Plasma chemical method

The plasma chemical method for the thermal decomposition of solutions has been preferred over gas-flame heating for the following reasons [532] ... 

The unique advantage of the plasma chemical method is the ability to collect the condensate, which can be used for raw material decomposition or even liquid-liquid extraction processes. The condensate consists of a hydrofluoric acid solution, the concentration of which can be adjusted by controlling the heat exchanger temperature according to a binary diagram of the HF - H20 system [534]. For instance, at a temperature of 80-100°C, the condensate composition corresponds to a 30-33% wt. HF solution. 

Figure 3. The non-forming carbon fibers bundle (a) and its field emission image (c). The carbon fibers bundle etched by plasma-chemical method (b) and its field emission image (d).

Synthetic, Plasma Chemical Method, Original and Water-Washed... 

The plasma-chemical method produces nitric acid as a by-product which can be reused to form more of the nitrate solution for further plasma decomposition (7-104). The high-qrrahty ceramics produced in plasma are of special interest for the synthesis of... 

Alternatively, gas-phase doping can be achieved by plasma-chemical methods (Bauer and Bilger, 1982). Interaction of the plasma or of the neutral gas with surfaces containing dopants is used to introduce dopant atoms into the gas phase. In the case of doping by ion implantation, dopant ions are accelerated to an energy of typically 10-100 keV and are allowed to impinge... 

The plasma chemical method is relatively often used now for preparing many nanopowders for production of refractory compounds (nitrides, oxides, carboni-trides, and their compositions) [6]. The process of preparing aluminum nitride nanopowder by this technique is based on evaporation of aluminum in high temperature nitrogen flow, following chemical interaction, and subsequent condensation of reaction product. It means that this process could be considered as a kind of combustion synthesis. 

Below are presented some general conclusions on the characteristics and prospects of the plasma-chemical methods for the conversion of methane from the review [212] ... 

More recently, new surface treatments using non-isothermal, low-temperature plasma have drawn a great deal of interest. Plasma-chemical methods suitable for coating and surface treatment replace conventional galvanic methods, because they are not as harmful to the environment as the classical ones (see Section 5.4.2). 

The concept of macroscopic kinetics avoids the difficulties of microscopic kinetics [46, 47] This method allows a very compact description of different non-thennal plasma chemical reactors working with continuous gas flows or closed reactor systems. The state of the plasma chemical reaction is investigated, not in the active plasma zone, but... 

In plasma chemical vapor deposition (PCVD), the starting materials are typically SiCl, O2, 2 6 GeCl (see Plasma technology). Plasma chemical vapor deposition is similar to MCVD in that the reactants are carried into a hoUow siUca tube, but PCVD uses a moving microwave cavity rather than a torch. The plasma formed inside the microwave cavity results in the deposition of a compact glass layer along the inner wall of the tube. The temperatures involved in PCVD are lower than those in MCVD, and no oxide soots are formed. Also, the PCVD method is not affected by the heat capacities or thermal conductivities of the deposits. 

The first experiments on the plasma chemical decomposition of fluoride solutions containing tantalum or niobium to obtain tantalum and niobium oxides were reported about fifteen years ago [524]. Subsequent publications were devoted to further development and expansion of the method for other refractory rare metals such as titanium and zirconium [525 - 532]. 

The plasma chemical decomposition method is based on rapid heating, decomposition and hydrolysis of fluoride compounds to obtain powdered oxides following interaction with water. Rakov and Teslenko [533] showed that the following hydrolysis equilibrium... 

Niobium oxide obtained by plasma chemical decomposition is an ultra-fine powder with a specific surface area, as determined by the BET method, of about 20-30 m2/g. The estimated average particle size does not exceed 0.1 pm. 

This method is one of the dry methods in which no chemical reaction is involved. Preparation of ultrafine particles by physical vapor deposition (PVD) dose not require washing and calcination, which are indispensable for chemical preparation such as in CP and DP methods. As waste water and waste gases are not by-produced, the arc plasma (AP) method is expected to grow in popularity as one of the industrial production methods for gold catalysts and as a clean preparation method. 

Soltanpour PN, Johnson GW, Workman SM, Jones JB, Jr., Miller RO. Inductively coupled plasma emission spectrometry and inductively coupled plasma-mass spectroscopy. In Bartels JM (ed.), Methods of Soil Analysis Part 3 Chemical Methods. Madison, WI Soil Science Society of America and Agronomy Society of America 1996, pp. 91-139. 

Cohn, and their associates in Harvard during World War II in their efforts to isolate serum proteins for clinical use. Traces of the organic solvents were removed during the freeze-drying of the different preparations. In the U.K. plasma fibrinogen was obtained by Kekwick and his colleagues by low-temperature precipitation with ether. Serum proteins acquired by these chemical methods were mixtures. 

The various methods of preparation employed to prepare nanoscale clusters include evaporation in inert-gas atmosphere, laser pyrolysis, sputtering techniques, mechanical grinding, plasma techniques and chemical methods (Hadjipanyas Siegel, 1994). In Table 3.5, we list typical materials prepared by inert-gas evaporation, sputtering and chemical methods. Nanoparticles of oxide materials can be prepared by the oxidation of fine metal particles, by spray techniques, by precipitation methods (involving the adjustment of reaction conditions, pH etc) or by the sol-gel method. Nanomaterials based on carbon nanotubes (see Chapter 1) have been prepared. For example, nanorods of metal carbides can be made by the reaction of volatile oxides or halides with the nanotubes (Dai et al., 1995). 

Wet chemical methods involve sophisticated sample preparation and standardization with National Bureau of Standards reference materials but are not difficult for the analytical chemist nor necessarily time consuming (Figure 1). The time from sample preparation to final results for various analytical methods, such as GFAA (graphite furnace atomic absorption), ICP (inductively coupled plasma spectroscopy), ICP-MS (ICP-mass spectrometry), and colorimetry, ranges from 0.5 to 5.0 h, depending on the technique used. Colorimetry is the method of choice because of its extreme accuracy. Typical results of the colorimetric analysis of doped oxides are shown in Tables I and II, which show the accuracy and precision of the measurements. 

Metals contained in samples are determined by a wide variety of analytical methods. Bulk metals, such as copper in brass or iron in steel, can be analyzed readily by chemical methods such as gravimetry or electrochemistry. However, many metal determinations are for smaller, or trace, quantities. These are determined by various spectroscopic or chromatographic methods, such as atomic absorbance spectrometry using flame (FAAS) or graphite furnace (GFAAS) atomization, atomic emission spectrometry (AES), inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), x-ray fluorescence (XRF), and ion chromatography (IC). 

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