Abstract
The proposed method, based on measuring the chemical reaction rate in solid phase, is, therefore, limited to such systems where reaction between nanocrystalline materials and a gas phase occurs. Additionally, assumptions of the model of reaction between nanocrystalline materials and a gas phase, where the surface chemical reaction rate is the rate limiting step, are used. As an example of such a reaction, nitriding (with ammonia) of the prereduced industrial iron catalysts for ammonia synthesis of different average crystallite sizes was used. To measure the reaction rate, the differential reactor equipped with systems for thermogravimetric measurements and analysis of the chemical composition of the gas phase was used. The crystallites mass and size distributions for the analyzed samples of catalyst were determined.
Highlights
Particle or grain size distribution is an important parameter in many processes and its precise measurement is required to accurately control the course of these processes
The grain size distribution (GSD) determination became the fundamental measurement when dealing with the nanomaterials, because properties of these materials depend on diameter of nanoparticles [1,2,3,4]
Crystallite size distribution can be measured by X-ray diffraction method of WarrenAverbach or the method proposed in Vogel’s work [12], by Journal of Nanomaterials electron microscopy (SEM, TEM), by methods using results of gas adsorption/desorption measurements, for example, by BET method, by optical methods used to count single particles passing through a laser beam, or by the chemical method already described [13]
Summary
Particle or grain size distribution is an important parameter in many processes and its precise measurement is required to accurately control the course of these processes. The method for determining the size distribution of crystallites, which is intended to measure the width of the diffraction peak at two levels: in the fifth and four fifths of the peak height instead of the previously applied FWHM was proposed [7]. This method enables one to obtain information on the size distribution of grains in different crystallographic directions. This may be due to the fact that, for example, agglomerates of small crystallites are in the “surface” method treated as one large crystallite
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