Search results

Porous titanium is used in many bioimplant and electrode applications because of its interconnected pore structure and good corrosion resistance. The purpose of this paper is to study the anodic polarization behavior of porous titanium in different electrolytes and clarify the influences of the porosity and macro‐pore size on the corrosion resistance.

The porous titanium with 10‐70% porosities and average macro‐pore sizes in the range of 100‐500 μm was prepared by the powder metallurgy method using polymethyl methacrylate (PMMA) as a space holder. Electrochemical corrosion tests were performed on porous titanium as well as solid titanium (with the same irregular and isolated micro‐pore structures as that on the interconnected spheroidal macro‐pore walls of porous titanium) in the 0.1 M H₂SO₄, 1 M NaOH and 0.9% NaCl (37 °C) solutions.

It was found that porous titanium exhibited an active‐passive transition behavior in the 1 M NaOH and 0.1 M H₂SO₄ solutions. In contrast, a self‐passivation transition behavior was observed in the 0.9% NaCl solution (37 °C).

The paper demonstrates that both the porosity and macro‐pore size of porous titanium play an important role in determining the corrosion rate, rather than the corrosion potential.

Porous medium has always been introduced as an environment for increasing heat transfer in cooling systems. However, increase in heat transfer and resolving pressure drop in the fluid flow have been focused on by researchers.The purpose of this paper is to study the effects of creating porous micro-channels inside porous macro-blocks to optimize system performance in channels.

To simulate flow field, a developed numerical code that solves Navier–Stokes equations by finite volume method and semi-implicit method for pressure linked equations (SIMPLE) algorithm will be used together with bi-disperse porous medium (BDPM) method. Working fluid is air with Pr = 0.7 in laminar state. Influence of permeability changes by creation of micro-channels containing porous medium in vertical, horizontal and cross-shape patterns will be investigated.

By creating porous micro-channels inside macro-blocks, not only does the heat transfer increase significantly but the pressure also drops remarkably. Increase in performance evaluation criteria (PEC) is more evident in lower Reynolds numbers that can increase the PEC to 75 per cent by creating cross-shape micro-channels. By changing the permeability of micro-channels, PEC will increase by reducing the pressure drop but it has minor changes in Nu.

The current work is applicable to optimizing system performance by decreasing the pressure drop and increasing the heat transfer.

The developed patterns are useful in increasing the system performance including the increase in heat transfer and decrease in pressure drop in systems such as air coolers required in electrical circuits.

Development and optimization of system performance by new patterns using BDPM in comparison to the previous patterns.

Pyrolysis for coal gas generation changes the composition, pore structure, permeability and adsorption capacity of coal. This work aims to discuss the utilization of coal pyrolysis on enhancing coalbed methane (CBM) production in the Gujiao area, Shanxi province, China.

This research was conducted mainly by the methods of thermogravimetry mass spectrometry (TG-MS) analysis, liquid nitrogen adsorption experiment and methane isothermal adsorption measurement.

The results can be concluded as that 400-700°C is the main temperature range for generating CH₄. Pore volume and specific surface area increase with increasing temperature; however, the proportion of micro pore, transition pore and macro pore has no difference. The optimum temperature for enhancing CBM production should be letter than 600°C because the sedimentation of tar and other products will occupy some pores and fissures after 600°C.

Here in, to accurately recognize the suitable maximum temperature for heating development, a method enhancing CBM production, TG-MS, was adopted to analyze the products and the weight loss of coals with different ranks in the Gujiao area at temperature of 30-1,100°C. And then the pore structure, porosity, permeability, methane adsorption capacity and thermal maturity of coals during pyrolysis were investigated with increased temperature from 30°C to 750°C. On these bases, the favorable condition for enhancing CBM production and the thermal evolution of coal were recognized.

Hydroxyapatite‐polymer composite materials are being researched for the development of low‐load bearing implants because of their bioactive and osteoconductive properties, while avoiding modulus mismatch found in homogenous materials. For the direct production of hydroxyapatite‐polymer composite implants, selective laser sintering (SLS) has been used and various parameters and their effects on the physical properties (micro and macro morphologies) have been investigated. The purpose of this paper is to identify the most influential parameters on the micro and macro pore morphologies of sintered hydroxyapatite‐polymer composites.

A two‐level full factorial experiment was designed to evaluate the effects of the various processing parameters and their effects on the physical properties, including open porosity, average pore width and the percentage of pores which could enable potential bone regeneration and ingrowth of the sintered parts. The density of the sintered parts was measured by weight and volume; optical microscopy combined with the interception method was used to determine the average pore size and proportion of pores suitable to enable bone regeneration.

It was found that the effect of build layer thickness was the most influential parameter with respect to physical and pore morphology features. Consequently, it is found that the energy density equation with the layer thickness parameter provides a better estimation of part porosity of composite structures than the energy density equation without the layer thickness parameter. However, further work needs to be conducted to overcome the existing error of variance.

This work is the first step in identifying the most significant SLS parameters and their effects on the porosity, micro and macro pore morphologies of the fabricated parts. This is an important step in the further development of implants which may be required.

The purpose of this paper is to verify the feasibility and evaluate the compressive properties of Ti6Al4V implants with controlled porosity via electron beam melting process. This process might be a promising method to fabricate orthopedic implants with suitable pore architecture and matched mechanical properties.

Ti6Al4V implants with controlled porosity are produced using an electron beam melting machine. A scanning electron microscope is utilized to examine the macro‐pore structures of the Ti6Al4V implants. The compressive test is performed to investigate the mechanical properties of the porous implants.

The fabricated samples show a fully interconnected open‐pore network. The compressive yield strength of the Ti6Al4V implants with the porosity of around 51 percent is higher than that of human cortical bone. The Young's modulus of the implants is similar to that of cortical bone.

The surface of samples produced by electron beam melting process is covered with loosely spherical metal particles. Polishing and ultrasonic cleaning have to be used to remove the loose remnants.

This paper presents the potential application in the fabrication of orthopedic or dental implants using electron beam melting process.

The purpose of this paper is a theoretical modeling use of electrochemical impedance spectroscopy (EIS) technique for different cases that could describe the possible electrochemical behaviour on steel coated with metallic and oxide thin films (of nickel) deposited by magnetron sputtering, and compare them to know if the theoretical analysis resembles the real case. It is extremely important to clarify that such simulations do not consider the use of the constant phase element (CPE) for the analysis. Therefore, the goal for the theoretical models should be to gain acceptance in electrochemical research.

In order to obtain the equivalent circuits to explain the different possible behaviours of the films and their protective properties in sour media, EIS experimental data were correlated with data from the simulation software. The different nickel and nickel oxide thin films were tested after their deposition by magnetron sputtering on low‐carbon steel and after they had then been exposed to the sour media electrolyte of NaCl 3 wt% + H₂S (saturated).

The EIS simulation starts from the laboratory evaluation of nickel and nickel oxide thin films as anticorrosive protection for low‐carbon steel exposed to sour media. From these results, it is found that the nickel and nickel oxide films could adopt seven different behaviours, and all are possible to occur.

The equivalent circuits proposed will give an insight into the corrosion phenomena for different metals coated with thin films and exposed to sour media, because all of the simulations are made on the basis of real EIS results.

The electrical analysis in the simulation diagram did not consider the use of the CPE to adjust the plots. In consequence, the values of all parameters for the seven different adjustments obtained through the simulations establish a reference for the explanation of the corrosion phenomena. They are also a tool with which to predict the possible behaviour of a thin film deposited on metal and exposed to electrolytes that are as aggressive as sour media.

The purpose of this paper is to develop a new bio‐plotter using a rapid freeze prototyping (RFP) technique and to investigate its potential applications in fabricating tissue scaffolds.

The development of cryogenic bio‐plotters including design steps of hardware as well as software is addressed. Effects of structural parameters and process parameters on the properties of tissue scaffolds are demonstrated through simulation and experimental results.

The paper finds that the RFP method is suitable to fabricate macro‐ and micro‐porous scaffolds, especially for temperature‐sensitive polymers. In addition, through simulation and experiment results, it also shows that macro‐ and micro‐porous properties could be manipulated by structural parameters and process parameters, respectively.

This paper shows that the chamber temperature is an important process parameter that can provide the means to control the micro‐porous structure of the scaffold. However, if the temperature is set too high, the fiber is frozen so rapidly that it cannot be fused with other fibers of the previous layer. On the other hand, if the temperature is too low, the fiber is not solidified fast enough. So, the chamber temperature, together with extruding pressure and nozzle velocity, must be optimized, which will be further investigated in future work.

The RFP technique is successfully proposed to construct 3D tissue scaffolds. In addition, a new cryogenic bio‐plotter is designed and developed, in which general algorithms of rapid prototyping method are presented and implemented, facilitating the fabrication of tissue scaffolds with various cross‐hatching patterns in a RFP process.

To discuss the effects of metal matrix composite (MMC) journal structure on the pressure distribution and, consequently, on the load‐carrying capacity of the bearing are predicted using feed forward architecture of neurons.

The inputs to the networks are the collection of experimental data. These data are used to train the network using the Batch Back‐prop, Online Back‐prop and Quickprop algorithms.

The neural network (NN) model outperforms the available experimental model in predicting the pressure as well as the load‐carrying capacity.

The experiment specimens used in this study have been made of MMC with aluminum based reinforced with SiC ceramic particles, using the stir casting technique. Various composite journal structures can be investigated.

The simulation results suggest that the neural predictor would be used as a predictor for possible experimental applications on modelling journal bearing system.

This paper discusses a new modelling scheme known as artificial NNs. An experimental and a NN approach have been employed for analysing MMC journal structure for hydrodynamic journal bearings and their effects on the system performance.

The influence of flood conditions upon traditional cob construction is little understood. This paper aims to investigate the ability of cob materials to resist flood situations and documents basic failure mechanisms. This work also seeks to investigate the wettability characteristics of cob materials utilising environmental scanning electron microscopy.

This paper takes the form of a literature review and case study underpinning laboratory experiments.

Cob walls that are suitably compacted, straw reinforced and are composed and manufactured of the correct materials appear to have the ability to resist total failure when subjected to initial flood conditions, however, the duration to which these structures will remain intact has still to be ascertained, and testing is ongoing. A correlation appears to exist between the rate of cob material's compaction and the duration to which the structural integrity of the walls was retained when the samples were submerged in water. In addition, the use of straw reinforcing increased the duration to which the wall could be submerged before failure. Un‐reinforced cob walls that were submerged in simulated floodwaters, exhibited an undercutting pattern of deterioration prior to failure. The materials for cob construction exhibited both hydrophobic and hydrophilic characteristics. This would have an influence on the material's ability to saturate and dehydrate, and also have an impact on moisture transfer mechanisms. Unsaturated cob wall/samples developed surface tension between hydrophilic surfaces and this is believed by the authors to increase inter‐particle bond strength within the material by the suction effect.

This paper is believed to be the first preliminary investigation into the effect of flooding on cob structures. Additionally, it utilises environmental scanning electron microscopy to reveal information about the surface characteristics of the materials and uses wettability studies to assess the hydrophilic and hydrophobic nature of the aforementioned.

The study aims to explore the composition and microstructure of clay functionally graded materials under the process of double-gradient direct ink writing (DIW).

The investigation focused specifically on the pore characteristics of barite-kaolin clay composite after three-dimensional (3D) printing and sintering as well as its bionic application in geophysical model.

The model with pore and material variations brought about spatial and nonlinear mechanical properties. Moreover, the vertical gradient and connected pores in the upper kaolin part simulated the natural phenomenon of the landslide model (take Chinese Majiagou landslides as an example). Both the thermal debinding behavior and the kaolin powder particles characteristics [large pore volume (0.019 cm³g^–1) and pore size (29.20 nm)] were attributed to the interconnection channels.

Hence, the macroscopic and microscopic pores achieved by dual-gradient DIW process make it possible to control the permeability and details of properties, precisely in the geological model.