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Identification of deposits
IDENTIFICATION OF DEPOSITS by Charles Rosenstein She#Case Ltd,, Jerusalem, Israel
and Stanley Hirsch Leeam Consultants Ltd., New Rochelle, N. Y. Unknown metal deposits are qualitatively determined by systematic spot testing (Table I) or by instrumental analysis. Before testing, lacquer and other protective coatings must be removed from parts with a suitable solvent. Dirty parts are cleaned with a paste made from ordinary kitchen cleansers and water, and are then rinsed well with water.
SPOT TESTING OF DEPOSITS Immerse the part in warm 50% by volume nitric acid. If the surface is attacked, note the color of the nitric acid solution and proceed to Table II. For thin deposits, the initial reaction of nitric acid on the deposit must be carefully observed, so that the deposit will be tested and not the base metal. When gold is thinly plated on brass and then placed in a nitric acid
Table I. Flow Chart for Systematic Spot Testing of Deposits Deposit:
///~..~Warm, 50% by
Not Attacked:
Attacked:
Aluminum Chromium Gold Palladium Platinum Rhodium
Blue---copper
Green--brass, nickel Yellow---bronz, iron Colorless--cadmium, indium lead, silver, zinc Cloudy--fin, fin alloys
I
Warm, concentrated
hydrochloricacid
Not Attacked:
Attacked:
Gold Palladium Platinum Rhodium
Aluminum(colorless) Chromium (green)
Gold
Not Attacked:
Palladium
Rhodium
Platinum
595
Table II. Deposits Attacked by 50% by Volume Nitric Acid Color of Nitric Acid Solution
Qualitative Test to Confirm Deposit
Colored: Blue--copper Green--brass, nickel Yellow--bronze, iron
Dissolve the deposit in warm 50% by volume nitric acid. A blue solution indicates copper. A yellow nitric acid solution indicates bronze or iron. Add ammonia until red litmus turns blue. A reddish-brown precipitate indicates iron. If iron is not present, the deposit is bronze. A green nitric acid solution indicates brass or nickel. Add ammonia until red litmus rams blue. Then add five drops 5% dimethylglyoxime in ethanol. A red precipitate indicates nickel. If nickel is not present, the deposit is brass. Copper and copper alloys are confirmed by adding ammonia to a nitric acid solution until red litmus turns blue. Then add five drops 5% benzoinoxime in ethanol. A green precipitate indicates copper or a copper alloy.
Colorless: Cadmium, indium, lead, silver, zinc
Dissolve the deposit in warm 50% by volume nitric acid. Add one drop concentrated hydrochloric acid. A cloudy sointionindicates silver. ff silver is not present, add one drop concentrated sulfi.tric acid to the nitric acid solution. A white precipitate indicates lead. If lead is not present, add ammonia to the nitric acid solution until red litmus turns blue. A white precipitate indicates indium. If indium is not present, add ammonia to the nitric acid solution until red litmus turns blue. Then add 10 drops 10% sodium sulfide solution. A yellow precipitate indicates cadmium; a white precipitate indicates zinc.
Cloudy: Tin, tin alloys
Dissolve the deposit in warm 50% by volume nitric acid. Add water, filter the solution, and note the color of the filtrate: copper and nickel alloys are blue-green; zinc and lead alloys are colorless. Confmn the constituent of the tin alloy by testing the filtrate with the above specific tests for copper, lead, nickel, and zinc.
solution, the brass will be attacked a n d insoluble gold flakes will be present in the solution. Specific qualitative tests in Table lI c o n f i r m the type of deposit. f f the surface is not attacked b y w a r m 5 0 % b y v o l u m e nitric acid, p r o c e e d to Table III. Place 10 drops o f w a r m c o n c e n t r a t e d h y d r o c h l o r i c acid on the part. If the deposit is attacked, it is either a l u m i n u m (colorless) or c h r o m i u m (green). If the deposit is not attacked, place t w o drops a q u a regia (250 ml nitric acid a n d 7 5 0 ml h y d r o c h l o r i c acid per liter) on it and c h e c k if the deposit dissolves. E a c h of the specific qualitative tests for gold, platinum, a n d p a l l a d i u m (Table III) m u s t be run to determine the type o f deposit. K n o w n coatings m a y be tested along with u n k n o w n ones in order to b e c o m e familiar with the reactions a n d colors o f a particular test.
596
Table III. Deposits Not Attacked by 50% by Volume Nitric Acid Deposit
Rhodium
Ten Drops Warm Concentrated HCl
Two Drops Aqua Regia
Not attacked
Not attacked
Aluminum
Attacked(colorless)
Chromium
Attacked (green)
Gold Palladium Platinum
Not attacked
Attacked
QualitativeTest to Confirm Deposit
Dissolve the deposit in aqua regia. Evaporate the solution to dryness, add 20 ml 10% by volume hydrochloric acid and one ml dimethylglyoxime in ethanol. A yellow precipitate indicates palladium. If palladium is not present, add two grams ammonittm chloride to the solution. A yellow precipitate indicates platinum. If platinum is not present, add 10 ml 10% oxalic acid to the solution, heat, filter the precipitate and dry. A gold-colored precipitate indicates gold or a gold alloy.
INSTRUMENTAL ANALYSIS Several instrumental methods (see chapter elsewhere in this Guidebook on chemical analysis of plating solutions) provide a quick and sensitive means of identifying unknown metallic deposits. Deposits are scraped off, filed, or stripped by immersion in a suitable solution.
Emission Spectrometry Emission spectrometry is useful in the qualitative detection of metals because of its accuracy, speed, and ease of operation. The sample is inserted into a graphite electrode in the form of filings, shavings, or a solution. A DC arc is usually used to excite the sample and cause it to emit a unique and characteristic set of spectral lines. It is necessary to identify only a few of the most intense lines of each element to confirm conclusively the presence of an element. Likewise, the lack of these lines signifies the absence of that element in the sample. Tables of characteristic wavelengths are available. An emission spectrograph of pure iron is a wavelength standard, as it labels and identifies the actual wavelengths from the deposit being determined. Spectra of the pure iron and other pure metals are photographed side by side with the spectrum of the sanaple.
X-Ray F l u o r e s c e n c e When a sample is exposed to X-rays of certain wavelengths, the various elements in the sample will give off more X-rays whose energies are characteristic of the elements in the sample. Qualitative analysis of these elements is performed by measuring the energies of these fluorescent X-rays.
Mass Spectrometry A mass spectrometer separates ions from an ionized sample according to their mass-to-charge ratios. Qualitative identification is obtained from these ratios.
597
Polarography The half-wave potential in polarograms is characteristic of the substance undergoing reduction at the microelectrode (dropping mercury electrode).
Atomic Absorption Spectroscopy Almost all metals can be analyzed by atomic absorption spectroscopy. Small amounts of an unknown deposit are needed for identification and different current density areas can be analyzed. Extensive sample pretreatment is unnecessary.
Electrodeposition: The Materials Science of Coatings and Substrates byJ.W. Dini 367 pages $105.00 The first comprehensive book on materials science and its relationship to electrodeposition and other coating technologies. Topics covered include hydrogen embrittlement, adhesion, diffusion, porosity, stressadditives, corrosion, and wear. Send Ordersto: METAL FINISHING, 650 Avenue of the Americas, New York, NY 10011 For faster service, call (212) 633-3199 or FAX your order to (212) 633-3140 All book orders must be prepaid. Please include $5.00 shipping and handling for delivery of each book via UPS in the U.S., $10.00 for each book shipped express to Canada; and $20.00 for each book shipped express to all other countries.
The Chemical Analysis of Electroplating Solutions by T.H. Irvine
182 pages
$50.00
Chapters in this work are divided into groups in accordance with the periodic table of elements. Though the procedures are traditional, theoretical aspects are included with other information. Anyone who studies this book carefully will derive a helpful understanding of what he or she is doing so that unexpected results can be searched out for causes and corrected. Send Orders to:
METAL FINISHING 650 Avenue of the Americas, N e w York, NY 10011 For faster service, call (21 2) 633-3199 or FAX your order to (21 2) 633-3140 All book orders must be prepaid. Pleaseinclude $5.00 shipping and handling for delivery of each book via UPS in the U.S., $10.00 for each book shipped expressto Canada; and $20.00 for each book shipped expressto all
598
and Stanley Hirsch Leeam Consultants Ltd., New Rochelle, N. Y. Unknown metal deposits are qualitatively determined by systematic spot testing (Table I) or by instrumental analysis. Before testing, lacquer and other protective coatings must be removed from parts with a suitable solvent. Dirty parts are cleaned with a paste made from ordinary kitchen cleansers and water, and are then rinsed well with water.
SPOT TESTING OF DEPOSITS Immerse the part in warm 50% by volume nitric acid. If the surface is attacked, note the color of the nitric acid solution and proceed to Table II. For thin deposits, the initial reaction of nitric acid on the deposit must be carefully observed, so that the deposit will be tested and not the base metal. When gold is thinly plated on brass and then placed in a nitric acid
Table I. Flow Chart for Systematic Spot Testing of Deposits Deposit:
///~..~Warm, 50% by
Not Attacked:
Attacked:
Aluminum Chromium Gold Palladium Platinum Rhodium
Blue---copper
Green--brass, nickel Yellow---bronz, iron Colorless--cadmium, indium lead, silver, zinc Cloudy--fin, fin alloys
I
Warm, concentrated
hydrochloricacid
Not Attacked:
Attacked:
Gold Palladium Platinum Rhodium
Aluminum(colorless) Chromium (green)
Gold
Not Attacked:
Palladium
Rhodium
Platinum
595
Table II. Deposits Attacked by 50% by Volume Nitric Acid Color of Nitric Acid Solution
Qualitative Test to Confirm Deposit
Colored: Blue--copper Green--brass, nickel Yellow--bronze, iron
Dissolve the deposit in warm 50% by volume nitric acid. A blue solution indicates copper. A yellow nitric acid solution indicates bronze or iron. Add ammonia until red litmus turns blue. A reddish-brown precipitate indicates iron. If iron is not present, the deposit is bronze. A green nitric acid solution indicates brass or nickel. Add ammonia until red litmus rams blue. Then add five drops 5% dimethylglyoxime in ethanol. A red precipitate indicates nickel. If nickel is not present, the deposit is brass. Copper and copper alloys are confirmed by adding ammonia to a nitric acid solution until red litmus turns blue. Then add five drops 5% benzoinoxime in ethanol. A green precipitate indicates copper or a copper alloy.
Colorless: Cadmium, indium, lead, silver, zinc
Dissolve the deposit in warm 50% by volume nitric acid. Add one drop concentrated hydrochloric acid. A cloudy sointionindicates silver. ff silver is not present, add one drop concentrated sulfi.tric acid to the nitric acid solution. A white precipitate indicates lead. If lead is not present, add ammonia to the nitric acid solution until red litmus turns blue. A white precipitate indicates indium. If indium is not present, add ammonia to the nitric acid solution until red litmus turns blue. Then add 10 drops 10% sodium sulfide solution. A yellow precipitate indicates cadmium; a white precipitate indicates zinc.
Cloudy: Tin, tin alloys
Dissolve the deposit in warm 50% by volume nitric acid. Add water, filter the solution, and note the color of the filtrate: copper and nickel alloys are blue-green; zinc and lead alloys are colorless. Confmn the constituent of the tin alloy by testing the filtrate with the above specific tests for copper, lead, nickel, and zinc.
solution, the brass will be attacked a n d insoluble gold flakes will be present in the solution. Specific qualitative tests in Table lI c o n f i r m the type of deposit. f f the surface is not attacked b y w a r m 5 0 % b y v o l u m e nitric acid, p r o c e e d to Table III. Place 10 drops o f w a r m c o n c e n t r a t e d h y d r o c h l o r i c acid on the part. If the deposit is attacked, it is either a l u m i n u m (colorless) or c h r o m i u m (green). If the deposit is not attacked, place t w o drops a q u a regia (250 ml nitric acid a n d 7 5 0 ml h y d r o c h l o r i c acid per liter) on it and c h e c k if the deposit dissolves. E a c h of the specific qualitative tests for gold, platinum, a n d p a l l a d i u m (Table III) m u s t be run to determine the type o f deposit. K n o w n coatings m a y be tested along with u n k n o w n ones in order to b e c o m e familiar with the reactions a n d colors o f a particular test.
596
Table III. Deposits Not Attacked by 50% by Volume Nitric Acid Deposit
Rhodium
Ten Drops Warm Concentrated HCl
Two Drops Aqua Regia
Not attacked
Not attacked
Aluminum
Attacked(colorless)
Chromium
Attacked (green)
Gold Palladium Platinum
Not attacked
Attacked
QualitativeTest to Confirm Deposit
Dissolve the deposit in aqua regia. Evaporate the solution to dryness, add 20 ml 10% by volume hydrochloric acid and one ml dimethylglyoxime in ethanol. A yellow precipitate indicates palladium. If palladium is not present, add two grams ammonittm chloride to the solution. A yellow precipitate indicates platinum. If platinum is not present, add 10 ml 10% oxalic acid to the solution, heat, filter the precipitate and dry. A gold-colored precipitate indicates gold or a gold alloy.
INSTRUMENTAL ANALYSIS Several instrumental methods (see chapter elsewhere in this Guidebook on chemical analysis of plating solutions) provide a quick and sensitive means of identifying unknown metallic deposits. Deposits are scraped off, filed, or stripped by immersion in a suitable solution.
Emission Spectrometry Emission spectrometry is useful in the qualitative detection of metals because of its accuracy, speed, and ease of operation. The sample is inserted into a graphite electrode in the form of filings, shavings, or a solution. A DC arc is usually used to excite the sample and cause it to emit a unique and characteristic set of spectral lines. It is necessary to identify only a few of the most intense lines of each element to confirm conclusively the presence of an element. Likewise, the lack of these lines signifies the absence of that element in the sample. Tables of characteristic wavelengths are available. An emission spectrograph of pure iron is a wavelength standard, as it labels and identifies the actual wavelengths from the deposit being determined. Spectra of the pure iron and other pure metals are photographed side by side with the spectrum of the sanaple.
X-Ray F l u o r e s c e n c e When a sample is exposed to X-rays of certain wavelengths, the various elements in the sample will give off more X-rays whose energies are characteristic of the elements in the sample. Qualitative analysis of these elements is performed by measuring the energies of these fluorescent X-rays.
Mass Spectrometry A mass spectrometer separates ions from an ionized sample according to their mass-to-charge ratios. Qualitative identification is obtained from these ratios.
597
Polarography The half-wave potential in polarograms is characteristic of the substance undergoing reduction at the microelectrode (dropping mercury electrode).
Atomic Absorption Spectroscopy Almost all metals can be analyzed by atomic absorption spectroscopy. Small amounts of an unknown deposit are needed for identification and different current density areas can be analyzed. Extensive sample pretreatment is unnecessary.
Electrodeposition: The Materials Science of Coatings and Substrates byJ.W. Dini 367 pages $105.00 The first comprehensive book on materials science and its relationship to electrodeposition and other coating technologies. Topics covered include hydrogen embrittlement, adhesion, diffusion, porosity, stressadditives, corrosion, and wear. Send Ordersto: METAL FINISHING, 650 Avenue of the Americas, New York, NY 10011 For faster service, call (212) 633-3199 or FAX your order to (212) 633-3140 All book orders must be prepaid. Please include $5.00 shipping and handling for delivery of each book via UPS in the U.S., $10.00 for each book shipped express to Canada; and $20.00 for each book shipped express to all other countries.
The Chemical Analysis of Electroplating Solutions by T.H. Irvine
182 pages
$50.00
Chapters in this work are divided into groups in accordance with the periodic table of elements. Though the procedures are traditional, theoretical aspects are included with other information. Anyone who studies this book carefully will derive a helpful understanding of what he or she is doing so that unexpected results can be searched out for causes and corrected. Send Orders to:
METAL FINISHING 650 Avenue of the Americas, N e w York, NY 10011 For faster service, call (21 2) 633-3199 or FAX your order to (21 2) 633-3140 All book orders must be prepaid. Pleaseinclude $5.00 shipping and handling for delivery of each book via UPS in the U.S., $10.00 for each book shipped expressto Canada; and $20.00 for each book shipped expressto all
598