Kinetics of hexagonal–cubic phase transformation of zinc sulfide in vacuo, in zinc vapor, and in sulfur vapor

Abstract

The kinetics of the hexagonal-cubic phase transformation of zinc sulfide have been studied in vacuo, in zinc vapor, and in sulfur vapor in the temperature range 800-900 "C by a powder X-ray diffraction technique. The transformation rate is enhanced in the presence of sulfur and zinc vapor. In vacuo and in sulfur vapor the reaction is nucleation-controlled with activation energies of 95.0 and 98.5 + 5 kcal, respectively. In zinc vapor the reaction is diffusion-controlled with the diffusion coefficient expressed asThe modes of catalytic action by sulfur and zinc vapor on the solid phase transformation reaction are discussed. Canadian Journal of Chemistry, 46, 2881 (1968) IIntroduction Experimental Our interest in the phase transformation of zinc sulfide stems from observations on sintering studies of ZnS powder (1) which indicated that the wurtzite-sphalerite transformation rate was enhanced by ambient vapors, viz. Zn and sulfur. This catalytic effect of a gas on a solid state reaction, while not a new one, appealed to us as a promising method for probing the nature of gas-solid interactions, especially the effect of an adsorbed species on the solid rather than the common inverse effect. Two modes of this catalytic action were visualized with their origins: (a) on the surface, where the most probable mode of action might be nucleation and (b) in the interior, where the action must involve solubility with subsequent transport or mobility steps. With regard to the latter mode, if the catalytic action is not entirely restricted to the surface, the Zn and sulfur vapor species possess a useful intrinsic parameter in their large relative difference in diameter, i.e. rs,/r,, --2.'Present address: Kinetics Research Group of Hungarian Academy of Sciences, Szeged, Hungary.2To whom correspondence on this paper should be addressed. 3Present address: Chemistry Department, Immaculata College, Immaculata, Pa. 4Present address: Chemistry Department, University of Western Ontario, London, Ontario.The ZnS powder used in this work was from two batches of BDH laboratory reagent, I and 11. In both cases, the X-ray diffractograrns showed (2) peak intensities characteristic of 80% wurtzite-20% sphalerite mixture. The particle radius of the powder is calculated to be 6.1 x cm from nitrogen adsorption measurements (3).The sulfide samples (ca. 200 mg) were annealed in a static system in vacuo or with sufficient zinc or sulfur to give the requisite pressure. The reaction chamber consisted of a quartz vessel of the design already described (4). After the anneal in the furnace at the appropriate temperature (4) and the removal of the powder from the quartz vessel, the sample was weighed, crushed in a mortar, and analyzed using a Norelco diffractometer model X-86.The extent of reaction was determined by a method similar to that used by Edwards and Lipson (5). This method assumes that the intensity of the (111) face of the cubic structure increases at the expense of the (100) and (101) planes of the hexagonal structure. The fact that the (002) ...

Mechanism of Flux Action in the Thermal Recrystallization of Zinc Sulfide

“…An activation energy of 61.5 kcal was obtained by Secco (17) for the lattice diffusion of zinc, that is the movement of zinc through normal zinc sites in the zinc sulfide lattice. A similar value for a lattice diffusion mechanism was given by Bansagi and co-authors (19). The results obtained in the present study are in very good agreement with the activation energy values given by Secco (t7).…”

I. Order–disorder transitions and solid state reaction kinetics in Na2SO4–K2SO4 system

“…Highly consistent linear plots of the above relationships gave (i) E, values of 500 1+-80 kJ/mol for recycled stored samples of K,Na(SO,), and (ii) E, values of 1000 2 150 kJ/mol for freshly prepared individual samples of K,Na(S04)2 and KNaSO, . These high E, values are consistent with activation energy values reported for phase transitions in K2S04 (18), ZnS (15), and anthranilic acid (19 …”

Effects of Temperature, Pressure, and Metal Promoter on the Recrystallized Structure and Optical Transmission of Chemical Vapor Deposited Zinc Sulfide

“…The degree of hexagonality and extent of crystallographic texture were quantitatively assessed in order to establish their relationship to optical transmission and to provide insight into possible mechanisms for crystallographic transformation during annealing and HIPping. Bansagi et al 40 and Xue and Raj 22 have suggested a simple measure of the degree of hexagonality in polycrystalline ZnS powders and hot-pressed compacts. The degree of hexagonality is determined by measuring the relative atomic fraction of hexagonal stacking or polytypic sequences in a sample.…”