Volclay Bentonite

Alternate Names: Volclay 325 Bentonite, Dioctahedral smectite

Description: 364CER,334,355,660,149,446,105,356,840,331,351

Oxide	Analysis	Formula
CaO	0.65%	0.10
Na2O	2.57%	0.35
MgO	2.67%	0.56
FeO	0.35%	0.04
Fe2O3	3.25%	0.17
Al2O3	21.08%	1.73
SiO2	63.02%	8.79
LOI	5.64%	n/a
Oxide Weight		784.55
Formula Weight		831.44

Notes

A micronized sodium bentonite.
The 325 mesh version of this is most suitable for porcelains and a possible substitute for the more expensive HPM-20 Volclay.

Dioctahedral smectite, an expanding layer silicate.
Gray and cream-colored clays (montmorillonites) for use as suspension agents, viscosifiers, gellants and binders.
Has lower iron content that HPM-20 bentonite.
However while they company refers to their 325 mesh product, the data sheet says that 90% passes 325 mesh?

Related Information

Could these bentonite particles cause specking in a porcelain?

The stated particle size of a material and fired appearance can both be misleading. For example, these are Volclay 325 bentonite particles fired to cone 8 oxidation. They are from a water washed sieve analysis test, the oversize particles from a 325 mesh screen (left) make up 2% of the total and 1% are from the 200 mesh screen (right). Although the 325 particles appear ominously dark, individually they are likely to small to produce apparent fired specks in a porcelain. However 200 mesh sizes can produce visible fired specks, but that fraction of oversize does not have nearly as high iron or flux content. Still, the finer darker particles could agglomerate, it might be better to use a cleaner bentonite to plasticize a porcelain.

Two plasticizers show vastly different potency

A comparison of the plasticity of two bentonites was done by diluting them with silica. The top sample is Volcay 325 mixed 25:75 with silica. It is a standard Wyoming sodium bentonite - mined, dried and ground. The bottom specimen is Hectalite 200, a highly refined white hectorite, mixed 50:50 with silica. Notice how much less plastic it is (even though at double the percentage).

Links

Materials	Hectalite 200
Materials	Hectabrite White magnesium-rich surface-modified highly purified sodium hectorite clay 4-5 times more efficient than raw bentonite.
Materials	HPM-20 Volclay Bentonite
Materials	Fuller's Earth
Typecodes	Clay Other Clays that are not kaolins, ball clays or bentonites. For example, stoneware clays are mixtures of all of the above plus quartz, feldspar, mica and other minerals. There are also many clays that have high plasticity like bentonite but are much different mineralogically.
URLs	http://www.colloid.com/ISG/TechData/Volclay%20325%20Mesh%20Tech%20Sheet.pdf Volclay 325 Data Sheet

Data

% Passing 325 Mesh Wet	90%
Apparent Viscosity (cps)	12 cps minimum @ 6.25% solids
pH for dry powder	8.5-10.5 @ 5% solids
% Passing 200 Mesh Wet	97%

By Tony Hansen
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