J.Am. Ceram Soc.,861962-6402003) urna Mullite-Aluminum Phosphate Laminated Composite Fabricated by tape castin 8 Department of Materials Science and Engineering, University of Illinois, Urbana, Illinois 61801 Mullite-aluminum phosphate (3Al,O3 2SiO,/AlPO4)lami- II. Experimental Procedure nated composites were fabricated by tape casting. a density of 1.56 g/cm, which corresponds to 61% Commercial mullite(KM 101, Kyoritsu Ceramics Materials density, and a bending strength of 1.5 MPa after Co. Ltd, Nagoya, Japan) powder was used. Aluminum phos- at 1600 C for 10 h. The aluminum phosphate functioned as a phate was synthesized by the organic, steric entrapment meth- porous, weak, and chemically stable interphase which was able od. To synthesize AlPO4, aluminum nitrate nonahydrate to deflect cracks in a laminated composite. To increase the [AI(NO3)3 9H2O, 98+%, Aldrich Chemical, Inc, Milwaukee, strength of the weak interphase material, 10 and 30 vol% of wI and diabasic ammonium phosphate [(NH4)2. HPO4, Fisher mullite were added Scientific, Fair Lawn, NJ were used as the Al and P source, respectively. The nitrates are first mixed in the distilled water. After 30 min of mixing, 5 wt% poly( vinyl alcohol)(PVA, 205S, Celanese, Ltd, Dallas, TX) solution was added to the solution followed by another 50 min of mixing. The solution was ther A LUMINUM PHOSPHATE(AlPO4)has long been known for its heated at 200% and 400C to remove the water. The partiall imilar structure and analogous polymorphic transformations dehydrated cake was dried at 150C overnight and finally to silica. The a(tetragonal)-B(cubic)cristobalite transforma- calcined at900°C tion, on heating, is known to be clearly first order, with a volum The laminated composites were made by the -casting hange of +4.44%. AlPO, is chemically inert, thermally stable ocess. A mixture of 60 wt% ethanol(ethyl alcohol USP, AAPER (mp=2000C), electrically neutral, and highly covalent. These ALCOL and Chemical, Shelbyville, KY)and 40 wt% methyl ethyl properties make AlPO4 an attractive candidate material for high ketone(99.8%, Fisher Scientific) was used as a solvent. Phosphate temperature applications. AlPO, is known to be difficult to sinter ester(Emphos PS-21A, Witco Chemicals, Houston, TX) was the dispersant. The binder was poly( vinyl butyral)(Butvar B90 because of its high degree of covalency. There are some reports Solutia Chemicals, New Milford, CT). Poly(ethylene glycol) concerning the volatilization of P2Os from AIPO. 3,5,6 Gitzen er(300NF, FCC grade, Union Carbide Chemicals and Plastics Co al. fabricated AlPO -bonded, alumina castables and noted that the inc, Danbury, CT) and dibutyl phthalate(99%, Aldrich)were used as plasticizers. A conventional tape-casting machine with double doctor blades was used. The speed of casting was I cm/s Laminated ceramic composites have been made by tape casting, The procedures for making laminated composites were as follows rolling, slip casting, and electrophorectic deposition, etc. Some powder solvent(48-h ball milling)- powder solvent typical laminated composite systems that have been fabricated clude Al, O, /ZrO2, Al,O, /LaPO4, Al,ZrO,/YPO4, etc plasticizer binder (24-h ball milling)- deairing(rotated at slow peed without balls)- casting cutting and laminating Crack deflection in the Al2O3/Zro2 laminated composite was thermocompression(80 C/(1 h)-345 MPa uniaxial pressing) attributed to residual stresses at the interface 7,9 Morgan et al. 8 binder removal(l°C/ min to I50°C→0.1° min to600°C/(2h) suggested that a monazite ( LapOahalumina interface is weak →CP(413.7MPa)→ sintering(l600°C/10h) enough to produce interfacial debonding when a crack approaches The particle size of synthesized AlPO4 powder before and after t. However, no laminated system has been made to date using I h attrition milling was measured using a centrifugal, automatic AlPOa as a crack deflecting interphase particle size distribution analyzer(Model CAPA-700, Horiba, In this study, the chemical stability and physical and mechanical Kyoto, Japan ). The specific surface area was measured by seve perties of AlPO4 were studied. Mullite-aluminum phosphate point BET analysis from nitrogen gas adsorption(Model ASAP (, 2SiO2/AlPO) laminated composites were investigated to 2400, Micrometrics, Norcross, GA). The sample was dried at see whether AlPO, could function as a crack-deflecting interphase 150 C overnight to remove the moisture before BET analysis. The n a ceramic composite system bulk density of the sintered material was measured by the Archimedes method (ASTM C373). To check for possible vola tilization of po. from the 2AIPO three different kinds of AlPOa were acid-treated, heated, and nalyzed in a Perkin-Elmer Model Plasma Il, inductively coupled asma(ICP) analyzer. The chemical compatibility between mul lite and alpo checked by a rigaku x F W. Zok--contributing editor Model D-Max automated diffractometer, Rigaku/USA, Danvers, MA). The two powders were mixed by 24-h ball milling, sintered 1600°C(10h),and 二二 eceived June 6, 2002; approved June 12, 2003. diffraction(XRD). The microstructures of the lami ites were examined by scanning electron microsc mnv ise M. Mode S-530, Hitachi, Osaka, Japan)
Mullite–Aluminum Phosphate Laminated Composite Fabricated by Tape Casting Dong-Kyu Kim* and Waltraud M. Kriven** Department of Materials Science and Engineering, University of Illinois, Urbana, Illinois 61801 Mullite–aluminum phosphate (3Al2O32SiO2/AlPO4) laminated composites were fabricated by tape casting. AlPO4 had a density of 1.56 g/cm3 , which corresponds to 61% of theoretical density, and a bending strength of 1.5 MPa after sintering at 1600°C for 10 h. The aluminum phosphate functioned as a porous, weak, and chemically stable interphase which was able to deflect cracks in a laminated composite. To increase the strength of the weak interphase material, 10 and 30 vol% of mullite were added. I. Introduction ALUMINUM PHOSPHATE (AlPO4) has long been known for its similar structure and analogous polymorphic transformations to silica.1 The (tetragonal) 3 (cubic) cristobalite transformation, on heating, is known to be clearly first order, with a volume change of 4.44%.2 AlPO4 is chemically inert, thermally stable (mp 2000°C3 ), electrically neutral, and highly covalent. These properties make AlPO4 an attractive candidate material for hightemperature applications.4 AlPO4 is known to be difficult to sinter because of its high degree of covalency.4 There are some reports concerning the volatilization of P2O5 from AlPO4. 3,5,6 Gitzen et al. 5 fabricated AlPO4-bonded, alumina castables and noted that the castables gave excellent serviceability in temperature ranges to 1870°C. Laminated ceramic composites have been made by tape casting, rolling, slip casting, and electrophorectic deposition, etc. Some typical laminated composite systems that have been fabricated include Al2O3/ZrO2, 7 Al2O3/LaPO4, 8 Al2O3/ZrO2/YPO4, 9 etc. Crack deflection in the Al2O3/ZrO2 laminated composite was attributed to residual stresses at the interface.7,9 Morgan et al. 8 suggested that a monazite (LaPO4)–alumina interface is weak enough to produce interfacial debonding when a crack approaches it. However, no laminated system has been made to date using AlPO4 as a crack deflecting interphase. In this study, the chemical stability and physical and mechanical properties of AlPO4 were studied. Mullite–aluminum phosphate (3Al2O32SiO2/AlPO4) laminated composites were investigated to see whether AlPO4 could function as a crack-deflecting interphase in a ceramic composite system. II. Experimental Procedure Commercial mullite (KM 101, Kyoritsu Ceramics Materials Co. Ltd., Nagoya, Japan) powder was used. Aluminum phosphate was synthesized by the organic, steric entrapment method.10,11 To synthesize AlPO4, aluminum nitrate nonahydrate [Al(NO3)39H2O, 98%, Aldrich Chemical, Inc., Milwaukee, WI] and diabasic ammonium phosphate [(NH4)2HPO4, Fisher Scientific, Fair Lawn, NJ] were used as the Al and P source, respectively. The nitrates are first mixed in the distilled water. After 30 min of mixing, 5 wt% poly(vinyl alcohol) (PVA, 205S, Celanese, Ltd., Dallas, TX) solution was added to the solution, followed by another 50 min of mixing. The solution was then heated at 200° and 400°C to remove the water. The partially dehydrated cake was dried at 150°C overnight and finally calcined at 900°C. The laminated composites were made by the tape-casting process. A mixture of 60 wt% ethanol (ethyl alcohol USP, AAPER ALCOL and Chemical, Shelbyville, KY) and 40 wt% methyl ethyl ketone (99.8%, Fisher Scientific) was used as a solvent. Phosphate ester (Emphos PS-21A, Witco Chemicals, Houston, TX) was the dispersant. The binder was poly(vinyl butyral) (Butvar B90, Solutia Chemicals, New Milford, CT). Poly(ethylene glycol) (300NF, FCC grade, Union Carbide Chemicals and Plastics Co. Inc., Danbury, CT) and dibuthyl phthalate (99%, Aldrich) were used as plasticizers. A conventional tape-casting machine with double doctor blades was used. The speed of casting was 1 cm/s. The procedures for making laminated composites were as follows: powder solvent (48-h ball milling) 3 powder solvent plasticizer binder (24-h ball milling) 3 deairing (rotated at slow speed without balls) 3 casting 3 cutting and laminating 3 thermocompression (80°C/(1 h) 3 34.5 MPa uniaxial pressing) 3 binder removal (1°C/min to 150°C 3 0.1°C/min to 600°C/(2 h)) 3 CIP (413.7 MPa) 3 sintering (1600°C/(10 h)). The particle size of synthesized AlPO4 powder before and after 1 h attrition milling was measured using a centrifugal, automatic, particle size distribution analyzer (Model CAPA-700, Horiba, Kyoto, Japan). The specific surface area was measured by sevenpoint BET analysis from nitrogen gas adsorption (Model ASAP 2400, Micrometrics, Norcross, GA). The sample was dried at 150°C overnight to remove the moisture before BET analysis. The bulk density of the sintered material was measured by the Archimedes method (ASTM C373). To check for possible volatilization of P2O5 from the reaction 2AlPO4 3 Al2O3 P2O5, three different kinds of AlPO4 were acid-treated, heated, and analyzed in a Perkin-Elmer Model Plasma II, inductively coupled plasma (ICP) analyzer. The chemical compatibility between mullite and AlPO4 was checked by a Rigaku X-ray diffractometer (Model D-Max automated diffractometer, Rigaku/USA, Danvers, MA). The two powders were mixed by 24-h ball milling, sintered at 1600°C/(10 h), and analyzed for existing phases by X-ray diffraction (XRD). The microstructures of the laminated composites were examined by scanning electron microscopy (SEM, Model S-530, Hitachi, Osaka, Japan). F. W. Zok—contributing editor Manuscript No. 186902. Received June 6, 2002; approved June 12, 2003. *Member, American Ceramic Society. **Fellow, American Ceramic Society. 1962 journal J. Am. Ceram. Soc., 86 [11] 1962–64 (2003)
November 200 Communications of the American Ceramic Sociery 1963 Table L. Experimental Analysis of AlPO, after Three Different heat treatments Al(at%) P(at%) P: AIP Standard AlPO4(Aldrich, 99.99%) 21 1600°c(10h,air→1400°C/(100h) 21 r-treated AIPOA 1800C/(5 h), air-treated AlPO 21.56 24.30 Flexural strengths were measured by three-point bend testing with a screw-driven machine(Model 4502, Instron Corp, Canton, MA). The flexural strength and work of fracture values were determined after testing three to five samples. The specimen size mm, and the crosshead speed was 0. 1 mm/min 2 Theta II. Results and discussion e Kyoritsu KM 101 mullite had a particle size and specific vol% mullite and 50% AlPO4, after sintering at 1600oC for 10 h. So Fig. 1. X-ray diffraction profiles for a crushed pellet composed surface area of 0. 8 um and 8.5 m/g, respectively. The crystalline AlPO4 powder had particle sizes of 10 and 0.9 um, before and after 1-h attrition milling, respectively. The amorphous and crys- lline form of AlPO, powder had specific surface areas of 136 and 87 m-/g, respectively, after 1-h attrition milling. Because of the Mullite concern for decomposition of AlPO4 at high temperature, ICP analyses were done for three different kinds of AlPO,, and the results are summarized in Table I. The three samples were()a standard AlPO,(Aldrich, 99.99%),(ii)AlPO, which was heat- treated at 1600C/(10 h)in air, followed by an anneal at 1400oC/ (100 h)in air; and (iii) AlPO4 which was heat-treated at 1800C/(5 h)in air. If the reaction 2AIPO4-AL2O3+ P2Os occurs and P2O5 AIPOA evaporates at high temperature, the relative amounts of Al in the sample will increase. Table I compares the atom percent of Al and P for the three different AlPO specimens. This table indicates that there were almost no differences in the relative amounts of the two elements in the three different aluminum phosphates. One is led to the conclusion that aluminum phosphate is chemically stable at high temperatures. Table II summarizes the tape-casting formulations for the mullite and AlPOA. The solid loading was 25.1 vol% for both of 10 microns the powders In the case of the AlPO, tapes, 30% extra solvent was The results(Fig. 1) indicate that mullite and aluminum phosphate sintered at 1600C for 10 h are completely compatible with each other, without formation of any third phas Figure 2 is a scanning electron micrograph(SEM) of the 3A1,03 2SiO,/AlPO a laminated composite sintered at 1600C for porous, weak AlPO4 interphase and had a tortuous crack path in 10 h. The mullite layer is dense and the AIPOa layer is clearly the composite. These observations imply that AlPO4 can function porous. A single-phase AlPO a pellet sintered at 1600 C/(10 h) had as a porous and weak interphase material in a laminated composite a measured density of 1.56 g/cm, which corresponded to 61% of causing crack deflection to occur, and hence increase the overall theoretical densi ity, and a three-point bending strength of 1. 5 MPa toughness of a composite The low sinterability of the AlPO4 is consistent with the literature The overall thermal expansion coefficients of mullite and AlPO Mullite sintered under the same condition had a density and are 5.3 X 10-/K and 2. x 10-6/K, respectively. 2 Some residual three-point bending strength of 3. 11 gcm'(98% of theoretical tress may exist at the interfaces between the matrix and porous density)and 308 MPa, respectively. Figure 3 shows typical crack AlPO4 interphase due to thermal expansion coefficients mismatch. deflection in the mullite-aluminum phosphate laminate system However, we have fabricated numerous mullite and AlPO4 laminated after three-point bend testing. The crack is well-deflected along the samples and could find no line-broadening or peak shifts Table Il. Tape Casting Formulations for Mullite and AlPO Solvent Plasticizers MEK Dispersant Powder Extra additions Comments 25.1 576 13 5.7 4.7 5.6 30 vol% solvent Too high viscosity hyl alcohol USP, AAPER ALCOL and -21A, Witco); PVB= poly(vinyl butyral)( Butvar B90, Solutia), PG d polyethylene glycol) ooN F. Fcc Gonad c, Union Carbide dP ie dibutyl (99%, Aldrich Chemical)
Flexural strengths were measured by three-point bend testing with a screw-driven machine (Model 4502, Instron Corp., Canton, MA). The flexural strength and work of fracture values were determined after testing three to five samples. The specimen size was 3 mm (H) 4 mm (W) 40 mm (L), the supporting span was 30 mm, and the crosshead speed was 0.1 mm/min. III. Results and Discussion The Kyoritsu KM 101 mullite had a particle size and specific surface area of 0.8 m and 8.5 m2 /g, respectively. The crystalline AlPO4 powder had particle sizes of 10 and 0.9 m, before and after 1-h attrition milling, respectively. The amorphous and crystalline form of AlPO4 powder had specific surface areas of 136 and 87 m2 /g, respectively, after 1-h attrition milling. Because of the concern for decomposition of AlPO4 at high temperature, ICP analyses were done for three different kinds of AlPO4, and the results are summarized in Table I. The three samples were (i) a standard AlPO4 (Aldrich, 99.99%); (ii) AlPO4 which was heattreated at 1600°C/(10 h) in air, followed by an anneal at 1400°C/ (100 h) in air; and (iii) AlPO4 which was heat-treated at 1800°C/(5 h) in air. If the reaction 2AlPO4 3 Al2O3 P2O5 occurs and P2O5 evaporates at high temperature, the relative amounts of Al in the sample will increase. Table I compares the atom percent of Al and P for the three different AlPO4 specimens. This table indicates that there were almost no differences in the relative amounts of the two elements in the three different aluminum phosphates. One is led to the conclusion that aluminum phosphate is chemically stable at high temperatures. Table II summarizes the tape-casting formulations for the mullite and AlPO4. The solid loading was 25.1 vol% for both of the powders. In the case of the AlPO4 tapes, 30% extra solvent was added because of its high viscosity. Chemical compatibility between AlPO4 and mullite was studied by X-ray diffractometry. The results (Fig. 1) indicate that mullite and aluminum phosphate are completely compatible with each other, without formation of any third phase. Figure 2 is a scanning electron micrograph (SEM) of the 3Al2O32SiO2/AlPO4 laminated composite sintered at 1600°C for 10 h. The mullite layer is dense and the AlPO4 layer is clearly porous. A single-phase AlPO4 pellet sintered at 1600°C/(10 h) had a measured density of 1.56 g/cm3 , which corresponded to 61% of theoretical density, and a three-point bending strength of 1.5 MPa. The low sinterability of the AlPO4 is consistent with the literature.4 Mullite sintered under the same condition had a density and three-point bending strength of 3.11 g/cm3 (98% of theoretical density) and 308 MPa, respectively. Figure 3 shows typical crack deflection in the mullite–aluminum phosphate laminate system after three-point bend testing. The crack is well-deflected along the porous, weak AlPO4 interphase and had a tortuous crack path in the composite. These observations imply that AlPO4 can function as a porous and weak interphase material in a laminated composite, causing crack deflection to occur, and hence increase the overall toughness of a composite. The overall thermal expansion coefficients of mullite and AlPO4 are 5.3 106 /K and 2.3 106 /K, respectively.12 Some residual stress may exist at the interfaces between the matrix and porous AlPO4 interphase due to thermal expansion coefficients mismatch. However, we have fabricated numerous mullite and AlPO4 laminated samples and could find no line-broadening or peak shifts. Fig. 1. X-ray diffraction profiles for a crushed pellet composed of 50 vol% mullite and 50% AlPO4, after sintering at 1600°C for 10 h. Fig. 2. SEM micrograph of a 3Al2O32SiO2/AlPO4 laminated composite sintered at 1600°C for 10 h. Table I. Experimental Analysis of AlPO4 after Three Different Heat Treatments Al (at.%) P (at.%) Standard AlPO4 (Aldrich, 99.99%) 21.41 24.77 1600°C/(10 h), air 3 1400°C/(100 h), air-treated AlPO4 21.56 25.03 1800°C/(5 h), air-treated AlPO4 21.56 24.30 Table II. Tape Casting Formulations for Mullite and AlPO4 † Powder Solvent‡ Dispersant‡ (PS) Binder‡ (PVG) Plasticizer‡ Extra additions Comments Eth (60%) MEK (40%) PG DP Mullite 25.1 57.6 1.3 5.7 4.7 5.6 – – AlPO4 25.1 57.6 1.3 5.7 4.7 5.6 30 vol% solvent Too high viscosity † All ingredients are in volume percent. ‡ Eth ethanol (ethyl alcohol USP, AAPER ALCOL and Chemical); MEK methyl ethyl ketone (99.8%, Fisher Scientific); PS phosphate ester (Emphos PS-21A, Witco); PVB poly(vinyl butyral) (Butvar B90, Solutia); PG poly(ethylene glycol) (300NF, FCC Grade, Union Carbide); DP dibutyl phthalate (99%, Aldrich Chemical). November 2003 Communications of the American Ceramic Society 1963
Communications of the American Ceramic Sociery Vol 86. No. 1I interphases had bending strengths of 154, 155, and 184 MP respectively. Some typical load versus displacement curves three-point bending tests of the three different composites presented in the Fig. 4. All the composites showed"stepped versus displacement curves. Mullite IV. Conelusions The amorphous and crystalline forms of AlPO4 powders which AlPO4 ific surface area of 13 I-h attrition milling, were entrapment method. AlPO4 was chemically stable and did not disproportionate at high temperatures. Mullite and aluminum phosphate were compatible with each other without the formation of a third phase, after sintering at 1600.C/(10 h). The aluminum a three-point bending strength of 1.5 MPa after sintering at 500 microns 1600C/(10 h). The tape-casting formulations for the mullite and AlPO4, using 25 1 vol% powder loading, worked well for making Fig. 3. SEM micrograph showing crack deflection along the AlPO a laminated composite. The aluminum phosphate functioned as a terphase in the 3AlO, 2SiO2/AlPO4 laminated composite porous and weak interphase material in laminated configurations As the amount of mullite in the interphase increased from 0 to 10 to 30 vol%, the strength of the composite changed from 154 to 155 to 184 MPa, respectively. References 0.14 0% mullite 10% mullite 如Bm知mr址m: 30% mullite 2A. J. Leadbetter and T. W. Smith,"The a-B Transition in the Cristobalite Phase of SiOz and AlPO4, L. X-ray Studies, Philos Mag, 33 [1 105-12(1976). 4J. V. Bothe Jr. and P. W. Brown, "Low-Temperature Formation of Aluminum Orthophosphate, " J Am Ceram Soc., 76[2]362-68(1993 w. H. Gitzen, L. D. Hart, and G. Maczura, "Phosphate-Bonded Alumina Castables: Some Properties and Applications, "Am. Ceram. Soc. Bull, 35[6]217-23 P. E. Stone, E. P. Egan Jr, and J.R. Lehr,"Phase Relationships in the System Cao-Al O3-P2Os," J.A. Ceram. Soc., 39 [3]89-98(1956). O. Prakash, P, Sakar, and P S Nicholson, "Crack Deflection in Ceramic/Ceramic Lamin 0.1 P E. D Morgan and D B Mars Ceramic Composites of Monazite an m D. H Kuo and W. M. Riven, "A Strong and Damage-Tolerant Oxide Laminate J.Am. Ceram.Soc,8092421-24(1997) Fig. 4. Load versus displacement curve for the 3AL20, 2SIO2/AlPOA ow. M. Kriven, S. J. Lee, M. A. Gulgun, M. H. Nguyen, and D. K,Kim interphase composition of pure AlPO4 and 10 ""Synthesis of Oxide Powders via Polymeric Steric Entrapment"(invited review aper pp 99-110 in Ceramic Transacti and 30 vol% mullite added, respectively. nthesis of Ceramics, Glasses, Composites Ill. Edited by J. P. Singh, N. P. Ansel, th of the interphase material, 10 and 30 dded to the alPOa interphase. The com J. D. Cawley and W.E. Lee, "Oxide Ceramics"; Pp. 47-117 in Materials Science d Technology, Vol. 11, Structure and Properties of Ceramics. Edited by M. Swai O CH, New York, 1994
To increase the strength of the interphase material, 10 and 30 vol% of mullite were added to the AlPO4 interphase. The composites with pure AlPO4 and 10 and 30 vol% mullite-added interphases had bending strengths of 154, 155, and 184 MPa, respectively. Some typical load versus displacement curves for three-point bending tests of the three different composites are presented in the Fig. 4. All the composites showed “stepped” load versus displacement curves. IV. Conclusions The amorphous and crystalline forms of AlPO4 powders which have specific surface area of 137 and 87 cm2 /g, respectively, after 1-h attrition milling, were synthesized by an organic, steric entrapment method. AlPO4 was chemically stable and did not disproportionate at high temperatures. Mullite and aluminum phosphate were compatible with each other without the formation of a third phase, after sintering at 1600°C/(10 h). The aluminum phosphate had a density of 61% of the theoretical density and had a three-point bending strength of 1.5 MPa after sintering at 1600°C/(10 h). The tape-casting formulations for the mullite and AlPO4, using 25.1 vol% powder loading, worked well for making a laminated composite. The aluminum phosphate functioned as a porous and weak interphase material in laminated configurations. As the amount of mullite in the interphase increased from 0 to 10 to 30 vol%, the strength of the composite changed from 154 to 155 to 184 MPa, respectively. References 1 W. R. Beck, “Crystallographic Inversions of the Aluminum Phosphate Polymorphs and Their Relations to Those of Silica,” J. Am. Ceram. Soc., 32 [4] 147–51 (1949). 2 A. J. Leadbetter and T. W. Smith, “The – Transition in the Cristobalite Phase of SiO2 and AlPO4, I. X-ray Studies,” Philos. Mag., 33 [1] 105–12 (1976). 3 D. E. C. Corbridge, Phosphorus: An Outline of Its Chemistry, Biochemistry and Technology; p. 141. Elsevier, New York, 1985. 4 J. V. Bothe Jr. and P. W. Brown, “Low-Temperature Formation of Aluminum Orthophosphate,” J. Am. Ceram. Soc., 76 [2] 362–68 (1993). 5 W. H. Gitzen, L. D. Hart, and G. Maczura, “Phosphate-Bonded Alumina Castables: Some Properties and Applications,” Am. Ceram. Soc. Bull., 35 [6] 217–23 (1956). 6 P. E. Stone, E. P. Egan Jr., and J. R. Lehr, “Phase Relationships in the System CaO–Al2O3–P2O5,” J. Am. Ceram. Soc., 39 [3] 89–98 (1956). 7 O. Prakash, P. Sakar, and P. S. Nicholson, “Crack Deflection in Ceramic/Ceramic Laminates with Strong Interfaces,” J. Am. Ceram. Soc., 78 [4] 1125–27 (1995). 8 P. E. D. Morgan and D. B. Marshall, “Ceramic Composites of Monazite and Alumina,” J. Am. Ceram. Soc., 78 [6] 1553–63 (1995). 9 D. H. Kuo and W. M. Kriven, “A Strong and Damage-Tolerant Oxide Laminate,” J. Am. Ceram. Soc., 80 [9] 2421–24 (1997). 10W. M. Kriven, S. J. Lee, M. A. Gu¨lgu¨n, M. H. Nguyen, and D. K. Kim, “Synthesis of Oxide Powders via Polymeric Steric Entrapment” (invited review paper); pp. 99–110 in Ceramic Transactions, Vol. 108, Innovative Processing and Synthesis of Ceramics, Glasses, Composites III. Edited by J. P. Singh, N. P. Bansel, and K. Niihara. American Ceramic Society, Westerville, OH, 1999. 11M. A. Gu¨lgu¨n, W. M. Kriven, and M. H. Nguyen, “Processes for Preparing Mixed-Oxide Powders,” U.S. Pat. No. 6 482 387, November 19, 2002. 12J. D. Cawley and W. E. Lee, “Oxide Ceramics”; pp. 47–117 in Materials Science and Technology, Vol. 11, Structure and Properties of Ceramics. Edited by M. Swain. VCH, New York, 1994. Fig. 3. SEM micrograph showing crack deflection along the AlPO4 interphase in the 3Al2O32SiO2/AlPO4 laminated composite. Fig. 4. Load versus displacement curve for the 3Al2O32SiO2/AlPO4 laminated composite with an interphase composition of pure AlPO4 and 10 and 30 vol% mullite added, respectively. 1964 Communications of the American Ceramic Society Vol. 86, No. 11