Zone-Melting Techniques
Transcript of Zone-Melting Techniques
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Zone-Meliing Techniques M'ith development of the transistor,
solid state electronics came of age. Trie evolution of this exciting new industry was stimulated by a major technological advance in chemical purification known as zone refining, a "zone-in eltiiig" technique. The zone-melting process, simple in conception, yet spectacular in results, has permitted the electronic conduction properties of solids t o be exploited on a truly prodigious seule. It has not only allowed the preparation of exceptionally pu re solids, but it has allowed the preparation of solids with controlled solute concentrations and controlled solute distributions.
The application of zone refining to purifying metals, semiconductors, organic and inorganic chemicals, halide salts, and sea water has yielded favorable results. This technique has allowed semiconductor materials to be prepared in which the harmful impurities have been reduced to less than one part in ΙΟ10. Besides its broad industrial application, zone melting is a powerful research tool in the study of structure-sensitive and impurity-sensitive properties of solids.
Purification or separation by repea t ed fractional crystallization is based on the well-known fact that a freezing crystal differs in composition from its l iquid. The basic zone-refining technique resulted from the additional idea of melting par t , rather than all, of a charge at a given time. Repeated passage of a molten zone in one direction along the charge causes segregation of the solutes t o one end or the other depending on the partition coefficient of the solutes between the two phases; thus, a portion of the charge becomes very pure after a number of zone passes. Other zone-melting techniques enable the introduction of a particular solute concentration and the control of solute distributions in the solid.
This book, the first on the subject, was written by \V. G. Pfann, the inventor of zone melting. It has an easy-flowing style that is a pleasure to read. Pfann has prepared the book for students, scientists, engineers, and manufacturers, in a manner that will arouse their interest and with contents that will satisfy this diverse audience.
T h e author covers fully the theory and practice of zone melting. He first deals with the basic zone-melting proc
ess, leading then to the quantitative analysis of batch and continuous zone refining. This is followed by a description of an array of ingenious practical methods by which purification can be achieved. The remainder of the book deals with other zone-melting techniques—techniques by which solute segregation can be either prevented or manipulated in a controlled way during crystal growth.
This book contains information not published elsewhere. It is a basic prerequisite for any person interested in crystal growth or contemplating solid state materials research or preparation.
Zone Melt ing. W. G. PFANN. xvi + 236 pages. John Wiley & Sons, Inc.. 440 Fourth Ave., New York 16, N. Y. $7.50. Reviewed by \V. A. Tiller, Westinchouse Electric Go.
Automatic Control Anyone who designs systems which
are to b e automatically controlled or operates automatically controlled equipment or services it should have as much understanding of automatic control theory as possible. Unfortunately, the exact presentation of automatic control theory can only be accomplished through the liberal use of differential equations, and many who are closely associated with automatic control have too little mathematical training to follow a mathematical presentation of the subject. "Automatic Control, Principles and Practice" is designed to fill the needs of such people. Minimum prerequisites for reading it profitably are a good understanding of algebra and of elementarv phvsics. At the same time, readers with considerably more background will find it interesting and worth-while reading.
The book begins with a description of the control system and its characteristics, introducing the reader to the factors that determine the type of control equipment and adjustments required for a particular system. This leads naturally into a description of the types of control action, starting with simple two-position action and progressing up the series of more complex types to proportional plus reset plus rate action. Simple formulas are
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given which permit calculating the proper settings for the various control responses in i€?rnis oi ui·'1 .iiCiisviraOiC characteristics of the system.
T h e next section of the book is devoted to a discussion of frequency response methods. It covers procedures used in obtaining the data, methods for presenting the data, criteria for stability of the control system, and simple calculations involving frequency response data. Simple formulas for calculating the proper settings for controller responses from frequency response data a re included.
Since a controller must consist of real mechanical components, the next section describes the physics of springs, levers, diaphragms, bellows, nozzle-flapper systems, and other mechanical components found in pneumatic controllers. Λ similar discussion of the physics of components found in hydraulic control equipment follows. The next section attempts to give the reader an understanding of the electrical components used in control gear.
After describing a number of force balance systems and computing circuits, the author discusses primary measuring elements. He is careful to point out the time constants of these and the factors that influence the time constants. The operating principles of a few well-chosen types of commercially available controllers are also described. The discussion of final control elements is limited to valves of various types.
A number of types of control systems, including averaging control, cascade control, ratio control, totalizing control, and time schedule control, are discussed. Finally, some typical industrial applications to operations such as steam generation, water treatment, and gasoline refinery control are analyzed.
i n its J^OV pages, tuis υοοκ covers control theory as it relates to automatic control of chemical processes. It is probably the best nonmathematical treatment of this subject available. While it is carefully written, well illustrated, logically arranged, and non-mathematical, it is not eas_y reading because of the large amount of material covered in the volume.
Automatic Control, Principles a n d Practice. Werner G. I\>lzbock. iv -f- 28 pages. Reinhold Publishing Co. , 430 Park Ave., New York 22, N . Y. Reviewed by Ralph H. Munch, Monsanto Chemical Co.
(Continued on page 111)
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PRODUCTION (Continued from page 81)
of uranium, surrounded by magnes ium fluoride slag, is found in the cup a t t h e bottom. The slag is knocked off, and the last traces are removed b y washing in acids and other solutions.
• Vacuum Cast . The pure uranium billet is still a long way from being a finished fuel e lement for use in a nuclear reactor. It must b e vacuum cast into rods, which are then carefully tempered, machined, and sealed into finned "cans" of aluminum or magnesium alloy. Because one faulty fuel rod can cause an expensive shutdown in an atomic power plant, t h e specifications are high. Testing is exhaust ive. Complete records on each rod are kept so that the history of a specific rod can b e traced back through t h e plant if necessary.
The new canning factory a t Spring-fields puts this exacting process on a l most an assembly line basis. This work plus the cost of t h e o re and t h e chemical processing adds u p to a n average $60,000 p e r ton of fabricated fuel element.
Springfields has supplied most of t h e fuel elements used in British reactors, except for those m a d e of enriched materials, which will continue t o be made a t Dounreay, Scotland. Wi th the new plant , Springfields will b e able to meet present demand for fuel elements, and the time needed to construct new power plants will ensure that t he UKAEA will h a v e time to expand to meet its needs . If demand is too great, a new plant •ÎT-» ο τ ι nfVi<=»7- l r*r»af ir\r\ m io rV i f r-»r-»cciV»1v V»<*
rvijf u*"*. in anv case trie Li IC A y*. A feels confident that it can supply fuel elements fcr Britain's nuclear p o w e r program, as well a s for any reactors Britain sells ab road .
• Yttrium m e t a l , once considered too brit t le for structural uses, has been m a d e into a pliant, easily formed material by Bureau of Mines metallurgists. Though not revealing product ion techniques, BuMines says the process is similar to the Kroll process for titan ium and zirconium. Nietal made b y the bureau contains about 0.02*7^ oxygen, which is t h e principal offender limiting ductility.
BOOKS (Continued from page 87)
Cilove Boxes and Shielded Cells for Handling Radio-Active Materials. G. N. WALTON, xii 4 -515 pages. Academic Press, Inc., I l l Fifth Ave., New York 3, Ν. Υ. 1958. $16.80.
Papers from the 1957 Harwell Symposium and the United Kingdom Atomic Energy Authority on operating experiences in handling radioactive materials. Designed as a textbook on radiation shielding.
Electronic Apparatus for Biological Research. P. Ε. Κ. DONALDSON et al. xi 4- 718 pages. Academic Press, Inc., I l l Fifth Ave., New York 3, Ν. Υ. 1958. $20.
A handbook for biological research workers concerned with design, construction, and maintenance of electronic equipment.
Paperbound Elasticity, Plasticity and Structure of
Matter. 2nd. ed. R. HOUWINK. vxii 4-368 pages. Dover Publications, Inc. 920 Broadway, New York 10, Ν. Υ. 1958. $2.45.
The Theory of the Properties of Metals and Alloys. N. F. Μοττ and H. JONES. χ + 326 pages. Dover Publications, Inc., 920 Broadway, New York 10, Ν. Υ. 1958. $1.85.
Current Research and Development in Scientific Documentation. No. 3. National Science Foundation, Washington 25, D. C. 1958. Free.
Power Reactors. U. S. Atomic Energy Commission Technical Information Service, iii 4- 02 pages. U. S. Government Printing Office, Washington 25, D. C. 1958. 65 cents.
Productive Uses of Nuclear Energy. Report on Prospects for Nuclear Energy in Puerto Rico. viii 4- 87 pages. National Planning Association. 1606 New Hampshire Ave., N.W., Washington, D. C. 1958. $1.25.
The Water Pollution Control Program of the_U. S^Public Health Service.^ 1957-Iyo8. Public Health Service Publication No. 631. 26 pages. U. S. Government Printing Office, Washington 25, D. C. 1958. 25 cents.
The Unfixed Pressure Vessel Code Simplified. ROBERT CHOSE. 48 pages. The Unfired Pressure Vessel Code Simplified, P. O. Box 91, Leonia, N. J. 1958. $6.50.
ASTM Standards on Gaseous Fuels. ASTM Committee D-3 on Gaseous Fuels, vi 4- 198 pages. American So-cietv for Testing Materials. 1916 Race St.,'Philadelphia 3, Pa. 1958. $3.00.
Specifications and Tests for Electrode-posited Metallic Coatings. American Society for Testing Materials and Elec-troplaters' Society. vii 4- 116 pages. ASTM, 1916 Race St., Philadelphia 3, Pa. 1958. $2.25.
Fundamentals of Pipe Drafting. CHARLES H. THOMPSON. 66 pages. John Wrilev & Sons, Inc., 440 Fourth Ave., New York 16, Ν. Υ. 1958. $3.50.
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