Author Topic: Secondary standard for oxygen  (Read 5684 times)

Jeff C.

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Secondary standard for oxygen
« on: April 06, 2015, 11:25:54 PM »
Hi all, I'm planning to measure the oxygen dissolved in Cu matte (Cu-Fe-S). The oxygen concentration would be in the range between 0.1 to 1.5wt%. And I'm looking for a secondary standard with similar amount of oxygen in there. Been going through NIST website, the closest one would be synthetic Cu2O (about 10wt% O)...also found some steel standards with only trace amount of oxygen (<100ppm). Haven't come across anything in between.

Suggestions are appreciated!!!  :)

Probeman

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Re: Secondary standard for oxygen
« Reply #1 on: April 07, 2015, 08:33:46 AM »
Hi all, I'm planning to measure the oxygen dissolved in Cu matte (Cu-Fe-S). The oxygen concentration would be in the range between 0.1 to 1.5wt%. And I'm looking for a secondary standard with similar amount of oxygen in there. Been going through NIST website, the closest one would be synthetic Cu2O (about 10wt% O)...also found some steel standards with only trace amount of oxygen (<100ppm). Haven't come across anything in between.

Suggestions are appreciated!!!  :)

Hi Jeff,
I assume you want this secondary std to check the accuracy of measuring trace oxygen in Cu-Fe sulfides (matte?)?  Are you attempting to characterize the oxidation state of the sulfur in that setting?  It's a tough question for sure. 

I suspect your best bet, considering the general relative lack of low level oxygen standards, would be to obtain some CuFe2 and/or FeS2 single crystals which one might have confidence (for reasons of synthetic purity or thermodynamic considerations perhaps?) that because they are perfect crystals and give a proper XRD patterns, therefore they might be oxygen free?

I have some vacuum remelted Fe metal that is stated to have 310 PPM of oxygen and 10 PPM of N, but of course besides being a very different matrix, the problem is surface oxidation for pure Fe...

Can anyone say whether synthetic (or natural for that matter!), simple sulfides should be essentially oxygen free to EPMA sensitivity levels?   
john
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debel

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Re: Secondary standard for oxygen
« Reply #2 on: April 07, 2015, 11:38:42 AM »
Bismoclite (Bi oxychloride) has 6.1 wt% O in it.
Bi2O3 (an important synthetic) has ~10 wt% O.
The absorption correction may be a problem.

Jeff C.

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Re: Secondary standard for oxygen
« Reply #3 on: April 07, 2015, 07:48:03 PM »
Hi all, I'm planning to measure the oxygen dissolved in Cu matte (Cu-Fe-S). The oxygen concentration would be in the range between 0.1 to 1.5wt%. And I'm looking for a secondary standard with similar amount of oxygen in there. Been going through NIST website, the closest one would be synthetic Cu2O (about 10wt% O)...also found some steel standards with only trace amount of oxygen (<100ppm). Haven't come across anything in between.

Suggestions are appreciated!!!  :)

Hi Jeff,
I assume you want this secondary std to check the accuracy of measuring trace oxygen in Cu-Fe sulfides (matte?)?  Are you attempting to characterize the oxidation state of the sulfur in that setting?  It's a tough question for sure. 

I suspect your best bet, considering the general relative lack of low level oxygen standards, would be to obtain some CuFe2 and/or FeS2 single crystals which one might have confidence (for reasons of synthetic purity or thermodynamic considerations perhaps?) that because they are perfect crystals and give a proper XRD patterns, therefore they might be oxygen free?

I have some vacuum remelted Fe metal that is stated to have 310 PPM of oxygen and 10 PPM of N, but of course besides being a very different matrix, the problem is surface oxidation for pure Fe...

Can anyone say whether synthetic (or natural for that matter!), simple sulfides should be essentially oxygen free to EPMA sensitivity levels?   
john

Thanks for your quick response John.

Yes, indeed I need this secondary standard for checking the accuracy and at this stage I'm not trying to determine the oxidation state of the S in matte phase yet.

We do have synthetic CuFeS2 and FeS2 in our Taylor Block and I've been using them as primary standards for Cu, Fe and S and assume they are oxygen free or at the level below the detection limit of our JEOL8200.

I heard silicon can take some oxygen but not sure to what extent?

Jeff C.

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Re: Secondary standard for oxygen
« Reply #4 on: April 07, 2015, 07:53:24 PM »
Bismoclite (Bi oxychloride) has 6.1 wt% O in it.
Bi2O3 (an important synthetic) has ~10 wt% O.
The absorption correction may be a problem.

Thanks for the suggestion, debel.

Yes, for Bi2O3, the absorption correction is a concern to me.

John Donovan

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Re: Secondary standard for oxygen
« Reply #5 on: April 07, 2015, 08:33:56 PM »
I heard silicon can take some oxygen but not sure to what extent?

The native oxide layer on pure Si depends on exposure time to air, but initially forms rapidly at room temperature to around 1 to 2 nm, but continues to grow for many months thereafter and can approach 3 to 6 nm or more after a year or two.
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John Donovan

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Re: Secondary standard for oxygen
« Reply #6 on: April 07, 2015, 09:44:20 PM »
Bismoclite (Bi oxychloride) has 6.1 wt% O in it.
Bi2O3 (an important synthetic) has ~10 wt% O.
The absorption correction may be a problem.

Thanks for the suggestion, debel.

Yes, for Bi2O3, the absorption correction is a concern to me.

Remember, for most trace elements, the uncertainty of the background correction accuracy overwhelms the uncertainty of the matrix correction accuracy.

I agree that in some circumstances, (e.g., O ka in certain matrices) the accuracy of the absorption correction can be a significant source of uncertainty, but usually the accuracy of the background correction is the dominant source of error for trace elements, due to the uncertainty of the background characterization.

Consider this:  the matrix correction is always a multiplicative (percent relative) source of error while the background correction is always a subtractive (absolute) source of error...
John J. Donovan, Pres. 
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"Not Absolutely Certain, Yet Reliable"