Papers by Keyword: Porous Structure

Abstract: This work is devoted to finding of a solution of the actual problem of modern solar power engineering that consists in incomplete conversion of the Planck spectrum of solar radiation using photoelectric conversion. Concentrated solar power being an alternative faces other limiting features such as high cost of building and maintenance, large areas occupied by these plants, the need of precise adjustment of mirrors-lenses systems and also its detrimental effect on nature, birds in particular. An intensification of vaporization from the surface of water can become a solution. In this work a thin layer made of graphene nanoflakes was used as an absorbing media for solar radiation that intensifies evaporation. Also it acts as a catalyst for transmission of water through porous substrate that was made of wood. Results for these experiments were compared with evaporation from free surface. The possibility of using of these porous substrates for the purpose of desalting and purifying water was also experimentally studied.

Abstract: The prospects for the use of foam glass in construction were described. The modern compositions of foaming mixtures for foam glass synthesis were considered. Compositions for studying the influence of the foaming mixture components on the formation of foam glass porous structure were developed, their internal structure and properties were studied. The role of each component of the mixture on its foaming was revealed. Glycerol is a pore-forming agent, which decomposes and produces foaming gases. Waterglass is a stabilizing agent reducing glycerol combustion process. Recommendations on the application of the described patterns in the foam glass synthesis were given.

Abstract: The porous nanostructured hydroxyapatite (HA) has the high specific surface area and loading capacity that is useful for enhancing bioactivity, sinterability, densification, and the capacity for loading the drug, protein, heavy metals, etc. For the first time, the bipolar membrane in electrochemical method was developed for the synthesis of hydroxyapatite nanosheet-assembled porous structures. The bipolar membrane was installed in the electrolysis cell to separate the cell into two chambers. The bipolar membrane prevented the OH^- ions to move away from the cathode chamber and the H+ ions to go to the cathode chamber. In this condition, HA was formed in the cathode chamber while the other calcium phosphate was formed in the anode chamber. The pH increase of solution rapidly leads to more effective the formation of the nanostructured HA. The higher the electrolysis time and the current density the greater the tendency of nanostructured HA formation. The mechanism of HA hydroxyapatite nanosheet-assembled porous structures formation includes the agglomeration formation of the spherical-like particles, the formation of agglomeration nanosheet structures, and the formation of HA hydroxyapatite nanosheet-assembled porous structures.

Abstract: The fabrication of porous GaN (PGaN) by UV-assisted electrochemical etching with a variations of current densities (40, 60, and 80 mA/cm²) for 60 min in electrolytes consisting of 4% KOH are reported. Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-Ray (EDX), Atomic Force Microscopy (AFM) and X-ray Diffraction (XRD) were used to characterize the morphological and structural characteristics of the PGaN. All PGaN sample prepared by electrochemical etching technique produced a hexagonal-like pore shape. FESEM images demonstrated that the pore uniformity and porosity are affected significantly by the current density. The PGaN sample fabricated with 80 mA/cm² produces a uniform and high porosity structure compared to other PGaN sample. This shows that the morphology and structural characteristic of PGaN are increase with the increase of current density. The EDX result revealed significant Ga and N atom presence in all samples. However, the O atom only presence in sample etched with 80 mA/cm² implying that the etching process is occur vigorously in this sample. The AFM verified that the surface roughness and the pore depth are increased as current density increased. There were relatively large variations of the peak intensities for 2Theta-scan patterns as exposed by XRD. The peak shift for PGaN sample relative to as-grown was inconsistent and the changed was relatively small. Raman intensity found to be enhanced with the increase in current density and among the PGaN sample, the E₂(high) peak for sample prepared with 60mA/cm² and 80mA/cm² was observed to be slightly shifted to lower frequency. The PL spectra displayed that the porosity has high impact on the PL peak intensity. . Overall, this proved that with the usage of low power UV light, the pore structure still can be produced as good as pore structure fabricated with high power UV light.

Abstract: The improvement of the thermal insulating material thermophysical characteristics of the thermal protection elements by studying the porous structure is a promising direction of research. The article describes the effects of the porosity and coupling of the porous structure on the thermophysical characteristics of thermal insulating materials. The article uses standard systematized techniques and instruments of scientific research applied in thermophysics. The research methodology of highly-porous material thermophysical properties is based on performance of empirical laboratory investigations of the samples obtained. It was found that for the pore structure effect on the material characteristics it is rational to use the following complex indices: porosity, number of pores, pore position in space, the pore form, pore formation energy. The article shows the effect of the porous structure on the thermophysical characteristics of the material. The complex parameters of the porous structure, which will allow to develop a new method of control of the porous structure, are proposed. As a result of the experiment planning method, the regression equation of an effective coefficient of thermal conductivity for porous thermal protection structures was developed. It was established that for a more even distribution of the mixture in a volume it is necessary to minimize the size of the dispersed components, thereby increasing the area of their contacts. The experimental method revealed that the moisture evaporation caused the formation of pores inside the clay. The shape of the pores was determined using electron microscope MMP-2P, both on the sample section and surface. The clearest clay has the greatest porosity (no iron oxide and calcium oxide). The pores have a spherical shape in it. The presence of impurities reduces the material porosity due to the increased clay viscosity.

Abstract: Hydrochar has already been applied directly or indirectly in various applications. It has electrochemical and catalytical properties, and can be used for sorption, ion exchange and complexing. It can also be applied as the CO₂ adsorbent, electrode material for supercapacitors and fuel cells, and as a fossil fuel. The studied hydrochar samples produced under different reaction times were chemically activated by NaOH. The obtained hydrochar samples pre-and post-activation were studied and compared depending on HTC reaction time.

Abstract: Synthetic polymers are widely used in biomedical applications due to their advantages compared to other materials including low cost and ease of processability, good corrosion resistance and high properties to weight ratio. Among several polymeric biomaterials, polyethylene is a biocompatible polymer which has a long history of being utilized in many biomedical applications ranging from simple components to advanced implants. Although dense polyethylene is known to be a bioinert material which does not interact with host tissue, polyethylene in its appropriate porous form has been shown to be able to integrate well with surrounding host tissues and could widen its uses as bioactive implants. Porous polyethylene structure which was fabricated by three dimensional printing (3DP) is demonstrated. Its manufacturing technique, properties and clinical applications as tissue integrated implants which permitted soft or hard tissue ingrowth in tissue regeneration and replacement is discussed.

Abstract: The operational properties of thermal insulation materials directly depend on their structure. The processes of pore formation occur inside the material after high-temperature treatment, which makes their studying more expensive and complicated. On the basis of experimental data, a computer simulation program for the process of pore formation has been developed, which makes it possible to simulate the processes of changing the structure of foam glass during heat treatment without repeated laboratory experiments.

Abstract: Theoretical principles of the formation of highly organized porous structure of cellular concrete are developed, based on model concepts of the dynamics of the expanding gas cavity in the liquid phase as a single control cell. The peculiarities of controlling the formation of cellular structure of aerated concrete based on the balance of forces in a three-phase disperse system on the model "gas pore - molding mixture" are revealed and a coalescing-aggregate scheme for porosity formation of the aerated concrete mixture is proposed. It is shown that, in accordance with the refined Rayleigh-Plesset equation, the determining factor in the formation of the cellular structure of aerated concrete is the pressure over the mixture to be poroused, the effect of the porosity being achieved by reducing the external pressure to the vacuum level. The division of pores by size in anaerated concrete mixture is proposed. The maximum pore size is determined by the capillary Laplace constant. The prospects of aerated concrete technology are associated with a decrease in the maximum and average size of cellular pores, as well as methods for eliminating pores of air entrainment and segmented pores. Reducing of the size of the pores will be reflected in the decrease of the Bond quantity and in the increase of the importance of capillary forces in the formation of the porous structure of aerated concrete. The concepts of the types of cellular structures are developed, depending on the average density and their boundaries for cellular concrete are established.

Abstract: Trabecular bone, widely presented in the ends of long bones and chine, is a typically porous structure which provides a multifunction such as light weight, undertaking load, impact energy buffer and hosting marrow cells. The structure of trabecular is a dominant factor for the strength of cancellous bone. The prediction of the trabecular bone’s mechanical properties depending on the trabecular structure is very useful for the diagnosis and treatment of osteoporosis. The object of this study is to establish a relationship between the mechanical properties and topological, morphological parameters of trabecular bone. The 50 3-D data of cancellous bone are selected from the CT images of three caput femurs and disposed in BoneJ, through which the BV/TV, SMI and genus parameters of each samples are obtained. The deformation behaviors of trabecular bone are simulated in ABAQUS through uniaxial compression on the 3-D model derived from stack images. Then linear-regression analyses are conducted on the BV/TV, genus, SMI and apparent Young’s modulus, resulting a high correlation (R^2=0.84) between the Young’s modulus and the hybrid parameter derived from SMI and normalized genus, corresponding to morphological and topological parameter of the samples respectively. The result indicates that it’s promising to establish the relationship between mechanical properties of trabecular bone and their topological and morphological parameters.