Growth Of Solid Particles Research Articles

Nanoframes as a Resilient Candidate for a Broader Spectra of Catalysis Challenges

Metal nanoframes have gained tremendous attention in the domain of modern research and development due to their distinctive 3D spatial structure, efficient physiochemical properties, and comparatively good activity. Different strategies have been implicated by the researchers to design nanoframes of varying chemical natures and shapes. Most of the synthetic protocols being adopted to design nanoframes consist of two main steps: nucleation and the growth of solid particles and, secondly, excavation of the interiors. In this context, many synthetic methods are overviewed. To show their unprecedented performance or activity, a few applications in catalysis, biomedicine, theranostics, SERS, the sensing of different materials, the reduction of CO2, etc., are also discussed.

Conversion of liquid chitosan-based nanoemulsions into inhalable solid microparticles: Process challenges with polysaccharide

Solid particles ≤5 μm are essential to allow lower lung deposition and macrophage phagocytosis of anti-tubercular drugs. Decorating liquid nanoemulsion of anti-tubercular drug with macrophage-specific chitosan and chitosan-folate conjugate and spray drying the nanoemulsion with lactose produced oversized solid particles due to polysaccharide binding effects. This study designed solid nanoemulsion using lactose as the primary solid carrier and explored additives and spray-drying variables to reduce the binding and particle growth effects of chitosan. Deposition of magnesium stearate on lactose negated chitosan-inducible excessive lactose-liquid nanoemulsion binding and solid particle growth. Moderating the adhesion of chitosan-decorated liquid nanoemulsion onto lactose produced smooth-surface solid microparticles (size: 5.45 ± 0.26 μm; roughness: ∼80 nm) with heterogeneous size (span: 1.87 ± 1.21) through plasticization of constituent materials of nanoemulsion and lactose involving OH/N-H, C-H, CONH and/or COO moieties. Smaller solid particles could attach onto the larger particles with minimal steric hindrance by smooth surfaces. Together with round solid particulate structures (circularity: 0.919 ± 0.002), good pulmonary inhalation beneficial for treatment of pulmonary tuberculosis as well as other diseases is conferred.

Effects of Temperature and Time on Microstructural Evolution of Semisolid 5A06 Aluminum Alloy: Preparation of Semisolid Billets in Ellipsoid Solid Phase

To shorten the semisolid billet process and reduce its cost, the effects of isothermal temperature and soaking time on the microstructural evolution and coarsening rate during directly heating room temperature hot-rolled 5A06 aluminum alloy to semisolid temperature were investigated. Samples cut from the hot-rolled plates were heated to semisolid temperatures ranging from 580 to 620 °C, and soaking for 5-30 min. The microstructure of samples was characterized by optical microscopy, scanning electron microscopy with energy-dispersive x-ray spectroscopy, and Image-Pro Plus software. The results showed that the microstructure contained ellipsoidal solid grains with the quantitative parameters of the average grain size of 143 µm and averaged shape factor of 0.55 under an optimal condition of 615 °C for 20 min. Recrystallization occurred within 5 min of holding time, increasing temperature can promote recrystallization, which is beneficial to spheroidization of solid phase, and it will also accelerate melting and the growth of solid particles. Extending soaking time, the liquid phase increased gradually and the change of solid particles was complicated. Abnormal accumulation of liquid phase was found, which will lead to the formation of irregular structure. The reasonable coarsening rate constants ranged from 1319 to 3454 μm3 s−1 under the desired treatment parameters. The segregation of Mg occurred at the grain boundaries, as well as around the inclusions within the grains.

Effect of charging solid particles on their growth process and parameters of microwave discharge in liquid n-heptane

A zero-dimensional non-stationary model of a microwave discharge in liquid n-heptane at atmospheric pressure with continuous argon injection into the plasma region is presented. The model includes equations for the kinetics of neutral and charged plasma components, equations describing the formation and growth of solid particles from the decomposition products of n-heptane, and an equation for the microwave field strength in plasma. The description of the coagulation process takes into account the electrostatic repulsion of solid particles due to their charge. The kinetics of charged particles is described taking into account their death on the surface of negatively charged solid particles formed in plasma. To determine the coefficients of the reaction rates in mechanisms of direct electron impact, the electron energy distribution function obtained by solving the Boltzmann equation is used. Calculations have shown that the plasma quasineutrality is mainly supported by the charge of solid particles, and the electron concentration is 1–2 orders of magnitude less than the total ion concentration. An increase in the averaged microwave field was noted in comparison with the case that does not take into account charging. Charging of the solid particles does not affect the composition of the main gas-phase products, but leads to the suppression of the coagulation process for large solid particles, which leads to a change in the size distribution function of the solid particles formed in the plasma.

Microstructure evolution of hot pressed AZ91D alloy chips reheated to semi-solid state

AZ91D magnesium alloy chips, which were directly collected on the spot of machining process, were recycled to prepare billet via hot pressing for semi-solid processing. The semi-solid microstructure evolution of the billet during reheating was investigated. The results indicate that there are three stages during reheating to semi-solid state: the dissolution of Mg17Al12 and diffusion of Al into α-Mg matrix, the melting of the region with high content of solute and formation of isolated solid particles, and spheroidization and growth of solid particles. Meanwhile, a number of entrapped liquid droplets form within solid particles. In addition, the number and size of entrapped liquid droplets rely on the holding time in the semi-solid temperature range. With increasing isothermal holding time, the solid fraction remains unchanged when the solid-liquid system reaches the dynamic equilibrium at last, while the solid particles become more globular and the average size of solid particles increases owing to the decreasing of interfacial energy and the effect of interfacial tension.

Kinetics of the dissolution and growth of a finely dispersed solid phase in stirred apparatuses

A mathematical model is considered for the kinetics of dissolution and growth of solid particles by the diffusion mechanism in apparatuses with the stirring of a liquid phase. The mathematical model of the kinetics is based on the concept of the pseudolaminar boundary layer on the surface of a particle. The reliability of the developed mathematical model is verified by experimental data on rubber crumb degassing and silver halide crystallization in stirred apparatuses.

A New Paradigm of Crystallization Arising from Non-standard Nucleation Pathways

There is increasing evidence that large classes of colloid materials crystallize via a non-standard nucleation mechanism involving intermediate metastable phases. In this paper recent work on the microscopic derivation of the phase diagram and free energy barriers in the nucleation of protein crystals, and on the kinetics of growth of solid particles in the post-nucleation regime is reviewed. The extent to which combined structural and density fluctuation give rise to favourable crystallization pathways involving an intermediate fluid phase is assessed and the connection with experiments in microgravity at ISS (PROMISS-2 and NANOSLAB-2) is discussed.

Reduced discrete population balance model for precipitation of barium sulfate nanoparticles in non-ionic microemulsions

A discrete population balance model is formulated in order to analyze the precipitation process of barium sulfate nanoparticles taking place in the droplets of a water-in-oil microemulsion. The model accounts for the distribution of reactants over the droplet population in terms of discrete numbers of the reacting ionic species (Ba2+, SO42−), as well as for the nucleation and growth of solid particles in terms of discrete BaSO4-molecular units. The introduction of physically motivated assumptions leads to a considerable reduction of complexity of the population balance model. The kinetic parameters for nucleation and growth are estimated by fitting of simulated particle size distributions to recently published experimental data by Niemann et al. [B. Niemann, P. Veit, K. Sundmacher, Nanoparticle precipitation in reverse microemulsions: particle formation dynamics and tailoring of particle size distributions, Langmuir 24 (1), 2008, 4320–4328] and Adityawarman et al. [D. Adityawarman, A. Voigt, P. Veit, K. Sundmacher, Precipitation of BaSO4 nanoparticles in a non-ionic microemulsion: identification of suitable control parameters, Chem. Eng. Sci. 60 (12), 2005, 3373–3381]. The obtained parameter values support the conclusion that particle nucleation follows a heterogeneous mechanism and that the nanostructure of the microemulsion has a significant effect on the particle growth mechanism. The considered microemulsion-assisted precipitation process allows the generation of nanoparticle morphologies which are not attainable by classical bulk phase precipitation processes.

Coagulation, fragmentation and radial motion of solid particles in protoplanetary disks

The growth of solid particles towards meter sizes in protoplanetary disks has to circumvent at least two hurdles, namely the rapid loss of material due to radial drift and particle fragmentation due to destructive collisions. In this paper, we present the results of numerical simulations with more and more realistic physics involved. Step by step, we include various effects, such as particle growth, radial/vertical particle motion and dust particle fragmentation in our simulations. We demonstrate that the initial dust-to-gas ratio is essential for the particles to overcome the radial drift barrier. If this value is increased by a factor of 2 compared with the canonical value for the interstellar medium, km-sized bodies can form in the inner disk (<2 AU) within 104 yrs. However, we find that solid particles get destroyed through collisional fragmentation. Only with the unrealistically high-threshold velocities needed for fragmentation to occur (>30 m/s), particles are able to grow to larger sizes in disks with low α values. We also find that less than 5% of the small dust grains remain in the disk after 1 Myr due to radial drift, no matter whether fragmentation is included in the simulations or not. In this paper, we also present considerable improvements to existing algorithms for dust-particle coagulation, which speed up the coagulation scheme by a factor of ~ 104.

Analytical Model for Heat Transfer Phenomena in Cup-Cast Method

Cup-cast method is a new method deals with semi-solid slurry preparation recently developed by the authors. In this method, suspension of globular solid particles in molten metal is prepared by controlling the nucleation and growth of solid-particles through the simplest and quickest techniques. In this method, heat transfer phenomenon plays an important role in governing the shape, size, and fraction of solid particles. In the current study, a heat transfer model was proposed and applied to Al-A356 alloy semi-solid slurry preparation. The heat transfer model was based on heat balance consideration between cup and slurry and it was in a good agreement with experimental results.

Semi-Solid Slurry Preparation without Additional Stirring, Cup-Cast Method

The needs for high-strength and lightweight structural materials have increased in automotive and aerospace structural applications. Semi-solid processed light alloys have satisfied these requirements because of processing advantages and significant weight reduction. Conventional semi-solid casting methods have got a wide variety of problems and difficulties. The cup-cast method that has been just developed is a novel process that make semi-solid casting as easy as pouring the water from a pitcher into a drinking glass, and avoid all the problem and difficulties of other semi-solid casting processes. Cup cast method is based on the heat and mass transfer and spherical equiaxed particles with controlling the nucleation and growth of solid particles were produced. In this study the different factor of this method was optimized by micro-structural investigation on the Al-A356 alloy. Pouring height and temperature, duration of pouring, and cup coating had played important roles in this method.

Computational Modeling of Phase Connectivity in Solid-Liquid Phase Microstructures During Grain Growth.

A Monte Carlo simulation method for modeling grain growth of solid particles in a liquid phase was developed to analyze the connectivity of a solid phase in a solid-liquid system on a two or three dimensional lattice. The mean size, contiguity and connectivity of the solid particles were analyzed as a function of the fraction of solid phase (fS) and interface energy (γSL) between solid and liquid phases. The differences between results from 2D and 3D simulations were also examined. The connectivity increased with increasing fS and γSL, 3D simulations producing a much larger connectivity than 2D simulations. The unrealistically low values obtained from 2D simulations proved that 3D simulation is necessary for a reliable analysis of phase connectivity. The connectivity results from 3D simulations could be divided into two groups; in the first group, the microstructures were close to 100% connectivity, while in the second group, the connectivity decreased. This decrease was caused by grain growth, lowering of fS and γSL and increasing of the distance from the edge plane. A plot of connectivity vs. contiguity indicated that there was a critical value of contiguity (approximately 5%) above which close to 100% connectivity could be maintained, and below which the connectivity decreased approximately linearly. Our computational method may be applied to the design of microstructures of materials containing solid and liquid phases when a particular connectivity is desired.

Influence of the physicochemical properties on the growth of solid particles by granulation in fluidized bed

This work aims at investigating the effects of the physicochemical properties, such as the viscosity and the wettability of a granulating liquid on solid particles surfaces, on the agglomeration kinetics of solid particles in a fluidized bed. A series of batch experiments are carried out in a fluidized bed granulator at 50°C with 2 kg of solid particles. The use of solutions of Sodium CarboxyMethylCellulose (CMC) as binder with different concentrations leads to the study of the viscosity of the solution. The effect of the surface tension is investigated by adding different concentrations of a nonionic surfactant to the binding solution. The effect of the contact angle is then studied by using nonhydrophobic or partly or totally hydrophobic particles. The growth of agglomerates appears to be favored when the interfacial tension increases and the contact angle decreases. The viscosity of the solution has less effect than the interfacial parameters. The results point out that the dominant forces in the granulation process are the capillary forces. When an aqueous solution is pulverized into a fluidized bed containing hydrophobic particles, most of the binder is elutriated and collected in the cyclone. This shows that the main mechanism is in this case spray drying. As this process occurs at low temperature, it is useful for drying thermosensitive solutions.

Transient liquid phase bonding process using liquid phase sintered alloy as an interlayer material

An attempt was made of using a liquid phase sintered alloy, which will be a liquid phase coexisting with solid particles at the bonding temperature, as an interlayer for bonding metals. With an aim of revealing the fundamental features of this modified TLP bonding, investigated were the kinetics concerned with the isothermal solidification process and the growth of solid particles in Fe-4.5wt%P and Fe-1.16wt%B interlayers for bonding pure iron. The movement of the bond interface was linearly dependent on t1/2 with higher slope than expected in the normal TLP bonding. The higher slope is attributed to the contribution of the solid particles distributed in the interlayer. The solid particles have shown no growth. However, when pure Fe particles are allowed to coexist with the liquid of equilibrium composition, they grows very rapidly. Discussion was made on the growth kinetics of the pure Fe particles.

A nucleation experiment in low gravity conditions: Monitoring and collection of Mg and Zn particles

Abstract An experiment on the nucleation and growth of solid particles from the condensation of vapor in low gravity conditions was performed onboard NASA's KC-135 Microgravity Research Aircraft. In addition to the systems to monitor relevant physical parameters, two systems have been developed and used to observe the growth process of the particles and to extract these particles for further microscopic analyses. A dynamic light scattering system is used to measure the in situ mean particle size while a second independent system allows the collection of the nucleated particles directly from the condensation front. These samples have been analyzed in the lab using Scanning Electron Microscopy (SEM). Mean particle sizes are approximately 300 nm and 150 nm for Mg and Zn particles, respectively. Evidence for particle-particle coagulation of Mg into “fractal” like clusters is seen while Zn shows no evidence for any coagulation over the conditions explored.

Formation and growth of solid particles in shear flow

Formation and growth of solid particles of Sn-15% Pb and Al-40% Zn were studied using a Couette type viscometer in isothermally and continuously cooled shear flows. Solid particles come mainly from broken dendrites in the initial stage of solidification. With increase of solid fraction, solids grow in an equiaxial and merging way in the flow of the partially solidified alloy. Mergence happens between two particles of small misorientation, and merging growth is performed by the growth of protruding parts on the solid-liquid interfaces of the solids.

Stochastic modeling of nucleation and coagulation growth processes for NH 4Cl

The growth of solid particles by coagulation or during nucleation is modeled stochastically. Particle growth simulated by either mechanism is found to result in a high porosity. The average porosity (defined as the fraction of the volume occupied by voids) resulting from coagulation is 0.92, and that for cluster scavenging is also 0.92 at a supersaturation ratio of 6.2. A cross sectional porosity scan for coagulated aggregates is predicted to be 0.84, in very close agreement with experimental observations for NH 4Cl. Consideration of the standard deviation of the mean porosity shows that, with either growth mechanism, the trends are established early in the development of an aggregate. Thus, observations from simulations of small aggregates can be safely extended to much larger aggregates.

Comments on Growth of Solid Particles by Turbulence in Collapsing Clouds

Comments on Growth of Solid Particles by Turbulence in Collapsing Clouds

Grain Formation in the Expanding Envelopes of T Tauri Stars

The possibility of the nucleation in the expanding envelopes of T Tauri stars is investigated by using the nucleation theory by Becker and Doring. The nucleation time scale r,. in .the gas is investigated assuming that only graphite is condensable. The expansion time scale roxo of the gas ejected from a T Tauri star is calculated assuming that the gas flow is steady and spherically symmetric. The time scale r,. is compared with roxp for Xo=l0- 2 (Xo is the concentration of carbori by mass) assuming that the gas expands adiabatically, and the mass­ loss rate needed for nucleation is found to be larger than those observed in T Tauri stars. Thi~ suggests that nucleation around T Tauri stars is rather difficult. § I, Introduction It is generally believed that grains ·are contained m interstellar and proto­ planetary gas clouds. The importance of the existence of grains has been pointed out in connection with the cooling mechanism during the contraction of the gas cloud and with the origin of protoplanets. 1> In spite of the importance, however, the formation of grains has not yet been understood well. A few authors have .Pointed out the possibility that grains are formed in atmospheres of cool stars or in expanding shells of active stars such as T Tauri stars, planetary nebulae, novae and supernovae.2>-4> This is a:lso suggested by the infrared excesses of active stars. 5>-u> Hoyle and Wickramasinghe 2>•8> have investigated the conditions for the forma­ tio'n and the growth of solid particles in the static stellar atmospheres of N-type stars. Kamijo14) and Donn et al. 15> have re-examined Hoyle and Wickramasinghe's mechanism in cool carbon stars. On the other hand, Fix16 > has studied the forma­ tion of grains in the adiabatically . pulsating atmosphere. He has shown that if the pulsation period is longer than a few months, the grains are condensed in expanding phases of pulsation. In this paper we will investigate the possibility of the formation of grains in the expanding envelopes of T Tauri stars using the nucleation theory by Becker and Doring 17> and others. 18>-20> The reasons why we take notice ofT Tauri stars are as follows: Firstly, some of them are known as infrared stars 11> so that grains may exist in the circumstellar spaces around T Tauri stars. The mass-loss rates are known from the observations together with the initial velocities of ejected matter and stellar radii. 21 > Hence we can easily compare our estimation with

The Growth of Solid Particles in Fe-20 wt% Cu Alloy during Sintering in the Presence of a Liquid Phase

The Growth of Solid Particles in Fe-20 wt% Cu Alloy during Sintering in the Presence of a Liquid Phase