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CHROMIUM
"Hard" or "Industrial" chromium are terms
used to describe thick (0.1 - 60 mils) of chromium metal.
They are used for engineering purposes rather than decorative
applications which are generally very thin (0.005 - 0.050
mils) and are usually applied over bright nickel. Industrial
chromium is used to improve performance of new equipment or
to rebuild and refurbish used equipment - often to a standard
better than new.
Electrodeposited industrial chromium is an extremely hard,
non-stick, and, depending on the plating conditions, reflective
coating. Chromium retains its hardness even after heating
to 400°C and resists tarnishing at temperatures above
300°C. As an electrodeposited coating, chromium is highly
stressed and forms a network of fine, shallow cracks that
are covered and sealed by the next layer of plated chrome.
Resistance to corrosion in an oxidizing environment is excellent.
On exposure to an oxidizing atmosphere chromium forms a thin,
though transparent oxide film that provides an additional
layer of protection. Chromium is resistant to attack by water,
nitric acid, sulfuric acid, hydrogen sulfide, and nearly all
organic acids, but corrodes quickly in hydrochloric and other
chloride based acid solutions.
| Physical Properties of Electrodeposited
Chromium |
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| Melting Point |
1890° ± 10°C |
| Density |
6.9 - 7.29 g/cm3; |
| Electrical Resistivity |
13 - 67 micro ohm-cm. |
| Coefficient of Liner Expansion |
7.4 - 11.0 micrometer/meter/°C |
| Tensile Strength |
15,000 - 100,000 PSI |
| Modules of Elasticity |
15 - 37 x 106 PSI |
| Microhardness |
800 - 1350 kg/mm² |
| Specific Heat |
0.1039 cal/g/°C @ 0°C |
| Latent Heat of Fusion |
31.75 cal/g |
| Latent Heat of Vaporization |
1472 cal/g |
| Thermal Conductivity |
0.65 cal/cm²/sec/cm/°C |
| Normal Total Emissivity |
0.015 at 20°C |
TIN
Electrodeposited tin from an alkaline stannate bath is light
gray to white in color with a slight matte surface. Tin is
often recommended as a bearing surface for lubricated sliding
or rotating surfaces against a variety of materials including
chromium, cast iron and steel.
Tin has a number of qualities that make it an excellent coating
for bearing surfaces. It reduces friction by acting as a dry
lubricant and retaining additional lubricating oil. It is
soft (2.0 Mohs Scale) and ductile so that if one area becomes
burnished, surrounding tin can flow in to the exposed areas
to "heal" the surface. Foreign particles that might
otherwise scuff or score the bearing surfaces are temporarily
embedded in the time till they can be washed out of the working
surface areas by lubricating oil. Finally, if the tin eventually
wears off the surface and into the lubricating oil, it won't
cause additional problems for lube oil viscosity or create
other wear inducing compounds.
| Physical Properties of Electrodeposited Tin |
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| Melting Point |
231.97°C |
| Density |
7.29 g/cm³ |
| Electrical Resistivity |
11.1 microohm-cm @ 20°C |
| Microhardness |
8-10 kg/mm² |
NICKEL
Electrodeposited pure nickel has some outstanding properties
that cause it to be specified for many new and rebuild engineering
applications. It is soft, ductile, machinable, and dense and
can be applied to thicknesses of 100 mils. Electroplated nickel
deposits exhibit good salt spray corrosion resistance and
have excellent fretting corrosion resistance against steel.
Deposits can have very low internal stresses.
| Physical Properties of Electrodeposited Nickel |
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| Melting Point |
1455°C |
| Density |
8.93 g/cm³ |
| Electrical Resistivity |
7-12 microohm-cm @ 20°C |
| Coefficient of Liner Expansion |
13.6 micrometer/meter/°C |
| Tensile Strength |
72,000 - 120,000 PSI |
| Microhardness |
300-400 kg/mm² |
| Thermal Conductivity |
(20-200°C) |
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