GB702774A - Electro-conductive products and production thereof - Google Patents

Abstract

In the method of providing glass or refractory bases with an electroconductive coating by coating the base while at a temperature above 400 DEG F. but below its fusion temperature with a compound which forms the film, the coating operation is carried out while the water content of the atmosphere adjacent the surface to be coated is below 0.01 pounds per pound of atmosphere. Best results are obtained when the water content is below 0.005 lb. per lb. of atmosphere, preferably about 0.00025-0.001 lb. per lb. of atmosphere. When the humidity of the general atmosphere is excessive the water content of the atmosphere adjacent the surface to be coated must be adjusted to and maintained at the above limits. This control of the atmosphere results in a greater uniformity in the conductivity, transparency, clarity, and adhesion of the film. The working data and results are given of experiments carried out on glass plates in atmospheres containing 0.003-0.03 lbs. water per lb. atmosphere using coating solutions composed as follows, (A) stannic chloride pentahydrate 900 gms., methanol 63 ccs., phenyl hydrazine 21 gms., and dioctyl sodium sulphosuccinate solution 30 ccs., the latter being formed by mixing dioctyl sodium sulphosuccinate 10 gms., methanol 45 ccs., water 5 ccs., and (B) anhydrous stannic chloride 1000 ccs., methanol (anhydrous) 2000 ccs., ammonium and fluoride 60 gms., and butyl carbitol acetate 3000 ccs. These show that the specific resistivity of the film is increased by more than 50 per cent. when the water content is 0.012 lbs. per lb. atmosphere, and increases still further as the water content increases. Experiments, the data of which are given, show that the adverse effect of high humidity may be partly compensated for by adjusting the distance from spray to base, but too great a reduction of this distance is not practicable, and in examples a distance of 15 inches is used. The compressed air used in the spray gun should contain no suspended droplets of water, and should contain less than 0.005 lb. water per lb. air or not more than the water content of the atmosphere. In an example a glass sheet was heated to 1230 DEG F. and then held in an atmosphere with a water content of 0.003 lb. per lb. air and temperature of 75 DEG F. and sprayed with solution (A) from a distance of 15 inches for about 4 seconds, about 8 ccs. of the solution being sprayed on to the glass. The sheet may then be tempered. The specific resistivity of the coating was 0.0025 ohm/cm. Other solutions may be used, e.g. an aqueous solution of stannic chloride containing at least 40 per cent. by weight stannic chloride, the water content being 5-150 per cent. of the weight of the stannic chloride. Frequently an alcohol is added in the proportion of 5-50 per cent. of the weight of stannic chloride, a list of suitable alcohols being given. Aldehydes, water-soluble ketones, or up to 10 per cent. of fluorides may also be present. Other suitable solutions are, (C) stannic chloride pentahydrate 90 per cent. by weight 40 per cent. aqueous solution of formaldehyde 10 per cent. by weight, (D) stannic chloride pentahydrate 900 gms., phenyl hyrazine hydrochloride 21 gms., methanol 90 ccs., (E) anhydrous stannic chloride 1000 ccs., methanol 5000 ccs., ammonium bifluoride 100 gms. Anhydrous solutions, e.g. B, E, are less affected by humidity variation than are the aqueous solutions. The coating may be carried out in an atmosphere of nitrogen, carbon dioxide, or the like, and vapours of stannic chloride &c. may be used instead of the spraying solutions. Although it is preferred to use stannic chloride other tin halides, stannous oxalate, stannous acetate, cadmium bromide, cadmium acetate or indium trichloride may be used, suitable solutions being (F) stannous acetate 4 gms., methanol 30 ccs., 12 normal hydrochloric acid to dissolve the acetate, (G) zinc acetate 20 gms., water 50 gms., phenyl hydrazine hydrochloride 5 gms., (H) two parts by volume anhydrous stannic chloride, one part glacial acetic acid, (I) cadmium acetate 150 gms., water 100 gms., (J) cadmium bromide 75 gms., water 100 gms., one volume of 30 per cent, aqueous hydrogen peroxide per volume of cadmium bromide solution, (K) saturated indium trichloride in methanol. Suitable bases include glass, mica, metal oxides such as alumina, porcelain, glass fibres, quartz, silicates e.g. of aluminum and calcium, stone, and metals such as tungsten, molybdenum, chromium, iron, and steel. The coated articles may be used as windscreens, electrical resistors, insulators, grid leaks, mirrors, radio tube valves, and electrical heating elements, e.g. in cooking utensils, and the coating on metal may be used as a rectifier film.