Alumina Crucible Research Articles

Prediction of Ce(III) Electrodeposition at Various Electrochemical Conditions in Molten LiCl-KCl Eutectic

Molten salt is one of the widely used liquid media for a selective extraction through electrolysis. In the nuclear industry, pyroprocessing which utilizes LiCl-KCl molten salt in its core unit processes is suggested as a candidate of non-proliferative fuel recycling process. In an electrorefiner, the uranium metal is selectively collected on a solid electrode through the electrochemical reduction of uranium ion dissolved in LiCl-KCl. The deposit shows a dendritic characteristic which dramatically increases an electroactive surface area of the working electrode. As the surface area increases, current density decreases, and the overall electrochemical condition including potential gradient and exchange current along the diffusion layer is, therefore, changed as well in a real time. Despite of its critical influence on the precision of process simulation, there is no model which reflects this transient change of the electrode. In this work, cerium is selected as a surrogate of uranium. Its behaviors of electrodeposition at various conditions (time, current, concentration, and overpotential) are investigated, and a methodology for quantitative prediction of deposit formation on the working electrode is suggested. All sample preparation and experiments were carried out in a glove box filled with high purity argon gas (99.9999 % Ar, [H2O] and [O2] < 1ppm). Oxidation or hydrolysis was completely avoided in advance. 44 wt.% of LiCl and 56 wt.% of KCl (both 99 % purity, anhydrous, Sigma-Aldrich) were mixed for the preparation of LiCl-KCl eutectic. This eutectic and CeCl3 (99.99 % purity, anhydrous, Sigma-Aldrich) were put together into an alumina crucible. This sample was placed in a high temperature furnace which sustained the temperature 773 ± 2 K. Two 1 mm diameter tungsten rods were used as working and counter electrodes, and a silver wire was immersed in 1 wt.% AgCl-LiCl-KCl as the reference electrode. All electrochemical experiments were performed with a potentiostat (Autolab, PGSTAT302N). Prior to the electrodeposition, cyclic voltammetry (CV) was measured to obtain redox peak of cerium and to check the existence of impurity in a system. Then chronoamperometry (CA) was carried out at a fixed potential of -2.05 V (vs. 1 wt.% Ag/AgCl), which is slightly more negative value than that of the reduction peak for successful electrodeposition. As shown in Figure 1, CA plots showed three different characteristics as the concentration of Ce(III) increased. At low concentration (< 0.45 wt.%, black plots), almost constant or gradual increase of current flow was observed. On the other hand, at high concentration (0.48 wt.% >, red plots), the magnitude of current flow increased drastically with illustrating clear linear slope. Therefore, it can be interpreted that, under the same condition of applied potential, the larger the concentration, the greater the current flow due to more electroactive species around the electrode, and thus the larger the growth of the surface area with the larger amount of electrodeposition. At the concentration between 0.45 wt.% and 0.48 wt.% of Ce(III), the CA plot expressed an intermediate behavior which can be shifted from one to the other characteristic at any time depending on the formation of deposit. Even though the CA plots showed different characteristics based on the concentration parameter, they all sketched linear trend. The amount of charge transferred which corresponded to the amount of metal deposit was able to be expressed as a function of time with slope and y-intercept. The slopes of CA plots at high concentration condition were directly proportional to the concentration. The y-intercept, the first plateau of CA plot, could be defined from the current of reduction peak of CV, which is proportional to the concentration. The current signal of reduction peak was affected by immersed depth of working electrode and overpotential. In conclusion, under assumption of no physical detachment or loss of electrodeposit, the preliminary prediction of the amount of electrodeposit was possible with three parameters (time, concentration, and overpotential) which were substantially related to the determination of induced current during CA experiment. This prediction should be achieved in a scrupulous way with consideration of concentration parameter because of different behaviors of electrodeposition. Figure 1

OSL properties of KMgF3:Tm3+ for dosimetric applications as OSL dosimeter

The optically stimulated luminescence (OSL) properties of undoped and Tm3+-doped KMgF3 fluoroperovskite have been investigated for the first time. KMgF3 compounds were synthesized by solid state reaction method and two different procedures were employed to improve the contact among the reagents, namely, the compressed powder was put either in an alumina crucible or in a platinum foil. The maximum OSL emission was found in samples prepared in an alumina crucible and doped with 0.5% mol of thulium. The radioluminescence (RL) spectrum shows two emission peaks at 455 and 360 nm, which can be ascribed to the 1D2–3F4 and 1D2–3H6 transitions of Tm3+ cations. The OSL dosimetric properties of the most promising composition, namely, KMgF3:Tm3+ (0.5% mol), have also been determined and analyzed. This compound exhibits good linearity in the dose range from 0.1 up to 100 Gy and satisfactory repeatability with a percentage standard deviation of 2.4%. Therefore, an OSL fading of approximately 75% in the first 36 h of storage is observed and then, the response remains almost constant. These characteristics, together with a minimum detectable dose of 0.04 Gy and the rapid erasing of the OSL signal after 100 s of stimulation, which makes feasible to bleach completely the residual OSL in order to restore the sample between dose measurements, suggest the potential of this perovskite as OSL dosimeter.

Preparation and characterization of monoclinic rod-shaped ZrO2 whiskers via sulfate flux

Monoclinic rod-shaped ZrO2 whiskers were prepared in liquid conditions using a sulfate flux with ZnSO4 and Na2SO4 in an alumina crucible. TG-DSC, XRD, SEM, TEM, HRTEM, SAED and EDS were employed to characterize the structure, morphology and growth mechanism of the as-synthesized whiskers. The results demonstrated that both the heating temperature and holding time influence the formation of ZrO2 whiskers. When the heating temperature and holding time were 900 °C and 30 min, the ZrO2 whiskers were elongated along the [01¯1] direction, had an average length and diameter of 600 nm and 70 nm, and exhibited a well-crystallized, one-dimensional structure and smooth surface with no distinct defects. The growth of the whiskers was dominated by the liquid-solid (LS) growth mechanism, affording anisotropic growth through dissolution/recrystallization.

Solution combustion synthesis of the nanocrystalline NCM oxide for lithium-ion battery uses

In this study, the NCM cathode with a chemical composition of were synthesized through a solution combustion method. In this method, metal nitrates and urea were used as precursors and fuel, respectively. The powder obtained from combustion were transferred into a alumina crucible and insert to the muffle furnace and calcined at 750 °C for 15 h. The crystallite size of the sample was calculated with sherer equation to be about 41 nm. The prepared cathode were characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry analysis (TGA), differential scanning calorimetry (DSC) and battery charge-discharge test. The initial charge and discharge capacities of electrode containing 94% active material at a rate of 0.05 C in voltage window of 2.5–4.3 V at room temperature was obtained 168.03 and 150.01 mAh g−1, respectively.

Influence of crucible material on the microstructure and properties of iron rich glass-ceramics

Slag glass melting is usually performed on a laboratory scale in crucibles, which are economically viable tools for the production of slag glass-ceramics. In this work, quaternary CaO-Al2O3-MgOSiO2 (CAMS) glass-ceramics were prepared by melting the tailing of Bayan Obo mine tailing, blast furnace slag, and fly ash in alumina and graphite crucibles. The effect of the crucible material on the microstructure and properties of the glass-ceramics was investigated using differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and inductively coupled plasma atomic emission spectroscopy. Results indicated that the contents of Al2O3 and Fe2O3 in the initial glass were significantly changed by the corrosion of the alumina crucibles during the glass melting process and by the reducing action of the graphite crucibles. The main crystal phases of glass-ceramics melted in alumina crucibles and graphite crucibles were Ca (Mg, Fe, Al) (Si, Al)2O6, coesite and Ca (Mg, Al) (Si, Al)2O6, respectively. According to these findings, we conclude that the microstructure and properties of the glass-ceramics are affected by the crucibles.

Thermal properties and crystallization of MgO–FeOx–P2O5 glasses

Differential scanning calorimetry (DSC), dilatometry and X-ray diffraction have been used to study thermal behavior and stability of glasses prepared simultaneously in Al2O3 or Pt crucibles in compositional series (40 − x)MgO–xFe2O3–60P2O5 within the concentration range of x = 0–40 mol% Fe2O3. Mossbauer spectra showed that all glasses with Fe2O3 contained both Fe(II) and Fe(III) ions. The contamination glasses from alumina crucibles ranged from 0.3 to 0.9 mol% Al2O3. The replacement of MgO by Fe2O3 resulted in a gradual decrease in glass transition temperature and dilatometric softening temperature, whereas thermal expansion coefficient did not change significantly. The DSC curves showed that all glasses crystallize on heating in the broad temperature range ≈ 560–900 °C. Crystallization temperature decreases with increasing Fe2O3 content. The highest tendency toward crystallization was found for the glass containing 40 mol% Fe2O3. X-ray diffraction measurements showed that the major compounds formed by glass crystallization were Mg(PO3)2, Fe(PO3)3, Fe3(P2O7)2 and FePO4. All thermoanalytical studies showed differences in thermal behavior of glasses prepared in Al2O3 or Pt crucibles.

In crucible reduction of mill scale by lean grade coal: Study of time, temperature and arrangement for optimum reduction conditions

The research work involves the reduction of mill scale by lean grade coal with limestone powder (90% lean grade coal + 10% limestone powder) in an alumina crucible. The ratio of mill scale and coal with limestone powder was taken in the ratio of 1: 1.25 and all raw materials of particle size ranging between 90 to 150 microns. Study of the effect of reduction time (60, 90, 120 minutes), temperature (850, 900, 950°C) and arrangements (mixed, central, alternate concentric) in crucible have been investigated. It has been found out the mill scale sample reduced for 90 minutes at 900°C in the alternate concentric way, showed the optimum conditions for reduction, in which metallic iron found to be 64.64% and the corresponding degree of metallization is 96.0516%. With the increase in time and temperature, reduction increases and later becomes constant or shows very slow inclination in reduction value.

Switching on a Spin Glass: Flux Growth, Structure, and Magnetism of La11Mn13-x-yNixAlySn4-δ Intermetallics.

Reactions of tin and manganese in a lanthanum/nickel eutectic melt in alumina crucibles produce La11Mn13-x-yNixAlySn4-δ (0 ≤ x ≤ 3.6; 2.5 ≤ y ≤ 4.9; 0.6 ≤ δ ≤ 1.1) phases with the stoichiometry dependent on the reactant ratio. These compounds crystallize in a new tetragonal structure type in space group P4/mbm, with a = 8.4197(1) Å, c = 19.2414(3) Å, and Z = 2 for La11Mn8.2Ni0.8Al4Sn3.3. The structure can be viewed as an intergrowth between La6Co11Ga3-type layers and Cr5B3-type La/Sn slabs. This system represents a unique playground to study the itinerant magnetism of diluted icosahedral Mn layers. The dilution of manganese sites in the Mn/Ni/Al layer with nonmagnetic elements has a significant effect on magnetic properties, with low Mn content analogues being paramagnetic and higher Mn content analogues such as La11Mn10Al3Sn3.4 exhibiting spin-glass behavior with a freezing transition at 20 K. The lack of long-range magnetic ordering is confirmed by heat capacity and resistivity measurements.

Effect of Alumina Incorporation on the Surface Mineralization and Degradation of a Bioactive Glass (CaO-MgO-SiO₂-Na₂O-P₂O₅-CaF₂)-Glycerol Paste.

This study investigates the dissolution behavior as well as the surface biomineralization in simulated body fluid (SBF) of a paste composed of glycerol (gly) and a bioactive glass in the system CaO-MgO-SiO2-Na2O-P2O5-CaF2 (BG). The synthesis of the bioactive glass in an alumina crucible has been shown to significantly affect its bioactivity due to the incorporation of aluminum (ca. 1.3–1.4 wt %) into the glass network. Thus, the kinetics of the hydroxyapatite (HA) mineralization on the glass prepared in the alumina crucible was found to be slower than that reported for the same glass composition prepared in a Pt crucible. It is considered that the synthesis conditions lead to the incorporation of small amount of aluminum into the BG network and thus delay the HA mineralization. Interestingly, the BG-gly paste was shown to have significantly higher bioactivity than that of the as-prepared BG. Structural analysis of the paste indicate that glycerol chemically interacts with the glass surface and strongly alter the glass network architecture, thus generating a more depolymerized network, as well as an increased amount of silanol groups at the surface of the glass. In particular, BG-gly paste features early intermediate calcite precipitation during immersion in SBF, followed by hydroxyapatite formation after ca. seven days of SBF exposure; whereas the HA mineralization seems to be suppressed in BG, probably a consequence of the incorporation of aluminum into the glass network. The results obtained within the present study reveal the positive effect of using pastes based on bioactive glasses and organic carriers (here alcohols) which may be of interest not only due to their advantageous visco-elastic properties, but also due to the possibility of enhancing the glass bioactivity upon surface interactions with the organic carrier.

Recovery of plutonium and cerium from alumina crucible

Plutonium recovery is inevitable from plutonium bearing alumina crucibles generated over the years as part of carbon analysis during chemical quality control of nuclear fuels. This is a challenging task owing to the complex nature of matrix. The first stage of methodology development of plutonium recovery involved usage of CeO2 bearing crucibles. Cerium distribution in alumina crucible was investigated by examination of surface morphology. Various aqueous recovery routes were tested initially with CeO2 bearing crucibles and 4 M HF–8 M HNO3–NH4NO3 was found to be most promising (60% recovery). The same route yielded 90% plutonium recovery from alumina crucibles.

The Effect of Temperature on the Chromizing Process for Ferritic-Martensitic Steel

The formation of protective Cr2O3 layer was usually retarded in the high temperature steam oxidation of boiler tube materials. This condition makes the oxidation rate higher than that in dry condition. Therefore in this work, chromizing process is introduced to diffuse chromium on the surface of boiler steel so that it can act as a reservoir for the formation of Cr2O3 layer. The chromizing process was conducted on T91 steel by exposing it into alumina crucible. The crucible was exposed at different temperature (600°C-1050°C) under argon environment in the crucible that contains the chromizing mixture powder of masteralloy Cr, activator NH4Cl and filler Al2O3. It was found that Cr diffusion was happened at higher temperature and it formed Cr carbide on the surface. It also clarified that this chromizing process can prevent the retardation of Cr2O3 layer.

Effect of Alumina Addition on Li6.75La2.75Ca.25Zr1.5Nb.5O12 Lithium Garnet

Lithium-conducting garnets are a promising solid state electrolyte in the cubic phase for lithium (Li) batteries because of their stability with lithium, wide electrochemical stability window, and high conductivity (~1 mS cm-1). Aluminum (Al) is a widely studied dopant due to its ability to stabilize the cubic phase because of the occurrence of unintentional doping from alumina crucibles used during synthesis. The quantity of aluminum in the material is critically important to sintering conditions and performance in both the bulk and at the grain boundaries. Al can diffuse into the structure of garnets and dope the Li site while removing three total Li for charge balance. Another possibility is the Al reacts with excess lithium or lithium that has left the structure during high temperature processing. This allows for a liquid phase to form, enabling better densification during sintering. In this work, the aluminum content in Li6.75La2.75Ca.25Zr1.5Nb.5O12 was varied and calcined in magnesia crucibles to limit Al contamination. One weight percent of alumina (0.1 moles) was added before the solid state reaction, producing a conductivity of 2.96 x 10-4 S cm-1 after sintering at 1100°C. Specifically in the sample with 0.1 Al added when sintered at 1100°C for 12 hours, the Al contributed to an increase in grain boundary conductivity to 1.96x10-3 S cm-1 and a decrease in total activation energy to 0.35 eV versus samples without any added aluminum. The varying Al content showed little variance in bulk conductivity over several sintering conditions, while showing a wide divergence of 2.72x10-3 S cm-1, in grain boundary conductivity. Possible explanations are discussed with structural, chemical, and EIS measurements detailed.

The Influence of the Valence Electron Concentration on the Structural Variation of the Laves Phases MgNi2–xGex

The influence of the partial substitution of Ni atoms by the similarly sized but electron‐richer Ge atoms with a similar electronegativity in the binary Laves phase MgNi2 is investigated. A small degree of substitution in MgNi2–xGex (x = 0.1) leads to the change of the hexagonal MgNi2‐type structure (C36) to the cubic C15 type, whereas higher amounts of Ge lead to the formation of the two new Laves phases Mg2Ni3Ge and MgNi1.30(5)Ge0.70, which were synthesized by the direct reaction of the elements in alumina and niobium crucibles using an induction furnace. The crystal structures of the two phases were determined by single‐crystal X‐ray diffraction. Mg2Ni3Ge (hR18‐MgNi2–xGex, x = 0.5) crystallizes in the Y2Rh3Ge‐type structure, which is an ordered variant of the cubic Laves phase MgCu2: space group R3m, a = 5.0300(7), c = 11.330(2) Å. hP36‐MgNi2–xGex with x = 0.70(6) crystallizes as a superstructure of the hexagonal Laves phase MgZn2: space group P63/mcm, a = 8.6946(2), c = 7.8127(3) Å. MgNi1.3Ge0.7 represents a new structure type. Gradual substitution of Ni by Ge in the Laves phase MgNi2 corresponds to an increase in the valence electron concentration (VEC) in the ternary phase system and leads to the series MgCu2 (C15 type), hR18‐Mg2Ni3Ge (superstructure of MgCu2 type), and hP36‐MgNi1.3Ge0.7 (superstructure of MgZn2 type). The electronic structures are discussed based on band structure calculations, and the results are compared to the pristine Laves phase MgNi2, MgCu2, and MgZn2 with VEC = 2/3, 4/3 and 2, respectively.

Synthesis and Characterization of Cerium- and Lanthanum Containing Bioactive Glass

Synthesis and characterization of bioglass® of general composition (45-X-Y) SiO2, 24.5 Na2O, 24.5 CaO and 6.0 P2O5 (wt %) was modified by addition of X= (0-1) wt % of CeO2 and Y= (0-1) wt % of La2O3 respectively. These five samples were prepared in alumina crucible via melting route at a temperature of 1400±5 °C with air as a furnace atmosphere. These glass samples were immersed in simulated body fluid (SBF) for different time period and their bioactivity were determined by Fourier transform infrared spectroscopy (FTIR) analysis. Surface morphology was studied by using Scanning electron microscope (SEM). Bioactivity, pH measurement of bioactive glass was carried out and mechanical properties of these glasses increased with increasing concentration of CeO2 and La2O3.

Facile synthesis of highly dispersed Fe(II)-doped g-C3N4 and its application in Fenton-like catalysis

In this work, highly dispersed Fe(II)-doped g-C3N4 was successfully prepared by simple calcination of a Fe+3/melamine precursor in a semi-closed alumina crucible at 550°C without atmosphere protection. The morphology, structure, and chemical composition of the products were characterized fully. Thermogravimetric analysis/Differential thermic analysis (TGA/DTA), 57Fe Mossbauer, and electron paramagnetic resonance measurements were used to evaluate the changes in the chemical composition of the 10%-Fe/melamine precursor as a function of the calcination temperature, revealing that reduction of Fe+3 to Fe+2 occurs progressively at temperatures between 310°C and 550°C. The prepared Fe-doped g-C3N4 materials exhibit high activity in the Fenton-like degradation of cationic methylene blue within a wide pH range, as well as high reusability and low iron leaching. The catalysts display high activity in the degradation of cationic rhodamine B, anionic indigo carmine (IC), and neutral phenol. Electrospray ionisation mass spectrometry (ESI-MS) measurements confirmed that all selected substrates were successively oxidized into different intermediate compounds before mineralization, exhibiting great potential for application in the degradation of environmental pollutants.

Minimizing Phosphorus Pickup During Melting and Casting of Lightweight Fe–Mn–Al–C Steels

High manganese and aluminum austenitic steels continue to be of great interest as lightweight alternatives to quenched and tempered martensitic steels for high energy absorbing applications in the military and automotive industries. However, the presence of phosphorus in levels greater than about 0.006 wt%P increases the kinetics of κ-carbide precipitation and reduces both ductility and notch toughness. Previous studies have shown that phosphorus pickup of up to 0.02 wt%P is possible even when high purity charge materials are used, suggesting that commonly used refractories may be a source of fugitive phosphorus. The current study investigates the interaction between two commercially available refractories and a high manganese and aluminum steel during melting and casting. Two commercially produced revert samples of chemistry Fe-30Mn-9Al-1.6Si-0.9C-0.5Mo (0.002%P) were melted under protective atmosphere in high purity alumina crucibles lined with phosphate- and silicate-bonded refractories, respectively. Phosphorus pickup in the steel melted on the phosphate-bonded refractory was more than 0.14 wt%P with heavy phosphorus segregation and κ-carbide precipitation on grain boundaries. The steel melted in contact with the silicate-bonded refractory showed no phosphorus pickup, less carbide precipitation on grain boundaries, and no evidence of any phosphide eutectic. The effect of melt residence time during casting was also studied as a function of refractory choice. Results showed that when the phosphate refractory was used to coat the ladles, this resulted in only a slight increase in phosphorus; however, Si increased from 0.74 to 0.97 wt%Si. A small increase in hardening was observed for castings poured from phosphate-bonded ladles. Notch toughness was highest for the specimens poured from the phosphate-bonded refractory ladles, and this is attributed to an increased amount of carbon in solid solution. Aging for 10 h at 530 °C sharply reduced the breaking energy from an average of 150 to <5 J. The results show that phosphorous pickup can be significant when phosphate-bonded refractories are used, especially during melting when the steel is in contact with these refractories for extended periods of time. Therefore, phosphate-bonded refractories should be avoided when melting and casting Fe–Mn–Al–C steels.

Nickel–Silver Monotectic in Alumina Crucible for Use with Contact Thermometry

Previously, the authors have published work describing a pure Ni fixed point within alumina crucibles. The success of this study stimulated working with the Ni–Ag monotectic point in alumina crucibles. Similar to eutectic points, the Ni–Ag monotectic temperature is an invariant point but it differs from a eutectic reaction in such a way that the monotectic phase change takes place from Ni–Ag liquid solution to Ni–Ag solid solution and Ag rich Ni–Ag liquid solution. In the phase diagram references, the Ni–Ag monotectic phase transition temperature is assigned to be about 20 $$^{\circ }$$ C below the pure Ni melting/freezing point. As is the case for pure Ni, mechanical stability is one of the concerns. Therefore, proper cell design is necessary to avoid breakage of the alumina crucible. The techniques used for the fabrication and measurement of the pure Ni cell were applied to the Ni–Ag cell as well. The cells have been successfully fabricated and the temperature measurement at the fixed point was carried out for more than 20 thermal cycles in total. A Pt/Pd thermocouple was used to measure the temperature and was calibrated from the tin point to the gold point to measure the ITS-90. Freezing plateaus are realized with the technique of “recurrent offset freezing method with reserved solid”. The duration of each freezing plateau is a minimum of 30 min. The monotectic transformation temperature for the best performed cell is determined as 1428.27 $$^{\circ }$$ C with a combined uncertainty of ±0.06 $$^{\circ }$$ C ( $${k}=1$$ ).

Facile synthesis of silicon nitride nanowires with flexible mechanical properties and with diameters controlled by flow rate

Ultralong Si3N4 nanowires (NWs) were successfully synthesized with size controlled in N2 gas by using an efficient method. The diameters of the Si3N4 NWs increased when the flow rate of N2 gas increased, with average diameters of 290 nm from flow rates of 100 ml/min, 343 nm from flow rates of 200 ml/min and 425 nm from flow rates of 400 ml/min. Young’s modulus was found to rely strongly on the diameters of the Si3N4 NWs, decreasing from approximately 526.0 GPa to 321.9 GPa; as the diameters increased from 360 nm to 960 nm. These findings provide a promising method for tailoring these mechanical properties of the NWs in a controlled manner over a wide range of Young’s modulus values. Vapour-liquid-solid (VLS) mechanisms were used to model the growth of Si3N4 NWs on the inner wall of an alumina crucible and on the surface of the powder mixture. Alumina may be an effective mediator of NW growth that plays an important role in controlling the concentrations of Si-containing reactants to support the growth of NWs on the inner wall of the alumina crucible. This approach offers a valuable means for preparing ultralong Si3N4 NWs doped with Al with unique properties.

Microstructure formation and interface characteristics of directionally solidified TiAl-Si alloys in alumina crucibles with a new Y2O3 skull-aided technology

The microstructure evolution and interface characteristics of a directionally solidified Ti-43Al-3Si (at.%) alloy in an alumina (Al2O3) crucible with new Y2O3 skull-aided technology were investigated. The Y2O3-skull that is in contact with the TiAl-melt is relatively stable, which results in a more controlled reaction between the skull and the melt than in the case of an Al2O3 crucible is used. A thin reaction layer was formed between the mould and the melt through mutual diffusion. The layer thickness increased with increasing reaction time. The thickness of this layer was less than 80 μm for reaction times up to 5800 s. Y2O3 particles were not found in the specimen because the mould coating was prepared with fine Y2O3 powder without a binder, which prevented the Y2O3 particles splitting from the coating as a consequence of thermal physical erosion. The oxygen content of the TiAl-alloy increased with increasing reaction time. The total oxygen content of the solidified specimen was less than that of the specimen solidified in the Al2O3 crucibles. This new Y2O3 skull-aided technology is expected to improve the surface quality of TiAl-alloys and reduce the reaction between the crucible/mould and molten TiAl alloys during directional solidification processing with longer contact times.

Oxidation Comparison of Alumina-Forming and Chromia-Forming Commercial Alloys at 1100 and 1200\xa0\xb0C

21 Commercial alumina-forming and chromia-forming high-temperature alloys were tested at 1100 and 1200 °C for up to 1000 h. Exposure was performed in air using 100-h cycles on ~2-mm-thick test coupons placed in highly sintered alumina crucibles. Visual appearance, gross mass gain and amount of spallation were monitored after every 100 h. Investigation of topography and cross sections was performed in LOM and SEM with EDS at breakaway oxidation or at 1000 h depending on what occurred first. In order to investigate the earlier part of the oxidation process in more detail, separate samples from all materials were exposed under the same conditions for a single 100-h cycle and were then investigated in the same manor.