Particle Generation Rate Research Articles

Silane reduced chemical vapor deposition tungsten as a nucleating step in blanket W

The SiH4–WF6 nucleation step of chemical vapor deposition blanket tungsten has been studied in the 10–100 Torr pressure range. The deposition rate, particle generation rate, and step coverage were studied as a function of the process parameters. The deposition rate was found to be mass transfer limited over the entire range of process conditions. Deposition rates from 300 to over 70 000 Å/min were observed. An in situ detector was used to measure gas phase particle levels. Particle generation rates were found to range from 0 to 108 particles/s over the parameter range studied. The strongest dependence seen was on the SiH4/WF6 flow ratio. At ratios of less than one, no detectable particles were produced. The particle generation rate increases rapidly at ratios above one. The particle rate also increases with increasing temperature and pressure. The step coverage was found to be ∼85% for 1000 Å films in 3:1 aspect ratio trenches. Overall, the results indicate that SiH4 nucleation in the 10–100 Torr range is an attractive alternative to the ≤1 Torr processes commonly in use today.

Generation of Submicrometer Particles in Dry Sliding Contact

The generation of submicrometer-sized particles during dry sliding between stainless steel surfaces is investigated by means of a laser spectrometer for particle counting and scanning tunnelling microscopy for asperity topography characterization. It has been found that, when the submicrometer wear increases with increasing sliding distance or with an initially rougher surface, the number of particles having a submicrometer size is a power function of that size. The two wear coefficients in the power function are determined empirically for the case of stainless steel contact. Different from the generation pattern of several-micrometer particles, the generation rate of submicrometer particles continuously increases until reaching the equilibrium surface condition. The asperity topography measurement shows the micrometer-sized asperities also have subasperities whose sizes are about one order of magnitude smaller. An asperity model similar to Archard’s is thus proposed for estimation of submicrometer wear. The dominant wear mechanisms are brittle fracture and plastic deformation combined with adhesion transfer. The asperity contact can be considered as a plastic-elastic deformation system with subasperities deformed plastically all the time and the micrometer asperities first deformed plastically and then deformed elastically because of the significant increase of microhardness on the soft surface in a metal pair. When the microhardness ratio between two rubbing surfaces reaches a stable value, the generation of submicrometer particles reaches the maximum rate and the wear grows steadily.

Particulate generation in silane/ammonia rf discharges

The rate of particle generation in a SiH4/NH3 rf discharge has been studied as a function of the discharge operating parameter space, electrode geometry, and power supply coupling mode. Measurements of the bulk quantity of particles produced in the discharge reveal that the mode of coupling (capacitive or dc) as well as the electrode temperature significantly affects particle generation rates. Laser light scattering measurements made as a function of the plasma power density indicate that particle generation abruptly ceases at a threshold value sufficient to induce spark breakdown at the cathode. Based on these observations, it is shown that particle growth in plasmas can be modeled entirely as a heterogeneous process. The initiation of particle growth is shown to be consistent with an electron surface desorption model involving vibrational excitation of surface clusters. Propagation of growth in the gas phase is shown to be consistent with an eliminative ion-molecular condensation reaction, and the pressure dependence of this mechanism is exploited to estimate a value for the rate constants for SiH4 and NH3 condensation in SiN:H particle growth.

Changes in stream benthic organic matter following watershed disturbance

Benthic organic matter was collected quarterly from streams draining a 9‐yr‐old clearcut, an 18‐yr‐old “old‐field”, a 25‐yr‐old successional forest, and two reference watersheds at Coweeta Hydrologic Laboratory in the Appalachian Mountains of North Carolina. USA. Samples were separated into large benthic organic matter (LBOM >1 mm) and fine benthic organic matter (FBOM <1 mm). An additional survey of large (>5 em diam.) and small (1–5 cm diam.) wood was conducted. Standing stocks of LBOM ranged from 124 to 235 g AFDM m−2 (ash tree dry mass) and were significantly higher in streams draining reference watersheds and the successional forest than in either the recent clearcut or old‐field. Reference sites exhibited LBOM peaks in late autumn and spring. No seasonal patterns were observed in disturbed streams. Standing stocks of FBOM averaged 113 to 387 g AFDM m−2, and the stream draining the successional forest had significantly higher FBOM levels than the other sites. In reference streams, FBOM abundance peaked in spring. In disturbed streams, FBOM standing stocks were highest in summer or late autumn. Standing stocks of large wood ranged from 0 to 3956 g AFDM m−2 and were significantly higher in the reference streams than in streams draining the old‐field or successional forest. Small wood averaged 11 to 342 g AFDM m−2 and was significantly lower in the stream draining the old‐field than at the other sites. Comparisons of organic matter inputs with standing stocks indicated that disturbed streams at Coweeta receive less material and process it faster than reference streams. Disturbed streams also appear to be less retentive than reference streams and exhibit a gradual decline in FBOM during the winter when large, long‐duration storms combined with low particle generation rates deplete accumulated FBOM.

「水素プラズマ‐金属」反応における超微粒子発生速度に及ぼすアーク磁気回転の影響

The authors developed a new technique for the preparation of ultrafine metal particles based on the “hydrogen plasma-metal” reaction process. In this technique, an arc column generated in hydrogen atmosphere revolves on the surface of a molten metal by a magnetic field.The generation rate of ultrafine particles of iron, copper and silver increased with increasing the revolution rate of the arc column. It is estimated that the apparent reaction interface of the arc column and the surface of molten metal is extended by the revolution of the arc.

Size and Generation Rate of Sidestream Cigarette Smoke Particles

Sidestream cigarette smoke generated using an automatic smoking machine (SEM-II) and Kentucky 2R1 reference cigarettes was analyzed for particle generation rate and size distribution. Part of the sidestream smoke was sampled with an Andersen Cascade Impactor, following dilution with about 29 to 54 liters/min of laboratory air. The remaining sidestream smoke was further diluted 1,000-fold with vapor phase from filtered sidestream smoke before analysis with an Electrical Aerosol Analyzer and Condensation Nuclei Counter. The smoking parameters of primary dilution ratio and puff pressure were varied in the experiments. The number median diameter of sidestream cigarette smoke was about 0.10 μm, and the mass median diameter was typically 0.16 μm, about half the size of fresh mainstream smoke. Additionally, the size distribution of sidestream smoke was significantly broader than that of mainstream smoke. The particle generation rate of sidestream smoke depended on smoking conditions and varied from 1.4 × 109 to ...

STEADY-STATE MODELLING OF A LATEX REACTOR TRAIN FOR THE PRODUCTION OF STYRENE-BUTADIENE RUBBER

A mathematical model is developed for the emulsion copolymerization of styrene and butadiene carried out in a continuous train of stirred tank reactors. The model predicts copolymer composition, conversion, molecular weight averages, and long chain branching frequencies, as well as the latex particle size distribution for all reactors in the train. It is capable of simulating closely the behaviour of industrial SBR processes. Several simulation studies are performed. Topics investigated include: process operating modifications to improve productivity; the effect of chain transfer agent flow rate and number of reactors on the molecular weight development; the effect of process modifications on the development of the particle size distribution down the reactor train; and the effect of reactor design on particle generation rates.

アークプラズマ法による金属超微粒子発生装置について

A production system of ultrafine metal particles has been designed and manufactured to examine its industrialization. In this system, metal powders are produced by arc melting in hydrogen and inert gases. The particle generator, a kind of arc furnace, was newly improved so as to produce fine particles and to feed a raw metal rod.The generation rate of ultrafine metal particles became higher with the increasing partial pressure of hydrogen in atmosphere. The generation rate of iron particles was about 30g/h in 50% hydrogen atmosphere (5kW). The diameters of Fe, Cu and Al particles were found to be from 10 to 100nm by the use of a transmission electron microscope.

A model and the methodology for determining wear particle generation rate and filter efficiency in a diesel engine using ferrography

A mathematical model was developed that describes the wear particle concentration as a function of time in a diesel engine. This model contains engine and lubrication system parameters that determine the concentration of wear particles in the engine sump. These variables are the oil system volume, oil flow rate, particle generation rate, filtering efficiency and the initial particle concentration. The model was employed to study the wear particle concentrations in the sump and the mass of particles in the filter for the Cummins VT-903 diesel engine. In addition, the model was used to develop a testing methodology for determining wear particle generation rates and filter efficiencies from used oil analysis. This testing methodology uses ferrography together with computer programs to yield accurate statistical information on the data as curve fitted to the model. The test set-up incorporated a remote-controlled sampling system that enabled the accurate and periodic taking of oil samples over an engine test approximately 5 h in duration. Results of this research indicate that equilibrium wear particle concentrations increase with an increase in engine speed and load. The wear particle generation rate and filter efficiency as determined by the test methodology were found to decrease with an increase in engine speed and load. After oil and filter changes, the wear particle generation rate and filter efficiency continually increased with cumulative engine time up to approximately 11 h. The test methods used to obtain the results above were found to be repeatable to within ±15% and could conceivably be employed to determine wear parameters on other diesel engines as well as the effects that other engine variables such as lubricants, oil temperature, coolant temperature and engine components have on the wear parameters.

An overview of recent advances in quantitative ferrography as applied to diesel engines

Ferrography is being applied to laboratory and field engines to understand better the wear processes taking place. Methods used to make ferrography quantitative and sensitive to a wide range of debris concentrations are presented. An equation describing the time-varying debris concentration in the engine was applied to ferrography data in order to calculate the particle generation rate and the filtering efficiency of a paper filter. Results using this technique in the laboratory are discussed. A medium duty truck engine from new to its present mileage of over 80000 mile was monitored every 50 h using analytical ferrography. The results of this study are presented.

A laser anemometer seeding technique for combustion flows with multiple stream injection

In nonpremixed combustion systems, fuel and oxidant are injected into the reaction chamber via two or more separate streams. Velocity measurements by laser anemometry within the chamber may be biased by individual streams unless the seeding concentrations of both streams are uniform and constant. In order to meet this requirement, a seeding technique has been developed to disperse 1-μm metal oxide particles at a controllable rate. Evaluations of the steadiness of particle generation indicate rms fluctuations are within 1.5% of the particle generation rate. Demonstration of the technique has been conducted in both nonreacting and reacting flows.

On the number concentration of aerosols in towns

A simple model of the aerosol plume generated by a town is developed under the assumption that the generation rate of particles is proportional to the town population. Thus the volume concentration of aerosols in towns is predicted for various meteorological conditions. The effects of localized sources of aerosols, such as industrial chimney stacks, are considered.

Soot measurements in laminar ethylene diffusion flames

Soot measurements were made in laminar ethylene diffusion flames for various fuel and air flow rates in a Wolfhard-Parker burner. Simultaneous light scattering and extinction measurements yielded spatially resolved particle number densities, particle size, and soot volume fraction. Laser doppler velocity measurements and temperature measurements allowed the flow field and particle trajectories to be determined. Soot production rates were found to be highest near the base of the flame in a region of temperature 1200–1400°C. Particle generation rates were greatest, however, near the flame zone. Small flames had the highest initial soot volume fractions and particle sizes, but larger flames produced more soot flux further up.

Soot formation in a laminar diffusion flame

Light scattering and extinction measurements have been made to measure profiles of soot volume fraction, particle number density and average size in a laminar ethylene diffusion flame. Velocity profiles by laser Doppler anemometry and temperature profiles were also obtained in order to solve the species conservation equations and deduce the soot formation and particle generation rates. Soot volume fraction and particle diameter profiles peak some 5 mm on the fuel side of the peak temperature and increase with height. Number densities drop steeply from the reaction zone to the sooting zone and are relatively invariant with height. Soot particle trajectories show strong entrainment of particles from the reaction zone into the fuel side of the flame. The soot formation rates and particle generation rates peak in different regions. The picture that emerges is that particles are generated in the reaction zone and move into the fuel side of the flame where the main increase in soot volume takes place.

Precipitation of sparingly soluble salts: A model of agglomeration controlled growth

AbstractA model describing the role played by agglomeration in the growth of precipitates of sparingly soluble salts is presented. The model predicts that the mean size of the precipitate should increase with the agglomeration and unit particle generation rates, and that the resulting size distributions may be log normal. These findings qualitatively confirm previous experimental results. The model also shows that the precipitate size characteristics can be described in terms of a single parameter, a dimensionless drawdown time.