GB2154247A - Use of alcohol for increasing the current efficiency and quality of chromium-iron alloy plating - Google Patents

Abstract

An electrolytic process of plating an article with a chromium and iron alloy by the electrodeposition of chromium and iron from an aqueous bath solution containing dissolved CrO3 electrolyte and dissolved iron electrolyte, the bath solution having enhanced current efficiency by reason of including methyl alcohol in the bath solution in an amount within the range from 0.25mls to 80mls of alcohol/l. of bath solution. The solution may be a sulphate-catalyzed bath solution and may also contain dissolved trivalent chromium compounds.

Description

SPECIFICATION Use of alcohol for increasing the current efficiency and quality of chromium-iron alloy plating Background and summary This invention relates to chromium-iron alloy plating, the more particularly to electrolytic chromium-iron alloy plating, wherein chromium and iron in a plating bath solution are electrodeposited on the article plated.

Over the years, a number of different plating bath solutions have been proposed for chromium electrodeposition. A commonly used bath solution in a chromic acid bath, resulting from dissolving CrO3 in water, and which further contains a sulfate catalyst, or a mixture of catalysts, such as sulfate and silicofluoride.

This invention is bottomed on the discovery that the addition of alcohol, i.e., methyl alcohol, to a chromium and iron plating bath solution containing dissolved chromium and iron electrolyte significantly increases the current efficiency realized during the plating process and the quality of the alloy plated. A further advantageous result is that chromium-iron platings or coatings are produced tending to have a more uniform thickness, which offers the possibility of reducing the required thickness of a plating in a given application. It has also been observed that the inclusion of the alcohol affects the initial stages of chromium and iron deposition, by speeding up the plating that occurs. By including alcohol in the bath solution, improved results are obtained from bath solutions containing the usual catalysts.

A general object of this invention, therefore, is to provide an improved electrolytic process of chromium-iron alloy-plating, and improved chromium-iron plating bath solutions.

More particularly, an object of the invention is to provide improvements in an electrolytic process of chromium-iron alloy plating, and a chromium-iron plating bath solution, which relies upon the incorporation in the bath solution of chromium and iron electrolytes, and methyl alcohol, to produce a chromium-iron alloy coating.

Various other objects, advantages and features of the present invention will become more fully apparent from a reading of the following description, which is to be taken in conjunction with accompanying examples included for the purpose of illustration.

Detailed description of the invention Describing a conventional electrolytic plating process, a chromium plating bath solution may be prepared from a chromium electrolyte, such as Crop, water, and a suitable catalyst such as sulfate ion obtained by introducing H2S04 to the bath solution. A plating tank, vessel, or cell containing the bath solution is provided with one or more anodes, which may be of lead, and one or more cathodes, which constitute the articles to be plated, and a current is established between the anode and cathode structures. The plating process may typically be carried out at temperatures ranging from 20 -80 . With the passage of time, chromium in the electrolyte solution becomes deposited on the cathode structure. The present invention may be carried out using conventional equipment and conventional temperatures.

Chromium in the past has been carried out on various types of cathode substrates. Such include nickel substrates, low-carbon steel substrates, iron substrates, copper substrates, etc. As far as has been observed, the present invention is applicable to all of such commonly employed substrates.

As indicated earlier, the present invention is based on the discovery that the inclusion of methyl alcohol in chromium based electrolytic plating baths has been found to produce significant improvement in the current efficiency of the chromium plating process. Other results noted have been the production, by reason of the inclusion of such alcohol, of more even coatings, and an acceleration in chromium deposition at the initial stages of the plating process.

The amount of alcohol employed in a typical chromium based plating bath solution is not substantial. In general terms, beneficial results might be expected with alcohol inclusions ranging from 0.25 to 80 mls. of alcohol/l. of bath solution.

Currently efficiency, as the term is used herein, is calculated by determining the mass of the material deposited on the cathodic substrate during the plating process (which may be calculated by determining the weight gain in the plated article) and dividing this quantity by the theoretical mass that would be electrodeposited under 100% efficient conditions, which assumes that all the electrons transferred by the current employed in the electroplating are effective to reduce metal ions in the electrolyte of the bath solution to metal atoms deposited on the cathode structure.

Set forth below are several examples. In these examples, and when describing the composition of different bath solutions, quantities indicated are for each liter (I.) of bath solution.

Example Electroplating was performed in apparatus including a vessel containing 25 mls. of plating bath solution.

The article plated, or cathode speciment, was a rectangular piece of sheet material having a combined surface area on opposite sides thereof of 2 cm.2. One hollow cylindrical lead anode placed in a position surrounding the cathode speciment had a surface area submersed in the bath solution of 24 cms.2. Using apparatus as described, plating was performed on a stainless steel substrate, i.e., cathode specimens of stainless steel composition, for a period of 1 hour. The temperature of the bath solution was maintained at 40"C. A current density with direct current was maintained at 0.25A (amperes)/cms.2. Plating, utilizing the conditions just described, was performed employing various bath solutions containing, in addition to distilled water, 250 grs. CRO3, 2mls. H2SO4 (conc.), and varying amounts of methyl alcohol. All chemicals were reagent grade.In most instances, several platings were performed with each composition of bath solution. The following table summarizes results obtained from the various platings that were performed.

TABLE I MethylAlcohol Content Average Current increase in ofBath Solution Efficiency Current Efficiency (mls.) { /0) due to Methyl Alcohol 0 22.0 0.84 22.4 +10.9 0.89 25.7 +16.8 0.95 26.0 +18.2 1.00 25.4 +15.5 1.05 24.9 +13.2 Scratch marks were made with an engraving tool on faces of various cathode specimens employed in the above platings, prior to the plating process. It was observed that in platings produced utilizing bath solutions containing methyl alcohol, such scratch marks were not discernable, whereas with platings produced without the inclusion of methylalcohol, they were clearly discernable.

Example II In another group of platings, bath solutions were prepared from electrolytes containing both trivalent and hexavalent chromium, and the salt of another metal, namely, diva lent iron (FeCI2-4H2O). The temperature of the bath solution was 42"C. Plating time was 5 min. The cathode speciments were nickel coated. Three different series of platings were performed, utilizing aqueous bath solutions with compositions as indicated in Table II set forth below. Other than as above indicated, operating conditions and equipment were the same as in Example I.

TABLE II MethylAlcohol Cr03 FeCI24H20 CrCl36 H2 0 Average ofBath Solution content content content Current (mls.l (grs.) (grs.) (grs.) Efficiency Series a 20 250 62.6 72.2 52 Series b 20 250 143 0 70 Series 20 250 71.2 0 42 All coatings deposited were shiny, except series b had dull edges. Coatings produced were iron and chromium alloy coatings.

Example 111 Another series of platings were performed on nickel plated substrates, i.e., cathode specimens. The bath solution, in addition to water, contained the following: 150 grs. CrO3; 42.7 grs. FeCl2.4H2O, 38.4 grs, CrCI3-6H2O,0.6 mls./H2SO4, 12 mls. methyl alcohol. Plating time was 5 min. Other than as specified, the apparatus and operating conditions were as in Example The platings obtained were uniformly shiny. Averages current efficiency was 40%.

Example IV A bath solution was prepared containing, in addition to water, the following: 250 grs. Crow, 72 grs.

CrCI3-6H2O,60 grs. FeCI2-4H2O,1 ml. H2SO4, and 20 mls. methyl alcohol. Such bath solution was used in the plating of nickel coated cathode specimens, utilizing different plating times, as set forth in Table Ill below.

Except as otherwise indicated, apparatus and operating conditions were as set forth in Example 1. In Table Ill the results obtained from the platings are indicated.

TABLE Ill Plating Time Current Efficiency Appearance ofDeposits (min.) {%) 3 42 uniformly shiny 3 41 uniformly shiny 3 43 uniformly shiny 10 48 shiny except on edge 45 45 shiny except on edge While not fully understanding the mechanics of what occurs in the electroplating bath solution, it is felt that the results may at least partially be explained by considering the following equation representative of a reaction that is believed to occur in a chromic acid bath solution which includes methanol; 4CrO3 + 3CH3OH + 12H+ = 3HCOOH + 4Cr+++ + 9H2O With this reaction occurring, formic acid is produced, believed to have a catalytic effect in the electrodeposition of chromium. Additionally, it will be noted that hexavalent chromium by the reaction is converted to trivalent chromium, which is part of the reduction reaction which occurs with the electrodeposition of chromium atoms on the cathode.

While various specific examples have been set forth, this is for purpose of illustration and not limitation, as obviously other electroplating bath solutions are possible following the herein disclosed invention.

Accordingly, it is desired to cover all modifications and variations of the inventions as would be apparent to ne skilled in the art.

Claims (5)

1. An electolytic process of plating an article with a chromium and iron alloy by the electrodeposition of chromium and iron from an aqueous bath solution containing dissolved CrO3 electrolyte and dissolved iron electrolyte, the bath solution having enhanced current efficiency by reason of including methyl alcohol in the bath solution in an amount within the range of from 0.25 mls to 80 mls of alcohol/l. of bath solution.

2. The process of claim 1, wherein the bath solution is a sulfate-catalyst bath solution.

3. The process of claim 1 wherein the bath solution also contains dissolved trivalent chromium electrolyte.

4. The process of claim 2, wherein the bath solution further includes chlorine ions introduced as salts of iron/or chromium.

5. An electrolyte process of plating an article, as claimed in any preceding claim, substantially as hereinbefore described and exemplified.