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Letters
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Letters to www.finishing.com/Letters by Ted Mooney
s month we toss in a little bit of just about everything in the inorganic finishing milieu. We're sure that there are at least a few topics here that will interest you, and there is certainly at least one topic that could benefit from your take on it.
TI
vace-.- coa..... GUIAIOII
I am researching the "how to" of vacuum deposition coating of aluminum on plastics and metals. I have purchased the "Handbook of Deposition Technolo• gies for Films and Coatings" and have 2 academic questions. Say I am currently at 29.92 in. Hg and need to get to 10-6 Torr. What is a Torr? What is it equivalent to in in. Hg? Second, can the process be done in an inert gas such as argon? Mark Robidoux, [email protected], Malvern, Pa,
One Torr is equal to 1 mm of Hg; therefore, 29.92 in. Hg is equal to 760 mm Hg or 760 Torr, which is atmospheric pressure at sea level. 1 x 10-6 Torr is 0.000001 Torr. Vacuum deposition of aluminum can be done using different physical vapor deposition methods. First is evaporation, which does not re• quire an argon atmosphere. Second is cathodic arc, which does not require argon. Third is sputtering, which does require an argon atmosphere. Fourth is ion vapor deposition, which I believe does use argon. Typically, when argon is used in a vacuum, the gases are pumped out of the vacuum chamber until a pressure in the 10-6 Torr range is reached. Argon is then backfilled into the chamber until a pressure of 10-4 to 10-2 is reached. The argon is usually used to create some kind of plasma. Argon is specifically used because it is a noble gas and doesn't react with the material being deposited. Similarly, helium, neon, krypton, and xenon can be used. Hope this helps. John Davis, jdavisfPiontechinc.com, Veeco Ion Tech, Fort Collins, Colo.
Here, you need to go to the metric system. The ideal air pressure at sea level is 760 mm Hg or 760 Ted Mooney is an independent consulting engineer based in Brick, N.J. 100
Torr. You need to evacuate the chamber using a mechanical pump and then a diffusion pump to go down to 10-6 Torr or 10-3 milliTorr (mT). The process cannot be done at atmospheric pressure if that is what you are implying with your question about argon. This is because most metals do not vaporize at these high pressures. The metals will just keep boiling in the molten pool. Typically, this process will not provide desirable coatings above 10- 1 Torr or 100 mT. Mandar Sunthankar, [email protected], IonEdge Corp., Ft. Collins, Colo.
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Anyone out there know of a process to electroplate niobium onto a stainless steel substrate? Is thick film sputter coating of niobium doable and, if so, what thicknesses of deposited material are reason• able? Michael Auld, [email protected], Synergetics Inc., St. Charles, Mo.
Reasonable thickness for sputter coating depends on the application requirements. Usually, up to 10 microns is trivial. Up to 0.001 in. (25 microns) is relatively simple although it might not be feasible if you want the coating to withstand lots of bending. Above 0.001 in. is doable but it depends on the requirements of the coating, the coating process, etc. John Davis, jdavisfPiontechinc.com, Veeco Ion Tech, Fort Collins, Colo.
It shouldn't be much of a problem to sputter niobium onto your substrate to a thickness of 0.001 in. or so. You can also look at cathodic arc or E-beam deposition. The cheapest approach is E-beam. Ca• thodic arc coatings have the best adhesion, but the process produces droplets of material that leave holes in the coating, though not that many with niobium. If the coater uses an unbalanced magne• tron for the sputter system the sputter deposited coating can have nearly as good adhesion as the cathodic arc deposited coating. Jim Treglio, ismtechfiPixpres.com, ISM Technologies, Poway, Calif.
~Fln"hlng
NIW ....... ORR OLD ULVANIDD 1I0OI'
I'm in the roofing business and have a concern about covering an old galvanized roof with new steel roof• ing panels (painted) even though there is a primer on the bottom surface because there is some rusting on the old roof. Is there a sealant that might provide a barrier in these spots? Or maybe I'm overly con• cerned about early corrosion. Any opinions? Dick Shipman, [email protected] Port Townsend, Wash.
Galvanized coatings are zinc, which is sacrificial to steel. So, while the galvanizing on the old roofwill realistically do infinitely little to retard eventual rusting of the new roof, it will certainly not acceler• ate it. Rust is not "contagious" per se, but it is porous and spongy and thus it tends to retain water. So I would agree with your intuition that it would be a good idea to brush away any loose rust and then apply some primer paint to those spots. The above is theoretical "book knowledge," not practical roofing experience, so take it only for what it's worth. Ted Mooney, P.E., [email protected], Finishing Technology, Brick, N.J.
c_nN8 DU~ SlLVIIIISILVIR CllLOIIIDI WI.
I am an undergraduate physics major at GWU cur• rently doing a joint research program with the med• ical school and I am experiencing a slight problem. I expect that this question is going to be a cinch for you guys to answer, but I say it's dumber not to ask! I need to create a silver-silver chloride wire. The electrodeposition process I am using now is not sat• isfactory. I do not get a thick enough coating nor do I get any durablity. What method do you suggest in order to create a better silver/silver chloride elec• trode? Right now I am running 30 rnA through a 2 M HCl solution. I treat the silver wire in 3 M HN03 first. I do reverse polarity twice while I am deposit• ing giving about 2 min per run (in each direction). Is this even the correct way of doing it? Also, if you can refer me to any good literature, I would appreciate it. Pirouz Shamszad, Presidential Scholar, Physics, [email protected], The George Washington University, Washington
I finally dug this out for you. I make my own silver/silver chloride reference electrodes some• times. Preage the silver wire, which must be 99.99% pure Ag, in a silver nitrate solution acidified with a little nitric acid, then with it as the anode, and a platinum wire as the cathode, plate it in 1 M HCI. Use a current density of5 to 10 mNcm2 • After a good coating is obtained, age the electrode overnight in February ZOOO
distilled water. You do not say what size wire you are using but I suspect the problem is that your current density is too high. (This procedure is from "Experiments in Physical Chemistry" by Shoemaker et aI, McGraw Hill, 1981. It's a handy book for lab stuff like this.) Dave Wichern, [email protected], Berkeley, Calif.
PLAn. WITH PIIOTOfIXIR AS IILIC1'IIOLYn
Is there any chance that I could use exhausted photofixer as a plating bath? It is rich in silver salts but it does have acetic acid as well. I'm an EE and can make any voltage at any current neede
Virtually all real industrial silver plating is done out ofcyanide baths, which are not for amateurs, but there are some proprietary noncyanide processes beginning to be used in specialized cases. It is vaguely possible that you could achieve a usable finish for limited purposes from some kind of nitrate or other noncyanide process that you could build with the photofixer as a starting point. There are some formulas in hobbyist books and some old plat• ing books but a trip to a large technical library would be required. While there, be sure to read up in detail about the dangers of fulminates. It strikes me that it would not be a surprise if you generated some explosive silver fulminates playing around with this stuff.
Ted Mooney, P.E., [email protected], Finishing Technology, Brick, N.J.
SlLVIR IXI"RACTION . . . . PM011I.......c . . . .
I am looking for information on how to extract the silver from used fixer from a photographic process. Just something simple I play with at home. What type of electrodes should I use? What voltage and current should I apply? I have found a lot of infor• mation on this site but could not find what I need. Joe Devlen, [email protected], Wetland, Onto
The former owner or the former manager of Film Recovery Systems in Chicago should have available time on their hands to answer your question. Last I heard they were serving life terms for first-degree murder because one of their employees died doing what you want to do. The point being that until you've had extensive training in the safe operation of a silver recovery operation, and unless a trained coworker is standing by with a Scott Air-pak to rescue you if something goes wrong, you shouldn't 101
attempt it. So I don't want to advise you what voltage and what anode material to use, etc. Ted Mooney, P.E., [email protected], Finishing Technology, Brick, N.J.
I won't ask for instuctions again but will you tell me what the hazard is. Is it poison gas, poison liquid, or an explosion hazard? Joe Devlen, [email protected], Welland, Onto
The basic issue is that silver recovery requires cyanide-based chemistry. Cyanide is a poison as a liquid, of course; even more importantly it releases deadly hydrogen cyanide gas if accidentally acidi• fied. And yes, I can foresee explosion hazards from silver fulminates as well. So the answer to your question is "all of the above." Ted Mooney, P.E., [email protected], Finishing Technology, Brick, N.J.
You will find that companies like mine contract out silver reclamation services in order to avoid problems with employee exposures and related lia• bilities. We use a recovery service and we are cur• rently evaluating a larger (10 gal fixer per day) recovery unit. These devices are self-contained and do an excellent job of recovering silver from fixer for a nominal cost to us. Industry, of course, needs to invest in these devices in order to comply with wastewater discharge limits. Rick Alexander, [email protected], Fashion Engravers, Gaffney, S.C.
..... _ .... AIIODIZI_ I've being doing colored anodizing at home for some time with good results. Now, before anybody tells me this is a dangerous thing to do at home, I've bought a plating manual and I know the safety rules, and the parts that I'm doing are small (100 in2 or less). What I would like to know is how the process of hard anodizing differs from cosmetic anodizing; what temperature, acid concentration, current density; and if there is something that I can add to the acid solution to get a harder anodic film without chang• ing the conditions. Alvaro Fogassa, {[email protected], Bridgeport, Conn.
There are two major differences: temperature and electrical. Temperature 32°F ± 1° (± 2° for lower quality work). This requires an excellent chilling system. Regarding electrical needs, hard anodizing nor• mally requires 40 V minimum with more modem units using a minimum of 60 V. This will normally 102
require a slightly larger amperage capability or the ramp up time will be longer. There are lots of additives that will give you a poor man's hard anodize. The properties are not identical to those of a good hard anodize, but some people find that the product is acceptable for their use. If you are not a business with a waste disposal permit, most companies will not sell to you because of the cradle-to-grave liabilities. Glycolic acid is a common additive for several older formulations. James Watts, [email protected], Fla.
Do you know an inexpensive way to keep the solution cold? I use a 5-gal container as a tank. I'm using about 15 Alfl}. Should I raise it to 25 Alft2? I'm using 15% acid and I've notice that ifllower the acid concentration to 10% I can get a harder film. Alvaro Fogassa, {[email protected] Bridgeport, Conn.
Try to find a used lab chiller. This will run around $500 if you are fortunate enough to find one. You could make a coil out of seamless 316 stainless steel tubing to go into the acid tank. Use a copper coil in a chilling tank; connect with plastic tubing and a small cheap pump. Use dry ice and methyl alcohol in your chilling tank. This goes to about -40°F. The alcohol is infinitely reuseable. Use propylene glycol rather than ethylene glycol since if you spill it, it is nonhazardous. The EPA gets upset about antifreeze spills. You will have to control the temperature of your anodize tank with a temperature controller or manually adjust the flow with a valve. Do not put any more dry ice in the bucket than sufficient to keep some in it. Saves a buck or two. Dry ice will last for days in a taped styrofoam cooler inside a card• board box that is also taped. Additional thoughts: take the stainless steel coil out of the bucket and rinse it off. Sulfuric acid attacks stainless steel above 65°F. And, no, you cannot put the dry ice in the acid. The temperature will be uncontrollable and it will form a lot of car• bonates, changing the conductivity of the solution. No, you cannot use it in a double boiler manner, as plastic is a poor conductor of cold and gets worse as the plastic gets thicker. James Watts, [email protected], Fla.
For a good 2-mil low-temperature hardcoat, 40 VDC is too low. Hardcoating is normally done at 35 to 40 Alft2 , and it can require up to 75 VDC to maintain that current density throughout the pro• cess. At these high-power levels, racking becomes much more critical. Chris Jurey, [email protected], Luke Engineering and Mfg. Co. Inc., Wadsworth, Ohio Metel Finishing
CNROM. PllUNflI'ROII I I " WHIILS
I bought a wheels and tires package from a company in California. Everything has been fine until today. When I was washing my car I noticed that one of my wheels has a small piece of chrome peeling off. I know I have some type of warranty or something. My wheels cost me about $2,000 and I don't think the chrome is supposed to just peel off after a while. What should I do? I am trying to contact the com• pany at the moment. Nick Johnson, [email protected], Bowling Green, Ky.
No, the chrome is not supposed to peel. Any rep• utable firm will replace the wheels at no cost to you. Even ifyou dragged the wheel edge along a curb, the chrome coating should adhere to the underlying base metal. Tom Pullizzi, pullizzi@{inishing.com, Bayside Electrical Testing Inc., Beach Haven, N.J.
I agree with Tom. The chrome plating should not peel from the wheel. Go back to the plating company and make a complaint.
Anders Sundman, [email protected], Sweden TAlI. COVIIIS ............ IIALU'
I have a facility that is looking into energy savings for their heated tanks. They would like to know which system works better, using tank lids or those large floating ping pong balls. The tank lids will save evaporation and energy but they seem hard to use; the ping pong balls float there, but do they really work and are you often losing them to the bottom of the tank? Any experience with either would be a great help. James Hanley, [email protected], Seattle
I had the same question, so I tried both. The floating balls seemed like a really good idea but, after some use, I did find disadvantages to them. While I never lost any to the bottom ofthe tank they were constantly hiding in the cavities of the parts I was immersing. When you have a 190· part in your hand, fishing a little ball out of it is tricky. Also, I think a lot depends on the purpose of the tank. For my caustic tank they were okay except as noted above. But for my nickel tank, I found that they prevented my seeing what was going on in the tank. Being able to see was more important than any heat loss. In all, I found the balls to be more hindrance than help. You may have to try them, but my expe• rience led me back to tank covers. Paul Norman, [email protected], Cobra Co., Odessa, Texas
Paul Norman's comments were interesting, espe• cially about the balls preventing him seeing "what was happening." As you know, those "balls" come in different sizes and in both hollow (cheaper) and solid construction. The complaint I used to get about the hollow ones is that some eventually get pinholed and sink to the bottom. (Personally, I find that hard to believe as the specific gravity of polypropylene is about 0.95 and is, hence, lighter than water.) I assume that these tanks are being "vented." The first question is: "Is the air flow sufficient or perhaps too much?" If the tanks' ventilation systems were designed by Hoyle and the Ventilation Manuals, the chance is fairly good that the air flow is or could be excessive. As lids can be a pain in the neck (weight, size, lifting problems, breakage, etc.) consider a half-lid. Why? Because obviously it would be easier to buy, use, and support. Also because you could essentially halve your cfm consumption, with consequent en• ergy savings on fan motors quite apart from reduc• ing the BTU losses. Remember that ventilation often means air dilution and often that dilution is exces• sive. Also contributory is the hood design. Freeman Newton, [email protected], Acid Ventilation Industrial Design, White Rock, B.C., Can.
I agree, the covers are a big pain and the blow• molded hollow balls get damaged. For this reason we made special flying-saucer-shaped solid PP balls that float. You might look for something similar in your part of the world.
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Khozema Vahanwala, [email protected], India
How do I size a fume scrubber for a bright dip tank, and what is the best material to build it from since it is washing NOx fumes? Guillermo Luna, [email protected], CENSA, Mexico City
Bright dip is probably the most noxious and dif• ficult plating process tank to exhaust. It should have a minimum exhaust rate of 250 cfmlft2 of area of solution. If the area of the tank suffers any cross drafts, 250 might not be enough. Little things make a lot of difference. The ratio of length-to-width; the type of hood; exhausted on 1,2,3, or 4 sides. Things like a PVC backsplash behind the tank and the tanks on either side significantly aid in the fume capture. Wings as little as 3 in. significantly aid in the capture. A small cover that covers as little as 6 in. of the front of the tank significantly reduces the effective area of the tank and can easily be moved just prior to moving the rack into the tank. Push air 103
will cut the required exhaust 20% if it is properly designed, maintained, and operated. The hood needs to be able to resist hot fumes. Depending on how it is designed, the distance from the edge of the solution, etc., it can be made out of heavier-than-normal PVC on the part that is next to the tank. 316 stainless steel is also common. CPVC will withstand the temperature and the chemicals but is hard to weld and costs more. Polypropylene welds do not like hot nitric acid, so I personally would not use polypropylene unless I had plastic welding repair of good quality in house. The scrub• ber can be made of PVC but should have a neutral• ization system on it to kill the nitric acid before it can go up the stack. I normally recommend that a person buy a scrub• ber that is rated at 2,000 cfm larger than calculated so it can be sped up by changing pulleys. The speed up costs more in electricity as fans become less efficient above a given volume for that fan. The media in the scrubber is normally rated fairly tightly, so a large increase or decrease in cfm from the rated flow lowers efficiency. It is better to slow down a unit than to have bought one that is just a little bit too small as the fumes from the bright dip will rust nearly any metal half way across the pro• cess floor. Metal buildings do not like bright dip. It is a vile, nasty process that produces beautiful work. James Watts, [email protected], Fla.
Up until recently I was an advocate of nitric• based bright dips. I had my platers take them out and switch to phosphoric-based dips and they love me for it. I'd much rather overcome the slight drop in effectiveness than the dangers associated with those nasty concoctions. Jim Conner, {[email protected], Salisbury, Md.
As the man says, 250 cfm/ft2 of tank area is a must; however, bright dip fumes (e.g., dipping in a sheet of aluminum) can suddenly really increase in volume. Excess airflow may not be necessary but a good hood design is a must. To capture the sudden cloud of fumes, some people have fully enclosed the bright dip tank (stainless) and even had curtains at each end. This shrouding goes up, say, 6 ft or more and the actual fumehood slots are at high level and on the very (flat) top. In this manner one encloses and surrounds the expanding fume cloud and allows it be efficiently removed without using too much airflow nor requiring a big scrubber, either. The essence of all good exhausting of fumes is capture! I assume you have a small operation. Consider having the freeboard in the tank always over 6 in. Shroud, iffeasible, the sides ofthe tank (Le., extend the sides using PVC sheet) by about 12 in. Ensure that the hood has the normal low level slot and a higher level slot. Ensure, too, that the slots are adjustable. If the hood is, say, 4 ft away from the end of the tank, then push-pull is probably necessary. If prop• erly designed the fumes will roll under the push air curtain until they reach the hood. PVC is eminently okay. Don't use PP due to stress cracking. Use stainless steel if you want to. Assum• ing that you are also doing some sulfuric anodizing, why not use a common scrubber for both? There was a case of one of these scrubbers where sodium hy• droxide was sprayed into the scrubber. To my hor• ror, when I visited this company, the operator was instead just using plain water and yet the scrubber still met air management requirements!
Freeman Newton, [email protected], Acid Ventilation Industrial Design, White Rock, B.C., Can. MF
Recovery and Refining of Precious Metals try C W Ammcn 328 pages $60.00 This book uses a very basic approach to introduce the subject of precious met.ll refining from primary and secondary sources. Working examples of recovery of cle.ln scrap, silver from sterling silver scrap, .md gold from "yellow gold" scrap are given, using step-by-step procedures. This book is a practical guide to recovering, testing, extracting, and refining precious metals. Send Orders to: METAL FINISHING 660 White Plains Rd., Tarrytown, NY 10591-5153 For f;lster service, call (914) 333-2578 or FAX your order to (914) 333-2570 All book ordrn mu.. I.... l'r~I'JI.I.l'lu llld"'k $5.00 .hll'l'lIIl: JII,f hJII,lIin~ for .It'I,,,,·rr of rJt'I1 hook ,·j.II·I'S CmoKU; ~nd 520.00 (or rJ,h hook 'hll'l
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Letters to www.finishing.com/Letters by Ted Mooney
s month we toss in a little bit of just about everything in the inorganic finishing milieu. We're sure that there are at least a few topics here that will interest you, and there is certainly at least one topic that could benefit from your take on it.
TI
vace-.- coa..... GUIAIOII
I am researching the "how to" of vacuum deposition coating of aluminum on plastics and metals. I have purchased the "Handbook of Deposition Technolo• gies for Films and Coatings" and have 2 academic questions. Say I am currently at 29.92 in. Hg and need to get to 10-6 Torr. What is a Torr? What is it equivalent to in in. Hg? Second, can the process be done in an inert gas such as argon? Mark Robidoux, [email protected], Malvern, Pa,
One Torr is equal to 1 mm of Hg; therefore, 29.92 in. Hg is equal to 760 mm Hg or 760 Torr, which is atmospheric pressure at sea level. 1 x 10-6 Torr is 0.000001 Torr. Vacuum deposition of aluminum can be done using different physical vapor deposition methods. First is evaporation, which does not re• quire an argon atmosphere. Second is cathodic arc, which does not require argon. Third is sputtering, which does require an argon atmosphere. Fourth is ion vapor deposition, which I believe does use argon. Typically, when argon is used in a vacuum, the gases are pumped out of the vacuum chamber until a pressure in the 10-6 Torr range is reached. Argon is then backfilled into the chamber until a pressure of 10-4 to 10-2 is reached. The argon is usually used to create some kind of plasma. Argon is specifically used because it is a noble gas and doesn't react with the material being deposited. Similarly, helium, neon, krypton, and xenon can be used. Hope this helps. John Davis, jdavisfPiontechinc.com, Veeco Ion Tech, Fort Collins, Colo.
Here, you need to go to the metric system. The ideal air pressure at sea level is 760 mm Hg or 760 Ted Mooney is an independent consulting engineer based in Brick, N.J. 100
Torr. You need to evacuate the chamber using a mechanical pump and then a diffusion pump to go down to 10-6 Torr or 10-3 milliTorr (mT). The process cannot be done at atmospheric pressure if that is what you are implying with your question about argon. This is because most metals do not vaporize at these high pressures. The metals will just keep boiling in the molten pool. Typically, this process will not provide desirable coatings above 10- 1 Torr or 100 mT. Mandar Sunthankar, [email protected], IonEdge Corp., Ft. Collins, Colo.
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Anyone out there know of a process to electroplate niobium onto a stainless steel substrate? Is thick film sputter coating of niobium doable and, if so, what thicknesses of deposited material are reason• able? Michael Auld, [email protected], Synergetics Inc., St. Charles, Mo.
Reasonable thickness for sputter coating depends on the application requirements. Usually, up to 10 microns is trivial. Up to 0.001 in. (25 microns) is relatively simple although it might not be feasible if you want the coating to withstand lots of bending. Above 0.001 in. is doable but it depends on the requirements of the coating, the coating process, etc. John Davis, jdavisfPiontechinc.com, Veeco Ion Tech, Fort Collins, Colo.
It shouldn't be much of a problem to sputter niobium onto your substrate to a thickness of 0.001 in. or so. You can also look at cathodic arc or E-beam deposition. The cheapest approach is E-beam. Ca• thodic arc coatings have the best adhesion, but the process produces droplets of material that leave holes in the coating, though not that many with niobium. If the coater uses an unbalanced magne• tron for the sputter system the sputter deposited coating can have nearly as good adhesion as the cathodic arc deposited coating. Jim Treglio, ismtechfiPixpres.com, ISM Technologies, Poway, Calif.
~Fln"hlng
NIW ....... ORR OLD ULVANIDD 1I0OI'
I'm in the roofing business and have a concern about covering an old galvanized roof with new steel roof• ing panels (painted) even though there is a primer on the bottom surface because there is some rusting on the old roof. Is there a sealant that might provide a barrier in these spots? Or maybe I'm overly con• cerned about early corrosion. Any opinions? Dick Shipman, [email protected] Port Townsend, Wash.
Galvanized coatings are zinc, which is sacrificial to steel. So, while the galvanizing on the old roofwill realistically do infinitely little to retard eventual rusting of the new roof, it will certainly not acceler• ate it. Rust is not "contagious" per se, but it is porous and spongy and thus it tends to retain water. So I would agree with your intuition that it would be a good idea to brush away any loose rust and then apply some primer paint to those spots. The above is theoretical "book knowledge," not practical roofing experience, so take it only for what it's worth. Ted Mooney, P.E., [email protected], Finishing Technology, Brick, N.J.
c_nN8 DU~ SlLVIIIISILVIR CllLOIIIDI WI.
I am an undergraduate physics major at GWU cur• rently doing a joint research program with the med• ical school and I am experiencing a slight problem. I expect that this question is going to be a cinch for you guys to answer, but I say it's dumber not to ask! I need to create a silver-silver chloride wire. The electrodeposition process I am using now is not sat• isfactory. I do not get a thick enough coating nor do I get any durablity. What method do you suggest in order to create a better silver/silver chloride elec• trode? Right now I am running 30 rnA through a 2 M HCl solution. I treat the silver wire in 3 M HN03 first. I do reverse polarity twice while I am deposit• ing giving about 2 min per run (in each direction). Is this even the correct way of doing it? Also, if you can refer me to any good literature, I would appreciate it. Pirouz Shamszad, Presidential Scholar, Physics, [email protected], The George Washington University, Washington
I finally dug this out for you. I make my own silver/silver chloride reference electrodes some• times. Preage the silver wire, which must be 99.99% pure Ag, in a silver nitrate solution acidified with a little nitric acid, then with it as the anode, and a platinum wire as the cathode, plate it in 1 M HCI. Use a current density of5 to 10 mNcm2 • After a good coating is obtained, age the electrode overnight in February ZOOO
distilled water. You do not say what size wire you are using but I suspect the problem is that your current density is too high. (This procedure is from "Experiments in Physical Chemistry" by Shoemaker et aI, McGraw Hill, 1981. It's a handy book for lab stuff like this.) Dave Wichern, [email protected], Berkeley, Calif.
PLAn. WITH PIIOTOfIXIR AS IILIC1'IIOLYn
Is there any chance that I could use exhausted photofixer as a plating bath? It is rich in silver salts but it does have acetic acid as well. I'm an EE and can make any voltage at any current neede
Virtually all real industrial silver plating is done out ofcyanide baths, which are not for amateurs, but there are some proprietary noncyanide processes beginning to be used in specialized cases. It is vaguely possible that you could achieve a usable finish for limited purposes from some kind of nitrate or other noncyanide process that you could build with the photofixer as a starting point. There are some formulas in hobbyist books and some old plat• ing books but a trip to a large technical library would be required. While there, be sure to read up in detail about the dangers of fulminates. It strikes me that it would not be a surprise if you generated some explosive silver fulminates playing around with this stuff.
Ted Mooney, P.E., [email protected], Finishing Technology, Brick, N.J.
SlLVIR IXI"RACTION . . . . PM011I.......c . . . .
I am looking for information on how to extract the silver from used fixer from a photographic process. Just something simple I play with at home. What type of electrodes should I use? What voltage and current should I apply? I have found a lot of infor• mation on this site but could not find what I need. Joe Devlen, [email protected], Wetland, Onto
The former owner or the former manager of Film Recovery Systems in Chicago should have available time on their hands to answer your question. Last I heard they were serving life terms for first-degree murder because one of their employees died doing what you want to do. The point being that until you've had extensive training in the safe operation of a silver recovery operation, and unless a trained coworker is standing by with a Scott Air-pak to rescue you if something goes wrong, you shouldn't 101
attempt it. So I don't want to advise you what voltage and what anode material to use, etc. Ted Mooney, P.E., [email protected], Finishing Technology, Brick, N.J.
I won't ask for instuctions again but will you tell me what the hazard is. Is it poison gas, poison liquid, or an explosion hazard? Joe Devlen, [email protected], Welland, Onto
The basic issue is that silver recovery requires cyanide-based chemistry. Cyanide is a poison as a liquid, of course; even more importantly it releases deadly hydrogen cyanide gas if accidentally acidi• fied. And yes, I can foresee explosion hazards from silver fulminates as well. So the answer to your question is "all of the above." Ted Mooney, P.E., [email protected], Finishing Technology, Brick, N.J.
You will find that companies like mine contract out silver reclamation services in order to avoid problems with employee exposures and related lia• bilities. We use a recovery service and we are cur• rently evaluating a larger (10 gal fixer per day) recovery unit. These devices are self-contained and do an excellent job of recovering silver from fixer for a nominal cost to us. Industry, of course, needs to invest in these devices in order to comply with wastewater discharge limits. Rick Alexander, [email protected], Fashion Engravers, Gaffney, S.C.
..... _ .... AIIODIZI_ I've being doing colored anodizing at home for some time with good results. Now, before anybody tells me this is a dangerous thing to do at home, I've bought a plating manual and I know the safety rules, and the parts that I'm doing are small (100 in2 or less). What I would like to know is how the process of hard anodizing differs from cosmetic anodizing; what temperature, acid concentration, current density; and if there is something that I can add to the acid solution to get a harder anodic film without chang• ing the conditions. Alvaro Fogassa, {[email protected], Bridgeport, Conn.
There are two major differences: temperature and electrical. Temperature 32°F ± 1° (± 2° for lower quality work). This requires an excellent chilling system. Regarding electrical needs, hard anodizing nor• mally requires 40 V minimum with more modem units using a minimum of 60 V. This will normally 102
require a slightly larger amperage capability or the ramp up time will be longer. There are lots of additives that will give you a poor man's hard anodize. The properties are not identical to those of a good hard anodize, but some people find that the product is acceptable for their use. If you are not a business with a waste disposal permit, most companies will not sell to you because of the cradle-to-grave liabilities. Glycolic acid is a common additive for several older formulations. James Watts, [email protected], Fla.
Do you know an inexpensive way to keep the solution cold? I use a 5-gal container as a tank. I'm using about 15 Alfl}. Should I raise it to 25 Alft2? I'm using 15% acid and I've notice that ifllower the acid concentration to 10% I can get a harder film. Alvaro Fogassa, {[email protected] Bridgeport, Conn.
Try to find a used lab chiller. This will run around $500 if you are fortunate enough to find one. You could make a coil out of seamless 316 stainless steel tubing to go into the acid tank. Use a copper coil in a chilling tank; connect with plastic tubing and a small cheap pump. Use dry ice and methyl alcohol in your chilling tank. This goes to about -40°F. The alcohol is infinitely reuseable. Use propylene glycol rather than ethylene glycol since if you spill it, it is nonhazardous. The EPA gets upset about antifreeze spills. You will have to control the temperature of your anodize tank with a temperature controller or manually adjust the flow with a valve. Do not put any more dry ice in the bucket than sufficient to keep some in it. Saves a buck or two. Dry ice will last for days in a taped styrofoam cooler inside a card• board box that is also taped. Additional thoughts: take the stainless steel coil out of the bucket and rinse it off. Sulfuric acid attacks stainless steel above 65°F. And, no, you cannot put the dry ice in the acid. The temperature will be uncontrollable and it will form a lot of car• bonates, changing the conductivity of the solution. No, you cannot use it in a double boiler manner, as plastic is a poor conductor of cold and gets worse as the plastic gets thicker. James Watts, [email protected], Fla.
For a good 2-mil low-temperature hardcoat, 40 VDC is too low. Hardcoating is normally done at 35 to 40 Alft2 , and it can require up to 75 VDC to maintain that current density throughout the pro• cess. At these high-power levels, racking becomes much more critical. Chris Jurey, [email protected], Luke Engineering and Mfg. Co. Inc., Wadsworth, Ohio Metel Finishing
CNROM. PllUNflI'ROII I I " WHIILS
I bought a wheels and tires package from a company in California. Everything has been fine until today. When I was washing my car I noticed that one of my wheels has a small piece of chrome peeling off. I know I have some type of warranty or something. My wheels cost me about $2,000 and I don't think the chrome is supposed to just peel off after a while. What should I do? I am trying to contact the com• pany at the moment. Nick Johnson, [email protected], Bowling Green, Ky.
No, the chrome is not supposed to peel. Any rep• utable firm will replace the wheels at no cost to you. Even ifyou dragged the wheel edge along a curb, the chrome coating should adhere to the underlying base metal. Tom Pullizzi, pullizzi@{inishing.com, Bayside Electrical Testing Inc., Beach Haven, N.J.
I agree with Tom. The chrome plating should not peel from the wheel. Go back to the plating company and make a complaint.
Anders Sundman, [email protected], Sweden TAlI. COVIIIS ............ IIALU'
I have a facility that is looking into energy savings for their heated tanks. They would like to know which system works better, using tank lids or those large floating ping pong balls. The tank lids will save evaporation and energy but they seem hard to use; the ping pong balls float there, but do they really work and are you often losing them to the bottom of the tank? Any experience with either would be a great help. James Hanley, [email protected], Seattle
I had the same question, so I tried both. The floating balls seemed like a really good idea but, after some use, I did find disadvantages to them. While I never lost any to the bottom ofthe tank they were constantly hiding in the cavities of the parts I was immersing. When you have a 190· part in your hand, fishing a little ball out of it is tricky. Also, I think a lot depends on the purpose of the tank. For my caustic tank they were okay except as noted above. But for my nickel tank, I found that they prevented my seeing what was going on in the tank. Being able to see was more important than any heat loss. In all, I found the balls to be more hindrance than help. You may have to try them, but my expe• rience led me back to tank covers. Paul Norman, [email protected], Cobra Co., Odessa, Texas
Paul Norman's comments were interesting, espe• cially about the balls preventing him seeing "what was happening." As you know, those "balls" come in different sizes and in both hollow (cheaper) and solid construction. The complaint I used to get about the hollow ones is that some eventually get pinholed and sink to the bottom. (Personally, I find that hard to believe as the specific gravity of polypropylene is about 0.95 and is, hence, lighter than water.) I assume that these tanks are being "vented." The first question is: "Is the air flow sufficient or perhaps too much?" If the tanks' ventilation systems were designed by Hoyle and the Ventilation Manuals, the chance is fairly good that the air flow is or could be excessive. As lids can be a pain in the neck (weight, size, lifting problems, breakage, etc.) consider a half-lid. Why? Because obviously it would be easier to buy, use, and support. Also because you could essentially halve your cfm consumption, with consequent en• ergy savings on fan motors quite apart from reduc• ing the BTU losses. Remember that ventilation often means air dilution and often that dilution is exces• sive. Also contributory is the hood design. Freeman Newton, [email protected], Acid Ventilation Industrial Design, White Rock, B.C., Can.
I agree, the covers are a big pain and the blow• molded hollow balls get damaged. For this reason we made special flying-saucer-shaped solid PP balls that float. You might look for something similar in your part of the world.
.... --.....
Khozema Vahanwala, [email protected], India
How do I size a fume scrubber for a bright dip tank, and what is the best material to build it from since it is washing NOx fumes? Guillermo Luna, [email protected], CENSA, Mexico City
Bright dip is probably the most noxious and dif• ficult plating process tank to exhaust. It should have a minimum exhaust rate of 250 cfmlft2 of area of solution. If the area of the tank suffers any cross drafts, 250 might not be enough. Little things make a lot of difference. The ratio of length-to-width; the type of hood; exhausted on 1,2,3, or 4 sides. Things like a PVC backsplash behind the tank and the tanks on either side significantly aid in the fume capture. Wings as little as 3 in. significantly aid in the capture. A small cover that covers as little as 6 in. of the front of the tank significantly reduces the effective area of the tank and can easily be moved just prior to moving the rack into the tank. Push air 103
will cut the required exhaust 20% if it is properly designed, maintained, and operated. The hood needs to be able to resist hot fumes. Depending on how it is designed, the distance from the edge of the solution, etc., it can be made out of heavier-than-normal PVC on the part that is next to the tank. 316 stainless steel is also common. CPVC will withstand the temperature and the chemicals but is hard to weld and costs more. Polypropylene welds do not like hot nitric acid, so I personally would not use polypropylene unless I had plastic welding repair of good quality in house. The scrub• ber can be made of PVC but should have a neutral• ization system on it to kill the nitric acid before it can go up the stack. I normally recommend that a person buy a scrub• ber that is rated at 2,000 cfm larger than calculated so it can be sped up by changing pulleys. The speed up costs more in electricity as fans become less efficient above a given volume for that fan. The media in the scrubber is normally rated fairly tightly, so a large increase or decrease in cfm from the rated flow lowers efficiency. It is better to slow down a unit than to have bought one that is just a little bit too small as the fumes from the bright dip will rust nearly any metal half way across the pro• cess floor. Metal buildings do not like bright dip. It is a vile, nasty process that produces beautiful work. James Watts, [email protected], Fla.
Up until recently I was an advocate of nitric• based bright dips. I had my platers take them out and switch to phosphoric-based dips and they love me for it. I'd much rather overcome the slight drop in effectiveness than the dangers associated with those nasty concoctions. Jim Conner, {[email protected], Salisbury, Md.
As the man says, 250 cfm/ft2 of tank area is a must; however, bright dip fumes (e.g., dipping in a sheet of aluminum) can suddenly really increase in volume. Excess airflow may not be necessary but a good hood design is a must. To capture the sudden cloud of fumes, some people have fully enclosed the bright dip tank (stainless) and even had curtains at each end. This shrouding goes up, say, 6 ft or more and the actual fumehood slots are at high level and on the very (flat) top. In this manner one encloses and surrounds the expanding fume cloud and allows it be efficiently removed without using too much airflow nor requiring a big scrubber, either. The essence of all good exhausting of fumes is capture! I assume you have a small operation. Consider having the freeboard in the tank always over 6 in. Shroud, iffeasible, the sides ofthe tank (Le., extend the sides using PVC sheet) by about 12 in. Ensure that the hood has the normal low level slot and a higher level slot. Ensure, too, that the slots are adjustable. If the hood is, say, 4 ft away from the end of the tank, then push-pull is probably necessary. If prop• erly designed the fumes will roll under the push air curtain until they reach the hood. PVC is eminently okay. Don't use PP due to stress cracking. Use stainless steel if you want to. Assum• ing that you are also doing some sulfuric anodizing, why not use a common scrubber for both? There was a case of one of these scrubbers where sodium hy• droxide was sprayed into the scrubber. To my hor• ror, when I visited this company, the operator was instead just using plain water and yet the scrubber still met air management requirements!
Freeman Newton, [email protected], Acid Ventilation Industrial Design, White Rock, B.C., Can. MF
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