Mechanism of tetraborate and silicate ions on the growth kinetics of microarc oxidation coating on a Ti6Al4V alloy.

The growth kinetics mechanism of microarc oxidation (MAO) coatings on Ti6Al4V alloy was studied by designing a binary mixed electrolyte with various SiO3 2- and B4O7 2- ion ratios via scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and potentiodynamic polarization. When the ratio of B4O7 2- in the electrolyte is 100%, B4O7 2- dissolves molten TiO2 at a high temperature, exposing nano-scale filamentary channels in the barrier layer of MAO coating, resulting in the repeated nucleation of microarc in the same area. When the ratio of SiO3 2- in the binary mixed electrolyte reaches 10%, the amorphous SiO2 formed by SiO3 2- at high temperatures from discharge blocks discharge channels and induces microarc nucleation in other regions, thus inhabiting the discharge cascade phenomenon. When the ratio of SiO3 2- in the binary mixed electrolyte increases from 15% to 50%, the amounts of molten oxides cover some of the pores formed by the primary microarc discharge, so part of the secondary discharge preferentially generates in the uncovered pores. Finally, the discharge cascade phenomenon occurs. Moreover, the thickness of the MAO coating obtained in the binary mixed electrolyte containing B4O7 2- and SiO3 2- shows a power function with time.

Incorporation of inorganic elements onto titanium-based implant surfaces by one-step plasma electrolytic oxidation: an efficient method to enhance osteogenesis.

In the field of dental and orthopedic implantation, the core issue is achieving good and stable osseointegration rapidly as well as for long-term, which is associated with a series of biological activities involving osteogenesis. Various surface modification methods have been applied to ameliorate the performance of titanium-based implants, among which plasma electrolytic oxidation (PEO) is very promising and has gained popularity in recent years. PEO produces thick, microporous, ceramic oxide layers on Ti and Ti alloys, which are described as "crater-like" or "volcano-like" morphology, and the physicochemical properties of PEO coating highly depend on PEO parameters. Furthermore, by adjusting the composition of the electrolytes of PEO, this technology enables the formation of element-incorporated coatings, exhibiting great potential. Plenty of studies reported in the literature revealed that multiple elements positively influence osteogenesis, but the issue of dose-dependent efficiency and safety concentration still requires careful consideration. Since osteoimmunomodulatory properties are regarded as the new target of implants, the osteoimmunomodulatory function of PEO coatings in the aspect of macrophage polarization has been discussed as well. The aim of this review is to describe the current state of different element-incorporated PEO coatings and their effect on the physicochemical and osteogenic properties of implants, intending to offer solutions for the development of implants that efficiently promote osseointegration.

Study on the wetting interface of Zr-Cu alloys on the SiC ceramic surface.

A Zr-Cu alloy, as a new type of filler metal, is proposed for brazing SiC ceramic under special working conditions. The wetting angle of Zr-Cu alloy/SiC ceramic at different temperatures and holding times was investigated by a high-temperature wetting tester. The composition of the wetting interface was tested by XRD, and the interfacial reaction layer was analyzed with SEM and EDS. The results show that the wetting angle decreases sharply with the change in temperature from 1100 °C to 1175 °C and remains unchanged when the temperature is higher than 1175 °C, about 34 ± 1°. The dynamic wetting angle of Zr-Cu/SiC at 1200 °C with the increase in holding time conforms to the law of exponential decay, and the equilibrium wetting angle is 5°. The transition layer with a certain thickness is formed during the spreading process of the Zr-Cu alloy at a high temperature, and the microstructure of the interfacial reaction layer mainly consists of ZrC and Zr2Si.

Assessment of a novel nanostructured flocculant with elevated flocculation and antimicrobial activity.

In this work, a novel process involving the preparation of nanochitosan-grafted flocculants (CPAM-g-NCS) to treat low turbid and salmonella suspensions simultaneously was introduced. Nanotechnology was employed to enhance the adsorption-adhesion and sterilization abilities of dual-functional flocculants. The monomers of chitosan, acrylamide, methacryloyl ethyl trimethyl ammonium chloride, and sodium tripolyphosphate were utilized for flocculants copolymerization. Then, using fourier-transform infrared spectroscopy, nuclear magnetic resonance hydrogen spectrum, and thermogravimetric and differential scanning calorimetry analysis, the successful synthesis of CPAM-g-NCS was verified. Scanning electron microscopy and size analysis suggested that nanostructured flocculants with irregular morphology and nanocolloids of 60.44 nm were formed. CPAM-g-NCS was applied to treat a series of simulated low turbid and salmonella suspensions. The simulation results showed that the minimum residual turbidity of 1.97 NTU and optical density of 0.16 (initial 0.89) can be achieved at dosages of 2.5 and 8.75 mg L-1, respectively, which were superior to conventional organics flocculants. Mechanistic studies suggested that the excellent adsorption property, and large numbers of quaternary ammonium and amino groups of nanoflocculants contributed to the superior flocculation and antibacterial performance of CPAM-g-NCS.

FEM Simulation and Verification of Brazing SiC Ceramic with Novel Zr-Cu Filler Metal.

Zr-Cu filler metal is proposed for SiC ceramic under special working conditions, as a novel type of the active filler metal, the difference of physical and chemical properties between SiC ceramic and Zr-Cu filler metal leads to greater residual stress in the joint, which affects the mechanical properties of brazing SiC ceramic joint. Based on the finite element method (FEM) simulation, the residual stress of the joint is simulated to guide the design of Zr-based filler metal and formulation of brazing process. The residual stress distribution of SiC ceramic joints brazed at 1200 °C with different thickness of the filler metal and cooling rate is simulated by ANSYS software. The simulation results of the residual stress are verified by brazing experiments and XRD measurements. The results show that the simulated residual stress of the joint is mainly axial compressive stress. The axial compressive stresses are the lowest when the filler metal thickness is 0.1 mm and the cooling rate is 2 °C /min, and increase with the increase of the filler metal layer thickness and cooling rate. The shear strength of the brazed SiC ceramic joint that achieves the highest with 2 °C /min is about 72 MPa, and then decreases with the increase of cooling rate. The experimental test of residual stress in different locations of the brazed SiC ceramic joint basically coincide with the FEM simulation.

Effects of rare-earth oxides on the microstructure and properties of Fe-based friction materials synthesized by in situ carbothermic reaction from vanadium-bearing titanomagnetite concentrates.

In this work, we prepared an iron-based frictional material from vanadium-bearing titanomagnetite concentrates by in situ carbothermic reaction with improved tribological properties. Effects of different amounts of rare-earth oxides on the microstructure and properties of the Fe-based friction materials were investigated. The microstructure of the Fe-based friction material consisted of an Fe matrix, hard particles (mainly TiC) and a lubricating phase (graphite). The moderate addition of rare-earth oxides improved the microstructure and properties of the Fe-based friction material significantly. Particularly, the friction coefficient decreased from 0.61 to 0.48-0.56 and the wear rate reduced from 7.8 × 10-7 cm3 J-1 to 2.6 × 10-7∼4.9 × 10-7 cm3 J-1. Addition of La2O3 (≤0.2 wt%) or CeO2 (≤0.4 wt%) contributed to sintering densification and improved the relative density, hardness and wear resistance. The dominant wear mechanism changes from severe abrasive wear and oxidative wear to mild oxidative wear. However, when rare-earth oxide addition was increased further, the microstructure, relative density, hardness, and wear performance of the Fe-based friction materials deteriorated. Consequently, the optimal additions of La2O3 and CeO2 were 0.2 wt% and 0.4 wt%, respectively.

Correction: Zr-Cu alloy filler metal for brazing SiC ceramic.

[This corrects the article DOI: 10.1039/C8RA05480K.].

Zr-Cu alloy filler metal for brazing SiC ceramic.

The Zr-Cu filler metal is mainly used for the joining of SiC ceramic as a nuclear fuel cladding material. The physical and chemical properties of the alloy, the interfacial reaction between the Zr-Cu filler metal and SiC ceramic, the residual stress of the SiC joint and the thermal neutron absorption cross section of the filler metal are considered during the design of the Zr-Cu filler metal. 80Zr-20Cu (wt%) is used as the filler metal in these experiments, showing good wettability and brazing properties with SiC ceramic.

Influence of Mn on the iron-based friction material directly prepared by in situ carbothermic reaction from vanadium-bearing titanomagnetite concentrates.

In this work, we prepared an iron-based frictional material from vanadium-bearing titanomagnetite concentrates by in situ carbothermic reaction with improved tribological properties. Effects of Mn content (1-4 wt%) on the microstructure and properties of iron-based friction material were investigated. The microstructure and properties of iron-based friction material with Mn are significantly improved. In particular, the friction coefficient decreases from 0.54 to 0.40-0.49 and the wear rate reduces from 1.899 × 10-7 cm3 J-1 to 0.229 × 10-7 cm3 J-1 - 1.309 × 10-7 cm3 J-1. Appropriate Mn addition (1-3 wt%) contributes efficiently to the sintering densification and increasing laminated pearlites. Comparatively, the density, hardness and wear resistance are improved. The dominant wear mechanism changes from severe abrasive wear to mild abrasive wear and oxidative wear is also enhanced. However, when Mn content increases to 4 wt%, the microstructure, relative density, hardness and wear performance of iron-based friction material are deteriorated. Consequently, the optimal addition of Mn is 3 wt% in the iron-based friction material.