DSC data variability
Morgan Bruns
Dietenberger, Mark A -FS
I am still trying to participate in the forum after Isaac invited me to the group. My new gmail account is not working quite right with the forum, so I am responding this way.
For heat capacity and heat of pyrolysis of dried vegetative material as function of temperature we used the modulated feature of TA’s MDSC, a concept that is incompatible with combined TGA and DSC in the Combustion and Flame paper. To account for mass loss of the vegetative material we used a TGA set at the same temperature profile at 3.5 K/min, the same as that in the MDSC test.
We spent quite a bit of time on its calibration and getting close agreement with the sapphire standard.
Our paper on evaluating the Cp and heats of reactions for pyrolysis for 12 live leaves is nearly complete (going through internal reviews) and about ready for submission to a journal.
I note that the newest TA instrument on the modulated DSC has an option for evaluation of thermal conductivity. I wonder who has it.
Regards, Mark Dietenberger
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Stanislav I. Stoliarov
Dr. Stanislav I. Stoliarov, Professor
University of Maryland
Department of Fire Protection Engineering
3104C J.M. Patterson Bldg.
4356 Stadium Dr.
College Park, MD 20742
Phone: 301.405.0928
Fax: 301.405.9383
Email: sto...@umd.edu
To view this discussion on the web visit https://groups.google.com/d/msgid/macfp-condensed-phase-discussions/BLAPR09MB6370A79B30B3E0435435D35ECF030%40BLAPR09MB6370.namprd09.prod.outlook.com.
Isaac Leventon
On Friday, October 16, 2020 at 9:05:35 PM UTC-4, Dr. Stas wrote:
Hi Mark,Will you be able to use the MDSC and your methodology to perform measurements on the black PMMA? If you perform these measurements quickly (within a month or so), we should be able to add them to the depository and reference your paper for methodology details.Stas--------------------------------------------------------
Dr. Stanislav I. Stoliarov, Professor
University of Maryland
Department of Fire Protection Engineering
3104C J.M. Patterson Bldg.
4356 Stadium Dr.
College Park, MD 20742
Phone: 301.405.0928
Fax: 301.405.9383
Email: sto...@umd.edu
On Fri, Oct 16, 2020 at 7:42 PM 'Dietenberger, Mark A -FS' via MaCFP Condensed Phase Discussions <macfp-condensed-phase-discu...@googlegroups.com> wrote:
I am still trying to participate in the forum after Isaac invited me to the group. My new gmail account is not working quite right with the forum, so I am responding this way.
For heat capacity and heat of pyrolysis of dried vegetative material as function of temperature we used the modulated feature of TA’s MDSC, a concept that is incompatible with combined TGA and DSC in the Combustion and Flame paper. To account for mass loss of the vegetative material we used a TGA set at the same temperature profile at 3.5 K/min, the same as that in the MDSC test.
We spent quite a bit of time on its calibration and getting close agreement with the sapphire standard.
Our paper on evaluating the Cp and heats of reactions for pyrolysis for 12 live leaves is nearly complete (going through internal reviews) and about ready for submission to a journal.
I note that the newest TA instrument on the modulated DSC has an option for evaluation of thermal conductivity. I wonder who has it.
Regards, Mark Dietenberger
From: macfp-condensed-phase-discu...@googlegroups.com <macfp-condensed-phase-discu...@googlegroups.com> On Behalf Of Morgan Bruns
Sent: Friday, October 16, 2020 4:11 PM
To: MaCFP Condensed Phase Discussions <macfp-condensed-phase-discu...@googlegroups.com>
Subject: DSC data variability
One of the things from the report that really stands out to me is the variability of the DSC data. The good news is that I think it's a clear lesson that we need to be careful when using DSC data from the literature. The bad news is that have a lot to learn about how to do DSC if we are ever going to get meaningful results that can be used to extract pyrolysis model parameters such as specific heat capacities and heats of pyrolysis.
A good place to start might be to sort through all of the README files on GitHub and just tabulate all of the clear differences in how the data were obtained (e.g., how many participants used covered sample pans versus uncovered sample pans?). Also, is anyone aware of any good papers looking at the process of DSC especially for polymer pyrolysis? I know that Stas has done some work on this, for instance here: http://dx.doi.org/10.1016/j.combustflame.2013.02.012.
I'm certainly not an expert in DSC experiments, but it would be great if we could come together as a community and figure out some guidelines for DSC best practices.
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Dietenberger, Mark A -FS
Thank you Stas and Isaac. Had you offered those samples of PMMA while we were in the middle of our MDSC experiments with the vegetation, we could have fit them into our work. When our staff heard of the PMMA request, it was like, are you kidding? It is so much work, of several weeks, of trying to get the calibration right and compensating for the poor instrument design. I suspect the older DSC data in general are in the same boat, with the large errors involved with the folks not paying close attention like we did with our instrument. If you want to get the heat capacity and heat of pyrolysis with smaller errors, and minimal preparation time, and minimal technical expertise, you just need to get the newer instruments being built. However, I have my issues with them also, from the theoretical point of view.
I like the modulation of the heat source to where we could fit a fourier series on it, as it helps separates the Cp from the heat of pyrolysis, (and from K). The TA MDSC has essentially 2 modulations, the one with constant heat (infinite period), and the one at around period of 100 seconds, that works well with their heat source. For the theory of heat conductive modulation, this paper describes it well,
https://www.sciencedirect.com/science/article/pii/0360132377900415
Just only pay attention to Equation 1 and Figure 2, and don’t worry about the rest of the paper. If you have MATLAB, the Equation 1 can be repeated for a multilayer slab, which in a DSC includes the heat source, the aluminum pan, and then the sample itself (which would have the unknown Cp and K). You are sitting there thinking how to best to use the formulas for test method, and then you start realizing the limitations of all those DSC instruments.
I have my own ideas on how to reduce the heat period, that is sorely needed, perhaps down to 1 second, that involves the redesign of the heat source and the pan itself.
I wonder who else thought the same thing?
Mark
Stanislav I. Stoliarov
Mark,
My concern with modulated DSC has always been an increased impact of contact resistance (of contact between the sample and the pan). For certain materials, we see that the sample lags its temperature sensor even when it is heated at a constant rate of 10 K/min with sample mass of 3 to 4 mg. I would argue that this effect is more significant when the temperature is modulated, especially at high frequency.
StasDr. Stanislav I. Stoliarov, Professor
University of Maryland
Department of Fire Protection Engineering
3104C J.M. Patterson Bldg.
4356 Stadium Dr.
College Park, MD 20742
Phone: 301.405.0928
Fax: 301.405.9383
Email: sto...@umd.edu
To view this discussion on the web visit https://groups.google.com/d/msgid/macfp-condensed-phase-discussions/BLAPR09MB6370B235C61B8B6BD1AADCCECF1F0%40BLAPR09MB6370.namprd09.prod.outlook.com.
Dietenberger, Mark A -FS
Stas,
Good point. I recalled from the Carlslaw and Jaeger heat conduction text, about the contact resistance having its own transfer function like the Equation 1 in the linked paper. That would mean one or two additional parameters to fit for a multilayer material. We also have the Lasercomp’s (bought out by TA) FOX 600 for large samples, where they included the contact resistance in the determination of thermal conductivity. But it required two samples of differing thicknesses. In our case of live leaves, contact resistance was a real problem due to the surface roughness.
As for heat capacity the DSC instrument needs to operate slowly enough such that the heat source, pan, and sample acts effectively like a lumped material, and so then overrides the concerns of contact resistance (ie. the normalized frequency is very low in Figure 2 of the linked paper). That is one advantage of having a long period of 100 seconds, or low frequencies, that we used. In our case of the leaves, the heat of pyrolysis (actually negative due to charring) occurred over a wide temperature range, enough for us to have several heating cycles within this temperature range, especially using the overall heating rate of 3.5 K/min. It took us several tries to get this right within the limitations of the instrument design, sensitivity, and accuracy.
Do you have a suggestion to where we should publish the paper? It needs to reach the appropriate audience…
Mark
Stanislav I. Stoliarov
Dr. Stanislav I. Stoliarov, Professor
University of Maryland
Department of Fire Protection Engineering
3104C J.M. Patterson Bldg.
4356 Stadium Dr.
College Park, MD 20742
Phone: 301.405.0928
Fax: 301.405.9383
Email: sto...@umd.edu