Dilatometer method

The only one that is not readily accessible by DTA is the expansion coefficient. It is determined by use of a thermal expansion apparatus, i.e.- a dilatometer. Methods and uses of thermal expansion will be described in a succeeding section. 

Among these techniques, the capacitance dilatometer method may be very sensitive. The change in the sample length produces a capacitance change between the two electrodes of a capacitor one plate of the capacitor is kept in a fixed position while the other is fixed onto one end of the sample. At the maximum elongation of the sample, the two capacitor plates are practically in contact. When the sample contracts the capacitance varies as 1 /AL. One of the main difficulties in this measurement is the realization of a dilatation-free support. 

Measurement of the inactive or unfree moisture in the soil by means of the dilatometer method." J. Agr. Research, 8 195-217. 

K Measurement of volume change as a function of pressure a. Dilatometer method (Bekkedahl, 1949) (sample immersed in mercury) b. Piston-cylinder method (Warfield, 1980) (cylindrical sample in bore of rigid container under varying pressure) Combined measurement of speed of longitudinal and shear waves (Hartmann, 1980) K = p(ul lush)... 

While the dilatometer method is the preferred method of determining the glass transition temperature, it is a rather tedious experimental procedure and measurements of Tg are often made in a differential scanning calorimeter (DSC). In this instrument (18), the heat flow into or out of a small (10-20 mg) sample is measured as the sample is subjected to a programmed linear temperature increase (typically 10 C/min). The heat flow is proportional to the specific heat of the sample. At the glass transition, there is an increase in the heat flow into the sample due to the increase in specific heat at this point. Values obtained in this manner are only a few degrees higher than the dilatometer values. 

The dilatometer method has been used for fused salts by heating in a hard glass or silica glass dilatometer (e.g. in a Lorenz furnace, 2.VI C) until the meniscus comes to a mark on the neck. The expansion of the glass must be taken into account that of silica glass is small (0 016 per cent of the volume for 100° C.) but can be introduced if necessary. 

Capacitance dilatometer methods are substantially more sensitive than the strain gauge technique (Slavin, 1972 Lacheisserie, 1975) but accurate low temperature calibration requires considerable care, as does the mounting of highly anisotropic materials (Tb and Dy) for rotation measurements (Keeler and Pearson, 1978). 

Photoinitiated polymerization has been carried out using the laser interferometry method (one of the dilatometer methods [24]), the principal and geometric schemes of which are presented in Figures 5.15 and 5.16, respectively. 

Methods of determining coefficient of thermal expansion include ASTM D696 (dilatometer method), ASTM E228 (dilatometer methods of plastics in the temperature range of -30°C to -l-30°C), and ASTM E831 (determination by thermomechanical analysis). 

Refractoriness-under-Load. The ability of a material to withstand specified conditions of load, temperature and time. Details of variations in this test will be found in the following national standards Britain-B.S. 1902 USA-ASTM-C16 Germany-DIN 51064 France-AFNOR B49-105. B.S. 1902 specifies a dilatometer method (Pt. 4.8)... 

M. Sternitzke, G. Muller Substitutional and thermal expansion in MAlSi20e aluminosilicates with keatite structure , Eur. J. Mineral. 3, 769-776 (1991) F.H. Gillery, E.A. Bush Thermal contraction of / -eucryptite (Li20.Al20s.2Si02) by X-ray and dilatometer methods , J. Amer. Ceram. Soc. 42, 175-177 (1959)... 

I = complex impedance, B = conductivity bridge, C = capillary viscometer, P = pycnometer or dilatometer, V = volumetric glassware, I = instrument, U = method unknown... 

How does a dilatometer work to provide a means of measuring the rate of chain growth reactions From a practical perspective, what issues are likely to arise during this method of measurement ... 

The measurement of the linear expansion coefficient can be carried out by several methods (see Chapter 13), for example, by means of an interferometric dilatometer [77], a capacitance dilatometer [78] or a SQUID dilatometer [74]. The latter can achieve resolutions as small as 2 x l(T14m. 

Various systems have been used to measure the mercury level change in the stem during intrusion. Indirect methods include resistance or capacitance measurements along the stem of the dilatometer [39], These readings are taken in conjunction with pressure readings, to correlate the number of pores at a specific pore size. 

The decomposition of initiator can be followed by usual analytical methods and k can be determined. The efficiency factor/can be obtained by comparing the amount of initiator [I] decomposed with the number of polymer chain formed. The rate of polymerization can be determined by monitoring the change in a physical or chemical property of the system. Generally, dilatometry technique is used for determination of the rate of polymerization. Let the extent of polymerization be small and concentration of initiator be constant. Let r0, rt and r be the readings on dilatometer initially, at time t and at the completion of reaction, respectively. If reaction is first order in [M],... 

Dilatometric methods. This can be a sensitive method and relies on the different phases taking part in the phase transformation having different coefficients of thermal expansion. The expansion/contraction of a sample is then measured by a dilatometer. Cahn et al. (1987) used dilatometry to examine the order-disorder transformation in a number of alloys in the Ni-Al-Fe system. Figure 4.9 shows an expansion vs temperature plot for a (Ni79.9Al2o.i)o.s7Feo.i3 alloy where a transition from an ordered LI2 compound (7 ) to a two-phase mixture of 7 and a Ni-rich f c.c. Al phase (7) occurs. The method was then used to determine the 7 /(7 + 7O phase boundary as a function of Fe content, at a constant Ni/Al ratio, and the results are shown in Fig. 4.10. The technique has been used on numerous other occasions,... 

Dilatometry is a convenient method for measuring polymerization rate. The method is based on a decreasing volume of the examined system along with conversion of monomer to polymer. For simple polymerization, usually carried out in solution in capillary dilatometer, the decrease in volume, Av, is calculated from measurements of the decrease in the level of reacting mixture ho - h = Ah in capillary with radius, r. Using equation ... 

A dilatometer is used to measure the intrusion and extrusion volumes and several methods are used to measure the change in mercury level within the dilatometer stem as intrusion and extrusion take place. One method involves the use of platinum or platinum-alloy resistance wire placed coaxially in the stem of dilatometer tube. As the mercury level decreases, the amount of resistance wire exposed increases, thereby providing a voltage which increases linearly with decreasing mercury level. Very small current is used to minimize resistive heating of the mercury. Platinum or platinum-iridium alloy may be employed as the resistance wire because they do not amalgamate with mercury. 

Figure 20.1 illustrates a third method of measuring the mercury level. The mercury in the dilatometer stem constitutes one plate of a capacitor and a metal sheath coaxially surrounding the dilatometer serves as the second plate. The capacitance changes with the mercury level due to the variation of the effective plate area. 

Because of its low and regular thermal expansion, vitreous silica is employed in apparatus used to measure the thermal expansion of solids. A detailed account of the different methods used for this purpose has been published (227). The most common form of dilatometer utilizes a vitreous silica tube closed at the bottom and containing the test sample. A movable rod of vitreous silica, resting on the sample, actuates a dial indicator resting on the top of the rod. The assembly containing the sample is placed in a furnace, bath, or cooling chamber to attain the desired temperature. 

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