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Zircopax

Zirconium Silicate

OxideAnalysisFormula
SiO232.79%1.000
ZrO267.21%1.000
Oxide Weight183.34
Formula Weight183.34
Enter the formula and formula weight directly into the Insight MDT dialog (since it records materials as formulas).
Enter the analysis into an Insight recipe and enter the LOI using Override Calculated LOI (in the Calc menu). It will calculate the formula.
GSPT - Softening Point 2550C

Zircopax is a generic brand name of zirconium silicate or zircon (see Zircon for more information). It is primarily used in ceramic to opacify glazes. In North America, the most popular zirconium opacifiers fall under the brand names of Zircopax Plus, Superpax, Zircosil and Excelopax. These vary according to particle size, the finer the size the greater the scattering of light (and thus the better the opacification). In addition, the finer sized materials contain a little extra silica for maximum whiteness.

Of course, the amount of zircopax in a glaze determines the opacity. Small amounts (1-3%) may give no noticeable difference but are sometimes employed to improve glaze hardness. Since zircopax is refractory, the more that is added the more the degree of glaze melting (and melt viscosity) is going to be affected. Up to 15% or more might be needed to fully opacify a glaze. If higher amounts are needed the glaze formulation may need to be adjusted to reduce the amount of SiO2 or increase flux (to melt the glaze better).

Zircopax affects glaze melt viscosity, surface smoothness, thermal expansion and color development and can be implicated in a range of glazes faults associated with these. Please read the page on zircon for more information.

Zirconium prices are have increased rapidly in recent years, reflecting the world supply situation. Even though the material is very expensive, Zircopax is added to the body recipe of “porcellanato” tiles. It is a very effective body whitener, especially for casting porcelain. Excessive additions give the porcelain an artificial "white plastic" appearance.

Typical Properties:

Formula: ZrSio4 Weight: 183.1
Linear Coefficient of Expansion (25-700C cm/cm/degreeC): 42 x 10 -7
Specific gravity: 4.5

Particle Size: Zircopax Superpax Excelopax
Microns, Ave. 1.3 .74 .55
Bulk density lbs/cu ft 100 75 75
Surface area, m2/g 4.5 9.8 12.8


Mechanisms

Pictures

An example of G2571A cone 10R matte with 10% added zircopax (right). The zircopax version is very bright white compared to the original.

Opacifying a reduction dolomite matte

Opacifying a cone 10 reduction magnesia matte glaze. On the left: G2571A dolomite matte, a popular recipe (from Tony Hansen). Right: 10% Zircopax has been added. Both are on a buff stoneware (H550 from Plainsman Clays).

Can you make things from zircopax? Yes.

Only 3% Veegum will plasticize Zircopax (zirconium silicate) enough that you can form anything you want. It is even more responsive to plasticizers than calcined alumina is and it dries very dense and shrinkage is quite low. Zircon is very refractory (has a very high melting temperature) and has low thermal expansion, so it is useful for making many things. Of course you will have to have a kiln capable of much higher temperatures than are typical for pottery or porcelain to sinter it well.

How do you turn a transparent glaze into a white?

Right: Ravenscrag GR6-A transparent base glaze. Left: It has been opacified (turned opaque) by adding 10% zircopax. This opacification mechanism can be transplanted into almost any transparent glaze. It can also be employed in colored transparents, it will convert that coloration to a pastel shade, lightening it.

The action of Zircopax vs Tin Oxide at cone 10R on Plainsman H443. Notice Tin does not work. Also notice that between 7.5 and 10% Zircopax provides as much opacity at 15% (Zircon is very expensive).

Adding an opacifier can produce cutlery marking!

G2934 cone 6 matte (left) with 10% zircopax (center), 4% tin oxide (right). Although the cutlery marks clean off all of them, clearly the zircopax version has the worst problem and is the most difficult to clean. To make the best possible quality white it is wise to line blend in a glossy glaze to create a compromise between the most matteness possible yet a surface that does not mark or stain.

Can you throw zircopax on the potters wheel? Yes!

These crucibles are thrown from a mixture of 97% Zircopax (zirconium silicate) and 3% Veegum T. The consistency of the material is good for rolling and making tiles but is not quite plastic enough to throw very thin (so I would try 4% Veegum next time). It takes alot of time to dewater on a plaster bat. But, these are like nothing I could make from any other material. They are incredibly refractory (fired to cone 10 they look like bisqued porcelain), a have amazing resistance to thermal shock. I could pour molten metal into them and they will not crack. I can heat one area red hot and it will not crack. I can throw the red hot piece into water and it will not crack!

Out Bound Links

In Bound Links


By Tony Hansen

XML for Import into INSIGHT

<?xml version="1.0" encoding="UTF-8"?> <material name="Zircopax" descrip="Zirconium Silicate" searchkey="" 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="U" percent="67.210" tolerance=""/> </oxides> </material>


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