featurefocus

PLATING BATH OPERATIONPlating rate: After the initial make-up, the silver bath must be filteredcontinuously using a 5-µm or small-er spun-polypro cartridge and car-bon filter. The optimum cathodecurrent density for this non-cyanidesilver bath is 3–10 ASF. The cathodeefficiency is around 95%. Table 2lists the plating rate for various cur-rent densities.

MAINTENANCEBath maintenance typically compris-es regular addition of a silver com-plexor/stabilizer, pH adjustment,and continuous conventional andcarbon filtration. Silver is suppliedby the slab silver anode. Thismethod is cost effective because itplates out of the silver anodes ratherthan the solution. Rarely the silvermetal will drop too low and silverconcentrate must be added. A silver-stabilizing electrolyte is

added on a regular basis to complexthe silver dissolved from the anodes.Additions of silver stabilizer are madebased on ampere hours and hull celltests. Additions are usually requiredevery 500 ampere hours and therequired addition will be based on thesilver concentration. Typically a 1–2%daily addition of this electrolyte willbe required while plating. If the solu-tion sits idle for a week or longer, a 2%by volume addition of the electrolyteshould be made.

The sliver stabilizer and its break-down products can also be analyzedby high-performance liquid chro-matography. Years of industrialpractice with this non-cyanide silver

BATH SETUP AND SPECIFICATIONSThe bath is an alkaline, cyanide-freeliquid solution that contains silverions, electrolytes, and DI water. Themixed bath is a clear solution. The pHis adjusted using potassium hydroxide(KOH) and sulfuric acid. It is essentialto maintain pH between 8.5 and 9.2. Ifthe pH is too low, you will get theimmersion deposition of silver, and itwill be necessary to add 45% KOH toraise the pH to around 8.8. Also, do notlet the pH of the bath exceed 10.5.Plating specifications for rack and bar-rel baths are listed in Table 1.Note that the silver metal concen-

tration in both the rack and barrelformulations are about 50–60% ofthe concentration found in mostcyanide baths. Thus the silver drag-out losses are greatly reduced withthis non-cyanide bath comparedwith cyanide baths.

Today’s search for smaller grainsize includes silver, and nano sil-

ver electroplating is currently beingresearched. This article will includephotographic examples that showthe grain structure of the E-Brite50/50 alkaline non-cyanide silverprocess, including instances whenthe bath has not been filtered suffi-ciently. The filtering of the E-Brite50/50 process is important toachieve finer grain size. Also included in this article will be

a discussion on other physical charac-teristics of the E-Brite 50/50 process.The E-Brite 50/50 process is a pro-duction-proven method that is bothstable and reliable (see testimonial onnext page). Recently, a new develop-ment of plating on nickel substratesother than electroless nickel (EN) hasbeen achieved through utilizing anelectrolytic prep.

E-Brite 50/50 Alkaline Non-cyanideSilver Process Produces a Finer Grain

Structure than Cyanide Silver

BY ERIC OLANDER, PRESIDENT, ELECTROCHEMICAL PRODUCTS, INC. (EPI),NEW BERLIN, WIS.

Rack Plating Barrel Plating

Optimum Range Optimum Range

Silver metalpHTemperatureCathode current densityAnode current density

2.0 oz/gal8.868°F

3–10 ASF—

1.5–2.5 oz/gal8.5–9.560–75°F2–20 ASF2–10 ASF

2.4 oz/gal8.868°F

1–3 ASF—

2–2.5 oz/gal8.5–9.560–75°F0.5–5 ASF2–10 ASF

Agitation Air agitation on the anodes, plus cathode rod agitation or air agitation on the cathodes.

Filtration Continuous polypro-wound and carbon.

Table 1: Plating Specifications for Rack & Barrel Baths

Cathode current density (ASF) 5 10 15 20 25

Plating rate (µin/min) 12 21.6 32.4 43.2 54

Table 2: Plating Rate for Various Current Densities

52I metalfinishing I June 2009 www.metalfinishing.com

Feature Focus June 2009-proof-for-Eric-RT:Metal Multi Template USE THIS.qxd 11/2/2009 9:30 AM Page 1

lent. The bath does not immersioncoat on copper, and excellent adhe-sion can be achieve without the needfor a strike bath. With the introduction of pulse-

plating technology, it may be possi-ble to achieve nano-sized depositstructures using this non-cyanide sil-ver process. The crystalline structureof the silver coating is also character-ized by X-ray diffraction. The broad-er diffraction peak of the non-cyanide deposit suggests a finer grainthan that of a cyanide silver deposit.

Hardness: The hardness of non-cyanide silver coating is around95–110 KHN25, which is slightlyharder than the cyanide silver froma solution with no additives. Thehardness is measured on a cross-sec-tional sample with a Knoop dia-mond indenter at a load of 25g.

Electrical resistance: The electricalresistivity of the non-cyanide depositis around 3.0–3.5 µ�/cm, which isslightly higher than that of thecyanide silver deposit, and is suitablefor electrical applications.

Wear resistance: The wear resistivi-ty of the non-cyanide silver deposits

process shows that the breakdownproducts has no ill-effect on thephysical properties of silver deposits. Continuous conventional and

carbon filtration with 5-µm or finerfilters is critical for the successfuloperation of the non-cyanide silverprocess. Silver non-cyanide com-pounds are normally less stablethan the cyanide silver. Therefore,silver peroxide (AgO) particles canform when silver stabilizer is notpresent in sufficient quantities. TheSEM morphology of a normallyoperating silver deposit is shown inFigure 1. The deposit is smooth andhas a fine grain structure. If the sil-ver bath has not been filtered andhas idled for awhile, the silverdeposit tends to lead to bigger grainstructure and the deposit can bemore “rough,” which is shown inFigure 2.

PHYSICAL PROPERTIES OF NON-CYANIDE SILVER DEPOSITSAppearance: Parts have a slightlydull appearance, which is quicklyconverted to a bright white by dip-ping them momentarily in dilutesulfuric acid. The throwing is excel-

is superior to that of cyanide silverdeposits. The wear test, performedby Taber Abrader, abrades the silverdeposit with a load of 250g.

Purity: The purity of the non-cyanide silver deposit is around99.8%, which is characterized byAuger emission spectroscopy. E-Brite 50/50 alkaline non-cyanide sil-ver has always plated directly to mid-phos EN substrates with excellentadhesion. The reason for the adhe-sion of the silver onto the mid-phosEN process is the nickel platingstructure is amorphous while elec-troplated nickel is laminar. Recently,plated nickel substrates such asWoods, Watts, and sulfamate nickelcan be plated without a separatenickel strike. Following is a descrip-tion of the process:

1. E-Prep 242: 60 g/l 8 oz/gallon,

130–150°F, 4–8 V, cathodic cur-

rent 15–40 ASF, 40–50 seconds

2. Cold-water rinse

3. 5–20% by volume sulfuric acid

4. Cold-water rinse

5. Plate with E-Brite 50/50,

entering plating solution live

featurefocus

www.metalfinishing.com June 2009 I metalfinishing I 53

Figure 1: 50/50 grain structure with excellentfiltration. (Images courtesy of Universite deSherbrooke.)

Figure 2: Thick layer with average filtration.

Figure 3: Thin layer with average filtration. Figure 4: Bath set idle and inadequate filtration.

TESTIMONIALJoe Miller, Plant Manager, Helwig Carbon Corp.: “EPI’s non-cyanide sil-ver plating bath replaced our existing cyanide silver plating bath. We made theswitch due to [the] high cost associated with Homeland Security compliance. I esti-mate we saved $19,030!!! Besides the obvious fact [that] we have a safer work envi-ronment, other benefits include lower operating cost and further reduced costs asso-ciated with environmental compliance. EPI’s Bob Campbell and Sid Arthur pro-vided excellent customer service and technical support to assure a smooth transition.I was impressed with on-site support to get us up and running! Both gentlemen spentample time on operator training and continue to be readily available if necessary.The first day up, we were able to test a wide variety of our product line. All results

Feature Focus June 2009-proof-for-Eric-RT:Metal Multi Template USE THIS.qxd 11/2/2009 9:30 AM Page 2

CONCLUSIONSThe E-Brite 50/50 process can platea finer grain deposit than cyanidesilver when using the correct filtra-tion. This allows plating directlyonto nickel substrates using an elec-trolytic prep, while allowing manyother benefits to accrue for the sil-ver electroplater. There is a newdrive to eliminate cyanide if you listthe substance in your Departmentof Homeland Security (DHS)report. The E-Brite 50/50 processeliminates the cyanide, saving timeand the cost of DHS reporting,resulting in a new tangible benefit.

BIO Eric Olander is the president ofElectrochemical Products, Inc. (EPI), aNew Berlin, Wis.-based manufacturer ofISO-9000-certified chemicals for the metalplating and finishing industry. Olanderalso holds the position of chairman of the2009 SUR/FIN Steering Committee. Hemay be reached via e-mail aterico@epi.com.

ACKNOWLEDGEMENTS Images for this article were supplied by theUniversite de Sherbrooke.

featurefocus

54 I metalfinishing I June 2009 www.metalfinishing.com

Feature Focus June 2009-proof-for-Eric-RT:Metal Multi Template USE THIS.qxd 11/2/2009 9:30 AM Page 3