Papers by Keyword: Porosity

Abstract: Cellulose hydrogel was prepared by using the NaOH/ Thiourea/ H₂O as solvent system, cellulose aerogels were obtained by freeze-drying technology. The results showed that cellulose aerogel had porous network structure. Freeze-drying method was an effective way to prepare cellulose aerogel, and the volume shrinkage was 20.41%-28.36%. Bulk cellulose aerogel had low density, high porosity and fine mechanical strength. The density was low to 0.233g/cm³, and the porosity was up to 84.88%. The compressive strength was 5.7-8.2MPa. Cellulose aerogel had good heat insulation performance and thermal conductivity could be as low as 0.029 W/ (m·K). This work provided a foundation for the possibility of applying cellulose aerogels in the insulating material field.

Abstract: In order to study the chemical composition of volcanic rock and physical properties in Hainan province, used the method of X-ray fluorescence, analysises on its chemical composition, and researched the physical properties of volcanic rocks including density test, porosity test, acoustic test, resistance test. The results showed that: the volcanic rock is tholeiitic at the cavity of lava area in Hainan province, P-wave velocity and S-wave velocity would change with the changing of porosity.

Abstract: The present study was carried out to investigate the effect of shielding gases (Ar, CO₂, Ar+5%CO₂, Ar+10%CO₂, Ar+20%CO₂, Ar+2%O₂, Ar+5%O₂ and Ar+10%O₂) and arc voltage (16-24V) on the bead shape and porosity formation of galvanized steel pipe welds made by a gas metal arc welding process. It was confirmed that the bead height was lowered and bead width was wider with increasing voltages. Bead shapes made by Ar was narrow and convex due to a high surface tension while those made by mixture gas compositions such as Ar+CO₂ and Ar+O₂t became wider and smoother due to a lower surface tension. The pores were generated the least at low arc voltages of 16-20V and they were more formed over 22V. It was confirmed that Ar produced the most porosity while active and mixture gases such as CO₂ and Ar+10%CO₂ , Ar+5%O₂ and Ar+10%O₂ produced little pores by forming ZnO in the weld pool.

Abstract: New porous polyimide films were elaborated by vapor induced phase separation process. The influence of different parameters such as the nature of the solvent, the molecular weight of the porous agent, and relative humidity on the structure of the film was investigated. It was shown that the porous film prepared from NMP presents the most original morphology with micro-and nanopores. Moreover, such structure is only obtained when the porous agent used has a high molecular weight. The synthesized porous film was swelled in protic ionic liquid for fuel cell application. The performed conductivity measurements as a function of temperature have shown that the conductivity of the impregnated polyimide film increases when the temperature rises up to 150 °C following Arrhenius behavior.

Abstract: In this study aluminium dross, an industrial waste product from the aluminum casting industry which contains mostly aluminum, aluminium oxide, and volatile gases such as ammonia (NH₃), methane (CH₄) and hydrogen (H₂). In this study it is used as an admixture in cement paste to observe its effects on the porosity and bulk density of the material. The parameters used in the study include; the effects when different quantities of aluminium dross are added to portland cement (portland cement:aluminium dross by weight; 1: 0.05, 1: 0.10, and 1: 0.20) and the effect of different sized particles of aluminium dross (average diameter of aluminium dross particles; <45, 60, and 90 μm) on porosity and bulk density of cement paste. According to the study, as the amount of aluminium dross content in cement paste increases, the area fraction of porosity in the cement paste increases; yet the bulk density of cement paste decreases. In addition, when the particle size of aluminium dross decreases both of the pores size in the cement paste and bulk density of cement paste decrease.

Abstract: The metal friction materials of copper matrix with and without resin using hot press were investigated to study their hardness, porosities, bending strengths, microstructures, coefficient of frictions, and wear mechanisms. The experiment results show that the hardness and bending strength of the friction materials with increase of amount of copper increase, but the porosity decreases. The resulting coefficient of frictions show more stable and their values are about 0.5~0.6. In addition, the wear mechanism of friction material shows mainly grit abrasive and adhesion, which cause the coefficient of friction to become stable. On the other hand, when the copper matrix containing resin is used, the resulting porosity of friction materials becomes higher and the bending strength decreases. This shows that the wear mechanisms of grit abrasive, roughness, and adhesion cause the coefficient of friction to produce a higher value.

Abstract: Multifractal spectrums of sinter with different alkalinity were analyzed by multifractal software. The results show that sinter pore structure change from uniform to non-uniform with the improvement of alkalinity, Δα increases from 0.53 to 0.55. The structure of sinter pore is mainly microscopic by competition between macropores and micropores, Δf changes from 0.14 to-0.44. The distribution of sinter pores is quantitatively characterized by multi-fractal spectrum, which is consistent with transmission electron microscopy image.

Abstract: Many studies have shown that during laser welding, shielding gases play a key role in many aspects. In this paper, a series of contrast experiments about CO₂ laser welding of TA15 TI-alloy were completed by using He and Ar as shielding for different pressure, respectively. The experiments results reveal that the porosities in the weld have strong relation with weld penetration, and the shielding gas have great influences on the weld penetration. So the porosities mainly form in the center of welds which are under critical penetration and lack of penetration, and have no direct relation with the type and pressure of shielding gas.From the contrast images of penetrating process, it is known that when He as shielding gas, the sizes of keyholes on the back welds are quite larger than the sizes when Ar. This means more vapor erupting from bottom keyhole and porosities not easy to form. At the same pressure, the opening times of keyholes when He as shielding gas are longer than the times when Ar. Long opening times of keyholes make the shielding gas within keyhole not easy to be involved into the molten pool and form the porosities.

Abstract: The paper studied a compound desulphurization gypsum waterproof agent, which could modify the water-resistance performance of gypsum products on the basis of their microstructural properties. The waterproof mechanics were the synthesis results of superficial hydrophobic of hydrophobic emulsion, hindrance water of film forming matter and reducing the porosity in materials. The experiment results showed that the water-absorption rate of gypsum hardened body can be reduced to 3.5% and that the compressive strength reserve rate was 89.7% after 24h.

Abstract: Geotextiles have been commonly used globally, making the control of material selection to influence geotextiles properties an important research topic. This study aims to explore the effects of the ratio of high-strength polyethylene terephthalate (HPET) fiber to Kevlar fiber on hybrid geotextiles. At the first stage, HPET and polyethylene terephthalate (PET) fiber are combined to make HPET/PET hybrid geotextile and then tested for porosity and water permeability, determining the optimum HPET/PET ratio. At the second stage, with a content of 60 % PET fibers, HPET fibers and Kevlar fibers are mixed with various ratios to form Kevlar/HPET/PET hybrid geotextiles. The experimental results show that with an increase in the content of HPET fibers, the porosity and water permeability of the Kevlar/HPET/PET hybrid geotextile decrease.