Mixing up a new composite material - metal mixed with its oxide to create lanxides, a new ceramic composite

Science News, Dec 21, 1985 by Ivars Peterson

A metal's oxide coating is as familiar as rust on an iron surface or the thin aluminum oxide film protecting an aluminum sheet. Now a small company has developed a novel process for mixing a metal with its oxide to create a new class of composite materials. Called lanxides, these materials, unlike other ceramic composites, appear to be tough rather than brittle and relatively inexpensive to produce -- qualities that potentially make them useful for armor plating.

The process was discovered and developed by Marc S. Newkirk and his colleagues at the Lanxide Corp. in Newark, Del. The Department of Defense (DOD) provided most of the funding for the research. Details of the project, classified for three years, were released for the first time at a recent Materials Research Society meeting in Boston.

This discovery, says materials scientist Rustum Roy of Pennsylvania State University in University Park, may rank higher than the discovery of the transistor. "It's a major new way to make materials," he says. Roy's laboratory, at the request of DOD, was involved in testing the company's process and studying the material's microscopic structure.

Lanxides are formed in the reaction between a molten metal and oxygen in air or some other vapor-phase oxidant. Normally, such a situation produces an unwelcome scum on the metal's surface. However, by controlling the molten metal's temperature and by adding traces of suitable dopant metals, an inch-thick layer of a metal oxide composite can be grown on the liquid's surface.

In the case of aluminum, the product consists of an interconnected aluminum oxide (alumina) network with metal filling in the gaps. This kind of microstructure is unique, says Roy. What isn't clear is exactly how this structure is physically and chemically created. Somehow metal must soak into the oxide layer while it is being formed.

Under the right conditions, a lanxide composite is considerably stronger than sintered alumina. This makes such a composite potentially useful for armor plating, rocket or jet engines and other applications where a light but tough material is needed.

So far, only the aluminum-alumina composite has been publicly described in detail. However, according to a report in the Dec. 12 NATURE, other lanxide materials have been developed. Newkirk says "hundreds" of inventions arising from the new technology are being patented. The company will release further information at several professional meetings next year and in the JOURNAL OF MATERIALS RESEARCH.