• Materials for Ceramics

Covia Nepheline Syenite

Notes

Their data sheet describes this as a naturally occurring, silica-deficient sodium-potassium alumina silicate. The higher total alumina and alkali contribution available from nepheline syenite produces ceramic ware with greater impact and flexural strength and improved resistance to the stresses of thermal extremes and mechanical shock. The lower melting eutectic and increased fluxing power make possible body compositions which mature at temperatures as low as cone 3-5. It is the higher alkali to alumina ratio and greater chemical reactivity that accelerate the melt and promote a faster maturation. It will increase the rate of vitrification over a wider firing range, ensure smooth glazed surfaces even at lower temperatures and help to reduce the deformation typically encountered in fast fire cycling. When the objective is improved translucency, this will combine with and consume the available free crystalline silica to create highly translucent wares.

The author's experience with this material is nothing but positive. Many decades of reliable quality and availability in a body and glaze flux of higher quality than anything else available. This is a great company!

Grades available: A-200, A-270, A-400, ASTM E-11

Property: Test Method Unit Values
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Mineral Petrographic Microcline/Albite/Nepheline
Specific Gravity ASTM C128 2.61
Melting Point ASTM C-24 1868F/1020C
Bulk Density ASTM C-29 38-55 lbs/cu ft
Free Silica < 0.1%

Related Information

Which is the champion melter of American/Canadian feldspars?

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Feldspars are employed in glaze recipes as melters. So comparing their melt fluidities should be helpful in deciding if one can substitute for another (of course, if possible, a soda-predominant feldspar should be substituted for another soda spar). Feldspars don't melt alone at cone 6 (2200F) so we mixed each with 15% Ferro Frit 3195 (we consider a feldspar a material that sources KNaO). Nepheline Syenite, this is A270, is the champion melter here. Other similar ones can be spotted easily. In the end, degree of melt is a valid consideration in determining if one feldspar is a viable substitute for another in a recipe. Even if the feldspar you want to substitute does not melt as much a little frit can be added to the recipe to make up for the difference (e.g. 3-5%).

Melt fluidity: Cornwall Stone vs. Nepheline Syenite

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Three Cornwall Stone shipments (from 2011 and 2014) fired at cone 8 in melt flow GLFL testers and compared to Nepheline Syenite. Each contains 10% Ferro Frit 3134.

Melt flow comparison between Nepheline Syenite 270 and 400 mesh

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This Nepheline Syenite GLFL test for melt flow did not demonstrate much of a difference in melting at cone 9 between 270 and 400 mesh materials.

Warnings on back of Covia nepheline syenite bag 2021

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It is stated as non-hazardous in accordance with GHS criteria. Although like feldspar in chemistry, mineralogically nepheline syenite powder is a gound igneous rock, it does not contain quartz.

Covia nepheline syenite bag as of 2021

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Demonstrate casting-rate control:

By slip-casting nepheline syenite

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What would it take to cast pure Nepheline Syenite? A clay addition. This 10:90 bentonite:Nepheline has enough shrinkage and leather-hard strength to enable pulling itself away from the plaster mold. This bowl was just extracted; it cast without cracks to 3mm thickness in about 15 minutes. The defloculated slip required more water than normal but it pours and drains really well. This is a demonstration of how much control technicians can have over casting rate. The amount and type of plastic clay added can take this material from being completely water permeable, zero leather-hard strength and non-castable to water impermeable, very high leather-hardness but very slow casting. Only a testing program is needed to determine the minimum bentonite percentage needed to achieve reliable casting (it is likely less than 10%).

For example, 95%+ nepheline slurries can be made using Veegum. How did this bowl fire? As a vitreous product around cone 1. And, on aging for a month, the rheological properties of the slurry did not change.

Covia Nepheline Syenite (from Canada):

Here is what it does from cone 3 down to 05

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These SHAB test fired bars are 95% nepheline syenite (5% Veegum added). By cone 02 (bar stamped #4) is self-glazing and glass-like with a total shrinkage (plastic to fired) of 15% (less than some porcelains). At cone 03 (the #5 bar) the porosity is 3% (a stoneware). This is not an absolute indication of the materials' melting profile because of the Veegum, it behaves as a powerful flux and melting catalyst.

The Blue Mountain nepheline syenite deposit in Havelock, Ontario, is a major, high-purity industrial mineral source mined since 1955 for glass, ceramics, and filler applications. This 99% pure, iron-poor deposit consists of albite, microcline, and nepheline. It has less than 0.1% free SiO₂ and Fe₂O₃! The deposit is approximately 400 feet deep.

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