Superplastic Forming of SiAlON Ceramics

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66409/1/j.1151-2916.1994.tb04645.x.pd

New minerals tsangpoite Ca5(PO4)2(SiO4) and matyhite Ca9(Ca0.5□0.5)Fe(PO4)7 from the D'Orbigny angrite

Tsangpoite, ideally Ca5(PO4)2(SiO4), the hexagonal polymorph of silicocarnotite, and matyhite, ideally Ca9(Ca0.5□0.5)Fe(PO4)7, the Fe-analogue of Ca-merrillite, were identified from the D'Orbigny angrite meteorite by electron probe microanalysis, electron microscopy and micro-Raman spectroscopy. On the basis of electron diffraction, the symmetry of tsangpoite was shown to be hexagonal, P63/m or P63, with a = 9.489(4) Å, c = 6.991(6) Å, V = 545.1(6) Å3 and Z = 2 for 12 oxygen atoms per formula unit, and that of matyhite was shown to be trigonal, R3c, with a = 10.456 (7) Å, c = 37.408(34) Å, V = 3541.6 (4.8) Å3 and Z = 6 for 28 oxygen atoms per formula unit. On the basis of their constant association with the grain-boundary assemblage: Fe sulfide + ulvöspinel + Al-Ti-bearing hedenbergite + fayalite-kirschsteinite intergrowth, the formation of tsangpoite and matyhite, along with kuratite (the Fe-analogue of rhönite), can be readily rationalised as crystallisation from residue magmas at the final stage of the D'Orbigny meteorite formation. Alternatively, the close petrographic relations between tsangpoite/matyhite and the resorbed Fe sulfide rimmed by fayalite + kirschsteinite symplectite, such as the nucleation of tsangpoite in association with magnetite ± other phases within Fe sulfide and the common outward growth of needle-like tsangpoite or plate-like matyhite from the fayalite-kirschsteinite symplectic rim of Fe sulfide into hedenbergite, infer that these new minerals and the grain-boundary assemblage might represent metasomatic products resulting from reactions between an intruding metasomatic agent and the porous olivine-plagioclase plate + fayalite-kirschsteinite overgrowth + augite + Fe sulfide aggregates. Still further thermochemical and kinetics evidence is required to clarify the exact formation mechanisms/conditions of the euhedral tsangpoite, matyhite and kuratite at the grain boundary of the D'Orbigny angrite.Fil: Hwang, Shyh Lung. National Dong Hwa University; República de ChinaFil: Shen, Pouyan. National Sun Yat-sen Universit; República de ChinaFil: Chu, Hao-Tsu. Central Geological Survey; República de ChinaFil: Yui, Tzen-Fu. Institute of Earth Sciences; República de ChinaFil: Varela, Maria Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; ArgentinaFil: Iizuka, Yoshiyuki. Institute of Earth Sciences; República de Chin

Fabrication, microstructural characterization, and deformation of superplastic silicon aluminum oxygen nitrogen ceramics.

Superplastic SiAlON materials, including hot-pressed \alpha\sp\prime-, \alpha\sp\prime+\beta\sp\prime-, and \beta\sp\prime-SiAlON, have been developed for the first time. These ceramics have submicron grain sizes, excellent biaxial formability, and novel flow characteristics. The investigation of kinetics and reaction pathways has established the special roles of ternary eutectic SiO\sb2-Y\sb2O\sb3-Al\sb2O\sb3 liquid and AlN in fabricating these materials at low temperature reaction hot-pressing. Formability, which is especially enhanced by the inclusion of \beta\sp\prime-SiAlON, has been demonstrated by punch-stretch testing at 1550\sp\circC to large biaxial strains. The general deformation mechanism is found to be Newtonian viscous flow at lower flow stresses, and changes to shear thickening flow at a characteristic stress. This novel shear thickening transition can be rationalized by transient grain interlocking under compressive stress conditions. Extensive TEM work has also been conducted on these superplastic SiAlONs to examine microstructural development at various stages of processing and deformation. Epitaxial growth of \alpha\sp\prime-SiAlON on $\alpha$-Si\sb3N\sb4 and epitaxial growth of \beta\sp\prime-SiAlON on $\beta$-Si\sb3N\sb4, on supersaturated \beta\sp\prime-SiAlON, and even on $\alpha$-Si\sb3N\sb4 have all been identified. In addition, \beta\sp\prime-SiAlON grains were found to rotate and align themselves with the biaxial stretching directions. No evidence of cavitation was detectable after biaxial stretching in any of these materials. These observations have provided additional insight to the formability and alloy design of superplastic ceramics. They also have broader implications on the microstructural control of tough SiAlONs.PhDApplied SciencesMaterials scienceUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/128997/2/9308346.pd

Nucleation and Growth of Α′-SiAlON on Α-Si 3 N 4

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66248/1/j.1151-2916.1994.tb07041.x.pd

Microstructure of chromium spinel and pyrite as indicators of thermomechanical history of chromitite from Kenting melange, Taiwan

Transmission electron microscopy was used to characterize the microstructure of chromium spinel and pyrite in the serpentinized chromitite occurrence of the Kenting melange at Hengchun, southern Taiwan. The deformation episodes of the Hengchun chromitite were then inferred from the defect microstructures on the basis of the known creep behaviour of analogue spinel materials and pyrite. Dislocations arranged as dipoles, tangles and subgrain boundaries were found in chromium spinel indicating that the chromium spinel was probably plastically deformed and polygonized later in the upper mantle. The dislocations arranged as dipoles, loops, tangles and subgrain boundaries in pyrite correspond probably to later episodes of the ocean floor metamorphism during which dynamic recrystallization of pyrite occurred, together with brittle deformation of chromium spinel. The breccias of chromium spinel and pyrite are in part due to brittle deformation during emplacement of the ophiolite at a convergent plate boundary.Les chromitites serpentinisées du mélange de Kenting contiennent des spinelles chromifères et de la pyrite. L'étude au microscope électronique en transmission de ces minéraux a permis de caractériser leurs microstructures. Les épisodes de déformation ainsi mis en évidence dans la chromite sont comparés avec les données connues sur le comportement thermomécanique des spinelles et de la pyrite. On montre de cette manière l'origine ophiolitique des chromites. L'analyse des dislocations dans les spinelles chromifères montre qu'elles ont été déformées plastiquement et polygonisées dans le manteau supérieur. Les dislocations en dipôle, en boucles, en échevaux et en "sous-joints" dans les pyrites correspondent aux derniers épisodes de métamorphisme du plancher océanique. Pendant cet épisode a eu lieu une recristallisation dynamique des pyrites et une déformation cassante des spinelles. Les brèches de spinelles chromifères et des pyrites sont en partie le résultat d'un stade de déformation cassante pendant la mise en place des chromitites ophiolitiques à la frontière convergente des plaques.Hwang Shyh-Lung, Shen Pouyan, Chu Hao-Tsu, Jeng Ruey-Chang. Microstructure of chromium spinel and pyrite as indicators of thermomechanical history of chromitite from Kenting melange, Taiwan. In: Bulletin de Minéralogie, volume 111, 5, 1988. pp. 457-469

Kuratite IMA 2013-109

The information given here is provided by the IMA Commission on New Minerals, Nomenclature and Classification for comparative purposes and as a service to mineralogists working on new species.Fil: Hwang, Shyh-Lung. National Dong Hwa University. Department of Materials Science and Engineering; República de ChinaFil: Shen, Pouyan. National Sun Yat-sen University. Institute of Materials Science and Engineering; República de ChinaFil: Chu, Hao-Tsu. Central Geological Survey; República de ChinaFil: Yui, Tzen-Fu. Academia Sinica. Institute of Earth Sciences; República de ChinaFil: Varela, Maria Eugenia. Consejo Nacional de Investigaciones Cienti­ficas y Tecnicas. Centro Cientifico Tecnologico San Juan. Instituto de Ciencias Astronomicas de la Tierra y del Espacio; ArgentinaFil: Iizuka, Yoshiyuki. Central Geological Survey; República de Chin