High-Pressure Physics
The study of high-pressure physics includes any type of physical research in which unusually high pressures are used. There is no specific definition for "high pressures," but the term usually refers to pressures that can be produced only with some degree of difficulty. Indeed, much of the history of high-pressure research is the story of efforts to construct instruments by which greater and greater pressures can be produced and by which changes in materials caused by these pressures can be observed and measured.
High-pressure research is of interest in many fields of physics, because most physical properties undergo some kind of change with increased pressure. One of the earliest examples of high-pressure research was that conducted by the English physicist John Canton in 1762. Canton demonstrated that water can be compressed by applying pressure to it. Certainly the most famous names in pre-twentieth century high-pressure research are those of the French physicists Èmile Hilaire Amagat and Louis Paul Cailletet. Amagat in particular invented a device in the 1880s that could produce pressures of 3,000 atmospheres (44,000 pounds per square inch). All attempts to exceed that limit failed, however, and interest in high-pressure research declined until the turn of the century.
Renewed attention to high-pressure problems came about in the early 1900s almost entirely as the result of the work of Percy W. Bridgman. While working toward his doctorate at Harvard in 1905, Bridgman experienced a failure in the high-pressure apparatus with which he was working. He decided to turn his attention to the construction of a better device for producing high pressures. Bridgman was extraordinarily successful in this effort. Over the next 30 years, he developed better and better devices, the best of which could produce pressures 140 times greater than that of Amagat's equipment.
Bridgman's successes were achieved when he took a totally new approach to the design of equipment. He abandoned the piston-in-cylinder technique common to much previous high-pressure research in favor of new equipment whose strength increases as pressure increases. Perhaps the ultimate accomplishment from Bridgman's work was the diamond anvil press developed in 1957. This device is capable of producing pressures of a half million atmospheres (7 million pounds per square inch).
Bridgman was born in Cambridge, Massachusetts, on April 21, 1882. He attended public schools in neighboring Newton and then entered Harvard. He earned his bachelor's (1904), master's (1905), and doctoral (1908) degrees from Harvard, and then immediately accepted an appointment to the teaching staff there. He remained at Harvard until his retirement in 1954. He died in Randolph, New Hampshire on August 20, 1961.
Bridgman was awarded the Nobel Prize for physics in 1946 for his work on high-pressure physics. In addition to his research, Bridgman was very interested in problems of the philosophy of science and wrote a number of important books and papers on the subject. The Logic of Modern Physics (1927) and The Nature of Physical Theory (1936) are the best known of these.
Scientists have now recorded a number of changes in physical properties that result from high pressures. In addition to a decrease in volume, high pressures cause variations in electrical, magnetic, optical, and chemical properties. For example, some substances undergo phase changes as pressures on them increase. Water is one such substance, capable of existing in seven different phases under various pressures. Electrical conductivity also tends to be a function of pressure; in many metals, conductivity increases approximately ten percent for every increase of 10,000 atmospheres of pressure applied.
One of the most important practical applications of high-pressure research has been the production of synthetic diamonds. With Bridgman serving as a consultant, scientists at the General Electric Company synthesized the first industrial-grade diamonds in 1955 using a device that produced 100,000 atmospheres of pressure.
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