Corrosion and corrosion control

For many years, the solid metals and their alloys have been widely used for fabrication of the implants replacing hard human tissues or their functions. To improve fixation of solid implants to the surrounding bone tissues, the materials with porous structures have been introduced. By tissue ingrowing into a porous structure of metallic implant, the bonding between the implant and the bone has been obtained. Substantial pore interconnectivity, in metallic implants, allows extensive body fluid transport through the porous implant. This can provoke bone tissue ingrowth, consequently, leading to the development of highly porous metallic implants, which could be used as scaffolds in bone tissue engineering. The goal of this study was to develop and then investigate properties of highly porous titanium structures received from powder metallurgy process. The properties of porous titanium samples, such as microstructure, porosity, Young's modulus, strength, together with permeability and corrosion resistance were investigated. Porous titanium scaffolds with nonhomogeneous distribution of interconnected pores with pore size in the range up to 600 μm in diameter and a total porosity in the range up to 75% were developed. The relatively high permeability was observed for samples with highest values of porosity. Comparing to cast titanium, the porous titanium was low resistant to corrosion. The mechanical parameters of the investigated samples were similar to those for cancellous bone. The development of high-porous titanium material shows high potential to be modern material for creating a 3D structure for bone regeneration and implant fixation.

Highly porous titanium scaffolds for orthopaedic applications

Porous titanium has long been desired as a bone substitute material because of its ability to reduce the stress shielding in supporting bone. In order to achieve the various pore structures, we have evolved a moldless process combined with a space holder technique to fabricate porous titanium. This study aims to evaluate which pore size is most suitable for bone regeneration using our process. The mixture comprising Ti powder, wax binder and PMMA spacer was prepared manually at 70 °C which depended on the mixing ratio of each group. Group 1 had an average pore size of 60 μm, group 2 had a maximum pore size of 100 μm, group 3 had a maximum pore size of 200 μm and group 4 had a maximum pore size of 600 μm. These specimens were implanted into rabbit calvaria for three and 20 weeks. Thereafter, histomorphometrical evaluation was performed. In the histomorphometrical evaluation after three weeks, the group with a 600 μm pore size showed a tendency to greater bone ingrowth. However, after 20 weeks the group with a pore size of 100 μm showed significantly greater bone ingrowth than the other groups. This study suggested that bone regeneration into porous titanium scaffolds is pore size-dependent, while bone ingrowth was most prominent for the group with 100 μm-sized pores after 20 weeks in vivo.

https://iopscience.iop.org/article/10.1088/1748-6041/11/1/015012/pdf

Bone ingrowth of various porous titanium scaffolds produced by a moldless and space holder technique: an in vivo study in rabbits.

The sintering of wet processed Mars global simulant green bodies is explored Green bodies shaped using slip casting, throwing on a potter’s wheel and additive manufacturing, including material extrusion (robocasting) and layerwise slurry deposition (LSD) are sintered in terrestrial and simulated Mars atmosphere A sintering schedule is developed using hot stage microscopy, water absorption, sintering shrinkage and sintering mass loss Sintered parts are characterized in respect to their density, porosity, phase composition, microstructure and mechanical properties Densification behavior for different green bodies was generally similar, enabling the fabrication of larger green bodies (tiles, cups, bowls) and parts with fines details (test cubes and cuneiform tables) with low water absorption Sintered LSD discs had a bending strength between terracotta and typical porcelains with 575/533 ​MPa in terrestrial/simulated Mars atmosphere Clay ISRU for sintered ceramics can be considered an eminently favorable construction technology for soft and hard ISRU on Mars

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Sintering of ceramics for clay in situ resource utilization on Mars

The use of lightweight concrete has continuously increased because it has a primary benefit of reducing dead load in a concrete infrastructure. Various properties of lightweight concrete, such as compressive strength, elastic modulus, sound absorption performance, and thermal insulation, are highly related to its pore characteristics. Consequently, the identification of the characteristics of its pores is an important task. This study performs a comparative analysis for characterizing the pores in cementitious materials using three different testing methods: a water absorption test, microscopic image processing, and X-ray computed tomography (X-ray CT) analysis. For all 12 porous cementitious materials, conventional water absorption test was conducted to obtain their water permeable porosities. Using the microscopic image processing method, various characteristics of pores were identified in terms of the 2D pore ratio (i.e., ratio of pore area to total surface area), the pore size, and the number of pores in the cross-sectional area. The 3D tomographic image-based X-ray CT analysis was conducted for the selected samples to show the 3D pore ratio (i.e., ratio of pore volume to total volume), the pore size, the spatial distribution of pores along the height direction of specimen, and open and closed pores. Based on the experimental results, the relationships of oven-dried density with these porosities were identified. Research findings revealed that the complementary use of these testing methods is beneficial for analyzing the characteristics of pores in cementitious materials.

/pdf/characterization-of-porous-cementitious-materials-using-8of01777pr.pdf

Characterization of Porous Cementitious Materials Using Microscopic Image Processing and X-ray CT Analysis.

A method to estimate the pore free density and the open and closed porosities of a PM specimen by helium pycnometry is introduced. The findings of the method as applied to pressed and sintered specimens of a commercially pure iron powder in the density range from 6·7 to 7·5 g cm−3 are presented and compared with the values obtained on the same specimens using the standard oil impregnation and water immersion method. It was found that the observed density values by the two methods were similar, but that the open and closed porosity values were not. In general, the pycnometric method indicated substantially higher open porosity values and correspondingly lower closed porosity values than the standard method at all densities.

F. J. Semel

Papers

Porosity analysis of PM materials by helium pycnometry