Materials under pressure
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oduction On Earth, pressures can range from one bar (10–4 GPa) at the surface, to a few hundreds of bars (on the order of 10–2 GPa) at the bottom of the oceans, to around 3.6 × 106 bar (360 GPa) at the Earth’s center1 (Figure 1). In comparison, the pressure at the center of the sun is estimated to be around 26.5 × 106 GPa. For many years, scientists have been motivated to attain ever higher pressures in the laboratory, to reproduce and study some of the phenomena seen in real life, and to create novel materials with new and unique properties.2–6 The applied pressure can be varied almost continuously by more than seven orders of magnitude above ambient pressure, and its influence can have a profound effect on the electronic structure, bonding, and coordination environments of atoms, the rates and types of possible reactions, and the microscopic to macroscopic volumetric response and deformation to such loads. The state of matter can be changed in a controlled way. In addition, advances in instrumentation are enabling completely new regions of phase space to be explored by experiment, while at the same time giving enhanced access to the information required to solve materials-related issues. The definition of “high pressure” depends on the field of interest. Pressures can be small, at just a few tens of MPa, as in the investigation of biological systems such as the extremophile organisms that live at the bottom of the oceans or the study of protein folding, or they can be in excess of 1 TPa, which are not
found naturally on Earth, but are achievable in shock compression experiments that are leading to the discovery of novel states of matter and novel physicochemical phenomena.7 The theme of this issue is “Materials under pressure.” It presents an overview of recent advances in high-pressure experimental methods and instrumentation (such as diamond anvil cells [DACs],8 multianvil presses,9 or the Paris-Edinburgh press10 [Figure 2]) to study matter in materials science, physics, chemistry, engineering, and biology.
Superhard materials In their article in this issue, Sumiya reports on current progress in the development of ultrahard materials for abrasives, cutting tools, and wire dies.11 This work extends the discussion of the March 2003 issue of MRS Bulletin on “Superhard coating materials”12 toward the nanoscale, illustrating binderless nanopolycrystalline diamond and cBN phases. The physical properties of these synthetic ultrahard materials surpass those of microscopic and single-crystal materials through loss of binder and the absence of cleavage and anisotropy.13 Sumiya discusses the industrial significance of the high-pressure and -temperature sintering processing of these materials, their influence on the microstructure, as well as their mechanical properties. They also discuss how these tie to the eventual improved application of both nanophase diamond and cBN in high-precision machining of
Anita Zeidler, University of Bath, UK; [email protected] Wilson A. Crichton, European Synchrotron Radiation Facility, Fran
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