Zircon
Formula: ZrO2.SiO2
| DENS - Density (Specific Gravity) |
4.3-4.7 |
| HMOH - Hardness (Moh) |
7.5 |
| MLPT - Melting Point (MP) |
2550C |
| SLBY - Solubility |
Insoluble in water, weakly soluble in acids |
Zirconium silicate (or zircon) is extremely stable and will survive to very high temperatures in a glaze melt without dissolving (although small amounts do dissolve). Zircon is the generic name for zirconium silicate, the trade names are different (for example, zircopax). The refractive index of zircon is high (particularly with micronized zircon, size less than 5 microns).
Zircon is normally used in glazes for opacification (converting a transparent glaze to an opaque). Up to 20% may be required to opacify some transparent glazes, amounts beyond this reach saturation where crystallization begins to occur. The exact amount needed varies between different glaze types. It is thus most effective at low temperatures. Tin oxide can be a more effective opacifier than zircon (it has various advantages and disadvantages). Opacification can be a complex subject, and there are many other mechanisms for opacifiation (see Opacity in the glossary).
Individual zircon particles are angular, very hard and refractory (amazingly, they do not dissolve into the glaze melt even when ball milled to exceedingly small particle sizes). High amounts of zircon opacifier can cause cutlery marking (because of abrading angular micro-particles projecting from the glaze surface).
Zircon lowers glaze thermal expansion, but not by the same mechanism as other oxides that dissolve in the melt. Its low expansion will thus tend to reduce crazing. Thus, if the presence of zircon reduces thermal expansion enough that there is a danger of shivering, the glaze formulation may need to be adjusted to accommodate the zircon addition. It is often best to exclude the chemistry of the zircon materials from participation in glaze chemistry calculations, it is better to treat them simply as an addition and take into consideration their effect on glaze properties on a physical rather than chemical level.
Zircon stiffens the glaze melt and this often needs to be taken into account (since the chemistry of a zircon-containing glaze might suggest that it is more fluid that it really is). Glazes lacking melt fluidity can experience problems with crawling, blistering and pinholing since they are lacking in the ability to heal disruptions. Adjustment of the glaze chemistry may be needed (increasing the flux content while maintaining the SiO2:Al2O3, for example).
Many people do not fully appreciate the relationship between glaze color and opacifier content. Transparent glazes have depth, thus any colorants present produce deep and rich color (if the glaze does not crystallize of course). But when an opacifier is added to the glaze, the color depth is affected (according to the percentage employed). Thus a rich blue can turn into a dull pastel blue in a fully opacified glaze. The degree of color in a transparent colored glaze varies according to thickness whereas opacified colors to not suffer this problem (although this phenomenon is considered a benefit by many for its decorative appeal).
Because of its high thermal stability zircon is also employed in making various hi-tech porcelain bodies and materials. It is a major source for the production of zirconium oxide ZrO2.
Zircon sand (which is milled to produce zirconium silicate powders) has become so expensive in 2011 that major manufacturers are considering or are already diluting their products with other materials (like kaolin). So 'heads up' if your glaze is not as opacified as it was before! Also, use care in pretesting zircon materials, they vary in quality.
Mechanisms
Body Thermal Expansion - Low A very low expansion material. Glaze Opacifier - White Zirconium silicate is by far the most popular opacifier in glazes. It is available from many manufacturers. Opax, Ultrox, Zircopax and Superpax are examples of trade names of zirconium silicate and zirconium oxide products. The finer the milling of the material the better the opacity and the cleaner the color that will be produced.
Out Bound Links
In Bound Links
- (Hazards - Unspecified)
Zirconium Compounds Toxicity
The hazards of these materials in the ceramic indu... - (Materials - Parent)
Ultrox - Zirconium Silicate Glaze Opacifier
- (Materials - Alternative)
Opax - Zirconium Oxide, Zirconia
- (Materials - Related)
Calcined Alumina - Al2O3 - Aluminum oxide
Alumina Calcined, Calcnd Alum, Ground Alumina, Corundum
- (Materials - Parent)
Magnesium Zirconium Silicate - MgO.ZrO2.SiO2 or MgZrSiO5 - Low density zirconium opacifier
- (Materials - Parent)
Zircopax - Zirconium Silicate
- (Materials - Parent)
Calcium Zircon Silicate - CALCIUM ZIRCONIUM SILICATE
- (Oxides - Material source)
ZrO - Zirconium Oxide, Zirconia
- (Materials - Parent)
Superpax - Zirconium silicate
- (Materials - Parent)
Zirconium Spinel
SYNTHETIC ZIRCONIUM SILICATE
- (Materials - Parent)
Zircopax Plus - Zirconium Silicate Opacifier
- (Oxides - Material source)
ZrO2 - Zirconium Dioxide
XML for Import into INSIGHT
<?xml version="1.0" encoding="UTF-8"?>
<material name="Zircon" descrip="" searchkey="Zirconium Silicate" loi="0.00" casnumber="366497-20-3">
<oxides>
<oxide symbol="SiO2" name="Silicon Dioxide, Silica" status="" percent="32.790" tolerance=""/>
<oxide symbol="ZrO2" name="Zirconium Dioxide" status="" percent="67.210" tolerance=""/>
</oxides>
</material> | 
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