Controllably Introducing Exposed Surfaces to Nanocrystalline CeO2 Catalysts by High-Pressure Treatment

Controllably introducing highly active exposed surfaces into catalysts is a promising way to improve their properties. In addition to the widely used bottom-up method by limited crystal growth and topdown method by etching, in this study, a high-pressure treatment method is used to introduce fully crystalline clean, highly active exposed planes on submicrometer- or tens of nanometer-sized brittle catalysts. This treatment is based on a mechanism at the submicrometer or tens of nanometer scale, in which the catalysis materials are still brittle (they become ductile only when reaching the size of a couple of nanometers by the strong size effect) but do not crack randomly under high pressure like macrosized materials do. In fact, the catalyst displays a predominant cracking orientation, which is likely a highly active exposed plane, in the predominant dislocation orientation under high pressure. In this work, we used a CeO2 catalyst as a model system to show the mechanism that leads to an obvious photocatalytic property enhancement. Currently, since most catalysts have already been prepared at the submicrometer or tens of nanometer level, we believe that our findings provide a potential route to further improve their properties through a high-pressure treatment.

Research on Parameter Optimization of Micro-Milling Al7075 Based on Edge-Size-Effect

In the process of micro-milling, the appearance of the edge-size-effect of micro-milling tools cannot be ignored when the cutting parameters are smaller than the cutting edge arc radius (r0) of the micro-milling tool or close to it, and it could easily lead to low cutting efficiency and poor surface quality of the micro-slot. Through micro-milling experiments on Al7075-T6 materials, the change of milling force in the plough zone and shear zone during micro-milling was studied, and the minimum cutting thickness (hmin) range was determined to be 0.2r0–0.4r0 based on r0 of the micro-milling tool. Subsequently, the effect of fz/r0 (fz denotes feed rate per tooth) on the top burr formation of the micro-slot, the surface roughness (Ra) of the micro-slot bottom, and the milling force was studied, and a size-effect band of micro milling was established to determine the strong size-effect zone, transition size-effect zone, and the weak size-effect zone. Finally, two different fz/r0 in the strong size-effect zone and the weak size-effect zone are compared, which proves that the main purpose of the cutting parameters optimization of micro-milling is to avoid cutting parameters locating in the strong edge-size-effect zone. The above conclusions provide a theoretical basis for the selection of micro-milling cutting parameters, and an important reference in improving the surface quality of micro-milling.

Ab initio investigation of supported Au–Mn nanowires

We present an ab initio study of surface supported Au–Mn nanowires. Three different substrates are discussed: Cu(110), stepped Cu(111) and Si(001) surface. The emergence of stable antiferromagnetic (AFM) solutions in Au–Mn nanowires was found in all three cases. We found the nonzero magnetic moments of Mn atoms, however, the bulk of manganese is paramagnetic. The critical temperature of the Au–Mn wires is calculated by means of kinetic Monte Carlo simulation. The strong size-effect of the critical temperature is demonstrated.

Discrete dislocation dynamics simulations of twin size-effects in magnesium

ABSTRACTA dislocation-{101̅2} twin boundary (TB) interaction model was proposed and introduced into discrete dislocation dynamics simulations to study the mechanical behavior of micro-twinned Mg. Strong strain hardening was captured by current simulations, which is associated with the strong TB’s barrier effect. In addition, twin size effects with small TB spacing leading to a strong yield stress, were observed to be orientation dependent. Basal slip orientation produces a strong size effect, while prismatic slip does a weak one.

Size Effect on the Behavior of Thermal Elastohydrodynamic Lubrication of Roller Pairs

In order to investigate the size effect on elastohydrodynamic lubrication (EHL) of roller pairs, complete numerical solutions for both the Newtonian fluid and the Eyring fluid thermal EHL problems of roller pairs under steady state conditions have been achieved. It can be seen that there is no size effect on the isothermal EHL performance; however, there is a very strong size effect on the thermal EHL performance. Results show that the term of shearing heat is the most important factor for the film temperature when the size of a contact changes. Comparison between the Newtonian solution and the Eyring solution has been made under some operating conditions. It is interesting to see that the effective viscosity of the Eyring fluid is nearly the same as that of the Newtonian fluid when the size of a contact is large enough. The non-Newtonian effect, therefore, can be ignored when the size of a contact is very large. It is equally interesting to see that the thermal effect can be ignored when the size of a contact is very small. In addition, the influence of the velocity parameter, the load parameter, and the slide-roll ratio on the lubricating performance for various sizes of contacts has been investigated.

Size effects of nanoindentation creep

The size effects on indentation creep were studied on single-crystal Ni3Al, polycrystalline pure Al, and fused quartz samples at room temperature. The stress exponents were measured by monitoring the displacement during constant indentation loads after correction for thermal drift effects. The stress exponents were found to exhibit a very strong size effect. In the two metals Al and Ni3Al, the stress exponent for very small indents is very small, and for Al, this even approaches unity, suggesting that linear diffusional flow may be the controlling mechanism. The stress exponents in these two metals rise rapidly to over 100 as the indent size gets larger, indicating a rapid change of the dominating mechanism to climb-controlled to eventually glide-controlled events. In fused quartz, the stress exponent also exhibits a sharply rising trend as the indent size increases. The stress exponent is also close to unity at the smallest indents studied, and it rises rapidly to a few tens as the indent size gets larger.

Different Relaxation Modes of Epitaxial Thin Film Alloys With A Large Size Effect

In epitaxial layers, the mechanism of stress relaxation under consideration is in general dislocations. This paper will present experimental evidences for other modes of relaxation. which may occur in some situations especially where a strong size effect or misfit is present. In fact the stress is the driving force for intermixing, twinning, and phase transformation, which are not expected to occur in the bulk. All these experimental results have been sustained by numerical simulations that will also be presented.