Search Results (4)

The mineralogical studies of rare-element (REL) pegmatites are important for unraveling the ore-forming process and evaluating REL mineralization potential. The Chinese Altai orogenic belt hosting more than 100,000 pegmatite dykes is famous for rare-metal resources worldwide and diverse REL mineralization types. In this paper, we present the results of EMPA and LA-ICP-MS for muscovite from the typical REL pegmatite dykes of the Chinese Altai. The studied pegmatites are Li-Be-Nb-Ta, Li-Nb-Ta, Nb-Ta, Be-Nb-Ta, Be and barren pegmatites. The Li⁺ accompanied with Fe, Mg and Mn substitute for Al³⁺ at the octahedral site in muscovite from the REL pegmatites, and the substitution of Rb by Cs at the interlayer space is identified in muscovite from the Be pegmatites. The P and B contents increase with evolution degree and the lenses from the Nb-Ta pegmatite are produced at late fluid-rich stage with high fluxes (P and B). The enrichment of HFSE in muscovite indicates a Nb-Ta-Sn-W rich pegmatite magma for the Be-Nb-Ta pegmatite. From barren pegmatite, beryl-bearing zone, to spodumene-bearing zone, the evolution degrees of pegmatite-forming magmas progressively increase. In the Chinese Altai, the possible indicators of muscovite for REL mineralization types include Rb (ca. 400–600 ppm, barren pegmatite; ca. 1200–4000 ppm, Be pegmatite; >4500 ppm, Li pegmatite), Cs (ca. 5–50 ppm, barren pegmatite; ca. 100–500 ppm, Be pegmatite; >300 ppm, Li pegmatite) and Ge (<3 ppm, barren pegmatite; ca. 4–6 ppm, Be pegmatite; ca. 6–12 ppm, Li pegmatite) coupled with Ta, Be (both <10 ppm, barren pegmatite) and FeO (ca. 3–4 wt%, Be pegmatite; ca. 1–2.5 wt%, Li pegmatite). The plots of Nb/Ta vs. Cs and K/Rb vs. Ge are proposed to discriminate barren, Be- and Nb-Ta-(Li-Be-Rb-Cs) pegmatites. The Li, Be, Rb, Cs and F concentrations of forming liquid are evaluated based on the trace element compositions of muscovite. The high Rb and Cs contents of liquid and lower Be contents than beryl saturation value indicate that both highly evolved pegmatite magma and low temperature at emplacement contribute to beryl formation. The liquids saturated with spodumene have large variations of Li, possibly related to metastable state at Li unsaturation–supersaturation or heterogeneous distribution of lithium in the system. Full article

In this study, brazing AA6061 to Q235 steel using flame brazing was performed with 70.9 wt.% CsF-0.5 wt.% RbF-28.6 wt.% AlF₃ fluxes doped with GaF₃, ZnF₂, Zn(BF₄)₂ and Ga₂O₃ nanoparticles, matched with a Zn-15Al filler metal, and the spreadability of the filler metal and the mechanical properties of brazed joints were investigated at the same time. The results showed suitable amounts of GaF₃, ZnF₂, Zn(BF₄)₂ and Ga₂O₃ doped into the base flux could strengthen the filler metal in wetting and spreading on the surface of aluminum alloy and steel to different degrees. The suitable ranges of GaF₃, ZnF₂, Zn(BF₄)₂ and Ga₂O₃, respectively, were 0.0075–0.01 wt.%, 0.0075–0.01 wt.%, 0.0075–0.01 wt.% and 0.009–0.01 wt.%, and the maximum spreading area was obtained via doping with GaF₃. The shear strength of brazed joints reached the peak at 126 MPa when 0.075 wt.% GaF₃ was added. Comparative tests proved that the activity of the CsF-RbF-AlF₃ flux doped with GaF₃ was the best. The reason was that the CsF-RbF-AlF₃-GaF₃ flux was competent in removing oxides of the base metal and decreasing the interfacial tension, in virtue of the activity of Ga³⁺ as well as F⁻. Full article

The effect of trace amounts of GaF₃ and Ga₂O₃ nanoparticles on the wettability and spreadability of CsF-AlF₃ flux matched Zn-15Al filler metal were comparatively studied on 6061 aluminum alloy and Q235 low-carbon steel. The experimental results indicate that appropriate amounts of GaF₃ and Ga₂O₃ added into the flux could significantly promote the Zn-15Al filler metal to wet and spread on the surface of 6061 aluminum alloy and Q235 low-carbon steel. The optimum ranges for GaF₃ and Ga₂O₃ were 0.0075–0.01wt.% and 0.009–0.01 wt.%, respectively. Comparative analysis showed that the activity of CsF-AlF₃ flux bearing GaF₃ was higher than that bearing Ga₂O₃. The reason for this is that the former flux has a stronger ability to remove oxides of the base metal and reduce the interfacial tension of the molten filler metal and the base metal. Full article

In this study, a Ga₂O₃ nano-particle was added into CsF-RbF-AlF₃ flux to develop a highly active flux for brazing aluminum alloy to steel, and the spreadability and wettability of Zn-Al filler metal that matched the CsF-RbF-AlF₃ flux-doped Ga₂O₃ nano-particle on the steel were investigated. The results showed that the spreadability and wettability of the CsF-RbF-AlF₃ flux-doped Ga₂O₃ nano-particle could be remarkably improved when matching Zn-Al filler metals on both aluminum and low-carbon steel, for which the optimal content is in the range of 0.001–0.003 wt.% of Ga₂O₃. An investigation and analysis on the mechanism of reactions among CsF-RbF-AlF₃-doped Ga₂O₃ nano-particle flux and filler metal or base metals showed that the Ga₂O₃ nano-particle is selectively absorbed by the interface of molten Zn-2Al filler metal and base metal, which released the surface-active element Ga to enrich the molten Zn-2Al filler metal and decreased the interfacial tension, so as to promote the enlargement of its spreading area during the brazing process. It was concluded that adding a trace amount of Ga₂O₃ nano-particle into CsF-RbF-AlF₃ flux is a meaningful way to improve the activity of flux for brazing aluminum to steel compared with adding ZnCl₂, which poses the risk of corrosion on aluminum. Full article