【摘要】 <正> 一、前言 自从德拜(Debye),谢尔(Scherrer)于1916年首先发明粉晶照相以来,一直被广泛应用于科学研究、生产实践,对于矿物研究与鉴定起了极其重要的作用。粉晶照相法虽有其局限性,如:线条的重合,低级晶系图谱复杂等,但却有其优点,如:操作简单,强度可靠,不受单晶的限制等,则是别的方法所不及的。迄今照相技术,计算方法,鉴定手段等仍在继续不断地得到有关研究人员的改进。更多还原

【Abstract】 To index X-ray powder diffraction lines of an unknown crystal is, in general, based on the known cell constants, or on the high symmetry of crystals. The constants and A in the d-calculating formula can be cancelled by the ratio method. The experimental d(A)-values are expressed by the reciprocals of the squares of the d(A)-values, i.e. d*2hkl. By dividing the rear d*2hkl, by those of the first, second, third etc., in the order of the initial descending d( A.) -values we acquire the ratio values.In order to reduce the calculation, we take first ten or twenty lines in diffraction patterns and take three dividings with the 1st, 2nd and 3rd d*nkl as divisors.For isometric crystals, there is a maximum common factor (M. C. F. ) in the ratio d*2(hkl)n/d*2(hkl)m,i.e. a*2(=d*2100). For tetragonal, trigonal or hexagonal crystals, the ratios of d*2koo, d*2oko and d*2kko are either the same as those in isometric or showing some particular values ; c can be found after the determination of a and b. For orthorhombic,d*2(hkl)n/d*2(hkl)m =h2n + k2n/(b/a)2 + I2n/(c/a)2/h2m + k2m(b/a)2 + I2m/(c/a)2 and for monoclinic,Calculations of the ratios show that the more the approach of b/a’s and c/a’ s of two crystals, the more the approach of their respective ratios of the d*2hkl’s, The essential of the method is to find the b/a(=A) and c/a(=C) from the given d (A)-values by calculating and comparing the ratios of the k*2hkl (Qhkl). These ratios are arranged systematically with A, C as coordinates in order to facilitate the locating of A &C of an unknown. Sixty orthorhombic minerals of known A & C were calculated and the ratios of the nearest A and C may be discriminated, as in A = 0.904, C = 0.780 & A = 0.904, C=0.784; A=0.8919, C = 0.354 & A= 0. 983, C = 0.355 and hence the method is practicable. The same and high reliabilities of both a,b,c and d(A)-values are necessary. The accuracy of calculations depends on that of a, b, c and d(A)-va-lues,found experimentally. For monoclinic crystals the angle varies from 90°to 120°.更多还原