Simultaneous mass and temperature-change

Timken, M. D., Chen, J. K. and Brill, T. B. (1990). Thermal decomposition of energetic materials. 37. SMATCH FT-IR (simultaneous mass and temperature-change FT-IR) spectroscopy. Applied Spectrosc., 44, 701-6. [148]... 

Variations on the theme of fast thermolysis/FTIR spectroscopy include temperature profiling/FTIR spectroscopy, in which the temperature changes of the condensed phase are measured simultaneously with the gas evolution fast-heat-and-hold/FTIR spectroscopy [378], in which isothermal decomposition is studied following rapid heating to a selected temperature and Simultaneous Mass and Temperature Change (SMATCH)/FTIR spectroscopy [379], which has clearly established the connection between the microscale fast thermolysis approach and steady-state combustion of the bulk material. In T-jump/FTIR spectroscopy the thermal decomposition of a material can be studied isothermally after heating at 2000°C/s [376]. 

Since TG and DTA complement each other, it is an obvious move to attempt both investigations simultaneously [173]. TG-DTA measures mass and energy changes as a function of temperature or time. Depending on the atmospheric conditions (vacuum, inert or air conditions) thermal or oxidative stability is measured. Typical TG-DTA... 

Humidification and dehumidification involve the transfer of material between a pure liquid phase and a fixed gas that is insoluble in the liquid. These operations are somewhat simpler than those for absorption and stripping, for when the liquid contains only one component, there are no concentration gradients and no resistance to transfer in the liquid phase. On the other hand, both heat transfer and mass transfer are important and influence one another. In previous chapters they have been treated separately here and in drying of solids (discussed in Chap. 24) they occur together, and concentration and temperature change simultaneously. 

The main difference between metals and polymers is related to the fact that transitions from one state to another in polymers occur (as a result of changing of environmental conditions, primarily temperature) not as jumps but continuously. This leads to the absence of a clearly defined line or transition front. Additionally, because of die low heat and temperature conductivity of polymeric materials, a change in material properties may take place over a large volume,or even simultaneously throughout the whole mass of an article, although the local transition rates and degrees of conversion may be different. Thus it is necessary to develop a macrokinetic model of the transition. This model must describe the combined effects of non-stationary heat transfer and reaction kinetics and is used to determine the temperature and conversion fields. 

Simultaneous measurements of the rate of change, temperature and composition of the reacting fluid can be reliably carried out only in a reactor where gradients of temperature and/or composition of the fluid phase are absent or vanish in the limit of suitable operating conditions. The determination of specific quantities such as catalytic activity from observations on a reactor system where composition and temperature depend on position in the reactor requires that the distribution of reaction rate, temperature and compositions in the reactor are measured or obtained from a mathematical model, representing the interaction of chemical reaction, mass-transfer and heat-transfer in the reactor. The model and its underlying assumptions should be specified when specific rate parameters are obtained in this way. 

One needs to describe nonequilibrium phenomena by the simultaneous consideration of mass, temperature, and time of the local states while accounting for the given time and energy dissipation due to temperature changes. The time scale over which microscopic changes occm is much smaller than the time scale associated with macroscopic changes. Temperature fluctuations in a microstate will be different from those in a macroscopic state in which the properties are the averages of many microstate values. 

Solution of Equation (10.2.1) provides the pressure, temperature, and concentration profiles along the axial dimension of the reactor. The solution of Equation (10.2.1) requires the use of numerical techniques. If the linear velocity is not a function of z [as illustrated in Equation (10.2.1)], then the momentum balance can be solved independently of the mass and energy balances. If such is not the case (e.g., large mole change with reaction), then all three balances must be solved simultaneously. 

Simultaneous thermogravimetric and differential thermal analysis (TG/DTA) is a useful technique for the solid-state characterization of pharmaceutical materials. Such characterization includes the determinations of loss on drying, phase transition temperatures, thermal stability, and whether or not water is bound or unbound. TG/DTA combines the measurement of a change in mass of a sample as a function of temperature (TG) with the temperature difference of a sample compared with an inert reference material as a function of temperature (DTA). 

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