Effect of the La addition content on valence electron structure and properties of ZrB2 ceramics

Abstract

ZrB 2 is a combined bonding compound composed of strong covalent bonds which make it difficult to sinter and densify. Thus, rare earth or other metal elements are usually used to be sintering additives to improve its sintering properties. To forecast properties of ZrB 2 solid solutions with addition of lanthanum, their valence electron structure (VES) was calculated by using the empirical electron theory (EET) of solids and molecules, and the effect of lanthanum with various proportion on the VES and properties of ZrB 2 ceramics has been studied. The results show that with the increase of the lanthanum addition content, the hybridization steps of Zr and B atoms of ZrB 2 solid solutions are still A16 and 5, respectively. The hybridization step of lanthanum is always A1. The covalent electron numbers and bonding energy of the strongest bonds of the ZrB 2 matrix decrease with the lanthanum addition content increase. These suggest that the addition of lanthanum will improve the fracture toughness and decrease the hardness, crystal cohesive energy and melting point of ZrB 2 . In a word, its sintering properties are improved, and its densities are increased.

The Carbon Source Analysis for Diamond Crystal Growth from Fe-C System at High Pressure-High Temperature

“…TFDC considers the electron density being continuous as the boundary criterion of atoms, so the electron density should also be continuous on the contacting surfaces of the atoms from different phases. If the difference of valence electron density (∆ρ) of two adjacent planes is less than 10%, it is assumed that the electron density of interface is continuous at the first order of approximation [8,9]. The lower the ∆ρ of two adjacent planes, the closer the valence electron structure of interface, and the lower the driving force for transforming one structure into another.…”

“…EET suggests that all covalent electrons in an unit cell should be distributed on its all covalent bonds [7], and the number of covalent electrons on one crystal plane should be equal to all covalent electrons of covalent bonds on this plane. So the covalent electron density of a certain crystal plane can be calculated as following [8]…”

“…Based on known crystal structure, the valence electron structure (VES) of solids and molecules can be calculated according to the empirical electron theory of solids and molecules (EET) [7], and the covalent electron density of a certain crystal plane can also be calculated [8]. The Thomas-Fermi-Dirac theory modified by Cheng (TFDC) considers the electron density being continuous as the boundary criterion of atoms [9].…”

“…According to the crystal structure and lattice constant at HPHT, selecting all hybrid levels of atoms in the cell, VESs of diamond, graphite and Fe 3 C are analyzed by the bond length difference (BLD) method on the basis of EET. The calculation method can be found in Ref [8]. According to EET, the state group of every existing atom must satisfy 0.005…”

Influence and Theory Analysis of Ti, Zr, B on the Refining Effect of Aluminum Alloy

“…Lattice constant about Al 3 Ti, Al 3 Zr, TiB 2 , ZrB 2[9][10][11][12] and EET theory, each substance valence electronic structure and bond energy can be calculated. They are shown in table 2 to table 5.…”