Philosopher’s wool, commonly known as zinc oxide (ZnO), is an intriguing inorganic chemical compound with a range of practical applications. Found naturally as the mineral zincite, zinc oxide is predominantly produced synthetically in modern industry. Renowned for its mild astringent and antiseptic properties, it serves as an effective topical protectant in various medical and cosmetic products.
This versatile compound has earned its place in diverse fields, from skincare to pharmaceuticals, due to its beneficial effects on the skin and its ability to aid in healing processes. In this article, we delve into the properties, applications, and significance of zinc oxide, exploring why it continues to be a valuable substance in both natural and synthetic forms.
Synonyms:
- Zinc oxide
- Oxozinc
- Calamine
- Zinc White
- Chinese white
- Flowers of zinc
Zinc is a naturally-occurring metallic element. Like other minerals, zinc also exists as a component of the building blocks of our body and is necessary for maintaining our normal health and metabolism.
It also helps in maintaining our immune, enzymatic systems and normal cell functioning. It is required for protein synthesis, collagen formation and skin healing. Zinc and one of its various compounds, zinc oxide, have been used in medicinal and industrial applications for time immemorial.
Physical properties
Zinc white crystallizes mainly in two forms which are cubic zinc blende and hexagonal wurtzite as the unit cell. It is powdery in texture. The most common and stable structure under ambient conditions is wurtzite.
Zincblende (ZnS) can be stabilized by growing zinc oxide (ZnO) on substrates which has a cubic lattice structure. The oxide and zinc centers are tetrahedral.
| Molecular Weight | 81.406 g/mol |
| Density | 5.606 g/cm3 |
| Melting Point | 1,974 °C |
| Boiling Point | 2,360 °C |
| Refractive index | n1=2.013, n2=2.029 |
| Magnetic susceptibility (Xm) | −27.2·10−6 cm3/mol |
| Band gap | 3.3 eV |
Chemical properties
The chemical formula of Philosopher’s wool or zinc oxide is ZnO.
- It is white solid
- Crude zinc oxide is yellow-grey in color
- Exists as a granular Solid form
- Insoluble in water
- It has no characteristic smell
- It is an amphoteric oxide
- Dissolves in acids and alkalis
It can be dissolved in most acids, such as hydrochloric acid:
ZnO + 2 HCl → ZnCl2 + H2O
Solid zinc oxide will also dissolve in alkalis to produce soluble zincates:
ZnO + 2 NaOH + H2O → Na2[Zn(OH)4]
Production
It is mainly synthesized in 4 ways:
- Wet chemical process
- Direct process
- Indirect process
- Laboratory synthesis
The ordinary white powder of zinc oxide can be prepared in the laboratory by electrolyzing a solution of sodium bicarbonate (NaHCO3) using zinc as an anode. In this process zinc hydroxide [Zn(OH)2] and hydrogen gas (H2) is produced. The zinc hydroxide on heating decomposes into zinc oxide (ZnO):
Zn + 2 H2O → Zn(OH)2 + H2 ↑
Zn(OH)2 → ZnO + H2O
History
It was used by early humans, in processed and unprocessed forms, as paint or medicinal ointment, but their composition. The use of Pushpanjan, probably zinc oxide, as a healing salve for eyes and open wounds, is described in the Indian Ayurveda (a natural system of medicine) medical text in the Charaka Samhita.
As a part of rituals, Alchemists would burn zinc in the air and collect the residue, which formed into white woolly tufts. They called it Lana philosophical in Latin, meaning Philosopher’s wool.
Uses of Philosopher’s wool
Philosopher’s wool has various applications in our daily life, nearly all of us had used it in some form. They have many health as well as industrial uses. It is also used as a food preservative to protect it from bacterial and fungal attacks.
Health uses
It has wide applications in health and health-related product manufacturing.
- Treat skin diseases
- Treat and prevent diaper rash
- Treat dandruff
- Baby lotions
- Bath soaps
- Foot powders
- First aid tapes
- Acne treatment
- Used in dental cement
- In pastes
- In bandages
- In sunscreens and sun lotions to protect the skin from harmful sun rays
- In treating sunburn (suntan)
- Antifungal additives in food (as nanoparticles NPs)
- Zinc oxide nanoparticles are antibacterial (as nanoparticles NPs)
Those people allergic to ZnO should not use products made of zinc oxide. It may lead to skin irritation, redness of the skin, or worsening rashes.
Industrial uses
- Used as a white pigment in paints
- Manufacturing of rubber
- Products of photocopying
- Used in coating (as anticorrosive for metals)
- Ceramic industry
- Li-ion battery and supercapacitors
- Piezoelectricity
- Spintronics
- Zinc oxide nanorod sensor
- Electronics
- Methane reforming
- Glass
- Cement
- Lubricants
- Batteries
- Ferrites
- Fire retardants
- Corrosion prevention in nuclear reactors