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Glossary of MinSE


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Z

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Also called electrogalvanizing.    An electroplating process in which zinc is deposited on the surface of an object from cyanide,  alkaline non-cyanide,  or acidic chloride baths.   Pure zinc anodes are used.    Zinc plating is applied mainly to steels for corrosion protection and decoration purposes, but the technique has poor levelling capability.    Zinc plated coatings are pure, very ductile and up to 12 µm thick, compared with 80-125 µm for hot dip galvanised layers.

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Also called an oxygen probe.   Used for detecting small levels of oxygen in gas carburising furnaces and thereby obtaining an estimate of carbon potential.   From the following reaction:

CO  à C(Fe) + 1/2 O2 

carbon potential can be seen to be proportional to (pCO)/p(O2)1/2.   The zirconium sensor generates an  e.m.f. when brought into contact with oxygen, using air as a reference.   One design of sensor has the following relationship:

e.m.f = 4.9593 x 10-5 T log10 (pO2/0.209)

where T is the absolute temperature of the sample point and pO2 is  the partial pressure of oxygen.    Hence, the measured e.m.f may be directly related to carbon potential.   Also see gaseous carburising. This method has also received rigorous investigation for controlling gaseous nitriding atmospheres; see:  S. Bőhmer et al, Surf. Eng., 1994, 10 (2) 129-135.

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