Particle size temperature effect

It is now possible to model the wafer-level performance for most CMP processes. These models cover only some of the important tool or process design issues, such as relative velocities and pressure dependencies additional work is needed to predict the results for other parameters such as slurry composition or particle size, temperature dependencies, pad properties, and other effects. Die-level modeling has been used effectively to identify... 

Thus, reactions considered here are those taking place under actual process conditions. Reactions (1) and (2) were studied separately in the TGA at different temperatures and with different particle sizes. Also, effect of the gas-phase reactant concentration was studied to evaluate the reaction order. In a few experiments the effects of the presence of H2O in the feed gas on reaction (1) and that of H2 on reaction (2) were investigated. 

Industrially, catalyst activity maintenance is often screened via "temperature increase requirement" (TIR) experiments. In these experiments, constant conversion is established and the rate of temperature increase required to do so is used as a measure of the resistance of the catalyst to deactivation. However, this type of operation may mask the effect of particle size, temperature, temperature profile, and heat of reaction on poison coverage, poison profile, and the main reaction rate. This masking may be particularly important in complicated reactions and reactor systems where the TIR experiment may produce positive feedback. 

The intraparticle transport effects, both isothermal and nonisothermal, have been analyzed for a multitude of kinetic rate equations and particle geometries. It has been shown that the concentration gradients within the porous particle are usually much more serious than the temperature gradients. Hudgins [17] points out that intraparticle heat effects may not always be negligible in hydrogen-rich reaction systems. The classical experimental test to check for internal resistances in a porous particle is to measure the dependence of the reaction rate on the particle size. Intraparticle effects are absent if no dependence exists. In most cases a porous particle can be considered isothermal, but the absence of internal concentration gradients has to be proven experimentally or by calculation (Chapter 6). 

Based on experiments with pure hydrocarbons and synthetic silica-alumina catalyst, it has been estimated that the cracking-rate constant at 932°F. should decrease by a factor of to when particle diameter is increased from about 0.5 mm. to 4 mm. (74). The influence of particle size on effective activity is especially pronounced at very high cracking temperatures (49). This behavior is in line with predictions because, with increasing temperature, reaction rate on the catalyst surface increases more rapidly than the rate of diffusion of reactants into the pores. Cracking of unsymmetrical diarylethanes is an exceptional case in which the reaction appears to depend entirely upon the number of collisions of the hydrocarbon with the external area of the catalyst particles (208). 

There are a number of conflicting studies concerning the effect of particle size and particle-size distribution of the sample on the peak areas and Al in values. Speil et al. (2) found that the peak areas under the kaolin dehydration peak varied from 725-2080 mm2 over the particle-size range of 0.05-0.1 to 5-20 ju. It was also found that the A7 in values varied from 580-625°C. However, Norton (89) found that the A7 io values remained essentially constant but that the temperature at which the dehydration reaction was completed varied from 610-670°c >ver a particle-size range of <0.1 to 20-44 p. Grimshawet al. (90) agreed with the latter study in that, with particle sizes down to 1 fi, the thermal characteristics of the kaolin samples were independent of particle size. This effect is illustrated in Table 5.5. 

Reference [85] gives many details of the effect of reaction variables such as the temperature at which the AIBN is added the effects of different levels of AIBN, PVP, and styrene on particle size the effect of adding either toluene or water to the reaction medium the addition of water initially or after nucleation and the effect of the level of divinylbenzene and the method of its addition. 

Fig. 1. Comparison between experimental and model predictions at different temperatures and particle sizes, for effective...

Eliminating the pore diffusion resistances Pore diffusion resistances can be identified by the effect of the particle size on conversion. If the conversion is a function of the particle size, then the rate data are veiled by pore diffusion effects. To eliminate pore diffusion effects, the careful experimenter is advised to measure the conversion as a function of the particle diameter. If the conversions increase with decreasing particle diameters at constant space-time, then the data are veiled by pore diffusion limitations. The use of Arrhenius plots to elucidate the particle size temperature optimums is shown in Figure 7.7. 

Many factors affect the sulfur capture the most important are Ca/S ratio, recycle ratio, temperature, sorbent type and sorbent particle size. The effects of these parameters will be discussed later in the paper. 

The DoE shows the initial mannitol mass fraction and the initial droplet size to have the highest influence on the final particle size. Smaller effects are caused by the drying temperature as well as by quadratic initial mannitol mass fraction and a two-factor interaction between the initial droplet size and the initial mannitol mass fraction. The corresponding equation yields [34]... 

Figure C2.17.10. Optical absorjDtion spectra of nanocrystalline CdSe. The spectra of several different samples in the visible and near-UV are measured at low temperature, to minimize the effects of line broadening from lattice vibrations. In these samples, grown as described in [84], the lowest exciton state shifts dramatically to higher energy with decreasing particle size. Higher-lying exciton states are also visible in several of these spectra. For reference, the band gap of bulk CdSe is 1.85 eV.

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