Plasma equilibrium

A brief description of a low-density non-equilibrium plasma is given followed by a review of its characteristic features and of tire relevant collisionprocesses in tire plasma. Principles for tire generation of plasmas in teclmical devices are discussed and examples of important plasma chemical processes and tlieir technical applications are presented. 

A non-tliennal, non-equilibrium plasma is characterized by an electron temperature much larger tlian tire ion temperature and tire neutral gas temperature (T T. Typical non-tliennal, non-equilibrium plasmas... 

The talk will briefly review some of these developments ranging from high temperature equilibrium plasmas to cool plasmas, PECVD, ion implantation, ion beam mixing and ion assisted etching and deposition. Brief consideration will also be given to sputtering and ionised cluster beam deposition techniques in inorganic synthesis. 

Low Temperature (Non Equilibrium) Plasmas The rigorous classification of plasma treatments is difficult, however, from the viewpoint of the treated surface there are three broad categories ... 

Nozaki, T., Kimura, Y., and Okazaki, K., Carbon nanotubes and hydrogen co-production from methane using atmospheric pressure non-equilibrium plasma, Proc. 16th ESCAMPIG and 5th... 

Since pyrolysis converts waste into CO, CH4, and H2, the product gases can be processed in an atmospheric pressure non-equilibrium plasma reformer to improve the energy-recovery potential of the product gas. Energy-recovery options include heat and chemical energy recovery. 

In non-thermal plasmas, also known as non-equilibrium plasmas, there is a significant difference in temperature between electrons and ions/neutrals. Non-thermal plasmas can initiate a chemical reaction even at relatively low temperatures by generating free radicals (i.e., H, O, OH, CH3, etc), which propagate the reaction. 

Surface Modification. Plasma surface modification can include surface cleaning, surface activation, heat treatments, and plasma polymerization. Surface deaning and surface activation are usually performed for enhanced joining of materials (see Metal SURFACE treatments). Plasma heat treatments are not, however, limited to high temperature equilibrium plasmas on metals. Heat treatments of oiganic materials are also possible. Plasma polymerization crosses the boundaries between surface modification and materials production by producing materials often not available by any other method. In many cases these new materials can be applied direcdy to a substrate, thus modifying the substrate in a novel way. 

To characterize the kinetic stabilities of complexes, the rate constants should be used, determined for the exchange reactions occurring between the complexes and endogenous metal ions (e.g. Cu2+ and Zn2+). Similarly to the equilibrium plasma models, the development of a kinetic model is needed for a better understanding of the relation between the extent of in vivo dissociation and the parameters characterizing the rates of dissociation, the rates of distribution in the extracellular space and the rates of excretion of the Gd3+ complexes. 

Such approaches rely on so-called relative sensitivity coefficients (RSFs), ratios of the difference between the sensitivity of various elements, and these cannot be considered as fundamental constants. In fact, they provide no more than a quantitative measurement of the deviation of the method s result from the amount of substance, as issued from primary methods (if available). Other near-equilibrium plasma methods for the analysis of solids (glow discharge, sputtered neutrals secondary ion mass spectrometry) produce quite acceptable results for analytical practice. 

We will now develop the transport equations in L-space from the above Green functions. Following the Keldysh approach in //-space, the transport equations for non-equilibrium plasmas and radiation have been given by DuBois [29]. A similar transport equation for a system of ions may be found in Kwok [30], which is based on the Green function associated with ion positions. In a separate paper [31], we will derive the appropriate transport equations for the coupled system of electrons, ions, and electromagnetic fields. 

Dissociation of molecular oxygen in non-equilibrium plasmas has been subject of numerous experimental investigations, mostly at pressures below about lOmbar26-31 ... 

A plasma is an efficient way to dissociate gas molecules to produce non-equilibnum concentrations of gas-phase species, such as the high concentrations of atomic hydrogen needed for diamond growth. Plasmas can be generated by a number of energy sources (microwave, radio-frequency, or direct-current electric fields), and can be either cold (non-isothermal, or nonequilibrium plasmas) or hot (isothermal, or equilibrium plasmas). The major characteristics of these plasmas are summarized in Table 3. 

Continuous Infusion (IV) Steady state (equilibrium) plasma drug concentration is reached after continuous infusion for 4-5 half-lives. c o CD 2X mg/hour... 

The temperatiue difference between electrons and heavy neutral particles due to Joule heating in the collisional weakly ionized plasma is conventionally proportional to the sqirare of the ratio of the electric field ( ) to the pressure p). Only in the case of small values of E/p do the temperatiues of electrons and heavy particles approach each other. Thus, this is a basic requirement for local thermodynamic equilibrium (LTE) in plasma. Additionally, LTE conditions require chemical equilibrium as well as restrictions on the gradients. The LTE plasma follows the maj or laws of equilibrium thermodynamics and canbe characterized by a single temperature at each point of space. Ionization and chemical processes in such plasmas are determined by temperature (and only indirectly by the electric fields through Joule heating). The quasi-equilibrium plasma of this kind is usually called thermal plasma. Thermal plasmas in nature canbe represented by solar plasma (Fig. 1-4). 

Numerous plasmas exist very far from the thermodynamic equilibrium and are characterized by multiple different temperatures related to different plasma particles and different degrees of freedom. It is the electron temperature that often significantly exceeds that of heavy particles (7 > To). Ionization and chemical processes in such non-equilibrium plasmas are directly determined by electron temperature and, therefore, are not so sensitive to thermal processes and temperature of the gas. The non-equilibrium plasma of this kind is usually called non-thermal plasma. An example of non-thermal plasmas in nature is the aurora borealis (Fig. 1-2). 

The non-equilibrium EEDF for different discharge systems and different plasma conditions will be discussed in Chapter 3. Sometimes, however (even in non-equilibrium plasmas), the EEDF is determined mostly by the electron temperature and, therefore, can be described by the quasi-equilibrium Maxwell-Boltzmarm distribution function ... 

The three-body recombination process (2-37) is the most important one in high-density quasi-equilibrium plasmas. Concentrations of molecular ions are very low in this case (because of thermal dissociation) for the fast mechanism of dissociative recombination described earlier, and the three-body reaction dominates. The recombination process starts with the three-body capture of an electron by a positive ion and formation of a highly excited atom with a binding energy of about. This highly excited atom then gradually loses energy in electron impacts. The three-body electron-ion recombination process (2-37) is a reverse one with respect to the stepwise ionization (see Section 2.1.7). For this reason, the rate coefficient of the recombination can be derived from the stepwise ionization rate coefficient kl (2-25) and from the Saha thermodynamic equation for ionization/recombination balance (see Chapter 3) ... 

The Einbinder formula can be generalized to non-equilibrium plasma conditions when the electron temperature exceeds that of aerosol particles (Tj, > T ) (Fridman, 1976) ... 

A detailed description of non-equilibrium plasma-chemical systems and processes generally requires an application of kinetic models. The application of statistical models leads sometimes to significant errors (Slovetsky, 1980). In some specific systems, however, statistical approaches can be not only simple but also quite successful in describing non-equilibrium plasma, which is discussed next. 

A second example is related to strongly non-equilibrium plasma gasification processes,... 

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