Papers by Keyword: Surface Energy

Abstract: Surface energies of indium doped ZnO were calculated to explain the polarized growth of ZnO nanodisks due to indium doping. Calculation results show that the surface energy of ZnO (0001) surface is much larger than that of ZnO (10 1 0) surface, leading to a preferred growth direction of [0001] for pure ZnO. At a doping rate of 1/8, the surface energies of indium doped ZnO are greatly reduced, but the surface energy of (0001) surface is still larger than that of (10 1 0) surface. At a doping rate of 1/4, the surface energies are decreased further, and the surface energy of (0001) surface is lower than that of (10 1 0) surface. Hence, growth of ZnO along [10 1 0] direction is made possible by heavy indium doping.

Abstract: Diamond-Like carbon (DLC) films were prepared under different bias voltage by direct current magnetic filter cathode vacuum arc deposition (DC-MFCVAD). Bias voltages changed from 0 to -200 V. The study intends to investigate the effect on the properties of DLC films for biomedical applications. X-ray photoelectron spectrum (XPS) was used to investigate composition of the films. Nano-scratch tests were used to characterize effects of bias voltage to adhesion. Furthermore, the wettability of the DLC films was investigated by contact angle measurements using four common liquids. Finally, platelet adhesion experiments were done to evaluate the interaction of blood with DLC films. The results showed that the adhesion, wettability and hemo-compatibility of DLC films were affected by bias voltage.

Abstract: Previously, various surface treatments have been used to enhance the ability of titanium surfaces to induce calcium phosphate (Ca-P) formation in simulated body fluid (SBF). However, there were no systematic investigations on the key factors of the surface treatments to control such ability. In this work, three factors are studied for their roles in controlling Ca-P precipitation in SBF: surface roughness, surface chemistry and surface energy. Four kinds of single-step chemical treatments on Ti surfaces were carried out, including alkali treatment (AT), nitric acid treatment (NT), hydrogen peroxide treatment (HPT), and heat treatment. The experimental results show that the surface energy is the most likely controlling factor of Ca-P formation ability.

Abstract: This paper investigates the surface texture evolution during α−γ−α phase transformation. After austenite annealing of the cold rolled sheets a weak texture was formed at the surface of ultra low carbon steel alloyed with Mn and Al. This texture consists of <100>//ND and <110>//ND fiber orientations with an intensity of approximately 2 X random. This surface texture is confined to a mono-layer of surface grains which are in direct contact with the metal/vapour interface. In order to interpret this surface effect, two alternative mechanisms were considered: (i) one assumption attributes the occurrence of the specific surface texture to the minimization of the outer surface energy and (ii) according to an alternative hypothesis the release of elastic work parallel to ND in the surface area is responsible for the observed surface fibers. After analyzing the experimental data it is concluded that the evidence in support of hypothesis (i) is the more convincing in this experiment.

Abstract: O-doped Diamond-Like carbon (O-DLC) films were prepared by direct magnetic filtered cathodic vacuum arc deposition (DC-MFCVAD) under different O2 gas flow at room temperature (R.T.). Raman spectra were used to characterize structure of films. The wettabilities of the O-DLC films also were investigated by contact angle measurements using four common liquids. For studying films’ interaction with blood, platelet adhesion experiment in vitro was done to characterize anticoagulant property of the O- DLC films from an aspect. Furthermore, ultraviolet spectrophotometer was employed to measure the optical band gap of the synthesized films. All of the results showed that O-DLC films have good anticoagulant property, oxygen doping can prevent graphite-like tendency of DLC films and increase band gap in a way, this kind of film materials may be become a new candidated biomaterials.

Abstract: Amorphous carbon (a-C) and carbon nitrogen (a-CN) films were synthesized using plasma immersion ion implantation and deposition (PIII-D) under different N2 flow at room temperature (R.T.). Lifshitz-van der Waals/acid-base approach (LW-AB) was introduced in order to study films’ surface energy deeply. The results showed that the capability of the surface of the film on receive electron changed with N2 flow, which effected platelet adhesion of film strongly. Hall effects tests were employed to characterize the electrical properties of the films. The results showed that the as-deposited films exhibited n-type semiconductor characteristic, and carrier concentration of the films decreased with N2 flow increasing. Raman spectra with 514nm laser-source were employed to analyze the structural of the films.

Abstract: The effect of cutting fluids on surface characteristics of glass
one of homogenuious brittle materials
are discussed. In water both fracture stress and tough ness are greatly decreased and many uncontrollable cracks are easily generated and propagate in maching.The other hand, in spindle oil, both the stress and toughness becomes lager, and the crack generation and propagation also restrained than those in water. In order to obtain the defect free surface of glass by machining, both the generation of cracks and propagation should be controlled or restrained. Since they are greatly affected by the surface and/or at the crack tip energy of glass, some methods for increasing the energy are proposed.

Abstract: More than fifty years ago Frank proposed that a dislocation with a Burgers vector larger than a critical value would have an open core. Since then, there has been controversy as to whether micropipes in SiC are examples of open core screw dislocations. In this work open core dislocations in 4H-SiC material are investigated by AFM. The results are interpreted on the basis of Frank’s theory and the surface energy of SiC is estimated from the critical value of Burgers vector. Finally, the extracted surface energy is compared with the results of other research.

Abstract: In order to examine mode-I & II type fracture behavior of ceramic joints, the interface element was proposed as a simple model which represents the mechanism of failure in an explicit manner. It was applied to the analyses of four point bending test and asymmetrical four point bending test for SiC/SiC composite specimen joined by ARCJoinTTM. By using a new type interface potential, which is a coupled function of opening and shear deformations, both the bending and asymmetrical bending tests were simulated. From comparison with experiments, surface energy at the interface between the joint and composite was estimated to be about 30 N/m regardless of the fracture mode. Also, from the comparison between the predicted strength and the experiments for the tensile test of lap joint of SiC/SiC composites, it was found that the proposed method was considered to have a great potential as a tool to study the failure problems whose fracture type was a mixture of mode-I & II.

Abstract: A new formulation for an adhesive force between a substrate and an indenter is presented. The boundary condition taking into account surface stresses is used for the present analysis. The surface stress is originated from surface energy. A paraboloidal indenter is pressed to the substrate, and then adhesion occurs between both surfaces. Surface energy and surface stress will vary at the adhesion surface, and then the surfaces deform in a concave way. An attractive force occurs to keep the contact of two adhesion surfaces. In the present paper, an effect of surface stress on the adhesive force will be clarified.