CA1213558A - Method of purifying trivalent chromium electroplating baths - Google Patents
Method of purifying trivalent chromium electroplating bathsInfo
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- CA1213558A CA1213558A CA000432829A CA432829A CA1213558A CA 1213558 A CA1213558 A CA 1213558A CA 000432829 A CA000432829 A CA 000432829A CA 432829 A CA432829 A CA 432829A CA 1213558 A CA1213558 A CA 1213558A
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- ions
- electrolyte
- trivalent chromium
- metal ions
- dimethyldithiocarbamate
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D21/00—Processes for servicing or operating cells for electrolytic coating
- C25D21/16—Regeneration of process solutions
- C25D21/18—Regeneration of process solutions of electrolytes
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- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Electroplating And Plating Baths Therefor (AREA)
- Removal Of Specific Substances (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A method for purifying trivalent chromium electrolytes containing deleterious contaminating metal ions in concentrations which detrimentally affect the performance of the electrolyte producing chromium deposits which are commercially unsatisfactory due to the presence of dark streaky or spongy deposits. In accordance with the method disclosed, a selective precipitation of such detrimental metal ions includ-ing iron, copper, nickel, zinc and lead ions is selectively and effectively achieved by the addition of controlled effective amounts of bath soluble and compatible dimethyldithiocarbamate and diethyldithio-carbamate ions and mixtures thereof and the resultant precipitate is thereafter removed such as by filtra-tion.
A method for purifying trivalent chromium electrolytes containing deleterious contaminating metal ions in concentrations which detrimentally affect the performance of the electrolyte producing chromium deposits which are commercially unsatisfactory due to the presence of dark streaky or spongy deposits. In accordance with the method disclosed, a selective precipitation of such detrimental metal ions includ-ing iron, copper, nickel, zinc and lead ions is selectively and effectively achieved by the addition of controlled effective amounts of bath soluble and compatible dimethyldithiocarbamate and diethyldithio-carbamate ions and mixtures thereof and the resultant precipitate is thereafter removed such as by filtra-tion.
Description
METHOD OF PVRIFYING TRIVALENT
CHROMIUM ELECTROPI~TING BATHS
_ BACKGROUND OF THE II~VENTION
The present invention broadly relates to trivalent chromium electrolytes, and more particularly to a method of purifying and restoring the perEormance of such electrolytes which have been rendered deficient in producing commercially acceptable chromium electro-deposits due to the progressive accumulation and in-crease in concentration of contaminating metal ions such as nickel, zinc, iron, copper and lead during normal commercial operation of the bath. When one or more of such metal ion impurities attain concentrati~n levels which adversely affect the per-formance of the electrolytel the resultant chromium electrodeposit is rendered commercially objectionable due to the presence of black streaks, clouds and hazes which is sometimes further accompanied by a spongy deposit and a 1QSS or reduction in the cover-ing power of the electrolyte.
In order to overcome the detrimental effect of such metal ion contamination in trivalent chromium electroplating baths, it has heretofore been proposed in accordance with United States Patent ~o. 4,038,160 to add small amounts of water soluble ferrocyanide compounds to the electrolyte to effect a precipita-tion ~2~ 3 of such contaminating metal ions which can convenient-ly be removed by filtration. While the purification technique as disclosed in the aforementioned United S-tates patent has been found effective in many instan-ces, the presence of residual amounts of the ferro-cyanide precipitating agent adversely affects the performance of the electrolyte rendering the bath inoperative for producing commercially acceptable chromium deposits. When an excess of the ferrocyanide agent is present in the bath, a further treatment is required to remove such excess which can be performed by the intentional addition of contaminating metal ions to effect a precipitation of the residual ferrocyanide compound. It will be appreciated that the treatment proposed in the aforementioned United States patent requires precise analysis of the contaminants in the bath in order that a precise quantity of the precipi tating agent can be added which is not only tedious and time consuming but also requires skilled operating personnel. The to~ic nature of the ferrocyanide pre-cipitate requires special waste disposal measures which also is objectionable.
It has also been proposed to effect an elec-trolytic purification of contamina-ted trivalent chro-mium electrolytes employing a cathode on which a codepositi.on of such contaminating metal ions is effected by electrolyziny the bath over a prolonged time period. While such an electrolytic purification ~ ~3~
techni~ue is somewhat effective for reducing copper ion contamination, i-t has been found relatively in-effective for removing nic~el and zinc ions and only partially effective for removiny iron.
It has heretofore been suggested to employ dithiocarbamates for precipitating heavy metals from electroplating rinse waters employing a pH generally on the al~aline side. Suxprisingly, in accordance with the discovery comprising the present invention, it has been found tha-t selected dithiocarbama-te com~
pounds can be employed for purifying aqueous acidic trivalent chromium electrolytes which preferentially react with and precipitate the detrimental metal ions found in trivalent chromium electrolytes without sig-ni~icantly removing the chromium ions which are pres-ent in concentrations of about 50 times or more greater than the level of con-taminating metal ions present in the bath. Moreover, such trivalent chromium electro-lytes frequently contain metal ions such as vanadium as a desirable constituen-t for controlling and reduc-ing the formation of detrimental hexavalent chromium ions which also surprisingly are not significantly removed by the use of such selected dithiocarbamate additives. Moreover, trivalent chromium electrolytes are on the acid side usually ranging in pH from about 1.5 up to abou-t 5 which is substantially below the ~35i~
alkaline pH range heretofore proposed for treatment of electroplating rinse waters.
The unexpected results of the present inven-tion are further evidenced by the fact that certain dithiocarbamate compounds such as dibutyldithiocarbamate are unsatisfactoryO Similarly, dimethyl glyoxine, a compound well known as a precipitating agent for nickel ions, has been found ineffective for precipitating appreciable amounts of contaminating nickel ions from trivalent chromium baths and, moreover, the precipitate formed is of a gelatinous character which tends to cling to the tank walls and work piece surfaces causing unacceptable plate deposits and a fouling of the fil-tration equipment. Similar sulfide contai.ning com-pounds such as, for e~ample, sodium thiocarbonate (Na2CS3) and sodium thiocyanate (NaSCN) when incorpora-ted in trivalent chromium electrolytes cause serious defects in the chromium deposit including dark blue to black discoloxa-tion of low current density recess areas
CHROMIUM ELECTROPI~TING BATHS
_ BACKGROUND OF THE II~VENTION
The present invention broadly relates to trivalent chromium electrolytes, and more particularly to a method of purifying and restoring the perEormance of such electrolytes which have been rendered deficient in producing commercially acceptable chromium electro-deposits due to the progressive accumulation and in-crease in concentration of contaminating metal ions such as nickel, zinc, iron, copper and lead during normal commercial operation of the bath. When one or more of such metal ion impurities attain concentrati~n levels which adversely affect the per-formance of the electrolytel the resultant chromium electrodeposit is rendered commercially objectionable due to the presence of black streaks, clouds and hazes which is sometimes further accompanied by a spongy deposit and a 1QSS or reduction in the cover-ing power of the electrolyte.
In order to overcome the detrimental effect of such metal ion contamination in trivalent chromium electroplating baths, it has heretofore been proposed in accordance with United States Patent ~o. 4,038,160 to add small amounts of water soluble ferrocyanide compounds to the electrolyte to effect a precipita-tion ~2~ 3 of such contaminating metal ions which can convenient-ly be removed by filtration. While the purification technique as disclosed in the aforementioned United S-tates patent has been found effective in many instan-ces, the presence of residual amounts of the ferro-cyanide precipitating agent adversely affects the performance of the electrolyte rendering the bath inoperative for producing commercially acceptable chromium deposits. When an excess of the ferrocyanide agent is present in the bath, a further treatment is required to remove such excess which can be performed by the intentional addition of contaminating metal ions to effect a precipitation of the residual ferrocyanide compound. It will be appreciated that the treatment proposed in the aforementioned United States patent requires precise analysis of the contaminants in the bath in order that a precise quantity of the precipi tating agent can be added which is not only tedious and time consuming but also requires skilled operating personnel. The to~ic nature of the ferrocyanide pre-cipitate requires special waste disposal measures which also is objectionable.
It has also been proposed to effect an elec-trolytic purification of contamina-ted trivalent chro-mium electrolytes employing a cathode on which a codepositi.on of such contaminating metal ions is effected by electrolyziny the bath over a prolonged time period. While such an electrolytic purification ~ ~3~
techni~ue is somewhat effective for reducing copper ion contamination, i-t has been found relatively in-effective for removing nic~el and zinc ions and only partially effective for removiny iron.
It has heretofore been suggested to employ dithiocarbamates for precipitating heavy metals from electroplating rinse waters employing a pH generally on the al~aline side. Suxprisingly, in accordance with the discovery comprising the present invention, it has been found tha-t selected dithiocarbama-te com~
pounds can be employed for purifying aqueous acidic trivalent chromium electrolytes which preferentially react with and precipitate the detrimental metal ions found in trivalent chromium electrolytes without sig-ni~icantly removing the chromium ions which are pres-ent in concentrations of about 50 times or more greater than the level of con-taminating metal ions present in the bath. Moreover, such trivalent chromium electro-lytes frequently contain metal ions such as vanadium as a desirable constituen-t for controlling and reduc-ing the formation of detrimental hexavalent chromium ions which also surprisingly are not significantly removed by the use of such selected dithiocarbamate additives. Moreover, trivalent chromium electrolytes are on the acid side usually ranging in pH from about 1.5 up to abou-t 5 which is substantially below the ~35i~
alkaline pH range heretofore proposed for treatment of electroplating rinse waters.
The unexpected results of the present inven-tion are further evidenced by the fact that certain dithiocarbamate compounds such as dibutyldithiocarbamate are unsatisfactoryO Similarly, dimethyl glyoxine, a compound well known as a precipitating agent for nickel ions, has been found ineffective for precipitating appreciable amounts of contaminating nickel ions from trivalent chromium baths and, moreover, the precipitate formed is of a gelatinous character which tends to cling to the tank walls and work piece surfaces causing unacceptable plate deposits and a fouling of the fil-tration equipment. Similar sulfide contai.ning com-pounds such as, for e~ample, sodium thiocarbonate (Na2CS3) and sodium thiocyanate (NaSCN) when incorpora-ted in trivalent chromium electrolytes cause serious defects in the chromium deposit including dark blue to black discoloxa-tion of low current density recess areas
2~ and also significantly reduce the covering power of the ba-th.
SUMMARY OF THE INVENTION
The benefits and advantages of the present invention are achieved by employing dimethyldithio-carbamate and diethyldithiocarbamate ions as well as mixtures thereof as a purifying agent for trivalent chromium electrolytes by ~hich a selective preferential reaction and precipitation of detrimental contaminating ions is effected producing a precipitate of a somewhat crystalline character which can readily be removed and separated from the treated electrolyte by conventional filtration equipmentO Due to the instability of dimethyldithiocarbamic acid and diethyldithiocarbamic acid, it is preferred to introduce the corresponding ions into the bath as bath soluble alkali metal and ammonium salts such as the sodium salt for economic considerations. The additive agent is preferably introduced in the form of a concentrated aqueous solu-tion to facilitate dispersion in the electrolyte. The specific quantity of the purifying agent added during the purification treatment will vary depending upon the magnitude of contaminating metal ions present in the electrolyte. The quantity employed is therefore calculated to be sufficient to at least remove a suf-ficient quantity of such metal ion contaminants to reduce their concentration to a level at which the performance of the electrolyte is restored. Typically, concentrations of the precipitating agent relative to the concentration oi contaminating metal ions in an amount of about ~:1 g/l are employed.
Additional benefits and advantages of the present invention will become apparent upon a reading of the Description of the Preferred Embodiments taken in conjunction with the specific examples provided.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The purification method of the present inven-tion is particularly effective for purifyi~g trivalent chromium electrolytes which generally contain trivalent chromium ions in a concentration of about 0.2 to about 0.8 molar, complexing agents for complexing the chro-mium ions to maintain them in solution such as formate ions, acetate ions or mixtures thereof present in con-centrations to provide a molar ratio of complexing agent to chromium ions usually of about 1:1 to about
SUMMARY OF THE INVENTION
The benefits and advantages of the present invention are achieved by employing dimethyldithio-carbamate and diethyldithiocarbamate ions as well as mixtures thereof as a purifying agent for trivalent chromium electrolytes by ~hich a selective preferential reaction and precipitation of detrimental contaminating ions is effected producing a precipitate of a somewhat crystalline character which can readily be removed and separated from the treated electrolyte by conventional filtration equipmentO Due to the instability of dimethyldithiocarbamic acid and diethyldithiocarbamic acid, it is preferred to introduce the corresponding ions into the bath as bath soluble alkali metal and ammonium salts such as the sodium salt for economic considerations. The additive agent is preferably introduced in the form of a concentrated aqueous solu-tion to facilitate dispersion in the electrolyte. The specific quantity of the purifying agent added during the purification treatment will vary depending upon the magnitude of contaminating metal ions present in the electrolyte. The quantity employed is therefore calculated to be sufficient to at least remove a suf-ficient quantity of such metal ion contaminants to reduce their concentration to a level at which the performance of the electrolyte is restored. Typically, concentrations of the precipitating agent relative to the concentration oi contaminating metal ions in an amount of about ~:1 g/l are employed.
Additional benefits and advantages of the present invention will become apparent upon a reading of the Description of the Preferred Embodiments taken in conjunction with the specific examples provided.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The purification method of the present inven-tion is particularly effective for purifyi~g trivalent chromium electrolytes which generally contain trivalent chromium ions in a concentration of about 0.2 to about 0.8 molar, complexing agents for complexing the chro-mium ions to maintain them in solution such as formate ions, acetate ions or mixtures thereof present in con-centrations to provide a molar ratio of complexing agent to chromium ions usually of about 1:1 to about
3:1, and conductivity salts such as the salts of alkali metal or alkaline earth metals and strong acids such as hydrochloric acid and sulfuric acid present in amounts up to about 300 g/l or higher to achieve the requisite conductivity. Among such conductivity salts are 20 fluoboric acid as well as the alkali metal, alkaline earth metal and ammonium bath soluble salts thereof.
Such trivalent chromium electrolytes can optionally and preferably further contain ammonium ions present at molar ratios of total ammonium ion to chromium ion of from about 2:1 up to about 11:1 as well as halide ~ .
~ 6 ions including chloride and bromide ions present at a molar ratio of about 0.8:1 up to about 10:1 of halide ions to chromium ions present. Metallic re-ducing agents of the types as disclosed in Canadian Patent Application ~o. 389,254, filed ~ovember 2, 1981, comprising vanadium ions are also desirably included in amounts to provide a vanadium ion concentration of from about 0.015 up to about 6.3 g/l.
Such trivalent chromium electrolytes can also optionally and advantageously contain buffering agents of which boric acid present in concentrations of about 0.15 molar up ~o bath solubility has been found par-- ticularly satisfactory. Wetting agents can also be advantageously employed of the general types used in nickel and hexavalent chromium electrolytes in concen-trations of from about 0.05 up to about 1 g/l.
Trivalent chromium electrolytes also contain hydrogen ions to provide a pH on the acid side general-ly ranging from about 2.5 up to about 5.5.
The beneficial results of the present inven-tion are also obtained employing the purification additive in trivalent chromium electrolytes of the types as generally and specifically described in United States Patents No. 3,954,574; 4,107,004;
~ t`;i~
~3~
Such trivalent chromium electrolytes can optionally and preferably further contain ammonium ions present at molar ratios of total ammonium ion to chromium ion of from about 2:1 up to about 11:1 as well as halide ~ .
~ 6 ions including chloride and bromide ions present at a molar ratio of about 0.8:1 up to about 10:1 of halide ions to chromium ions present. Metallic re-ducing agents of the types as disclosed in Canadian Patent Application ~o. 389,254, filed ~ovember 2, 1981, comprising vanadium ions are also desirably included in amounts to provide a vanadium ion concentration of from about 0.015 up to about 6.3 g/l.
Such trivalent chromium electrolytes can also optionally and advantageously contain buffering agents of which boric acid present in concentrations of about 0.15 molar up ~o bath solubility has been found par-- ticularly satisfactory. Wetting agents can also be advantageously employed of the general types used in nickel and hexavalent chromium electrolytes in concen-trations of from about 0.05 up to about 1 g/l.
Trivalent chromium electrolytes also contain hydrogen ions to provide a pH on the acid side general-ly ranging from about 2.5 up to about 5.5.
The beneficial results of the present inven-tion are also obtained employing the purification additive in trivalent chromium electrolytes of the types as generally and specifically described in United States Patents No. 3,954,574; 4,107,004;
~ t`;i~
~3~
4,169,022 and 4,196,063.
During conventional commercial operation employing such trivalent chromium electrolytes, a pro-gressive contamination of the electrolyte occurs as a result of drag-in, dissolution in the electrolyte of unprotected surfaces of the receptacles or tanks con-taining the electrolyte, dissolution of the metallic surfaces o~ the work pieces being plated, dissolution of exposed portions of the work racks durlng immersion in the electrolyte, as well as contamination from the water and chemicals employed for replenishing and makeup of the electrolyte. As a result, a pxogressive buildup in the concentration of contaminating metal ions such as ions of nickel, zinc, iron, copper and lead occurs which, by experimentation, has indicated that coneentrations of nickel ions in amounts of about 150 ppm or higher are harmful and cause defects in the chromium electrodeposit. While the presence of iron ions in amounts up to about 500 ppm are beneficial to the trivalent chromium electrolyte in that they tend to promote coverage of the ehromium deposit, concen-trations of above abou~ 1,000 ppm (above 1 g/l) are generally harmful to the chromium deposit~ Similarly, concentrations of copper ions in amounts above about 15 ppm and zine ions above about 10 ppm and higher are harmful. When combinations of such metal ions are present in the bath, the harmful effects of the indi-vidual ions are cumulative and lower concentrations of the individual metal ions produce defects in the chro-mium deposit which is evidenced by the presence of black streaks~ clouds, and hazes. Under severe con-taminating conditions, the covering power of the elec-trolyte is also adversely affected.
In accordance with the present invention, dimethyldithiocarbamate and/or diethyldithiocarbamate ions preferably in the form of an aqueous concentrate of the alkali metal and ammonium salts thereof of which the sodium salt constitutes the preferred mater-ial,, are introduced into the contaminated trivalent chromium electrolyte in an amount sufficient to pre-cipitate at least a portion of such metal ions reducing their level to an innocuous concentration in which satisfactory plating performance is again restored.
The non-toxic precipitate can readily be disposed of ~ by conventional disposal techniques in contrast to the toxic precipitate produced with ferrocyanide compounds Unlike with the use of ~errocyanide precipitating agents, excess amounts of the purifying agent of the present invention do not detrimentally affect the quality of the chromium deposit and any unreacted quantities of the purifying agent remaining in the electrolyte following the treatmentare progressively decomposed and/or removed during the normal electrolysis of the electrolyte during conventional plating operations.
. ~ 9 ~Z~3~
The purifying agent is preferably introduced into the electrolyte in the form of a concentrated aqueous solution to facilitate uniform dispersion thereof in the presence of agitation as opposed to the addition in the form of a dry bath soluble powder. The liquid concentrate will usually contain about 30 percent by weight of the purification agent and is usually ad-justed to provide a pH of above about 8, preferably above about 9 to provide stability during storage.
When commercial dimethyldithiocarbamate and diethyl-dithiocarbamate products are employed, it is usually desirable to carbon filter or otherwise purify such commercial mixtures to remove any undesirable reaction by-produc~s therein which may adversely affect the performance of the electrolyte following the purifica-tion treatment.
The purification agent of the present inven-tion is useful over a wide pH operating range. Gener-ally, trivalent chromium electrolytes operate at a ~ pH ranging from a~out 2 to about S.5 and more typically, from about 3 to about 4. The purifying agent of the present invention operates well within the foregoing pH ranges as well as at at pH as low as about 1.5.
In order to further illustrate the present invention, the following specific examples are pro-vided. It will be understood that the examples are , 1 0 ~3~
provided for illustrative purposes and are not intended to be limitlng of the scope of the invention as herein described and as set forth in the subjoined claims.
EX~MPLE 1 An aqueous acidic trivalen-t chromium test electrolyte ~as prepared having the following compo-. sition:
INGREDIENT CONCENTRATION
__ : Cr~3 24.2 g/l NH4COOH 44.0 g/l NaBF4 ~,55.0 g/l NH~Cl 150.0 g/l H3BO3 57.1 g/1 VOSO4 1.0 g/l Wetting agent*2.0 cc/l *Wetting agent comprises equivalent of 0.13'l4 g/l dihexyl ester of sodium sulfosuccinic acid and 0.244 g/l of sodium sulfate derivative of 2-ethyl-1-hexanol.
Contamination of the electrolyte with iron, copper and nickel ions was effected by the addition of the cor.responding sulfate salts to produce an iron ion concentration of about 0.312 g/l, a copper ion concen-tration of about 0.032 g/l and a nickel ion concen-tra-tion of about 0.110 g/l. To 1 liter of the foregoing electrolyte containing the contaminating metal ions, 2.5 y/l of sodium diethyldithiocarbamate trihydrate L3~3 was added and the resultant solutlon was stirred for approximately 10 minutes at 75F at a pH of about 3.2 and then allowed to stand quiescent for a period of 2 hours. The resultant solution was then filtered through a carbon filter and analyzed for metallic contamination.
Upon analysis, the iron ions concentration was found to be 0.168 g/l; the copper ion concentration was 0.012 g/l; the nickel ion concentration was found to be 0.0~2 g/l. Accordingly, about ~6.2 percent of the contamina-ting iron ions were removed; about 62.5 percent of the contaminating copper ions were removed; about 62 percent of the contaminating nickel ions were removed.
E~5AMPLE 2 A 400 milliliter sample of the trivalent chromium test electrolyte as described in Example 1 was adjusted by the addition of contaminating metal sal-ts to provide an iron ion concentration of about 0.312 g/l, a nickel ion concentration of about 0.120 g/l and a copper ion concentration of about 0.080 g/l.
To the electroly-te containing the dissolved contami-na-ting metal ions, 3.5 g/l o~ sodium diethyldithio-carbamate trihydrate were added and the solution stirred for approximately one-half hour at 120F at a pH of about 3. The solu-tion was then allowed to s-tand quiescent for about 2 hours at 75F whereafter it was filtered through a carbon filter. Analysis of the filtrate revealed that the iron ion concentration was reduced to about 0.072 ~/1, the nickel ion concen-tration was reduced to about 0.010 g/l while the copper ion concentration was nil. Accordingly, about 77 per-cent of the iron ion contamina-tion was removed, about 91.7 percent of the nickel ion contamination was removed while substantially 100 percent of the copper ion con-centration was removed.
In order to evaluate the effect of pH on the effec-tiveness of the purifying agent of the present invention, the same test electrolvte as described in Example 2 containing the same level of contaminating metal ions was raised to a pH of about 4 by the addi-tion of ammonium hydroxide. The solution was there-after treated in the same manner as described inExample 2. Analvsis of the filtrate revealed that the iron ion concentration in the treated electrolyte was reduced to about 0.012 g/1, and the nickel ion and copper ion concentrations were nil. Accordingly, about 96.2 percent of the iron ions were removed ~hile substantially 100 percent of the nickel and copper ions were removedO The results of Example 3 indicate that the additive agent is of an increased effectiveness at a pH of 4 in comparison to a pH of about 3 as employed in Example 2.
135~8 A trivalent chromium test electrolyte was prepared of a composition similar to that described in Example 1 with the exception that the trivalent chromium ion concentration was 21.7 g/l, the ammonium formate concentration was about 51.0 g/l and the boric acid concentration was about S0.8 g/l with the remain-ing ingredients the same as described in Example 1.
The electrolyte was adjusted for a pH of about 3.5 and the concentration of contaminating ions was as follows: iron ions about 0.298 g/l; nickel ions about 0.188 g/l and zinc ions about 0.047 g/l.
A test panel which had been plated in a conventional Watts-type bright nickel bath at a current density of about 45 ASF at 145F for a period of 10 minutes to provide a bright nickel deposit of about 0.3 mil thickness, after water rinsing was plated in the foregoing contaminated trivalent chromium electro-lyte for a period of 3 minutes at 75F and a cathode current density of about 100 ASF. The chromium de-posit was iridescent in the intermediate cbrrent den-sity areas and had black streaks in the high current density areas. The chromium deposit was considered unacceptable from a commercial standpoint due to the high level of contaminating metal ions therein.
The contaminated trivalent chromium electro-lyte was thereafter treated by the addition of 3.8 g/l ~3~
of sodium diethyldithiocarbamate trihydrate for a period of 1 hour at 75F with continuous stirring.
The electrolyte after settling, was thereafter ~iltered through a carbon filter and the filtrate was analyzed for residual metal ion contaminants present in the treated electrolyte. Upon analysis, the iron ion con-centration was found to be about 0.164 g/l, the nickel ion concentration was nil and the zinc ion concentra-tion was found to be about 0.0004 g/l. Accordlngly, about 45 percent of the iron ions were removed, about 100 percent of the nickel ions were removed while about ~ ?
99 percent of the zinc ion contaminant was removed.
~ nickel plated test panel of the type here-inabove described was then plated in the treated and filtered solution under the same conditions as employed for the untreated solution. The chromium deposit was overall bright and of normal and uniform appearance.
The plating deposit was considered entirely commercial-ly acceptable, The plating test further indicates 2~ that the presence of excess sodium diethyldithiocar-bamate in the electrolyte following the treatment does not adversely affect the performance of the trivalent chromium plating solution. This example clearly evidences the effectivenesss of the present invention in rejuvena-ting a metal ion contaminated trivalent chromium electrolyte the performance of which has heen ~3~
rendered c~mmexcially unsatisfactory whereby the elec trolyte is restored to provide satisfactory chromium depositsO
An experimental treatment of a commercial trivalent chromium electrolyte comprising a 4,000 gal-lon bath was made having a nominal composition corres-ponding to that described in Example 1. The perfor-mance of the electrolyte had become impaired due to the accumulation of iron and nickel contaminating ions during normal electroplating operations. Analyses of samples of the electrolyte before treatment and fol-lowing treatment were made for iron ions, nickel ions and vanadium ions present as a reducing agent. The results of the analyses are as follows:
Before Treatment After Treatment Fe 1.310 g/l 1.000 g/l Ni 0.501 g/l 0.351 g/l V 0.238 g/l 0.238 g/l The purification treatment of the contam-inated electrolyte was carried out by the addition of 30 gallons of a solution containing a concentration of about 350 g/l of sodium diethvldithiocarbamate. While the bath was being continuously filtrated, but wi-thout undergoing electrolysis, the solution of additive agent was added. In~ediately following the addition of -the aqueous additive solution, a dark precipitate formed which, surprisingly, instead of increasing filter back pressure actually resulted in a reduction in filter back pressure. As a result, the precipitate was easily removed and satisfactory operation of the electrolyte was restored within about 1 hour after treatment providing commercially satisfactory chromium deposits~ The precipitate recovered by the filtration was analy~ed and found to contain about 66.7 mol per-cent iron die~hyldithiocarbamate and 33.3 mol percent nickel diethyldithiocarhamaté.f The selectivity of -the additive agent for extracting contaminating metal ions is evidenced by the fact that no vanadium and no chro-mium was extracted rom the bath during treatment.
Slmilar tests employing ferrocyanide precipitating agents evidences a significant removal of both chro-mium and vanadium which are desirable constituents in the trivalent chromium electrolyte.
While it will be apparent that the preEerred embodiments of the invention disclosed are well calcu-la-ted to fulfill the objects above stated, it will be appreciated that the invention is susceptible to modi-fication, variation and change without departing from the proper scope or fair meani.ng of the subjoined claims.
During conventional commercial operation employing such trivalent chromium electrolytes, a pro-gressive contamination of the electrolyte occurs as a result of drag-in, dissolution in the electrolyte of unprotected surfaces of the receptacles or tanks con-taining the electrolyte, dissolution of the metallic surfaces o~ the work pieces being plated, dissolution of exposed portions of the work racks durlng immersion in the electrolyte, as well as contamination from the water and chemicals employed for replenishing and makeup of the electrolyte. As a result, a pxogressive buildup in the concentration of contaminating metal ions such as ions of nickel, zinc, iron, copper and lead occurs which, by experimentation, has indicated that coneentrations of nickel ions in amounts of about 150 ppm or higher are harmful and cause defects in the chromium electrodeposit. While the presence of iron ions in amounts up to about 500 ppm are beneficial to the trivalent chromium electrolyte in that they tend to promote coverage of the ehromium deposit, concen-trations of above abou~ 1,000 ppm (above 1 g/l) are generally harmful to the chromium deposit~ Similarly, concentrations of copper ions in amounts above about 15 ppm and zine ions above about 10 ppm and higher are harmful. When combinations of such metal ions are present in the bath, the harmful effects of the indi-vidual ions are cumulative and lower concentrations of the individual metal ions produce defects in the chro-mium deposit which is evidenced by the presence of black streaks~ clouds, and hazes. Under severe con-taminating conditions, the covering power of the elec-trolyte is also adversely affected.
In accordance with the present invention, dimethyldithiocarbamate and/or diethyldithiocarbamate ions preferably in the form of an aqueous concentrate of the alkali metal and ammonium salts thereof of which the sodium salt constitutes the preferred mater-ial,, are introduced into the contaminated trivalent chromium electrolyte in an amount sufficient to pre-cipitate at least a portion of such metal ions reducing their level to an innocuous concentration in which satisfactory plating performance is again restored.
The non-toxic precipitate can readily be disposed of ~ by conventional disposal techniques in contrast to the toxic precipitate produced with ferrocyanide compounds Unlike with the use of ~errocyanide precipitating agents, excess amounts of the purifying agent of the present invention do not detrimentally affect the quality of the chromium deposit and any unreacted quantities of the purifying agent remaining in the electrolyte following the treatmentare progressively decomposed and/or removed during the normal electrolysis of the electrolyte during conventional plating operations.
. ~ 9 ~Z~3~
The purifying agent is preferably introduced into the electrolyte in the form of a concentrated aqueous solution to facilitate uniform dispersion thereof in the presence of agitation as opposed to the addition in the form of a dry bath soluble powder. The liquid concentrate will usually contain about 30 percent by weight of the purification agent and is usually ad-justed to provide a pH of above about 8, preferably above about 9 to provide stability during storage.
When commercial dimethyldithiocarbamate and diethyl-dithiocarbamate products are employed, it is usually desirable to carbon filter or otherwise purify such commercial mixtures to remove any undesirable reaction by-produc~s therein which may adversely affect the performance of the electrolyte following the purifica-tion treatment.
The purification agent of the present inven-tion is useful over a wide pH operating range. Gener-ally, trivalent chromium electrolytes operate at a ~ pH ranging from a~out 2 to about S.5 and more typically, from about 3 to about 4. The purifying agent of the present invention operates well within the foregoing pH ranges as well as at at pH as low as about 1.5.
In order to further illustrate the present invention, the following specific examples are pro-vided. It will be understood that the examples are , 1 0 ~3~
provided for illustrative purposes and are not intended to be limitlng of the scope of the invention as herein described and as set forth in the subjoined claims.
EX~MPLE 1 An aqueous acidic trivalen-t chromium test electrolyte ~as prepared having the following compo-. sition:
INGREDIENT CONCENTRATION
__ : Cr~3 24.2 g/l NH4COOH 44.0 g/l NaBF4 ~,55.0 g/l NH~Cl 150.0 g/l H3BO3 57.1 g/1 VOSO4 1.0 g/l Wetting agent*2.0 cc/l *Wetting agent comprises equivalent of 0.13'l4 g/l dihexyl ester of sodium sulfosuccinic acid and 0.244 g/l of sodium sulfate derivative of 2-ethyl-1-hexanol.
Contamination of the electrolyte with iron, copper and nickel ions was effected by the addition of the cor.responding sulfate salts to produce an iron ion concentration of about 0.312 g/l, a copper ion concen-tration of about 0.032 g/l and a nickel ion concen-tra-tion of about 0.110 g/l. To 1 liter of the foregoing electrolyte containing the contaminating metal ions, 2.5 y/l of sodium diethyldithiocarbamate trihydrate L3~3 was added and the resultant solutlon was stirred for approximately 10 minutes at 75F at a pH of about 3.2 and then allowed to stand quiescent for a period of 2 hours. The resultant solution was then filtered through a carbon filter and analyzed for metallic contamination.
Upon analysis, the iron ions concentration was found to be 0.168 g/l; the copper ion concentration was 0.012 g/l; the nickel ion concentration was found to be 0.0~2 g/l. Accordingly, about ~6.2 percent of the contamina-ting iron ions were removed; about 62.5 percent of the contaminating copper ions were removed; about 62 percent of the contaminating nickel ions were removed.
E~5AMPLE 2 A 400 milliliter sample of the trivalent chromium test electrolyte as described in Example 1 was adjusted by the addition of contaminating metal sal-ts to provide an iron ion concentration of about 0.312 g/l, a nickel ion concentration of about 0.120 g/l and a copper ion concentration of about 0.080 g/l.
To the electroly-te containing the dissolved contami-na-ting metal ions, 3.5 g/l o~ sodium diethyldithio-carbamate trihydrate were added and the solution stirred for approximately one-half hour at 120F at a pH of about 3. The solu-tion was then allowed to s-tand quiescent for about 2 hours at 75F whereafter it was filtered through a carbon filter. Analysis of the filtrate revealed that the iron ion concentration was reduced to about 0.072 ~/1, the nickel ion concen-tration was reduced to about 0.010 g/l while the copper ion concentration was nil. Accordingly, about 77 per-cent of the iron ion contamina-tion was removed, about 91.7 percent of the nickel ion contamination was removed while substantially 100 percent of the copper ion con-centration was removed.
In order to evaluate the effect of pH on the effec-tiveness of the purifying agent of the present invention, the same test electrolvte as described in Example 2 containing the same level of contaminating metal ions was raised to a pH of about 4 by the addi-tion of ammonium hydroxide. The solution was there-after treated in the same manner as described inExample 2. Analvsis of the filtrate revealed that the iron ion concentration in the treated electrolyte was reduced to about 0.012 g/1, and the nickel ion and copper ion concentrations were nil. Accordingly, about 96.2 percent of the iron ions were removed ~hile substantially 100 percent of the nickel and copper ions were removedO The results of Example 3 indicate that the additive agent is of an increased effectiveness at a pH of 4 in comparison to a pH of about 3 as employed in Example 2.
135~8 A trivalent chromium test electrolyte was prepared of a composition similar to that described in Example 1 with the exception that the trivalent chromium ion concentration was 21.7 g/l, the ammonium formate concentration was about 51.0 g/l and the boric acid concentration was about S0.8 g/l with the remain-ing ingredients the same as described in Example 1.
The electrolyte was adjusted for a pH of about 3.5 and the concentration of contaminating ions was as follows: iron ions about 0.298 g/l; nickel ions about 0.188 g/l and zinc ions about 0.047 g/l.
A test panel which had been plated in a conventional Watts-type bright nickel bath at a current density of about 45 ASF at 145F for a period of 10 minutes to provide a bright nickel deposit of about 0.3 mil thickness, after water rinsing was plated in the foregoing contaminated trivalent chromium electro-lyte for a period of 3 minutes at 75F and a cathode current density of about 100 ASF. The chromium de-posit was iridescent in the intermediate cbrrent den-sity areas and had black streaks in the high current density areas. The chromium deposit was considered unacceptable from a commercial standpoint due to the high level of contaminating metal ions therein.
The contaminated trivalent chromium electro-lyte was thereafter treated by the addition of 3.8 g/l ~3~
of sodium diethyldithiocarbamate trihydrate for a period of 1 hour at 75F with continuous stirring.
The electrolyte after settling, was thereafter ~iltered through a carbon filter and the filtrate was analyzed for residual metal ion contaminants present in the treated electrolyte. Upon analysis, the iron ion con-centration was found to be about 0.164 g/l, the nickel ion concentration was nil and the zinc ion concentra-tion was found to be about 0.0004 g/l. Accordlngly, about 45 percent of the iron ions were removed, about 100 percent of the nickel ions were removed while about ~ ?
99 percent of the zinc ion contaminant was removed.
~ nickel plated test panel of the type here-inabove described was then plated in the treated and filtered solution under the same conditions as employed for the untreated solution. The chromium deposit was overall bright and of normal and uniform appearance.
The plating deposit was considered entirely commercial-ly acceptable, The plating test further indicates 2~ that the presence of excess sodium diethyldithiocar-bamate in the electrolyte following the treatment does not adversely affect the performance of the trivalent chromium plating solution. This example clearly evidences the effectivenesss of the present invention in rejuvena-ting a metal ion contaminated trivalent chromium electrolyte the performance of which has heen ~3~
rendered c~mmexcially unsatisfactory whereby the elec trolyte is restored to provide satisfactory chromium depositsO
An experimental treatment of a commercial trivalent chromium electrolyte comprising a 4,000 gal-lon bath was made having a nominal composition corres-ponding to that described in Example 1. The perfor-mance of the electrolyte had become impaired due to the accumulation of iron and nickel contaminating ions during normal electroplating operations. Analyses of samples of the electrolyte before treatment and fol-lowing treatment were made for iron ions, nickel ions and vanadium ions present as a reducing agent. The results of the analyses are as follows:
Before Treatment After Treatment Fe 1.310 g/l 1.000 g/l Ni 0.501 g/l 0.351 g/l V 0.238 g/l 0.238 g/l The purification treatment of the contam-inated electrolyte was carried out by the addition of 30 gallons of a solution containing a concentration of about 350 g/l of sodium diethvldithiocarbamate. While the bath was being continuously filtrated, but wi-thout undergoing electrolysis, the solution of additive agent was added. In~ediately following the addition of -the aqueous additive solution, a dark precipitate formed which, surprisingly, instead of increasing filter back pressure actually resulted in a reduction in filter back pressure. As a result, the precipitate was easily removed and satisfactory operation of the electrolyte was restored within about 1 hour after treatment providing commercially satisfactory chromium deposits~ The precipitate recovered by the filtration was analy~ed and found to contain about 66.7 mol per-cent iron die~hyldithiocarbamate and 33.3 mol percent nickel diethyldithiocarhamaté.f The selectivity of -the additive agent for extracting contaminating metal ions is evidenced by the fact that no vanadium and no chro-mium was extracted rom the bath during treatment.
Slmilar tests employing ferrocyanide precipitating agents evidences a significant removal of both chro-mium and vanadium which are desirable constituents in the trivalent chromium electrolyte.
While it will be apparent that the preEerred embodiments of the invention disclosed are well calcu-la-ted to fulfill the objects above stated, it will be appreciated that the invention is susceptible to modi-fication, variation and change without departing from the proper scope or fair meani.ng of the subjoined claims.
Claims (7)
1. A method for purifying an aqueous acidic trivalent chromium electrolyte containing a detrimental amount of contaminating metal ions which comprises the steps of adding to the contaminated electrolyte a soluble and compatible purifying agent selected from the group consisting of dimethyldithiocarbamate ions, diethyldithiocarbamate ions, and mixtures thereof in an amount effective to precipitate at least a portion of the detrimental contaminating metal ions to reduce their concentration in the electrolyte to a level at which satisfactory performance of the electrolyte is restored and thereafter removing the precipitate from the electrolyte.
2. The method as defined in claim 1 in which the dimethyldithiocarbamate ions and diethyldi-thiocarbamate ions are added in the form of electro-lyte soluble and compatible alkali metal and ammonium salts thereof.
3. The method as defined in claim 1 in which the dimethyldithiocarbamate ions and diethyldi-thiocarbamate ions are added as the sodium salts thereof.
4. The method as defined in claim 1 in which the dimethyldithiocarbamate ions and diethyldi-thiocarbamate ions are added in the form of an aqueous solution.
5. The method as defined in claim 1 includ-ing the further step of uniformly distributing the purifying agent throughout the electrolyte.
6. The method as defined in claim 1 in which the step of removing the precipitate from the electrolyte is performed by filtration.
7. The method as defined in claim 1 in which the purifying agent is added to the electrolyte in a weight ratio of about 8.1 purifying agent to contaminating metal ions present.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US40321282A | 1982-07-29 | 1982-07-29 | |
| US403,212 | 1982-07-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1213558A true CA1213558A (en) | 1986-11-04 |
Family
ID=23594912
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000432829A Expired CA1213558A (en) | 1982-07-29 | 1983-07-20 | Method of purifying trivalent chromium electroplating baths |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPS5941500A (en) |
| AU (1) | AU542415B2 (en) |
| CA (1) | CA1213558A (en) |
| DE (1) | DE3327011A1 (en) |
| FR (1) | FR2537164A1 (en) |
| GB (1) | GB2124258B (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107857389A (en) * | 2017-11-06 | 2018-03-30 | 广州超邦化工有限公司 | The method for handling Electrodeposition of Zn-ni Alloy In Alkaline Bath waste water |
| CN108218129A (en) * | 2018-01-26 | 2018-06-29 | 广州超邦化工有限公司 | The processing method of chemical nickle-plating wastewater |
| CN108315774A (en) * | 2018-02-06 | 2018-07-24 | 广州超邦化工有限公司 | The processing method of nickel and copper impurity in a kind of trivalent chromium chrome plating liquid |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS633128A (en) * | 1986-06-23 | 1988-01-08 | Sanyo Electric Co Ltd | Control circuit for burner |
| JPS6362900A (en) * | 1986-09-03 | 1988-03-19 | Shinko Electric Ind Co Ltd | Regenerating agent for gold plating and method for regenerating gold plating solution with said agent |
| JPH01174822A (en) * | 1987-12-29 | 1989-07-11 | Katsunori Tanada | Timer device for burner |
| US6398845B1 (en) | 2000-02-10 | 2002-06-04 | Sumitomo Chemical Company, Limited | Method for purifying aluminum |
| JP5218742B2 (en) * | 2008-03-07 | 2013-06-26 | 奥野製薬工業株式会社 | Method for removing metal impurities from trivalent chromium plating bath |
| JP5182115B2 (en) * | 2009-01-21 | 2013-04-10 | 東ソー株式会社 | Heavy metal immobilization treatment method, treatment agent used therefor, and production method thereof |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3518171A (en) * | 1969-07-24 | 1970-06-30 | Metalux Corp The | Purification of nickel electroplating solutions |
| CA955035A (en) * | 1970-02-05 | 1974-09-24 | Osaka Soda Co. | Treatment process for removal of metals and treating agent therefor |
| BE794336A (en) * | 1972-02-10 | 1973-05-16 | Parker Ste Continentale | PROCESS FOR PURIFYING METAL COATING BATHS |
| GB1455580A (en) * | 1973-12-13 | 1976-11-17 | Albright & Wilson | Electrodeposition of chromium |
| US4107004A (en) * | 1975-03-26 | 1978-08-15 | International Lead Zinc Research Organization, Inc. | Trivalent chromium electroplating baths and method |
| GB1558169A (en) * | 1975-07-03 | 1979-12-19 | Albright & Wilson | Chromium electroplating |
| GB1580137A (en) * | 1977-05-24 | 1980-11-26 | Bnf Metals Tech Centre | Electrolytic deposition of protective chromite-containing coatings |
| AU513298B2 (en) * | 1978-06-02 | 1980-11-27 | International Lead Zinc Research Organization Inc. | Electrodeposition of black chromium |
-
1983
- 1983-07-20 AU AU17129/83A patent/AU542415B2/en not_active Ceased
- 1983-07-20 CA CA000432829A patent/CA1213558A/en not_active Expired
- 1983-07-26 JP JP13666283A patent/JPS5941500A/en active Granted
- 1983-07-26 GB GB08320069A patent/GB2124258B/en not_active Expired
- 1983-07-27 FR FR8312433A patent/FR2537164A1/en active Pending
- 1983-07-27 DE DE19833327011 patent/DE3327011A1/en active Granted
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107857389A (en) * | 2017-11-06 | 2018-03-30 | 广州超邦化工有限公司 | The method for handling Electrodeposition of Zn-ni Alloy In Alkaline Bath waste water |
| CN107857389B (en) * | 2017-11-06 | 2020-06-09 | 广州超邦化工有限公司 | Method for treating alkaline zinc-nickel alloy electroplating wastewater |
| CN108218129A (en) * | 2018-01-26 | 2018-06-29 | 广州超邦化工有限公司 | The processing method of chemical nickle-plating wastewater |
| CN108315774A (en) * | 2018-02-06 | 2018-07-24 | 广州超邦化工有限公司 | The processing method of nickel and copper impurity in a kind of trivalent chromium chrome plating liquid |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2124258A (en) | 1984-02-15 |
| JPS6158560B2 (en) | 1986-12-12 |
| AU1712983A (en) | 1984-02-02 |
| JPS5941500A (en) | 1984-03-07 |
| DE3327011C2 (en) | 1989-04-20 |
| GB8320069D0 (en) | 1983-08-24 |
| GB2124258B (en) | 1986-01-29 |
| AU542415B2 (en) | 1985-02-21 |
| DE3327011A1 (en) | 1984-02-02 |
| FR2537164A1 (en) | 1984-06-08 |
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