scholarly journals Pyrometallurgy and Electrometallurgy of Rare Earths – Part A: Analysis of Metallothermic Reduction and its Variants

2021 ◽  
Author(s):  
Muhammad Musaddique Ali Rafique
Keyword(s):  
Rare Earth ◽  
High Temperature ◽  
Rare Earths ◽  
Direct Reduction ◽  
Energy Requirement ◽  
Rare Earth Oxide ◽  
Mixed Salt ◽  
Metallothermic Reduction ◽  
Critical Material ◽  
Indirect Electrolysis

Rare earths are classified as most important and critical material for US economy and defense by Congress and a mandate has been set to increase their in-house production, domestic resource utilization and decrease reliance on foreign resources and reserves. They are widely available in earth crust as ore (bastnaesite (La, Ce)FCO3, monazite, (Ce, La, Y, Th)PO4, and xenotime, YPO4), but their so-called economic reserves are sparsely located geographically. They may be produced by various means such as beneficiation (physical, chemical, mechanical, or electrical), reduction (direct or indirect), electrolysis (of aqueous or molten / fused single or mixed salt systems) at high temperature or hydrometallurgy. Out of these, direct reduction also known as metallothermic reduction (La and Ca reduction) is mostly utilized. Its variant, high temperature electrowinning of fused salts is also practiced widely. These processes are material and application specific. In this study, author will employ thermodynamics (Ellingham diagrams, free energy of formation, reduction potential, Nernst equation, Pourbaix (Eh-pH) diagrams, E-pO-2 diagrams), kinetics and energetic of a chemical reaction (chemical metallurgy) to reduce rare earth oxide / salt to rare earth metals (REO/RES – REM). It is shown that materials and energy requirement vary greatly depending on type of mineral ore, production facility, and beneficiation / mineral processing method selected. Aim is to reduce dependence on coal deposits. It is anticipated this route will be able to produce rare earths with > 35% yield and > 98% purity which be described in subsequent studies and patents.

scholarly journals On the resistance of rare earth oxide-doped YSZ to high temperature volcanic ash attack

2016 ◽  
Vol 307 ◽  
pp. 534-541 ◽  
Author(s):  
J. Xia ◽  
L. Yang ◽  
R.T. Wu ◽  
Y.C. Zhou ◽  
L. Zhang ◽  
...  
Keyword(s):  
Rare Earth ◽  
High Temperature ◽  
Volcanic Ash ◽  
Rare Earth Oxide

High temperature stability of Hf-based gate dielectric stacks with rare-earth oxide layers for threshold voltage control

2008 ◽  
Vol 92 (11) ◽  
pp. 112912 ◽  
Author(s):  
James M. LeBeau ◽  
Jesse S. Jur ◽  
Daniel J. Lichtenwalner ◽  
H. Spalding Craft ◽  
Jon-Paul Maria ◽  
...  
Keyword(s):  
Rare Earth ◽  
High Temperature ◽  
Threshold Voltage ◽  
Gate Dielectric ◽  
Temperature Stability ◽  
Voltage Control ◽  
Rare Earth Oxide ◽  
High Temperature Stability ◽  
Oxide Layers

Creep Behavior of Multi-Cation α-SiAlON Partially Stabilized Produced with an Yttrium-Rare Earth Oxide Mixture(CRE2O3)

2005 ◽  
Vol 498-499 ◽  
pp. 575-580
Author(s):  
Claudinei dos Santos ◽  
Kurt Strecker ◽  
M.J.R. Barboza ◽  
Sandro Aparecido Baldacim ◽  
Francisco Piorino Neto ◽  
...  
Keyword(s):  
Solid Solution ◽  
Rare Earth ◽  
High Temperature ◽  
Liquid Phase ◽  
Creep Behavior ◽  
Rare Earth Oxide ◽  
Si3n4 Ceramic ◽  
Creep Tests ◽  
Oxide Mixture ◽  
Metallic Cations

a−SiAlON (a’) is a solid solution of a−Si3N4, where Si and N are substituted by Al and O, respectively. The principal stabilizers of the a’-phase are Mg, Ca, Y and rare earth cations. In this way, the possible use of the yttrium-rare earth oxide mixture, CRE2O3, produced at FAENQUIL, in obtaining these SiAlONs was investigated. Samples were sintered by hotpressing at 17500C, for 30 minutes, using a sintering pressure of 20 MPa. Creep behavior of the hot-pressed CRE-a-SiAlON/b-Si3N4 ceramic was investigated, using compressive creep tests, in air, at 1280 to 1340 0C, under stresses of 200 to 350 MPa, for 70 hours. This type of ceramic exhibited high creep and oxidation resistance. Its improved high-temperature properties are mainly due to the absence or reduced amount of intergranular phases, because of the incorporation of the metallic cations from the liquid phase formed during sintering into the Si3N4 structure, forming a a’/b composite.

scholarly journals High pressure sintered ZrO2-6%wt REO

2007 ◽  
Vol 39 (1) ◽  
pp. 17-24
Author(s):  
C. Kuranaga ◽  
G.S. Bobrovnitchii
Keyword(s):  
Fracture Toughness ◽  
High Pressure ◽  
Rare Earth ◽  
High Temperature ◽  
Room Temperature ◽  
Rare Earth Oxide ◽  
Micro Hardness ◽  
Oxide Mixture ◽  
Sintering Conditions ◽  
High Temperature High Pressure

The sintering conditions employed in this work are innovative, due to the use of an alternative technology to process ZrO2-REO (rare earth oxide mixture), so called high temperature - high pressure (HPHT). A pressure of 5GPa was used, temperatures of 1100, 1200, and 1300 o C, for times of 2 and 5 minutes. The best results were obtained for samples sintered at 5GPa/1300 o C/5min., where a micro-hardness of 4.8GPa, fracture toughness of 5.3MPa.m ?, density of 97.9%, and 88% in volume of a tetragonal phase retained at room temperature were achieved.

Evaluation of the Effect of Heavy Rare Earth Elements on Electrical Resistivity of Zirconia-Yttria Ceramics

2005 ◽  
Vol 498-499 ◽  
pp. 305-310 ◽  
Author(s):  
Dolores Ribeiro Ricci Lazar ◽  
Valter Ussui ◽  
E.N.S. Muccillo ◽  
Ana Helena A. Bressiani ◽  
José Octavio A. Pascoal
Keyword(s):  
Electrical Resistivity ◽  
Rare Earth ◽  
Rare Earths ◽  
Chemical Elements ◽  
Resistivity Measurement ◽  
Density Measurement ◽  
Rare Earth Oxide ◽  
Electrical Resistivity Measurement ◽  
Heavy Rare Earth ◽  
Oxide Systems

The use of yttria concentrates was investigated in this study for synthesis and processing of zirconia based ceramics applied as solid electrolyte materials. Terbium, dysprosium, holmium, erbium and ytterbium are the chemical elements, classified as heavy rare earths, that can be found in those concentrates due to their association with yttrium ores. The ceramic characteristics were compared to zirconia-yttria and zirconia-yttria-heavy rare earth oxide systems, containing 3 and 9 mol% of dopant. Powders were prepared by the coprecipitation route and ceramic processing conditions were established to attain relative densities up to 95%. The characterization of assintered pellets was performed by apparent density measurement by Archimedes method, X-ray diffraction, scanning electron microscopy and electrical resistivity measurement by impedance spectroscopy. It was observed that the presence of heavy rare earths in a concentrate containing 85 wt% of yttria has no significant influence on the total ionic resistivity of zirconia based ceramics.

Effects of Rare Earth Oxides on Microstructures and Properties of Magnesia Refractories

2008 ◽  
Vol 368-372 ◽  
pp. 1158-1160 ◽  
Author(s):  
Bao Guo Zhang ◽  
Zhou Fu Wang ◽  
Shao Wei Zhang ◽  
Xi Tang Wang ◽  
Zi Wei Xu
Keyword(s):  
Mechanical Properties ◽  
Solid Solution ◽  
Rare Earth ◽  
High Temperature ◽  
Mechanical Strength ◽  
Grain Boundaries ◽  
Bulk Density ◽  
Rare Earth Oxide ◽  
Rare Earth Oxides ◽  
Microstructure And Mechanical Properties

The effects of Y2O3, La2O3 and Nd2O3 on the sintering, microstructure and mechanical properties of magnesia refractories were investigated. Addition of rare earth oxide (ReO) to magnesia refractories increases the bulk density, decreases the porosity and improves the mechanical strength of the refractories. The improved sinterability was attributable to the vacancies generation associated with the solid-solution reactions between MgO and ReO. In the samples with ReO, rare earth silicate phases form at magnesia grain boundaries, providing additional bonding between magnesia grains and between magnesia grains and matrix. Consequently, the samples with ReO showed much higher high temperature strengths than those without ReO.

scholarly journals Rare earth oxide coatings to decrease high temperature degradation of chromia forming alloys

2004 ◽  
Vol 7 (1) ◽  
pp. 135-139 ◽  
Author(s):  
Stela Maria de Carvalho Fernandes ◽  
Lalgudi Venkataraman Ramanathan
Keyword(s):  
Rare Earth ◽  
High Temperature ◽  
Rare Earth Oxide ◽  
Oxide Coatings
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