Thermobalance commercial

Experimental factors. In the previous section it was stated that the precise temperature regions for each reaction of the thermal decomposition of copper sulphate pentahydrate is dependent upon experimental conditions. When a variety of commercial thermobalances became available in the early 1960s it was soon realised that a wide range of factors could influence the results obtained. Reviews of these factors have been made by Simons and Newkirk30 and by Coats and Redfern31 as a basis for establishing criteria necessary to obtain meaningful and reproducible results. 

The different types of thermobalances which are used today in research laboratories and in industry are usually bound to and designed for specific applications. They may either be commercially available instruments, or assembled from individual components or completely homemade6,7 13 1S. As an example, the set-up of a modern thermobalance is shown schematically in Fig. 5. This type of instrument with its... 

The historical aspects ofTG have been discussed by Duval (3-5), Wend-Iandt (7), Keattch (23), and others (107-109). Perhaps thejirst thermobalance was that described by Nernst and Riesenfeld (I20X whp used a Nernst quartz torsion microbalance. equipped wit an electric furnace, to study the mass-loss on heating of Iceland spar. opal, zirconia, and other minerals. The Japanese Honda was apparently the first to use the term ihermobalance for an instrument he described in 1915 (9). The French school of thermo-gravimetry began with Urbain in 1912 when he modified two-pan analytical balance into a cril e thermobalance (24). This was followed by the work of Guichard (1923) (10), Vallet (1936), Chevenard (1936), Duval (1950), and many others.The first commercial thermobalance in the United States, which prompted funner work in TG. was that described by Mauer (31) in 1954,... 

Obviously, all these requirements cannot be met in every thermobalance. However, a number of commercially available instruments do incorporate these features. 

Most of the commercial thermobalances now available use computer data reduction techniques to process the raw TG data (see Chapter 12). A dedicated microcomputer system plots the resultant data using a plotter or dot-matrix printer. Scaling and offset of the curve can be carried out as well as other mathematical operations such as differentiation, curve peak integration, and so on. 

A large number of reviews and books have been written describing various commercial and noncommercial thermobalances. Mention should be made of the reviews by Gordon and Campbell (2), Duval (16), Lewin (17), Jacque et al. (18), Saito (19), Vaughan (20), Wendlandt (21, 22), and others. Books containing descriptions of thermobalances include those by Duval (23, 24), Garn (25), Keattch (26), Anderson (27), Wendlandt (28), Saito (29), and... 

Guichard s work was followed by the investigations of Vallet (32), Dubois (33), and others (23). Perhaps the greatest impetus to the French school of thermogravimetry was the development of the Chevenard (34) recording thermobalance. This balance had been under development since 1936 and became commercially available in 1945 it was the first automatic (photographically) recording instrument. In the hands of Duval and co-workers (23, 24), it became the standard instrument for work in this field. 

Two other important milestones in the development of the modern thermobalance occurred in 1958 and 1964. A multifunctional instrument, called the Derivatograph. was described by Paulik 35) et al. in 1958. The instrument could record not only the TG curve, but also its first derivative (DTG) and the differential thermal analysis jDTA) curve. In 1964. Weide-mann (3) described the Mettler system, which was perhaps the most sophisticated thermobalance ever commercially available. This system is described in detail by Wiedemann and Bayer (8). 

The Mettler TA1 thermoanalyzer, as developed by Wiedemann (3, 60), was perhaps the most elaborate and versatile of any thermobalance ever constructed. It is no longer available commercially, having been superseded by the Mettler TA 2000 and TA 3000 systems. However, because of its uniqueness, the Mettler TAl is described here. 

The method of thermogravimetry is basically quantitative in nature in that the mass-change can be accurately determined- However, the temperature ranges in which the mass-changes occur are qualitative in that they depend on the instrumental and sample characteristics. With the wide use of commercial thermobalances, TG data of a sample can be correlated from laboratory to laboratory if similar conditions of pyrolysis are employed. 

Another apparatus, which permits the recording of simultaneous ETA. DTA. and TG DTG. is shown in Figure 8.50 (192). The system consists of a commercial DTA apparatus and thermobalance manufactured by Netzsch-Geratebau, Selb, West Germany. For ETA measurements, an inert carrier gas is passed over the sample S and the standard material I situated in the isothermal region of the furnace F. The radioactive emanation released from the sample is carried into a measuring cell. The alpha-activity of the emanation E is counted by means of a silicon surface barrier detector D connected... 

Wendlandt has also described an EC apparatus that can be incorporated into the furnace of a commercial thermobalance so that concurrent EC-TG measurements can be made (110). This sample holder was later modified so that concurrent EC-DTA measurements could also be carried out (112). A high-temperature EC furnace and sample holder, for use up to... 

Thermogravimetry (TG), the technique in which the mass of a sample is monitored against time or temperature, is performed with a ThermoGravimetric Analyser (TGA) or thermobalance. Recently, a survey of this technique and the available commercial equipment was given toy Wunderlich [1]. 

Balances. Balances must remain precise and accurate continuously under extreme temperature and atmospheric conditions, and should deliver a signal suitable for continuous recording. These requirements may be met in many ways the two books by Duval and Wendlandt (see bibliography) show at least ten different commercial thermobalances that perform satisfactorily. The basic characteristics of such balances will be illustrated by describing one, the Cahn Electrobalance (Ventron Instruments... 

The similarities of TG and DTA are obviously great, at least instrumentally. As a consequence, many commercial instruments are designed to perform both types of analysis the heating device, temperature-control unit, atmospheric control, and recording device are essentially used in common and are contained in a single control unit, only the thermobalance and DTA sample compartments being separate. 

Some commercial instruments have been developed which combine a thermobalance with a thermal analyzer in a single heating process, recording TG, DTG, and DTA curves simultaneously. Representatives of this kind of equipment are the De-rivatograph (Hungarian Optical Works) shown in Figure 3.7 and the STA system (simultaneous thermal analysis system) of Stanton Redcroft Ltd. (UK). 

Honda [42, 43] laid the broad foundations of modern thermogravimetry, introducing the thermobalance International Union of Pure and Applied Chemistry (lUPAC) was established The first commercial thermogravimeter was produced [35]... 

The quality of the furnace atmosphere deserves careful attention. Most commercial thermobalances operate at atmospheric pressure. Vacuum and high-pressure studies normally require specialized equipment, either commercial or home-... 

The heart of the thermogravimetric analyzer is the thermobalance, which is capable of measuring the sample mass as a function of temperature and time. The relationship between the components of a thermobalance varies from one instrument to another. A schematic representation as shown in Figs. 3.1a and 3.1b indicates typical thermocouple placements relative to the sample. The three standard sample and furnace positions relative to the balance are depicted in Fig. 3.1a. Figure 3.2 shows actual examples of currently available commercial instruments. 

Figure 3.2. Three examples of commercial thermobalances, including typical thermocouple placement (a) a top-loading model (courtesy of Netzsch Instruments) (b) a side loading model (courtesy of Mettler-Toledo) (c) a bottom-loading model (courtesy of TA Instruments).

Principles and Characteristics Simultaneous thermal analysis techniques, such as TG-DSC/DTA offer vital information on polymer structure based on heat flow behaviour and mass change [290], but little direct information on the composition of evolved gas products. A more complete thermal profile is provided when a thermal analyser is coupled to an identification tool. Henderson et al. [433] have recently described TG-DSC/DTA with evolved gas analysers (MS and FTIR). The skimmer coupling is the most advanced commercial way of combining a thermobalance or simultaneous TG-DSC/DTA instrument with a quadrupole mass spectrometer [338]. For descriptions of interface techniques in this coupled instrumentation, cfr. ref. [411]. Simultaneous TG-DSC-MS is capable of operation up to 2000°C [434]. 

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