Hans Flandorfer

Individual solutions for control and data acquisition with the PC

Abstract Individual and flexible solutions for control and data acquisition are an important tool for measurements in scientific research, since very often self-constructed or adapted commercial measuring devices are applied. Software which is purchased together with the instruments is in many cases not suitable for research applications, which require comprehensible procedures with high precision and reproducibility. Suitable programmed commercial solutions are either not available or too expensive. This paper presents the adaptation and automation of a high temperature Calvet-type microcalorimeter. It allowed us to perform programmable drop calorimetry with automated additions of samples under controlled atmosphere and temperature as well as signal acquisition at low cost, which does not require any special knowledge of electronics or programming. We were able to integrate several instruments for measuring and controlling via their communication interfaces (IEEE, I/O-port) by means of the program Laboratory Virtual Instrument Engineering Workbench (LabView, National Instruments). The program runs on a conventional Pentium-PC under Windows98. It allowed us to construct user interfaces for the input of control parameter and observation of running measurements as well as the import of acquired data to the evaluation software HiQ (National Instruments).

Calorimetric investigations of the two ternary systems Al-Sn-Zn and Ag-Sn-Zn

Abstract Using a Calvet type calorimeter, the enthalpy of mixing in the two ternary systems, Al–Sn–Zn and Ag–Sn–Zn was determined at 973 K. In the Al–Sn–Zn system, the investigations were carried out along three cross-sections with constant molar ratios of Sn: Zn = 1: 2, 1: 1 and 2: 1 and an aluminium content between 0 and 100 at.%. For the Ag–Sn–Zn system, the measurements have been done at constant molar ratios of Ag: Sn = 1: 3, 1: 1 and 3: 1 with zinc contents between 0 and 50 at.%. The substitutional solution model of Redlich–Kister according to the CALPHAD method was used for a least-square fit of the experimental data in order to get an analytical expression for the integral enthalpy of mixing. The ternary extrapolation models of Kohler, Muggianu, and Toop were applied on the binary data to compare measured, fitted, and extrapolated values.

Phase relationships in the In-rich part of the In-Pd system

Abstract A detailed literature overview concerning the In-rich cubic phase in the In–Pd system is given. Powder X-ray diffraction, metallography including EPMA and thermal analyses of samples around the composition In70Pd30 were performed in order to evaluate the phase relationships. Our results showed that the compound In3Pd (partially filled γ-brass structure type) hitherto reported in phase diagram compilations does not exist as an equilibrium phase. Therefore the In-rich part of the phase diagram presented here was changed replacing In3Pd by In7Pd3. The general phase relations correspond to those reported earlier for In3Pd but the temperatures of related invariant reactions were slightly enhanced. The homogeneity range of In7Pd3 is below 0.5 at.%. The crystal structure of the binary intermetallic compound In7Pd3 was determined by single crystal X-ray diffraction using a CCD-diffractometer at room temperature. Refinements finally yielded a body centered cubic structure (space group: Im 3 m ; Pearson symbol: cI40, Z=4) with a=9.4359(4) A. For the entire data set of 240 independent reflections residual values are R=0.0222 and Rw=0.0484. The structure is isotypic to Sn7Ir3 with In on the Sn sites and Pd on the Ir sites. Our results are in excellent agreement with a single crystal structure determination reported earlier.

Lead-free solder materials: experimental enthalpies of mixing in the Ag–Cu–Sn and Cu–Ni–Sn ternary systems

Abstract The partial and integral enthalpies of mixing of molten, ternary Ag–Cu–Sn alloys were determined at 500, 700 and 900 °C using a Calvet-type microcalorimeter. Five sections in a compositional range from pure Sn to about 40 at.% Sn were investigated. The data were fitted using a Redlich–Kister–Muggiano polynomial, where the binary interaction parameters were taken from the literature. Additionally, the temperature dependence of the ternary interaction parameters was described analytically by a linear function. In the ternary Cu–Ni–Sn system, the enthalpies of mixing were determined at 1250 °C in five sections, starting from pure Sn to about 40 at.% Sn. Again, the ternary interaction parameters were fitted using the substitutional Redlich–Kister–Muggiano model. For both ternary systems and all mentioned temperatures, isoenthalpy curves were constructed for the integral molar enthalpy of mixing.

Novel ytterbium-zinc-silicides and germanides grown from zinc-flux

Abstract Novel ternary ytterbium-zinc-silicides and germanides have been synthesized using pure zinc metal as a flux-solvent. The new compounds, YbZn 2 Si 2 and YbZn 2 Ge 2 crystallize with the BaAl 4 or ThCr 2 Si 2 -type. Yb(Zn,Si) 2 and Yb(Zn,Si) 2− x crystallize with the ThSi 2 and the GdSi 2− x type, respectively. Crystal properties were characterized using X-ray single crystal analysis via Gandolfi and Weissenberg film techniques, by flat specimen X-ray powder diffractometry and in some cases by automatic four circle X-ray single crystal diffractometry. Depending on the heating and cooling program in the synthesis, various lattice parameter values were obtained suggesting the existence of homogeneity regions. Both the Yb-Zn-silicides and the germanide show a temperature independent Pauli-type paramagnetic behaviour down to liquid He temperature consistent with the XAS-measurements revealing an Yb 2+ ground state.

Enthalpy Effect of Adding Cobalt to Liquid Sn-3.8Ag-0.7Cu Lead-Free Solder Alloy: Difference between Bulk and Nanosized Cobalt

Heat effects for the addition of Co in bulk and nanosized forms into the liquid Sn-3.8Ag-0.7Cu alloy were studied using drop calorimetry at four temperatures between 673 and 1173 K. Significant differences in the heat effects between nano and bulk Co additions were observed. The considerably more exothermic values of the measured enthalpy for nano Co additions are connected with the loss of the surface enthalpy of the nanoparticles due to the elimination of the surface of the nanoparticles upon their dissolution in the liquid alloy. This effect is shown to be independent of the calorimeter temperature (it depends only on the dropping temperature through the temperature dependence of the surface energy of the nanoparticles). Integral and partial enthalpies of mixing for Co in the liquid SAC-alloy were evaluated from the experimental data.

On the stability of hexagonal Ge7Nb10

Abstract Our studies on the Ge–Nb system reveal the existence of a hexagonal compound with the composition Ge 7 Nb 10 that is stable with respect to disproportionation and which was found to crystallize in the space group P6 3 /mmc . A hexagonal phase of the approximate composition Ge 3 Nb 5 has been mentioned by different authors but has been commonly regarded as C- or N-stabilized and therefore not included in the binary phase diagram. A single crystal X-ray study of the compound revealed a Mn 5 Si 3 -type based structure where half of the 2b interstitial positions are filled with Ge. X-ray powder diffraction studies and electron probe microanalysis were used to determine the composition ranges of the phases. Various experiments were carried out in order to confirm the thermodynamic stability of this compound and to rule out stabilization by hetero-elements. These studies included the use of different starting materials, different sample preparation techniques and different annealing procedures. The results show strong indications, that Ge 7 Nb 10 is formed as a binary phase which is stable with respect to disproportionation and should therefore be included in the binary phase diagram.

The tin-rich copper lithium stannides: Li3Cu6Sn4 and Li2CuSn2

Abstract The Sn rich ternary intermetallic compounds Li3Cu6Sn4 (CSD-427097) and Li2CuSn2 (CSD-427098) were synthesized from the pure elements by induction melting and annealing at 400°C. Structural investigations were performed by powder- and single-crystal XRD. Li3Cu6Sn4 crystallizes in space group P6/mmm; it is structurally related to but not isotypic with MgFe6Ge6 (a = 5.095(2) Å, c = 9.524(3) Å; wR2 = 0.059; 239 unique F2-values, 17 free variables). Li3Cu6Sn4 is characterized by two sites with a mixed Cu:Sn occupation. In contrast to all other Cu-Li-Sn compounds known so far, any mixed occupation was found for Cu-Li pairs only. In addition, one Li site is only half occupied. The second Sn rich phase is Li2CuSn2 (space group I41/amd, a = 4.4281(15) Å, c = 19.416(4) Å; wR2 = 0.033; 213 unique F2-values, 12 atom free variables); it is the only phase in the Cu-Li-Sn system which is noted for full ordering. Both crystal structures exhibit 3D-networks which host Li atoms in channels. They are important for understanding the lithiation mechanism in Cu-Sn electrodes for Li-ion batteries.

Enthalpy of mixing of liquid systems for lead free soldering: Ni–Sb–Sn system

Highlights ► First paper providing enthalpy of mixing determined by calorimetry for Ni–Sb. ► First paper providing enthalpy of mixing determined by calorimetry for Ni–Sb–Sn. ► Full report of measured values for readers own evaluation. ► Isoenthalpy plot and detailed discussion of possible ternary interactions.

New intermetallic phases in the Cu–Li–Sn system: the lithium-rich phases Li3CuSn and Li6Cu2Sn3

Abstract The Li-rich ternary intermetallic compounds with the idealized end-member compositions Li3CuSn (CSD-427099) and Li6Cu2Sn3 (CSD-427100) were synthesized from the pure elements by induction melting in Ta crucibles and annealing at 400°C. Both powder and single-crystal XRD investigations were performed. Li3CuSn crystallizes in space group P6/mmm [a=4.5769(2), c=8.461(2) Å; wR2=0.073 for 180 unique F2-values and 25 free variables]. All atoms are located along [00z], [1/3 2/3 z] and [2/3 1/3 z]; individual sites are arranged in layers parallel to (00.1). One site is fully, one partially occupied by Sn atoms. Fully but mixed occupation with Cu and Li atoms was found for one site. The remaining electron-density distribution resulting from the strong anisotropic displacement parallel to the c axis is considered in four further sites, which are mixed occupied with (Li, Cu, □), but modelled solely by Li atoms. The crystal structure exhibits analogies with that of Li2CuSn (F4̅3m); comparable layers occur parallel to {111} but the stacking sequence and packing density differs adopting cubic symmetry. In Li6Cu2Sn3 [space group R3̅2/m, a=4.5900(2), c=30.910(6) Å; wR2=0.039 for 253 unique F2-values for 25 free variables] all atoms are arranged again at (00z), (1/3 2/3 z) and (2/3 1/3 z). Three sites are fully occupied (two by Sn atoms, a further one by Li atoms). Three additional positions are mixed occupied by Cu and Li atoms. The crystal structure is closely related to that of the binary phases Li13Sn5 and Li5Sn2; the substitution of Li by Cu atoms and vice versa is evident. The structural relationship to Li13Ag5Si6, which is permeable for Li ions, makes the title compound interesting as anode material in Li-ion batteries.