Printer-friendly version
Glossary of MinSE


Browse the glossary using this index

Special | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O
P | Q | R | S | T | U | V | W | X | Y | Z | ALL

V

:

Also called evaporation coating.    A method of applying thin metallic or ceramic coatings to substrates at low temperature.   The process is usually carried out under high vacuum conditions (≈10-5 to 10-6 torr).  The coating material can be vapourised using a variety of heat sources; the most common are resistance heaters for low melting point materials, like aluminium, zinc sulphide and antimony, and electron beam heaters for high melting point materials like nickel, molybdenum and aluminium oxide.   The process is highly directional (diagram) and the quality of coating adherence is poor compared to those produced by ion plating.   Hence, such coatings have limited tribological application.   Some coatings like aluminium oxide and zirconium nitride can be produced reactively by evaporating the metal constituent in a partial pressure of oxygen and nitrogen respectively.   For recative deposition the chamber pressure maybe as high as 10-2 torr.   Designs also exist that enable two or more metals to be evaporated simultaneously, enabling the synthesis of alloy coatings.    Aluminium coatings are widely used for decorative purposes on many substrates, including plastics.    They are also widely used in the auto industry for mirrors and lamp reflectors.    In the electronics industry capacitors are fabricated using coatings of the oxides of cerium, silicon, tantalum, titanium and aluminium, while resistors comprising composite coatings of chromium plus silicon dioxide are frequently used.  The latter undergo a post-deposition heat treatment at ≈430°C to develop the required resistance.   The majority of vacuum coatings are less than 1 µm thick.    

Hungary flag Vákuum bevonatolás

:

Also called low pressure pasma spraying (LPPS).  A plasma spraying process performed in a chamber that is firstly evacuated to ≈10-2 Torr and secondly progressively back filled with an inert gas to ≈100 Torr.   The plasma torch is often "warmed-up" before the latter working pressure is reached.  VPS has gained popularity because the resulting coatings are denser (>90% of theoretical) than those achieved during conventional plasma spraying, conducted at atmospheric pressure.  The latter method is sometimes called "APS";  air plasma spraying.

Hungary flag Vákuum plazma fémbevonatolás

:

Degreasing of a surface achieved by exposure to the action of vapourised organic solvents.  Maybe combined with spraying or immersion in hot liquid solvent in conjunction with ultrasonic agitation.

Hungary flag Gőzöléses zsírtalanítás

:

 See vacuum coarting, plasma assisted PVD, PVD and CVD

Hungary flag Gőzöléses bevonatolás

:

A surface finishing operation in which the objects under treatment are embedded in a vibrating container containing an abrasive medium.    Also see tumbling.

Hungary flag Vibrációs megmunkálás

:

Also called diamond pyramid hardness (DPN).  A square based pyramid indenter, made of diamond,  whose apex has an included angle of 136° is used to indent the surface of a metal or ceramic under the application of a known load.  Following indentation, the average indentation diagonal (d) is measured and Vickers Hardness Number (VHN) is obtained from tables or can be calculated.   VHN is the ratio of the load (P) to surface (projected) area of the indentation, and is usually expressed in kg/mm2.    VHN can be calculated using the formula:

VHN = load/contact area = 1.854 P/d2 = kg/mm2

Nowadays, it is becoming popular to express Vickers hardness in G.Pa; this is achieved by expressing P in Newtons rather than  kilogrammes  (1 kg = 9.80665 N).

VHN is widely used in the heat treatment and surface engineeering sectors and both macro and microindentation versions exist.  Vickers microhardness is especially useful for obtaining hardness-depth profiles of surface engineered materials like nitrided and carburised steels.

Hungary flag Vickers keménység

:

A strongly adherent glassy substance applied to (mainly) steels and grey cast-irons as an inexpensive abrasion and corrosion resistant coating.    Vitreous enamel is prepared by smelting together an intimate mixture of refractory materials.   For example, silica, titania, feldspar and china clay together with an appropriate fluxing agent such as borax, sodium silicoborate and nitrates or carbonates of lithium, sodium and potassium.  Melting together of these materials produces a substance resembling glass in texture, but often containing gas bubbles.   The material is then rapidly solidified, e.g., by pouring into water, crushed and ball milled into a fine powder called "frit".  Cast-iron surfaces are prepared by grit blasting, while steels are pickled in acid and given a nickel dip coating.   Frit can be applied to cast-iron surfaces by sieving it onto the surface and heating the objects in a furnace to 900°C; this is called the "dry process".   A more common approach is to apply the frit as a slurry by spraying or dipping; after drying, the frit is fused by heating to ≈750-850°C.    Items are then allowed to cool slowly.   Formerly in wide-use for cook-ware and other house-hold implements;  enamelling is nowadays largely superseded by PTFE coatings.   

Hungary flag Porcelán bevonat

:

See vacuum plasma spraying

Hungary flag VPS


Theme by NewSchool Learning