The conversion of SrSO3 to SrSO4 is indicative of presence of O2 in the test tube. Either one of two things could be the root cause of this observation:

1) You have some leak in the piping/ tubing connections.

2) The N2 gas required to keep the inert environment for pyrolysis to happen is not 100% N2 but has some O2 in it. Remember that N2 is typically produced by air separation unit (ASU) and there is some possibility the ARU does not produce 100% pure N2. Try to use another supplier of the N2 gas.

Hope this helps answer your question.

Professor Yehia Khalil

Yale University

USA

Thank you, prof. Khalil. I checked the all of connections. No leak has been found. The N2 gas I used is high purity nitrogen. And high purity argon is also used in my experiment. The same results were obtained. I do try my best to clean the O2. If trace O2 in high purity nitrogen or argon will turn SrSO3 to SrSO4, how could I eliminate the influence of O2? Besides, if SrSO3 will be oxidized so easy,  Is it possible that preparation SrO from SrSO3 by pyrolysis in industrial production?

The Gmelin Handbook of Inorganic Chemistry suggests that 4SrSO3 will decompose to 3SrSO4 and SrS.

As previous speakers indicated, you have either

1/ oxygen presence, which can be reduced by better purging (slightly elevated temp?), high purity gasses, positively no leaks...you if you increase weight of your starting material and find same amount of SrSO4, your oxygen contamination is static. If you have same ratio, not same amount, you used more oxygen and there is source in the system...

2/ unstable product, that decomposes, either in your setup, or after removal, when exposed to ambient.

In any case, how did you characterized your product, how sure are you of the stoichiometry you announced? What method, what precision and what is main source of the errors. Those are the questions you need to ask yourself. 

The colleagues gave possible answers to your questions which you your self answered in your questions. However i would like to add some comments:

-If the oxygen free pryrolysis of SrSO3 favors the formation of  SrSO4 then it may be not possible to directly get SrO this way. Then it may be a two step process. That is by oxidizing Sr S in oxygen arm environment.

- If the sealing of the reactor is not sufficient and it is not tight enough against oxygen, it is most probable to get directly SrSO4.

- Another important factor which must be given highest care is the absorbed oxygen and water moisture at the surface of the reactor tubes and sealing.

- One has not to forget that the staring material is inform of powder which has a very large surface area and consequently absorbs a lot of oxygen which poison the source.

Then you have to make very string elaboration to your reactor by using very tight gas and vacuum fittings and valves. I thin using gum for fitting is not very suitable. You have to build your apparatus for hight purity and sealing condition.

The you have to develop a working procedure to a void the contamination of the reactor and the substances by oxygen.

You have to release the oxygen and water moisture fro the apparatus and  materials by preheating and pumping at relatively elevated temperature.

You can increase the quantity of the material such that if  apart is converted to SrSO4 the rest will be converted to SrO by continuing the reaction.

wish you success

Thank you for everybody. I have found the result of generating SrSO4 finally. As it's said by Dr. Merola, SrSO3 could turn to SrSO4 and SrS at high temperature. I can not found any data of pyrolysis of  SrSO3. But according to the data of CaSO3, there are two route of SrSO3 pyrolysis, 4CaSO3=3CaSO4+CaS at lower temperature, CaSO3=CaO+SO2 at higher temperature. So, if I put the sealing Al2O3 tube with SrSO3 specimen to the furnace reached at 1000 deg C, could  the higher-temperature -reaction happen? The Al2O3 tube could suffer the such huge change of temperature.

And I got something that once SrSO3 and Mg salts pyrolyze together, SO2 in SrSO3 could submit. why? Thanks again. 

You could also check (or control to some degree) your furnace atmosphere by adding another material.

For example, adding Ti-metal powder to your furnace at 1000C will create an oxygen partial pressure of approximately 10^-28. See the attached Ellingham diagram.

If you notice no more Ti-metal after your furnace run, you know that the oxygen atmosphere exceeded that partial pressure.

Dear Chen,

To run high temperature reactions at such elevated temperature you can use also quartz tubes. 

I think you are correct that you may need to get the tube and furnace up to a high temperature first.  It does appear that the disproportionation reaction takes place at lower temperature and so this reaction occurs as you are heating the system up to temperature.  

Really, It is a good discussion.

I hope that Dr. Chen Siming found the solution of his problem.

Yes, SrSO3 could turn to SrSO4 and SrS at high temperature. As well as 4SrSO3 may decomposed  to 3SrSO4 and SrS.

Good luck

Yes. I want to find a way to prepared SrO from SrSO3. But up to now, the pyrolysis of SrSO3 is impossible, even the temperature raised to 1100 deg C or added Mg salt (I have found something reported that SO2 can release with Non-water Mg salt additive ). How could I get SrO from SrSO3? Thanks for your helping.