DE1496966A1 - Plating process - Google Patents

Description

Plating Process The invention relates to an improved one Process for depositing or applying a shiny or light-colored finish made of nickel or a nickel-phosphorus alloy onto a metal object or a with a metal coating provided with the plating without jam of brightening agents or

; Yivalizing agents such as pyrophosphate, phosphonic acid or ## hosphinic acid, is obtained. The technique of electroplating metal objects by immersing the workpiece in a solution of a salt, the plating metal and passing an electric current through the solution from an anode preferably consisting of the plating metal is known. The technique of "electraless" plating by immersion of a metal object in a bath containing a salt of the ni The metal to be beaten and contains an alkaline hypophosphite, whereby no electric current is impressed from an external source, is also known. In this case, pure nickel is beaten on a metal piece of metal that is immersed in a bath containing a nickel and a relative 3-ratio, low concentration of hypophosphite (sodium , Ammonium or potassium).

According to the invention, a weak electrical current is a direct current or a --echselstrom can be used to beschlaunigen to-ÖAS deposition of nickel or a nickel-phosphorus alloy e- * nem metal workpiece which is immersed in a bath containing a nickel salt and a hypophosphite, preferably sodium hypophosphite. Since an electrical - "., Rom is used, this method can nevertheless be called the" electrical non-electrical "method, the electrical current used for plating in the usual way is too weak Electro-non-electrical processes have a crystalline character, whereas it is assumed that the precipitates produced by the non-electrical process are amorphous.The electrical-non-electrical coating is less porous and more resistant to tarnishing than the non-electrical coating Coating. An important feature of the electric-n'Lcf # t- EIF-ktr-4-chrn procedure used weak current consists in that it increases the working life of the solution and has a retarding or non-driving effect by preventing the sodium hypophosphite from causing spontaneous decomposition of the dades.

If the n-3 standing lines are followed, the result is a shiny or light-colored plating, the thickness of which is partially enclosed b # w. enclosed areas, for example deep crevices or inside coves is essentially the same.

including the precipitation of nickel or a nickel phosphorus alloy on the wark piece to exhaust the nickel salt and hypophosphite in the bath leads, the restoration of the solution required $ either by periodic eats £ '- adding a nickel compound and --Ines hyfiofjhosphite or by circulating it again the electrolyte through an auxiliary tank by means of a device as it is in the Drawing is shown for example.

Purposes and advantages of the invention emerge from the following description, in which the invention is explained by way of example with reference to the drawing. Fig. 1 is a schematic view of an apparatus for use with an impressed direct current; Fig. 2 is a similar view of an apparatus for use with an alternating current.

The device shown in FIG. 1 has a main working tank 10 which contains a quantity 12 of an electrolyte into which one or more Katuden work pieces, 14 and one or more nickel electrodes 16 are immersed. A suitable direct current jellyfish 9, for example a battery 20, is connected to the anodes and the cathodes in the tank 10 , preferably via an automatic switching device 22 in order to switch the current on and off periodically. For example, the switch 22 can be set so that the current is switched on for 30 seconds and then switched off for 30 seconds, or it can be set in such a way that switch-on periods and switch-off periods of different durations are maintained. The wetted areas of the work pieces 14 should be much larger than those of the anodes 16 and should, for example, never have a size ratio of 10 to 1 , so that the anodes 16 have a relatively high current density.

An auxiliary tank 30 is provided to keep the electrolyte in the tank 10 at its strength or concentration. Electrolyte fluid from the main tenk 10 flows by gravity into a quantity 32 into the! Tank 30 through pipe 34. Nickel anades 36 are in the set 32 dissolved in order to increase the nickel content in it. 9 whereby the Dissolving the nickel is supported by direct current from a suitable source, for example a battery 38 , the terminals are connected to the nickel anodes 36 and a copper cathode 40, which is converted into a -10% solution of sulphurous acid or hydrochloric acid in a porous vessel 42 is or are immersed. The enriched electrolyte in the quantity 32 is pumped back to the main tank 10 via a filter 44 and connecting pipes by means of a pump 46 which is driven by some suitable device, not shown. The nickel anodes 36 in the auxiliary tank 30 constantly replenish the nickel content of the plating bath. In order to replenish the hypophore content when it is used up, fresh hypophore solution can be added to the quantities 32 at certain time intervals Alternating current is used, as described below, workpieces 14 are used as both electrodes, the workpieces being selected so that the wetted areas of the two electrodes are essentially equal to one another , This leads to-essentially the same. metal deposits-on the electrodes * '.- A Rheastat 50 and a'Transformator-52 can be used to: control the current supplied to the plating bath. When carrying out the invention, the following ingredients are for - the bath # w-esentlicht Wanigetensein-Nickelnelz - (for example, 9 dqs sulfate and / or the chloride) a hypophosphite (preferably sodium) Ein-Zittetaalz (for example Na, triumzitr.a: t.) V TO keep the nickel layer in solution, For example, the following formula can be used, nickel sulfate (and /. Or chloride) -: 30 gr .. yes liter sodium citrate 30 gr: per liter Natriumhyp-aphosphit 15 gr per liter of the metal salts of the citrate and the hypophosphite are accordingly in the weight ratios 2 1 2 t 1 yet.. If a low-voltage current is sent through dop electrolytes (097 'to 3 Amp. Yes 929 cm 2 cathode area a.he.he), the process for temperatures of the electrolyte down to 490C .. effective »One Nickel anode should be used with a surface area no more than one tenth of the surface area of the cathode, the relatively high anode current density serving to prevent nickel from being deposited on the anode from solution.

Currents that are weaker than 097 amps per 929 cm 2 cathode area have a certain effect on the extent or the speed and the quality of the -deposited metal ', but the advantage is "the self-from #, - the use a current density of less than, -.> 9.7 Amp4-. gives .-. negligible * The effective range of current densities for the realization of the invention - goes approximately from 2 0.7-bi.a-3-Amp. yes 929 cm cathode area, wo4u1..a4n-S of about-: 2 Amp, .- an Opt-, Imum- is ** One of the factors that determine the current density in any case # Is the pressure on the electrodes voltage. It has been found that an impressed voltage of about l »5 volts erforderlich.ist to overcome the electrical potential # which is present in the" not "elektrischeit (alectrolose) 11Plattierungszellen * the invention is described below with reference to a test example To explain in more detail the effectiveness of a Niederäspannungestramen with an autokatolyt To demonstrate a bath at a temperature of 49 0 C , two solutions were prepared in accordance with the formula given above using the method. -take # that there was no hypophite in one. A direct current of 0.7 amps per 929: cm 2 cathode area was applied. The results were as follows Solution - current result Without hypophosphite- 097 Amp. No precipitation with hypophosphite 0 no precipitate with hypophosphite 027 Amp. shinier or lighter colored continuous coating Similar results were obtained using AC current of 097 amps, g where-in. in this case the anode and the cathode were workpieces. From this - en tests results Examples sichg that the process no electroplating -is (in the Sinny-like is used H'andel-this term in), but a method in which s the desired results of the threshold conditions are obtained which is required for electroplating. The weak current applied (direct current or alternating current) obviously supports the gelvanic potential of the hypophoaphite and activates it in order to perform the function that it could not perform without such support energy.

The - inconsistency in the thickness of the plating deposited on a workpiece - which has deep recesses - is improved by - periodically interrupting the applied current. For example, the current can be switched on and off in periods of a few seconds, and the switch-on periods need not be of the same length as the 9 switch-off periods. For example, a brass tube was made using an intermittent current of 3.0 amps per 929 cm 2 of cathode area at a temperature of about 82-C, the tube being 1.8 m in length and 6.3 in diameter -mm had a pure, shiny or light nickel coating on the inside andt- he outside without using an internal electrode. The - .. pipe was first cleaned in the usual way with an alkaline cleaning agent, followed by a fresh water rinse, a short immersion in acid (1 part nitric acid »2 parts sulfuric acid) and a second rinse. Tube was then immersed on copper wires in a "non-electric" bath and a DC current of 3 amps was applied for a few minutes, after which current was applied intermittently (switched on for 2 seconds, switched off for 2 seconds) for one hour Continuous coating of nickel or nickel phosphor was deposited on the entire inner surface and the entire outer surface of the tube. When a thicker inner coating is desired, a flow of the electrolyte through the tube should be promoted or pre-strengthened in order to flush out used electrolyte and thereby 'To ensure the evenness of the precipitation.

The effectiveness of interrupting the current can be compared with the theory It is explained closely that the cat, hade, .the. ana-de and the electrolyte form a cell # which are charged with special electrical energy by the imposed current can be. This particular accumulated charge of energy is quickly discharged when the electricity from the outside is switched off.

The particular substances mentioned above are usually preferred because they are commercially available. However, other substances can be used with or in place of the substances mentioned. Accordingly, nickel ammonia sulfate, nickel citrate or nickel addition are effective in practicing the invention. Similar salts of cobalt (including the hlorids and sulfates) may be completely or partially replacing the above used Nickelaalze * When a cobalt salt is mixed with a nickel salt, which deposited metal is a Nickelphoapharlegierung.

Sodium hypophosphite is the most commercially available hypophosphite, but the electrically non-electrical process can be carried out if this salt is partially or completely replaced by ammonium hypophosphite-potassium hypophosphite, calcium hypophosphite-berilum hypophosphite, or phosphorous acid Care must be taken that the ratio of nickel ions to hypophosphite ions is kept essentially constant.

The concentration of the electrolyte bath as described above and in accordance with the case given above. The bath is not critical, but the bath is effective if the solution is concentrated to a multiple of the stated strength or is diluted to half its original strength (for example by pre-evaporation).

By the 11electrical-nonelectrical method according to the above description, a shiny or '. bright nickel coating creates without the help of chemical "hallucinations" and without instability the conditions that are common in * non-electrical "processes. The method described is furthermore not sensitive to special conditions but can be used at temperatures of 49 ° C. up to the boiling point and with a pH value of 290 to 9.0, the preferred value being about 4.5. The process is cheap and convenient to control, and the un-beaten coatings adhere very well and are brilliantly continuous and evenly distributed on bases of any metal including parts made of aluminum or alloys — but only zinc or cadmium or magnasium alloys .

Claims (2)

Patent claims 1, a method for depositing a coating on a metal surface, characterized in that the surface to be coated is immersed as a cathode in an electrolyte which contains an aqueous solution of at least one nickel layer such as nickel sulfate, nickel chloride, nickel ammonium sulfate, nickel citrate and nickel acetate, and also sodium citrate and at least one hypophosphite such as sodium hypophosphite, ammonium hypophosphite, potassium hypophosphite, calcium hypophosphite or barium hypophosphite anthältp where nickel salts sodium citrate and hypophosphite are used in approximate weight ratios of 2: 2: 1, and that an anode is immersed in the electr, alyte direct current of 0.7 and a up to 3.0 Amp. per 929 cm 2 wetted cathode area is sent through your electrolyte and the electrodes. 2. Method according to claim 19, characterized in that sodium hypophosphite is used as the hypophosphite. - 3. The method according to claim 2, characterized in that: nickel sulfate and nickel chloride are used as nickel salts and a solution of these salts in the ratio of 30 gr. Nickel sulfate and nickel chloride 30 gr. Sodium citrate and 15 gr. Sodium hypophosphite as the electrolyte per liter of water is used. 4. Method according to one of Claims 1 to 3, characterized in that a wetted area of the anode is used which is approximately one tenth that of the cathode. 5. The method according to any one of claims 1 to 49 da. characterized in that the current is interrupted at frequent time intervals. 6. The method according to any one of claims 1 to 59, characterized in that direct current is used as the current. 7 * Method according to one of Claims 1 to 39, characterized in that alternating current is used as the current and that anode and cathode with approximately the same wetted areas are used.