Barium carbonate powder is dense and white, and is made of mineral barite (BaSO4) or barium chloride. Carbonate forms were subsequently obtained by precipitation. BaCO3 has several crystal forms, α It is the most stable.
Barium carbonate is very thermally stableB and will not be easily separated unless at least some CO is present (i.e., reduced) in the kiln atmosphere. BaCO3 is reduced to unstable baco2 in the reaction:
BaCO3 + CO – > BaCO2 + CO2
Although baco2 has a high melting temperature, it will be easy to decompose in glaze melting (Jiefang Bao glass building). It decomposes even more easily when the glaze melts in a reducing atmosphere. When BaCO3 is present in a small amount (e.g., 5% or less), the dissolution process occurs most rapidly. Even if there is a large amount, the glaze matrix can be cured with two types, one participating in the glass microstructure and the other acting as a refractory filler, opaque agent and matting agent (especially in low-temperature glaze). When barite is used as filler, the effect is sometimes mistaken for real barite frosting. This may leach toxic Bao (other oxides will make it opaque or produce low fire matte, such as Cao, MgO, alumina, zircon).
When barium carbonate decomposes, it will produce gas, and sometimes many pinholes or blisters will be produced on the glaze. There are barium frits available (for example, fusion f-403 has 35% Bao). Using one of them as a raw material to replace it is a classic application of glaze chemistry calculation. The synthesized glaze will be more fusible, with better clarity and fewer defects.
In art ceramics, barium carbonate is generally used to produce the classic barium crystal frosting, and Bao is easy to form a crystalline phase in the cooling process. This depends on the appropriate kiln temperature, cooling cycle and chemical properties of the main glaze (a slightly reducing atmosphere is also beneficial). Some people have observed that barium crystallizes very well in some formulations, and it occurs even if it is cooled very quickly. Among other chemicals, barium can also initiate crystal development. For example, adding some barium carbonate to metal glazes can benefit.
Bao can usually be derived from barium blocks (such as cc-257 iron) instead of the original barium carbonate, as long as the proportion is not too high. Don’t think that
every kind of glaze needs a package. In some formulations, Bao can replace SRO or Cao, or even MgO (of course, using glaze chemistry software), without losing color or surface (for example, bright glossy blue).
Barium carbonate is usually added in a small amount (0.2-0.8%) to clayey soil to prevent burning surface scum or weathering. It is slightly soluble in water and provides Ba + + ions to connect with SO4 – ions in water to form BaSO4 (barium sulfate). This new molecular form of sulfate is much less soluble (2-3 mg / L), so it stays inside (rather than migrating to the surface during drying). However, the company tries to reduce the use of barium (even high clay with high soluble salt), because barium sulfate will produce sulfuric acid during the firing process and corrode the refractory materials of the kiln. In order to obtain the best dissolution effect, it is best to add barium to water first and mix it for as long as possible, then either add water to other dry ingredients (for plastic bodies) or add other ingredients to water (for slips).