THE EFFECTIVE MODULI OF COMPOSITE REINFORCED BY SPHERICALCOATING PARTICLES

The effective moduli of composite reinforced by spherical coating particles are investigated by the four phase spheroidal model and the theory of equivalent media. The theoretical predicting formulae of bulk modulus and shear modulus have been derived for this kind of composite in this paper. These formulae can reduce to the results of three phase spheroidal model which had been obtained by others for composite reinforced by particles.

3D Raman mapping as an analytical tool for investigating the coatings of coated drug particles

The properties of dry-coated paracetamol particles(fast-dissolving model drug)with carnauba wax particles as the coating agent(dissolution retardant)were investigated.Raman mapping technique was used to non-destructively examine the thickness and homogeneity of coated particles.The results showed that the wax existed in two forms on the surface of the paracetamol particles,forming a porous coating layer:i)whole wax particles on the surface of paracetamol and glued together with other wax surface particles,and ii)deformed wax particles spread on the surface.Regardless of the final particle size fraction(between 100 and 800 mm),the coating thickness had high variability,with average thickness of 5.9±4.2 mm.The ability of carnauba wax to decrease the dissolution rate of paracetamol was confirmed by dissolution of powder and tablet formulations.The dissolution was slower for larger coated particles.Tableting further reduced the dissolution rate,clearly indicating the impact of subsequent formulation processes on the final quality of the product.

Enhancement of Heat-Resistance of Carbonyl Iron Particles by Coating with Silica and Consequent Changes in Electromagnetic Properties

Silica-coated carbonyl iron particles （CIPs） are fabricated with the Stober method to improve their heat-resistance and wave-aSsorption properties. The morphology, heat-resistance, electromagnetic properties and microwave absorption of raw-CIPs and silica-coated CIPs are investigated using a scanning electron microscope, an energy dispersive spectrometer, a thermal-gravimetric analyzer, and a network analyzer. The results show that the heat-resistance of silica-coated CIPs is better than that of raw CIFs. The reflection losses exceeding -lOdB of silica-coated CIPs are obtained in the frequency range 9.5-12.4 GHz for the absorber thickness of 2.3 mm, and the same reflection losses of uncoated CIPs reach the data in the lower frequency range for the same thickness. The enhanced microwave absorption of silica-coated CIPs can be ascribed to the combination of proper electromagnetic impedance match and the decrease of dielectric permittivity.

CVD Coating of Oxide Particles for the Production of Novel Particle-Reinforced Iron-Based Metal Matrix Composites

This paper focuses on surface metallization of oxide particles by means of titanium nitride (TiN) thin films for the production of highly wear-resistant metal matrix composites (MMC) on Fe-base for wear protection applications. These powder-metallurgically produced materials consist of a metallic matrix with embedded oxide hard-particles such as alumina or zirconia. The poor wettability of these oxides by iron-base melts and the resulting weak bonding between the components lead to porous materials and weak tribomechanical properties, thus limiting the material’s application range. To counteract such problems, this paper describes a processing route in which the oxide particles are pre-metallized by application of a thin TiN coating by means of chemical vapor deposition (CVD). This surface metallization should increase the wettability and bonding behavior between the ionically bonded particles and the iron-base alloy, which should improve the mechanical and tribological properties. Therefore, a CVD device for coating ceramic particles was constructed and is described in this paper. Furthermore, coatings deposited on the ceramic sub-strates were investigated by means of RBS, SEM and XRD. In addition, the feasibility of producing metal matrix composites (MMC) by admixing the TiN-coated oxide particles with a Fe-base alloy and their further densification by supersolidus liquid-phase sintering is demonstrated.

Influence of cycle time distribution on coating uniformity of particles in a spray fluidized bed by using CFD-DEM simulations

Cycle Time Distribution(CTD)plays a critical role for determining uniformity of particle coating in spray fluidized beds.However,the CTD is influenced by both geometrical structure and operating conditions of fluidized bed.In this study,a spray fluidized bed of coating process is simulated by a comprehensive Computational Fluid Dynamics-Discrete Element Model(CFD-DEM).To achieve different behaviors of CTD,some modifications are designed on a pseudo-2D internally circulating fluidized bed,which traditionally composes of a high-velocity upward bed and low-velocity downward bed.These modifi-cations include making the air distributor slope and/or laying a baffle in the downward bed.First,the CTD and evolution of particle size distribution under different bed structures are compared.The CTD directly influences the coating uniformity.By making the particles flowing along a parallel direction in the downward bed through the geometrical modifications,the CTD becomes narrower and the coating uniformity is significantly improved.Second,under the optimized bed structure,the influence of oper-ating conditions on the coating uniformity is studied.Properly increasing the fluidization gas velocity and the fluidization gas temperature and reducing the liquid spray rate can improve the coating uniformity.

SIMULATION OF FLUIDIZED BED WITH TOP LIQUID SPRAYING

Simulation of the drying process in a top spraying fluidized bed is conducted.A wetting coefficient describing the wetted part of the particle surface is introduced.Using experimental data and the data regression method,the modified function of the wetting coefficient is calculated.And this function is introduced to the mathematical model,which describes the heat and mass transfer process in a liquid sprayed gas fluidized bed.Through modeling,the gas humidity and temperature profiles as well as the particle temperature profile can be obtained.Compared with the experimental results,the wetting coefficient and the mathematical model are verified.

A review of TRISO-coated particle nuclear fuel performance models

The success of high temperature gas cooled reactor depends upon the safety and quality of the coated particle fuel. The understanding and evaluation of this fuel requires the development of an integrated mechanistic fuel performance model that fully describes the mechanical and physicochemical behavior of the fuel particle under irradiation. In this paper, a review of the analytical capability of some of the existing computer codes for coated particle fuel was performed. These existing models and codes include FZJ model, JAERI model, Stress3 model, ATLAS model, PARFUME model and TIMCOAT model. The theoretic model, methodology, calculation parameters and benchmark of these codes were classified. Based on the failure mechanism of coated particle, the advantage and limits of the models were compared and discussed. The calculated results of the coated particles for China HTR-10 by using some existing code are shown. Finally, problems and challenges in fuel performance modeling were listed.

Manufacture of HTR Fuel Element

The HTR Fuel Element R & D Program,set in 1987,aims to develop the manufacturetechnology of HTR fuel element and to produce the fuel element for the first core of our 10MW experimental reactor.Now the work on laboratory scale is phased out.In this paper,the fuel element manufacture technology is described and the test results are given.

Swelling and diffusion model of a hydrophilic film coating on controlled-release urea particles

Controlled-release urea was fabricated by coating urea particles with a polymer latex in a fluidized bed. The latex film coated on the urea particle surface was hydrophilic and swelled in water. The film swelling in water and urea solution and properties of the swollen film were studied. The film swelling in urea solution followed the Lagergren＇s pseudo-first order kinetics with the swelling coefficient depending on the film material and experimental conditions. The effects of swelling on film structure and permeability were studied. The film permeability coefficient decreased with increasing swelling ratio with an approx- imately linear relationship. Based on the film formation process and structure of the swollen film. a film structure model consisting of dense and swollen phases was proposed. The permeability coefficient of the spherical film and cumulative release of urea from the coated particles were calculated from the swelling ratio of the spherical film. which was determined from the expansion curve of the coated particle during the release process, The calculated and measured release curves agreed well, This research indicates that the swelling of the hydrophilic film and the controlled-release mechanism are important factors in the development of controlled-release urea.

Irradiation Testing of Coated Particle Fuel at HANARO

TRISO （Tri-structural iso-tropic）-coated particle fuel is being developed to support the development of a VHTR （very high temperature reactor） in Korea. From August 2013, the first irradiation testing of coated particle fuel was begun to demonstrate and qualify TRISO fuel for use in the VHTR in HANARO （high-flux advanced neutron application reactor） at KAERI （Korea Atomic Energy Research Institute）. This experiment is currently undergoing under an atmosphere of a mixed inert gas without on-line temperature monitoring and control combined with on-line fission product monitoring of the sweep gas. The irradiation device contains two test rods, one contains nine fuel compacts and the other five compacts and eight graphite specimens. Each compact has 263 coated particles. After a peak bum-up of about 4% and a peak fast neutron fluence of about 1.7 × 1021 n/cm2, PIE （post irradiation examination） will be carried out at KAERI＇s irradiated material examination facility. This paper describes the characteristics of coated particle fuels, and the design of the test rod and irradiation device for the coated particle fuels, and discusses the technical results of irradiation testing at HANARO.

SIMULATION OF PARTICLE COATING IN THE SUPERCRITICAL FLUIDIZED BED

Fluidized bed technology using supercritical carbon dioxide both as a fluidizing gas and as a solvent for the coating material makes possible the production of thin, uniform and solvent-free coatings. But operation at low fluidizing velocities, which is favorable to facilitate gas cleaning under the high pressure conditions, may lead to uneven distribution of the coating in the fluidized bed and to unstable operation due to agglomeration. Therefore a model has been developed which describes local fluid dynamics within the high pressure fluidized bed. Based on this model, the coating process is described and the distribution of the coating inside the fluidized bed is calculated. Furthermore a submodel for the calculation of local concentrations of liquid paraffin has been set up, which may be used as a basis for the prediction of agglomeration and thus stability of operation.

PARTICLE COATING BY CHEMICAL VAPOR DEPOSITION IN A FLUIDIZED BED REACTOR

Aluminum coatings were created onto glass beads by chemical vapor deposition in a fluidized bed reactor at different temperatures. Nitrogen was enriched with Triisobutylaluminum (TIBA) vapor and the latter was thermally decomposed inside the fluidized bed to deposit the elemental aluminum. To ensure homogeneous coating on the bed material, the fluidizing conditions necessary to avoid agglomeration were investigated for a broad range of temperatures. The deposition reaction was modeled on the basis of a discrete particle simulation to gain insight into homogeneity and thickness of the coating throughout the bed material. In particular, the take-up of aluminum was traced for selected particles that exhibited a large mass of deposited aluminum.

Scalable gas-phase processes to create nanostructured particles

The properties of nanoparticles are often different from those of larger grains of the same solid material because of their very large specific surface area. This enables many novel applications, but properties such as agglomeration can also hinder their potential use. By creating nanostructured particles one can take optimum benefit from the desired properties while minimizing the adverse effects. We aim at developing high-precision routes for scalable production of nanostructured particles. Two gas-phase synthesis routes are explored. The first one - covering nanoparticles with a continuous layer - is carried out using atomic layer deposition in a fluidized bed. Through fluidization, the full surface area of the nanoparticles becomes available. With this process, particles can be coated with an ultra-thin film of constant and well-tunable thickness. For the second route - attaching nanoparticles to larger particles - a novel approach using electrostatic forces is demonstrated. The micron-sized particles are charged with one polarity using tribocharging. Using electrospraying, a spray of charged nanoparticles with opposite polarity is generated. Their charge prevents agglomeration, while it enhances efficient deposition at the surface of the host particle. While the proposed processes offer good potential for scale-up, further work is needed to realize large-scale processes.

Research on the Silicon Carbide Layer of Coated Fuel Particles

The 10MW high temperature gas-cooled test reactor (HTR-10) under construction at INET uses whole ceramic fuel elements. The main barrier which prevents fission product release is the SiC layer of the coated fuel particles. Fabrication of high quality SiC layers is one of the key R&D tasks for the HTR-10 fuel element. The SiClayer was deposited on the fuel particles in a 50 mm conical fluidized bed using the CVD (chemical vapour deposition) technique. The density, thickness, strength and elastic modulus of the SiC layer were measured. The microstructure was observed using SEM (scanning electron microscope ). Parameters were established for manufacturing the SiC layer of the coated fuel particles to be used in the HTR-10. It was found that the traditional density measurement by the sink-float method is questionable in the low density region and that the SiC layer may be contaminated by uranium under certain conditions.

Experimental observation of surface phonon absorption in Zn fine particles coated with ZnO

FINE particles have attracted much attention in the past few years due to their unique physical and chemical properties. For gas-evaporated fine metallic particles, a thin oxide layer is usually formed on their surface. According to Ruppin’s prediction, a dielectric coating on metallic particles should have a series of surface modes between ωTO and ωLO, the long-wavelength transverse and longitudinal optical phonon frequencies of the dielectric. The frequency of

A novel coated-particle design and fluidized-bed chemical vapor deposition preparation method for fuel-element identification in a nuclear reactor

Particle coating is an important method that can be used to expand particle-technology applications. Coated-particle design and preparation for nuclear fuel-element trajectory tracing were focused on in this paper. Particles that contain elemental cobalt were selected because of the characteristic gamma ray spectra of 60Co. A novel particle-structure design was proposed by coating particles that contain elemental cobalt with a high-density silicon-carbide （SiC） layer. During the coating process with the high-density SiC layer, cobalt metal was formed and diffused towards the coating, so an inner SiC–CoxSi layer was designed and obtained by fluidized-bed chemical vapor deposition coupled with in-situ chemical reaction. The coating layers were studied by X-ray diffractometry, scanning electron microscopy, and energy dispersive X-ray spectroscopy techniques. The chemical composition was also determined by inductively coupled plasma optical emission spectrometry. The novel particle design can reduce the formation of metallic cobalt and prevent cobalt diffusion in the coating process, which can maintain safety in a nuclear reactor for an extended period. The experimental results also validated that coated particles maintain their structural integrity at extremely high temperatures （～1950 °C）, which meets the requirements of next-generation nuclear reactors.