Refractory Nanoparticles Research Articles

Nonstationary convective mixing in a drop of melt bypassed by plasma flow

A simple phenomenological model is proposed that takes into account nonstationary convective mixing transfer of a gas or refractory solid nanoparticles from a near-surface layer of a melt drop into the volume, which is driven by a shear flow arising when a plasma flow bypasses the drop. It is shown that this phenomenon can lead to significant intensification of the mass transfer in comparison to the process of diffusion.

Modification of cast aluminum-matrix composite materials by refractory nanoparticles

The effect of SiO2 and Al2O3 oxide ceramic nanoparticles on the solidification of model samples based on a commercial D16 alloy is studied. The composite samples are fabricated by reaction casting when titanium, nickel, and ceramic powders are mixed with an aluminum melt. The grain size in a matrix, the size and shape of Al3Ti intermetallic inclusions, and the interphase distances in eutectics are determined with optical and scanning electron microscopes. A certain modifying effect of oxide ceramic nanoparticles on the structure of model CMs during their in situ formation is detected, and the inoculation effect of SiO2 added to a melt on the reaction products is most pronounced.

Coatings for thermo-reinforcement of heatproofing materials and quasiplastic ceramics

Thermo-reinforcing coatings based on ceramic-forming polymers and oxygen-free modifying refractory nanoparticles are investigated. It is established that thermo-reinforcing coatings increase the working temperatures of fibrous heat-insulating materials by 300–500°C and increase the thermal and mechanical properties by a factor two or three. A new multifunctional glass-ceramic composite thermo-reinforced material which can be used in heat-insulating, heat-proofing, and sound-absorbing structures in aerospace and power engineering has been developed.

Determining aerosol particle size distributions using time-resolved laser-induced incandescence

The particle size distribution within an aerosol containing refractory nanoparticles can be inferred using time-resolved laser-induced incandescence (TR-LII). In this procedure, a small volume of aerosol is heated to incandescent temperatures by a short laser pulse, and the incandescence of the aerosol particles is then measured as they return to the ambient gas temperature by conduction heat transfer. Although the cooling rate of an individual particle depends on its volume-to-area ratio, recovering the particle size distribution from the observed temporal decay of the LII signal is complicated by the fact that the LII signal is due to the incandescence of all particle size classes within the sample volume, and because of this, the particle size distribution is related to the time-resolved LII signal through a mathematically ill-posed equation. This paper reviews techniques proposed in the literature for recovering particle size distributions from TR-LII data. The characteristics of this problem are then discussed in detail, with a focus on the effect of ill-posedness on the stability and uniqueness of the recovered particle size distributions. Finally, the performance of each method is evaluated and compared based on the results of a perturbation analysis.

Volume Crystallization of a Nickel Droplet Containing Refractory Nanoparticles upon Its Impact onto a Substrate

A mathematical model is developed for nonequilibrium volume crystallization of a metallic droplet modified by mechanically activated refractory nanoparticles upon its impact onto a solid substrate. The model takes into account the kinetics of heterogeneous and homogeneous nucleation during melt cooling. Specific features of crystallization of a liquid metal (nickel) depending on the concentration and size of modifying particles are examined numerically. A typical feature of the process considered is the maximum supercooling of the melt, whose magnitude depends on the particle size and cooling intensity. Homogeneous nucleation is almost absent. The calculated radii of droplets solidified on the substrate are in good agreement with available experimental data.