TA Instrumentation

The equipment used in DTA studies is shown schematically in Fig. 16.16. The sample is loaded into a crucible, which is then inserted into the sample well (marked S). A reference sample is made by placing a similar quantity of inert material (such as AI2O3) in a second crucible. This crucible is inserted in the reference well, marked R. The dimensions of the two crucibles and of the cell wells are as nearly identical as possible furthermore, the weights of the sample and the reference should be virtually equal. The sample and reference should be matched thermally and arranged symmetrically with the furnace so that they are both heated or cooled in an identical manner. The metal block surrounding the wells acts as a heat sink. The temperature of the heat sink is slowly increased using an internal heater. The sink in turn simultaneously heats the sample and reference material. A pair of matched thermocouples is used. One pair is in contact with the sample or the sample container (as shown) the other pair is in contact with the reference. The output of the differential thermocouple, or AT, is amplified and sent to the data 

Modern DTA instruments have the ability to change atmospheres from inert to reactive gases, as is done in TGA. As is the case with TGA, the appearance of the DTA thermal curve depends on the particle size of the sample, sample packing, the heating rate, flow characteristics inside the furnace, and other factors. Thermal matching between the sample and the reference is often improved by diluting the sample with the inert reference, keeping the total masses in each crucible as close to each other as possible. 

Sample crucibles are generally metallic (Al, Pt) or ceramic (silica) and may or may not have a lid. Many metal pans with lids have the lid crimped on using a special tool. Best results are obtained when the area of contact between the sample and the pan or crucible is maximized. Samples are generally in the 1-10 mg range for analytical applications. 

The peak area in DTA is related to the enthalpy change. A//, to the mass of sample used, m, and to a large number of factors like sample geometry and thermal conductivity. These other factors result in the area. A, being related to the mass and A// by an empirically determined calibration constant, K  

Unfortunately, K is highly temperature-dependent in the DTA experiment, so it is necessary to calibrate the peak area in the same temperature region as the peak of interest. This may require multiple calibration standards and can be time consuming. As we shall see, the calibration constant K for DSC is not temperature dependent therefore DTA is usually used for qualitative analysis, while DSC is used for quantitative measurements of AH and heat capacity. 

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The friction coefficient at PVA gel/OTS modified quartz is 0.300 while that at PVA gel/unmodrfied quartz is 0.076. Frictions were measured by using a rheometer (ARES, TA instruments) as a function of sliding velocity in water and these values were calculated from the experimental resultsoflowestsbdingvelodty,7.5 x 10 m/s. 

Gel formation was monitored using a controlled-stress rheometer (Carri-Med CS 50, TA Instruments, Guyancourt, France) with cone-and-plate geometry (cone diameter 4 cm, angle 3°58 ). The bottom plate was fitted with a Peltier temperature controller that... 

In the broadest sense, thermal analysis (TA) measures physical changes in a material as a function of temperature. TA instruments measure variables in a sample such as heat flow, weight, dimensions, etc. A typical fingerprint of a compound might be the endothermic peak on a thermogram indicating a sample s crystalline melt. 

Anonymous. DMA 983 Dynamic Mechanical Analyzer. Brochure. New Castle, DE TA Instruments 1995. 

Figure 1 Example of an OIT experimental curve. Reproduced from Marcus and Blaine [4], by kind permission of TA Instruments.

S.M. Marcus and R.L. Baine, Estimation of bias in the oxidative induction time measurement by pressure DSC, Application note TA-228, TA Instruments, Inc., New Castle, DE, USA. 

Measurements of differential scanning calorimetry (DSC) were obtained on a TA Instruments 2910 thermal analysis system (Fig. 2). Samples of approximately 1-2 mg were accurately weighed into an aluminum DSC pan, and covered with an aluminum lid that was crimped in place. The samples were then heated over the range of 20-140 °C, at a heating rate of 10 °C/min. Valproic acid was found to boil at 227 °C. 

Thermal decomposition was performed using a SDT Q-600 simultaneous DSC-TGA instrument (TA Instruments). The samples (mass app. 10 mg) were heated in a standard alumina 90 il sample pan. All experiments were carried out under air with a flow rate of 0.1 dm3/min. Non-isothermal measurements were conducted at heating rates of 3, 6, 9, 12, and 16 K/min. Five experiments were done at each heating rate. 

Fig. 1.26. Instrument DSC 2920 with DTA-measuring cell. This installation is not designed for low temperatures, but can be modified for this purpose. (Commercial standard installations for low temperatures have not been found by the author.) (Schema and photograph TA Instruments, Inc. New Castle DE 19720, USA.)...

The purpose of differential thermal systems is to record the difference in the enthalpy changes that occurs between the reference and the test sample when both are heated in an identical fashion. Several publications are available concerning the theoretical aspects and applications of various thermal analysis techniques, including the DSC [71-74]. Commercial instruments are available from a number of companies including Perkin-Elmer, TA Instruments, Toledo-Mettler, SET ARAM, Seiko, and Polymer Laboratories. 

TA instruments has developed automated thermogravimetric analysis and related kinetic programs that enable a rapid determination of decomposition rates to be made. The following excerpt from a TA application brief [57] explains the method ... 

Estimation of Polymer Lifetime by TGA Decomposition Kinetics, TA Instruments Thermal Analysis Application Brief TA-125, pp. 1-4. 

TA Instruments CSL2 Controlled Stress Rheometer D-E 10 2 -109 10 6-5 x 103 good TA Instruments, New Casde, Del. 

Another resonant frequency instrument is the TA Instmments dynamic mechanical analyzer (DMA). A bar-like specimen is clamped between two pivoted arms and sinusoidally oscillated at its resonant frequency with an amplitude selected by the operator. An amount of energy equal to that dissipated by the specimen is added on each cycle to maintain a constant amplitude. The flexural modulus, E is calculated from the resonant frequency, and the makeup energy represents a damping function, which can be related to the loss modulus, E". A newer version of this instrument, the TA Instruments 983 DMA, can also make measurements at fixed frequencies as well as creep and stress—relaxation measurements. 

The TA Instruments CSL2 rheometer can perform low frequency oscillatory measurements as well as steady-state viscosity determinations, even though it has a simple mechanical system. The sinusoidal wave form is generated mathematically in the computer rather than with an electromechanical drive system. The stress is controlled, and the resulting strain is determined and stored in memory. The computer analyzes the wave form and calculates the viscosity and elasticity of the specimen at the frequency of the test. As of this writing (1996), the oscillation software covers a frequency range of 10-4 -40 Hz. This range could be increased as faster software and computers become available. 

A differential scanning calorimeter (DSC), Dupont Instrument, Model DSC2910, was used to determine the glass transition temperatures. Thermo-gravimetric analyses were carried on a thermogravimetric analyzer (TGA), TA Instruments, Model Hi-Res TGA 2950. 

Technical data, R. W. Thomas and M. W. Cadwallader, TA Instruments Hotline, Wilmington, Del., June, 1990. 

C(CH2OH)4 0.4 mole %/TA Instrument Waters Assoc., Inc. (Model 200)... 

The compositions of the composites were determined simply by weighing the tared solid sample. Melting endotherms and glass transition temperatures were determined using a TA Instruments 2910 modulated differential scanning calorimeter (DSC) operated with a 3°C/min ramp rate, a 0.75 °C oscillation amplitude, and a 60-s oscillation period. 

Fig. 1.25. Scheme of a DTA measuring cell. 1, Crucible with sample 2, sample 3 thermocouple (reference crucible not enlarged) 4, gas inlet 5, ceramic support (TA Instruments, Newcastle, DE, USA)... 

Fig. 1.45.1. Artist s view of a DSC cell in Tzero technology as used in modulated DSC (MDSC) processes. 1, Sample and reference table made from one piece of constantan 2, chromel thermocouples directly connected to the constantan tables 3, Tzero sensor from chromel-constantan in the middle between sample and reference table (TA Instruments, New Castle, DE, USA...

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