Dilatometric method

Method ATSFAAR Apparatus Q)de No. Measurement units Test suitable for meeting following standards Notes 

Temperature of deflection under load or heat deflection or distribution temperature (Martens Method) °C ASTMD648-04[01]  

Melt flow index (or rate) 1002013 10.02017 ASTMD1238[14] ASTMD2116[15] ASTMD3364[16] UNI EN ISO 1133 [17]  

Melting point (Fischer Johns) 070173C °c ASTM Also measured from differential thermal analysis peak 

Dilatometric Method.—Since, in the majority of cases, transformation at the transition point is accompanied by an appreciable change of volume, it is only necessary to ascertain 

If the transformation occurred immediately the transition point was reached, the sudden expansion and contraction would 

Immerse the bulb of the dilatometer completely in the water of a thermostat, the initial temperature Fig. 104. 2jO After about five or ten 

These experiments generally require a considerable period of time. 

Experiment.—Detei-mim the Temperature of Formation of Astracanite from the Simple Salts. 

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Glass-transition temperatures are commonly determined by differential scanning calorimetry or dynamic mechanical analysis. Many reported values have been measured by dilatometric methods however, methods based on the torsional pendulum, strain gauge, and refractivity also give results which are ia good agreement. Vicat temperature and britde poiat yield only approximate transition temperature values but are useful because of the simplicity of measurement. The reported T values for a large number of polymers may be found ia References 5, 6, 12, and 13. 

The reactions are accompanied by a considerable volume change, and a dilatometric method was employed by Bell and Higginson (1949), who added acetaldehyde-water mixtures (containing about equal quantities of MeCHO and MeCH(OH)2) to an excess of acetone, and thus measured kj, in presence of a large number of acid catalysts. The direct hydration of acetaldehyde in aqueous buffer solutions is inconveniently fast at room temperatures, but ( (j + A ) was measured dilatometrically at 0°C by Bell and Darwent (1950), who established the existence of general acid-base catalysis. 

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,... 

Water has also been shown to be essential for the liquid phase polymerization of isobutylene with stannic chloride as catalyst (Norrish and Russell, 87). The rates of reaction were measured by a dilatometric method using ethyl chloride as common solvent at —78.5°. With a mixture consisting of 1.15% stannic chloride, 20 % isobutylene, and 78.8% ethyl chloride, the rate of polymerization was directly proportional to the amount of added water (up to 0.43% of which was added). A rapid increase in the rate of polymerization occurred as the stannic chloride concentration was increased from 0.1 to 1.25% with higher concentrations the rate increased only gradually. It was concluded that a soluble hydrate is formed and functions as the active catalyst. The minimum concentration of stannic chloride below which no polymerization occurred was somewhat less than half the percentage of added water. When the concentration of the metal chloride was less than about one-fifth that of the added water, a light solid precipitated formation of this insoluble hydrate which had no catalytic activity probably explains the minimum catalyst concentration. The addition of 0.3% each of ethyl alcohol, butyl alcohol, diethyl ether, or acetone in the presence of 0.18% water reduced the rate to less than one-fifth of its normal value. On the other hand, no polymerization occurred on the addition of 0.3 % of these substances in the absence of added water. The water-promoted reaction was halved when 1- and 2-butene were present in concentrations of 2 and 6%, respectively. 

For kinetic investigations of homogeneous polymerizations, a variety of methods and apparatus has been developed. The dilatometric method is especially worthy of mention on account of its simplicity and general applicability (Fig. 2.3). 

Dilatometric technique can also be used for determination of polymerization rate in the case of multimonomer polymerization. However, in this case calibration of the dilatometric method is more complex. The substrates and products are both polymers with similar molecular weights. Difference in density during the course of polymerization is connected only with the conversion of double bonds to the single bonds. It is difficult to obtain a macromolecular product in which double bonds are fully converted to single bonds. Calibration must be based on simultaneous measurements of Ah and independent method (e.g., IR spectroscopy) and calculation of (1/dp l/d]vi). 

Benrath184 used a dilatometric method to follow the acid-catalysed hydrolysis of acetamide, whereas Leisten212 and Rabinovitch and Winkler187 both analysed for the liberated ammonia by the formol method281. 

Figure 2. Change in size with increased water adsorption at 22° C. I (O) pellet of zeolite NaA (dilatometric method) 2 ( ) crystals NaA (x-ray method, paramerter a length of arrows shows the error in x-ray measurements) 8 ( ) pellet of fired clay (dilatometric method).

Benson, S. W., and A. M. North A simple dilatometric method of determining the rate constants of chain reactions. II. The effect of viscosity on the rate constants of polymerization reaction. J. Am. Chem. Soc. 81, 1339 (1959). 

Solid Fat Index—Dilatometric Method (SFI) (Cd 10-57) estimates the percentage of solids in a semi-solid fat on the basis of changes in volume with temperature. This method utilizes glass dilatometers, and is the primary method in the United States. Totox Value an estimate of the degree of oxidation of a fat or oil, calculated as ... 

Burnett (2), using a dilatometric method to study the polymerization in heptane, reported a first-order dependence of the reaction rate on the monomer and the a-TiCl3 concentration, but little or no dependence on the aluminum alkyl. A settling period was observed which could not be correlated with the various components of the reaction system. An activation energy, measured after the settling period, was found to be 7.7 kcal./mole. 

Dilatometric Methods. Usually applied to liquid systems in which the volume of the system depends on the extent of the reaction. The reaction vessel is called a dilatomeler. ... 

Rate coefficients of hydrolysis and other nucleophilic reactions of epoxides have been measured by various authors (49, 150—154]. The data are reviewed insofar as they are of interest with respect to acid—base catalysis. Measurements have been done mainly by the dilatometric method or by continuous titration of the base formed in the reaction. Table 9 contains rate coefficients, referring to rate eqn. (44), and... 

The SFC and SFI values can be determined by dilatometric methods or by pulsed NMR. The dilatometric method is still considered the most accurate, but NMR provides reliable information much more quickly. 

The dilatometric method is time-consuming and subject to the bias introduced by the convention described. More recently pulsed Nuclear Magnetic Resonance (pNMR) has been used to measure the relative amounts of liquid and solid fat in a sample, based upon the difference in rates of relaxation of protons in the two phases after the sample has been pulsed (AOCS Method Cd 16-81). With proper calibration this gives a direct determination of the percentage of solid fat, and the results are termed sohd fat content (SFC). The analysis takes less time than dilato-metry, but the equipment is more expensive. 

Experimental Measurement of Bate of Cure. The rate of cure was measured eiqperimentally in several studies (54-58). Three of Ihese (54, 57, 58) used file dilatometric method to determine the rate of... 

The reaction of oarboxylate with various substrates is an example of a system which necessitates a careful search for products. Early examples of these reactions demonstrated that direct nucleophilic attack takes place. For example, using a dilatometric method, formate was found to catalyze strongly the hydrolysis of acetic anhydride whereas propionate and butyrate slow down the reaction (Kilpatrick, 1928). These results are attributable to mixed anhydride formation with the total rate being determined by the reactivity of the mixed anhydride. The reaction of acetate with 2,4-dinitrophenyl benzoate results in the formation of an unstable mixed anhydride, as was shown in an experiment in which 0 labeled acetate was used the benzoic acid product contains 75% of the O label (Bender and Neveu, 1958). The other 25 % of the O label is presumed to be lost to acetate by solvent attack at the benzoyl carbon if direct nucleophilic interaction is the sole path. 

The dilatometric method evidently gives no indication whatever of critical points in this alloy. On the expansion curve there is no sign of any definite irregularity. 

If dilatometric methods are used, accurate results can be obtained only if no-load is applied to the sample. However, this makes the measurement of contractions more difficult. 

I. The Dilatometric Method.—Since, in the majority of cases, transformation at the transition point is accompanied by an appreciable change of volume, it is only necessary to ascertain the temperature at which this change of volume occurs, in order to determine the transition point. For this purpose the dilatometer is employed, an apparatus which consists of a bulb with capillary tube attached, and vrhich constitutes a sort of large thermometer (Fig. 159). Some of the substance to be examined is passed into the bulb A through the tube B, which is then sealed off. The rest of the bulb and a small portion of the capillary tube is then filled with some liquid, which, of course, must be without chemical action on the substance under investigation. A liquid, however, may be employed which dissolves the substance, for, as we have seen (p. 58), the transformation at the transition point is, as a rule, accelerated by the presence of a solvent. On the other hand, the liquid must not dissolve in the substance under examination, for the temperature of transformation would be thereby altered. 

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