TECHNOLOGY
N e w Cell Uses Less M e r c u r y N e w d e N o r a fluent a m a l g a m eel! uses unit cells in filter press-like a r r a n g e m e n t ; e a c h unit has a steel screen Electroluminescence m a y s o m e d a y s u p p l a n t c a t h o d o l u m i n e s c e n c e in TV picture tubes C I N C I N N A T I . - A new mercury cell for chlor-alkali production uses a cathode of amalgam flowing down a vertical screen. At the 107th meeting of the Electrochemical Society here May 1 to 5, Vittorio de Nora, Impianti Elettrochimici, Milan, Italy, said his organization has built a large experi mental cell of this type, but so far there have been no commercial installations. The cell is actually made up of a number of unit cells connected in a parallel electrical circuit and placed next to each other like plates in a filter press. Each unit cell contains a verti cal steel screen down which .the amalgam flows. Mercury is introduced through a horizontal steel pipe with a lengthwise slot into which the screen is fastened. T h e holes in the screen keep the fit from being a ight one and «provide even distribution of the mer cury along the top of the screen. Anodes are vertical graphite rods. The two electrodes are separated by a diaphragm to prevent mixing of the anode and cathode products with con sequent safety hazards. Although permeable, there is little flow of liquid through the diaphragm. Pressure is kept equal on both sides and liquid enters and leaves on the anode side in contrast to diaphragm cells in which liquid is fed into one side of the cell and withdrawn from the other. Current efficiency of the fluent amalgam cell, as de Nora has named it, is above 9 6 % and the average voltage is less than 4.3 at normal load. Ad vantages are lower operating and initial costs with smaller mercury require ments. (No small matter considering the price of mercurv jumped from $ 1 8 7 - $ 189 to $ 3 2 5 - 8 3 3 0 before dropping to $ 3 1 8 - $ 3 2 0 per flask dur ing 1 9 5 4 ) . Titanium. A commercial electro lytic process for titanium is an intrigu ing possibility, but so far none has pro gressed beyond the pilot-plant stage. Production of the metal is not enough, it must b e prepared in a form suitable for working. Generally, titanium ob tained b y electrolysis of potassium titanium fluoride in sodium chloride appears as large thin plate-like crystals which average about 3 / 4 inches in length, but may grow as long as l 3 / 4 2074
inches and attain a width of ; \ s inches, according to Q. H. McKenna, Horizons. Plate-like crystals are easily com pacted and are therefore the desired form. Under certain conditions, how ever, an amorphous powder may be produced. Also, at times when the cell is operated at a temperature as high as 880° C massive cubic crystals are formed (normal operating tempera ture is about 750° C ) . By increasing current density when concentration is increased, and controlling other condi tions carefully, satisfactory operation of the cell can be achieved at an ν poinl between 660° and 880 J C. Beryllium by Chelation. Recently developed chelation techniques are now being used in an improved process for production of beryllium hydroxide, first step in preparing metallic beryl lium. In manufacturing beryllium hy droxide, sulfated ore is leached with water to give a solution containing beryllium, aluminum, iron, and minor impurities together with some sulfuric iieid. Formerly individual steps of separating iron from solution, separat ing aluminum from solution, and pre cipitating beryllium are now combined in a single operation where impurity chelation and complexing, and beryl lium precipitation are carried out simultaneously, says C. W. Schwenzfeier, Jr., Brush Beryllium. An added advantage is that the hydroxide is of the granular alpha type, easily separated by standard filtration. A major portion of the aluminum is separated by treating with ammonium hydroxide so that easily separated am monium alum is formed. Mother liquor from this step, which still con tains troublesome quantities of alu minum, is pumped continuously to the prime controller in a three-unit pro portioning flowmeter. The prime con troller governs flow of caustic soda liquor and chelating agent streams which are combined with the main stream in a kettle. Heavv metals, such as iron and nickel, are converted into chelates, alu minum into sodium aluminate, and beryllium into sodium beryllate. All of these are soluble in the basic solu tion. Heating to 100° C, however, re sults in the hydrolysis of sodium beryl-
late to the alpha form of beryllium hy droxide which is insoluble. Molybdenum Metal. Metal prep aration b y the reduction of an oxide or other compound with an active metal such as sodium or aluminum is an old technique. In searching for a better method of producing metallic molybdenum, F. E. Block and H. L. Gilbert, LT. S. Bureau of Mines, Albany. Oregon, found that calcium reduction of molybdenum dioxide gave a metallic powder. This is to be expected be cause molybdenum's melting point is over 2600° C. Surprisingly, however, molybdenum trioxide did give metallic particles in a preliminary test. Final technique adopted employed a bomb made from llVo-inch inside diameter stainless steel pipe with a wall n / v , - i n c h thick. Flanges were provicr:\ to close the ends and a mag nesia lii mg was used. Commercial calciur» metal had to be vacuum sub limed to reduce the nitrogen content and it then h a d to be cut so that the pieces passed a ] /4-inch mesh screen. As a safety measure the charge was prepared in about 50 increments con sisting of one pound MoO a , one pound calcium, and 50 grams iodine each. The b o m b was fired electrically in a remote location with adequate protec tion for the crew. In twelve hours the bomb was cool enough to open. An average recovery of 97 r/ r molybdenum in a single mass of metal was obtained. Less expensive magnesium was sub stituted for calcium in some tests, but Block says it is not very satisfactory. Forging of molybdenum ingots is not readily done because of the metal's oxygen content, hut preliminary studies indicate small amounts of aluminum, thorium, or carbon will improve ductilitv. Krol! Hafnium. Using the Kroll process, several hundred pounds ol relatively pure hafnium have been pre pared b y Block's colleagues, H. L. Gilbert and M . M. Barr. Hafnium is normally associated with zirconium in ores in quantities about 2 % as great as the zirconium. Separation of the two metals is difficult because of their very similar properties. The Kroll process has been success fully used for titanium and zirconium, it consists of the reduction of the metallic chloride with magnesium. Calcined hafnium oxide was briquetted with carbon black using dextrine as a hinder. Dried briquettes were chlorin ated at 900° C in a 12-inch diameter shaft chlorinator. The crude tetra chloride formed is very sensitive to oxidation and hydrolysis and requires special handling to prevent its deteri-
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Here's new convenience and safety for usin hydrogen peroxide in organic reactions
V
DU PONT BULLETIN DESCRIBES EFFICIENT HYDROGEN
PEROXIDE-RESIN
TECHNIQUE
Peracetic acid can n o w be formed simply by passing a mixture of hydrogen peroxide and acetic acid through a cation exchange resin bed. Here are a few of the possible uses for this n e w Du Pont development: Epoxidation Hydroxylation Quinone formation Esters from ketones Lactones f r o m ketones Ketone cleavage Sulfur oxidation Nitrogen oxidation Polynuclear cleavage Phenol p r e p a r a t i o n Polymerization
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NOTE: D u P o n t will be glad to h e l p you improve your products and processes involving hydrogen peroxide. For p r o m p t advice o n your specific application, just write to E. I. du P o n t de N e m o u r s & Co. (Inc.), Electrochemicals Depc.,Wilmington 98, D e l .
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E. I. du Pont de Nemours & Co. (inc.) Electrochemicals Dept., Peroxygen Products Div. CEN-5 16, Wilmington 9 8 , Delaware. Please send my copy o f technical bulletin "Hydrogen P e r o x i d e - R e s i n Technique for the Preparation of Peracetic Acid."
HYDROGEN PEROXIDE "Albone" 35 . . . hydrogen peroxide, 3 5 % "Aibone" 50 . . . hydrogen peroxide, 5 0 %
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TECHNOLOGY
Constant Voltage
NYLAB'S Eliminates αϊ! storage butteries and storage battery accessories for SPECTROPHOTOMETERS (especially the Beckman Model DU) and GENERAL LABORATORY APPLICATIONS * 5 volts to 10 volts d c up to 6 amperes Lower Voltages from a divider
2076
oration in the atmosphere. Heating the crude product a n d sublimating it in an atmosphere of helium was neces sary to remove impurities formed b e fore it was placed in t h e reduction furnace. In the reduction furnace t h e tetrachloride w a s resublimated into a crucible containing molten magnesium. Operation temperature was about 850° ('. A 40% excess of magnesium was required. This was removed later by vacuum distillation. Sponge metal is reactive when ex posed to air. By first exposing it to a mixture of air and helium, the most reactive centers oxidize slowly without igniting the entire sponge. Consum able electrode a r c methods enable one to melt sponge to form ingots which can then be forged and rolled into sheets. Oxygen content of the metal renders it too hard to b e classified as cold ductile. Electroluminescence, In a conven tional television picture t u b e the light producing image is emitted by a catliodoluminescent phosphor excited by a beam of electrons. Investigation of phosphors for this type tube is the subject of much of t h e increasing amount of chemical research of the electronic industry, b u t recently a different type of luminescence is attract ing interest—electroluminescence. This form of luminescence is pro duced when a suitable phosphor is placed in a fluctuating electrical field. Sometimes it is enhanced, or activated, by ultraviolet light and it is then called photoluminescence. If "picture frame TV," using a flat, thin picture tube ever becomes a reality, electroluminescence or photoelectroluminescence will prob ably be used. Apparatus for studying these phenomena usually employs a thin layer of phosphor between two flat electrodes, one of which is trans parent. The transparent electrode is rendered conducting by coating with a thin transparent layer of some mate rial such as titanium dioxide. An electroluminescent phosphor does not emit light continuously, but inter mittently with the fluctuations of the current. Emission intensity of single crystals of zinc sulfide subjected to halt wave rectified 60 cycle sinusoidal volt age reaches o n e peak at the voltage maximum (at the 90° position in the phase angle) and another just before the point where t h e voltage falls to zero (usually about 150°). Taking special care to eliminate re flectance within the crystal, D. R. Frankl, Sylvania Electric, finds that the spectral distribution of both peaks from zinc sulfide phosphors is about the same and is roughly independent of voltage. The light appears blue to the
eye but measurement shows that it contains green a n d yellow also. He notes that the 90° peak intensity and the current increase at about the same rate as t h e voltage amplitude, indicating that the ratio of photons emitted to electrons traversing the crystal at the 90° phase peak is roughly independent of voltage. Photoconductivity. Electrical con ductivity of cadmium sulfide is in creased by the action of light and it also becomes luminescent. T h e wave length of maximum photoconductivityis longer than that of maximum optical absorption. Most explanations of this behavior have assumed that either the mobility or the lifetime of an elec tron in the conductive bands is de pendent upon the light's wavelength. Experiments by John Larnbe, Naval Research Laboratory, Washington, D. C , show that lifetime of conduction electrons is about 10 times larger at 5200 A. than it is at 4800 A. This information, together with optical absorbance data, suggests that it is the lifetime of conduction electrons which plays the major role in determining spectral response of photoconductivity. Vapor Screens. Ordinary lumines cent screens in cathode-ray tubes, formed by settling powdered phos phors, are limited in their resolution and contrast because of scattered light from the p o w d e r particles. A contin uous transparent phosphor coating is therefore advantageous, b u t attempts to obtain one by vacuum evaporation and condensation of phosphors have failed because of loss of activator mate rial. More encouraging results have been obtained by actually producing the phosphor b y vapor reaction at the heated glass surface, according to D . A. Cusano and F . J. Studer, General Electric. T h e surface to be coated is supported in a q u a r t z t u b e held at 400° to 700° C temperature. A p o w d e r consisting of zinc, zinc chloride, a n d manganese chloride is slowly introduced into an electrically heated evaporator at the bottom of the tube, while hydrogen sulfide is introduced at a point some what higher in the tube. An activated zinc sulfide layer be comes so firmly bonded to the glass that it can b e put through the same polishing operations as t h e glass itself. So far, brightness has been much less than that of white phosphors. Direct current excitation cells m a d e in this m a n n e r show only short flashes of light w h e n the current is put on or turned off. However, ultraviolet light causes photoluminescence which can be greatly increased by applying d.c. voltage.
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