HW3Solutions - 1. Problem W3.49 from Callister (8 points)...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
MSE280: Introduction to Engineering Materials Homework 3: Solutions 1. (a) This portion of the problem asks that we specify which type of interstitial site the Be 2+ ions will occupy in BeO if the ionic radius of Be 2+ is 0.035 nm and the O 2- ions form an HCP arrangement. Since, from Table 3.4, r O 2- = 0.140 nm, then Problem W3.49 from Callister (8 points) r Be 2 + r O 2 = 0.035 nm 0.140 nm = 0.250 As r C / r A is between 0.225 and 0.414, the coordination number for Be 2+ is 4 (Table 3.3) therefore, tetrahedral interstitial positions are occupied. (b) We are now asked what fraction of these available interstitial sites are occupied by Be 2+ ions. Since there are two tetrahedral sites per O 2- ion, and the ratio of Be 2+ to O 2- is 1:1, one-half of these sites are occupied with Be 2+ ions. Problem 4.6 from Callister (8 points) We are asked to sketch portions of a linear polypropylene molecule for different configurations (using two-dimensional schematic sketches). (a) Syndiotactic polypropylene (b) Atactic polypropylene
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
(c) Isotactic polypropylene Problem 4.9 from Callister (8 points) For an alternating copolymer that has a number-average molecular weight of 100,000 g/mol and a degree of polymerization of 2210, we are to determine one of the repeat unit types if the other type is ethylene. It is first necessary to calculate m using Equation 4.6 as m = M n DP = 100,000 g/mol 2210 = 42.25 g/mol Since this is an alternating copolymer we know that chain fraction of each repeat unit type is 0.5; that is f e = f x = 0.5, f e and f x being, respectively, the chain fractions of the ethylene and unknown repeat units. Also, the repeat unit molecular weight for ethylene is m s = 2( A C ) + 4( A H ) = 2(12.01 g/mol) + 4(1.008 g/mol) = 28.05 g/mol Now, using Equation 4.7, it is possible to calculate the repeat unit weight of the unknown
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 6

HW3Solutions - 1. Problem W3.49 from Callister (8 points)...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online