Monthly Tech-Tip from Tony Hansen SignUp

No tracking! No ads!

1-9 | A | B | C | D | E | F | Frits | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

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?

Tap picture for full size and resolution

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

Tap picture for full size and resolution

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
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
Follow me on

Got a Question?

Buy me a coffee and we can talk



https://digitalfire.com, All Rights Reserved
Privacy Policy