Protection of titanium metal by nanohydroxyapatite coating with zirconia and alumina second phases

In this study hydroxyapatite (HA)/zirconia/alumina composite coatings on titanium metal was carried out using Sol-Gel dip coating and calcination process. Hydroxyapatite-Alumina-Zirconia sol, coated samples in three processes by changing final sol stirring time, aging time, calcination temperature of synthesized powder and prepared coating and rate of coating. Some parts of prepared sol were also synthesized and became powder in all three processes. Scanning electron microscopy was used to estimate the particle size of the surface and for morphological analysis. The functional group and crystallization characteristics of the powders were analyzed using (FTIR) and X-Ray diffraction (XRD). Results show that the morphology of HA-Alumina-Zirconia coatings is more homogenous in the second process with 2 hours final sol stirring time, 20 hours aging time under stirring at 60, 675°C calcination temperature for coating and 850°C for powder and 60mm/min rate of dip coating.     

Synthesis of silicon-substituted hydroxyapatite by a hydrothermal method with two different phosphorous sources

Silicon-substituted hydroxyapatite (Si-HA) with up to 1.8 wt% Si content was prepared successfully by a hydrothermal method, using Ca(NO₃)₂, (NH₄)₃PO₄ or (NH₄)₂HPO₄ and Si(OCH₂CH₃)₄ (TEOS) as starting materials. Silicon has been incorporated in hydroxyapatite (HA) lattice by partially replacing phosphate (PO₄³⁻) groups with silicate (SiO₄⁴⁻) groups resulting in Si-HA described as Ca₁₀(PO₄)_6−x(SiO₄)_x(OH)_2−x. X-ray diffraction (XRD), Fourier transform IR spectroscopy (FTIR), inductively coupled plasma AES (ICP-AES) and scanning electron microscopy (SEM) techniques reveal that the substitution of phosphate groups by silicate groups causes some OH⁻ loss to maintain the charge balance and changes the lattice parameters of HA. The crystal shape of Si-HA has not altered compared to silicon-free reference hydroxyapatite but Si-incorporation reduces the size of Si-HA crystallites. Based on in vitro tests, soaking the specimens in simulated body fluid (SBF), and MTT assays by human osteoblast-like cells, Si-substituted hydroxyapatite is more bioactive than pure hydroxyapatite.     

Synthesis of high surface area nanocrystalline MgO by pluronic P123 triblock copolymer surfactant

Nanocrystalline magnesium oxide with high surface area was prepared by a simple precipitation method using pluronic P123 triblock copolymer (Poly(ethylene glycol)-block, Poly(propylene glycol)-block, Poly(ethylene glycol)) as surfactant. The prepared samples were characterized by X-ray Diffraction (XRD), N₂ adsorption (BET), Fourier transform infrared spectroscopy (FTIR), Thermal, differential thermal gravimetric and differential thermal analyses (TG/DTG/DTA) and Scanning electron microscopy (SEM). The obtained results revealed that the addition of surfactant is effective to prepare magnesium oxide with high surface area and affects the morphology of the prepared samples. The results showed that the magnesium oxide calcined at different temperatures ranging from 600 to 800 °C possessed a high surface area in the range of 133.9–78.1 m² g^?1. In addition, the magnesium oxide prepared with the addition of surfactant showed a narrower pore size distribution compared to the sample prepared without the addition of a surfactant.     

Tuning and optimization of structure and surface properties of thin and fine hydrophilic nanofibrous substrates through low-pressure heat-press treatment

The properties of electrospun nanofibrous membranes (ENMs), including pore size, surface roughness, and hydrophilicity, significantly affect crosslinking, thickness, and morphology of the polyamide selective layer formed on top of ENM substrate in thin film composite membranes, and, ultimately the performance of membranes. We produced polyamide 66 nanofiber layers with a thickness of 10 μm and a fiber diameter of 55 nm, considerably thinner and finer than usual ENM substrates. We then subjected this thin layer to post-production treatment using the efficient low-pressure heat-press (LPHP) method at a pressure of 3 kPa at three different temperatures and two different time intervals. It was found that the morphology of the nanofiber layer was preserved, and its structural characteristics, including pore structure, surface roughness, wettability, crystallinity, and specific surface area, were favorable with LPHP treatment. The optimal conditions were obtained with treatment at 190°C for 3600 s, in which the roughness of the nanofiber substrate decreased from 64 to 25 nm. Using these substrates offers new, less-explored opportunities for optimizing the LPHP treatment of the substrate. These substrates are proposed for a new generation of TFC membranes in a continuous production line, with the possibility of scaling up for pressure- and osmosis-driven membranes.     

Curing behavior of dicyandiamide/epoxy resin system using different accelerators

Various amounts of dicyandiamide (Dicy), two grades of epoxy resins, i.e. Epiran 06 and Epikote 828, and three different accelerators including benzyl dimethyl amine (BDMA), 3-(4-chlorophenyl)-1,1-dimethyl urea (Monuron) and 2-methyl imidazole (Im) were used in curing of Dicy/epoxy resin system. Both of the used epoxy resins were based on diglycidyl ether of bisphenol A (DGEBA). The effects of type and concentration of accelerators on curing behavior were studied by differential scanning calorimetry (DSC) method in dynamic or non-isothermal mode. The optimum concentration of Dicy for curing of epoxy resins was obtained based on the glass transition temperature of the cured epoxy/Dicy formulations. The maximum glass transition temperature of 139 °C was obtained at the stoichiometric ratio of Dicy to epoxy of 0.65. The results showed that BDMA has a broader curing peak in DSC and starts the cure reaction earlier than the others. However, Monuron has a narrow curing reaction peak with good cure latency. The tensile properties of Dicy-cured Epiran 06 and Epikote 828 epoxy resins reinforced with chopped strand mat showed that these two epoxy resins have similar mechanical properties. For composites based on the Epiran 06 and Epikote 828 reinforced with 40 wt % glass chopped strand mat, tensile strength and modulus were 156 and 153.4 MPa and 11.6 and 12.4 GPa, respectively.     

Solid-phase electrochemical reduction of graphene oxide films in alkaline solution

Graphene oxide (GO) film was evaporated onto graphite and used as an electrode to produce electrochemically reduced graphene oxide (ERGO) films by electrochemical reduction in 6 M KOH solution through voltammetric cycling. Fourier transformed infrared and Raman spectroscopy confirmed the presence of ERGO. Electrochemical impedance spectroscopy characterization of ERGO and GO films in ferrocyanide/ferricyanide redox couple with 0.1 M KCl supporting electrolyte gave results that are in accordance with previous reports. Based on the EIS results, ERGO shows higher capacitance and lower charge transfer resistance compared to GO.     

Mutations Closer to the Active Site Improve the Promiscuous Aldolase Activity of 4‐Oxalocrotonate Tautomerase More Effectively than Distant Mutations

The enzyme 4‐oxalocrotonate tautomerase (4‐OT), which catalyzes enol–keto tautomerization as part of a degradative pathway for aromatic hydrocarbons, promiscuously catalyzes various carbon–carbon bond‐forming reactions. These include the aldol condensation of acetaldehyde with benzaldehyde to yield cinnamaldehyde. Here, we demonstrate that 4‐OT can be engineered into a more efficient aldolase for this condensation reaction, with a >5000‐fold improvement in catalytic efficiency (k_cat/K_m) and a >10⁷‐fold change in reaction specificity, by exploring small libraries in which only “hotspots” are varied. The hotspots were identified by systematic mutagenesis (covering each residue), followed by a screen for single mutations that give a strong improvement in the desired aldolase activity. All beneficial mutations were near the active site of 4‐OT, thus underpinning the notion that new catalytic activities of a promiscuous enzyme are more effectively enhanced by mutations close to the active site.     

The effect of natural flow of aquifers and associated dispersion on the onset of buoyancy‐driven convection in a saturated porous medium

Carbon dioxide injection into deep saline aquifers is an important option for managing CO₂ emissions. Injected CO₂ dissolves into formation brines from above, increasing brine density and creating an unstable hydrodynamic state favorable for natural convection. Long‐term buoyancy‐driven flow of high‐density CO₂‐saturated brine leads to faster trapping through improved dissolution and can reduce the risk of CO₂ leakage from storage sites. We investigate the role of natural flow of aquifers and associated dispersion on the onset of convection. A linear stability analysis of a transient concentration field in a laterally infinite, horizontal, and saturated porous layer with steady horizontal flow is presented. The layer is subjected to a sudden rise in CO₂ concentration from the top and is closed from the bottom. Solution of the stability equations is obtained using a Galerkin technique and the resulting equations are integrated numerically. We found simple scaling relationships that follow t_Dc～60(1 + Pe_T)Ra^‐2 for the onset time of convection and a～0.05Ra/(1 + Pe_T) for the wavenumber of the initial instabilities. Results reveal that transverse dispersion increases the time to onset of convection for the entire range of Ra. Furthermore, transverse dispersion decreases the critical wavenumber of the instabilities. These results facilitate screening candidate sites for geological CO₂ storage. © 2008 American Institute of Chemical Engineers AIChE J, 2009