Chemical elements
  Zinc
    Isotopes
    Energy
    Production
    Application
    Physical Properties
    Chemical Properties
      Zinc Fluoride
      Zinc Chloride
      Zinc Oxychlorides
      Zinc Bromide
      Zinc Iodide
      Zinc Hypochlorite
      Zinc Perchlorate
      Zinc Bromate
      Zinc Iodate
      Zinc Periodate
      Zinc Oxide
      Zinc Hydroxide
      Zincates
      Zinc Peroxide
      Zinc Sulphide
      Zinc Hydrosulphite
      Zinc Thiosulphate
      Zinc Sulphite
      Zinc Sulphate
      Zinc Dithionate
      Zinc Tetrathionate
      Zinc Pentathionate
      Zinc Selenide
      Zinc Selenites
      Zinc Selenate
      Zinc Telluride
      Zinc Tellurate
      Zinc Chromite
      Zinc Chromate
      Zinc Dichromate
      Zinc Molybdate
      Zinc Tungstate
      Zinc Nitride
      Zinc Azide
      Zinc Amide
      Zinc Ammoniate
      Zinc Nitrite
      Zinc Nitrate
      Basic Zinc Nitrates
      Zinc Phosphide
      Zinc Hydrophosphide
      Zinc Hypophosphite
      Zinc Phosphite
      Zinc Thiophosphite
      Zinc Orthophosphate
      Zinc Pyrophosphate
      Ammonium Zinc Orthophosphate
      Zinc Thiophosphates
      Zinc Arsenide
      Zinc Arsenite
      Zinc Arsenates
      Zinc Metantimonate
      Thioantimony Salts of Zinc
      Zinc Carbonate
      Zinc Thiocarbonate
      Zinc Cyanide
      Zinc Thiocyanate
      Zinc Silicide
      Zinc Silicates
      Zinc Borates
      Zinc Perborate
    PDB 12ca-1ai0
    PDB 1aiy-1b6z
    PDB 1b71-1bs8
    PDB 1bsk-1cao
    PDB 1caq-1ctt
    PDB 1ctu-1de6
    PDB 1def-1dy0
    PDB 1dy1-1ed6
    PDB 1ed8-1exk
    PDB 1eyf-1fj9
    PDB 1fjg-1g0e
    PDB 1g0f-1gkq
    PDB 1gkr-1ha5
    PDB 1hbm-1hso
    PDB 1hsz-1i6v
    PDB 1i73-1im5
    PDB 1iml-1jcv
    PDB 1jcz-1jy8
    PDB 1jyb-1kh4
    PDB 1kh5-1kys
    PDB 1kzo-1llm
    PDB 1llu-1m7j
    PDB 1m9j-1mwo
    PDB 1mwq-1ndv
    PDB 1ndw-1nyq
    PDB 1nyr-1os4
    PDB 1os9-1p9w
    PDB 1paa-1pud
    PDB 1pv8-1q9l
    PDB 1q9m-1qv6
    PDB 1qv7-1r6o
    PDB 1r79-1ro9
    PDB 1ror-1sfo
    PDB 1sg0-1t3k
    PDB 1t4k-1tkh
    PDB 1tkj-1u0l
    PDB 1u10-1ums
    PDB 1umt-1v67
    PDB 1v6g-1vrq
    PDB 1vs0-1wew
    PDB 1wfe-1wwf
    PDB 1wwg-1xb1
    PDB 1xb8-1xpz
    PDB 1xq0-1y5w
    PDB 1y5x-1ylk
    PDB 1ylo-1z8r
    PDB 1z93-1zkx
    PDB 1zl6-258l
    PDB 2a03-2afo
    PDB 2afs-2atq
    PDB 2au3-2bfz
    PDB 2bg2-2c3a
    PDB 2c4r-2cij
    PDB 2cim-2czr
    PDB 2d0w-2djw
    PDB 2dkc-2e1b
    PDB 2e1s-2eer
    PDB 2eex-2em4
    PDB 2em5-2eoj
    PDB 2eok-2erq
    PDB 2esf-2fa7
    PDB 2fac-2fpx
    PDB 2fqp-2g84
    PDB 2g87-2gvf
    PDB 2gvi-2han
    PDB 2hap-2huc
    PDB 2hue-2imc
    PDB 2imr-2j65
    PDB 2j6a-2jq5
    PDB 2jr7-2kfn
    PDB 2kft-2l75
    PDB 2lgv-2nx9
    PDB 2nxa-2oc8
    PDB 2occ-2osm
    PDB 2oso-2p53
    PDB 2p57-2pow
    PDB 2ppb-2q8j
    PDB 2qa1-2qp6
    PDB 2qpj-2r71
    PDB 2r74-2sod
    PDB 2srt-2v86
    PDB 2v87-2vp7
    PDB 2vpb-2vyo
    PDB 2vz5-2wey
    PDB 2wfq-2wx0
    PDB 2wx1-2xam
    PDB 2xan-2xr9
    PDB 2xrg-2ytd
    PDB 2yte-2z30
    PDB 2z3g-2zet
    PDB 2zh0-3a32
    PDB 3a36-3aoi
    PDB 3at1-3bk1
    PDB 3bk2-3byr
    PDB 3byw-3cia
    PDB 3ciz-3d08
    PDB 3d09-3dbu
    PDB 3dc3-3dp6
    PDB 3dpe-3e1w
    PDB 3e1z-3ebh
    PDB 3ebi-3epk
    PDB 3epl-3f28
    PDB 3f2b-3fhe
    PDB 3fhp-3ful
    PDB 3fum-3g9y
    PDB 3ga3-3gpu
    PDB 3gpx-3h2w
    PDB 3h3e-3hfy
    PDB 3hgz-3hsn
    PDB 3hso-3i8v
    PDB 3i9b-3ij6
    PDB 3ijf-3ixe
    PDB 3iz0-3k34
    PDB 3k35-3kiy
    PDB 3kj1-3kvt
    PDB 3kwa-3lat
    PDB 3lcn-3lrr
    PDB 3ls1-3m1n
    PDB 3m1v-3mek
    PDB 3men-3mru
    PDB 3ms0-3n63
    PDB 3n64-3nin
    PDB 3nis-3ny2
    PDB 3ny3-3ohc
    PDB 3ohd-3oyl
    PDB 3oym-3pih
    PDB 3pki-3r0d
    PDB 3rj7-3t74
    PDB 3t87-3u9g
    PDB 3ua7-3v24
    PDB 3v25-4agl
    PDB 4agm-4dih
    PDB 4dii-4efs
    PDB 4eg2-4fc8
    PDB 4fgm-6tli
    PDB 6tmn-9nse

Zinc Oxide, ZnO






Zinc Oxide occurs naturally as zincite or red zinc ore crystallised in the hemimorphic group of the hexagonal system, with a hardness of 4-4.5 and a density of 5.5-5.55.

Zinc oxide is prepared on the large scale by heating the metal to near its boiling-point. The vapours burn in the air and a white woolly mass of oxide condenses. It has been known under various names: pompholix and nix alba, or philosophical wool, in ancient times; zinc white, and occasionally flowers of zinc, in modern.

Proposals have been made to prepare it commercially by heating zinc sulphate or various zinc minerals with carbon, and by electrolysing a solution of sodium sulphate between zinc electrodes. The zinc hydroxide formed in the latter process is finally calcined to the oxide.

Amorphous zinc oxide is also obtained by igniting zinc hydroxide or carbonate.

A crystalline oxide results from igniting zinc nitrate, and zinc oxide also sublimes in crystals when (a) zinc is heated to redness in a current of steam; (b) zinc chloride is heated in a current of steam; (c) zinc oxide is heated in a slow current of hydrogen; (d) zinc oxide is heated in a current of oxygen; (e) zinc oxide is volatilised in the electric furnace.

Gorgeu, by heating zinc sulphate with an alkaline sulphate, obtained transparent, nacreous, greenish-yellow or greenish hexagonal prisms that belonged to the hexagonal system and were identical with zincite in hardness and density. He also obtained good crystals by heating equal parts of zinc fluoride and potassium fluoride in the presence of steam.

The artificial crystals are usually hexagonal, though some crystals, artificially produced during the distillation of zinc, belong to the regular system. Moissan obtained his crystals in long transparent needles.

According to Brugelmann, the density of amorphous zinc oxide, prepared by igniting the hydroxide or carbonate, is 5.47, and of the crystals obtained by igniting the nitrate, 5.78.

The specific heat of zinc oxide has been given as 0.12480. Ordinary amorphous zinc oxide is a white powder with a creamy tint, that goes yellow when hot and white again on cooling. The yellow tint in some commercial samples has been traced to cadmium sulphide. Zinc oxide has been said to lose part of its oxygen on heating, and the yellow lower oxide to remain stable if no oxygen is present during cooling. Crystalline samples often have a yellow tinge. The yellow colour is said to appear whether the oxide is heated in an atmosphere of oxygen or carbon dioxide or nitrogen, or in a partial vacuum.

At 18° C., 236,000 parts of water dissolve 1 part of zinc oxide. The precipitated oxide retains small quantities of moisture at high temperatures. Even after ignition it dissolves in ammonium chloride solution or in a solution of ammonia and ammonium carbonate. Acids readily dissolve it.

Hydrogen begins to reduce zinc oxide at 454° C., and the reduction can be carried to completion in dry hydrogen, though the reversible character of the reaction

H2+ZnOZn+H2O

renders this difficult. Zinc oxide is also reduced by carbon at a red heat and by heating with magnesium.

The reduction of zinc oxide by carbon is metallurgically important.

According to Boudouard, carbon monoxide is the immediate agent of reduction. The reduction of zinc oxide by carbon monoxide begins at a lower temperature than the reduction by carbon in an atmosphere of nitrogen. According to Lemarchands, zinc oxide can be reduced directly by carbon, and the reduction of the oxide is normally effected simultaneously by carbon and carbon monoxide. The amount of carbon entering into the reaction is intermediate between the quantities required by

ZnO+C = Zn+CO
and
2ZnO+C = 2Zn+CO2,

because the reduction of zinc oxide by carbon monoxide

ZnO+CO = Zn+CO2

is more rapid than the reduction of carbon dioxide by carbon. The reaction

ZnO+CZn+CO

proceeds from left to right at 600° C. The reverse reaction is only observable at much higher temperatures. Carbon monoxide can reduce zinc oxide at temperatures as low as 350°-400° C.

Zinc oxide and carbon are converted into zinc vapour and carbon monoxide at 1033° C.

Sulphur dioxide has no action on heated zinc oxide, but chlorine converts it into the chloride.

It is said to dissociate when heated with metallic zinc.

The heat of formation of zinc oxide has been frequently determined, and, according to de Forcrand, it varies from 80.29 to 84.7 Cal. for solid zinc and gaseous oxygen. Apparently the values are higher, as the temperatures at which the oxide is prepared are greater. This may be connected with increasing polymerisation as the temperature of the oxide is raised. Dilute sulphuric acid dissolves zinc oxide much less rapidly when it has been raised to a red heat than when it has been prepared at 350° C. The strongly heated oxide also dissolves relatively slowly in alkaline hydroxides.

Its heat of solution in aqueous hydrofluoric acid has been given as 21.820 Cal.

Zinc oxide is used as a polishing powder, especially for glass. It is employed in the manufacture of dental cements, crystalline glazes, glass, and porcelain. As a pigment it has the advantage over lead compounds of not darkening under the action of hydrogen sulphide.

Zinc ointment, which contains zinc oxide, is a familiar pharmaceutical product.


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