Zinc oxide

Description

Zinc oxide (ZnO) is a common inorganic compound with a large number of uses. It is insoluble in water but soluble in dilute acids and bases. Its melting point is extremely high—1975 oC, where it also decomposes.
ZnO exists in two common crystalline forms: wurtzite and zincblende. The zincblende structure is shown here, but wurtzite is more stable under ambient conditions.
ZnO occurs in the mineral zincite, but most of the commercial product is made by the high-temperature oxidation of metallic zinc or zinc ores. It is used extensively in diverse industries such as rubber, ceramics, medicine, food, pigments, and coatings. It absorbs ultraviolet light and is probably an ingredient in the sunscreen you used this past summer.

Chemical properties

Zinc oxide is an amorphous, white or yellowish-white powder. It is a fine white powder that becomes yellow at temperatures above 3000℃. It is an amphoteric oxide that reacts with acids and dissolves in alkaline solution with formation of zincates. Its density and oil absorption value are 5.6 g/cm³ and 10-25 g oil/100 g ZnO, respectively.

Physical properties

White or yellowish-white powder; odorless; bitter taste; hexagonal crystal; refractive index 2.008; density 5.606 g/cm³; melts at 1,975°C; practically insoluble in water, 1.6 mg/L at about 30°C; soluble in dilute acids, ammonia solu 990 tion, and alkali hydroxides.

The Uses of Zinc oxide

Zinc oxide has a wide range of uses and can be used:
(1) As a pigment and paint. Zinc oxide is a largely inert white compound that is widely used as a filler or extender, as well as a white pigment. It can react with certain types of acidic paint resins, resulting in the formation of a brittle film when it dries.
(2) Used to protect, soothe, and repair the skin. It is an active ingredient in sunscreens that reflects UVA and UVB rays and relieves skin irritation. It is included in the list of sunscreen chemicals approved by the U.S. Food and Drug Administration (FDA).
(3) Used as an activator for vulcanization accelerators in natural and synthetic rubber.
(4) Used as a skin protectant. It is a cream, ointment, or paste that can treat or prevent skin irritations such as cuts, burns, or diaper rash.
(5) Used as a material in the production of ceramics, glass, cement, and lubricants.
(6) As a nutritional supplement, it is added to some foods and animal feed.

Background

Zinc oxide is an inorganic compound used in a number of manufacturing processes. It can be found in rubbers, plastics, ceramics, glass, cement, lubricants, paints, ointments, adhesives, sealants, pigments, foods, batteries, ferrites, fire retardants, and first-aid tapes. It occurs naturally as the mineral zincite, but most zinc oxide is produced synthetically. It is also widely used to treat a variety of other skin conditions, in products such as baby powder and barrier creams to treat diaper rashes, calamine cream, anti-dandruff shampoos, and antiseptic ointments.

Indications

For adjunctive treatment of diaper dermatitis. Also, it can be used to treat minor skin irritations (eg, cuts, burns, and scrapes, poison ivy). Zinc oxide can be used in ointments, creams, and lotions to protect against sunburn and other damage to the skin caused by ultraviolet light.

Definition

zinc oxide: A powder, white whencold and yellow when hot, ZnO; r.d.5.606; m.p. 1975°C. It occurs naturallyas a reddish orange ore zincite,and can also be made by oxidizinghot zinc in air. It is amphoteric,forming zincates with bases. It isused as a pigment (Chinese white) and a mild antiseptic in zinc ointments.An archaic name is philosopher’swool.

Definition

Zincite is a mineral form of zincoxide, ZnO.

What are the applications of Application

ZnO is used primarily for its anti-bacterial and fungicidal properties. Also, in the United States, ZnO is regarded as a Category I skin protectant and a Category III sunscreen.

Manufacturing Process

Most of the ZnO used today is produced from sphalerite, ZnS, as the starting ore by either the direct, US process, or the indirect, French process. In the US process a compound containing ZnO is reduced with coal to zinc vapor, which is oxidized to ZnO powder. The French process takes place in two steps. Zinc metal is first vaporized and the vapor is then oxidized with the ZnO powder being collected.

General Description

Crude zinc oxide is a yellow-gray granular solid with no odor. Zinc oxide has a specific gravity of 4.4. Zinc oxide is insoluble in water. The primary hazard is the threat posed to the environment. Immediate steps should be taken to limit its spread to the environment. Prolonged inhalation of the dust may result in metal fume fever with symptoms of chills, fever, muscular pain, nausea and vomiting.

Air & Water Reactions

Slowly decomposed(hydrolyzed) in water. Insoluble in water.

Reactivity Profile

ZINC OXIDE is insoluble in water. What little solubility Zinc oxide has yields aqueous solutions that are neutral in pH. Intimate mixtures of zinc oxide and chlorinated rubber with or without hydrocarbons or chlorinated solvent react violently, even explosively upon heating [Chem. Trade J., 1962, 151, 672]. Slow addition of zinc oxide to cover the surface of linseed oil varnish caused generation of heat and ignition, [Chem. Trade J., 1933, 92, 278].

Hazard

Exposure to zinc oxide fumes from welding and other operations can cause metal fume fever. Its symptoms are chills, fever, cough, and tightness in the chest.

Health Hazard

Exposures to zinc oxide metal fume cause several health disorders. The symptoms of toxicity include, but are not limited to, fever, chills, muscle ache, nausea, fever, dry throat, cough; lassitude (weakness, exhaustion), metallic taste, headache, blurred vision, low back pain, vomiting, malaise (vague feeling of discomfort), chest tightness, dyspnea (breathing diffi culty) and decreased pulmonary function. The overexposure to zinc oxide fumes in workplaces produce symptoms known as metal fume fever or “zinc shakes”; an acute, selflimiting condition. Chronic exposure to zinc oxide may cause respiratory tract irritation with nasopharyngitis and laryngitis.

Fire Hazard

Some may burn but none ignite readily. Containers may explode when heated. Some may be transported hot.

Agricultural Uses

Zinc oxide (ZnO) is a zinc fertilizer. It is a white powder when cold and yellow when hot, and contains approximately 78% zinc.
Zinc oxide occurs in nature as a reddish-orange colored zincite, and is made by oxidizing hot zinc in air. It is an amphoteric oxide forming zincates, by reacting with bases and zinc salts with acids. It is used as a white pigment and as a mild antiseptic in ointments. An archaic name of zinc oxide is philosopher's wool.
Foliar applications with zinc oxide reduce the foliage damage. Zinc oxide, applied by way of seed coatings, root dips or tree injections, corrects the zinc deficiency. Dipping potato seeds in 2% zinc oxide suspension overcomes zinc deficiency satisfactorily. A similar method is used for pre-plant dipping of the roots of rice seedlings.

Pharmaceutical Applications

The pharmaceutical and cosmetic industries use ZnO in powders and ointments because of its bactericidal properties. It is also used to form dental cements by its reaction with eugenol.
Zinc oxide is used as a raw material for many products: stearates, phosphates, chromates, bromates, organic dithiophosphates, and ferrites (ZnO, MnO, Fe2O3). It is used as a source of zinc in animal feeds and in electrogalvanization . It is also used for desulfurizing gases.

Industrial uses

Zinc oxide has many uses. By far the most important is in the rubber industry. Almost half the world’s ZnO is used as an activator for vulcanization accelerators in natural and synthetic rubber. The reactivity of the ZnO is a function of its specific surface area, but is also influenced by the presence of impurities such as lead and sulfates. The ZnO also ensures good durability of the vulcanized rubber, and increases its thermal conductivity. The ZnO content is usually 2–5%.
In paints and coatings, zinc oxide is no longer the principal white pigment, although its superb white color is used by artists. It is used as an additive in exterior paints for wood preservation. It is also utilized in antifouling and anticorrosion paints [2.82]. It improves film formation, durability, and resistance to mildew (having a synergistic effect with other fungicides) because it reacts with acidic products of oxidation and can absorb UV radiation.
In the field of glass, ceramics, and enamels, ZnO is used for its ability to reduce thermal expansion, to lower the melting point, and to increase chemical resistance. It can also be used to modify gloss or to improve opacity.

Pharmacokinetics

Zinc oxide has astringent, soothing and protective properties and is used in topical preparations for eczema, slight excoriations, wounds and haemorrhoids. It also reflects ultraviolet radiation and can be used as a physical sunscreen.

Materials Uses

The highest purity material is calcined with additives such as Bi2O3 and used in the manufacture of varistors. The photoconducting properties of ZnO are used in photoreproduction processes. Doping with alumina causes a reduction in electrical resistance; hence, it can be used in the coatings on the master papers for offset reproduction.
Zinc oxide is used as a catalyst in organic syntheses (e.g., of methanol), often in conjunction with other oxides. It is present in some adhesive compositions.

Toxicity

Acute oral toxicity (LD50): 7950 mg/kg [Mouse].

Safety Profile

Moderately toxic to humans by ingestion. Poison experimentally by intraperitoneal route. An experimental teratogen. Other experimental reproductive effects. Human systemic effects by inhalation of freshly formed fumes: metal fume fever with chills, fever, tightness of chest, cough, dyspnea, and other pulmonary changes. Mutation data reported. A s h and eye irritant. Has exploded when mixed with chlorinated rubber. Violent reaction with Mg, linseed oil. When heated to decomposition it emits toxic fumes of ZnO. See also ZINC COMPOUNDS.

Synthesis

Zinc ore is roasted and purified at 1000°C. The two methods of manufacture are (1) French, an indirect method and (2) American, a direct method. ZnO is in the form of transparent hexagonal crystals. The refractive index of this material is 2.0 with whiteness due to the scattering of light by the ultrafine particles. The coverage on the skin of ZnO is subordinate to that of TiO2.8 This material is soluble in acid and alkali with good heat and light stability.

Potential Exposure

Zinc oxide is primarily used as a white pigment in rubber formulations and as a vulcanizing aid. It is also used as an antiinflammatory agent; in photo copying; paints, chemicals, ceramics, lacquers, and varnishes; as a filler for plastic; in cosmetics; pharmaceuticals, and calamine lotion. Exposure may occur in the manufacture and use of zinc oxide and products, or through its formation as a fume when zinc or its alloys are heated. HC may have been used as a Choking/Pulmonary Agent.

Carcinogenicity

In general, genotoxic studies have not found evidence for mutagenicity of zinc.

Absorption

No significant percutaneous absorption from topically applied zinc oxide.

Metabolism

Intended for local use only, no systemic absorption.

Shipping

UN3077 Environmentally hazardous substances, solid, n.o.s., Hazard class: 9; Labels: 9-Miscellaneous hazardous material, Technical Name Required.

Incompatibilities

Incompatible with linseed oil, magnesium. Contact with chlorinated rubber (@ 215C) may cause a violent reaction. Slowly decomposed by water.