Dilatometers, density measurements

In general, different techniques for volume-, expansion-, and density-measurement have been developed over time. The highest accuracy is obtjdned with push-rod dilatometers, which have been developed by different companies and are commercially available. Newer devices are also suited for measurements of molten materials and up to a temperature of about 3000 K. Most of the available literature data for the solid state has been measured using such dilatometers, e.g., [47]. 

A dilatometer can also be considered as a piezometer of variable volume, where the change in volume can be achieved using pistons. Older devices often used mercury as a liquid piston with the consequent environmental risk and moderate accuracy ( 0.5-1%) of density measurements (Ravich and Borovaya, 1971a-b Urusova, 1975). 

SFI measures by volume, the ratio of crystalline (solid) phase verses liquid phase in the fat sample. It is performed manually using a glass dilatometer, and measures the increase in volume as the fat sample expands upon heating, starting with frozen sample. Density measurements are taken at a series of standardized temperature check points. 

Dilatometer Basically it is a pyrometer equipped with instruments to study density as a function of temperature and/or time. It can measure the thermal expansion or contraction of solids or liquids. They also study polymerization reactions it can measure the contraction in volume of unsaturated compounds. It basically is a technique in which a dimension of a material under negligible load is measured as a function of temperature while it is subjected to a controlled temperature program. 

A volume increase is possible only when the whole sample briquet has already been deformed (the deformation of the sample being in fact measured as an expansion). When the expansion begins (see Figure 10, 385°C.), pore formation in the vitrinite sets in. The size of the pores formed in the dilatometer experiment is on the average smaller than in a loose bulk owing to the fact that deformation of single particles into void volumes is impossible in the dilatometer. Figure 13 compares the dependence of pore formation on bulk density for three coke types. 

In dilatometry, specific volumes V or densities of materials are measured by use of a pycnometer, dilatometer, or density-gradient column. The data obtained are then interpreted through the equation... 

A more satisfactory method is to measure F directly in a dilatometer. In fact the direct measurement of F is the simplest and best method for obtaining the density of mixtures containing volatile materials. The requirements for measuring excess volumes directly are similar to those for measuring excess enthalpies, except that the presence of a vapour space even as small as 10 or 10 cm may lead to considerable error. A simple apparatus used by Swinton and colleagues is shown in Figure 16. The vessel is first filled with mercury while... 

A more direct method is provided by a dilatometer, basically a pressure vessel connected to a mercury reservoir and a glass capillary column. Changes in the height of the mercury in the column are directly related to the change in density of the fluid in the pressure vessel. The apparatus is calibrated using pure water, with its known volumetric properties. Of course, no brief description can give any idea of the multitude of details of operation and correction factors that go into making precise measurements. 

Pycnometer pik- na-m9-t9r [Gk pyknos + ISV -meter] (1858) n. A container whose volume is precisely known, used to determine the density of a liquid by filling the container with liquid and then weighing it. The same instrument may be used to measure the density of particular matter, such as plastic pellets, by immersing it in a liquid that is inert to, and significantly less dense than the solid matter. A dilatometer is a special pycnometer equipped with instruments to study specific volume as a function of temperature. 

Where the sub-index 0 indicates initial conditions and T is the induction period. kdim in equation 1 has been measured with precision by Kothe and Fischer as fcdim = 2.51x10 exp (-93,500/(/f2)) L moP -s with R in J moP °K and T, the temperature, in °K. In order to obtain initial estimates of the value of fedsma we performed reactions for the system S-MA in presence of OH-TEMPO [N]) in a capillary dilatometer in order to measure the induction period and the conversion - time curve after induction. Different compositions of the pair S-MA and of the nitroxide mixture increased its volume by thermal expansion until thermal equilibrium was established. At that point zero time was marked and the volume contraction of the reaction mixture with time was correlated with conversion via standard calculations that use the density of the monomer mixture and the polymer. ° Table 1 contains a summary of the results and Figure 3... 

Sample density can be measured using a variety of methods density-gradient column, dilatometry, pycnometry, and flotation or buoyancy. The density-gradient column approach is probably used most frequently to determine sample densities for crystallinity measurements. When thermostated and appropriately calibrated with floats, this approach permits measurements to accuracies of 0.2 mg/cm or better. Dilatometers are well suited for measuring specific volumes and following crystallization, as a function of temperature. 

The degree of crystallinity can be determined by number of techniques. These techniques involve the measurement of density, volume in dilatometer, ratio of the intensity of absorption bands corresponding to crystalline and amorphous fractions in infrared (IR) spectroscopy, heat of fusion/ crystallization in differential scanning calorimetry (DSC), and area under the diffraction peaks in wide-angle x-ray diffraction (WAXD). The response parameters used to monitor the process of crystallization in these techniques are different and require the data on the properties of the 100% crystalline polymer. These methods are useful for quantitative evaluation of the degree of crystallinity. 

Fig. 4.27. Melting curves of a sample of low density PE ( Lupolen 1800S ) crystallized by stepwise cooling (melt at 115 °C 100 °C 75 °C 50 °C 25 °C), obtained in measurements of the specific heat using a differential calorimeter (left) and of the expansion coefficient / , registered in a dilatometer right) [45]...

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