Zinc Oxide
Pure Source Of Zinc, ZnO
Chemistry
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Miscellaneous
- Family: Flux Source
- Region: North America
- Mined At: Unspecified
- Raw Mineral: No
- Generic: Yes
Notes
Zinc oxide is a fluffy white to yellow white powder a very fine particle size coupled with high surface area. It is made using one of two processes which produce different densities. The French process vaporizes and oxidizes zinc metal, the American process smelts a coal/zinc sulfide mix and oxidizes the zinc fumes.
Ceramic grades normally employ a larger particle size.
It is soluble in strong alkalis and acids.
It can be an active flux in smaller amounts. It generally promotes crystalline effects and matteness/softness in greater amounts. If too much is used the glaze surface can become dry and the heavily crystalline surface can present problems with cutlery marking. Other surface defects like pitting, pinholing, blistering and crawling can also occur (because its fine particle size contributes to glaze shrinkage during drying and it pulls the glaze together during fusion).
Calcined zinc oxides are available and apparently produce less glaze surface defect problems. You can calcine zinc on your own in a bisque kiln, it at around 815C. Calcining a mix of zinc and kaolin produces a more workable powder. However calcined zinc tends to rehydrate from atmospheric water (and get lumpy in the process).
Zinc oxide sublimes at 1800C but it reduces to Zn metal in reduction firing and then boils at around 900C (either causing glaze defects or volatilizing into the atmosphere). Note that electric kilns with poor ventilation often have local reduction.
While it might seem that zinc would not be useful in reduction glazes, when zincless and zinc containing glazes are compared it is often clear that there is an effect (e.g. earlier melting). Thus some zinc has remained, perhaps because it was within the melt when reduction started or its after effects are responsible.
The use of zinc in glazes is limited by its price, its hostility to the development of certain colors and its tendency to make glazes more leachable in acids (although zinc is not considered a hazardous substance).
Zinc oxide is used in glass, frits, enamels and ferrites. Zinc oxide is also used in large quantities in the rubber and paint industries; in insulated wire, lubricants, and advanced ceramics.
Properties
Glaze Opacifier - White
Zinc oxide will produce opacity or whiteness, especially at low temperatures, if the calcium content is low. It does not opacify as well in boron glazes. It works well in combination with tin.
Data
- Specific Gravity: 5.6
Suppliers
- LANSCO COLORS
- Union Miniere Cobalt & Energy Products
- Zinc Corporation of America
Authors
- Tony Hansen (Owner)
XML
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<material name="Zinc Oxide" descrip="Pure Source Of Zinc, ZnO" generic="1" rawmineral="0" searchkey="" loi="0.00">
<families>
<family name="Flux Source"/>
</families>
<regions>
<region name="North America"/>
</regions>
<oxides>
<oxide symbol="ZnO" name="Zinc Oxide" status="" percent="100.000" tolerance=""/>
</oxides>
<suppliers>
<supplier name="LANSCO COLORS" country="US" url="http://www.pigments.com/" label=""/>
<supplier name="Union Miniere Cobalt & Energy Products" country="BE" url="http://www.um.be" label=""/>
<supplier name="Zinc Corporation of America" country="US" url="http://www.zinccorp.com/" label=""/>
</suppliers>
<notes>
<note>Zinc oxide is a fluffy white to yellow white powder a very fine particle size coupled with high surface area. It is made using one of two processes which produce different densities. The French process vaporizes and oxidizes zinc metal, the American process smelts a coal/zinc sulfide mix and oxidizes the zinc fumes.
Ceramic grades normally employ a larger particle size.
It is soluble in strong alkalis and acids.
It can be an active flux in smaller amounts. It generally promotes crystalline effects and matteness/softness in greater amounts. If too much is used the glaze surface can become dry and the heavily crystalline surface can present problems with cutlery marking. Other surface defects like pitting, pinholing, blistering and crawling can also occur (because its fine particle size contributes to glaze shrinkage during drying and it pulls the glaze together during fusion).
Calcined zinc oxides are available and apparently produce less glaze surface defect problems. You can calcine zinc on your own in a bisque kiln, it at around 815C. Calcining a mix of zinc and kaolin produces a more workable powder. However calcined zinc tends to rehydrate from atmospheric water (and get lumpy in the process).
Zinc oxide sublimes at 1800C but it reduces to Zn metal in reduction firing and then boils at around 900C (either causing glaze defects or volatilizing into the atmosphere). Note that electric kilns with poor ventilation often have local reduction.
While it might seem that zinc would not be useful in reduction glazes, when zincless and zinc containing glazes are compared it is often clear that there is an effect (e.g. earlier melting). Thus some zinc has remained, perhaps because it was within the melt when reduction started or its after effects are responsible.
The use of zinc in glazes is limited by its price, its hostility to the development of certain colors and its tendency to make glazes more leachable in acids (although zinc is not considered a hazardous substance).
Zinc oxide is used in glass, frits, enamels and ferrites. Zinc oxide is also used in large quantities in the rubber and paint industries; in insulated wire, lubricants, and advanced ceramics.
</note>
</notes>
<testdata>
<testitem testname="0" value="5.6"/>
</testdata>
</material>
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