El-Geassy A A, Abdel Halim K S, Alghamdi Abdulaziz S
Central Metallurgical Research and Development Institute (CMRDI), P.O. Box 87, Helwan 11421, Egypt.
College of Engineering, University of Ha'il, P.O. Box 2440, Hail 55476, Saudi Arabia.
Materials (Basel). 2023 Mar 29;16(7):2736. doi: 10.3390/ma16072736.
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 [Fe(MoO)]. An XRD phase analysis indicated that iron molybdate was the only phase that was identified in precursor A, while iron molybdate and FeO 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 H at 600-850 °C using microbalance, and the O 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 [Fe(MoO)] and FeO 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 MoFe intermetallic alloys. The mechanism of the reduction reactions was predicted from the apparent activation energy values ) 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 MoFe intermetallic alloys can be successfully fabricated via a gas-solid reaction technique at lower temperatures.
纳米结构的钼铁金属间化合物由前驱体合成，前驱体中钼与铁的摩尔比分别为72/28%和30/70%，分别记为前驱体A和B。这些前驱体通过七水合钼酸铵（AHM）和草酸亚铁的热水溶液共沉淀制备。将干燥的沉淀物用热重-差示扫描量热法（TG-DSC）进行热处理，以跟踪其在高达700℃（10°K/分钟）的氩气气氛中焙烧时的行为。TG曲线表明，前驱体A和B热处理后的失重分别为32.5%和55.5%。DSC热流曲线表明，在AHM和草酸亚铁热分解过程中，分别在196.9℃和392.5 - 400℃出现吸热峰。在427.5℃检测到的放热峰是由于纳米级钼酸铁[Fe(MoO)]的生成。X射线衍射（XRD）相分析表明，钼酸铁是前驱体A中唯一鉴定出的相，而前驱体B中生成了钼酸铁和FeO。通过压制纳米级前驱体制备压块，在500℃焙烧3小时。使用微量天平在600 - 850℃的氢气中对焙烧后的压块进行等温还原，并将还原反应导致的氧失重作为时间的函数连续记录。研究并讨论了还原温度和前驱体组成对前驱体还原行为的影响。用X射线粉末衍射（XRD）、反射光显微镜（RLM）和扫描电子显微镜（SEM-EDS）对部分还原和完全还原的压块进行了检查。根据前驱体组成，[Fe(MoO)]和FeO的还原反应在生成MO/Fe金属间合金之前，通过形成中间低价氧化物进行。基于在还原早期、中期和末期鉴定和表征的中间相，给出了化学反应方程式以跟踪MoFe和MoFe金属间合金的形成。根据在不同还原度下计算得到的表观活化能值预测还原反应的机理。此外，应用从气固反应模型推导的数学公式来证实还原机理，该机理很大程度上取决于前驱体组成和还原温度。然而，可以报道，纳米结构的MoFe和MoFe金属间合金可以通过气固反应技术在较低温度下成功制备。
