Sample thermal history

Even when DSC and XRD are both used, quite separate instruments are involved. This leads to difficulties in reconciling results owing to differences in sample thermal history/conditioning, sample dimensions and sample temperature control and uniformity. These difficulties can be entirely overcome by coupling XRD and DSC together in the same instrument and making both types of measurement simultaneously on the same sample. 

Recently Moore and Petrie (5) have demonstrated that control of sample thermal history can result in transition from ductile to brittle behavior for polyethylene terephthalate. This transition in behavior was related to volume relaxation of the glassy state. 

In contrast to this, distinct differences were observed for the thermal cis-trans isomerization depending on the samples thermal history the increase in the trans-isomer content was followed by measuring the change in the absorption at =378 nm (Fig. 8). ... 

Sample synthesis was carried out as previously des-cribed, using either solution or interfacial polycondensation. Characterization was as in reference 3 DSC and polarizing microscopy were carried out using controlled sample thermal history as described in references 4,5. 

Fig. 1. The Nematic-Isotropic Biphase. Nematic fraction fjj measured by NMR on slow cooling from the isotropic phase (sample thermal history as in ref. 5). Comparison with jTxN IN be DSC peak width and Tc-T2 or biphase observed by microscopy (scanning rate 10 C/min. thermal history as in ref. 5). Sample DDA-9 Mn=4,000.

For a property which manifests a change at the glass transition (specific volume for example), the experimentally determined value below T is dependent on the sample thermal history. For example, for faster cooling rates, the glass is observed to have a greater specific volume. In addition, for... 

Depending on the sample thermal history, a cold-crystallization exothermic peak may or may not be observed dnring the DSC, and if it does not appear the value of = 0. 

A dsc scan of a typical commercial ionomer shows two endotherms at about 50 and 98°C, respectively. The size of the lower peak can be correlated with stiffness and yield point. The thermal history of the sample influences the relative size of the lower peak and moves it to higher temperatures, while the upper peak decreases in size but remains at the same temperature. Room temperature aging also increases the size of the lower endotherm. 

Electrical Properties. The electrical properties of siUcon carbide are highly sensitive to purity, density, and even to the electrical and thermal history of the sample. 

The influence of the thermal history on the location and intensity of the a peak of PTEB can be observed in Fig. 18. It can be seen that the intensity of this relaxation measured on both E" and tanS bases decreases considerably on passing from the liquid crystalline sample... 

On the contrary, the phase structure and the thermal history do not have important effects on the location and intensity of the /3 relaxation. This relaxation is very broad in all the samples and overlaps the y relaxation. The activation energy of the /3 peak is about 85 kJ mol for the three samples, of the same order of magnitude as that of other polyesters [38,40]. Finally, the y relaxation is found in the three samples of PTEB with no remarkable influence of the thermal history. 

In conclusion, the different thermal histories imposed to PTEB have a minor effect on the /3 and y relaxations, while the a. transition is greatly dependent on the annealing of the samples, being considerably more intense and narrower for the specimen freshly quenched from the melt, which exhibits only a liquid crystalline order. The increase of the storage modulus produced by the aging process confirms the dynamic mechanical results obtained for PDEB [24], a polyester of the same series, as well as the micro-hardness increase [22] (a direct consequence of the modulus rise) with the aging time. 

Thermal transitions can be studied by DSC. The crystallization transition is usually sharp with a good baseline. The melting transition is more complex and often not a single transition (Fig. 3.19)48 as it depends on the thermal history of the sample and the structural changes that can take place upon heating. In warming, solid-state transitions can take place in the unit cell, the lamellae can thicken, and secondary crystallization can also take place. The heats of crystallization and... 

Sample Preparation. Samples for mechanical studies were made by compression molding the polymers at 150°C between Teflon sheets for 15 minutes followed by rapid quenching to room temperature in air. These will be referred to as PQ (press-quenched or simply quenched) samples. The thickness of the PQ samples was around 10 mils (0.25 mm). The thermal history of all of the PQ samples (HBIB, HIBI, and LDPE) were essentially the same. They were used within one week after they were pressed. Samples for morphology, SALS and SEM studies were prepared from toluene solutions. These films were cast on a Teflon sheet at 80 C from a 1% (by weight) solution in toluene. These films were about 5 mils in thickness. When the polymer films had solidified (after 5 hrs), they were stored in a vacuum oven at 80°C for two days to remove residual solvent. These samples will be designated by TOL (solution cast from toluene). 

A comparison of the dynamic mechanical properties of our HB at 35 Hz has been made to that of LDPE in Figures 14 A and B. The thermal and sample preparative history affects the mechanical properties of HB films to such an extent that in order to make a meaningful comparison one has to describe the exact history of the samples. Such a thermal history dependence has been examined for LDPE(54,57) and recently for HB.(12) Shown in Figures A and B are the mechanical spectra for HB-PQ, HB-Tol, and LDPE-PQ films. The compression molded films were prepared 1 to 2 days prior to the test. The solution cast film (from toluene), HB-Tol, was annealed at 80°C for 2-3 days and stored at room temperature for 1 week... 

The cracking susceptibility of a micro-alloyed HSLA-100 steel was examined and compared to that of a HY-100 steel in the as-received condition and after heat treatment to simulate the thermal history of a single pass weld. Slow strain rate tensile tests were conducted on samples of these alloys with these thermal histories in an inert environment and in an aqueous solution during continuous cathodic charging at different potentials with respect to a reference electrode. Both alloys exhibited reduced ductilities at cathodic potentials indicating susceptibility to hydrogen embrittlement. The results of these experiments will be presented and discussed in relation to the observed microstructures and fractography. 

Mullane E, Russel SS, Gounelle M (2002) Iron isotope fractionation within a differentiated asteroidial sample suite. 65 Annual Meteoritical Society Meeting, abstract number 5157 Mullane E, Russel SS, Gounelle M, Mason TED (2003a) Iron isotope composition of Allende and Chainpur chondrules effects of equilibration and thermal history. Lunar Planet Sci Conf XXXIV, abstract number 1027... 

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