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Nepheline Syenite

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Nepheline Syenite A-270

Like feldspar, Nepheline Syenite is used as a flux in porcelains, vitreous and semi-vitreous clay bodies, and in glazes. Nepheline syenite contributes high alumina without associated free silica in its raw form. This makes it an excellent tile filler and melter, especially for fast firing. Nepheline syenite fluxes and forms silicates with free silica in bodies without contributing any free silica itself, thereby stabilizing the expansion curve of the fired body. Floor and wall tile bodies benefit from lower absorption and moisture expansion, better mechanical strength and lower thermal expansion than other alumina sources. Nepheline syenite is valuable in glass batches to acheive the lowest melting temperature while acting as a source of alumina.

Nepheline Syenite has been a standard in the ceramic industry for many years, and is very popular for its whiteness. For example, it is possible to make a very white vitreous medium temperature porcelain (as low as cone 4) by mixing a plastic kaolin with nepheline syenite and silica.

In pugged bodies nepheline syenite can be responsible for stiffness changes during aging. It is also more challenging to maintain stable deflocculated slurry bodies using nepheline syenite than with other feldspars.

Because of its sodium content, high nepheline syenite glazes tend to craze (because of the high thermal expansion of Na2O). However bodies fluxed with nepheline syenite do not necessarily exhibit greater expansion than other feldspar bodies.

Nepheline syenite begins melting around cone 1 and is one of the lowest melting feldspars.

Since nepheline syenite has more alumina than most feldspars, substituting it into recipes means that on one hand a lower melting temperature is achieved while on the other a more viscous melt results because of the extra alumina.

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