REFSAN BARIUM CARBONATE
REFSAN BARIUM CARBONATE
RAW MATERIALS AND OXIDES

REFSAN BARIUM CARBONATE (5135)

Brand : REFSAN
Price : 24,53TL
ÇOKALAZÖDE BOYA

BARIUM CARBONATE

 

Barium carbonate powder is dense and white and is manufactured either from the mineral barite (BaSO4) or from barium chloride. Subsequently a precipitation process is used to get the carbonate form. There are several crystalline forms of BaCO3, alpha is the most stable.

Barium carbonate is very stable thermally and does not readily disassociate unless at least some CO is available in the kiln atmosphere (i.e. reduction). BaCO3 is reduced to the unstable BaCO2 in the reaction:

BaCO3 + CO -> BaCO2 + CO2

While BaCO2 has a high melting temperature, it will break down much readily in a glaze melt (liberating the BaO for glass building). It decomposes even more readily during glaze melting in a reduction atmospheres. The dissolution process happens most quickly if BaCO3 is present in small amounts (e.g. 5% or less). Even if present in larger amounts, the glaze matrix can solidify with both types, one participating in the glass microstructure and the other acting as a refractory filler, opacifier and matting agent (especially in low temperature glazes). Effects produced when baria is acting as a filler are sometimes mistaken for those of a true baria crystal matte. Such will likely leach toxic BaO (other oxides will opacify or produce a low fire matte i.e. CaO, MgO, Alumina, Zircon).

Barium carbonate produces gases as it decomposes and these can sometimes cause many pinholes or blisters in glazes. There are barium frits available (e.g. Fusion F-403 has 35% BaO), incorporating one of them to source it instead is a classic application of glaze chemistry calculations. The resultant glaze will be more fusible and will have better clarity and fewer defects.

In art ceramics barium carbonate is popular for the production of classic barium crystal mattes, BaO readily forms crystalline phases during cooling. These are dependent on adequate kiln temperatures, cooling cycle and the chemistry of the host glaze (a slightly reducing atmosphere is also beneficial). Some have observed that in some formulations, barium crystallizes so well that it will occur even with very rapid cooling. Barium can act to initiate crystal development in other chemistries, for example metallic glazes can benefit by the addition of some barium carbonate.

BaO can often be sourced from a barium frit (like Ferro CC-257) instead of raw barium carbonate, provided that the percentage is not too high. Do not assume that BaO is necessary in every glaze in which it appears. In some recipes BaO can be substituted for SrO or CaO and even MgO (using glaze chemistry software of course) without losing the color or surface (bright glossy blues, for example).

 

CHEMICAL ANALYSIS

 

Unit

Result

Purity

%

99.21

InsoIubIe In HCL

%

0.16

Sulphur ( SO4)

%

0.29

Chlorine  (As CI)

%

0.01

Iron

%

0.004

Grain Size (After Sieve)

%

0.18

  

MOISTURE

0.28 % max.