Recording dilatometer

The dilatometer stem is coaxially enclosed in an open-ended stainless-steel sheath which serves as one plate of a capacitor in a manner similar to the sheath used in the high-pressure porosimeter. When connected to the capacitance bridge of the porosimeter, the filling apparatus, using its own low-pressure transducer, measures the intruded volume and continuously plots the data on an X-Y recorder up to 24 psia. 

Dilatometer. Reliable kinetic data on gamma-induced emulsion polymerization can be obtained only when the polymerization rate is measured continuously (7). The recording dilatometer used in our previous work had some disadvantages. A mercury meniscus traveled down a precision capillary, releasing a thin platinum wire within the capillary. The electrical resistance of this assembly was used as a measure for the... 

Handling of the dilatometer, determination of final conversion, and evaluation of the recordings of the millivoltmeter were described earlier... 

Volume measurements needed to calculate the SFI are made by observing and recording the position of the dye solution meniscus in the graduated capillary tube at one temperature (typically 60°C) or two temperatures at which the sample is fully molten, and at desired measurement temperatures (which will be lower than the clear point of the sample). The sample is brought to the first measurement temperature from 0°C after a standardized tempering procedure. This and subsequent measurement temperatures must be approached from below to avoid supercooling effects. Temperature is controlled by immersing the whole dilatometer in constant temperature water baths or an ice-water bath. 

The emulsion polymerization of acrylonitrile is quite complex because of the high solubility of the monomer in water (7.4% at 25 C) and the insolubility of the polymer in the monomer. Hummel et al. (1967), using a sophisticated recording dilatometer, showed that the rate-conversion curves... 

A more detailed fundamental study was reported by Hummel et al. (1962 Hummel, 1963). Using a sensitive recording dilatometer of their own design they could follow the variation of tbe rate of polymerization with time and conversion. There was an abrupt rise in the rate for tbe first few percent conversion attributed to particle formation. There followed a constant rate period up to about 30% when the free monomer phase disappeared. An increase in rate to a maximum was then observed, ascribed to tbe gel effect, followed by a steady decrease in rate due to monomer depletion and slower diffusion of the monomer to the active sites in the highly viscous particles. The particle sizes were rather small, about 500 A diameter, compared with those often obtained with chemical initiation (e.g., Zimmt, 1959). This presumably explains the comparatively close adherence to the simple Smith-Ewart picture up to the appearance of the gel effect. 

Acres and Dalton (1963a) also studied the emulsion polymerization of methyl methacrylate initiated by Co y radiation using a recording dilatometer. Only the conversion-time curves were measured with constant dose rate, varying monomer concentration, and with constant monomer concentration at different dose rates. Except at the lowest monomer concentration a clear gel effect was observed, with linear rates up to that point. The linenr rates increased with increasing monomer concentration up to about 0.4 mol/liter and then leveled oif. The dependence of the rate, before the gel effect, on the dose rate was 0.4 and, unlike their findings with styrene, not dependent on the monomer concentration. Their results were consistent with those of Hummel ei al. that methyl methacrylate follows, with y radiation, the generally accepted Smith-Ewart Case 2 kinetics except for the marked gd effect. 

The course of the y-induced emulsion polymerization was followed with a highly sensitive self-recording dilatometer. The variation of the over-all reaction rate with time in the emulsion polymerization of MM A, EA, and MA deviated... 

The experimental device consists in a Carlo-Erba Serie 200 porosimeter, a data acquisition unit Hawlett Packard 3497A. a microcomputer PC connected to a printer. The sample is set in a pirex dilatometer having a fitting calibrated capillary. This is filled with mercury under the pressure. Variations in mercury level in the capillary tube are followed by a needle held in contact with the mercury surface. The needle comes down thanks to a motor device can generate electrical impulses corresponding to needle variations of 0.1 mm. These impulses are transmitted to a data acqisition unit and then to a microcomputer which would record the... 

A dilatometer constructed by Sauer is shown in Fig. 45. The sensing element is a linear variable differential transformer, whose rectified output is recorded directly. A pivot arm connects the transformer (A) to the bearing arm (B) and a micrometer screw allows for calibration and adjustment of the transformer. By adjustment of the compensating screw, the pivot arm can be moved so that the contact point (B) is exactly one sample length from the fulcrum. Temperatures above and below ambient can be obtained by circulating gas round the specimen. 

Mitchell [3] demonstrated the use of a recording dilatometer for the determination of the crystallisation rate. He used as the rate characteristic the time necessary to reach 50 % of the ultimate change in volume due to crystallisation. This time is called the crystallisation half-time value. ... 

The potential of the crystallisation half-time values to distinguish between IR batches from various sources and made under different conditions, was studied. A continuously recording dilatometer was built for these experiments. This apparatus, the measuring method and some results are described in the following sections. 

The determinination of the rate of polymerization of vinyl acetate in solution has been carried out in a mercury recording dilatometer. In this procedure, the solution of the monomer and 2,2 -azobis(2,4-dimethylvaleronitrile) is placed in the dilatometer, degassed, and sealed at a pressure of approximately 10 mm Hg. The dilatometer is maintained at 50.0 0.02°C. The total shrinkage is calculated using 0.892 gm/ml as the density of the monomer and 1.166 gm/ml as that of the polymer. The rate of polymerization is usually determined from the rate of shrinkage in the conversion range of 5-7% [62]. 

D 240 (1992) Test method for heat of combustion of liquid hydrocarbon fuels by bomb calorimetry D 696 (1998) Standard Test Method for Coefficient of Linear Expansion of Plastics between — 30 °C and 30°C with a Vitreous Silica Dilatometer D 1519 (2000) Test method for rubber chemicals - melting range D 1826 (1994) Test method for calorific (heating) value of gases in natural gas range by continuous recording calorimeter... 

The usual method of measuring a is to record mechanically the change in length of a test piece as it is heated in an instrument called a push-rod dilatometer, which is illustrated in Figure 34.14. The data that are obtained are plotted as A///o versus T as shown in Figure 34.15. The slope of a line at any temperature is a. Accuracies of commercial dilatometers can be as good as 0.5%. 

Polymerization rates were determined by recording capacitance dilatometry . In these experiments S (1.90 g), AN (1.1 g), and the appropriate solvent (50 ml) were heated in the dilatometer with tBPP (0.06 g) and ZnCla (0.22 g) when required. 

Fig. 8. Schematic diagram of dilatometer 1 linear filament galvanometer bulb (4V, 0.5 A) 2,3 biconcave lenses (focal length 21 mm, aperture 20.5 mm) 4 capillary of the dilatometer 5 Ge photodiode (Philips GAP 12) 6 light source cylinder (length, 70 mm diameter, 37 mm) and photodiode cylinder (length 125 mm diameter. 37 mm) 7 mobile block 8 precision threaded rod (thread 0.5 mm) 9 drive motor (G.K. Keller NHS 12 R, 0--220V) 10 change-over relay (MBLE R1A/120/KKK) 11 counterbalance weight, 12 galvanometric relay (AOIP RP 221) 13 worm screw 14 helicoidal potentiometer 15 recorder 16,17 selsyn motor 18,19 revolution counter [Ref. (SO)]...

Figure 8.8 A mercury-based dilatometer (24). Bulb A contains the polymer (about 1 g), capillary B is for recording volume changes (Hg -r polymer), G is a capillary for calibration, sealed at point F. After packing bulb A, the inlet is constricted at E, C contains weighed mercury to fill all dead space, and D is a second constriction.

In other cases when an inert liquid can be found and the temperature of a solid-solid phase transition is not extreme, a dilatometer approach can be used. A change in volume of a solid at a phase transition is observed. Usually, a record of... 

The standard load applied is either 45.36 kg or double this weight The standard specimen can be a cylinder or a square prism. The dimensions of the cylindrical specimen are 50 mm in diameter and 50 mm in height The dimensions of the prismatic specimen are 38 mm x 38 mm x 114 mm [2]. The sample is kept in a carbon granule furnace between refractory plates and in contact with a dilatometer. The dilatometer is in turn attached to an extensom-eter to measure deformation. A specified load is applied on top of the sample. The furnace is then heated at a standard rate of 10°C per minute. As it is heated, a record of the height of the sample is made. Figure 19.1 shows such a record. 

---