Question

1. High temperature heating elements are made out of an intermetallic often called molydisilicide. Answer the following questions using the Mo-Si phase diagram shown below. Weight Percent Silicon Temperature, 130 Mo Atomic Percent Silicon a) Calculate the maximum wt.% silicon that is soluble in solid molybdenum. b) Write a eutectic reaction (upon cooling) and give its temperature and composition. How many different eutectics occur in this system? c) Write a peritectic reaction (upon cooling) and give its temperature and composition d) Give the phases present, the composition of each phase, and the amount in mol %) of cach phase present at 1000°C when a Mo-55 at.% Si liquid is cooled from 2000'C. c) Does MoSiz melt congruently or incongruently? Explain in one sentence. 1) MoSiz heating elements can be used in air because they form a protective layer of amorphous SiO, which covers the surface. Why is this silica layer protective?

Answer 1

head Date (a) maximuon wt% of = 57. ering Silicon (6) Euk chic Reaction : - EL Most Mosiz at 1906oc. Self era! CELUJE There are enfectic 1 450) Mo 13 different types of reactions occur in this system. (c) Poritectic reaction - L+Mo - Mo.si at 2023°c. Composition 54 to 26% of si - hence 951.40 74% of Mo at 1000c it is solid phase of Mosi, and (een position - Mosina Composition at 1ooo'c :- Masin = 400 si - Mosi = 67%. Si Amount of Phases (by leaves rule) ir Mosi = (67-55) x 100 = 44.444 (67-40) Mosi = 55.40 xico = 55.55%. 67-40

Page No. Daten Date (e) Yes, Mosi, melt incongruently.. because cate this composition (67% si will melt, not the compound of both. mosi (2 Because Silicon dioxide (sio) is a good inowator. it increases the thermal stability. it to is also used as Refractory element in ceramics also that's why ceramics can withstand upfo 1760°c
in the question various reactions, their temperature and compositions, weight percent were asked. Then asked about congruent process and also asked about importance of silicon dioxide in the practical use.