A novel, integrated, fast, and inexpensive process for the preparation of dense Ba(1−x)EuxAl2Si2O8 thin ceramic specimens for damage sensor applications is reported. The processing approach involves a combination of combustion synthesis for the preparation of the powders and spark plasma sintering (SPS) for the consolidation of the specimens to densities close to 100% of relative density. The synthesis of the porous powders by combustion resulted in particle (agglomerate) sizes that were on average 421 nm, as determined from dynamic light scattering, and in the almost complete reduction of the initial Eu3+ activators to Eu2+. The powders densified to grain sizes of around 250 nm due to a collapse of the porous powder structure and minimal grain growth during SPS. Thermal treatment of the powders and sintered specimens improved the intensity of the emissions at 373 and 745 nm and diminished the emission at 485 nm. The luminescence phenomena from the specimens were a result of two mechanisms: (1) the removal of strain in the lattice due to thermal treatment, and (2) a charge transfer mechanism between Eu2+ and Eu3+.

The friction and wear characteristics of thin diamond-like carbon (DLC) coatings have been investigated extensively in recent years mostly in laboratory bench tests. These coatings are known to provide significant friction reduction in the absence of lubricants. In the presence of lubricants, the friction benefits of these coatings are not clearly demonstrated. The current investigation is focused on exploring the friction reduction potential of a DLC coating obtained from a supplier in laboratory bench tests and in a motored valve train test. The DLC coating was deposited on the bucket tappet. In laboratory bench tests, results showed significant friction reduction in the absence of any lubricant but not in the presence of engine oil. In motored valve train tests a significant reduction in friction torque was observed when compared against a slightly rougher uncoated bucket, but no reduction was observed when compared against uncoated bucket tappet with comparable surface finish. Under boundary lubrication conditions, no lubricantderived surface films were present on the DLC-coated surface. However, under mixed lubrication conditions, evidence of patchy antiwear surface films could be observed on DLCcoated buckets. The antiwear film appears to be primarily composed of calcium phosphate.

Articles you may be interested inEnhancement of thermal conductivity of silver nanofluid synthesized by a one-step method with the effect of polyvinylpyrrolidone on thermal behavior Appl. Phys. Lett. 102, 231907 (2013); 10.1063/1.4809998 Effect of particle size on the thermoluminescence properties of Ba 0.97 Ca 0.03 SO 4 : Cu AIP Conf. Proc. 1512, 446 (2013); 10.1063/1.4791103 Unusual metallic behavior in nanostructured cobalt ferrite at superparamagnetic regime J. Appl. Phys. 112, 063926 (2012); 10.1063/1.4754855Thermal conductivity of polyethylene glycol nanofluids containing carbon coated metal nanoparticles Nanofluids consist of nanoparticles dispersed in heat transfer carrier fluid and are typically used for enhancing thermal conductivity in devices and systems. This study investigated the synthesis of iron and copper nanoparticle-based thermal fluids prepared using a two-step process. Chemical precipitation was used for the synthesis of the powders, and ultrasonic irradiation was used to disperse the nanoparticles in the carrier fluid ͑ethylene glycol͒. The size distributions of the nanopowders in the carrier fluid were determined using dynamic light scattering resulting in average particle sizes of around 500 nm. The crystallite sizes of the powders were below 20 nm. Thus, both types of nanofluids are comparable with regard to crystallite size, particle size, and morphology resulting in a direct comparison of material properties and their effect on thermal conductivity of the nanofluids. A guarded hot parallel-plate method and dynamic tests were used to compare the thermal conductivities of the nanofluids. It was shown that thermal conductivity can be enhanced by up to 70% for copper nanofluids. It was also demonstrated that for a given particle concentration, copper nanofluids are superior in thermal conductivity compared to iron nanofluids.