October 2005 Laminated silicon Nitride the stacks and therefore their thermal conductivity decrease 9. the range of 20-30 W/mK, which is typical for a dense silicon Thus, with increased precursor content, the overall density nitride material The thermal conductivities of the stacks laminated with the pre-ceramic polymer are lower than that of the tapes laminated by compression(Fig. 12). With increasing precursor content in Acknowledgments the interlayers (i.e. 0, 30, 50, and 60 vol%), the thermal con- pplying the mate ductivity decreases. This corresponds well with the density of the rials: SKW Trostberg. Zschimmer& Schwarz( Germany) tered stacks, which also decreases with increasing precursor content(see Section I(2)). A lower density indicates a higher level of porosity, which reduces the thermal conductivity of the References Das and T.R. Curlee. "The Cost of Silicon Nitride powder and the eco- However, the influence of the interlayers containing the pre cursor material has to be taken into account The mean values of J.D. Cawley, A.H. Heuer, W.S.Newman,and B.B. Mathewson, "Con in thermal properties, but the error bars are quite high. The Blded s 1 aat rigg of laminated Engineering Materials,"Am.CeramSoc. the results of cer60 are consistent with the observed decrease Cer60. This indicates that for high precursor contents(50 vol% 77 [10]82-6(1998)pe Casting: Past, Present, Potential,"Am Ceram Soc. Bull thermal conductivity of composition Cer50 is lower than that of or greater), either the processing is less reliable or the effects of a2 ol. 17A. Edited:12mam上 Kramer. vch he precursor are stronger. Perhaps a different chemical com- position of the interlayer in comparison with that of the ta SA. Roosen, "Laminieren von keramischen grunfolien: grenzen und moglichkei material causes the strong decrease in thermal conductivity The evaluation of the chemical composition of the grain- Edited by J. G. Heinrich, W Hermel. G. Ziegler,and H. Riedel. Wiley-VCH boundary phase is very complicated, and should be carried D Cawley and Z Liu, "Applying Tape Casting to Layere out in further work 7G. Kleer R. Goller. W. Doll. J. G. Heinrich. and O Rosenfelder. "Stren Euro-Ceramics Il. Dt. Keram. Ges. Koln 1991 IV. Summary R. Goller. G. Kleer, and J. Kriegesmann. ""Bruchmechanische untersuchungen m siliciuminfiltrierten siliciumcarbid (SiSiC). "Keran. Zeitschrift, 46 Green tapes with simple geometries can easily be laminated by 235-9(994). compression with 14 MPa at room temperature. After lamina- L. Mohr, P. Desai and T Starr, "Effect on Processing Parameters on Po- ysilazane Preceramic Binders in a Ceramic Composite System, "Ceram. Eng Sc laminated components, the single layers could no longer be de- T. 12 (9-10)2095-104(1991). ch and J. G. Heinrich. ""Aqueous Tape Casting of Silicon Nitride, tected. Nevertheless, the bending strength when the tensile stress ar Ceram. Soc 22 1312427-34(2002) Characterization is applied parallel to the stacking direction was approximately Water-Based Slurries for the Tape Casting Process, "Ceram. Int, 28[6] 675-83 640 MPa and higher than perpendicular to it (490 MPa), where s the thermal conductivity showed no change in the measuring allieDsignal. Ceraset SN. Technical Bulletin Allied Signal Composites Inc, 30 W/mK. The mechanical anisotropy may have been caused Beha Sor in M.uk: red aramis: P An. Caram, So 2 5 n 557-4 193,ge layers introduced by dust or cu 4. S. Reed. Principles of Ceramic Processing. John Wiley Sons. New York, ting debris mination is possible. Pastes containing a liquid pre-ceramic 6E. Kroke Y. Li c. Konetschny. E. Lecomte. C. Fasel. and R. Riedel. "si- polymer improve the lamination process. The pastes show a complex rheological behavior, which partly fulfills the needs of 97-9(2000) the screen-printing process. By using these precursor-contai ich.""Properties of Silicon Cracking of Laminates Subjected to ained. Variation of the precursor content shows that a 30-50 vol% range is best suited. With these compositions, similar me- chanical properties as in the case of lamination by Ceramics(Part 3). J. Ceram. Soc. Jpl, 108[3]230-5( could be achieved. The measurements revealed that--probably 2 R Riedel and M. Seher lization Behaviour of Amorphous Silicon Nitride, "J. Eur. Ceran. Soc., 11[1]21-5(1991) because of some pores or inclusions in the interlayers--the same 2G. Ziegler, J. Heinrich, and G. Wotting. "Review: Relationships Between anisotropic properties exist as in the case of the stacks made by essing, Microstructure and Properties of Dense and Reaction-Bonded Silicon ompression. The homogeneous microstructure in most areas of the laminated samples leads to the assumption that by prevent M. Kitayama, K. Hirao, M. Toriyama, and S Kanzaki, "Thermal Conduc- tivity of B-Si3N4: 1. Effect of Various Microstructural Factors, "J. Am. Ceram. ing dust and cutting debris between the tapes during by bot Soc,82[l1310512(1999 direction-independent properties can be achieved tari. "High Thermal Conductivity Non-Oxide Ceramics, J. Ceram. were affected mostly by a changed sintering behavisotro laminating methods. The thermal properties were resulting Engineering Properties of Nitrides; pp. 812-20 in Engineered aterials Handbook, Vol. 4. Edited by S J. Schneider Jr. ASM Internation n a small residual porosity in the tape material after sintering Ohio. 19the range of 20–30 W/mK, which is typical for a dense silicon nitride material.24 The thermal conductivities of the stacks laminated with the pre-ceramic polymer are lower than that of the tapes laminated by compression (Fig. 12). With increasing precursor content in the interlayers (i.e. 0, 30, 50, and 60 vol%), the thermal con￾ductivity decreases. This corresponds well with the density of the sintered stacks, which also decreases with increasing precursor content (see Section III(2)). A lower density indicates a higher level of porosity, which reduces the thermal conductivity of the material. However, the influence of the interlayers containing the pre￾cursor material has to be taken into account. The mean values of the results of Cer60 are consistent with the observed decrease in thermal properties, but the error bars are quite high. The thermal conductivity of composition Cer50 is lower than that of Cer60. This indicates that for high precursor contents (50 vol% or greater), either the processing is less reliable or the effects of the precursor are stronger. Perhaps a different chemical com￾position of the interlayer in comparison with that of the tape material causes the strong decrease in thermal conductivity. The evaluation of the chemical composition of the grain￾boundary phase is very complicated, and should be carried out in further works. IV. Summary Green tapes with simple geometries can easily be laminated by compression with 14 MPa at room temperature. After lamina￾tion, an excellent joint was obtained. In the green and sintered laminated components, the single layers could no longer be de￾tected. Nevertheless, the bending strength when the tensile stress is applied parallel to the stacking direction was approximately 640 MPa and higher than perpendicular to it (490 MPa), where￾as the thermal conductivity showed no change in the measuring direction. The calculated thermal conductivity is approximately 30 W/mK. The mechanical anisotropy may have been caused by small defects between the layers introduced by dust or cut￾ting debris. By using suitable pastes to join single tapes, a pressureless lamination is possible. Pastes containing a liquid pre-ceramic polymer improve the lamination process. The pastes show a complex rheological behavior, which partly fulfills the needs of the screen-printing process. By using these precursor-containing lamination aids, high-quality laminated samples can be ob￾tained. Variation of the precursor content shows that a 30–50 vol% range is best suited. With these compositions, similar me￾chanical properties as in the case of lamination by compression could be achieved. The measurements revealed that—probably because of some pores or inclusions in the interlayers—the same anisotropic properties exist as in the case of the stacks made by compression. The homogeneous microstructure in most areas of the laminated samples leads to the assumption that by prevent￾ing dust and cutting debris between the tapes during lamination, direction-independent properties can be achieved by both the laminating methods. The thermal properties were isotropic and were affected mostly by a changed sintering behavior, resulting in a small residual porosity in the tape material after sintering. Thus, with increased precursor content, the overall density of the stacks and therefore their thermal conductivity decreased. Acknowledgments The authors are grateful to the following companies for supplying the mate￾rials: SKW Trostberg, Zschimmer&Schwarz (Germany). References 1 S. Das and T. R. Curlee, ‘‘The Cost of Silicon Nitride Powder and the Eco￾nomic Viability of Advanced Ceramics,’’ Am. Ceram. Soc. Bull., 71 [7] 1103–11 (1992). 2 J. D. Cawley, A. H. Heuer, W. S. Newman, and B. B. Mathewson, ‘‘Computer￾Aided Manufacturing of Laminated Engineering Materials,’’ Am. Ceram. Soc. Bull., 75 [5] 75–9 (1996). 3 R. E. Mistler, ‘‘Tape Casting: Past, Present, Potential,’’ Am. Ceram. Soc. Bull., 77 [10] 82–6 (1998). 4 H. Hellebrand, ‘‘Tape Casting’’; pp. 189–265 in Materials Science and Tech￾nology, Vol. 17A, Edited by R. W. Cahn, P. Haasen, and E. J. Kramer. VCH Verlagsges, Weinheim, 1996. 5 A. Roosen, ‘‘Laminieren von keramischen gru¨nfolien: grenzen und mo¨glichkei￾ten bestehender und neuer verfahren’’; pp. 113–8 in Werkstoffwoche ‘98, Vol. 7, Edited by J. G. Heinrich, W. Hermel, G. Ziegler, and H. Riedel. Wiley-VCH, Weinheim, 1999. 6 J. D. Cawley and Z. Liu, ‘‘Applying Tape Casting to Layered Manufacturing Processes,’’ Ceram. 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Technical Bulletin Allied Signal Composites Inc., Newark, DE, 1999. 13J. S. Sung, K. D. Koo, and J. H. Park, ‘‘Lamination and Sintering Shrinkage Behavior in Multilayered Ceramics,’’ J. Am. Ceram. Soc., 82 [3] 537–44 (1999). 14J. S. Reed, Principles of Ceramic Processing. John Wiley & Sons, New York, 1995. 15T. Hanemann, M. Schulz, and M. Ade, ‘‘Controlled Crosslinking of Poly￾ureasilazane’’; Proceedings of Materials Week, Mu¨nchen, 2001. 16E. Kroke, Y. Li, C. Konetschny, E. Lecomte, C. Fasel, and R. Riedel, ‘‘Si￾lazane Derived Ceramics and Related Materials,’’ Mater. Sci. Eng. Rep., 26 [4–6] 97–9 (2000). 17B. Bitterlich and J. G. Heinrich, ‘‘Properties of Silicon Nitride Mixed with a Preceramic Polymer’’; Proceedings of Materials Week, Mu¨nchen, 2001. 18C. Hillman, Z. Suo, and F. F. Lange, ‘‘Cracking of Laminates Subjected to Biaxial Tensile Stresses,’’ J. Am. Ceram. Soc., 79 [8] 2127–33 (1996). 19K. Yokoyama and S. Wada, ‘‘Solid–Gas Reaction During Sintering of Si3N4 Ceramics (Part 3),’’ J. Ceram. Soc. Jpn., 108 [3] 230–5 (2000). 20R. Riedel and M. Seher, ‘‘Crystallization Behaviour of Amorphous Silicon Nitride,’’ J. Eur. Ceram. Soc., 11 [1] 21–5 (1991). 21G. Ziegler, J. Heinrich, and G. Wo¨tting, ‘‘Review: Relationships Between Processing, Microstructure and Properties of Dense and Reaction-Bonded Silicon Nitride,’’ J. Mater. Sci., 22 [9] 3041–86 (1987). 22M. Kitayama, K. Hirao, M. Toriyama, and S. Kanzaki, ‘‘Thermal Conduc￾tivity of b-Si3N4: I, Effect of Various Microstructural Factors,’’ J. Am. Ceram. Soc., 82 [11] 3105–12 (1999). 23K. Watari, ‘‘High Thermal Conductivity Non-Oxide Ceramics,’’ J. Ceram. Soc. Jpn., 109 [1] 7–16 (2001). 24S. Hampshire, ‘‘Engineering Properties of Nitrides’’; pp. 812–20 in Engineered Materials Handbook, Vol. 4, Edited by S. J. Schneider Jr. ASM International, Ohio, 1991. & October 2005 Laminated Silicon Nitride Stacks 2721