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The group c s amples were prepared using the same

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Unformatted text preview: t t e r n s . There was little or no evidence of intercalation as determined from the X-ray data on the group C samples. T h e X RF a nalysis of the samples resulted in inconsistantly high and low values for the ratios of A g/Ti w hich varied over different portions of the sample. the X - r a y diffraction and X R F r e s u l t s , the Ag + Rased o n T iSZ s amples which were cooled slowly from 1 000 C w ere not intercalated to any significant d e g r e e . It is possible that the silver was distributed over the surface of the T iSZ c rystalline powder in such a way that very little or no crystalline silver was present which is supported by the absence of pure silver X-ray diffraction lines. P age - 3 3 - C HAPTER 4 D IFFERENTIAL SCANNING CALORIMETRY 4 -1 G eneral Discussion Differential scanning calorimetry (DSC) is a technique whereby a sample material and a reference material are heated or cooled while a quantity which is proportional to the differential enthalpic change (or change in heat capacity) between the sample and reference materials is measured. The data are recorded as a function of time or temperature. Enthalpic changes are caused by fundamental changes in s t a t e , chemical composition, molecular reactivity of the materials, etc. The shape of the enthalpy change vs temperature or time is basically a function o f t he reaction kinetics but is also influenced by sample packing, geometric shape of the sample and reference, the heating r a t e , atmosphere, temperatures of the sample and reference, thermal contacts at all interfaces, as well a s the time constants of the electronics, etc. The sample and reference materials are placed in identical containers which may or may not be hermetically sealed, then placed in thermal contact with a heat source. A uniform linear rate of heating is usually desired because of the time dependence of the measured quantity. Thermocouples are used to monitor the temperatures of the sample and reference. P age - 3 4 - 4-2 T wo Standard Methods of DSC...
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