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The impact of trivalent oxide nanoparticles on the microstructure and performance of magnesite-dolomite refractory bricks
Accepted Manuscript The impact of trivalent oxide nanoparticles on the microstructure and performance of magnesite-dolomite refractory bricks Salman Ghasemi-Kahrizsangi, Ebrahim Karamian, Ahmad Ghasemi-Kahrizsangi, Hassan Gheisari Desheikh, Ali Soheily PII:
S0254-0584(17)30193-1
DOI:
10.1016/j.matchemphys.2017.03.001
Reference:
MAC 19547
To appear in:
Materials Chemistry and Physics
Received Date: 17 January 2017 Revised Date:
25 February 2017
Accepted Date: 1 March 2017
Please cite this article as: S. Ghasemi-Kahrizsangi, E. Karamian, A. Ghasemi-Kahrizsangi, H.G. Desheikh, A. Soheily, The impact of trivalent oxide nanoparticles on the microstructure and performance of magnesite-dolomite refractory bricks, Materials Chemistry and Physics (2017), doi: 10.1016/ j.matchemphys.2017.03.001. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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The Impact of Trivalent Oxide Nanoparticles on the Microstructure and Performance of Magnesite-Dolomite Refractory Bricks Desheikh4, Ali Soheily5
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Salman Ghasemi-Kahrizsangi1*, Ebrahim Karamian2, Ahmad Ghasemi-Kahrizsangi3, Hassan Gheisari
1, 2, 4, 5-Advanced Materials Research Center, Faculty of Materials Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran.
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3- Special Alloy Company, No.27, In front of Isfahan Tile Co., Shohadaye Kashi St., IsfahanNajafabad Ave., Isfahan City, Iran.
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Corresponding author*: E-mail address: [email protected]
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Abstract: In this research, the impact of trivalent oxide nanoparticles on the microstructure and performance of the magnesite-dolomite refractory bricks was examined. Up to
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4 wt. % Fe2O3, Al2O3, and Cr2O3 nanoparticles were added to the specimens as additives. Physical and mechanical properties such as bulk density (BD), apparent porosity (AP), hydration resistance (HR), and cold crushing strength (CCS) were
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examined. XRD and SEM analysis were used to detect the ceramic phase’s formation and microstructure analysis, respectively. Results show that the use of Fe2O3, Al2O3, and Cr2O3 nanoparticles improve the physical and mechanical
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properties of the MgO-CaO materials. Also, it revealed that specimens contain Fe2O3 and Al2O3 nanoparticles improve hydration resistance through the liquid phase sintering mechanism by formation some low melting phases such as C2F(2CaO.Fe2O3), C3A(3CaO.Al2O3), and C12.A7(12CaO·7Al2O3). However the specimens contain Cr2O3 nanoparticles improve the hydration resistance through
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the solid state sintering mechanism by formation phases such as CaCr2O4 and MgCr2O4. In general, hydration resistance improvement trend of the MgO-CaO specimens includes trivalent nanoparticles is Al2O3
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Phase.
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Keywords: Nanoparticles, Trivalent, Hydration Resistance, Solid State, Liquid
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1. Introduction:
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Typically, magnesite-dolomite refractory bricks are composed of 50-80 wt. % of magnesia (MgO) [1]. Recently, magnesite-dolomite or Mag-Dol refractory bricks have been used instead of MgO-Cr2O3 and MgO-C refractory bricks [2]. There are two ways for produce magnesite-dolomite refractory bricks. The first way is using
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fused and sintered clinker of magnesite (MgCO3) and dolomite (Mg.Ca (CO3)2) as starting material for produce the magnesite-dolomite refractory bricks which would
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results in more homogenous products with more favorable properties. Another way is mixing magnesite and dolomite together and calcined them at high temperature that let to produce an in–situ Mag-Dol refractory bricks [3, 5]. These refractory bricks have a lot of advantages such as high refractoriness, good thermal shock resistance, high chemical resistance at high-temperature, thermodynamic stability
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in the presence of carbon, and an appropriate abrasion resistance. Magnesitedolomite refractory bricks are widely used in different industries such as metallurgy and cement kilns [1, 5, and 6-11]. Also, Mag-Dol refractory bricks have
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been considered to be one of the effective refractory types for processing clean steel products, due to these refractory bricks are beneficial to removing inclusions
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from molten steels [3, 5, and 6]. Magnesite-dolomite refractory bricks have become one of the attractive steel making refractories due to the increasing demands of molten steel purity, the awareness of environmental protection and resource shortage grows [4-6]. Despite of aforementioned advantageous, the use of magnesite-dolomite refractory bricks has been restricted due to their trend to hydration when exposed to the humid atmosphere [1-6, 12-14]. Some researcher reported that physical properties of magnesite-dolomite refractory bricks could be improved by using pitch, tar, flake, and vein graphite minerals [2, 5]. Also, the
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hydration resistance of Mag-Dol refractory bricks can be improved by surface phosphate (H3PO4) coating or by treating in a CO2atmosphere which leads to cover the surface of CaO grain by formation of a dense layer (CaCO3) and protect CaO
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grain from hydration [15]. Several researcher examined the improvement of hydration resistance of magnesite-dolomite refractory bricks through the addition of different oxide additives, such as V2O5 [16], CuO [17], FeTiO3 [18], La2O3 [19, 20], TiO2 [2], Ce2O [8, 20], ZrO2 [6,10, and 13], NiO [21], BaO [22],CaF2 [23], talc
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[24], and Fe2O3 [1, 3, 5, 6, 9, 25, and 29]. Recently, several researchers started to engineer the quality of the refractory bricks and castables by using Nano-sized
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materials in the composition due to the reported benefits of adding nanoparticles (such as oxides and non-oxides) to ceramic bodies [30-33]. According to reports, properties such as the strength, corrosion, oxidation, hydration and thermal shock resistance of a refractory is improved if one can favorably tailor the interaction of Nano-phases with the other particles [34-42]. Taking the above, in the research, the
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impact of trivalent oxide nanoparticles such as Fe2O3, Al2O3, and Cr2O3 on the microstructure and performance of magnesite-dolomite refractory bricks were
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investigated.
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2. Experimental Procedure: 2.1. Materials:
In this research, magnesite and dolomite from Birjand and Zefreh mines in Iran, respectively) was used as the raw materials and the details of them[chemical analysis was performed by XRF spectrometry using a Philips Model PW 2400 XRF instrument with a Rh target tube] are mentioned in Table 1. Also, synthesized
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Nano-particles of Fe2O3, Al2O3, and Cr2O3 were used as additives (Supplier: US Research Nanomaterials, Inc, Table 2, Figures 1a-c and 2a-c). Hydraulic oil (Supplier: Crown Oil Co.) was used as a binder and the details of it mentioned in
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Table 3. Different samples of magnesite-dolomite refractory composition were formulated with varying Nano-particles additive concentration between 0 and 4 wt. % (Table 4). An acrylic copolymer (Zephrym PD3315) and acetone (as a dispersant agent and dispersion medium, respectively) were used to make an
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appropriate and stable suspension of Nano-particles.
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2.2. Methods:
In order to achieve a homogeneous batch, all the raw materials, additives, and binder were thoroughly mixed in a Hobert mixer for each composition (Table 5). Mixed batches were compacted to the cylindrical shape of dimension 50 mm *50 mm at the specific pressure of 180 MPa using a hydraulic press (LEISE, Italy).
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Then all specimens were fired in a shuttle kiln at 1650 °C for 3h. Different physical and mechanical properties of the fired specimens were examined. An average of three test results is mentioned in the results and discussion section. The ceramic phase’s formation of the samples was detected by the X-ray diffraction
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technique (XRD; MXP21VAHF Advance model) with CuKα radiation (λ=1.5406 Å) operated at 40 kV and 30 mA. The scans were performed in the 2θ range from
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10 to 110 with a step scan of 0.05 and 1.5 s per step in a continuous mode. Also, the microstructure of fractured surfaces of the samples was analyzed by MLA250FEI Quanta scanning electron microscopy equipped with energy dispersive spectrometer (SEM-EDS). The liquid displacement method using the Archimedes principle in a Kerosene medium (ASTM C-20) was used in order to the measurement of the bulk density (BD) and apparent porosity (AP) values. Also, the ASTM C-132-97 was used for determined the cold crushing strength (CCS) of the
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specimens. The hydration resistance of powdered specimens is evaluated in terms of the change in the mass of the powdered samples before and after treating them in autoclave device (temperature=25°C, relative humidity= 95%, and pressure 25
(Eq. 1) [13, 37]
M2 (g) = mass gain after hydration test. M1 (g) = mass gain before hydration test. 3. Results and Discussion
Bulk Density (BD) and Apparent Porosity (AP):
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3.1.
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HR (%) = [(M2-M1)/M1]*100
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bar) according to the following equation:
The impact of Al2O3 and Fe2O3 Nano-particles addition on the bulk density (BD) and apparent porosity (AP) of the specimens sintered at 1650 °C for 3h is shown in Fig.3a-b. It can be seen that the bulk density(BD) starting to increase from 0.5 wt.
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% of Fe2O3and Al2O3 Nano-particles, and finding its higher amount (3.38g/cm3 and3.35 g/cm3) at4 wt. %, respectively. These variations are due to these reasons: First; new phase formation with high density (such as C2F=3.77 g/cm3, C3A= 3.82
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g/cm3, and C12.A7 =2.68 g/cm3).
Second; because of the higher true density of Fe2O3 (5.24 g/cm3) and Al2O3
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(3.89g/cm3), in comparison to the CaO (3.34g/cm3) and MgO (3.58g/cm3) phases [2, 4]. Also, another densification mechanism is correlated microstructural [5]. Low melting point related to the Fe2O3(Tm=1565°C) and Al2O3(Tm=2072°C) Nanoparticles in comparison with MgO(Tm=2582°C) and CaO (Tm=2572°C) which leads to the formation of an Fe2O3 and Al2O3 bridge that allows an appropriate mass transport between MgO(magnesia) and CaO(calcia) particles [3, 5, and 6]. Also, the used of aluminum and iron oxides nanoparticles change the grain boundary between assemblage and the morphology of the CaO(calcia) and
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MgO(magnesia) particles, changing the di-hedral angle (ɵ). The lowering of the dihedral angle (ɵ) means free surface energy (ϒss) will be smaller, which will simplification grain-to-grain contact and ultimately direct-bond formation [5, 6,
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and 39]. This tendency increases the densification of specimens. But for the specimens contain Cr2O3 nanoparticles it can be seen that the bulk density (BD) begins to increase from 0.5wt. % of Cr2O3 Nano-particles (3.18g/cm3), and finding
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its higher amount at 4 wt. %( 3.41g/cm3). These variations can be attributed to: First; a good compaction of the specimens on filling up of the inter-granular
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porosity between magnesia and calcia grains.
Second; a better sintering of the specimens due to the presence of fine nano-Cr2O3. Third; The higher true density of Cr2O3 (5.22g/cm3) [4], in comparison to the calcia (3.35 g/cm3) and magnesia (3.58 g/cm3) or due to a possible new phases formation [such as MgCr2O4 (4.43g/cm3) and CaCr2O4 (4. 43g/cm3)] [43, 44]. For
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the apparent porosity variation it shows that values decrease with increasing Cr2O3Nano-particles content up to 1.5 wt.% and for further Cr2O3Nan-oparticles (1.5 up to 4 wt.%) the apparent porosity increased. This variation is because of the large differences in thermal expansion coefficients (α) between magnesia (∼13.5 ×
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10−6 ◦C−1), calcia (∼13.8× 10–6◦C−1) and MgCr2O4 (∼8.5× 10−6 ◦C−1) [4], it can
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generate excessive micro-cracks formation in the microstructure, provoking a porosity increment.
3.2.
Phase Analysis:
Fig.4-7 shows the XRD patterns of samples without, 1.5%, and 4 wt. % Fe2O3, Al2O3, and Cr2O3 nanoparticles, respectively. Lime (CaO) (JCPDS 04-0777) and magnesia (MgO) (JCPDS 04-0829) were the main crystalline phases in all the
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samples. Also, for MC sample Ca (OH) 2 (JCPDS 04-0733) phase is formed during sample preparation. In the sample with 1.5 and 4 wt. % nano Fe2O3 and Al2O3: MgO, CaO, C2F (2CaO.Fe2O3) (JCPDS 47-1744), C3A (3CaO.Al2O3) (JCPDS 38-
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1429), and C12.A7 (12CaO·7Al2O3) (JCPDS 09-0413) were the main crystalline phases. CaO reacted with Fe2O3 and Al2O3 Nano-particles and formed C2F (2CaO.Fe2O3), C3A (3CaO.Al2O3), and C12.A7 (12CaO·7Al2O3) phases. These phases have low melting point (lower than 1500◦C) [1-3]. The aforementioned
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phases at the firing temperature (1650◦C) are in the melting state that is the source of glassy phase in the microstructure [5, 6]. The presence of Nano Fe2O3 and Al2O3
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in MgO-CaO samples forms liquid phase above 1500◦C at the grain boundary and promotes sintering through the liquid Phase sintering mechanism [1, 5-7]. Increasing additives concentration helps to create more liquid phases among the grains. Thus, wettability of the grain increases and led to grain growth through solution and precipitation [1, 5, and 39]. With increasing the additive content the
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amount of glassy phases increases. But for the samples contains 1.5 and 4 wt. % Nano Cr2O3: MgO, CaO, CaCr2O4 (JCPDS 9-146), and MgCr2O4 (JCPDS 10-0351) were the main crystalline phases. CaO and MgO reacted with Cr2O3 Nano-particles
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and formed CaCr2O4 and MgCr2O4 phases with melting point 2170 ◦C and 2350◦C, respectively [43, 44]. The aforementioned phases at the sintering temperature
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(1650◦C) are in the solid state [4]. Also, Cr2O3phase peaks not exist. It revealed that all added Cr2O3had reacted with CaO (calcia) and MgO (magnesia) to form CaCr2O4 and MgCr2O4 phases which preferred to locate on intragranular and intergranular area of MgO (magnesia) and CaO (calcia) particles. The peaks intensity of the CaCr2O4 and MgCr2O4 phases for specimens contain more Cr2O3 Nano-particles (MCCr4) are higher than specimens contains lower than of Cr2O3 Nano-particles.
3.3.
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SEM/EDX Analysis:
Fig.8a-d shows the microstructure analysis (SEM) of the fractured surfaces of the samples without and with 4 wt. % Fe2O3, Al2O3, and Cr2O3 nanoparticles,
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respectively. In the sample without addition, there is a lot of pores and porosity (Fig. 8a). EDX analyses do not show the phases but the elements, so XRD and
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EDX (Table 6) results confirm that the presence of some low melting point phases that were formed by reaction of CaO with Al2O3 and Fe2O3 Nano-particles to generate C2F (2CaO.Fe2O3), C3A (3CaO.Al2O3), and C12.A7 (12CaO·7Al2O3) for MCF3 and MCA3 samples. MgO (dark gray), CaO (light gray), and low melting phases (white area) were observed in the microstructure (Fig. 8b-c). By increasing
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the Al2O3 and Fe2O3 Nano-particles to 4wt. % the grain size has increased and the amount, and the size of the pores is decreased and a homogeneous microstructure with low apparent porosity was created. In the presence of Al2O3 and Fe2O3 Nano-
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particles the grain growth takes place (Fig.8d). Because of the near ionic radius of Fe3+ (0.69 Å), Al3+ (0.67 Å), and Ca2+ (0.95 Å) result in the formation of cationic
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vacancies in CaO (calcia) (Equation 2 and 3) [5]. This phenomenon led to high atomic mobility, encouraging precipitation of low melting point phases from CaO (calcia) [C2F (2CaO.Fe2O3), C3A (3CaO.Al2O3), and C12.A7 (12CaO·7Al2O3)] and increase the direct bond formation.
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Fe2O3 2 + + 3
(Eq: 2) [1, 5, and 6]
Al2O3 2 + + 3
(Eq: 3) [1, 5, and
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6]
One of the key parameters in decreasing the sintering temperature of direct-bonded
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samples is lowering the di-hedral angle (ɵ) between calcia (CaO) particles [39]. The addition of Nanoparticles must be more effective in decreasing the di-hedral angle (ɵ) and encouraging direct bonding in comparison to micro-particles. In this work, this phenomenon can be explained as follows: during the sintering process the nanoparticles (Al2O3 and Fe2O3) react with the calcia in matrix leading to the
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formation some low melting point phase’s in a faster way. Consequently, the capillary force from the wetting liquid eliminate porosity and reduce interfacial area. Since, diffusion rates in liquid are relatively high this phenomenon led to in faster bonding and densification with its corresponding improvement in physical
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and mechanical properties [5, 39]. Also, for specimen contains 4 wt. % Cr2O3 Nano-particles a homogeneous microstructure composed mainly of a well-
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distributed phases is observed. By energy dispersive X-ray spectroscopy analysis (EDX), as a second phase, there are two phases surrounded by the magnesia (MgO) and calcia (CaO) ground mass (Fig.8d). The first one corresponds to light gray particles composed by Ca and Cr elements as it was identified by EDX. This phase is a spinel compound found in the XRD analysis and identified as CaCr2O4. The last phase corresponds to bright grey particles composed by Mg and Cr elements (Table 6). From the energy dispersive X-ray spectroscopy analysis
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(EDX) and XRD analysis this phase was confirmed as an MgCr2O4. During the microstructural analysis (SEM), it was observed that CaCr2O4 and MgCr2O4 are homogeneously dispersed through the entire matrix. As the Cr2O3 Nano-particles
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contents were increased, some coarse agglomerations composed by CaCr2O4 and MgCr2O4 were formed. This microstructural characteristic described above can be correlated to the decreased mechanical resistance (such as cold crushing strength) at higher Cr2O3 Nano-particles content since CaCr2O4 and MgCr2O4 agglomerates
Cold Crushing Strength:
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3.4.
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could be acting as stress concentrates thus making the matrix weaker.
Fig.9 shows the impact of Fe2O3, Al2O3, and Cr2O3 Nano-particles addition on the cold crushing strength (CCS) of the samples. The contents of the cold crushing strength mentioned for the samples containing Nano Fe2O3 and Al2O3 were much higher than those measured by the MC sample. This is due to the progress of a
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stronger bonding structure and microstructure correction. As a result, the connection between the cold crushing strength (CCS) behavior and the microstructural specification can be explained as follows;
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High cold crushing strength (CCS) contents are creating for compositions with high proportions of continuous bonding in their microstructure. Higher diffusion
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rates of Nano-particles led to this continuous bonding. Also, it observed that cold crushing strength (CCS) for the samples contains Cr2O3 Nano-particles is higher than samples contains Fe2O3 and Al2O3 nanoparticles. For the specimens contains Cr2O3 Nano-particles a sharp increase in the strength value is obtained with addition Cr2O3 Nano-particles up to 1.5wt%.The maximum cold crushing strength was found for the MCCr1.5 specimen (782 kgf/cm2). It was observed that higher Cr2O3 Nano-particles concentrations (from 2 to 4 wt. %) decreased the cold
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crushing strength of the MgO–CaO refractory specimens. This cold crushing strength variation may be due to the following reasons: A) The lower apparent porosity registered for MCCr0.5, MCCr1, and MCCr1.5
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specimens.
For MCCr2 to MCCr4 formulation corresponding to 2 up to 4 wt. % of Nano Cr2O3, there is a gradual diminish the in cold crushing strength (CCS). This variation
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trend can be explicated due to the creating of coarse agglomerates and a large thermal expansion coefficient (α) (MgO=∼13.5*10-6/◦C, CaO=∼13.8* 10-6/◦C,
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MgCr2O4= ∼8*10-6/◦C) miss-match between divers phases existed in the matrix. The different thermal expansion coefficient (α) between phases results in the creating peripheral micro-cracks around agglomerates; these micro-cracks could be a decrement to mechanical performance (CCS) (Fig.9). Hydration Resistance:
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3.5.
Fig.10 shows the impact of Fe2O3, Al2O3, and Cr2O3 Nano-particles addition on the hydration resistance of magnesite-dolomite specimens. Refractories contain magnesia (MgO) and calcia (CaO) particles can hydrate in humid atmosphere. The
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CaO and MgO grain react easily with moisture in atmosphere and formation CaO (OH) 2 and Mg (OH) 2 phases (Eq. 4 and 5), volume expansion of the resultant can
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cause severe damage to the materials [2-5]. CaO + H2O = Ca (OH) 2
(Eq.4) [3, 5, and 6]
MgO+H2O
(Eq.5) [3, 5, and 6]
= Mg (OH) 2
Several approach such as using pitch, tar, flake, and vein graphite minerals, treating magnesite-dolomite bricks in a CO2atmosphere or addition of different oxide additives such as V2O5, CuO, FeTiO3, La2O3, TiO2, Ce2O, ZrO2, and Fe2O3
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have been tested to improve the performance of magnesite-dolomite refractories. All methods lead the access of calcia and magnesia to the moisture to decrease. From Fig. 10 it can be seen that the mass gain of magnesite –dolomite specimens
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decreased with addition of Fe2O3, Al2O3, and Cr2O3 Nano-particles. For MC sample the mass gain after 96 h was 3.2%, which was decreased with increasing the amount of trivalent nanoparticle additives. Increasing the amount of additives reduces the weight gain because of the more grain growth and lower grain
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boundary and porosity for the samples contain Nano Fe2O3 and Al2O3, and covered free CaO and MgO phases. The amount of hydration is related to the absorption of
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water on the crystal defect and grain boundary surface. It is reported that the hydration resistance of CaO contains materials is strongly dependent on the content of free CaO in materials and its microstructure [10, 13]. In general, when Nano Fe2O3 and Al2O3 was added they created some low melting point phases such as C2F (2CaO.Fe2O3), C3A(3CaO.Al2O3), and C12.A7 (12CaO·7Al2O3) located at grain
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boundaries and the triple point of calcia (CaO) and magnesia(MgO) grains thus preventing the hydration resistance of the magnesite-dolomite samples. But for the impact of Cr2O3 Nano-particles on the improvement of magnesite-dolomite
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hydration resistance it can be explanation that a solution process in which Cr3+cations are added to CaO (MgO) to form a solid solution is performed:
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Cr2O3 2CroMg + V//Mg + 3Oo
Cr2O3 2CroCa + V//Ca+ 3Oo
(Eq: 6) (Eq: 7)
The main notice in reactions 4 and 5 is the formation of Ca or Mg vacancies. These vacancies formations (in reactions 4 and5) affects the calcined materials by creating new surfaces, due to the role of the electrostatic repulsion force (ERF) between anions in vacancies thus enhancement the surface energy and promoting
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solid solution reactions and the firing process. These effects enhancement the powder density, so as to increment the hydration resistance of the samples. In terms of a preference of cations to create a solid solution with calcia and magnesia,
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improvement of the hydration resistance of the samples via a diminish of the Ca2+
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and Mg2+ content in the solid of calcia and magnesia with Cr3+cations was desired.
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4. Conclusions:
The use of trivalent Fe2O3and Al2O3 Nano-particles lead to improve the densification and thereby increase the hydration resistance of magnesitedolomite samples through the liquid phase sintering mechanism by formation low melting phases such as C2F (2CaO.Fe2O3) ,C3A
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(3CaO.Al2O3), and C12.A7 (12CaO·7Al2O3). The use of trivalent Cr2O3 Nano-particles lead to improve the densification and thereby increase the hydration resistance of magnesite-dolomite samples
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through the solid state sintering mechanism by formation phases such as CaCr2O4 and MgCr2O4 and solid phase sintering mechanism.
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The improvement trend of the hydration resistance of specimens includes various oxide nanoparticles is Al2O3< Fe2O3< Cr2O3.
In
order to enhancement the performance of the magnesite-dolomite
refractory bricks, the addition of nanoparticles was more effective because of its intrinsic properties such as a high specific surface area, size effect and higher activity.
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[12]. S. A. Suvorov, M. I. Nazmiev, R. S. Polovinkina, I. G. Maryasev,”Water- resists limemagnesia clinker". Journal of Refractories and Industrial Ceramics, 47(2006), pp.38-40.
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[13]. S. Ghsemi -Kahrizsangi, M .Barati, H. Gheisari, A. Shahraki, and M. Farooghi,” Densification and properties of ZrO2 nanoparticles added magnesia – doloma refractories “.Ceramic International, 29(2016), 2016. [14]. M. Chen, A. Jin, N. Wang, J. Yu," synthesis of hydration –resistance of CaO refractory by addition of MgO”, Developments in Chemical Engineering and Mineral Processing”, 14(2006), pp. 409-416. [15]. Min Chen, Nan Wang, Jingkun Yu, Akira yamaguchi،” Effect of Porosity on Carbonation and Hydration of CaO Material”. Journal of the European Ceramic Society, Vol, 27.2007, pp, 1953-1959.
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[16]. A. Ghosh, T.K. Bhattacharay, B. Mukherjee, S.K. Das," densification and properties of lime with V2O5 additions", Ceramic International, 30(2004), pp. 2117-2120. [17]. A. Ghosh, T.K. Bhattacharay, B. Mukherjee, S.K. Das," the effect of CuO addition on the sintering of lime", Ceramic International, 27(2001), pp. 201-203.
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[18] .A.G.M.O tham, M. A. Abuel, M. A. Serry،” Hydration –resistant lime refractories from egyption lime stone and ilmenite raw materials”،Ceramics International, 27(2001),pp. 801-807.
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[19].N. M. Ghonemi, M. A. Mandourand M. A. Serry,” phase composition, microstructure and properties of sintered La2O3–doped lime and dolomite grains”, Ceramic international, 16(1990)215-223. [20] .N.M. Ghoneim, M.A. Mandour, M.A. Serry, "Sintering of lime doped with La2O3 and CeO2", Ceramics International, 15 (1989) 357–362. [21]. R. Jingti, X. Bao, "Effect of NiO addition on the sintering properties of dolomite clinker", Journal of synthetic crystals 42(2013)1620-1625. [22]. L. Liu, M. Chen, L. Xu, X. Yin, W. Sun, “Effect of BaO addition on densification and mechanical properties of Al2O3-MgO-CaO refractories", Metals 6(2016)84. [23]. Zh. Han, D. X. Feng, Z. H. Zhong, Y. Jun, N. J. hua, “Effect of CaF2 on the defects formation and sintering properties of MgO-CaO materials”, Journal of Synthetic Crystals, (2014)01.
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[24] A.G.M. Othman, "Effect of talc and bauxite on sintering, microstructure and refractory properties of Egyptian dolomitic magnesite", British Ceramic Transactions, 102 (2003), pp. 265– 271. [25]. J. Lee, H. Cole, S. LEE, "Effect of Fe2O3 additions on the hydration resistance of CaO”, Journal of ceramic processing research, 13(2012), pp. 646-650.
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[26]. Yeprem," Effect of iron oxide addition on the hydration resistance and bulk density of doloma", Journal of the European Ceramic Society, 2007, pp. 1651-1655. [27]. E. J. Koval, G. L. Messing, R. Bradt,” Effects of raw material properties and Fe2O3 additions on the sintering of dolomites”, Ceram. Bull., 63(1984) 274–277.
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[28]. G.B. Qiu, B. Peng, M. Guo, and M. Zhang,” Regeneration utilization of spent MgO-CaO bricks for argon oxygen decarburization furnace”, J. Chin. Ceram. Soc., 41(2013) 1284.
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[29]. G. Qiu, B. Peng, X. Li, M. Guo, M. Zhang," Hydration resistance and mechanism of regenerated MgO–CaO bricks", Journal of the Ceramic Society of Japan 123 (2015)90-95. [30]. L.B. Khoroshavin, V.A. Perepelitsyn, on the nanotechnology of refractories, Refractory and Industrial Ceramic 40 (1999) 553–557. [31] E. Y, Pivinskii, P.V. Dyakin, Y. Yu, Pivinskii, S.V. Vikhman, "Nanoparticles and their effective use in the technology of highly concentrated binding suspensions (hcbs) and refractory castables", Refractory and Industrial Ceramic. 44 (2003) 314–318.
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[32]. S. Tamura, T. Ochiai, S. Takanaga, T. Kanai, H. Nakamura, "Nano-tech refractories 1: the development of the nanostructural matrix, in: Proceedings of UNITECR'03 Congress, 19–22 October, Osaka, Japan, (2003)517–520. [33]. D. V. Kuznetsov, D. V. Lysov, A. A. Nemtinov, A. S. Shaleiko, V. A. Korolkov, " Refractories in heat units Nano-materials in refractory technology", Refractories and industrial ceramics, 51(2010).
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[34]. H.R. Zargar, C. Oprea, G. Oprea, T. Troczynski, "The effect of nano- Cr2O3 on solidsolution assisted sintering of MgO refractories", Ceramics International, 38 (2012), pp. 6235– 6241. [35] R. Rekha Das,” Effect of Micron and Nano MgAl2O4spinel Addition on the Properties of Magnesia-Carbon Refractories”, MSC Thesis, (2010). [36]. S. Adak, A.S. Bal, A.K. Chattopadhyay, P.B. Panda, R.P. Rana, Effect of nano-titania addition on the properties of magnesia–carbon system, in: Proceedings of the 54th International Colloquium on Refractories, Aachen, Germany, (2011).pp. 180–183. [37]. S. Ghasemi. Kahrizsangi, H.Gh.Dehsheikh,” Effect of Spinel (MgAl2O4) nanoparticles addition on the Properties of MgO-CaO Refractory Ceramic Composite”, international journal of material research, (2016). [38]. A. K. Singh, R. Sarkar,” Nano mullite bonded refractory castable composition for high temperature applications”, Ceramics International, 42 (2016) 12937– 12945.
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[39]. C. Gómez Rodríguez, T.K. Das Roy, S. Shaji, G.A Castillo Rodríguezb, L. García Quiñonez, Edén Rodríguez, J. O. González, J.A. Aguilar-Martínez,” Effect of addition of Al2O3 and Fe2O3 nanoparticles on the microstructural and physico-chemical evolution of dense magnesia composite”, Ceramics International, 41, ( 2015,) 7751–7758.
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[40].L. Lu, L. Di, Ch. Ding ,Ch. Zhang, D. Yang,” Effect of Nano-ZrO2 Addition on Microstructure, Mechanical Property and Thermal Shock Behaviour of Dense Chromic Oxide Refractory Material”, Transactions of the Indian Ceramic Society ,74, (2015 )3.
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[41]. E. Rodríguez, F.H. Moreno, J.A. Aguilar-Martínez, A.E. Montes-Mejía, J.J. Ruiz-Valdés, Rodrigo Puente-Ornelas, J.E. Contreras," effect of nano-titania (n-Tio2) content on the mechano-physical properties of a magnesia refractory composite" Ceramics International, 42 (2016) 8445–8452.
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[42] C. Gogtasa, H. F. Lopeza, K. Sobolev," Effect of nano-YSZ and nano-ZrO2 additions on the strength and toughness behavior of self-flowing alumina castables", Ceramics international, l42 (2016)1847–1855. [43] .S. Hshimoto, A. Yamaguchi, and Y. Takahashi,”growth and characterization of needle-like b-CaCr2O4 crystals”, materials research bulletin, Vol.32, No.11, pp.1593-1602, 1997.
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[44] .A. Azhari, F. Golestani-Fard, H. Sarpoolaky, "Effect of nano iron oxide as an additive on phase and microstructural evolution of mag-chrome refractory matrix", Journal of the European Ceramic Society ,29 (13) (2009) 2679–2684.
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Table1; Chemical composition and physical properties of raw materials Magnesite Dolomite
SiO2
0.95
0.7
Al2O3
1.6
2.8
Fe2O3
0.6
TiO2
0.2
CaO
2.7
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Oxide
MgO
Physical properties Bulk density(g/cm3) Apparent porosity(%)
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57.2 37.2
0.3
0.44
3.28-3.3 3.75-3.80
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0.2
93.2
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Alkalis
0.8
2.85-3.1 3.80-3.85
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Density (g/cm3) 5.24 2.9 5.22
Size (nm) 40-50 50±55 50-60
SSA ( m2/g) 115 90 80>
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Fe2O3 Al2O3 Cr2O3
Purity (%) 98> 99> 99.8>
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Oxide
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Table 2; Properties of the nanoparticles Color red white green
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Values -32 845 Insol. 10 Pale yellow
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Properties Pour Point(°C) Relative Density(15°C) Water Solubility Viscosity(40°C) Appearance
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Table 3; Physical and chemical properties of hydraulic oil
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Table 4; Batch composition with sample code
3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
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0 0.5 1 1.5 2 2.5 3 3.5 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Nano Cr2O3
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35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35
Nano Al2O3
Nano Fe2O3
0 0 0 0 0 0 0 0 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0 0 0 0 0 0 0
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MC MCF0.5 MCF1 MCF1.5 MCF2 MCF2.5 MCF3 MCF3. MCF4 MCA0.5 MCA1 MCA1.5 MCA2 MCA2.5 MCA3 MCA3.5 MCA4 MCCr0.5 MCCr1 MCCr1.5 MCCr2 MCCr2.5 MCCr3 MCCr3.5 MCCr4
Hydraulic Oil(wt. %)
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CaO (wt. %)
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Sample code
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.5 1 1.5 2 2.5 3 3.5 4
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Table 5; Mixing sequence of MgO-CaO refractory samples sequence
1 Coarse and medium magnesite and dolomite
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2 Addition of hydraulic oil
3 Addition of nano-particles and fine magnesite and
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dolomite
Mixing time(min)
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Steps Mixing
2 5 10
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Table 6; EDX analyses of A) CaO, B) MgO, C) 2CaO.Fe2O3, D)3CaO.Al2O3, E)
Point C 40.77 32.17 -
Cr Fe
-
-
26.71
Au
0.44
0.53
Point D 28.74 38.45 32.51
0.34
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Point E 31.21 37.81 30.57
Point F 42.11 0.12 18.13 -
Point G 45.65 20.30 0.8 -
-
-
39.40 -
32.60 -
0.41
0.23
0.65
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Point B 35.05 64.42 -
-
-
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O Mg Ca Al
Point A 35.26 64.30 -
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Element
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12CaO·7Al2O3 , F) CaCr2O3 , and G) MgCr2O4 points.
0.3
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Fig1.TEM images of the a) Fe2O3, b) Al2O3, and C) Cr2O3 nanoparticles.
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Fig 2. XRD patterns of the a) Fe2O3, b) Al2O3, and c) Cr2O3 nanoparticles.
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Fig3. Variation of the a) bulk density and b) apparent porosity of the magnesite-dolomite
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refractory specimens as a function of nanoparticles addition.
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Fig.4 XRD pattern of the MC sample.
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Fig.5 XRD pattern of the A) MCF1.5 and b) MCF4 samples.
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Fig.6 XRD pattern of the A) MCA1.5 and b) MCA4 samples.
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Fig.7 XRD pattern of the A) MCCr1.5 and b) MCCr4 samples.
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Fig8. SEM images of the fractured surfaces of the samples a) without, b) 4wt% Fe2O3, c) 4wt% Al2O3, and d) 4wt% Cr2O3 nanoparticles.
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Fig9. Variation of the cold crushing strength of the magnesite-dolomite refractory specimens as a function of nanoparticles addition
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Fig10. Effect of nanoparticles addition on the improvement of magnesite-dolomite specimens hydration resistance.
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Highlights: 1- Fe2O3and Al2O3 improve MgO-CaO densification via liquid phase sintering mechanism.
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2- Cr2O3 improve MgO-CaO hydration resistance via solid state sintering mechanism.
3- Magnesite-dolomite hydration resistance improvement trend is Al2O3<
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Fe2O3< Cr2O3.
S0254-0584(17)30193-1
DOI:
10.1016/j.matchemphys.2017.03.001
Reference:
MAC 19547
To appear in:
Materials Chemistry and Physics
Received Date: 17 January 2017 Revised Date:
25 February 2017
Accepted Date: 1 March 2017
Please cite this article as: S. Ghasemi-Kahrizsangi, E. Karamian, A. Ghasemi-Kahrizsangi, H.G. Desheikh, A. Soheily, The impact of trivalent oxide nanoparticles on the microstructure and performance of magnesite-dolomite refractory bricks, Materials Chemistry and Physics (2017), doi: 10.1016/ j.matchemphys.2017.03.001. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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The Impact of Trivalent Oxide Nanoparticles on the Microstructure and Performance of Magnesite-Dolomite Refractory Bricks Desheikh4, Ali Soheily5
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Salman Ghasemi-Kahrizsangi1*, Ebrahim Karamian2, Ahmad Ghasemi-Kahrizsangi3, Hassan Gheisari
1, 2, 4, 5-Advanced Materials Research Center, Faculty of Materials Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran.
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3- Special Alloy Company, No.27, In front of Isfahan Tile Co., Shohadaye Kashi St., IsfahanNajafabad Ave., Isfahan City, Iran.
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Corresponding author*: E-mail address: [email protected]
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Abstract: In this research, the impact of trivalent oxide nanoparticles on the microstructure and performance of the magnesite-dolomite refractory bricks was examined. Up to
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4 wt. % Fe2O3, Al2O3, and Cr2O3 nanoparticles were added to the specimens as additives. Physical and mechanical properties such as bulk density (BD), apparent porosity (AP), hydration resistance (HR), and cold crushing strength (CCS) were
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examined. XRD and SEM analysis were used to detect the ceramic phase’s formation and microstructure analysis, respectively. Results show that the use of Fe2O3, Al2O3, and Cr2O3 nanoparticles improve the physical and mechanical
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properties of the MgO-CaO materials. Also, it revealed that specimens contain Fe2O3 and Al2O3 nanoparticles improve hydration resistance through the liquid phase sintering mechanism by formation some low melting phases such as C2F(2CaO.Fe2O3), C3A(3CaO.Al2O3), and C12.A7(12CaO·7Al2O3). However the specimens contain Cr2O3 nanoparticles improve the hydration resistance through
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the solid state sintering mechanism by formation phases such as CaCr2O4 and MgCr2O4. In general, hydration resistance improvement trend of the MgO-CaO specimens includes trivalent nanoparticles is Al2O3
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Phase.
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Keywords: Nanoparticles, Trivalent, Hydration Resistance, Solid State, Liquid
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1. Introduction:
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Typically, magnesite-dolomite refractory bricks are composed of 50-80 wt. % of magnesia (MgO) [1]. Recently, magnesite-dolomite or Mag-Dol refractory bricks have been used instead of MgO-Cr2O3 and MgO-C refractory bricks [2]. There are two ways for produce magnesite-dolomite refractory bricks. The first way is using
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fused and sintered clinker of magnesite (MgCO3) and dolomite (Mg.Ca (CO3)2) as starting material for produce the magnesite-dolomite refractory bricks which would
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results in more homogenous products with more favorable properties. Another way is mixing magnesite and dolomite together and calcined them at high temperature that let to produce an in–situ Mag-Dol refractory bricks [3, 5]. These refractory bricks have a lot of advantages such as high refractoriness, good thermal shock resistance, high chemical resistance at high-temperature, thermodynamic stability
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in the presence of carbon, and an appropriate abrasion resistance. Magnesitedolomite refractory bricks are widely used in different industries such as metallurgy and cement kilns [1, 5, and 6-11]. Also, Mag-Dol refractory bricks have
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been considered to be one of the effective refractory types for processing clean steel products, due to these refractory bricks are beneficial to removing inclusions
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from molten steels [3, 5, and 6]. Magnesite-dolomite refractory bricks have become one of the attractive steel making refractories due to the increasing demands of molten steel purity, the awareness of environmental protection and resource shortage grows [4-6]. Despite of aforementioned advantageous, the use of magnesite-dolomite refractory bricks has been restricted due to their trend to hydration when exposed to the humid atmosphere [1-6, 12-14]. Some researcher reported that physical properties of magnesite-dolomite refractory bricks could be improved by using pitch, tar, flake, and vein graphite minerals [2, 5]. Also, the
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hydration resistance of Mag-Dol refractory bricks can be improved by surface phosphate (H3PO4) coating or by treating in a CO2atmosphere which leads to cover the surface of CaO grain by formation of a dense layer (CaCO3) and protect CaO
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grain from hydration [15]. Several researcher examined the improvement of hydration resistance of magnesite-dolomite refractory bricks through the addition of different oxide additives, such as V2O5 [16], CuO [17], FeTiO3 [18], La2O3 [19, 20], TiO2 [2], Ce2O [8, 20], ZrO2 [6,10, and 13], NiO [21], BaO [22],CaF2 [23], talc
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[24], and Fe2O3 [1, 3, 5, 6, 9, 25, and 29]. Recently, several researchers started to engineer the quality of the refractory bricks and castables by using Nano-sized
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materials in the composition due to the reported benefits of adding nanoparticles (such as oxides and non-oxides) to ceramic bodies [30-33]. According to reports, properties such as the strength, corrosion, oxidation, hydration and thermal shock resistance of a refractory is improved if one can favorably tailor the interaction of Nano-phases with the other particles [34-42]. Taking the above, in the research, the
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impact of trivalent oxide nanoparticles such as Fe2O3, Al2O3, and Cr2O3 on the microstructure and performance of magnesite-dolomite refractory bricks were
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investigated.
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2. Experimental Procedure: 2.1. Materials:
In this research, magnesite and dolomite from Birjand and Zefreh mines in Iran, respectively) was used as the raw materials and the details of them[chemical analysis was performed by XRF spectrometry using a Philips Model PW 2400 XRF instrument with a Rh target tube] are mentioned in Table 1. Also, synthesized
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Nano-particles of Fe2O3, Al2O3, and Cr2O3 were used as additives (Supplier: US Research Nanomaterials, Inc, Table 2, Figures 1a-c and 2a-c). Hydraulic oil (Supplier: Crown Oil Co.) was used as a binder and the details of it mentioned in
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Table 3. Different samples of magnesite-dolomite refractory composition were formulated with varying Nano-particles additive concentration between 0 and 4 wt. % (Table 4). An acrylic copolymer (Zephrym PD3315) and acetone (as a dispersant agent and dispersion medium, respectively) were used to make an
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appropriate and stable suspension of Nano-particles.
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2.2. Methods:
In order to achieve a homogeneous batch, all the raw materials, additives, and binder were thoroughly mixed in a Hobert mixer for each composition (Table 5). Mixed batches were compacted to the cylindrical shape of dimension 50 mm *50 mm at the specific pressure of 180 MPa using a hydraulic press (LEISE, Italy).
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Then all specimens were fired in a shuttle kiln at 1650 °C for 3h. Different physical and mechanical properties of the fired specimens were examined. An average of three test results is mentioned in the results and discussion section. The ceramic phase’s formation of the samples was detected by the X-ray diffraction
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technique (XRD; MXP21VAHF Advance model) with CuKα radiation (λ=1.5406 Å) operated at 40 kV and 30 mA. The scans were performed in the 2θ range from
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10 to 110 with a step scan of 0.05 and 1.5 s per step in a continuous mode. Also, the microstructure of fractured surfaces of the samples was analyzed by MLA250FEI Quanta scanning electron microscopy equipped with energy dispersive spectrometer (SEM-EDS). The liquid displacement method using the Archimedes principle in a Kerosene medium (ASTM C-20) was used in order to the measurement of the bulk density (BD) and apparent porosity (AP) values. Also, the ASTM C-132-97 was used for determined the cold crushing strength (CCS) of the
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specimens. The hydration resistance of powdered specimens is evaluated in terms of the change in the mass of the powdered samples before and after treating them in autoclave device (temperature=25°C, relative humidity= 95%, and pressure 25
(Eq. 1) [13, 37]
M2 (g) = mass gain after hydration test. M1 (g) = mass gain before hydration test. 3. Results and Discussion
Bulk Density (BD) and Apparent Porosity (AP):
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3.1.
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HR (%) = [(M2-M1)/M1]*100
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bar) according to the following equation:
The impact of Al2O3 and Fe2O3 Nano-particles addition on the bulk density (BD) and apparent porosity (AP) of the specimens sintered at 1650 °C for 3h is shown in Fig.3a-b. It can be seen that the bulk density(BD) starting to increase from 0.5 wt.
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% of Fe2O3and Al2O3 Nano-particles, and finding its higher amount (3.38g/cm3 and3.35 g/cm3) at4 wt. %, respectively. These variations are due to these reasons: First; new phase formation with high density (such as C2F=3.77 g/cm3, C3A= 3.82
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g/cm3, and C12.A7 =2.68 g/cm3).
Second; because of the higher true density of Fe2O3 (5.24 g/cm3) and Al2O3
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(3.89g/cm3), in comparison to the CaO (3.34g/cm3) and MgO (3.58g/cm3) phases [2, 4]. Also, another densification mechanism is correlated microstructural [5]. Low melting point related to the Fe2O3(Tm=1565°C) and Al2O3(Tm=2072°C) Nanoparticles in comparison with MgO(Tm=2582°C) and CaO (Tm=2572°C) which leads to the formation of an Fe2O3 and Al2O3 bridge that allows an appropriate mass transport between MgO(magnesia) and CaO(calcia) particles [3, 5, and 6]. Also, the used of aluminum and iron oxides nanoparticles change the grain boundary between assemblage and the morphology of the CaO(calcia) and
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MgO(magnesia) particles, changing the di-hedral angle (ɵ). The lowering of the dihedral angle (ɵ) means free surface energy (ϒss) will be smaller, which will simplification grain-to-grain contact and ultimately direct-bond formation [5, 6,
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and 39]. This tendency increases the densification of specimens. But for the specimens contain Cr2O3 nanoparticles it can be seen that the bulk density (BD) begins to increase from 0.5wt. % of Cr2O3 Nano-particles (3.18g/cm3), and finding
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its higher amount at 4 wt. %( 3.41g/cm3). These variations can be attributed to: First; a good compaction of the specimens on filling up of the inter-granular
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porosity between magnesia and calcia grains.
Second; a better sintering of the specimens due to the presence of fine nano-Cr2O3. Third; The higher true density of Cr2O3 (5.22g/cm3) [4], in comparison to the calcia (3.35 g/cm3) and magnesia (3.58 g/cm3) or due to a possible new phases formation [such as MgCr2O4 (4.43g/cm3) and CaCr2O4 (4. 43g/cm3)] [43, 44]. For
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the apparent porosity variation it shows that values decrease with increasing Cr2O3Nano-particles content up to 1.5 wt.% and for further Cr2O3Nan-oparticles (1.5 up to 4 wt.%) the apparent porosity increased. This variation is because of the large differences in thermal expansion coefficients (α) between magnesia (∼13.5 ×
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10−6 ◦C−1), calcia (∼13.8× 10–6◦C−1) and MgCr2O4 (∼8.5× 10−6 ◦C−1) [4], it can
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generate excessive micro-cracks formation in the microstructure, provoking a porosity increment.
3.2.
Phase Analysis:
Fig.4-7 shows the XRD patterns of samples without, 1.5%, and 4 wt. % Fe2O3, Al2O3, and Cr2O3 nanoparticles, respectively. Lime (CaO) (JCPDS 04-0777) and magnesia (MgO) (JCPDS 04-0829) were the main crystalline phases in all the
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samples. Also, for MC sample Ca (OH) 2 (JCPDS 04-0733) phase is formed during sample preparation. In the sample with 1.5 and 4 wt. % nano Fe2O3 and Al2O3: MgO, CaO, C2F (2CaO.Fe2O3) (JCPDS 47-1744), C3A (3CaO.Al2O3) (JCPDS 38-
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1429), and C12.A7 (12CaO·7Al2O3) (JCPDS 09-0413) were the main crystalline phases. CaO reacted with Fe2O3 and Al2O3 Nano-particles and formed C2F (2CaO.Fe2O3), C3A (3CaO.Al2O3), and C12.A7 (12CaO·7Al2O3) phases. These phases have low melting point (lower than 1500◦C) [1-3]. The aforementioned
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phases at the firing temperature (1650◦C) are in the melting state that is the source of glassy phase in the microstructure [5, 6]. The presence of Nano Fe2O3 and Al2O3
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in MgO-CaO samples forms liquid phase above 1500◦C at the grain boundary and promotes sintering through the liquid Phase sintering mechanism [1, 5-7]. Increasing additives concentration helps to create more liquid phases among the grains. Thus, wettability of the grain increases and led to grain growth through solution and precipitation [1, 5, and 39]. With increasing the additive content the
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amount of glassy phases increases. But for the samples contains 1.5 and 4 wt. % Nano Cr2O3: MgO, CaO, CaCr2O4 (JCPDS 9-146), and MgCr2O4 (JCPDS 10-0351) were the main crystalline phases. CaO and MgO reacted with Cr2O3 Nano-particles
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and formed CaCr2O4 and MgCr2O4 phases with melting point 2170 ◦C and 2350◦C, respectively [43, 44]. The aforementioned phases at the sintering temperature
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(1650◦C) are in the solid state [4]. Also, Cr2O3phase peaks not exist. It revealed that all added Cr2O3had reacted with CaO (calcia) and MgO (magnesia) to form CaCr2O4 and MgCr2O4 phases which preferred to locate on intragranular and intergranular area of MgO (magnesia) and CaO (calcia) particles. The peaks intensity of the CaCr2O4 and MgCr2O4 phases for specimens contain more Cr2O3 Nano-particles (MCCr4) are higher than specimens contains lower than of Cr2O3 Nano-particles.
3.3.
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SEM/EDX Analysis:
Fig.8a-d shows the microstructure analysis (SEM) of the fractured surfaces of the samples without and with 4 wt. % Fe2O3, Al2O3, and Cr2O3 nanoparticles,
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respectively. In the sample without addition, there is a lot of pores and porosity (Fig. 8a). EDX analyses do not show the phases but the elements, so XRD and
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EDX (Table 6) results confirm that the presence of some low melting point phases that were formed by reaction of CaO with Al2O3 and Fe2O3 Nano-particles to generate C2F (2CaO.Fe2O3), C3A (3CaO.Al2O3), and C12.A7 (12CaO·7Al2O3) for MCF3 and MCA3 samples. MgO (dark gray), CaO (light gray), and low melting phases (white area) were observed in the microstructure (Fig. 8b-c). By increasing
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the Al2O3 and Fe2O3 Nano-particles to 4wt. % the grain size has increased and the amount, and the size of the pores is decreased and a homogeneous microstructure with low apparent porosity was created. In the presence of Al2O3 and Fe2O3 Nano-
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particles the grain growth takes place (Fig.8d). Because of the near ionic radius of Fe3+ (0.69 Å), Al3+ (0.67 Å), and Ca2+ (0.95 Å) result in the formation of cationic
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vacancies in CaO (calcia) (Equation 2 and 3) [5]. This phenomenon led to high atomic mobility, encouraging precipitation of low melting point phases from CaO (calcia) [C2F (2CaO.Fe2O3), C3A (3CaO.Al2O3), and C12.A7 (12CaO·7Al2O3)] and increase the direct bond formation.
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Fe2O3 2 + + 3
(Eq: 2) [1, 5, and 6]
Al2O3 2 + + 3
(Eq: 3) [1, 5, and
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6]
One of the key parameters in decreasing the sintering temperature of direct-bonded
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samples is lowering the di-hedral angle (ɵ) between calcia (CaO) particles [39]. The addition of Nanoparticles must be more effective in decreasing the di-hedral angle (ɵ) and encouraging direct bonding in comparison to micro-particles. In this work, this phenomenon can be explained as follows: during the sintering process the nanoparticles (Al2O3 and Fe2O3) react with the calcia in matrix leading to the
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formation some low melting point phase’s in a faster way. Consequently, the capillary force from the wetting liquid eliminate porosity and reduce interfacial area. Since, diffusion rates in liquid are relatively high this phenomenon led to in faster bonding and densification with its corresponding improvement in physical
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and mechanical properties [5, 39]. Also, for specimen contains 4 wt. % Cr2O3 Nano-particles a homogeneous microstructure composed mainly of a well-
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distributed phases is observed. By energy dispersive X-ray spectroscopy analysis (EDX), as a second phase, there are two phases surrounded by the magnesia (MgO) and calcia (CaO) ground mass (Fig.8d). The first one corresponds to light gray particles composed by Ca and Cr elements as it was identified by EDX. This phase is a spinel compound found in the XRD analysis and identified as CaCr2O4. The last phase corresponds to bright grey particles composed by Mg and Cr elements (Table 6). From the energy dispersive X-ray spectroscopy analysis
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(EDX) and XRD analysis this phase was confirmed as an MgCr2O4. During the microstructural analysis (SEM), it was observed that CaCr2O4 and MgCr2O4 are homogeneously dispersed through the entire matrix. As the Cr2O3 Nano-particles
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contents were increased, some coarse agglomerations composed by CaCr2O4 and MgCr2O4 were formed. This microstructural characteristic described above can be correlated to the decreased mechanical resistance (such as cold crushing strength) at higher Cr2O3 Nano-particles content since CaCr2O4 and MgCr2O4 agglomerates
Cold Crushing Strength:
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3.4.
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could be acting as stress concentrates thus making the matrix weaker.
Fig.9 shows the impact of Fe2O3, Al2O3, and Cr2O3 Nano-particles addition on the cold crushing strength (CCS) of the samples. The contents of the cold crushing strength mentioned for the samples containing Nano Fe2O3 and Al2O3 were much higher than those measured by the MC sample. This is due to the progress of a
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stronger bonding structure and microstructure correction. As a result, the connection between the cold crushing strength (CCS) behavior and the microstructural specification can be explained as follows;
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High cold crushing strength (CCS) contents are creating for compositions with high proportions of continuous bonding in their microstructure. Higher diffusion
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rates of Nano-particles led to this continuous bonding. Also, it observed that cold crushing strength (CCS) for the samples contains Cr2O3 Nano-particles is higher than samples contains Fe2O3 and Al2O3 nanoparticles. For the specimens contains Cr2O3 Nano-particles a sharp increase in the strength value is obtained with addition Cr2O3 Nano-particles up to 1.5wt%.The maximum cold crushing strength was found for the MCCr1.5 specimen (782 kgf/cm2). It was observed that higher Cr2O3 Nano-particles concentrations (from 2 to 4 wt. %) decreased the cold
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crushing strength of the MgO–CaO refractory specimens. This cold crushing strength variation may be due to the following reasons: A) The lower apparent porosity registered for MCCr0.5, MCCr1, and MCCr1.5
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specimens.
For MCCr2 to MCCr4 formulation corresponding to 2 up to 4 wt. % of Nano Cr2O3, there is a gradual diminish the in cold crushing strength (CCS). This variation
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trend can be explicated due to the creating of coarse agglomerates and a large thermal expansion coefficient (α) (MgO=∼13.5*10-6/◦C, CaO=∼13.8* 10-6/◦C,
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MgCr2O4= ∼8*10-6/◦C) miss-match between divers phases existed in the matrix. The different thermal expansion coefficient (α) between phases results in the creating peripheral micro-cracks around agglomerates; these micro-cracks could be a decrement to mechanical performance (CCS) (Fig.9). Hydration Resistance:
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3.5.
Fig.10 shows the impact of Fe2O3, Al2O3, and Cr2O3 Nano-particles addition on the hydration resistance of magnesite-dolomite specimens. Refractories contain magnesia (MgO) and calcia (CaO) particles can hydrate in humid atmosphere. The
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CaO and MgO grain react easily with moisture in atmosphere and formation CaO (OH) 2 and Mg (OH) 2 phases (Eq. 4 and 5), volume expansion of the resultant can
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cause severe damage to the materials [2-5]. CaO + H2O = Ca (OH) 2
(Eq.4) [3, 5, and 6]
MgO+H2O
(Eq.5) [3, 5, and 6]
= Mg (OH) 2
Several approach such as using pitch, tar, flake, and vein graphite minerals, treating magnesite-dolomite bricks in a CO2atmosphere or addition of different oxide additives such as V2O5, CuO, FeTiO3, La2O3, TiO2, Ce2O, ZrO2, and Fe2O3
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have been tested to improve the performance of magnesite-dolomite refractories. All methods lead the access of calcia and magnesia to the moisture to decrease. From Fig. 10 it can be seen that the mass gain of magnesite –dolomite specimens
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decreased with addition of Fe2O3, Al2O3, and Cr2O3 Nano-particles. For MC sample the mass gain after 96 h was 3.2%, which was decreased with increasing the amount of trivalent nanoparticle additives. Increasing the amount of additives reduces the weight gain because of the more grain growth and lower grain
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boundary and porosity for the samples contain Nano Fe2O3 and Al2O3, and covered free CaO and MgO phases. The amount of hydration is related to the absorption of
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water on the crystal defect and grain boundary surface. It is reported that the hydration resistance of CaO contains materials is strongly dependent on the content of free CaO in materials and its microstructure [10, 13]. In general, when Nano Fe2O3 and Al2O3 was added they created some low melting point phases such as C2F (2CaO.Fe2O3), C3A(3CaO.Al2O3), and C12.A7 (12CaO·7Al2O3) located at grain
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boundaries and the triple point of calcia (CaO) and magnesia(MgO) grains thus preventing the hydration resistance of the magnesite-dolomite samples. But for the impact of Cr2O3 Nano-particles on the improvement of magnesite-dolomite
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hydration resistance it can be explanation that a solution process in which Cr3+cations are added to CaO (MgO) to form a solid solution is performed:
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Cr2O3 2CroMg + V//Mg + 3Oo
Cr2O3 2CroCa + V//Ca+ 3Oo
(Eq: 6) (Eq: 7)
The main notice in reactions 4 and 5 is the formation of Ca or Mg vacancies. These vacancies formations (in reactions 4 and5) affects the calcined materials by creating new surfaces, due to the role of the electrostatic repulsion force (ERF) between anions in vacancies thus enhancement the surface energy and promoting
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solid solution reactions and the firing process. These effects enhancement the powder density, so as to increment the hydration resistance of the samples. In terms of a preference of cations to create a solid solution with calcia and magnesia,
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improvement of the hydration resistance of the samples via a diminish of the Ca2+
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and Mg2+ content in the solid of calcia and magnesia with Cr3+cations was desired.
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4. Conclusions:
The use of trivalent Fe2O3and Al2O3 Nano-particles lead to improve the densification and thereby increase the hydration resistance of magnesitedolomite samples through the liquid phase sintering mechanism by formation low melting phases such as C2F (2CaO.Fe2O3) ,C3A
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(3CaO.Al2O3), and C12.A7 (12CaO·7Al2O3). The use of trivalent Cr2O3 Nano-particles lead to improve the densification and thereby increase the hydration resistance of magnesite-dolomite samples
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through the solid state sintering mechanism by formation phases such as CaCr2O4 and MgCr2O4 and solid phase sintering mechanism.
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The improvement trend of the hydration resistance of specimens includes various oxide nanoparticles is Al2O3< Fe2O3< Cr2O3.
In
order to enhancement the performance of the magnesite-dolomite
refractory bricks, the addition of nanoparticles was more effective because of its intrinsic properties such as a high specific surface area, size effect and higher activity.
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References:
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[2]. S. Ghasemi. Kahrizsangi, A. Gh. Kahrizsangi, H. Gh. Dehsheikh, E. Karamian, A. Soheily,” Effect of Nano-TiO2 Additions on the Densification and Properties of Magnesite–Dolomite Ceramic Composite”, Iranian Journal of Science and Technology, Transaction A,(2016). [3]. F. Kashaninia, H. S.arpoolaky, R. Naghizadeh, A.R. Bagheri, M and Zamanipour," improving hydration resistance of magnesia-doloma refractories by iron oxide addition", Iranian Journal of Materials and Science & Engineering, 8 (2011), pp.34-40.
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[5]. S. Ghasemi –Kahrizsangi, A.Nemati, A. Shahraki, M. Farooghi,” Densification and Properties of Fe2O3 Nanoparticles added CaO Refractories”, Ceramics International, 42(2016), pp. 12270-12275. [6]. S. Ghsemi Kahrizsangi, A.Nemati, A. Shahraki and M. Farooghi,” The Effect of NanoAdditives on the Hydration Resistance of Materials Synthesized from the MgO-CaO System “International Journal of Engineering, Transactions A: Basics”, 29(2016), pp.539-545. [7]. S. Chen, G. Chen, J. Cheng," Effect of additive on the hydration resistance of material synthesized from the magnesia-calcia system", Journal of American ceramic society, 83(2000), pp.1810-1812.
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[8]. H. Zhang, H. Zhao, J. Zhen, j. Yu, and J. Nie.”Defect Study of MgO-CaO Material doped With CeO2”. Journal of the Advances in Materials Science and Engineering, 20(2013), pp. 1-5. [9]. Gui-bo Qiu, Ben Peng, Chang-sheng Yue, Min Guo, Mei Zhang,” Properties of regenerated MgO–CaO refractory bricks: Impurity of iron oxide “, Ceramic International. 42(2016), pp. 2933–2940.
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[10]. M. Chen, C. Lu, J. Yu, Improvement in performance of MgO–CaO refractories by addition of Nano-sized ZrO2, Journal of the European Ceramic Society. 27 (2007), pp. 4633–4638. [11]. H. Yin, Y. Ma, J. Yan,”Effect of MgO coating on hydration resistance of MgO-CaO clinkers",Journal of Materials Science Forum, 695(2011), pp. 324-327.
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[19].N. M. Ghonemi, M. A. Mandourand M. A. Serry,” phase composition, microstructure and properties of sintered La2O3–doped lime and dolomite grains”, Ceramic international, 16(1990)215-223. [20] .N.M. Ghoneim, M.A. Mandour, M.A. Serry, "Sintering of lime doped with La2O3 and CeO2", Ceramics International, 15 (1989) 357–362. [21]. R. Jingti, X. Bao, "Effect of NiO addition on the sintering properties of dolomite clinker", Journal of synthetic crystals 42(2013)1620-1625. [22]. L. Liu, M. Chen, L. Xu, X. Yin, W. Sun, “Effect of BaO addition on densification and mechanical properties of Al2O3-MgO-CaO refractories", Metals 6(2016)84. [23]. Zh. Han, D. X. Feng, Z. H. Zhong, Y. Jun, N. J. hua, “Effect of CaF2 on the defects formation and sintering properties of MgO-CaO materials”, Journal of Synthetic Crystals, (2014)01.
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[24] A.G.M. Othman, "Effect of talc and bauxite on sintering, microstructure and refractory properties of Egyptian dolomitic magnesite", British Ceramic Transactions, 102 (2003), pp. 265– 271. [25]. J. Lee, H. Cole, S. LEE, "Effect of Fe2O3 additions on the hydration resistance of CaO”, Journal of ceramic processing research, 13(2012), pp. 646-650.
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[28]. G.B. Qiu, B. Peng, M. Guo, and M. Zhang,” Regeneration utilization of spent MgO-CaO bricks for argon oxygen decarburization furnace”, J. Chin. Ceram. Soc., 41(2013) 1284.
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[29]. G. Qiu, B. Peng, X. Li, M. Guo, M. Zhang," Hydration resistance and mechanism of regenerated MgO–CaO bricks", Journal of the Ceramic Society of Japan 123 (2015)90-95. [30]. L.B. Khoroshavin, V.A. Perepelitsyn, on the nanotechnology of refractories, Refractory and Industrial Ceramic 40 (1999) 553–557. [31] E. Y, Pivinskii, P.V. Dyakin, Y. Yu, Pivinskii, S.V. Vikhman, "Nanoparticles and their effective use in the technology of highly concentrated binding suspensions (hcbs) and refractory castables", Refractory and Industrial Ceramic. 44 (2003) 314–318.
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[32]. S. Tamura, T. Ochiai, S. Takanaga, T. Kanai, H. Nakamura, "Nano-tech refractories 1: the development of the nanostructural matrix, in: Proceedings of UNITECR'03 Congress, 19–22 October, Osaka, Japan, (2003)517–520. [33]. D. V. Kuznetsov, D. V. Lysov, A. A. Nemtinov, A. S. Shaleiko, V. A. Korolkov, " Refractories in heat units Nano-materials in refractory technology", Refractories and industrial ceramics, 51(2010).
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Table1; Chemical composition and physical properties of raw materials Magnesite Dolomite
SiO2
0.95
0.7
Al2O3
1.6
2.8
Fe2O3
0.6
TiO2
0.2
CaO
2.7
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Oxide
MgO
Physical properties Bulk density(g/cm3) Apparent porosity(%)
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57.2 37.2
0.3
0.44
3.28-3.3 3.75-3.80
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0.2
93.2
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Alkalis
0.8
2.85-3.1 3.80-3.85
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Density (g/cm3) 5.24 2.9 5.22
Size (nm) 40-50 50±55 50-60
SSA ( m2/g) 115 90 80>
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Fe2O3 Al2O3 Cr2O3
Purity (%) 98> 99> 99.8>
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Oxide
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Table 2; Properties of the nanoparticles Color red white green
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Values -32 845 Insol. 10 Pale yellow
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Properties Pour Point(°C) Relative Density(15°C) Water Solubility Viscosity(40°C) Appearance
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Table 3; Physical and chemical properties of hydraulic oil
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Table 4; Batch composition with sample code
3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
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0 0.5 1 1.5 2 2.5 3 3.5 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Nano Cr2O3
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35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35
Nano Al2O3
Nano Fe2O3
0 0 0 0 0 0 0 0 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0 0 0 0 0 0 0
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MC MCF0.5 MCF1 MCF1.5 MCF2 MCF2.5 MCF3 MCF3. MCF4 MCA0.5 MCA1 MCA1.5 MCA2 MCA2.5 MCA3 MCA3.5 MCA4 MCCr0.5 MCCr1 MCCr1.5 MCCr2 MCCr2.5 MCCr3 MCCr3.5 MCCr4
Hydraulic Oil(wt. %)
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CaO (wt. %)
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Sample code
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.5 1 1.5 2 2.5 3 3.5 4
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Table 5; Mixing sequence of MgO-CaO refractory samples sequence
1 Coarse and medium magnesite and dolomite
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2 Addition of hydraulic oil
3 Addition of nano-particles and fine magnesite and
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Mixing time(min)
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Steps Mixing
2 5 10
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Table 6; EDX analyses of A) CaO, B) MgO, C) 2CaO.Fe2O3, D)3CaO.Al2O3, E)
Point C 40.77 32.17 -
Cr Fe
-
-
26.71
Au
0.44
0.53
Point D 28.74 38.45 32.51
0.34
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Point E 31.21 37.81 30.57
Point F 42.11 0.12 18.13 -
Point G 45.65 20.30 0.8 -
-
-
39.40 -
32.60 -
0.41
0.23
0.65
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Point B 35.05 64.42 -
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O Mg Ca Al
Point A 35.26 64.30 -
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Element
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12CaO·7Al2O3 , F) CaCr2O3 , and G) MgCr2O4 points.
0.3
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Fig1.TEM images of the a) Fe2O3, b) Al2O3, and C) Cr2O3 nanoparticles.
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Fig 2. XRD patterns of the a) Fe2O3, b) Al2O3, and c) Cr2O3 nanoparticles.
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Fig3. Variation of the a) bulk density and b) apparent porosity of the magnesite-dolomite
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refractory specimens as a function of nanoparticles addition.
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Fig.4 XRD pattern of the MC sample.
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Fig.5 XRD pattern of the A) MCF1.5 and b) MCF4 samples.
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Fig.6 XRD pattern of the A) MCA1.5 and b) MCA4 samples.
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Fig.7 XRD pattern of the A) MCCr1.5 and b) MCCr4 samples.
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Fig8. SEM images of the fractured surfaces of the samples a) without, b) 4wt% Fe2O3, c) 4wt% Al2O3, and d) 4wt% Cr2O3 nanoparticles.
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Fig9. Variation of the cold crushing strength of the magnesite-dolomite refractory specimens as a function of nanoparticles addition
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Fig10. Effect of nanoparticles addition on the improvement of magnesite-dolomite specimens hydration resistance.
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Highlights: 1- Fe2O3and Al2O3 improve MgO-CaO densification via liquid phase sintering mechanism.
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2- Cr2O3 improve MgO-CaO hydration resistance via solid state sintering mechanism.
3- Magnesite-dolomite hydration resistance improvement trend is Al2O3<
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Fe2O3< Cr2O3.