Zinc and compounds: Overview
Description
Zinc is mainly used as a protective coating for iron and steel (galvanising). It is further used for the production of zinc alloys (e.g. brass), rolled zinc, zinc dust (a pigment and a reducing agent), and zinc compounds (e.g. zinc oxide).
- Zinc oxide is the industrially most important zinc compound. It is used in rubber (vulcanising, pigment), photocopy paper, chemicals and paints. Other uses are in floor coverings, in glasses, enamels, fabrics, plastics, lubricants, in rayon manufacture, and in pharmaceuticals (powders and ointments for external application on burns, skin infections and for skin protection).
- Zinc acetate is used in wood preserving, as a mordant in dyeing, as a feed additive, as a food additive, as a component of adhesives, as a glaze for painting on porcelain, and as a reagent in testing for albumin, tannin, phosphate and blood. It is a pharmaceutical necessity for zinc eugenol dental cement for temporary fillings.
- Zinc carbonate is used as a fire-proofing filler for rubber and plastic compositions exposed to flame temperature, as a feed additive, as a pigment, in cosmetics and lotions, and in the manufacturing of zinc salts, porcelains, pottery, and rubber.
- Zinc chloride is used in fluxes (soldering and welding), for fire proofing, as a wood preservative, and in medicine (cauterising agent). It is used alone or with phenol and other antiseptics for preserving railway ties, and as a herbicide and foliar treatment on sidewalks, patios, and fence rows. It is used in the manufacturing of parchment paper, artificial silk, activated carbon, cold water glues, magnesia cements, cement for metals and for facing stone, dental cements, and golf balls. It is used as a mordant in printing and dyeing textiles, as electrolyte in dry cell batteries, as a corrosion inhibitor in water treatment, as an agent in the vulcanisation of rubber, and as a chemical intermediate for pesticides and micronutrients in agriculture. It is used in mercerising cotton, sizing and weighting fabrics, carbonising woollen goods, producing crepe and crimping fabrics, and preserving anatomical specimens. Zinc chloride is a primary ingredient in smoke bombs, as used by the military for screening purposes, crowd dispersal, and fire-fighting exercises.
- Zinc chromate is primarily used in paints for priming metals to resist corrosion. It is also used in varnishes and automotive paint pigments.
- Zinc cyanide is used in metal plating, in producing insecticides, electroplating, removing ammonia from producer gas, and gold extraction. It is also used as a chemical reagent, and in medicine and chemical analysis.
- Zinc fluoride is used in the fluorination of organic compounds, in the manufacturing of phosphors for fluorescent lights, in preserving wood, in electroplating baths, in galvanising steel, and making ceramics. It is also used as a termite repellent, in medication, and in glazes and enamels for porcelain.
- Zinc phosphide is used in rat and field mice poison, as a stomach poison for mosquito larvae and agricultural pests, and for control of crickets.
- Zinc potassium chromate is used as a rust inhibitor in metal paints and as an artist's colour.
- Zinc sulfate is used as a reagent in analytical chemistry and for paper bleaching, as a component of spinning bath in the manufacture of rayon, and as a chemical intermediary for the manufacture of carbamate fungicides, zinc metal, and other zinc compounds. It is used in skin fresheners, glue, textile dyeing and printing, and preservatives for wood and hides. It is also used as a fireproofing agent, a fertiliser ingredient, a feed supplement, a herbicide, a miticide, as a soil treatment on lawns, and in sewage against animal pathogenic bacteria. Zinc sulfate can be used as a supplement for humans, animals and plants with zinc deficiency.
- Zinc sulfide is used as a pigment for paints, oil cloths, linoleum, leather, and dental rubber, in white and opaque glass, plastics, dyeing, and in fungicides. It is used as a semiconductor, a photoconductor for solar cells, a pigment in paper, in infra-red thin film and transmitting devices, in detinning, and in optical filter coating. It is used as a phosphor in TV and X-ray screens, and in luminous dials of watches.
A range of organic zinc compounds exists (e.g. zinc soaps, Ziram, and Zineb) which are used as fungicides, antiseptics, water-repellents, lubricants, and for water-proofing textiles, papers, and concrete.
Substance details
Substance name: Zinc and compounds
CASR number: 7440-66-6
Molecular formula: Zn
Synonyms: Zinc dust, zinc powder, blue powder. Zinc acetate (CASR# 557-34-6), zinc carbonate (CASR# 3486-35-9), zinc chloride (CASR# 7646-85-7), zinc chromate (CASR# 13530-65-9), zinc cyanide (CASR# 557-21-1), zinc fluoride (CASR# 7783-49-5), zinc hydroxide (CASR# 20427-58-1), zinc oxide (CASR# 1314-13-2), zinc phosphide (CASR# 1314-84-7), zinc potassium chromate (CASR# 11103-86-9), zinc sulfate (CASR# 7733-02-0), and zinc sulfide (CASR# 1314-98-3).
Physical properties
Zinc is easily obtained from its ores. The main minerals are sulfides (sphalerite, wurtzite). Zinc is a bluish-white, lustrous metal. It is brittle at ambient temperatures but is malleable at 100 to 150°C. It can also be rolled at these temperatures. It is a reasonable conductor of electricity. Zinc forms many alloys. Brass, an alloy with copper, is an example.
Atomic Number: 30
Atomic Mass: 65.4
Melting Point: 420°C
Boling Point: 907°C
Specific Gravity: 7.14
The properties of zinc compounds vary greatly:
- Zinc acetate comes in the form of white granules. It is slightly efflorescent and has a faint vinegar odour. It decomposes at 200°C.
- Zinc carbonate comes as colourless crystals, or a white, crystalline powder. It is odourless and evolves carbon dioxide at 300°C.
- Zinc chloride comes in the form of hygroscopic white granules, white crystals, fused pieces, or rods. It is odourless but its white fume has an acrid odour. The melting point of pure zinc chloride is 275°C and its boiling point is 756°C. Its specific gravity is 2.9 and its vapour density is 4.7.
- Zinc chromate can be a yellow, fine powder or yellow prisms. It is odourless.
- Zinc cyanide is either a white powder, or colourless, rhombic crystals. It has the odour of bitter almonds. It decomposes at 800°C.
- Zinc fluoride can exist as colourless crystals, needles, or a white crystalline mass. It has a melting point of 872°C and a boiling point of 1502°C. Its specific gravity is 4.95.
- Zinc oxide is a white solid which turns yellow on heating. Its melting point is 1975°C and its specific gravity is 5.6.
- Zinc phosphide comes in the form of dark grey crystals, or a lustrous or dull powder. It has a faint phosphorus or garlic odour. Its melting point is greater than 420°C and it boils at 1100°C.
- Zinc potassium chromate is a yellow powder.
- Zinc sulfate comes in the form of colourless rhombic crystals, transparent prisms or small needles. It is efflorescent in dry air.
- Zinc sulfide comes in the form of colourless hexagonal crystals, or white/greyish-white or yellow powder.
Chemical properties
Zinc is insoluble in water but reacts readily with non-oxidising acids, forming zinc (II) and releasing hydrogen. It also dissolves in strong bases. It reacts readily when heated with oxygen to give zinc oxide. Direct reactions with halogens will also occur. Pure zinc in air forms a layer which protects the metal from corrosion. In dry air, this protective layer is an oxide layer and in wet air it is a carbonate-hydroxide layer.
Zinc ions found in aquatic environments are in the (II) oxidation state. It is rarely encountered as the free zinc (II) ion due to its strong tendency to form complexes with inorganic and organic compounds freely available in nature. Water solubility of zinc compounds varies, with zinc acetate, zinc nitrate, zinc sulfate, zinc chloride, zinc chlorate and zinc perchlorate all readily soluble in water. Zinc oxide, zinc carbonate and zinc sulfide are practically insoluble in water. Properties of selected zinc compounds follow.
- Zinc acetate is soluble in water and alcohol. It crystallises from dilute acetic acid.
- Zinc carbonate is soluble in dilute acids, alkalies and in ammonium salt solutions. It is insoluble in water, ammonia, pyridine, alcohol and acetone.
- Zinc chloride is very soluble in water, and quite soluble in alcohol and acetone. It is also soluble in hydrochloric acid, glycerol and ether. It is insoluble in ammonia. It is very deliquescent. Its fumes are corrosive to metals.
- Zinc chromate is insoluble in cold water and acetone, and soluble in acid and ammonia. It is corrosive because of its oxidising potency.
- Zinc cyanide is insoluble in alcohol, and soluble in ammonium solutions, solutions of alkali cyanides and hydroxides.
- Zinc fluoride is soluble in water, and quite soluble in alcohol and acetone. It is also soluble in ammonium hydroxide, alkali, hydrochloric acid and nitric acid, slightly soluble in aqueous hydrofluoric acid, and insoluble in ammonia.
- Zinc hydroxide can be precipitated from zinc solutions by addition of bases. It dissolves in aqueous sodium hydroxide and concentrated ammonia.
- Zinc oxide is formed when burning zinc metal in air or by pyrolysis of zinc carbonate or zinc nitrate.
- Zinc phosphide is practically insoluble in alcohol and water, and slightly soluble in benzene. It is stable when dry. It reacts with acids and more slowly with water. It reacts violently with acids when heated (> 400 °C) to form phosphine gas.
- Zinc sulfate is soluble in water, methanol and glycerol. It is insoluble in alcohol. Insoluble sulfates are formed when zinc sulfate is combined with lead, barium, strontium, and calcium salts.
- Zinc sulfide is insoluble in water and alkalies, and soluble in dilute mineral acids.
Further information
The National Pollutant Inventory (NPI) holds data for all sources of Zinc and compounds in Australia.
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