Influence of the Processes Parameters on the Properties of The ...
Influence of the Processes Parameters on the Properties of The ...
Influence of the Processes Parameters on the Properties of The ...
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Chapter 3.<br />
Analytical Methods and Designs <str<strong>on</strong>g>of</str<strong>on</strong>g> Experiments<br />
Differential scanning calorimetry (DSC) is a <str<strong>on</strong>g>the</str<strong>on</strong>g>rmoanalytical technique in which <str<strong>on</strong>g>the</str<strong>on</strong>g> difference in<br />
<str<strong>on</strong>g>the</str<strong>on</strong>g> amount <str<strong>on</strong>g>of</str<strong>on</strong>g> heat required to increase <str<strong>on</strong>g>the</str<strong>on</strong>g> temperature <str<strong>on</strong>g>of</str<strong>on</strong>g> a sample and reference is measured as a functi<strong>on</strong><br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> temperature. Both <str<strong>on</strong>g>the</str<strong>on</strong>g> sample and reference are maintained at nearly <str<strong>on</strong>g>the</str<strong>on</strong>g> same temperature throughout <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
experiment. Generally, <str<strong>on</strong>g>the</str<strong>on</strong>g> temperature program for a DSC analysis is designed such that <str<strong>on</strong>g>the</str<strong>on</strong>g> sample holder<br />
temperature increases linearly as a functi<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> time.<br />
<strong>The</strong> technique was developed by Wats<strong>on</strong> and O’neill [1962] and was introduced commercially at<br />
<str<strong>on</strong>g>the</str<strong>on</strong>g> 1963, Pittsburgh C<strong>on</strong>ference <strong>on</strong> Analytical Chemistry and Applied Spectroscopy [ISO - Internati<strong>on</strong>al<br />
Organizati<strong>on</strong> for Standardizati<strong>on</strong>, 1963]. Heat-flux DSC and power-compensated DSC are <str<strong>on</strong>g>the</str<strong>on</strong>g> two types <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
DSC that have been widely used.<br />
One <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> big advantages <str<strong>on</strong>g>of</str<strong>on</strong>g> DSC is that samples are very easily encapsulated, usually with little<br />
or no preparati<strong>on</strong>, ready to be placed in <str<strong>on</strong>g>the</str<strong>on</strong>g> DSC cell, so that measurements can be quickly and easily made<br />
[Gabbott, 2008]. <strong>The</strong> specific heat <str<strong>on</strong>g>of</str<strong>on</strong>g> a material changes slowly with temperature in a particular physical<br />
state, but alters disc<strong>on</strong>tinuously at a change <str<strong>on</strong>g>of</str<strong>on</strong>g> state. As well as increasing <str<strong>on</strong>g>the</str<strong>on</strong>g> sample temperature, <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
supply <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>rmal energy may induce physical or chemical processes in <str<strong>on</strong>g>the</str<strong>on</strong>g> sample, e.g. melting or<br />
decompositi<strong>on</strong>, accompanied by a change in enthalpy, <str<strong>on</strong>g>the</str<strong>on</strong>g> latent heat <str<strong>on</strong>g>of</str<strong>on</strong>g> fusi<strong>on</strong>, heat <str<strong>on</strong>g>of</str<strong>on</strong>g> reacti<strong>on</strong> etc.<br />
In a heat flux DSC, <str<strong>on</strong>g>the</str<strong>on</strong>g> sample material, enclosed in a pan and an empty reference pan are placed<br />
<strong>on</strong> a <str<strong>on</strong>g>the</str<strong>on</strong>g>rmoelectric disk surrounded by a furnace. <strong>The</strong> furnace is heated at a linear heating rate and <str<strong>on</strong>g>the</str<strong>on</strong>g> heat<br />
is transferred to <str<strong>on</strong>g>the</str<strong>on</strong>g> sample and reference pan through <str<strong>on</strong>g>the</str<strong>on</strong>g>rmoelectric disk (cf. Figure 3.1). <strong>The</strong> temperatures<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> two <str<strong>on</strong>g>the</str<strong>on</strong>g>rmometers are compared, and <str<strong>on</strong>g>the</str<strong>on</strong>g> electrical power supplied to each heater adjusted, so that <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
temperatures <str<strong>on</strong>g>of</str<strong>on</strong>g> both <str<strong>on</strong>g>the</str<strong>on</strong>g> sample and <str<strong>on</strong>g>the</str<strong>on</strong>g> reference remain equal to <str<strong>on</strong>g>the</str<strong>on</strong>g> programmed temperature, i.e. any<br />
temperature difference which would result from a <str<strong>on</strong>g>the</str<strong>on</strong>g>rmal event in <str<strong>on</strong>g>the</str<strong>on</strong>g> sample is ‘zero’. <strong>The</strong> analogical<br />
signal, <str<strong>on</strong>g>the</str<strong>on</strong>g> rate <str<strong>on</strong>g>of</str<strong>on</strong>g> energy absorpti<strong>on</strong> by <str<strong>on</strong>g>the</str<strong>on</strong>g> sample (e.g. W/s), is proporti<strong>on</strong>al to <str<strong>on</strong>g>the</str<strong>on</strong>g> specific heat <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
sample since <str<strong>on</strong>g>the</str<strong>on</strong>g> specific heat at any temperature determines <str<strong>on</strong>g>the</str<strong>on</strong>g> amount <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>rmal energy necessary to<br />
change <str<strong>on</strong>g>the</str<strong>on</strong>g> sample temperature by a given amount. In o<str<strong>on</strong>g>the</str<strong>on</strong>g>r words, <str<strong>on</strong>g>the</str<strong>on</strong>g> measuring principle is to compare <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
rate <str<strong>on</strong>g>of</str<strong>on</strong>g> heat flow to <str<strong>on</strong>g>the</str<strong>on</strong>g> sample and to an inert material which are heated or cooled at <str<strong>on</strong>g>the</str<strong>on</strong>g> same rate.<br />
1.2 First Order Transiti<strong>on</strong>s<br />
(A)-Apparatus<br />
(B)-Principle<br />
Figure 3.1: Differential scanning calorimetry.<br />
Changes in <str<strong>on</strong>g>the</str<strong>on</strong>g> sample, which are associated with absorpti<strong>on</strong> or evoluti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> heat, cause a change<br />
in <str<strong>on</strong>g>the</str<strong>on</strong>g> differential heat flow which is <str<strong>on</strong>g>the</str<strong>on</strong>g>n recorded as a peak. <strong>The</strong> area under <str<strong>on</strong>g>the</str<strong>on</strong>g> peak is directly<br />
proporti<strong>on</strong>al to <str<strong>on</strong>g>the</str<strong>on</strong>g> enthalpy change and its directi<strong>on</strong> indicates whe<str<strong>on</strong>g>the</str<strong>on</strong>g>r <str<strong>on</strong>g>the</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>rmal event is endo<str<strong>on</strong>g>the</str<strong>on</strong>g>rmic or<br />
exo<str<strong>on</strong>g>the</str<strong>on</strong>g>rmic. Analysis <str<strong>on</strong>g>of</str<strong>on</strong>g> a DSC <str<strong>on</strong>g>the</str<strong>on</strong>g>rmogram enables <str<strong>on</strong>g>the</str<strong>on</strong>g> determinati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> two important parameters: <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
transiti<strong>on</strong> temperature peak (taken at <str<strong>on</strong>g>the</str<strong>on</strong>g> maximum T m or at <str<strong>on</strong>g>the</str<strong>on</strong>g> <strong>on</strong>set T <strong>on</strong>set ), and <str<strong>on</strong>g>the</str<strong>on</strong>g> enthalpy <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
melting/crystallizati<strong>on</strong> (H m /H c ). <strong>The</strong> extrapolated <strong>on</strong>set temperature (T <strong>on</strong>set ) corresp<strong>on</strong>ding to <str<strong>on</strong>g>the</str<strong>on</strong>g> transiti<strong>on</strong><br />
temperature at zero heating rate can be obtained by plotting peak temperatures as a functi<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> heating rate<br />
[Ruegg et al., 1977].<br />
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