Dynamic Young's modulus of open-porosity titanium measured by the electromagnetic acoustic resonance method

As biological implants, porous titanium with adjustable mechanical properties can solve the stress-shielding effect. In this paper, porous titanium was prepared by the powder metallurgy method, where urea powders as the second phase were removed by heat treatment. Pore morphology (such as pore size and character) was controlled by the character of urea powders. The dynamic Young's moduli of such porous titanium with different morphology was measured by the electromagnetic acoustic resonance method. From the semi-log plots of Young's modulus versus the porosity, it was found that with increased porosity this modulus firstly decreases linearly, then decreases rapidly and goes to zero at certain porosity. However, the Young's modulus was independent of pore size. The relationship between Young's modulus and the porosity was explained by a parallel model based on the Minimum Solid Area method. The value of linear slop `b' and the percolation limit `P_C' were used for predicting the trend of Young's modulus varied with the porosity and pore size. So porous titanium with appropriate Young's modulus can be chosen as a candidate for bone substitutes.     

Microstructure and Mechanical Properties of Silicon Nitride Ceramics with Controlled Porosity

Porous silicon nitride ceramic with a porosity from 0–0.3 was fabricated by partial hot-pressing of a powder mixture of α-Si₃N₄ and 5 wt% Yb₂O₃ as sintering additive. Irrespective of the porosity, the samples exhibited almost the same microstructural features including grain size, grain aspect ratio, and pore size. Porosity dependences of Young's modulus, flexural strength, and fracture toughness ( K _{I C} ) were investigated. All these properties decreased with increasing porosity. However, because of the fibrous microstructure, the decreases of flexural strength and fracture toughness were moderate compared with the much greater decrease of Young's modulus. Thus, the strain tolerance (fracture strength/Young's modulus) increased with increasing porosity. The critical energy release rate also increased slightly with an increasing volume fraction of porosity to 0.166 and remained at the same level with that of the dense sample when the porosity was 0.233. They decreased as porosity increased further.     

Elastic Properties of Model Porous Ceramics

The finite-element method (FEM) is used to study the influence of porosity and pore shape on the elastic properties of model porous ceramics. Young's modulus of each model is practically independent of the solid Poisson's ratio. At a sufficiently high porosity, Poisson's ratio of the porous models converges to a fixed value independent of the solid Poisson's ratio. Young's modulus of the models is in good agreement with experimental data. We provide simple formulas that can be used to predict the elastic properties of ceramics and allow the accurate interpretation of empirical property–porosity relations in terms of pore shape and structure.     

METAL POROSIMETER FOR DETERMINING THE PORE VOLUME OF HIGHLY VITRIFIED WARE1

A metal porosimeter of the McLeod-Gage type has been developed for use in determining the porosity of highly vitrified ware. The glass capillary is welded directly on to the 20% chrome-steel metal cap. The metal construction gives a rugged apparatus that can be safely handled for routine work. It is as sensitive as the similar glass apparatus of Washburn and Bunting, but is not structurally delicate. A photograph and drawing with details are included. The suggestion is made that the results obtained by these types of apparatus be expressed as “per cent pore volume,” and that the results obtained by water soaking be specifically named “per cent water absorption” to distinguish between them. Results are given to show that for fairly vitrified ware, the water boiling method gives much lower porosity than the method using air as the fluid.     

High-Temperature Young's Modulus of Alumina During Sintering

High-temperature Young's modulus of a partially sintered alumina ceramic has been studied dynamically during the sintering process. Comparative, room-temperature Young's modulus data were obtained for a suite of partially sintered alumina compacts with different porosities. The dynamic Young's modulus of a 1200°C partially sintered material was observed to decrease linearly with temperature, but then above 1200°C it increased sharply as sintering and densification of the alumina became dominant. The evolution of the Young's modulus due purely to sintering exhibited an exponential relationship with porosity in excellent agreement with room-temperature measurements of equivalent porous alumina ceramics.     

POROSITY: VI. DETERMINATION OF POROSITY BY THE METHOD OF GAS EXPANSION*

Theory of the method. —The pore volume is measured by allowing the gas which fills the pores to expand into a measured volume and measuring the accompanying fall in pressure. Applicability. —The method is in general applicable to pieces of any size and shape and to all classes of porous bodies or materials. A new porosimeter. —For rapid work with shaped test pieces a new porosimeter is described. The new instrument measures accurately both pore volume and bulk volume. A complete porosity determination can be made in 5 minutes. No weighing is required. The results on ceramic bodies arc reproducible to one unit in the first decimal place of the per cent porosity. Considerably higher accuracy than this can be secured if desired. Results. —The results obtained with the new method are in all cases higher, in a number of cases very much higher, than those obtained by the methods of liquid absorption in current use. For fired bodies the same results are obtained with dry air, hydrogen or helium as the pore filling gas. The results show conclusively that complete filling of all the pores in a reasonable time can not be secured by any of the current methods using a liquid as the pore filling agent.     

Elasticity and Internal Friction of Polycrystalline Yttrium Oxide

Young's modulus and internal friction of polycrystalline yttrium oxide were determined from room temperature to 1658°C by sonic techniques. A linear relation was found between volume fraction porosity and Young's modulus at room temperature. The effect of porosity on room temperature internal friction is also discussed. Young's modulus decreased linearly with increasing temperature to 1000° to 1100°C, where a slight anomaly was observed accompanied by an internal friction peak. The modulus was again linear from 100° to 13500°C. Above this temperature a rapid decrease in elastic modulus occurred with a rapid increase in internal friction.     

Evolution of Mechanical Properties of Porous Alumina during Free Sintering and Hot Pressing

This comparative study addresses the influence of microstructural evolution on mechanical properties of porous alumina sintered with and without the application of uniaxial pressure. A complete set of data on Young's modulus, long-crack fracture toughness, and fracture strength for two alumina powders as a function of density was obtained. The evolution of fracture strength with increased density was modeled using a porosity-dependent crack-tip fracture toughness, linked to the contact area of grains and a porosity-dependent size of the largest defect. The defect shape factor was found independent of porosity. A uniaxial pressure of 13 MPa during densification had negligible effect on the relation of strength to porosity.     

Structural Properties of Dried Potatoes,Mushrooms, and Strawberries as a Function of Freeze-Drying Pressure

The structural and thermophysical properties of freeze-dried agricultural products (potatoes, mushrooms, and strawberries) were investigated to determine whether these properties were affected by freeze drying conditions. The true density of freeze-dried products was measured with a helium stereopycnometer, and apparent density was obtained by measuring their geometric characteristics. Porosity and pore size distribution were also measured with a mercury porosimeter. The mechanical properties of freeze-dried agricultural products were obtained using a universal testing machine. Dried products were equilibrated in saturated salt solutions of constant water activity and scanned with a differential scanning calorimeter (DSC) for the evaluation of glass transition temperature. Simple mathematical models were developed in order to correlate the structural and mechanical properties with process conditions. The apparent density and mechanical properties of freeze-dried products increased with the applied freeze-drying pressure, whereas the porosity decreased. The glass transition temperature decreased with the increment of moisture content and it was not highly influenced by process conditions.     

Porosity and mechanical properties of cement mortar

The effect of volume fraction porosity on the mechanical properties of cement mortar is studied. It is shown that both the Young's modulus and fracture toughness decrease with porosity. Although the flexural strength also decreases with porosity the linear relationship is largely fortuitous. Maximum size pores do not act as critical flaws in controlling flexural strength. The critical crack size is several times larger than the maximum pore size due to stable crack growth according to the crack growth resistance curve concept applied to cement mortar.     

三维针刺CFRP复合材料的制备及显微结构研究

以三维针刺碳毡作为预制体,采用树脂浸渍-热压固化工艺快速制备了碳纤维增强树脂基复合材料(CFRP)。通过光学和扫描电子显微镜观察了材料的显微结构,使用阿基米德方法测定材料的密度和气孔率,并利用压汞仪分析了材料的孔隙分布。结果表明,树脂浸渍-热压固化是一种理想的制备CFRP复合材料的方法,制备出的材料密度可达1.45 g/cm3,孔隙率仅为3%,且孔隙主要为由热应力引起的纤维束内贯穿裂纹和基体-纤维界面脱粘两类。     

Application of a stochastic network pore model to oil-bearing rock with observations relevant to oil recovery

Mercury porosimeter experiments have been traditionally used to investigate the pore structure of oil bearing rocks, although interpretation based upon the oversimplified parallel-bundle model is inadequate to explain many practical aspects of oil recovery. A technique for stochastically assigning the sizes of tubular pore segments placed in a network configuration of interconnected pores has been used to model pore structure and a trial and erro procedure has been devised which gives directly the size distribution of segments comprising the network which will exactly reproduce any observed merc porosimeter penetration curve. The theory is applied to porosimeter tests on a core sample from the Agha Jari Field (Iran). It is evident that the pore distribution function according to a network interpretation comprises a very much greater proportion of larger pores than is inferred from the parallel model. This distortion of the pore size distribution is shown to arise from the inaccessibility of larger segments when surrounded by small pores, a phenomenon that cannot be represented by the parallel-bundle approach. As a quantified interconnecting pore model, the network analysis has potential for investigating oil retention mechanisms in a reservoir, and the probable micro-scale water displacement behaviour of the pore network deduced to rep the core sample is described. Low recovery factors seem to be related to water flowing preferentially through pathways made of larger pores. Entrapment likely in large pores isolated by surrounding smaller ones.     

Influence of pore former on porosity and mechanical properties of Ce0.9Gd0.1O1.95 electrolytes for flue gas purification

Single layered porous Ce_0.9Gd_0.1O_1.95 electrolytes were fabricated by tape casting using different types, shapes and sizes of pore formers and their respective strength and stiffness were compared. The sintered bodies were characterized by scanning electron microscopy, mercury porosimetry, impulse excitation technique (Young modulus) and flexural strength measurements, to investigate the role of the different pore formers on the properties of the compounds. The compared techniques used to evaluate porosity give consistent results. The ratio between open and total porosities, evaluated from mercury porosimetry, varies depending on the used pore formers. The stiffness and strength of the compounds show an exponential dependency to the total porosity. By considering the open porosity instead (functional porosity), we observe that samples with platelets shaped pore formers have higher in-plane strength than spherical pore formers. An optimum can be found in term of Weibull strength and strain of samples obtained with the various pore formers by considering the dependency on the functional open porosity instead of the total porosity.     

Electrospun nanofibrous polyvinylidene fluoride-co-hexafluoropropylene membranes for oil–water separation

Effective separation of oil from water is of significant importance globally for various applications such as wastewater treatment, oil spill cleanup, and oil purification. Among the numerous approaches for oil removal, membrane separation is considered one of the most promising approaches due to its selectivity and ease of operation. Electrospinning is a promising technique for producing polymeric membranes with tunable structures with interconnected pores, large surface area, and high porosity. In this study, hydrophobic poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofibrous membranes were electrospun and used for this purpose. The effects of various parameters (e.g., polymer concentration, applied voltage, tip to collector distance, and feed rate) were investigated to find the optimum electrospinning conditions. Further, the electrospun membranes were characterized according to average fiber diameter, morphology, average pore size, and wettability to identify the combinations most likely to succeed in oil–water filtration. The physical–chemical properties of the membranes (i.e., thickness, areal density, porosity, average pore size, water/oil contact angle, hydrostatic pressure head, and oil filtration flux) were studied based on standard test methods. The separation efficiency of eight electrospun membranes with various pore sizes and average fiber diameters were tested for diesel/water mixtures. A linear relation was found between the initial oil flux and the average pore size of the membranes. The maximum oil filtration flux of about 224 L/m²/h, achieving over 75% oil recovery in 10 min, was obtained for the electrospun membrane with the average pore size of 4.5 μm. The membranes were successfully used for eight consecutive oil–water separation cycles without noticeable loss of flux.     

Influence of chemical degradation on mechanical behavior of a petroleum cement paste

Cement paste used in the Oil Industry is generally subjected to chemical degradation due to flow of acid fluids in various situations. The present study focuses on the evolution of thermo-hydro-mechanical (THM) behavior with chemical degradation of petroleum cement paste. Triaxial compression tests with different confining pressures (0, 3, 10 and 20 MPa) are carried out on a standard oil cement paste in sound state and completely degraded state by ammonium nitrate solution under a temperature of 90 °C. The results obtained show that the material in its initial state exhibits a small elastic phase and a strong capacity of compaction. The mechanical behavior depends on the load induced pore water pressure. Because of the increase in porosity caused by chemical degradation, the mechanical strength (cohesion and friction angle) and Young's modulus decrease. The dependence of mechanical strength and Young's modulus on confining pressure is smaller in the chemically degraded cement paste than in the sound one. In fine, the mechanical behavior of the whole material becomes more ductile. As a result, such effects of chemical degradation should be taken into account when modeling such cement paste materials exposed to such chemical degradations.     

Elastic Properties of Silica Xerogels

To calculate elastic constants, longitudinal and tranverse acoustic wave velocities were measured for silica xerogels as a function of relative humidity (rh). The silica xerogels studied are microporous with open porosity of 53 vol%. The longitudinal wave velocity exhibits a minimum at about 35% rh. The transverse wave velocity decreases to a constant value for 35% rh. Consequently, Young's modulus is a minimum at about 35% rh, whereas the shear modulus decreases to a constant value at 35% rh. The bulk modulus and Poisson's ratio exhibit minimum values at about 15% rh. Young's modulus decreases from 4.91 to 3.42 GPa at 35% rh and then increases to 3.60 GPa at 55% rh. Poisson's ratio decreases from 0.184 to 0.164 at 15% rh and then increases to 0.272 at 55% rh. Below 35% rh, silica xerogels adsorb a monolayer of hydroxyls, whereas above 35% rh silica xerogels show pore filling.     

Flexural strengths of polymer modified cement pastes prepared by a novel curing process

Polymer modified cement pastes prepared by a short two stage curing process yielding flexural strengths of approximately 30 MPa are described. The presence of the polymer which gives the improved flexural strength, resulted in a decrease in pore size and porosity and also a marked increase in the work of fracture, whereas very little change was observed in the values of Young's modulus.     

Elastic and Anelastic Response of Polycrystalline UO2-PuO2

A sonic resonance technique was used to investigate the room-temperature elastic and anelastic properties of physically mixed U_0.8PU_0.2O₂ as a function of density, stoichiometry, and cation homogeneity. The effect of porosity on the elastic moduli was linear and is described by E =2102.7 (1–2.03 P )± 13.5 Kbars for the Young's modulus, G =823.5(1–2.05 P )± 9.1 kbars for the shear modulus, and B = 1584.8(1–1.89 P )± 59.1 kbars for the bulk modulus, where P is the volume fraction porosity. Poisson's ratio was 0.28 and was not a function of porosity. The Debye temperature of U_0.8Pu_0.2O₂ computed from the Young's and shear moduli for theoretically dense specimens was 379°K. Variation of the O/M ratio from 1.968 to 2.006 produced no significant change in either the damping capacity or the elastic moduli of single-phase 80%UO₂-20% PuO₂ solid solutions. An approximate 24% decrease of the room-temperature Young's and shear moduli and an approximate increase by a factor of 14 in the internal friction were observed with gross modifications of plutonium cation homogeneity. Preliminary results suggest that internal friction measurements might be used to assay the homogeneity of UO₂-PuO₂ solid solutions.     

Characterization of 3D elastic porous polydimethylsiloxane (PDMS) cell scaffolds fabricated by VARTM and particle leaching

In this study, elastic porous polydimethylsiloxane (PDMS) cell scaffolds were fabricated by vacuum‐assisted resin transfer moulding (VARTM) and particle leaching technologies. To control the porous morphology and porosity, different processing parameters, such as compression load, compression time, and NaCl particle size for preparing NaCl preform, were studied. The porous structures of PDMS cell scaffolds were characterized by scanning electron microscopy (SEM). The properties of PDMS cell scaffolds, including porosity, water absorption, interconnectivity, compression modulus, and compression strength were also investigated. The results showed that after the porogen–NaCl particles had been leached, the remaining pores had the sizes of 150–300, 300–450, and 450–600 μm, which matched the sizes of the NaCl particles. The interconnectivity of PDMS cell scaffolds increases with an increase in the size of NaCl particles. It was also found that the smaller the size of the NaCl particles, the higher the porosity and water absorption of PDMS cell scaffolds. The content of residual NaCl in PDMS/NaCl scaffolds reduces under ultrasonic treatment. In addition, PDMS scaffolds with a pore size of 300–450 μm have better mechanical properties compared to those with pore sizes of 150–300 and 450–600 μm. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42909.     

Preparation of blend polyethersulfone/cellulose acetate/polyethylene glycol asymmetric membranes for oil–water separation

Blend PES/CA hydrophilic membranes were prepared via a phase-inversion process for oil–water separation. PEG-400 was introduced into the polymer solution in order to enhance phase-inversion and produce high permeability membranes. A gas permeation test was conducted to estimate mean pore size and surface porosity of the membranes. The membranes were characterized in terms of morphology, overall porosity, water contact angle, water flux and hydraulic resistance. A cross-flow separation system was used to evaluate oil–water separation performance of the membranes. From FESEM examination, the prepared PES/CA membrane presented thinner outer skin layer, higher surface porosity with larger pore sizes. The outer surface water contact angle of the prepared membrane significantly decreased when CA was added into the polymer solution. The higher water flux of the PES/CA membrane was related to the higher hydrophilicity and larger pore sizes of the membrane. From oil–water separation test, the PES/CA membrane showed stable oil rejection of 88 % and water flux of 27 l/m² s after 150 min of the operation. In conclusion, by controlling fabrication parameters a developed membrane structure with high hydrophilicity, high surface porosity and low resistance can be achieved to improve oil rejection and water productivity.