To enhance the insulating properties of a thermal barrier coating, one has to focus on new materials with lower intrinsic thermal conductivity than established yttria-stabilized zirconia. Substances with pyrochlore structure were investigated. Starting from lanthanum zirconate, substitutions of the lanthanum by other trivalent rare-earth elements were made, and the thermal conductivity and the thermal expansion coefficient of the manufactured materials were measured. A complete substitution of the lanthanum led to increased thermal expansion coefficients, whereas the partial substitution did not show an appreciable effect. The thermal conductivities of the modified materials were lower than that of the pure lanthanum zirconate for temperatures <1000°C for all amounts and elements of substitution. A comparison of the observed values with calculated values of the thermal conductivities showed a relatively good agreement.N. Padture-contributing editor Manuscript No. 186991.

In application as a thermal barrier coating (TBC), partially stabilized zirconia (Zr) approaches some limits of performance. To further enhance the efficiency of gas turbines, higher temperature capability and a longer lifetime of the coating are needed for the next generation of TBCs. This paper presents the development of new materials and concepts for application as TBC. Materials whose compositions have the pyrochlore structure or doped Zr are presented in contrast with new concepts like nanolayers between the top and bond coat, metal-glass composites, and double-layer structures. In the last concept, the new compositions are used in a combination with Zr, as a double, multi, or graded layer coating. In this case, the benefits of Zr will be combined with the promising properties of the new top coating. In the case of metal-glass composites, the paper will be focused on the influences of different plasma spraying processes on the microstructure. The performance of all these different coating systems has been evaluated by burner rig tests. The results will be presented and discussed.

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Single-crystal Raman spectra in the range 4000-35 cm −1 and the results of group theoretical treatment including Cartesian symmetry coordinates of nickel iodate dihydrate, Ni.IO 3 / 2 · 2H 2 O, (space group Pbca, Z = 4) are presented and discussed with respect to the strength of the HO -H· · ·OIO 3 hydrogen bonds and the extent of intramolecular (intraionic) coupling of the stretching vibrations of both the hydrate H 2 O molecules and the iodate IO 3 − ions. The energies and relative intensities of the IO stretching modes in the various species of the unit-cell group D 2h reveal that the iodate ions of the title compound behave as if they possess pseudo C 2v site symmetry with a at least partly uncoupled IO stretch due to the significantly shortest (175.5 pm) IO arm and a symmetric (n s ) and an antisymmetric stretching vibration (n as ) due to the remaining IO 2 group (r I -O = 184.2 and 186.0 pm). The respective site-group modes decrease in the order n 3a $ n IO.1/ (mean value of the respective unit-cell group modes: 804 cm −1 / > n 1 $ n s (772 cm −1 / > n 3b $ n as (744 cm −1 ) (n 1 and n 3 as for distorted C 3v IO 3 − ions). For the IO 3 − bending modes (430-300 cm −1 ) and the lattice modes below 300 cm −1 the true vibrational modes are not known. The normally used assignment to a symmetric (n 2 ) and an asymmetric bending vibration (n 4 ) as for C 3v IO 3 − ions is at least questionable.The hydrogen-bond distances calculated from the wavenumbers of the OD stretching modes of matrixisolated HDO molecules do not fully agree with the data of a neutron diffraction study performed in 1972.

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Das Standard‐Wärmedämmschichtmaterial Ytttriumoxid‐stabilisiertes Zirkonoxid (YSZ) ist für den Langzeiteinsatz auf eine maximale Temperatur von etwa 1200°C beschränkt. Dementsprechend kann ein weiterer Anstieg der Gaseinlaßtemperatur und damit der Effizienz von Gasturbinen kaum mit YSZ‐Beschichtungen erreicht werden. In einem Auswahlprozeß wurden besonders Perowskit‐ (ABO3, A = Sr,Ba, B = Zr) und Pyrochlor(A2B2O7, z.B. A = La oder andere Seiten‐Erd‐Elemente, B = z.B. Zr)‐Materialien als mögliche Kandidaten für Wärmdämmschichten identifiziert. Grundlegende physikalische Eigenschaften (z.B. Wärmeausdehnungskoeffizient, Temperaturleitfähigkeit und Wärmeleitfähigkeit) von einigen Kandidaten wurden an gesinterten, dichten Proben bestimmt. Die Möglichkeit zur Optimierung der Eigenschaften durch spezifische Zusammensetzungen wird diskutiert. Von den vielversprechenden Materialien wurden Pulver, die für das Plasmaspritzen geeignet sind, über das Sprühtrocknen hergestellt. Neue WDS‐Systeme, die aus über das atmosphärische Plasmaspritzen abgeschiedenen neuen Materialien und mit Vakuumplasma‐gespritzten Haftvermittlerschichten bestanden, wurden in einem Gasbrennerteststand untersucht. Besonders La2Zr2O7‐Beschichtungen zeigten vielversprechende Ergebnisse. Eine weitere Verbesserung konnte durch den Einsatz von lagigen oder gradierten Schichten mit einer YSZ‐Schicht an der Haftvermittlerschicht und dem neuen Material als oberste Schicht erzielt werden. Erste Ergebnisse von thermischen Zykliertests bei 1250 und 1350°C Oberflächentemperatur werden präsentiert.