Papers by Keyword: Microporous Structure

Abstract: Aging mechanism of dam concrete under the action of freeze-thaw damage was analyzed by testing macro and micro performance. The results show that compressive, splitting tensile and flexural strengths reached 58.4%, 61.3% and 57.8% of the initial values after 150 cycles. Strength is the most sensitive indicator of freeze-thaw damage, followed by weight loss rate, relative dynamic elastic modulus and ultrasonic velocity. After freeze-thaw damage, concrete structure becomes loose, porous amount gradually increased and pore size especially over 25nm expanded. Microcracks not only exist in the hydration products, but also destroy the bubbles structure in air entrained concrete, which is the main cause of freeze-thaw damage.

Abstract: Activated carbons are prepared from hemp stem with KOH as activating agent under different ratio of KOH to carbon conditions. The BET(Brunauer Emmett and Teller) specific surface area of the hemp stem-based activated carbons first increases and then decreases with the increasing ratio of KOH to carbon. The specific surface area, micropore surface area and volume of the activated carbons reach a maximum of 1589.27m²/g 1420.52m²/g, 89% of the total area, 0.751m³/g at the ratio of 4.5:1. The micropore size distribution shows the activated carbons contain a large number of ultramicropore and supermicropore.

Abstract: The research on microcellular polymer foam (MPF) is significant in plastic processing industry. In this study, polymethyl methacrylate (PMMA) was considered to be the foam matrix via a preliminary experiment. It is because that compared with other polymers, it is easier to swell and plasticize with supercritical CO2 (SCCO2). Moreover, its absorbability in SCCO2 is much higher. The above research provides guidance for the preparation of microcellular polymer blend foams. In order to study the foam process and the optimum experimental conditions, the average cellular sizes were measured by controlling the saturation pressure, temperature and the soak time on the basis of the orthogonal experiment. The microporous structure was observed by scanning electron microscope (SEM). Then the optimum amount of nano-fillers was achieved by solution and melt blending. In addition, the mechanical properties of MPF were measured to explore the change in foaming. The obtained results would provide better insight to planners and operators in the field of chemical engineering to handle the uncertainties effectively.

Abstract: To eliminate the release-delayed phenomenon of macromolecular drug delivery system at the early stage, biodegradable implantable drug delivery system with micro-porous structure was designed by Bio-MEMS technology in this paper. Water absorption and degradation characters of polylactic acid - polyglycolic acid (PLGA) material with different monomer ratio were studied. Drug release model was built by mass transfer equation and the Finite Element Method. Influencing factors about the cumulative amount of release drug were analyzed. And the results suggest that with more ratio of polylactic acid(PLA), PLGA would have more greater amount of water absorbed as well as a longer degradation time. Better linearity of cumulative amount of release drug would be achieved by reducing the diameter and number of micro-porous.

Abstract: In the present study, nickel foams with an open cell microporous structure were fabricated by the so-called space-holding particle sintering method, which included the adding of a particulate polymeric material (PMMA). The average pore size of the nickel foams approximated 10.5 μm; and the porosity ranged from 70 % to 80 %. The porous characteristics of the nickel foams were observed using scanning electron microscopy and the mechanical properties were evaluated using compressive tests. For comparison, nickel foams with an open-cell macroporous structure (pore size approximately 1.3 mm) were also presented. Results indicated that the nickel foams with a microporous structure possess enhanced mechanical properties than those with a macroporous structure.

Abstract: Micro-porous nickel (Ni) with an open cell structure was fabricated by a special powder metallurgical process, which includes the adding of a space-holding material. The average pore size of the micro-porous Ni samples approximated 30 μm and 150 μm, and the porosity ranged from 60 % to 80 %. The porous characteristics of the Ni samples were observed using scanning electron microscopy (SEM) and the mechanical properties were evaluated using compressive tests. For comparison, porous Ni samples with a macro-porous structure prepared by both powder metallurgy (pore size 800 μm) and the traditional chemical vapour deposition (CVD) method (pore size 1300 μm) were also presented. Results indicated that the porous Ni samples with a micro-porous structure exhibited different deformation behaviour and dramatically increased mechanical properties, compared to those of the macro-porous Ni samples.

Abstract: The three different structures of titanium oxide film were prepared: (1) The commercial pure titanium was treated with heating in air at 700°C for half hour and gotten a dense rutile film on titanium (HS Samples); (2) The commercial pure titanium was treated by chemically treating and gotten a layer of amorphous titania gel on the Ti surface (TS Samples); (3) After chemically treating, the samples were heated in air at 700 °C for half hour, and gotten nano-particles coalesced microporous titanium oxide (rutile) film on titanium surface (XS sample). The dense rutile and amorphous titania gel did not induce apatite formation on their surfaces in SBF solution for 48 hours, whereas the nano-particles coalesced microporous rutile structure induced apatite formation on their surfaces. Mechanical test and histological examination were investigated after the samples implanted in dogs limbs for 3 months. The results of push-out test are 12.96, 29.48 and 35.83 MPa respectively for HS, TS and XS sample. Histological results showed that TS sample and XS sample contacted the bone directly, without any intervening fibrous tissue, and there was a fibrous tissue layer between the bone and HS samples.