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Glossary of MinSE


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Maybe carried out using 100% hard wood charcoal, but more often, the commercal carburising pack compositions comprise 6 to 20wt-% activating compounds bound to hard wood charcoal and/or coke by molasses, tar or oil.   Barium carbonate has been a principal activator; due to its toxicity this is being discontinued in the United States because of industrial control legislation.  Calcium, sodium and potassium carbonates are suitable alternatives.   The activator(s) serve to create carbon dioxide via the reaction:  

CaCO3  --> CaO +  CO2

which then reacts with the charcoal/coke:

 CO2  + C <==> 2 CO

The CO is then reduced to carbon at the steel surface where it is dissolved in the austenitic phase:-

Hungary flag szilárd közegben, ládában cementálás

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(i) an obsolete term for pack carburising; (ii) Any pack method that results in the diffusional formation of a surface layer (or layers) enriched in interstitial or intermetallic compounds.   Such processes include, pack boriding, pack aluminising and pack chromising.   All these processes involve embedding components within a powdered pack contained inside a vessel, which is then placed inside a furnace.    Sometimes inert or reducing gases are passed through the pack (e.g., pack aluminising and pack chromising) in other cases no external gases are required (e.g., pack boriding).    Process control is difficult with such techniques, especially with regard to controlling the activity or potential of the diffusiong specie(s).   Pack constituents may be costly and are often used several times.   After each diffusion cycle the powders become depleted in constituents and their activity or potential reduced.    Industrial users therefore implement methods of "topping-up" powders with new constituents.   This calls for stringent management of the powders.   A detailed knowledge of the effect of various substrate compositions on pack life must also be accumulated. Also see minor thermochemical diffusion techniques.

Hungary flag szilárd közegben cementálás

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Carried out by embedding components in a mixture of powders comprising, Al, Cr, Cr2O3 (the sources of Al and Cr) and NH4Cl. (the activator).  The process is conducted at temperatures ≈950-1100°C for 2-4 hours.  The thickness of the layer produced does not exceed 100 µm.

Hungary flag szilárd közegben krómaluminizáció

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Conventional packs comprise a mixture of chromium metal or ferrochromium powder and an an activator such as NH4Cl, NH4Br or NH4I.  A gas tight container is required and hydrogen is passed through the pack which is heated between 850 and 1050°C for up to 12 hours.   In a more recent development, components are packed in a mixture of FeCl3 and metallic chromium powders, which on heating react to produce (probably) CrCl2; argon or nitrogen is passed through the pack to prevent ingress of oxygen.  CrCl2 is reduced to Cr at the surface of the steel components.  In both cases chromium diffuses into the steel and produces a surface layer whose constitution depends upon the steel substrate composition (see: Chromising ).

Hungary flag szilárd közegben krómozás

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Sherardizing is carried out in a powdered medium consisting, as a rule, of zinc powder or dust with additions of zinc chloride or ammonium chloride to provide activation.   Sometimes an inert substance (e.g. aluminium oxide, fireclay or high-silica sand) is added to act as a diluent and prevent sintering togther of the zinc particles.  Temperatures ≈400-800°C for 2-4 hours are typical.  The process can be further assisted by rotation of the charge (tumbling).  The thickness of the diffusion layer is  ≈ 30 to 200 µm.     Also see sheradizing.

Hungary flag szilárd közegben horganyzás

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Siliconising carried out by embedding components in a powdered mixture comprising silicon mixed with silicon carbide, silico-calcium or ferrosilicon.   The diluent is usually  alumina or magnesium oxide, while NH4Cl, NH4I, NH4F, KF or NaF act as the activator phase.  The process requires ≈4-6 hours at 950 to 1200°C. 

Hungary flag szilárd közegben szilikonizálás

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An electroplating process in which palladium is deposited from tetra-amino palladium nitrate solutions, which contains ≈10-15g/l of palladium. The process uses platinum or platinised titanium anodes. Typical coating thicknesses are in the range of 2 to 5 µm.   Palladium plating is used as a substitute for gold or rhodium plating, especially in the finishing of copper electrical contacts on circuit boards.   It has a Vickers hardness of 200-300 kg/mm2 which is higher than that of electroplated gold; hence palladium plating imparts reasonable wear resistance.     It also finds use for the high temperature oxidation protection of refractory metals, such as tantalum and molybdenum

Hungary flag Palládiumozás

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See vacuum carburising

Hungary flag vákuum cementálás

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See closed loop partial-pressure control..

Hungary flag atmoszférikusnál kisebb nyomás ellenőrzés

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Any vacuum deposition process whereby one of the constituents of the final coating is vapourised or atomised from the solid state within the vacuum chamber, prior to deposition.  The two methods of vapourisation/atomisation are evaporation and sputtering.   In general plasma assisted processes like ion plating can be regarded as PVD, but for these cases a more exact definition is plasma assisted PVD. 

Hungary flag Fizikai gőz bevonatolás


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