Slight Porosity Research Articles

Investigation on glassy skin formation of porous polystyrene fibers electrospun from DMF

Micrometer and submicrometer diameter of polystyrene (PS) fibers were electrospun from various dimethyl for- mamide (DMF) solutions at different weight fractions under 35% relative humidity. Increasing polymer fraction in the solu- tion results in a gradual morphological transition from beads-with-incipient to bead-free fibers and also increases the diameter. The formation of uniform glassy skin presumably due to radial capillary flow within the liquid jet was confirmed by scanning electron microscope. The thickness of the skin varies with the weight fraction of PS; therefore, it was normal- ized with respect to average fiber diameter (AFD). The skin gets thinner as the weight fraction of PS increases. In addition, the fibers exhibit highly porous internal structure and smooth surface along with slight porosity. The development of poros- ity is attributed to liquid-liquid phase separation of water molecules in atmospheric moisture and DMF.

Effect of Carbon Particle Size on Electrochemical Performance of EDLC

The effect of particle size on the electrochemical performance of electrical double-layer capacitors (EDLCs) has been studied using carbon derived from silicon carbide powders with to grains at temperatures from 800 to . For the same synthesis temperature, similar pore texture and microstructure of carbide-derived carbons produced from different powders have been observed. Nanoparticles exhibited a slight porosity modification with a larger pore volume and surface area as compared to micrometer particles ( and ). Capacitances as high as associated with a small resistance and time constant have been reached for nano- and sub-micrometer particles synthesized at low temperatures and tested in a tetraethylammonium tetrafluoroborate in acetonitrile solution. This result suggests that small particles facilitate the migration of the ions inside the porous electrodes, allowing them to reach the whole pore volume due to a shorter transport distance within the particle.

In-depth RBS study of optical layers based on nanostructured silicon

The particular structure of porous silicon (PS), which can be described as an amorphous matrix in which silicon nanocrystals are embedded, makes this material very suitable for its use in many different fields, including optoelectronics and biological applications. In the present work, Rutherford backscattering spectroscopy (RBS) measurements and optical characterization are carried out on PS layers in order to determine their in-depth compositional profile, homogeneity, porosity, oxidation degree and overall optical behavior. The experimental results show quite good in-depth homogeneity of the PS layers since only slight porosity and oxidation degree gradients have been observed, further supported by optical measurements. Additionally, RBS measurements were used to confirm the existence of a layer of low porosity at the PS/silicon interface independently of the formation current density.

Feasibility study of producing alumina foam by plasma spraying

Plasma spraying was utilized as a tool to produce alumina (AI2 O3) foam based on a new methodology. Blended powder of A12 O3 and calcium oxide (CaO) of different composition was plasma sprayed on predesigned moulds. The sprayed specimens were subsequently treated in water and glycerol in an ultrasonic cleaner at 80°C selectively to dissolve CaO and retain the A12 O3 matrix. Microstructural investigation showed a slight porosity similar to that observed in the plasma-sprayed coatings in the assprayed untreated specimens, which after treatment in water and glycerol exhibited a considerable increase in the extent of porosity. X-ray diffractometry (XRD) studies confirmed the dissolution of CaO, giving rise to porosity, as exhibited by the presence of peaks corresponding to CaO in the as-sprayed material and its absence after water and glycerol treatments.

Mineral evolution and element mobility during episyenitization (dequartzification) and albitization in the postkinematic Bohus granite, southwest Sweden

The petrography and geochemistry of two subsurface occurrences of pervasively albitized and episyenitized (i.e. dequartzified) granite in the central part of the postkinematic Sveconorwegian Bohus granite, in southwestern Sweden, were studied. The altered granite is whitened and consists of an albite-microcline framework with a very fine-grained interstitial assemblage of illite + hematite + ankerite ± anatase. Textural relations indicate that the initial dissolution of magmatic quartz, accompanied by albitization of plagioclase, left a vuggy reservoir rock, which facilitated fluid penetration and thereby further alteration. The subsequent stage is characterized by infilling of vugs by the very fine-grained authigenic assemblage and by concomitant alteration of igneous minerals such as magnetite, ilmenite and biotite. Deuteric alteration products of magmatic minerals are affected by these two alteration stages, implying that episyenitization occurred widely after emplacement and cooling of the host granite. Mass balance calculations, with reference to adjacent unaffected granite, evince mainly Si loss and Na gain, reflecting the observed mineralogical changes. The volume decrease is estimated to be ~ 9%, owing to compaction accompanying the dequartzification and a slight porosity increase. The calculations revealed a slight enrichment in HREEs ± Y, essentially hosted by xenotime and a thorite-xenotime solid solution, both exsolved during recrystallization of monazite. Oxidation of ferrous iron and partial loss of chalcophile elements reflect oxidizing conditions. The alteration episode is Permo-Carboniferous and is possibly associated with circulation of oxidizing fluids through the Bohus granite.

Computed tomography used in weld inspections at NASA : Murray, S.H. Welding Journal, Vol. 69, No. 2, pp. 33–39 (Feb. 1990)

This paper describes an application of computed tomography (CT) for an evaluation of a series of welding-end hydraulic accumulators in use at Kennedy Space Center, which were suspected of possibly containing fatigue cracks in their welds, the failure which could result in a high-velocity or high-volume leakage of hydraulic fluid. The accumulator welds were evaluated in terms of incomplete penetration, porosity, and incomplete fusion. Out of 43 accumulators examined, six were given the ranking of 'good', i.e., having no incomplete penetration, and only slight porosity and incomplete fusion. These were selected for use in most critical locations of the hydraulic system used to load the Magellan spacecraft into the payload bay of the Space Shuttle Discovery, with the resulting successful loading and subsequent launching of the Magellan spacecraft.

Parkinsonite, (Pb,Mo, □)8O8Cl2, a new mineral from Merehead Quarry, Somerset

AbstractParkinsonite, ideally (Pb,Mo,□)8O8Cl2, is a new mineral from the Merehead Quarry, Cranmore, Somerset, England. It occurs as compact clusters or patches of red to purplish red bladed crystals, which have an adamantine lustre and a perfect {001} cleavage and occupy fractures and cavities in carbonate vughs in veins of manganese and iron oxide and hydroxide minerals. Associated minerals are mendipite, diaboleite, chloroxiphite, wulfenite, cerussite and hydrocerussite. Discrete crystals were not found; intergrown crystalline aggregates are the usual form of occurrence. The maximum grain size is about 300 × 100 µm, but most grains are appreciably smaller. Parkinsonite was synthesized using high purity chemicals. The measured density of the synthetic material is 7.32 g/cm3; the calculated density is 7.39 g/cm3, the difference being due to minor impurity and slight porosity in the synthetic sample. Parkinsonite is translucent. Reflectance spectra were obtained in air and in oil. Refractive indices calculated from these (at 589 nm) are for Ro, 2.58, and Re', 2.42, i.e. uniaxial negative. VHN50 is 113–133 from which the calculated Mobs hardness is 2–2.5.X-ray studies show that parkinsonite is tetragonal with space group I4/mmm, I4̄2m, I4̄m2, I4/mm, or I422 and a 3.9922(3), c 22.514(2) Å. It has a cell volume of 358.82(5) Å3 with Z = 1. The strongest six lines of the X-ray powder diffraction pattern are [d in Å (I) (hkl)] 2.823, 2.813(100) (110,008); 5.63(85) (004); 2.251(33) (116, 0.0.10); 2.988(27) (105); 3.750(15) (006); 1.994(11) (200,118). Averaged electron microprobe analyses give the empirical formula Pb6.34Mo0.89□0.77O8.02Cl1.98 on the basis of 10 atoms [O + Cl]. The name is for Reginald F. D. Parkinson, mineral collector of Somerset, UK, who first found the mineral.

A model for predicting evolution of pore size distributions in UO 2 fuel

The model generalizes the description of Dollins and Nichols by including pore size distributions. A thermal densification formulation is also derived. The results show that at T< 900° C, densification is independent of temperature and is mainly due to interstitial migration. In the range 1000–1350°C, vacancy diffusion and fission spike/pore interaction also interfere. Here, the densification rate decreases as the temperature rises and a slight porosity growth appears around 1300°C. Above 1500°C, pore coalescence is stimulated and the densification rates are enhanced. The predicted evolutions of pore size distributions, under irradiation at low temperatures and during resintering tests, are in reasonable agreement with experimental data.

POROSITY AND PERMEABILITY OF RESERVOIRS AND CAPROCKS IN THE EROMANGA BASIN, SOUTH AUSTRALIA

When effective porosity and permeability are measured at simulated overburden pressure, and grain size variation is taken into account, two distinct relationships are evident for Eromanga Basin reservoirs. Reservoirs in the Hutton Sandstone and Namur Sandstone Member behave such that significant porosity reduction can be sustained with retention of high permeability, whereas permeability of reservoirs in the Birkhead Formation and Murta Member is critically dependent on slight porosity variations. Logging tool responses are compared with core-derived data to show in particular the effects of grain size and clay content on the gamma ray, sonic, and density tools, where clay content is assessed from cation exchange capacity measurements. Sonic and density crossplots, constructed to provide comparison with a water-saturated 'reference' reservoir, are advantageous in comparing measured effective porosity from core plugs at overburden pressure with porosity calculated from logs. Gamma ray and sonic log responses of the Murta Member in the Murteree Horst area are clearly distinct from those of all other reservoirs, perhaps partly due to differences in mineralogy and shallower depth of burial compared with other formations.