Blackening


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Blackening

 

a type of oxide coating for iron and steel products, used for corrosion protection and for decorative purposes. The most common method of blackening is to immerse the products in a concentrated alkaline solution containing sodium nitrate or sodium nitrite as an oxidizer. As the concentration of the alkali is increased (other conditions being equal), the thickness of the oxide film also increases. A thin coating (20 to 40 angstroms) does not alter the external appearance of the surface nor does it provide practical protection for the metal against corrosion. Thick coatings (2.5 micrometers), which are black or grayish black, have poor mechanical strength. The best thickness is 0.6 to 0.8 micrometer. Blackening is a special case of blueing.

References in periodicals archive ?
First, the hen party is generally a female only affair (the male equivalent is the stag party), whereas the blackening is celebrated by both men and women, often together.
in its annual music poll bestowed album-of-the year honors on "The Blackening.
We guessed it was the blackening, but they hadn't given us any warning of when they were going to do it.
Consequently, the series of figure 3's is inserted in addition to the blackening, so that the incorporation of sesquialtera proportion should not escape attention and resolution.
Postgraduate student Sheila Young is also keen to attend a blackening, where brides and grooms are kidnapped - together or separately before their wedding - and covered in food slops before being paraded round their villages.
It's the memory of such accidents that turn some people off to the idea of blackening fish on purpose.
Also to claim she had reached this state after 18 months is patently absurd, smokers take 20 to 30 years with direct inhalation of the tar to come close to the internal blackening she describes.
On the Fourth of July weekend last year, fireworks caused three small fires, each blackening less than one acre, the Forest Service said.
For the blackened shrimps: a little olive oil; Worcestershire sauce to taste; a little lemon juice; Tabasco to taste; a little Schreiber's blackening spice; a little sugar; 8 large shrimps, butterflied if wished.