Difference between revisions of "Zinc oxide"

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Zinc oxide is a white oxide of zinc used an additive in many products. It has the formula ZnO.

Properties

Physical

Zinc oxide is white, powdery substance. It is insoluble in water. It will decompose before melting when heated to 1975°C, or to 950°C with carbon.

Chemical

Zinc oxide is amphoteric. It reacts with acids to form salts of zinc, and with bases to form zincates. It is used industrially to make zinc sulfide through reaction with hydrogen sulfide.^[1]

Crystalline zinc oxide is thermochromic, changing from white to yellow when heated and in air reverting to white on cooling. This color change is caused by a small loss of oxygen to the environment at high temperatures to form the non-stoichiometric Zn_1+xO, where at 800 °C, x = 0.00007.

Availability

Like most chemicals, zinc oxide can be purchased from scientific suppliers like Elemental Scientific in pure form.^[2] It can also be purchased from art and ceramic suppliers, since it is used as a pigment and in glazes.

Preparation

Zinc oxide can be made in the lab by heating zinc carbonate or zinc hydroxide at high temperatures.

A more clean method involves electrolyzing a solution of sodium bicarbonate with a zinc anode. Zinc hydroxide and hydrogen gas are produced. The zinc hydroxide is pyrolyzed to zinc oxide.

It is also a side product of zinc melting. If the floating slag becomes yellow at high temperatures, then it contains zinc oxide.

Projects

• Thermochromism demonstration
• Make zinc oxide eugenol
• Make zinc metal
• Grow large crystals via hydrothermal growth^[3]
• Ceramic materials

Handling

Safety

Zinc oxide is non-toxic, but it's generally best to avoid breathing it in as it could potentially irritate the airways. Impure zinc often contains cadmium, which is extremely toxic to oneself and the environment.

Storage

Zinc oxide does not require special storage, though it should be kept away from any acidic vapors.

Disposal

Zinc oxide poses little toxicity to the environment, though it may contain traces of cadmium.

References

1. ↑ http://en.wikipedia.org/wiki/Zinc_oxide
2. ↑ http://www.elementalscientific.net/store/scripts/prodView.asp?idproduct=2857
3. ↑ http://onlinelibrary.wiley.com/doi/10.1111/j.1151-2916.1964.tb14632.x/abstract

Relevant Sciencemadness threads

• Making Zinc Oxide