Spark Plasma Parameters for Titanium Diboride and Titanium Electrodes. Numerical Simulation and Experiment

Abstract

Numerical simulation was used to compare the effect of pure titanium and TiB₂ on the spark plasma parameters in air and the intensity of spectral lines at various erosion rates, power densities at the discharge axis, and excitation potentials of singly charged Ti II ions. The model incorporates the equation of mass transfer at the discharge axis and quasiequilibrium conditions for calculating plasma composition on assumption of local thermodynamic equilibrium (LTE). Temperature at the discharge axis was calculated using the energy balance equation taking into account the energy acquired by electrons in an external field and energy losses in inelastic collisions (ionization and excitation of atoms and ions, dissociation of molecules). The system of nonlinear equations was solved in the cycle to obtain self-consistent values of temperature and particle concentration. Temperature was 500–1000 K higher with TiB₂ electrodes than that with Ti electrodes in all ranges of powers and erosion rates. 3D plots of temperature, electron concentration, particle densities, and line intensities were built as functions of discharge power density and erosion rates of electrodes. The temperature, electron concentration, intensity of spectral lines of atoms and singly and doubly charged ions of pure titanium and titanium in its boride were nonlinear functions of the discharge power and the erosion rate of electrodes.  The nature of changes in the concentration of particles differs significantly from changes in the intensity of lines emitted by these particles. The calculated parameters agree with the experiment within the measurement error and certain simplifications adopted in the model. The results obtained can be used both for analyzing the composition of new materials and for spectral diagnostics of electrode erosion.