Zinc Oxide – Manufacturing and Applications

Zinc Oxide

You may have used or seen many cosmetic products such as sunscreen lotion, lipsticks, ointments, hand creams, etc. When you apply them, they appear to stick to your skin. But have you ever thought about what makes them sticky?

It is a naturally occurring compound, zinc oxide. But do you know what zinc oxide is used for other than in cosmetics? What are its properties? How is it manufactured in laboratories?

This article will let you know the answers to all these questions. Have a look!

What Is Zinc Oxide?

Generally speaking, zinc oxide is an inorganic compound. It is also known as zinc white or Calamine. It exists in powdered form and is white. This white powder is insoluble in water. In nature, it is found in the form of a mineral named zincite. It is a slightly antiseptic and astringent chemical compound that reacts as a topical shielding agent.

It has a wide application in medicinal products and numerous manufacturing processes. Because of its wide usage, nowadays, zinc oxide is generated synthetically.

What Is the Structure of Zinc Oxide?

Zinc oxide crystallizes in two main shapes, i.e., hexagonal wurtzite and cubic zincblende. The commonly found and most stable form among these two is wurtzite. Zinc exists in Zn(+2) in both forms, and both have tetrahedral geometry at their centers.

Because of its elastic softness, the zinc oxide formula ZnO is used in medicinal creams. Zn-O bonds, being polar in nature, result in electrically charged planes.

The molecular structure of zinc oxide is O = Zn

Manufacturing of Zinc Oxide

Metallurgical Process:

There are two ways to manufacture the ZnO compound named zinc oxide.

1. Direct Process:

This process involves the reduction of zinc ore in the presence of coal. The zinc vapors are oxidized in the same reactor in the next step. Both these steps take place in a single cycle. Samuel Wetherill developed this process.

2. Indirect Process:

In this process, in a furnace, metallic zinc is melted and vaporized at 910°C. ZnO is produced by the immediate reaction of zinc vapor and oxygen. The zinc oxide particles are conveyed via a cooling tube and collected at a bag filter station. The indirect process was popularized by LeClaire in 1844 and has been termed the French process since then.

Chemical Process:

There are many chemical ways to manufacture the ZnO compound named zinc oxide.

1. Mechanochemical Process:

It is the cheapest and most simple process. In this process, anhydrous ZnCl₂ and Na₂CO₃ are reacted to ZnCO₃. This ZnCO₃ is calcined at a temperature of 400–800°C to produce ZnO and CO₂.

ZnCl₂ + Na₂CO₃ → ZnCO₃ + 2NaCl

ZnCO₃ → ZnO + CO₂

2. Controlled Precipitation:

5ZnSO₄(aq) + 10NH₄HCO₃(aq) → Zn₅(CO₃)₂(OH)₆(s) + 5(NH₄)₂SO₄(aq) + 8CO₂(g) + 2H₂O(l)

Zn₅(CO₃)₂(OH)₆(s) → 5ZnO(s) + 2CO₂(g) + 3H₂O(g)

There are some more ways to manufacture zinc oxide chemically.

What Are the Properties of Zinc Oxide?

The properties of zinc oxide are categorized into two classes, i.e., physical properties and chemical properties.

1. Physical Properties:

• The zinc oxide formula is ZnO.
• It exists in white-coloured powder form.
• The molecular mass of ZnO is 81.408 g/mol.
• It is an odorless compound with a solid white appearance.
• The density of the ZnO compound name zinc oxide is 5.606 g/cm3.
• Zinc oxide has a melting point of 1975°C, while its boiling point is 2360°C.
• It isn’t very pleasant to taste and has a hexagonal-shaped crystal structure.
• Solubility of zinc oxide: it is insoluble in water, soluble in acids and alkalis, and insoluble in alcohol.
• ZnO is a moderately soft substance on the Mohs scale, with an approximate hardness of 4.5.
• Zinc oxide is stable under recommended storage conditions.
• It shows a refractive index of 2.02.

2. Chemical Properties:

• When heated to decomposition, zinc oxide emits toxic fumes.
• The pH of zinc oxide manufactured according to the indirect metallurgy process is 6.95, while zinc oxide manufactured by the direct process is 7.37.
• The heat capacity of zinc oxide is 40.26 J/mol °C at 25°C.
• Enthalpy of formation of zinc oxide is -356.1 kJ/mol at 419.5 – 907°C.
• Zinc oxide shows amphoteric properties. It forms zinc salts when reacted with acids, while it forms zincates when treated with alkalies.
• When zinc oxide undergoes strong heating, it undertakes a yellow color which vanishes on cooling.
• Zinc oxide reacts steadily with fatty acids in fats and oils. The products obtained are lumpy masses of zinc stearate, oleate, etc.

What Is Zinc Oxide Used For?

Zinc oxide is used for the following purposes:

• Paint coatings
• Cigarette Filters
• Paint pigments
• Laser diodes
• Spintronics
• Breakfast Cereals
• Light-emitting diodes (LEDs)
• Piezoelectricity; delivering Alternating Current (AC) by strengthening and delivering zinc oxide nanowires.

What Are the Application Areas of Zinc Oxide?

Zinc oxide has wide applications in many industries. Some of the applications are given below:

1. Rubber Industry:

You might get shocked, but it is a fact that over 50% of the manufactured zinc oxide is utilized in the rubber industry. ZnO compound name zinc oxide is utilized in the vulcanisation of rubber to fabricate many things such as shoe soles, tires, hockey pucks, etc. It is used with stearic acid during the process of vulcanisation of rubber.

2. Ceramic Industry:

Ceramics and concrete industries utilize high thermal conductivity, low expansion coefficient, and high thermal strength of ZnO particles. Because of being an elastic material in the ceramic industry, ZnO has a low expansion coefficient. On adding in small amounts, ZnO gives a glossy surface to the products. On the other hand, zinc oxide provides a matte finish touch to the products in moderate amounts. 

Zinc oxide addition provides a longer processing time and water resistance properties to concrete material. It also maneuvers in quick-setting cement.

3. Medicine Industry:

Zinc oxide has soothing, astringent, and protective properties. It is used in topical preparations for slight excoriations, eczema, hemorrhoids, and wounds. It also reflects ultraviolet radiation and can be used as a physical sunscreen. Zinc oxide is low in toxicity and biodegradable. It is the reason it is highly used in the biomedical field. The medical applications of ZnO nanoparticles have stretched horizons. It is mainly used as food powders, ointments, zinc soaps, dental inlays, etc. Zinc oxide is an indispensable compound in manufacturing products in this industry.

4. Food Industry:

ZnO is currently listed as normally safe by the US Food and Drug Administration. As zinc is an essential micronutrient element, it is used as a food additive. The birth of nanotechnology led to zinc oxide developing many products with antimicrobial agent properties. ZnO nanoparticles have also presented many potential applications in food preservation and its industry. ZnO nanoparticles have been absorbed in polymeric patterns to provide an antimicrobial scheme to the packaging substance and improve some wrapping properties.

5. Pigment Industry:

Although TiO2 has been used nowadays, ZnO is still a key element of the paint and pigment industry. Generally, it is operated as a white pigment. But, recently, ZnO has been facing a high downfall because of not matching certain standards and specifications. At the same time, ZnO can be used as energy-saving window coatings. 

Not every electrical appliance consists of ZnO and can increase the electrical conductivity of the appliances by dropping them with Al or Ga. ZnO also provides the capacity to reflect infrared radiation.

6. Coating Industry:

The use of ZnO for the functionalization of textile substrates is at a hike since it can provide distinctive multifunctional properties, such as antimicrobial activity, photocatalytic self-cleaning, UV protection, hydrophobicity, flame retardancy, moisture management and thermal insulation, and electrical conductivity. Paints based on zinc oxide can retain their flexibility. Therefore, zinc oxide is highly preferable in the coating industry.

Conclusion

From the above article, you are well-versed that ZnO is a widely usable inorganic compound. What is zinc oxide used for? It acts as an additive in dietary supplements, cosmetics, ceramics, plastics, cement, glass, paints, lubricants, adhesives, ointments, pigments, sealants, batteries, meats, first-aid tapes and fire retardants, ferrites, and in various products and materials.

Frequently Asked Questions

1. What are the applications of zinc oxide in the cosmetic industry?

Some applications of the ZnO in the cosmetic industry are:

• It is a broad-spectrum UV absorber, making it useful in producing many cosmetic items like ointments, moisturizers, lip products, etc.
• It is effective against UVA and UVB.
• It assists cosmetic products in sticking to the skin easily.
• Active ZnO is used as an active ingredient in products for treating acne.
• It is used in treatment lotions because of its antifungal and antibacterial properties.
• It is also used in nappy rash creams, anti-dandruff shampoos, deodorants, etc.

2. Is zinc oxide usable as a water disinfectant?

Some reasons that make zinc oxide usable as a water disinfectant are:

• ZnO nanoparticles have antibacterial properties that help in disinfecting the water.
• ZnO nanoparticles are very small, can handle harsh conditions, and are safe for consumption.
• ZnO disinfectant water is based on removing reactive oxygen species present in water, releasing Zn(II) and thus damaging the cell walls of bacterias present in water.

3. What are the catalytic applications of zinc oxide?

Some catalytic applications of zinc oxide are:

• As a catalyst, ZnO is used in the manufacturing of methanol.
• During the production of iso-butyl from synthesis gas, alkali promoted ZnO.
• The mixture of zinc and chromium oxides proceeds the hydrogenation of carbon monoxide.
• ZnO is also used to catalyze the manufacture of caprolactam, which then continues to obtain nylon 6.