Zinc Oxide

2020-11-20

Zinc oxide is an inorganic compound with the formula ZnO. Synthetic ZnO is primarily used as a white powder that is insoluble in water, or naturally as the mineral zincite. The powder is widely used as an additive in numerous materials and products including plastics, ceramics, glass, cement, rubber (e.g., car tires), lubricants, paints, ointments, adhesives, sealants, pigments, foods (source of Zn nutrient), batteries, ferrites, fire retardants, and first aid tapes. ZnO occurs as white powder known as zinc white or as the mineral zincite. The mineral usually contains manganese and other impurities that confer a yellow to red colour. Crystalline zinc oxide is thermochromic, changing from white to yellow when heated and in air reverting to white on cooling. This colour change is caused by a small loss of oxygen to the environment at high temperatures to form the non-stoichiometric Zn1+xO, where at 800 °C, x = 0.00007. Zinc oxide is also an amphoteric oxide. It is nearly insoluble in water and alcohol, but it is soluble in (degraded by) most acids, such as hydrochloric acid. [1]

Uses [1]

There are many applications for zinc oxide powder. Most applications exploit the reactivity of the oxide as a precursor to other zinc compounds. For material science applications, zinc oxide has high refractive index, high thermal conductivity, binding, antibacterial and UV-protection properties. Consequently, it is added into materials and products including plastics, ceramics, glass, cement, rubber, lubricants, paints, ointments, adhesive, sealants, pigments, foods, batteries, ferrites and fire retardants.

Rubber Industry

About 50% of ZnO use is in the rubber industry. Zinc oxide along with stearic acid is used in the vulcanisation of rubber. In addition, ZnO additive protect rubber from fungi and UV light.

Concrete Industry

Zinc oxide is widely used for concrete manufacturing. Addition of ZnO improves the processing time and the resistance of concrete against water.

Medical Uses

Medical uses of zinc oxide include the production of calamine via a mixture of zinc oxide with about 0.5% iron (III) oxide (Fe2O3). Calamine is then used to produce calamine lotion. There are also two minerals, zincite and hemimorphite, which have been historically called calamine. When mixed with eugenol, a ligand, zinc oxide eugenol is formed, which has applications as a restorative and prosthodontics in dentistry. Reflecting the basic properties of ZnO, fine particles of the oxide have deodorising and antibacterial properties and for that reason are added into materials including cotton fabric, rubber, and food packaging. Enhanced antibacterial action of fine particles compared to bulk material is not intrinsic to ZnO and is observed for other materials, such as silver. This property is due to the increased surface area of the fine particles. Zinc oxide is 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. In addition, it is a component in tape (called “zinc oxide tape”) used by athletes as a bandage to prevent soft tissue damage during workouts. Zinc oxide can be used in ointments, creams, and lotions to protect against sunburn and other damage to the skin caused by ultraviolet light. When used as an ingredient in sunscreen, zinc oxide sits on the skin’s surface and is not absorbed into the skin, and blocks both UVA (320–400 nm) and UVB (280–320 nm) rays of ultraviolet light.

Cigarette Filters

Zinc oxide is a constituent of cigarette filters for removal of selected components from tobacco smoke. A filter consisting of charcoal impregnated with zinc oxide and iron oxide removes significant amounts of HCN and H2S from tobacco smoke without affecting its flavour.

Food Additive

Zinc oxide is added to many food products, including breakfast cereals, as a source of zinc, a necessary nutrient. Some pre-packaged foods also include trace amounts of ZnO even if it is not intended as a nutrient.

Pigment

Zinc white is used as a pigment in paints and is more opaque than lithopone, but less opaque than titanium dioxide. It is also used in coatings for paper. Chinese white is a special grade of zinc white used in artists’ pigments. It is also a main ingredient of mineral makeup.

Coatings

Paints containing zinc oxide powder have long been utilised as anticorrosive coatings for metals. They are especially effective for galvanized iron. Iron is difficult to protect because its reactivity with organic coatings leads to brittleness and lack of adhesion. Zinc oxide paints retain their flexibility and adherence on such surfaces for many years. Plastics, such as polyethylene naphthalate (PEN), can be protected by applying zinc oxide coating. The coating reduces the diffusion of oxygen with PEN. Zinc oxide layers can also be used on polycarbonate (PC) in outdoor applications. The coating protects PC form solar radiation and decreases the oxidation rate and photo-yellowing of PC.

Corrosion prevention in nuclear reactors

Zinc oxide depleted in the zinc isotope with the atomic mass 64 is used in corrosion prevention in nuclear pressurised water reactors. The depletion is necessary, because 64Zn is transformed into radioactive 65Zn under irradiation by the reactor neutrons.

Routes of Exposure [2]

Exposure to zinc oxide can occur through inhalation, ingestion, and eye or skin contact. Exposure to the chemical may occur through the following operations:

  • The manufacture and transportation of zinc oxide
  • Use as a white pigment in rubber formulations and as a vulcanising agent
  • Use in cosmetics, ointments, and electronic devices
  • Use as a UV absorber in plastics, ceramics, floor tile, and glass
  • Use in seed treatments, food additives, photoconductors, and in colour photography

Health Effects

Zinc oxide dust is primarily a nuisance dust, but exposures to high concentrations can result in respiratory system effects in humans. Volunteers inhaling 600 mg/m (3) zinc oxide dust for 10 minutes exhibited persistent rales, decreased vital capacity, coughing, upper respiratory tract irritation and substernal pain. Studies have reported that exposures to concentrations up to 430 mg/m (3) zinc oxide resulted in chest pain [ACGIH 1991, p. 1755]. Inhalation of zinc oxide fume can result in metal fume fever. In itself, this is a self-limiting condition characterised by flu-like symptoms, which resolve within 24 to 48 hours. Repeated exposures to zinc oxide by skin contact have resulted in papular-pustular skin eruptions in the axilla, inner thigh, inner arm, scrotum and pubic areas. Epidemiologic studies of zinc refinery workers found no correlation between industrial zinc exposures and lung or other types of cancer.

Acute Effects [2]

Acute exposure: Acute exposure to zinc oxide can result in coughing, substernal pain, upper respiratory tract irritation, rales, chills, fever, nausea, and vomiting.

Chronic Effects [2]

Chronic exposure: Chronic exposure to zinc oxide by skin contact may result in papular-pustular skin eruptions in the axilla, inner thigh, inner arm, scrotum and pubic areas.

Safety

First Aid Measures [2]

  • Eye Contact: Check for and remove any contact lenses. In case of contact, immediately flush eyes with plenty of water for at least 15 minutes. Get medical attention if irritation occurs.
  • Skin Contact: Wash with soap and water. Cover the irritated skin with an emollient. Get medical attention if irritation develops.
  • Inhalation: If inhaled, remove to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen. Get medical attention.
  • Ingestion: Do NOT induce vomiting unless directed to do so by medical personnel. Never give anything by mouth to an unconscious person. Loosen tight clothing such as a collar, tie, belt or waistband. Get medical attention if symptoms appear.

Exposure Control/Personal Protection [1]

  • Engineering Controls: Use process enclosures, local exhaust ventilation, or other engineering controls to keep airborne levels below recommended exposure limits. If user operations generate dust, fume or mist, use ventilation to keep exposure to airborne contaminants below the exposure limit.
  • Personal Protection: Safety glasses, lab coat, dust respirator (Be sure to use an approved/certified respirator or equivalent), gloves.

Regulation [3]

~h2United States:

The Occupational Safety and Health Administration (OSHA)has set a Time Weighted Average (TWA) concentration limit for zinc oxide of 15mg/m3.

Australia [4]

Australia Exposure Standards have set a TWA for zinc oxide (fume) of 5mg/m3.

References

http://en.wikipedia.org/wiki/Zinc_oxide

http://www.osha.gov/SLTC/healthguidelines/zincoxide/recognition.html

http://www.sciencelab.com/msds.php?msdsId=9927329

jr.chemwatch.net