FI63785C - LOESNING INNEHAOLLANDE ETT KROM (III) TIOCYANATKOMPLEX FOER ELKTROPLAETERING AV KROM ELLER EN KROMLEGERING - Google Patents

Description

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England-England (GB) 2U73U / 77 (71) International Business Machines Corporation, Armonk, Nev York 1050U, USA (72) Donald John Barclay, Battery, Winchester, William Morris Morgan,

Eastleigh, Hampshire, England-England (GB) (TU) Oy Kolster Ah (5U) Chromium (ill) thiocyanate complex solution for electroplating chromium or chromium alloy - Lösning innehällande ett chromium (III)

The invention relates to a solution containing a chromium (III) thiocyanate complex used for electroplating chromium or a chromium alloy. BG patent 1 431 639 describes an electroplating solution of chromium or chromium alloy in which the chromium source is an aqueous solution of a chromium (III) thiocyanate complex, and a method for plating a chromium or chromium-containing alloy by conducting an electroplating current at the anode and cathode.

The preferred complex disclosed in the above-mentioned patent publication is a chromium (III) aquothiocyanate complex prepared by equilibrating with chromium perchlorate and sodium thiocyanate in aqueous solution. The general formula of the complex thus formed is ((H 2 O) 6_nCr (III) (NCS) n) (3 "n), where n is 1 to 6 2 63785

It can be seen that lower index numbers are always positive, while upper index numbers can be positive, negative, or zero.

Previously, an electro-plating solution of chromium or chromium alloy has been disclosed, wherein the chromium source is an aqueous solution containing a chromium (III) thiocyanate complex having at least one ligand other than thiocyanate or water in the inner coordination space of the complex. It can be seen that the chromium (III) substances in solution are octahedral and have six ligands attached to the chromium atom. These ligands form and fill an inner coordination space for the chromium atom and are inert to the extent that they exchange very slowly with unbound ligands in solution. Thus, for example, the reaction (Cr (H 2 O) 5 (NCS)) + 2 (NCS) "-> (Cr (H 2 O) 5 (NCS)) + 2 + (NCS) _ very slow. The slowness of reactions of this nature complicates the chromium (III ) chemistry and makes equilibration necessary at high temperatures, see also Basolo and Pearson, "Mechanism of Inorganic Reactions: A Study of Metal Complexes in Solution," published by Wiley.

The linear thiocyanate anion NCS has unique catalytic properties. It is able to form a coordination bond with metal ions through its nitrogen atom and to the metal with its sulfur atom, and its electron density is largely localized around these three atoms.

The thiocyanate anion is thought to catalyze the electron transfer reaction:

Cr (III) + 3e ~ -> Cr (0) by forming multiligand bridges between the thiocyanate-Cr (III) complex and the cathode surface. The electroactive intermediate can be labeled as follows:

Cr (III) - NCS - M

wherein M is the metal surface of the cathode Cr (0) when the initial single layer of chromium is plated. The "hard" nitrogen forms a coordination bond with the Ce (III) ion and the "soft" sulfur with the metal surface M of the cathode. Multiligand crosslinking with thiocyanate in the electrochemical oxidation of chromium (II) using mercury electrodes is described in Inorganic Chemistry 9, 1024 (1970).

3,63785

A particularly preferred electroplating solution of chromium or chromium alloy, as previously proposed, is one in which the chromium source is an aqueous solution of a chromium (III) sulfothiocyanate complex. More specifically, a chromium (III) sulfatothiocyanate complex is formed from a chromium (III) thiocyanate complex of the formula ((Η, Ο), n Cr (III) (SO.) (NCS) 3-2m-n 2 6-2m-n 4 mn. of a mixed complex in which m is 0, 1 or 2 and n is at least 1, but 2m + n is not greater than 6.

This aqueous solution of chromium (III) sulfothiocyanate complex is prepared by equilibrating an aqueous solution of chromium sulfate (CR2 (SO2) ^ ♦ 151 ^ 0) and sodium or potassium thiocyanate.

An electroplating solution of chromium or chromium alloy has also been previously disclosed, wherein the chromium source is an aqueous solution of a chromium (III) chlorothiocyanate complex. More specifically, the chromium (III) chlorothiocyanate complex consists of a chromium (III) thiocyanate complex of the formula << H2 °> 6-mn Cr (III> C1m (NCS) n> 3-mn, where m is zero or positive and n is at least 1, but m + n is not greater than 6. This aqueous solution of chromium (III) chlorothiocyanate complex can be prepared by equilibrating an aqueous solution of chromium chloride (Cr Cl 3.6H 2 O) and sodium or potassium thiocyanate.

Chromium is commercially plated with an aqueous chromic acid bath made of chromium oxide (CrO 2) and sulfuric acid. Such baths in which chromium is hexavalent pose a significant health hazard due to the formation of chromic acid fumes. In addition, the appearance of the resulting coatings is unsatisfactorily turbid if the plating current is interrupted for any reason. In addition, detachment of precipitated chromium occurs. Thus, the interruption of the plating current can cause considerable losses and it is difficult to perform cylindrical chromium plating except as very thin chromium coatings and to guarantee the coverage of the coating and its strong adhesion to the objects to be coated.

Additional disadvantages of chromic acid plating baths continue to be the low precipitation rate due to low efficiency, the limited ability to obtain uniform coatings on uneven objects, and the limited ability to obtain uniform coatings over a wider area of 4,637,885. Precipitation of metals at high current density sites such as edges is greater and "combustion" occurs under certain conditions. It should also be noted that the chromic acid plating bath has a very high chromium content, 100-200 g / l. However, because chromium salts are relatively expensive, chromium concentrations should be kept as low as possible to minimize bath manufacturing costs and reduce "bath shift" with the workpiece. Reducing bath displacement losses in the manufacture of decorative chrome coatings is important because the displacement can be as much as six or more times the weight of the plated metal combined.

Several experiments have been performed on the use of trivalent chromium salts in the precipitation of chromium or chromium-containing alloys.

GB Patent 1,144,913 describes a chromium plating solution containing chromium chloride in a dipolar, proton neutral solvent (such as dimethylformamide) and water. GB Patent 1,333,714 discloses another solution containing Chromium ammonium sulfate in a dipolar proton-neutral solvent and water.

However, such solutions have limitations that prevent their use in industry. Objects with a particularly complex shape cannot be plated satisfactorily, and the use of a dipolar, proton-neutral solvent requires a power supply unit that can provide a voltage of up to 20 volts. Reducing the amount of dipolar, proton-neutral solvent causes an unstable bath. In addition, the solutions are relatively expensive. Plating solutions also contain 0.5-1.5 M chromium ions, which is a relatively high concentration. There are also health risks associated with the use of dimethylformamide.

U.S. Patent No. 3,917,517 describes a cran or crude alloy plating solution consisting of chromium chloride or sulfate with hypophosphite ions in addition to the dipolar, proton neutral solvents or their solvents disclosed in both of the aforementioned GB patents. The addition of hypophosphite ions to a diatomaceous earth chromium plating solution is reported to "reduce or eliminate" a number of disadvantages associated with dipolar solutions containing proton-neutral solvents. The preferred plating temperature is reported to be 25 ° to 5 ° C with a maximum of 35 ° C for the chromium chloride solution and 55 ° C for the chromium sulphate solution, the chromium concentrations being reported to be 0.5-1.75 micrometers per minute, corresponding to the best speeds achieved with hexavalent chromic acid plating solutions. preferably 0.7-1.3 M.

DE Patents 2,612,443 and 2,612,444 disclose an aqueous plating solution containing chromium sulfate with hypophosphate or glycine ions as "weak complexing agents".

The solutions disclosed in these patents further require chloride or fluoride ions, respectively. The maximum plating speed was about 0.15 micrometers per minute and the preferred temperature range was about 25-35 ° C. The preferred chromium content for decorative plating is reported to be 1 M.

DE 2 550 615 also describes a trivalent electroplating solution containing chromium sulphate or chloride, ammonium sulphate or chloride, boric acid and in addition numerous alternative "weak complexing agents" including glycine ions and hypophosphate ions. However, in the examples, the concentrations of chromium ions and the concentrations of additional buffer materials are relatively high.

GB Patents 1,455,580 and 1,455,841 relate to another procedure which has been used to precipitate chromium from aqueous solutions of trivalent salts. In these patents, the chromium source is chromium chloride, chromium sulfate or chromium fluoride. In addition, bromide, ammonium and formate or acetate ions are noted to be essential. Precipitation rates are reported to be 0.15 micrometers per minute and temperatures in the range of 15-30 ° C. Chromium concentrations range from 0.1 to 1.2 M, with a recommended concentration of 0.4 M chromium ions.

The present invention relates to a solution containing a chromium (III) thiocyanate complex for electroplating chromium or a chromium alloy. The solution according to the invention is characterized in that the chromium source of the solution consists of a balanced aqueous solution of said chromium (III) thiocyanate complex and a buffering agent, preferably an amino acid, formate or acetate, in which the buffering agent forms one of the ligands of the complex.

63785

The buffering agent is preferably an amino acid such as glycine, Ni 2 Cl 2 COOH. Amino acids are strong buffers, but they can also form complexes with metal ions such as chromium (III) ions during equilibration by coordination of their nitrogen or oxygen atoms. Thus, an amino acid-chromium (III) -thiocyanate complex mixture is obtained by equilibrating the amino acid with a chromium (III) -thiocyanate complex.

The electroplating solution according to the invention has been found in practice to have a number of very advantageous properties which improve the catalytic properties of the chromium (II) thiocyanate plating solutions described above. First, the plating range can be expanded; glossy deposits have been obtained in the range of 10-1000 + mA / cm. Second, plating speeds of up to 0.9 micrometers per minute have been achieved. Third, there is a very wide temperature range in which shiny chromium can be precipitated, i. 20-70 ° C, and fourth, the chromium ion content in the solution is very low.

It is hypothesized that in previous experiments to precipitate chromium from trivalent solutions, the formation of hydroxychrome (III) on the cathode prevented precipitation at high current densities. The precipitation of chromium from the solution according to the invention is facilitated both by the catalytic effect of the thiocyanate and by the buffering effect of the amino acid at the cathode, which amino acid is released from the chromium atom when the charge is discharged at the cathode.

Other buffering agents can be used, such as formates, acetates, etc. However, the combination of catalytic properties and strong buffering effect of the complexing buffering agent is the factor that provides significant improvements.

The chromium (III) thiocyanate complex used in the invention may be a chromium (III) sulfothiocyanate complex or a chromium (III) chlorocyanate complex.

It goes without saying that by adding nickel, cobalt or other metal salts to the solution, mixtures of chromium and these metals can be plated. It should also be noted that chromium and chromium alloys can be precipitated when using photoresist plates.

The invention is illustrated by the following examples.

7 63785

Example 1

The plating solution according to the invention is prepared by forming a 0.05 M aqueous solution of chromium chloride (CrCl. This solution is saturated with boric acid (H 2 BO 4) (50 g / l) and equilibrated at 80 ° C for 1 hour with 0.075 M sodium thiocyanate (NaNCS), 0.16 M Glycine (N 2 CO 2 COOH), 0, With 5 M potassium chloride (KCl) and 2M potassium bromide. Potassium chloride and bromide are added to improve the conductivity of the solution. The equilibrated solution is cooled, the pH is adjusted to 3.0 by adding dilute sodium hydroxide and 1 g / l of sodium lauryl sulphate (wetting agent) is added.

The plating solution is placed in a Hull cell equipped with a flat platinum-plated titanium anode and a flat platinum-plated titanium anode and a flat, brass Hull cell test cathode. The ion exchange membrane is not used to separate the anode and cathode and the temperature of the solution is 22 ° C. A plating current of 5A is passed through the solution for 2 minutes. Shiny chromium precipitates from a current density of 2 2 to a peak of 10 mA / cm (580+ mA / cm).

Example 2

By equilibrating glycine with chromium (III) thiocyanate to form an equilibrated aqueous solution of glycine chromium (III) sulfothiocyanate-mixed complex, this effect can be demonstrated as follows »prepare the solution in two steps A jp 9: (A) Prepare a plating solution by forming a 0.075 M chromium sulphate solution (Cr (SO 2)). ) 2 · I5H2O). This solution is saturated with boric acid (H.JBO3) (80 g / l) and equilibrated at 80 ° C for one hour with 0.15 M sodium thiocyanate and 0.8 M sodium sulphate. Sodium sulfate is added to improve the conductivity of the solution. The finished solution is cooled, its pH is adjusted to 2.5 by adding dilute sodium hydroxide solution and 0.6 g / l of sodium lauryl sulphate (wetting agent) is added. This plating solution is placed in the normal Hull cell shown in Example 1 and the temperature of the solution is maintained at 25 ° C. A plating current of 5 A is passed through the cell for 2 minutes. 2 shiny chromium in the current density range of 5-125 mA / cm precipitates on the plate of the Hull cell.

63785 δ (Β) The solution prepared in A is re-equilibrated at 80 ° C for one hour by adding 5 g / l glycine (0.065 M). The pH is adjusted to 2.5 by adding dilute sodium hydroxide solution. A current of 5A is passed through solution (B) at 25 ° C in a normal Hull cell for 2 minutes. Shiny chromium precipitates 2 in the range 5-275 mA / cm.

(C) The solution prepared in (A) was re-equilibrated at 80 ° C for 1 hour by adding 10 g / l glycine (0.13 M). The pH is adjusted to 2.6 by adding dilute sodium hydroxide solution.

An electric current of 1.6 A is passed through the solution (C) at a temperature of 47 ° C and using a cathode with an area of 12 cm2 (130 mA / 2 cm) for 30 minutes. A layer of chromium with a thickness of 10 micrometers (i.e. 0.33 micrometers per minute) precipitates.

(D) The temperature effect is demonstrated as follows: solution (B) is heated to 45 ° C and an electric current of 5A is passed through the solution in a normal Hull cell for 2 minutes. Shiny chromium 2 precipitates in the range of 12-400 mA / cm.

Example 3

The plating solution is prepared essentially as described in Example 1 of GB 1 431 639, i. 150 g of sodium dichromate (Na2Cl2 <07) are added to 485 ml of perchloric acid (HClO2) and 525 ml of water. Add about 400 milliliters of hydrogen peroxide dropwise until the solution turns deep blue.

When this state is reached, the solution is boiled until its volume is halved, whereupon hydrogen peroxide is removed and the desired chromium perchlorate solution (CrfClO 2) is left. This solution forms a chromium (III) source solution for plating. 10 g of glycine are dissolved in water and the pH is adjusted to 2.0 by adding perchloric acid. To the glycine solution add 100 ml of chromium source solution and readjust the pH to 2.0 with sodium hydroxide solution and make up to 1 liter with water. This solution is equilibrated at 80 ° C by the addition of sodium thiocyanate (0.3 M) and sodium perchlorate (1M) over 1 hour. The solution is cooled to 40 [deg.] C., saturated with boric acid (H2 O4) (70 g / l) and 1 g / l of sodium lauryl sulphate are added.

The following plating results are obtained with the solution (A) prepared in Example 3. Shiny chromium can be precipitated in the temperature range of 25-70 ° C.

4, 9 63785

The best results are obtained at temperatures above 35 ° C.

(B) The solution is placed in a Hull cell and heated to 70 ° C. The brass Hull cell cathode is plated at a total current of 10 A for two minutes using a planar platinum-plated titanium anode. Shiny chromium precipitates on the brass plate from a current density of 2 2 to a peak of 20 mA / cm (1000 + mA / cra). There were no signs of burning or poor adhesion.

(C) The solution is heated to 70 ° C and a 6.3 mm diameter brass rod 2 is plated at a current density of 300 mA / cm for 10 minutes. The rod was moved during plating. The thickness of the chromium precipitate measured by weighing was 9 micrometers.

(D) The solution was heated to 70 ° C and a 6.3 mm diameter brass rod 2 was plated at a current density of 135 mA / cm for 10 minutes. The rod was moved during plating. The thickness of the chromium precipitate measured by weighing was 6 micrometers.

Example 4

A plating solution was prepared as in Example 2C except that 1 M sodium perchlorate was used to improve the conductivity of the solution instead of 0.8 M sodium sulfate. A shiny chromium precipitate having a thickness of 0.85 micrometers was plated on both sides of a 2 x 5 cm brass strip under the following conditions: pH = 2.55, temperature 46 ° C, current 2 A and time 2.5 minutes. The current density was 100 mA / cm and chromium precipitated at 0.3 micrometers per minute. Example 5

A plating solution according to the invention was prepared by the following steps, in which the indicated amounts of ingredients correspond to one liter of plating solution: 1) 60 g of boric acid (H 2 BO 4) was added to 600 ml of deionized or distilled water, the mixture was heated and stirred until dissolution occurred. The pH of the solution was adjusted to 2-2.4 with 10% NaOH or 10% B2SO 4.

2) 33.12 g of chromium (III) sulfate (Cr 2 SO 4) 2 was added to the boric acid solution prepared in step 1.

3) To the solution prepared in Step 2 was added 32.43 g of sodium thiocyanate (NaNCS). The solution was heated to 85 ° -5 ° C and kept at this temperature for 90 minutes with stirring.

4) After cooling to room temperature, 10 g of glycine (NH 3 CH 2 COOH) was added to the solution and its pH was adjusted as in 10 65785 in step 1. The solution was warmed to 85 ° -5 ° C and kept at this temperature for 90 minutes with stirring.

5) The solution was cooled to room temperature and 140 g of sodium perchlorate (NaClO 2 O) was added with heating and stirring until dissolution occurred.

6) The pH of the solution was adjusted to 2.5 as in step 1.

7) Deionized or distilled water was added to the solution until a volume of up to 1 liter was reached.

8) To the solution was added 1 g of sodium lauryl sulfate or 0.1 g of FC.98 (wetting agent, manufactured by 3 M Corporation) and stirred until dissolution occurred.

The solution was then ready for plating.

The bath can be used in a certain range of current density, pH and temperature. Suitable values are for a current density of 50-150 FIM / Λ cm, a pH of 2.0-4.0 and a temperature of 25-60 ° C. At a current density of 105 mA / cm 2, a pH of 3.5 and a temperature of 50 ° C, 0.6 micron of chromium precipitated in 2 minutes (efficiency 20-23%).

The current density of the anode must be about 40 mA / cm. The anodes can be platinum titanium or carbon. A fume hood must be used because electrochemical decomposition of the thiocyanate ion occurs at the cathode.