Bone ash is a white material produced by the calcination of bones. Typical bone ash consists of about 55.82% calcium oxide, 42.39% phosphorus pentoxide, and 1.79% water. The exact composition of these compounds varies upon the type of bones being used, but generally the formula for bone ash is: Ca5(OH)(PO4)3. Bone ash usually has a density around 3.10 g/mL and a melting point of 1670°C (3038°F). Most bones retain their cellular structure through calcination.
Bone ash has many uses, such as in fertilizers, polishing compounds, or the production of ceramics in the form of bone china. In addition, bone ash can be used as a protective coating for metal equipment, tools, or around a floor as moulding. In this context, bone ash is well established as a sealant for seams or cracks.
As a powder coating, bone ash has many unique characteristics. First of all, the powder has high thermal stability, so it maintains its form in extremely high temperatures. The powder coating itself adheres to metal well and does not drip, run, cause much corrosion, or create noticeable streaks. Using the bone ash is easy as well, as it comes in a powder form, is easy to clean up, and does not separate into smaller parts (therefore requiring no extra mixing).
The raw material for bone china is about 50% bone ash derived from animal bones. These bones undergo multiple processing stages during which all meat is removed and the bone is completely cleaned. Once cleaned, the bone is heated to about 1000°C (1832°F) so that all additional organic material is removed from the bone and the bone becomes sterilized. Lastly, the newly sterilized bone is ground with water into fine particles which can be used as a raw material for bone china. Bone ash plays an important role in the creation of bone china, as the phosphate of the bone generates beta tricalcium phosphate, and other compounds from the bone create a calcium crystal called anorthite. Although synthetic alternatives such as dicalcium phosphate and tricalcium phosphate have been produced, the majority of bone china is still made using natural bone ash.
Bone ash can be used alone as a fertilizer or it can be treated with sulfuric acid, which ultimately allows the fertilizer to permeate the soil better. In addition to the nutrients to be found in the bone ash, the fact that the ash is dry and finely powdered makes it an excellent plant fertilizer.
- This article incorporates text from The Modern World Encyclopædia: Illustrated (1935); out of UK copyright as of 2005.
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