Expansion probes

Thermal analysis on a DuPont 900 thermomechanical analyzer provided additional information on transition temperatures. A blunt-end expansion probe was used with heating rates in the range of 5°-10°C/min. 

Figure 12 shows the use of the IMS-2 Thermomechanical System with an expansion probe to establish the average coefficient of linear expansion of the Process 1 residue in the temperature range from 60°C to 140°C. As is shown in the figure, the expansion coefficient was calculated to be 4.56 X 10". An exploratory run using the expansion probe in the TMS-2 Thermomechanical Analyzer... 

Figure 16.39 Schematic of a TMA. Three types of sample probes are shown with samples in place (dark colored areas are the samples). The expansion probe and sample are shown as they would be located in the furnace. (Courtesy of NETZSCH Instmments, Inc., Burlington, MA, www.netzsch-thermal-analysis.com.)...

Degree of swelling— increase in thickness of the sample with absorption of a solvent as measured by the expansion probe. See Section 4.6.5 and Eq. (4.8). 

Expansion probes are used primarily to measure CLTE and under negligible load, 2.5-3 mm in diameter the same probe can be rounded to form a hemispherical probe some suppliers also provide a macroprobe with 6mm diameter... 

Irregular-shaped sample expansion behavior can be directly measured using a volumetric dilatometer by embedding the sample (a few grams or more) in aluminum oxide powder or placed it into a buoyancy fluid in a volumetric dilatometer made of fused quartz or sapphire an expansion probe is used to measure the difference in the expansion of the dilatometer with and without sample as a function of temperature... 

Flat bulk sample Expansion probe Small load Linear expansivity Temperature CLTE (a) and Tg... 

Irregular-shaped bulk sample Expansion probe Sample smaller than probe, Linear displacement Temperature Softening temperature... 

Figure 10.7 Schematic presentation of the Perkin-Elmer thermal mechanical analyser (top). Bottom left expansion probe for measurement of linear thermal expansion coefficient. Bottom right penetration probe for measurement of stiffness.

We measured the coefficient of thermal expansion, CTE, of RX-55-AE-5 using a TA Instruments Model 2940 TMA that was controlled by a TA 500 Thermal Analyzer equipped with a TMA Mechanical Cooling Accessory [6,7]. A quartz micro-expansion probe sat on top of all samples with a force of 0.01 Newtons (N). The change in the length of the sample was as it was heated or cooled was measured by a linear transformer that converted the vertical distance of the quartz motion probe and was recorded by the TA Instrument software. Ultra high purity nitrogen carrier gas was used at a constant flow rate of 100 cm /min. Samples were heated at a linear heating rate of 3°C /min. 

As adhesive compositions are most often obtained by mixing an organic binder with inorganic fillers and various additives, thermomechanical analysis is generally conducted with an expansion probe. The... 

At this stage, we do not know how much of 2p.j, 3p.j, 4p.j,. .. np.j this wavefunction contains. To probe this question another subsequent measurement of the energy (corresponding to the H operator) could be made. Doing so would allow the amplitudes in the expansion of the above f"= P.i... 

Future development of SAM-based analytical technology requires expansion of the size and shape selectivity of template stmctures, as well as introduction of advanced chemical and optical gating mechanisms. An important contribution of SAMs is in miniaturization of analytical instmmentation. This use may in turn have considerable importance in the biomedical analytical area, where miniature analytical probes will be introduced into the body and target-specific organs or even cell clusters. Advances in high resolution spatial patterning of SAMs open the way for such technologies (268,352). 

Instruments based on the contact principle can further be divided into two classes mechanical thermometers and electrical thermometers. Mechanical thermometers are based on the thermal expansion of a gas, a liquid, or a solid material. They are simple, robust, and do not normally require power to operate. Electrical resistance thermometers utilize the connection between the electrical resistance and the sensor temperature. Thermocouples are based on the phenomenon, where a temperature-dependent voltage is created in a circuit of two different metals. Semiconductor thermometers have a diode or transistor probe, or a more advanced integrated circuit, where the voltage of the semiconductor junctions is temperature dependent. All electrical meters are easy to incorporate with modern data acquisition systems. A summary of contact thermometer properties is shown in Table 12.3. 

We note first that not all amorphous substances actually exhibit a negative a in the experimentally probed temperature range. In such cases, it is likely that the contraction coming from those interactions in these materials is simply weaker than the regular, anharmonic lattice thermal expansion. Other contributions to the Griineisen parameter will be discussed later as well. 

Figure 9. Action spectra acquired in the F Cl B—X, 3-0 spectral region and with the probe laser tuned to the F Cl E—B, 9-1 transition. Both spectra were recorded using the same source conditions, but with the lasers intersecting the expansion at Z = 8.8, (a), and Z = 19.1, (b). Monomer rotational temperatures of 2.34(3) K and 1.09(10) K were measured at the two distances [62].

Another method is to measure the disappearance rate of the excited parent molecules, that is, the intensity changes of the disk-like images at various delay times (therefore, at various photolysis laser positions) along the molecular beam. This is very useful when the dissociation rate is slow and the method described above cannot be applied. This measurement requires a small molecular beam velocity distribution and a large variable distance between the crossing points of the pump and probe laser beams with the molecular beam. The small velocity distribution can be obtained through adiabatic expansion, and the available distances between the pump and probe laser beams depend on the design of the chamber. For variable distances from 0 to 10 cm in our system and AV/V = 10% molecular beam velocity distribution, dissociation rates as slow as 3 x 103 s 1 under collisionless condition can be measured. 

On macroscopic length scales, as probed for example by dynamic mechanical relaxation experiments, the crossover from 0- to good solvent conditions in dilute solutions is accompanied by a gradual variation from Zimm to Rouse behavior [1,126]. As has been pointed out earlier, this effect is completely due to the coil expansion, resulting from the presence of excluded volume interactions. 

The idea is simple consider a polycrystalline material that is subjected to locally varying strain. Then every crystal is probing its local strain by small compression or expansion of the lattice constant. The superposition of all these dilated lattices makes the observable line profiles - and as a function of order their breadth has to increase linearly. According to Kochendorfer the polycrystalline material becomes inhomogeneous or heterogeneous . 

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