D.Y. Li

A first-principles study on the mechanical and thermodynamic properties of (Nb1−xTix)C complex carbides based on virtual crystal approximation

Effects of component and temperature on mechanical and thermodynamic properties of (Nb1−xTix)C complex carbides were studied. The results show that it is easier to mix a small amount of NbC with TiC to form Ti-rich complex carbides than mixing small amounts of TiC with NbC to form Nb-rich complex carbides. Elastic modulus, hardness, ductility and fracture toughness of the complex carbide can be optimized by controlling the fractions of Nb and Ti in the complex carbide. The electronic property analysis on the complex carbides reveals that strong metal–metal and metal–carbon interactions exist in NbC, while strong metal–carbon interactions but weaker metal–metal interactions in TiC. The metal–metal interactions in the complex carbides attenuated when Nb is replaced by Ti. The bulk modulus and linear thermal expansion coefficient of the complex carbides demonstrate that a small amount of Ti atoms in the complex carbides may effectively alleviate the loss of the bulk modulus at elevated temperatures.

Understanding the low corrosion potential and high corrosion resistance of nano-zinc electrodeposit based on electron work function and interfacial potential difference

Nano-electrodeposition has been demonstrated to be more effective in protecting materials from corrosion, compared to conventional electrodeposition. However, debate still exists regarding why nanocrystalline electrodeposits show more negative corrosion potentials but lower corrosion rates than those of coarse-grained electrodeposits. In this work, we investigated corrosion behaviors of electrodeposited nanocrystalline and microcrystalline zinc coatings in a 3.5 wt% NaCl solution, and related them to the electron work functions of the coatings in order to understand the addressed issue based on the electron stability. It is demonstrated that the corrosion potential (ϕm) of a deposit depends on its electron work function (φm) and the contact potential difference at the electrodeposit/solution interface (Δmsψ). φm reflects the stability of electrons in the deposit, while Δmsψ reflects the environmental influence on the chemical stability of the deposit, which affects the actual corrosion rate. The present study shows that electrons in the nanocrystalline zinc coating are less confined due to its high-density grain boundaries, corresponding to lowered φm. However, Δmsψ of the nanocrystalline coating is more positive than that of coarse-grained one, leading to a lower corrosion rate. This study helps end the debate and provide relevant information for optimize nanocrystalline electrodeposits.

Electron work function – a probe for interfacial diagnosis

A poor interface or defected interfacial segment may trigger interfacial cracking, loss of physical and mechanical functions, and eventual failure of entire material system. Here we show a novel method to diagnose local interphase boundary based on interfacial electron work function (EWF) and its gradient across the interface, which can be analyzed using a nano-Kelvin probe with atomic force microscope. It is demonstrated that a strong interface has its electron work function gradually changed across the interface, while a weaker one shows a steeper change in EWF across the interface. Both experimental and theoretical analyses show that the interfacial work function gradient is a measure of the interaction between two sides of the interface. The effectiveness of this method is demonstrated by analyzing sample metal-metal and metal-ceramic interfaces.

Incorporating TiO2 nanotubes with a peptide of D-amino K122-4 (D) for enhanced mechanical and photocatalytic properties

Titanium dioxide (TiO2) nanotubes are promising for a wide variety of potential applications in energy, biomedical and environmental sectors. However, their low mechanical strength and wide band gap limit their widespread technological use. This article reports our recent efforts to increase the mechanical strength of TiO2 nanotubes with lowered band gap by immobilizing a peptide of D-amino K122-4 (D) onto the nanotubes. Topographies and chemical compositions of the peptide-coated and uncoated TiO2 nanotubular arrays were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy (XPS). Properties of the peptide-coated and uncoated TiO2 nanotubular arrays, including hardness, elastic modulus, electron work function and photocurrent, were evaluated using micromechanical probe, Kelvin Probe and electrochemical system. Effect of the peptide on surface conductivity was also investigated through current mapping and I–V curve analysis with conductive atomic force microscopy. It is demonstrated that the peptide coating simultaneously enhances the mechanical strength, photocatalytic and electrical properties of TiO2 nanotubes.

Elevate the corrosion potential of Zn coatings using ceramic nanoparticles

It was observed that adding TiC nanoparticles (NPs) to zinc coating increased its corrosion resistance. To understand the beneficial role of TiC nanoparticles in suppressing corrosion, we studied the electrochemical behavior of TiC NP-added nanocomposite zinc coating, in comparison with those of coarse-grained and nanocrystalline zinc coatings, in simulated seawater. The surface electrochemical stability and surface electron stability, which are respectively reflected by corrosion potential and electron work function (EWF), were investigated. It is demonstrated that the increased corrosion resistance of nanocomposite zinc coating is ascribed to the fact that the TiC nanoparticles raise surface electron work function of the coating, corresponding to elevated surface electron stability.