Structure of Unsupported Small Palladium Nanoparticles

A tight binding molecular dynamics calculation has been conducted to study the size and coordination dependence of bond length and bond energy of Pd atomic clusters of 1.2–5.4 nm in diameter. It has been found that the bond contraction associated with bond energy increases in the outermost layer about 0.24 nm in a radial way, yet in the core interior the bond length and the bond energy remain their corresponding bulk values. This surface bond contraction is independent of the particle size

Erosion wear behaviour and model of abradable seal coating

International audienceThe abradable seal coating for an aircraft turbine engine is mostly composed of metal phase, self-lubricating non-metal phase and many pores. The erosion wear resistance is one of the most important properties of the coating. The erosion wear behaviour and mechanism of several kinds of middle temperature seal coatings were investigated by a CMS-100 self-made vacuum sand erosion machine. The results show that the relationship between the erosion mass loss and the erosion time is linear, the coatings hold a maximum erosion rate at 60° impact angle, and the relation between the erosion rate and the impact speed is an exponential function. The speed exponent increases with the increase of the impact angle. At 90° impact, the abrasive particles impinging on the coating surface produce indentations and extruded lips, and then the lips are work-hardened and fall off; and flattened metal phase grains are impacted repeatedly, loosed and debonded. At 30° impact, the micro-cutting, plowing and tunneling via pores and non-metal phase are involved. The model of the erosion mechanism is advanced on the basis of the above-mentioned erosion wear behaviour

Effect of Rare Earth Y on Properties of Nanosized 90W-7Ni-3Fe Composite Powder Fabricated by Spray Drying-Hydrogen Reduction

(W,Ni,Fe) composite oxide powder synthesized by spray drying was reduced at 700∘C for 90 minutes in H2 atmosphere. The effect of rare earth Y on H2 reduction of (W,Ni,Fe) composite oxide powder was studied. Phase composition, crystalline size, and particle morphology of the reduced powder have been measured by X-ray diffraction and scanning electron microscope (SEM). Fsss particle size and special surface area of the reduced powder were also measured and analyzed. The result showed that new phase Y(Ni0.75W0.25)O3 appeared in the reduced powder and particle morphology was nearly spherical or polyhedron by Y additions. The higher the rare earth element content was, the bigger the influencing on particle morphology was. When the rare earth Y content was under 0.8%, with the increase of the rare earth element content, dBET, Fsss, and crystal sizes of the reduced powder decreased greatly

Modeling the Size-Dependent Solid-Solid Phase Transition Temperature of Cu2S Nanosolids

The present study provides a simple model to predict the favored phase of Cu2S nanosolids upon variation of their size, shape, and temperature. Insight into the phase stability at the nanoscale will aid in the design of new nanomaterials. A study of the solid-solid phase transition demonstrated that the low-chalcocite to high-chalcocite transition temperature of Cu2S nanowires increases with increasing wire diameter consistent with recent experimental data.(31) At ambient temperature, the high-chalcocite phase is the most stable phase for nanofilms with a thickness below 1.5 nm, nanowires With a diameter below 3 tun and nanoparticles smaller than 4.5 nm, all in agreement with experimental observations.status: publishe

Friction and wear behaviour and abradability of abradable seal coating

International audienceThe friction and wear behaviour of several kinds of middle temperature abradable seal coatings used in aircraft turbine engine was investigated. Their abradability was evaluated by sliding worn volume. The mechanisms of the sliding wear of the coatings are abrasive wear, adhesive wear and oxidation wear, but the weight of the adhesive wear and abrasive wear is different in different coatings and under different test loads. The results show that the abradability decreases with the increase of the hardness for a given kind of coating. Even if the hardness is close, the abradability is very different in different kinds of coatings. So, only by the hardness can the level of abradability not be not judged and the coating not be chosen and designed. The abradability of M313 type of coating is the best, M310 is close to M601 and M307 with low hardness is fairly good, but M307 with high hardness is the worst

An Ensemble and Iterative Recovery Strategy Based kGNN Method to Edit Data with Label Noise

Learning label noise is gaining increasing attention from a variety of disciplines, particularly in supervised machine learning for classification tasks. The k nearest neighbors (kNN) classifier is often used as a natural way to edit the training sets due to its sensitivity to label noise. However, the kNN-based editor may remove too many instances if not designed to take care of the label noise. In addition, the one-sided nearest neighbor (NN) rule is unconvincing, as it just considers the nearest neighbors from the perspective of the query sample. In this paper, we propose an ensemble and iterative recovery strategy-based kGNN method (EIRS-kGNN) to edit data with label noise. EIRS-kGNN first uses the general nearest neighbors (GNN) to expand the one-sided NN rule to a binary-sided NN rule, taking the neighborhood of the queried samples into account. Then, it ensembles the prediction results of a finite set of ks in the kGNN to prudently judge the noise levels for each sample. Finally, two loops, i.e., the inner loop and the outer loop, are leveraged to iteratively detect label noise. A frequency indicator is derived from the iterative processes to guide the mixture approaches, including relabeling and removing, to deal with the detected label noise. The goal of EIRS-kGNN is to recover the distribution of the data set as if it were not corrupted. Experimental results on both synthetic data sets and UCI benchmarks, including binary data sets and multi-class data sets, demonstrate the effectiveness of the proposed EIRS-kGNN method

Formation and growth mechanism of tungsten oxide microtubules

Tungsten oxide microtubules, arrayed in a radial flower-like structure, were synthesized by simply using W powders reacting with Ni(NO3)(2) center dot 6H(2)O at a elevated temperature. The formed microtubules, with lengths more than 100 pin and outer diameters of 1-5 mu m, have irregular open ends, showing clear grooves along the growth direction on the tubule surface. A novel aggregation mechanism based on chemical-vapor-deposit process was proposed to describe the growth process of the synthesized tubules, and the possible mechanism for the arrangement of the radial flower-like morphology was discussed