Papers by Keyword: Niobium

Abstract: Abstract: Appropriate ratio of mixing digestion solvent which consist of HF and HNO3 have been tested firstly and combine with the high-pressure sealed microwave heating method, the titanium ore samples can be quickly and completely digested into solution. Then the elements content of zirconium, niobium, vanadium, chromium can be determined at the same time by applying the inductively coupled plasma atomic emission spectrometry (ICP-OES) method under hydrofluoric acid media condition.This method has solved the problem that the titanium ore matrix and impurities of zirconium oxide, niobium oxide, chromium oxide and other insoluble oxides are all difficult to digeste under normal conditions by the acid. Through fluoride ion complex reaction, make sure the easy hydrolysis of titanium ore matrix and niobium, zirconium and other elements to form the shape of the complex ion, even in the low acidity of the solution does not produce the hydrolysis reaction, so that it can greatly reduce the detection solution acidity to eliminate the blank background and acidity effects. The experiments investigated the impacts between the sample digestion conditions such as microwave heating procedures, reagents ratio, amount, and the titanium matrix as well as coexistent elements. Besides, it optimized the detection parameters of the ICP spectrometer under the conditions of using unconventional resistance to hydrofluoric acid PTFE nebulizer. Spectral interferences and matrix effects have been eliminated by selecting the appropriate analyte spectral lines as well as the integrated use of matrix matching and synchronization of the background correction method. The results show that the background equivalent concentration is 0.0002% ～ 0.0008%, and the detection limit is 0.0029 ～ 0.0018%, trace element recovery rate is 91.0% and ～108.0%, RSD is ≤ 4.71%.

Abstract: Using high-pressure sealed microwave heating method, the WC-Co based cemented carbide samples were digested completely by nitric acid and phosphoric acid (VHNO3: VH3PO4 = 5:1). Then the digestion solution was diluted with water to a constant volume, and directly using inductively coupled plasma atomic emission spectrometry (ICP-OES) determination of the content of 0.005 to 10% Co and 0.005 ~ 1% of Fe, Nb, Ta, V, Cr, Mo and Ni. This paper examine the best digestion conditions, including reagent composition, ratio, and microwave control parameters, etc., then establish a set of microwave digestion and by complex reactions with inorganic reagents to stabilize the high tungsten matrix digestion method, in order to quickly and completely digest the tungsten-cobalt-based samples and avoid the generation of tungsten acid precipitation resulting in the loss of some of the analyte and impact of organic complex agents on the spectral determination. The results showed that: the control parameters of using 5 min to heat the sample to 130 °C and keep for 5 min, then heated to 190 °C in 5 min and keep for 15 min is better to maintain the digestion. By optimizing elemental analysis line, ICP measurement parameters and matrix matching and synchronization of background correction method, the high tungsten matrix effects and spectral interference are eliminated; ensure the detection performance of the method. Background equivalent concentration of 5μg/L (Nb) ~ 18μg/L (Fe), elements of the detection limit of 4μg/L (Nb) ~ 13μg/L (Fe), which used for the determination of impurities in the alloy or elements with the results is RSD <3%, recovery 97.0% ~ 103.5% corresponding with the national standard examination method.

Abstract: The studies emphasis on the development of niobium alloyed ductile iron with higher strength comparing to unalloyed ductile iron. 0.5wt% to 2wt% niobium were added into mixture of ductile iron casting containing pig iron, carburizer and steel scrap, and nodulized through 1.6wt% Fe-Si-Mg addition in CO2 sand casting process. Samples were then machined according to TS EN 10001 standards for tensile test and ASTM E23 for Charpy impact test. In addition, Rockwell hardness test was also performed. Microstructure observations were made after 2% Nital chemical etched and the phase structures were validated through XRD analysis. It was found that addition of niobium in ductile iron provide significant enhancement in mechanical properties when compared to unalloyed ductile iron. Addition of higher amount of niobium had further increased the strength and impact toughness properties. The enhancement of the mechanical properties is expected to further expand the applications of ductile iron.

Abstract: In this paper, porous Ti14Nb4Sn alloys were fabricated using a space holder sintering method, resulting in a porosity of ~70%. Scanning electron microscopy (SEM) analyses revealed a combination of both macropore and micropore structures. The fabricated titanium alloy scaffolds exhibited a similar structure to that of natural bone, which is expected to improve bone implant longevity. Bacterial cells of Pseudomonas aeruginosa ATCC 9027 were employed for the in vitro test.

Abstract: In present article, the low intensity magnetic separation process was studied for the low-grade niobium minerals by microwave magnetic roasting. The influence of magnetic density, particle size of grinding and dispersant addition on the magnetic separation effect of sinter ore with the best magnetisability was investigated emphatically. The results show that the iron recovery was decreased and the iron grade increased gradually with decreasing the magnetic density and particle size of grinding. The magnetic separation result of sinter ore was optimal under the magnetic density of 80KA / m and the grinding grain-size of 33 μm. Fine grinding can effectively make Fe separated from Nb, especially when the dispersant(industrial alcohol) was used in the process of magnetic separation , resulting in the improvement of the grade of iron from 57.2% to 60.5% and enrichment of Nb in the tailing ore(the grade of Nb was 5.01%). After the acid pickling of tailing ore containing Nb, the grade of Nb in the extract was improved to 12.36%, which was enriched four times more than that of low-grade niobium ore before microwave magnetic roasting.

Abstract: The thickness-ratio effects of Ni/Nb bi-layer electrodes were studied for power device applications. The reaction microstructure and electrical contact property were investigated after annealing at 1000 °C and compared with the results of an Ni electrode. Microstructure-related problems of the Ni electrode could be successfully resolved without sacrificing ohmic contact behavior by the addition of Nb to a Ni based electrode. Carbon precipitation was reduced with increasing Nb thickness by the formation of carbides, which led to good adhesion between the electrode and a wiring pad. High shear strength of the bonded wire was also obtained by the elimination of the carbon precipitates on the electrode surface.

Abstract: The separation of niobium and iron from the low grade niobium ore was researched by the technology process of reductive roasting and magnetic separation. Experiments of reductive roasting and magnetic separation were carried out in order to investigate the separation effect at different conditions of roasting temperature and addition amount of coal powders. The results show that the separation of niobium and iron can be realized, meanwhile the niobium can be enriched in the magnetic tailings. The main mineral phase of niobium in magnetic tailings changes into NbC from (Ce,Nd)NbTiO₅ when the roasting temperature exceeds 1150°C. By magnetic separation after roasting with adding 37.5% coal powders at 1050°C, w(T.Fe) of the reduced iron is 86.11%, the percentage metallization is 87.6%, and the yield ratio of iron is 77.4%. Meanwhile, w(Nb₂O₅) of the magnetic tailings is 7.35% which is 2.4 times higher than low grade niobium ore, and the yield ratio of niobium is 98.1%.

Abstract: Plate steel S460 is intercritically rolled during the final stages of industrial processing. A series of experiments to represent the preliminary stages of an intercritical simulation were completed and the isothermal austenite to ferrite transformation kinetics investigated. The growth of the ferrite grains was interpreted using the classic JMAK model and the effect of processing history also examined. A double austenite deformation at 1323 K, to a true strain of 0.2, led to the most acceptable starting microstructure for the extended simulation. The role of niobium in this preliminary simulation is also considered.

Abstract: For the re-concentration minerals of RE dressing tailings in Bayan Obo mine, Fe and P compounds were selectively reduced by the methods of coal-based direct reduction in reactionary pot. The metal and slag in sponge iron obtained from reduction was melted and separated. Compared to that in re-concentration minerals, the content of valuable elements oxide in melt-separation slag was enriched to about 2.5 times. Therefore, melt-separation slag can be used as the basic material to extract the valuable elements.

Abstract: This paper presents the changes on phase structures of niobium alloyed ductile iron after austempering process which started by austenitizing process at 900°C and held at 350°C for 1 hour, 2 hours and 3 hours in salt bath furnace. The phase structure were observed by light microscope, and then verified through X-Ray diffraction (XRD). The phase structure of as cast niobium alloyed ductile iron mainly consists of graphite nodules embedded in ferrite and pearlite phases with presence of niobium carbide. Austempering process resulted in the structure of graphite nodules embedded in ferrite platelets and bainitic structures. Increasing the austempering holding times had resulted in coarsening of the ferrite platelets structures and transformation from lower bainite to upper bainite structures.