Production of Hydroxyapatite on the Surface of Ti6Al7Nb Alloy as Compared to Ti6Al4V Alloy

Ti6Al4V is very commonly used for the production of dental implants. Titanium alloys whose mechanical and corrosion properties are equal or better than those of Ti6Al4V might present interest as plausible future materials, too. Ti6Al7Nb alloy was tested and compared to Ti6Al4V in this work. Samples of both alloys were oxidized in a water solution containing calcium acetate (Ca(CH3COO)2) and calcium glycerophosphate (Ca(PO4CH(CH2OH)2)) by Plasma Electrolytic Oxidation (PEO) for 20 min. After that, the samples were hydrothermally treated (HTT) in water (pH = 7) and in potassium hydroxide (KOH) solution (pH = 11) for 2 hours at 200°C in a pressurized reactor. The content and morphology of hydroxyapatite (HA) layers formed on the surface of both alloys after the PEO and subsequent HTT treatments were studied. The surface morphologies, elemental composition, and phase components were characterized by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and X-Ray Diffraction (XRD), respectively. The surface roughness was measured by Atomic Force Microscope (AFM), and thickness measurements were made by SEM and thickness gauge. Corrosion measurements were performed for the comparison of the corrosion behavior of the two alloys

Theoretical Description of Carbon Felt Electrical Properties Affected by Compression

Electro-conductive carbon felt (CF) material is composed by bonding together different lengths of carbon filaments resulting in a porous structure with a significant internal surface that facilitates enhanced electrochemical reactions. Owing to its excellent electrical properties, CF is found in numerous electrochemical applications, such as electrodes in redox flow batteries, fuel cells, and electrochemical desalination apparatus. CF electro-conductivity mostly arises from the close contact between the surface of two electrodes and the long carbon fibers located between them. Electrical conductivity can be improved by a moderate pressing of the CF between conducting electrodes. There exist large amounts of experimental data regarding CF electro-conductivity. However, there is a lack of analytical theoretical models explaining the CF electrical characteristics and the effects of compression. Moreover, CF electrodes in electrochemical cells are immersed in different electrolytes that affect the interconnections of fibers and their contacts with electrodes, which in turn influence conductivity. In this paper, we investigated both the role of CF compression, as well as the impact of electrolyte characteristics on electro-conductivity. The article presents results of measurements, mathematical analysis of CF electrical properties, and a theoretical analytical explanation of the CF electrical conductivity which was done by a stochastic description of carbon filaments disposition inside a CF frame

Electric and Hydraulic Properties of Carbon Felt Immersed in Different Dielectric Liquids

Electroconductive carbon felt (CF) material, having a permeable structure and significant electroconductive surface, is widely used for electrodes in numerous electrochemical applications such as redox flow batteries, fuel cells, electrochemical desalination apparatus, etc. The internal structure of CF is composed of different lengths of carbon filaments bonded together. This structure creates a large number of stochastically oriented and stochastically linked channels that have different lengths and cross sections. Therefore, the CF hydraulic permeability is similar to that of porous media and is determined by the internal empty volume and arrangement of carbon fibers. Its electroconductivity is ensured by the conductivity of the carbon filaments and by the electrical interconnections between fibers. Both of these properties (permeability and electrical conductivity) are extremely important for the efficient functioning of electrochemical devices. However, their influences counter each other during CF compressing. Increasing the stress on a felt element provides supplementary electrical contacts of carbon filaments, which lead to improved electrical conductivity. Thus, the active surface of the felt electrode is increased, which also boosts redox chemical reactions. On the other hand, compressed felt possesses reduced hydrodynamic permeability as a result of a diminished free volume of porous media and intrinsic channels. This causes increasing hydrodynamic expenditures of electrolyte pumping through electrodes and lessened cell (battery) efficiency. The designer of specific electrochemical systems has to take into account both of these properties when selecting the optimal construction for a cell. This article presents the results of measurements and novel approximating expressions of electrical and hydraulic characteristics of a CF during its compression. Since electrical conductivity plays a determining role in providing electrochemical reactions, it was measured in dry conditions and when the CF was immersed in several non-conductive liquids. The choice of such liquids prevented side effects of electrolyte ionic conductivity impact on electrical resistivity of the CF. This gave an opportunity to determine the influences of dielectric parameters of electrolytes to increase or decrease the density of interconnectivity of carbon fibers either between themselves or between them and electrodes. The experiments showed the influence of liquid permittivity on the conductivity of CF, probably by changing the density of fiber interconnections inside the felt

The study of hydroxyapatite growth kinetics on CP – Ti and Ti65Zr treated by Plasma electrolytic oxidation process

The kinetics of hydroxyapatite growth on titanium alloys (CP–Ti and Ti65Zr) was studied. Specimens were treated by Plasma Electrolytic Oxidation (PEO) and immersed into the Hanks' solution. The PEO method was performed at AC mode with the current density of 4 A/dm2 in an electrolyte containing calcium acetate and calcium glycerophosphate, allowing the inclusion of calcium and phosphorus in the obtained oxide layer, which promotes the osseointegration when applied to bone tissue. The treated specimens were immersed in the Hanks’ solution with different exposure times, followed by studying changes in morphology, chemical, and phase composition. In addition, the surface wettability was tested, and the corrosion behavior of the treated samples was investigated. Tiny HA crystals can be seen on the surface of CP-Ti samples treated by PEO for 5 and 30 min. The morphology with a distinct layer of HA was obtained for the Ti65Zr sample after 5 min of PEO treatment. As for the immersion times, the highest crystal growth velocity was observed for the Ti65Zr of 5 min of PEO and 14 days of immersion. The change in morphology and EIS analysis confirms the observed behavior. Finally, based on the XRD analysis for the Ti65Zr of 5 min PEO treatment samples, the Srilankite phase in an amount of 60% is responsible for the crystal growth, resulting in the best crystal growth velocity and good corrosion properties (Rp = 0.732 MΩ cm2)

Investigation of the Effectiveness of Dental Implant Osseointegration Characterized by Different Surface Types

Different surfaces were obtained by Plasma Electrolytic Oxidation (PEO) of the Ti–6Al–4V alloy; followed by hydrothermal treatment (HT). The surfaces were studied by scanning electron microscopy (SEM); Energy Dispersive Spectroscopy (EDS); X-ray Diffraction (XRD); Brunauer–Emmett–Teller (BET) absorption and abrasion wear tests. The resulting surface contains hydroxyapatite (HA); which contributes to superior implant osseointegration. Treated implants were introduced into rabbits and their osseointegration was studied after two and six months. It was established that implant surface area increases due to pore formation. Pore formation and hydroxyapatite on the surface of the implant qualitatively change contact osseogenesis processes with reduced duration of osseointegration of implants. The treatment of the surface of the implants by the combination of PEO and HT provided better results in the medico-biological investigations than PEO alone. Abrasion tests demonstrated that the HA will be preserved after the procedure of implantation; ensuring effective osseointegration

Biofuel Production by Fermentation of Water Plants and Agricultural Lignocellulosic by-Products

While at present most energy crops are depriving human feedstock, fermentation of agricultural residues and fast growing water plants possesses a good prospect to become a significant source for bio-fuel; as both substrates are widely available and do not require agricultural areas. Water hyacinth for instance can be cultivated in fresh, brackish or wastewater and owing to its rapid growth and availability. Since owing to its natural abundance it is considered to be an invasive plant in most continents, its utilization and use as a renewable energy source may also contribute for its dilution and control. Agricultural lignocellulosic surplus by-products are also a promising fermentable substrate for bioethanol production, as it decreases both disposal expenses and greenhouse gases emissions. This paper describes a scheme and methodology for transformation of any lignocellulosic biomass into biofuel by simple cost effective operation scheme, integrating an innovative process of mechanochemical activation pre-treatment followed by fermentation of the herbal digest and ethanol production through differential distillation. Under this approach several complex and costly staged of conventional ethanol production scheme may be replaced and by genetic engineering of custom fermenting microorganisms the fermentation process becomes a fully continuous industrial process

Biofuel Production by Fermentation of Water Plants and Agricultural Lignocellulosic by-Products

While at present most energy crops are depriving human feedstock, fermentation of agricultural residues and fast growing water plants possesses a good prospect to become a significant source for bio-fuel; as both substrates are widely available and do not require agricultural areas. Water hyacinth for instance can be cultivated in fresh, brackish or wastewater and owing to its rapid growth and availability. Since owing to its natural abundance it is considered to be an invasive plant in most continents, its utilization and use as a renewable energy source may also contribute for its dilution and control. Agricultural lignocellulosic surplus by-products are also a promising fermentable substrate for bioethanol production, as it decreases both disposal expenses and greenhouse gases emissions. This paper describes a scheme and methodology for transformation of any lignocellulosic biomass into biofuel by simple cost effective operation scheme, integrating an innovative process of mechanochemical activation pre-treatment followed by fermentation of the herbal digest and ethanol production through differential distillation. Under this approach several complex and costly staged of conventional ethanol production scheme may be replaced and by genetic engineering of custom fermenting microorganisms the fermentation process becomes a fully continuous industrial process