Papers by Keyword: Platelet

Abstract: Platelet mixer is a type of high-efficient equipment which can mix fluids through platelet micro-channels by cross-bedded injection. It overcomes disadvantages that the fluid is centralized around the inlet and it improves the diffusion. In this work, the platelet mixer is used for pre-mixer in a rocket engine, and the diffusion of oxygen and air in pre-mixer is analyzed. The high speed jet leads to a strong shear force near the inlet which produces counter-rotating stream-wise vortices around the jet. The angle between the direction of jet and radial direction influences both the stream-wise vortices and diffusion. The vortices intensity increases as the angle increase from 0^o to 20^o.

Abstract: A possibility of the SrAl₁₂O₁₉ platelet formation in the Al₂O₃ – ZrO₂ ceramic using SrCO₃ or Sr₃Al₂O₆ is evaluated. An impact of two techniques of platelet synthesis on mechanical properties of the material is investigated. Defects revealed in the sintered ceramic material are analyzed. Recommendations on the best method of the SrAl₁₂O₁₉ phase formation in ceramic materials are given based on the structural and X-ray diffraction analyses as well as on mechanical tests. It is shown that an addition of 3 wt% SrAl₁₂O₁₉ into the ZTA ceramic results in an increase in fracture toughness by up to 30 % in comparison with the initial material.

Abstract: Observation on the effect of adding titanium oxide (TiO₂) and magnesium oxide (MgO) on the sintering of α-alumina (Al₂O₃) has been performed. In this study, technical alumina used as basic material in which the sample is formed by the pressureless sintering/cold press and sintered at 1500°C which is lower than alumina sintering temperature at 1700°C. Elemental analysis, observation of microstructure, hardness, fracture toughness and density measurements were carried out to determine the physical and mechanical properties of alumina. The results indicate a change in the microstructure where the content of the platelet structure are much more than the equilateral structure. At sintering temperature of 1500°C, neck growth occurs at ceramics grain, supported by the results of the density test which indicate perfect compaction has occurred in this process.

Abstract: Solar thermal propulsion is a kind of space propulsion technology with great potential applications. Due to the difficulty of hydrogen storage in orbit, ammonia becomes an ideal candidate propellant as its stability and easier storage. In solar thermal propulsion system, the working temperature is usually above 2300K, and in this condition the dissociation of ammonia will occur. Thus, using ammonia as a single component propellant to compute and analysis the performance of thruster is not precise, and the mixture components produced from ammonia dissociation must be taken into account. In this paper a novel heat exchanger configuration with platelet technology is designed, and based on finite-rate chemical reaction method and computational fluid dynamics, the dissociation process of ammonia in the heat exchanger and nozzle is simulated. Then the influence to the specific impulse of the solar thermal propulsion system is comparatively analyzed. The simulation result indicates that the main productions of the dissociation are N₂ and H₂, and the mole fraction of other components is small value that can be neglected. The specific impulse considering dissociation reaction is higher than not considering, so that this research can estimate the performance of solar thermal propulsion with ammonia propellant more precisely.

Abstract: Platelet alumina powders have been synthesized by introducing AlF₃ as crystalline transformation additive. The influence of the additive contents on the phase transformation of the start material Al (OH)₃ was studied by SEM, the effect of calcination temperatures on the phase transformation and microstructure of alumina powder were investigated by TG-DSC, XRD and SEM. The results indicate that uniform platelet powders could be abtained while more than 15% AlF₃ was introduced. When the calcination temperature higher than 1100°C pure α-Al₂O₃ could be synthesized, comparing to the tranditional preparation of platelet alumina powders, the remarkable advantages of the method are low calsination temperature, small particle size and simple process.

Abstract: Polyrotaxane-immobilized surfaces were prepared as a platform of dynamic surfaces, which can prevent from non-specific interaction with plasma proteins and platelet, and then modulate cellular functions via specific interaction with receptor protein-ligand binding through movable polyrotaxane backbone. The immobilization of the polyrotaxane was carried out via two-step protocol, in which the polyrotaxane with tetraethyleneglycol dodecanethiol (TEGDT) anchoring group at both terminals was fixed onto Au substrate via Au-S bond, followed by the fixation of TEGDT molecule onto the Au substrate to complete the loop formation of polyrotaxane on the Au substrate with the help of self-assembled monolayer formation of TEGDT. Their surface properties were characterized by means dynamic contact angle measurements, and preliminary studies as biomaterials were performed in terms of plasma protein adsorption onto their surfaces.

Abstract: A dense alumina body with anisotropic grains was fabricated from anisotropic particles (platelets) after heating at 1650°C for 15 min under applying pressure of 60 MPa using a PECS technique. When the alumina was cut on the vertical plane to the load direction while sintering, the breakdown voltage was 15 KV/mm and thermal conductivity was 36 W/mK. On the other hand, a porous alumina body was also synthesized from alumina platelets. The uniaxial pressure in fabricating the green compact body had an influence on the relative density of the alumina body after heating. The relative density and compressive strength of the compact that was uniaxially pressed at 1 MPa were 75 %, respectively. In addition, the relative density and compressive strength of compact that was uniaxially pressed at 3 MPa were 64 %, respectively. The thermal conductivity of the porous alumina with 64% in porosity was 0.8 W/Km.

Abstract: α-Al2O3 platelets were successfully synthesized in molten NaCl-KCl salt using the pre-calcined Al(OH)3 powders as starting materials, and the effect of milling medium on the powder characteristics was investigated, with the purpose of obtaining high performance sintered ceramics. When anhydrous alcohol was used as milling medium, the synthesized product at 900°C was porous α-Al2O3 with a small amount of amorphous Al2O3. While deionized water was used, single-phase and dense α-Al2O3 platelets were developed at 900°C. It was related with different solubility of NaCl-KCl salt in anhydrous alcohol and deionized water during milling. When the synthesized α-Al2O3 platelets were used as seeds in sintered ceramics, fracture toughness was developed.

Abstract: The in vitro blood compatibility of a new nickel free high nitrogen austenitic stainless steel Fe-Cr-Mn-Mo-N (BIOSSN4) was studied by the kinetic clotting time test and the platelet rich plasma adhesion test in this paper. In comparison with 316L stainless steel, the kinetic clotting time of BIOSSN4 steel are longer, and only causes less activation of platelets in platelet adhesion test, which was indicated by their morphology and low spreading. The experimental results reveals that the BIOSSN4 stainless steel has better blood compatibility, the blood compatibility mechanism of steels was analyzed based on surface tension and interfacial tension between the steels and blood.