Dilatometer system

The quality of the mirror blanks was controlled in various inspection procedures. The GTE values were measured according to the sampling plan shown in Fig. 4.44. Sample rods with a length of 100 mm were cut from ce-ramized Zerodur and measured with a high-precision dilatometer system. In Fig. 4.45 the results for mirror 2 are represented in a bar chart. 

The specimen [50-mm diameter and 50-mm-high (4) or a prism 38 mm x 38 mm x 114 mm (3)] is placed in a furnace between refractory plates and in contact with a dilatometer system, which is in turn attached to an extensometer to measure deformation. A specified load is applied to the specimen, and the material is then heated to the maximum test temperature or until a particular percentage deformation is reached. Methods of measurement include EN 993-8 1997 and ASTM 832-00. 

In the laboratory test a refractory specimen of nominal size 50 mm in diameter and 50 mm high is placed in furnace, in contact with a dilatometer system connected to an extensometer, and heated to the test temperature with a specific stress applied, nominally around 0.2 MPa for dense refractories. Once at temperature, the deformation of the sample over time is monitored. Results are represented graphically as a curve of creep percent versus time. 

For compressive stress-strain, the test specimen is placed between load columns in the furnace. A dilatometer system, to which the extensometer is attached, is located in the test specimen as shown. Other arrangements may use optical or averaging extensometers. This means the specimen deformation and hence strain can be measured. It is important to load the specimen slowly during the test to simulate the slow stress build due to thermal expansion in a refractory lining. 

The dilatometer is generally made of glass and is the vessel where the mercury is intruded into the sample pores. The design is dependent on the pressure source and monitoring system of the instrument. The dilatometer consists of a sample holder and a calibrated stem, which is used to measure the amount of mercury intruded into the sample. The sample in the dilatometer must be cleaned from adsorbed species by degassing the material in a vacuum [42], Most commercial instruments degas the sample in the instrument before mercury intrusion. Once the sample is degassed, the dilatometer (sample holder and stem) are filled with mercury. 

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 ... 

Alternative procedures are to use a dilatometer to measure volume change or to calculate Poisson s ratio from measurement of two moduli. Laufer et al5 concluded that for soft rubbers the dilatometer is the best approach and describe a suitable apparatus. Kugler et al6 have given a review of attempts at measurement and describe an optical system which they employed on a series of filled rubbers. It would seem reasonable that modem instrumentation, such as a video extensometer, could be used but this does not appear to have been reported. 

Figure 7.6 Two example LVDT stages offered by Theta Industries. Top constant force system, used for vertically mounted dilatometers and parallel plate viscometers. Bottom horizontally mounted dual pushrod system with leaf springs.

At the point at which the cavitation threshold has been passed, the generation of cavitation bubbles results in a sudden increase of the volume of the sonicated liquid. This volume change can be detected and measured with a system similar to Mikhailov s acoustic dilatometer, by measuring the liquid rise in a capillary tube connected to the sonicated vessel [119,142-144]. This method can be very sensitive and is a good and simple way to determine the cavitation threshold. In principle, it could also be used for quantitative measurements but it suffers from two drawbacks. First, it does not distinguish between gaseous cavitation, vaporous cavitation, and dead bubbles which may become occluded at surfaces. Second, part of the liquid rise in the capillary might also be the result of expansion caused by the temperature increase which accompanies sonication of the liquid. 

Referring to Fig. 6.1, total volume of the dilatometer or the reaction system is... 

Actually, in both cases the interval of monomers concentrations in which reaction systems keep their homogeneity is practically coincides (of course with definite correction by temperature course of investigated processes since polymerization kinetics as it was mentioned earlier was measured at 60°C, and viscosimetry studies were carried out at 30°C). Moreover, undoubtedly the correspondence of "transition region" of monomer concentrations values was also traced at which compression of macroradicals balls and their turning obtained by mentioned independent methods (dilatometer and viscosimetry) was observed. 

Degree of Crystallinity. The degree of crystallinity (1 — A) of the cast films was calculated from the ratio of the observed heat of fusion by DSC to the heat of fusion (AHu) of 100% crystalline PTHF. A AHu of 3800 cal/mole was obtained by analyzing the melting point depression data of PTHF-diluents systems (6) and was used in the calculation. As shown in Figure 8, the degree of crystallinity decreases with increased PS content in the block copolymers. Moreover, the data for ST and STS copolymers show approximately the same (1 — A) vs. PS content relationship. The degree of crystallinity was also determined for isothermally crystallized samples. In dilatometers, the cast films were melted at 80 °C for 1 hr and then crystallized at 20°C for 104 min. The... 

Volume Relaxation. Isothermal volume relaxation was assessed for the a-PS/PPO blend system using a precision mercury dilatometer up to a final aging time of proximately 2 days. Four aging temperatures of Tg-lS C, T,-30°C, Tg-4S C, and Tg-60 C were used, and the resulting relaxation rates ( Pv = (l/V)dV/dlog(ti) ) (7P) are presented in Figure 3 (initial curvature in volume rdaxation plots was not used in... 

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