US 3260659 A
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J y 12, 1966 R. WILLING ETAL 3,
STRIPPING 0F CHROMIUM FROM BERYLLIUM Filed June 12, 1963 INVENTOR.
ROBERT WILLING NY S. SOUILLACE ANTHO BY L 1 ATTORNEY United States Patent Office 3,260,659 Patented July 12, 1966 Inc.
Filed June 12, 1963, Ser. No. 287,325 1 Claim. (Cl. 204-146) This invention relates to a method for removing chromium plate from a metal substrate and more specifically to a method for removing chromium plate from beryllium substrate by the use of relatively concentrated sulfuric acid.
Removal of chromium plate from a substrate without affecting the substrate metal permits salvaging the substrate for re-use with little or no damage to the substrate. Chromium is extremely difficult to remove from beryllium and similar metals without causing damage to the beryllium surface and subsequent loss of dimension. Some attempts at removing chromium plate from beryllium have resulted in methods which are either injurious to the beryllium or which require abnormally long stripping periods. Some of these processes remove chromium from beryllium but during the process the relatively expensive metal suffers surface damage.
The process of this invention is practiced by immersing a material or instrument having beryllium substrate plated with chromium into a concentrated sulfuric acid (over a range of 96% to 100%, with the optimum being 98%) under controlled conditions.
The material which is to be stripped of chromium is immersed in the sulfuric acid environment. Temperature control is maintained within reasonable tolerances; voltage must be maintained within a specified. maximum to prevent attack on the beryllium substrate and within a specified minimum to prevent decreasing the speed of the sulfuric acid composition in stripping away the chromium. As the stripping environment becomes concentrated by the stripped trivalent chromium the rate of stripping is reduced. Therefore it may be desirable to provide means for periodically renewing the sulfuric acid medium in which the beryllium substrate material is immersed.
Therefore it is an object of this invention to provide a process for removing chromium plate from beryllium.
It is still another object of this invention to provide a process for removing chromium plate from a beryllium substrate by the use of relatively concentrated sulfuric acid.
Another object of this invention is to provide a process for removing chromium plate from a beryllium substrate by the use of a sulfuric acid composition so that beryllium surface damage and dimension loss are reduced.
Another object of this invention is to remove chromium plate from a beryllium substrate economically and efficiently.
Other objects, features, and advantages of the present inventive process will appear from a reading of the following description -of several examples of the process of the invention including a more preferred process, the said description being given in connection with the accompanying drawing, of which the figure is an illustration of means for practicing the inventive process.
Referring now to the figure, the vessel 1 comprised of a conducting material, stainless steel, lead, black iron, etc., is filled with a non-aqueous chemical compound 2 such as sulfuric acid, with an optimum concentration of 98% (range of 96% to 100% T'he substantially non-aqueous solution is maintained at approximately room temperature over a preferred range of from 60 F. to 110 F. The temperature may be increased either by heating the solution by external means or by passing alternating current through the solution. Other means may also be employed to heat the solution. The most preferred temperature is approximately F. A piece of equipment 3 having preferably a beryllium substrate 5 and a chromium plate 4 plated on top of substrate 5 is immersed in the solution. A direct voltage supply 7 such as a battery with a potentlometer so that the voltage may be varied over a desired range is connected to the beaker and to material or piece of equipment 3. The negative electrode of the DC. voltage supply is connected to the vessel by clip means 9 which may be any suitable clamp for gripping the side of the vessel 1. The positive electrode is similarly connected by clip means 8 to equipment 3. An insulator 6 is provided inside vessel 1 to prevent the equipment 3 from making contact with vessel 1 which serves as the negative electrode. If the vessel is comprised of a non-conducting material such as glass or a plastic, it is necessary to provide a negative electrode in the vessel solution. The voltage is maintained over a preferred range of from seven volts to eleven volts and more preferably at approximately nine volts. High voltages initiate an attack on the beryllium layer 5 and lower voltages tend to decrease the efiiciency of the chromium stripping solution and also cause some attack on the beryllium. It was observed during the experiments that the current density of the solution drops to zero as the chromium plate 4 is removed from the beryllium surface 5. The process is completed when the chromium has been stripped from the beryllium surface. During the experiments it was observed that within the range of variables indicated for temperature, voltage, and solution concentration, that the rate of chromium plate removal was within the range of from 25 micro inches to 10 0 micro inches per minute per surface. After the chromium has been removed the piece of equipment is removed from the solution. The solution may be used to strip other pieces of equipment until the solution becomes concentrated in trivalent chromium at which time the rate of stripping is substantially reduced and it becomes necessary to renew the solution.
Summary A process for stripping chromium plate, or other similar metals from a beryllium substrate without attack and resultant loss of initial dimensions of the beryllium is economically desirable due to the high cost of the beryllium metal and due to the fabrication effort which usually is involved in the production of precisely plated equipment in the beryllium metal. A process for stripping chromium plate, etc., from a beryllium substrate is practiced by immersing'the equipment having a chromium plated layer into a solution maintained at approximately ambient temperature. The solution is contained in a vessel which may also serve as a negative electrode if comprised of a conducting metal. A positive electrode is connected to the piece of equipment from which the chromium will be stripped. The two electrodes are connected to a direct voltage source which provides a potential difference of approximately nine volts from the minus to the plus electrode during the stripping process. The solution used is the substantially non-aqueous solution, H (optimum 98%). Previous solutions and processes use solutions which either attack the beryllium surface or consume so much time as to render them uneconomical.
Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and-example only and is not to be taken by way of limitation, the spirit and scope of this invention being limited only by the terms of the appended claim.
3 4 We claim: from said positive electrode to the negative electrode A process for stripping chromium from material comis maintained Within a range of from 7 to 11 volts. prised of chromium plate on beryllium comprising the steps of: References Cited by the Examiner immersing said material in a sulfuric acid solution hav- 5 UNITED STATES PATENTS ing a concentration of from 96% to 100%, 2,185853 1/1940 Mason 2O4 146 maintaining said solution within a temperature range of from 60 F. to 110 F., OTHER FERENCES making a connection t said m teri l so as t k Journal Electrodepositors Technical Society, vol. 14,
it a positive electrode in said solution and passing an 10 1938, P- electrical current from said positive electrode to a a negative electrode in electrical contact with said so- JOHN MACK Prlmary Emmmer' lution, the potential for passing said electrical current R. MIHALEK, Assistant Examiner.