Molybdenum Crucible Research Articles

Growth of YAG:Nd laser crystals by Horizontal Directional Crystallization in Protective Carbon‐Containing Atmosphere

AbstractLaser‐quality yttrium‐aluminum garnet single crystals doped with neodymium (YAG:Nd) of a concentration up to 1 at. % is grown by the method of horizontal directional crystallization from a molybdenum crucible in the protective reducing atmosphere based on argon, СО, and hydrogen. It is found that the content of carbon impurity in the grown crystals does not exceed 5·10−3 wt %, the content of molybdenum being on the level of 1.5·10−3 wt %. The optical quality of the crystals depends on the composition of the growth atmosphere and annealing. It is shown that, besides the bands of neodymium ion absorption, the crystals are characterized by the intense absorption in the UV edge of the spectrum at 370 nm wavelength, and by the wide absorption band with a maximum at 580 nm caused by formation of F and F+‐centers. The absorption at 370 and 580 nm can be eliminated by annealing. The structure perfection of the crystals is characterized by the rocking curve half‐width (β) which value varies within the limits of 10–14 arc. sec for (001) plane. Laser testing demonstrates the parameters comparable with those of YAG:Nd crystals grown by the Czochralski method from iridium crucible.

Synthesis of magnesium oxide and zinc oxide powders in a glow discharge plasma at atmospheric pressure

Investigation of the processes involved in the synthesis of magnesium oxide and zinc oxide powders using the thermal effects of an atmospheric-pressure glow discharge plasma in an inert gas flow are described. The discharge operates in a repetitively pulsed mode with pulse repetition rate of several tens of kilohertz and pulse duration up to 12 μs, discharge current of 600 mA and voltage up to 300 V. These parameters lead to thermal erosion of magnesium or zinc inserts in a molybdenum crucible. The chemical and phase composition of the erosion products were determined using TEM/EDS and X-ray diffraction analysis, and the composition of the plasma was assessed by optical emission spectrometry. This experimental approach allows fabrication of powders of these metal oxides with characteristic particle size 10–50 nm, and the formation of coatings of these materials in a one-step process.

Optical and laser characteristics of Сo-doped magnesium-aluminum spinel crystals grown using molybdenum crucible

Single crystals of Co-doped magnesium-aluminum spinel (MALO:Co) are used for Q-switching of laser radiation at λ = 1.54 μm. Usually, they are grown by the Czochralski method from iridium crucibles that are too expensive. This investigation demonstrates the possibility of obtaining MALO:Co single crystals by the horizontal directional crystallization method using a molybdenum crucible in Ar + (CO, H2) protective reducing medium.The obtained MALO:Co crystals have the spinel structure of MgO‧xAl2O3 with 1 ≤ x < 1.15, and the impurity of molybdenum in them does not exceed 0.019 wt%. Co2+ ions replace Mg2+ ions in the [MgO4] tetrahedral environment. This is confirmed by the broad absorption bands (λmax ≈ 600 nm and λmax ≈ 1400 nm) in Vis-IR spectra. The absorption bands in the UV region of the spectrum are shown to originate from the complexes of point defects that can be eliminated by subsequent annealing in oxidizing/reducing environment. Experimentally shown is the possibility to obtain monoimpulses with the energy of ∼ 1–2 mJ and ∼10–15 ns duration at a wavelength of ∼1.54 μm in passive Q-switches based on MALO:Co crystals.

Preparation of Synthetic Titania Slag Relevant to the Industrial Smelting Process Using an Induction Furnace

A high titania slag that is used as a feedstock for TiO2 manufacturing is obtained by ilmenite smelting (FeO.TiO2). The composition of the slag obtained by smelting is dependent on the composition of the mineral used for slag preparation, i.e., ilmenite in our study. At the laboratory scale, ilmenite slags are mostly obtained by using ilmenite as the raw material. An easy and simple way would be to prepare the synthetic slag using the individual components and heating them to high temperature in a furnace. The titania slag has a high oxidizing nature and requires an inert atmosphere to prevent oxidation of the slag as well as the molybdenum crucible. This paper describes the preparation of synthetic ilmenite slag using an induction furnace and the study of the composition and the phases formed in the slag. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and inductively coupled plasma-optical emission spectroscopy (ICP-OES) were used as analytical techniques for studying the slag. A comparison between obtained synthetic slag and industrial ilmenite slag was performed to test the possibility of preparing slags in the laboratory as per the required composition. The slags show similar phase formation as obtained in industrial ilmenite slags, which means that the synthetic slags are identical to the industrial slags.

Study of dynamic refractory wear by slags containing very high FeO contents under steelmaking conditions

ABSTRACT The wear of industrial refractory materials was studied in contact with slag containing high amounts of FeO using the rotating finger technique. The thermodynamic equilibrium of the refractory slag systems was also determined in Thermo-calc® and FactSage™. The studied refractories were alumina spinel, zirconia, graphite, silicon carbide (SiC), magnesia-carbon (MgO-C), chromite (Cr2O3), and MgO-Spinel (MgO–Al2O3). The fingers were rotated in a FeOx (90wt%) – SiO2 (5wt%) – CaO (5wt%) slag for 3 hours in a molybdenum crucible at 100 RPM at 1700K. The wear of the refractory fingers was determined by dimensional changes and changes in composition of the slags. Only MgO-spinel refractories exhibited resistance to the slag. The thermodynamic equilibrium calculations were able to predict the experimental behavior when appropriate databases were used, with the exception of the chromite slag.

Synthesis, Crystal and Electronic Structures, and Electrical Properties of the Fifth Member of the Rb2(Mo9S11)(Mo6nS6n+2) Series: Rb10Mo39S43, an Atypical Reduced Molybdenum Sulfide Containing Mo9 and Mo30 Clusters.

The new compound Rb10Mo39S43 has been synthesized as single crystals by a solid-state reaction in a sealed molybdenum crucible at 1500 °C. It constitutes the fifth member of the homologous series of the trigonal (space group R3̅c) compounds Rb2n(Mo9S11)(Mo6nS6n+2). Consequently, its crystal structure is based on an equal mixture of Mo9S11 and Mo30S32 cluster units interlinked through Mo-S bonds with the Rb+ cations localized in the voids between the Mo9S11 and Mo30S32 units. The coexistence of the two high-nuclearity Mo9 and Mo30 clusters in the crystal structure leads to an unusual c parameter of 163.96(1) Å, and thus, Rb10Mo39S43 is the first ternary and multinary compound in solid-state chemistry to have such a large parameter. Contrary to the first four members, Rb10Mo39S43 was not found to be superconducting down to 2 K. First-principles calculations showed that the electronic structures of this series of compounds can be determined from those of the Mo9 and Mo6n clusters and that fewer interactions between clusters in Rb2n(Mo9S11)(Mo6nS6n+2) occur when n increases.

A re-assessment of the nitrogen geochemical behavior in upper oceanic crust from Hole 504B: Implications for subduction budget in Central America

The geochemical behavior of N during seawater-oceanic crust alteration remains poorly constrained. Yet, it is a central parameter to assess the flux of N to subduction zones. Most studies proposed that hydrothermally altered basaltic rocks are enriched in N relative to fresh basalts. However, published data from DSDP/ODP Hole 504B, a reference site for the composition of the oceanic crust, suggest that seawater alteration leads to the N depletion of the upper ocean crust. To better address this issue, we analyzed N concentration and isotope composition of 21 altered basalts from the lavas and sheeted dikes sampled by Hole 504B. These new analyses show significant N enrichment (up to 14.1 ppm) relative to fresh degassed MORB (∼1 ppm). The differences observed between earlier and modern data are interpreted as resulting from analytical artifact due to the earlier use of a molybdenum crucible for N extraction. Furthermore, our new data show a progressive decrease of N concentration with depth, from 14.1 to 1.4 ppm. Nitrogen isotope compositions display a large range, with δ15N values from −0.9 to +7.3‰, and most likely reflect multiple stages of alteration with fluids of various compositions. In contrast to N concentration, δ15N values do not show a global depth trend but oscillate around a mean value of 3.0 ± 2.2‰ (1SD). The N concentration shows a positive correlation with bulk rock δ18O values, suggesting that N behavior during alteration process is mainly controlled by temperature. We propose that N speciation in the hydrothermal fluid is dominated by NH3/NH4 at low temperature (<200°C) but is transformed to N2, associated with H2, at higher temperature (>200°C). These new data are used to re-evaluate the global flux of N input into Central American subduction zone, showing that the upper basaltic crust represent about 20% of the total N buried in subduction zone. A comparison with previous results obtained on N degassed in volcanic arc illustrates that, in “warm” subduction zone like Central America, up to 50% of the subducted N may be transferred to the deep mantle. This contrasts with “cold” subduction environments, where >80% of the N inputs escape sub-arc slab devolatilization and supports that the geothermal gradient plays a major role in determining the N fate in subduction zones.

Stimulation of densification during the reduction of U3O8 to UO2 by atmosphere control

A reduction process in the head-end for pyroprocessing has been adopted to avoid oxidation attack on the molybdenum crucible during sintering. The reduction process is employed to reduce U3O8 pellets to UO2 prior to sintering. This allows elimination of the oxygen source, which causes oxidation attack during sintering, thereby permitting the use of a metallic crucible. However, little densification occurs due to the low reduction temperature limited by the INCONEL crucible. Consequently, the amount of material scraps from the pellets increases, thus creating an additional processing burden due to its high radioactivity. To reduce the amount of scraps, densification should be enhanced. This study suggests a simple atmospheric control strategy and clarifies its effects. With the atmospheric control, a higher bulk density and better attrition resistance were obtained in comparison to without this strategy. This can be explained in terms of O/U ratio dependent diffusion kinetics during the reduction of U3O8 to UO2.

The role of thermal processes and target evaporation in formation of self-sputtering mode for copper magnetron sputtering

The main focus of the article is the study of function mechanisms of a magnetron sputtering system (MSS) with a heat-insulated metal target in a self-sputtering gasless mode. A distinctive feature of the studied case is that the target evaporation takes place along with its sputtering. The research has been carried out on a copper target sample in molybdenum crucible. It has been found that because of evaporation the MSS can function stably using metal vapors without sputtering gas. The pressure in the chamber is 0.01 Pa. The current-voltage characteristics and spatial distribution of the copper atoms concentration near the target have been determined at the power density from 14 to 72 W/cm2. The minimum power density necessary for a stable gasless self-sputtering mode is 19.4 W/cm2. Herewith the evaporated particles constitute approximately 87% of the total number of copper atoms near the target.It has been found that the erosion coefficients of metal targets at evaporation reach several tens of atoms per ion, which is an order of magnitude higher than the sputtering yield. Due to this, the coatings deposition under self-sputtering conditions takes place without reducing a deposition rate as compared to the case with sputtering gas.

A new method for production of titanium vapor and synthesis of titanium nitride coatings

It is proposed to synthesize on machine parts and cutting tools wear-resistant titanium nitride coatings with the help of the hollow-cathode glow discharge, a molybdenum crucible for titanium evaporation being used as the anode of the discharge and a process vacuum chamber being used as the hollow cathode. The research revealed that at the anode surface area less than a critical value S* = (2 m / M ) 1/2 S , where S is the area of the chamber walls, m is the mass of electrons and M is the mass of ions, the anode fall of potential is positive and grows from ∼50 V at argon pressure p = 0.2 Pa to ∼2 kV at p = 0.02 Pa. At the discharge current I = 0.6 A electrons accelerated by the anode fall of 0.9 kV transport into the crucible with the inner diameter of 12 mm the power of ∼0.54 kW, which allows the titanium evaporation and the coating deposition rate of 5 µm·h −1 on a substrate distanced from the crucible at 100 mm. After the argon is replaced with the nitrogen, titanium nitride coating without titanium droplets is synthesized the deposition rate amounting to about the same value.

Studies on calcium reduction of yttrium fluoride

The reduction of yttrium fluoride (YF3) by calcium in a molybdenum crucible was investigated. A visual observation technique was used to monitor the reduction process. It was observed that the reaction initiated immediately after the melting of calcium. Based on the results, a two-step reduction sequence was attempted. First, the charge was heated to 950°C to minimise the calcium loss by vaporisation and to ensure completion of reaction. The products were then fast heated to 1600°C for slag/metal separation. Molybdenum content of yttrium was found to be in a range of 3.5–4.75 wt-%, which is much lower than the equilibrium content predicted by Mo–Y phase diagram. The yttrium/molybdenum interface was studied using an electron probe microanalyser, which confirmed that the overall equilibrium was not reached, indicating the possibility of lowering the molybdenum contamination further by process optimisation.

High-voltage discharge in supersonic jet of plumbum vapor

During study of vacuum discharge in plumbum evaporating from molybdenum crucible in identical geometry of discharge gap and the same crucible temperature existence of two different discharge forms were observed. These two forms are vacuum arc with current above 10 A and voltage about 15 V and high-voltage discharge with current about 10 mA and voltage of 340 V. Plumbum was placed in heat-isolated crucible (cathode). Electron-beam heater was situated under the crucible. At the temperature of 1.25 kK that corresponds to plumbum saturated vapor pressure about 0.1 kPa voltage from power source (380 V, 200 A) was applied to anode and high-voltage discharge initiated with characteristics mentioned above. After a few seconds this discharge could turn into arc or could exist hundreds of seconds until total plumbum evaporation. Glow of discharge could take the form of a cone, harness or plasma bunch that hanged at the appreciable distance from the electrodes. The estimations of plasma parameters are presented.

Growth and characterization of large-scale Ti:sapphire crystal using heat exchange method for ultra-fast ultra-high-power lasers

Large-scale titanium-doped sapphire (Ti:sapphire) crystal was grown in a 380 mm diameter molybdenum crucible using the heat exchange method (HEM) and characterized. The diameter of the core Ti:sapphire single crystal was estimated to be slightly larger than 200 mm. A Ti:sapphire crystal wafer 157 mm in diameter and 28 mm thick was obtained. Characterization based on X-ray diffraction spectroscopy, Raman spectroscopy, and absorption and fluorescence spectroscopy was carried out. The as-grown Ti:sapphire crystal had high intrinsic quality and a large figure of merit (FOM) without additional annealing. The high optical quality of the as-grown Ti:sapphire crystal indicated it is suitable for ultra-fast ultra-high-power lasers in chirped pulse amplification systems.

Drawability and frictional behavior of pure molybdenum sheet in deep-drawing process at elevated temperature

Forming of pure molybdenum crucible is greatly demanded for its broad application in production of single crystal sapphire. To fabricate molybdenum crucible and other sheet metal products of molybdenum, it is necessary to determine the limiting draw ratio and frictional data with the aid of finite element analysis to reduce the massive experiments. To ensure the accuracy of finite element analysis, it is crucial to determine the reproducible frictional data. In this study, an evaluation methodology combined hot deep-drawing test with numerical simulation used to investigate the formability and tribological behavior of pure molybdenum at elevated temperature. For calculation of friction coefficient, the isothermal deep-drawing tests were carried out at the temperature ranging from 993 to 1143 K under lubricated and dry conditions. According to the predicted relation between frictional coefficient and forming temperature, the influences of forming temperature, lubrication, and blank diameter on friction are discussed, and the limiting draw ratios of molybdenum sheet at various temperatures are obtained. It is found that there is a significant improvement in drawability of pure molybdenum from 1.2 at room temperature to 1.98 at 1143 K by using boron nitride lubricant. However, the effect of forming temperature on the formability of molybdenum sheet is not significant under dry friction condition. Compared with the experimental results, the method used for evaluation of the formability and friction characteristic in hot deep drawing of molybdenum sheet is verified efficiently.

Crystal Growth and Magnetic properties of RMg3 (R = La, Ce and Nd)

We have successfully grown the single crystals of RMg3 (R = La, Ce and Nd) compounds by Bridgman method, in a sealed molybdenum crucible. These compounds crystallize in the cubic BiF3-type structure with the space group Fm3̄m. The powder x-ray diffraction pattern clearly revealed that the samples were single phase without any impurity. The crystals were oriented by means of Laue back reflection method for the magnetic and transport measurements. It has been found that CeMg3 orders antiferromagnetically at TN = 2.6 K, while NdMg3 shows two magnetic orderings with TN1 = 6.8 K and TN2 = 2.8 K respectively. The magnetic part of the electrical resistivity of CeMg3 exhibited a double peak structure and the magnetization measurement revealed a reduced magnetic moment of 0.5 μB/Ce. The heat capacity measurement of CeMg3 measured down to 0.5 K exhibited an enlarged Sommerfeld coefficient of 370 mJ/K2 mol. From the Schottky heat capacity we have estimated the crystal electric field split energy levels of CeMg3 and NdMg3.

Synthesis, Crystal and Electronic Structures, and Thermoelectric Properties of the Novel Cluster Compound Ag3In2Mo15Se19

Polycrystalline samples and single crystals of the new compound Ag3In2Mo15Se19 were synthesized by solid-state reaction in a sealed molybdenum crucible at 1300 °C. Its crystal structure (space group R3̅c, a = 9.9755(1) Å, c = 57.2943(9) Å, and Z = 6) was determined from single-crystal X-ray diffraction data and constitutes an Ag-filled variant of the In2Mo15Se19 structure-type containing octahedral Mo6 and bioctahedral Mo9 clusters in a 1:1 ratio. The increase of the cationic charge transfer due to the Ag insertion induces a modification of the Mo–Mo distances within the Mo clusters that is discussed with regard to the electronic structure. Transport properties were measured in a broad temperature range (2–1000 K) to assess the thermoelectric potential of this compound. The transport data indicate an electrical conduction dominated by electrons below 25 K and by holes above this temperature. The metallic character of the transport properties in this material is consistent with electronic band structure calculations carried out using the linear muffin-tin orbital (LMTO) method. The complex unit cell, together with the cagelike structure of this material, results in very low thermal conductivity values (0.9 W m–1 K–1 at 300 K), leading to a maximum estimated thermoelectric figure of merit (ZT) of 0.45 at 1100 K.

Enthalpy of formation of the CaLi2 phase

The solution calorimetric method was used for the determination of the formation enthalpy of the CaLi2 intermetallic phase and the heat of solution of the components. The phase was prepared in a glove box with high purity argon protective atmosphere by means of melting proper amounts of calcium and lithium in a molybdenum crucible at 350 °C (623 K). The X-ray structure analysis confirms the existence only the CaLi2 phase in the alloy. With the application of liquid aluminum and tin as the metallic bath, the calorimetric investigations were conducted at 746 °C (1019 K) and 399 °C (672 K), as well as 853 °C (1126 K). On the basis of the data from this study and from the literature, the temperature dependencies of the heat of solution of the calcium and lithium in the liquid aluminum and tin were determined in the form of linear equations. The formation enthalpies of the CaLi2 intermetallic phase obtained in these two types of investigations are comparable to each other and they are equal to −2.7 ± 1.3 and −2.9 ± 1.7 kJ/g-atoms for the Al and Sn-bath, respectively.

Near-Net-Shape Molybdenum Parts Produced by Plasma Spray Forming

Complex and thin-walled refractory metallic parts including molybdenum (Mo) rocket nozzle and crucible were fabricated using plasma spray forming (PSF) followed by hot isostatic pressing (HIPing). Optical microscope (OM), scanning electron microscope (SEM), Archimedes method, Vickers hardness and tensile tests have been employed to study microstructure, density, micro-hardness and mechanical properties of the parts. A lamellar structure consisting of vertical columnar grains, micron-sized pores, partially melted particles and rough interlamellar contacts with gaps of sub-micron sizes between lamellae were found in PSF Mo deposits. Relative density, micro-hardness and ultimate tensile strength (UTS) of the deposits were about 89%, 150 HV0.025 and 44 MPa, respectively. After low-pressure and two-step HIPing, those changed up to about 92%, 250∼400 HV0.025 (interior ∼ exterior layers), 93 MPa, and 97%, 325 HV0.025 and 170 MPa, respectively. Moreover, a four-stage mechanism of HIPing for PSF parts including heating up, recrystallization, lamellae movement, plastic yielding and creep has been proposed and discussed in detail.

ChemInform Abstract: Synthesis of Tantalum Tellurides: The Crystal Structure of Ta2Te3.

Abstract Ta2Te3 was prepared by reducing TaTe2 with tantalum at 1350 K in a sealed molybdenum crucible. Ta2Te3 disproportionates above 1420 K yielding the ditelluride and as yet unknown Ta6Te5. The stability limit for the substitutional sesquitellurides NbxTa2−xTe3 is reached at x ≈ 1 . The novel layered-type structure of Ta2Te3 (C 2/m, N=4; a=2049.5(3) pm, b=349.96(4) pm, c=1223.7(2) pm, β=143.74(1)0 (Guinier), N(I0)=762 with I0>2σ(I0), 32 variables, R=0.032) can be considered a stuffed variant of a molybdenite structure type. It consists of corrugated layers ∞ 2 ( Te-Ta 4 3 - Te ) which, according to the shortest interlayer contacts TeTe (372.9 pm), order via van der Waals interactions. Extended homonuclear bonding regions (297.1 pm ≤ dTaTa≤ 309.7 pm) within the metal layers contribute to the stability of the metallic sesquitelluride.

Organized Formation of 2D Extended Covalent Organic Frameworks at Surfaces

The development of nanoscale masking for particle deposition is exceedingly important to push the future of nanoelectronics beyond the current limits of lithography. We present the first example of ordered hexagonal covalent nanoporous structures deposited in extended arrays of near monolayer coverage across a Ag(111) surface. The networks were formed from the deposition of the reagents from a heated molybdenum crucible between 370 and 460 K under ultrahigh vacuum (UHV) onto a cleaned Ag(111) substrate and imaged using a scanning tunneling microscope (STM). Two surface covalent organic frameworks (SCOFs) are presented; the first is formed from the deposition of 1,4-benzenediboronic acid (BDBA) and its dehydration to form the boroxine-linked SCOF-1, the second is formed from the co-deposition of BDBA and 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) to form a dioxaborole-linked SCOF-2 network. The networks were found to produce nanoporous structures of 15 A for SCOF-1 and 29 A for SCOF-2, which agreed with theoretical pore sizes determined from DFT calculations. Both SCOFs were found to have exceptional thermal stability, maintaining their structure until approximately 750 K, which was found to be the polymer degradation temperature from thermal gravimetric analysis (TGA).