Riff Fenton on wed 4 feb 98
ordered some cobalt carb. the other day and mentioned to my
supplier that I thought I might shop around for a better
price on this expensive stuff. "oh", he said, "you can find
a better price, but it is a lower percentage."
say what?
"ya, ours is about 79%...theirs only about 40% or so."
Now I thought that cobalt carbonate was cobalt carbonate.
I mean, do supply houses dilute it? What else is in it?
Should we ask? or do we not want to know? Is cobalt carbonate
for $14.00 a lb that much different from cobalt carbonate for
$28.00 a lb?
Riff
Tom Buck on thu 5 feb 98
Surely, percent cobalt in a material is important, and one should always
demand an analysis (chemical composition by weight of components).
There are TWO commerical cobalt materials made for industry
generally, paint and ceramics being important, (not for potters, we get
what comes):
cobalt II carbonate basic with a simple formula of
2CoCO3.3Co(OH)2.H2O which if pure would have a Cobalt (elemental) content
of 55% but it is not likely to be much above 95% pure, more probably
around 90% pure, so 50% would be a good ballpark amount.
and cobalt oxide, in one of two forms, or a mix of the two
depending on source and enduse. Cobalt III oxide Co2O3 (steel gray
or black). Cobalt II oxide CoO (grayish, sometimes green-brown). Since
both oxides are usually produced by calcining the carbonate (above), and
since the specific oxide produced depends on the kiln atmosphere, there is
some variation in the product from such an operation.
In CoO, the cobalt content is over 75% (max 78.5%); in Co2O3, the
cobalt content is 72% max. So, if the commercial grade is 90%
oxide, the material would contain at least 65% elemental cobalt, perhaps
as much as 70% Co.
With cobalt pigment fetching high prices, one should always
question the purity of the material being offered.
Tom Buck ) tel: 905-389-2339 & snailmail: 373 East
43rd St. Hamilton ON L8T 3E1 Canada (westend Lake Ontario, province of
Ontario, Canada).
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