Yzinc oxideIt is a chemical compound with the formula ZnO. It is an inorganic chemical used as an ingredient in over-the-counter medicines. It is also mainly used as an additive in pigments and semiconductors in various industries.
Zinc oxide occurs naturally in trace amounts, a mineral found primarily in New Jersey, USA. The crystal has a hexagonal crystal structure (mindat.org and Hudson Institute of Mineralogy, 2017).
Figure 1: Structure of zinc oxide.
There are several methods to synthesize zinc oxide, the main routes being the French and American methods.
In the French process, the metallic zinc is vaporized and the vapor is oxidized with preheated air. The US process uses various crude zinc compounds that are reduced with charcoal and produce zinc fumes. The zinc fumes are then oxidized with oxygen from the air, similar to the French process.
Another way to synthesize zinc oxide is the wet process, which consists of purifying zinc sulfate or chloride by precipitation with carbonate. The precipitate is then calcined to obtain zinc oxide (zinc oxide formula, S.F.).
ZnSO44+NaCO3→ ZnCO3+NaSO4→ ZnO + CO2(800ºC).
Physical and chemical properties of zinc oxide.
Zinc oxide is a white solid, odorless and with a bitter taste (National Center for Biotechnology Information, 2017). Its appearance is shown in Figure 2.
Figure 2: Appearance of Zinc Oxide.
Zinc oxide has two possible structures: hexagonal and cubic, but hexagonal crystals are the most common. The compound has a molecular weight of 81.38 g/mol and a density of 5.606 g/ml. Its melting point is 1975°C, where it begins to decompose (Royal Society of Chemistry, 2015).
ZnO is an amphoteric oxide that can be dissolved in acids or bases by reactions:
ZnO + 2OH-zinc+2+H2O
Zinc oxide is insoluble in water (0.0004 g per 100 ml of water at 17 °C). The low solubility it creates creates aqueous solutions with a neutral pH. Reacts violently with aluminum and magnesium powders causing fire and explosion hazard.
Intimate mixtures of zinc oxide and chlorinated rubber, with or without hydrocarbons or chlorinated solvents, react violently, even explosively, when heated.
The slow addition of zinc oxide to coat the surface of the linseed oil varnish causes heat generation and ignition.
reactivity and hazards
Zinc oxide is a stable, non-flammable compound and not incompatible with other chemical compounds, but it emits toxic fumes when heated. The compound is not toxic or hazardous if swallowed or if it comes in contact with the skin or eyes, however the compound does present an inhalation hazard.
Especially with zinc oxide particles, a harmful concentration of airborne particles can be reached quickly. Inhalation of vapors can cause metal fume fever with the following symptoms:
- sore throat
- fever or high body temperature
- Muscle pains.
The fume substance is irritating to the respiratory tract. The effects may be delayed. Symptoms of metal fume fever only appear after a few hours (NIOSH, 2015).
In case of inhalation, the victim must remain in a well-ventilated place. If inhalation is severe, the victim should be evacuated to a safe area as soon as possible.
Loosen tight clothing such as a shirt collar, belt, or tie. If breathing is difficult for the victim, oxygen should be administered.
If the victim is not breathing, mouth-to-mouth resuscitation is given. Always keep in mind that it can be dangerous for the rescuer to give mouth-to-mouth resuscitation if the inhaled material is toxic, infectious, or corrosive (Zinc Oxide Material Safety Data Sheet, 2013).
Despite the use of zinc oxide as a medicine, it is highly toxic to the environment, especially to aquatic organisms. Immediate measures must be taken to limit its spread in the environment in accordance with current regulations.
Today, nanotechnology is active in various fields of science through its effects on materials and devices using various techniques at the nanoscale (Vaseem Mohammad (Ph.D.), 2010).
Nanoparticles are part of nanomaterials, which are defined as individual particles with a diameter of 1-100 nm.
Nanoparticles have become in recent years a common material for the development of new cutting-edge applications in the areas of communication, energy storage, sensing, data storage, optics, transmission, environmental protection, cosmetics, biology and medicine, due to its important optical, electrical and magnetic properties.
Notably, the unique properties and utility of nanoparticles also derive from a variety of attributes, including the similar size of nanoparticles and biomolecules such as proteins and polynucleotides. Additionally, nanoparticles can be made from a variety of metals.
Metal oxide nanoparticles, including zinc oxide, are versatile platforms for biomedical applications and therapeutic interventions.
There is an urgent need to develop new classes of anticancer agents and recent studies have shown that ZnO nanomaterials hold great promise (John W. Rasmussen, 2010).
These nanoparticles have antibacterial, anticorrosive, antifungal and UV filtering properties. Some of the synonyms for zinc oxide nanoparticles are Oxydatum, Cinci Oxicum, Permanent White, Ketocinc and Oxocinc (AZoNano, 2013).
Zinc oxide is a product widely used topically in dermatology for skin care. In the United States, it is the main ingredient in sunscreens due to its reflective properties.
Zinc oxide is one of the safest ingredients to protect the skin from the harmful effects of ultraviolet (UV) rays. UV rays penetrate the skin and damage the tissues, accelerate the aging process and dry out the skin.
These rays also increase the risk of skin cancer. Zinc oxide sunscreens filter UV rays, preventing them from penetrating the skin and causing cell damage.
Zinc oxide is also effective in healing the skin. It can be used to heal wounds, reduce sensitivity associated with sunburn, and soothe chapped skin.
People who are zinc deficient often experience slower wound healing cycles. When zinc oxide is applied to the wound area, it provides the body with the extra zinc it needs to repair skin cells. Zinc oxide helps keep the wound area moist and clean.
Lotions and creams that contain zinc oxide are effective astringents for the skin. Zinc oxide can be applied to prevent excess oil from building up on the surface.
It is sometimes used to treat acne; It is believed to reduce the appearance of blemishes and skin irritation and inflammation, thereby reducing the number and severity of acne breakouts.
The National Institutes of Health reports that topical and oral zinc appear to be a safe and effective treatment for acne (PEARSON, 2015).
Zinc ointment may work best for this common skin condition when used in combination with the topical antibiotic erythromycin.
Due to its antibacterial and deodorant properties, doctors often treat diaper rash with zinc oxide ointment. For optimal effectiveness, it is usually applied at each diaper change.
Keeping the diaper area clean and allowing the skin to dry completely before applying zinc oxide ointment will help minimize the severity of diaper rash.
According to the American Academy of Dermatology, zinc oxide ointment can relieve the symptoms of melasma. Melasma is a common skin condition that causes brown patches on the face, mainly on the top of the nose, cheeks, lips, and the forehead of the chin.
About 90% of melasma cases occur in women. It is more common in people with darker skin tones.
Minor skin irritations such as cuts, burns, scabs, and poison ivy often benefit from the anti-inflammatory properties of zinc oxide ointment. You can apply a thin layer of zinc oxide to the affected skin as many times as needed to soothe irritation and promote healing.
The protective effects of zinc oxide ointment on the skin make it one of the best over-the-counter treatments for hemorrhoids.
Hemorrhoids are swollen veins in the anal canal caused by too much pressure in the pelvic and rectal areas. Hemorrhoids are usually not serious, but they can cause significant discomfort.
2- Rubber industry
More than 50% of zinc oxide is used in the rubber industry. Due to the vulcanization process, the equipment has higher tensile, swelling and abrasion resistance and is elastic in a wider temperature range.
In its simplest form, vulcanization occurs by heating rubber with sulfur (Encyclopædia Britannica, 2018).
Two ingredients that play important roles in vulcanization chemistry are known as "activators", usually zinc oxide and stearic acid.
These compounds react together and with accelerators to form a zinc sulfide compound, which in turn is the primary intermediate in adding sulfur to a diene elastomer and forming sulfur bonds to make items like tires, shoes, and even hockey pucks ( Ghent, 2016).
3- Pigments and Colors
Along with linseed oil (a drying oil useful as a vehicle), zinc oxide has been used as a pigment since the 18th century, leading to the rapid expansion of the European paint industry. Basic white pigments include zinc oxide, zinc sulfide, lithopone, and titanium dioxide (Encyclopædia Britannica, 1998).
4- solar cells
One very important use is that zinc oxide is widely used as a buffer layer in CIGS (Indium Gallium Selenide) solar cells. Some current experiments focus on the effect of ZnO thickness on the maximum power output of the cells.
Zinc oxide (ZnO) is an interesting material in terms of conductivity. It crystallizes in a wurtzite structure and its association is an ionic and covalent mixture. High purity single crystals are insulators.
Zinc oxide is the most piezoelectric of all materials and is widely used as a transducer in electronic devices. (Piezoelectricity is the property of a crystal to become polarized when subjected to pressure.)
Zinc oxide is a good semiconductor when there are aluminum impurities in the glass. Polycrystalline zinc oxide semiconductor ceramics are good conductors and obey Ohm's Law.
The addition of small amounts of other oxides, such as barium and chromium, gives zinc oxide ceramics non-ohmic electrical properties.
6- Other uses
The addition of zinc oxide helps in the processing of the concrete and also improves the resistance to water.
Zinc oxide is used in cigarette filters and as an additive in cereals. It is also used in xerography as a photoconductive foil and as a corrosion inhibitor.
The future of high-quality zinc oxide is sure to be exciting. The potential advances for non-medical applications exceed even current medical applications.
Zinc oxide nanorods, spintronic and piezoelectric sensors are promising fields and should be considered in the not too distant future.
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