《复合材料 Composites》课程教学资源（学习资料）第五章 陶瓷基复合材料_Al2O3-SiC-6

Ceramics international 21(1995)1-4 Usefulness of Alumina-coated SiC Whiskers in the Preparation of whisker-reinforced Alumina Ceramics A Kato, * H. Nakamura Department of Chemical Science and Technology, Faculty af Engineering, K yushu University, Fukuoka 812, Japan N. Tamari, T. Tanaka &l. Kondo Osaka National Research Institute, Osaka, Ikeda-shi, Osaka 563, Japan (Received 10 November 1993; accepted 10 December 1993) Abstract: Alumina coated siC were used as the starting material for the fabrication of SiC-whisker ed alumina ceramics. Sintering density and the dispersion state of Sic were improved by using alumina coated SiC whiskers, Mechanical strength increased 1.5 times by using alumina coated SiC whiskers 1 INTRODUCTION alumina ceramics were prepared by using alu mina-coated whiskers. Mechanical strength value In order to increase the strength and reliability of were also determined whisker-reinforced ceramics, it is important to dis- perse the whiskers uniformly in the matrix. When 2 EXPERIMENTAL PROCEDURE hiskers coated with the matrix substance are used as a raw material, it is expected that the Commercial Sic whiskers (TW$400, average di agglomeration of whiskers in the matrix can be ameter: 1. 2 um, average length: 40 um, Toka educed and a more uniform dispersion can be Carbon Co, Ltd. were coated with alumina hy- obtained. Furthermore in th here the drate from aluminum sulfate aqueous solution by ubstance of the whiskers is different from that of homogeneous precipitation techniques. The coat the matrix, the pre-coating of the whiskers with ing was carried out at 70C under the following the matrix substance provides the same surface conditions: suspension of Sic whiskers =9.0 g/l, properties for them as for the matrix substance, [AL2(SO4)3]=0-075 mol/, [urea]= 10-8 mol/l, stir- thus reducing the difficulties in powder handling ring rate of the reacting solution 850 rpm. The during wet molding coated particles were calcined at 1150C for 1 h in Based on these viewpoints, the authors have an Ar atmosphere. By this calcination the alumina studied the method to coat whiskers with the hydrate changed to a-Al2O3. The ratio of coated matrix substance with the intention to use them as alumina/Sic whisker was 40/60 (in vol). The cal- a raw material for whisker-reinforced ceramics. 1, 2 cined powder is shown in Fig. 1 Recently, Kapolnek and Dejonghe3 reported that Alumina-coated or uncoated Sic whiskers were in the production of whisker-dispersed ceramics, mixed with fine a-Al2O3 powders(AKP-50 of Sumi- the use of matrix-coated whiskers was effective for tomo Chemical Co, Ltd, >99.99% purity, Mg the uniform dispersion of whiskers 10 ppm, particle size 0-1-0. 3 um, surface area 10.7 In the present study, SiC-whisker-reinforced m"g)in ethanol to give the volume ratio SiC/AlO =1/9 or 3/7. The preparation of Sic whisker- To whom correspondence should be addressed Al,O, powder mixtures was carried out as follows Ceramics Internationa! (272-8842/95/$9.50 1995 Elsevier Science Limited, England and Techna S.r. 1. Printed in Great Britain

Ceramics International 21 (1995) 14 Usefulness of Alumina-coated Sic Whiskers in the Preparation of Whisker-reinforced Alumina Ceramics A. Kate,* H. Nakamura, Department of Chemical Science and Technology, Faculty c$ Engineering, Kyushu University, Fukuoka 812, Japan N. Tamari, T. Tanaka & I. Kondo Osaka National Research Institute, Osaka, Ikeda-shi, Osaka 563, Japan (Received 10 November 1993; accepted 10 December 1993) Abstract: Alumina coated SIC whiskers were used as the starting material for the fabrication of Sic-whisker-reinforced alumina ceramics. Sintering density and the dispersion state of Sic whiskers were improved by using alumina coated Sic whiskers. Mechanical strength increased 1.5 times by using alumina coated BC whiskers. 1. In INTRODUCTION order to increase the strength and reliability of whisker-reinforced ceramics, it is important to dis￾perse the whiskers uniformly in the matrix. When whiskers coated with the matrix substance are used as a raw material, it is expected that the agglomeration of whiskers in the matrix can be reduced and a more uniform dispersion can be obtained. Furthermore, in the case where the substance of the whiskers is different from that of the matrix, the pre-coating of the whiskers with the matrix substance provides the same surface properties for them as for the matrix substance, thus reducing the difficulties in powder handling during wet molding. Based on these viewpoints, the authors have studied the method to coat whiskers with the matrix substance with the intention to use them as a raw material for whisker-reinforced ceramics. 1,2 Recently, Kapolnek and Dejonghe3 reported that in the production of whisker-dispersed ceramics, the use of matrix-coated whiskers was effective for the uniform dispersion of whiskers. In the present study, Sic-whisker-reinforced * To whom correspondence should be addressed. alumina ceramics were prepared by using alu￾mina-coated whiskers. Mechanical strength values were also determined. 2. EXPERIMENTAL PROCEDURE Commercial Sic whiskers (TWS400, average di￾ameter: 1.2 pm, average length: 40 pm, Tokai Carbon Co., Ltd.) were coated with alumina hy￾drate from aluminum sulfate aqueous solution by homogeneous precipitation techniques.2 The coat￾ing was carried out at 70°C under the following conditions: suspension of Sic whiskers = 9.0 g/l, [Al,(SO,)3] = 0.075 mol/l, [urea] = 10.8 mol/l, stir￾ring rate of the reacting solution = 850 t-pm. The coated particles were calcined at 1150°C for 1 h in an Ar atmosphere. By this calcination the alumina hydrate changed to a-Al2O3. The ratio of coated alumina/Sic whisker was 40/60 (in vol). The cal￾cined powder is shown in Fig. 1. Alumina-coated or uncoated Sic whiskers were mixed with fine c~-Al2O3 powders (AKP-50 of Sumi￾tomo Chemical Co., Ltd., >99.99% purity, Mg < 10 ppm, particle size 0.1-0.3 pm, surface area 10.7 m2/g) in ethanol to give the volume ratio SiC/Al,O, = l/9 or 3/7. The preparation of Sic whisker￾Al203 powder mixtures was carried out as follows: Ceramics International 0272-8842/95/$9.50 0 1995 Elsevier Science Limited, England and Techna S.r.1. Printed in Great Britain

A. Kato, H. Nakamura, N. Tamari, T. Tanaka, I. Kondo Al, O3-coated SiC whiskers(A) a-Al2O3 powde or uncoated SiC whiskers (B) (AKP-50) Dispersion in ethanol ultrasonic Dispersion ultrasonic (Solid 1 vol%) agitation in ethanol agitation (A): 15 min (Solid 1 Vol%) (B): 60 min Mixing-ultrasonic itation(15 min) Evaporation Drying under stirring of ethanol g-type atbp.784°C) The powder mixtures prepared are shown in Table 1. Raw powders for Sic-whisker-reinforced Table 1 alumina ceramics Hot-pressing was used for densification. the resulting powders were packed in a graphite mold No. Sic whisk Constituent of raw powders vo|%) pressed at 30 MPa, then heated at around 60° C/min to l800°for30 min and allowed to ar-Al2Oa powder cool after the pressure was released The size of uncoated SiC whiskers 10 Cr-AI2O3+Al2O3-coated SiC whiskers AlO, +uncoated SiC whiskers 30 a-Al2O3+AI2O3-coated SiC whiskers the sintered specimen was approximately 20 mm X 40mm×5mm wig ot pressed disks thus prepared were polished a #f 200 diamond wheel and their densities were measured by the Archimedes method. Hot- pressed disks were cut into bars with nominal dimensions of 3 mm x 4 mm x 40 mm. The bars were prepared for flexure tests by grinding three 5 um surfaces and beveling the edges(to be in tension) with a# 800 diamond grind plate. Room-temper- ature flexural strength was measured in a three- point-bending mode, with a span of 30 mm, at a loading rate of 0.5 mm/min. The measurement was carried out on four bars from each hot pressed disk 3. RESULTS AND DISCUSSION Figure 2 shows the Si distribution on the surface i: 1 00 s6 56d si 2]m perpendicular to the hot-press axis of the sintered bodies. From this picture, one can observe that the use of alumina- coated Sic whiskers improves Fig. 1. Calcined product, Reaction condition: [ SiC]=9 g/l, [Al(So4)3]=0075 mol, [urea]= 10-8 mol/, Temp =70C, he dispersion state of Sic whiskers Stirring rate = 850 rpm, volume of reaction solution= 500 ml Sintered density and mechanical properties of Calcination condition: 1150%C. I h in a: the four samples are summarized in Table 2. The

2 A. Kato, H. Nakamura, N. Tamari, T. Tanaka, I. Kondo Al,O,-coated Sic whiskers (A) or uncoated SIC whiskers (B) CY-A&O~ powder (AKP-50) Dispersion in ethanol (Solid 1 ~01%) ultrasonic agitation (A): 15 min (B): 60 min Dispersion in ethanol (Solid 1 Vol%) ultrasonic agitation (60 min) Mixing -ultrasonic agitation (15 min) Drying under stirring with wing-type stirrer The powder mixtures prepared are shown in Table 1. Hot-pressing was used for densification. The resulting powders were packed in a graphite mold, pressed at 30 MPa, then heated at around 60Wmin to 1800°C for 30 min and allowed to cool after the pressure was released. The size of Fig. 1. Calcined product. Reaction condition: [Sic] = 9 g/l, [Al,(SO,),] = 0.075 mol/l, [urea] = 10.8 mol/l, Temp.= 7O”C, Stirring rate = 850 rpm, volume of reaction solution = 500 ml. Calcination condition: 1 150°C, 1 h in Ar. Table 1. Raw powders for Sic-whisker-reinforced alumina ceramics No. SIC whisker (vol%) Constituent of raw powders 1 10 cu-AI,OB powder + uncoated SIC whiskers 2 10 a-AlpOB + Al,O,-coated Sic whiskers 3 30 a-AIIOB + uncoated SIC whiskers 4 30 c”-AI,OB + A&O,-coated Sic whiskers the sintered specimen was approximately 20 mm X 40mmX5mm. Hot-pressed disks thus prepared were polished with a # 200 diamond wheel and their densities were measured by the Archimedes method. Hot￾pressed disks were cut into bars with nominal dimensions of 3 mm X 4 mm X 40 mm. The bars were prepared for flexure tests by grinding three surfaces and beveling the edges (to be in tension) with a # 800 diamond grind plate. Room-temper￾ature flexural strength was measured in a three￾point-bending mode, with a span of 30 mm, at a loading rate of 0.5 mmmin. The measurement was carried out on four bars from each hot￾pressed disk, 3. RESULTS AND DISCUSSION Figure 2 shows the Si distribution on the surface perpendicular to the hot-press axis of the sintered bodies. From this picture, one can observe that the use of alumina-coated SIC whiskers improves the dispersion state of SIC whiskers. Sintered density and mechanical properties of the four samples are summarized in Table 2. The

Alumina-coated Sic whisk Un-coated SiC whisker Al2 03-coated SiC whisker 10vo|% SiC x588Bus,aKv188以 x88aa含·5,kv18 No.1 No. 2 30vo|% SiC x800 0000 B, Oky own x5BR日5,8HV1aH No. 3 No 4 50m Fig. 2. Distribution of Si element of sintered body. (XMA mapping of Si Kg )(Surface perpendicular to hot press axis. strength of the SiC-whisker-reinforced alumina strength of whisker-reinforced ceramics is affected prepared from alumina-coated Sic whiskers are by many factors including the bonding strength at comparable with those of SiC-whisker-reinforced the alumina-SiC interface, the morphology and lumina prepared by conventional powder pro- size of the whiskers, the orientation state of the cessing method from finer SiC whisker and whiskers, sintering aid, etc. Thus, further investi- alumina powder containing 0. 25 wt% MgO. The gations are needed to get stronger composites However. Table 2 shows that the use of alumina Table 2. Density and mechanical properties of sic whisker-reinforced alumina coated SiC whiskers gave a higher sintered density when the SiC content was 30 vol% and signifi- Sample no. Density cantly higher flexural strengths. These improve g/cm2(%TD. strength(MPa) ments may be due to the more uniform dispersion of Sic whiskers which was described above and 3899 shows the advantage of the use of alumina-coated (999%) 3911 Sic whiskers as a starting material (100%) 4. CONCLUSIONS In the preparation of whisker-reinforced ce (996%) the use of matrix-coated whiskers is effective see Table in improving the dispersion of whiskers in the b %T D was calculated on the basis of theoretical densi- resulting composite and hence improving the ties 3.21 g/cm for Sic and 3- 98 g/cm for Al2 O3 mechanical properties

Alumina-coated SC whiskers 3 1 Oval% SC 3Ovol% Sic 1 No.1 1 1 No.21 AlpO,-coated Sic whisker 1 No.31 I No.41 c I I I 50 CI m Fig. 2. Distribution of Si element of sintered body. (XMA mapping of Si K,.) (Surface perpendicular to hot press axis.) strength of the Sic-whisker-reinforced alumina prepared from alumina-coated SIC whiskers are comparable with those of Sic-whisker-reinforced alumina prepared by conventional powder pro￾cessing method from finer SIC whisker and alumina powder containing 0.25 wt% Mg0.4 The Table 2. Density and mechanical properties of SE￾whisker-reinforced alumina Sample no.’ 1 2 3 4 Density* g/cm3(% T.D.) 3.899 (99.9 %I 3.911 (100 %) 3.638 (97.0 %I 3.734 (99.6 %) Flexural strength (MPa) 289 369 400 568 a see Table 1. b % T.D. was calculated on the basis of theoretical densi￾ties 3.21 g/cm3 for SIC and 3.98 g/cm3 for AI,O,. strength of whisker-reinforced ceramics is affected by many factors including the bonding strength at the alumina-sic interface, the morphology and size of the whiskers, the orientation state of the whiskers, sintering aid, etc. Thus, further investi￾gations are needed to get stronger composites. However, Table 2 shows that the use of alumina￾coated SIC whiskers gave a higher sintered density when the Sic content was 30 ~01% and signifi￾cantly higher flexural strengths. These improve￾ments may be due to the more uniform dispersion of SIC whiskers which was described above and shows the advantage of the use of alumina-coated Sic whiskers as a starting material. 4. CONCLUSIONS In the preparation of whisker-reinforced ceramics, the use of matrix-coated whiskers is effective in improving the dispersion of whiskers in the resulting composite and hence improving the mechanical properties

A. Kato, H. Nakamura. N. Tamari. T. Tanaka, I. Kona REFERENCES morphology of coated body. J. Ceram. Soc. 0(1993)7738 3. D. KAPOLNEK, D. DEJoNGHE. L C. Particulate NAKAMURA, H. Kato, A, Effect of crystallization composites from coated powders. J. Eur. Ceram. Soc., 7 of alumina hydrate in preparation of alumina coated (1991)3455 composite particles. Ceram Inter, 18(1992)201-6 4. SMITH, S M.& SINGH, J P, Processing and charac 2. NAKAMURA, H& Kato. A, Preparation of alumina terization of sic-whisker -reinforced alumina-matrix com hydrate-coated Sic whisker-effect of reaction condition osites. J. Am. Ceram. Soc., 76(1993)497-502

4 A. Kate, H. Nakamura, N. Tamari, T. Tanaka, I. Kondo REFERENCES 1. NAKAMURA, H. & KATO, A., Effect of crystallization of alumina hydrate in preparation of alumina coated composite particles. Ceram Inter., 18 (1992) 201-6. 2. NAKAMURA, H. & KATO, A., Preparation of alumina hydrate-coated Sic whisker-effect of reaction condition on the morphology of coated body. J. Ceram. Sot. Japan, 101 (1993) 773-8. 3. D. KAPOLNEK, D. & DEJONGHE, L. C., Particulate composites from coated powders. J. Eur. Ceram. Sot., 7 (1991) 345-51. 4. SMITH, S. M. & SINGH, J. P., Processing and charac￾terization of Sic-whisker-reinforced alumina-matrix com￾posites. J. Am. Ceram. Sot., 76 (1993) 497-502