Zhang Jiuxing

Fracture toughness of sintered Mo–La2O3 alloy and the toughening mechanism

Abstract The K IC of sintered Mo–La 2 O 3 alloy and pure molybdenum was tested and the micro-structure was investigated by SEM, TEM and AES. The results show that the K IC of Mo–La 2 O 3 alloy reaches 24.76 MPa m 1/2 , which is 2.5 times as much as that of pure Mo. The sintered Mo–La 2 O 3 alloy and pure molybdenum have similar equiaxed grain structure. The AES analysis revealed that the same content of interstitial impurities exist on grain boundaries of Mo–La 2 O 3 alloy and pure molybdenum. A toughening mechanism was proposed to be that large number of dislocations were pinned around La 2 O 3 particles, shortening the efficient slip length and decreasing the dislocation pile-up on grain boundaries of Mo. The improvement of toughness of Mo–La 2 O 3 alloy was attributed to the relief of stress concentration at the grain boundaries of Mo–La 2 O 3 alloy and the weaker tendency to intergranular fracture on grain boundaries.

A study of diffusion behavior of elements lanthanum and oxygen in Mo–La2O3 cathode

Abstract The diffusion behavior of elements lanthanum and oxygen in Mo–La2O3 cathode has been carried out by using Auger Electron Spectroscopy. Lanthanum and oxygen ions (La3+ and O2+) diffuse from the grain boundaries to the surface. The experimental results were analyzed by kinetics of grain boundary diffusion. In the temperature range 1123 K–1423 K, the diffusion coefficients of La3+ and O2+ ions were found to fit with the following expression: D La =3.6703×10 −16 exp (−1.01639×10 5 / RT ) m 2 s −1 D O =1.5122×10 −16 exp (−8.13066×10 4 / RT ) m 2 s −1

A study of chemical behavior of lanthanum in La2O3–Mo thermionic cathode materials

The chemical reaction of La2O3 and Mo2C in La2O3–Mo cathode materials has been studied by thermal analysis, X-ray diffraction, scanning electron microscopy and in-situ X-ray photoelectron spectroscopy (XPS). The thermal analysis and X-ray diffraction results show that molybdenum is one of the reaction products of lanthanum oxide and molybdenum carbide. In-situ XPS results show that chemical state of lanthanum changes during heating. We proved, for the first time, that reacted metallic lanthanum appears at the surface of this kind of cathode material at high temperature.

A study of the effect of chemical state of lanthanum on the emission properties of La2O3–Mo filament

Abstract The ion implanting method has been used for implanting metallic lanthanum into the surface of molybdenum wires to study the effect of chemical state of lanthanum on the emission properties of the filaments. The chemical reaction of La 2 O 3 and Mo 2 C can take place during the operating of the La 2 O 3 –Mo filament, and the metallic lanthanum layer improves emission capabilities of the La 2 O 3 –Mo filament. During filament carbonizing and operating, to control the evaporation rate of lanthanum from the filament surface is very important. On the basis of experimental results, the optimum carbonizing and operating temperatures have been presented. On application of the new technique, the life of this filament has exceeded the minimum life for practical uses.