Zinc Oxide: Uses, Grades and Safety

Zinc oxide is an inorganic white powder made of zinc and oxygen. It's one of the most widely used zinc compounds, mainly as a white pigment, a filler and an activator in rubber. In Hindi it's simply called जिंक ऑक्साइड, and painters and rubber shops often just say "zinc white".

• Formula: ZnO
• CAS number: 1314-13-2
• Molar mass: about 81.4 g/mol
• Appearance: soft, odourless white powder
• Melting point: about 1,974 °C, where it decomposes
• Solubility: practically insoluble in water, but it dissolves in acids and strong alkalis

It turns slightly yellow when strongly heated and goes back to white on cooling. That's normal and doesn't mean the powder is spoiled.

Azlok currently lists zinc oxide powder as technical grade. The main listing is a 100 g pack labelled Industrial and Utility Grade, meant for technical and industrial work. A second listing, sold simply as Zinc Oxide Powder, doesn't state a grade or pack size in its name, so check the product page before ordering.

For the current rate across packs, see today's price per kg.

Most zinc oxide sold in India goes into a handful of trades.

• Rubber: an activator in sulphur vulcanisation, used with stearic acid in tyres, footwear soles, hoses and rubber sheets.
• Ceramics and glass: a flux and opacifier in glazes. It gives gloss and helps colours develop.
• Paints and putties: a white pigment and mildew-resistant filler in some primers and wall putties.
• Cosmetic manufacturing: used in powders and creams, but only cosmetic-grade material that meets Indian cosmetic rules belongs in those products.
• Lab and school work: a simple example of an amphoteric oxide, since it reacts with both acids and alkalis.

Zinc oxide is a fine, light powder that clumps when damp, so how you mix it matters more than how much you use.

1. Weigh it, don't scoop by eye. A 100 g pack is bulky, and a spoon of loose powder can weigh half as much as a packed one.
2. Rubber compounding: standard recipes use about 3 to 5 parts zinc oxide per 100 parts rubber (phr), along with roughly 1 to 2 phr stearic acid. Add it early in the mixing so it disperses fully.
3. Glazes: zinc oxide is added as a percentage of the dry glaze recipe. Follow a tested recipe, because too much can cause crawling and pinholes. Some potters calcine the powder first to reduce shrinkage.
4. Paints and putties: make a smooth paste with a small amount of the liquid first, then stir that paste into the rest. Dumping dry powder into a full tin leaves lumps.
5. Sieve before use if the powder has sat for a while. A kitchen-style mesh is fine for craft work, as long as it's kept only for chemicals.

Zinc oxide is fairly easy to handle, but the dust and fumes need respect.

• Wear a dust mask, safety glasses and gloves when pouring or sieving. The powder is very fine and floats in the air.
• Never heat it, or zinc-coated metal, to the point of fuming in a closed room. Breathing zinc fumes can cause "metal fume fever", a flu-like illness.
• Keep it away from strong acids and strong alkalis, which react with it.
• Store it in a tightly closed container in a dry place, away from moisture so it doesn't cake.
• Keep it away from children and pets, and away from food and kitchen use.
• Zinc compounds are harmful to aquatic life. Don't rinse large amounts down drains or into soil. Sweep up spills dry and dispose of them as solid waste, as your local rules allow.

For hobby rubber work, a few glaze tests or patching putty, the 100 g technical pack is enough and stays fresh. Opening a large sack for a small job only invites moisture.

Don't buy technical grade for anything that goes on skin, into food or into analytical lab work. Those need a grade made and tested for that purpose. If you run a rubber unit, a pottery studio or a paint line and need 25 kg or more, send your requirement through our bulk inquiry page. Tell us the grade, the monthly quantity and any specification you work to, such as purity or particle size.