Thermal processes, basic principles

In Section 13.2, we introduce the materials used in OLEDs. The most obvious classification of the organic materials used in OLEDs is small molecule versus polymer. This distinction relates more to the processing methods used than to the basic principles of operation of the final device. Small molecule materials are typically coated by thermal evaporation in vacuum, whereas polymers are usually spin-coated from solution. Vacuum evaporation lends itself to easy coaling of successive layers. With solution processing, one must consider the compatibility of each layer with the solvents used for coating subsequent layers. Increasingly, multilayered polymer devices arc being described in the literature and, naturally, hybrid devices with layers of both polymer and small molecule have been made. 

This chapter contains a discussion of two intermediate level problems in chemical reactor design that indicate how the principles developed in previous chapters are applied in making preliminary design calculations for industrial scale units. The problems considered are the thermal cracking of propane in a tubular reactor and the production of phthalic anhydride in a fixed bed catalytic reactor. Space limitations preclude detailed case studies of these problems. In such studies one would systematically vary all relevant process parameters to arrive at an optimum reactor design. However, sufficient detail is provided within the illustrative problems to indicate the basic principles involved and to make it easy to extend the analysis to studies of other process variables. The conditions employed in these problems are not necessarily those used in current industrial practice, since the data are based on literature values that date back some years. 

Hoffmann, W. (2000). "The Basic Principles of Thermal Process Safety Towards a Better Communication Between Safety Experts and Process Chemists." Process Chem. Pharm. Ind., 389-408. 

The basic principles describing the efFects of CT complexes on the energy profile along the reaction coordinate stem from the theory of electron transfer. Redox processes may occur (i) as ground-state thermal reactions, (ii) by direct irradiation of the CT band, and (iii) upon photoexcitation of one of the redox partners followed by diffusional complex formation [4, 24], as depicted in Chart 3. 

A. G. Buekens and J. G. Schoeters, Basic principles of waste pyrolysis and review of Enropean processes.. In J. L. Jones and S. B. Radding (eds) Thermal Conversion of Solid Wastes and Biomass, ACS Symposium Series 130, American Chemical Society, Washington DC, 1980. 

Although MBE continues to be the best technique for controlled deposition of thin layers (10-100 A) of materials, the MOCVD process does offer the advantage for rapid deposition over large areas of substrates. The basic principles of the MOCVD technique is the thermal decomposition of volatile molecular precursors to the desired combined form (or even the constituent metal itself) on a selected substrate at not too high a temperature. In addition to the volatility of the precursor and its facile decomposition to the desired combined form for deposition, the whole operation should not, from the practical point of view, involve any toxic/hazardous byproducts, that might entail any environmental problems. 

The analytical chemist will find Chapters 4 and 5 most beneficial to a fundamental understanding of the basic principles of the ECD. The ECD is somewhat simple to operate to an experienced analyst, but the process of electron capture can be quite complex. The authors have done an excellent job in presenting these principles in a very understandable fashion. With the knowledge from these chapters the analytical chemist can use the ECD to obtain fundamental properties associated with thermal attachment to molecules. 

Tompkins (1978) concentrates on the fundamental and experimental aspects of the chemisorption of gases on metals. The book covers techniques for the preparation and maintenance of clean metal surfaces, the basic principles of the adsorption process, thermal accommodation and molecular beam scattering, desorption phenomena, adsorption isotherms, heats of chemisorption, thermodynamics of chemisorption, statistical thermodynamics of adsorption, electronic theory of metals, electronic theory of metal surfaces, perturbation of surface electronic properties by chemisorption, low energy electron diffraction (LEED), infra-red spectroscopy of chemisorbed molecules, field emmission microscopy, field ion microscopy, mobility of species, electron impact auger spectroscopy. X-ray and ultra-violet photoelectron spectroscopy, ion neutralization spectroscopy, electron energy loss spectroscopy, appearance potential spectroscopy, electronic properties of adsorbed layers. 

All thermal separation processes follow this order of events. The basic principles of thermal separation processes Me now formulated and will be discussed in detail. 

The basic principles of mass transfer are discussed in detail in [1.95-1.97]. Thermal separation processes are actually mass transfer processes matter is transported between phases and across phase interfaces. Mass transfer is caused by differences in concentration within a phase and by disturbances of the phase equilibrium. The time taken to return to the phase equilibrium depends mainly on mass transfer, but also on heat transfer (heat is transported not only by convection and radiation at higher temperature, but also by mass). For the design of thermal separation processes, along with a knowledge of phase equilibria, it is also important to have a detailed understanding of how equilibrium is reached and the time required, taking into account restrictions in the mass transfer rate. 

Process simulation Process simulation software is used for the planning and layout of processes in entire systems or plant units. The range of competence of these software systems typically comprises the calculation of procedural basic operations, mainly in chemical and thermal process engineering according to the principle of the conservation equations for mass, matter, momentum and enthalpy in consideration of the principles of thermodynamics. A typical example is the calculation of the matter and heat transmission in rectification columns. Here, the acquisition of correspondingly reliable matter data is often difficult. Therefore, the simulation results are generally accompanied by the respective experimental studies. 

AG Buekens, JG Schoeters, SPEJ 29 41, 1973 Basic Principles of Waste Pyrolysis, Review of European Processes in Thermal Conversion of Solid Wastes and Biomass. ACS Symp. Ser Vol. 30, 1980, p 397. 

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