A plate of single crystal Si and polycrystalline Si are polished together. Then
ID: 288855 • Letter: A
Question
A plate of single crystal Si and polycrystalline Si are polished together. Then a diamond is used to make a 1 mm scratch on each of them to the same length.
a. Name three experimental conditions other than temperature which could affect the results of an indentation hardness or toughness test of a ceramic (there are more than three).
b. Si is hard therefore it is tough. Support or refute this answer.
c. If you performed a strength test on only one sample each of the polycrystalline and single crystal Si described above in 2, how would you expect the fracture stresses to compare and why?
d. If you did the same experiment again, but made 100 identical samples each of scratched single and polycrystalline Si, then performed the strength test, how do you expect the two populations to compare and why?
Explanation / Answer
a. Factors
b. Compared with the other pure metals silicon is hard and brittle crystalline solid. It is one of the most abundant element in the earth crust. It has high boiling (2,355 °C) and melting point (1,410 °C ). The coordination number increases with pressure creating a cubic crystal structure. Its Hardness value is 6.5 in Moh's hardness scale. Silicon also improves the hardness and thus wear resistance of aluminium.
c. The single crystal is also know as monocrystalline. It has a homogenous crystal framework. As the name suggest it has a single crystal , unbroken edges with no grain boundaries and also are rare in nature.
Polycrystalline consist of large number of small crystals. The mobility of the charge is greater in polycrystalline than single crystal and so the material shows the great stability under electic field and light induces stress. But in the industry monocrystalline is more efficients semi-conductor than polycrystalline.
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