Chemical vapor condensation method

Ullrafine particles (UFPs) of metal and semiconductor nitrides have been synthesized by two major techniques one is the reactive gas condensation method, and the other is the chemical vapor condensation method. The former is modified from the so-called gas condensation method (or gas-evaporation method) (13), and a surrounding gas such as N2 or NII2 is used in the evaporation chamber instead of inert gases. Plasma generation has been widely adopted in order to enhance the nitridation in the particle formation process. The latter is based on the decomposition and the subsequent chemical reaction of metal chloride, carbonate, hydride, and organics used as raw materials in an appropriate reactive gas under an energetic environment formed mainly by thermal healing, radiofrequency (RF) plasma, and laser beam. Synthesis techniques are listed for every heal source for the reactive gas condensation method and for the chemical vapor condensation method in Tables 8.1.1 and 8.1.2, respectively. 

The chemical vapor condensation method was applied for the preparation of ferromagnetic nanoparticles with a core-sheU structure by the pyrolysis of iron pentacarbonyl ([Fe(CO)5]) [176, 177]. Among the factors which strongly affect the characteristics of finally formed particles is the decomposition temperature of the precursor at the tubular furnace. During decomposition of the precursor vapor in the heated furnace, nuclei are formed and grown to form the observable particles. A saturation vapor pressure ratio increases with an increase of the decomposition temperature. A higher saturation vapor pressure ratio results in the larger particle formation. The relationship between decomposition temperature and particle size... 

Rapid solidification and devitrification of amorphous metals and metallic glasses Combustion-flame chemical vapor condensation processes (Kear) Induction-heating chemical vapor condensation processes DC and RF magnetron sputtering, inclusive of the method of thermalization Laser ablation methods Supercritical fluid processing... 

Nanomaterials are also prepared by chemical vapor deposition (CVD) or chemical vapor condensation (CVC). In these processes, a chemical precursor is converted to the gas phase and then it undergoes decomposition to generate the nanoparticles. These products are then subjected to transport in a carrier gas and collected on a cold substrate, from where they are scraped and collected. The CVC method may be used to produce a variety of powders and fibers of metals, compounds, or composites. The CVD method has been employed to synthesize several ceramic metals, intermetallics, and composite materials. 

Building on our experience with IGC and CVC, we have replaced the heat source by a flame in the Combustion Flame - Chemical Vapor Condensation (CF-CVC) technique. This technique offers several advantages over previous methods and has the potential to continuously generate non-agglomerated powders at high rates typical for industrial processes. These advantages have been exploited in other research and commercial flame synthesis processes for the production of diamond, carbon black, other particulates, and a variety of thin films, but not to date for the large scale production of nanoscale powders. 

Carbon Composites. In this class of materials, carbon or graphite fibers are embedded in a carbon or graphite matrix. The matrix can be formed by two methods chemical vapor deposition (CVD) and coking. In the case of chemical vapor deposition (see Film deposition techniques) a hydrocarbon gas is introduced into a reaction chamber in which carbon formed from the decomposition of the gas condenses on the surface of carbon fibers. An alternative method is to mold a carbon fiber—resin mixture into shape and coke the resin precursor at high temperatures and then foUow with CVD. In both methods the process has to be repeated until a desired density is obtained. 

Evaporation of metal atoms followed by condensation, possibly after reaction with another substrate, is the key step of chemical vapor deposition (CVD) processes, which today are wide-spread. If the metal used is silicon, this method leads to the basis of the data processing industry. 

Coating and thin films can be applied by a number of methods. In thermal or plasma spraying, a ceramic feedstock, either a powder or a rod, is fed to a gun from which it is sprayed onto a substrate. For the process of physical vapor deposition (PVD), which is conducted inside an enclosed chamber, a condensed phase is introduced into the gas phase by either evaporation or by sputtering. It then deposits by condensation or reaction onto a substrate. A plasma environment is sometimes used in conjunction with PVD to accelerate the deposition process or to improve the properties of the film. For coatings or films made by chemical vapor deposition (CVD), gas phase chemicals in an appropriate ratio inside a chamber are exposed to a solid surface at high temperature when the gaseous species strike the hot surface, they react to form the desired ceramic material. CVD-type reactions are also used to infiltrate porous substrates [chemical vapor infiltration (CVI)]. For some applications, the CVD reactions take place in a plasma environment to improve the deposition rate or the film properties. 

Chemical Activities by the Surface Vapor Pressure Method. Surface pressure measurements in the transition region between the condensed and gaseous monolayer states of a single lipid component spread as a monolayer on water yield a value of ir which is independent of the surface area. This value—the surface vapor pressure, irv—is analogous to the vapor pressure of a liquid in equilibrium with its vapor. When a second lipid component is in the surface, the limits of miscibility in the condensed phase may be determined on the basis of the surface vapor pressure dependence on the mole fraction in the condensed phase (8). 

SiC-precursor processing can be subdivided into gas (chemical vapor deposition, CVD) and condensed phase methods. CVD, because of microelectronic applications, has spawned an entire field. It will be discussed here only very briefly. We will focus more intensively on the use of silicon-containing organometaUic precursors as condensed phase sources of ceramic materials. 

In general, vapor deposition methods refer to any process in which materials in a vapor state are condensed on a surface to form a solid-phase. These processes are normally used to form coatings to alter the mechanical, electrical, thermal, optical, corrosion resistance and wear resistance properties of various substrates. Recently, vapor deposition methods have been widely explored to fabricate various nanomaterials such as NS-T102. Vapor deposition processes usually take place in a vacuum chamber. If no chemical reaction occurs, this process is called physical vapor deposition (PVD) otherwise, it is called chemical vapor deposition (CVD). In CVD processes, thermal energy heats the gases in the coating chamber and drives the deposition reaction. 

DEHUMIDIFICATION - The condensation of water vapor from air by cooling below the dewpoint or removal of water vapor from air by chemical or physical methods. 

These methods have been widely used for nanoparticle fabrication techniques. These methods have been widely utilized for nanoparticles fabrication techniques which was subjected for both vaporization and condensation techniques. This method can play a vital role in both physical and chemical methods of synthesis of nanoparticles. The synthesized nanoparticles are subjected to various characterization techniques to identify whether they are the same size, if they are the same size the preparation method is physical vapor condensation. But if they are different particle sizes then we can conclude it with physical vapor condensation (Ghorbani et al., 2011). 

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