Occurrence and Uses
Zinc sulfide occurs in nature in two crystalline forms, the minerals, wurtzite, and sphalerite. Sulfide ore is the principal zinc mineral.
The most important use of Zinc sulfide is as a pigment. As lithopone, a mixture with barium sulfate, it forms a low gloss interior house paint. The pigment, “mineral white” is made by combining zinc sulfide with zinc oxide. Zinc sulfide is incorporated into phosphors to produce luminescence when irradiated with light. It is used in making luminous dials, x-ray and television screens, and fluorescent lights. Also, it is used in making white and opaque glass and as a base for color lakes (which consist of an organic pigment with an inorganic carrier).
Physical Properties
Zinc sulfide is white to gray-white or pale yellow powder. It exists in two crystalline forms, an alpha (wurtzite) and a beta (sphalerite). The wurtzite form has hexagonal crystal structure; refractive index 2.356; density 3.98 g/cm3; melts at 1,700°C; practically insoluble in water, about 6.9 mg/L; insoluble in alkalis; soluble in mineral acids. The sphalerite form arranges in cubic crystalline state; refractive index 2.368; density 4.102 g/cm3; changes to alpha form at 1,020°C; practically insoluble in water, 6.5 mg/L; soluble in mineral acids, insoluble in alkalis. When zinc sulfide contains water, it slowly oxidizes to sulfate on exposure to air.
Uses
Zinc sulfide is well known as an optical coating material for its high refractive index (~2.35 at 500 nm) and very broad transmittance range from 400 nm up to 14 µm. It allows for coatings in the IR and VIS range with good environmental durability, and can be evaporated rapidly from e-beam and resistance heated sources. It is used as a semiconductor and in photo optic applications.
Copperactivated zinc sulfides are the most widely used phosphors for safety purposes.
Zinc sulfide and white lead are sometimes used in coating materials because of their fungicidal properties and to neutralize acid to protect against corrosion.
Production
Zinc sulfide is mined from natural deposits and concentrated by various processes.
Also, zinc sulfide may be prepared in the laboratory by passing hydrogen sulfide through an aqueous solution of a soluble zinc salt, such as zinc chloride or zinc nitrate. The precipitate is filtered, washed, and dried.
Chemical Properties
Yellowish-white powder. ZnS exists in two crystalline forms,
α (wurtzite) and β (sphalerite). Stable if kept
dry. α: d 3.98. β: d 4.102, changes to α form at
1020C. Sublimes at 1180C. Soluble in acids; insoluble
in water.
Uses
Zinc sulfide (ZnS) is used as a pigment and to make white glass, rubber, and plastics. It is
an ingredient in pesticides, luminous paints, and X-ray and television screens.
Uses
Pigment for paints, oilcloths, linoleum, leather, dental rubber, etc., especially in the form of lithopone; mixed with ZnO as "mineral white." Anhydrous zinc sulfide is used in x-ray screens and with a trace of a radium or mesothorium salt in luminous dials of watches; also television screens.
Uses
Zinc Sulfide is used as a friction material to carry sulfur, which hardens rotor surfaces and thereby reduces wear. Also in printing inks, UV-hardened systems, powder coatings, adhesives, insulating & sealing compounds, thermoplastic pigmentation, thermosets, flame resistant plastics, glass-fiber reinforced plastics, pigment concentrates, elastomers,. textile fibers, paper, mastics, lubricants, electroluminescent lamps, infrared windows, domes and optical elements.
Production Methods
Production is similar to that of lithopone. A Na2S solution is mixed with a zinc salt solution under precisely controlled conditions. The resulting zinc sulfide precipitate is calcined and processed to give the finished product. Na2S + ZnSO4 →ZnS + Na2SO4.
Definition
zinc sulphide: A yellow-whitewater-soluble solid, ZnS. It occursnaturally as sphalerite (see also zincblende) and wurtzite. The compoundsublimes at 1180°C. It is used as apigment and phosphor.
General Description
A yellowish-white powder in a liquid. Insoluble in water and denser than water. Primary hazard is to the environment. Immediate steps should be taken to limit spread to the environment. Easily penetrates the soil to contaminate groundwater and nearby waterways.
Air & Water Reactions
Insoluble in water.
Reactivity Profile
These sulfides are rather inert, dissolve into acid, insoluble in water and alkalis.
Health Hazard
Inhalation of material may be harmful. Contact may cause burns to skin and eyes. Inhalation of Asbestos dust may have a damaging effect on the lungs. Fire may produce irritating, corrosive and/or toxic gases. Some liquids produce vapors that may cause dizziness or suffocation. Runoff from fire control may cause pollution.
Fire Hazard
Some may burn but none ignite readily. Containers may explode when heated. Some may be transported hot.
Industrial uses
Zinc sulfide(Sachtolith) is mainly used in plastics. Functional properties such as lightening and hiding power are criteria for the use of Sachtolith. It has proved to be very useful for coloring many thermoplasts. During the dispersion process it does not cause abrasion of metallic production machinery or adversely effect the polymer, even at high operating temperatures or during multistage processing. Even ultrahigh molecular mass thermoplasts can be colored without problems. In glass-fiber-reinforced plastics, the soft texture of Sachtolith prevents mechanical fiber damage during extrusion. Sachtolith is also used as a dry lubricant during the fabrication of these materials.
The low abrasiveness of Sachtolith prolongs the operating life of stamping tools used in the manufacture of industrial rubber articles. The lightfastness and ageing resistance of many elastomers are improved by using Sachtolith. It is also used as a dry lubricant for roller and plain bearings, and as a white pigment for greases and oils.
Toxicology
The use of zinc sulfide and barium sulfate in contact with foods is permitted by the FDA (United States) and in most European countries. Some restrictions apply in France, Italy, the United Kingdom, and Czechoslovakia.
Soluble zinc is toxic in large amounts, but the human body requires small quantities (10–15 mg d−1) for metabolism. Zinc sulfide is harmless in the human due to its low solubility. The acid concentration in the stomach and the rate of dissolution following ingestion are not sufficient to produce physiologically significant quantities of soluble zinc. LD50 values in the rat exceed 15 g kg−1. No cases of poisoning or chronic damage to health have been observed in the manufacture of zinc sulfide pigments.
