Papers by Keyword: Hydrothermal Treatment

Abstract: The effect of hydrothermal treatment time on sealing and corrosion resistance of the AA7475-T761 anodized aluminium alloy has been investigated in this study. The hydrothermal treatments tested are environmental compatible without chromium ions involved. Anodizing was carried out by a tartaric-sulphuric anodizing (TSA) process and this was followed by hydrothermal treatments for partial sealing, in various solutions. The effect of propyleneglycol (PRG) and/or cerium ions in the hydrothermal treatment solution was evaluated. Four treatment times were tested, specifically, 2.5, 5.0, 7.5 and 10 min. The corrosion resistance of the anodized and treated samples was evaluated by Electrochemical Impedance Spectroscopy (EIS) and the anodic layers formed were characterized by Scanning Electron Microscopy (SEM). The EIS results showed that the hydrothermal treatments in solutions with cerium ions resulted in similar impedances for periods of treatment from 5 to 10 min whereas in the solutions with PRG the impedance increased with time of treatment from 2.5 to 10 min showing a slower kinetics of anodic layer sealing. However, the fastest kinetics of sealing were associated to the treatments that combined two steps, one in PRG and other in cerium containing solutions with similar impedances obtained from 2.5 to 10 min of treatment. Surface evaluation by SEM showed that the porosities in the anodic layer were not sealed for the periods of hydrothermal treatments corresponding to 2.5 min. The presence of cerium in hydrothermal treatment had a beneficial effect on the stability of the anodic layer formed and provided a healing effect on the corroding sites.

Abstract: Tetrabromobisphenol A (TBBPA) is widely used as a flame retardant and relatively persistent in the environment. There has been increasing interest in the developing alternative approach for its degradation and debromination. In this study, we explored the debromination of TBBPA by alkaline hydrothermal treatment with reactive minerals, namely iron powder, layered double hydroxide (LDH) and gibbsite. The effects of hydrothermal temperatures and time, the initial TBBPA concentrations, and additive amounts of reactive minerals on debromination were investigated. As a comparison, the conventional hydrothermal treatment with no additive as the control group was included. The UV-vis absorption spectra of TBBPA before and after debromination were studied as well. The results showed that increasing temperature was helpful for the improvement of debromination. It significantly increased by 223.5, 54.3 and 78.1% with increasing temperature from 140 to 160 °C for the control, iron power and LDH groups, respectively. When the hydrothermal time was shorter than a critical value, the debromination rate increased with time rising. A maximum rate of 79.9% was achieved for iron powder group after reaction for 8 h. The preferred initial TBBPA concentration was determined as 60 ppm for all groups. The optimum amounts of reactive minerals were not consistent and determined as 0.08 g for iron powder, 0.32 g for LDH and 0.16 g for gibbsite, respectively. The maximum absorption bands of TBBPA increased as the pH was raised. They were located at 209 and 308 nm for neutral TBBPA and increased to 211 and 311 nm for TBBPA-Na₂CO₃. New absorption bands in the wavelength region of 225-275 and 300-350 nm were observed, when TBBPA was subjected to hydrothermal treatment. Keywords: Brominated flame retardants (BFRs); tetrabromobisphenol A (TBBPA); debromination; hydrothermal treatment; UV-vis absorption spectra

Abstract: Dental implant made of pure titanium (Ti) has become one important option to restore the function of lost tooth. However, because of insufficient hardness, it is always scratched during oral hygieneprocedures. To improve its surface hardness,titanium nitride (TiN) coating was prepared. Soft tissue - implant interface is important for blocking bacteria invasion, therefore surface modification is necessary to improve biocompatibility of TiN for fibroblasts.In the present study, TiN coating was modified by hydrothermal treatment incalcium acetate (CaAc) solution and effect of hydrothermal treatment temperature was studied. After treatment,calcium (Ca) wassuccessfully combined into TiN surface and the surface morphology, roughness and hardness were not changed below 140 °C. It is expected that, surface modification with Ca by hydrothermal treatment could made TiN a promising dental implant coating.

Abstract: Porous graphene is a collection of graphene-related materials which exhibits properties distinct from those of graphene, and it has widespread potential applications in various fields. Several approaches have been developed to produce porous graphene. However, the large-scale production of porous graphene nanosheets still remains a great challenge. Moreover, the costs of some methods are prohibitive for its commercial production and the processes are too complicated and time-consuming. In this work, we propose a simple and green method by which graphene nanosheets can be etched by sodium hydroxide under autogenous pressure at 180 °C. The morphologies and surface elements of the porous graphene nanosheets and sizes of pores were characterized. It is demonstrated that the one-step etching of graphene nanosheets is an effective method to obtain large-scale porous graphene nanosheets with high and uniform porosity. The pores in the porous graphene nanosheets were 6 nm depth (the same as the thickness of the graphene nanosheets) and 30-50 nm width.

Abstract: The surface topography and biocompatibility of titanium mesh treated with inositol hexakisphosphate (IP6) was studied. At high concentration of IP6, micro-grooved titanium surface with width of ~ 8 μm was formed. Then, calcium phosphate coating was deposited on the micro-grooves by a second hydrothermal treatment. Furthermore, cell culture results showed that micro-grooved surface could guide cell elongation and stretching along the grooves. Calcium phosphate modified micro-grooved titanium surface enhanced the cell viability compared with the unmodified surface. Therefore, IP6 modification may be a good candidate for improving the biocompatibility of titanium implants.

Abstract: The Ce_0.5Zr_0.5O₂ nanocomposites (CZ) were prepared by co-precipitation(CP), fractional precipitation (FP) and fractional precipitation with hydrothermal treatment (FP-HT). The samples were characterized by X-ray diffraction (XRD), Brunauer-Emmet Teller method (BET), H₂-temperature programmed reduction (H₂-TPR), and thermogravimetric analysis (TG) under H₂-N₂. XRD results displayed that all samples formed a single solid solution-like ceria-zirconia phase. BET results revealed CZ prepared by FP-HT (CZ-FP-HT) had the highest surface area. H₂-TPR and TG analysis under H₂-N₂ showed CZ-FP-HT exhibited the strongest redox ability and oxygen storage capacity. Moreover, three-way catalysts of Pd-Rh supported on CZ -FP-HT and commercial CZ with same composites were prepared, and their three-way catalytic activity were also studied by engine evaluation. Pd-Rh/CZ-FP-HT showed a bit of higher oxygen storage capacity, catalytic activity and better thermal stability than Pd-Rh/CZ-commercial.

Abstract: The effects of micro-arc oxidation (MAO) voltage (370V, 400V, 420V) on the surface morphology, adhesion of film/substrate, corrosion resistance and fretting friction and wear properties after micro-arc oxidation and heat-treatment for 48h of TiNi alloy were investigated. The results show that, as the voltage gradually increases: (1) micro-arc oxidation coatings form, when the voltage increase to 420V, the coating shows a significant micro-arc oxidized porous characteristics; (2) the Ca/P ratio in the coatings also increases, so the Ca/P ratio can be controlled by adjusting the voltage of micro-arc oxidation; (3) the corrosion resistance of MAO coatings can be significantly improved by increasing the output voltage, the corrosion rate and the corrosion potential of 420V are smaller two magnitude than 370V’s; (4) the coating of 420V shows lower friction coefficient with higher resistance, narrower wear scar width; (5) the MAO coatings have formed different types of hydroxyapatite crystals (HA) after immersed in high temperature and pressure reactor for 48h, and the phase composition of the coating are mainly apatite.

Abstract: Cerium Oxide (CeO₂) nanocubes are synthesized by using hydrothermal treatment method in the presence of four different types of ionic liquid such as acetate anion, phosphate anion, and dicyanamide anion. Ceria nanocubes has been consisted with average size of 16 to 31 nm in diameter and characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), and surface analyzer and porosimetry analysis (ASAP). Ceria nanocubes have higher photocatalytical ability in the degradation of methylene blue as compared to commercial ceria nanoparticles which are confirmed through ultraviolet-visible spectroscopy (UV/Vis).

Abstract: Titanium and its alloys have been employed in bone plates/screws, which must be removed after recovery. Conduction of bone occurs on the surface of Ti alloys that reside in the body for a long period. This can lead to re-fracture of cured bone in removal operations. On the other hand, bone has been reported not to be formed on the surface of Zr alloys. The purpose of this study was to synthesize Zr-containing TiO₂ film on commercial purity titanium (CP-Ti) by chemical-hydrothermal treatment. In addition, apatite formation on the films in Hanks’ solution and bone conduction in the tibiae of rats were also investigated. CP-Ti substrates were chemically treated with H₂O₂/HNO₃ aqueous solutions at 353 K for 20 min. The substrates were hydrothermally treated with ZrOCl₂/NH₃/hydroxy acid aqueous solutions in a Teflon-lined autoclave at 453 K for 12 h. The hydroxy acid was selected to be C₃H₆O₃ (lactic acid), C₄H₆O₆ (tartaric acid) or C₆H₈O₇ (citric acid). In the hydrothermal treatment without hydroxy acid, the surface product was anatase-type TiO₂. In contrast, when hydroxy acid was added the surface of Ti was covered homogeneously with a Zr-containing TiO₂ film. Some of the Zr (OH)₄ sol in the solution is thought to have dissolved into the solution by coordinate bonding with hydroxy acid carboxyl groups, leading to incorporation of Zr as ZrO₂ into the TiO₂. The product films suppressed the apatite precipitation in the Hanks’ solution soaking. In animal test, the small amount of ZrO₂ effectively suppressed the bone conduction.

Abstract: In this study, we conferred superhydrophilic properties on anodized TiO₂ coatings using a hydrothermal treatment, and developed a method to maintain this surface until implantation. The osteoconductivity of these coatings was evaluated with in vivo tests. A hydrothermal treatment made the surface of as-anodized samples more hydrophilic, up to a water contact angle of 13 deg. Storage in PBS(-) led to a reduction in the water contact angle, because of the adsorption of the inorganic ions in the solution, and the sample retained its high hydrophilicity for a long time. As the water contact angle decreased, the hard tissue formation ratio increased continuously up to 58 %, which was about four times higher than the hard tissue formation ratio on as-polished Ti.