Question

Unit cell dimensions for polyethylene may be assumed to be as follows: a-0.741 nm, b=0.496 nm, c=0.254 nm, a=ß=y= 90° The wavelength of CuK radiation is 0.1542 nm. 17.1 A flat-plate X-ray diffraction pattern was obtained from an unoriented sample of polyethyl- ene using CUKK, radiation. It consisted of three rings of radius 22.2, 36.6 and 19.7 mm. The specimen-to-film distance was 50 mm. Calculate the d-spacing of the planes giving rise to these reflections. It is thought that these reflections are from (hk0) type planes. Draw a scale diagram of the unit cell of polyethylene projected along the c-axis. Measure the spacing of the low-index (hk0) type planes and hence identify the planes giving rise to the observed reflections

Answer 1

Solution o741 n M a Given b 046 hM CE 02S4nM 6.1542 nm wavelengthAàeut The 22.2. mns Bragg's Law 1 Spacing geven structure is mnimum hke blanef Orthorhombic ICfce) elles ton is d-Spacing fey (hkR)=C myni mu m 0.549+0.246 +0.o645)2 IO78 n 2545)

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