İsmail Duman

Synthesis of niobium borides by powder metallurgy methods using Nb2O5, B2O3 and Mg blends

Niobium boride powders having NbB, NbB2 and Nb3B4 phases in various amounts and single phase NbB powders were successfully synthesized by using powder metallurgy methods from related metal oxide raw materials in the presence of a strong reducing agent. Nb2O5, B2O3 and Mg powder blends were milled at room temperature by a high-energy ball mill for different time. Subsequently, undesired MgO phase was removed from the milled powders by HCl leaching to constitute NbB–NbB2–Nb3B4 as final products and they were subjected to an annealing process at 1500 °C for 4 h to observe probable boride transformation. Characterization was carried out by XRD, DSC, PSA, SEM/EDX, TEM and VSM. The effects of milling time (up to 9 h) on the formation, microstructure and thermal behavior of the final products were investigated. Reduction reaction took place after milling stoichiometric powder blends for 2 h. Nano-sized NbB–NbB2–Nb3B4 powders in high purity were obtained in the absence of any secondary phase and any impurity via mechanochemistry by milling for 5 h and leaching with 4 mol/L HCl. After annealing, pure and nano-sized NbB–NbB2–Nb3B4 powders transformed to a single NbB phase without leaving behind NbB2 and Nb3B4 phases.

Beneficiation of brass ashes

Abstract Slags formed during brass smelting contain a significant amount of metallic value. The glassy and oxidized portion of the ground slag, usually referred to as “brass ash”, consists of compounds such as ZnO, ZnO·SiO 2 , Cu-Zn, CuO, Cu and Zn/Cu/B oxide, and its colored-metal content may vary between 28÷52% Zn and 8÷16% Cu. These ashes are classified as harmful wastes, due to their high Zn content, and are considered to be secondary raw materials that should be treated accordingly, from an economical viewpoint. The aim of this experimental study is to investigate the possibilities of beneficiating brass ashes by treating it with H 2 SO 4 or (NH 4 ) 2 CO 3 + NH 4 OH mixtures. Effects of temperature, air sparging and addition of oxidizing agents, such as MnO 2 and Fe 2 (SO 4 ) 3 , are investigated on copper and zinc leaching recovery. As a result of both acidic and alkaline leaching experiments, it is observed that more than 90% of Zn and more than 65% of Cu was leached out. Two separate process flow sheets are proposed for the possible treatment of brass ashes.

Effects of La2O3 Addition on the Microstructure and Properties of Activated Sintered W-Ni Compacts

In order to improve the properties of Ni activated sintered W compacts, La2O3 was added to a W-1 wt.% Ni matrix alloy. W-1 wt.% Ni-0.5 wt.% La2O3 and W-1 wt.% Ni-1 wt.% La2O3 composites were fabricated by mechanical alloying and activated sintering methods. The effects of La2O3 content and mechanical alloying duration on the microstructural and physical properties of activated sintered W-Ni compacts were investigated. The results showed that La2O3 particles have a significant effect on the density/microhardness values and wear amounts of the samples. The relative density value of 96.39 % and microhardness value of 4.08±0.28 GPa of W-1 wt.% Ni samples increased to respectively 98.09 % and 5.45±0.29 GPa with the addition of 1 wt.% La2O3. Wear rate of 3.26±0.81 (mm3N-1m-1)x10-9 of the W-1 wt% Ni samples decreased to 2.10±0.24 (mm3N-1m-1)x10-9 with the addition of 0.5 wt.% La2O3. Furthermore, grain sizes decreased and microhardness values increased with increasing mechanical alloying duration.