Diffractometric method for determining the degree of crystallinity of materials
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RACTION AND SCATTERING OF IONIZING RADIATIONS
Diffractometric Method for Determining the Degree of Crystallinity of Materials D. G. Chukhchin, A. V. Malkov, I. V. Tyshkunova, L. V. Mayer, and E. V. Novozhilov Lomonosov Northen (Arctic) Federal University, Arkhangelsk, 163002 Russia e-mail: [email protected] Received October 2, 2015
Abstract—A new method for determining the degree of crystallinity of a material from X-ray diffraction data has been developed. The method is based on estimating the rate of change in function I = f(2θ) in the entire range of scattering angles. A calculation is performed using the ratio of the integral modulus of the first derivative of intensity with respect to angle 2θ to the integral area under the diffraction pattern curve. The method was tested on two substances with known amorphous and crystalline components. A linear relationship is revealed between the specified ratio of crystalline and amorphous parts and the calculated crystallinity index. The proposed method allows one to estimate impartially and compare the degree of crystallinity for samples of different nature. DOI: 10.1134/S1063774516030081
INTRODUCTION Diffraction methods are the main source of data on material structure at the atomic level. Diffraction patterns of materials containing a crystalline component exhibit characteristic peaks, the height and position of which are used to estimate the crystallinity index. In addition, recording X-ray diffraction patterns, one can observe a transition from one structural modification of material to another, which manifests itself in a shift of X-ray peaks [1, 2]. Quantitative X-ray diffraction analysis can be used to determine the degree of crystallinity of different substances. Cellulose―a natural polymer with a high content of crystalline component―was one of the first materials on which such studies were performed. A special issue of Cellulose (April, 2014) was devoted to the 100th anniversary of the publication of Debye’s study [3] on determining the degree of crystallinity of materials. The formula proposed by Debye to calculate the degree of crystallinity, based on estimating the X-ray scattering by the crystal structure of materials and crystal sizes, is still valid; it is used by researchers along with other methods for determining this characteristic [4]. In a number of known methods for determining the degree of crystallinity of materials, an X-ray diffraction pattern is arbitrarily divided into two parts (phases) under the assumption that one of them is crystalline and the other is amorphous and the areas under the corresponding curves are calculated; these areas are considered to be proportional to the phase volumes in further analysis [5]. The Segal method [6]
is based on measuring intensities at two points of cellulose diffraction pattern, assigned presumably to the crystalline and amorphous phases of material. This simple approach was previously widely used to calculate the degree of crystallinity of cellulose; however, it is currently considered insufficiently re
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