Heating rate programme

Figure 5.4-57. Programmable DTA plot.s for variou.s heating rates 4-nitrobenzoic acid (reprinted from Grewer (1994), Thermal hazards of chemical reactions , Copyright (1994) with permission from Elsevier Science). 

The mechanical programmers were replaced by electronic programmers. These depended mainly on different solid state time-logic RC circuits to increase the power to the column oven to supply the desired heating rates. This allowed multilinear pro-... 

At SINTEF charcoals from birch and oak wood were produced at atmospheric pressure in a 3.7 L stainless steel retort placed in a Nabertherm muffle oven. The muffle oven is equipped with a programmable temperature controller, which provides control of the heating rate, temperature, and reaction time. The retort has a capacity of proximately 1 kg of dry wood per batch. The typical dimensions of the feedstock pieces were 3 cm x 3 cm x 5 cm. During heating and cooling, the retort was purged with Nj to prevent air leakage into the system. 

Organic contaminants were analyzed by gas chromatography using a CHROMPACK CP 9000 model and a DB-1 column (30 m x 0.25 mm, 0.32 pm film thickness) with the following temperature programme initial 120 °C, heating rate 5 C, final 320 C, hold for 10 minutes. For calibration solutions with two concentration levels (10 and 100 pg/ml), following DIN 38402, were used. Fluoroanthene was taken as internal standard. 

TPD experiments were performed using an NEVA NAG 110 mass spectrometer with a glass-made vacuum system. Prior to every TPD measurement the sample was heated up at 1173K for Ih under vacuum (10 torr) to remove the adsorbed impurities. The typical water vapor adsorption pressure was around 20 torr and the heating rate was 10 l min. The temperature programmer used in our experiments was Chino, model KP. 

In so-called power-compensation DSC, sample and reference are completely isolated from each other (Fig. 3.2). Both the sample and reference crucible have their own heating element and temperature sensing element. With the aid of a temperature programmer, both sample and reference are heated and always have the same temperature. As soon as changes in the sample occur, extra (or less) heat will be needed to maintain the set heating rate. With the aid of specialized electronic circuitry, extra (or less) power is now sent to the sample holder in order to keep the temperature difference zero. In this way, power and consequently heat flow and enthalpy changes are measured. 

A commercially available temperature programmer, dc amplifier, and two-point recorder were employed. Furnace heating rates of from 0 to 30cC/min were possible. 

These controlling features for the Rheovibron , a combination of multiprogrammer, programmable calculator, and lock-in analyzer, are used to provide a programmed heating rate, continuous sample tensioning, measurement of the phase angle between stress and strain, and acquisition and reduction of the data. 

The operation of the furnace is controlled by a temperature programmer which ensures a linear heating profile over a range of heating rates. A variety of electronic control circuits based on the PID (proportional integral differential) principle are used to provide linear heating profiles. The parameters of the PID circuit are normally set by the manufacturer for optimum performance under... 

Ideally, integration of equation 5.9 should reproduce the TG curve of a given sample. Integration can be performed easily if a hyperbolic temperature programme of the form IT=r-st is used, where r and s are constants. For a linear heating programme with constant heating rate, (j), equation 5.9 becomes... 

Heating rate Rate of temperature increase in response to a temperature programme. 

This provides one way of measuring heat capacity in a linear rising temperature experiment one simply divides the heatflow by the heating rate. If the temperature programme is replaced by one comprising a linear temperature ramp modulated by a sine wave, this can be expressed as... 

In an MTDSC experiment, a repeated temperature modulation is superimposed on the normal linear temperature programme [1-5,74]. The modulation amplitude and frequency, and the underlying heating rate can be chosen independently. 

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