Effect of Deposition Parameters

Effect of Pressure. CVD graphite with greater uniformity, better coverage, and improved quality is generally obtained at low deposition pressure. Pressure controls the thickness of the surface 

At higher pressure (i.e., atmospheric), the reactant gas must be diluted with an non-reactive gas, such as hydrogen or argon, to prevent vapor-phase precipitation, while generally no dilution is necessary at low pressure. However, atmospheric-pressure reactors are usually simpler and cheaper, and, with proper control of the deposition parameters, satisfactory deposits may be obtained. 

Effect of C/H Ratio. The carbon-to-hydrogen (C/H) ratio of the gas mixture (CH4 and H2) entering the reaction chamber is an important factor in the control of the nature of the deposition. Higher C/H ratios (such as 1/4) favor laminar deposition and lower ratios (such as 1/14) favor isotropic deposition. 

Effect of Temperature. Generally, isotropic deposits are obtained at higher temperatures ( 1400°C) and laminar and columnar deposits at lower temperatures. 

In summary, isotropic deposits are obtained at high temperature, low pressures, and low C/H ratio. The opposite conditions favor the deposition of laminar and columnar deposits. 

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It should be noted that although the effect of deposition parameters on the electrochemical deposition of sol-gel films has been thoroughly investigated by many different groups aiming at tuning the thickness and other properties (e.g., hydrophobicity, roughness, and corrosion resistance) of the films, the manipulation of the deposition process is still based on experience in different systems. 

Luft and Tsuo have presented a qualitative summary of the effects of various plasma parameters on the properties of the deposited a-Si H [6]. These generalized trends are very useful in designing deposition systems. It should be borne in mind, however, that for each individual deposition system the optimum conditions for obtaining device quality material have to be determined by empirical fine tuning. The most important external controls that are available for tuning the deposition processs are the power (or power density), the total pressure, the gas flow(s), and the substrate temperature. In the following the effects of each parameter on material properties will be discussed. 

Besides the already mentioned techniques, a low-temperature plasma has been adopted to enhance the reaction in CVC. Through the synthesis of AIN UFPs by an RF-plasma-enhanced CVC using trimethylaluminum [A1(CH3)3] and NH3 as reactants, the effect of experimental parameters on the rate of powder formation, particle size, and structure was examined (60). A high RF current was primarily connected to a high electron density, which activated the gas-phase reaction to promote the powder formation rate. The increase of both susceptor temperature and A1(CH3)3 concentration also increased the powder formation rate and enhanced the grain growth, where both mechanisms—coalescence by particle collision and vapor deposition on to particle surfaces—were believed to occur. 

Only one group has reported CD of SbiSes. The solution used was potassium an-timonyl tartrate, complexed with triethanolamine and ammonia. Selenosulphate was used as the Se source. No XRD pattern was found, as for the sulphide deposited under equivalent conditions. The bandgap was 1.88 eV, and resistivity O-cm [13,14]. Continued study of this deposition showed the effect of various parameters on deposition rate and film thickness (the latter typically reaching 1 p.m) [15]. This study also described some photoelectrochemical behavior of these films (Chap. 9). 

In processing VGO it has been argued that the heavy poly-aromatic structures characterised by the Ramsbottom Carbon Residue (RCR, Table 1) can be considered as coke precursors [8]. An increase of the boiling point of those structures via condensation reactions or dehydrogenation reactions is responsible for coke deposition onto the catalyst. In order to increase our level of understanding of these processes we consider first the effects of catalyst parameters on the coke formation. 

The general problem has been to extend the usefulness of the induction parameter model proposed by Oran et al. (1). This induction parameter model (IPM) is proposed as a means to enable one to estimate, relatively easily, the energy necessary to achieve ignition when using a thermal heating source Much of the calibration of this model, for example the effect of deposition volume (quench volume), can be done with one-dimensional models, and shock tube experiments. There are phenomena, however, which must be studied in two or three dimensions. Examples are turbulence and buoyancy. This paper discusses the effect of buoyancy and possible extensions to the IPM. 

Martonen TB, Katz IM. Deposition patterns of aerosolized drugs within human lungs effects of ventilatory parameters. Pharm Res 1993, 10, 871-878. 

Fig.5 shows the calculated curvature and temperature evolution for an FGM deposit with thickness of about 180 im, which is consistent with the experimental results shown in Fig.4 except for the transient oscillations. Fig.6 (a) shows the calculated stress distributions in 2-layer and FGM deposits. The gradual stress variation in the FGM can be observed. In Fig.6 (b) effects of model parameters such as the substrate temperature and elastic modulus of YPSZ on the stress distribution in 2-layer deposits are demonstrated. As the substrate temperature is raised from 600 to 825K, the tensile stress in the NiCrAlY layer is significantly reduced. If a value of elastic modulus of 190GPa of a dense bulk material was used, the compressive residual stress in the YPSZ is excessively overestimated. This example clearly demonstrates the importance of using realistic values for modeling thermal and mechanical behavior of sprayed deposits. 

Parametric Study. A study of the effect of process parameters on the deposition of boron using the static filament apparatus was conducted. The parameters studied include system pressure, reactant gas flow, ratios, electrode separation, and configurations, and field strengths. The evaluation of certain parameters has been quantitative and was based on the weight of boron deposited or on the thickness of the deposit at the midpoint of the filament. Other parameters were evaluated by a qualitative description of the deposit. 

In the classic semi-manual electrophoretic technique used mainly in bioanalysis, a small slab or strip of plastic material covered by a porous substance (a gel) is impregnated with an electrolyte buffer. The two extremities of the covered gel system are dipped into two independent reservoirs containing the same electrolyte and linked to the electrodes of a continuous voltage supply (Eigure 8.1). The sample is deposited in the form of a transverse band, which is cooled and then bedded between two isolating plates. Under the effect of several parameters that... 

Leach, C. 1999. Effect of formulation parameters on hydrofluoroalkane-beclomethasone dipropionate drug deposition in humans. J. Allergy Clin. Immunol. 104 (6) S250. 

Computer Simulations Illustrating the Effects of Process Parameters on the Non-Uniform Deposit Distribution Due to Resistive Substrate... 

Daley and Lundgren (lO) evaluated the performance of various instruments for aerosol measurement. The effects of several parameters including temperature, humidity, particle collection characteristics, linearity and mass sensitivity were studied. The observed linear response limits ranged from 0.2 to 6 (jg/mm r and no relationship between linearity limit and point of complete saturation was apparent. The mass sensitivity was found to be dependent upon deposit size and location and decreased for particles size beginning at - 2 pm in diameter reaching essentially zero at 20 Jm. However, viscous coating appeared to improve sensitivity in this range. 

The role of asphaltene deposition in miscible flooding processes is also examined. Experimental data together with coupled equation of state models and Flory-Huggins polymer solution theory have been used to illustrate the effect of various parameters such as solvent type, solvent/oll ratio and pressure on the amount of asphaltene precipitation during addition of solvents to heavy oil. 

An estimation of the effect of different parameters on the current density distribution can be made from Fig. 3.2, which shows the dependencies of the current densities at the closer, / > and further, if, part of the cathode from the anode on the cell voltage, (/, for different solution resistivity. As can be seen, the increase of the conductivity of the electrolyte leads to the more uniform current density distribution of deposits at the electrode surface. A similar but less pronounced effect of the increase of the cathodic Tafel slope can be seen, while the change of /q does not affect the current density distribution. It is necessary to note that a soluble anode is considered in this case and, hence, the anodic and cathodic exchange current densities are the same. 

Some understanding of the corrosion of aluminium alloys used as cladding on research and test reactor fuel has been obtained from the CRP. Aluminium corrosion is extremely complex and the variables affecting localized corrosion (pitting and crevice corrosion) act both independently and synergistically. Additional information about the effects of deposited particle composition on the corrosion behaviour of aluminium alloys is needed. Surface finish affects the corrosion of aluminium alloys, and more information is required with respect to this parameter. Additional data on the effects of certain impurity ions in basin water on localized corrosion behaviour are necessary to better identify the ions that cause corrosion. A goal would be to develop an equation for pitting as a function of water chemistry parameters. 

Rahman, M. Amsarani, R. Mooney, D. A. MacElroy, J. M. D. Dowling, D. P., Effect of Process Parameters on Chemistry, Growth Rate and Nano-Sized Particulate Formation of Atmospheric Plasma Deposited, nm Thick Siloxane Coatings. J. Nanosci. Nanotech. 2009, 9,3506-3513. 

C. Agraflotis, A. Tsetsekou, The effect of processing parameters on the properties of y-aluminia washcoats deposited on ceramic honeycombs, J. Mater. Sci. 2000, 35, 951-960. 

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