Presence Of Microporosity Research Articles

Surface topography of hydroxyapatite affects ROS17/2.8 cells response.

Hydroxyapatite (HA) has been used in orthopedic, dental, and maxillofacial surgery as a bone substitute. The aim of this investigation was to study the effect of surface topography produced by the presence of microporosity on cell response, evaluating: cell attachment, cell morphology, cell proliferation, total protein content, and alkaline phosphatase (ALP) activity. HA discs with different percentages of microporosity (< 5%, 15%, and 30%) were confected by means of the combination of uniaxial powder pressing and different sintering conditions. ROS17/2.8 cells were cultured on HA discs. For the evaluation of attachment, cells were cultured for two hours. Cell morphology was evaluated after seven days. After seven and fourteen days, cell proliferation, total protein content, and ALP activity were measured. Data were compared by means of ANOVA and Duncan's multiple range test, when appropriate. Cell attachment (p = 0.11) and total protein content (p = 0.31) were not affected by surface topography. Proliferation after 7 and 14 days (p = 0.0007 and p = 0.003, respectively), and ALP activity (p = 0.0007) were both significantly decreased by the most irregular surface (HA30). These results suggest that initial cell events were not affected by surface topography, while surfaces with more regular topography, as those present in HA with 15% or less of microporosity, favored intermediary and final events such as cell proliferation and ALP activity.

Characterization of the Mississippian chat in south-central Kansas

To understand production from low resistivity-high porosity Mississippian chat reservoirs in south-central Kansas it is necessary to understand the nature of deposition and diagenesis, how tectonics is a factor, the lithofacies controls on petrophysical properties, and log response to these properties. The initial mudstones to sponge-spicule wacke-packstones were deposited in transgressive-regressive (T-R) cycles on a shelf to shelf margin setting, resulting in a series of shallowing-upward cycles. Sponge-spicule content appears to increase upward with increasing cycle thickness. After early silicification, inter- and post-Mississippian subaerial exposure resulted in further diagenesis, including sponge-spicule dissolution, vuggy porosity development in moldic-rich rocks, and autobrecciation. Meteoric water infiltration is limited in depth below the exposure surface and in distance downdip into unaltered, cherty Cowley Formation facies. Areas of thicker preserved chat and increased diagenesis can be correlated with structural lineaments and, in some areas, with recurrent basement block movement. Combination of folding or block fault movement prior to or during development of the basal Pennsylvanian unconformity, sponge-spicule concentration, and possibly thickness of overlying bioclastic wacke-grainstones resulted in variable reservoir properties and the creation of pods of production separated by nonproductive cherty dolomite mudstones. These events also resulted in alteration of the depositional cycles to produce a series of lithofacies that exhibit unique petrophysical properties. From bottom to top in a complete cycle seven lithofacies are present: (1) argillaceous dolomite mudstone, (2) argillaceous dolomite mudstone that has chert nodules, (3) clean dolomite mudstone that has nodular chert, (4) nodular to bedded chert, (5) autoclastic chert, (6) autoclastic chert that has clay infill, and (7) bioclastic wacke-grainstone. The uppermost cycle was terminated by another lithofacies, a chert conglomerate of Mississippian and/or Pennsylvanian age. The chert facies exhibit porosities ranging from 25 to 50% and permeabilities greater than 5 md. The (Begin page 86) cherty dolomite mudstones, argillaceous dolomite mudstones, and bioclastic wacke-grainstones exhibit nonreservoir properties. Reservoir production, numerical simulation, and whole core data indicate fracturing can be present in chat reservoirs and can enhance permeability by as much as an order of magnitude. Capillary pressure data indicate the presence of microporosity and can explain high water saturations and low resistivity observed in wire-line logs. Relative permeabilities to oil decrease rapidly for saturations greater than 60% and may be influenced by dual pore systems. Archie cementation exponents increase from 1.8 for mudstones to more than 2.5 in the cherts that have increasing sponge-spicule mold and vug content. Detailed modified Pickett plot analysis of logs reveals critical aspects of chat character and can provide reliable indices of reservoir properties and pay delineation. Models developed provide additional insight into the chat of south-central Kansas and understanding of the nature of controls on shallow-shelf chert reservoir properties.

The influence of phosphorus on shrinkage porosity in cast irons

In this paper, the influence of phosphorus on the formation and presence of microporosity in gray cast iron is examined. The microporosity is ascribed to the formation and presence of the phosphide eutectic(s) in the microstructure during solidification. Samples with high phosphorus content have higher levels of microporosity. The role of alloying elements like chromium and molybdenum on the formation and presence of the phosphide eutectic in the microstructure and overall microporosity is examined. The influence of pouring temperature in controlling the formation of the phosphide eutectic is highlighted. Since cast irons have great use in cylinder liners for automotive applications the practical relevance of using phosphorus is of significant interest.

Relations between Pore Structure Parameters and Their Implications for Characterization of MCM-41 Using Gas Adsorption and X-ray Diffraction

Structural parameters for ordered mesoporous materials are shown to be strongly interrelated as a result of their well-defined structures. Equations for mesoporous materials with hexagonal arrays of uniform pores (e.g., MCM-41 and SBA-15) are presented, which can be used to calculate the pore size, pore wall thickness, and specific surface area on the basis of several quantities, which are easily available from X-ray diffraction and gas adsorption data (i.e., the interplanar spacing, primary mesopore volume, and micropore volume). The influence of assumptions about the pore shape, pore wall density, and the presence of microporosity or disordered nonmesostructured domains on the evaluation of structural parameters is examined. It is suggested that because of very large specific surface areas and primary mesopore volumes for many MCM-41 materials, the existence of extensive disordered domains is not a common feature of MCM-41. Examination of X-ray diffraction (XRD) patterns and nitrogen adsorption isotherm...

Critical discussion of simple adsorption methods used to evaluate the micropore size distribution

The well-known simple adsorption methods used to evaluate the micropore size distribution from low pressure adsorption isotherms were examined by employing model isotherms for slit-like graphite micropores obtained from nonlocal density functional theory. It was shown that in the range of pore sizes from about 0.4 to 0.9 nm, the Horvath Kawazoe (HK) method satisfactorily reproduces the shape of the micropore size distribution, but the pore sizes are underestimated. In the case of micropores wider than 0.9 nm, the method fails as the formation of the monolayer on the pore walls produces a peak corresponding to 0.6 nm micropores on the HK pore size distribution. Therefore, the HK method indicates the presence of microporosity even for nonporous samples. The Dubinin-Astakhov adsorption isotherms were also examined and it was shown that their application to represent local adsorption isotherms for homogeneous pores is questionable. However, the adsorption potential distributions seem to be promising for micropore analysis.

Low cycle fatigue behaviour of electron beam and friction welded joints of an α-β titanium alloy

Fusion welds in titanium alloys, with intermediate {beta} stabilizing additions, show poor mechanical properties due to large fusion zone grain size coupled with a brittle plate martensitic microstructure and hydrogen induced microporosity. These problems, associated with fusion welding, have been reported to be overcome by friction welding. The alloy used in this study is a Soviet composition (VT9) of the {alpha}-{beta} class with the nominal chemical composition Ti-6.5Al-3.3Mo-1.6Zr-0.3 Si (in weight percent), intended to be used as discs and blades in compressor stages of gas turbine engine where low cycle fatigue (LCF) loading is experienced. Electron beam welding of the alloy was largely unsuccessful for the reasons described above. Fatigue properties of such welds had large scatter due to the presence of microporosity. A continuous drive friction welding technique was investigated to overcome this problem These welds showed encouraging results in that microporosity, a problem in the electron beam welding, was not observed and the mechanical properties were at par or better than those of the base metal. This paper deals with the study of stress controlled LCF behavior of friction welds and electron beam welds of the {alpha}-{beta} titanium alloy at ambient temperature and the results are compared withmore » those of base metal.« less

Carbon Surface: Area, Porosity, Chemistry, and Energy

Data from the adsorption of nitrogen at 77 K are interpreted in terms of surface area and porosity, for a range of carbon blacks and two porous carbons, using the BET, αs, and Dubinin–Radushkevich methods. Heat of immersion (ΔHi) data, for nonpolar (n-heptane) and polar (water) liquids are correlated with surface structure and chemistry, respectively. An average value of ΔHi≈ 107 mJ m−2is obtained for the dispersion interaction of nonporous carbon blacks by immersion inton-heptane. Where nitrogen adsorption data indicate the presence of microporosity, higher values of ΔHiare observed which are thought to contain a contribution due to enhanced adsorption forces within pores. Data from samples of one specific black, which had been oxidized to varying levels using an oxygen/ozone fluidized bed apparatus, are presented showing a linear relationship between the surface oxygen levels and their polar interaction with water.

Relationship between carbon black surface chemistry and energy

Nitrogen adsorption data are interpreted in terms of surface area and porosity, for a range of carbon blacks and porous carbons, using the BET, αs and Dubinin–Radushkevich methods. The relative merits of these approaches for identifying and isolating adsorption in micropores, from adsorption on external surface, are considered. Heat of immersion (ΔimmH) data, for non-polar (n-heptane) and polar (water) liquids are related to surface structure and chemistry, respectively.An average value of ΔimmH≈ 107 mJ m–2 is obtained for the dispersion interaction of non-porous carbon blacks by immersion into n-heptane. Where nitrogen adsorption data indicate the presence of microporosity, higher values of ΔimmH are observed which are thought to contain a contribution due to enhanced adsorption forces within these pores. This indicates that the adsorption mechanism within the porosity is one of either primary or secondary micropore filling. Calculation of surface energy (γds) data from nitrogen spreading pressures also supports this conclusion.An approximately linear relationship is observed between the surface oxygen levels of several commercially available carbon blacks and their polar interaction with water. This linear relationship is confirmed by ΔimmH data for samples of one specific black which had been oxidised to varying levels, measured by X-ray photoelectron spectroscopy, (XPS), using an oxygen–ozone fluidised bed apparatus. This oxidation process is shown to lead to the development of carboxylic acid groups on the carbon surface; these have been identified using XPS chemical shift data, IR spectroscopy and pH measurement.

Measurement of the diffusion coefficient of oxygen in a polymeric substance in a polymeric substance

The permeability of a polymer film to gases is determined by the solubility and diffusion coefficient of the gas in the polymeric substance as well as by the presence of microporosity and cracks in a real polymer. The latter play an especially important role in crystalline polymers and, because of this, it becomes unreliable to measure the diffusion coefficients of gases by the membrane method [1]. In the present work, the radiothermoluminescence method (RTL) has been used to determine the diffusion coefficients of oxygen in solid crystalline polypropylene (PP) and polyethylene (PE). This method, proposed by Buben and Nikol'skii [2, 3], is based on the observation of the shape of the curve for the disappearance of the thermoluminescence of the polymer containing oxygen. It has been shown [2, 3] that as the concentration of oxygen dissolved in the polymer increases, the intensity of the β-maximum, positioned in the region of the glass temperature T g, decreases and, simultaneously, there is an increase in the intensity of the low-temperature γ-maximum. Thus, by using this method, it is possible to work with a small amount of the substance and with quite thin films.