J.C. Han

Oxidation and ablation of 3D carbon-carbon composite at up to 3000 °C

Abstract The reactivity of fine-weave pierced 3D carbon-carbon composites in air at temperatures up to 3000 °C was studied. The corrosion morphology and microstructure of oxidized samples were investigated by XPS, SEM, and XRD techniques, and the non-equilibrium nature of the oxidation process was pointed out. A thermochemical ablation model of Cue5f8C composites controlled by gas phase diffusion and reaction kinetics was developed.

Increasing sp3 hybridized carbon atoms in germanium carbide films by increasing the argon ion energy and germanium content

We have prepared germanium carbide (Ge1−xCx) films on Si(0 0 1) by radio frequency (RF) reactive sputtering a pure Ge(1 1 1) target in a CH4/Ar mixture discharge, and found that the sp3 hybridized carbon atoms in the Ge1−xCx film can be significantly increased in two ways. One is by increasing the Ge content via increasing the RF power during the film deposition, which can lead to a transition from sp2 C–C to sp3 C–Ge bonding in the film. Another is by increasing the Ar ion energy in a discharge Ar/CH4 gas by applying the negative bias voltage, which plays an important role in inducing the compressive stress in film. We find that when the compressive stress increases above a critical value of 2.2 GPa, an abrupt transition from sp2 C–C to sp3 C–C bonding occurs in the Ge1−xCx film, which is a consequence of energy minimization.

ELECTROSTATIC IMAGE METHOD FOR DIPOLE MOMENT OF A CHAIN OF TWO UNEQUAL CONDUCTING SPHERES

Abstract When a chain of two unequal conducting spheres is immersed in a uniform electric field, the distribution of the induced charge on the spheres is influenced strongly by the electrostatic interaction between the spheres. This influence relies on their radii and the orientation of the applied field. Here, we employ the electrostatic image method to calculate the induced charge and the dipole moment of the chain, and require that the net charge of the chain be zero. It is shown that the moment of a smaller sphere adhering on a larger one can be ignored for some field orientations, while for others it becomes large. In certain cases, the larger sphere behaves like an isolated body.

Fractal model of the dipole moments of conducting particle chains

Abstract A self-similar fractal model is developed for calculating the dipole moments of linear chains of equally spaced conducting spheres immersed in uniform electric field. We assume that chains may be treated as larger equivalent spheres with same dipole moment and that two such imaginary spheres behave like two real ones. The effective radii of the equivalent spheres are determined from a fractal generating process. In this process, only the knowledge of particle pair is required. The fractal dimension is determined, which is only a function of the spacing of the spheres. The longitudinal and transverse dipole moments are expressed as simple functions of the fractal dimension and the number of the spheres in a chain. The results for touching spheres are in excellent agreement with the known numerical calculations of the image method. Comparison is made with the nearest-neighbor approximation, which is extended to the transverse case here. The fractal model is acceptable.

Fractal characterization of the dipole moments of dielectric particle chains

Abstract A simple self-similar fractal model is presented for obtaining the dipole moments of dielectric particle chains subjected to uniform electric field. The chains are replaced by equivalent spheres, and the effective radii of these spheres are determined from a fractal generating process. The dipole moments are determined in terms of the effective radii and are expressed as simple functions of the fractal dimension and the number of the particles in chain. The computed results for the longitudinal dipole moments are consistent with the previous calculations of the linear multipole expansion. The many-sphere nature of the moments of chains is well understood.