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Effects of microsilica addition on the microstructure and properties of alumina foams
Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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Ceramics International journal homepage: www.elsevier.com/locate/ceramint
Short communication
Effects of microsilica addition on the microstructure and properties of alumina foams Keke Huang a, Yuanbing Li a,n, Shujing Li a, Li Wang b, Shihan Wang a a b
The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology (WUST), Wuhan, 430081 PR China Yi Xing Hongye Insulation Engineering Co., Ltd, Yixing, 214200 PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 8 June 2016 Received in revised form 12 July 2016 Accepted 19 July 2016
Cellular alumina foams with porosity of 93.3–94.4% were fabricated by thermo-foaming of powder dispersions in molten D-glucose anhydrous. Up to 8 wt% microsilica was added to ceramic mixtures to explore its effect on the microstructure and properties of the sintered foams. The dispersions revealed a shear thinning and viscosity of the dispersions increased as microsilica addition increased. The shrinkage of samples decreased from 19.70% to 17.82%, the densities of samples decreased from 0.267 to 0.206 g/ cm3 and compressive strength decreased from 1.65 to 0.96 MPa when microsilica addition increased from 0 to 8 wt%. Furthermore, the curves of cell size distribution had a transformation from bimodal to unimodal and the amount of small windows in the foam reduced due to the addition of microsilica. & 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: Alumina Foams Microstructure Pore size distribution Compressive strength
1. Introduction Highly porous ceramics have attracted more and more attention because of their excellent properties such as high permeability, high surface area, high-temperature stability, low weight, and low thermal conductivity [1]. They are considered as candidate materials for filtration of molten metals and hot gases, thermal and acoustic insulation, catalytic carriers as well as biomaterials. During the past years, several methods have been developed to prepare ceramic foams, including replica [2], foam-gelcasting [3,4], freeze casting [5] and thermo-foaming method [6,7]. Among these, thermo-foaming method is the most attractive because it is a solvent and surfactant free process, totally avoids the use of synthetic and toxic processing additives and applicable to preparations of ceramics foams with high porosity and homogenous foam structure from top to bottom. Vijayan et al. [6] prepared alumina foams with porosity of 97.84–93.29 vol% by thermo-foaming of powder dispersions in molten sucrose followed by organic burnout and sintering. However, the final microstructure and properties of the ceramic foams produced by thermo-foaming method depend greatly on the viscosity of dispersions. The incorporation of microsilica could influence the viscosity of dispersions. In this work, up to 8 wt% microsilica was added to ceramic mixtures to examine its effect on the microstructure and properties of alumina n
Corresponding author.
foams. In addition, the reaction between Al2O3 and SiO2 in raw materials forms mullite at high temperature, which accompanies volume expansion. This could counteract the shrinkage of samples during the sintering.
2. Experimental procedure
α-Alumina powder (Kaifeng Special Refractories Co., Ltd., China, d50 ¼2.373 mm), microsilica powder (Elkem 951 U, SiO2 content Z94.0% d50 ¼ 0.602 mm) and analytical reagent grade D-glucose anhydrous (Sinopharm Chemical Reagent Co., Ltd., China.) were used as starting materials. The D-glucose monohydrate (80 g) and the powder mixture of alumina powder and microsilica (96 g) were mixed for 5 h in a polyurethane bottle rotating at a speed of 400 rev/min with corundum balls as the abrasive media. The addition of the microsilica powder was in the range of 0–8 wt%. The D-glucose anhydrous–powder mixtures were heated in a mold at 195 °C under stirring to form powder dispersions in molten Dglucose monohydrate. The dispersions were then kept at 130 °C in an air oven for foaming and setting. The demolded foamed bodies were cut into rectangular bodies and then sintered at 1550 °C for 3 h in air atmosphere. The heating rate used was 1 °C/min from room temperature to 600 °C and from 600 °C to 1550 °C. Particle size was measured by laser particle size analyzer (Mastersizer2000, Malvern Instruments Ltd., UK). The viscosity of the dispersions was evaluated at 130 °C using a rheometer (MCR
http://dx.doi.org/10.1016/j.ceramint.2016.07.134 0272-8842/& 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: K. Huang, et al., Effects of microsilica addition on the microstructure and properties of alumina foams, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.07.134i
2
K. Huang et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
301 Anton Paar Physics, Germany) with a cylindrical spindle measurement system (CC17-SN28332). The density of sintered foams was calculated by mass and dimension at a minimum of five samples with regular shapes. A Micromeritics AccuPyc1330 was used to measure the true density of sintered samples. The total porosity was calculated by the following formula:
⎛ ρ ⎞ Pt (%) = 100⎜⎜ 1 − b ⎟⎟ ρt ⎠ ⎝
Fig. 1. Rheological flow curves of dispersions containing different microsilica contents.
(1)
where Pt, total porosity; ρb, bulk density; ρt, true density. The linear shrinkage was calculated from measuring the sizes of samples before and after sintering. Microstructures of the sintered samples were observed using a scanning electron microscope (SEM, JSM-6610, JEOL, Japan). Cell and window size of the samples were measured using a micro-image analysis and process program (MIAPS, Precise, China) from the SEM microstructure. Compressive strength was examined using a universal testing machine (ETM, Wance, China) at a crosshead speed of 0.5 mm/min with 50 mm 40 mm 12 mm samples (ASTM standard C365/C365M05). Five samples were used to calculate the average compressive strength.
3. Results and discussion
Fig. 2. XRD patterns of the fired samples.
Fig. 3. The effect of microsilica addition on linear shrinkage and density of the fired samples.
Fig. 1 shows the rheological flow curves of dispersions with different fractions of microsilica powder at 130 °C. It could be seen that all the dispersions revealed a shear thinning and viscosity of the dispersions increased as microsilica addition increased. XRD patterns of sintered samples containing different microsilica additions are given in Fig. 2. For the sample without fumed silica, the corundum phase was observed only. With increasing microsilica content, the peak intensity associated with mullite enhanced gradually and their peak width became narrower, indicating that mullite crystals developed more perfectly. The effect of microsilica addition on the bulk density and linear shrinkage of the samples sintered at 1550 °C is shown in Fig. 3. The shrinkage of samples decreased from 19.70% to 17.82% when microsilica addition increased from 0 to 8 wt%. The decrease in shrinkage may be attributed to the volume expansion from the reaction between Al2O3 and SiO2 in raw materials. As seen in Fig. 3, the densities of samples decreased from 0.267 to 0.206 g/cm3 with the increase in microsilica addition. The corresponding porosity values were in the range from 93.3% to 94.4%. The Pore structures of sintered samples are presented in Fig. 4a–c. The foam showed interconnected cellular morphology. The spherical cells were connected through circular shaped windows. Comparing Fig. 4b–c with a, the amount of small windows in the foam fabricated with microsilica was less than those of the foam fabricated without microsilica. The windows were derived from the rupture of bubbles, which were affected by the viscosity of the dispersion. With the addition of microsilica, viscosity of the dispersion increased and hence the rupture of bubbles becomes more difficult. As a result, the amount of this kind of small windows decreased. As seen in Fig. 4d, the foam samples obtained from 8 wt% microsilica addition had dense strut and close packed grains on the cell wall surface. The cell size distribution of sintered samples obtained from various microsilica additions are illustrated in Fig. 5a. The median pore diameter of sintered samples without microsilica additions was about 659 mm. The cell size distribution of sintered foams without microsilica exhibited two noticeable peaks, where the cell
Please cite this article as: K. Huang, et al., Effects of microsilica addition on the microstructure and properties of alumina foams, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.07.134i
K. Huang et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
3
Fig. 4. SEM micrographs of sintered samples: (a) 0 wt%, (b) 4 wt%, (c) 8 wt%, (d) the strut region (8 wt%).
size were about 800 and 1200 mm, and the cell size mainly centralized on 800 mm. Meanwhile, the cell size distribution of sintered foams with 8 wt% microsilica addition exhibited only a peak where cell size was about 600 mm, and the median pore diameter is 576 mm. This suggested that the curves of cell size distribution changed from bimodal to unimodal due to the addition of microsilica. Moreover, cell size decreased with increasing microsilica addition. Fig. 5b shows the window size distribution of fired samples obtained from different microsilica additions. The window size distribution was between 7 mm and 355 mm. For samples without microsilica, quantitatively 91% windows lay in the range of 0–140 mm and 9% windows lay in the range of 140–360 mm. For samples with 8 wt% microsilica addition, 69% windows lay in the range of 0–140 mm and 31% windows lay in the range of 140–360 mm. This was consistent with what observed in microstructures. Typical load–displacement curves recorded during the compression of the foams are shown in Fig. 6a. Load–displacement curves of samples were similar to that of cellular ceramic [8,9], which was characterized by an initial linear phase followed by a long distance of plateaus due to the progressive collapse of the structure. The maximum load reached during the test was used to calculate the compressive strength of the sintered foam. Compressive strength of sintered samples decreased from 1.65 to 0.96 MPa with increasing microsilica addition, as shown in Fig. 6b.
When microsilica addition was 8 wt%, an average compressive strength of sintered samples with porosity of 94.4% was 0.96 MPa. Considering the high porosity, sintered foams with 8 wt% microsilica addition exhibited a relatively high-compressive strength. Thus, it is possible to adjust microsilica addition to obtain ceramic foams with high strength and small cell size.
4. Conclusions Cellular ceramic foams with and without microsilica addition were obtained by the thermo-foaming of powder dispersions in molten D-glucose anhydrous. The addition of microsilica affected the flow curves of the dispersions, the shrinkage after firing, the phases that form during sintering and the microstructure of the samples. With microsilica addition to dispersions, the viscosity increased, and the rheological behavior is altered. The linear shrinkage of samples decreased from 19.70% to 17.82%, the densities of samples decreased from 0.267 to 0.206 g/cm3 and compressive strength decreased from 1.65 to 0.96 MPa when microsilica addition increased from 0 to 8 wt%. Additionally, the curves of cell size distribution had a transformation from bimodal to unimodal and the amount of small windows in the foam reduced due to the addition of microsilica.
Please cite this article as: K. Huang, et al., Effects of microsilica addition on the microstructure and properties of alumina foams, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.07.134i
K. Huang et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
4
Fig. 6. (a) Typical compressive test data for sintered samples; (b) Compressive strength of sintered samples. Fig. 5. Cell and window size distribution of sintered foams obtained from various microsilica additions.
Acknowledgements This work was supported by the National Natural Science Foundation of China (51502213).
References [1] S. Barg, C. Soltmann, M. Andrade, D. Koch, G. Grathwohl, Cellular ceramics by direct foaming of emulsified ceramic powder suspensions, J. Am. Ceram. Soc. 91 (2008) 2823–2829. [2] I. Sopyan, J. Kaur, Preparation and characterization of porous hydroxyapatite through polymeric sponge method, Ceram. Int. 35 (2009) 3161–3168.
[3] F.K. Yang, C.W. Li, Y.M. Lin, C.A. Wang, Effects of sintering temperature on properties of porous mullite/corundum ceramics, Mater. Lett. 73 (2012) 36–39. [4] X.G. Deng, J.K. Wang, J.H. Liu, H.J. Zhang, F.L. Li, H.J. Duan, L.L. Lu, Z. Huang, W. G. Zhao, S.W. Zhang, Preparation and characterization of porous mullite ceramics via foam-gelcasting, Ceram. Int. 41 (2015) 9009–9017. [5] S.Q. Ding, Y.P. Zeng, D.L. Jiang, Fabrication of mullite ceramics with ultrahigh porosity by gel freeze drying, J. Am. Ceram. Soc. 90 (2007) 2276–2279. [6] S. Vijayan, R. Narasimman, C. Prudvi, K. Prabhakaran, Preparation of alumina foams by the thermo-foaming of powder dispersions in molten sucrose, J. Eur. Ceram. Soc. 34 (2014) 425–433. [7] K.K. Huang, Y.B. Li, Y. Zhao, S.J. Li, Y.W. Li, S.B. Sang, Effects of foaming temperature on the preparation and microstructure of alumina foams, Mater. Lett. 165 (2016) 19–21. [8] F.A.C. Oliveira, S. Dias, M.F. Vaz, J.C. Fernandes, Behaviour of open-cell cordierite foams under compression, J. Eur. Ceram. Soc. 26 (2006) 179–186. [9] S. Meille, M. Lombardi, J. Chevalier, L. Montanaro, Mechanical properties of porous ceramics in compression: on the transition between elastic, brittle, and cellular behavior, J. Eur. Ceram. Soc. 32 (2012) 3959–3967.
Please cite this article as: K. Huang, et al., Effects of microsilica addition on the microstructure and properties of alumina foams, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.07.134i
Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
Short communication
Effects of microsilica addition on the microstructure and properties of alumina foams Keke Huang a, Yuanbing Li a,n, Shujing Li a, Li Wang b, Shihan Wang a a b
The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology (WUST), Wuhan, 430081 PR China Yi Xing Hongye Insulation Engineering Co., Ltd, Yixing, 214200 PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 8 June 2016 Received in revised form 12 July 2016 Accepted 19 July 2016
Cellular alumina foams with porosity of 93.3–94.4% were fabricated by thermo-foaming of powder dispersions in molten D-glucose anhydrous. Up to 8 wt% microsilica was added to ceramic mixtures to explore its effect on the microstructure and properties of the sintered foams. The dispersions revealed a shear thinning and viscosity of the dispersions increased as microsilica addition increased. The shrinkage of samples decreased from 19.70% to 17.82%, the densities of samples decreased from 0.267 to 0.206 g/ cm3 and compressive strength decreased from 1.65 to 0.96 MPa when microsilica addition increased from 0 to 8 wt%. Furthermore, the curves of cell size distribution had a transformation from bimodal to unimodal and the amount of small windows in the foam reduced due to the addition of microsilica. & 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: Alumina Foams Microstructure Pore size distribution Compressive strength
1. Introduction Highly porous ceramics have attracted more and more attention because of their excellent properties such as high permeability, high surface area, high-temperature stability, low weight, and low thermal conductivity [1]. They are considered as candidate materials for filtration of molten metals and hot gases, thermal and acoustic insulation, catalytic carriers as well as biomaterials. During the past years, several methods have been developed to prepare ceramic foams, including replica [2], foam-gelcasting [3,4], freeze casting [5] and thermo-foaming method [6,7]. Among these, thermo-foaming method is the most attractive because it is a solvent and surfactant free process, totally avoids the use of synthetic and toxic processing additives and applicable to preparations of ceramics foams with high porosity and homogenous foam structure from top to bottom. Vijayan et al. [6] prepared alumina foams with porosity of 97.84–93.29 vol% by thermo-foaming of powder dispersions in molten sucrose followed by organic burnout and sintering. However, the final microstructure and properties of the ceramic foams produced by thermo-foaming method depend greatly on the viscosity of dispersions. The incorporation of microsilica could influence the viscosity of dispersions. In this work, up to 8 wt% microsilica was added to ceramic mixtures to examine its effect on the microstructure and properties of alumina n
Corresponding author.
foams. In addition, the reaction between Al2O3 and SiO2 in raw materials forms mullite at high temperature, which accompanies volume expansion. This could counteract the shrinkage of samples during the sintering.
2. Experimental procedure
α-Alumina powder (Kaifeng Special Refractories Co., Ltd., China, d50 ¼2.373 mm), microsilica powder (Elkem 951 U, SiO2 content Z94.0% d50 ¼ 0.602 mm) and analytical reagent grade D-glucose anhydrous (Sinopharm Chemical Reagent Co., Ltd., China.) were used as starting materials. The D-glucose monohydrate (80 g) and the powder mixture of alumina powder and microsilica (96 g) were mixed for 5 h in a polyurethane bottle rotating at a speed of 400 rev/min with corundum balls as the abrasive media. The addition of the microsilica powder was in the range of 0–8 wt%. The D-glucose anhydrous–powder mixtures were heated in a mold at 195 °C under stirring to form powder dispersions in molten Dglucose monohydrate. The dispersions were then kept at 130 °C in an air oven for foaming and setting. The demolded foamed bodies were cut into rectangular bodies and then sintered at 1550 °C for 3 h in air atmosphere. The heating rate used was 1 °C/min from room temperature to 600 °C and from 600 °C to 1550 °C. Particle size was measured by laser particle size analyzer (Mastersizer2000, Malvern Instruments Ltd., UK). The viscosity of the dispersions was evaluated at 130 °C using a rheometer (MCR
http://dx.doi.org/10.1016/j.ceramint.2016.07.134 0272-8842/& 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: K. Huang, et al., Effects of microsilica addition on the microstructure and properties of alumina foams, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.07.134i
2
K. Huang et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
301 Anton Paar Physics, Germany) with a cylindrical spindle measurement system (CC17-SN28332). The density of sintered foams was calculated by mass and dimension at a minimum of five samples with regular shapes. A Micromeritics AccuPyc1330 was used to measure the true density of sintered samples. The total porosity was calculated by the following formula:
⎛ ρ ⎞ Pt (%) = 100⎜⎜ 1 − b ⎟⎟ ρt ⎠ ⎝
Fig. 1. Rheological flow curves of dispersions containing different microsilica contents.
(1)
where Pt, total porosity; ρb, bulk density; ρt, true density. The linear shrinkage was calculated from measuring the sizes of samples before and after sintering. Microstructures of the sintered samples were observed using a scanning electron microscope (SEM, JSM-6610, JEOL, Japan). Cell and window size of the samples were measured using a micro-image analysis and process program (MIAPS, Precise, China) from the SEM microstructure. Compressive strength was examined using a universal testing machine (ETM, Wance, China) at a crosshead speed of 0.5 mm/min with 50 mm 40 mm 12 mm samples (ASTM standard C365/C365M05). Five samples were used to calculate the average compressive strength.
3. Results and discussion
Fig. 2. XRD patterns of the fired samples.
Fig. 3. The effect of microsilica addition on linear shrinkage and density of the fired samples.
Fig. 1 shows the rheological flow curves of dispersions with different fractions of microsilica powder at 130 °C. It could be seen that all the dispersions revealed a shear thinning and viscosity of the dispersions increased as microsilica addition increased. XRD patterns of sintered samples containing different microsilica additions are given in Fig. 2. For the sample without fumed silica, the corundum phase was observed only. With increasing microsilica content, the peak intensity associated with mullite enhanced gradually and their peak width became narrower, indicating that mullite crystals developed more perfectly. The effect of microsilica addition on the bulk density and linear shrinkage of the samples sintered at 1550 °C is shown in Fig. 3. The shrinkage of samples decreased from 19.70% to 17.82% when microsilica addition increased from 0 to 8 wt%. The decrease in shrinkage may be attributed to the volume expansion from the reaction between Al2O3 and SiO2 in raw materials. As seen in Fig. 3, the densities of samples decreased from 0.267 to 0.206 g/cm3 with the increase in microsilica addition. The corresponding porosity values were in the range from 93.3% to 94.4%. The Pore structures of sintered samples are presented in Fig. 4a–c. The foam showed interconnected cellular morphology. The spherical cells were connected through circular shaped windows. Comparing Fig. 4b–c with a, the amount of small windows in the foam fabricated with microsilica was less than those of the foam fabricated without microsilica. The windows were derived from the rupture of bubbles, which were affected by the viscosity of the dispersion. With the addition of microsilica, viscosity of the dispersion increased and hence the rupture of bubbles becomes more difficult. As a result, the amount of this kind of small windows decreased. As seen in Fig. 4d, the foam samples obtained from 8 wt% microsilica addition had dense strut and close packed grains on the cell wall surface. The cell size distribution of sintered samples obtained from various microsilica additions are illustrated in Fig. 5a. The median pore diameter of sintered samples without microsilica additions was about 659 mm. The cell size distribution of sintered foams without microsilica exhibited two noticeable peaks, where the cell
Please cite this article as: K. Huang, et al., Effects of microsilica addition on the microstructure and properties of alumina foams, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.07.134i
K. Huang et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
3
Fig. 4. SEM micrographs of sintered samples: (a) 0 wt%, (b) 4 wt%, (c) 8 wt%, (d) the strut region (8 wt%).
size were about 800 and 1200 mm, and the cell size mainly centralized on 800 mm. Meanwhile, the cell size distribution of sintered foams with 8 wt% microsilica addition exhibited only a peak where cell size was about 600 mm, and the median pore diameter is 576 mm. This suggested that the curves of cell size distribution changed from bimodal to unimodal due to the addition of microsilica. Moreover, cell size decreased with increasing microsilica addition. Fig. 5b shows the window size distribution of fired samples obtained from different microsilica additions. The window size distribution was between 7 mm and 355 mm. For samples without microsilica, quantitatively 91% windows lay in the range of 0–140 mm and 9% windows lay in the range of 140–360 mm. For samples with 8 wt% microsilica addition, 69% windows lay in the range of 0–140 mm and 31% windows lay in the range of 140–360 mm. This was consistent with what observed in microstructures. Typical load–displacement curves recorded during the compression of the foams are shown in Fig. 6a. Load–displacement curves of samples were similar to that of cellular ceramic [8,9], which was characterized by an initial linear phase followed by a long distance of plateaus due to the progressive collapse of the structure. The maximum load reached during the test was used to calculate the compressive strength of the sintered foam. Compressive strength of sintered samples decreased from 1.65 to 0.96 MPa with increasing microsilica addition, as shown in Fig. 6b.
When microsilica addition was 8 wt%, an average compressive strength of sintered samples with porosity of 94.4% was 0.96 MPa. Considering the high porosity, sintered foams with 8 wt% microsilica addition exhibited a relatively high-compressive strength. Thus, it is possible to adjust microsilica addition to obtain ceramic foams with high strength and small cell size.
4. Conclusions Cellular ceramic foams with and without microsilica addition were obtained by the thermo-foaming of powder dispersions in molten D-glucose anhydrous. The addition of microsilica affected the flow curves of the dispersions, the shrinkage after firing, the phases that form during sintering and the microstructure of the samples. With microsilica addition to dispersions, the viscosity increased, and the rheological behavior is altered. The linear shrinkage of samples decreased from 19.70% to 17.82%, the densities of samples decreased from 0.267 to 0.206 g/cm3 and compressive strength decreased from 1.65 to 0.96 MPa when microsilica addition increased from 0 to 8 wt%. Additionally, the curves of cell size distribution had a transformation from bimodal to unimodal and the amount of small windows in the foam reduced due to the addition of microsilica.
Please cite this article as: K. Huang, et al., Effects of microsilica addition on the microstructure and properties of alumina foams, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.07.134i
K. Huang et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
4
Fig. 6. (a) Typical compressive test data for sintered samples; (b) Compressive strength of sintered samples. Fig. 5. Cell and window size distribution of sintered foams obtained from various microsilica additions.
Acknowledgements This work was supported by the National Natural Science Foundation of China (51502213).
References [1] S. Barg, C. Soltmann, M. Andrade, D. Koch, G. Grathwohl, Cellular ceramics by direct foaming of emulsified ceramic powder suspensions, J. Am. Ceram. Soc. 91 (2008) 2823–2829. [2] I. Sopyan, J. Kaur, Preparation and characterization of porous hydroxyapatite through polymeric sponge method, Ceram. Int. 35 (2009) 3161–3168.
[3] F.K. Yang, C.W. Li, Y.M. Lin, C.A. Wang, Effects of sintering temperature on properties of porous mullite/corundum ceramics, Mater. Lett. 73 (2012) 36–39. [4] X.G. Deng, J.K. Wang, J.H. Liu, H.J. Zhang, F.L. Li, H.J. Duan, L.L. Lu, Z. Huang, W. G. Zhao, S.W. Zhang, Preparation and characterization of porous mullite ceramics via foam-gelcasting, Ceram. Int. 41 (2015) 9009–9017. [5] S.Q. Ding, Y.P. Zeng, D.L. Jiang, Fabrication of mullite ceramics with ultrahigh porosity by gel freeze drying, J. Am. Ceram. Soc. 90 (2007) 2276–2279. [6] S. Vijayan, R. Narasimman, C. Prudvi, K. Prabhakaran, Preparation of alumina foams by the thermo-foaming of powder dispersions in molten sucrose, J. Eur. Ceram. Soc. 34 (2014) 425–433. [7] K.K. Huang, Y.B. Li, Y. Zhao, S.J. Li, Y.W. Li, S.B. Sang, Effects of foaming temperature on the preparation and microstructure of alumina foams, Mater. Lett. 165 (2016) 19–21. [8] F.A.C. Oliveira, S. Dias, M.F. Vaz, J.C. Fernandes, Behaviour of open-cell cordierite foams under compression, J. Eur. Ceram. Soc. 26 (2006) 179–186. [9] S. Meille, M. Lombardi, J. Chevalier, L. Montanaro, Mechanical properties of porous ceramics in compression: on the transition between elastic, brittle, and cellular behavior, J. Eur. Ceram. Soc. 32 (2012) 3959–3967.
Please cite this article as: K. Huang, et al., Effects of microsilica addition on the microstructure and properties of alumina foams, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.07.134i