Recently, the words “metamict” or “metamictization” have been increasingly used instead of “amorphous” or “amorphization” in acknowledgment of the fact that the first recognized example of the transition from the crystalline to the aperiodic state was in natural materials—minerals. The term (originally “metamikte” from Greek for “mix otherwise” because of their complex compositions) was first defined by Broegger in a Danish encyclopedia as one of three classes of amorphous substances: porodine (= colloidal), hyaline, and metamikte. Minerals considered to be metamict were judged amorphous because of their conchoidal fracture and isotropic optical properties; however, well-developed crystal faces evidenced the prior crystalline state.

Hamberg was the first to suggest that metamictization is a radiation-induced, periodic-to-aperiodic phase transition caused by alpha particles which originate from constituent radionuclides in the uranium and thorium decay series. Rinne and Vegard confirmed by x-ray diffraction studies that metamict minerals were either amorphous or finely crystalline. Later work supported the idea of a radiation-induced transformation. The work of Stackelberg and Rottenbach established that the decrease in density, refractive indices, and birefringence correlated with the breakdown of the structure with increasing alpha-decay dose. Stackelberg and Rottenback tried to test this hypothesis directly by bombarding a thin slab of zircon with alpha particles. The results were inconclusive because the slab fractured, but this must have been one of the first experiments in which an “ion beam” was used to “modify” a material.

At the Savannah River Plant (SRP), construction of what will be the world's largest solidification facility for nuclear waste has been under way since 1983. Beginning in 1990, the nearly 100 million liters of liquid high-level nuclear waste now stored on the site will be made into a durable borosilicate glass in this Defense Waste Processing Facility (DWPF).

In developing a slurry-fed melting process for the DWPF, we made advances in understanding both glass processing and glass durability. This article focuses on what we learned and what further advances are likely to be made.

Generally speaking, the goal of any glass technologist is to make a good glass and to make it well. In the glass industry a good product is whatever people will buy. To make it well means, above all, to make the product as economically as possible. Thus, the commercial glass technologist will control the composition of the melter feed material very closely to ensure that only the components necessary for glass performance are included, and in the least expensive form possible. The commercial glass technologist may also tolerate low yields or specify several stages of post-melt processing if it is necessary to produce a product to demanding specifications.

To the nuclear waste glass technologist, however, a good product is one which will be stable in geologic environments for millions of years.

The Materials Division in the Aerospace Technology Directorate of the National Aeronautics and Space Administration (NASA)-Lewis Research Center has a distinguished history of contributions to advanced materials research and development. Located in Cleveland, Ohio, the Lewis Research Center was originally built for aircraft piston engine research during World War II as a part of NASA's predecessor, the National Advisory Committee on Aeronautics. After the war, with its need for immediate engineering solutions ended, attention at Lewis turned to a variety of more fundamental research problems. As early as the 1950s, a portion of the experimental effort at Lewis sought new materials to withstand the extremely high temperatures within turbojet engines. The needs for materials to withstand ever more severe temperature/environment extremes continue, and recognition of these needs, in part, motivates the current materials research effort at NASA-Lewis. The Materials Division structure reflects the strengths as well as the diversity of research areas being investigated. Each of the eight branches making up the Materials Division is briefly sketched below.

The Microgravity Materials Science Laboratory is a unique facility with the purpose of allowing industry, university, and government researchers to prepare for materials processing experiments to be done in the “microgravity” environment aboard the Space Shuttle.