Chromium Plating Bath Research Articles

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クロムメッキ液中のFの自動制御

クロムメッキ液中のFの自動制御

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クロムメッキ液中の硫酸の分析

The values of analysis of sulfuric acid in chromium plating baths, especially in a high concentrated bath containing fluosilicic acid, were given with the results of higher than true values. The measuring process was by centrifugal precipitation method as follows: the precipitate of barium sulfate, which had been obtained by precipitating sulfuric acid with barium chloride, was settled in a measuring tube by a centrifugal separator and the volume of deposits was measured.It was found that these higher values of analysis were due to the deposition of precipitates of barium chromate and barium hexafluosilicate together with barium sulfate; and the values depended on the contents of chromium (VI) oxide and potassium hexafluosilicate as well as that of sulfuric acid in the plating bath. Therefore, the values of analysis of sulfuric acid by centrifugal precipitation method was apparently observed with higher results by the higher contents of deposits other than barium sulfate.It was further found that the total volume of these mixed precipitates also depended on the chemical conditions of the bath, besides the contents of constituents; and considerably slight errors of values were observed when the bath reached a chemically stable state.

クロムメッキの浴電圧

The bath voltages of chromium plating were studied at various concentrations of CrO3 and under various plating conditions.The following results were obtained:(1) A higher bath voltage was required for a CrO3 bath of lower concentration. When the voltage of CrO3 250g/l bath was taken as the standard, the voltage required was about 2 times for 50g/l bath, about 4 times for 25g/l bath, and about 6 times for 12.5g/l bath at 1l beaker test.(2) Assuming that the hypothetical value of resistance voltage of chromium plating bath calculated from its conductivity is Eohm and the real value is E'ohm, the following relation was derived:k=Eohm/E'ohm=K/K'=(2.4±0.2)l1/3where K and K': Hypothetical and real cell constants, respectivelyl: Distance between electrodes(3) Accordingly, k was called cell constant ratio.

クロムメッキ浴の電流効率におよぼす分極特性の影響について

The effects of polarization characteristics on current efficiency of chromium plating bath were studied and the following results were obtained:1) In the solution containing fluorides, the electrode reaction for electrodeposition of metallic chromium plating was retarded, and the intermediate products in cathodic reduction such as black chromium plating were likely to be deposited so that the increase of current efficiency was inhibited.2) In the solution containing fluorides, the electrode reaction for electrodeposition of metallic chromium plating was more detarded with the drop of the bath temperature, and the deposition of intermediate products in cathodic reduction was likely to be promoted so that the increase of current efficiency was inhibited.3) In the solution containing sulfuric acid, the current efficiency was greatly increased with the drop of the bath temperature.4) In the solution containing the mixture of sulfuric acid and fluorides, the current efficiency of the mixed solution was likely to make a compromise between the both efficiencies of each of solutions containing sulfuric acid and fluorides, respectively.

クロムメッキの電流効率

The current efficiency for chromium plating from low concentration CrO3 baths was measured and the following results were obtained.(1) The highest current efficiency of 22% was obtained in a chromium plating bath of CrO3 50g/l at 50Amp/dm2 and 55°C containing H2SO4 0.6-1.5g/l and Na2SiF6 1.0g/l as catalyzers.(2) However, the above bath composition did not correspond with the composition for highest brightness and covering power.(3) The current efficiency of the low concentration chromium bath containing CrO3 50g/l, H2SO4 0.5g/l, and Na2 SiF6 0.5g/l was between that of Sargent Bath and that of fluorosilicate bath under various plating conditions.

クロムメッキ浴の陰極分極特性

The cathodic polarization characteristics of chromium plating baths, to which various anions had been added, were measured by potentiostatic method for the investigation of their cathodic reactions.The following results were obtained:1) The cathodic reaction of black chromium plating bath in the potential range of the 4 th branch consisted of electrodeposition of hydrated chromium oxide film and black chromium plating as seen in pure chromic acid solution.2) Metallic chromium was directly deposited from the stage of chromate film without parsing through the stages of hydrated chromium oxide film and black chromium plating.3) The deposition process and properties of the deposits were varied according to kind and amount of anions added to the chromium plating bath; and also they depended upon the conditions of electrolysis.

クロムメッキ液中の3価クロムおよび鉄の分析

クロムメッキ液中の3価クロムおよび鉄の分析

クロム-モリブデン合金メッキ層のカタサと耐摩耗性

Chromium-molybdenum alloy electrodeposits were obtained from the Sargent's chromium plating bath, to which molybdenum salt had been added, under the similar plating conditions to those of the Sargent bath with no addition of the salt. Chromium-molybdenum alloy deposits (containing more than 3% of molybdenum) of about 50μ in thickness gave hardness of Hv 1, 000-1, 300, which was higher than that of the conventional hard chromium plating, and their abrasion resistance was also 2-3 times as high as that of the latter.The relation between the molybdenum content of these deposits and the hardness or the amount of abrasion could be expressed by the following equations, respectively.Hardness (Hv)=95.8x+715Amount of abrasion (mg)=-3.8x+33.3where x=Molybdenum content of the deposits (%)As shown in the above equations, the hardness increased about 100Hv and the amount of abrasion decreased about 4mg with the increase in 1% of molybdenum content in the deposits.

ケイフッ化物系クロムメッキ浴に関する二, 三の実験

A chromium plating bath principally composed of chromic anhydride with a large content of fluosilicate (K2SiF6 of 3-55g/l) was studied with respect to the current density.The following results were obtained:(1) The solubility of potassium fluosilicate in chromic acid solution was increased by means of preliminary electrolysis.(2) In the electrolysis for an extremely short time, the current efficiency was always higher than that of the Sargent Bath. However, the efficiency was above 50% on the side of higher temperature and higher current density.When the time for electrolysis was longer, it was difficult to maintain such a high current efficiency, but the efficiency was likely to be higher than that of the Sargent Bath.(3) This plating had a wider range of brightness than the Sargent Bath. Burnt deposits were not produced in this plating even under a high current density as 200amp./dm2.

各種素地金属のクロムメッキ浴中での陰極腐食

Cathodic corrosion in chromium plating baths was observed for several metals such as iron and copper and also on the surface of bright or non-bright nickel plating.The test solutions were(a) Aqueous solution of single chromic acid(b) Two sorts of aqueous solutions containing each one of sulfuric and fluosilicic acids.The results obtained were as follows:(1) The potential region for cathodic corrosion in chromium plating baths corresponded with that for reduction of Cr6+→Cr3+ in chromium electrode reaction.(2) The corrosion velocities of substrate metals were increased with the increase in concentrations of catalytic anions to be added.(3) Bright nickel plating was more corroded than other metals in the bath containing sulfuric acid. On the other hand, both of iron and bright nickel plating were remarkably corroded in the bath containing fluosilicic acid.(4) When the pulsation of current wave form of power source for rectified current for the plating was more rippled, the cathodic corrosion was more promoted.

The behaviour of the lead anode in chromium-plating baths

Possible reactions accounting for the oxidation of the lead anode in CrO 3 solutions are formulated and their theoretical potentials calculated from free energy data. The implications of these equations are discussed and certain conclusions are drawn. The passivation of lead in CrO 3 solutions of different concentrations has been studied using both the cyclic galvanostatic and potentiostatic techniques. Oxidation with constant current gives rise to potential/time curves having four distinct arrests. These correspond to the consecutive formation of PbO, Pb(OH) 2, PbCrO 4 and PbO 2 before the evolution of oxygen. The same conclusion is obtained from forward potentiostatic experiments in which polarization is directed towards positive potentials. A fifth oxidation arrest is recorded in backward potentiostatic polarization curves and is ascribed to the oxidation of PbO and Pb(OH) 2 to a higher valent lead oxide, PbO n, where 1 < n < 2. Anode decay curves obtained after current interruption show two arrests at potentials very near to those of the systems PbO n/PbO 2 and Pb/PbCrO 4 under the prevailing conditions. Following a change in slope at ca +0·85 V, the potential tends ultimately to that of the Pb/Pb(OH) 2 system. Sulphate additions do not affect the shape of the decay curves and it is concluded that the behaviour of the lead anode in chromium-plating baths is practically the same as that in pure chromic acid solutions. X-ray diffraction patterns of material formed upon oxidizing lead in CrO 3 solutions show characteristic d-lines for PbO, PbCrO 4 and PbO 2.

ケイフッ酸系黒色クロムメッキ浴の検討

Various kinds of black chromium plating baths have hitherto been reported in literatures. However, the bath composition is not yet established in actual practice at present. Physical and chemical properties of these deposits and the mechanism of their coloration are not also thoroughly researched.The authors examined black chromium plating baths in the literatures and found out that the bath containing hydrogen silicofluoride gave the plating with least powdery deposit and strongest adhesion; but its unevenness in color was most enormous among the platings from these kinds of baths.Plating conditions for the most even black color were researched and the following results were obtained.(1) The optimum composition of bath and plating conditions were as follows:CrO3 300g/l Bath temperature above 10°CH2SiF6 above 1g/l DK 30-50amp./dm2(2) Sulfuric acid should completely by removed, because its presence limited the range of black color. Hydrogen silicofluoride should be supplied to the bath according to its electrolytic comsumption.(3) Higher throwing power was obtained by coating the substrate with copper or nickel, and then, immediately plating black chromium on that coating.

ケイフッ酸系黒色クロムメッキ浴の改良

Addition of nitric ions to the black chromium plating bath containing hydrogen silicofluoride was most effective for blackness of platings as described in the previous report (Part 2). Then, platings from the bath containing hydrogen silicofluoride and nitric ions were studied and it was observed that the bath was very stable and gave platings, having extremely good characteristics.The results obtained were as follows.(1) Thermal resistance: Resistant at 500°C for 5hr. on nickel plated substrate.(2) Adhesion: Satisfactory results in tape-test and 180° bending test.(3) Wear resistance: Lower than that of nickel platings, and much lower than that of chromium platings (equivalent to a few divisions of the latter).(4) Hardness: Lower than that of nickel platings.(5) Adhesion of paints: Satisfactory results for some kinds of paints.(6) Corrosion resistance: No rust was observed in continuous salt-spray test for 64hr.

ケイフッ酸系黒色クロムメッキ浴の添加剤

Bath composition and plating conditions of black chromium plating bath containing hydrogen silicofluoride were given in the previous report (Part 1). The addition of hydrogen silicofluoride to this bath was intended to give higher blackness and evenness in coloration but these effects were not com- plete in the results.Then, effects of further addition agents to the above bath were studied and found that the addition of nitric and formic ions among acid radicals and barium ion among metallic ions was most effective for color in platings; and no other agents were effective.Bath composition and plating conditions for giving the most even and black coloration were as follows:Cr2O3……300g/lH2SiF6……1g/lAddition agents……3-5g/lBath temperature……above 10°CDk……30-50amp./dm2

Rapid analysis of plating baths by a direct-reading thermometric method

Methods are described for the rapid analysis of plating baths by measurement of the heat evolved in a reaction between the reagent and the component to be determined. The novel feature of the method is the use of reagents which have zero heat of mixing, so that the temperature scale can be directly calibrated in concentration units for a particular determination. A determination takes only 5 min and the precision is equal to that of the classical methods. Procedures are given for the analysis of nickel and chromium plating baths.

EDTA滴定によるクロムメッキ液中の3価クロムの定量

EDTA滴定によるクロムメッキ液中の3価クロムの定量

クロムメッキ浴の種類と耐食性

An acetice acid salt spray test was carried out on the copper-nickel-chromium plated steel panels with thicker chromium layer in three types of chromium plating bath, each of which differed in tendency to cracking. From the corrosion data fallowing conclusions were obtained.i) Thicker chromium plated in high concentrated crack-free chromium bath consistently increases corrosion resistance. However, it is feared that in the actual outdoor exposure the visible cracks induced by residual tensile stress in the chromium layer may appear along the high current density areas of plated parts.ii) Thicker chromium plated in micro-cracked chromium plating bath containing fluoride also seems to be very effective in increasing corrosion resistance.In this case the stress is released by micro-cracking, visible macro-cracking does not occur even in the high current density areas.

装飾クロムメッキの耐食性に及ぼすクロムメッキの影響

The effects of chromium layer on the corrosion protection of decorative chromium plated steel panels were investigated. In this series of corrosion study the Sargent type chromium plating baths were used with varied chromic acid concentrations.Accelerrated corrosion test of the nickel-chromium plated steel panels showed that the effect of increasing chromium thickness is greatly changed with the type of underlying nickel layer. Thus the plated panel with underlayer of Ni-Cr alloy of relatively rich ductility but high internal tensile stress loses corrosion resistance with increasing chromium thickness. This is clearly due to the crazing of nickel layer along the cracks of outer chromium layer, although the tendancy decreases with an increase of chromic acid concentration in the chromium plating bath.On the contrary, the plated panels with the underlayer of levelling bright nickel showed little deterioration with chromium thickness increase, even in the low concentrated chromium bath.Furthermore in this case, increase of chromium thickness by using high concentrated chromium plating bath increases corrosion resistance.Then, the corrosion resistance test of copper-nickel-chromium layer of the same thickness as the above nickel chromium plating was carried out, and is found that in the case of Ni-Cr alloy as intermediate layer, the presence of copper layer depresses deteriorating effect caused by the increase of chromium thickness.