Zinc sulfide blende

Zinc sulfide, ZnS, sphalerite (zinc blende) zinc sulfide, ZnS, wurtzite zinc selenide, ZnSe zinc telluride, ZnTe, cubic zinc telluride, ZnTe, hexagonal zinc polonide, ZnPo zinc aluminum selenide, ZnAl2Se4 zinc indium selenide, ZnIn2Se4 zinc indium telluride, Znhi2Te4. 

There are two forms of zinc sulfide that have structures known as wurtzite and zinc blende. These structures are shown in Figures 7.7a and 7.7b. Using the ionic radii shown in Table 7.4, we determine the radius ratio for ZnS to be 0.39, and as expected there are four sulfide ions surrounding each zinc ion in a tetrahedral arrangement. Zinc has a valence of 2 in zinc sulfide, so each bond must be 1/2 in character because four such bonds must satisfy the valence of 2. Because the sulfide ion also has a valence of 2, there must be four bonds to each sulfide ion. Therefore, both of the stmctures known for zinc sulfide have a tetrahedral arrangement of cations around each anion and a tetrahedral arrangement of anions around each cation. The difference between the structures is in the way in which the ions are arranged in layers that have different structures. 

FIGU RE 7.7 The zinc blende (a) and wurtzite (b) structures for zinc sulfide. 

St. Joseph Also known as St. Joe. A process for extracting zinc from zinc sulfide ore by electrothermic reduction, practised by the St Joseph Lead Company at its Josephtown refinery in the United States, in the 1930s. A mixture of zinc blende with coke was heated by passing electricity through the mixture. The zinc vapor thus produced was condensed in a bath of molten zinc. The name has also been applied to a similar lead extraction process. 

The zinc that is produced today starts as the zinc sulfide (ZnS) minerals zinc blende or sphalerite or from zinc carbonate (ZnCO ) known as smithsonite or calamine. In the electrolytic process, these minerals are dissolved in water to form the electrolyte in the cell where the zinc cations are attracted and collected at the cathode and deposited as a dull, brittle type of zinc. 

Unit cells of these two structures are shown in Figure 1.37 and Figure 1.38, respectively. They are named after two different naturally occurring mineral forms of zinc sulfide. Zinc blende is often contaminated by iron, making it very dark in colour and thus lending it the name of Black Jack . Structures of the same element or compound that differ only in their atomic arrangements are termed polymorphs. 

Wurtzite structure. Zinc sulfide can also crystallize in a hexagonal form called wurtzite that is formed slightly less exothermically than the cubic zinc blende (sphalerite) modification (Afff = —192.6 and —206.0 kJ mol-1, respectively) and hence is a high temperature polymorph of ZnS. The relationship between the two structures is best described in terms of close packing (Section 4.3) in zinc blende, the anions (or cations) form a cubic close-packed array, whereas in wurtzite they form hexagonal close-packed arrays. This relationship is illustrated in Fig. 4.13 note, however, that this does not represent the actual unit cell of either form. 

The luminescent properties can be influenced by the nature of the activators and coactivators, their concentrations, the composition of the flux, and the firing conditions. In addition, specific substitution of zinc or sulfur in the host lattice by cadmium or selenium is possible, which also influences the luminescent properties. Zinc sulfide is dimorphic and crystallizes below 1020 °C in the cubic zinc-blende structure and above that temperature in the hexagonal wurtzite lattice. When the zinc is replaced by cadmium, the transition temperature is lowered so that the hexagonal modification predominates. Substitution of sulfur by selenium, on the other hand, stabilizes the zinc-blende lattice. 

Cation holes can also be created by coactivation with trivalent metal ions or by incorporation of oxygen [5.313]. The luminescence band of self-activated zinc sulfide with the zinc-blende structure exhibits a maximum at 470 nm. On transition to the wurtzite structure, the maximum shifts to shorter wavelengths. In the mixed crystals zinc sulfide-cadmium sulfide and zinc sulfide-zinc selenide, the maximum shifts to longer wavelengths with increasing cadmium or selenium concentration. 

The zinc blende and wurtzite structures. Zinc sulfide crystallizes in two distinct lattices hexagonal wurtzite (Fig. 4.2a) and cubic zinc blende (Fig. 4.2b). We shall not elaborate upon them now (see page 121), but simply note that in both the coordination number is 4 fbr both cations and anions. The space groups are Ptync and F43m. Can you tell which is which ... 

SPHALERITE BLENDE. Also known as zinc blende, this mineral is zinc sulfide, tZn, Fc)S, practically always containing some iron, crystallizing in the isometric system frequently as tetrahedrons, sometimes as cubes or dodecahedrons, but usually massive with easy cleavage, which is dodecahedral. It is a brittle mineral with a conchoidal fracture hardness, 2.5-4 specific gravity, 3.9-4.1 luster, adamantine to resinous, commonly the latter. It is usually some shade of yellow brown or brownish-black, less often red, green, whitish, or colorless streak, yellowish or brownish, sometimes white transparent to translucent. Certain varieties... 

The melt used in this work was prepared from the residue of hydrogen-donor extraction of Colstrip coal with tetralin solvent in such a way as to simulate the composition of an actual spent melt. The extraction was conducted in the continuous bench-scale unit previously described (17) at 412°C and 50 min residence time. The residue used was the solvent-free underflow from continuous settling (17) of the extractor effluent. The residue was then precarbonized to 675°C in a muffle furnace. The melts were blended to simulate the composition of a spent melt from the direct hydrocracking of the Colstrip coal by blending together in a melt pot zinc chloride, zinc sulfide, and ammonium chloride, ammonia, and the carbonized residue in appropriate proportions. Analysis of the feed melt used in this work is given in Table I. 

Zinc Zinc blende Zinc sulfide ZnS Sulfide is roasted in air and the oxide produced is heated with carbon... 

The principal source of zinc is zinc sulfide or zinc blende. This ore occurs mainly in Australia, Canada and the US. The zinc ore is first concentrated by a process called froth flotation. The crushed ore is fed into tanks of water containing a chemical frothing agent. Air is blown through so that the whole mixture froths up. The rock particles become soaked with water and sink to the bottom of the tank. However, the zinc sulfide particles, into which the water cannot soak, are carried to the top of the tank by the air bubbles and are skimmed off and dried. This ore now contains 55-75% of zinc sulfide. The zinc sulfide is then heated very strongly in a current of air in a furnace (Figure 10.16) to convert it to the oxide ... 

The PT structure has filled P layers and one T layer filled between P layers. Zinc sulfide has two modifications zinc blende or sphalerite... 

The structure of cubic zinc sulfide (zinc blende, sphalerite) may be described as a ccp of S atoms, in which half of the tetrahedral sites are filled with Zn atoms the arrangement of the filled sites is such that the coordination numbers of S and Zn are both four, as shown in Fig. 10.1.7. The crystal belongs to space group 7 2 — / 43m. Note that the roles of the Zn and S atoms can be interchanged by a simple translation of the origin. 

Zinc is not a very common metal and as we notice from Table 3.1, its availability on earth s crust is low. It is found mainly as zinc sulfide in ores such as sphalerite and zinc blende, and as carbonates in smithsonite and silicate in calamine. The oxide is extracted by roasting these ores. The first discovery of zinc based CBPC as a dental material occurred... 

Other AZ stmcture types include cesium chloride, CsCl (Fig. 3.11) two polymorphs of zinc sulfide-wurtzite and zinc blende and NiAs. Although these stmcture t) pes are... 

Zinc selenide (yellow) and telluride (brown) have similar stractures to those of the sulfide, both existing in both wurtzite and zinc blende modifications. The selenide is used with zinc sulfide as a phosphor. It has the interesting property that it can act as a bine-green solid state laser bine-green laser action in solids is rare (most solid-state lasers function towards the red end, 635 nm or more, of the spectrum). At room temperature, laser action with the selenide at a wavelength of 525 nm (green) is observed and at -196°C at 495 nm (bine). Unfortunately the laser is relatively short-lived. Zinc telluride is a wide band gap semicondnctor whose electron transport properties in the form of thin films of stoichiometric and nonstoichiometric forms have been mnch studied. Its applications in optoelectronics, for example, as an optical recording material, have been reviewed. ... 

Zinc never occurs as a free element in the earth. Some of its most important ores include smithsonite, or zinc spar or zinc carbonate (ZnC03) sphalerite, or zinc blende or zinc sulfide (ZnS) zincite, or zinc oxide (ZnO) willemite, or zinc silicate (ZnSi03) and franklinite [(Zn,Mn,Fe)0 (Fe,Mn2)03]. 

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