Bone Ash
Formula: Ca5(OH)(PO4)3
| DENS - Density (Specific Gravity) |
3.10 |
| MLPT - Melting Point (MP) |
1670C |
Bone ash is TriCalcium Phosphate in the form of Hydroxyapatite Ca5(OH)(PO4)3. This reacts when making bone china to give Anorthite (CaAl2Si2O8) and Ca3(PO4)2.
2*Ca5(OH)(PO4)3 --> 3*Ca3(PO4)2 + Ca(OH)2
Real bone ash is obtained by calcinating bone up to approximately 1100°C and then cooling and milling. This material is still manufactured today since some of its important properties are due to the unique cellular structure of bones that is preserved through calcination. Real bone ash has excellent non-wetting properties, it is chemically inert and free of organic matters and has very high heat transfer resistance.
Bone ash has traditionally been added to porcelain to achieve a high degree of translucency (thus the name 'bone china'). The manufacture of bone china is difficult to master because the clays are non-plastic, ware is unstable in the kiln, and it is difficult to burn consistently to the body's narrow firing range.
Up to 1-2% bone ash can be used in enamels for opacification (more will usually cause pinholes). In glazes, as with enamels, too much or too high a temperature will cause blistering. In this use the phosphorus' influence toward a stiff melt generally checks the fluxing action of the calcia.
Bone ash or calcium phosphate are used to opacify opal glass (1-3%) because the P2O5 content forms colorless compounds with iron impurities.
Mechanisms
Glaze Opacifier - White Low temperature glazes sometimes employ bone ash for opacity because of the milky quality it produces. It can also be used to assist tin oxide where a less shiny surface can be tolerated. Glaze Surface Texture - Texture Bone ash encourages strong glaze textures; however, too much can produce crazing or blistering.
Out Bound Links
- (URLs)
Synthetic Bone Ash
http://www.murlinchemical.com/syn1.html - (URLs)
Ebonex Corp.
http://www.ebonex.com/ba_pro.htm - (URLs)
Interesting history of Bone Ash
http://www.ebonex.com/hist.htm - (Materials - Related)
Tricalcium Phosphate - Ca3(PO4)2 or 3CaO.P2O5
Tri-Calcium Phos, Tribasic Calcium Phosphate, Synthetic Bone Ash, Calcium Orthophosphate
- (Typecodes)
1: GNM - Generic Material
- (Typecodes)
1: FLS - Flux Source
- (MDT - Member)
Enamel Industry
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Crystal Glazes
These materials are specially defined for makers o... - (MDT - Member)
UK
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Ron Roy
This is the traditional Ron Roy materials file. He... - (Typecodes - Unspecified)
1: OPA - Opacifier
- (Glossary - Unspecified)
Bone China
True bone china is a special type of porcelain tha... - (MDT - Member)
North America
The decision about what materials to include in th... - (MDT - Member)
Glass Industry
The materials included in this MDT were selected i... - (MDT - Member)
New Zealand
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In Bound Links
XML for Import into INSIGHT
<?xml version="1.0" encoding="UTF-8"?>
<material name="Bone Ash" descrip="" searchkey="Calcium Phosphate" loi="0.00" casnumber="68439-86-1">
<oxides>
<oxide symbol="CaO" name="Calcium Oxide, Calcia" status="U" percent="55.820" tolerance=""/>
<oxide symbol="P2O5" name="Phosphorus Pentoxide" status="" percent="42.390" tolerance=""/>
</oxides>
<volatiles>
<volatile symbol="H2O" name="Water" percent="1.790" tolerance=""/>
</volatiles>
</material> | 
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