I am asking about BET measurment of my samples prepared at 105 C in which temperature should I made degassing in order to conserve the same thermochemical proprities .thank you
Depends what your sample is. You didn't provide any information.
Sometimes it is useful to do a TGA in inert atmosphere to see if your sample decomposes at some temperature.
105 oC is quite low temperature for degassing anyway, so just depends what your sample is....
Then it seems quite insensitive to temperature. See the Figure 4 of the attached link.
I would go for 200-300 oC of heating under vacuum.
In any case, better to perform a TG analysis and/or measure at different degassing temperatures, just to be sure.
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652001000400006
Be sure to know what your sample temperature limits are. Also one thing that doesn't get mentioned enough, especially for porous samples, is sensitivity to thermal shock. Some samples encounter structural collapse if you heat it too fast. Somewhere like 5-10C/min shouldn't be a problem.
You have TG of your sample, weight loss if is quite low... and little bit strange that it always decreases... in any case, I think nothing happens below 400 oC.
How about measuring the isotherm a few times, with different degassing temperatures? For example: 150, 200, 250 and 300 oC... is a little extra work, but should be fruitful. I hope everybody tries this with their samples.
You should observe the surface area to increase with degassing temperature (loss of volatiles and water). If a some point area decreases, it means that structure collapsed and T was too high.
Have a shot and let us know!
As I have seen the TG of your sample the weight loss is continuous and that should be specified that to what it is attributed. I have performed the BET analysis of many samples and as the suggested by the instrumental engineer the degassing temperature for any sample is enough within the range of 300-400 C. the decrease in mass observed in TG profile may be attributed to decomposition of some chemical species on the surface. but that does not mean the surface properties like surface area and pore volume will vary much. And as the main objective of the BET analysis is to estimate the surface properties i will suggest to degas the sample in range 300-400 C as it is applicable to most of the samples.
Thanking you
I am surprised by your TGA trace showing a continuous weight loss, this may be due to carbonation of the surface. With activated carbons when trying to determine the microporosity by first performing a pre-adsorption with nonane an outgassing temperatura of 300°C is enough to recover the original isotherm. So in my work when posible I use 300°C as being suffiently high to remove any loosely bound adsorbed species.
Best regards,
Malcolm
Dear Khallok
Your TGA results are very strange as your sample is degrading with the rise in temperature. I am also working on HA but my results are different from you and comparable to the previous reported data.
You are working on porous or non-porous HA?
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