Papers by Keyword: Particle Size

Abstract: Sand-milling machine was firstly utilized to crush and disperse the raw materials. A homogenous and well-dispersed mixture of TiO₂ and BaCO₃ (<30nm) was obtained. The solid state reaction temperature can be reduced by 200°C for nanosized reactants compared with coarse ones. In order to increase tetragonality of nanosized BaTiO₃, an innovative two-step calcination method, which includes solid state reaction process between reactants at a low temperature T₁ and phase transition process at a high temperature T₂, was subsequently adopted. The microstructure evolution of BaTiO₃ by two-step calcination was investigated as a function of T₂ and corresponding dwelling time t₂. Pure-perovskite BaTiO₃ nanopowders with the mean particle size as small as 75nm and tetragonality (c/a ratio) higher than 1.0096 could be fabricated by two-step calcination through altering T₂ and/or its dwelling time t₂.

Abstract: Ti-6Al-4V (wt.%) alloy rods were prepared successfully using a low-cost and short powder metallurgy process that involves mixing TiH₂ and Al₆₀V₄₀ powders, compacting the powder blend and extruding the powder compact at elevated temperatures. The microstructure and mechanical properties of Ti-6Al-4V alloy and the effects of particle size, oxygen content and heat treatment on them were investigated. The results showed that the microstructure and homogeneity of the extruded rods were strongly affected by the particle size of TiH₂/Al₆₀V₄₀ powder blends. By changing tumbler mixing into low-energy ball milling, the TiH₂/Al₆₀V₄₀ particle sizes decreased, and the volume fraction of undissolved V rich particles in the microstructure of the extruded rod substantially decreased from 8.6% to zero. High yield strength and ultimate tensile strength of 1154 and 1353 MPa respectively with a moderate elongation to fracture of 3.6% are achieved with the Ti-6Al-4V rod prepared by using the powder blend. The extruded Ti-6Al-4V rod prepared using the ball milled powder had a very high strength, but limited ductility due to a high oxygen content. Solution treatment and aging slightly increase the strength of Ti-6Al-4V rods at the cost of dramatic decrease of ductility.

Abstract: The additive manufacturing of titanium parts by laser metal deposition (LMD) offers a promising alternative to conventional machining of aviation parts. The technology enables the production of near net shape parts with higher deposition rates than powder bed-based processes. Ti-6Al-4V powder is fed directly into a high-power laser beam in order to form a deposition track on the underlying material. For three dimensional parts several tracks are stacked on top of each other. In this paper the material evolution from powder to a solid wall during LMD is investigated. Powder properties as well as the microstructure in deposited structures are thoroughly described and analyzed. The gained knowledge provides a deeper process comprehension and is an important step towards high-quality additive manufacturing of Ti-6Al-4V. At first, the influence of powder particle size on the LMD process is quantified by creating two powder fractions with different sieving procedures. The used material is recycled Ti-6Al-4V powder from a powder bed-based AM process with particle sizes up to 150 µm. The powder is characterized according to current standards; apparent density, tap density and the flowability are determined as well as the particle size distribution. Additionally, the particle morphology is analyzed using electron beam microscopy. In order to link the powder properties to the LMD process and to identify impact factors to the feeding behavior the mass flow of both powder fractions is measured. Secondly, walls are manufactured with the characterized powder and the resulting microstructure is analyzed. Because of the layer-wise deposition and the resultant periodic heat input each layer experiences several thermal cycles. As a result various solid phase transformations occur during the deposition of consecutive tracks. In addition the thermal boundary conditions change with increasing wall height and a heterogeneous microstructure is observed. It consists of non-equilibrium phases (martensitic or massive α) and α+β lamellae. Based on an existing numerical model the thermal history of each layer is estimated and an explanation is presented for the complex sequence of solid phase transformations in each area of the structure.

Abstract: In this work, liquid crystal emulsion with aloe vera (AV) was formulated and characterised its physical properties. A direct titration method was used to determine the composition of liquid crystal emulsion in a system consisting of water/mixed Tween 80: Span 85/hexane. AV gel was added to produce AV liquid crystal emulsion (AVLCE), which was then subjected to various characterisation such as microscopic analysis, stability test, rheological test and particle size analysis. Results showed that the application of AVCLE employed better performances in terms of stability, particle size and moisturizing. This study suggest that the formulated AVLCE may be suitable to be used as topical application on wounded skin.

Abstract: The aim of this paper is to investigate the behavior of the recycled polymer containing the filler. The recycled polymer under investigation is polypropylene with a glass fiber filler. During grinding of plastic waste particles are formed which have a different size, shape and surface, from larger pieces to dust particles. Several recycled mixtures were made, all from original material. Samples with different particle size of recycled material were subsequently tested by mechanical testing. Included tests were Charpy impact test and Shore hardness test. Testing was conducted at different temperatures; ambient 23 °C and increased temperatures 60 ° and 100 °C. The results show a very large effect on Charpy properties and a lesser influence on the hardness of these mixtures. Mixture of smallest dust particles indicates larges change of measured properties.

Abstract: The crystal structure, microscopic morphology, particle size distribution and UV shielding properties of layered double hydroxides (LDHs) with different particle size were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), laser particle size analysis and ultraviolet and visible (UV-vis) spectrophotometer. The effects of LDHs with different particle size on the physical, rheological properties and UV aging resistance of bitumen were investigated by conventional physical properties and dynamic rheological characteristics. The results indicated that the particle size of LDHs had a little effect on the physical properties, and it had some influence on rheological properties of bitumen, but its influence on the UV aging resistance of bitumen was different significantly. When UV aging time was 9d, the viscosity aging indexes of bitumen modified by LDHs with different particle size (80nm, 115nm and 180nm) decreased by 48.2%, 58.1% and 63.8% compared with the pristine bitumen, respectively. LDHs with the particle size of 180 nm showed better improvement than other two kinds of LDHs on UV aging resistance of bitumen.

Abstract: Gas atomization is one of the most cost-effective methods for preparing spherical powders. The Cu-9.7Sn-0.2P alloy powder for 3D printing was prepared by a self-developed double nozzle gas atomization technique with different deliver tube diameters, and the particle size and shape of the powder were characterized. Results show that the powder particles are mostly nearly spherical, mixed with a few irregular powders. The average O. Bluntness of the powders are 60~70%, the average Outgrowths are lower than 18%. The deliver tube diameter affects the powder characteristics directly. The increase of the diameter increases the particle size of the powder and reduces the sphericity. At the same time, the adhesion of the satellite powder decreases, the flowability becomes better and the oxygen content drop. The surface and internal structure of the powder are mainly cellular and dendritic structures.

Abstract: This research paper studies the influence of preparation method of recycled polymer material with glass fibers on the tensile properties of the final product. The recycled material was made from polypropylene, which originally contained 30 % of glass fibers. It was divided into fractions using size of the crushed particles. These fractions ranged from large particles, similar to the original material, to small dust particles. Measurements were performed at various temperatures. It was found that the mixture of dust particles showed a large decrease in measured properties. It is mainly due to shortening of the large glass fibers, so that it no longer fulfills its function as reinforcing filler. Conversely, mixture with larger particles did not show a significant decrease in properties compared to the original material.

Abstract: Porous cordierite is among the special porous ceramic due to its extensive properties. In this research, porous cordierite was fabricated through gelcasting method. A mixture of raw materials (SiO₂, Al₂O₃ and MgO) was melted at 1550 °C followed by quenching in water to produce a glass. Then the formed glass powder were milled for 1, 3, 5, 7 and 9 hours to obtain various particle sizes of cordierite powder. Cordierite powder produced was then used to prepare 3-D porous cordierite ceramic using gelcasting method. The cordierite pellets were characterized. Surface morphology was analysed via Scanning Electron Microscope (SEM) to observe the pore structure of porous cordierite formed from powder with various particle sizes.

Abstract: The development of the new technologies has also brought new possibilities of the wood processing, wood shaping and wood materials tending. By reason of increased human need for wood products the industry has shifted from the production in the workshops throught manufactures up to fabrications. This fact also causes increasing of the wood dust amount in the spaces of the production shops or halls, and by that also increased danger of the explosion of the wood dust. At the adequate initiatory source, sufficient amount of flammable material, oxidant and essential pressure, the explosion can occur and last for several miliseconds, therefore people rescue in the endangered spaces in case of explosion is impossible. One of the parameters which influence properties of the flammable wood dust is its particle size. The article deals with the particle size influence of the wood dust at its minimal temperature of ignition in the stired state. On the basis of the experimental measures the influence of the minimal action of the thermal energy for the activation of the ignition process of the wood dust in the stired state at the reacting of pressure and variousness of grit size is assessed.