Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/20—Electroplating: Baths therefor from solutions of iron

Definitions

• the present invention provides a process for electrodepositing iron.
• the process is especially adapted to plating iron to build up to desired dimensions, worn or otherwise undersize parts of machines that are subject to severe operating conditions and where accurate dimensioning by machining is required.
• the base on which the iron is plated may itself be iron, or it may be steel, copper, brass, etc.; generally, apparently, any material that conducts electricity or can be made to conduct electricity.
• the temperature of the bath, the bath composition and the current density must be controlled carefully and the plates produced by the sulfate baths are not regarded as of as high a quality as those of the chloride baths.
• the chloride baths must be operated at temperatures approaching that of boiling water. Such high temperatures are a nuisance in a commercial plating shop. Also in commercial plating it is necessary in the majority of cases that parts of the pieces being plated be stopped off, i. e., covered with a protecting material to prevent plating on them, and the materials that are desirable for stopping-01f do not stand well these high temperatures.
• the chloride baths are quite corrosive and extensive measures are needed to guard the plating tank and accessory apparatus'against their corrosive actions.
• neither the sulfate bath nor the chloride bath, nor a bath of a mixture of the two, as these have been known before, is capable of producing, reliably, and day after day under factory conditions, plates that are generally suitable for surfaces that are subject to severe operating conditions. With each of them there is considerable tendency to oxidation of the bath, and considerable insoluble ferric products are formed. Stillfurther, the iron deposited from either a sulfate or a chloride bath, or a mixture of the two, tends to be brittle.
• the brittleness can be reduced by subsequent-heat treatment, but the results of the heat treatment are not always uniform, and sometimes at least such high temperatures are required to reduce the brittleness to the desired degree that the hardness of the deposit is reduced.
• the adherence of the iron plate to the base or foundation on which it is deposited, the bonding as it is called is too weak and uncertain, when produced under 2,745,806 Patented May 15, 1956 the conditions existing in commercial operations at least", to permit the process to be used where the plate is to be subjected to such high stresses and strains as occur in modern machinery.
• none of the plating processes heretofore known seem able to produce deposits or plates of iron that are useable generally by industry, or at least to do so commercially.
• the present process is one that is practical and well adapted for large scale production in commercial plating plants.
• the plate or deposit of the method or process of the present invention adheres strongly to metal bases (i. e. is well *bonded), and adheres adequately to permit the plate to be used where the stresses are high, except where steps may be taken to prevent strong bonding (e. g. where a plate removable from the base on which it is laid down is desired): means for preventing adhesion or bonding of a plate to the base on which it is laid down are Well known of course.
• the iron plate of this process is dense, tends to be machineable without great difliculty, may be relatively hard or may be relatively soft as desired, and may be brittle or may be relatively ductile as initially laid down (i. e. as plated) depending on the particular form of the process employed, and if too brittle is readily made ductile and tough by heat treatment that does not materially reduce the hardness of the plate.
• machineable mean of course workable by a cutting operation, as on a lathe for example, as distinguished from an abrasive operation such as grinding or honing.
• the plate or deposit of the process is smooth, is substantially free from pits and impurities, has a fine grain structure, and the grain-size need not increase materially with increasing thickness of the plate so that thick plates can be laid down that are substantially homogeneous throughout.
• the deposit or plate of the present process is suitable for substantially any use, including providing machine parts and other articles with surfacings or facings on which machine work must be done, say to bring them to rather exact dimensions, and that are subject to heavy duty, such as, for example, the journal portions of heavy high-speed shafts and the bearings which support such shafts, and members that are subject to severe reciprocating wear conditions, such as the internal walls of engine cylinders.
• the operating temperature of the bath may be relatively low.
• gentle agitation of the bath by pumping or by some other simple form of agitator may be desirable in some instances in order to maintain the bath properly homogeneous and of uniform temperature throughout, as will be understood from general electroplating practices.
• each of the various factors or elements of the process is operable throughout such a relatively wide range of values, and those which tend to change during plating tend to change so slowly, that the operations are readily controlled.
• iron or steel is used for the anode, at least preferably in order that the anode may feed the bath with iron to more or less completely replace the iron taken from the bath to form the plates.
• a sludge forms at the anodes, and to avoid this sludge reaching and perhaps contaminating the plate, I usually interpose a porous partition between the anode and the work or article being plated; preferably to this end I-put a porous bag around the anode in which this anode sludge collects; if more than one anode is used, a bag may be provided for each anode or a group of anodes may be enclosed in a single bag.
• the materials to be used for making up the bath include deleterious metals in substantial quantities, it is best that those materials be purified before being used.
• some foreign metals finding their way into the bath can be removed by exposing the bath to large surfaces of iron metal, such as a quantity of steel wool in a bag suspended in the bath or in a purification column through which the bath is pumped, while electrolysis, ,i. e. working the bath for a time in the same way as plating is done but with dummy cathodes substituted for the work, appears to remove many impurities or foreign metals.
• various organic materials are undesirable in the bath.
• organic impurities can be reduced to harmless concentrations by the use of activated carbon.
• the fiuoborate radical here concerned is, of course, what may be regarded as the radical of borofluoric (tetrafiuoroboric, hydrofiuoboric) acid, HBF4.
• the fluoborate content increases the rate of corrosion of the anode during plating over what is would be otherwise and permits errosion to such an extent that the anode or anodes can supply the bath with all the iron necessary to maintain the iron concentration within the desired range.
• the fiuoborate restrains the precipitation of iron in ferric form to the degree required for the production of an iron plate that is machineable without great difiiculty and that is suitable for heavy duty. Further, the fluoborate improves the efficiency of material used to reduce ferric compounds to ferrous form, and also tends to prevent rapid clogging of the filters. About the same quantity of fluoborate as appropriately restrains precipitation, is suitable for anode corrosion and for the other services of the fluoborate, and where this is not sufficiently true for practical purposes, an adjustment can be made readily.
• the fiuoborate radical BF4 content of the present plating bath should not be less than about ten (10) grams per liter of the bath, a already stated above. With very low concentrations of this radical the plates tend to be rough, and with less than about ten (10) grams per liter there is a material tendency for the precipitation of ferric compounds in undesirable quantities and the rate of anode corrosion tends to be too low for This last is especially true when the variables of the bath are correlated to produce a relatively hard plate. On the other hand, with much more than about one hundred (100) grams of this radical per liter of the bath, the dissolution or corrosion rate of the iron anode becomes so high as to tend to be troublesome.
• ammonium radical, NH4 in the present bath also acts to restrain the production of iron in the ferric condition through atmospheric oxidation of ferrous iron. More importantly however it also causes the plate to be somewhat harder than it would be otherwise. It also tends to give plates fine grain structures. It is used therefore, speaking generally, when a relatively hard plate is needed but not otherwise. For example, a quite hard plate is desired generally for lining the inner walls of engine cylinders, and in such a case I usually use ammonium radical in the bath. The effect of ammonium radical becomes noticeable at a concentration of about three and one-half (3.5) grams per liter of solution, and speaking generally the higher the concentration the harder the plate. However at concentrations of much more than about thirteen and one-half (13.5) grams per liter of solution, the plate produced tends to be highly stressed in its as-plated condition and there is considerable tendency for it to crack.
• the chloride radical, Cl has several effects. It tends to improve the conductivity of the bath, and thereby permits higher current densities for a given voltage and therewith raises the rate at which the plate can be laid down. It also tends to increase the throwing power of the bath, to reduce the tendency to treeing and a nodular form of growth of the plate, to reduce the grain size of the plate, to the production of a plate that is softer than it would be otherwise, and to the production of plates that are tough and ductile in the as-plated condition or that can be made tough and ductile by heating to temperature too low, or for periods too short, to substantially reduce the hardness of the plate.
• the plates would tend to be coarse grained, and brittle in the as-plated condition and generally tend to remain permanently brittle unless heated to such temperature and for such periods as would materially reduce the hardness of the plates.
• ammonium radical When used along with ammonium radical it also tends to relieve the high stresses in the plate and the cracking of the plate which otherwise tend to follow from the ammonium radical, while the ammonium radical tends, contrawise, to offset the tendency of chloride radical to produce a relatively soft plate.
• the quantity of chloride radical should not, preferably, be much less than six and one-half (6.5) grams per liter of solution, and its effects increase with increasing concentrations of the radical.
• chloride radical enlarges noticeably the range of current densities at which it is possible to produce plates that are not too highly stressed for some purposes even with ammonium radical present up to a concentration of about thirteen and one-half (13.5) grams per liter of solution.
• the maximum possible concentration of chloride radical seems to be limited only by the quantity that can be taken into the bath without introducing an undesired substance (for example, a deleterious cation accompanying the chloride), or producing an undesirably high concentration or an undesirably low concentration of some other desired constituent of the bath (for example, too high a concentration of ammonium radical if the chloride is introduced in the form of ammonium chloride). Accordingly as a practical matter I use usually less than about one hundred (100) grams of chloride radical, C1, per liter of solution.
• the sulphate radical, S04 in the reactions of the present baths, when used has a number of effects. E. g. it tends to offset the tendency of chloride radical to make the plate relatively soft, i. e. the sulfate tends to make the plate harder than it would be otherwise. Also sulfate radical tends to increase the conductivity of the bath to a slight extent, and when a large part of the iron of the bath is present as ferrous sulfate, sulfate radical tends to lower the rate of change of the iron to ferric form. Also in coaction with fluoborate radical, sulfate radical tends to raise the secondary anode corrosion rate.
• the iron can be provided in the initial bath in the form of salts (e. g. ferrous fluoborate, ferrous chloride, ferrous sulfate), although this is not necessary.
• concentration of the iron in the bath, calculated as the metal, Fe is not of primary importance. Speaking generally, it may be large or it may be small. From about thirty to about one hundred twenty (120) grams per liter of solution is sufficient.
• the sodium lauryl sulfate in the bath reduces the discharge of spray from the bath, and also helps to prevent the formation of pits in the plate.
• sodium lauryl sulfate other sodium salts of the fatty alcohol sulfates, or mixtures of such salts, or other equivalent surface active agents, may be used as before pointed out. Insofar as the effects of such surface active agents may be deemed harmful, or not desirable or unnecessary in any particular instance, none need be used. Very small quantities are sufiicient for the purposes indicated. About one-teenth (0.1) of a gram per liter of solution produces a material effect.
• the higher the temperature of the bath during the plating operations the higher may be the current density at the cathode, i. e. at the work of article being plated, and accordingly the more rapidly can a plate of a given thickness be produced.
• Temperatures well about 160 F. can be used, and perhaps temperatures as high as up to boiling may be acceptable for some types of plates, but the higher the temperature the largr tends to be the apparent grain-size of the plate; raising the temperature about 5 F. may cause a perceptible increase in the apparent grain size.
• the higher the temperature the higher is the rate of evaporation of the bath and the higher the rate of formation of ferric compounds, and above about 155 F.
• the current density at the anode and the current density at the cathode may differ widely from each other. Further, the current density at the anode can change over a wide range without materially affecting the character of the plate being laid down. This last makes it possible to use an anode continuously or repeatedly unit it has been largely consumed.
• an anode current density higher than about one hundred fifty (150) amperes per square foot at least tends to induce excessive polarization at the anode.
• raising the bath temperature permits raising the anode current density for the same effects.
• an anode current density of. about one hundred twenty amperes per square foot is quite generally satisfactory.
• the cathode current density i. e. the current density at the work or area being plated
• the cathode current density i. e. the current density at the work or area being plated
• the higher the bath temperature the higher may be this current density too, speaking generally, for a plate of a given character.
• the cathode current density i. e. the current density at the work or area being plated
• a cathode current density of ninety (90) amperes per square foot may be satisfactory, while a plate one-eighth 4;) inch thick plated under the same conditions but with even a somewhat lower cathode current density, e. g. eighty (80) amperes per square foot, may crack, either during the plating or days later, and heat treating the latter plate at temperatures in the neighborhood of, say, 600 F., even for long periods does not seem to relieve the stresses sufficiently to assure it against cracking subsequently.
• a cathode current density of forty ,(40) amperes per square foot with the same bath temperature is capable of producing plates one-eighth /s) inch thick and more that are tough and ductile after such heat treatment. and otherwise quite satisfactory even for heavy duty service.
• about one hundred twenty (120) amperes per square foot seem to be about the greatest cathode current density likely to be'desirable, even for the thinnest plates for example, considering also convenience of operation.
• the low limit for the cathode current density, the threshold value for plating as it were is apparently something of the order of about five amperes per square foot.
• cathode current density used the lower will be the rate at which the plate is built up to the thickness it is desired to have. Taking everything into consideration, a cathode current density of about forty (40) amperes per square foot is generally satisfactory for all purposes, and this is the density I now prefer.
• pH values for the plating bath as from about five (5), and more preferably from about four (4), as a maximum for ordinary plating purposes, to about two (2) although it is conceivable that with a bath temperature as high as the boiling point deposits of a sort may be laid down at a pH of, say, one and eight-tenths (1.8), or possibly down to one and one half (1.5).
• pH values within the lower portion of the pH range are more suitable when the bath temperatures are high and vice versa, and high cathode current densities are permissible with high bath temperature accompanied by low pH values while a lower cathode current density is required for low bath temperatures accompanied by high pH values.
• a plate may be produced that has some ductility, at least after a heat treatment of a sort that does not reduce the hardness of the plate materially, while with a bath at room temperature, a pH of from three and onehalf (3.5) to four (4) and a cathode current density even as low as about fifteen amperes per square foot, the resulting plate may be not only hard. but also highly stressed internally and brittle, and
• the softest and most ductile plates in the as-plated condition are obtained from a bath devoid of ammonium radical or sulfate radical (other than such sulfate radical as may be contained in a surface active agent) and having pH value in the neighborhood of three and two-tenths (3.2) to three and one-half (3.5).
• a bath is made initially, it may not have a desired pH, or it may depart from the desired pH value during operations.
• the pH may be raised by treating the bath with steel wool for example (e. g.
• steel wool in a bag can be suspended in the bath until the correction has been made), or by adding, say, ammonium hydroxide, NHiOH, or ferrous carbonate, FeCOa, etc., to the bath. Or the pH can be lowered at any time by adding, say, an appropriate acid, such as sulphuric acid, H2804, or hydrochloric acid, HCl, etc.
• an appropriate acid such as sulphuric acid, H2804, or hydrochloric acid, HCl, etc.
• the iron plates of this process may be relatively soft and ductile, as plated, or may be harder, rather highly stressed internally, and even rather brittle, as plated, depending on the particular radicals and concentrations of the radicals employed in the bath,
• the plate can be made quite tough and ductile and its internal stresses relieved materially by heat treatment.
• the heating may be to temperatures too low to reduce the hardness of the plate materially even when held at the elevated temperature for a considerable period.
• holding the plate (or an article on which a plate has been formed) at about six hundred degrees Fahrenheit (600 F.) for two or three hours is satisfactory for substantially all purposes and brings about substantially no reduction in hardness of the plate.
• this tendency of higher temperatures to reduce the hardness of the plate can be offset by shortening the period at which the plate is held at the higher temperature, and speaking generally, the higher the temperature the shorter need be the period.
• heating to a temperature of about seven hundred and fifty degrees Fahrenheit (750 F.) for a period of fifteen (15) minutes is about the equivalent in result so far as concerns the plate, to heating to six hundred degrees Fahrenheit (600 F.) for a period of three hours.
• the metal on which the plate is formed is one which absorbs hydrogen during the plating operation, i.
• the permissible periods of heating to the higher temperatures if the maximum hardness of the plate is to be achieved may be too short to drive absorbed hydrogen from the article itself, or too short to heat the base article to the proper temperature to drive off its hydrogen, or both.
• heating to the lower temperatures for longer periods, rather than to a higher temperature for a short period is necessary if embrittlement of the underlying base metal is to be avoided.
• heating to about six hundred degrees Fahrenheit (600 F.) for about two (2) to three (3) hours is generally sufiicient for most practical purposes. The manner in which the article with its plate is heated is not of primary importance.
• the oven may be heated to the requisite temperature before the plated article is placed in it. After the article has been held at the elevated temperature for the appropriate time, it can be allowed to cool naturally, say at room temperature.
• aqueous bath or solution of the radicals indicated can be made up in various ways of course, as will be understood, and the manner in which it is formed is not of primary importance excepting that it is desirable that the fluoborate radical be formed or dissolved in the water of the solution in advance of any other constituent of the bath other than, say, such ferrous iron as may accompany the fluoborate radical as a cation.
• the fluoborate radical prevents the formation of insoluble or diificultly soluble ferric compounds that may be formed otherwise.
• the bath is made up of such salts at least,- it best be purified before use, and preferably the bath is made up in a tank other than the plating tank in order to keep the plating tank free of the purifying material and possible precipitates and contaminants of the materials used in making the bath.
• the bath may be made up and purified in the following manner: First, take about one-half /2) the required quantity of water heated to, say, between 120 F.
• sufi'icient steel wool say No. 3 or No. 4 steel wool
• the purpose of adding the steel wool is to precipitate various impurities that may have accompanied the make-up salts, to reduce to the ferrous condition ferric iron that may be'present, and to neutralize acid usually contained in the make-up salts.
• the reaction with the steel wool can be hastened by holding the solution at an elevated temperature, say at from 120 F., to 150 F.; with a temperature of 130 F.
• the reaction will be completed overnight.
• Considerable gassing and a tendency to spray tiny droplets of the solution into the atmosphere accompanies this reaction; to suppress the spray the make-up tank can be covered, or a small quantity of one or more of the surface active agents mentioned above can be added, say about four one-hundredths (.04) gram per liter of the solution.
• the pH of the solution has risen to four (4) or higher, add to the solution from three (3) to five (5) grams per liter of activated carbon and a like quantity of cellulose filter-aid, and stir the solution gently periodically or continuously to-keep the carbon and filter-aid suspended in the solution until impurities accompanying the make-up materials, as these are available on the market usually, are absorbed.
• this treatment removes almost completely any surface-active agent that may have been added to suppress spraying.
• run the solution through a filter to remove the undissolved matter in it.
• dissolve it in a small quantity of hot water and add this solution to the filtered solution.
• add sufficient water to bring upthe whole to the volume the plating bath is to have, and thoroughly mix the whole.
• add concentrated sulphuric acid, H2804 as may be necessary to lower the pH of the bath to the desired value, for example, to within the range from three and threetenths (3.3) to'three and seven-tenths (3.7).
• the bath is then ready to operate. However a few hours of operation or pre-plating electrolysis may improve its performance. It may be noticed that the stirring referred to above, as well as all other stirring or other agitation to which a finished bath may be subjected, is best gentle, i. e. carried on in such a manner as not, ordinarily, to disturb any more than possible any deleterious precipitates that may fall to the bottom of the plating tank, or carry air into the bath because air in the bath promotes the formation of ferric compounds.
• a bath is allowed at any time to stand for any considerable period without plating being done in it, it is well,'before plating is started or resumed, to circulate it for a little time through steel Wool, activated carbon and a filter to remove deleterious substances that may have formed in it.
• it in maintaining a bath in good operating condition, it is well, as before indicated, that it v be filtered and purified either at frequent intervals or continuously during the plating cycles. This can be done by circulating the bath at intervals or continuously during plating through activated carbon and a filter. Water is added from time to time as necessary to maintain the volume of the bath. Under the operating conditions particularly recommended however, there is little loss of the radicals in plating, other than mechanical losses, i. e.
• a deficiency of sulfate radical can be made up by adding ferrous sulfate for example, or should the ferrous sulfate concentration become objectionably high, it can be reduced in manners already pointed out.
• ferrous sulfate is crystallized out however, ammonium radical, if there is any in the bath, may be lost with it. Reduction of ammonium radical concentration lost in this way or otherwise can be made up by, say, the addition of ammonium chloride to the bath.
• Loss of chloride radical can be made up by the addition of, say, ferrous chloride, or more or less made up by the addition of ammonium chloride if the bath is one containing ammonium radical.
• the pH value of the bath tends to change usually during plating, the direction and rate of change being dependent on various factors, such as the relative sizes of the anode and the cathode, and the anode polarization. As it may rise too high, it can be lowered by, for example, adding sulphuric acid to the bath; as it may fall too low, the pH can be raised by, for example, treating the bath with steel Wool; for example, by suspending a mass of steel wool in a porous bag in the bath.
• the pH value of a bath can well be determined and corrected at least daily; While ferric iron tends to form from atmospheric oxidation, on the other hand the plating operations may reduce ferric iron to the ferrous condition; and accordingly in a given bath the ferric iron concentration may tend to reach a certain fixed value. As its value may become too high, it can be reduced by treating the bath with steel wool; for example, in the manner described above for correcting pH value. At least until its net rate of formation and an equilibrium concentration have been determined in a particular bath and under the particular conditions of operating that bath, and an appropriate periodic or continuous correction applied, the ferric iron concentration can well be determined every few days and correction made as frequently. Assuming that the baths are constituted and operated as prescribed above, little or no attention need be paid to the concentration of iron, as metal, in them, and with the attention indicated above they willoperate for indefinitely long periods.
• a good bath for such a plate may consist of the following ingredients in the quantities stated per liter of solution by volume: fluoborate radical calculated as BF4, about forty-five and four-tenths (45.4) grams; chloride radical, Cl, about eighty-nine and twotenths (89.2) grams; iron, Fe, about eighty-four and nine-tenths (84.9) grams; sodium lauryl sulfate or equivalent, about two-tenths (0.2) gram; water sufficient to make one liter of solution by volume.
• fluoborate radical calculated as BF4, about forty-five and four-tenths (45.4) grams
• chloride radical, Cl about eighty-nine and twotenths (89.2) grams
• sodium lauryl sulfate or equivalent about two-tenths (0.2) gram
• water sufficient to make one liter of solution by volume.
• a relatively hard plate e. g. a plate suited for the inner walls of engine cylinders.
• a suitable bath for such a plate is one consisting of the following ingredients in the quantities stated per liter of solution by volume: fiuoborate.
• radical calculated as BF4, about forty-five and fourtenths-(45.4) grams; ammonium radical, NH4, about six and three quarters (6.75) grams; chloride radical, Cl, about thirteen and one-quarter (13.25) grams, sulfate radical, S04, about one hundred thirty-eight and twotenths (138.2) grams; iron, Fe, about ninety-four and nine-tenths (94.9) grams; sodium lauryl sulfate or equivalent, about two-tenths (0.2) gram; water sufiicient to make one (1) liter of solution by volume.
• a plating tank maintain the bath at a temperature between F. and F.
• a process for electrodepositing iron which comprises electrolyzing an aqueous acid solution consisting essentially of ferrous iron, not more than 3 grams per liter of ferric iron, and at least 26 grams per liter of acid radical selected from the group consisting of chloride radical and a combination of chloride and sulphate radicals, in such combination the chloride radical being present in the amount of from 6 /2 to 100 grams per liter, and from to 100 grams per liter of fluoborate radical.
• a process for electrodepositing iron which comprises electrolyzing an aqueous acid solution consisting essentially of ferrous iron, not more than 3 grams per liter of ferric iron, and at least 26.6 grams per liter chloride radical, and from 10 to 100 grams per liter of fiuoborate radical.
• a plating bath for the electrodepositing of iron consisting essentially of an aqueous solution containing per liter of solution about 45 grams of fluoborate radical, about 89 grams of chloride radical, about grams of ferrous iron, not more than 3 grams of ferric iron, and about .2 gram of sodium lauryl sulfate, and water sufiicient to make 1 liter by volume.
• a plating bath for the electrodepositing of iron consisting essentially of an aqueous solution containing per liter of solution about 45 grams of fluoborate radical, about 6.75 grams of ammonium radical, about 13.25 grams of chloride radical, about 138 grams of sulfate radical, about grams of ferrous iron, not more than 3 grams of ferric iron, about .2 gram of sodium lauryl sulfate, and water suflficient to make 1 liter of solution by volume.
• the process of electrodepositing iron comprising electrolyzing an aqueous acid solution as defined in claim 13, wherein the temperature of the solution is substan tially maintained between 135 F. and 150 F., the pH value of the solution being maintained between 3 and 4, the current density at the area being plated being maintained at about 40 amperes per square foot, and the current density at the anode being maintained at less than amperes per square foot.
• the process for electrodepositing iron comprising electrolyzing an aqueous acid solution as defined in claim 14, wherein the temperature of the solution is substantially maintained between F. and F., the pH value of the solution being maintained between 3 and 4, the current density at the area being plated being maintained at about 40 amperes per square foot, and the current density at the anode being maintained at less than 100 amperes per square foot.

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• 0
  • NL NLAANVRAGE7410367,B patent/NL180512B/xx unknown
  • BE BE522608D patent/BE522608A/xx unknown
  • DE DENDAT1048755D patent/DE1048755B/de active Pending
  • NL NL100872D patent/NL100872C/xx active
• 1953
  • 1953-01-16 US US331725A patent/US2745800A/en not_active Expired - Lifetime
  • 1953-08-28 FR FR1146512D patent/FR1146512A/fr not_active Expired
  • 1953-09-16 CH CH327296D patent/CH327296A/de unknown
  • 1953-10-14 ES ES0211670A patent/ES211670A1/es not_active Expired
• 1954
  • 1954-01-15 GB GB1298/54A patent/GB755635A/en not_active Expired

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