Meiling Zhou

Effects of double filling of La and Ce on thermoelectric properties of CemLanFe1.0Co3.0Sb12 compounds by spark plasma sintering

Double-filled skutterudite compounds CemLanFeCo3Sb12 with (m+n)=0.2–0.4 were synthesized by spark plasma sintering using powders of Co, Sb, Fe, and rare-earth Ce and La as starting materials, and the thermoelectric properties were studied in detail. The dominant phases of all the samples are the skutterudite with small amount of Sb as an impurity phase, and the amount of Sb decreases in double-filled compound. The lattice constant is enhanced linearly up to (m+n)=0.30 with increasing filling fraction and then unchanged. The Seebeck coefficient and thermal conductivity of double-filled compounds are generally higher than single-filled samples whatever the filling fraction is. Among all the samples, Ce0.1La0.2FeCo3Sb12 shows the highest Seebeck coefficient of 150μVK−1 at 773K and the lowest thermal conductivity of 1.81W∕mK at 673K, and the maximum ZT value reaches 0.60 at 773K due to its lower thermal conductivity.

A Study of Scandia Doped Tungsten Nano-Powders

Abstract Scandia and rhenium doped tungsten powders were prepared by solid-liquid doping combined with two-step reduction method. The particle size of doped tungsten and distribution of scandia and rhenium were studied by SEM, EDS, XRD and granularity analysis. Experimental results showed that scandia distributed evenly on the surface of tungsten particles. Addition of scandia and rhenium decreased the particle size of doped tungsten, and the more the content of scandia and rhenium, the smaller the doped tungsten particles. Tungsten powders doped with 3% Sc2O3 and 3% Re (mass fraction) had an average size of about 80 nm in diameter. The mechanism of the decrease in the tungsten particle size was discussed.

Secondary emission property of CeO2-Y2O3-Mo cathode

Secondary emission has been used in many fields stimulated by the development of vacuum electronic technology, especially in the field of high power magnetron. The development of high power magnetron needs cathodes which could provide high secondary emission yield (Vasilyva, 1996). As a novel cathode which is expected to be applied in magnetron, CeO2-Y2O3-Mo cermet cathode has be prepared by liquid-liquid doping combined with a fast sintering, spark plasma sintering technique.

Preparation of the REO-Mo secondary emitter with sub-micro structure by SPS method

Millimeter wave magnetron has exhibited promising prospect in its application. Due to intensive electron back-bombardment in millimeter wave magnetron, Ba-W dispenser cathodes may not be ideal long-acting electron source in such devices. The traditional Th-W cathode encounters fatal shortcoming of radioactivity. REO-Mo metal-ceramic cathode is one of the hopeful cathodes for millimeter wave magnetron because of their shortage of natural radioactivity background and lower cost than recently developed Ir-La alloy cathode. Investigations from Wang showed the low susceptivity of REO-Mo metal ceramic cathodes to electron bombardment and the dependence of secondary emission property on the distribution of different ingredient and microstructure of materials. Therefore, in this work, attempts are made to prepare the REO-Mo metal ceramic cathodes with fine sub-micro structure on the basis of precursor rare oxide doped molybdenum powder synthesized by a sol-gel and two-step method.

Recent progress of rare earth oxide doped Molybdenum secondary electron emission cathodes

In this paper, the effect of different preparation process on the secondary electron emission performance was investigated. The different doping methods and preparation techniques such as Solid-Solid doping(SS), Liquid-Solid (LS) doping, Liquid-Liquid (LL) doping, Spark Plasma Sintering (SPS), Air Plasma Spray (APS) method, were introduced into this kind of materials. The microstructure of samples was observed with Hitachi S-3500N Scanning Electron Microscopy, equipped with Oxford Inca EDX equipment. The self-designed apparatus was used to evaluate secondary electron emission yields (δ) of samples in the ultra-high vacuum chamber. The secondary emission properties were measured at 600°C in order to avoid the influence of the thermionic emission.

Scandia doped tungsten matrix for impregnated cathode

Abstract As a matrix for Sc-type impregnated cathode, scandia doped tungsten with a uniform distribution of Sc2O3 was obtained by powder metallurgy combined with the liquid-solid doping method. The microstructure and composition of the powder and the anti-ion bombardment behavior of scandium in the matrix were studied by means of SEM, EDS, XRD, and in-situ AES methods. Tungsten powder covered with scandium oxide, an ideal scandium oxide-doped tungsten powder for the preparation of Sc-type impregnated cathode, was obtained using the liquid-solid doping method. Compared with the matrix prepared with the mechanically mixed powder of tungsten and scandium oxide, Sc2O3-W matrix prepared with this kind of powder had smaller grain size and uniform distribution of scandium. Sc on the surface of Sc2O3 doped tungsten matrix had good high temperature stability and good anti-ion bombardment capability.

Emission property of RE2O3 doped Mo cathode materials

Single La₂O₃, Ce₂O₃ doped Mo with low content of RE₂O₃ has good thermionic emission property. The zero-field emission current densities at 1450 degC of 6.87A/cm and 5.03 A/cm2 could be obtained for La₂O₃(4wt%)-Mo and Ce203(4wt%)-Mo, respectively.La₂O₃-Mo, Ce₂O₃-Mo cermet cathode containing high content of RE₂O₃ shows a certain secondary emission property. A layer of RE₂O₃ could be formed at surface of the cathode and plays an important role in the emission.

Secondary Electron Emission from REO-Mo Metal Cermet Cathode

The secondary electron emission of REO-Mo metal cermet cathodes have been investigated in this paper. The enhancement of secondary emission yields is related to the annealing technology, which leads to the improvement of the supplement of electron

The thermoelectric properties of (Ce,La)/sub y/Fe/sub 1.0/Co/sub 3.0/Sb/sub 12/ compounds by solid state reaction and spark plasma sintering

Filled skutterudite compounds (Ce,La)/sub y/FeCo/sub 3/Sb/sub 12/ with y=0.1/spl sim/0.3 were synthesized by solid state reaction-spark plasma sintering (SPS) using powders of Co, Sb, Fe and rare earth Ce as starting materials, and the thermoelectric properties of the compounds were also studied. It is shown that there is a little Sb in filled skutterudite compounds (Ce,La)/sub y/FeCo/sub 3/Sb/sub 12/ with y=0.1/spl sim/0.3 at 900 K. The lattice constant and the Seebeck coefficient of the compounds increases with the filling fraction of the Ce and La, while the thermal conductivity and electrical conductivity is greatly reduced The compounds had a minimum value of thermal conductivity with y=0.3, indicating that it is the coupling rattling and the irregular distribution between the two filler ions of La and Ce that give rise to the mass change of atom and the additional phonon scattering produced by lattice aberration when the Sb voids in the skutterudite structure were filled by Ce and La. The compound of Ce/sub 0.1/La/sub 0.2/Fe/sub 1.0/Co/sub 3.0/Sb/sub 12/ with Co-rich had a maximum value of the dimensionless figure of merit ZT=0.46 at 773 K.

Thermionic property of RE/sub 2/O/sub 3/ doped molybdenum and pattern recognition application on this kind of material

La/sub 2/O/sub 3/-Mo as one of the attractive alternatives for ThO/sub 2/2-W thermionic cathode has exhibited better performance. However, La/sub 2/O/sub 3/-Mo cathode can not provide stable emission current . In order to improve its emission stability, a better understanding on its emission mechanism is still required. The key to the emission model is the chemical state of rare earth lanthanum on the surface of carbonized La/sub 2/O/sub 3/3-Mo surface. The chemical state of lanthanum on the surface of La/sub 2/O/sub 3/3-Mo cathode and its role in the emission stability improvement was studied in this paper. In addition, in order to get the thermionic cathode possessing high emission property, either single rare earth oxide of La/sub 2/O/sub 3/3,Y/sub 2/O/sub 3/, and Sc/sub 2/O/sub 3/ or a mixture of these rare earth oxides doped molybdenum cathodes have been produced by powder metallurgy method. Furthermore, computer pattern recognition technique has been used to optimize the composition of the material and cathode preparation technique.