Effects of nanocrystalline calcium oxide particles on mechanical, thermal, and electrical properties of EPDM rubber

In this research, the effect of calcium oxide (CaO) nanocrystalline particles filled ethylene propylene diene monomer (EPDM) rubber composites is investigated, at different weight percentages (1.0, 2.0, 4.0, and 8 wt%) of CaO nanocrystalline particles using two methods of mixing. In one case conventional mixing on twin roll-mill was used, in the other case ultrasonic mixing as a pre-mixing was applied. CaO particles are synthesized by the precipitation method. The average crystallite size of CaO is 100 ± 20 nm. Adding CaO nanocrystalline particles increases the thermal stability of EPDM and the glass transition temperature. The hardness of EPDM rubber gradually increases with increasing the amount of CaO particles, the maximum hardness 64.2 observed in 8 wt% of CaO particles for both cases almost 26% higher than neat EPDM. Tensile strength decreases, while the maximum % modulus of the ultrasonic mixed sample was 1.48 MPa which is 24% higher than EPDM.

The Role of Transfer Layer on the Sliding Wear Behavior of a Cu-15Ni-8Sn Alloy Under Different Loads

We studied the microstructure of the transfer layer and its effect on the wear mechanism and wear property of an aged Cu-15Ni-8Sn alloy against GCr15 bearing steel during dry sliding by changing the applied load. The results indicate that the aged Cu-15Ni-8Sn alloy shows different wear behavior and wear properties when the applied load changed, where the average friction coefficient and specific wear rate decrease quickly with increasing applied load in steady wear condition. The sample tested under relatively high applied load shows the best wear performance owing the thickest oxide layer exists in the transfer layer. The main wear mechanisms were found changing with varied applied. The metallic nanocrystalline particles and the relative ductile copper oxides promotes the formation of a thick and densified oxide layer. The change of the thickness and morphology of the oxide layer under different load can significantly affect the wear mechanisms.

Rapid aqueous-phase synthesis of highly stable K0.3Bi0.7F2.4 upconversion nanocrystalline particles at low temperature

Lanthanide-doped K0.3Bi0.7F2.4 nanocrystalline particles are synthesized through an ultrafast (only 1 min) and aqueous-phase chemical method at low temperature (room temperature ∼ 90 °C), which can be used as pigments for anti-counterfeiting.

Waste free Technologies for Production of Nanocrystalline Cellulose and its Composites

In this paper, waste-free technologies are proposed for the production of nanocrystalline cellulose (NCC), its semi-finished products and composites. The following optimal conditions for the cellulose hydrolysis stage were found: concentration of sulfuric acid 40 wt.%, temperature 80oC, duration 1 h, acid to cellulose ratio 7. After hydrolysis stage, the depolymerized cellulose was separated from the acid, washed, diluted with water and disintegrated to release individual nanocrystalline particles. Finally, the diluted dispersion of NCC was evaporated to obtain a commercial product such as concentrated NCC paste. For the production of composites, the acid in unwashed hydrolyzed cellulose was neutralized and precipitated with calcium base (e.g. calcium hydroxide) in order to obtain a white pigment, calcium sulfate (CS). Moreover, the spent sulfuric acid and acidic wastewater were collected and treated with a special auxiliary reagent to reuse and convert the acid into a valuable by-product, selling of which significantly reduces the cost of NCC. The wastewater collected after washing, neutralization and evaporation was purified and returned back to the technological cycle. To reduce the production cost, expensive stages - disintegration and evaporation of diluted dispersion, should be eliminated; as a result, cheap semi-finished products containing aggregates of NCC or its composite with inorganic particles of CS were manufactured along with by-product.

Квантовые точки "ядро--оболочка" Ge/Si в матрице оксида алюминия: влияние температуры отжига на оптические свойства

Structures with Ge/Si nanoparticles (quantum dots) in an alumina matrix are interesting for researchers due to the combination of two main semiconductors, as well as the use of a matrix with high dielectric permittivity and strong oxygen oxygen–metal bonding. Nanoperiodic multilayer structures in the sequence substrate/Al2O3/Ge/Si/Al2O3 . . .Al2O3 (period — Al2O3/Ge/Si, the number of periods was up to 20) annealed at different temperatures were prepared in this work. It was shown that nanocrystalline particles of both Ge and Si were observed in the structures after annealing. Nanocrystal sizes and quantity were determined by the thicknesses of deposited layers and the annealing temperatures. The results obtained by various optical techniques indicate a quantum-size effect in the structures, which is confirmed by high-resolution microscopy.

Sol-Gel Synthesis of TiO2 Nanocrystalline Particles with Enhanced Surface Area through the Reverse Micelle Approach

Titania nanocrystalline particles were synthesized by hydrolysis-condensation of titanium tetraisopropoxide in water-in-oil micellar solutions of water/cyclohexane/Triton X-100 system, and the effects of reflux time and water-to-surfactant molar ratio on the particle uniformity, crystallinity, and surface area were studied. Several characterization techniques including TEM and SEM, as well as X-ray diffraction and FT-IR spectroscopy, helium pycnometry, and nitrogen physisorption, were employed to evaluate the particle density and dimensions, crystallite size, surface area value, and the porosity features in the as-prepared condition and also after thermal treatment at 500°C. The results show that all treated samples are dense nanocrystalline anatase particles with BET surface area values over 100 m2·g−1 and primary particle size of 10–15 nm. However, for the as-prepared samples, as the reflux time increases, a better purification of particles from the synthesis environment is resulted, leading to denser and more crystalline powders with smaller particle size and higher BET surface area values culminating in 179 m2·g−1 for 24 hours of refluxing. Moreover, decreasing the water-to-surfactant molar ratio from 10 to 5 and 2 increases the particles surface area to 239 and 224 m2·g−1, respectively, at the expense of slight density and crystallinity degradation and considerable prolongation of surfactant removal step. Supportively, the comparison between photocatalytic activities of as-prepared samples also evidences the effectiveness of reflux time extension on improving the sample features and enhancing their functionality. This study can highlight how the earlier synthesis steps can influence the evolution of the structure of the final products.