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Question

here is the problem :

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8. Consider the eutectic reaction in the SiO2-Al2O3 system, write down the reaction and identify all the phases present and their compositions.

9. If 60wt%Al2O3-40wt%SiO2 is cooled from the liquid state to room temperature.  At what temperature will solidification be complete? How much cristobalite will be present in the material at 1500OC.

10. What overall composition would be required to give a material made up of 50wt% mullite and 50wt% alumina at 1400OC.

Consider the eutectic reaction in the SiO2-Al2O3system, write down the reaction and identify all the phases present and their compositions. If 60wt%Al2O3-40wt%SiO2is cooled from the liquid state to room temperature. At what temperature will solidification be complete? How much cristobalite will be present in the material at 1500OC. What overall composition would be required to give a material made up of 50wt% mullite and 50wt% alumina at 1400OC.

Explanation / Answer

8 all phases are liquid, crystobalite, crystobalite+liquid, crystobalite + mullite, mullite+liquid, alumina + liquid, compound mullite

9) at 1587 K now of the 40% silica by wt amount in mullite is 0.667*(60/101) *60 = 23.76 % therefore in form of cristobalite we have 16.24%

10) net wt of silica = (60/211)*50 + 50 = 14.2% therefore wt% of alumnia = 85.8%

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