centre of excellence poemes, iees (cleps), bulgarian academy of sciences sources: , eric weisstein

Centre of Excellence POEMES, IEES (CLEPS), BULGARIAN ACADEMY OF SCIENCES

Sources: http://www.e-thermal.com

http://www.tainst.com, Eric Weisstein

http://scienceworld.wolfram.com

Differential Thermal Analysis

Methods


Differential Scanning Calorimetry (DSC) temperatures and heat flows associated with thermal transitions. phase transitions/changes, dehydration, gas evolution, melting, crystallization. heats of fusion and of reactions, Arrhenius parameters (E, k and n). oxidation stability, direct measurement of heat capacity.

Sources: http://www.e-thermal.com, http://www.tainst.com, Eric Weisstein, http://scienceworld.wolfram.com

Differential Thermal Analysis Methods

Thermogravimetric Analysis (TGA) and DTGA weight changes (losses) as a function of temperature under a controlled atmosphere. moisture or volatiles, thermal stability and composition, simultaneous DSC / TGA.

Dynamic Mechanical Analysis (DMA) mechanical properties as a function of time, temperature, and frequency. dimension change measurements as a function of temperature or force. stress / strain, stress relaxation, creep.

Differential Thermal Analysis DTA difference in temperature and heat flows between the sample and a reference. temperature control program, qualitative analyses of thermal processes.


Source: http://www.npl.co.uk/npl/cmmt/cog/thermal.html

Differential Scanning Calorimetry (DSC)

Two designs of DSC instruments produce comparable data .

endothermic / exothermic processes or changes in heat capacity. minimal sample amounts (liquids / solids), 30 min analysis, easy sample preparation. wide range of temperatures, hermetically closed or in an atmosphere. linear heating ramp, faster heating = higher sensitivity but lower resolution.

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Differential Scanning Calorimetry (DSC)


The two schemes of DSC devices produce comparable data – Power compensated and Heat flux plate. They comprise two pans with volumes of some ml which are in contact to heaters and thermo sensors. The sample is colored in red on the figure, the empty pan is the reference. The sample weight is measured precisely.

The temperature program is a simple linear rise with time, the maximum temperatures can exceed 1200oC and sample cooling is possible. Using high sweep rates, a higher sensitivity, but lower resolution is achieved and vice versa. The specific heats of the occurring endothermic/exothermic processes or the changes in heat capacity can be determined for some mg of sample only.

No special sample preparation is required, the sample can be in a form of powder, granules, paste or a liquid. The sample pan can be hermetically closed during the test, or an inert oxidative or reductive atmosphere can be ensured. A routine analysis takes only about 30 min.



Temperature modulated DSC (TMDSC)

The Temperature modulated DSC (TMDSC) is a modification of DSC.

A fast sinusoidal modulation is applied over the slower linear heating ramp. The modulation is of low amplitude (about one degree). The output signal is processed by FFT analysis. The slow linear sweep ensures a high resolution combined by the high sensitivity provided by the fast modulation.

The method is perfect for differentiation of overlapping transitions. It allows to separate heat capacity related (reversible - crystal melting) from kinetic (non-reversible – evaporation, decomposition) heat flows. Blends of two or more materials can be studied. The thermal conductivity of insulating materials can be determined.

By TMDSC determination of heat capacity along with changes in heat capacity during transitions is also possible.




Temperature modulated DSC (TMDSC)

sinusoidal modulation over the linear heating ramp, differentiation of overlapping transitions (fast) (slow) (FTA)

separates heat capacity related (reversible - crystal melting) and kinetic (non-reversible – evaporation, decomposition) heat flows. blends of two or more materials, determine thermal conductivity of insulating materials. determination of heat capacity along with changes in heat capacity during transitions.

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DSC curves for non cured and cured positive plates

200 – 300oC: dehydration 327oC: metalic Pb melting 360oC: hydrocarbonates 420oC: hydrocarbonates 410oC: hydrocarbonates

non cured

cured

dehydration

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Source: G. Papazov, M. Matrakova, to be published


DSC curves for non cured and cured positive plates


Four broad endothermic peaks are observed in the thermograms along with a sharp endothermic peak due to metallic lead melting at 327oC.

The couple of overlapping peaks at 200-300oC are related to the dehydration of the paste and the peaks at 360oC and above – to the destruction of lead hydrocarbonates.

After curing, the shape of the thermogram changes significantly. The amount of crystalline water and the type of its bonds are important for the properties of the paste.

Centre of Excellence POEMES, IEES (CLEPS), BULGARIAN ACADEMY OF SCIENCES CThermogravimetric (TGA) and DTGA

analysis

TGA and DTG curves for a non cured positive plate

TGA and DTG curves for a cured positive plate

up to 200oC: moisture 270oC: dehydration 340oC: hydrocarbonate 370oC: hydrocarbonate

up to 200oC: moisture 260oC: dehydration 340oC: hydrocarbonate 370oC: hydrocarbonate

non cured

cured

dehydration

dehydration



CThermogravimetric (TGA) and DTGA analysis


The presented curves correspond to TGA (weight loss in % vs temperature) and DTG (rate of loosing weight vs. temperature).

The samples are the same as for the above DSC curves (non cured and cured positive plates).

Up to 200oC the moisture from the sample is evolved.

The main weight loss is due to dehydration occurring at 270oC.

Smaller weight losses are observed due to the destruction of hydrocarbonates at 340oC and 370oC.


TGA and DTG curves for a positive plate

TGA and DTG curves for a cured positive plate

TGA and DTG curves for a formed positive plate

260oC: dehydration340oC: hydrocarbonate380oC: hydrocarbonate

Up to 350oC: dehydration 510oC: 570oC:



TGA and DTG curves for a positive plate

The cured plate (containing 4PbO.PbSO4) looses weight due to dehydration at about 260oC and due to the destruction of hydrocarbonates at 340 and 380oC.

The curves for the positive plate after formation (containing PbO2) are rather different. Weight losses due to dehydration are observed at 350oC.



Thermograms of various PbO2 types obtained by DSC

DSC is a powerful method to investigate the phase composition and the properties of PbO2. In combination with XRD and SEM it provides unique information.

The thermal spectra of four PbO2 samples are shown on the next figure. The red curve is for chemical b-PbO2 (Merck), the black one for a mixture of b-PbO2 with few % of a-PbO2, and the green and the blue curves are for electrochemically prepared PbO2 – freshly prepared PAM (green) and PAM at the end of cycle life (blue).Two exothermic peaks are observed on the figure at about 200 and 280oC. They are due to crystallization processes occurring in the partially hydrated zones of their particles. Amorphous PbO2 is observed mainly in electrochemically obtained PbO2.Six endothermal peaks are observed at higher temperatures. First, between 300 and 400 oC chemically bound water contained in the PbO2 PAM particles is evolved. At temperatures above 400oC a-PbO2 and b-PbO2 are thermally decomposed to a variety of non stoichiometric lead oxides.


Thermograms of various PbO2 types obtained by DSC

Peaks 1, 2 (exo) - up to 200oC – crystallization of amorphous PbO2.

Peaks 3, 4 (endo) - 300-380oC - PbO(OH)2 PbO2

Peaks 5, 6, (endo) - 380 - 480oC - -PbO2 PbOx (A)

Peaks 7, 8 (endo)- above 480oC - PbOx (A) PbOx (B)

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Thermograms of PbO2 samples from PAM sublayers (SGTP)

On the next figure thermal spectra of PbO2 PAM samples from a SGTP are shown. The samples are taken from one electrode at different distances from the current collector in the middle.

The area of Peak 6 which is related to b-PbO2 decomposition decreases slowly from the surface towards the current collector.

On the red curve for the sample in the AMCL a new hump is observed (in white). The shape of the curve changes completely in the corrosion layer what is an indication about phase composition changes.


Thermograms of PbO2 samples from PAM sublayers (SGTP)

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Peak 4 (endo) - 300-380oC - PbO(OH)2 PbO2

Peaks 6 (endo) - 380 - 480oC - -PbO2 PbOx (A)

Peaks 7, 8 (endo) - above 480oC - PbOx (A) PbOx (B)

Peaks 4A, 4B (endo) - 385oC and 430oC - PbOx (C) PbOx (D)


DSC of PAM with declined capacity and after capacity recovery



Peak 6 (endo) - 380 - 480oC - -PbO2 PbOx (A)

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Source: B. Monahov, M. Matrakova, to be published


TGA / DTG, PAM, before and after capacity recovery

Source: B. Monahov, M. Matrakova, to be published


Peak 6 (endo) - 380 - 480oC - -PbO2 PbOx (A)

Peak 9 (endo) - 510oC - PbOx Pb3O4 + a-PbOy

Peak 10 (endo) - 560oC - PbOx Pb3O4 + a-PbOy

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Battery knowledge contributed by thermal techniques

1. Fundamentals of the processes taking place in the plates during production and service life (phase transitions, hydration, dehydtration and their impact on battery performance).

2. Fundamentals of the processes taking place during the COC and of the processes related to battery thermal runaway.

3. Rate of temperature changes in the cell and temperature distribution along the plate during charge and discharge.

4. Dependence of battery temperature changes on cycle life.

5. Estimation of heating rate, thermal efficiency and thermal capacity of the battery / cell (or its components).

6. Thermal modeling of batteries in EV and stationary applications.

centre of excellence poemes, iees (cleps), bulgarian academy of sciences sources: , eric weisstein

Documents

thermal transitions

iees cleps

centre of excellence

thermal stability

decomposition heat flows

modification of dsc

fft analysis

routine analysis