Increase In Open Porosity Research Articles

EFFECT OF POROSITY ON PARTICLE EROSION WEAR BEHAVIOR OF LAB. SCALE SICF/SIC COMPOSITES

The use of silicon-based ceramics and composites as combustor liners and turbine vanes provides the potential of improving next-generation turbine engine performance, through lower emissions and higher cycle efficiency, relative to today's use of super alloy hot-section components. As a series of research for FOD resistant, a particle erosion wear test was carried out for continuous Pre- SiC fiber-reinforced SiC matrix composites with a new concept of lab. scale fabrication by LPS process. The result shows that aperture (some form of porosity) between fiber and interface has a deleterious effect on erosion resistance. Aperture along the fiber interfaces consequently causes a severe wear in the form of fiber detachment. Wear rate increase proportional as contents of open porosity increases. For nearly full dense composite materials of about 0.5 % porosity, are about 200 % more wear-resistant than about 5 % porous composites. Grain growth and consolidate condition of matrix which directly affects to FOD resistant are also discussed.

Chemico-physical modifications induced by plasma and ozone sterilizations on shape memory polyurethane foams

Thermally activated shape memory polyurethane foams are promising materials for minimally invasive surgical procedures. Understanding their physical and chemical properties, in vitro response and effects of sterilization is mandatory when evaluating their potential as biomaterials. In this work, we report on the characterization of two Cold Hibernated Elastic Memory (CHEM) foams before and after two novel low-temperature sterilization techniques (plasma and ozone). Foams have different transition temperatures (T(trans)), as determined by Tandelta peaks in DMA tests, that depend on their chemical composition: both foams possess excellent shape recovery ability (Recovery Rate up to 99%) in conventional shape recovery tests. Plasma sterilization (Sterrad sterilization system) resulted in a slight increase of open porosity, but no effects on bulk chemical and thermo-mechanical properties were observed. Ozone sterilization had a stronger effect on foams morphology, both in terms of an evident rupture of pore walls and surface oxidation. These modifications affected both thermomechanical and shape recovery behavior. Furthermore, plasma sterilized foams cytocompatibility was investigated with L929 fibroblast cell line in vitro, showing a good adhesion and proliferation, as confirmed by SEM observation and Alamar blue assay. The obtained results contribute to define the role of shape memory foams as biomaterials and open novel questions on the role of sterilization technique effects on cellular solids.

Improvement of thermal properties of fired clays by introduction of vegetable matter

Porous bricks produced by extrusion were obtained by adding vegetable matter of various compositions and shapes. The main objective of this article is precisely to investigate the possibilities offered by vegetable matter. During firing, the burning of the vegetable matter created pores and an increase in open porosity ranging from 11% to 18% was obtained. The linear shrinkage and mass loss of bricks were acceptable. The mechanical properties were studied by the three-point bending method and sound wave propagation. The results obtained showed that the rigidity of the material and its thermal conductivity decreased by up to 32%, as the porosity increased. An improvement of up to 18—48% in the thermal resistance of industrial perforated bricks could be expected, depending on their nature. Porosity obtained by adding wheat straw provided the best compromise between thermal and mechanical properties.

Properties of pore structure of thin-layer external plasters under ageing in simulated environment

The basic and commonly used four types of thin-layer facade plasters on cement and silicate binders were subjected to 400 cycles of accelerated ageing in the simulate chamber. The main attention was focused on the character of pore structure evolution during of ageing process. To reach this objective, examinations of the microstructure by the mercury intrusion method and total porosity by the densitometry method were carried out in time per 100 cycles. During the study, the main emphasis was put on the open porosity and changes of dimensional groups of pores. On the ground of the hysteresis of the mercury pressure by mercury intrusion porosimetry testing, the presence of pores with capillary entrance was suggested. In view of this, the cylindrical and spherical model of porous structure has been defined. The contribution of capillary and spherical pores vary in time together with properties such as: average pore radius, length of cylindrical pores and their tortuosity. The changes of these values confirm that atmospherical ageing influences plasters’ binders in two zones. It appears on the one hand by the decrease of total porosity, length and diameter of capillaries but on the other hand by the increase of open porosity and the decrease of pores’ tortuosity. It indicates the tightening character of the inside pore structure of the examined plasters and at the same time it gives diverse effect in its external zone.

Shape memory polymer foams for cerebral aneurysm reparation: Effects of plasma sterilization on physical properties and cytocompatibility

Shape memory polyurethanes (SMPUs) represent promising candidate materials for aneurysm embolization, since they could enable clinical problems still associated with these clinical procedures to be overcome. In this work, we report on the characterization of physicochemical, thermomechanical and in vitro interface properties of two SMPU foams (Cold Hibernated Elastic Memory, CHEM), proposed as a material for embolization devices in minimally invasive procedures. Moreover, because device sterilization is mandatory for in vivo applications, effects on the properties of the foams after plasma sterilization were also evaluated. Both foams (CHEM 3520 and CHEM 5520) showed excellent shape recovery ability (recovery rate, R r , up to 99%) in conventional shape recovery tests, performed at constant heating rate. Transition temperatures ( T trans ), determined by tan δ peaks in dynamic mechanical analysis (DMA), were 32.2 and 45.1 °C, for CHEM 3520 and 5520, respectively. The value of T trans affects shape memory ability in the recovery test at 37 °C, which simulates the behavior after implantation of the device: in fact, R r was significantly higher for lower T trans foam ( R r ≈ 82% and R r ≈ 46%, respectively, for CHEM 3520 and CHEM 5520). After plasma sterilization performed by a Sterrad ® sterilization system, an increase in open porosity was observed: this is probably due to the sterilization cycle; however, no effects on shape recovery behavior were observed. Furthermore, plasma treatment had no significant effect on L929 cells in in vitro cytotoxicity tests, performed on cell culture medium extracts in contact with foams for up to 7 days. Moreover, direct cytocompatibility tests showed a good colonization and growth from L929 cells on CHEM foams, suggesting the effectiveness of an in vivo healing process. All these results seem to suggest that CHEM foams could be advantageously used for manufacturing devices for mini-invasive embolization procedures of aneurysms.

Fabrication of porous alumina ceramics from powder mixtures with sol–gel derived nanometer alumina: Effect of mixing method

This work concerns a systematic study investigating the effect on microstructure, porosity and bending strength of the addition of small amounts of very fine sol–gel derived nanoalumina on a micron-sized alumina powder for the production of highly porous ceramics. Different ways of mixing, with the nanomaterial being either in powder form (γ-alumina) or in sol state (boehmite sol), were investigated for this purpose. It was observed that when small amounts of nanomaterial (4–6 wt%) are added both the bending strength and open porosity increase to a level depending significantly on mixing method and level of dispersion of nanoparticles into the coarse matrix. The increase in strength can reach 100% in case the nanomaterial is added in powder form and 500% in case of mixing in sol state.

Effect of coloring with various metal oxides on the microstructure, color, and flexural strength of 3Y‐TZP

The purpose of this study was to investigate the effect of cerium and bismuth coloring salts solutions on the microstructure, color, flexural strength, and aging resistance of tetragonal zirconia for dental applications (3Y-TZP). Cylindrical blanks were sectioned into disks (2-mm thick, 25-mm in diameter) and colored by immersion in cerium acetate (CA), cerium chloride (CC), or bismuth chloride (BC) solutions at 1, 5, or 10 wt %. The density, elastic constants, and biaxial flexural strength were determined after sintering at 1350 degrees C. The crystalline phases were analyzed by X-ray diffraction before and after aging in autoclave for 10 h. The results showed that the mean density of the colored groups was comparable with that of the control group (6.072 +/- 0.008 g/cm(3)). XRD confirmed the presence of tetragonal zirconia with a slight increase in lattice parameters for the colored groups. A perceptible color difference was obtained for all groups (DeltaE* = 2.57 +/- 0.48 to 14.22 +/- 0.98), compared with the control. The mean grain size increased significantly for the groups colored with CC or CA at 10 wt %, compared with the control group (0.318 +/- 0.029 mm). The mean biaxial strength of CA1%, CA5%, and BC1% groups was not significantly different from that of the control group (1087.5 +/- 173.3 MPa). The flexural strength of all other groups decreased linearly with increasing concentration for both cerium salts (860.7 +/- 172 to 274.4 +/- 67.3 MPa). The resistance to low temperature degradation was not affected by the coloring process. Coloring with cerium or bismuth salts produced perceptible color differences even at the lowest concentrations. A decrease in flexural strength at the higher concentrations was attributed to an increase in open porosity.

Effect of holding time on the basic properties of biomorphic SiC ceramic derived from beech wood

Liquid silicon infiltration processing to manufacture biomorphic silicon carbide is a low-cost route and the resulting products have high strength. Holding time is an important factor to fabricate biomorphic ceramics with various strengths and open porosity. In this study, biomorphic SiC ceramics were prepared by infiltrating liquid Si into biocarbon template from beech at 1550 °C for different reaction time (holding time I), and sequentially removing Si at 1700 °C for different time (holding time II). The resulting products have coarse surfaces of the pore walls because of recrystallization of formed SiC. The porosity decreases and the bending strength and fracture toughness enhances as prolonging reaction time. Both bending strength and fracture toughness generally decline, while open porosity increases and the density decreases with removing of unreacted Si in the samples. While removing Si time is prolonged from 20 min to 60 min, the average bending strengths of the axial and radial samples decline by 41.3% and 54.4%, respectively. The average fracture toughness decreases by 45.9% for the axial samples and by 49.7% for the radial samples. The key factors to affect properties of the resulting products are the formed SiC and the residual silicon. The difference of the porosity and density of the axial and radial samples is decided by the relationship of the direction of the channels of samples and the direction of infiltration.

The structure and properties of zinc titanate doped with strontium

Doped and undoped zinc titanate powders were prepared by a conventional solid state reaction technique using metal oxides. The characteristics of zinc titanate samples were found to depend on the heating conditions and the amounts of additions. It is shown that they are semiconductors, and the formation of SrTiO 3, α-Zn 2TiO 4, rutile phase, morphology roughness and open porosity increase with increasing the amounts of doped Sr. The electrical resistivities of doped and undoped zinc titanate reveal a transition from semiconductor behavior to metal-like behavior as the temperature increased. All samples represent the V-type resistivity–temperature characteristic and possess the typical PTCR characteristics above room temperature.

Microstructure and density changes in Li 2O during irradiation in BEATRIX-II, Phase I and II

BEATRIX-II Phase I and II were in-situ tritium recovery experiments to characterize the behavior of ceramic breeders irradiated to high burn-up using the fast flux test facility (FFTF). A thin-walled, Li 2O-sintered ring specimen and single crystals specimen were irradiated to total lithium burn-ups of about 5 at%. Scanning electron microscopy of the ring specimen in Phase II revealed a substantial increase of open porosity and platelet-shaped grains and a decrease in grain size for most parts of the specimens. At the top end of the specimen hexagonal-shaped bubbles were observed in addition to the increase of porosity and the decrease of grain size. The increase of open porosity and the decrease of grain size were considered to arise from a significant link-up of the bubbles. Such increase of open porosity led to volumetric swelling in the order of 20%. Fracture surfaces of the single crystals exhibited morphological changes resembling blisters.

Porous Alumina by Hot Isostatic Pressing

ABSTRACTProduction of porous alumina ceramics by capsule-free hot isostatic pressing of bimodally distributed alumina powders with a large size difference (>10) and reaction sintering of alumina powder and boron oxide formed by oxidation of boron nitride during sintering were investigated. The influence of the composition of bimodally distributed alumina and alumina-boron nitride mixture of powders on open and closed porosity was studied.HIP treatment at 1600°C provided sintering of only fine-grained powder. A small loss in open porosity (about 4%) is observed with increasing of the fine powder weight fraction up to 0.4.Reaction sintering of a fine-grained alumina powder with boron oxide gives significant (about 30%) increase of open porosity.

Accelerated irradiation testing of SYNROC and its constituent minerals using fast neutrons

Fast neutron irradiation is being used to produce displacement damage in SYNROC B, SYNROC C, barium hollandite, zirconolite and perovskite, to simulate the actinide decay damage which will accumulate during long term disposal of SYNROC containing radioactive waste. Fast neutron and actinide decay damage is correlated by equating the calculated displacements per atom for the two cases, on the basis of 10 wt% waste addition. The macroscopic, microscopic and crystal structure effects are being measured on all five materials for ‘SYNROC ages’ up to 10 6 years, obtained by irradiating to a fast neutron dose of 4.8 × 10 20 n/ cm 2 (⩾ 1 MeV). Materials variables include the fabrication method and the presence or absence of simulated radwaste. All materials have exhibited a volume expansion and a corresponding decrease in density with increasing fast neutron dose. For the same dose, the volume expansions increase in the order barium hollandite ≅ hot pressed SYNROC B < perovskite ≅zirconolite ≅ SYNROC C< cold pressed and sintered SYNROC B. Microcracking occurs in SYNROC at expansions greater than 4 vol%, producing only a small increase in open porosity. For SYNROC C the neutron dose is equivalent to a SYNROC age of 2 × 10 5-years.

The effect of porosity on the thermal conductivity of nuclear graphite

During service in a high-temperature reactor, graphite will be oxidized by impurities such as water vapour present in the helium coolant. Oxidation will affect the thermal conductivity of the graphite and hence the fuel temperature. This report describes experiments on the effect of oxidation at 1000°C by water vapour of a semi-isotropic moulded graphite. The value of thermal conductivity at room temperature decreases with increasing weight loss, but not linearly, the decreases being most rapid at low weight losses. The percentage change in thermal conductivity is approximately linear with the increase in open porosity.

Dry recovery of ceramic uranium dioxide waste material

Three dry recovery routes of ceramic uranium dioxide waste material were studied: (a) calcination of waste material to U 3O 8 and blending with the original UO 2 powder; (b) calcination to U 3O 8, then reduction to UO 2 and blending with the original UO 2 powder; (c) grinding the waste material to a fine powder and blending with the original UO 2 powder. The first route resulted in an increased open porosity and decreased closed porosity of the sintered UO 2 pellets. The second recovery route had almost no effect on the quality of the sintered pellets, while the third route caused an increase in open porosity up to about 15–18 wt% of the added scrap material and increased closed porosity for higher concentrations of the added recovery material. Effects of sieving the recovered scrap powders were also investigated. No effects were observed for the first and second recovery routes, while for the third route more pronounced effects were obtained for coarsely ground powders.

Alteration in concrete properties depending on conditions and setting period after hydrothermal treatment

The ultimate compressive strengths of specimens exposed to hydrothermal treatment increase steadily during hardening under moist conditions. Hardening in extremely moist conditions (in wet chips, for example) is particularly effective. After 14 days hardening in an atmosphere with a humidity of 95% and a temperature of 18–22°C, the strength of the concrete rises by 16–28% and can reach standard values. Where the hardening temperature is about 8–15°C, conditions of maximum moisture should be obtained so that the rate of increase of the strength will be of the same order. Determinations of water absorption give a picture of the structural changes in concrete for various types of conditions during hardening. When the concrete dries out, its open porosity increases by 10–30%. Hardening in moist conditions after hydrothermal treatment raises the frost resistance of concretes without additives. Hardening in the air has no beneficial effect. Concretes containing a complex plasticizer (sulfite liquor) or an air-entraining agent (air-entraining resin) also exhibit a frost resistance several times greater than additive-free concretes after hydrothermal treatment. If concretes are to attain their design properties after hydrothermal treatment, the most important factor is the provision of a very humid atmosphere for hardening in the initial stage. The duration of such a stage is about 14 days.