Abstract:The paper deals with the nucleation mechanism of the loss of thermodynamic equilibrium in systems of high energy density, namely, in current-carrying conductors and in cathode micropoints. The limiting value of energy is discussed which may be introduced into a current-carrying conductor prior to its explosion, as well as the characteristic sizes of droplets during subsequent dispersion, times of delay of micropoint explosions, and other effects accompanying such a mechanism of destruction.
The mechanism of decay of the superheated metastable metal produced by a thin foil explosion was investigated experimentally. The decay of the metastable metal was indicated by the occurrence of bubbles detected using soft x-ray backlighting. The experiments were carried out on a research facility comprising three current generators. One of them was used to initiate the explosion of a test foil, and the other two, X-pinch backlighting sources, were used for diagnostics. In the experiments, an upper limit has been determined for the decay time of the metastable state of a superheated metal. For aluminum, at a foil thickness of 6 μm and a deposited energy of 1.49 ± 0.08 eV/atom, the metastable state decay time was about 90 ns; for copper, at the same foil thickness and a deposited energy of 1.46 ± 0.07 eV/atom, it was about 250 ns. Analysis of the experimental results based on the classical nucleation theory has made it possible to estimate the work required for the formation of a critical bubble, the radius of the critical bubble, and the Tolman length, which characterizes the effect of the surface curvature on the surface tension. The work required for the formation of a critical bubble has been estimated to be 16.6 ± 1.5 eV for aluminum and 18.3 ± 1.2 eV for copper. The critical bubble radius and the Tolman length turned out to be several nanometers for both test metals.
A new approach has been presented herein to prepare nano titanium carbide based on the underwater electrical explosion approach. Scanning electron microscopy and x-ray photoelectron spectroscopy were used to investigate the morphology and composition of the electrical explosion products. A numerical model was established to investigate the nanoparticle formation process. The results show that the average diameter of the formed nanoparticles was ∼60 nm and approximately conformed to a lognormal distribution. Compared with the nanoparticles prepared by electrical explosion in gas, the nanoparticles prepared by the underwater electrical explosion had a smaller size distribution range and better sphericity. During the formation process of nanoparticles, the distribution of nanoparticles formed in a narrow temperature range near the specific temperature directly determined the characteristics of the final electrical explosion products. The specific temperature was ∼3400 K, which was also the specific temperature of the saturation ratio, the nucleation rate, the average diameter of the formed nuclei, the number of monomers, and the number of the formed nanoparticles. The diameters of nanoparticles obtained in the experiment were mainly concentrated between 50 and 70 nm, and the calculated diameters of the nanoparticles were mainly concentrated between 55 and 65 nm; therefore, the data obtained through the model were consistent with the experimental ones. These provide a way to synthesize the nano titanium carbide and a method to estimate their size and distribution, and it is hoped for understanding the evolution of the titanium wire underwater electrical explosion and the formation of nanoparticles.
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