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A QUICK ROUTE FOR THE SYNTHESIS OF PMN-PZT POWDERS
A. Izadpanahi, S. Baghshahi, A. Shalbaf Zadeh,
Volume 13, Issue 3 (9-2016)
Abstract

In the following research, Lead magnesium niobate relaxor ferroelectric (PMN-PZT) ceramic powders were synthesized using the combustion method grand urea as the fuel for the first time. The starting materials used were lead nitrate, magnesium acetate, niobium oxide, zirconium nitrate, titanium oxide.

    The raw materials were first mixed using the general formula of (1-x)Pb(Mg1/3Nb2/3)O3-xPb(Zr0.52Ti0.48)O3, with  x=0.3. The synthesized powders were characterized using XRD, SEM and FTIR spectroscopy techniques. The X-ray diffraction patterns revealed that the structure of the prepared samples were tetragonal at 500,600,700 and 800 oC. However, the monoclinic phase was detected in the samples calcined at 800 oC and the amount of pyrocholore phase also drastically decreased at this temperature. The band gap widths of the samples were measured via UV spectroscopy in the wave number range of 400-4000cm-1. The results show that by increasing the calcination temperature, the band gap width of the prepared samples decreases. SEM micrographs verify that by rising the calcination temperature, the structure of the prepared samples becomes more homogenous.


Effect of Temperature-Time on simultaneous hydrogen reduction of molybdenum and tungsten oxides
Iman Babaei Nezhad, Hossein Aghajani, Seyed Hossein Seyedein, Mohammad Reza Aboutalebi,
Volume 21, Issue 0 (3-2024)
Abstract
The Mo-30 wt% W solid solution is a well-established molybdenum-based alloy. A recent approach to alloying Mo and W involves the simultaneous reduction of their oxides by hydrogen. Several studies have reported the production of Mo-W alloys via the reduction of mixed oxides. But the alloying mechanism and the effects of key reduction parameters on alloy formation remain uninvestigated. In the present study, the simultaneous hydrogen reduction of MoO₃–WO₃ mixed oxides was investigated as a potential route for producing pre-alloyed Mo–W powders. In this study pre-alloyed Mo-30 wt% W is. The effects of reduction temperature and holding time on phase evolution, morphology, and alloy formation were systematically examined. The chosen temperature range is 600-1050°C. The influence of time on phase formation and morphology during the hydrogen reduction of molybdenum and tungsten oxides is examined over a 30-360 minute period. Other parameters such as heating rate (20℃min ), bed height (10mm), H₂ flow rate (500mlmin ), and material weight (14.3g) were kept constant. The reduced samples are analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effects of temperature and time on the reduction processes are closely linked. Results indicate the formation of MoO₂ and WO₂ phases at 600°C after 60 minutes of hydrogen reduction. No Oxide phases were detected in XRD analysis of the sample that was reduced at 800°C for 180 minutes. Therefore, tungsten and molybdenum coexist in all particles of the samples. Mass transfer between Mo and W takes place during the reduction of oxides to the metallic phase. But isothermal reduction does not yield a homogeneous alloy. In these studies, for T > 800°C, increasing time has minimal effect on alloying these elements. At T=800°C, a significant change in morphology occurs at t>180 min. At T=800°C, a notable morphological change occurs after t>180 min. These changes are caused by the CVT mechanism. The optimal conditions for achieving chemical homogeneity in the alloy powder particles after reduction were identified as: 600°C for 60 min, 600 to 1050 for 240 min, and 180 min at 1050°C. This cycle leads to the formation of homogeneous alloy powder particles. The achieved homogeneity is attributed to providing sufficient time for mass transport between molybdenum and tungsten oxide particles through gaseous chemical species formed within this temperature range.

 
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