lise of High Vacuum Techniques Increasing A STAKF
LECENT advance» in high vacuum tech Rnology and know-how wort* discussed by 250 experts in the field invited to Cam bridge, Mass., Oct. 30 and 31 to partici pate in a High Vacuum Symposium under the joint sponsorship of the National Research Corp. and the Division of Industrial and Engineering Chemistry of
the
AMERICAN*
CHEMICAL.
SOCIETY.
Previously considered useful only in the laboratory, high vacuum techniques are being used on an expanding basis by the chemical processing industries, and the impression was gained that high vacuum applications in industrial processes are rapidly approaching the "bonanza" stage. Scientific
Aspects
The opening session was devoted to scientific aspects of high vacuum, with Saul Dushman, assistant director of the General Klectric Research Laboratories, presiding. An introductory historical paper was given by Dr. Dushman, re viewing the development of high vacuum techniques and the relatively simple laws that describe the behavior of gases in this region. T h e remaining papers of the ses sion indicated the critical importance of accurate and rapid vacuum measurement, which is several magnitudes behind the vacuums now attainable. T h e present frontier of vacuum measurement is ap proximately 10 ~8 mm. Kg. Laboratory tests involving slow degradation of photo electric emissivity from tungsten surfaces due t o formation of monolayers of the re sidual gas have indicated achievement of vacuums approaching 10 ~ 1 2 mm. Hg (10 , s atm.). At these vacuums, the number of molecules loft in the evacuated area is of the order of 100 per cubic centimeter. High vacuum distillation was the topic of the second session. Large tonnage
vacuum distillation of petroleum residues was reported by W. W. Kraft, t h e Luramus Co., in the first paper. These opera tions were carried out at pressures of 20 and 1 mm. Hg, vacuums which were admittedly short of the range properly characterized as high vacuum, but which did contain some of the technical require ments in pumping and low pressure drop in the still column that are eharacteristic of the more extreme range. A new de velopment in still design was reported by ,J. R. Bowman, Mellon Institute of In dustrial Research, the operating prin ciple consisting of a heated tube main tained above the boiling point of the liquid and enclosing a cooled rotating inner cylinder. Vapor in the annular space condenses on the inner element and is im mediately flung off by centrifugal force». Operating characteristics of the still make it suitable for pressures down to 10 microns (0.01 mm. Hg). High rectifying capac ity, of the order of 40 plates for a column 30 inches long, can be obtained. Thermal requirements vary in almost direct pro portion to the equivalent number of plates, since the effect of adding one plate is achieved by an equivalent increase in the evaporation-condensation heat require ment per unit throughput. A small laboratory molecular still with a through put of about 200 ml. per hour and suited for distillation of samples as small as 50 ml. was described by K. C. D. Hickman, Distillation Products, Inc., and a model of the still was shown to the group. The final paper of the session was also presented by Dr. Hickman and reported a system for readily evaluating the thermal decomposi tion hazard inherent in different types of distillation equipment. Controlling vari ables in the expression developed were distillation pressure and time of exposure
Left. Great Britain was represented by these visitors shown with the chairman of the symposium, Riclu/ni S. Morse (center), National Research Corp.: J, C. Sivallotc, H. C. Raine· R. F. Fisher, all of imperial Chemical indus tries, Ltd., and G. R. H. Geoghegan9 British Ministry af
VOLUME
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46.NOVEMBER
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of the distilland t o the vaporizing ele ment. Kngineering aspects of high vacuum generation were rrovered in the third session. Topics treated were measure ment and control o f leakage, design cri teria, installation a.nd maintenance prac tices, and pumping «peed studies. Applicalions and Dehytl
in ration
\letallnrgy
T h e last two sessions related respectively to vacuum metallurgy and vacuum de hydration. T h e v a c u u m metallurgy of magnesium, copper, and titanium were covered, and a. fundamental study, most of which appeared to be still in the stage of theoretical analysis, of the sintering of copper powder was described. Ulti mate objective of t h e latter investigation was improvement of powder metallurgy methods to obtain products with physical properties approaching those of east metals. In aiiotlior paper, studies in vacuum heat treating of steel and beryl lium-copper spring** were reported. The session on vacuum, dehydration included a discussion of low temperature drying techniques, information obtained in de velopment of a commercial process for manufacture o f orange juice and powder, and a fundamental study of vacuum de hydration using liquid absorbents. Numerous questions and comments dur ing the sessions and many individual dis cussions at other times revealed a wide range of industrial interest in high vacuum processes. T h e impression was gained that in the coming decade low pressures may very well become as firmly established in industrial importance as the high pres sure operations that have materialized in the oast 20 to 30 years.
Supply» Right. 'Speakers on high vacuum engineering: J, C. Hecker, Distillation Products, Inc., presiiled: Β. B. Dayton, Distillation Products* Inc.; C E. Normand 9 Carbide and Carbon Chemicals Corp. ς R. Mr. Jacobs, Standard Oil Co. (Ind.): and H. C. Weingartrver, ISaCl Research Corp.
1947
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