Showing papers on "Vaporization published in 1989"

Preparation of Organometallic Compounds from Highly Reactive Metal Powders

Abstract: The formation of novel organometallic compounds by the reaction of organic substrates with finely divided metal powders represents a powerful tool for the synthetic chemist. The direct reaction with a zerovalent metal is the only viable method of synthesis for many of these compounds. Accordingly, chemists have been actively developing new methods for increasing the reactivity of metal powders toward organic substrates. Three principal approaches have been developed in recent years: the metal vaporization method, sonochemistry, and the preparation of finely divided metal powders by the reduction of metal salts. A number of new methods of synthesis have resulted from these studies.

Pressure-temperature phase diagram of elemental carbon

Abstract: Carbon atoms form very strong bonds to each other yielding solid crystalline materials like graphite and diamond. Because of the high bonding energies, the vaporization and melting temperatures are very high. Different kinds of atom-to-atom bonding make many solid forms possible, ranging from pure graphite to pure diamond, as well as many types of molecules in liquid or gaseous carbon. Rigorous conditions of high temperature, high pressure, or both, are required to change a given elemental phase of carbon to another. Currently the vapor-pressure line of graphite, the P, T equilibrium line between graphite and diamond, and the graphite/diamond/liquid triple point are fairly well established. The triple point (or points) for graphite (or carbynes)/vapor/liquid remain controversial. At pressures less than 0.1 GPa liquid carbon seems to be a poor electric conductor while at higher pressures it is a good one. Current experimental and theoretical evidence indicate that diamond is stable against collapse to metallic forms (unlike Si and Ge) up to pressures over 350 GPa, and possibly as high as 2300 GPa. The latest static and shock compression experiments on diamond indicate that it melts to a conducting liquid at about 5000 K at pressures of 15 to 30 GPa, but does not melt at about 6000 K at 125 GPa. This suggests that the melting temperature of diamond increases with pressure, and that at the melting temperature liquid carbon is slightly less dense than diamond.

Framework for a Unified Model for Nucleate and Transition Pool Boiling

Abstract: An area and time-averaged model for saturated pool boiling heat fluxes has been developed. In the model, which is valid in the upper end of nucleate boiling and in transition boiling, the existence of stationary vapor stems at the wall is assumed. The energy from the wall is conducted into the liquid macro/micro thermal layer surrounding the stems and is utilized in evaporation at the stationary liquid-vapor interface. The heat transfer rate into the thermal layer and the temperature distribution in it are determined by solving a two-dimensional steady-state conduction equation. The evaporation rate is given by the kinetic theory. The heater surface area over which the vapor stems exist is taken to be dry. Employing experimentally observed void fractions, not only the nucleate and transition boiling heat fluxes but also the maximum and minimum heat fluxes are predicted from the model. The maximum heat fluxes obtained from the model are valid only for surfaces that are not well wetted and includes the contact angle as one of the parameters.

Particle behavior in thermal plasmas

Abstract: In this overview, effects exerted on the motion and on heat and mass transfer of particulates injected into a thermal plasma are discussed, including an assessment of their relative importance in the context of thermal plasma processing of materials. Results of computer experiments are shown for particle sizes ranging from 5–50 μm, and for alumina and tungsten as sample materials. The results indicate that (i) the correction terms required for the viscous drag and the convective heat transfer due to strongly varying properties are the most important factors; (ii) noncontinuum effects are important for particle sizes <10 μm at atmospheric pressure, and these effects will be enhanced for smaller particles and/or reduced pressures; (iii) the Basset history term is negligible, unless relatively large and light particles are considered over long processing distances; (iv) thermophoresis is not crucial for the injection of particles into thermal plasmas; (v) turbulent dispersion becomes important for particle <10 μm in diameter; and (vi) vaporization describes a different particle heating history than that of the evaporation process which, however, is not a critical control mechanism for interphase mass transfer of particles injected into thermal plasmas.

Origin of precursors of organic molecules during evaporation of meteorites and mafic terrestrial rocks

Abstract: THE accretion of the Earth was characterized by high-temperature transformations of planetesimal matter during high-velocity impacts. In the final stages of the Earth's growth, up to 30% of planetesimal mass and the corresponding mass of the target were evaporated1-3. Here we look at the effect of laser-pulse heating on meteorite materials and silicates in order to simulate the vaporization which occurs during impacts and to study the chemical composition of the gases produced. In our experiments, the residual gas mixture consisted of both oxidized and reduced components: CO, CO2, SO2, H2O, H2, N2, H2S, COS, CS2, various hydrocarbons from C1 to C6, HCN and CH3CHO. In addition, we find that the composition of the gas mixtures is qualitatively similar for all samples. Our data give an idea of the chemical composition of gases that may have been released into the Earth's early atmosphere by impact devolatilization. In the gas mixtures produced by these experiments we measured weight per cents of ∼10−3 for HCN, ∼10−4 for CH3CHO and ∼10−2 for hydrocarbons. Impact vaporization is no less effective for the formation of HCN than is the formation of HCN by impact reprocessing of the atmosphere4. For the production of aldehyde and hydrocarbons, impact vaporization is even more effective. The gas mixtures formed by vaporization of silicates provide favourable conditions for abiotic synthesis of organic compounds.

Heats of vaporization of fluids

Abstract: I. The Heat of Vaporization of Pure Substances. 1. The thermodynamics of vapour-liquid equilibrium in a single-component system. 2. Experimental determination of the heat of vaporization. 3. Expression of the heat of vaporization as a function of temperature. 4. Expression of the heat of vaporization using vapour pressure equations. 5. Calculation of the heat of vaporization using the reference substance concept. 6. Empirical methods for prediction of the heat of vaporization at 298.15K and the normal boiling temperature. 7. A survey of methods for determination of the heat of vaporization and recommendations. 8. The main uses of the heat of vaporization: a critical survey. II. The Heats of Vaporization of Mixtures. 1. Definitions and basic relationships. 2. Relationships between different types of heats of vaporization. 3. Methods of calculating the differential heats of vaporization. 4. Methods of calculating the integral heats of vaporization. 5. Experimental determination of the heats of vaporization of mixtures. 6. The heats of vaporization of azeotropic mixtures. 7. The heats of vaporization of solvents from solutions on nonvolatile components. 8. The heats of vaporization of systems with associating components. Appendix: Calculation of the pVT properties and thermodynamic functions of fluids in the subcritical region. Index.

Laser droplet heating: fast and slow heating regimes

Abstract: The heating of a laser-irradiated droplet is analyzed theoretically and numerically by solving the heat transport equation. Two regimes of droplet heating are considered, slow and fast heating. In the slow heating regime, the thermal diffusion term plays an important role and the droplet may not experience explosive vaporization during the lifetime of the laser pulse. In the fast heating regime, the vaporization term plays the dominant role and the temperature profile inside the droplet is similar to the heat production profile except for a thin shell near the surface. Numerical results are presented for the case of water droplets irradiated by 10.6microm laser radiation.

Oscillatory vaporization of fuel droplets in an unstable combustor

Abstract: The effects of oscillating gas pressure and velocity on droplet vaporization rates during combustion instability are examined. Droplets are continuously injected through the pressure cycle, and the behavior of each droplet is calculated. Individual droplet vaporization rates are combined to give the total vaporization rate for a spray. Heat conduction and convection within the droplet interior are considered and found to have very significant effects compared to the infinite-conductivity or rapid-mixing models of the past. The gain or response function associated with the oscillatory vaporization rate component in phase with the pressure is shown to be sufficiently large to sustain instability.

Emission spectroscopy of plasma during laser welding of AISI 201 stainless steel

Abstract: The rates of vaporization of alloying elements from the weld pool were related to the emission spectra of the plasma during pulsed laser welding of AISI 201 stainless steel under various welding conditions. The temperature distribution in the plasma was determined from the spectra obtained from various locations in the plasma plume. The extent of ionization of the plasma was calculated from the electron temperatures To understand the role of surface active elements, emission spectra and the vaporization rate of iron that resulted from the welding of ultrapure iron samples were compared with those from the welding of oxidized samples or samples that were doped with sulfur or oxygen.

Vaporization device for continuous introduction of liquids into a mass spectrometer

Abstract: This invention is designed to serve as an interface between a liquid chromatograph and a conventional or tandem mass spectrometer (LC/MS, LC/MS/MS). It may also be used for liquid sampling without prior separation of analytes by a liquid chromatograph. This invention differs from prior art in that vaporization of the analytical sample (LC eluent) occurs through the action of condensing pressurized steam on the exterior of a low thermal mass metal capillary, while the aqueous LC eluent is flowing through the metal capillary. The steam is obtained by heating a small volume of water sealed within the device. LC eluent entering the capillary results in localized cooling and subsequent condensation of the pressurized steam on the outer surface of the capillary. The process of condensation deposits energy to the capillary equivalent to the latent heat of vaporization of water. This energy results in flash vaporization of the LC eluent within the capillary. Condensed water flows along the outer wall of the metal capillary where it is returned to the trapped liquid reservoir for re-vaporization. Energy coupling to the LC eluent is substantially more efficient than methods used in prior art interface devices. This invention minimizes overheating of temperature sensitive analytes separated by the LC and rapidly self compensates for changes in eluent flow or eluent composition without the need for adjustment in operating temperature. This invention eliminates the need for aerosol desolvation prior to ionization.

Properties of carbon films deposited by pulsed laser vaporization from pyrolytic graphite

Abstract: Amorphous carbon films have been deposited on silicon 〈111〉 and quartz substrates by pulsed ruby laser vaporization from pyrolytic graphite. Depositions have been carried out at different substrate temperatures, and the properties of the deposited carbon films have been studied using IR and UV–VIS transmission, ellipsometry, and laser-Raman spectroscopies. Chemical and electrical resistivity measurements have also been performed. It is shown that the film properties depend critically on the substrate temperature and that at the substrate temperature of 50 °C films with substantial proportion of sp 3 hybridized orbitals are obtained.

High temperature thermodynamic studies of some gaseous thorium fluorides

Abstract: The gaseous species ThF, ThF2, ThF3, and ThF4 were generated in a heated effusion beam source, and were identified and characterized by mass spectrometry. An oxygen impurity in the sample also led to the characterization of the gaseous oxyfluoride ThOF. Reaction equilibria involving these species were studied over large temperature ranges, leading to the derivation of both enthalpy and entropy data for these species. The vapor pressure and vaporization thermodynamics of ThF4(s) were also determined. Derived bond dissociation energies in ThF4 oscillate about a mean value of 670±25 kJ mol−1, with a distinct pattern similar to other metal tetrafluorides. Absolute entropies calculated from the equilibrium data indicate moderate electronic level contributions for the odd‐electron molecules ThF and ThF3, but not for the even‐electron species ThF2 and ThF4. Furthermore, the experimental entropy of ThF4 is compatible with a regular tetrahedral configuration, rather than the distorted configuration of lower symmet...

Method and means for vaporizing liquids by means of heating a sample capillary tube for detection or analysis

Abstract: This disclosure is concerned with method and apparatus for vaporizing liquid solutions in order to detect, quantitate, and/or determine physical or chemical properties of samples present in liquid solution. Mixtures may be separated by an on-line liquid chromatographic column and the methods used for detection, quantitation, identification, and/or determination of chemical and physical properties include mass spectrometry, photoionization, flame ionization, electron capture, optical photometry, including UV, visible, and IR regions of the spectrum, light scattering, light emission, atomic absorption, and any other technique suitable for detecting or analyzing molecules or particles in a gaseous or vacuum environment. The method and apparatus involves controlled partial vaporization of the solution. Methods are disclosed for controlling the degree of partial vaporization and the temperature at which this vaporization occurs, and for maintaining this degree of vaporization essentially constant even though the solvent flow rate and/or composition may vary in either a controlled or an uncontrolled fashion. This GOVERNMENT SUPPORT The invention described herein was made in the course of work under a grant or award from the Department of Health and Human Services (formerly Health Education and Welfare). CROSS REFERENCE TO RELATED APPLICATIONS

An evaluation of the point-source approximation in spray calculations

Abstract: This paper presents an evaluation of the errors involved in the coupling between the gas and liquid phases in spray computations. The point-source approximation is investigated for stagnant and convective droplet vaporization. In the stagnant case, it is shown that the calculated vaporization rate may be in error if the gas-phase grid size is comparable to the droplet size. In the convective case, it is shown that a doublet should be added to the point-source approximation if the gas-phase grid size is comparable to the droplet size. The calculation of the transfer number using an average fuel mass fraction at the location of the droplet is shown to lead to errors as large as 10-50% or even prevent convergence of the solution. The errors are reduced to 0-10% when the conditions of the approaching flow, upstream of the front mass fraction layer, are employed in the evaluation of the transfer number.

Inhibition of coke formation during vaporization of heavy hydrocarbons

Abstract: An improved process for vaporizing a crude petroleum feedstock, preferably one boiling in the vacuum gas oil range or higher, prior to thermal cracking to olefins, wherein such feedstock is preheated, in one or more stages, in the convection section of a tubular steam cracking furnace, characterized by conducting the preheating in the presence of a small amount of hydrogen, preferably at a hydrogen/feed ratio of from about 0.01 to about 0.15 wt. %, so as to inhibit coke formation.

High capacity multicomponent liquid vaporizer

Abstract: An apparatus for vaporizing a multicomponent liquid consists of a vaporization chamber into which liquid is injected through a nozzle with sufficient velocity to ensure multiple impingements with the heated surfaces of the chamber so that the vaporization is substantially complete. The apparatus may have a plurality of injection nozzles, each responsive to a valve. The valves are sequentially operated by a control circuit to provide a substantially continuous stream of liquid to the vaporization chamber.

Production of sodium vapor from exposed regolith in the inner solar system

Abstract: The likely supply of sodium to the lunar exosphere by impact vaporization, by charged particle sputtering, and by photon stimulated desorption has been calculated. These were each compared to the supply of sodium needed to maintain the observed sodium exosphere about the Moon. The two processes already known to act on the lunar regolith, impact vaporization and charged particle sputtering, appear to be sufficient to explain the observed column density of sodium in the lunar atmosphere. Photon-stimulated desorption, given the estimates for the yield of sodium due to this process available in the literature, would produce 100 to 1000 times more sodium than is observed. If impact vaporization is the main source of sodium to the atmosphere of Mercury, then sodium photo-ions in the exosphere of Mercury are efficiently recycled to the planet.

Stability and Erosion of Melt Layers Formed During Plasma Disruptions

Abstract: Melting and vaporization of metallic reactor components such as the first wall and the limiter/divertor may be expected in fusion reactors due to the high energy deposition resulting from plasma in...

pulsed laser-induced vaporization from the surface of a binary oxide (zinc ferrite) and its implications for synthesis of thin films

Abstract: The nature of pulsed ruby laser‐induced vaporization from the surface of a binary oxide represented by ZnxFe3−xO4 (x∼1) is studied via morphological (scanning electron microscopy), compositional (energy‐dispersive analysis of x ray), structural (small‐angle x‐ray diffraction), and microstructural (conversion electron Mossbauer) examination of the laser‐processed surface and correlation of the related surface modification to the properties of thin films deposited therefrom, and subjected to similar examination. Zinc ferrite (ZnxFe3−xO4) films have been deposited on single‐crystal Al2O3 substrates and the dependence of the film properties on the oxygen partial pressure and substrate temperature during deposition is studied to explore optimized conditions for deposition of near single‐phase stoichiometric films.