Chemical combination among metals has been studied for a long time. In the early days, chemists had much difficulty in understanding how metals could combine at all among themselves, often in several different proportions, since this often seemed to be at variance with elementary notions of valency. Indeed, in the last century a distinction was proposed between daltonides and berthollides, the former being compounds with simple ratios of the numbers of constituent atoms… consistent with Dalton's atomic theory!… the latter, called after a skeptical French chemist, being the name reserved for compounds with a wide composition range which scarcely seemed explicable on any reasonable atomic model. A few nostalgic souls still employ these distinctions.

An early classic on the subject was a book published by two Italian chemists in 1918. British metallurgist C.H. Desch also wrote a monograph on intermetallic compounds in 1914 (the year when the name “physical metallurgy” was first proposed, and the chemical bias of metallurgy shifted toward a physical one), and he declared that “attempts to form a theory of the constitution of intermetallic compounds… have been comparatively unsuccessful.” When he returned to the subject 20 years later, he felt much more cheerful about the state of the theory because in the meantime Hume-Rothery had introduced the concepts of atomic size factor, electron/atom ratio, and electronegativity (a concept also associated with the name of Linus Pauling) into the discussion of intermetallic phases, or compounds. Today, a battery of sophisticated physical concepts is used to make sense of both binary and multielement intermetallic compounds and they are no longer regarded as chemical anomalies.

A renaissance in research and development of solid lubricants has taken place during the past 10 years. This renaissance has been driven by the needs of advanced technological applications, for which liquid lubricants alone have become either ineffective or undesirable. Increasing the efficiency of jet and automobile engines, which entails engine operation at significantly higher temperatures, and increasing the longevity of space vehicles have been central technology drivers.

In the past 10 years, many new solid lubricants have been developed to address these needs for higher temperature operation and longer life. Their development, for the most part, has taken advantage of what is known concerning their mechanism of action. Although this mechanistic knowledge is incomplete, particularly at high temperatures, significant advances in material performance have been made. In addition, new methods of applying solid lubricant coatings, namely plasma and ion-beam-assisted vacuum deposition methods, have recently come into their own and produced improved materials.

This article will highlight developments in the 1980s which produced new solid lubricants and the advanced technologies which these materials will enable.

Several reviews of solid lubricants survey the area in more detail than is possible here. For overview purposes, this article will briefly describe the classes of materials used as solid lubricants, their mechanism of action, and areas of application.

From the beginning of the activity in high temperature superconductivity (near the end of 1986), there were efforts to grow single crystals of the compounds. The push for single crystals arose because earlier work on Chevrelphase superconductors (e.g., PbMo6S8) or re-entrant superconductors (ErRh4B4) showed that the properties of complex superconductors were easily masked by impurities, grain boundaries, imperfectly averaged properties, etc.

As early as the so-called “Woodstock of Physics” (the American Physical Society Meeting in New York, March 1987), a single-crystal, x-ray diffraction structure was given for YBa2Cu3O7-x (YBCO-123, with Tc = 93 K), the composition of which had been announced only three weeks earlier. The sample qualified as a single crystal because a single grain had been separated out for the x-ray study, although it was too small for any other measurements.

But, single crystal studies are not infallible, and may not always be the best route. For instance, the aforementioned x-ray work on YBCO gave the wrong structure because the x-ray scattering length from oxygen atoms is too small to yield enough scattering intensity to locate them. It remained for neutron-scattering work with large powdered samples to give the correct orthorhombic structure, having Cu-O chains and warped Cu-O planes (see Figure 1).

The following is an edited version of NASA Astronaut Bonnie J. Dunbar's Plenary Address at the 1990 MRS Fall Meeting.

I've often been asked, “Why a materials scientist in space?” I hope my presentation tonight will provide a little more insight on “why.” I don't think it's unusual at all. I look at myself as a continuum between outer space and inner space. I've been equally fascinated looking at the stars as at atomic structures under scanning electron microscopes. So to me it's not an unusual experience. In addition, materials scientists and engineers are needed to operate in space.

Tonight I would like to do several things. I'd like to talk to you about where we've been in space, where we are, and where we hope to go. I'll emphasize the materials aspect of it, not only in how we achieved space, but how we hope to exploit the microgravity environment of space. I have with me “home movies” of a Shuttle Mission I flew on in January 1990. You'Il share with me the experience of performing research as well as retrieving the long-duration exposure facility (LDEF) with a robotic arm.