19900161 DZ In ternational Workshop A0 Irsee -Germany September 7-9, 1994 P4 Fqq-.o4- 444 REPORT DOCUMENTATION PAGE Form Approved OMB No. 0704-0188 Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503. 1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED 1994 Conference Proceedings 4. TITLE AND SUBTITLE 5. FUNDING NUMBERS Mullite and Mullite Ceramics F6170894W0696 6. AUTHOR(S) Conference Committee 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT NUMBER Institut fur Werkstoff-Forschung des DLR Porz-Wahnheide, Linder Hohe N/A Koln 51147 Germany 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING/MONITORING AGENCY REPORT NUMBER EOARD PSC 802 BOX 14 CSP 94-1021 FPO 09499-0200 11. SUPPLEMENTARY NOTES 2 Volumes -Journal of the European Ceramic Society and International Workshop Abstracts 12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE Approved for public release; distribution is unlimited. A 13. ABSTRACT (Maximum 200 words) The Final Proceedings for Mullite and Mullite Ceramics, 7 September 1994 -9 September 1994 14. SUBJECT TERMS 15. NUMBER OF PAGES 420 (Estimated) EOARD 16. PRICE CODE N/A 17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19, SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT OF REPORT OF THIS PAGE OF ABSTRACT UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89) Prescribed by ANSI Std. 239-18 298-102 International Workshop Mullite'94 OMCE OF AEizOSPACi EUROPEAN' 1ZRESEARZCH AND DEVELOPMENT'J ,,We wish to thank the United States Air Force European Office of Aerospace Research and Development (EOARD) and the German Aerospace Research Establishment (DLR) for their contribution to the succes of this conference" Characterization of low temperature mullitization T. Ban, S. Hayashi,A . Yasumori, and K. Okada Tokyo Institute of Technology, Tokyo, Japan Various mullite precursors have been prepared by various synthetic methods using the various starting materials. It is generally considered that mullite forms directly from the amorphous phase at around 10000C when the precursor is chemically homogeneous, but spinel phase forms preceeding to mullite when the precursor is less chemically homogeneous. Recently, Nishio and Fujiki'), Hulling and Messing2), and Schneider3) independently showed mullitization at below 800'C. Since this new mullitization reaction is unclear yet in this study, low temperature mullitization reaction was characterized by magic-angle spinning nuclear magnetic resonance (MAS NMR), small angle X-ray scattering (SAXS) and powder X-ray diffraction (XRD) methods. The precursor sample was prepared basically by Nishio and Fujiki method'). At first, 0.1 mole of aluminium nitrate nonahydrate, 0.2 mole of aluminium isopropoxide, and 0.1 mole silicon ethoxide were dissolved in 7.9 mole of de-ionized water and stirred for 2 days at the ambient temperature. The solutions were gelatinized and dried to xerogel at various temperatures from 700 to 250'C. A part of xerogels were further heat-treated at 250'C for 16 hours. Low temperature mullitization was found to occur only when the precursor samples were dried and heat-treated at 250'C. Mullite started to crystallize as low as 4500C. Amount of mullite formed did not increase up to 8000C but significantly increased between 8000 and 1000'C. Two peaks at -90 ppm and -105 ppm were observed in the 29Si MAS NMR spectra of the sample, which showed low temperature mullitization. By SAXS measurement of the sample, existence of the particles in two different sizes was found. Two different structures in polymerization of Si0 tetrahedra in the sample, i.e. unpolymerized and polymerized Si0 4 4 tetrahedral structures were suggested from these results. The interface between these structures was considered to play an important role for nucleation of mullite phase at low temperature. References 1) T. Nishio and Y. Fujiki, J. Ceram. Soc. Jpn., 99 [8] 654-9 (1991) 2) J.C. Hulling and G.L. Messing, J. Non-Cryst. Solids, 147/148 213-21 (1992) 3) H. Schneider, private communication (1993) EXAFS studies of Cr-doped mullite ceramics K.R. BauchspieJP'), A. Kulikov2), and H. Schneider3) School of Mathematical and Physical Science, Murdock University, Perth, W.A., Australia '# 2)R ussian Academy of Sciences, Vladivostoc, Russia 3)G erman Aerospace Research Establishment, Cologne, Germany Results of extended X-ray absorption fime structure (EXAFS) measurements of the Cr K edge of Cr-doped mullite (up to»> 10 wt% Cr 0 ) are presented. The experiments were carried out on 2 3 Beamline 7C at Photon Factory, National Laboratory of High Energy Physics (KK), in Tsukuba, Japan. The X-ray absorption spectra were normalized by first subtracting a pre-edge background and then fitting a smoothly-varying cubic spline background in the region of the EXAFS. For all measured spectra the magnitude of the Fourier transform, which is related to the radial distribution function (RDF), is characterized by two pronounced peaks. The first peak is ascribed to the nearest-neighbour oxygen atoms making up the octahedra surrounding the central Cr atoms and the second peak is assumed to be due to aluminium. In order to get a more quantitative view, the EXAFS spectra were last-squares fitted to a model function, which was based on standard Gaussian lineshapes for the RDFs of oxygen and aluminium. It turned out that the aluminium peak could not be fitted satisfactorily with a Gaussian RDF alone. The discrepancy can be reduced by assuming that there exists an additional contribution to the Gaussian RDF of aluminium. Obviously, the additional contribution results from Cr atoms that do not occur at 'regular' octahedral lattice sites. Since these Cr atoms are not in the center of the aluminium coordination shell, the AI-RDF seen by those Cr atoms is broadened and slightly asymmetric. The data analysis showed that the contributions from both Cr-atom positions did not correlate significantly. Therefore, inclusion of the additional term is justified. The aluminium coordination shell is at >>3 .27 A from the first Cr atoms while it is between >>2. 8 A and >>3.7 A from the second. The interpretation of the EXAFS with the occurrence of two different Cr3+ lattice sites in mullite is in excellent agreement with previous electron paramagnetic resonance (EPR) and crystal field spectroscopic results: These investigations yielded strong evidence for a Cr3+ incorporation at 'regular' (M( 1)) and 'interstitial' octahedral positions. Processing of mullite-based long fiber composites via slurry routes and by oxidation of Al:Si powder J. Brandt' andA . Kristofferson1), and Robert Lundbereg2 1)S wedish CeramicI nstitute, Goteborg,S weden2 2)V olvo Aero CorporationA B, Trollhdttan, Sweden A novel technique to synthesize mullite by oxidation of Al:Si alloy powder has been utilized for the manufacture of A10 long-fiber reinforced mullite composites. It includes (1) slurry 2 3 infiltration/fiber winding of continuous A10 yams (ALMAX) and (2) slurry infiltration/ slip 2 3 casting of ZrO coated sapphire fibers (Saphicon). The nonaqueous slurry used consisted of 2 Al:Si alloy, mullite and additives. During reaction bonding of the green matrices, the A1:Si alloy oxidizes and converts to mullite, below 1400TC in air. One advantage of this technique is that the oxidation causes an internal volume expansion of the matrix. This minimizes the sensitivity to crack formation due to reduced shrinkage stresses between the fibers and the matrix. Si:A! spinel formation in A1 0 -SiO precursor-mullitization processes 2 3 2 Akshay Kr. Chakravorty,H eadX -ray/Dilatometry Section, Central Glass & Ceramic Research Institute, Calcutta - 700 032, India Mullite formation processes in three different kinds of monophasic gels, hybrid gel, spray dried/pyrolyzed powder and three types of diphasic gels (all have 3:1) show great variations. Intermediate spinel formation directs mullitization reaction in most cases. In some kinds of monophasic gels or powder it does not form at all but t-mullite formation is evident at 980'C exotherm. In order kinds, it develops shaply with exhibition of 980'C exotherm. From DTA analysis, alkaliketching experiments, and RDS study, the composition of this Si-Al spinel is found to be analogous to that of 3:2 mullite. Purely heterogeneous diphasic gel does not exhibit 980'C exotherm but form y- A1 0 and a- 2 3 A1 0 prior to mullitization. Formation of former phase is confirmed by AEM, followed by 2 3 EDS analysis. However, insitu diphasic gels forms only Si bearing spinel other than pure Al- spinel. Formation of mixtures of Al-spinel and Si-Al spinel out of four different insitu diphasic gels (varying in Al/Si ratios) have been monitored by QXRD techniques. The results reveal that intensities of both 460 and 670 20 Cuk peaks of spinel phase/phases increase with 0 temperature. Measured X-ray intensity at each peak is found to be greater than that of the expected y- A10 2 3 formation. This apparent excess intensity evidently substantiates the view that silica is present in the spinel and formation of it is also possible in heated diphasic gel. But unlike to monophasic gel it forms as early as 600'C and increases predominantly with exhibition of an exotherm at - 1280'C and thereafter it transforms to o-mullite with exhibition or another exotherm at - 1320'C. Finally, the reasons behind the various paths of mullitizations have been discussed. Mullite fiber/mullite matrix composites K.K. Chawla, J.-S. Ha, and Z.R. Xu Departmento fM aterials and Met.Eng., New Mexico Tech, Socorro, NM, USA Mullite fiber/mullite matrix composites represent an important type of oxide/oxide composites that can have potentially very attractive high temperature properties. This work shows how to achieve tough mullite/mullite composites without fiber degradation or interfacial reaction. Colloidal processing of mullite matrix to lower the composite consolidation temperature and engineering of the interface between mullite fiber and mullite matrix by using thick BN (1 mm) or BN/SiC double coatings on mullite fibers were employed. This allowed deformation mechanisms conducive to toughness enhancement such as fiber/matrix debonding and fiber pullout come into play. Significant improvements in the mechanical properties, especially those related to toughness and a noncatastrophic failure were achieved in mullite fiber/mullite matrix composites. * This work was supported by the U.S. Office of Naval Research, contract No. N0014-89-J1459. Multiple thoughening in reaction bonded mullite/SiC/ZrO composites 2 N. Claussen'1, and S. Wu2) 1) Technische UniversitatH amburg-Harburg,H amburg, Germany 2)C urrently with the MaterialsR esearch Center, Lehigh University, Bethlehem PA, US.A Low shrinkage mullite/SiC/A1 0 /ZrO composites were fabricated based on the RBAO 2 3 2 technology. A powder mixture of 40 vol% Al, 30 vol% A10 and 30 vol% SiC was attrition 2 3 milled in acetone with TZP balls which introduce a substantial ZrO wear debris into the 2 mixture. The precursor powder was isopressed at 300-900 MPa and heat treated in air by two different cycles resulting in various phase ratios in the final products. During heating, Al oxidizes to A1 0 completely, while SiC oxidizes to SiO only on its surface. Fast 2 3 2 densification (at >1300'C) and mullite formation (at 1400'C) prevent further oxidation of the SiC particles. Because of the volume expansion associated with the oxidation of Al (28%), SiC (10%), and the mullitization (4.2%), sintering shrinkage is effectively compensated. The reaction bonded composites exhibit low linear shrinkages and high strengths: shrinkages of 7.2%, 4.8%, and 3%, and strengths of 610 MPa, 580 MPa, and 490 MPa, corresponding to compaction pressures of 300 MPa, 600 MPa, and 900 MPa, respectively, were achieved in samples containing 49-55 vol% mullite. HIPing improves significantly the mechanical properties: a fracture strength of 490 MPa and a toughness of 4.1 MPa .m1/2 increased to 890 MPa and 6 MPa m-i2, respectively. These strength and Ki, data are at least a factor of three higher than those usually obtained for conventional mullite. More than 80 % of the dispersed tetragonal ZrO particles transform on fracture, however, this alone cannot explain the strong 2 increase. Hence we speculate that both nano- and ZrO -toughening are active. 2 Supported by Deutsche Forschungsgemeinschafi (DFG) under Contract No. Cl 52/12-3. Sol-gel mullite matrix-SiC and -mullite 2D woven fabrics composites with or without zirconia containing interphase. Elaboration and properties Ph. Colomban, and E. Mouchon ONERA-OM, Chatillona nd CNRS-LASIR, Thiais, France Many advanced aerospace systems require or would benefit from new low density materials for structural applications. This is particularly true for those applications requiring materials temperatures above 800'C, e.g. aircraft engine parts. For these applications the most promising classes of new materials are ceramics woven fabrics-reinforced ceramic matrix composites. Strong and very tough ceramic and glass-ceramic matrix composites have been prepared using mainly one-dimensional fiber reinforcements. One of the most interesting matrix is mullite. The interest of the mullite matrix arises from its high thermal and chemical stability and from its relatively low dilatation coefficient. Its mechanical properties are good up to 1300-15000C and its low toughness can be improved by zirconia dispersion. The mullite solid solution domain is increased in the case of sol-gel synthesis and mullite glass-ceramic can be obtained. In this paper we compare the properties of composites made with Nicalon NLM202 (Nippon Carbon) SiC or with Nextel 440 (3M) or Sumica (Sumitomo) mullite fibers. The method used to make composites is a three-stage process [1]: /) the first is the preparation of an interface gel precursor impregnated fabrics by in situ gelification of a mixture of alkoxides, ii) the second is the deposit of a fine and reactive amorphous powder of matrix precursor on the impregnated fabrics, iii) the third step is the hot-pressing of the stacked fabrics in a carbon mold. Three or five sheets are used. Composites have been studied by SEM and TEM. Three points flexural strength was measured at R.T. and at 900'C, in air. Local Young's modulus, microhardness and interfacial shear stress have been determined at R.T. Micro-Raman spectra and X microanalysis were used to study the fiber-interface reactions. Using a mixture of aluminium-silicon ester and tributylborate as interface precursor, we obtain a carbon free SiC-mullite sliding interface. The use of a complementary ZrO -GeO gel interface precursor allows to obtain dense composites (open 2 2 porosity <4%) at moderate temperature (-1300'C) exhibiting good mechanical properties (ultimate value of the linear behaviour -180 MPa, even after 30 days annealing in air). The effects of a zirconia interphase on the mechanical properties of mullite-mullite composite is also discussed. The achievement of a R.T. and 900'C non-brittle composite is related to the absence of reaction between the zirconia interphase and the fibers. Microwave properties are discussed. [1] Ph. Colomban, M. Menet, E. Mouchon, C. Courtemanche and M. Parlier, Patent Fr 2672 283, EP 92400235-5, US (pending)