John W. Cahn
Encyclopedia
National Medal of Science
The National Medal of Science is an honor bestowed by the President of the United States to individuals in science and engineering who have made important contributions to the advancement of knowledge in the fields of behavioral and social sciences, biology, chemistry, engineering, mathematics and...
. He was a professor in the department of Materials Science at MIT from 1964-1978. Since 1977, he has held a position at the National Institute of Standards and Technology
National Institute of Standards and Technology
The National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory, otherwise known as a National Metrological Institute , which is a non-regulatory agency of the United States Department of Commerce...
(formerly the National Bureau of Standards, NBS). Dr. Cahn has had a profound influence on the course of materials and mathematics research during his career. One of foremost authorities on thermodynamics
Thermodynamics
Thermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...
, Cahn has applied the basic laws of thermodynamics to describe and predict a wide range of physical phenomena.
Biography
Cahn received a bachelor's degree in Chemistry in 1949 from the University of MichiganUniversity of Michigan
The University of Michigan is a public research university located in Ann Arbor, Michigan in the United States. It is the state's oldest university and the flagship campus of the University of Michigan...
. He later earned a Ph.D in Physical Chemistry in 1953 from the University of California at Berkeley. His doctoral Thesis was titled "The Oxidation of Isotopically Labelled Hydrazine" and his thesis advisor was R.E. Powell.
In 1954, Dr. Cahn joined the Chemical Metallurgy research effort at the General Electric
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
laboratory in Schenectady, NY, led by David Turnbull. Turnbull had done pioneering work on the kinetics
Chemical kinetics
Chemical kinetics, also known as reaction kinetics, is the study of rates of chemical processes. Chemical kinetics includes investigations of how different experimental conditions can influence the speed of a chemical reaction and yield information about the reaction's mechanism and transition...
of nucleation
Nucleation
Nucleation is the extremely localized budding of a distinct thermodynamic phase. Some examples of phases that may form by way of nucleation in liquids are gaseous bubbles, crystals or glassy regions. Creation of liquid droplets in saturated vapor is also characterized by nucleation...
, and there was a focus in the group on understanding the thermodynamics
Thermodynamics
Thermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...
and kinetics of phase transformations in solids.
In 1964, Cahn became a professor in the Department of Metallurgy (now Materials Science) at the Massachusetts Institute of Technology
Massachusetts Institute of Technology
The Massachusetts Institute of Technology is a private research university located in Cambridge, Massachusetts. MIT has five schools and one college, containing a total of 32 academic departments, with a strong emphasis on scientific and technological education and research.Founded in 1861 in...
. He left MIT in 1978. In 1969, Cahn began a long professional relationship with his graduate student Francis Larché, whose work focussed on the effect of mechanical stress on the thermodynamics of solids. The Larche-Cahn approach is the cornerstone of the treatment of the thermodynamics of stressed materials. Good examples of this phenomenon are the regions near a coherent precipitate—or the stress field around a dislocation.
In 1972, Cahn worked with David W. Hoffman to formulate a vector-based thermodynamics to describe the thermodynamics of interfaces, a formulation which is necessary to account for anisotropic materials. This is also known as the capillary vector formulation of interface energies. The mathematics of this treatment involves the concept of norms
Norm (mathematics)
In linear algebra, functional analysis and related areas of mathematics, a norm is a function that assigns a strictly positive length or size to all vectors in a vector space, other than the zero vector...
, although Cahn and Hoffman were unaware of it at the time.
In 1975, Cahn worked with his graduate student Sam Allen on phase transition
Phase transition
A phase transition is the transformation of a thermodynamic system from one phase or state of matter to another.A phase of a thermodynamic system and the states of matter have uniform physical properties....
s in Iron alloys, including order-disorder transitions. This work led to the Allen-Cahn equation.
Since 1984, he has held an affiliate professor position at the University of Washington
University of Washington
University of Washington is a public research university, founded in 1861 in Seattle, Washington, United States. The UW is the largest university in the Northwest and the oldest public university on the West Coast. The university has three campuses, with its largest campus in the University...
.
Work
The spinodal
In 1957, Cahn worked with John E. Hilliard to develop the Cahn-Hilliard Equation which describes the thermodynamic forces driving phase separation in many systems. Their joint theory of spinodal decompositionSpinodal decomposition
Spinodal decomposition is a mechanism by which a solution of two or more components can separate into distinct regions with distinctly different chemical compositions and physical properties...
is of interest for two primary reasons. First, it is one of the few solid-state transformations for which there is any plausible quantitative theory. The reason for this is the inherent simplicity of the reaction. Since there is no thermodynamic barrier to the reaction inside of the spinodal region, the decomposition is determined solely by diffusion. Thus, it can be treated purely as a diffusional problem, and many of the characteristics of the decomposition can be described by an approximate analytical solution to the general diffusion equation. In contrast, theories of nucleation and growth have to invoke the thermodynamics of fluctuations. And the diffusional problem involved in the growth of the nucleus is far more difficult to solve, because it is unrealistic to linearize the diffusion equation. From a more practical standpoint, spinodal decomposition provides a means of producing a very finely dispersed microstructure that can significantly enhance the physical properties of the material.
Solidification
In the theory of crystal growth, Cahn concluded that the distinguishing feature is the ability of the surface to reach an equilibrium state in the presence of a thermodynamic driving force (typically in the form of the degree of undercooling). He also concluded that for every surface or interface in a crystalline medium, there exists a critical driving force, which, if exceeded, will enable the surface or interface to advance normal to itself, and, if not exceeded, will require the lateral growth mechanism.Thus, for sufficiently large driving forces, the interface can move uniformly without the benefit of either a heterogeneous nucleation or screw dislocation mechanism. What constitutes a sufficiently large driving force depends upon the diffuseness of the interface, so that for extremely diffuse interfaces, this critical driving force will be so small that any measurable driving force will exceed it. Alternatively, for sharp interfaces, the critical driving force will be very large, and most growth will occur by the lateral step mechanism.
Droplets & surfaces
In 1977, Cahn published a simple mathematical treatment of the thermodynamics of wettingWetting
Wetting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together. The degree of wetting is determined by a force balance between adhesive and cohesive forces.Wetting is important in the bonding or adherence of...
: the interaction between a liquid in contact with a solid surface. This paper laid out a simple formulation for describing the wetting transition
Wetting transition
-Wetting transitions:The macroscopic parameter characterizing wetting of a solid surface with a liquid is contact angle. Various contact angles can co-exist on the same solid substrate. When contact angle experiences change we observe a wetting transition. Wetting transitions occurring on flat and...
—the point at which a liquid changes from forming a droplet on a surface to spreading out evenly as a liquid film over the surface. This theory had wide-ranging implications for many materials processing techniques
Quasicrystals
In 1982, Dan ShechtmanDan Shechtman
Dan Shechtman is the Philip Tobias Professor of Materials Science at the Technion – Israel Institute of Technology, an Associate of the US Department of Energy's Ames Laboratory, and Professor of Materials Science at Iowa State University. On April 8, 1982, while on sabbatical at the U.S...
observed a new crystalline structure with puzzling features. Cahn contributed to the theory of how such a structure could be thermodynamically stable and became co-author of the seminal paper which introduced quasicrystals. His competence in this new domain is widely acknowledged.
Glass transition
In 2004, Cahn and Bendersky presented evidence that an isotropic non-crystalline metallic phase (dubbed "q-glass") could be grown from the melt. This phase is the first phase, or "primary phase," to form in the Al-Fe-Si system during rapid cooling. Interestingly, experimental evidence indicates that this phase forms by a first-order transition. TEM images show that the q-glass nucleates from the melt as discrete particles, which grow spherically with a uniform growth rate in all directions. The diffraction pattern shows it to be an isotropic glassy phase. Yet there is a nucleation barrier, which implies an interfacial discontinuity (or internal surface) between the glass and the melt.Research in Retirement
In his retirement, Cahn has accepted a position at the University of WashingtonUniversity of Washington
University of Washington is a public research university, founded in 1861 in Seattle, Washington, United States. The UW is the largest university in the Northwest and the oldest public university on the West Coast. The university has three campuses, with its largest campus in the University...
as an Affiliate Professor in the departments of Materials Science and Engineering and Physics. In his office in the new Physics/Astronomy Tower, Dr. Cahn is working on a project that includes a glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
that grows from a melt like a crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
-- as if by a first-order transition.
Personal life
Dr. Cahn has three children and six grandsons. He now lives in Seattle, WA with his wife, Anne Hessing CahnAnne Hessing Cahn
Anne Hessing Cahn is political author, who holds a doctorate in political science from MIT. She is notable for her criticism of the CIA among other US agencies and leaders, particularly Team B and other aspects of the last days of the Cold War....
.
Honors & awards
2011The Kyoto Prize, Inamori Foundation
2002
Bower Prize, Franklin Institute
2001
Emil Heyn Medal, German Metallurgical Society
2001
Honorary Life Member, American Ceramic Society
1999
Bakhuys Roozeboon Lecturer and Gold medal, Netherlands Academy of Sciences
1999
Finalist, World Technology Award for Materials, The Economist
1999
Fellow, World Technology Network, National Museum of Science and Technology, London
1998
National Medal of Science
1998
Member, National Academy of Engineering
1998
Distinguished GE Lecturer in Materials Science at RPI
'69 & `98
MacDonald Lecturer, Canadian Metallurgical Society
1996
Doctor Honoris Causis, Universite d'Évry, France
1995
Harvey Prize
Harvey Prize
The Harvey Prize is awarded by the Technion in Haifa, Israel. It is awarded in different disciplines of Science, Technology, Human Health, and Contributions to Peace in the Middle East. Two awards - each of $75,000 - are given away annually...
, Technion.
1994
Rockwell Medal; Hall of Fame for Engineering, Science and Technology, and Medal, International Technology Institute.
1994
Gold Medal, Honorary Member, Japan Institute of Metals.
1993
Inland Steel Lecture, Northwestern University.
1993
Hume-Rothery Award, TMS.
1993
Cyril Stanley Smith Lecturer, University of Chicago.
1992
Honorary member, MRS-India.
1991
Michelson and Morley Prize, Case Western University.
1990
Honorary Sc. D., Northwestern University; Hilliard Lecturer.
1989
Sauveur Award, ASM International.
1987
Distinguished Physics Lecturer, Boston University.
1986
Stratton Award, National Bureau of Standards.
1985
Von Hippel Award, Materials Research Society.
1984
Gold Medal, US Department of Commerce.
1983
Distinguished Lecturer, University of Connecticut.
1982
Golick Lecturer, University of Missouri, Rolla, MO.
1981
Fellow, Japan Society for the Promotion of Science.
1981
Dickson Prize, Carnegie-Mellon University.
1980
Honorary Professor, Jiao Tong University, Shanghai, China.
1979
Van Horn Lecturer, Case-Western University.
1978
Dorn Lecturer, Northwestern University.
1977
Acta Metallurgica Gold Medal.
1974
Fellow, American Academy of Arts and Sciences.
1973
Member, National Academy of Sciences.
1968
Institute of Metals Lecturer, AIME.
1966
S. B. Meyer Award, American Ceramic Society.
1960-61
Guggenheim Fellowship spent at the University of Cambridge, Goldsmith Laboratory.
1951
Allied Chemical and Dye Fellowship at University of California, Berkeley.