F. Aldinger

Fabrication and electrical and thermal properties of Ti2InC, Hf2InC and (Ti,Hf)2InC

Abstract In this paper we report on the characterization of predominantly single phase, fully dense Ti2InC (Ti1.96InC1.15), Hf2InC (Hf1.94InC1.26) and (Ti,Hf)2InC ((Ti0.47,Hf0.56)2InC1.26) samples produced by reactive hot isostatic pressing of the elemental powders. The a and c lattice parameters in nm, were, respectively: 0.3134; 1.4077 for Ti2InC; 0.322, 1.443 for (Ti,Hf)2InC; and 0.331 and 1.472 for Hf2InC. The heat capacities, thermal expansion coefficients, thermal and electrical conductivities were measured as a function of temperature. These ternaries are good electrical conductors with a resistivity that increases linearly with increasing temperatures. At 0.28 μΩ m, the room temperature resistivity of (Ti,Hf)2InC is higher than the end members (∼0.2 μΩ m), indicating a solid solution scattering effect. In the 300 to 1273 K temperature range the thermal expansion coefficients are: 7.6×10−6 K−1 for Hf2InC, 9.5×10−6 K−1 for Ti2InC, and 8.6×10−6 K−1 for (Ti,Hf)2InC. They are all good conductors of heat (20 to 26 W/m K) with the electronic component of conductivity dominating at all temperatures. Extended exposure of Ti2InC to vacuum (∼10−4 atm) at ∼800xa0°C, results in the selective sublimation of In, and the conversion of Ti2InC to TiCx.

Rapid synthesis of the Bi-2212 phase by a polymer matrix method

A method that leads to the Bi-2212 phase after a short thermal treatment of metal acetates is presented. The thermal treatment consists in a calcination (2 h at + 2 h at ), pressing and sintering (1 or 3 h at ). TGA and DTA provide valuable data about the decomposition of the polymer and metal - polymer complex and the formation and decomposition of the carbonates in the intermediate compounds. In contrast with the most common sol - gel methods, the use of polyethylenimine yields relatively large particles (ca ).

Phase diagram studies in the system Ag-“Bi2Sr2CaCu2O8”

Abstract The phase relations in the system of Ag and the high-temperature superconducting phase “Bi 2 Sr 2 CaCu 2 O 8 ” (2212) are studied up to a Ag content of 50 mol percent in air. The most significant observation is that the temperature of the complete melting of 2212 decreases significantly from about 895°C to some 865°C with increasing Ag content. Therefore, at constant sinter temperature between 895°C and 865°C the amount of liquid in the sample depends significantly on the Ag concentration.

Microstructure, crystal structure and electrical properties of Cu0.1Ni0.8Co0.2Mn1.9O4 ceramics obtained at different sintering conditions

Details of the formation of Cu0.1Ni0.8Co0.2Mn1.9O4 ceramics under different sintering conditions have been studied by optical microscopy, scanning electron microscopy (SEM), electron probe and energy dispersive spectroscopy (EDX) microanalyses, X-ray diffraction (XRD) and electrical resistivity measurements. Microstructure studies of samples sintered at 1170xa0°C for 1 h indicated the presence of a secondary phase besides the main spinel phase with modified composition. XRD measurements showed that the spinel phase exhibits a tetragonally distorted spinel structure (space group I41/amd, a=5.9410(5) A, c=8.4196(15) A). The secondary phase (solid solution based on NiO) crystallizes with the NaCl-type structure (space group , a=4.1872(3) A). The content of the secondary phase in ceramics is 10.61 mass%. For NiMn2O4 ceramics, prepared under the same sintering conditions, the decomposition with Ni1−xMnxO solid solution (NaCl-type structure) and spinel phase formation have been observed. The tetragonal modification of the spinel phase for NiMn2O4 ceramics is more preferable (space group I41/amd, a=5.9764(5) A, c=8.4201(8) A). The distribution of atoms in the structure has been proposed for both ceramics. According to XRD results the Cu0.1Ni0.8Co0.2Mn1.9O4 ceramic samples, sintered at 920xa0°C for 8 h (program 1), at 920xa0°C for 8 h and at 750xa0°C for 24 h (program 2), at 920xa0°C for 8 h, at 1200xa0°C for 1 h and at 920xa0°C for 24 h (program 3) and at 920xa0°C for 8 h, at 1200xa0°C for 1 h, at 920xa0°C for 24 h and at 750xa0°C for 48 h (program 4), contain a single phase with the cubic spinel structure (space group ). Small residuals of the secondary phase for the ceramics, prepared via programs 3 and 4, have been observed by SEM investigations. The structure transformations of the spinel phase for Cu0.1Ni0.8Co0.2Mn1.9O4 ceramics sintered at 1170xa0°C are attributed to a Jahn–Teller-type distortion due to a compositional change as a result of the secondary phase separation.

Phase equilibria and diffusion paths in the Ti-Al-O-N system

Abstract To provide a basis for the calculation of high-temperature phase reactions in the Ti–Al–O–N system a thermodynamic dataset using the CALPHAD method (CALculation of PHAse Diagrams) was developed. Analytical Gibbs energy descriptions for the system phases were taken from literature or optimized in this work. The solid solution series Al 2 TiO 5 –Ti 3 O 5 (tialite) was modeled with the sublattice description (Al +3 ,Ti +3 ,Ti +4 ) 2 (Al +3 ,Ti +3 ,Ti +4 ) 1 (O −2 ) 5 . The nine energy parameters resulting from the applied Compound Energy Formalism could be reduced to four independent parameters. Reciprocal reactions and the condition of electroneutrality were taken into account. Based on the optimized binary and ternary phase diagrams extrapolating calculations on quaternary compositions were carried out and compared with experimental work. The results show good agreement with the phase assemblages in the microstructure of ceramics in the Ti–Al–O–N system. Additionally, the oxidation behavior of γ-TiAl can be explained qualitatively.

Thermodynamic modelling in the ZrO2–La2O3–Y2O3–Al2O3 system

Abstract The thermodynamic database for the ZrO2 – La2O3 – Y2O3 – Al2O3 system has been derived using previous descriptions for the six binary systems and the ternary ZrO2 – La2O3 – Al2O3 system. The parameters of the Y2O3 – Al2O3 system were adjusted due to changes in the Y2O3 thermody-namic parameters. The thermodynamic parameters of the La2O3 – Y2O3 system were slightly changed to get consistency between calculations and new experimental results for the ZrO2 – La2O3 – Y2O3 ternary system. Diverse kinds of phase diagrams of the ZrO2 – La2O3 – Y2O3 and La2O3 – Y2O3 – Al2O3 ternary systems have been calculated. The present thermodynamic description of the quaternary system is consistent with available experimental results for lower-order systems. It was used to calculate isoplethal sections for compositions related to thermal barrier coating (TBC) and its interaction with thermally grown oxide Al2O3. The T0-lines have been calculated for diffusionless transformations between fluorite, tetragonal, monoclinic and pyrochlore phases in the ZrO2 – LaO1.5 system as well as driving forces for partitioning of non-equilibrium phase into equilibrium phase assemblages. These data could be applied for determination of desirable ranges of material composition for TBC.

The increase of pinning in (Bi,Pb)2Sr2Ca2Cu3O10+d bulk ceramics

Considering the phase equilibrium diagram of the Bi2O3-PbO-SrO-CaO-CuO system, ceramics of the 2223 phase with the composition Bi1.8Pb0.4Sr2Ca2Cu3O10+d have been transformed by a simple annealing procedure into multi-phase samples. The transformation results in a four-fold increase of the critical current density at 2 T and 30 K (three-fold at 1 T and 50 K), which is believed to express an enhanced pinning capacity of the material. The nature of the pinning centres produced is not yet clarified.

Thermodynamics of liquid and undercooled liquid Al-Ni-Si alloys

Abstract The partial and the integral enthalpies of mixing of liquid Al–Ni–Si alloys have been determined by high-temperature isoperibolic calorimetry for three sections with constant concentration ratios of Ni and Si at 1575±3 K. With a view to a direct use of the thermodynamic properties, the values of the integral enthalpy of mixing of the ternary alloys together with the literature values of the constituent binaries Al–Ni, Ni–Si and Al–Si are analytically described by the thermodynamically adapted power series according to the right-hand Colinet geometry using a least-squares regression analysis. A regular association model adequately describes the thermodynamic properties of liquid and undercooled liquid Al–Ni–Si alloys. The Δ H ( x Al , x Ni , x Si ), Δ S ( x Al , x Ni , x Si ) and Δ G ( x Al , x Ni , x Si ) functions show the existence of essential contributions of ternary interactions among the alloy components. The strongest tendency toward chemical short-range ordering in the liquid state occurs near to compositions corresponding to the intermetallic compound Ni 2 AlSi.

The influence of the phase equilibria on the critical temperatures T C of the high-T C Bi-Sr-Ca-Cu-O and Y-Ba-Cu-O compounds

The phase equilibria of YBa2Cu3O7−d (123 phase) strongly influence its oxygen content and consequently its critical temperature Tc. With increasing content of BaCuO2 or CuO, Tc decreases. Whereas, if Y2BaCuO5 (211 phase) is in equilibrium with the 123 phase, the oxygen content and Tc of which is high. Bi2+x(Sr,Ca)3Cu2O8+d exhibits an extended single phase region and its Tc is strongly affected by its chemical composition. In addition, the oxygen content of the phase is a function of the temperature and influences the Tc of the phase.

Enthalpy of mixing of liquid Al-Cu-Si alloys

Abstract The partial and the integral enthalpies of mixing of liquid Al–Cu–Si alloys have been measured by high temperature calorimetry at 1575±3 K. Results for three sections with constant concentration ratios of Al and Si are given in tabular form. A least-square regression analysis of the integral enthalpy of mixing data results in the following relationships (in kJ mol−1; T=1575±3 K): Δ H =x Al x Cu α Al–Cu +x Al x Si α Al–Si +x Cu x Si α Cu–Si +x Al x Cu x Si α Al–Cu–Si α Al–Cu =(−75.6±6.5)+(−63.8±8.8)x Al +(232±33)x 2 Al +(−131±28)x 3 Al α Al–Si =−12.6+2.5x Si α Cu–Si =(−16.2±2.2)+(97.7±37.1)x Cu +(−1138±208)x 2 Cu +(3514±489)x 3 Cu + (−4748±515)x 4 Cu +(2216±199)x 5 Cu α Al–Cu–Si =(−241.7±8.8)+(1165±32)x Al +(891±34)x Si +(−935±30)x 2 Al +(−640±35)x 2 Si + +(−1563±52)x Al x Si . The minimum of ΔH changes with composition from −14.5 kJ mol−1 (Cu–25at.%Si) to −17.3 kJ mol−1 (Al–60at.%Cu). The presence of additional ternary interactions or ternary associates in the liquid state could not be observed.