US3755094A

US3755094A - Anode compositions

Info

Publication number: US3755094A
Application number: US00196206A
Authority: US
Inventors: E Seyb; M Kalt; H Chessin
Original assignee: M&T Chemicals Inc
Current assignee: M&T HARSHAW
Priority date: 1971-11-05
Filing date: 1971-11-05
Publication date: 1973-08-28
Anticipated expiration: 1990-08-28

Abstract

In accordance with certain of its aspects, this invention relates to novel processes and to a lead base alloy suitable for anode production consisting essentially of lead and tin and at least one metal selected from the group consisting of tellurium, thallium, and cadmium and containing 90-99 percent by weight of lead, 1-7 percent by weight of tin, and at least one metal selected from the group consisting of tellurium, thallium, and cadmium in an amount of 0.005-5.0 percent by weight sufficient to bring the total weight of the lead base alloy anode to 100 percent.

Description

United States Patent [191 Seyb et al. I

[ ANODE COMPOSITIONS [22] Filed: Nov. 5, 1971 [2]]. Appl. No.: 196,206

Related US. Application Data [62] Division of Ser. No. 830,851, June 5, 1969,

[73] Assignee: M & T Chemicals Inc., New York,

abandoned.

[52] US. Cl 204/51, 204/293 [51] Int. Cl C231) 5/06, BOlk 3/06 [58] Field of Search t. 204/51, 293

[56] References Cited UNITED STATES PATENTS 1,766,87l 6/l930 Beckinsale et al. 75/166 C 2,060,534 ll/l936 Singleton et al. 75/166 R 2,841,541 7/1958 Smith 204/51 2,729,602 l/l956 Van Houton 204/55 R Aug. 28, 1973 FOREIGN PATENTS OR APPLICATIONS 508,604 7 7/1939 Great Britain 75/166 B OTHER PUBLICATIONS Transactions of the Electrochemical Soc., Vol. 80, pp. 59 and 60 by Bray et al., 1941.

Primary Examiner-F. C. Edmundson Attorney-Lewis C. Brown, Kenneth G Wheeless et al. I

57 f ABSTRACT In accordance with certain of its aspects, this invention relates to novel processes and to a lead base alloy suitable for anode production consisting essentially of lead and tin and at least one metal selected from the group 9 Claims, No Drawings 1 ANODE COMPOSITIONS This application is a divisional application of Ser. No. 830,85l, filed June 5, 1969,'now abandoned.

This invention relates to novel anodes, novel anode compositions, and to the preparation of such anodes and their use in electroplating processes. More particularly, this invention relates to the preparation and use of novel lead base alloy anodes containing 90-99 percent by weight of lead, 1-7 percent by weight of tin,

and at least one metal selected from the group consist-- in order to provide anodes which carry a higher surface current density than conventional anodes of equal cross-sectional area and to reduce the build-up upon the anode of undesirable deposits such as chromate deposits. During the course of chromium plating operations, lead anodes become heavily coated with lead ox: ides (mainly lead dioxide, PbO When left standing in a solution containing chromic acid, a lead anode ordinarily becomes coated with lead chromate and such coatings act to partially insulate the anode, thusinterfering with the normal distribution of the chromium deposited on the cathode. Such defects are especially undesirable in industrial chromium plating where irregularities in current distribution may produce wide variations in chromium plate thicknesses. During conventional operations, therefore, it may become necessary to remove such incrustations from conventional lead anodes by wire brushing or by chemical treatment using solutions containing hydrochloric acid or aqueous solutions containing alkali-metal pyrophosphate or other cleaning agents.

it is an object of the present invention to provide an improved lead alloy anode which is essentially free of antimony, bismuth, and arsenic. Another object of the invention is to provide an improved chromium electroplating process using a lead base alloy anode whichis particularly resistant toattack by chromic acid. A further object of the invention is to provide a lead base alloy anode which gives superior chromium electrodeposits and is characterized by particularly long life when subjected to the corrosive attack of chromic acid and other chromium plating bath chemicals.

In accordance with certain of its aspects, this invention relates to novel processes and to a lead base alloy suitable for anode production consisting essentially of lead and tin and at least one metal selected from the group consisting of tellurium, thallium, and cadmium and containing 90-99 percent by weight of lead, 1-7 percent by weight of tin, and at least one metal selected from the group consisting of tellurium, thallium, and cadmium in an amount of 0005-50 percent by weight sufficient to bring the total weight of the lead base alloy anode to 100 percent.

The lead base alloy anodes of the invention are particularly characterized by the substantial absence of antimony, bismuth, and arsenic from the alloy. The lead base alloy anodes of the invention are preferably at least ternary alloys consisting essentially of lead, tin, and tellurium or thallium, or cadmium, or combinations of one or more of these last three metals. Typical lead base alloy anodes may about 90-98 percent by weight of lead, about 2-5 percent by weight of tin, and the remainder tellurium (typically in amounts sufficient to saturate the alloy) or thallium (typically in amounts up to 1 percent by weight), or cadmium (typically in amounts up to 2 percent by weight). Higher percentages of tin, tellurium, thallium, or cadmium may be used according to the invention, but cost considerations generally do not justify the use of excessive amounts of these metals.

The lead base alloy anode compositions are prepared by melting the metals together or by adding and dissolving the metals for a particular alloy in molten lead and then cooling the resulting lead base alloy anode composition. 1

The leadbase alloy anodes prepared according to the invention have good hardness properties, excellent electricalproperties (including good initial resistance during startup'periods in chromium plating process) and are particularly resistant to attack by chromic acid during the chromium electroplating process. The lead base alloy anodes'are exceptionally resistant to attack 'in' chromic acid which contains additives such as sulfates, fluorides, and especially mixed radicals such as sulfate SO, and silicofluoride SiFf.

Typical lead alloy anode compositions which may be employed according to the invention and which have been found superior to prior art lead base anodes include the following examples which are summarized in 30 Table I. In Table I all parts are given in percent by weight based upon the total weight of the lead base alloy.

TABLE I Typical chromium plating baths in which the lead base alloy anode compositions of the invention may be employed may contain from about -600 g/l of chromic acid (as Crll Illustrative acidic aqueous chromium plating baths which may be employed include the following bath compositions:

Preferred Component Amount Concentrations l Chromic acid 750-600 50 Sulfate ion (e.g. from sulfuric acid) 1-10 2.5 [I Chromic acid l50-600 2S0 Sulfate ion (e.g. from sulfuric acid) 0.5-5 1 Silicofluoride ion (e.g. from H,SiF.) l-l0 2 [ll Chromic acid 150-600 400 Sulfate ion (e.g. from strontium sulfate) 1-5' 2 Silieofluoride ion (e.g. from H,SiF.) 2-8 5 Another aspect of the invention relates to a process for electrodepositing chromium from an aqueous acidic chromium electroplating bath which contains at least one chromium compound providing chromium metal ions for electroplating chromium which comprises passing current from a lead base alloy anode consisting essentially of lead, tin, and at least one metal selected from the group consisting of tellurium, thallium,

was greater than 0.50 grams per square centimeter were classified as poor. As can readily be seen from Table II, lead base alloy anode compositions prepared in accordance with the invention herein showed good resistance to attack in chromic acid solutions. In addition, the lead base alloy anode compositions of the invention possess excellent initial-resistance characteristics and provide excellent chromium plated articles.

TAB LE 11 Lead Base Alloy Anode Compositions l 2 3 4 5 6 7 8 9 Ex. No. Control Meta] (Percent by Weight) Pb 97.95 96.0 97.0 96.995 94.0 96.225 94.525 94.50 100.0 Sn 2.0 2.0 2.0 2.0 3.0 3.0 4.0 4.0 Te 0.05 0 0 0.005 0 0.025 0.025 0.05 0 Tl 0 0 1.0 0.5 1.0 0.75 0 0.50 0 Cd 0 2.0 0 0.5 2.0 0 1.450 0.95 0

TOTAL 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00

Anode Weight Loss GJcm. 0.27 0.22 0.27 0.25 0.20 0.22 0.19 0.20 0.79

and cadmium, wherein said lead base alloy anode contains 90-99 percent by weight lead, l-7 percent by weight tin, and the remainder of said lead base alloy anode consists of at least one metal selected from the group consisting of tellurium, thallium, and cadmium to a cathode through said aqueous acidic chromium plating solution to produce a chromium surface on at least a portion of said cathode.

Chromium electroplating is ordinarily carried out with the novel lead base alloy anode of the invention using bath temperatures of l-95 C. and plating currents of l-60 amperes per square decimeter (asd).

The following examples are submitted for the purpose of illustration only and are not to be construed as limiting the scope of the invention in any way.

GENERAL PROCEDURE Lead base alloy anodes were prepared by melting the indicated amounts of lead and tin together and then adding the indicated amount of tellurium, thallium, and

cadmium to obtain a metal solution. The so-formed alloy was then' cast into cold molds or extruded to the desired shape of the anode.

All of the lead base alloy anode compositions described in the illustrative examples possess superior hardness and resistivity against attack from chromic acid solutions when compared with the control anodes.

Resistance to chromic acid attack was measured by immersing an anode into a solution of chromic acid containing 240 g/l of chromic acid and the mixed radicals, sulfate, and silicofluoride at a temperature of 43 C. for a time of 120 hours. During this time the solutions were electrolyzed with an anode current density of amperes per square decimeter (asd) foreight.

Another control consisting of a binary alloy containing 90 percent Pb and 10 percent Sb exhibited a corresponding loss of 0.70 g/cm.

As can be seen from Table II, lead-base alloy anodes of the invention possess good resistance to attack in chromic acid solutions.

We claim: 1. A process for electrodepositing chromium from an aqueous acidic chromium electroplating bath which contains at least one chromium compound providing hour periods and then let stand for 16 hours. At the end of 120 hours, the anodes were removed and the weight loss of each determined. The loss of anode weight was measured after removal of deposits formed on said anode by side reactions such as the reaction of the chromium metal ions for electroplating chromium which comprises passing current from a lead base alloy anode consisting essentially of lead, tin, and at least one member selected from the group consisting of tellurium, thallium, and cadmium, wherein said lead base alloy anode contains 90-99 percent by weight lead, l-7 percent by weight tin, and the remainder of said lead base alloy anode consists of at least one member selected from the group consisting of tellurium, thallium, and cadmium to a cathode through said aqueous acidic chromium-plating solution to produce a chromium surface on at least a portion of said cathode.

2. A process as claimed in claim 1 wherein the chromium electroplating bath contains sulfate SO, and silicofluoride SiF,.

3. A process as claimed in claim 1 wherein the lead base alloy anode contains 0.000-005 percent tellunum.

4. A process as claimed in claim 1 wherein the lead' base alloy anode contains 0.000-l.0 percent thallium. 5. 'A process as claimed in claim 1 wherein the lead base alloy anode contains 0.0002.0 percent cadmium.

anode with the chromic acid. Anodes wherein the loss of anode material was less than 0.35 grams per square centimeter of immersed anode surface were considered good and anodes wherein the loss of anode material 6. A process as claimed in claim 1 wherein the lead base alloy anode contains 0.000-005 percent tellurium. and 0.000-l.0 percent thallium.

7. A process as claimed in claim 1 wherein the lead base alloy anode contains 0.000-0.05 percent tellurium and 0000-20 percent cadmium.

A process as claimed in claim 1 wherein the lead base alloy anode contains 0.0000.05 percent tellubase alloy anode contains 0.000-l.0 percent thallium rium, 0.000l.0 percent thallium, and 0.0002.0 perand 0.0002.0 percent cadmium. cent cadmium.

9. A process as claimed in claim 1 wherein the lead

Claims

2. A process as claimed in claim 1 wherein the chromium electroplating bath contains sulfate SO4 and silicofluoride SiF6 .
3. A process as claimed in claim 1 wherein the lead base alloy anode contains 0.000-0.05 percent tellurium.
4. A process as claimed in claim 1 wherein the lead base alloy anode contains 0.000-1.0 percent thallium.
5. A process as claimed in claim 1 wherein the lead base alloy anode contains 0.000-2.0 percent cadmium.
6. A process as claimed in claim 1 wherein the lead base alloy anode contains 0.000-0.05 percent tellurium and 0.000-1.0 percent thallium.
7. A process as claimed in claim 1 wherein the lead base alloy anode contains 0.000-0.05 percent tellurium and 0.000-2.0 percent cadmium.
8. A process as claimed in claim 1 wherein the lead base alloy anode contains 0.000-1.0 percent thallium and 0.000-2.0 percent cadmium.
9. A process as claimed in claim 1 wherein the lead base alloy anode contains 0.000-0.05 percent tellurium, 0.000-1.0 percent thallium, and 0.000-2.0 percent cadmium.