I am looking to test thermal expansion forces of small elastomer particles (~1mm diameter) and am planning to use Dynamic Mechanical Analysis for this test. The current plan is to machine a shallow cylindrical aluminum pan which I will fill with these particles, sized so that the upper compression plate of the DMA can fit cleanly inside like a plunger on a piston. This is to minimize radial distortion as the particles will be constrained within the dish. Tests will be isostrain temperature ramps to measure the thermal expansion forces of these particles as they increase in temperature. Assuming we perform this test many times and account for voids between the particles by assuming some random packing factor, is this a reasonable approach to collecting this force data? Measuring individual particles seems like the measurements would be too close to the minimum sensitivity of the instrument.
Put the particles between 2 quartz rods or cylinders and measure. The quartz does not expand till 1400 C.
Using an Al pan and upper compression plate of DMA as a plunger are really smart ideas. But, large distortions might come up in force during your measurement when the upper plate of DMA touchs to the pan wall. Another problem would be you never assume the number of force transfer points between particles and upper plate (and also particle to particle). But, force transducer will automatically detect and compute the response of sample by regarding a full-contact with the sample... You should try anyway and please let us know results of your attempt.
Good Luck...
It does not sound feasible to me, but take a look at ISO 17744.
I think using a dedicated TMA would be better, and pvT even better still.
Does your DMA act as a TMA? Because you have to be able not to use the dynamic load and keep your contact force and also static load to the minimum. TMAs usually operate from 1 mN up to only 3 N. I would suggest the use of alumina pans, and not aluminium because in temperature the aluminum will undergo thermal expansion, too.
Denise Besghini Yes, we can set the DMA in an transient isostrain mode with no dynamic oscillations. We are also trying to set the static load as small as possible as you say. Do you have a recommendation of how to select a reasonable static load value?
I am not too concerned with thermal expansion as we are only going up to temperatures of 180C, and I believe the linear expansion will be less than 0.5% if my math is right.
Peter Farrington The intent is essentially a pvT test as you suggest. Holding constant the volume and measuring pressure as the temperature increases. Is there a particular concern you have about this setup that would make it infeasible?
Ali Durmus The pan is machined such that the DMA probe fits neatly inside with a small (
I would do anyway an experiment with only the pan to create a baseline in the used temperature range and then eventually subtract the contribution of the pan. It is what is generally made in TMA, even with alumina pan.
I did experiments with some polymer microspheres using a force of 30 mN, to ensure good contact, without compromising the expansion, because I measured that using much higher forces compromised the expansion. But I think the force that you can reach depends on the shell thickness, the modulus of the elastomer and therefore how much your particles can withstand a load without deformation. If you can make experiments in a range of loads using similar quantities of sample I would do that at first
The test conditions are such that DMA cannot provide good measurement accuracy for thermal expansion forces. An additional complication is the variability of the coefficient of thermal expansion. It may be first to try to melt the particles, and then form a block sample (tablet) from the melt. In this case, a diameter of 5 mm will be sufficient for correct measurements.
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