Spinel grains

Zitmer E (1997) Presolar material in meteorites an overview. In Astrophysical Implications of the I aboratory Study of Presolar Materials. Bematowicz TJ and Zinner E (eds) AIP, New York, p 3-26 Zinner EK, Gopel C (2002) Aluminium-26 in H4 chondrites implications for its production and its usefulness as a fine-scale chronometer for early solar system events. Meteorit Planet Sci 37 1001-1013 Zinner E, Amari S, Guitmess R, Nguyen A, Stadermann FJ, Walker RM, I wis RS (2003) Presolar spinel grains from the Murray and Murchison carbonaceous chondrites. Geochim Cosmochim Acta 67 5083-5095... 

Laurich-Mclntyre, S.E. and Bradt, R.C., Room temperature strengths of individual tabular alumina and sintered spinel grains (aggregates) , UNITECR 93 Congress, Sao Paulo, Brazil, 1993. 

Zinner E., Amari S., Guinness R., Nguyen A., Stadermann F., Walker R. M., and Lewis R. S. (2003) Presolar spinel grains from the Murray and Murchison carbonaceous chondrites. Geochim. Cosmochim. Acta (in press). 

In terms of sheer numbers, probably the most abundant variety of CAl in most chondrites consists largely of spinel and calcic pyroxene. Some of these contain lesser amounts of anorthite, melilite, hibonite, and perovskite, but pyroxene-spinel-rich assemblages are almost universal. These objects range in size from a few tens of micrometers up to 1-2 cm (in CV3 chondrites). Large or small, from whatever kind of chondrite, the essential structure consists of small spinel grains or dense nodules of spinel grains or even chains of spinels, enveloped in a continuous thin rim of aluminum diopside that binds the entire structure together. 

Figure 15.8. Microstructure showing MgAl204 spinel grains in a CaMgSlAIO glass matrix and an entrapped glass pocket within a grain. ...

Both, spinel and pyrochlore accommodate excess dopants, the concentrations of which exceed their solubility limits in ZnO, and therefore they concentrate at grain boundaries [113]. The microstructure of a ZnO varistor will then comprise ZnO grains, a bismuth-rich phase, and spinel grains, which can be located either inter- or intragranularly (Figure 1.5). 

Tabie 5 Properties of Sintered and Fused Spinel Grains... 

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