A Novel Hydro-Thermal Synthesis of Nano-Structured Molybdenum-Iron Intermetallic Alloys at Relatively Low Temperatures

Abstract

Nano-structured Mo/Fe intermetallics were synthesized from precursors that contained 72/28% and 30/70% molar ratios of Mo/Fe, which were given as precursors A and B, respectively. These precursors were prepared from the co-precipitation of aqueous hot solutions of ammonium heptamolybdate tetrahydrate (AHM) and ferrous oxalate. The dry precipitates were thermally treated using TG-DSC to follow up their behavior during roasting, in an Ar atmosphere of up to 700 °C (10° K/min). The TG profile showed that 32.5% and 55.5% weight losses were measured from the thermal treatment of precursors A and B, respectively. The DSC heat flow profile showed the presence of endothermic peaks at 196.9 and 392.5–400 °C during the thermal decomposition of the AHM and ferrous oxalate, respectively. The exothermic peak that was detected at 427.5 °C was due to the production of nano-sized iron molybdate [Fe2(MoO4)3]. An XRD phase analysis indicated that iron molybdate was the only phase that was identified in precursor A, while iron molybdate and Fe2O3 were produced in precursor B. Compacts were made from the pressing of the nano-sized precursors, which were roasted at 500 °C for 3 h. The roasted compacts were isothermally reduced in H2 at 600–850 °C using microbalance, and the O2 weight loss that resulted from the reduction reactions was continuously recorded as a function of time. The influence of the reduction temperature and precursor composition on the reduction behavior of the precursors was studied and discussed. The partially and completely reduced compacts were examined with X-ray powder diffraction (XRD), a reflected light microscope (RLM), and a scanning electron microscope (SEM-EDS). Depending on the precursor composition, the reduction reactions of the [Fe2(MoO4)3] and Fe2O3 proceeded through the formation of intermediate lower oxides, prior to the production of the MO/Fe intermetallic alloys. Based on the intermediate phases that were identified and characterized at the early, intermediate, and final reduction degrees, chemical reaction equations were given to follow up the formation of the MoFe and MoFe3 intermetallic alloys. The mechanism of the reduction reactions was predicted from the apparent activation energy values (Ea) that were computed at the different reduction degrees. Moreover, mathematical formulations that were derived from the gas–solid reaction model were applied to confirm the reduction mechanisms, which were greatly dependent on the precursor composition and reduction temperature. However, it can be reported that nano-structured MoFe and MoFe3 intermetallic alloys can be successfully fabricated via a gas–solid reaction technique at lower temperatures.

Characterization of the Polyetheretherketone Weldment Fabricated via Rotary Friction Welding

“…The heat capacities of welded parts fabricated using RFW with the burn-off length of 1.8 mm and 1 mm are about 0.94 mW/mg and 0.50 mW/mg, respectively [29]. This result shows the molecular orientation [30,31] in the weld interface of the welded parts fabricated using RFW with a burn-off length of 1.8 Figure 15 shows the DSC traces of welded parts. The heat capacities of welded parts fabricated using RFW with the burn-off length of 1.8 mm and 1 mm are about 0.94 mW/mg and 0.50 mW/mg, respectively [29].…”

Mechanical Performance and Microstructural Evolution of Rotary Friction Welding of Acrylonitrile Butadiene Styrene and Polycarbonate Rods

“…The heat capacities for the friction-welded parts welded by rotation speeds of 330 rpm, 490 rpm, 650 rpm, 950 rpm, and 1350 rpm are −1.002 mW/mg, −0.8127 mW/mg, −0.626 4mW/mg, −1.759 mW/mg, and -2.287 mW/mg, respectively. The DSC curve for the friction-welded parts welded by a rotation speed of 1350 rpm shows an endothermic peak [31] between 400 to 440 °C and an exothermic peak [32] between 600 to 700 °C. This means that higher rotation speed contributes to higher molecular orientation in the weld joints, showing that the friction-welded parts have better mechanical properties.…”

Rotary Friction Welding of Dissimilar Polymer Rods Containing Metal Powder

“…As can be seen, the heat capacity [34] for RFW of PLA-containing Al powder and the PLA-containing Al powder rod and RFW of PLA-containing Cu powder and the PLA-containing Cu powder rod is about 2.737 mW/mg and 2.541 mW/mg. This means that the welded part fabricated by RFW of the PLA-containing Al powder and the PLA-containing Al powder has a higher molecular orientation in the welded joints than that of the welded part fabricated by RFW of the PLA-containing Cu powder and the PLA-containing Cu powder [35,36]. Figure 12 shows the surface hardness of RFW specimens in comparison to pure materials.…”