Band 111, Heft 10

A new method was developed for quickly preparing a highemissivity silicon boride compound of SiB x (x = 3, 4, 5, 6) by highly exothermic Ti-TiO 2 -Si-Al chemical oven preheating. The SiB x combustion synthesis process and adiabatic combustion temperature were investigated. A large exothermic reaction occurred at the combustion temperature of 1 700 K. X-ray diffraction results indicate that an SiB x phase and a substantial amount of unreacted Si were identified in the products. By increasing the boron content until the Si-B ratio reached to 1 : 6, the diffraction peaks primarily indicated SiB 6 , SiB 4 , and Si 11 B 33 in the final product. According to the spectra and quantitative results, the atomic chemical composition ratio of Si and B was close to the nominal composition. Thus, this method offers an efficient way to produce Si-B compounds with less time and energy consumption than current methods.

CdS nanoparticles are synthesized by a simple chemical coprecipitation technique using glucose as a capping/complexing agent and their structural, morphological, electrical and magnetic properties are studied. X-ray diffraction results reveal the pure phase formation of CdS nanoparticles along with a wurtzite structure. The interaction of the glucose with CdS nanoparticles is evident from the distinct absorption bands and peaks in the Fourier transform infrared spectra. Field effect scanning electron microscope and high resolution transmission electron microscope images depict weakly aggregated spherical nanoparticles of size ~2- 20 nm. The selective area electron diffraction pattern exhibits well-resolved diffraction rings representing the polycrystalline nature of the nanoparticles. The optical band gap has been calculated using Tauc’s plot and found to be 2.58 eV, which is higher than the band gap of the bulk phase wurtzite CdS. The existence of the excitonic peak and the blue-shift in the absorption threshold confirm the quantum confinement in the synthesized nanoparticles. The temperature dependence of d. c. conductivity is studied and observed a linear response through current-voltage characteristics. Weak ferromagnetism is also observed in the synthesized CdS nanoparticles irrespective of the diamagnetic nature of CdS in bulk form. The observation of weak ferromagnetism in the synthesized nanoparticles proposes them as a potential candidate for diluted magnetic semiconductors.

Ti-6Al-4V alloy cylinder samples were subjected to rotary forging at temperatures ranging from room temperature to 1 473 K. The microstructure and texture were examined by means of electron back-scatter diffraction and X-ray diffraction. The results indicated that the rotary forging could remarkably promote formability at elevated temperatures but not room temperature. For the 1 073 K and 1173 K samples, dynamic recrystallization led to a notable grain refinement effect and produced a typical basal texture. With the further increase of deforming temperature to 1 473 K, dislocation slip contributed the main deformation and the effect of grain refinement was weakened. The martensitic transformation took place during the cooling process of the 1 473 K sample, forming a strip type microstructure and a special texture different from basal texture.

In this study, copper/ZrO 2 surface composites were produced using nano-particles via friction stir processing in order to enhance surface tribological properties. The present research aimed to generate copper matrix composites and analyze the effect of processing parameters on the evolving microstructure, microhardness, and wear-resistance behavior. It is worth noting that the processed composite layer had more homogeneity in the four-pass process. In comparison to the base metal and non-powder samples, it had higher mechanical characteristics. Based on the results, the highest recorded hardness, approximately 288 HV, was found in a four-pass state with powder. Remarkably, it showed a double peak compared to 80 HV in the base metal. The lowest friction coefficient of four-passes with the powder sample was about 0.47, which showed a significant efficiency in comparison to the friction coefficient of base metal that was about 0.81.

In this paper, brass/steel/brass clad-composite was fabricated using a cold roll-bonding process. Composite sheets were roll-bonded at reduction ratios between 37 and 72% at room temperature from strips of 150 mm in length and 30 mm wide, in one pass without lubrication. The threshold deformation for successful bonding was at a thickness reduction of 48% and peel strengths of the bonds were measured to be approximately 12 N cm -1 , and it was found to escalate with an increase in the rolling reduction. The optimum reduction in thickness was ~66% wherein the peel strength was ~33 N cm -1 . Various techniques such as optical and electron microscopy were implemented to analyze and investigate the effects of the reduction in thickness and the joining mechanism. The results showed that an increased reduction in thickness in rolling leads to an increase in the joining strength. Furthermore, increasing the brass plate thickness negatively affects the joining strength. A Cu peak on the peeled-off steel surface and the presence of Fe on the peeled-off brass surface strongly suggest that the major bonding between brass and steel was mechanically induced metallurgical bonding.

Boron-added steel has been used in several automotive components in which the energy absorbed in impact testing is an important requirement. Previous thermodynamic studies have shown that boron addition promotes significant change in equilibrium phases, increasing the volume fraction of precipitated phases, mostly due to increased carbide stability and formation of borocarbides. As volume fraction, size and distribution of precipitates influence the absorbed energy in impact testing of steels, it is important to study M 23 (B,C) 6 borocarbide precipitation and coarsening kinetics and its effects on Charpy V-notch absorbed energy of boron steels. In the present work, borocarbide coarsening kinetics were evaluated using optical microscopy in samples heat-treated at 880 0 C for different times. The borocarbide coarsening kinetics data suggest that growth is controlled by an interfacial reaction mechanism. The Charpy V-notch absorbed energy decreases with increasing borocarbide section size and the embrittlement was successfully described by an empirical equation.

In this work, we fabricate a highly efficient photocatalytic AgBr/Ag 2 CO 3 heterojunction through the co-precipitation method. The obtained samples were characterized by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, ultraviolet-visible diffuse reflectance spectra and X-ray photoelectron spectroscopy. The photocatalytic activities of obtained samples can be assessed by visible light (λ ≥ 400 nm) degradation of rhodamine B solution. X-ray diffraction revealed that the crystallinity of the AgBr/Ag 2 CO 3 heterojunction was significantly higher than pure AgBr and Ag 2 CO 3 . Moreover, the AgBr/ Ag 2 CO 3 heterojunction prepared at pH = 6 has the best photocatalytic performance, it can raise the degradation degree of rhodamine B over 95% at 20 min. Finally, a possible photocatalytic mechanism is discussed.

The non-isothermal crystallization kinetics with heating rates ranging from 10 K s -1 to 80 K s -1 and the isothermal crystallization kinetics during annealing from the glass transition temperature to the crystallization onset temperature of a Zr 57 Cu 15.4 Ni 12.6 Al 10 Nb 5 amorphous alloy were studied in detail using X-ray diffraction and differential scanning calorimetry. During non-isothermal crystallization, it is more difficult to nucleate than to grow, and the crystallization resistance increases first and then decreases. During isothermal crystallization of the alloy from 713- 728 K, there are two exothermic peaks corresponding to a diffusion-controlled growth process with decreasing nucleation rate and increasing nucleation rate. From 733- 748 K, only one exothermic peak appears, and the growth process is controlled by the interface with decreasing nucleation rate. Isothermal crystallization is a process in which the crystallization resistance increases. The resistance of isothermal crystallization is less than that of non-isothermal crystallization.

In the last decade, biocidal materials have been extensively researched and applied as a coating for various touchscreen devices, in medicine and civil engineering. This research addresses important practical issues in application of surface- modified biocidal glass in water, and inspects optical properties in the spectral range between 350 nm and 500 nm, the range important for bacteria fluorescence detection. Testing of biocidal efficiency has been conducted in an environment rich with microorganisms and algae. To incorporate silver ions in soda lime glass plates, an ion-exchange process in a molten bath was used. The optical characterization of as-synthesized samples indicates very high transparency, above 90% at 440 nm, specifically important for escherichia coli detection. fter 140 days in the bioreactor, it was found that glass heated for 15 min at 350 0 C produced best results, maintaining transparency above 85% in spectral range from 350 nm to 1000 nm.

In this study, the synergistic effects of 2-mercaptobenzotiazole molecules and zinc nitrate on the corrosion behavior of carbon steel were investigated using electrochemical techniques in 3.5% NaCl solution. The experimental results revealed that combination of 2-mercaptobenzoimidazole (MBT) and zinc nitrate with ratio of 100 ppm : 100 ppm, resulted in the least corrosion current (1.03 lA cm -2 ) and the highest corrosion inhibition efficiency. Polarization results showed that the inhibition mechanism of inhibitor was mixed-type (anodic and cathodic mechanism) corrosion inhibition which was predominantly influenced by a reduction in dissolution rate of the substrate (decrease in anodic current density). Electrochemical impedance spectroscopy analysis yielded more accurate results about the formation mechanism and stability of the inhibitor film over prolonged time. The precipitation of chelate from inhibitor molecules and zinc cations on steel surface was found to be the main mechanism for increasing the corrosion resistance of steel substrate.

To find good candidate materials for degradable bridgeplugs used in shale oil or gas exploitation, a novel hot extruded Mg-4Y-1Zn-1Cu alloy with long period stacking order (LPSO) phase and excellent mechanical properties and rapid degradation rate was fabricated. Compared with the Mg-4Y-1Zn alloy, the compressive properties of Mg-4Y- 1Zn-1Cu alloy are dramatically enhanced by adding Cu, with a compressive strength of 480 MPa, which can be attributed to the formation of fine-grains and the strengthening LPSO phase distributed within the substrate. Furthermore, Mg-4Y-1Zn-1Cu alloy shows a rapid degradation rate as demonstrated by immersion tests and polarization curves, with about 30 times higher corrosion rate than Mg- 4Y-1Zn alloy, which can be attributed to the 14H-type LPSO phase containing Cu with high corrosion potential and high fraction grain boundaries.