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Native Materials - Petrographic Analysis To Oxides


curt

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Hi All,

 

I have recently obtained some petrographic analyses of some raw materials (basically rocks!) that I am thinking about incorporating into my ongoing native materials work. 

 

The petrographic analysis provides a mineralogical breakdown of the rocks, eg, x% of plagioclase, y% of actinolite, etc., and I suspect is the kind of thing normally done for miners or other industrial users of these materials.

 

However, this is not information I can use (at least not directly) in my glaze software (Insight), which requires a Seger-formula style oxide breakdown of the material, ie, SiO2, Al2O3, MgO etc. etc. in order to incorporate it as a raw material in glaze or clay body formulas.

 

Now, I am nobodies chemist, but I suspect that if I know the mineralogical breakdown, there is somehow or somewhere a way to convert this information into an oxide-based breakdown.  Has anyone seen such a place or resource, or converter, which would do this?  Or have any other thoughts how I could get this information into a usable form?

 

 

 

 

 

 

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Do you know what type of plagioclase you have? According to the wikipedia article, plagioclase is a series of minerals, made up of variable proportions of anorthite and albite. The chemical composition can vary a lot depending on the type. For example, anorthite contains 35.84% alumina and 44.40% silica, while albite contains 20.35% alumina and 67.39% silica.

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Not precisely although I can make an educated guess based on other samples I have and some knowledge of the geochemistry of the area. And since plagioclase is only one of several minerals in the particular rock, if I am slightly off the consequences are not that severe.

 

In any case, that was just an example - for the moment lets just pretend that I do know exactly how much silica and how much alumina are there. The question I am trying to answer is: how much silica oxide and alumina oxide does that silica and alumina turn in to at temperature?

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Guest JBaymore

Curt,

 

If you own the Level II version of Insight, the info on how to do this is on the paid Digitalfire reference site, I think.  I don't think that is on the free info part that is available there .... but you should check. 

 

If you have the percent composition based on oxides (as in X% SiO2 / X% CaCO3) , with a little math (or with glaze calc software) that can be converted to molecular relationship with the fluxes unified.  No time now... day of critiques ...more later.

 

best,

 

...............john

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Guest JBaymore

Silica is silicone dioxide/SiO2, right? Surely it is not turning into anything.

 

Silicon ......  not "silicone".  Unless that is an English English thing ;) .  As in "Aluminum" :) .

 

best,

 

.................john 

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"Silica is silicone dioxide/SiO2, right? Surely it is not turning into anything."

 

yes, I agree with you in potter-speak. And if I was getting the chemical analysis in oxide terms it would all be straightforward.

 

However the kinds of analyses I have been getting were not made for potters. They give ELEMENTAL breakdowns, eg how much silicon, how much aluminum, etc, not the breakdowns of COMPOUNDS such as silicon dioxide, aluminum oxide etc. I am out of my depth here, but it appears that attaching oxygen to other elements changes their percentages in a mineral (compared to the percentages of elements).

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Curt,

 

If you own the Level II version of Insight, the info on how to do this is on the paid Digitalfire reference site, I think. I don't think that is on the free info part that is available there .... but you should check.

 

If you have the percent composition based on oxides (as in X% SiO2 / X% CaCO3) , with a little math (or with glaze calc software) that can be converted to molecular relationship with the fluxes unified. No time now... day of critiques ...more later.

 

best,

 

...............john

Thanks John I do have Insight Level 2 and will have a look. I was not aware that there was a part of the reference site that was for paying subscribers only (maybe I have been using it without knowing!)

 

I can get from oxide percentages to molecular with a bit of trial and error in Insight ;-)

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Curt, it sounds like you may have figured out how to convert between element percentages and oxide percentages, but for anyone reading this who wants to know, here (I think) is how you would do it:

Suppose your material contains X% of an element R, which forms an oxide RaOb. Then 100g of your material contains X grams of R. To find the number of R atoms in moles, divide this by the relative atomic mass, A[R]. The number of oxide molecules in moles will therefore be X/A[R]/a, since each oxide molecule contains a atoms of R. To find the mass of the oxide in grams, multiply this by the relative atomic mass of the oxide, A[RaOb]. Thus the percent of oxide is (X/A[R]/a) x A[RaOb].

Since A[RaOb] = a A[R] + b A[O], we can rewrite this as X x (1 + b A[O]/(a A[R])).

For example, the molecular formula for aluminium oxide (alumina) is Al2O3, and the relative atomic masses of aluminium and oxygen are 26.98 and 16.00 respectively, so to convert the percentage of aluminium into the percentage of alumina, multiply this by 1 + 3x16.00/(2x26.98) =  1.89.

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(...a few hours of fossicking around on the internet later...)

 

Thanks for the comments.  I eventually found out what needs to be done to convert elements to oxides, after visiting the geologist's Diagon Alley on the web.  Peter, it is pretty much what you said, although I was hoping to find a spreadsheet or a website where someone would have already done all those calculations for me and I and could just plug in my elements and go.  No luck on that yet, so at this point I am still up for some spreadsheet work myself I think, but I will keep looking. 

 

David, I did look at Rhodes, but he was teasingly unhelpful, pointing to a seed when what I needed was the tree.  To be fair to him, though, my copy of Clay and Glazes dates from the mid-70s, when I think most were talking about card-punch machines rather than spreadsheets.

 

If anyone discovers that magic spreadsheet or website I am looking for to convert elemental breakdowns to oxide breakdowns please sing out!  :rolleyes:   

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