Papers by Keyword: Pore

Abstract: In the experiments of different process parameters (laser power, scanning speed and scanning distance),the low-time defects of forming part were studied by microscope,including air bubble, pore, micro-crack and macro-crack. The formation mechanism of bubble-defect was analyzed.Linear energy density (E=P/v) was introduced as synthetic parameter.According to analysis and test verification, the optimum technological parameters of 316L stainless steel were laser power 190-210KW, laser speed 800-1000mm/s and scanning interval 0.9-0.11mm,and the linear energy density was about 200J/m. There were no cracks, no bubbles, a small amount of porosity, and the product density reached 99.7%.

Abstract: With different process parameters (laser power, scanning speed and scanning distance),the low-time defects of forming part were studied by microscope,including air bubble, pore, micro-crack and macro-crack. The formation mechanism of pore-defect was analyzed. The micro-structure and composition of the pore-defect were studied by means of SEM and EDS. The results showed that the porosity mainly included circular air porosity, irregular process porosity and oxide inclusion.Linear energy density (E=P/v) was introduced as synthetic parameter.According to analysis and test verification, the optimum technological parameters of 316L stainless steel were laser power 190-210KW, laser speed 800-1000mm/s and scanning interval 0.9-0.11mm,and the linear energy density was about 200J/m. There were no cracks, no bubbles, a small amount of porosity, and the product density reached 99.7%.

Abstract: Light scattering caused by pores detrimentally affects the optical transparency of transparent ceramics. Herein, Mie theory has been used to calculate the cross-section of pore scattering in transparent ceramics, and the influence of wavelength, pore size distribution and refractive index has been discussed in detail. For wavelength between 200 nm and 2000 nm, the scattering cross-section decreases with increasing wavelength, which means that pore scattering is more detrimental to short-wavelength transparency. With ZOLD function simulating the pore size distribution inside the ceramic, it has been found that the scattering is strongest when the most-probable diameter d_m equals the incident light wavelength λ. And FWHM (full width at half maximum) parameter a also affects the scattering cross-section. a between 0.003 and 0.7 is necessary for obtaining high optical transparency in visible wavelength range. The method presented in this work is available for the estimation of scattering effect in different kinds of materials, which may be useful for future design of high-transparency ceramics.

Abstract: Evolution behavior of pores in 7050 aluminum alloy during hot compression process has been investigated by finite element (FE) numerical simulation. The representative volume element (RVE) model containing one isolated pore is built, in which the gas in pore is treated as ideal gas. Effects of initial pore inner pressure and deformation temperature on pore evolution have been investigated. The simulation results indicate that stress concentration exists around the pore in the compressing process. At the simple compression condition, the inner pressure of the pore increases but the volume decreases as the bulk metals deforms. However, the volume reaches a plateau after the yield point of bulk metal. The plateau volume depends on the initial inner pressure of the pore and the flow stress of the bulk metal. Since the inner pressure of the pore balances with the flow stress of bulk metal at the interface, the temperature affects the evolution behavior of the pore through its influence on the flow stress of the bulk metal primarily.

Abstract: In this study, production processes for porous alumina, and the characteristics of the material, were investigated. Porous alumina was produced by a wet-shaping process in which air bubbles were introduced into the slurry. The feature of this production process is that many pores are produced by slip casting carried out using whipped slurry, where only the conditions of the slurry are adjusted. The advantage of this process is its simplicity. From the results, it is made clear that a green compact of porous alumina can be produced by changing the amount of solvent and binder, and also that a sintered compact of porous alumina can be produced by a low sintering temperature, such as 1473 K. The four point bending strength of porous alumina is about 515 MPa when the porosity is about 30 %. The excellent characteristics of the sintered compact of porous alumina are shown by the observation results of the fracture surface in this production process. The dense alumina body is sintered while maintaining the fine grains, and with the micro pores remaining in the grain boundary.

Abstract: Fibre-reinforced ceramic composite materials offer excellent thermal, mechanical and chemical properties. Due to their intrinsic fibre structure and porosity, they offer a great damage tolerance. Therefore, they provide superb attenuation characteristics, as do polymer composites. The current compound systems consisting of ceramic components feature a rather low capacity for energy absorption in relation to their weight; this is a fact in dire need of a fundamental change. In regards to the development of new hybrid ceramic/polymer material compounds basic research of the material design and binding behaviour of the different components is necessary. The advantage of this development allows for a selective implementation of positive characteristics of one component in an integrated compound-system. This opens up completely new possible are-as of application, such as wear and tear resistant and chemically inert, energy absorbing elements for the construction of reactors or areas of medical technology. During the investigation, a few selected fibre-reinforced ceramic composite materials with a specific porosity were produced, while adjusting the amount of resin/hardening agent used, as well as modifying other parameters. This was followed by tests regarding the wetting with a polyurethane component. The characterisation and analysis of the hybrid compounds on a microscopic scale is achieved by means of optical microscopic examinations. The characterisation of the mechanical attenuation characteristics on the other hand is realised by means of DM(T)A. The flexural strength is determined by utilising a “three-point-bending test”.

Abstract: The pore distribution in cement mortar, which is highly related to compressive strength and permeability, vary with water-cement ratios and curing periods. This study used magnetic resonance imaging (MRI) to observe the pore distribution. Compressive strength tests, the rapid chloride-ion permeability test, and electrical resistivity tests were performed to determine the influence of pore distribution on durability. The results reveal that lower water-cement ratios and longer curing periods contributes to fewer pores in mortar specimens. SEM images illustrated how this may be influenced by the rate at which the hydration product, C-S-H colloids, is generated. In addition, the results of durability testing indicate that porosity and compressive strength, total charge passed, and resistivity display linear relationships, as porosity increases, the total charge passed increases, resistivity decreases, and compressive strength declines. The linear regression determined that the R² of all relationships exceeded 0.90, thereby demonstrating the feasibility of applying MRI to assess the durability of concrete.

Abstract: Here a novel technique was employed to fabricated three-dimensionally porous polystyrene (PS) films via ultrasound assisted template method. In contrast to spin-coated thin film, different morphologies appeared on the films prepared by casting PS/toluene solution on glass substrates. By varying either systematic parameters or intrinsic parameters, surface structures changed from two-dimension flat pores to three-dimension sponge pores. The influences of ultrasonic intensity, frequency, irradiation time, film thickness and toluene content in water bath on surface morphologies were extensively studied. Scanning electron microscopy and white-light confocal microscopy showed that PS casted films with thickness of 200μm have a higher porosity and lower surface roughness within micrometer range. The contact angle measurement indicated slight changes of surface hydrophilicity with toluene content in water bath. Suitable toluene content favored multilayer formation of PS film and led to monodisperse pore distribution analyzed by ImageJ.

Abstract: Coal is a natural porous media, its porosity and structural integrity influenced the gas adsorption and desorption characteristics greatly, as well as physical and mechanical properties of coal. Scanning electron microscopy (SEM) is applied to acquire SEM image of four kinds of coal samples at different zoom levels, and the box dimension can be worked out based on the pore preprocessing of SEM images. Then, the numerical value of box dimension is used to describe the development degree of the four kinds of coal sample and four development degrees’ sequence. At last, the intrinsic relevance between fractal dimension and other parameters is analyzed through mathematic method. The results show as follows: coal sample has self-similarity characteristic; the fractal dimension is related to both the total number of pores and porosity degree; the data of the coal pore, analyzed through fractal dimension, are consistent with that through traditional method; what’s more, fractal dimension has more advantages in describing accuracy and simplicity.

Abstract: Although plaster belonged to the first structural materials, they are still getting further enhancements. Nowadays different companies are producing and selling plasters that differ either in their composition or purpose. This article is comparing plasters presented on the market in the Czech Republic. Those are lightweight, renovation and even most common lime-cement plasters. Among the studied characteristics were: basic physical properties (for comparison were measurement of two methods: vacuum water saturation and helium pycnometry); they water vapor transport parameters and heat transport parameters. Lightweight and renovation plasters had shown the biggest porosity, lowest thermal conductivity and the highest diffusion resistance factor.