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The forming region and mechanical properties of SiO2-Al2O3-MgO glasses
Journal of Non-Crystalline Solids xxx (xxxx) xxx–xxx
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The forming region and mechanical properties of SiO2-Al2O3-MgO glasses Ren Gaoa, Huanping Wanga,⁎, Qingong Zhua, Qinghua Yanga, Xingguo Suna, Bingpeng Lia, Shiqing Xua,⁎, Xianghua Zhangb a b
College of Materials Science and Engineering, China Jiliang University, Hangzhou 310018, PR China Laboratory of Glasses and Ceramics, UMR 6226 CNRS-University of Rennes, Rennes Cedex 35042, France
A R T I C L E I N F O
A B S T R A C T
Keywords: SiO2-Al2O3-MgO glasses Forming regions Bending strength Compression strength Optical band gap
The glasses of 93.9% (xSiO2-yAl2O3-zMgO)-5% CaO-1% B2O3-0.1% Fe2O3 were prepared, and the relationship between mechanical properties and structural stability were characterized by means of Raman spectroscopy and optical band gap values. The glass forming region is found to be x = 50–70%, y = 10–25% and z = 15–32%. As x = 65%, y = 10% and z = 25% (SAM-4), the investigated glass possesses the optimum volume density, oxygen packing density, optical band gap, banding strength, compression strength and compression modulus, which are 2.517 g/cm3, 77.047 mol/l, 3.56 eV, 77.04 MPa, 202.74 MPa and 106.70 GPa, respectively. Meanwhile, starting from the representative point of SAM-4 to radiate around, the volume density, oxygen density, Raman intensity and mechanical properties of the glasses are all decreasing constantly, and the optical band gap of the glasses is increasing on the contrary. Moreover, the optical band gap value and Raman spectroscopy of SAM-4 all prove that the number of oxygen bonds in the bridge reach the maximum and the highest structural stability is achieved, which further shows that it is an important reason why its mechanical properties is significantly improved.
1. Introduction Over the past decades, the high strength and high modulus glass fibers are widely used in military industry, wind power generation, medical and other fields [1,2]. Now the SiO2-Al2O3-MgO glass fibers, as a kind of high strength and modulus glass materials, have been received more and more attention in the field of fan blade manufacturing [3], and the strength representative of fan blade materials on the global market is mainly United States S-2 glass [4], Japanese T glass [5], Russia BM glass [6] and the series of Chinese HS glass [7]. The tensile strength of the S-2, T, BM and HS glass fibers are 4600, 4500, 4450 and 4650 MPa, respectively, and their monofilament modulus are namely 75, 70, 68 and 80 GPa, whose properties are relatively the best in the all glass fibers [4,5]. However, the present study has not discussed the composition influence on the mechanical properties of SiO2-Al2O3-MgO glass fibers and the effect on the structural stability of the SiO2-Al2O3-MgO glasses. The mechanical properties and structural stability of glass fibers are closely related to the composition of the glasses. For example, Ulrike et al. investigated the effect of different glass compositions within the CaO-Al2O3-SiO2 system on its elastic properties, and found that the density and Young's modulus of CaO-Al2O3-SiO2 glasses increase with the content of SiO2 increasing from 60.5 to 63 wt% and decrease with ⁎
the content of CaO increasing between 21.4 and 25.4 wt% [8–11]. Moreover, Nicolas et al. discussed the influence of TiO2 and Nb2O5 content on the optical and mechanical properties of the SiO2-NaO-BaO glass fibers, and draw the conclusion that the high linear refractive index and the increase of the hardness for the increasing oxygen atom concentration are responsible for the formation of a denser glass network dominated by corner linked NbO6 and TiO6 octahedral [12–15]. Wang et al. founded the high Bi2O3 content, which is from 25–36 mol%, could improve the structural stability of the Bi2O3-SiO2Al2O3 glass fibers [16–19]. The addition of CaO can provide a large degree of polarization of the oxygen ion to ease the oxygen ion competition in silicon and aluminum, thereby reducing the possibility of glass crystallization [20]. Meanwhile, the addition of B2O3, due to the presence of the boron oxide triangle under the high temperature condition, can reduce the high temperature viscosity of the glasses, thus increasing the fluidity of the glasses [21]. And the Fe2O3 doped the silicate glasses, which as a modified colorant, plays a role in clarifying and defoaming of the glass fluid [22]. Based on the relatively excellent properties of the SiO2Al2O3-MgO glass and little research on its composition and structural stability, we would discuss the forming region of 93.9% (xSiO2-yAl2O3zMgO)-5% CaO-1% B2O3-0.1% Fe2O3 glasses and its mechanical properties and structural stability by changing the value of x, y and z.
Corresponding authors. E-mail addresses: [email protected] (H. Wang), [email protected] (S. Xu).
http://dx.doi.org/10.1016/j.jnoncrysol.2017.05.004 Received 6 December 2016; Received in revised form 26 April 2017; Accepted 10 May 2017 0022-3093/ © 2017 Elsevier B.V. All rights reserved.
Please cite this article as: Gao, R., Journal of Non-Crystalline Solids (2017), http://dx.doi.org/10.1016/j.jnoncrysol.2017.05.004
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Table 1 The chemical composition of SiO2-Al2O3-MgO glasses (mass fraction/%). Sample
(x)SiO2
(y)Al2O3
(z)MgO
CaO
B2O3
Fe2O3
SAM-1 SAM-2 SAM-3 SAM-4 SAM-5 SAM-6 SAM-7 SAM-8 SAM-9 SAM-10 SAM-11 SAM-12 SAM-13 SAM-14 SAM-15 SAM-16 SAM-17 SAM-18 SAM-19 SAM-20 SAM-21 SAM-22 SAM-23 SAM-24 SAM-25
65 65 65 65 60 60 60 60 55 55 55 55 55 53 50 50 53 70 70 70 70 75 75 75 75
25 20 15 10 25 20 15 10 30 25 20 15 10 27 25 20 15 20 15 10 5 20 15 10 5
10 15 20 25 15 20 25 30 15 20 25 30 35 20 25 30 32 10 15 20 25 5 10 15 20
5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1
Fig. 1. The forming region of 93.9% (xSiO2-yAl2O3-zMgO)-5% CaO-1% B2O3-0.1% Fe2O3 glasses.
transducer and micro cracks on the surface of the specimens may influence the accuracy of mechanical property indices. Therefore, we carried out high precision grinding and polishing on glass surface, and the results of the above tests used the average of the three samples. To quantitatively evaluate the errors, the deviation of bending strength, compression strength and compression modulus are reflected through the standard deviation error. The equation is expressed as below [23,24]:
2. Experiment procedures
σ=
Glass samples of composition 93.9% (xSiO2-yAl2O3-zMgO)-5% CaO1% B2O3-0.1% Fe2O3 (x = 50–75%, y = 5–30% and z = 1 – x − y, mass fraction/%) were prepared by the traditional powder melting method. The compositions of the SiO2-Al2O3-MgO glasses are given in Table 1. The glass batch was made of SiO2, Al2O3, MgO, CaO, B2O3 and Fe2O3 with purity greater than 99.99% Aladdin chemistry. The glass were melted in platinum crucibles in an electric furnace at 1650 °C for 5 h, and the melts were stirred occasionally by using a fused quartz stirring rod to make the contents more homogenously dispersed and to decrease the amount of bubbles trapped inside. Then the SiO2-Al2O3MgO glasses were immediately placed into an electric annealing furnace for 2 h at 900 °C and then cooled to room temperature at 2 °C/min. Eventually the SiO2-Al2O3-MgO glasses forming region was determined by the X-ray diffraction. The different components of the SiO2-Al2O3-MgO glasses were cut into a number of similar strips and flakes. The dimension for the measuring the bending strength was 30.00 × 3.00 × 3.00 mm (the strips), and the size for the measuring compression strength and modulus was 10.00 × 10.00 × 2.00 mm (the flakes). Volume density of the samples was measured by the conventional Archimedes principle using distilled water. The transmission spectra of the SiO2-Al2O3-MgO glasses were recorded at room temperature using a fiber optics UV–vis spectrometer (Model-AVASPEC 3648) in the range of 200–800 nm. Meanwhile, Raman measurements were carried out using the 785 nm line of the Ar+ laser as an excitation source operating at 1.0 W power. The measurements were done with a DILOR XY triple spectrometer, equipped with an 1800 g/mm holographic gratings and CCD detector cooled by liquid N2. The measurements were performed in backscattering geometry under an Olympus microscope with ×100 objective and confocal entrance optics (confocal hole 880 μm, entrance slit 180 μm) in multi-window mode. The measuring time was 600 s per spectral window. The bending strength was measured with the WDW-2E universal testing machine. Meanwhile, the compression strength and modulus were measured with the CMT5105 electromechanical universal testing machine. Several factors, such as multiple internal reflections with the
1 N−1
N
∑ Xi − X2 i=1
(1)
3. Results and discussion 3.1. Glass forming region The final forming region of the glasses is characterized by ternary phase diagrams, as shown in Fig. 1, which is obtained by the XRD patterns in Fig. 2. It is found that sample 2, 3, 4, 5, 6, 7, 10, 11, 12, 15, 16, 17, 18, 19 and 20 could be formed glasses, and sample 1, 8, 9, 13, 14, 21, 22, 23, 24 and 25 were appearing to crystallization or formed non-glassy state. Thus, the forming region of SiO2-Al2O3-MgO glasses is designated that SiO2 content is between 50 and 75%, Al2O3 content is between 10 and 25% and MgO content is between 10 and 32%, which is within the area of the blue triangle. Meanwhile, the rest of the area is not the forming zone and tends to crystallize. These results indicated that the forming region of 93.9% (xSiO2-yAl2O3-zMgO)-5% CaO-1% B2O3-0.1% Fe2O3 glasses is x = 50–70%, y = 10–25% and z = 15–32%. Fig. 3 shows the differential thermal analysis of the SiO2-Al2O3-MgO glasses, from which we can see that the glass transition temperature (Tg) is between 904 °C and 960 °C. So the annealing temperature of the glass is determined at 900 °C. 3.2. Raman spectra and optical band gap The Raman spectra of the SiO2-Al2O3-MgO glasses taken at room temperature have been shown in Fig. 4, and the Raman intensity of the SiO2-Al2O3-MgO glasses is characterized in Fig. 5. From the above two Figures, the spectra are normalized to have the same area in the range 200–1550 cm− 1 and the SAM-4 (x = 65%, y = 10% and z = 25%) has the maximum peak value at 470 cm− 1, 1020–1060 cm− 1 and 1350 cm− 1. These results indicate that the SAM-4 has the most internal bridge oxygen bonds, therefore it possesses the most stable structure. It is because that the bridge oxygen bond react the glass structure of the tightness and structural stability to a certain extent [25]. Meanwhile, the strong and broad band at 450–475 cm− 1 arises from the symmetric banding vibration of SieOeSi, and the high-frequency band at about 2
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Fig. 4. The Raman spectra of different compositions SiO2-Al2O3-MgO glasses.
Fig. 5. The Raman intensity values of the SiO2-Al2O3-MgO glasses at 1350 cm− 1. Fig. 2. The XRD patterns of different compositions SiO2-Al2O3-MgO glasses.
Fig. 6. The optical transmission of the SiO2-Al2O3-MgO glasses. Fig. 3. The differential thermal analysis of SiO2-Al2O3-MgO glasses.
transforming the Eqs. (2) and (3) [27], and the optical band gap Eopt is estimated with the interception on horizontal axis by extrapolating the linear plot to zero coordinate. The Eopt of the SiO2-Al2O3-MgO glasses are shown in Table 2.
1350 cm− 1 arises from optic-like telescopic vibration of O]Si]O antiasymmetric, which are all consistent with the number increase of the oxygen bonds within the glasses [26]. The transmittance spectra of different components glasses were characterized in Fig. 6. Based on the results from Fig. 6, the linear relationship between (αhc/λ)2 and Energy are shown in Fig. 7 by
α= 3
−ln T t
(2)
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Fig. 7. The linear fitting graph of optical transmission of the SiO2-Al2O3-MgO glasses.
Fig. 8. The optical band gap value of the SiO2-Al2O3-MgO glasses.
[28,29]. Fig. 8 also shows that the optical band gap of the glasses is decreasing with the content of Al2O3 increasing. It is because that the Al2O3 has a wide band gap. With the increase of the content of Al2O3, the defect of the glasses will continue to increase and more energy with electrons will be absorbed, which will increase the optical band gap of the glasses, and these results are similar with Barajas and Iordanova et al. [30,31]. The effect of the content of MgO on the optical band gap of the glasses is similar to the content of SiO2. In Fig. 5, from the point of SAM-4 to the surrounding divergence, whether the content of MgO rises or falls, the Raman intensity are decreasing, which leads the network structure of the glasses more loosely and increases the optical band gap of the glasses. Thus, it will decrease the structural stability of the glasses further.
Table 2 The cut-off wavelength and the optical bad gap of the SiO2-Al2O3-MgO glasses. Sample
λcut-off (nm)
Eopt (eV)
SAM-2 SAM-3 SAM-4 SAM-5 SAM-6 SAM-7 SAM-10 SAM-11 SAM-12 SAM-15 SAM-16 SAM-17 SAM-18 SAM-19 SAM-20
427.5 417.6 415.5 416.5 443.5 436.5 431.6 420.6 431.6 452.5 432.5 447.5 431.6 430.5 428.6
3.72 3.62 3.56 3.94 3.72 3.85 4.17 4.10 3.95 4.18 4.11 4.27 3.85 3.83 3.82
3.3. Density and oxygen packing density Density is explained in terms of a competition between the masses and size of the various structural units present in the glass, which is related to how tightly the ions and ionic groups are packed together in the structure. Meanwhile the density closely related to the oxygen packing density. The values of density measured for the samples using Archimedes principle are given in Table 3, and the molar oxygen atomic packing density (OPD) is calculated using the formula [32]:
where α is the diffuse emission absorption coefficient, T is transmittance (%) and t is thickness of glasses.
αhv = Ahv−Eg n
(3)
where α is diffuse emission absorption coefficient, h is Planck's constant, v is frequency, Eg is the optical band gap and n is a constant band gap and n is a constant associated with different types of electronic transitions (n = 1/2, 2, 3/2 or 3 for direct allowed, indirect allowed, direct forbidden and indirect forbidden transitions, respectively). Then according to the results of the above characterizations, the optical band gap values of the SiO2-Al2O3-MgO glasses are shown in Fig. 8. As revealed in Fig. 8, the SAM-4 possesses the minimum value, which is 3.56 eV. Taking the point of SAM-4 as the center to the periphery, the optical band gap increases with the increase or decrease of the content of SiO2. From point of the SAM-4 to around the divergence, since the Si]O]Si peak continues to weaken which was shown in Fig. 5, the number of oxygen bridge bond in the internal of glasses is decreasing constantly, which leads the optical band gap continue to increase and decline the structural stability of the investigated glasses. Variation in the optical band gap is dependent of the structural modifications of the glass. Optical band gap characterizes the degree of strength that electrons are bound to the nucleus, namely the minimum energy required to create an intrinsic excitation, and the internal electrons maintain the structural of stability by means of their circular motion without leaving the atomic nucleus. The smaller the energy required, the smaller the energy consumption of the atomic structure maintained, so the glasses possess better structural stability
Table 3 The volume density and oxygen packing density of the glasses.
4
Sample
Number of oxygens C (number) [31]
Molecular weight M (g/ mol)
Volume density ρ (g/cm3)
Oxygen packing density (mol/ l)
SAM-2 SAM-3 SAM-4 SAM-5 SAM-6 SAM-7 SAM-10 SAM-11 SAM-12 SAM-15 SAM-16 SAM-17 SAM-18 SAM-19 SAM-20
2.005 1.911 1.817 2.052 1.958 1.864 2.005 1.911 1.817 1.958 1.864 1.798 2.052 1.958 1.864
65.157 62.261 59.366 67.122 64.229 61.333 66.194 63.299 60.404 65.265 62.370 60.032 66.086 63.191 60.296
2.401 2.453 2.517 2.319 2.304 2.400 2.231 2.289 2.311 2.212 2.257 2.156 2.336 2.356 2.366
73.885 75.296 77.047 70.894 69.526 73.548 67.578 69.111 70.241 66.365 67.760 64.590 72.534 73.006 73.151
± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.011 0.009 0.015 0.017 0.013 0.025 0.016 0.014 0.027 0.016 0.008 0.024 0.012 0.011 0.017
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Table 4 The mechanical properties of the glasses. Sample
B (MPa)
SAM-2 SAM-3 SAM-4 SAM-5 SAM-6 SAM-7 SAM-10 SAM-11 SAM-12 SAM-15 SAM-16 SAM-17 SAM-18 SAM-19 SAM-20
76.05 76.66 77.04 65.96 64.05 73.66 57.65 63.55 65.82 55.48 63.12 34.15 68.15 69.53 70.22
± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
σ (MPa) 3.56 5.79 4.67 7.33 3.68 8.09 4.57 1.99 4.69 4.02 2.64 6.48 4.67 1.75 4.59
192.87 197.98 202.73 184.00 168.34 187.87 159.61 164.12 180.96 155.81 163.51 146.99 187.45 187.55 189.15
± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
EC (GPa) 3.77 4.41 1.89 5.36 6.59 9.09 3.12 7.33 5.21 4.89 9.15 6.98 5.27 2.54 10.36
101.51 ± 4.74 104.20 ± 2.33 106.70 ± 8.04 96.84 ± 4.67 93.52 ± 2.69 98.88 ± 3.26 88.67 ± 4.69 91.18 ± 4.15 95.25 ± 1.98 86.56 ± 3.57 90.84 ± 2.49 81.66 ± 6.58 98.66 ± 3.17 98.71 ± 4.09 99.55 ± 7.49
Fig. 9. The oxygen packing density and volume density of the SiO2-Al2O3-MgO glasses.
⎛ρ⎞ OPD = 1000C ⎜ ⎟ ⎝M⎠
(4)
where ρ, M and C is density, molar mass fraction and molar oxygen atom number, respectively. According to Table 3, the volume density and oxygen packing density of different SiO2-Al2O3-MgO glasses are shown in the Fig. 9. The volume density and oxygen packing density of the glasses are varying from 2.156 to 2.517 g/cm3 and 64.590 to 77.047 mol/l, respectively. Among all the samples, the SAM-4 possesses the maximal values, which are 2.517 g/cm3 and 77.047 mol/l, individually. These results from the two variable quantities show the similarly trend, which is found to be that starting from the representative point of SAM-4 to radiate around, the volume density and oxygen packing density are all decreasing constantly. On one hand, according to Figs. 5 and 8, when starting from the representative point of SAM-4 to radiate around, the Raman intensity of the glasses are decreasing and the optical band gap values are increasing, which mean the glasses decrease the number of bridge oxygen bonds and reduce the structural stability, thus affecting the volume density and oxygen packing density of the glasses. On the other hand, the high SiO2 and low Al2O3 content increase the cohesion forces inside the network of the glass and thereby the network compactness of glassy matrix increases in the present system. This seems to be in agreement with a report from 1998, based on 80 glass composition, which has pointed out that the density of Na2O-Al2O3-SiO2 glass is almost dependent on the concentration of SiO2 and Al2O3 [33,34]. However, when the content of SiO2 is above 65%, the volume density and oxygen packing density of the glasses will drop rapidly. It is because that excess silicon will lead to SiO2-Al2O3-MgO glasses contains too much free oxygen, which will lead the glasses structure loose [35], thus affecting the density and oxygen packing density of the investigated glasses.
Fig. 10. The bending strength of the SiO2-Al2O3-MgO glasses.
According to Table 4, the bending strength of the investigated glasses with the change content of SiO2, MgO and Al2O3 is characterized as shown in Fig. 10. It reveals that the SAM-4 glass has the largest bending strength among all the samples, which is 77.04 MPa. Moreover, starting from the representative point of SAM-4 to radiate around, the bending strength of the glasses are continuing to decrease. It is because that, as the SAM-4 point around to disperse, the volume density and oxygen packing density are gradually decreasing, which will reduce the compactness of the glasses. At the same time, from Figs. 5 and 8, they show the reasons for the changes in the structure of the glasses, which are result in the change of the bending strength. Due to the decrease of Raman intensity and increase of optical band gap, the number of bridge oxygen bond decrease and the structure stability of the investigated glasses decrease substantially. Then it will decrease the bending strength of the glasses. Moreover, as the content of SiO2 is decreasing, the structural stability of the glasses is reducing fast. This is because that the volume of [AlO4] is much bigger than [SiO4], and the structure of the investigated glasses tends to be unstable and will reduce the bending strength of the investigated glasses [38]. Over all, as diverging from the sample 4 point to the periphery, the bending strength changes the most obviously with the change of the content of SiO2, and the content of MgO and Al2O3 have a relatively small impact on the bending strength of the glasses. The compression strength and the compression modulus of the investigated glasses are presented in Table 4. The compression strength and modulus of the SiO2-Al2O3-MgO glasses have been calculated according to the following equation [39].
3.4. Mechanical strength The results of bending strength experiments have been shown in Table 4. And the bending strength of the investigated glasses can be calculated by the following equation [36,37]:
B=
3FL 2bt 2
(5)
where the L, b, t, F and B is length of samples, width of samples, thickness of samples, yield stress and bending strength, respectively. 5
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Fig. 12. The compression modulus of the SiO2-Al2O3-MgO glasses.
Fig. 11. The compression strength of the SiO2-Al2O3-MgO glasses.
σ=
F bt 2
(6)
Foundation of Zhejiang Province (LZ14B010001) and the International S & T Cooperation Program of China (2013DFE63070).
Ec =
σ ε
(7)
References
where the b, t, F, σ, ε and Ec are the width of samples, thickness of samples, fracture stress, compression strength, strain and compression modulus, respectively. According to Table 4, the compression strength and compression modulus of the SiO2-Al2O3-MgO glasses with different content of SiO2, MgO and Al2O3 are characterized in Figs. 11 and 12. It is consistent with the law of the bending strength obviously, and the optimum composition points are all the SAM-4, which are 202.73 MPa and 106.70 GPa, respectively. It is because that the structural stability of the SAM-4 is the most stable, which is consistent with the bending strength of the glasses. Meanwhile, starting from the representative point of SAM-4 to radiate around, since glasses interior structure are instable, and the number of oxygen bonds in the bridge is decreased continuously, which will break its compression strength and modulus.
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4. Conclusions The composition of 93.9% (xSiO2-yAl2O3-zMgO)-5% CaO-1% B2O30.1% Fe2O3 (mass fraction/%) were investigated, and the forming region is found to be x = 50–70%, y = 10–25% and z = 15–32%, and the rest of the area are not the forming area and it turns out to be crystallization zone. As the x = 65%, y = 10% and z = 25% (SAM-4), the Raman intensity and optical band gap reach the maximum and minimum value respectively, which means the number of internal bridge oxygen bonds achieve maximal value, thus results in that the bending strength, compression strength and compression modulus reach the maximum. The bending strength, compression strength and compression modulus of the SAM-4 are 77.04 MPa, 202.74 MPa and 106.70 GPa, respectively. Starting from the representative point of SAM-4 to radiate around, the volume density, oxygen density, Raman intensity, bending strength, compression strength and compression modulus of the glasses are all decreasing constantly, and the optical band gap of the glasses are increasing on the contrary.
[21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39]
Acknowledgement This work was financially supported by the Natural Science
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The forming region and mechanical properties of SiO2-Al2O3-MgO glasses Ren Gaoa, Huanping Wanga,⁎, Qingong Zhua, Qinghua Yanga, Xingguo Suna, Bingpeng Lia, Shiqing Xua,⁎, Xianghua Zhangb a b
College of Materials Science and Engineering, China Jiliang University, Hangzhou 310018, PR China Laboratory of Glasses and Ceramics, UMR 6226 CNRS-University of Rennes, Rennes Cedex 35042, France
A R T I C L E I N F O
A B S T R A C T
Keywords: SiO2-Al2O3-MgO glasses Forming regions Bending strength Compression strength Optical band gap
The glasses of 93.9% (xSiO2-yAl2O3-zMgO)-5% CaO-1% B2O3-0.1% Fe2O3 were prepared, and the relationship between mechanical properties and structural stability were characterized by means of Raman spectroscopy and optical band gap values. The glass forming region is found to be x = 50–70%, y = 10–25% and z = 15–32%. As x = 65%, y = 10% and z = 25% (SAM-4), the investigated glass possesses the optimum volume density, oxygen packing density, optical band gap, banding strength, compression strength and compression modulus, which are 2.517 g/cm3, 77.047 mol/l, 3.56 eV, 77.04 MPa, 202.74 MPa and 106.70 GPa, respectively. Meanwhile, starting from the representative point of SAM-4 to radiate around, the volume density, oxygen density, Raman intensity and mechanical properties of the glasses are all decreasing constantly, and the optical band gap of the glasses is increasing on the contrary. Moreover, the optical band gap value and Raman spectroscopy of SAM-4 all prove that the number of oxygen bonds in the bridge reach the maximum and the highest structural stability is achieved, which further shows that it is an important reason why its mechanical properties is significantly improved.
1. Introduction Over the past decades, the high strength and high modulus glass fibers are widely used in military industry, wind power generation, medical and other fields [1,2]. Now the SiO2-Al2O3-MgO glass fibers, as a kind of high strength and modulus glass materials, have been received more and more attention in the field of fan blade manufacturing [3], and the strength representative of fan blade materials on the global market is mainly United States S-2 glass [4], Japanese T glass [5], Russia BM glass [6] and the series of Chinese HS glass [7]. The tensile strength of the S-2, T, BM and HS glass fibers are 4600, 4500, 4450 and 4650 MPa, respectively, and their monofilament modulus are namely 75, 70, 68 and 80 GPa, whose properties are relatively the best in the all glass fibers [4,5]. However, the present study has not discussed the composition influence on the mechanical properties of SiO2-Al2O3-MgO glass fibers and the effect on the structural stability of the SiO2-Al2O3-MgO glasses. The mechanical properties and structural stability of glass fibers are closely related to the composition of the glasses. For example, Ulrike et al. investigated the effect of different glass compositions within the CaO-Al2O3-SiO2 system on its elastic properties, and found that the density and Young's modulus of CaO-Al2O3-SiO2 glasses increase with the content of SiO2 increasing from 60.5 to 63 wt% and decrease with ⁎
the content of CaO increasing between 21.4 and 25.4 wt% [8–11]. Moreover, Nicolas et al. discussed the influence of TiO2 and Nb2O5 content on the optical and mechanical properties of the SiO2-NaO-BaO glass fibers, and draw the conclusion that the high linear refractive index and the increase of the hardness for the increasing oxygen atom concentration are responsible for the formation of a denser glass network dominated by corner linked NbO6 and TiO6 octahedral [12–15]. Wang et al. founded the high Bi2O3 content, which is from 25–36 mol%, could improve the structural stability of the Bi2O3-SiO2Al2O3 glass fibers [16–19]. The addition of CaO can provide a large degree of polarization of the oxygen ion to ease the oxygen ion competition in silicon and aluminum, thereby reducing the possibility of glass crystallization [20]. Meanwhile, the addition of B2O3, due to the presence of the boron oxide triangle under the high temperature condition, can reduce the high temperature viscosity of the glasses, thus increasing the fluidity of the glasses [21]. And the Fe2O3 doped the silicate glasses, which as a modified colorant, plays a role in clarifying and defoaming of the glass fluid [22]. Based on the relatively excellent properties of the SiO2Al2O3-MgO glass and little research on its composition and structural stability, we would discuss the forming region of 93.9% (xSiO2-yAl2O3zMgO)-5% CaO-1% B2O3-0.1% Fe2O3 glasses and its mechanical properties and structural stability by changing the value of x, y and z.
Corresponding authors. E-mail addresses: [email protected] (H. Wang), [email protected] (S. Xu).
http://dx.doi.org/10.1016/j.jnoncrysol.2017.05.004 Received 6 December 2016; Received in revised form 26 April 2017; Accepted 10 May 2017 0022-3093/ © 2017 Elsevier B.V. All rights reserved.
Please cite this article as: Gao, R., Journal of Non-Crystalline Solids (2017), http://dx.doi.org/10.1016/j.jnoncrysol.2017.05.004
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Table 1 The chemical composition of SiO2-Al2O3-MgO glasses (mass fraction/%). Sample
(x)SiO2
(y)Al2O3
(z)MgO
CaO
B2O3
Fe2O3
SAM-1 SAM-2 SAM-3 SAM-4 SAM-5 SAM-6 SAM-7 SAM-8 SAM-9 SAM-10 SAM-11 SAM-12 SAM-13 SAM-14 SAM-15 SAM-16 SAM-17 SAM-18 SAM-19 SAM-20 SAM-21 SAM-22 SAM-23 SAM-24 SAM-25
65 65 65 65 60 60 60 60 55 55 55 55 55 53 50 50 53 70 70 70 70 75 75 75 75
25 20 15 10 25 20 15 10 30 25 20 15 10 27 25 20 15 20 15 10 5 20 15 10 5
10 15 20 25 15 20 25 30 15 20 25 30 35 20 25 30 32 10 15 20 25 5 10 15 20
5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1
Fig. 1. The forming region of 93.9% (xSiO2-yAl2O3-zMgO)-5% CaO-1% B2O3-0.1% Fe2O3 glasses.
transducer and micro cracks on the surface of the specimens may influence the accuracy of mechanical property indices. Therefore, we carried out high precision grinding and polishing on glass surface, and the results of the above tests used the average of the three samples. To quantitatively evaluate the errors, the deviation of bending strength, compression strength and compression modulus are reflected through the standard deviation error. The equation is expressed as below [23,24]:
2. Experiment procedures
σ=
Glass samples of composition 93.9% (xSiO2-yAl2O3-zMgO)-5% CaO1% B2O3-0.1% Fe2O3 (x = 50–75%, y = 5–30% and z = 1 – x − y, mass fraction/%) were prepared by the traditional powder melting method. The compositions of the SiO2-Al2O3-MgO glasses are given in Table 1. The glass batch was made of SiO2, Al2O3, MgO, CaO, B2O3 and Fe2O3 with purity greater than 99.99% Aladdin chemistry. The glass were melted in platinum crucibles in an electric furnace at 1650 °C for 5 h, and the melts were stirred occasionally by using a fused quartz stirring rod to make the contents more homogenously dispersed and to decrease the amount of bubbles trapped inside. Then the SiO2-Al2O3MgO glasses were immediately placed into an electric annealing furnace for 2 h at 900 °C and then cooled to room temperature at 2 °C/min. Eventually the SiO2-Al2O3-MgO glasses forming region was determined by the X-ray diffraction. The different components of the SiO2-Al2O3-MgO glasses were cut into a number of similar strips and flakes. The dimension for the measuring the bending strength was 30.00 × 3.00 × 3.00 mm (the strips), and the size for the measuring compression strength and modulus was 10.00 × 10.00 × 2.00 mm (the flakes). Volume density of the samples was measured by the conventional Archimedes principle using distilled water. The transmission spectra of the SiO2-Al2O3-MgO glasses were recorded at room temperature using a fiber optics UV–vis spectrometer (Model-AVASPEC 3648) in the range of 200–800 nm. Meanwhile, Raman measurements were carried out using the 785 nm line of the Ar+ laser as an excitation source operating at 1.0 W power. The measurements were done with a DILOR XY triple spectrometer, equipped with an 1800 g/mm holographic gratings and CCD detector cooled by liquid N2. The measurements were performed in backscattering geometry under an Olympus microscope with ×100 objective and confocal entrance optics (confocal hole 880 μm, entrance slit 180 μm) in multi-window mode. The measuring time was 600 s per spectral window. The bending strength was measured with the WDW-2E universal testing machine. Meanwhile, the compression strength and modulus were measured with the CMT5105 electromechanical universal testing machine. Several factors, such as multiple internal reflections with the
1 N−1
N
∑ Xi − X2 i=1
(1)
3. Results and discussion 3.1. Glass forming region The final forming region of the glasses is characterized by ternary phase diagrams, as shown in Fig. 1, which is obtained by the XRD patterns in Fig. 2. It is found that sample 2, 3, 4, 5, 6, 7, 10, 11, 12, 15, 16, 17, 18, 19 and 20 could be formed glasses, and sample 1, 8, 9, 13, 14, 21, 22, 23, 24 and 25 were appearing to crystallization or formed non-glassy state. Thus, the forming region of SiO2-Al2O3-MgO glasses is designated that SiO2 content is between 50 and 75%, Al2O3 content is between 10 and 25% and MgO content is between 10 and 32%, which is within the area of the blue triangle. Meanwhile, the rest of the area is not the forming zone and tends to crystallize. These results indicated that the forming region of 93.9% (xSiO2-yAl2O3-zMgO)-5% CaO-1% B2O3-0.1% Fe2O3 glasses is x = 50–70%, y = 10–25% and z = 15–32%. Fig. 3 shows the differential thermal analysis of the SiO2-Al2O3-MgO glasses, from which we can see that the glass transition temperature (Tg) is between 904 °C and 960 °C. So the annealing temperature of the glass is determined at 900 °C. 3.2. Raman spectra and optical band gap The Raman spectra of the SiO2-Al2O3-MgO glasses taken at room temperature have been shown in Fig. 4, and the Raman intensity of the SiO2-Al2O3-MgO glasses is characterized in Fig. 5. From the above two Figures, the spectra are normalized to have the same area in the range 200–1550 cm− 1 and the SAM-4 (x = 65%, y = 10% and z = 25%) has the maximum peak value at 470 cm− 1, 1020–1060 cm− 1 and 1350 cm− 1. These results indicate that the SAM-4 has the most internal bridge oxygen bonds, therefore it possesses the most stable structure. It is because that the bridge oxygen bond react the glass structure of the tightness and structural stability to a certain extent [25]. Meanwhile, the strong and broad band at 450–475 cm− 1 arises from the symmetric banding vibration of SieOeSi, and the high-frequency band at about 2
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Fig. 4. The Raman spectra of different compositions SiO2-Al2O3-MgO glasses.
Fig. 5. The Raman intensity values of the SiO2-Al2O3-MgO glasses at 1350 cm− 1. Fig. 2. The XRD patterns of different compositions SiO2-Al2O3-MgO glasses.
Fig. 6. The optical transmission of the SiO2-Al2O3-MgO glasses. Fig. 3. The differential thermal analysis of SiO2-Al2O3-MgO glasses.
transforming the Eqs. (2) and (3) [27], and the optical band gap Eopt is estimated with the interception on horizontal axis by extrapolating the linear plot to zero coordinate. The Eopt of the SiO2-Al2O3-MgO glasses are shown in Table 2.
1350 cm− 1 arises from optic-like telescopic vibration of O]Si]O antiasymmetric, which are all consistent with the number increase of the oxygen bonds within the glasses [26]. The transmittance spectra of different components glasses were characterized in Fig. 6. Based on the results from Fig. 6, the linear relationship between (αhc/λ)2 and Energy are shown in Fig. 7 by
α= 3
−ln T t
(2)
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Fig. 7. The linear fitting graph of optical transmission of the SiO2-Al2O3-MgO glasses.
Fig. 8. The optical band gap value of the SiO2-Al2O3-MgO glasses.
[28,29]. Fig. 8 also shows that the optical band gap of the glasses is decreasing with the content of Al2O3 increasing. It is because that the Al2O3 has a wide band gap. With the increase of the content of Al2O3, the defect of the glasses will continue to increase and more energy with electrons will be absorbed, which will increase the optical band gap of the glasses, and these results are similar with Barajas and Iordanova et al. [30,31]. The effect of the content of MgO on the optical band gap of the glasses is similar to the content of SiO2. In Fig. 5, from the point of SAM-4 to the surrounding divergence, whether the content of MgO rises or falls, the Raman intensity are decreasing, which leads the network structure of the glasses more loosely and increases the optical band gap of the glasses. Thus, it will decrease the structural stability of the glasses further.
Table 2 The cut-off wavelength and the optical bad gap of the SiO2-Al2O3-MgO glasses. Sample
λcut-off (nm)
Eopt (eV)
SAM-2 SAM-3 SAM-4 SAM-5 SAM-6 SAM-7 SAM-10 SAM-11 SAM-12 SAM-15 SAM-16 SAM-17 SAM-18 SAM-19 SAM-20
427.5 417.6 415.5 416.5 443.5 436.5 431.6 420.6 431.6 452.5 432.5 447.5 431.6 430.5 428.6
3.72 3.62 3.56 3.94 3.72 3.85 4.17 4.10 3.95 4.18 4.11 4.27 3.85 3.83 3.82
3.3. Density and oxygen packing density Density is explained in terms of a competition between the masses and size of the various structural units present in the glass, which is related to how tightly the ions and ionic groups are packed together in the structure. Meanwhile the density closely related to the oxygen packing density. The values of density measured for the samples using Archimedes principle are given in Table 3, and the molar oxygen atomic packing density (OPD) is calculated using the formula [32]:
where α is the diffuse emission absorption coefficient, T is transmittance (%) and t is thickness of glasses.
αhv = Ahv−Eg n
(3)
where α is diffuse emission absorption coefficient, h is Planck's constant, v is frequency, Eg is the optical band gap and n is a constant band gap and n is a constant associated with different types of electronic transitions (n = 1/2, 2, 3/2 or 3 for direct allowed, indirect allowed, direct forbidden and indirect forbidden transitions, respectively). Then according to the results of the above characterizations, the optical band gap values of the SiO2-Al2O3-MgO glasses are shown in Fig. 8. As revealed in Fig. 8, the SAM-4 possesses the minimum value, which is 3.56 eV. Taking the point of SAM-4 as the center to the periphery, the optical band gap increases with the increase or decrease of the content of SiO2. From point of the SAM-4 to around the divergence, since the Si]O]Si peak continues to weaken which was shown in Fig. 5, the number of oxygen bridge bond in the internal of glasses is decreasing constantly, which leads the optical band gap continue to increase and decline the structural stability of the investigated glasses. Variation in the optical band gap is dependent of the structural modifications of the glass. Optical band gap characterizes the degree of strength that electrons are bound to the nucleus, namely the minimum energy required to create an intrinsic excitation, and the internal electrons maintain the structural of stability by means of their circular motion without leaving the atomic nucleus. The smaller the energy required, the smaller the energy consumption of the atomic structure maintained, so the glasses possess better structural stability
Table 3 The volume density and oxygen packing density of the glasses.
4
Sample
Number of oxygens C (number) [31]
Molecular weight M (g/ mol)
Volume density ρ (g/cm3)
Oxygen packing density (mol/ l)
SAM-2 SAM-3 SAM-4 SAM-5 SAM-6 SAM-7 SAM-10 SAM-11 SAM-12 SAM-15 SAM-16 SAM-17 SAM-18 SAM-19 SAM-20
2.005 1.911 1.817 2.052 1.958 1.864 2.005 1.911 1.817 1.958 1.864 1.798 2.052 1.958 1.864
65.157 62.261 59.366 67.122 64.229 61.333 66.194 63.299 60.404 65.265 62.370 60.032 66.086 63.191 60.296
2.401 2.453 2.517 2.319 2.304 2.400 2.231 2.289 2.311 2.212 2.257 2.156 2.336 2.356 2.366
73.885 75.296 77.047 70.894 69.526 73.548 67.578 69.111 70.241 66.365 67.760 64.590 72.534 73.006 73.151
± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.011 0.009 0.015 0.017 0.013 0.025 0.016 0.014 0.027 0.016 0.008 0.024 0.012 0.011 0.017
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Table 4 The mechanical properties of the glasses. Sample
B (MPa)
SAM-2 SAM-3 SAM-4 SAM-5 SAM-6 SAM-7 SAM-10 SAM-11 SAM-12 SAM-15 SAM-16 SAM-17 SAM-18 SAM-19 SAM-20
76.05 76.66 77.04 65.96 64.05 73.66 57.65 63.55 65.82 55.48 63.12 34.15 68.15 69.53 70.22
± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
σ (MPa) 3.56 5.79 4.67 7.33 3.68 8.09 4.57 1.99 4.69 4.02 2.64 6.48 4.67 1.75 4.59
192.87 197.98 202.73 184.00 168.34 187.87 159.61 164.12 180.96 155.81 163.51 146.99 187.45 187.55 189.15
± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
EC (GPa) 3.77 4.41 1.89 5.36 6.59 9.09 3.12 7.33 5.21 4.89 9.15 6.98 5.27 2.54 10.36
101.51 ± 4.74 104.20 ± 2.33 106.70 ± 8.04 96.84 ± 4.67 93.52 ± 2.69 98.88 ± 3.26 88.67 ± 4.69 91.18 ± 4.15 95.25 ± 1.98 86.56 ± 3.57 90.84 ± 2.49 81.66 ± 6.58 98.66 ± 3.17 98.71 ± 4.09 99.55 ± 7.49
Fig. 9. The oxygen packing density and volume density of the SiO2-Al2O3-MgO glasses.
⎛ρ⎞ OPD = 1000C ⎜ ⎟ ⎝M⎠
(4)
where ρ, M and C is density, molar mass fraction and molar oxygen atom number, respectively. According to Table 3, the volume density and oxygen packing density of different SiO2-Al2O3-MgO glasses are shown in the Fig. 9. The volume density and oxygen packing density of the glasses are varying from 2.156 to 2.517 g/cm3 and 64.590 to 77.047 mol/l, respectively. Among all the samples, the SAM-4 possesses the maximal values, which are 2.517 g/cm3 and 77.047 mol/l, individually. These results from the two variable quantities show the similarly trend, which is found to be that starting from the representative point of SAM-4 to radiate around, the volume density and oxygen packing density are all decreasing constantly. On one hand, according to Figs. 5 and 8, when starting from the representative point of SAM-4 to radiate around, the Raman intensity of the glasses are decreasing and the optical band gap values are increasing, which mean the glasses decrease the number of bridge oxygen bonds and reduce the structural stability, thus affecting the volume density and oxygen packing density of the glasses. On the other hand, the high SiO2 and low Al2O3 content increase the cohesion forces inside the network of the glass and thereby the network compactness of glassy matrix increases in the present system. This seems to be in agreement with a report from 1998, based on 80 glass composition, which has pointed out that the density of Na2O-Al2O3-SiO2 glass is almost dependent on the concentration of SiO2 and Al2O3 [33,34]. However, when the content of SiO2 is above 65%, the volume density and oxygen packing density of the glasses will drop rapidly. It is because that excess silicon will lead to SiO2-Al2O3-MgO glasses contains too much free oxygen, which will lead the glasses structure loose [35], thus affecting the density and oxygen packing density of the investigated glasses.
Fig. 10. The bending strength of the SiO2-Al2O3-MgO glasses.
According to Table 4, the bending strength of the investigated glasses with the change content of SiO2, MgO and Al2O3 is characterized as shown in Fig. 10. It reveals that the SAM-4 glass has the largest bending strength among all the samples, which is 77.04 MPa. Moreover, starting from the representative point of SAM-4 to radiate around, the bending strength of the glasses are continuing to decrease. It is because that, as the SAM-4 point around to disperse, the volume density and oxygen packing density are gradually decreasing, which will reduce the compactness of the glasses. At the same time, from Figs. 5 and 8, they show the reasons for the changes in the structure of the glasses, which are result in the change of the bending strength. Due to the decrease of Raman intensity and increase of optical band gap, the number of bridge oxygen bond decrease and the structure stability of the investigated glasses decrease substantially. Then it will decrease the bending strength of the glasses. Moreover, as the content of SiO2 is decreasing, the structural stability of the glasses is reducing fast. This is because that the volume of [AlO4] is much bigger than [SiO4], and the structure of the investigated glasses tends to be unstable and will reduce the bending strength of the investigated glasses [38]. Over all, as diverging from the sample 4 point to the periphery, the bending strength changes the most obviously with the change of the content of SiO2, and the content of MgO and Al2O3 have a relatively small impact on the bending strength of the glasses. The compression strength and the compression modulus of the investigated glasses are presented in Table 4. The compression strength and modulus of the SiO2-Al2O3-MgO glasses have been calculated according to the following equation [39].
3.4. Mechanical strength The results of bending strength experiments have been shown in Table 4. And the bending strength of the investigated glasses can be calculated by the following equation [36,37]:
B=
3FL 2bt 2
(5)
where the L, b, t, F and B is length of samples, width of samples, thickness of samples, yield stress and bending strength, respectively. 5
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Fig. 12. The compression modulus of the SiO2-Al2O3-MgO glasses.
Fig. 11. The compression strength of the SiO2-Al2O3-MgO glasses.
σ=
F bt 2
(6)
Foundation of Zhejiang Province (LZ14B010001) and the International S & T Cooperation Program of China (2013DFE63070).
Ec =
σ ε
(7)
References
where the b, t, F, σ, ε and Ec are the width of samples, thickness of samples, fracture stress, compression strength, strain and compression modulus, respectively. According to Table 4, the compression strength and compression modulus of the SiO2-Al2O3-MgO glasses with different content of SiO2, MgO and Al2O3 are characterized in Figs. 11 and 12. It is consistent with the law of the bending strength obviously, and the optimum composition points are all the SAM-4, which are 202.73 MPa and 106.70 GPa, respectively. It is because that the structural stability of the SAM-4 is the most stable, which is consistent with the bending strength of the glasses. Meanwhile, starting from the representative point of SAM-4 to radiate around, since glasses interior structure are instable, and the number of oxygen bonds in the bridge is decreased continuously, which will break its compression strength and modulus.
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20]
4. Conclusions The composition of 93.9% (xSiO2-yAl2O3-zMgO)-5% CaO-1% B2O30.1% Fe2O3 (mass fraction/%) were investigated, and the forming region is found to be x = 50–70%, y = 10–25% and z = 15–32%, and the rest of the area are not the forming area and it turns out to be crystallization zone. As the x = 65%, y = 10% and z = 25% (SAM-4), the Raman intensity and optical band gap reach the maximum and minimum value respectively, which means the number of internal bridge oxygen bonds achieve maximal value, thus results in that the bending strength, compression strength and compression modulus reach the maximum. The bending strength, compression strength and compression modulus of the SAM-4 are 77.04 MPa, 202.74 MPa and 106.70 GPa, respectively. Starting from the representative point of SAM-4 to radiate around, the volume density, oxygen density, Raman intensity, bending strength, compression strength and compression modulus of the glasses are all decreasing constantly, and the optical band gap of the glasses are increasing on the contrary.
[21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39]
Acknowledgement This work was financially supported by the Natural Science
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