The temary system MgO-SiO_2-Al2O3 contains the important low thermal expansion c

Question

The temary system MgO-SiO_2-Al2O3 contains the important low thermal expansion compound cordierite (Mg2Al4si5O18). How many grams of Al2O3 are required to prepare 1000 g of cordierite. For the composition 40MgO-55SiO_2-5Al2O3. trace the equilibrium crystallization path in Also determine the crystallization path if incomplete resorption of forstcrite occurs along the forsteritc-protoenstatite boundary. How do the compositions and temperatures of the eutectics compare for the equilibrium and nonequilibrium crystallization paths? What arc the compositions and amounts of each constituent in the final product for the two cases.

Explanation / Answer

The composition triangles on the phase diagram show that cordierite lies almost completely in the 5MgO.9Al2O3.4SiO2 triangle, so cordierite will consist mainly of spinal, mullite and Sapphirine.

The cordierite phase falls into three different shapes and cordierites will contain mixtures of phases (i) mullite,forsterite and cordierite, (ii) protoenstatite, enstatite and cordierite (iii) cristobalite, tridymite and cordierite.

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