Near-surface Layer Of Sample Research Articles

Application of end-face fiber optic sensor for thermooptical research

The principles of operation and implementation features of the developed fiber-optic device for pulsed thermoreflectometry based on an external Fabry-Perot interferometer are discussed. The possibility of studying local thermal processes in the near-surface layers of samples by changing the thermal reflection of probing radiation during pulsed laser heating is shown. Comparison of experimental data with modeling calculations showed the predominant influence of the thermal deformation mechanism in the case of metal samples.

Deoxygenation of esters over sulfur-free Ni–W/Al2O3 catalysts for production of biofuel components

Sulfur-free Ni–W/Al2O3 catalysts synthesized through incipient wetness impregnation technique were investigated in deoxygenation of methyl palmitate and ethyl caprate blend at 300 °C and P = 1 MPa (PH2 = 0.25 MPa) in a fixed-bed continuous flow reactor. Modification of Ni/Al2O3 catalysts by W (0.4–4.4 wt%) was found to give rise to higher both conversions of the feedstock and deoxygenation degree. In addition, this also resulted in a change in the selectivity of deoxygenation towards alkanes formed via direct hydrodeoxygenation route, compared to alkanes formed through decarboxylation/decarbonylation. Selectivity by alkanes with carbon chain length equal to those of an initial fatty acid formed via hydrodeoxygenation was found to increase with W content increasing. The synthesized catalysts were investigated by XRD, XPS, TEM, BET and H2-TPR techniques. According to XPS study of the reduced samples, tungsten was in 6+ oxidation state on the sample surface and W6+ content increased in the near-surface layer of samples with tungsten content increasing in catalysts.

Metallographic studies results of 20kH13 steel samples with textured relief, modified surface and protective coating

One of the possible ways to improve passive methods of the steam turbine blade material protection from water droplet erosion is to create “smart”-surface that combines the properties and characteristics that could not be implemented simultaneously when using one or another proven method of protection. To solve the problem of developing such surface, this article presents the metallographic researches results of the blade steel 20kH13 samples with various already used and promising passive methods of protection, consisting in the use of ion-plasma and polyurethane coatings, surface modification by means of diffusion saturation with nitrogen ions, creation of the structured surface relief by laser ablation. The results of the carried out researches have allowed to reveal both morphology of a possible “smart”-surface, and influence on a microstructure and characteristics of a near-surface layer of samples after treatments considered.

Change in oxygen concentration in Sr2RuO4 single crystals after laser processing

In order to check the possibility of realization of high-temperature superconductivity in strontium ruthenate, we studied experimentally the influence of laser radiation on single-crystal samples of Sr2RuO4. Results obtained by the technique of electron-probe X-ray microanalysis showed an enhancement of the oxygen concentration in the near-surface layer of samples, which may most probably be caused by the change in the ruthenium valence as a result of laser treatment.

A new method of formation of a durable microrelief on the surface of samples made of cobalt-chromium alloy

Experimental studies of strong local interaction between microplasma discharges and samples made of cobalt—chromium alloy were performed. It was established that, in the near-surface layer of samples treated with microplasma discharges, a remelted area with greatly changed physicochemical properties is formed. After microplasma treatment, the surface of samples becomes considerably rougher, which improves surface cohesion (adhesion) with various materials (ceramics, plastics, etc.) when durable composite structures are formed.

Effect of sterilization on the cutting efficiency of rotary nickel-titanium endodontic files

Objective. Nickel-titanium instruments that offer greater flexibility than instruments made of other metallic materials have been developed. This study evaluated the behavior in vitro of nickel-titanium rotary instruments under repeated sterilization cycles. Study Design. To investigate changes in cutting ability and superficial alterations, 36 ProFile instruments, 18 with a taper of .04 and 18 with a taper of .06, were exposed to different sterilization cycles. Samples were divided into 3 groups of 12 files each. The 12 group A samples were exposed to 14 cycles of sterilization for 30 minutes; the 12 group B samples were exposed to 7 cycles of sterilization for 30 minutes; the 12 group C samples were not sterilized and served as a control group. Chemical compositions of the near surface layers of samples of each group were determined by means of Auger spectroscopy. Results. The instruments that underwent the greatest number of sterilizations (group A) showed in-depth distributions of chemical composition that were different from those seen in the control group; this was the result of greater amounts of titanium oxide on the surfaces of the sterilized instruments. The files of group A showed a decrease in cutting efficiency in comparison with those of the control group. Conclusions. On the basis of this research on nickel-titanium files, we determined that repeated sterilizations under autoclave alter the superficial structure of such instruments. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1999;88:343-7)

Topographical change of high-temperature copper surface bombarded by Ar ions

Topographical changes of thin copper wires (chemical purity 99.9%, 30–50 μm in diameter) during 20 keV argon ion bombardment up to 4 × 10 19 ions cm −2 at several temperatures between room temperature and 1073 K have been studied using the Scanning Electron Microscope. It is observed that there is a notable difference in the surface topography of copper wires below 423 K and above 573 K. This experimental observation is related to the diffusion of metal atoms in near-surface layers of samples.