Papers by Keyword: Dissolution Behavior

Abstract: Ni60WC35 self-fluxing composite coating was fabricated by transverse-flow CO2 laser apparatus on 45 medium-carbon steel surfaces. The microstructure and phase transform behavior of WC reinforced particles under the laser cladding conditions was investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy-dispersive spectrometer (EDS). The results show that laser scanning speed has a great important influence on the microstructure of Ni-based WC composite coating, WC particles has a transition to the Ni-based coating. The main feature of WC particle is its edge hard phase has transformed into needle phase, and the needle phase areas increase with the decrease of the laser scanning speed. Some WC particles turn into needle clusters structure, and then white block phase. In addition, WC particle has some microscopic defects, and the surface priority defect can be dissolved. When the pool temperature rises to 1250°C, WC decomposition reaction become W2C and C. The elements diffusion can promote the dissolution of WC particles when the pool temperature rises continuously.

Abstract: We report our observations concerning the time evolution of surface morphology occurring during the in vitro immersion of bioactive glass surfaces in contact with phosphate buffer solution. We compare regions under intentionally produced residual stresses via micro-indentation to those where no indentation was performed. The sign of the residual stress is shown to be important for predicting dissolution behaviour; compression retards dissolution, whereas tension enhances dissolution. We analyze our results with a simple model for the work of bond dissociation. We report that a highly constrained residual compressive stress state, such as in an indent, leads to a work deficit in comparison to tension, which accounts for the slower dissolution rate of compressed bioactive glass. Such a mechanochemical effect suggests that the presence of residual stresses from the manufacture of biomedical implants and devices could lead to accelerated or delayed dissolution and that careful control of residual stresses should be sought for predictable performance in dissolvable materials.

Abstract: Biphasic tricalcium phosphate (BTCP) powders composed of α-tricalcium phosphate (α-TCP) and β-tricalcium phosphate (β-TCP) were prepared using amorphous calcium phosphate (ACP) precursor after heat treatment at 800oC. The in vitro dissolution behavior of the powders was examined after soaked in 0.1M NaAc-HAc buffer solution for different times. It was revealed that the Ca2+ and PO4 3- concentration, and pH value of the BTCP-soaked solution are higher than those of the α-TCP- and β-TCP-soaked solutions. The dissolution behavior of BTCP powders was explained. The specific dissolution behavior of BTCP powders can widen the biodegradation range of calcium phosphate family.

Abstract: Characterization of heat-treated CaTiO3 thin films of 10, 20, 30 and 50 nm in thickness and their change after immersion in a simulated body fluid were investigated by grazing incident angle X-ray diffractometry and Auger electron spectroscopy (AES). The CaTiO3 films were prepared on titanium substrate by sputter-deposition of CaTiO3 target followed by heating in an electric furnace at 873 K in air for 7.2 ks. The CaTiO3 films were immersed in 0.8% NaCl solution for 14 d. All the films before heat treatment were non-crystallized films and after heat treatment, only the 50-nm film was crystallized to perovskite-type CaTiO3. In AES in-depth profiles after heating, Ca diffusion was not observed in the 50-nm film, whereas Ca diffusion toward the Ti substrate was observed in the 10-, 20- and 30-nm films. After immersion for 14 d, the vicinity of surface of the 10, 20 and 30 nm thick CaTiO3 films were dissolved into the NaCl solution, while the 50-nm thick CaTiO3 film was scarcely dissolved. Since dissolution from biomaterials in a human body has possibility to harm, the CaTiO3 film should be deposited more than 50 nm in thickness and heat-treated at 873 K.

Abstract: Submicron α-tricalcium phosphate (α-TCP), β-tricalcium phosphate (β-TCP) and biphasic α/β-TCP powders were prepared by an amorphous calcium phosphate (ACP) precursor way. For the biphasic TCP powders, primary particle size was 300nm, α-TCP and β-TCP primary particles were homogeneously mixed in the submicron powders. When the TCP powders were soaked in acetate buffer solution with pH 5, the Ca ion concentration in the soaked solutions and the resulting morphology variations were measured and observed. The results showed that the dissolution behavior of the biphasic TCP powders was different from α-TCP and β-TCP, and had a higher dissolved Ca ion concentration. This is attributed to a high supersaturation which is cased by the distribution homogeneity of two phase primary particles in submicron powders. These demonstrate the biphasic TCP to have potential to extend biological applications of Ca phosphates.

Abstract: Bioactive glass-ceramics of the SiO2-CaO-P2O5-MgO system were fabricated by sol-gel-self propagating method. Two Gel-derived materials discs， 5S and 3S， were prepared by compression of powders. The materials obtained were examined in vitro with regard to the dissolution behavior and the formation ability of calcium phosphate layer on the surfaces of samples in simulated body fluid (SBF). Concentration of ions and pH value in SBF were determined by ICP-AES and micro acidity meter after 3S and 5S were immerged in SBF for intervals from 6h to 15 days and the surface characteristic of 3S and 5S soaked were determined by SEM. Experiment results showed that the formation ability of calcium phosphate on the surface of gel-derived materials depended on the speed of dissolution of samples, which related to original chemical composition and size of crystal on the surface of materials. With decreasing of Si content and increasing of Ca content, smaller crystal could be formed on the surface of 3S, which tended to dissolve more quickly in SBF. Solubility product of calcium phosphate can be reached more easily in the solution with high concentration of Ca and P and bone-like carbonate apatite formed easily on the surface of 3S.