Thermomechanical probes

The read-write heads have thermomechanical probes. The thermomechanical probes have a resistive region for locally heating a tip of the thermomechanical probe in response to electrical current being applied to the thermomechanical probes [98]. 

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 11.20. Schematic representation of a thermomechanical analyser (a) and (b) with various probe configurations (c)...

Using a thermomechanical analyzer (TMA) as the parallel-plate rheometer, the neat resin was laminated under identical conditions as did the prepreg to deteraiine the viscosity history. Throughout this study, the quartz probe (0.145 in. in diameter) which is attached to a linear variable differential transfomier for thickness monitoring exerted a constant force of 2... 

For softer, rubbery polymers, a different experimental procedure gives better results. For these experiments we have measured directly the penetration distance of a tiny weighted probe into the cross-sectioned surface of polymer samples. For this purpose we have made use of a Perkin-Elmer Thermomechanical Analyzer equipped with a tip modified to be small enough to provide measurements of the desired resolution. (We are currently using a conical diamond phonograph needle having a tip angle of 60°.)... 

TMA s were run over a temperature range of -20°C to 210°C on a Perkin Elmer Thermomechanical Analyzer IMS-1. They were run with a 40 mil diameter penetration probe loaded with 200 grgms to give a pressure of 394 psi. The program rate was lOC/min. under a helium atmosphere and the Y-axis sensitivity... 

Tdec), the temperatures for maximum degradation rate (Tmax), and char yield at 545 °C (CY) measured using the thermogravimetric analyses (TGA), and by the Tg measured using a thermomechanical analyzer (TMA) with a penetration probe. Tdec is noted as the point where the extrapolations of the two slopes in the TGA curve intersect. The Tg was measured using a thermomechanical analyzer (TMA) with a penetration probe. 

Thermomechanical Analyses (TMA) were recorded on a DuPont thermal analyzer. Model 943 TMA fitted with a penetrating tip probe, at 2g load and 10°C/mln temperature rise. Vertical displacement and the first derivative of that displacement with respect to time were recorded as a function of temperature. Dynamic Mechanical Analyses (DMA) were obtained on a DuPont 981 DMA Instrument. 

H. Wohljen and R. Dessy (1979) Surface acoustic wave probe for chemical analysis, III. Thermomechanical polymer analyzer , Analytical Chemistry, 51, 1470-5. 

Thermomechanical-analysis (TMA) testing is used to measure a material s expansion coefficient above and below the glass-transition temperature or Tg. Thermomechanical analysis continuously monitors the expansion of a probe on a sample as a function of temperature. The standard test method for TMA is ASTM D3386, Coefficient of Linear Thermal Expansion of Electrical Insulating Materials.In addition to the glass-transition temperature or Tg, the expansion coefficients above and below Tg are reported. 

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... 

Thermomechanical analysis (TMA), e.g. [50]. The sensitivity of TMA is comparable with that of DMT A. In contrast to DSC and DMT A, the measurement is not the average over the whole sample but an average of the properties of a certain part of the sample that is limited by the shape of the tip of the probe. Direct measurements of the expansivity are possible which give access to the free volume and the relaxation behavior of the polymer chains [93-95]. 

A schematic diagram illustrating a typical thermomechanical analyzer is shown in Fig. 4.146. This instrument was produced by the Perkin-Elmer Co. Temperature is controlled through a heater and the coolant at the bottom. Atmosphere control is possible through the sample tube. The heavy black probe measures the position of the... 

Dilatometry and thermomechanical analysis (TMA) are also techniques used to monitor the thermal behavior of fibers. They both employ a sensitive probe in contact with the surface of the sample, and the thermal transitions are detected either by a change in volume or modulus of the sample, respectively. In the latter case, the probe necessarily penetrates the sample surface. A variable transformer records the voltage output that is directly proportional to the degree of displacement of the probe during a thermally induced transition. TMA is a more sensitive technique than either DTA or DSC for detecting thermal transitions. 

Thermomechanical analysis (TMA) is the measurement of dimensional changes (such as expansion, contraction, flexure, extension, and calorimetric expansion and contraction) in a material. It is measured by the movement of a probe which is in contact with the sample in order to determine temperature-related mechanical behaviour in the temperature range of 180-800 °C. This occurs as the sample is heated, cooled (temperature plot), or held at a constant temperature (time plot). It also measures linear or volumetric changes in the dimensions of a sample as a function of time and force. 

In thermomechanical analysis (TMA), the change in mechanical properties is measured as a function of temperature and/or time. A probe in contact with the sample moves as the sample undergoes dimensional changes. The movement of the probe is measured with an LVDT. The sample deformations that can be measured are compression, penetration, extension, and flexure or bending. 

Other penetrometer-indentometers include transducers to sense the position and movement of the probe and microprocessors for temperature control and data collection and reduction. These instruments are used mainly to measure softening points, which are not glass transitions but are usually close to those values. Because a softening point is indicative of behavior under load, it is often more useful for predicting performance than the Tg. Penetrometer-indentometers can also be used to measure indentation hardness, creep, creep recovery, and modulus. Examples of such instruments include the TA Instruments, Mettler, Perkin-Elmer, Seiko, and Shimadzu thermomechanical analyzers (TMAs). They can be used to generate modulus and modulus-temperature data from indentation-time plots by applying the Hertz equation (eq. 36) (170,296), where E is the elastic or Young s modulus, jx the Poisson s ratio, r the radius of the hemispherical indentor, P the force on the indentor (mass load x g), h the indentation, and ifk the indentation hardness. 

Thermomechanical analysis (TMA) measures the deformation of a material contacted hy a mechanical prohe, as a function of a controlled temperature program, or time at constant temperature. TMA experiments are generally conducted imder static loading with a variety of probe configurations in expansion, compression, penetration, tension, or flexime. In addition, various attachments are available to allow the instrument to operate in special modes, such as stress relaxation, creep, tensile loading of films and fibers, flexural loading, parallel-plate rheometry, and volume dilatometry. The type of probe used determines the mode of operation of the instrument, the manner in which stress is apphed to the sample, and the amount of that stress. 

A temperature calibration procedure for TMA has been proposed (53-55) and subsequently included as an ASTM method (Test Method for Temperature Calibration of Thermomechanical Analyzers, E1363-90). It uses a penetration probe and the melting temperature of one or more standard materials. Pure metals with sharp melting points are the standards often used. An open DSC pan may be used to contain the calibrant material. Another potential material would be the selected shape memory alloy, reported to be reproducible to 1°C (56). Several reviews on temperature calibration for TMA have been published based on ASTM efforts in this area (54,55). Sircar (26) suggests that, when used for elastomer evaluation, temperature calibration for TMA should be conducted with low melting liquids as in DSC. For calibration of the expansion, one manufacturer s manual (TA Instruments) recommends aluminum for calibrating the linear expansion parameter. Other calibration standards suggested for the linear coefficient of thermal expansion (CTE) are lead (57) and copper (58). 

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