The methods of preparation for Bi8(A1C14)2 and Bi6C17 have been improved and the single crystal structures for these cluster compounds re-investigated and re-interpreted. In addition, conductivity measurements and band structure calculations using the tight-binding approximation have been performed on BieC17 and related subvalent bismuth halides. -Bi,(A1C14)2 consists of isolated A1C1, anions and rather undistorted square-antiprismctic Bi2+ clusters with an average Bi-Bi distance 0f~3.10 A. Relatively short intercluster Bi-Bi contacts of 3.90 A suggest weak bonding interactions between the Big+ units. In contrast, the structure determination of Bi6C17 implies that this structure should be regarded as being composed of discrete BkZ+ clusters and a polymeric Bi"'-Cl anionic lattice including infinite, distorted A[Bi2C1$+] chains. According to the experimental and theoretical results, the Bi6X7 (X = C1, Br) family of subvalent bismuth halide compounds are anisotropic semiconductors along the crystallographic c axis. The conductivity is mediated by the onedimensional &[BizCli'] chains. These are interconnected with the Bi$+ clusters, which are acting as electron resenroirs. The related BiX (X = Br, I) family of subvalent bismuth halides are shown to be anisotropic semiconductors in the crystallographic b direction. Subvalent bismuth chloride was at first formulated as BiCl[',21, but was later crystallographically shown to actually have the stoichiometry Bi6C17 and to exhibit an unusually complex structure with isolated Bi;+ clusters and chlorobismuthate(II1) c~rnplexes[~-~]. The authors described the structure as (Bi$')2(Bi2Cl$-)(BiCl~L)4, corresponding to the over-all stoichiometry Bi6C17. The 1 : 1 BiCl compound has so far not been synthesised, and it is interesting to note the following trend in the stoichiometry of the subvalent bismuth halides that have been isolated and characterized : Bi6C17Bi6Br7 BiBrAll these compounds have been structurally characterised in the solid ~t a t e [~- '~] and the Bi6X7 (X = C1 or Br) pair found to be structurally analogous. There are two main reasons for our interest in the latter two compounds. First, Bi6CI7 has been reported to be a metallic conductor, whereas the structural and chemical analogue Bi6Br7 is claimed to be an insulator [7]. Such a difference is very surprising considering the isostructurality and chemical simi-BiI Bi71Z, Bi912 larity of the two compounds. Second, the previous structural characterisations of Bi6C17 are incomplete in the sense that the chloride positions were not refined anisotropically. In this work, the crystal structure of Bi6C17 has been redetermined, and the conductivity of a single crystal determined. The new results have then been rationalised using band structure calculations.BiBr and the three different modifications of BiI are also structurally analogous and contain one-dimensional Bi2X4 double chains bridged by metal-metal bonded chains of interstitial, formally zero-valent Bi atom^ [^,^]. The more metal-rich subvalent bismuth iodide ...

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The requirement for economic reconditioning of the latest ALSTOM gas turbine generation with Single Crystal (SX) superalloys has lead to the development of advanced repair processes such as Diffusion Brazing or Transient Liquid Phase bonding. Diffusion Brazing (DB) of conventionally cast polycrystalline turbine components has been carried out for many years but the requirement for this joining and repair technique to be applied to DS and SX superalloys has emerged only more recently. The main concern for the use of a braze-repair process for the more highly loaded SX components is the ability to guarantee sufficient thermal and mechanical integrity throughout the component lifetime. Such high strength braze joints in SX superalloys can be achieved by combining a brittle phase-free and high γ′ content microstructure, while maintaining the crystallographical orientation of the SX parent material within the repair zone. Prior to the brazing process, a suitable crack surface preparation is essential, and this is achieved by the employment of specifically optimized Fluoride Ion Cleaning (FIC) process. This guarantees the complete removal of oxide from the crack surfaces and promotes the flow of the braze alloy for complete filling down to the crack tip. This paper presents the development of the DB process which has been specifically tailored for the repair of SX superalloys. The principles of the diffusion brazing process as applied to the CMSX-4 superalloy are discussed and the parameters which control the brazing kinetics are outlined. The optimization of the brazing heat treatment cycle will be presented. This paper also demonstrates the retention of the single crystal micro-structure in the repair zone, and demonstrates the test procedures developed to achieve the required thermal and mechanical integrity of braze repairs for application in SX gas turbine components.

The reactions were carried out in sealed, evacuated glass ampoules in a temperature gradient 170 -+ 100°C. Te,o] and Te4[Bi2BrR] were both obtained as black, cubclike crystals with a violet lustre in reflecting light. Both compounds were found to be readily hydrolyzed by moist air. The preparations were accompanied by the formation of several by-products. All of these were found to have a higher tellurium content than the characterized compounds and were predominantly formed when a greater than stoichiometric amount of tellurium was used in the reaction When the amount of tellurium did not exceed the stoichiometry for Te4[Bi&!120] and Te4[Bi2Br8], these two compounds were formed as the principal products in yields of over 40%. Crystal Structure of Te4[Bi6ClZnJThe crystal structure is built up of discrete Tea' and polymeric [Bi6C120]2p ions. Table 1 contains the crystallographic data and the atomic coordinates, Figure I The chlorobismutate ion [Bi6C120]2-has a remarkable and complex structure. It consists of two distorted BiClh octahedra around Bi( 1) and Bi(3) and trigonal-pyramidal BiCl; units around Bi(2). The two BiCI6 octahedra are connected by a common corner with Cl(1) in the bridging position, while a BiCl, group is attached to Ri(1) by a common Cl(4) atom. These groups are connected by C1 atoms C1(2), Cl(3) and Cl(5) via common octahedral edges and corners to a two-dimensional sheet extending parallel to the crystallographic a-b plane. The Bi-CI bond lengths are depicted in Figure 3 in the form o f a histogram, which highlights the great variation in the coordination of the Bi atoms. The Bi(l)-Cl and Bi(3)-CI distances range from 248.9(3) to 306.6(4) pm. indicating strong distortion of the BiC16 octahedra. The coordination of Bi(2) also shows marked deviation. Three short Bi-CI bonds are seen, with an average length of 248.3 pm. while the next nearest coordinating CI atoms are more than 70 pin more distant. Thus, the local

Te7[Be2Cl6] bildet sich aus Te, TeCl4 und BeCl2 in einer eutektischen Schmelze von Na2[BeCl4] / BeCl2 bei 250 °C in Form hydrolyseempfindlicher, schwarzer Kristalle. (Te4)(Te10) [Bi4Cl16] wird aus Te, TeCl4 und BiCl3 durch chemischen Gasphasentransport in geschlossenen, evakuierten Glasampullen im Temperaturgradienten 150 ° → 90 °C in Form silberglänzender, nadelförmiger Kristalle erhalten. Die Strukturen beider Substanzen wurden anhand von Einkristalldaten bestimmt (Te7[Be2Cl6]: orthorhombisch, Pnnm, Z = 2, a = 541, 60(3), b = 974, 79(6), c = 1664, 4(1) pm; (Te4)(Te10)[Bi4Cl16]: triklin, P1¯, Z = 2, a = 547, 2(3), b = 1321, 1(7), c = 1490(1) pm, α = 102, 09(5)°, ä = 95, 05(5)°, γ = 96, 69(4)°). Die Struktur von Te7[Be2Cl6] besteht aus eindimensional‐polymeren Tellur‐Kationen (Te72+)n in Form gefalteter Bänder, die [Be2Cl6]2—‐Anionen haben die Struktur eines Tetraederdoppels mit gemeinsamer Kante. Durch eine andere Art der Faltung gegenüber dem polymeren Te‐Kation wie es in den Strukturen von Te7[MOX4]X (M=Nb, W; X=Cl, Br) vorkommt, stellt das (Te72+)n‐Ion in Te7[Be2Cl6] eine neue, isomere Form dar. Die Struktur von(Te4)(Te10)[Bi4Cl16] enthält zwei verschiedene polymere Te‐Kationen. (Te102+)n besteht aus ebenen Te10‐Gruppen in Form von drei eckenverknüpften Vierringen, die zu einem gefalteten Band verbunden sind. (Te42+)n bildet im Gegensatz zu den bisher stets gefundenen diskreten, quadratisch‐planaren E42+‐Ionen (E = S, Se, Te) eine Kette aus rechtwinklig‐planaren Te4‐Ringen (Te—Te 274 und 281 pm), die durch 297 pm lange Te—Te‐Bindungen verknüpft sind. Das [Bi4Cl16]4—‐Anion ist ebenfalls bandförmig. Bi weist die Koordinationszahl sieben in Form eines auf einer Vierecksfläche überdachten trigonalen Prismas auf.