Particle evaporation

Mechanisms and Rates of Combustion. AH soHd fuels and wastes bum according to a general global mechanism (Fig. 2). The soHd particle is first heated. FoHowing heating, the particle dries as the moisture bound in the pore stmcture and on the surface of the particle evaporates. Only after moisture evolution does pyrolysis initiate to any great extent. The pyrolysis process is foHowed by char oxidation, which completes the process. 

Figure 7.16 AFM (above) and TEM images (below) of palladium particles evaporated onto a flat Si02 layer, left as deposited and right after cycles of heating in oxygen and hydrogen at 475 K (from Erlandsson et al. [46]).

A bathroom mirror is usually colder than the temperature of the steam rising from a hot bath. Each molecule of steam (gaseous water) has an enormous energy, which comes ultimately from the boiler that heats the water. The particles of steam would remain as liquid if they had less energy. In practice, particles evaporate from the bath to form energetic molecules of steam. We see this energy as kinetic energy, so the particles move fast (see p. 30). The typical speeds at which gas particles move make it inevitable that steam molecules will collide with the mirror. 

In the present paper non-conventional TEM methods to characterize small metallic particles are presented. The topographic information on the particles shape can be combined with micro-diffraction (using STEM) data to obtain a full characterization of the particle. The case of gold particles evaporated on a NaCl substrate is used as example. The particle shapes observed are discussed. It is shown that many particles have a crystal structure which is different from the bulk (Fee). 

There is some field evidence for the existence of organic films on the surfaces of particles. For example, Fig. 9.57 shows the results of electron microscopy of haze aerosol collected in Los Angeles (Husar and Shu, 1975). The droplets are wrinkled in appearance, and they suggest this is due to haze aerosol droplets being coated with an organic layer that collapsed when the water in the particle evaporated under vacuum. Husar and Shu propose that the wrinkled appearance is due to a nonvolatile layer of organics that shrunk after water evaporated from the particle during analysis ... 

When these heavy recoil nuclei are the result of a complete fusion of the projectile and target nuclei, they are usually called evaporation residues because they result from a deexcitation of the primary complete fusion product by particle evaporation (emission). In intermediate energy and relativistic nuclear collisions, the momentum transfer to the target nucleus is much less, and the energy of the recoiling nucleus is 5-100 keV/nucleon. Such recoils are usually called heavy residues ... 

A continuing effort among experimentalists who study nuclei far from beta stability is the measurement of the atomic mass surface As a manifestation of the nuclear force and the nuclear many body system, atomic masses signal important features of nuclear structure on both a macroscopic and microscopic scale It has thus been a challenge to nuclear theorists to devise models which can reproduce the measured mass surface and to predict successfully the masses of new isotopes Both the measured mass surface and that beyond it which can be predicted by these models serve as important input to a variety of fundamental and applied problems, e g, nucleosynthesis calculations, predictions of decay modes of exotic nuclei far from stability, nuclear de-excitation by particle evaporation, decay heat simulations, etc ... 

Although qualitatively similar to the experimental SME results, our previous simulation results had difficulties with particle evaporation [160]. Figure 1.34 illustrates particle evaporation. To overcome evaporation, the model parameters have been adjusted. 3D visualization techniques were also used to monitor the issue, and the full-blown 3D capabilities [157] allow for a detailed, nanostmctural analysis of the PFPE lubricant films. 

The linear velocity of the probe tip (1 msec" ) is low compared with the gas velocity, so that this distance must be measured in the direction of gas flow, and the full width of the spike can correspond only to the passage of 10 X 10 m of ionized gas over the probe. A crystallite of KCl with the observed diameter, if volatilized at 1 atm and 2500 K (the measured flame temperature) would produce a vapor sphere of 10" m radius or a cylinder 10 X 10" m long and 4.5 X 10" m in diameter. This suggests that the spikes are indeed caused by a trail of vapor left as the particle evaporates. 

Ingebrethsen, B.J. and S.B. Sears Particle size distribution of sidestream cigarette smoke 39th Tobacco Chemists Research Conference, Program Booklet and Abstracts, Vol. 39, Paper No. 47, 1985, p. 25. Ingebrethsen, B.J. and S.B. Sears Particle evaporation of sidestream cigarette smoke in a stirred tank J. Colloid Interface Sci. 131 (1990) 526-536. 

The behavior of inorganic salts when RH is decreased is different from that discussed in the Sections 9.2.2 and 9.2.3 (Figure 9.4). For example, for (NH4)2S04, as the RH decreases below 80% (the DRH of (NH4)2S04) the particle evaporates but not completely. The particle remains liquid until a RH of 37%, where crystallization finally occurs. This hysteresis phenomenon is characteristic of most salts. For such salts, knowledge of the RH alone is insufficient for calculation of the aerosol liquid water content in this regime. One needs to know the RH history of the particle. 

The first case discussed is for rapid mass transfer between the gas and aerosol phases, a — 1000. The deposition ratios are presented in Figure 19.8 as a function of and y. When no source of the organic species A is present (8 =0), and because the system starts from equilibrium, the gas-phase concentration of A cannot exceed its saturation value. Therefore in this case A does not condense at any time to the aerosol phase and the particles evaporate in an attempt to maintain equilibrium. This nonsymmetry in the system is depicted in Figure 19.8a, and for / > 1 (deposition velocity of the particles exceeds the deposition velocity of the vapor) the equilibration process does not significantly affect the deposition. The material in the aerosol phase is preferentially deposited... 

Calculated using the ALICE compound nuclear particle evaporation code (S). None observed. 

Within the first 8 h of curing, a recrystallization process occurs, which increases slightly the strength of cohesion (up to 2 kg cm ). After that, capillary water and water from the thin liquid films between particles evaporates and the latter are interlocked into a porous mass, as a result of which the cohesion strength increases from 2 to 4.8 kg cm . Then, evaporation of the wedge water and subsequent hardening of the porous mass follow. Consequently, the cohesion forces increase from 4.8 to 6.0 kg cm. ... 

Figure 9.8 illustrates a problem that can occur with any furnace element—sample contamination. The sample is a-SiC, which was heated in a tungsten furnace for 12 hours at 1300°C. The dark features are tungsten particles evaporated onto the surface during heat treatment. 

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