Although zinc oxide was known to the ancients, as a by-product of copper smelting, it was not until 1840 that it was established as a product. Courtoise, in France (hence French Process) made a ZnO pigment by combustion of zinc vapor in air. This replaced basic lead carbonate and remained the white paint pigment of choice until the mid 20th century when titanium dioxide grades were developed. At this time linoleum was a major ZnO use. Zinc oxide has continued to be the preferred accelerator for rubber vulcanization and, led by automobile tires, remains the dominant use for zinc oxide.
Automobiles are a significant user of zinc oxide, in addition to tires, rubber trim, mountings, hoses and belts, it is also an intermediate in zinc phosphate coatings and oil EP additive. Further uses include ferrites and varistors.
A characteristic of zinc oxide is the ability to find new applications and the market for photocopy grade zinc oxide that developed in the 1960’s is both an example and also a foretaste of future applications. In the early days of photocopying, copiers were much less sophisticated than today. The Electrofax system had a photoconductive zinc oxide coating on the copy paper which allowed simple equipment to be used. At one time this ZnO market was second only to rubber.
A further use was developed some twenty years later which also was based on electronic properties, varistors. Controlled growth of zinc oxide and dopants allows grain boundaries to form which control electrical current. Varistors switch from an insulator to conductor at a set voltage, they are used for circuit protection from small appliances to grid systems.
Zinc oxide was one of the first materials to be used in nano technology. Nano size zinc oxide is transparent to visible light but absorbs ultra violet, hence extensive use in sun screens.
Zinc oxide research in the 21st century has escalated. Both vapor and aqueous systems have been used to create a wide range of crystalline materials that are expected to have various high-tech uses. In addition to the crystalline shapes seen in French Process zinc oxide, nanowires and loops may be fabricated. Examples of potential uses are in blue lasers, transparent transistors and sensors. Zinc oxide is also the major hope for the next generation of LED based solid state lighting. This will be much more energy efficient and longer lived than present incandescent and fluorescent lighting.
A further area of research is in magnetic semiconductors to serve the next generation of further miniaturized computer memory.
In a few short years zinc oxide has come from a superceded white pigment to a major area for research in a range of exciting new applications.
Zinc oxide Manufacture
The world-wide market for commercial zinc oxide is primarily served by ‘French Process’ material, ie made by combustion of zinc vapor in air. A large proportion of the zinc originates with electrolytic zinc smelters and is of Special High Grade (SHG) quality. The vaporization of zinc is energy intensive, consequently the escalation of fuel costs have made this an increasingly large part of the overall cost of manufacture.
Integrated Resource Management has developed a zinc oxide manufacture process which minimizes energy costs. The features of the process are-
Minimal fuel usage due to recuperative and regenerative burner systems.
Optimized product yield due to design.
Low capital cost.
Flexibility of operation, the process may be campaigned from 5 day to 100 day periods.
Flexibility with respect to characteristics of product such as particle size.
Capable of sustaining exceptional purity of less that 4ppm lead.
Low operational and maintenance cost.
Such furnace operations work very efficiently with SHG zinc and natural gas fired burners. In addition the system may be readily modified to allow the use of secondary zinc materials and also alternate fuels.