Particles, rapid expansion

Crystallization Solutes may be crystallized from supercritical fluids by temperature and/or pressure changes, and by the PCA process described above. In the rapid expansion from supercritical solution (BESS) process, a SCR containing a dissolved solute is expanded through a nozzle or orifice in less than 1 ms to form small particles or fibers. A variety of inorganic crystals have been formed naturally and synthetically in SCR water. 

Depolymerization, e.g., polyethylene terephthalate and cellulose hydrolysis Hydrothermal oxidation of organic wastes in water Crystallization, particle formation, and coatings Antisolvent crystallization, rapid expansion from supercritical fluid solution (RESS)... 

Tsutsumi, A., Nakmoto, S., Mineo,T., and Yoshida, K., A Novel Fluidized-Bed Coating of Fine Particles by Rapid Expansion of Supercritical Fluid Solutions, Proc. 1st Int. Particle Technol. Forum, pp. 452-455, Denver, CO (1994)... 

As the weak interaction is the slowest of all, it was the first to find itself unable to keep up with the rapid expansion of the Universe. The neutrinos it produces, which serve as an indicator of the weak interaction, were the first to experience decoupling, the particle equivalent of social exclusion. By the first second, expansion-cooled neutrinos ceased to interact with other matter in the form of protons and neutrons. This left the latter free to organise themselves into nuclei. Indeed, fertile reactions soon got under way between protons and neutrons. However, the instability of species with atomic masses between 5 and 8 quickly put paid to this first attempt at nuclear architecture. The two species of nucleon, protons and neutrons, were distributed over a narrow range of nuclei from hydrogen to lithium-7, but in a quite unequal way. 

The Chinese scientists [123] have reported the preparation of nanoscale RDX (-50 nm) and nanoscale HMX (=70 nm) by an impinging method [124]. Researchers from China have also reported preparation and characterization of n-NTO and their data indicate that it decomposes at a lower temperature and at the same time, it is less sensitive to impact compared with m-NTO. This property of n-NTO is likely to be of tremendous significance for insensitive munitions [125]. The preparation of n-RDX particles with a mean size (=110-120 rim) but narrow distribution has also been reported by a novel method known as rapid expansion of supercritical solution (RESS) [126]. 

Micronization with supercritical fluids - Crystallization - Rapid expansion - Gas anti-solvent Recrystallization - Precipitation with compressed anti-solvent - Solution-enhanced dispersion - Particles from gas-saturated solutions 80 - 300 fine particles and powders from various products and of designed properties... 

Solid products require somewhat different treatment. In general, rapid expansion of SCFs [35] is the most effective approach, at least for small-scale reactions. RESS precipitation separates the product as fine particles, free for traces of the SCF and other volatile components of the reaction mixture. RESS is particularly useful for the precipitation of organometallic compounds with relatively weakly bound ligands (e.g., C2H4, T 2-H2) [12,13] see Figure 9.1-5. 

By utilizing the rapid expansion of supercritical solutions, small-size particles can be produced from materials which are soluble in supercritical solvents. In this process, a solid is dissolved in a pressurized supercritical fluid and the solution is rapidly expanded to some lower pressure level which causes the solid to precipitate. This concept has been demonstrated for a wide variety of materials including polymers, dyes, pharmaceuticals and inorganic substances. 

In the latest literature, the production by supercritical techniques of pharmaceuticals-loaded bio-polymer micro-particles is widely considered [34], All of these applications take advantage of the solvent or anti-solvent power of CO2. Various techniques have been proposed so far, such as the rapid expansion from supercritical solution (RESS) [35], the gas... 

A novel fluidized-bed coating process using the rapid expansion of supercritical solutions (RESS) is described for the encapsulation of fine particles [2,3]. This process exploits the capability of supercritical fluids to act as a selective solvent. Supercritical fluids are noteworthy in that their... 

A. Tsutsumi, S. Nakamoto, T. Mineo, K. Yoshida, A novel fluidized-bed coating of fine particles by rapid expansion of supercritical fluid solutions, Powder Technol. 85 (1995) 275-278. 

The rapid expansion of supercritical solutions (RESS) has been explored recently as a novel route for the production of small and monodispersed particles (1-2.). Particle formation involves nucleation, growth and agglomeration. In RESS, nucleation is induced by a rapid decompression growth and agglomeration occur within the expanding solution. The thermodynamics of the supercritical mixture influences the relative importance of these mechanisms, and thus play a key role in sizes or size distribution of final particles. 

Several new processes for formation of solid particles with defined particle size and particle size distribution using supercritical fluids were developed in the past years. Examples are crystallisation from supercritical fluids, rapid expansion of supercritical solutions (RESS), gas antisolvent recrystallisation (GASR), and PGSS (Particles from Gas Saturated Solutions)-process [1,2]. 

Production of fine, solvent free powders is of great importance in the pharmaceutical industry /5/. Conventional techniques produce particles with broad particle size distributions. Moreover, particles may be irregular or contain solvents. Hence the development of procedures such as Rapid Expansion of Supercritical Solutions (RESS) or the Gas Antisolvent Recrystallisation (GAS) is in progress /5, 6/... 

A pilot plant is presented, which has been built to prepare fine particles (< 4 pm) by the Rapid Expansion of Supercritical Solutions (RESS - process). In this study carbon dioxide loaded with anthracene was used. By varying process parameters, the particle size distribution can be influenced. Changes of the post-expansion pressure have no provable influence on the particle size distribution. 

The rapid expansion of supercritical solutions (RESS) was explored by several authors as a novel route to the formation of microparticles. Ohgaki [1] produces fine stigmasterin particles by the rapid expansion of a supercritical C02 solution. Amorphus fine particle and whisker-like crystals (0,05 - 3 pm) were obtained with different preexpansion pressures. Johnston [2] obtained submicron particles from different polymers. Loth [3] described the mirconisation of phenacetin with supercritical fluids. 

A pilot plant was built to study the influence of different process parameters on the particle size produced by RESS-process (Rapid Expansion of Supercritical Solutions). Particles smaller than 4 pm were obtained for the system carbon dioxide-anthracene. 

Early stages of the universe are listed in Table 15.2. Primeval matter was merging into elementary particles, huge amounts of energy were released and the big bang immediately caused a rapid expansion of the universe. Within about 1 s the temperature decreased markedly, matter and antimatter annihilated each other, quarks combined into mesons and baryons and enoimous amounts of energy were liberated causing further expansion. Formation of the first protons and leptons is assumed after about 1 s, when the temperature of the early universe was about lO K. 

Merging of primordial matter into elementary particles, such as protons and neutrons release of huge amounts of energy, beginning of rapid expansion... 

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