LaB6 Powder Research Articles

Features of the Real Structure of Lanthanum HexaboridePolycrystalline

The microstructure of lanthanum hexaboride (LaB6) polycrystalline has beenstudied by using transmission electron microscopy. This shows that theideal LaB6 polycrystalline can be obtained by sintering ingots at thetemperature of 2273 K for a holding time of 120 min in Ar pressure of 800 Torr,where the ingots are formed by pressing LaB6 powder at room temperatureat a pressure of 0.4-0.5 GPa. The particles in LaB6 polycrystallinehardly bind; there are only a few pores at the joint parts of threeparticles and a few impurities exist in some pores. The sintering processfor fabricating LaB6 polycrystalline is analysed and the formation ofthe pore and the impurities are studied from the point of surface tension.

Synchrotron Powder Diffraction using Imaging Plates: Crystal Structure Determination and Rietveld Refinement

The combination of intense X-ray synchrotron radiation and an imaging-plate area detector makes it possible to extract real-time structural information using Rietveld refinement of individual time slices. Powder diffraction data from capillary samples were collected using a flat imaging plate mounted perpendicular to, or at an oblique angle to, the incoming beam. Owing to the geometry of the experiments, several factors must be taken into account when Rietveld refinement of powder diffraction data obtained using a flat imaging plate is performed: (i) nonequal step sizes are obtained when the diffraction profiles are extracted; (ii) the refined zero-point correction is different from that for conventional diffraction geometry; (iii) the sample-detector distance is not constant, requiring a modified geometric term in the Lorentz factor; (iv) the geometric contribution to the instrumental resolution function must be considered. The geometric factors have been derived and are discussed. The Rietveld program XRS-82 and the profile extraction program ALLHKL have been modified to allow flat imaging-plate powder diffraction data to be refined. The Rietveld refinement of powder diffraction data of α-quartz collected using a 30 s exposure is presented. LaB6 powder diffraction data were collected using various settings. The profile variation with angle and the resolution function are described. Data were collected up to sin θ/λ = 1.29 Å−1 (d values down to 0.39 Å) using high energy and with the imaging plate inclined at an angle to the incoming beam.

Measurement of the Refraction Correction for Asymmetric Grazing Incidence Xrd From Rough Surfaces and Powders

The refraction effect at small incidence angles was investigated for solid Al2O3 disks of varying surface roughness, and Al2O3 and LaB6 powder layers of varying thickness and roughness using pseudo parallel beam optics. For the disks the peak shift Δ2θ correlated approximately inversely with ζmax, the maximum slope of a sinusoidal model of the surface roughness. For a disk polished with 3θm diamond, Δ2θ exceeded that predicted by the James equation. For the powder layers Δ2θ was very small for the thinnest layers. For thicker, rougher layers Δ2θ was larger and was probably due to displacement error from the 0.4° divergence of the Soller slit used and specular reflection of the diffracted beam from the Soller slit leaves.

Effect of production conditions on the corrosion resistance of lanthanum hexaboride powders and parts made from them

It has been established that hydrochloric acid treatment is an effective means of ridding an industrial lanthanum hexaboride powder of impurities. It is shown that acid treatment of industrial LaB6 powders substantially improves the corrosion resistance of parts made from them by powder metallurgy techniques. A mechanism of rupture of hot-pressed and sintered lanthanum hexaboride parts is proposed.

Kinetics of the densification of lanthanum hexaboride powder with and without a nickel addition during hot pressing

An investigation was carried out into the kinetics of the densification of LaB6 powder with and without a nickel addition. The effects of temperature, applied pressure, and holding time on the relative densities of the alloyed and unalloyed powders were determined. The results obtained are analyzed within the framework of the theory of volume viscous flow of a porous crystalline solid. It has been established that porous lanthanum hexaboride with and without a nickel alloying addition experiences densification as a result of creep of material controlled by dislocation slip. The energies of activation for creep of these materials and their Laplacian pressures were estimated.