Heating rates, thermogravimetry

Comparison of isothermal and8E/min heating rate thermogravimetry of a sample of PrOj analyzed in oxygen... 

The heating rate has only a small effect when a fast reversible reaction is considered. The points of inflexion B and C obtained on the thermogravimetric curve for copper sulphate pentahydrate (Fig. 11.2) may be resolved into a plateau if a slower heating rate is used. Hence the detection of intermediate compounds by thermogravimetry is very dependent upon the heating rate employed. 

This paper reviews recycling technologies of PMMA waste, its applications and its markets. It relates in detail experimentation on thermal and oxidative depolymerisation of PMMA scrap, under nitrogen and oxygen atmospheres, at different heating rates by thermogravimetry and differential scanning calorimetry techniques. 15 refs. 

Thermogravimetry Curves of Bromocriptine Mesilate, each at a heating rate of 20 C/min. and a Nitrogen Flow of 15 ml/min. 

Differential thermal analysis (DTA) was performed in air with an OD-102 Derivatograph (MOM, Hungary) using 100 mg samples at a heating rate of 10°C/min. Differential thermogravimetry (DTG) and thermogravimetry... 

A typical mass loss curve for the three heating rates is shown in Figure 2. The fractional residual (char) mass at 600°C is given for each species in Table I. Considerable data are available from the 1iterature particularly from thermogravimetry studies, on the influence of specimen and heating parameters on mass loss characteristics. 

The H/C ratio of the coke deposits was quantified by temperature programmed oxidation (TPO) in a 1 % oxygen helium mixture. Temperature was raised to 850° C at a heating rate of 10° min 1. The calculations of the H/C ratio involved the results from the measurements of carbon dioxide production and oxygen uptake (according to Ref. [8]). Coke deposits were also characterized by thermogravimetry and transmission electron microscopy. 

Thermogravimetry (TG) data were obtained on the NH4+- and H30+-exchanged ZSM-5 samples, as well as on a separately prepared NH -exchanged sample of similar composition, for confirmation purposes. A duPont Model 951 thermogravimetric analyzer was used in conjunction with a Model 990 Recorder-Controller. The TG curves were obtained on approximately 25 mg samples, at a heating rate of 10°C per minute, and under flowing air at a rate of 38 cnP per minute. 

The relation of weight-loss and ten rature variation at pine sawdust pyrolysis by thermogravimetry is shown in Fig. 2, where the continuous line is predicted result by model and the symbols are the experimental values. As constant heating rate is considered, the correlation of weight loss and tenq erature variation represents weight-loss evolution history. As can be seen from this figure, the kinetic model predicts well the weight-loss and tenqierature variation. 

Thermal behaviour of the substances was investigated by thermogravimetry (TG) with a Derivatograph-Q instrument. The powdered samples were placed on a platinum sample holder and studied under the following conditions mass of sample 100 mg, heating rate 10 degree/min, temperature range 300 to 1270 K. 

Thermogravimetry. Thermogravimetric analysis (TGA/DTG) was performed on a Seiko instrument. The samples were heated in platinum crucibles up to 1000°C with a heating rate of 3 C/mn in 60 mL/min under flowing dry air. 

Mass sensitivity as a critical parameter in thermogravimetry has been considered by Cahn and Peterson (47). Greater sensitivity of the thermobalance permits the use of smaller samples, with improved determination of mass plateaus of intermediate compounds and the use of faster heating rates. However, thermobalances with sensitivities greater than I jig can be attained only under two conditions (48) (1) sample Hangdown tubes of 9 mm inside diameter or less if used at atmospheric pressure and (2) larger-diameter tubes if used at reduced pressure (41 mm id at 150 Torr). Unfortunately, the use of the 9-mm tubes limits the sample size to 15-20 mg. 

Figure 10. Thermogravimetry of weddelite (CaC204.2H20) (heating rate 10 °C min in air)...

Thermogravimetry-mass spectrometry was done with a Perkin Elmer TAS 2 TGA connected by a capillary transfer line to a Hewlett Packard mass selective detector. A heating rate of 40 C7min was used so that the volatiles would rapidly desorb from the sample. Helium was used as a carrier gas at a pressure of 40 psi. The time traces of water and NMP were done at mass to charge ratios of 18 and 99 respectively. 

Figure 3. Thermogravimetry curves recorded on a commercial polycarbosilane (Dow Corning X9-6348) in Ar flow (lOOcm min ) at different heating rates.

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