Valentina Zin

The Synthesis and Effect of Copper Nanoparticles on the Tribological Properties of Lubricant Oils

Cu nanoparticles (NPs) are widely studied to understand how they work in lubricant oils to improve its tribological properties. This paper describes the synthesis and characterization of Cu NPs of different size (φ = 60 and 130 nm) carried out in EG and the dispersion procedure used to prepare nanolubricants containing different amounts of NPs (0.005 vol% -0.01 vol% -0.02 vol%). The base oil was a commercially available lubricant oil for internal combustion engines. In order to study the influence of different parameters such as particles size and concentration on tribological properties of nanolubricants, the Stribeck curves were recorded at 25°C in the three lubrication regions (elasto-hydrodynamic, mixed lubrication, and boundary lubrication) and the results discussed. It was found that Cu NPs with a 130-nm mean diameter were more effective in reducing the coefficient of friction in all the lubrication regimes with respect to smaller ones.

Thermal Shock and Oxidation Behavior of HiPIMS TiAlN Coatings Grown on Ti-48Al-2Cr-2Nb Intermetallic Alloy

A High Power Impulse Magnetron Sputtering (HiPIMS) method for depositing TiAlN environmental barrier coatings on the surface of Ti-48Al-2Cr-2Nb alloy was developed in view of their exploitation in turbine engines. Three differently engineered TiAlN films were processed and their performance compared. Bare intermetallic alloy coupons and coated specimens were submitted to thermal cycling under oxidizing atmosphere up to 850 °C or 950 °C, at high heating and cooling rates. For this purpose, a burner rig able to simulate the operating conditions of the different stages of turbine engines was used. Microstructures of the samples were compared before and after each test using several techniques (microscopy, XRD, and XPS). Coating-intermetallic substrate adhesion and tribological properties were investigated too. All the TiAlN films provided a remarkable increase in oxidation resistance. Good adhesion properties were observed even after repeated thermal shocks. HiPIMS pretreatments of the substrate surfaces performed before the coating deposition significantly affected the oxidation rate, the oxide layer composition and the coating/substrate adhesion.

Nanofluids characterization and application as nanolubricants in heat pump systems

In the last years, various applications have been proposed for nanofluids in the HVAC&R field; their use as primary and secondary fluids, also as lubricants, has been kept into account to improve systems performance. The present work was developed to test the applicability of nanofluids as lubricants in the compressors of heat pump systems, with the purpose to experimentally detect the possible positive effects of nanolubricants. Several nanolubricants, formed by polyolester or mineral oil as a base fluid, and titanium oxide (TiO2) or single-wall carbon nano-horns as nanoparticles, were studied in a dedicated test rig. In contrast with some published data, no improvement was detected with 0.05 to 0.5 wt% of TiO2 or 0.1 wt% of single-wall carbon nano-horns in tested commercial oils. All results will be discussed in depth in the article.

Effect of alumina coatings on corrosion protection of steels in molten lead

Lead alloys are attractive candidates as coolants for future generation nuclear reactors (fast reactors). Unfortunately, they easily corrode structural steels of reactors. To mitigate this phenomenon, surface protective coatings may be applied. In this study, T91 steel (Cr9Mo1) samples were coated with aluminum oxide coatings (Al-O) deposited by radio frequency magnetron sputtering. The alumina coatings were characterized using scanning electron microscopy–energy dispersive spectroscopy, x-ray diffraction, and tribological techniques. A corrosion test of coated steel samples was performed in stagnant lead at 550 °C for 1200 h and none of the samples revealed corrosion signs.