Open pore titanium foams via metal injection molding of metal powder with a space holder

Powder methods are highly applicable for the processing of more challenging metals and forms. Examples of materials that encompass both of these are metallic foams, which are advanced materials that consist of a network of interconnected or randomly spaced macropores separated by dense or microporous cell walls. These macropores can be either open or closed, or mix of those two, depending on the manufacturing process. One popular metal foam that has received a huge amount of interest in the last decade is Ti foam, due to it offering a unique combination of properties, such as high strength to weight ratio and high permeability combined with excellent biocompatibility. In this study the use of metal injection molding of titanium powder in combination with a space holder (to create large pore spaces) is examined for the production of open pore Ti foams for biomedical applications. Potassium chloride with two different particle shapes (spherical and cubic) was used as a space holder. It was found that feedstocks prepared with spherical KCl particles had a lower viscosity and better flowability compared to those made using cubic particles. Ti foams with a total porosity of 61.25% ± 0.29 were successfully produced. The structure of the foams produced was characterized using SEM and X-ray micro-computed tomography

Microporous Titanium through Metal Injection Moulding of Coarse Powder and Surface Modification by Plasma Oxidation

Titanium is one of the most attractive materials for biomedical applications due to having excellent biocompatibility accompanied by good corrosion resistance. One popular processing technique for Ti is Metal Injection Moulding (MIM). However, there are several issues associated with the use of this technique, such as the high cost of the fine powder used, the high level of contamination and consequent alteration to material properties, as well as the large volume shrinkage that occurs during sintering. In this study, the use of a relatively coarse Ti powder with a mean particle size of 75 μm to process Ti parts with the potential for biomedical applications by MIM will be examined, compared to a commercial Ti feedstock, and subsequently coated using Plasma Electrolytic Oxidation (PEO). The results show that samples produced with the coarse powder shrink 35% less and have a relative density 14% less with an average pore size three-times larger than that of the commercial feedstock. This helps increase the potential competitiveness of MIM in the production of biomedical parts, as it reduces cost, shrinkage and results in more intentionally-induced micropores, such as are desired for biomedical implants. PEO treatment of the samples yields a thick rough coating comprised of a mixture of rutile and anatase with interconnected microporous channels and openings resembling the mouth of a volcanic crater

Production and digital image correlation analysis of titanium foams with different pore morphologies as a bone-substitute material

Ti foams are mesoporous structured materials that are characterized by their high surface area and interconnected porosity with a huge potential for biomedical applications. In this study, we investigated the production of titanium foams with different pore morphologies as a bone-substitute material via the addition of different amounts, shapes, and sizes of the space holder. Furthermore, we also carried out strain analysis using digital image correlation (DIC) in order to analyse the strain distribution across the porous samples. In addition, the nature of the relationship between the amount of the space holder added and final amount of porosity in the foams produced was also examined. The results demonstrated that the relationship between the space holder amount and porosity in the samples follows a complex one-phase exponential decay function in an increasing form. Our findings also suggest that the shape of the space holder does not play a significant role in dictating the porosity of the foams produced in the current study. However, the space holder’s shape does have a substantial role in dictating the mechanical properties of the foams produced, where Ti foams produced using a cubic or irregular space holder were found to have a lower yield stresses than those made with the spherical space holder

Structural characterisation of porous copper sheets fabricated by lost carbonate sintering applied to tape casting

In this article, we describe experimental investigations of the structural characterisations of double-layered porous copper tapes of thickness down to 0.74 mm. The porous sheets were produced by a process combing tape casting and lost carbonate sintering (LCS) to control both the porosity and pores distribution of the sheets. By varying the values of processing parameters, double-layer (porous and dense) structured tapes with open cell structure and porosities ranging from 50.0 to 81.5% are produced. Scanning electron microscopy and actual size image analysis were employed to measure the pore size and surface porosity of the porous sample. The pore size distribution was characterised using Micro-CT scanner running Skyscan NRecon software and CTAn software. A helium pycnometer was employed to obtain the bulk porosity of the porous copper samples. Statistical analysis of these measurements was used to assess the efficiency and consistency of the space holder technique used to generate porosity, as well as to draw information about the influence that different processing routes have on the resulting mesostructure of the porous copper metal, and on its properties

Open Celled Porous Titanium

Among the porous metals, those made of titanium attract particular attention due to the interesting properties of this element. This review examines the state of research understanding and technological development of these materials, in terms of processing capability, resultant structure and properties, and the most advanced applications under development. The impact of the rise of additive manufacturing techniques on these materials is discussed, along with the likely future directions required for these materials to find practical applications on a large scale

Salt-concentrated acetate electrolytes for a high voltage aqueous Zn/ MnO2 battery

Aqueous rechargeable Zn/MnO2 batteries are attractive due to their low-cost, high safety and use of non-toxic materials. In term of electrolyte materials, it is anticipated that an aqueous electrolyte with a wider electrochemical window will improve the stability and energy density. In this work, we investigated salt-concentrated electrolytes based on relatively inexpensive acetate salts. An electrochemical window of 3.4 ​V was achieved in salt-concentrated 1 ​m Zn(OAc)2+31 ​m KOAc electrolyte. Its total ionic conductivity is 2.96 ​× ​10-2 ​S ​cm-1 while the ionic conductivity of Zn2+ ions is 7.80 ​× ​10-3 ​S ​cm-1, estimated by a current interrupt method. This electrolyte is regarded as a mild alkaline environment with a pH value of 9.76, causing the different storage mechanism for anode with Zn2+ ions and, cathode with OH- ions as the charge carriers respectively. A Zn/MnO2 battery was assembled using 1 ​m Zn(OAc)2+31 ​m KOAc electrolyte, self-supported α-MnO2-TiN/TiO2 cathode and Zn foil anode. The Zn/MnO2 battery can be charged to 2.0 ​V versus Zn/Zn2+ and delivers discharge capacity and energy density of 304.6 ​mAh·g-1 (calculated on the mass of MnO2) or 0.32 mAh·cm-2 (calculated on the area of electrode) and, 368.5 ​Wh·kg-1 (calculated on the mass of MnO2) or 232.7 Wh·kg-1 (calculated on the total active mass of electrodes and electrolyte) in the first cycle under a current density of 100 mA·g-1 (~ C/3, based on the mass of MnO2) or 0.1 mA·cm-2 (based on the area of electrode). During cycling, the coulombic efficiency can be maintained around 99% and reached 99.9% during the 14-340th cycles. After the cycling tests, almost no dendrites were observed on the Zn foil anode attributing to the super-high salt concentration in that acetate-based electrolyte, which will benefit the stability of aqueous Zn/MnO2 batteries