Study on flow characteristics of solid/liquid system in lysozyme crystal growth

During the process of lysozyme protein crystallization with batch method, the macroscopic flow field of solid/liquid system was observed by particle image velocimetry (PIV). Furthermore, a normal growth rate of (110) face and local flow field around a single protein crystal were obtained by a long work distance microscope. The experimental results showed that the average velocity, the maximal velocity of macroscopic solid/liquid system and the velocity of local flow field around single protein crystal were fluctuant. The effective boundary layer thickness delta(eff), the concentration at the interface Q and the characteristic velocity V were calculated using a convection-diffusion model. The results showed that the growth of lysozyme crystal in this experiment was dominated by interfacial kinetics rather than bulk transport, and the function of buoyancy-driven flow in bulk transport was small, however, the effect of bulk transport in crystal growth had a tendency to increase with the increase of lysozyme concentration. The calculated results, also showed that the order of magnitude of shear force was about 10(-21) N, which was much less than the bond force between the lysozyme molecules. Therefore the shear force induced by buoyancy-driven flows cannot remove the protein molecules from the interface of crystal.

The kinetic-theory for dilute solid liquid 2-phase flow

On the basis of a brief review of the continuum theory for macroscopic descriptions and the kinetic theory for microscopic descriptions in solid/liquid two-phase flows, some suggestions are presented, i.e. the solid phase may be described by the Boltzmann equation and the liquid phase still be described by conservation laws in the continuum theory. Among them the action force on the particles by the liquid fluid is a coupling factor which connects the phases. For dilute steady solid/liquid two-phase flows, the particle velocity distribution function can be derived by analogy with the procedures in the kinetic theory of gas molecules for the equilibrium state instead of being assumed, as previous investigators did. This done, more detailed information, such as the velocity probability density distribution, mean velocity distribution and fluctuating intensity etc. can be obtained directly from the particle velocity distribution function or from its integration. Experiments have been performed for dilute solid/liquid two-phase flow in a 4 x 6 cm2 sized circulating square pipe system by means of laser Doppler anemometry so that the theories can be examined. The comparisons show that the theories agree very well with all the measured data.

Controlled growth of silicon nanowires by solid-liquid-solid method and their formation mechanism

High quality silicon nanowires (SiNWs) were grown directly from n-(111) silicon single crystal substrate by using Au film as a metallic catalyst. The diameter and length of the formed nanowires are 30-60 nm and from several micrometers to sereral tens of micrometers, respectively. The effects of Au film thickness, annealing temperature, growth time and N-2 gas flow rate on the formation of the nanowires were experimentally investigated. The results confirmed that the silicon nanowires with controlled diameter, length, shape and orientation can be obtained via reasonably choosing and optimizing various technical conditions. The formation process of the silicon nanowires is analyzed qualitatively based on solid-liquid-solid growth mechanism.

Blue Luminescent Properties of Silicon Nanowires Grown by a Solid-Liquid-Solid Method

Silicon nanowires (SiNWs) were grown directly from n-(111) single-crystal silicon (c-Si) substrate based on a solid-liquid-solid mechanism, and Au film was used as a metallic catalyst. The room temperature photoluminescence properties of SiNWs were observed by an Xe lamp with an exciting wavelength of 350 nm. The results show that the SiNWs exhibit a strongly blue luminescent band in the wavelength range 400-480 nm at an emission peak position of 420 nm. The luminescent mechanism of SiNWs indicates that the blue luminescence is attributed to the oxygen-related defects, which are in SiOx amorphous oxide shells around the crystalline core of SiNWs.

Boundary conditions at the solid-liquid surface over the multiscale channel size from nanometer to micron

The boundary condition at the solid surface is one of the important problems for the microfluidics. In this paper we study the effects of the channel sizes on the boundary conditions (BC), using the hybrid computation scheme adjoining the molecular dynamics (MD) simulations and the continuum fluid mechanics. We could reproduce the three types of boundary conditions (slip, no-slip and locking) over the multiscale channel sizes. The slip lengths are found to be mainly dependent on the interfacial parameters with the fixed apparent shear rate. The channel size has little effects on the slip lengths if the size is above a critical value within a couple of tens of molecular diameters. We explore the liquid particle distributions nearest the solid walls and found that the slip boundary condition always corresponds to the uniform liquid particle distributions parallel to the solid walls, while the no-slip or locking boundary conditions correspond to the ordered liquid structures close to the solid walls. The slip, no-slip and locking interfacial parameters yield the positive, zero and negative slip lengths respectively. The three types of boundary conditions existing in "microscale" still occur in "macroscale". However, the slip lengths weakly dependent on the channel sizes yield the real shear rates and the slip velocity relative to the solid wall traveling speed approaching those with the no-slip boundary condition when the channel size is larger than thousands of liquid molecular diameters for all of the three types of interfacial parameters, leading to the quasi-no-slip boundary conditions.

A New Criterion Number for the Boundary Conditions at the Solid/Liquid Interface in Nanoscale

A simple, but important three-atom model was proposed at the solid/liquid interface, leading to a new criterion number, lambda, governing the boundary conditions (BCs) in nanoscale. The solid wall is considered as the face-centered-cubic (fcc) structure. The fluid is the liquid argon with the well-known LJ potential. Based on the concept, the two micro-systems have the same BCs if they have The same criterion number. The degree of the locking BCs is enhanced when lambda equals to 0.757. Such critical criterion number results in the substantial epitaxial ordering and one, two, or even three liquid layers are locked by the solid wall, depending on the coupling energy scale ratio of the solid and liquid atoms. With deviation from the critical criterion number, the flow approaches the slip BCs and there are little ordering structures within the liquid. Always at the same criterion number, the degree of the slip is decreased or the locking is enhanced with increasing the coupling energy scale ratio of the solid and liquid atoms. The above analysis is well confirmed by the molecular dynamics (MD) simulation. The slip length is well correlated in terms of the new criterion number. The future work is suggested to extend the present theory for other microstructures of the solid wall atoms and quasi-LJ potentials.

The solid-liquid extraction of yttrium from rare earths by solvent (ionic liquid) impreganated resin coupled with complexing method

A kind of solvent (ionic liquid) impreganated resin (IL-SIR) was developed herein for ameliorating imidazolium-type IL-based liquid-liquid extraction of metal ions. In this study, [C(8)mim][PF6] containing Cyanex923 was immobilized on XAD-7 resin for solid-liquid extraction of rare earth (RE). The solid-liquid extraction contributed to ameliorating mass transfer efficiency, i.e. shortening equilibrium time from 40 min to 20 min, increasing extraction efficiency from 29% to 80%. In additional, the novel IL-SIR could separate Y(III) from Sc(III), Ho(III), Er(III), Yb(III) effectively by adding water-soluble complexing agent.

Influences of Hydration Force and Elastic Strain Energy on the Stability of Solid Film in a Very Thin Solid-on-Liquid Structure

Since hydration forces become very strong at short range and are particularly important for determining the magnitude of the adhesion between two surfaces or interaction energy, the influences of the hydration force and elastic strain energy due to hydration-induced layering of liquid molecules close to a solid film surface on the stability of a solid film in a solid-on-liquid (SOL) nanostructure are studied in this paper. The liquid of this thin SOL structure is a kind of water solution. Since the surface forces play an important role in the structure, the total free energy change of SOL structures consists of the changes in the bulk elastic energy within the solid film, the surface energy at the solid-liquid interface and the solid-air interface, and highly nonlinear volumetric component associated with interfacial forces. The critical wavelength of one-dimensional undulation, the critical thickness of the solid film, and the critical thickness of the liquid layer are studied, and the stability regions of the solid film have been determined. Emphasis is placed on calculation of critical values, which are the basis of analyzing the stability of the very thin solid film.

Determination of the interdiffusion coefficients of liquid Zn and Sn using Ta/Zn-Sn/Si trilayers

In this paper we present a new method for measuring diffusion coefficients in liquid metals under convection-less conditions with solid/liquid-liquid/solid trilayer. The advantage of this kind of trilayer is that effects from gravity-induced convection and Marangoni-convection can be omitted, so that the diffusion coefficient is determined more accurately. The Ta/Zn-Sn/Si trilayer were prepared with a multi-target ion-beam sputtering deposition technique and annealed in an electric furnace under an argon atmosphere. The interdiffusion of liquid zinc and tin at 500 degrees degree C was investigated. The diffusion concentration profiles were determined by energy dispersive spectroscopy. The interdiffusion coefficients range from 1.0x10(-6)cm(2)/s to 2.8x10(-6)cm(2)/s, which is less than previous values measured by capillary reservoir technique under 1g-environment where various convection exist. The precise interdiffusion coefficients of liquid zinc and tin result from the removing of disturbances of various kinds of convection.

Kinetic study of hydrolysis of xylan and agricultural wastes with hot liquid water

We investigated the kinetics of hot liquid water (HLW) hydrolysis over a 60-min period using a self-designed setup. The reaction was performed within the range 160-220 °C, under reaction conditions of 4.0 MPa, a 1:20 solid:liquid ratio (g/mL), at 500 rpm stirring speed. Xylan was chosen as a model compound for hemicelluloses, and two kinds of agricultural wastes-rice straw and palm shell-were used as typical feedstocks representative of herbaceous and woody biomasses, respectively. The hydrolysis reactions for the three kinds of materials followed a first-order sequential kinetic model, and the hydrolysis activation energies were 65.58 kJ/mol for xylan, 68.76 kJ/mol for rice straw, and 95.19 kJ/mol for palm shell. The activation energies of sugar degradation were 147.21 kJ/mol for xylan, 47.08 kJ/mol for rice straw and 79.74 kJ/mol for palm shell. These differences may be due to differences in the composition and construction of the three kinds of materials. In order to reduce the decomposition of sugars, the hydrolysis time of biomasses such as rice straw and palm shell should be strictly controlled.

Determination of the interdiffusion coefficients of liquid Zn and Sn using Ta/Zn-Sn/Si trilayers

In this paper we present a new method for measuring diffusion coefficients in liquid metals under convection-less conditions with solid/liquid-liquid/solid trilayer. The advantage of this kind of trilayer is that effects from gravity-induced convection and Marangoni-convection can be omitted, so that the diffusion coefficient is determined more accurately. The Ta/Zn-Sn/Si trilayer were prepared with a multi-target ion-beam sputtering deposition technique and annealed in an electric furnace under an argon atmosphere. The interdiffusion of liquid zinc and tin at 500 degrees degree C was investigated. The diffusion concentration profiles were determined by energy dispersive spectroscopy. The interdiffusion coefficients range from 1.0x10(-6)cm(2)/s to 2.8x10(-6)cm(2)/s, which is less than previous values measured by capillary reservoir technique under 1g-environment where various convection exist. The precise interdiffusion coefficients of liquid zinc and tin result from the removing of disturbances of various kinds of convection.

Influence of Forced Convection on Columnar Microstructure During Directional Solidification of Al-Ni Alloys

This paper presents a summary of cellular and dendritic morphologies resulting from the upward directional solidification of Al - Ni alloys in a cylindrical crucible. We analysed the coupling of solid-liquid interface morphology with natural and forced convection. The influence of natural convection was first analyzed as a function of growth parameters (solute concentration, growth rate and thermal gradient). In a second step, the influence of axial vibrations on solidification microstructure was investigated by varying vibration parameters (amplitude and frequency). Experimental results were compared to preliminary numerical simulations and a good agreement is found for natural convection. In this study, the critical role of the mushy zone in the interaction between fluid flow and solidification microstructure is pointed out.

In situ formation by laser cladding of a TiC composite coating with a gradient distribution

An in situ method was developed to produce an Ni alloy composite coating reinforced by in situ reacted TiC particles with a gradient distribution, using one-step laser cladding with a pre-placed powder mixture on a 5CrMnMo steel substrate. Dispersed and ultra-fine TIC particles were formed in situ in the coating. Most. of the TiC particles, with a marked gradient distribution, were uniformly distributed within interdendritic regions because of the trapping effect of the advancing solid-liquid interface. In addition, the TiC-gamma-Ni interfaces generated in situ were found to be free from any deleterious surface reaction. Finally, the microhardness also showed a gradient variation, with the highest value of 1250 Hv0.2 and the wear properties of the coating were significantly enhanced.

Characteristics Of Energy Dissipation In Hyperconcentrated Flows

An equilibrium equation for the turbulence energy in sediment-laden flows was derived on the basis of solid-liquid two-phase flow theory. The equation was simplified for two-dimensional, uniform, steady and fully developed turbulent hyperconcentrated flows. An energy efficiency coefficient of suspended-load motion was obtained from the turbulence energy equation, which is defined as the ratio of the sediment suspension energy to the turbulence energy of the sediment-laden flows. Laboratory experiments were conducted to investigate the characteristics of energy dissipation in hyperconcentrated flows. A total of 115 experimental runs were carried out, comprising 70 runs with natural sediments and 45 runs with cinder powder. Effects of sediment concentration on sediment suspension energy and flow resistance were analyzed and the relation between the energy efficiency coefficient of suspended-load motion and sediment concentration was established on the basis of experimental data. Furthermore, the characteristics of energy dissipation in hyperconcentrated flows were identified and described. It was found that the high sediment concentration does not increase the energy dissipation; on the contrary, it decreases flow resistance.

Surface-induced melting of metal nanoclusters

We investigate the size effect on melting of metal nanoclusters by molecular dynamics simulation and thermo dynamic theory based on Kofman's melt model. By the minimization of the free energy of metal nanoclusters with respect to the thickness of the surface liquid layer, it has been found that the nanoclusters of the same metal have the same premelting temperature T-pre = T-0 - T-0(gamma(su) - gamma(lv) - gamma(sl))/(rhoLxi) (T-0 is the melting point of bulk metal, gamma(sv) the solid-vapour interfacial free energy, gamma(sl) the liquid-vapour interfacial free energy, gamma(sl),l the solid-liquid interfacial free energy, p the density of metal, L the latent heat of bulk metal, and xi the characteristic length of surface-interface interaction) to be independent of the size of nanoclusters, so that the characteristic length of a metal can be obtained easily by T-pre, which can be obtained by experiments or molecular dynamics (MD) simulations. The premelting temperature T-pre of Cu is obtained by AID simulations, then xi is obtained. The melting point T-cm is further predicted by free energy analysis and is in good agreement with the result of our MD simulations. We also predict the maximum premelting-liquid width of Cu nanoclusters with various sizes and the critical size, below which there is no premelting.