Crucible Material Research Articles

Some practical aspects of heat capacity determination by differential scanning calorimetry

Differential Scanning Calorimetry (DSC) is a widely accessible and versatile method for the determination of the heat capacities of organic materials as a function of temperature. In routine use, it is typically possible to obtain results with an accuracy better than 3 %. However, to achieve this level of accuracy, careful optimization of the experimental procedure for a specific apparatus must be performed. Using benzoic acid as a test substance, this work highlights some practical aspects of heat capacity measurements by DSC, such as crucible material and its geometry, heating rate, thermal lag, the selection of a suitable pre-stabilization stage before the measurement and the duration of the experiment, that can have a strong influence on the quality of the obtained results.

Effect of Crucible Material on Inclusions in 55SiCr Spring Steel

Effect of Crucible Material on Inclusions in 55SiCr Spring Steel

The Impact of Sample Homogeneity, Crucible Material, and Oxygen Partial Pressure on the Crystallization of Fe-Rich Oxidic Slag in CLSM Experiments

Crystallization tendency and the state of oxidic slags are important influencing factors for slag viscosity and therefore slag tapping. During the gasification process slag is constantly produced and flows down the gasifier walls until it is intercepted and stored for further treatment or a possible valorisation. The kinds of fuel used for gasification lead to different kinds of slag composition likewise. Slag viscosity is strongly influenced by the composition of the slag and the temperature. However, the process of crystallization represents another major influencing factor. Slag crystallization is also affected by several parameters, whose effects need to be considered in experimental studies. This study investigated the impact of the sample state, the chosen crucible material, and the oxygen partial pressure on the crystallization of a Fe-rich oxidic slag in the confocal laser scanning microscope (CLSM) experiment. Using sample powder may lead to heterogeneous nucleation and crystallization during heating due to heterogeneous melting of the compounds. The selection of crucible material is crucial to prevent alloy formation of Fe-species with Pt-crucibles under reducing atmosphere. Finally, the partial pressure of oxygen influences the crystallization tendency as well as the morphology of the crystallized phases. These parameters impede the reproducibility of results as well as the comparison with results deriving from other experiments like sample quenching. This contribution provides an enhanced understanding of the stated parameter effects on the experimental investigation of oxidic slags using the CLSM setup and yields advice to prevent experimental influence on the results.

Exploration of Multi-Component Vanadium and Titanium Pnictides Using Flux Growth and Conventional High-Temperature Methods.

The flux growth method was successfully employed to synthesize millimeter-sized single crystals of the ternary barium vanadium pnictides Ba5V12As19+x (x ≈ 0.02) and Ba5V12Sb19+x (x ≈ 0.36), using molten Pb and Sb, respectively. Both compositions crystallize in space group P3m and adopt a structure similar to those of the barium titanium pnictides Ba5Ti12Pn19+x (Pn = Sb, Bi), yet with a subtly different disorder, involving the pnictogen and barium atoms. Attempts to obtain an arsenide analog of Ba5Ti12Pn19+x using a Pb flux technique yielded binary arsenides. High-temperature treatment of the elements Ba, Ti, and As in Nb or Ta tubes resulted in side reactions with the crucible materials and produced two isostructural compositions Ba8Ti13−xMxAs21 (M = Nb, Ta; x ≈ 4), representing a new structure type. The latter structure displays fcc-type metal clusters comprised of statistically distributed Ti and M atoms (M = Nb, Ta) with multi-center and two-center bonding within the clusters, as suggested by our first-principle calculations.

Synthesis of tetragonal solid-state electrolyte Li7La3Zr2O12

Solid-state electrolyte (SSE) with tetragonal structure Li7La3Zr2O12 (LLZO) is prepared by solid state reaction. Investigation of heat treatment temperature and time are observed. Increasing temperature from 700 °C to 950 °C improves structure purity and stability. Synthesis at 700 °C show appearance of La2Zr2O7 phase, however 750 °C synthesis sample material is free of that impurity. Heat treatment time exhibits the biggest sintering time provide small amount of Li2CO3 impurity. Crucible material influences by formation of Li2ZrO3 and Li2CO3 impurities at 900 °C and 6 h synthesis.

Multifunctional optical thermometry based on the stark sublevels of Er3+ in CaO‐Y2O3: Yb3+/Er3+

AbstractA conventional high temperature solid state method was utilized to prepare CaO‐Y2O3, which is a potential candidate for manufacturing crucible material to melt titanium and titanium alloys with low cost. Meanwhile, Yb3+ ions and Er3+ ions were selected as the sensitizers and activators respectively to dope into CaO‐Y2O3, aimed at providing real‐time optical thermometry during the preparation process of titanium alloys realized using fluorescence intensity ratio (FIR) technology. The results reveal that a high measurement precision can be acquired by using the Stark sublevels of Er3+ 4F9/2 to measure the temperature with a maximum absolute error of only about 3 K. In addition, by analyzing the dependence of 4I13/2 → 4I15/2 transition on pump power of 980 nm excitation wavelength, it was found that the laser‐induced thermal effect has almost no influence on the temperature measurement conducted by using the FIR of the Stark sublevels of Er3+ 4I13/2, which means that a high excitation pump power can be used to obtain strong NIR emission and good signal‐to‐noise ratio for optical thermometry without the influence of the laser‐induced thermal effect. All the results reveal that CaO‐Y2O3: Yb3+/Er3+ is an excellent temperature sensing material with high measurement precision.

SiC-conversion coating from silica sol for improved oxidation resistance of carbon-fiber insulator in solar-cell ingot-growing crucibles

Carbon fibers, which have excellent mechanical and thermal properties, are used in many fields; however, they are very vulnerable to oxidation and have limited service life. Various studies have attempted to address this. In this study, a SiC–C composite material was prepared using a silica sol to coat the carbon surface and improve the oxidation resistance of a carbon-fiber insulator as a material for solar-cell ingot-growing crucibles. The SiC coating was formed on the carbon surface under various conditions by controlling the composition of the silica sol, and its characteristics were examined. Via SiC-conversion coating through a carbothermal reaction, a film of thickness 30–80 nm film was uniformly formed over the entire sample. In addition, the oxidation characteristics were enhanced by a factor of three to five, when compared with conventional carbon materials.

ARTEC-A furnace module for directional solidification and quenching experiments in microgravity.

A new experimental design for directional solidification experiments with high cooling rates under microgravity conditions is presented. The aerogel-based furnace module ARTEC (AeRogel TEchnology for Cast alloys) developed at DLR extends the earlier presented sounding rocket facility ARTEX by enabling a transition from low to high solidification velocities and a simultaneous operation of five independent furnaces in the same sounding rocket module. The furnaces for directional solidification are equipped with thermally insulating aerogels as a crucible material. Their optical transparency allows the control of the solidification parameters (velocity and temperature gradient) with optical methods in the lab. In ARTEC, a drastically increased solidification velocity is achieved by contacting the sample with a movable cooling-rod during processing. Therefore, a better theoretical understanding of the influence of a sudden change in solidification velocity on microstructure formation is obtained. Carrying out experiments in microgravity gives access to purely diffusive solidification conditions. Hence, convection free-growth can be compared with growth subject to natural (earth) and/or forced-convection (earth and space). Furthermore, alloys with high density differences in their alloy components and, hence, also between the primary solidifying phase and the surrounding liquid can be studied without the negative influence of fluid-flow or macrosegregation being present.

Metallothermic Al-Sc Co-Reduction by Vacuum Induction Melting Using Ca

Due to its enhancing properties in high-tech material applications, the rare earth element Scandium (Sc) is continuously gaining interest from researchers and material developers. The aim of this research is to establish an energy and resource efficient process scheme for an in situ extraction of Al-Sc master alloys, which offers usable products for the metallurgical industry. An AlSc20 alloy is targeted with an oxyfluoridic slag as a usable by-product. The thermochemical baseline is presented by modelling using the software tool FactSage; the experimental metal extraction is conducted in a vacuum induction furnace with various parameters, whereas kinetic aspects are investigated by thermogravimetric analysis. The Sc-containing products are analyzed by ICP-OES/IC concerning their chemical composition. Optimum parameters are derived from a statistical evaluation of the Sc content in the obtained slag phase. The material obtained was high in Ta due to the crucible material and remarkably low in Al and F; a comparison between the modelled and the obtained phases indicates kinetic effects inhibiting the accomplishment of equilibrium conditions. The formation of a Sc-rich Al-Sc phase (32.5 wt.-% Sc) is detected by SEM-EDS analysis of the metal phase. An in situ extraction of Al from Ca with subsequent metallothermic reduction of ScF 3 as a process controlling mechanism is presumed.

Unmolded Diatomite Based Heat Insulating Material for Aluminum Alloys

Results are provided for a study of diatomite of the Il’insk field (Sverdlovsk region) for preparation of unmolded insulation materials and their use as heat insulating materials in crucibles with molten aluminum. Use of diatomite as a heat insulating material makes it possible to reduce power consumption during holding molten aluminum in the resistance furnace crucible, prevents development of hydrogen porosity, and does not lead to melt saturation with silicon.

The influence of Prandtl numbers of melts and crucible materials on the features of crystal growth by the Bridgman method

The processes of crystallization of silicon and heptadecan in flat-bottomed cylindrical crucibles in conjugate convective heat transfer regime were studied numerically by the finite element method. Crystallization of silicon was investigated in a graphite crucible. Crystallization of heptadecane was investigated in a Plexiglas crucible. The possibility of existence of two convective vortices over a solidification front during the crystallization of silicon and heptadecane has been discovered. Crystallization of heptadecane was studied at two rates of lowering the crucible into the cold zone. Lowering of the crucible was simulated by moving the breakpoint in the temperature distribution on the outer side of the crucible walls. The breakpoint was the boundary of transition from the wall area heated to the initial temperature to the area with a given temperature gradient. Adaptive grids on triangles tracking the position of the crystallization front at each time step were used. The software package of developed by the authors was used.

NU-DIE ESR

Abstract Crucible Nu-Die ESR is a remelted version of H13 tool steel and offers better transverse toughness than standard H13. See also NUDIE V, Alloy Digest TS-276, October 1974, and NU-DIE XL, Alloy Digest TS-467, December 1986. This datasheet provides information on composition, physical properties, hardness, and elasticity. It also includes information on high temperature performance. Filing Code: TS-782. Producer or source: Crucible Materials Corporation.

Unshaped diatomite based heat insulating material for aluminum alloys

The results of the study of diatomites of the Ilinsky field (Sverdlovsk region) for the manufacture of unshaped insulation materials and their use as insulating materials in crucibles with aluminum melt are presented. The use of diatomite as a heat insulating material reduces the power consumption during the exposure of the aluminum melt in the crucible resistance furnace, prevents the appearance of hydrogen porosity and does not lead to saturation of the melt with silicon. Ill. 4. Ref. 7. Tab. 2.

Modification of silicophosphate glass composition, structure, and properties via crucible material and melting conditions

AbstractCeramic crucibles are known to corrode in contact with glass melts. Here, we investigate the effect of alumina and fused silica crucibles on the composition, structure, and properties of silicophosphate glasses. Glasses in the system 0.3 Na2O‐0.6 P2O5‐0.1 SiO2 were melted in platinum, alumina, or fused silica crucibles at 900°C or 1200°C for 0.5‐12 hours. Al2O3 and SiO2 were found to leach from the crucibles into the glass melt and alter the glass composition: Al2O3 content increased with melting temperature and time, resulting in up to 10 mol% Al2O3; SiO2 from fused silica crucibles was also introduced into the glass, resulting in a 25% higher SiO2 content compared to the nominal composition. Glass density, transition temperature, thermal expansion, and mechanical properties were strongly affected by these compositional changes. Based on vibrational spectroscopy, this is explained by increasing numbers of P–O–Al or P–O–Si bonds, resulting in a depolymerization of the phosphate network, and ionic cross‐linking by high field strength aluminum or silicon ions. With increasing alumina content, P–O–Si bonds were replaced by P–O–Al bonds. 31P and 27Al MAS NMR spectra revealed that aluminum is present in sixfold coordination exclusively and fully bonded to phosphate species, connecting phosphate groups by P–O–Al–O–P bonds.

The possibility of using high-quality fused magnesia in the manufacture of crucibles for vacuum-induction melting

The prospect of using crystalline fused magnesia (FL LC) in the manufacture technology of melting crucibles by the method of isostatic pressing is shown. It has been established that the production of a material based on MgO using concrete technology is limited to the hydration and loosening of the structure due to the formation and subsequent decomposition of brucite (native magnesia). The physical and mechanical characteristics of the obtained products are given. The effect of the CaO/SiO2 ratio on the corrosion and erosion resistance of products is considered. The raw material should have a molar ratio of these oxides of more than 1,7. Pressed crucibles were tested in the production of nickel, cobalt and tin based alloys in a vacuum induction furnace. The parameters of operation of products in the enterprise are shown. The effect of clogging by crucible materials during smelting of pure nickel has also been studied. The absence of contamination of the melt with crucible materials such as silicon dioxide, aluminosilicates and oxide films, etc., has been established.

ИССЛЕДОВАНИЕ МЕТАЛЛИЧЕСКОГО ТОПЛИВА U-10%Zr ДЛЯ ЯДЕРНО-ЭНЕРГЕТИЧЕСКИХ УСТАНОВОК

Currently, there is an increased interest in the development of uranium-zirconium metal fuel. Abroad, rods for fuel elements are manufactured by induction melting followed by injection casting. The casting of fuel rods is carried out in quartz test tubes with an inner coating of yttrium oxide. In the JSC “SSC RF - IPPE”, work was carried out on the manufacture and research of some basic properties of fuel slugs of the U-10%Zr alloy. Fuel slugs were made by melting of uranium and zirconium in an arc furnace, subsequent melting of ingots in quartz test tubes in a vacuum furnace and turning to the desired size on a lathe. Obtained slugs of U-10%Zr had a density of 16.35 g/cm3, lamellar structure consisting of the phases α-U and δ-UZr2. The results of studies on the interaction of fuel with materials of test tubes and crucibles have shown that yttrium oxide is the most suitable material for melting crucibles or coatings. It is also possible to use ZrO2-Y2O3, followed by grinding the fuel rods.

Study on N and B Doping by Closed Sublimation Growth Using Separated Ta Crucible

Boron (B) doping sources and crucible materials for stable, reproducible and high concentration B doping in fluorescent SiC (f-SiC) were investigated. When a Ta crucible was used with BN powder as a B doping source were used, B doping did not occur owing to too low C/Si ratio. On the other hand, when a C crucible and suitable Ta components inside the crucible were used, a high B concentration of 1.58 × 1019 cm-3 was obtained, owing to the high C/Si ratio. The results indicate that a C crucible with optimal Ta components and BN powder are suitable for high concentration B doping.

Stability of Tungsten Crucible against Uranium, Rare Earth, Cadmium, and Chlorides for Cathode Process in Pyroprocessing

The stability of W against U, rare-earth (RE) elements, Cd, and various chlorides was evaluated by melting and distillation testing. Three runs were performed with a W crucible to examine its reactivity: (i) RE melting by induction heating, (ii) salt distillation test of U-dendrite and various chlorides, and (iii) Cd distillation test from U–Cd alloy. The W crucible remained stable after the RE melting test using induction melting, exhibiting its applicability for induction heating systems. The salt distillation test with the W crucible at 1050°C exhibited the stability of W against U and various chlorides, showing no interaction. The Cd distillation test with the W crucible at 500°C showed that the crucible was very stable against Cd, maintaining a shiny surface. These results reveal that the W crucible is stable under operation conditions for both salt and Cd distillation, suggesting the high potential utility of W as a crucible material for application in cathode processes in pyroprocessing.

Structure and dynamics of glass-forming alloy melts investigated by application of levitation techniques

Abstract In this work results of studies on the short-range order and on the atomic dynamics in different stable and undercooled glass-forming metallic melts are reviewed. In order to undercool the melts deeply below the melting temperature and to avoid chemical reactions of the melts with crucible materials, the samples are containerlessly processed utilizing the electromagnetic or the electrostatic levitation technique. The short-range structure of the melts is studied by neutron diffraction, while the atomic dynamics are investigated by quasielastic neutron scattering. The relationship between short-range structure and atomic dynamics is discussed within the mode coupling theory of the glass transition. We will show that taking the time- and space-averaged structural information provided by measured partial structure factors as an input, mode coupling theory is able to explain the experimental results concerning the activation energies for self-diffusion and the coupling/decoupling behavior of the self-diffusion coefficients of the different alloy components.

Pyrolytic carbon coating of fused quartz by vacuum vapor transport

Fused quartz has excellent thermal and chemical properties as crucible material for single crystal growth from melt, and its high purity and low cost makes it especially attractive for the growth of high-purity crystals. However, in the growth of certain types of crystals, a layer of pyrolytic carbon coating is needed between the melt and the quartz crucible. In this article, we describe a method for applying pyrolytic carbon coating by vacuum vapor transport. The method is shown to be effective in yielding relatively uniform coating on a wide range of crucible sizes and shapes. The resultant pyrolytic carbon coating is characterized by optical attenuation measurements. In each coating process, the thickness of coating is shown to approach a terminal value with an exponential tail as the duration of pyrolysis increases, and the average thickness roughly increases linearly with the ratio of the volume of available hexane vapor to the surface area of pyrolytic coating. Quartz crucibles coated by this process have been used to successfully grow up to 2-in-diameter NaI single crystals, and the surface quality of NaI crystal was found to improve as the thickness of coating increases.