Ceramic flux

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Fluxes are substances, usually oxides, used in glasses, glazes and ceramic bodies to lower the high melting point of the main glass forming constituents, usually silica and alumina. A ceramic flux functions by promoting partial or complete liquefaction. [1] [2] The most commonly used fluxing oxides in a ceramic glaze contain lead, sodium, potassium, lithium, calcium, magnesium, barium, zinc, strontium, and manganese. These are introduced to the raw glaze as compounds, for example lead as lead oxide. Boron is considered by many to be a glass former rather than a flux.

Contents

Some oxides, such as calcium oxide, flux significantly only at high temperature. Lead oxide is the traditional low temperature flux used for crystal glass, but it is now avoided because it is toxic even in small quantities. It is being replaced by other substances, especially boron and zinc oxides. [3]

In clay bodies a flux creates a limited and controlled amount of glass, which works to cement crystalline phases together. Fluxes play a key role in the vitrification of clay bodies by lowering the overall melting point. The most common fluxes used in clay bodies are potassium oxide and sodium oxide which are found in feldspars. A predominant flux in glazes is calcium oxide which is usually obtained from limestone. The two most common feldspars in the ceramic industry are potash feldspar (orthoclase) and soda feldspar (albite).

Common oxides

List of commonly used ceramic oxides: [4]

See also

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<span class="mw-page-title-main">Manganese dioxide</span> Chemical compound

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<span class="mw-page-title-main">Lead glass</span> Variety of glass in which lead replaces the calcium content

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<span class="mw-page-title-main">Tin-glazing</span>

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<span class="mw-page-title-main">Soda–lime glass</span> Type of glass

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A pyrotechnic composition is a substance or mixture of substances designed to produce an effect by heat, light, sound, gas/smoke or a combination of these, as a result of non-detonative self-sustaining exothermic chemical reactions. Pyrotechnic substances do not rely on oxygen from external sources to sustain the reaction.

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This is a list of pottery and ceramic terms.

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<span class="mw-page-title-main">Forest glass</span>

Forest glass is medieval glass produced in northwestern and central Europe from approximately 1000–1700 AD using wood ash and sand as the main raw materials and made in factories known as glasshouses in forest areas. It is characterized by a variety of greenish-yellow colors, the earlier products often being of crude design and poor quality, and was used mainly for everyday vessels and increasingly for ecclesiastical stained glass windows. Its composition and manufacture contrast sharply with Roman and pre-Roman glassmaking centered on the Mediterranean and contemporaneous Byzantine and Islamic glass making to the east.

<span class="mw-page-title-main">Zirconium diboride</span> Chemical compound

Zirconium diboride (ZrB2) is a highly covalent refractory ceramic material with a hexagonal crystal structure. ZrB2 is an ultra-high temperature ceramic (UHTC) with a melting point of 3246 °C. This along with its relatively low density of ~6.09 g/cm3 (measured density may be higher due to hafnium impurities) and good high temperature strength makes it a candidate for high temperature aerospace applications such as hypersonic flight or rocket propulsion systems. It is an unusual ceramic, having relatively high thermal and electrical conductivities, properties it shares with isostructural titanium diboride and hafnium diboride.

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A secondary flux is a ceramic flux which does not act as a good flux alone, but is effective when used in combination with other fluxes. They also tend to act as "anti-fluxes" at lower temperatures, and may produce matt or opaque glazes under those conditions. For example, calcium oxide is generally used with sodium or potassium and by itself has little fluxing effect at pyrometric cone 6 but does act as a flux at cone 8.. When use calcium with lead it gives low melting temperature to glaz.

<span class="mw-page-title-main">Barium borate</span> Chemical compound

Barium borate is an inorganic compound, a borate of barium with a chemical formula BaB2O4 or Ba(BO2)2. It is available as a hydrate or dehydrated form, as white powder or colorless crystals. The crystals exist in the high-temperature α phase and low-temperature β phase, abbreviated as BBO; both phases are birefringent, and BBO is a common nonlinear optical material.

Ultra-high-temperature ceramics (UHTCs) are a type of refractory ceramics that can withstand extremely high temperatures without degrading, often above 2,000 °C. They also often have high thermal conductivities and are highly resistant to thermal shock, meaning they can withstand sudden and extreme changes in temperature without cracking or breaking. Chemically, they are usually borides, carbides, nitrides, and oxides of early transition metals.

References

  1. Daly, Greg (1995). Glazes and glazing techniques : a glaze journey (Reprinted ed.). London: A & C Black. ISBN   9780713642766.
  2. Obstler, Richard A. Eppler; Mimi (2005). Understanding glazes. Westerville, Ohio: The American Ceramic Society. ISBN   978-1-57498-222-0.{{cite book}}: CS1 maint: multiple names: authors list (link)
  3. "Flux".
  4. Hansen, Tony (July 20, 2022). "Oxides". Digitalfire. Retrieved July 20, 2022.

See also