is avoided. The threat of flooding limits flow rates in packed columns, holding design flow rates down to about 60%. The turbulent contact design is said to permit much higher rates—superficial gas velocities up to about 1200 ft. per minute, compared to a typical packed-column rate of about 200 ft. per minute. When feed rates fall below a critical rate, the spheres settle on each retaining grid and act much like conventional packing, Domtar says. The allowable range of feed rates, though, is a broad one. Liquid rates down to 9 gal. per minute per square foot at a gas velocity of 500 ft. per minute have been used successfully, according to the firm. The estimated top rate for economical operation is about 50 gal. per minute per square foot with a gas velocity of 1500 ft. per minute. For Papermaking. The absorber was developed at Domtar's central research laboratories, Cornwall, Ont., for use in the company's papermaking operations. A unit now in use at a Domtar pulping mill in Trenton, Ont., absorbs sulfur dioxide in a solution of soda ash to form sulfite cooking liquor. It handles as much as 25 gal. per minute per square foot of liquid at superficial gas velocities ranging from 500 to 1000 ft. per minute, according to Domtar. Pressure drop through the column is said to be about 10 in. of water. This three-stage column is 14 in. in diameter and 16 ft. tall. By comparison, a column packed with Raschig rings specified for this service would have to be 4 ft. in diameter and 30 ft. tall. Domtar has another Turbulent Contact Absorber in paper mill service, two more about to go into service. Aerotec's marketing plans are aimed at the papermaking market. The moving spheres aren't easily clogged when the feed streams contain solids or when precipitates form in the column itself, Aero tec says. This is important when making sulfite cooking liquor, since sulfur can precipitate in the absorber under some operating conditions halting the operation. As development work continues, Aerotec expects to extend the column's application to other chemical operations. A rubber-lined turbulent contact column is already on order for Armour Agricultural Chemical's wetprocess phosphoric acid facility at Fort Meade, Fla., for use as a scrubber
to remove hydrogen fluoride and other corrosive gases evolved when sulfuric acid contacts crushed phosphate-bearing rock. Aerotec rents pilot-size columns for field trials. Aerotec's line of Turbulent Contact Absorbers for the paper industry range in size from 1 ft. to 3.5 ft. in diameter. The spheres, made of either polyethylene or polypropylene, are l 1 / 2 in. in diameter. Standard column construction for pulping mill service is Type 316 stainless steel, but other materials can be used. One glass fiber-reinforced polyester pilot unit is now operating at a West Coast plant. Expanding Uses. Both firms are looking at further refinements in the turbulent contact approach. Domtar is investigating the effect of structure and operating changes on performance. Aerotec is looking at hollow stainless steel spheres to replace the polyolefins in corrosive or hightemperature operations—polypropylene spheres are limited to about 230° F. operating temperature. The thin-shell steel spheres would weigh about the same as the plastic spheres now in use—4.5 grams. The firm is also working on an improved demister, to cope with gas flows above 1000 to 1200 ft. per minute. The column's nonclogging feature opens the way for its use as an efficient gas scrubber, Aerotec points out. The company is studying its suitability for organic oxidation reactions in which heavy, flocculant precipitates form. The Turbulent Contact Absorber isn't Domtar's first venture into equipment marketing through licensing agreements. Since the 1930's, Babcock & Wilcox has marketed Domtardeveloped furnaces for the recovery of heat and chemicals from spent pulping liquor. Bauer Bros, manufactures the Centri-Cleaner cyclone pulp cleaner, developed by Domtar in 1951, and is currently working with the Canadian firm on other papermaking equipment developments. While the Turbulent Contact Absorber is the first Domtar design it has manufactured, Aerotec also markets a floating-bed scrubber, developed by Aluminium Company of Canada. This design, intended specifically for particulate matter collection, also uses lightweight spheres, but is based on a lower gas velocity and less free space in the bed of spheres. The Turbulent Contact Absorber was an outgrowth of this design.
Quartz Crystal Microbalance Measures Ultrathin Films An instrument which evolved from the needs of its own research group is now commercially available from Westinghouse's Scientific Equipment Department. The compact, ultrasensitive instrument is designed to measure evaporated films as thin as 10 - 8 gram per square centimeter, according to the Pittsburgh, Pa., firm. Called Model 701 quartz-crystal microbalance, the instrument measures changes in mass deposited on a crystal surface by measuring the corresponding change in resonant frequency of crystals. In operation one of two synthetic quartz crystals contained in the instrument is exposed to the vaporant source. The second crystal is placed close to the substrate being coated so that the crystal and substrate receive the depositing material at the same rate. According -to Westinghouse, the frequency of the exposed crystal, decreasing in proportion to the mass being deposited, is mixed with the frequency of the reference crystal. The resulting beat frequency represents the film thickness deposited. The frequency change in cycles per second is approximately equal to the film thickness in Angstrom units times the film density in grams per cubic centimeter, Westinghouse says. The instrument can measure directly the mass of extra thin films, either metal or dielectric, without correction for any other physical properties, Westinghouse claims. Furthermore, it can measure these films over a range of 0.05 to 40,000 A. with an accuracy of better than 1%. However, the instrument doesn't measure the uniformity or density of the deposited film, Westinghouse adds. Other measurement techniques are needed to control these factors in film deposition. However, the instrument does feature an electrical readout. Since the output signal corresponds to the instantaneous thickness of the deposited film, and the instrument can be used simultaneously with processing, Westinghouse says the instalment can be used either to measure or to control the processing rate of deposition. Investigation Tool. In addition to its use in deposition processing, Westinghouse says that the instrument is a valuable tool for many investigations in surface physics studies. Oxidation, AUG.
2 6, 1963
C&EN
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absorption and reaction rates, sputter ing yields, studies of films formed by other techniques, and measurement of deposited film thicknesses and prepa ration rates are among the potential uses cited by the company. When supplemented by other analytical tech niques, such as reflectance measuring and particle slicing, the instrument is suitable for resolving questions on the dynamics of thin-film growth, nucleation, and similar phenomena. These questions are fundamentally important to the associated problem of epitaxial film formation on arbitrary substrates— of particular interest in the field of microelectronics, according to Westinghouse. The films to be measured, either conducting or insulating, may have been formed by evaporation, sputter ing, or by other conventional means. The exposed crystal area is about 1.25 square centimeters. Total loading per 10-megacycle crystal depends on the density of the material being deposited - f o r example, 500 A. for gold; 36,400 A. for aluminum. The instrument uses solid-state cir cuitry, has a regulated power supply making it insensitive to line voltage. According to Westinghouse, it is suit able for all high-vacuum systems, rep resenting the smallest mass in the system, thus offering the least danger of contamination. Model 701 quartz crystal microbalance sells for $850 with replacement crystals priced at $5.50 each. Ε 30
C&EN PROGRESS REPORT
BRIEFS Bureau of Mines has just started an extended series of tests of a coal-fired gas turbine for generating electricity. If these Morgantown, W.Va., tests are successful, they could point the way to a new high-tonnage market for coal, according to the bureau. The turbine could mean increased efficiency in many power plants. Combined with conventional steam turbines, the new gas-powered turbine would make it possible to use more of the heat en ergy that becomes available when coal is burned.
Union Carbide's line of Ucar latexes has been increased by the introduction of Ucar 890. The New York firm explains that the new latex was de veloped as an improved back coating to impart higher strengths to fabrics. Carbide claims that commercial mill trials have demonstrated that it can be applied at lower costs than many com mercial latexes because no catalyst and less thickener is required. The pri mary use of Ucar 890 is expected to be in automotive and furniture up holstery.
Two new metal plating processes, in volving nickel, and cobalt and nickelcobalt alloy, have been developed at the Research and Development Di vision, Lockheed Missiles & Space
Co., Sunnyvale, Calif. The processes produce thin ferromagnetic films of almost pure metals on both metallic and nonmetallic bases. Such films have many uses in the electronics field, according to Lockheed. The solutions for these processes may be used con tinuously as all by-products are gase ous. Exclusive manufacturing rights for the processes in the U.S. and Canada have been granted Enthone, Inc., New Haven, Conn., with non exclusive rights throughout the world.
NEW EQUIPMENT A fully transistorized multipoint re corder is now offered by West Instru ment Corp., Schiller Park, 111. The new M 2 series can record up to 24 points on an 11-in. chart. Accord ing to the company, the transistorized amplifier offers the advantages of low internal temperature rise, no warm-up period, and no adjustments for vac uum tube aging. Ε 31
An electromagnetic flowmeter, which can be used in pipes up to 12 in. in diameter, is now available from Hays Corp., Michigan City, Ind. It is un affected by changes in fluid conduc tivity and can be used with clear liquids, opaque solutions, and slurries, according to the company. A per manent record and/or indication of flow is provided by the model. Ε 32
INDUSTRIAL CHEMICAL SPECIALTIES
Companies added these products to their lines during the past month Material Acrylic ester
Company Celanese Chemical Co. Pampa, Tex.
Sulfonates (Conco BOD)
Continental Chemical Co. Clifton, N.J.
Aluminum coating
Daynel Corp. of America Omaha, Neb.
Carboxylated latexes (Latex 815)
Dow Chemical Co. Midland, Mich.
Soluble silicone (SF-1075)
General Electric Co. Waterford, N.Y.
Available in commercial quantities unless otherwise noted.
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C&EN
AUG. 2 6, 1963
Features and Uses Propylene glycol monoacrylate available in semicommercial quantities for use in automotive and other coatings Biodegradable alkyl and aryl sulfonates available in slurry, liquid, and flake forms Offered in 11 colors for exterior use. Contains asbestos, aluminum flake, and alkyd resins Cure to a strong, tough rubber without vulcanization. For backsizing and laminating For use in cosmetics for nongreasy, water-repellent films
NEW Spectroquaiity® So/vent from MC&B
tetrahydrofuran T h e w i d e a c c e p t a n c e of our Spectroquality p-Dioxane h a s led us to the development of Tetrahydrofuran, Spectroqual ity. Like p-Dioxane, T e t r a h y drofuran is a cyclic ether, with comparable solvent properties. Because of its versatility, T e t rahydrofuran h a s wide appli cation as a s p e c t r o s o l v e n t , including use in such diverse fields as clinical chemistry a n d polymer chemistry. Specifications BP Dipole moment Ultraviolet cut-off I. R. Bands of maximum transmittance
bb U 1.70 220 w
amplifier. Strontium-90 is used in the probe. Operation of the instrument depends on the greater beta backscatter from the zinc compared with steel. Ε 34 A miniature vibrator, 2 in. long by 0.5 in. square, is being produced by Cleveland Vibrator Co., Cleveland, Ohio. Known as the Vibra-Mite, it is designed for use on feed tracks and small hoppers and bins to keep ma Ε 35 terials flowing smoothly.
A portable, nucleonic instrument for measuring the density of zinc on
steel has been developed by Burndept Ltd., Erith, Kent, England. The instrument is claimed to offer a rapid, accurate, and nondestructive method for assessing zinc content. The unit consists of a probe and a transistorized
Further useful information on keyed Equipment items men tioned is readily available . . .
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August 26, 1963
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A new laser crystal growing furnace is available from Research & Develop ment Products Co., Plainfield, N.J. The Model 4001 furnace has been de veloped for solid state experimental and production use, and phase equi librium studies as well as laser crystal growth. The furnace is made with a double shell construction, with the outer shell perforated, to assure good heat control and a relatively cool outer surface. Ε 33
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