Magnetic Properties of Bi-Magnetic Core/Shell Nanoparticles: The Case of Thin Shells

Bi-magnetic core/shell nanoparticles were synthesized by a two-step high-temperature decomposition method of metal acetylacetonate salts. Transmission electron microscopy confirmed the formation of an ultrathin shell (~0.6 nm) of NiO and NiFe2O4 around the magnetically hard 8 nm CoFe2O4 core nanoparticle. Magnetization measurements showed an increase in the coercivity of the single-phase CoFe2O4 seed nanoparticles from ~1.2 T to ~1.5 T and to ~2.0 T for CoFe2O4/NiFe2O4 and CoFe2O4/NiO, respectively. The NiFe2O4 shell also increases the magnetic volume of particles and the dipolar interparticle interactions. In contrast, the NiO shell prevents such interactions and keeps the magnetic volume almost unchanged.

Evolution of the Micropore Structure of Ammonium Perchlorate during Low-Temperature Decomposition and Its Combustion Characteristics

Ammonium perchlorate (AP) is a common oxidant in solid propellants, and its thermal decomposition characteristics at low temperatures (less than 240 °C) are key to the study of the thermal safety of propellants. Here, the low-temperature thermal decomposition characteristics of AP were investigated at 230 °C. The micromorphology of the low-temperature decomposition residues was characterized by scanning electron microscopy and 3D nano-computed tomography in order to analyse the evolution of microscopic pore structures, and the effect of the AP pore structure on combustion performance was then tested and analysed with a homemade closed bomb. The results demonstrate that the low-temperature decomposition of AP first occurs near the surface of the particles, simultaneously starting at multiple points and forming pores, and then gradually expands towards the interior until almost all of the pores connect with one other. Compared with ordinary AP, porous AP has a significantly improved combustion rate. When the ratio of porous AP to Al was 80:20, the peak pressure in the closed bomb was increased by 2.7 times; the rate of change in peak pressure increased 34 times, leading to a higher reaction speed and higher reaction intensity, and a typical explosion reaction occurred.

Corrosion of Stainless Steel by Urea at High Temperature

The corrosion mechanism of stainless steel caused by high temperature decomposition of aqueous urea solution has been investigated. The relationship between aqueous urea solution, its thermal decomposition products and the corrosion mechanism of stainless steel is studied by FTIR spectroscopy, SEM and stereo microscopy. The corroded steel samples, together with deposits, were obtained from the injection of aqueous urea solution on the steel plate at high temperatures. Uniform corrosion underneath the deposits was proposed as the main driver for corrosion of the steel samples. At the crevices, corrosion due to the used geometry and due to high temperature cycling could play an acceleration role as well.

EFFECT OF ZNO NANOPARTICLES ON PROPERTIES OF NANOCOMPOSITE COATING BASED ON ACRYLIC POLYMER EMULSION AND GRAPHENE OXIDE

Effect of ZnO nanoparticles on nanocomposite coatings based on R4152 and graphene oxide (GO) was studied.In presence of 2%wt. ZnO nanoparticle, abrasion resistance of coating increased by nearly 25% (from 75 to 92.9 L/mil) and temperature decomposition raised by 18oC. SEM images showed that nano ZnO can disperse homogenously in polymer matrix in presence of GO. Hence, photocatalytic activity of R4152/GO/ZnO nanocomposite coating was higher than that of R4152/ZnO nanocomposite coating. After 14 hours UV exposure, R4152/GO/ZnO nanocomposite coating can degrade over 80% methylene blue coated on its surface while 60% methylene blue was degraded by R4152/ZnO coatings.

Neutron diffraction study of the kinetics of low-temperature martensite decomposition in medium-carbon steel

It is found that the low-temperature decomposition of martensite in quenched medium-carbon steel occurs in two stages. In the first stage, the rate of decomposition is higher than that in the subsequent stage. Application of the neutron diffraction method allows the identification of two stages of transformation in the first stage of martensite decomposition. It is shown that the first stage is associated predominantly with carbon segregation at dislocations, and the second, with the outdiffusion of carbon from the supersaturated solid solution with the formation of dispersed particles of metastable carbides. It is shown that the change in the concentration of carbon and, accordingly, the degree of tetragonal lattice of martensite at aging and low tempering occurs to a certain limit, independent of the cooling rate during quenching and tempering temperature. This is due to the establishment of a relative equilibrium between a supersaturated solid solution and fine particles of metastable iron carbide. It is found that the determining process, which leads to a change in the microhardness the low-temperature decomposition, is the out diffusion of carbon from the supersaturated solid solution.