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The effect of complex nucleating agent on the crystallization, phase formation and performances in lithium aluminum silicate (LAS) glasses
Journal of Non-Crystalline Solids 521 (2019) 119486
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The effect of complex nucleating agent on the crystallization, phase formation and performances in lithium aluminum silicate (LAS) glasses Jiaqi Wu, Changwei Lin, Jianlei Liu, Lei Han, Hua Gui, Cui Li, Taoyong Liu, Anxian Lu
T
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School of Materials science and Engineering, Central South University, Changsha 410083, China
ARTICLE INFO
ABSTRACT
Keywords: LAS glass-ceramics Mechanism Crystallization temperature Complex nucleating agents
The glasses and glass-ceramics in Li2O-Al2O3-SiO2 system containing three complex nucleating agents (TiO2 + ZrO2 + P2O5) were prepared respectively. The effects of P2O5 content on crystallization mechanism and microstructure were researched by means of Differential Scanning Calorimetry, X-Ray Diffraction, Raman Spectra, Fourier Transform Infrared and Scanning Election Microscopy. Simultaneously, the effects of structure and composition on thermal expansion coefficient, transmittance, Vickers hardness, density, bending strength, and chemical stability were also discussed. The results indicated that P2O5 can promote the nucleation and crystallization process by forming AlPO4 and accelerating the precipitation of ZrTiO4. With the increase of P2O5 content (less 5 wt%), the promoting effect of elevated crystallization temperature on the process of grain grown enhanced gradually. Especially when P2O5 content is 5 wt%, the sample have the smallest crystals and the best performance, and there is a relatively low temperature and wide temperature range where could keep the grain size of P5 samples almost unchanged.
1. Introduction Glass-ceramic materials prepared by controlled crystallization of parent glasses with suitable nucleating agent are polycrystalline solids [1]. Lithium aluminum silicate (LAS, Li2O-Al2O3-SiO2) is one of the most valuable and extensively used glass ceramic systems due to the wide range of useful properties such as excellent mechanical properties as well as low thermal expansion coefficient (TEC) and high thermal shock resistance [2,3]. Such properties enable LAS glass-ceramics to be used in cookware, fireplaces, telescope mirror supports and so on [4,5]. The attractive properties of the LAS glass ceramics are not a material constant, which depend not only on the types of crystalline phases, but also on the chosen compositions of parent glass. Especially the addition of nucleating agent can obtain uniform distribution of crystals and lower crystallization temperature [6]. Since the works of Corning, on preparation of the LAS glass-ceramics called Pyroceram9606 by using TiO2 oxides as nucleating agents, a ripe theoretical system of LAS glass-ceramics has been achieved gradually [7,8]. The main crystalline phases in LAS-type glass ceramics are metastable solid solutions of βquartz/(β-eucryptite) based on the hexagonal structure or β-spodumene/(keatite). β-quartz solid solutions are equipped with the lower TEC to meet specific requirements due to the negative TEC of eucryptite (Li2O-Al2O3-2SiO2). However, β-quartz solid solutions are prone to
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transform into keatite at elevated crystallization temperature [9,10]. Hence the addition of nucleating agent is a key step in order to lower crystallization temperature and restrain the trend of transformation. The most repeatedly used nucleating agent are the ZrO2, TiO2 oxides and their mixture which has better performance on account of refining grain by the formation of ZrTiO4 [11,12]. Such as Höche T et al. [13] studied the effect of ZrO2 and TiO2 on the nucleation mechanism in a lithium aluminosilicate glass. In addition, the effect of the use of P2O5 oxides have been investigated specially in LAS glass-ceramics. A. de Pablos-Martín [14] et al. and Xingzhong Guo [15] et al. studied the crystallization mechanism by the calculated Avramis exponent in the Avrami formula according to DSC curves at different heating rates. Nevertheless, there are only a few literatures available on the theory of compound nucleating agents containing ZrO2, TiO2 and P2O5 oxides which are more effective nucleating agents than single or double nucleating agents. In this paper, the compound nucleating agents containing ZrO2, TiO2 and P2O5 oxides was used to prepare transparent LAS glass-ceramics with low thermal expansion coefficient, and the influence of the composite nucleating agent on mechanism in the process of crystallization was studied. Not only that, the minor amount of MgO was added to lower the melting point and low concentration of lithium was used to reduce cost of material.
Corresponding author. E-mail address: [email protected] (A. Lu).
https://doi.org/10.1016/j.jnoncrysol.2019.119486 Received 28 March 2019; Received in revised form 1 June 2019; Accepted 3 June 2019 0022-3093/ © 2019 Elsevier B.V. All rights reserved.
Journal of Non-Crystalline Solids 521 (2019) 119486
J. Wu, et al.
Infrared (FTIR, Nicolet6700, U.S.A) spectroscopy has been used in order to grasp the glass-ceramic fine structure in the range of 400–4000 cm−1, such as functional groups, by blending fine powdered of the samples with KBr in a ratio of 1: 100 and then pressed to form pellets. Raman spectra of the samples were examined by using Horiba Labram HR800 Raman Spectrometer. The structure of the main crystalline phase was showed by XRD patterns of powdered samples measured using X-ray diffraction (XRD, D/max 2500 model, Japan) with Cu Kα radiation in scanning angle (2θ) of 10–80°. In addition, the average value of grain size was calculated by combining the calculation result of Jade 6.0 after fitting and manual calculation result by the Scherrer method after measuring the full width of half maximum. The calculation formula is as follows:
Table 1 Chemical composition of the glass samples (wt%). Glass
SiO2
Al2O3
Li2O
MgO
ZrO2
TiO2
P2O5
Sb2O3
P2P3P4P5P6-
59 59 59 59 59
25.5 24.5 23.5 22.5 21.5
4 4 4 4 4
4 4 4 4 4
2 2 2 2 2
2 2 2 2 2
2 3 4 5 6
1.5 1.5 1.5 1.5 1.5
2. Experimental procedure 2.1. Glass preparation and heat treatment
where θ is a diffraction angle, λ is a wavelength of X-ray radiation, B is the full width of half maximum (FWHM), and K is a constant. To study the microstructure of the samples, they were polished with sandpaper and soaked in HF solution (10%) for 1.5 min, then were coated with a thin layer of platinum, electron micrographs were taken using SEM (Helios NanoLab G3 UC). Some mechanical properties were examined, such as the Vickers hardness by using micro-hardness tester (DHV-1000-CCD) and the bending strength obtained by three-point bending method using DD-1100 machine. The surface of the samples after polished and cleaned with anhydrous ethanal were measured with loads of 0.5 kg for 10 s, then calculated the average hardness of five position. The bending strength were obtained of glass ceramics at room temperature, and before the test, the samples were cut into dimensions of 5 mm × 5 mm × 25 mm, then calculated the average of three samples for each composition. The calculation formula of three-point bending method is as follows: where, δ is the bending strength, P is the breakage load, L is the sample span in the test, a is width and h is the thickness. The Archimedean method was used to calculate bulk density at room temperature with an error of ± 0.005 g/cm3, the calculation formula could be expressed as follows:
The horizontal dilatometer (Netzsch DIL 402EP, Germany) was employed to measure the thermal expansion coefficient, the glass transition temperature (Tg) and softening temperature (Tf) at a heating rate of 5 °C/min. The parent glass and glass-ceramics samples with no distinct defects were cut into dimensions of 5 mm × 5 mm × 50 mm, then measured among the temperature range of 30–900 °C and obtained the final value of TEC within the temperature range of 30–600 °C. Every date is measured from three samples for each composition. Transmittance spectra of glass-ceramics were surveyed with a HITACHIU-3310UV spectrophotometer from Japan during the wavelength range of 200–800 nm, and the surface of all samples (20 × 20 × 2 mm) was polished and cleaned by Ultrasonic Bath. Fourier Transform
= m1
Dwell time (h)
Crystallization temperature (°C)
Dwell time (h)
PX-1 PX-2 PX-3 PX-4 PX-5 PX-6 P2-7 P3-7 PY-7 PX-8 PX-9 PX-10
700 700 700 700 700 700 700 700 700 720 720 720
6 6 6 6 6 6 6 6 6 6 6 6
720 730 740 745 750 755 760 760 770 790 810 870
2 2 2 2 2 2 2 2 1.5 1.5 1.5 1.5
a
0 /(m1
m2 )
(3)
where, ρ0 is the density of the distilled water, m1 is the weight of the sample in the air, m2 is the weight of the sample in the distilled water. The chemical stability of the samples after erosion in alkaline (5% NaOH) or acidic solutions (10% HCl) for 8 h were also tested with the room temperature solution immersion method with an error of ± 0.02 g/cm3. The mass loss is calculated according to the following formula:
C = 100(G1
G2 )/S H
(4)
where, G1 is the weight of sample before soaking, G2 is the weight of sample after soaking, S is the surface area of sample before soaking, H is the soaking time.
Table 2 Heat treatments applied to LAS glass samples and their nomenclatures.a Nucleation temperature (°C)
(2)
= 3P L /2a h2
2.2. Analytical methods
Sample name
(1)
D = K /B cos
The initial materials of parent glass were analytical grade reagents SiO2, Li2CO3, Al2O3, TiO2, ZrO2, (NH4)2HPO4, MgO, and Sb2O3. The exact compositions in wt% were given in Table 1. The parent glass 100 g in weight nucleated by a mixture of TiO2, ZrO2 and P2O5 were melted in alumina crucibles at 1600–1620 °C for 2 h at a heating rate of 5 °C/min, then poured onto a preheated stainless-steel plate by an annealing around 580 °C for 2 h intended to eliminate the stresses. The addition of MgO oxides is in order to improve the melting properties while lowering the cost of material by partially replacing Li2O. Moreover, Sb2O3 was used as a refining agent which can enhance the parent glass performance by eliminating air bubbles. The thermal treatments of nucleation and crystallization depend on the characteristic glass temperatures such as glass transition temperature (Tg) and crystallization maximum temperature (Tp), were determined by Differential Scanning Calorimetry (DSC, Netzsch 404PC, Germany) thermograms. DSC curves were recorded in air at heating rates (10 °C/min) up to the maximum temperature of 1200 °C, and the measurement error is ± 2 °C. The details of thermal treatments are listed in Table 2.
3. Results and discussions 3.1. Crystallization behavior of the glass Fig. 1 shows the curves of the DSC analysis of parent glass prepared with different ratio of nucleating agent, it is noted that the temperature of exothermic peaks associated with the crystallization temperature (Tp) decreases first and then increases with the increase of P2O5 content in compound nucleating agents. From P2 to P6 samples, the temperatures of exothermic peak are 885 °C,874 °C, 860 °C, 846 °C and 867 °C, respectively. It indicates that a certain range of P2O5 used as a nucleating agent can lower crystallization peak temperature and promote the crystallization process of LAS glass, meanwhile, the crystallization peak
Note: X could be number 2,3,4,5 and 6. Y can be 3,4 and 5. 2
Journal of Non-Crystalline Solids 521 (2019) 119486
J. Wu, et al.
Fig. 1. DSC curves of glass sample with different P2O5 content.
temperature reaches the lowest when the addition P2O5 is 5 wt%. The reason for the variation tendency may be the different effects of P2O5 in glass, on the one hand, it can increase the stability of the structure by combining with (AlO4)5− and entering into silica network, thus has a reinforcement effect on network, finally inhibiting crystallization process, on the other hand, it can destroy silica tetrahedron and promote phase separation due to high coordination number, thus promote the crystallization [16]. When P2O5 content is less than 5 wt%, the latter plays a major role and promote the crystallization process. With the P2O5 content continuously to increasing, the effect of network reinforcement takes up more important role than phase separation, then having negative effect on crystallization process, so P6 sample has a higher crystallization temperature than P5 sample, as shown in Fig. 1. As revealed in Fig. 1, the variation trend of glass transition temperature (Tg) is same as Tp, first decreasing and then increasing. The value of Tg can obtain further confirmation in diagram of DSC and thermal expansion curves of parent glass, and only the P6 sample is shown as an example in Fig. 2 due to the similarity. The values of Tg and softening temperature (Tf) are obtained separately and they are about 685 °C, 746 °C, respectively. In generally, the nucleation temperature is identified as the range of from Tg to Tg + 50 °C, and less than Tf. Therefore, the optimum nucleation temperature of the parent glass is between 685 °C and 735 °C. Furthermore, according to the exothermic peak temperature shown in Fig. 1, a certain reference value of
crystallization temperature can be obtained. After some tests on the basis of the dates, the heat treatment system is determined finally, summarized in Table 2. 3.2. XRD analysis Glass ceramic powders formed from the parent glass after different heat treatments were determined by XRD, Fig. 3 shows the diffraction patterns of P2, P3, P4, P5 and P6 samples. On the whole, when the samples began to crystallize at low crystallization temperature, the main crystallization phase of the glass-ceramics is β-quartz and the lowest temperatures at which diffraction peaks were observed of the samples (P2, P3, P4, P5 and P6) are 745 °C, 740 °C, 730 °C, 720 °C and 730 °C, respectively, decreasing first and then increasing which is consist with the variation trend of Tp in DSC diagram. Then as the crystallization temperature rises, the relative amount of β-quartz also increases gradually, especially when crystallization temperature is 745 °C, the XRD patterns of all samples have well defined lines, shrill peak shapes and high degree of crystallinity, indicating the nucleating agents by a mixture of TiO2, ZrO2 and P2O5 have effective influence on crystallization at low crystallization temperatures. Finally, when the crystallization temperature continue to rise to 870 °C, the main crystal phase is basically transformed into β-spodumene. In term of single sample, such as Fig. 3(d) diagram, it shows that the main crystal phase is β-quartz at low crystallization temperatures by comparison with patterns of the standard β-quartz, but it appears an additional peak at 2θ ≈ 30° which corresponds to reflection by (111) plane of ZrTiO4 [17]. And with the increase of temperature, the shape of peak at 2θ ≈ 30° becomes shriller which reveals the more obviously formation of ZrTiO4 phase. Fig. 4 shows the grain size-crystallization temperature curves simulated by four or two different grain sizes in the sample with different P2O5 content and gives the slopes of simulated curves by line fitting in Origin9.0. The mean grain size is calculated by using Scherrer Formula, and the diffraction angle selected in the formula is at 2θ ≈ 26°. First, when the samples are heated at the same temperature such as 745 °C, the mean grain size of four samples (P3-4, P4-4, P5-4, P6-4) are about 69 nm, 60 nm, 53 nm and 63 nm, respectively. It reveals that with the growth in P2O5 content, the mean grain size descends at first and goes up later along, and P5 sample has the best effect on refining grain. Then, the effect of crystallization temperature on the mean grain size is shown in Fig. 4. It can be seen that the mean grain size is increased with the elevated crystallization temperature, and P5 sample has the smallest grain size, but the mean grain size of the P5 sample remains
Fig. 2. DSC and thermal expansion curves of parent glass (P6 sample). 3
Journal of Non-Crystalline Solids 521 (2019) 119486
J. Wu, et al.
Fig. 3. XRD patterns of: (a) P2, (b) P3, (c) P4, (d) P5, (e) P6 LAS glass-ceramics samples heat treated at different crystallization temperatures and (f) LAS glassceramics with a heat treatment temperature of 755 °C for 2 h.
basically unchanged in the temperature range of 740 °C to 750 °C which seems to violate the mechanism of elevated crystallization temperature promoting grain growth, but it is impossible. According to the research of Johnson [18], the nucleation process and growth process may occur simultaneously at a selected temperature because of changes in
dynamic and thermodynamic conditions by modifying the composition of the parent glass. Therefore, the crystals used to calculate the mean grain size in this paper includes both those that have been nucleated and to be nucleated at elevated crystallization temperature. These crystals have been nucleated can grow with increasing temperature so 4
Journal of Non-Crystalline Solids 521 (2019) 119486
J. Wu, et al.
Fig. 5. Raman spectra of glass-ceramics with a heat treatment temperature of 755 °C for 2 h. (the red number is the relative strengths of maximum peak per sample). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 4. The grain size-crystallization temperature curves simulated by four or two different grain sizes in the sample with different P2O5 content and the slopes of simulated curves by line fitting in Origin9.0.
of single nucleating agent or combination of two nucleating agents.
as to increase the mean grain size, while for new crystals formed by nucleation, their grain size is still small, which greatly reduces the mean grain size. Hence in a certain range of crystallization temperature, such as P5 sample at 740 °C to 750 °C, when the nucleation rate is approximately equal to the growth rate, it is possible to keep the mean grain size of P5 sample basically unchanged. Afterwards, as the temperature continues to rise, the nucleation process was gradually completed and the nucleation rate is much lower than the growth rate, so that the mean grain size of P5 sample increases rapidly. However, there are obvious differences on the slope of grain sizecrystallization temperature curves with various P2O5 content. According to Fig. 4, the slope of four curves (P3, P4, P5, P6) are 0.43, 0.70, 1.40, and 0.79, respectively, increasing first and then decreasing with the increase of P2O5 content, showing the sensitivity of grain growth will change with the crystallization temperature altered. When the P2O5 content is less than 5 wt%, the more P2O5 content, the stronger the promotion of nucleation process, and the more nucleation number, the faster the sample reaches the critical value duo to the limited total nucleation number, thus the faster the crystal grows with the elevated crystallization temperature, that is reflected in the gradual increase in the slope of curves. When the P2O5 content continues to increase to 6 wt %, the effect of P2O5 on nucleation process is weakened, it can be seen not only from a sudden increase in grain size of P6 sample, but also from a decrease in the slope of the curve. In a word, the P5 samples always obtain the smallest grain size and steady trend of change in a relatively low temperature and wide temperature range, therefore have the best effect. In order to study the detailed changes, the XRD patterns of five samples in 755 °C for 2 h are displayed in Fig. 3(f). The mean grain sizes of five samples are about 79 nm,73 nm, 66 nm, 60 nm and 71 nm, respectively, then further observations of grain morphology and size can be made in SEM(Fig. 9). The existence of ZrTiO4 in a low amount have been identified and its peak shape becomes more and more obvious with the increase of P2O5 content in Fig. 3(f). For the sake of better confirmation of presence of ZrTiO4 phase, Raman spectroscopy was carried out in Fig. 5, showing the bands at around 620 cm−1 and 789 cm−1 which corresponds to ZrTiO4 phase [19]. Thus, in the same heat treatment system, the more P2O5 content (less than 6 wt%), the more promoted the precipitation of ZrTiO4 phase which can refine grain by heterogeneous nucleation. To some extent, this shows why the effect of compound nucleating agent (TiO2 + ZrO2 + P2O5) is better than that
3.3. Structure and properties of glass-ceramics 3.3.1. Raman spectra analysis Fig. 5 demonstrates Raman spectra in the frequency range 100–1400 cm−1 of LAS glass-ceramics with various P2O5 content. In all Raman spectra there are two bands of β-quartz ss, a weaker band at 1074 cm−1 that is attributed to an antisymmetric stretching vibration of SieO bond and an intensive band at 478 cm−1 that is due to bending vibrations of Si-O-Si bond [20]. It can be seen that the relative strengths of maximum peak are 107, 140, 200, 230, and 296, respectively, gradually increasing, explaining that with the P2O5 content continuously to increasing, the glass network structure is gradually enhanced. There are also bands connected with ZrTiO4 and AlPO4 phase. The band at about 285 cm−1 in the Raman spectrum is characteristic of the lattice vibrations of AlPO4 and at about 130 cm−1 is due to stretching vibration of isolated PO43− tetrahedron [21]. There have low and insignificant peaks in sample of P2–6, but as the increase of P2O5 content, the peak shape at 285 cm−1 and 134 cm−1 becomes more sharper, revealing the obviously formation of AlPO4 phase. However, Raman spectroscopy can only qualitatively analyze the existence of functional groups, such as PO43−, it cannot achieve the effect of 31P NMR technique in accurately analyzing the glass structure. The 31P NMR technique [22,23] can be used to distinguish the types and structures of phosphorus compounds in samples when the higher accuracy is required. Simultaneously, the bands at 620 cm−1 along with bands at 789 cm−1 confirm the formation of ZrTiO4 phase [19]. With the growth of P2O5 content, the precipitation of ZrTiO4 phase become more and more obvious due to the sharper shape of peak at 620 cm−1 and 789 cm−1, indicating P2O5 can promote the precipitation of ZrTiO4 phase. According to written records [24], it proves the ZrTiO4 phase does not enter the network structure of the stuffed β-quartz ss, but promote heterogenous nucleation to achieve grain refinement. Thus, combined with XRD and DSC analysis, it can be known that the presence of P2O5 maybe promote precipitation of ZrTiO4 phase and formation of AlPO4 phase so as to get smaller grain size, but also have the negative effect on crystallization process by enhancing glass network structure, and with the P2O5 content continuously to increasing (more than 5 wt%), the effect of network reinforcement takes up more important role. 5
Journal of Non-Crystalline Solids 521 (2019) 119486
J. Wu, et al.
Fig. 6. Fourier-transform infrared spectroscopy of glass-ceramics with a heat treatment temperature of 755 °C for 2 h.
3.3.2. Structural study by infrared spectroscopy More information about the glass-ceramics fine structure can be acquired from FTIR spectroscopy. Fig. 6 illustrates the optical absorption of the five samples in the region of 400 cm−1-1400 cm−1. The spectrum can be divided in two ranges in the general case: one in the frequency range from 1500 cm−1 to 4000 cm−1 is not characteristic of the samples, including a wide band at about 3400 cm−1 and 1630 cm−1 connected with the presence of water as well as at about 2900 cm−1 attributed to symmetric vibration of –CH2 group, and the other in the low frequency range from 1500 cm−1 to 500 cm−1 is related to structure of the measured samples. Firstly, the band around 430 cm−1 is due to bending vibration of O-Si-O linkages [25] or the symmetric stretching vibrations of MgO6 octahedra and LiO4 tetrahedra [26]. Then, there is a weak absorption in the band between 550 cm−1 and 560 cm−1 related to the formation of the MgO4, by partially replacing Li+ with Mg2+ in the β-quartz ss due to their similar ionic radius, or hexacoordinated Al3+ ions [27]. While the band around 760 cm−1 corresponding to bending vibration of (AleOe) in [AlO4] [28] have an intensity absorption, demonstrating that aluminum atoms enter into the three-dimensional network structure of the β-quartz ss with the vast majority of [AlO4] and a small amount of hexacoordinated Al. The band at about 960 cm−1 could be assigned to vibration of the (SieOe) related with non-bridging oxygen ions. According to [27], the presence of nonbridging oxygen ions can be in keeping with the formation of hexacoordinated Al3+ ions in the vitreous residual phase, which confirms the existence of 6-fold coordinated Al3+ (AlPO4) in a more precise way. Finally, the maximum absorption band around 1000 cm−1-1100 cm−1 can be noticed in Fig. 6, its presence is related to asymmetric stretching vibrations of PeOeP groups [29] or stretching vibrations of SieOe(Si, Al) bond [30] which is characteristic of the tectosilicate in the β-quartz ss, by replacing Si with Al in the three-dimensional network structure. The IR spectra of five samples also have certain differences and variations with the P2O5 content continuously to increasing, such as around 1000 cm−1-1100 cm−1 and 950 cm−1 bands. When the band at 1000 cm−1-1100 cm−1, it can be seen that the absorption bands splits into two bands and the absorption peaks are sharper in P2-6 sample, illustrating the range of absorption is smaller, but with the growth in P2O5 content, the range of absorption get more wider, the absorption bands groups into one gradually, it may be caused by different bond strength of four Si-O-Si bond [31] or increase of PeOeP bond in [PO4]. Focus on the band around 950 cm−1 linked to Al3+, from P2–6 to P6–6, it can be seen that the bands are 946 cm−1, 948 cm−1, 952 cm−1, 957 cm−1 and 958 cm−1, respectively, gradually moving towards
higher wave number and having an increases of absorption intensity, revealing the gradually increase of Al3+ (AlPO4) content, which is consistent with Raman spectra analysis. 3.3.3. Transparency analysis The high transparency is typical characteristic of LAS glass-ceramics with β-quartz ss as main crystal phase because the grain size of the βquartz ss is generally 1/10 of the wavelength of visible light and the refractive index of crystal phase is nearly to that of glass. Fig. 7 demonstrates the visible spectral in the range of 300 cm−1–900 cm−1 of five crystallized samples with a heat treatment temperature of 755 °C, it can be learned that the P4-6 sample have maximum transparency, reaching around 84%, then followed by P5-6 sample with about 81%. With the P2O5 content continuously to increasing, the transparencies of samples show a trend of goes up first and then descends later along. As mentioned in the [32], the scattering effect of grain to light is the main factor affecting the transparency of glass-ceramics. According to Rayleigh scattering mode, the smaller the grain size, the lower the intensity of the scattering light, then the better the transparency. According to the XRD results above, the mean grain sizes of five samples are
Fig. 7. Transmittance spectra of glass-ceramics with a heat treatment temperature of 755 °C for 2 h. 6
Journal of Non-Crystalline Solids 521 (2019) 119486
J. Wu, et al.
79 nm,73 nm, 66 nm, 60 nm and 71 nm, respectively. Therefore, the results of transparency are basically consistent with analysis of grain size. However, P4-6 sample have higher transparency than P5-6, and P6-6 sample have the lowest transparency, which may be due to excessive phase separation effect caused by P2O5 in promoting the nucleation process of glass. The strong phase separation effect could aggravate the overall inhomogeneity and even generate the opacifying effect, which lead to the decrease of transparency. Especially when the P2O5 content is more than 4%, with the increase of P2O5 content, the phase separation effect caused by P2O5 is excessively increased, resulting in the opacifying effect, and then the intensity of scattering light increases, finally the transmission of visible light decrease. But when the P2O5 content is less than 4%, with the growth in P2O5 content, the grain size decreases and the transmission increase gradually, showing that the limited phase separation effect caused by P2O5 has a positive impact on the crystallization process. From the change of transparency, it can be seen that the general trend of grain size change, and the influence of phase separation effect caused by different P2O5 content on the crystallization process, especially its negative effect, that is, the opacifying effect caused by excessive phase separation due to the excess P2O5.
the more precipitate of crystal and the higher the crystallinity. 3.3.5. Physical and chemical property analysis In order to study structural change in more precise, some performances that can intuitively reflect the law of change in three-dimensional net structure are also measured, such as bending strength, Vickers hardness, density and chemical stability. With increasing P2O5 content in LAS glass ceramics, the effect of ratio changes in the composite nucleating agent (TiO2 + ZrO2 + P2O5) on the crystallization properties are revealed in Table 3. The bending strength and hardness of the glass-ceramics depend primarily on the microstructure, especially the degree of interlacing between grains determined by the grain content and size. As shown in Table 3, with the growth in P2O5 content, the hardness of glass-ceramics keeps same pace with the variation trend of bending strength, rising first and then falling, revealing that the better performances first and then worse performances, which is consistent with the results of XRD. When the P2O5 content is less than 5 wt%, the hardness and bending strength increase gradually because the increasing of crystal content of β-quartz and decreasing of grain size would hinder the propagation of small crack and formation of large crack. However, the P6-6 samples have the lower hardness and bending strength, it may be caused by excessive phase separation effect of P2O5. When the P2O5 content is more than 5 wt%, the strong phase separation effect may cause the disorder of the glass structure in the crystallization process and aggravate the overall inhomogeneity, which leads to the decrease of performance. This can also be seen by changing in transparency in Fig. 7. In addition, the corrosion resistance is an important measure of chemical stability, depending on the type of etch and on the properties of the glass itself, such as the tightness of the network structure, as well as the gaps, pores and other defects that may occur on the surface of the glass. As shown in Table 3, with the P2O5 content continuously to increase, the variation trend of measured mass loss descends at first and then goes up later along, indicating that the effect of acid or alkaline resistance gets better first and then gets worse. In general, the closer the connection between the glass network, the higher the tightness, and the better the corrosion resistance. According to the passage above, the more P2O5 content, the closer the connection between the glass network. Thus, the corrosion resistance of P6-6 sample should be better, but its stability is worse in reality, which may be due to some surface defects by the excessive phase separation effect from P2O5. It is basically consistent with the above results of hardness and bending strength. On the whole, it is acceptable range of the mass loss, the samples all have the stable chemical properties so that not easily corroded, and the effect of acid resistance is better than alkaline resistance. Density is an important physical property, which is related not only to the composition of parent glass, but also to the precipitation degree of crystal in LAS glass-ceramics. First, the higher the degree of crystal precipitation, the lower the density because the volume increases as crystal precipitation [33]. Then, in term of composition of parent glass, the atomic mass of P is large than atomic mass of other chemical elements replaced by P, so as to get the higher density with the increase of P2O5 content. Therefore, the effect of density should be considered by two factors. As shown in Table.3, it demonstrates that the density increases with the growth in P2O5 content, which may be result from the effect of increasing density caused by quality factor is greater than that of decreasing density caused by crystallization, especially when the content of P2O5 increases from 5 wt% to 6 wt%, not only the quality of parent glass increases, but also the crystallinity decreases shown in Fig. 3(f), so the growth of density is more larger.
3.3.4. The thermal expansion coefficient The low thermal expansion coefficient (TEC) is another typical characteristic of LAS glass-ceramics with β-quartz ss because of the negative TEC of β-quartz, thus, the higher the content of β-quartz ss, the lower value of TEC. As shown in Fig. 8, curves A, and B reveals the variation tendency of TEC (30 °C–600 °C) of parent glass and glass-ceramics, respectively. The curve A shows relatively gentle trend and finite change, indicating that the influences of P2O5 content on TEC of parent glass is limited. While curve B changes greatly with the of P2O5 content continuously to increasing, and the values of TEC are 2.0316 × 10−6/°C, 1.625 × 10−6/°C, 1.454 × 10−6/ °C, 1.022 × 10−6/°C and 1.3402 × 10−6/°C, respectively, descends at first and then goes up later along. As we all know, the TEC of glass-ceramics is related to microstructure and component, such as crystallinity, main crystal phase types and the ratio of volume fraction of main crystal phase with the residual glass phase [9]. As shown in Fig. 3(f), the β-quartz ss are the main crystal phase of five samples, and the crystallinity are 88.7%, 89.3%, 91.2%, 93.5% and 90.5%, respectively, calculated by Jade.6.0, demonstrating that with the growth in P2O5 content, the content of β-quartz ss increases first and then decreases. The result keeps pace with the TEC analyzes, which confirms that the higher the content of P2O5 (less 5 wt%),
3.3.6. SEM analysis Fig. 9 show the microstructure of the samples with a heat treatment temperature of 755 °C for 2 h, it can be seen that the shape of grain is spherical, which revealing that the main crystal phase is β-quartz solid solution rather than β-spodumene with the shape of striped. In addition
Fig. 8. Thermal expansion coefficient(30 °C–600 °C) of parent glass and glassceramics samples doped with different amount of P2O5. 7
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Table 3 TEC, bending strength, Vickers hardness, density, acid and alkali resistance of glass ceramics. Name
Bending strength (MPa)
Vickers hardness (GPa)
Density (g/cm3) ( ± 0.005)
Mass loss (Acid or Alkali) (×10−5 g/cm−2h) ( ± 0.02)
TEC (×10−6/°C, 25–600 °C)
P2-6 P3-6 P4-6 P5-6 P6-6
96.4 ± 0.4 101.2 ± 0.5 104.9 ± 0.3 109.1 ± 0.4 97.5 ± 0.3
6.38 6.58 6.95 7.01 6.68
2.516 2.519 2.523 2.528 2.539
6.31 6.72 5.82 5.21 5.76
2.032 1.625 1.454 1.022 1.340
± ± ± ± ±
0.02 0.03 0.03 0.02 0.04
to the spherical particles, there are also some fine nanoparticles, which may be related to the presence of ZrTiO4 phase and AlPO4 phase, that is especially evident in Fig. 9(d). They can be used as the carrier of heterogeneous nucleation so that promoting nucleating process and providing smaller grains by reducing the degree of supercooling. The existence of ZrTiO4 phase and AlPO4 phase also can be observed in Raman spectra analysis. In SEM photo (a), when the P2O5 content is 2 wt%, the size of the grain is large, the spacing between the crystals is wide and the arrangement is loose, but as the content continuously to increasing (less than 5 wt%), the size of the grains is getting smaller and the crystals are getting closer together. Especially when the P2O5 content is 5 wt%, the P5–6 sample have the smallest grain size and the most
or or or or or
10.2 9.78 8.37 7.31 8.92
± ± ± ± ±
0.136 0.075 0.081 0.101 0.091
closely aligned as shown in Fig. 9(d, f), thus have the best performance. But when the content continuously to increase to 6 wt%, it gets bigger grains. The variation trend of crystal size is same as the calculation results of XRD, which confirms that a certain amount of P2O5 can play the role of promoting crystallization procession and improving the performance by refining the grain. 4. Conclusion The crystallization mechanism, microstructure and performances of Li2O-Al2O3-SiO2 system glass ceramic containing complex nucleating agents (TiO2 + ZrO2 + P2O5) are researched. When the parent glass
Fig. 9. SEM images: (a) P2-6, (b) P3-6, (c) P4-6, (d) P5-6, (e) P6-6 and (f) P5-6 of LAS glass-ceramics with a heat treatment temperature of 755 °C for 2 h. 8
Journal of Non-Crystalline Solids 521 (2019) 119486
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was melted by using TiO2, ZrO2 and P2O5 in a ratio of 2:2:5 as nucleating agent, the sample can obtain the smallest grain size and steady variation tread of grain size in a relatively low temperature and wide temperature range (740 °C–750 °C), thus have the best effect. Moreover, the detailed change of performance and structure in samples with a heat treatment temperature of 755 °C for 2 h were studied. Such as the TEC, bending strength, Vickers hardness, density and the mass loss of Acid (Alkali) resistance of P5–6 sample are 1.022 × 10−6/°C (30–600 °C), 109 MPa, 6.95 GPa, 2.528 g/cm3, 5.21(7.31) × 10−5 g/cm−2 h, respectively. The influence of P2O5 on mechanism as following:
[5] M. Comte, Commercial Applications of Glass-Ceramics, from Glass to Crystal Nucleation, Growth and Phase Separation: From Research to Applications, EDP Sciences, 2017, pp. 361–374. [6] W. Holand, V. Rheinberger, M. Schweiger, Control of nucleation in glass ceramics, Philos. Trans. R. Soc. Lond. Ser. A 361 (1804) (2003) 575–589. [7] S. D. Stookey, US Patent 2920970, January (1960). [8] W. Pannhorst, Glastech. Ber. Glass Sci. Technol. 73 (C1) (2000) 28. [9] P.W. McMillan, Glass–Ceramics, Academic Press, New York, 1979. [10] Z. Strnad, Glass Science and Technology, Glass-Ceramic Materials, vol. 8, Elsevier, Amsterdam, Netherlands, 1986. [11] X. Gua, H. Yang, M. Cao, Nucleation and crystallization behaviour of LAS system glass-ceramics containing little and no fluorine, J. Non-Cryst. Solids 351 (2005) 2133–2137. [12] T. Hoche, et al., ZrTiO4 crystallization in nanosized liquid-liquid phase-separation droplets in glass – a quantitative XANES study, 13 (2011), p. 2550. [13] T. Höche, C. Patzig, T. Gemming, R. Wurth, C. Rüssel, Temporal evolution of diffusion barriers surrounding ZrTiO4 nuclei in lithia aluminosilicate glass–ceramics, Cryst. Growth Des. 12 (2012) 1556–1563. [14] A. de Pablos-Martín, et al., Crystallization kinetics of LaF3 nanocrystals in an oxyfluoride glass, J. Am. Ceram. Soc. 94 (8) (2011) 2420–2428. [15] X.Z. Guo, H. Yang, C. Han, F. Song, Crystallization and microstructure of Li2OAl2O3-SiO2 glass containing complex nucleating agent, Thermochim. Acta 444 (2) (2006) 201–205. [16] C.H.E.N. Dan-li, et al., Effect of nucleation agent P2O5 on crystallization of CaOAl2O3-SiO2 glass ceramics from yellow phosphorus furnace slag J, J. Synth. Cryst. 46 (11) (2017). [17] Richa Mishra, et al., Study on thermophysical properties and phase evolution in Nd doped Li2O-Al2O3-SiO2 glass nucleated by multiple nucleating agents, J. Non-Cryst. Solids 447 (2016) 66–73. [18] W.A. Johnson, R.F.J. Mehl, Trans. AIME 135 (1939) 416–458. [19] M. Andrianainarivelo, R.J.P. Corriu, D. Leclercq, P.H. Mutin, A. Vioux, Non-hydrolytic sol-gel process: zirconium titanate gels, J. Mater. Chem. 7 (2) (1997) 279–284. [20] O.S. Dymshits, A.A. Zhilin, V.I. Petrov, M. Ya, T.I. Chuvaeva Tsenter, V.V. Golubkov, Glas. Phys. Chem. 24 (1998) 79. [21] M. Rokita, et al., The AlPO4 polymorphs structure in the light of Raman and IR spectroscopy studies, J. Mol. Struct. 555 (2000) 351–356. [22] D.G. Gorenstein, Phosphorous-31 NMR，Spetroscopy Principles and Applications, Academic Press, Inc, London, 1984. [23] D.S. Argy Ropoulos, C. Heitner, H.I. Bolker, Y. Archipov, 31P-NMR spectroscopy in wood chemistry. Part V qualitative analysis of lignin functional groups, J. Wood Chem. Techn 13 (2) (1993) 187–203. [24] I. Alekseeva, O. Dymshits, et al., Raman spectroscopy quantifying the composition of stuffed b-quartz derivative phases in lithium aluminosilicate glass-ceramics, J. Non-Cryst. Solids 354 (2008). [25] H. Gui, et al., Glass forming, crystallization, and physical properties of MgO-Al2O3SiO2-B2O3 glass-ceramics modified by ZnO replacing MgO, J. Eur. Ceram. Soc 39 (2019) 1397–1410. [26] P. T A R T E, “Physics of Non-Crystalline Solids” (Wiley, New-York), (1964), p. 549. [27] L. Arnault, et al., Microstructural study of two LAS-type glass-ceramics and their parent glass, J. Mater. Sci. 35 (2000). [28] S.X. Huang, S. Li, F.N. Wu, Y.L. Yue, Effect of B2O3 on structure and properties of CaO-MgO-B2O3-Al2O3-SiO2 glasses, J. Inorg. Organomet. Polym. 25 (2015) 816–822. [29] C. Huang, E.C. Behrman, Structure and properties of calcium aluminosilicate glasses, J. Non-Cryst. Solids 128 (1991) 310–321. [30] M.A. Marzouk, H.A. El Batal, A.A. Ghany, F.E. Eldin, Ultraviolet, visible, ESR, and infrared spectroscopic studies of CeO2-doped lithium phosphate glasses and effect of gamma irradiation, J. Mol. Struct. 997 (2011) 94–102. [31] Lei Han, et al., Crystallization, structure and characterization of MgO-Al2O3-SiO2P2O5 transparent glass-ceramics with high crystallinity, J. Non-Cryst. Solids 481 (2018). [32] Jiin-lyh Shyu, Ching-Yueh Wang, Tzu-Yi Chang, Controlled phase transformations by particle size in spodumene and cordierite glass ceramics, J.Am.Ceram.Soc. 79 (7) (1996) 1971–1974. [33] M.D. Karkhanavala, F.A. Hummel, The polymorphism of cordierite, J. Am. Ceram. Soc. 36 (1953) 389–392.
1) The presence of P2O5 maybe promote precipitation of ZrTiO4 phase and formation of AlPO4 phase, so as to promote heterogenous nucleation by phase separation effect to get smaller grain size. 2) The presence of P2O5 also have the negative effect on refining grain size by enhancing glass network structure. When the P2O5 content is more than 5 wt%, the effect of network reinforcement takes up more important role, so as to get the bigger grain size. 3) when the P2O5 content is less than 5 wt%, with the P2O5 content continuously to increasing, the sensitivity of grain growth to crystallization temperature increases gradually, that is the more P2O5 content, the stronger the promotion of nucleation process, thus the faster the crystal grows with the elevated crystallization temperature. But while P2O5 content is more than 5 wt%, it could hinder crystallization process due to the strong network enhancement by P2O5 and could have the poor performance because of excessive phase separation effect of P2O5. Conflict of interest statement We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled. Acknowledgments This work has been supported by the project of the National Natural Science Foundation of China (Nos. 51672310, 51272288, 51172286). References [1] R.D. Rawlings, J.P. Wu, A.R. Boccaccini, Glass-ceramics: their production from wastes-a review, J. Mater. Sci. 41 (2006) 733–761. [2] P.F. James, Glass-ceramic: new compositions and uses, J. Non-Cryst. Solids 181 (1995) 1–15. [3] P.A. Tick, N.F. Borrelli, I.M. Reaney, Relationship between structure and transparency in glass-ceramic materials, Opt. Mater. 15 (1) (2000) 81–91. [4] G.H. Beall, L.R. Pinckney, Nanophase glass-ceramics, J. Am. Ceram. Soc. 82 (1) (1999) 5–16.
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The effect of complex nucleating agent on the crystallization, phase formation and performances in lithium aluminum silicate (LAS) glasses Jiaqi Wu, Changwei Lin, Jianlei Liu, Lei Han, Hua Gui, Cui Li, Taoyong Liu, Anxian Lu
T
⁎
School of Materials science and Engineering, Central South University, Changsha 410083, China
ARTICLE INFO
ABSTRACT
Keywords: LAS glass-ceramics Mechanism Crystallization temperature Complex nucleating agents
The glasses and glass-ceramics in Li2O-Al2O3-SiO2 system containing three complex nucleating agents (TiO2 + ZrO2 + P2O5) were prepared respectively. The effects of P2O5 content on crystallization mechanism and microstructure were researched by means of Differential Scanning Calorimetry, X-Ray Diffraction, Raman Spectra, Fourier Transform Infrared and Scanning Election Microscopy. Simultaneously, the effects of structure and composition on thermal expansion coefficient, transmittance, Vickers hardness, density, bending strength, and chemical stability were also discussed. The results indicated that P2O5 can promote the nucleation and crystallization process by forming AlPO4 and accelerating the precipitation of ZrTiO4. With the increase of P2O5 content (less 5 wt%), the promoting effect of elevated crystallization temperature on the process of grain grown enhanced gradually. Especially when P2O5 content is 5 wt%, the sample have the smallest crystals and the best performance, and there is a relatively low temperature and wide temperature range where could keep the grain size of P5 samples almost unchanged.
1. Introduction Glass-ceramic materials prepared by controlled crystallization of parent glasses with suitable nucleating agent are polycrystalline solids [1]. Lithium aluminum silicate (LAS, Li2O-Al2O3-SiO2) is one of the most valuable and extensively used glass ceramic systems due to the wide range of useful properties such as excellent mechanical properties as well as low thermal expansion coefficient (TEC) and high thermal shock resistance [2,3]. Such properties enable LAS glass-ceramics to be used in cookware, fireplaces, telescope mirror supports and so on [4,5]. The attractive properties of the LAS glass ceramics are not a material constant, which depend not only on the types of crystalline phases, but also on the chosen compositions of parent glass. Especially the addition of nucleating agent can obtain uniform distribution of crystals and lower crystallization temperature [6]. Since the works of Corning, on preparation of the LAS glass-ceramics called Pyroceram9606 by using TiO2 oxides as nucleating agents, a ripe theoretical system of LAS glass-ceramics has been achieved gradually [7,8]. The main crystalline phases in LAS-type glass ceramics are metastable solid solutions of βquartz/(β-eucryptite) based on the hexagonal structure or β-spodumene/(keatite). β-quartz solid solutions are equipped with the lower TEC to meet specific requirements due to the negative TEC of eucryptite (Li2O-Al2O3-2SiO2). However, β-quartz solid solutions are prone to
⁎
transform into keatite at elevated crystallization temperature [9,10]. Hence the addition of nucleating agent is a key step in order to lower crystallization temperature and restrain the trend of transformation. The most repeatedly used nucleating agent are the ZrO2, TiO2 oxides and their mixture which has better performance on account of refining grain by the formation of ZrTiO4 [11,12]. Such as Höche T et al. [13] studied the effect of ZrO2 and TiO2 on the nucleation mechanism in a lithium aluminosilicate glass. In addition, the effect of the use of P2O5 oxides have been investigated specially in LAS glass-ceramics. A. de Pablos-Martín [14] et al. and Xingzhong Guo [15] et al. studied the crystallization mechanism by the calculated Avramis exponent in the Avrami formula according to DSC curves at different heating rates. Nevertheless, there are only a few literatures available on the theory of compound nucleating agents containing ZrO2, TiO2 and P2O5 oxides which are more effective nucleating agents than single or double nucleating agents. In this paper, the compound nucleating agents containing ZrO2, TiO2 and P2O5 oxides was used to prepare transparent LAS glass-ceramics with low thermal expansion coefficient, and the influence of the composite nucleating agent on mechanism in the process of crystallization was studied. Not only that, the minor amount of MgO was added to lower the melting point and low concentration of lithium was used to reduce cost of material.
Corresponding author. E-mail address: [email protected] (A. Lu).
https://doi.org/10.1016/j.jnoncrysol.2019.119486 Received 28 March 2019; Received in revised form 1 June 2019; Accepted 3 June 2019 0022-3093/ © 2019 Elsevier B.V. All rights reserved.
Journal of Non-Crystalline Solids 521 (2019) 119486
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Infrared (FTIR, Nicolet6700, U.S.A) spectroscopy has been used in order to grasp the glass-ceramic fine structure in the range of 400–4000 cm−1, such as functional groups, by blending fine powdered of the samples with KBr in a ratio of 1: 100 and then pressed to form pellets. Raman spectra of the samples were examined by using Horiba Labram HR800 Raman Spectrometer. The structure of the main crystalline phase was showed by XRD patterns of powdered samples measured using X-ray diffraction (XRD, D/max 2500 model, Japan) with Cu Kα radiation in scanning angle (2θ) of 10–80°. In addition, the average value of grain size was calculated by combining the calculation result of Jade 6.0 after fitting and manual calculation result by the Scherrer method after measuring the full width of half maximum. The calculation formula is as follows:
Table 1 Chemical composition of the glass samples (wt%). Glass
SiO2
Al2O3
Li2O
MgO
ZrO2
TiO2
P2O5
Sb2O3
P2P3P4P5P6-
59 59 59 59 59
25.5 24.5 23.5 22.5 21.5
4 4 4 4 4
4 4 4 4 4
2 2 2 2 2
2 2 2 2 2
2 3 4 5 6
1.5 1.5 1.5 1.5 1.5
2. Experimental procedure 2.1. Glass preparation and heat treatment
where θ is a diffraction angle, λ is a wavelength of X-ray radiation, B is the full width of half maximum (FWHM), and K is a constant. To study the microstructure of the samples, they were polished with sandpaper and soaked in HF solution (10%) for 1.5 min, then were coated with a thin layer of platinum, electron micrographs were taken using SEM (Helios NanoLab G3 UC). Some mechanical properties were examined, such as the Vickers hardness by using micro-hardness tester (DHV-1000-CCD) and the bending strength obtained by three-point bending method using DD-1100 machine. The surface of the samples after polished and cleaned with anhydrous ethanal were measured with loads of 0.5 kg for 10 s, then calculated the average hardness of five position. The bending strength were obtained of glass ceramics at room temperature, and before the test, the samples were cut into dimensions of 5 mm × 5 mm × 25 mm, then calculated the average of three samples for each composition. The calculation formula of three-point bending method is as follows: where, δ is the bending strength, P is the breakage load, L is the sample span in the test, a is width and h is the thickness. The Archimedean method was used to calculate bulk density at room temperature with an error of ± 0.005 g/cm3, the calculation formula could be expressed as follows:
The horizontal dilatometer (Netzsch DIL 402EP, Germany) was employed to measure the thermal expansion coefficient, the glass transition temperature (Tg) and softening temperature (Tf) at a heating rate of 5 °C/min. The parent glass and glass-ceramics samples with no distinct defects were cut into dimensions of 5 mm × 5 mm × 50 mm, then measured among the temperature range of 30–900 °C and obtained the final value of TEC within the temperature range of 30–600 °C. Every date is measured from three samples for each composition. Transmittance spectra of glass-ceramics were surveyed with a HITACHIU-3310UV spectrophotometer from Japan during the wavelength range of 200–800 nm, and the surface of all samples (20 × 20 × 2 mm) was polished and cleaned by Ultrasonic Bath. Fourier Transform
= m1
Dwell time (h)
Crystallization temperature (°C)
Dwell time (h)
PX-1 PX-2 PX-3 PX-4 PX-5 PX-6 P2-7 P3-7 PY-7 PX-8 PX-9 PX-10
700 700 700 700 700 700 700 700 700 720 720 720
6 6 6 6 6 6 6 6 6 6 6 6
720 730 740 745 750 755 760 760 770 790 810 870
2 2 2 2 2 2 2 2 1.5 1.5 1.5 1.5
a
0 /(m1
m2 )
(3)
where, ρ0 is the density of the distilled water, m1 is the weight of the sample in the air, m2 is the weight of the sample in the distilled water. The chemical stability of the samples after erosion in alkaline (5% NaOH) or acidic solutions (10% HCl) for 8 h were also tested with the room temperature solution immersion method with an error of ± 0.02 g/cm3. The mass loss is calculated according to the following formula:
C = 100(G1
G2 )/S H
(4)
where, G1 is the weight of sample before soaking, G2 is the weight of sample after soaking, S is the surface area of sample before soaking, H is the soaking time.
Table 2 Heat treatments applied to LAS glass samples and their nomenclatures.a Nucleation temperature (°C)
(2)
= 3P L /2a h2
2.2. Analytical methods
Sample name
(1)
D = K /B cos
The initial materials of parent glass were analytical grade reagents SiO2, Li2CO3, Al2O3, TiO2, ZrO2, (NH4)2HPO4, MgO, and Sb2O3. The exact compositions in wt% were given in Table 1. The parent glass 100 g in weight nucleated by a mixture of TiO2, ZrO2 and P2O5 were melted in alumina crucibles at 1600–1620 °C for 2 h at a heating rate of 5 °C/min, then poured onto a preheated stainless-steel plate by an annealing around 580 °C for 2 h intended to eliminate the stresses. The addition of MgO oxides is in order to improve the melting properties while lowering the cost of material by partially replacing Li2O. Moreover, Sb2O3 was used as a refining agent which can enhance the parent glass performance by eliminating air bubbles. The thermal treatments of nucleation and crystallization depend on the characteristic glass temperatures such as glass transition temperature (Tg) and crystallization maximum temperature (Tp), were determined by Differential Scanning Calorimetry (DSC, Netzsch 404PC, Germany) thermograms. DSC curves were recorded in air at heating rates (10 °C/min) up to the maximum temperature of 1200 °C, and the measurement error is ± 2 °C. The details of thermal treatments are listed in Table 2.
3. Results and discussions 3.1. Crystallization behavior of the glass Fig. 1 shows the curves of the DSC analysis of parent glass prepared with different ratio of nucleating agent, it is noted that the temperature of exothermic peaks associated with the crystallization temperature (Tp) decreases first and then increases with the increase of P2O5 content in compound nucleating agents. From P2 to P6 samples, the temperatures of exothermic peak are 885 °C,874 °C, 860 °C, 846 °C and 867 °C, respectively. It indicates that a certain range of P2O5 used as a nucleating agent can lower crystallization peak temperature and promote the crystallization process of LAS glass, meanwhile, the crystallization peak
Note: X could be number 2,3,4,5 and 6. Y can be 3,4 and 5. 2
Journal of Non-Crystalline Solids 521 (2019) 119486
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Fig. 1. DSC curves of glass sample with different P2O5 content.
temperature reaches the lowest when the addition P2O5 is 5 wt%. The reason for the variation tendency may be the different effects of P2O5 in glass, on the one hand, it can increase the stability of the structure by combining with (AlO4)5− and entering into silica network, thus has a reinforcement effect on network, finally inhibiting crystallization process, on the other hand, it can destroy silica tetrahedron and promote phase separation due to high coordination number, thus promote the crystallization [16]. When P2O5 content is less than 5 wt%, the latter plays a major role and promote the crystallization process. With the P2O5 content continuously to increasing, the effect of network reinforcement takes up more important role than phase separation, then having negative effect on crystallization process, so P6 sample has a higher crystallization temperature than P5 sample, as shown in Fig. 1. As revealed in Fig. 1, the variation trend of glass transition temperature (Tg) is same as Tp, first decreasing and then increasing. The value of Tg can obtain further confirmation in diagram of DSC and thermal expansion curves of parent glass, and only the P6 sample is shown as an example in Fig. 2 due to the similarity. The values of Tg and softening temperature (Tf) are obtained separately and they are about 685 °C, 746 °C, respectively. In generally, the nucleation temperature is identified as the range of from Tg to Tg + 50 °C, and less than Tf. Therefore, the optimum nucleation temperature of the parent glass is between 685 °C and 735 °C. Furthermore, according to the exothermic peak temperature shown in Fig. 1, a certain reference value of
crystallization temperature can be obtained. After some tests on the basis of the dates, the heat treatment system is determined finally, summarized in Table 2. 3.2. XRD analysis Glass ceramic powders formed from the parent glass after different heat treatments were determined by XRD, Fig. 3 shows the diffraction patterns of P2, P3, P4, P5 and P6 samples. On the whole, when the samples began to crystallize at low crystallization temperature, the main crystallization phase of the glass-ceramics is β-quartz and the lowest temperatures at which diffraction peaks were observed of the samples (P2, P3, P4, P5 and P6) are 745 °C, 740 °C, 730 °C, 720 °C and 730 °C, respectively, decreasing first and then increasing which is consist with the variation trend of Tp in DSC diagram. Then as the crystallization temperature rises, the relative amount of β-quartz also increases gradually, especially when crystallization temperature is 745 °C, the XRD patterns of all samples have well defined lines, shrill peak shapes and high degree of crystallinity, indicating the nucleating agents by a mixture of TiO2, ZrO2 and P2O5 have effective influence on crystallization at low crystallization temperatures. Finally, when the crystallization temperature continue to rise to 870 °C, the main crystal phase is basically transformed into β-spodumene. In term of single sample, such as Fig. 3(d) diagram, it shows that the main crystal phase is β-quartz at low crystallization temperatures by comparison with patterns of the standard β-quartz, but it appears an additional peak at 2θ ≈ 30° which corresponds to reflection by (111) plane of ZrTiO4 [17]. And with the increase of temperature, the shape of peak at 2θ ≈ 30° becomes shriller which reveals the more obviously formation of ZrTiO4 phase. Fig. 4 shows the grain size-crystallization temperature curves simulated by four or two different grain sizes in the sample with different P2O5 content and gives the slopes of simulated curves by line fitting in Origin9.0. The mean grain size is calculated by using Scherrer Formula, and the diffraction angle selected in the formula is at 2θ ≈ 26°. First, when the samples are heated at the same temperature such as 745 °C, the mean grain size of four samples (P3-4, P4-4, P5-4, P6-4) are about 69 nm, 60 nm, 53 nm and 63 nm, respectively. It reveals that with the growth in P2O5 content, the mean grain size descends at first and goes up later along, and P5 sample has the best effect on refining grain. Then, the effect of crystallization temperature on the mean grain size is shown in Fig. 4. It can be seen that the mean grain size is increased with the elevated crystallization temperature, and P5 sample has the smallest grain size, but the mean grain size of the P5 sample remains
Fig. 2. DSC and thermal expansion curves of parent glass (P6 sample). 3
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Fig. 3. XRD patterns of: (a) P2, (b) P3, (c) P4, (d) P5, (e) P6 LAS glass-ceramics samples heat treated at different crystallization temperatures and (f) LAS glassceramics with a heat treatment temperature of 755 °C for 2 h.
basically unchanged in the temperature range of 740 °C to 750 °C which seems to violate the mechanism of elevated crystallization temperature promoting grain growth, but it is impossible. According to the research of Johnson [18], the nucleation process and growth process may occur simultaneously at a selected temperature because of changes in
dynamic and thermodynamic conditions by modifying the composition of the parent glass. Therefore, the crystals used to calculate the mean grain size in this paper includes both those that have been nucleated and to be nucleated at elevated crystallization temperature. These crystals have been nucleated can grow with increasing temperature so 4
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Fig. 5. Raman spectra of glass-ceramics with a heat treatment temperature of 755 °C for 2 h. (the red number is the relative strengths of maximum peak per sample). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 4. The grain size-crystallization temperature curves simulated by four or two different grain sizes in the sample with different P2O5 content and the slopes of simulated curves by line fitting in Origin9.0.
of single nucleating agent or combination of two nucleating agents.
as to increase the mean grain size, while for new crystals formed by nucleation, their grain size is still small, which greatly reduces the mean grain size. Hence in a certain range of crystallization temperature, such as P5 sample at 740 °C to 750 °C, when the nucleation rate is approximately equal to the growth rate, it is possible to keep the mean grain size of P5 sample basically unchanged. Afterwards, as the temperature continues to rise, the nucleation process was gradually completed and the nucleation rate is much lower than the growth rate, so that the mean grain size of P5 sample increases rapidly. However, there are obvious differences on the slope of grain sizecrystallization temperature curves with various P2O5 content. According to Fig. 4, the slope of four curves (P3, P4, P5, P6) are 0.43, 0.70, 1.40, and 0.79, respectively, increasing first and then decreasing with the increase of P2O5 content, showing the sensitivity of grain growth will change with the crystallization temperature altered. When the P2O5 content is less than 5 wt%, the more P2O5 content, the stronger the promotion of nucleation process, and the more nucleation number, the faster the sample reaches the critical value duo to the limited total nucleation number, thus the faster the crystal grows with the elevated crystallization temperature, that is reflected in the gradual increase in the slope of curves. When the P2O5 content continues to increase to 6 wt %, the effect of P2O5 on nucleation process is weakened, it can be seen not only from a sudden increase in grain size of P6 sample, but also from a decrease in the slope of the curve. In a word, the P5 samples always obtain the smallest grain size and steady trend of change in a relatively low temperature and wide temperature range, therefore have the best effect. In order to study the detailed changes, the XRD patterns of five samples in 755 °C for 2 h are displayed in Fig. 3(f). The mean grain sizes of five samples are about 79 nm,73 nm, 66 nm, 60 nm and 71 nm, respectively, then further observations of grain morphology and size can be made in SEM(Fig. 9). The existence of ZrTiO4 in a low amount have been identified and its peak shape becomes more and more obvious with the increase of P2O5 content in Fig. 3(f). For the sake of better confirmation of presence of ZrTiO4 phase, Raman spectroscopy was carried out in Fig. 5, showing the bands at around 620 cm−1 and 789 cm−1 which corresponds to ZrTiO4 phase [19]. Thus, in the same heat treatment system, the more P2O5 content (less than 6 wt%), the more promoted the precipitation of ZrTiO4 phase which can refine grain by heterogeneous nucleation. To some extent, this shows why the effect of compound nucleating agent (TiO2 + ZrO2 + P2O5) is better than that
3.3. Structure and properties of glass-ceramics 3.3.1. Raman spectra analysis Fig. 5 demonstrates Raman spectra in the frequency range 100–1400 cm−1 of LAS glass-ceramics with various P2O5 content. In all Raman spectra there are two bands of β-quartz ss, a weaker band at 1074 cm−1 that is attributed to an antisymmetric stretching vibration of SieO bond and an intensive band at 478 cm−1 that is due to bending vibrations of Si-O-Si bond [20]. It can be seen that the relative strengths of maximum peak are 107, 140, 200, 230, and 296, respectively, gradually increasing, explaining that with the P2O5 content continuously to increasing, the glass network structure is gradually enhanced. There are also bands connected with ZrTiO4 and AlPO4 phase. The band at about 285 cm−1 in the Raman spectrum is characteristic of the lattice vibrations of AlPO4 and at about 130 cm−1 is due to stretching vibration of isolated PO43− tetrahedron [21]. There have low and insignificant peaks in sample of P2–6, but as the increase of P2O5 content, the peak shape at 285 cm−1 and 134 cm−1 becomes more sharper, revealing the obviously formation of AlPO4 phase. However, Raman spectroscopy can only qualitatively analyze the existence of functional groups, such as PO43−, it cannot achieve the effect of 31P NMR technique in accurately analyzing the glass structure. The 31P NMR technique [22,23] can be used to distinguish the types and structures of phosphorus compounds in samples when the higher accuracy is required. Simultaneously, the bands at 620 cm−1 along with bands at 789 cm−1 confirm the formation of ZrTiO4 phase [19]. With the growth of P2O5 content, the precipitation of ZrTiO4 phase become more and more obvious due to the sharper shape of peak at 620 cm−1 and 789 cm−1, indicating P2O5 can promote the precipitation of ZrTiO4 phase. According to written records [24], it proves the ZrTiO4 phase does not enter the network structure of the stuffed β-quartz ss, but promote heterogenous nucleation to achieve grain refinement. Thus, combined with XRD and DSC analysis, it can be known that the presence of P2O5 maybe promote precipitation of ZrTiO4 phase and formation of AlPO4 phase so as to get smaller grain size, but also have the negative effect on crystallization process by enhancing glass network structure, and with the P2O5 content continuously to increasing (more than 5 wt%), the effect of network reinforcement takes up more important role. 5
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Fig. 6. Fourier-transform infrared spectroscopy of glass-ceramics with a heat treatment temperature of 755 °C for 2 h.
3.3.2. Structural study by infrared spectroscopy More information about the glass-ceramics fine structure can be acquired from FTIR spectroscopy. Fig. 6 illustrates the optical absorption of the five samples in the region of 400 cm−1-1400 cm−1. The spectrum can be divided in two ranges in the general case: one in the frequency range from 1500 cm−1 to 4000 cm−1 is not characteristic of the samples, including a wide band at about 3400 cm−1 and 1630 cm−1 connected with the presence of water as well as at about 2900 cm−1 attributed to symmetric vibration of –CH2 group, and the other in the low frequency range from 1500 cm−1 to 500 cm−1 is related to structure of the measured samples. Firstly, the band around 430 cm−1 is due to bending vibration of O-Si-O linkages [25] or the symmetric stretching vibrations of MgO6 octahedra and LiO4 tetrahedra [26]. Then, there is a weak absorption in the band between 550 cm−1 and 560 cm−1 related to the formation of the MgO4, by partially replacing Li+ with Mg2+ in the β-quartz ss due to their similar ionic radius, or hexacoordinated Al3+ ions [27]. While the band around 760 cm−1 corresponding to bending vibration of (AleOe) in [AlO4] [28] have an intensity absorption, demonstrating that aluminum atoms enter into the three-dimensional network structure of the β-quartz ss with the vast majority of [AlO4] and a small amount of hexacoordinated Al. The band at about 960 cm−1 could be assigned to vibration of the (SieOe) related with non-bridging oxygen ions. According to [27], the presence of nonbridging oxygen ions can be in keeping with the formation of hexacoordinated Al3+ ions in the vitreous residual phase, which confirms the existence of 6-fold coordinated Al3+ (AlPO4) in a more precise way. Finally, the maximum absorption band around 1000 cm−1-1100 cm−1 can be noticed in Fig. 6, its presence is related to asymmetric stretching vibrations of PeOeP groups [29] or stretching vibrations of SieOe(Si, Al) bond [30] which is characteristic of the tectosilicate in the β-quartz ss, by replacing Si with Al in the three-dimensional network structure. The IR spectra of five samples also have certain differences and variations with the P2O5 content continuously to increasing, such as around 1000 cm−1-1100 cm−1 and 950 cm−1 bands. When the band at 1000 cm−1-1100 cm−1, it can be seen that the absorption bands splits into two bands and the absorption peaks are sharper in P2-6 sample, illustrating the range of absorption is smaller, but with the growth in P2O5 content, the range of absorption get more wider, the absorption bands groups into one gradually, it may be caused by different bond strength of four Si-O-Si bond [31] or increase of PeOeP bond in [PO4]. Focus on the band around 950 cm−1 linked to Al3+, from P2–6 to P6–6, it can be seen that the bands are 946 cm−1, 948 cm−1, 952 cm−1, 957 cm−1 and 958 cm−1, respectively, gradually moving towards
higher wave number and having an increases of absorption intensity, revealing the gradually increase of Al3+ (AlPO4) content, which is consistent with Raman spectra analysis. 3.3.3. Transparency analysis The high transparency is typical characteristic of LAS glass-ceramics with β-quartz ss as main crystal phase because the grain size of the βquartz ss is generally 1/10 of the wavelength of visible light and the refractive index of crystal phase is nearly to that of glass. Fig. 7 demonstrates the visible spectral in the range of 300 cm−1–900 cm−1 of five crystallized samples with a heat treatment temperature of 755 °C, it can be learned that the P4-6 sample have maximum transparency, reaching around 84%, then followed by P5-6 sample with about 81%. With the P2O5 content continuously to increasing, the transparencies of samples show a trend of goes up first and then descends later along. As mentioned in the [32], the scattering effect of grain to light is the main factor affecting the transparency of glass-ceramics. According to Rayleigh scattering mode, the smaller the grain size, the lower the intensity of the scattering light, then the better the transparency. According to the XRD results above, the mean grain sizes of five samples are
Fig. 7. Transmittance spectra of glass-ceramics with a heat treatment temperature of 755 °C for 2 h. 6
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79 nm,73 nm, 66 nm, 60 nm and 71 nm, respectively. Therefore, the results of transparency are basically consistent with analysis of grain size. However, P4-6 sample have higher transparency than P5-6, and P6-6 sample have the lowest transparency, which may be due to excessive phase separation effect caused by P2O5 in promoting the nucleation process of glass. The strong phase separation effect could aggravate the overall inhomogeneity and even generate the opacifying effect, which lead to the decrease of transparency. Especially when the P2O5 content is more than 4%, with the increase of P2O5 content, the phase separation effect caused by P2O5 is excessively increased, resulting in the opacifying effect, and then the intensity of scattering light increases, finally the transmission of visible light decrease. But when the P2O5 content is less than 4%, with the growth in P2O5 content, the grain size decreases and the transmission increase gradually, showing that the limited phase separation effect caused by P2O5 has a positive impact on the crystallization process. From the change of transparency, it can be seen that the general trend of grain size change, and the influence of phase separation effect caused by different P2O5 content on the crystallization process, especially its negative effect, that is, the opacifying effect caused by excessive phase separation due to the excess P2O5.
the more precipitate of crystal and the higher the crystallinity. 3.3.5. Physical and chemical property analysis In order to study structural change in more precise, some performances that can intuitively reflect the law of change in three-dimensional net structure are also measured, such as bending strength, Vickers hardness, density and chemical stability. With increasing P2O5 content in LAS glass ceramics, the effect of ratio changes in the composite nucleating agent (TiO2 + ZrO2 + P2O5) on the crystallization properties are revealed in Table 3. The bending strength and hardness of the glass-ceramics depend primarily on the microstructure, especially the degree of interlacing between grains determined by the grain content and size. As shown in Table 3, with the growth in P2O5 content, the hardness of glass-ceramics keeps same pace with the variation trend of bending strength, rising first and then falling, revealing that the better performances first and then worse performances, which is consistent with the results of XRD. When the P2O5 content is less than 5 wt%, the hardness and bending strength increase gradually because the increasing of crystal content of β-quartz and decreasing of grain size would hinder the propagation of small crack and formation of large crack. However, the P6-6 samples have the lower hardness and bending strength, it may be caused by excessive phase separation effect of P2O5. When the P2O5 content is more than 5 wt%, the strong phase separation effect may cause the disorder of the glass structure in the crystallization process and aggravate the overall inhomogeneity, which leads to the decrease of performance. This can also be seen by changing in transparency in Fig. 7. In addition, the corrosion resistance is an important measure of chemical stability, depending on the type of etch and on the properties of the glass itself, such as the tightness of the network structure, as well as the gaps, pores and other defects that may occur on the surface of the glass. As shown in Table 3, with the P2O5 content continuously to increase, the variation trend of measured mass loss descends at first and then goes up later along, indicating that the effect of acid or alkaline resistance gets better first and then gets worse. In general, the closer the connection between the glass network, the higher the tightness, and the better the corrosion resistance. According to the passage above, the more P2O5 content, the closer the connection between the glass network. Thus, the corrosion resistance of P6-6 sample should be better, but its stability is worse in reality, which may be due to some surface defects by the excessive phase separation effect from P2O5. It is basically consistent with the above results of hardness and bending strength. On the whole, it is acceptable range of the mass loss, the samples all have the stable chemical properties so that not easily corroded, and the effect of acid resistance is better than alkaline resistance. Density is an important physical property, which is related not only to the composition of parent glass, but also to the precipitation degree of crystal in LAS glass-ceramics. First, the higher the degree of crystal precipitation, the lower the density because the volume increases as crystal precipitation [33]. Then, in term of composition of parent glass, the atomic mass of P is large than atomic mass of other chemical elements replaced by P, so as to get the higher density with the increase of P2O5 content. Therefore, the effect of density should be considered by two factors. As shown in Table.3, it demonstrates that the density increases with the growth in P2O5 content, which may be result from the effect of increasing density caused by quality factor is greater than that of decreasing density caused by crystallization, especially when the content of P2O5 increases from 5 wt% to 6 wt%, not only the quality of parent glass increases, but also the crystallinity decreases shown in Fig. 3(f), so the growth of density is more larger.
3.3.4. The thermal expansion coefficient The low thermal expansion coefficient (TEC) is another typical characteristic of LAS glass-ceramics with β-quartz ss because of the negative TEC of β-quartz, thus, the higher the content of β-quartz ss, the lower value of TEC. As shown in Fig. 8, curves A, and B reveals the variation tendency of TEC (30 °C–600 °C) of parent glass and glass-ceramics, respectively. The curve A shows relatively gentle trend and finite change, indicating that the influences of P2O5 content on TEC of parent glass is limited. While curve B changes greatly with the of P2O5 content continuously to increasing, and the values of TEC are 2.0316 × 10−6/°C, 1.625 × 10−6/°C, 1.454 × 10−6/ °C, 1.022 × 10−6/°C and 1.3402 × 10−6/°C, respectively, descends at first and then goes up later along. As we all know, the TEC of glass-ceramics is related to microstructure and component, such as crystallinity, main crystal phase types and the ratio of volume fraction of main crystal phase with the residual glass phase [9]. As shown in Fig. 3(f), the β-quartz ss are the main crystal phase of five samples, and the crystallinity are 88.7%, 89.3%, 91.2%, 93.5% and 90.5%, respectively, calculated by Jade.6.0, demonstrating that with the growth in P2O5 content, the content of β-quartz ss increases first and then decreases. The result keeps pace with the TEC analyzes, which confirms that the higher the content of P2O5 (less 5 wt%),
3.3.6. SEM analysis Fig. 9 show the microstructure of the samples with a heat treatment temperature of 755 °C for 2 h, it can be seen that the shape of grain is spherical, which revealing that the main crystal phase is β-quartz solid solution rather than β-spodumene with the shape of striped. In addition
Fig. 8. Thermal expansion coefficient(30 °C–600 °C) of parent glass and glassceramics samples doped with different amount of P2O5. 7
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Table 3 TEC, bending strength, Vickers hardness, density, acid and alkali resistance of glass ceramics. Name
Bending strength (MPa)
Vickers hardness (GPa)
Density (g/cm3) ( ± 0.005)
Mass loss (Acid or Alkali) (×10−5 g/cm−2h) ( ± 0.02)
TEC (×10−6/°C, 25–600 °C)
P2-6 P3-6 P4-6 P5-6 P6-6
96.4 ± 0.4 101.2 ± 0.5 104.9 ± 0.3 109.1 ± 0.4 97.5 ± 0.3
6.38 6.58 6.95 7.01 6.68
2.516 2.519 2.523 2.528 2.539
6.31 6.72 5.82 5.21 5.76
2.032 1.625 1.454 1.022 1.340
± ± ± ± ±
0.02 0.03 0.03 0.02 0.04
to the spherical particles, there are also some fine nanoparticles, which may be related to the presence of ZrTiO4 phase and AlPO4 phase, that is especially evident in Fig. 9(d). They can be used as the carrier of heterogeneous nucleation so that promoting nucleating process and providing smaller grains by reducing the degree of supercooling. The existence of ZrTiO4 phase and AlPO4 phase also can be observed in Raman spectra analysis. In SEM photo (a), when the P2O5 content is 2 wt%, the size of the grain is large, the spacing between the crystals is wide and the arrangement is loose, but as the content continuously to increasing (less than 5 wt%), the size of the grains is getting smaller and the crystals are getting closer together. Especially when the P2O5 content is 5 wt%, the P5–6 sample have the smallest grain size and the most
or or or or or
10.2 9.78 8.37 7.31 8.92
± ± ± ± ±
0.136 0.075 0.081 0.101 0.091
closely aligned as shown in Fig. 9(d, f), thus have the best performance. But when the content continuously to increase to 6 wt%, it gets bigger grains. The variation trend of crystal size is same as the calculation results of XRD, which confirms that a certain amount of P2O5 can play the role of promoting crystallization procession and improving the performance by refining the grain. 4. Conclusion The crystallization mechanism, microstructure and performances of Li2O-Al2O3-SiO2 system glass ceramic containing complex nucleating agents (TiO2 + ZrO2 + P2O5) are researched. When the parent glass
Fig. 9. SEM images: (a) P2-6, (b) P3-6, (c) P4-6, (d) P5-6, (e) P6-6 and (f) P5-6 of LAS glass-ceramics with a heat treatment temperature of 755 °C for 2 h. 8
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was melted by using TiO2, ZrO2 and P2O5 in a ratio of 2:2:5 as nucleating agent, the sample can obtain the smallest grain size and steady variation tread of grain size in a relatively low temperature and wide temperature range (740 °C–750 °C), thus have the best effect. Moreover, the detailed change of performance and structure in samples with a heat treatment temperature of 755 °C for 2 h were studied. Such as the TEC, bending strength, Vickers hardness, density and the mass loss of Acid (Alkali) resistance of P5–6 sample are 1.022 × 10−6/°C (30–600 °C), 109 MPa, 6.95 GPa, 2.528 g/cm3, 5.21(7.31) × 10−5 g/cm−2 h, respectively. The influence of P2O5 on mechanism as following:
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1) The presence of P2O5 maybe promote precipitation of ZrTiO4 phase and formation of AlPO4 phase, so as to promote heterogenous nucleation by phase separation effect to get smaller grain size. 2) The presence of P2O5 also have the negative effect on refining grain size by enhancing glass network structure. When the P2O5 content is more than 5 wt%, the effect of network reinforcement takes up more important role, so as to get the bigger grain size. 3) when the P2O5 content is less than 5 wt%, with the P2O5 content continuously to increasing, the sensitivity of grain growth to crystallization temperature increases gradually, that is the more P2O5 content, the stronger the promotion of nucleation process, thus the faster the crystal grows with the elevated crystallization temperature. But while P2O5 content is more than 5 wt%, it could hinder crystallization process due to the strong network enhancement by P2O5 and could have the poor performance because of excessive phase separation effect of P2O5. Conflict of interest statement We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled. Acknowledgments This work has been supported by the project of the National Natural Science Foundation of China (Nos. 51672310, 51272288, 51172286). References [1] R.D. Rawlings, J.P. Wu, A.R. Boccaccini, Glass-ceramics: their production from wastes-a review, J. Mater. Sci. 41 (2006) 733–761. [2] P.F. James, Glass-ceramic: new compositions and uses, J. Non-Cryst. Solids 181 (1995) 1–15. [3] P.A. Tick, N.F. Borrelli, I.M. Reaney, Relationship between structure and transparency in glass-ceramic materials, Opt. Mater. 15 (1) (2000) 81–91. [4] G.H. Beall, L.R. Pinckney, Nanophase glass-ceramics, J. Am. Ceram. Soc. 82 (1) (1999) 5–16.
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