Refractories molecular composition

Two types of models have been proposed that use this general picture as the basis for understanding volatile depletions in chondrites. Yin (2005) proposed that the volatile element depletions in the chondrites reflect the extent to which these elements were sited in refractory dust in the interstellar medium. Observations show that in the warm interstellar medium, the most refractory elements are almost entirely in the dust, while volatile elements are almost entirely in the gas phase. Moderately volatile elements are partitioned between the two phases. The pattern for the dust is similar to that observed in bulk chondrites. In the Sun s parent molecular cloud, the volatile and moderately volatile elements condensed onto the dust grains in ices. Within the solar system, the ices evaporated putting the volatile elements back into the gas phase, which was separated from the dust. Thus, in Yin s model, the chondrites inherited their compositions from the interstellar medium. A slightly different model proposes that the fractionated compositions were produced in the solar nebula by... 

Calcium polyphosphates of a metaphosphate composition [Ca(P03)2]n have properties and molecular structures which should yield a substance which is refractory in most environments but is rapidly degraded in systems containing active enzymes. None of the known systems of calcium phosphates yield fibrous crystals, although very short acicular crystals have been grown. (2 )... 

The sol-gel process uses a liquid reactive precursor material that is converted to the final product by chemical and thermal means. This precursor is prepared to form a colloidal suspension or solution (sol) which goes through a gelling stage (gel) followed by drying and consolidation. The process requires only moderate temperatures, in many cases less than half the conventional refractory-ceramic processing temperatures. It also permits close control of the composition and structure on the molecular level.P ... 

When preparing synthetic fibers it is usually preferable to avoid crystals that can undergo phase transitions in the temperature ranges of their intended application. This is one reason why amorphous inorganic phosphate fibers may not function well for an extended period. Attempts to prepare phosphate glass fibers have always met with failure in past years when refractory requirements were desired. Additionally, molecular weights in glasses are relatively small when compared to crystals of a similar composition. Two problems have usually been encountered. 

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