Chevenard thermobalance

Fig. 72. Thermogravimetric analyses of poly(l,3-phenylene oxide) [300]. 1, Aminco thermo balance, vacuum 0.3 mm, 3 degC min-1 2, Chevenard thermobalance, nitrogen, 2 degC min-1 3, Chevenard thermobalance, air, 2 degC min-1.

The effect of air buoyancy changes on the sample holder and certain balance components has been studied (3, 4, 12, 15, 29. 37, 48. 51, 52). Most of the studies have used the Chevenard thermobalance (3, 4, 37, 51, 52), but other balances have been studied as well (12, 15, 29, 37, 48). 

Figure 2.27. Effect of furnace top opening on apparent mass-change of Chevenard thermobalance at a heating rate of300°C/h (12) -----, one porcelain crucible, Coors 230-000 (about... 

Figure 2.29. Thermowetl and sample temperature in the decomposition of CaC204 H20 in nitrogen on a Chevenard thermobalance. One-gram sample heated at 300°C/h at a nitrogen flow rate of 400 ml/min. o, Thermowell temperature (+10° cal) b, sample temperature (36) (/) CaCjO, - H20 - CaC204 + HzO (2) CaC204 -> CaC03 + CO (3) CaCO -> CaO + C02.

Newkirk (12) found that if the balance mechanism of the Chevenard thermobalance was not properly thermally shielded, the oil in the dash pots became warm, causing an apparent mass-gain due to the decreased buoyancy of the oil. In the latest model of this balance, the oil dash pots have been replaced by a magnetic damping device. 

Figure 4. Principle of Chevenard thermobalance. C—counterweight F-—furnace /—fulcrum L—flight source M— mirror S—crucible support T—photographic recording drum.

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,... 

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. 

Kiss (88.89) coupled a Chevenard-type thermobalance with a type DR 10 spectrophotometer the evolved gases from ihe thermobalance were passed through a 10-cm-long infrared cell. A meihod was developed in which either... 

One of the factors limiting the accuracy of earlier models of thermobalances was the fact that the agate knife-edges and bearing surfaces on the balances were not sufficiently hard to withstand the continuous operation demanded. This led to the development of the Chevenard type of thermobalance, shown diagrammatically in Figure 4, where the agate system is replaced by a four-wire suspension (Duval [1963]). 

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