Anna V. Gubarevich

Onion-like carbon deposition by plasma spraying of nanodiamonds

Abstract A deposit of carbon nanoparticles based on an onion-like structure was fabricated from detonation nanodiamond powders by a novel plasma spraying process, electromagnetically accelerated plasma spraying (EMAPS). EMAPS was able to transform nanodiamonds to onion-like structured carbon within 300 μs through a thermal graphitization process in which the temperature of the particles would be in the range of 2700–4500 K. Synthesized onion-like carbon nanoparticles were spherical or polyhedral. The G-band in the UV–Raman spectra of the produced deposits was found to be a superposition of a characteristic band of well-formed carbon onions at 1571 cm −1 and the G-band of defective carbon onions at 1592 cm −1 . The availability of a plasma spraying process for developing solid lubricant coatings incorporating nanodiamond and onion-like carbon was demonstrated.

Diamond Powders Less Than 100 nm in Diameter as Effective Solid Lubricants in Vacuum

The frictional behavior of detonation nanodiamond and single-crystal fine diamond powders were studied to determine the effect of particle diameter on their lubricative and abrasive characteristics. In vacuum, nanodiamond with an average aggregate size of 75 nm and mechanically crushed single-crystal diamond powders with an average diameter of 50 nm formed a uniform lubricating layer while sliding against a SiC ball and showed very low friction coefficients of 0.03 and less than 0.01, respectively, under moderate conditions of 0.5 N applied load and 3.5 mm/s sliding speed. A clear tendency was observed for both the friction coefficient and specific wear rates to decrease with decreasing particle/aggregate size.

Process stages during solution combustion synthesis of strontium aluminates

Solution combustion synthesis (SCS) which includes the redox reaction between nitrates and organic fuels in solution is one of suitable methods for synthesis of oxide nanoparticles. In the present work, we investigated the SCS process in the Sr-Al-O system and found that it proceeds in the following stages. Stage 1 takes place just after evaporation of H2O but before start-up of combustion; stage 2: combustion reaction; stage 3: rapid cooling down to some temperature below that of furnace facilitated by vigorous evolution of gaseous products; and stage 4: warm-up to the furnace temperature. It has been found that Al(NO3)3 · 9H2O and CO(NH2)2 react at stage 1, while Sr(NO3)2 (whose decomposition temperature is about 925 K) react with Al(NO3)3 · 9H2O and CO(NH2)2 at stage 2 to give the nuclei of SrAl2O4. Upon completion of combustion, rapid cooling down caused by vigorous evolution of gases occurs at stage 3. The particles of newly formed SrAl2O4 did not grow significantly (20–50 nm) because of high temperature gradients. The particle sizes did not change meaningfully at stages 3 and 4, due to which the SCS process yielded fine SrAl2O4 nanoparticles (∼50 nm).

NiO-Al combustion synthesis as applied to joining Al2O3 ceramics

A method for joining Al2O3 ceramics has been investigated by utilizing NiO-Al volume combustion under various pre-heating gradients in air; the ignition temperature of the system has been made clear by changing starting composition, particle size of Al, and packing density of reaction powder compacts to optimize the conditions for ceramics joining. Combustion synthesized joining layers were mainly composed of NiAl2O4, Ni, and NiO. In order to prevent Al2O3 plates cracking during the combustion process, Al2O3 paste containing Al2O3 and water glass were deposited onto the Al2O3 surface, which formed intermediate layer joining the reactant layer and Al2O3 ceramics and decreased the temperature gradient between the two layers.

Volume combustion synthesis of NiAl as applied to ceramics joining

Volume combustion synthesis of NiAl has been applied to joining oxide ceramics. Combustion synthesized joint was found to contain largely the NiAl phase strongly attached to oxide ceramics via the Alrich zones formed at the boundary between combustion synthesized and intermediate layers.

Preparation and Optical Properties of Rare Earth Doped Y2O3 Nanoparticles Synthesized by Thermal Decomposition with Oleic Acid

The synthesis by thermal decomposition of rare earth doped yttrium oxide nanoparticles was investigated. The elements of the rare earth were europium, which showed strong fluorescence, and erbium, which indicated upconversion properties. Metal-oleate complex was used as a precursor. The results of Scherrer’s equation and SEM indicated that nanoparticles were successfully synthesized. Appropriate thermal decomposition time increased fluorescence intensity of europium activators by completion of thermal decomposition of oleic acid, while too long thermal decomposition time decreased the fluorescent intensity. Fluorescence of erbium activator was observed after annealing, while it was not observed before annealing because of stronger fluorescence of oleylamine.

Pneumatic Joint Design for Enhancing Spacesuit Flexibility

AbstractThe flexibility of spacesuits made of soft material is limited by high-pressure differences across the garment, which can induce strong tensile stress and stiffen soft materials. This paper describes a new single-axis pneumatic joint design for the enhancement of spacesuit flexibility. The joint is based on the implementation of an isotensoid shape that can theoretically carry interior pressure without circumferential stress. By introducing excess skin material into the isotensoid along a circumferential direction, local slack regions are generated, which enable expansion and contraction, resulting in a flexion motion with low resistance torque. Joint prototypes were fabricated from silicone rubber–coated Vectran woven fabric (Kuraray, Tokyo, Japan) and were subjected to flexion tests using a custom-made robotic arm. The torque measurement results showed that the increase in torque was low until the flexion angle reached 80° and rose rapidly at higher angles. It was concluded that the presence of ...