Molybdenum Trioxide Powder Research Articles

Preparation of MoO3 powder by hydrothermal method

Abstract Based on the raw material of ammonium tetramolybdate in the experiment, molybdenum trioxide was prepared by hydrothermal synthesis, and the effects of different pH, hydrothermal reaction time, filling degree, and calcination temperature on molybdenum trioxide powder were studied. Meanwhile, the molybdenum trioxide powder was characterized through scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and thermal analysis differential scanning calorimetry analysis so as to study the morphology and phase changes during the experiment. As is evident from the research findings, MoO3 powders with uniform and suitable size, smooth and clear surface, good dispersibility, and no adhesion can be obtained at the conditions of pH = 1, 16 h hydrothermal reaction, 90% of filling degree, and 550°C of calcination temperature. In the calcination process, MoO3 crystal undergone crystal transformation and was completely transformed from h-MoO3 to α-MoO3 at the calcination temperature of 350°C.

Preparation of low-radioactive high-purity enriched 100MoO3 powder for AMoRE-II experiment

This paper describes preparing radiopure molybdenum trioxide powder enriched with Mo-100 isotope for the AMoRE-II experiment. AMoRE-II, the second phase of the AMoRE experiments, will search for the neutrinoless double-beta decay (0νDBD) of the 100Mo isotope using over 100 kg of 100Mo embedded in 200 kg of ultra-pure Li2100MoO4 bolometric crystals. Efficient purification technology was developed and adapted to purify 100MoO3 powder with a 5 kg per month production capacity. Based on the ICP-MS analysis of purified powder, the 232Th and 238U were reduced to <9.4 μBq/kg and <50 μBq/kg, respectively. The concentrations of potassium, transition metals, and heavy metals were lower than 1 ppm. HPGe counting confirmed the reduction of progenies from the 232Th and 238U decay chains, reporting upper limits of <27 μBq/kg for 228Ac and <16 μBq/kg for 228Th. The 226Ra activity was acceptable at 110 ± 30 μBq/kg. In the last 3 years, 100 kg of pure 100MoO3 powder was produced. The production yield for the final purified product was above 90%, while irrecoverable losses were under 1.5%, and all by-products could be recycled further.

Measurement of the background activities of a 100Mo-enriched powder sample for an AMoRE crystal material by using fourteen high-purity germanium detectors

The Advanced Molybdenum-based Rare process Experiment (AMoRE) in its second phase will search for neutrinoless double-beta (0νββ) decay of 100Mo in 200 kg of molybdate crystals. To achieve the zero-background level in the energy range of the double-beta decay Q-value of 100Mo, the radioactive contamination levels in AMoRE crystals should be low. Enriched molybdenum trioxide powder, 100EnrMoO3, enriched to 95.73% abundance of the 100Mo isotope is used to grow the AMoRE crystals. A shielded array of fourteen high-purity germanium detectors with 70% relative efficiency each was used for the measurement of background activities in a sample of 9.6-kg powder. The detector system named the CAGe located at the Yangyang underground laboratory was designed for measuring low levels of radioactivity from natural radioisotopes or cosmogenic nuclides such as 228Ac, 228Th, 226Ra, 88Y, and 40K. The activities of 228Ac and 228Th in the powder sample were 0.88 ± 0.13 and 0.669 ± 0.089 mBq/kg, respectively. The activity of 226Ra was measured to be 1.19 ± 0.42 mBq/kg. The activity of 88Y was 0.101 ± 0.016 mBq/kg. The activity of 40K was found as 36.0 ± 4.1 mBq/kg.

Purification and recovery of 100MoO3 in crystal production for AMoRE experiment

The AMoRE collaboration searches for the neutrinoless double-beta decay of 100Mo with ultra-radiopure molybdate crystals operated as low-temperature scintillating bolometers. For such a rare event search experiment, the techniques for investigating and reducing radioactive background contaminants in detector materials are extremely crucial. This paper discusses techniques for deep purification of enriched molybdenum for growing the crystals and the recovery of 100MoO3 from the residual melt left after growing lithium molybdate crystals. The purities of enriched molybdenum trioxide powders before and after the purification and that of the recovered powder were tested with ICP-MS; results of these tests are presented.

Reduction of radioactive elements in molybdenum trioxide powder by sublimation method and its technical performance

We studied the effectiveness of the purification of molybdenum trioxide (MoO3) powder with the sublimation method. To utilize the method, we have designed sublimation apparatus to purify the powder and annealing apparatus to collect the fine powder, followed by the wet chemistry method. As part of purification R&D, MoO3 powder was purified using a low vacuum sublimation method to remove radioactive elements such as Ra, Th, U, etc. The purification was performed at different temperatures to determine the optimum conditions for high decontamination factors and high recovery efficiencies. After applying the sublimation method, the powder was dissolved in aqueous ammonia; recrystallized to obtain polyammonium molybdate (PAM); and annealed to acquire MoO3 fine powder. The phase of MoO3 powder was studied by using X-ray diffraction (XRD) techniques. The effectiveness of the purification techniques was checked with inductively coupled plasma mass spectrometry (ICP-MS) measurements and the radioactivity from Ra, Th, and U were measured with high purity germanium (HPGe) detectors at Yangyang underground laboratory in Korea. The purified MoO3 powder was used by the AMoRE (Advanced Mo-based Rare process Experiment) collaboration to grow scintillating crystals.

The effect of carrier gas flow rate on the growth of MoS2 nanoflakes prepared by thermal chemical vapor deposition

Molybdenum disulfide nanoflakes (MoS2) are superior material for their semiconducting properties. For bulk and monolayer MoS2 the band gap changes from indirect-to-direct, respectively. So, it exhibits promising prospects in the applications of optoelectronics and valleytronics, such as solar cells, transistors, photodetectors, etc. In this research, the influence of different Ar flow rates as the carrier gas, is investigated for growing MoS2 nanoflakes on silicon substrates using one-step thermal chemical vapor deposition by simultaneously evaporating of solid sources like sulfur and molybdenum trioxide powders. The structural and optical properties of the obtained nanoflakes are assessed by using X-ray diffraction pattern, scanning electron microscopy, UV–visible absorption, photoluminescence and Raman spectroscopy. It is shown that, Ar gas flow rate is strongly affects on the final products as few-layer MoS2 structures. Moreover, the abundance of MoS2 in comparison to MoO2 and MoO3 structures, in the obtained nanoflakes, is influenced by the Ar flow rate.

Preparation of industrial grade MoO2 by the reaction between industrial grade MoO3 and activated carbon

In this study, the reaction between industrial grade molybdenum trioxide powders and activated carbon has been investigated in order to produce industrial grade molybdenum dioxide (MoO2). Effects of activation carbon addition and reaction temperature on the product compositions are both illustrated. Increasing the reaction temperature can significantly improve the reaction rate. It is difficult for them to react completely when the temperature is lower than 550 °C. However, industrial grade MoO2 powders can be obtained when the temperature is up to 650 °C. It is also found that there is no intermediate product Mo4O11 formed during the reaction process of MoO3 by activated carbon, which is different from the case of hydrogen reduction of MoO3 to MoO2. The crystalline size of the obtained MoO2 becomes very small relative to that of the raw material MoO3.

Influence of propyl alcohol addition during processing of molybdenum trioxide powders: Observation of novel dual-wavelength excitation photochromism

The novel dual-wavelength excitation photochromic molybdenum trioxide (MoO3) powders are fabricated successfully via the hydrothermal method by the addition of propyl alcohol. The samples were fully characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible diffuse reflectance spectroscopy (UV–vis), and colorimetry. The characteristic spectrum of XRD demonstrates that the as-obtained products are highly pure. The results show that the flowerlike MoO3 sample with the inducer of propyl alcohol has better photochromic properties, which was analyzed by colorimetry. It is shown that both of the samples exhibit a strong adsorption band between 250 and 400nm in the UV range. Moreover, the UV–vis spectra shows that MoO3 synthesized with added propyl alcohol absorbs light not only between 250 and 400 nm but also displays an additional band between 500 and 800nm, demonstrating novel dual-wavelength excitation photochromic properties.

The Synthesis of α-MoO₃ by Ethylene Glycol.

This study investigated the use of ethylene glycol to form α-MoO3 (molybdenum trioxide) from ammonium molybdate tetrahydrate at various sintering temperatures for 1 h. During the sintering process, the morphologies of the constituents were observed using scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy was used to explain the reaction process. In this work, the results obtained using X-ray photoelectron spectroscopy (XRD) demonstrated that, when the molybdenum trioxide powder was treated thermally at 300 °C, the material exhibited crystallinity. The peaks were indexed to correspond with the (110), (040), (021), (111), and (060) crystallographic planes, and the lattice parameters of a, b, and c were about 3.961, 13.876, and 3.969 Å. Using these observations, we confirmed that orthorhombic α-MoO3 was formed for sintering temperatures from 300 to 700 °C. Pattern images were obtained by the selected area electron diffraction pattern (SAED) technique, and the d distance of the high resolution transmission electron microscopy (HRTEM) images were almost 0.39 and 0.36 nm, and the Mo 3d5/2, Mo 3d3/2, and O 1s of X-ray photoelectron spectroscopy (XPS) were located at 233.76, 237.03, and 532.19 eV, which also demonstrated that α-MoO3 powder had been synthesized.

Binder effect on the catalytic activity of MoO3 bulk catalyst reduced by H2 for n-heptane hydroisomerization

Two bulk catalysts containing about 70wt.% of molybdenum trioxide and alumina or silica as binder were prepared by a gel method. They were characterized by X-ray diffraction, Raman spectroscopy, TGA in air and textural properties. The MoO3 bulk catalysts were activated in situ by reduction with hydrogen and tested in the hydroisomerization of n-heptane using a fixed bed continuous flow microreactor coupled to gas chromatograph. The highest catalytic activity for hydroisomerization was obtained with the alumina-based bulk catalyst, although the silica-based bulk catalyst showed lower amounts of cracking products and a higher selectivity to dimethylpentanes. The bulk catalysts resulted more active than MoO3 powder. The results indicate that the acid–base properties of the binder have a desirable effect on the acidity of the molybdenum trioxide powder as hydroisomerization catalyst.

The Preparation Technique of Nanometer Molybdenum Trioxide by Hydrothermal Synthesis

The technique of hydrothermal synthesis is used to prepare nanometer molybdenum trioxide through controlling the parameters such as the acidification condition, the reaction temperature, the reaction time and so on. The technique is under high temperature and high pressure by water as the solvent. Synthesized molybdenum trioxide powder is characterized by XRD, SEM, and HRTEM. The optimal reaction time is 40h, the optimum reaction temperature is 170°C, and the optimum pH value is 1.0. The results indicate that powder has an ultrafine particle size, high purity, and narrow size distribution, good fluidity, light agglomerate and is perfect in crystal.

Preparation of Molybdic Acid Aggregates and Molybdenum Trioxide Powder with Controllable Size and Morphology

Molybdic acid aggregates were prepared by the reaction of ammonium molybdate with HNO_3 and HCl in a coexisting HAc or cetyl-trimethyl ammonium bromide (CTAB) solution,respec- tively.The results indicate that the size and morphology of as-prepared molybdic acid aggregates and annealed produets-α-MoO_3 powder were affected by the concentration of ammonium molybdate,HAc and CTAB.The molybdic acid aggregates with diameter of 1-2μm and length of several decades-micron can be obtained by the reaction of higher-concentration ammonium molybdate with HNO_3 in a coex- isting HAc or CTAB solution,repectively.After the as-prepared molybdic acid aggregates are annealed at 500-600℃for 3h,the nanometer-scaled lamellate and sub-micrometer MoO_3 powder are prepared. In addition,irregular molybdic acid aggregates rods are achieved by the reaction of lower-concentration ammonium molybdate with HCl in a coexisting CTAB solution.