TZM alloy Plate at a high temperature processing, surface oxide layer of TZM alloy sheet will adhere to impurities molybdenum oxide particles and MoO3 which is low melting point and has volatile uneven. If continue processing these impurities will be pressed into the TZM alloy plate layer, constitute defects on molybdenum alloy plate surface. In addition, in the rolling process, there may be some tiny microcracks. So the TZM alloy plate necessary to process alkali cleaning.
For cleaning alloy plate, generally choose to use caustic alkali fusion method. Putting NaOH and 3% nitrate in resistors bath and heated to 400 ℃ to melt. Then put TZM alloy plate into the solution, after a few minutes, remove the alloy into a cold water bath cleaning until the alloy becomes flushed white.
In the cleaning process, molybdenum oxide only, reacted with NaOH. But when there are nitrates which is strong oxidant, NaOH will react with the surface of the substrate, the reaction chemistry equation is as follows:
MoO3 + 2NaOH → 2NaMoO4 + H2O
MoO3 + 6NaOH → Na2MoO4 + 2Na2O + 6NO
2NO2 + 2NaOH → NaNO2 + NaNO3 + H2O
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