Metal Finishing Industry
Appendix A Glossary
abrasive blasting= A method to remove brittle materials such as millscale oxide, remains of paint etc. More generally referred to as grit blasting.
acid = Chemical substance whose water solutions exhibit a pH less than 7.
acid descaling = An alternative name for "pickling" a process using acid to dissolve oxide and scale.
activation = Process of removing last trace of oxide on a metal surface and a thin layer of the metal itself to ensure that the metal surface to be plated is electrochemically active. (see "etching")
addition agent = Material used to modify the character of the deposit, usually used only in small amounts.
alkaline descaling= A chemical process for removing scale. A typical descaling solution uses caustic soda with additives such as detergents and chelating agents.
alloying = The addition of one metal to another metal or non-metal or combinations of metals. For instance, steel is an alloy of carbon and iron. Other metals are added to steels to impart specific characteristics like strength or corrosion resistance.
"Alochrom" = A proprietary process applied to aluminum and its alloys to improve corrosion resistance or to prepare surfaces for painting. Treatment produces an adherent aluminum oxide with some absorbed chromate.
amalgamating = Process in which alloys are formed with mercury such as gold, silver, iron, copper and aluminum. Due to the toxicity of mercury, use of the technique is declining.
amorphous = Structure that is non-crystalline or without a regular structure.
ampere = The current that will deposit silver at the rate of 0.0011180 grams per second. Current flowing at the rate of one coulomb.
annealing = A heat treatment process which may be applied to all metals to soften them.
anode = The positive electrode in electrolysis, at which negative and positive ions are discharged, positive ions are formed, or other oxidizing reactions occur.
anodic coating = A protective, decorative, or functional coating formed by conversion of the surface of a metal in an electrolytic oxidation process.
anodic etching = A form of electrolytic etching where the workpiece is being etched is anodic in the electrolytic circuit (in electroplating, the workpiece is the cathode).
anodizing = A process generally applied to aluminum and its alloys to produce an adherent oxide film to impart corrosion resistance or surface hardness.
anolyte = The portion of an electrolyte in the vicinity of the anode. In a divided cell, the portion of the electrolyte that is on the anode side of the diaphragm.
aquablast = A surface cleaning process which can be applied to any material where an abrasive material is suspended in water. The resulting slurry is pressurized and ejected through a nozzle. Since higher pressures can be used in this process than in other types of blasting, surface metal can be quickly removed and leaving a good surface finish.
barrel plating (or cleaning) = Plating or cleaning in which the work is processed in bulk in a rotating container.
base metal = A metal that readily oxidizes or dissolves to form ions. The opposite of a base metal.
basis metal = Material upon which coatings are deposited.
blasting = See listing by specific medium (e.g., abrasive, dry, grit, shot, aqua).
borax treatment = A method of coating steel with a thin film of dry lubricant. After surface cleaning or acid pickling, the material is placed in a hot borax solution, allowed to come to solution temperature and removed and dried. The resulting alkaline coating imparts lubrication for subsequent drawing operations and provides minor corrosion protection.
boriding = A high temperature process used for surface hardening of mild low carbon steels.
bright chrome plating = Decorative chromium plate deposited directly on a nickel plate substrate.
bright dip= A solution used to produce a bright surface on a metal.
bright plating = A process that produces an electrodeposit that is luminous.
bright throwing power = The measure of the ability of a plating solution or a specified set of plating conditions to uniformly deposit bright electroplate upon an irregularly shaped cathode; in particular, those areas that are recessed and have a low current density area.
brightener = An addition agent that increases the brightness of the deposit.
bronzing = A chemical process generally applied to steel to impart the appearance of bronze (antimony chloride in hydrochloric acid followed by ammonium chloride in dilute acetic acid). The resulting "bronze" film does not have the corrosion resistance of true bronze.
brush plating = A method of plating that is applies the metal with a brush or pad within an anode that is moved over the cathode to be plated.
buffing = A specific type of mechanical polishing using a high speed disc made from layers of cloth, leather, or plastic impregnated with an abrasive. The workpiece is pressed against the disc for buffing.
building up = Electroplating for the purpose of increasing the dimensions of an article.
burnishing = A form of metal finishing where the surface is treated mechanically so that no appreciable metal is removed but the surface is smoothed.
burnt deposit = A rough or otherwise unsatisfactory deposit produced by the application of an excessive current density and usually containing oxides or other inclusions.
carbonitriding = A surface hardening technique for steel in which a hydrocarbon (e.g., butane or propane) and ammonia are injected into a furnace (750 - 800 degrees Celsius) containing the workpiece. The resulting atomic carbon and nitrogen react with the surface iron to form iron carbides and iron nitrides.
carburizing = A process used for certain types of ductile steel which increase surface hardness from two to six times. It generally is conducted in a heat resistant box containing an atmosphere of carbon monoxide, carbon dioxide, water vapor, methane, hydrogen, and butane in correct ratios and heated to 900 degrees Celsius.
case hardening = A family of surface hardening processes generally applied only to steels (see specific listings for carbonitriding, carburizing, chromium plating, cyanide hardening, electroless nickel plating, and nitriding).
casting = A general term covering a production technique where any metal is heated until it is molten and then poured into a mold, allowed to cool and solidify.
catalyst = An element or ion that promotes or assists in a reaction without affecting or changing the element.
cathode = The negative electrode in electrolysis at which positive ions are discharged, negative ions are formed, or other reducing actions occur.
cathodic etching = A technique applied to steel workpieces where the workpiece is make the cathode in an electrolytic cell with sulfuric acid as the electrolyte. The anode will generally be lead or stainless steel. When a current is applied, hydrogen will be evolved at the cathode and the surface metal oxide will be reduced. The technique is usually applied immediately prior to electroplating.
cathodic protection = A technique applied to steel where metals anodic to iron (e.g., zinc, aluminum, magnesium) are applied to the surface on the steel workpiece to provide a corrosion resistant surface. The process relies on the fact that where a cell exists between two metals with an electrolyte, one of the metals will corrode and in the process of corroding protect the other metal.
cation = A positively charged ion.
chemical polishing = A process carried out on mild- and low-alloy steel, stainless steel, aluminum. Special solutions are used to attack the surfaces of these metals in such a manner that the peaks or corners are affected in preference to the concave surfaces. The result is a general smoothing of the surface.
chromate coating (chromating) = A corrosion protection technique which has many variations and can be applied to steel, aluminum, magnesium, and zinc. It results in the formation of metal oxide on the surface of the workpiece which reacts to form metallic chromates. Chromating of aluminum and magnesium improves corrosion resistance considerably. With steel it is much less permanent.
chromium plating = This electrodeposition of chromium is generally applied to steel in all its forms. It is usually done for decorative purposes (bright chromium) or to provide a hard surface for engineering purposes (hard chromium). Chromium plate is nearly always deposited on top of a nickel deposit. The nickel deposit supplies corrosion resistance.
chromizing = A treatment applied to mild- and low-alloy steel only. It is a surface diffusion process in which chromium is alloyed with iron to create a chromium-rich surface layer. Thoroughly cleaned workpieces are placed in a heat resistant box with a proprietary powder of an unstable chromium compound. When the box is heated to over 1,000 degrees Celsius, the chromium decomposes into an active state which reacts with the iron to produce an alloy. The longer the workpiece is retained in the heated box the deeper the chromium alloy penetrates.
cold galvanizing = A term sometimes used to differentiate between electroplating zinc on steel from the hot dipping of steel in molten zinc. It can also refer to a form of painting with specialized paints which result in a film of up to 90 % powdered zinc. The purpose of all these processes is to provide corrosion resistance.
coloring = The production of desired colors onto a the workpiece using chemical or electrochemical action.
color anodizing = A process used only on aluminum and its alloys using dyes to color the anodic film. The anodic process produces a porous film which when fresh will absorb dyes. The anodizing is carried out using the sulfuric acid process. After completion of the anodizing the workpieces are rinsed in cold water and placed in a dye solution. After dyeing, the workpieces are again rinsed in cold water followed by immersion in nearly boiling water. The heat seals the anodic film and the surface remains permanently colored.
complex ion = An ion composed of two or more ions or radicals, both of which are capable of independent existence, that imparts the property of solubility necessary for electroplating.
complexing agent = A compound that will combine with metallic ions to form soluble ions. See complex ion.
concentration polarization = The increase in solution concentration at a membrane surface because of solution retentation.
contact plating = Deposition of a metal with the use of an internal source of current by immersion of the work in solution in contact with another metal.
contact tin plating = A form of electroless plating commonly used in the printed circuit board and general electronics industries to improve solderability of workpieces. The workpieces are immersed in a hot chemical solution containing unstable tin compounds. The tin reduces on the surface of the workpieces.
conversion coating = A coating produced by chemical or electro-chemical treatment of a metallic surface that provides a superficial layer containing a compound of the metal; for example, chromate coatings on zinc and cadmium or oxide coatings on steel.
copper plating = Copper is electrodeposited for conductivity in the printed circuit and electrical industries and for decorative purposes. There are four basic types of copper plating solutions; copper sulfate, copper cyanide, copper pyrophosphate, and copper fluoroborate.
corrosion = Corrosion occurs in all metals at some time and can be divided into four basic forms. Room temperature oxidation, the most common form, is most obvious in mild and low-alloy steels. The process is accelerated dramatically by comparatively small amounts of contaminants like chloride, sulfate, and fluoride. When exposed to high temperatures, metals will almost invariable result in oxidation of metal surfaces. Chemical corrosion is the result of attack by acids or alkaline compounds which dissolve the metal surface. Electrolytic corrosion occurs when two metals in contact with each other have different electrode potentials. It is a major contributor to most of the corrosion found in steels.
covering power = The ability of a plating solution, under a specified set of plating conditions, to deposit metal on the surfaces of recesses or deep holes ( to be distinguished from throwing power).
cromodizing = A name given to the chromating of steel where a film of iron chromate is formed on the surface. The corrosion protection provided by this treatment is of a very low order. "Phosphating" and oiling will probably provide superior resistance without the use of chromium.
current density (cd) = Current per unit area; usually expressed in amperes per square foot or amperes per square decimeter.
cyanide hardening = A surface hardening technique which uses molten cyanide salts to give workpieces a case containing carbon and nitrogen. Temperatures of 650 degrees to 800 degrees Celsius must be maintained for 20 - 30 minutes to be effective. The high toxicity of the cyanide makes this an expensive process due high treatment costs.
DC (Direct Current) = A flow of electricity from a positively charged terminal to a negatively charged terminal.
degreasing = A form of cleaning which generally uses chlorinated solvents. In the most common form, a liquid solvent is heated in an open topped container. As it boils a hot vapor rises above the liquid. The vapor is held within the container by means of a cooling coil which runs around the inside of the container a short distance below the rim. This cold zone causes the vapor to condense and return to the sump for reboiling continuously distilling itself.
When any cold component is placed in the container, the vapor immediately condenses on the surface. The solvent dissolves any grease on the surface and as more solvent condenses it runs off the workpiece carrying the soluble soils into the sump.
deposit = Refers to the metal coating deposited on the workpiece.
descaling = This term describes a process that can be applied to all materials to remove scale. Scale is generally produced during manufacture or storage. Sometimes it is easily seen in the form of rust or millscale, in other instances it is inconspicuous. Various methods are used for this process including blasting, pickling, acid or alkaline sodium hydride treatments, and polishing.
die-casting = A method of casting in which molten metal is poured, sometimes under pressure, into a mold or die. The die is made of metal and immediately after solidification of the casting the die opens and the casting is ejected.
diffusion coating = An alloy coating produced by applying heat to one or more metal coatings deposited on a metal.
distribution = Refers to the uniformity of the metal deposited from a plating process.
dragin = The water or solution that adheres to workpieces introduced into a bath.
dragout = The solution that adheres to a workpiece removed from a bath.
dry blasting = A general name given to any form of blasting where the abrasive agent is not carried in water.
dry-form lubrication = A form of painting applied to steel surfaces of workpieces subject to light wear or abrasion. It generally uses colloidal or molybdenum disulfide carried in a phenolic resin.
ductility = Refers to the flexibility of an electroplated deposit; this parameter is critical when bending and forming operations occur after plating.
dummy (dummy cathode) = A cathode in a plating solution that is not to be used after plating; often used for removal or decomposition of impurities.
effluent = Any gas or liquid emerging from a pipe or similar outlet; usually refers to waste products from chemical or industrial plants as stack gases or liquid mixtures.
electrocleaning = An electrochemical cleaning process by which a workpiece is first made the cathode in an electrolytic cell. When current is applied, the generation of hydrogen gas from the electrolysis of water at the surface of the workpiece results in a highly efficient scrubbing action. Following initial treatment as a cathode the circuit is reversed so that the workpiece is the anode. Oxygen gas, which is generated at the surface produces a final cleaning action.
electrode = A conductor through which current enters or leaves an electrolytic cell at which there is a change from conduction by electrons to conduction by charged particles of matter or vice versa.
electrode potential = The difference in potential between an electrode and the immediately adjacent electrolyte.
electroforming = A specific form of electroplating used where intricate shapes and relatively thin metal deposits are required. Molds of plastic, wax, or sometimes metals are made conductive by application of carbon or metallic powder and are plated by conventional methods. Nickel, copper, or precious metals are generally selected for this form of plating. The mold is generally removed at the completion of the plating process by one of a number of methods depending on the material from which the mold is constructed.
electrogalvanizing = Electrodeposition of zinc coatings.
electroless plating = The process of depositing metal from a water-based solution using chemical catalysts for the metal cation reduction process. In this process no external potential (electrical current) is applied.
electrolyte = A conducting medium in which the flow of current is accompanied by movement of matter;most often an aqueous solution of acids, bases, or salts, but includes many other media such as fused salts, ionized gases, and some solids.
electrolysis = Production of chemical changes by the passage of current through an electrolyte.
electrolytic etch = A technique generally applied to steels which attack the surface to produce a clean, oxide free material. It is often used prior to electroplating, especially chromium plating. Since it preferentially attacks edges it will open us small cracks in the surface of the workpiece. Due to this, this process can be used to inspect finishes for flaws.
electrolytic polishing = An electrochemical process usually applied to steels, aluminum, and aluminum alloys. This process produces a surface that is bright and highly reflective. In most instances this is used for decorative purposes and is often used in conjunction with some other form of metal finishing such as anodizing, plating, or lacquering.
electroplating = The process of depositing metal from an aqueous solution using an external potential (electrical current) for the metal cation reduction process; usually, the potential applied is DC, but can approach controlled AC with some sophisticated switching devices (pulsed electroplating).
electro-osmosis = See "reverse osmosis"
electrorefining = The process of anodically dissolving a metal from an impure anode and depositing it cathodically in a purer form.
electrowinning = The production of metals by electrolysis with insoluble anodes in solutions derived from ores or other materials.
emulsion cleaning = A cleaning technique which acts by emulsifying contaminants. Emulsions are mixtures of two liquids, with one liquid holding the other in a suspension similar to colloidal suspension. The liquids will typically have different polarities and will dissolve different types of materials. One of the liquids is usually water and the other will have non-polar properties. They can therefore be used to dissolve non-polar contaminants like oil and grease from metal surfaces.
etching = Etching is sometimes used a surface preparation technique prior to electroplating or for removal of metal such as in the printed circuit industry where material not required on the finished product is removed by a chemical solution. It can also be used as an inspection technique due to its ability to accentuate surface cracks and defects.
"ferrostan" process = A method of continuous electrolytic tin plating of steel strip in which cold reduced strip is continuously fed through the cleaning, etching, plating, and rinsing processes. The solution is generally acid sulfate which produces a matte finish.
filtration = A means of separation where constituents are separated usually by physical methods.
fire gilt process = A process used exclusively in the jewelry trade in which gold dissolved in mercury (gold amalgam) is wiped on surfaces to be plated. When the article is heated the mercury is driven off leaving a gold film. The process represents a considerable health hazard due to the emission of the mercury vapor.
flocculation = The combination or aggregation of suspended colloidal particles in such a way that they form small clumps; usually used in conjunction with additive chemicals (flocculants) to treat wastewater.
fluxing = A process used in the heating of metals which may be intended to reduce or eliminate oxidation, confine the products of oxidation, reduce their melting point, and improve fluidity of surface metal layers. Fluxing is generally used in casting, welding, and soldering.
foam blanket = An additive that forms a layer on the surface of electroplating baths that have poor anode/cathode efficiency, to prevent any mist or spray from escaping.
fouling = Deposition of materials on a membrane surface or within the pores because of soluablility limits (at the surface) or pore size and/or shape.
free cyanide = (1) Calculated - the concentration of cyanide or alkali cyanide present in solution in excess of that calculated as necessary to form a specified complex ion with a metal or metals present in solution. (2) Analytical - the free cyanide content of a solution as determined by a specified analytical method.
frosting = A type of metal finishing where a fine matte finish is produced by using techniques such as acid-etching, blasting, scratch brushing or barreling.
galvanic cell = An electrolytic cell capable of producing electrical energy by electrochemical action.
galvanic protection = A general term used in the corrosion protection of steel. Technically, it refers to a metal used to protect a metal higher than itself in electrode potential. In practice, it refers to the use of zinc to protect steel.
galvanizing = A corrosion protection technique applied only to mild steel, cast iron, and steel alloys in which workpieces are immersed in liquid zinc at 500 degrees Celsius. A zinc/iron alloy is formed at the surface of the workpiece giving it an adherent coating of zinc. Prior to galvanizing, the metal surface must be in a state of moderate cleanliness. This is generally accomplished by light acid pickling or blasting. Galvanized coatings are generally about 0.005 inches thick and can give protection for 10 to 20 years.
gilding = A process in which gold is coated on the surface of another base metal. Gold leaf, a layer beaten so thin it is porous to light, is glued or beaten onto the article to be gilded. A similar method applies a fine gold powder mixed with a flammable liquid solvent applied to the article like a paint. The solvent is allowed to evaporate or in some cases may be ignited.
gold plating = gold has two specific properties which make it valuable in industrial and commercial uses, it resists oxidation and corrosion to a very high degree and it retains its attractive color. The main advantage of gold plating over other methods of applying gold to surfaces, is that electroplated coatings do not have pores as gilded coatings do. This provides significantly longer lifespans and corrosion resistance.
grit blasting = A technique of abrasive cleaning or surface preparation using sharp particles (e.g., cast iron shot, aluminum oxide). It covers such processes as removal of scale, corrosion, paint and other surface films. Use of free silica presents a health threat and should be avoided.
hard chromium = Chromium plate for engineering rather than decorative applications; not necessarily harder than the latter, but generally thicker or heavier. See "chromium plating".
hard facing = A term referring to processes used to harden metal surfaces and impart wear resistance by a variety of heat treatments. See "metal spraying".
HCD (High Current Density) = High amperes per surface area.
hot dip coating = See "galvanizing".
hydrogen embrittlement = A defect which occurs during the electroplating process. Atomic hydrogen is produced at the cathode of the workpiece being plated. This atomic hydrogen is extremely reactive and has the capability of entering the interstices of the metal. Being unstable in the atomic state, the hydrogen will combine as rapidly as possible with other atoms to form molecular hydrogen. This molecular hydrogen, having a higher unit volume than atomic hydrogen results in internal pressure in the plated metal.
immersion plating = A plating technique similar to electroless plating where a more electropositive metal is dissolved in an electrolyte and is plated onto the surface of a less electronegative metal workpiece. The term immersion plating is used where a deposit is obtained and the plating process then stops. This is distinguished from electroless plating where the deposition of the metal being plated continues to deposit as long as the workpiece remains in the solution.
inchrom process = see "Chromizing".
indicator (pH) = A substance that changes color when the pH of the medium is changed; in the case of most useful indicators, the pH range within which the color changes is narrow.
indium plating = Indium is a metal not unlike lead but with friction and corrosion resistance properties that are unique. In fact, the sole purpose of indium plating is improving the friction characteristics of very high-rated bearings.
ion = An electrified portion of matter of atomic or molecular dimensions.
ion exchange = A reversible process by which ions are interchanged between a solid and a liquid with no substantial structural changes in the solid.
"kanigen plating" = First proprietary process for electroless nickel plating.
LCD (Low Current Density) = Low amperes per surface area.
lead plating = lead plating does not have many common uses except in the production of electrodes for lead acid batteries. Steel which has been plated with lead is much stronger mechanically and lighter than the same thickness of pure lead. It is also used as a base layer for indium plating. Lead plating solutions contain approximately 100 grams of lead per liter and 40 grams per liter of fluoroboric acid.
leveling = Electrodeposited materials tend to be concentrated at sharp corners, peaks, and ridges, due to the fact that current distributed on a surface will tend to concentrate at these irregularities more than in concave surfaces such as recesses. Therefore, when a workpiece with a rough surface is electroplated, the rate ofdeposition will be faster on convex irregularities resulting in an accentuation of the item's original roughness. To counteract this effect, additives are added to the electrolyte solution to produce a polarization effect concentrated at the peaks and ridges. This polarization effect lowers the current density at the peaks and reduces deposition rates. The net result is to smooth or "level" the surface of the workpiece.
mandrel = A form used as a cathode in electroforming; a mold or matrix.
mechanical plating = The application of an adherent metallic coating by mechanical means involving the compacting of finely divided particles of such metal to form coherent coatings.
membrane = A microporous structure that acts as a highly efficient filter that allows passage of water, but rejects suspended solids and colloidals; depending on membrane type, ions and small molecules might or might not be rejected.
metal spraying = The general term is applied to the spraying of one of several metals onto a metal substrate. In general, it is intended to produce three effects. The first, corrosion protection, usually involves the spraying of zinc or aluminum on structural steel components. It is also used on high tensile workpieces, such as those used in the aerospace industry, that can not be electroplated due to hydrogen embrittlement. The second purpose is "hard facing". Materials used in hard facing are tungsten bearing or tungsten carbide materials, cobalt, and nickel with small amounts of chromium, and high manganese chrome materials. These materials provide significant wear resistance. The third application is for salvage purposes. When engineering components are found to exhibit wear while in service, technical and economic considerations may make metal spraying to replace the wear a better alternative to replacement.
The most common method of metal spraying is "flame impingement". The technique uses powdered metal continuously fed into a high velocity flame. The flame atomizes the metal powder into a molten state and the particles are projected by the energy of the flame onto a prepared metal surface. Plasma coating is a similar method which uses radio frequency-induced plasmas at temperatures up to 30,000 degrees Celsius. This methods use is limited to high integrity components where excellent adhesion or sophisticated materials are required.
"Micro-chem" = A proprietary electrocleaning process used for "brightening" and "passivating" stainless steel. It is a form of electropolishing which gives a considerably smoother and shinier finish.
micro-throwing power = The ability of a plating solution or a specified set of plating conditions to deposit metal in tiny pores or scratches.
mil = One thousandth of an inch.
nickel plating = A very common form of electrolytic deposition that is generally used as an undercoating for subsequent deposits. There are three common solution for nickel plating: Watt's solution, Sulfuric acid, and electroless plating.
nitriding = A surface hardening process that is applied only to certain types of steel. This process creates a finish that is the hardest surface attainable using heat treatment processes. The process consists of maintaining a workpiece in a 500 degree Celsius ammonia atmosphere for up to 100 hours. Under these conditions atomic nitrogen combines with surface iron to form iron nitride. The nitrogen slowly diffusesaway from the surface as long as the proper temperature is maintained. The resulting case thickness is therefore dependent on length of heat treatment.
noble metal = A metal that does not readily tend to furnish ions and, therefore, does not readily dissolve nor easily enter into such reactions as oxidations; the opposite of a base metal.
nodule = A rounded projection formed on a cathode during electrodeposition.
passivation = The cleaning of stainless steel with nitric acid to remove carbon and other impurities.
pH adjustment = The act of changing the pH of an aqueous solution by adding acid or caustic.
phosphating = A process that converts the surface of a steel workpiece to iron phosphate usually prior to painting. Before phosphating, the surface of the workpiece must be free of rust and scale. This is usually accomplished with acid pickling, mechanical wire brushing, or blasting. Phosphating is a relatively short process, usually 5 to 20 minutes. Workpieces are generally painted or chromated within 24 hours of treatment since the phosphating provides little corrosion resistance.
pickling = A chemical treatment which removes oxide or scale from the surface of a metal. It most often refers to the use of sulfuric or hydrochloric acid to remove scale formed on mild and low-alloy steel during hot forming operations. Treatment of stainless steel or high nickel alloys is done with hydrofluoric acid, a particularly hazardous material that must be handled with extreme care.
plating = An electroplating or electroless plating process.
plating range = The current density range over which a satisfactory electroplate can be deposited.
pulse plating = A method of plating that uses a power source capable of producing square-wave current pulses.
rack plating = A frame for suspending and carrying current to articles during plating and related operations.
reducing agent = A compound that causes reduction thereby itself becoming oxidized.
reflowing = A technique used in the printed circuit board industry in which a component is heated in order to melt solder deposits and causing them to flow. It produces a bright, attractive looking material but its main purpose is for quality control. With reflowing, any defect on the substrate will not wet, clearly indicating areas where solder is missing.
rustproofing = A general term that refers to processes applied to steel. It can include painting or galvanizing, but most often refers to phosphating and similar low duty rust preventatives.
sacrificial protection = A corrosion protection technique that uses a metal of lower electrode potential to protect a metal of higher electrode potential. This is possible because in the presence of an electrolyte an electrochemical cell is established in which the lower potential metal acts as an anode and the metal that is being protected acts as the cathode. The anode corrodes and deposits onto the surface of the cathode. In practice, zinc and aluminum are the two metals most commonly used for this process.
sealing or anodic coating = A term commonly applied to any metal process having a subsequent treatment capable of affecting a previous process coating in order to reduce staining and corrosion of the workpiece or to improve the durability of color of the coating.
sensitizing = A relatively non-specific term used to cover a range of metal finishing processes that improve the treatability of a workpiece for subsequent processes. It often refers specifically to a part of electroless plating procedure on plastics or non-metal surfaces. After the surface has been etched it is reacted with solution that deposits a very thin film of a metal or metallic compound. The surface is then referred to as sensitized.
silver plating = Silver, the easiest metal to plate, is deposited for decorative purposes on household and jewelry items. Sometimes it is used by the electrical industry where it is plated over copper to improve corrosion resistance.
solder plating = The term covers deposition of an alloy of 60% tin and 40% lead that is widely used in the electrical and electronics industries. It provides two valuable features, corrosion resistance and "solderability".
stop-off = Method of protecting portions of a workpiece from chemical processes. Waxes, lacquers, or special tapes are applied to areas to prevent chemical attack or deposition.
strike = (1) A thin film of metal to be followed by other coatings. (2) To plate for a short time, usually at a high initial current density.
substrate = Surface material or electroplate upon which a subsequent electrodeposit or finish is made. See basis metal.
surface hardening = A general term referring to methods for making the surface of steel workpieces mechanically harder than their inner portions. Also see: "nitriding", "carburizing", "cyanide hardening", "carbonitriding".
throwing power = The ability to effect satisfactory coverage in recessed or blind (hole) areas of a part being plated.
total cyanide = The total content of cyanide expressed as the radical CN or as alkali cyanide, whether present as simple or complex ions; the sum of both the combined and free cyanide content of a solution.
ultrafiltration = The process that uses membranes to achieve separation of various constituents; a typical ultrafiltration membrane allows water, ions, and small molecules to pass through while rejecting large molecules and suspended solids.
vacuum deposition = A process in which certain pure metals are deposited on a substrate. The technique relies on the fact that, in a vacuum, pure metals can be vaporized at a low temperature in a closed container. The metal vapor will condense evenly on all surfaces to produce a metallic coating. Aluminum is the most successfully deposited material, producing a highly reflective finish.
vapor deposition = (1) Chemical - process for producing a deposit by chemical reaction, induced by heat orgaseous reduction of a vapor condensing on the substrate. (2) Physical - a process for depositing a coating by evaporating and subsequently condensing an element or compound, usually in a high vacuum.
wetting agent = A substance that reduces the surface tension of a liquid, causing it to spread more readily on a solid surface without it beading up.
workpiece = The part that is being electroplated or electroless plated.
zinc coating = See "galvanizing".
zinc phosphating = A process applied to freshly zinc plated workpieces that are immersed in a zinc phosphate solution acidified with phosphoric acid. The zinc surface deposit is converted to zinc phosphate. The workpieces are then immersed in a dilute chromic acid solution to seal the zinc phosphate deposits and prevent rust formation of unsightly zinc oxide.
zinc plating = Common form of plating used to provide corrosion resistance for steels.
zincate treatment = A treatment necessary for aluminum and its alloys before electroplating. After cleaning, etching in chromic or phosphuric acid to remove oxide and dipping in nitric acid to activate the surface, workpieces are immersed in a sodium zincate solution. Metallic zinc is deposited on the surface of the workpiece. It is then rinsed and immediately brought the final plating operation.