Papers by Keyword: Rare Earth Metals

Abstract: The paper provides a flow sheet of the phosphorus slag processing to produce precipitated silica (white soot). The process conditions for opening phosphorus slag at the I stage of leaching have been selected: the nitric acid concentration is 3.5 mol/dm³; the ratio S:L = 1:3.5; the temperature is 60 oС; and the process duration is 1 hour. The parameters of the white soot production II stage have been determined: the HNO₃ concentration is 6.5 mol/dm³; the ratio S:L = 1:3.5; the temperature is 50 oС; and the process duration is 1 hour. The temperature effect on the white soot structure and the specific surface have been established. At optimal process parameters, the white soot batches have been obtained with the main SiO₂ component content of 88.2 and 90.5 %, and a specific surface of 170 and 182 m²/g, respectively. The through recovery of silicon into a commercial product is 98.0 % of its initial content in slag.

Abstract: In connection with the search for new materials and the more extensive use of metals and alloys with special physical and chemical properties, rare-earth metals (REMs) are attracting increasing interest not only as alloying additives but also as the main components of structural materials. The Al-Fe alloys are of great practical interest, and the purpose of this work was to study the influence of microalloying by REMs on the mechanical and acoustic damping properties of Al-Fe alloys. REMs were selected as alloying components because of their properties and their widespread use in improving the structure and properties of structural alloys, including mechanical and acoustic damping properties. The results of these investigations are expected to enable the use of secondary Al (i.e., waste Al manufacture with a high Fe impurity concentration) as a base material for the development of structural alloys with improved mechanical properties for use in mechanical and electrical engineering applications. The use of secondary Al will provide economic advantages and will contribute to the conservation of resources.This work is actual because Al alloyed with Fe and REMs can be used as corrosion-resistant materials and conductive materials in electronics and for automotive and aircraft engines, wires, cables, rods, tires and other products of the electrical engineering industry, thus expanding the scope of applications of these alloys [1-4].

Abstract: A general trend in steelmaking industry is to increase strength, resistance to brittle fracture and fatigue properties of steel products at favorable price. Achieving fine-grained microstructure during austenite to ferrite transformation is a basic prerequisite to improve the mechanical properties. The desired transformation can be achieved in several ways one of which is the use of small non-metallic inclusions as heterogenous nucleation sites during solidification of steel. A great attention is focused on this concept in recent years. Rare earth metals are suitable for the formation of small inclusions similarly as in the case of conventional microalloying elements such as niobium, titanium, vanadium and other. Rare earth metals have a high affinity to oxygen and sulfur. The paper deals with the optimization of microstructure of 42CrMo4 low alloy structural steel used for machine parts exposed to higher stresses. The steel was alloyed with cerium in the form of mischmetal to achive fine-grained microstructure. Operational experiment was proposed and realized in accordance with results of laboratory experiment.

Abstract: The influence of rare-earth metals adsorbed in the surface of the metallic material subject to thermochemical processing as well as of those pre-added in the material matrix on the kinetics of layers growth is presented in the technical literature. It is generally concluded that the presence of rare earths is accelerating the kinetics of layer growth.

Abstract: The unique properties of rare earth elements (REE) have resulted in their being crucial to a growing number of emerging technologies. As the demand for REE currently exceeds annual production, the present worldwide crisis for REE will probably continue for the foreseeable future. Hence, it is highly likely that the availability of REE used in the metallurgy of cast iron will be significantly reduced and alternatives to REE usage may have to be developed. Graphite nodules nucleate heterogeneously on particles formed in the melt, having a duplex structure (sulphide as a core and oxide/silicate as a shell). Mg, Ca and REE appear to act in the nucleation first stage, while Si, Al, Mg, REE, Ca, Sr and Ba act predominately in the second stage. Generally, REE are employed in ductile irons to accomplish the following tasks: (a) neutralize tramp elements such as Ti, Pb, Bi, As etc; (b) assist in nodulizing or provide a supplementary effect to Mg to promote spheroidal graphite shapes; (c) assist in nucleating graphite. When anti-nodularising Thielman control factors (K) are less than 0.8, REE are usually not required since there are no trace elements to neutralize. REE are useful for K factors between 0.80 to 1.20 and are mandatory for K factors greater than 1.20. Theilman factors greater than 2.0 will always require REE. When Theilman factors are less than 0.80, REE _res levels of 0.01% are usually more than sufficient for ductile iron production. Three ductile iron inoculation alloys were selected for this research: (a) a conventional Ca bearing 75% FeSi inoculant (Ca-FeSi), used at a high consumption level; (b) an improved conventional Ca-FeSi alloy that incorporated active inoculating elements, such as Ba or REE, used at a medium consumption level, and (c) a combination of a commercial inoculant, such as Ca-FeSi alloy, used with a separate oxy-sulphide inoculant enhancer alloy addition. The last inoculation variant provided the best structural parameters and the lowest consumption level.

Abstract: The thermochemical processes of synthesis and purification of rare earth metals fluorides through the transfer of fluoroammonium complexes were discussed. By differential thermal calorimetry the temperature maxima of rates of formation and decomposition of complex compounds were defined and the values of the apparent activation energy processes were determined. It is possible the use of fluoroammonium systems to develop the preparation of anhydrous fluorides of rare earth metals.

Abstract: Magnetization and magnetoresistance (MR) studies were carried out on the [Gd/T_n multilayers with different thickness of Gd and Ti layers prepared by magnetron sputtering. The temperature interval of measurements was from 2 to 300 K, for the highest available magnetic field value of 100 kOe. A negative magnetoresistance was observed in all samples. The observed negative MR was analysed by using different magnetoresistance models.

Abstract: The chip formation process of four different titanium alloys has been studied in several cutting experiments. Alloys containing more than 50% of a-phase at room temperature and aged metastable b-alloys form segmented chips independent of the cutting conditions. Solution treated metastable b-alloys show a cutting parameter dependent change from continuous to segmented chip formation. Lanthanum has been added to all four alloys. The microstructure of these alloys consists of a titanium matrix and micrometer-size particles. The presence of grain boundary particles leads to enhanced grain stability at elevated temperatures. In addition, short chips are observed during metal cutting only in case pure metallic rare-earth metal particles are present.

Abstract: Magnetic, magnetoresistive and structural properties of Tb/Ti and Tb/Si nanoscale multilayers prepared by alternative deposition of Tb layers and Ti or Si spacers are comparatively studied. It was concluded that spin disorder scattering is responsible for the negative longitudinal magnetoresistance observed in multilayers of both types.