Dissociating plasmas

Potapkin et al. [54] showed this reaction to be a two-stage process, whereby H2S was first dissociated plasma-chemically and hydrogen produced. The hydrogen could then react with C02 to generate water and CO. The overall effect of C02 was to increase the conversion of H2S, but to reduce the hydrogen yield. 

Moiecuiar Dissociation Plasma Protein Weight Constant Half-Life Binding Trade Name (daitons) (nmoi/L) (hours) (%) ... 

Dissociation (plasma chemistry) The separation of a molecule into two or more fragments due to collision (Example collision of an electron with a molecule) or the adsorption of energy (Example photodissociation). See also Fragmentation. 

The SiH radical is tlie dominant growtli precursor for tlie fonnation of tlie a-Si H films in a low-temperature silane plasma [32]. Silane molecules are dissociated by energetic plasma electrons ... 

Gorse C and Capitelli M 1996 Non-equilibrium vibrational, electronic and dissociation kinetics in molecular plasmas and their coupling with the electron energy distribution function NATO ASI Series C 482 437-49... 

Decomposition of Zircon. Zircon sand is inert and refractory. Therefore the first extractive step is to convert the zirconium and hafnium portions into active forms amenable to the subsequent processing scheme. For the production of hafnium, this is done in the United States by carbochlorination as shown in Figure 1. In the Ukraine, fluorosiUcate fusion is used. Caustic fusion is the usual starting procedure for the production of aqueous zirconium chemicals, which usually does not involve hafnium separation. Other methods of decomposing zircon such as plasma dissociation or lime fusions are used for production of some grades of zirconium oxide. 

A considerable amount of carbon is formed in the reactor in an arc process, but this can be gready reduced by using an auxiUary gas as a heat carrier. Hydrogen is a most suitable vehicle because of its abiUty to dissociate into very mobile reactive atoms. This type of processing is referred to as a plasma process and it has been developed to industrial scale, eg, the Hoechst WLP process. A very important feature of a plasma process is its abiUty to produce acetylene from heavy feedstocks (even from cmde oil), without the excessive carbon formation of a straight arc process. The speed of mixing plasma and feedstock is critical (6). 

Chemical removal of surface material is produced through standard bond-breaking reactions. Typically chlorofluorocarbons (CECs) have been used, eg, CECl, CE2CI2, CE Cl, CE4, CHE, C2C1E. Eor example, CE dissociates into E atoms and fluorinated fragments of CE in a plasma ... 

After inorganic mercuric salts are absorbed and dissociated into the body fluids and in the blood, they are distributed between the plasma and erythrocytes. Aryl mercuric compounds and alkoxy mercuric compounds are decomposed to mercuric ions, which behave similarly. 

The molecules that are dissociated and the atoms that are ionized during plasma production can be in any state at the start. Steady-state plasmas are formed most often from gases, although Hquids, such as volatile organics, and soHds are also used. Gases and soHds routinely serve as sources of material in pulsed plasma work. 

The relative abundance of neutral SiH and H2 species have been measured as a function of power, pressure, flow rate, and dilution. For low power levels, eg, 5 W, up to 50% of the SiH gas is dissociated and the percentage increases to 80% for a power of 50 W. The decomposition of SiH gas proceeds more readily with lower flow rates. These observations, coupled with infrared (ir) measurements performed on the films, suggest that deposition under conditions in which the silane gas is not entirely decomposed leads to a majority of SiH units, whereas those deposited under conditions in which silane is strongly dissociated contain a majority of dihydride units leading to a deterioration of the semiconductor. Also, when the dwell time of SiH in the plasma region increases, the resultant film exhibits a pronounced peak at 2090 cm from the ir spectra corresponding to S1H2 inclusion. 

Table 1. Electron Impact Dissociative Processes Operative in Silane Plasma ...

Table 2. Reactions Within Plasma During Transport of Species Produced by Electron Impact Dissociation of Silane...

Eree radicals such as E can be used to etch siUcon at ambient temperature. The radicals are formed by dissociating compounds such as CE in a plasma. Thus,... 

Zircon is synthesized by heating a mixture of zirconium oxide and silicon oxide to 1500°C for several hours (163). The corresponding hafnium silicate, hafnon, has been synthesized also. Zircon can be dissociated into the respective oxides by heating above 1540°C and rapidly quenching to prevent recombination. Commercially, this is done bypassing closely sized zircon through a streaming arc plasma (38). 

In 1982 a study of the usefulness of DBBF in the production of a blood substitute was reported (99). A single modification achieved the dual goals of reduced oxygen affinity and restricted tetramer—dimer dissociation. This work was confirmed in 1987 (98). The product, called aa-hemoglobin, was formulated in Ringer s lactate. P q under physiologic conditions is 3.7 kPa (28.0 torr). Hill s parameter is 2.2, and the Bohr effect was reduced (100). Plasma retention was increased, and the product appeared to be less heterogeneous than some of the other derivatives under study. Its production was scaled up by Baxter Healthcare Corp., under contract to the U.S. Army. 

Chain reactions such as those described above, in which atomic species or radicals play a rate-determining part in a series of sequential reactions, are nearly always present in processes for the preparation of thin films by die decomposition of gaseous molecules. This may be achieved by thermal dissociation, by radiation decomposition (photochemical decomposition), or by electron bombardment, either by beams of elecuons or in plasmas. The molecules involved cover a wide range from simple diatomic molecules which dissociate to atoms, to organometallic species with complex dissociation patterns. The... 

All of the atomic species which may be produced by photon decomposition are present in plasma as well as the ionized states. The number of possible reactions is therefore also increased. As an example, die plasma decomposition of silane, SiH4, leads to the formation of the species, SiH3, SiHa, H, SiH, SiH3+ and H2+. Recombination reactions may occur between the ionized states and electrons to produce dissociated molecules either direcdy, or tlrrough the intermediate formation of excited state molecules. 

FIGURE 15.21 Hormone (H) binding to its receptor (R) creates a hormone receptor complex (H R) that catalyzes GDP-GTP exchange on the o -subunit of the heterotrimer G protein (G ), replacing GDP with GTP. The G -subunit with GTP bound dissociates from the /37-subunits and binds to adenylyl cyclase (AC). AC becomes active upon association with G GTP and catalyzes the formation of cAMP from ATP. With time, the intrinsic GTPase activity of the G -subunit hydrolyzes the bound GTP, forming GDP this leads to dissociation of G GDP from AC, reassociation of G with the /Sy subunits, and cessation of AC activity. AC and the hormone receptor H are integral plasma membrane proteins G and G are membrane-anchored proteins. 

Photochemical dissociation, 202 Photolyses, 200 Pine s wave function, 306 Plasma frequency, 306 Plasma model, 207, 304, 306, 318, 319, 323... 

Leptin is a cytokine produced and secreted by adipose tissue in proportion to the body fat content [3]. Mice and humans lacking leptin or its receptor develop a severe hyperphagia and a dramatic degree of obesity which is considerably more pronounced than that of the NDRKO mouse. Thus, leptin is the key adiposity signal in rodents and humans. Leptin secretion appears to reflect the metabolic status of the adipocyte rather than the sheer size of triglyceride deposits, and leptin levels may transiently be dissociated from total body fat. Nonetheless, over the course of a day with unrestricted food supply, plasma leptin levels reliably reflect the amount of total body fat. Local administration of leptin into the brain results in reduced food intake. The vast majority of patients with obesity have elevated serum levels of leptin. Thus, it is believed that the polygenic obesity is due to leptin resistance rather than to inadequate leptin secretion, or to a reduced blood/brain transport of the cytokine. 

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