CC BY
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AM&T
DOI: 10.17277/amt.2018.04.pp.016-018
The Study of Zinc Sulphide Produced by Different Methods of Impulse Actions
E.V. Petrov*, I V. Saikov, G.R. Saikova
Merzhanov Institute of Structural Macrokinetics and Materials Science of Russian Academy of Sciences, 8, Academician Osipyana St., Chernogolovka, Moscow region, 142432, Russia
* Corresponding author. Tel.: +7 49652 46 376. E-mail: petrov@ism.ac.ru
Abstract
The study of pulsed synthesis in a stoichiometric mixture of Zn+S was conducted by exposing a flat ampoule to the impact of a firing pin, by compressing a cylindrical ampoule, and also in a reactor using an exploding wire. The initiation of the reaction of the powder mixture in a flat ampoule was carried out by the impact action of the impact plate on the powder placed in the cells of the ampoule. With shock-wave action on a cylindrical ampoule, a concentrically converging detonation compression wave was formed, which ensured a comprehensive uniform compression of the ampoule with the powder. In the reactor, the reaction in the powder mixture was initiated by a wire that exploded under the action of an electric pulse applied to it. An X-ray phase analysis of the resulting products showed that in all cases the main product was hexagonal zinc sulphide. The investigation of the revealed structures by the method of electron microscopy showed that the morphology of the form of zinc sulphide reflected the type of crystal structure and the physicochemical conditions at the time of crystal formation.
Keywords
Pulsed impact; ampoule; reactor; zinc sulphide.
Introduction
Synthesis of materials with unique properties and their study under extreme conditions at high pressures is one of the objectives of modern science. Pulsed initiation of chemical reactions of synthesis in compositions consisting of powders of initial elements is one of the directions in shock wave processing of materials, accompanied not only by structural changes, but also by chemical transformations,. As a rule, such studies are experimental and characterized by the complexity of studying fast-acting physical-chemical processes directly in the process of impulse actions, which are characterized by high rates of deformation, pressures and temperatures. The analysis of the published data showed that studies of pulsed initiation of synthesis are conducted in the following directions -by exposing a flat ampoule to the impact of a firing pin, compressing the cylindrical ampoule, and also in the reactor by means of an exploding wire.
The uniqueness of exposing a flat ampoule to a metal impactor accelerated by explosive charge [1, 2], and compression of a cylindrical ampoule according to an axisymmetric loading scheme with a contact charge of explosives [3, 4], consists in the fact that a large
© E.V. Petrov, I.V. Saikov, G.R. Saikova, 2018
amount of energy is injected in the compressed mass of the powder in a short amount of time. Due to this, the synthesis occurs over times of the order of several microseconds with a high degree of plastic deformation of the contact regions.
The initiation of synthesis in a steel reactor by means of an electric wire explosion [5] is a method that represents the initiation of a fast-flowing synthesis reaction process in exothermic systems. It is the synthesis reaction, rather than decomposition that distinguishes the gasless and low-gas detonation of exothermic systems from the detonation of standard explosives, whose gaseous decomposition products are practically impossible to retain in their initial volume.
The purpose of this research is to study the synthesis of a stoichiometric mixture of Zn + S when loading a flat ampoule, shock-wave compression of an ampoule, and initiation in a reactor using an exploding wire.
Experimental
The object of the study was the exothermic system of zinc and sulfur, reacting with the formation of condensed reaction products. The initial powder of zinc
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Fig. 1. The diagram showing the experiment on loading a flat ampoule with an impactor
of PC-1grade in the size 1-11 microns had the spherical form. The sulfur powder grade 9990 class 1 with the size of 5-40 microns was in the form of separate conglomerates.
Initiation of the reaction of a Zn + S mixture in a flat ampoule was carried out by the impact of an impact plate accelerated by a hexogen charge on the powder placed in the ampoule cells (Fig. 1). The experiments were carried out in two versions: the shock-wave action of the plate through an intermediate medium (steel punch) and the impact of the projectile striking plate directly on the surface of the charge. The thickness of the gap between the impactor and the ampoule was 5 mm.
The procedure of shock-wave compression of the powder mixture in a cylindrical ampoule, shown in Fig. 2a, was as follows: a steel rod was placed inside the ampoule on one side closed by a flange, which was necessary to prevent the occurrence of the Mach effect. The powder mixture was poured into a gap of 6 mm in size between the wall of the ampoule and the rod. The ampoule was closed with a cover. A spall element was attached to the flange of the ampoule, designed to reduce the effect of shock wave unloading. After the initiation of the electric detonator, the charge of hexogen was detonated, as a result of which a compressional shock wave was formed concentrically
detonator
isolated contacts tap cover
exploding wire powder reactor body
bottom cover
a)
b)
Fig. 2. The scheme of the experiment:
a - shock-wave compression of the ampoule; b - initiation in the reactor using exploding wire
converging in the ampoule. The propagation of the detonation wave provided a comprehensive uniform compression of the ampoule with the powder.
Fig. 2b shows a diagram of the initiation experiment in a steel cylindrical reactor with an exploding wire, which was as follows: a wire was attached to two insulated contacts mounted into the top cover of the reactor. Then the top cover was screwed into the reactor body and the powder mixture was poured. The density of the Zn + S powder mixture in different experiments varied from 1400 kg/cm3 (bulk) to 2000 kg/cm3, and sometimes the density of the mixture was adjusted to 3620 kg/cm3 (cast Zn + S mixture). The reverse side of the reactor was closed with steel covers with a thickness of 1 to 15 mm. In the case of detonation of the Zn + S mixture, residual deformation of the thin end covers of the reactor was observed, which is characteristic of directional impulses. An electric impulse was applied to two isolated contacts, which exploded the wire, and the reaction in the powder mixture was initiated.
Results and discussion
In a flat ampoule after loading with an impactor, the ampoule cell collapsed, but the resulting product remained in a light gray color (wurtzite), both in cells with punches and in open cells of the ampoule. During the experiments on shock-wave compression, the ampoule was depressurized and the central rod extended. However, along the edges of the ampoule, the product formed during the interaction of Zn and S powders, which had a light gray color, was retained. After conducting the experiment in the reactor, a visual inspection showed the deformation of the bottom cover of the reactor. After opening the reactor, the resulting product had a light gray or yellow (sphalerite) porous structure. Large pores were located along the central part; the denser structure was located near the walls of the reactor. On the side of initiating the process, an air cavity was formed at the top cover of the reactor, and from the side of the cavity the synthesized material was covered with a shiny crust.
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a)
b)
Fig. 3. Diffractogram of Zn + S products in:
a - cylindrical ampoule; b - reactor
An X-ray phase study on the DRON-3M diffractometer of the products obtained in ampoules and reactor (Fig. 3) showed that for all experimental designs, the resulting product corresponded to the structure of the hexagonal (wurtzite) zinc sulfide phase. The diffractogram of the Zn + S product obtained in a flat ampoule completely corresponded to the diffractogram of the product obtained in the reactor (Fig. 3b). However, after the reaction, zinc sulfide can be formed in two modifications - hexagonal and cubic -in the reactor. The simultaneous presence of these two phases in the product, which was formed during the reaction of Zn and S powders, indicated crystallization at temperatures above or near the phase transition temperature [7].
The intensity of the peaks of zinc sulfide products after shock-wave compression of a cylindrical ampoule (Fig. 3a) was 6.5 times less on average compared to the product of zinc sulfide obtained in a flat ampoule and reactor (Fig. 3b), which means that the Zn + S mixture in the ampoule was subject to more intense exposure. As can be seen from the diagrams, the intensity of the X-ray lines responsible for pure zinc, sulfur and zinc oxide was extremely weak. From this we can conclude that the stoichiometric mixture of Zn + S in the process of the reaction almost completely turned into zinc sulfide.
Fig. 4. Zinc sulfide crystallites
The structure of hexagonal zinc sulfide has the form of crystallites with clearly defined edges (Fig. 4), which are compacted near the walls of the ampoule until the boundaries between them disappear. The form of crystallites was determined by the conditions of cooling, which determined the martensitic type of transformation of ZnS from the cubic phase to the hexagonal phase.
Conclusion
The studies showed that the synthesis in a stoichiometric Zn + S mixture is possible both with shock-wave loading of cylindrical and flat ampoules, and when initiated in the reactor with the help of an exploding wire. The resulting product in all experiments had the same hexagonal (wurtzite) structure, but in the reactor, when initiated with an exploding wire, zinc sulphide was obtained together with the cubic structure. The study of product structures showed that the morphology of the zinc sulfide form reflects the type of crystal structure and physico-chemical conditions at the time of the formation of crystals.
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