Rare‐earth zirconates have been identified as a class of low‐thermal‐conductivity ceramics for possible use in thermal barrier coatings (TBCs) for gas‐turbine engine applications. To document and compare the thermal conductivities of important rare‐earth zirconates, we have measured the thermal conductivities of the following hot‐pressed ceramics: (i) Gd2Zr2O7 (pyrochlore phase), (ii) Gd2Zr2O7 (fluorite phase), (iii) Gd2.58Zr1.57O7 (fluorite phase), (iv) Nd2Zr2O7 (pyrochlore phase), and (v) Sm2Zr2O7 (pyrochlore phase). We have also measured the thermal conductivity of pressureless‐sintered 7 wt% yttria‐stabilized zirconia (7YSZ)—the commonly used composition in current TBCs. All rare‐earth zirconates investigated here showed nearly identical thermal conductivities, all of which were ∼30% lower than the thermal conductivity of 7YSZ in the temperature range 25°–700°C. This finding is discussed qualitatively with reference to thermal‐conductivity theory.

have nearly the same thermal conductivities in the temperature range 25-700°C, all of which are approximately 30% lower than that of 7 wt% yttria-stabilized zirconia. These desirable thermal, mechanical, and physical properties of the rare-earth zirconates make them attractive candidates for use in thermal barrier coatings for gas-turbine engine applications. -(WU, J.; WEI, X.; PADTURE*, N. P.; KLEMENS, P. G.; GELL, M.; GARCIA, E.; MIRANZO, P.; OSENDI, M. I.; J. Am.

Low thermal conductivity ceramics in the ZrO2–GdO1.5 system have potential in structural (refractories, thermal barrier coatings, thermal protection) and nuclear applications. To that end, the thermal conductivities of hot-pressed xGdO1.5 ·(1 – x)ZrO2 (where x = 0.05, 0.15, 0.31, 0.50, 0.62, 0.75, 0.89, and 1.00) solid solutions were measured, for the first time, as a function of temperature in the range 25 to 700 °C. On the ZrO2-rich side, the thermal conductivity first decreased rapidly with increasing concentration of GdO1.5 and then reached a plateau. On the GdO1.5-rich side, the decrease in the thermal conductivity with increasing concentration of ZrO2 was less pronounced. The thermal conductivity was less sensitive to the composition with increasing temperature. The thermal conductivity of pyrochlore Gd2Zr2O7 (x = 0.5) was higher than that of surrounding compositions at all temperatures. A semiempirical phonon-scattering theory was used to analyze the experimental thermal conductivity data. In the case of pure ZrO2 and GdO1.5, the dependence of the thermal conductivity to the absolute temperature (T) was less than 1/T. Therefore, the minimum thermal conductivity theory was applied, which better described the temperature dependence of the thermal conductivity of pure ZrO2 and GdO1.5. In the case of solid solutions, phonon scattering by cation mass fluctuations and additional scattering by oxygen vacancies on the ZrO2-rich side and by gadolinium vacancies on the GdO1.5-side seemed to account for the composition and temperature dependence of the thermal conductivity.

Polylactic acid (PLA) surgical suture can be absorbed by human body. In order to avoid surgical site infections (SSIs), the drug is usually loaded on the PLA suture, and then the drug can release directly to the wound. Because the different types of wounds heal at different times, it is needed to control the drug release rate of PLA suture to consistent to the wound healing time. Two biopolymers, polyglycolide (PGA) and polycaprolactone (PCL), were selected as the carrier of ciprofloxacin (CPFX) drug, and then the CPFX-PCL/PGA was coated on the PLA suture. The degradation rate of drug-carrier can be controlled by adjusting the proportion of PCL/PGA, which can regulate the rate of CPFX drug release from PLA suture. The results show that the surface of PLA suture, coating with PCL/PGA, was very rough, which led to increased stitching resistance when we were suturing the wound. These materials, such as the PLA suture, the PCL/PGA carriers and the CPFX drug, were just physically mixed rather than chemically reacted, which was very useful for ensuring the original efficacy of CPFX drug. With the increasing of PCL in the carriers, both the breaking strength and elongation of these un-degraded sutures increased. During degradation, the breaking strength of all sutures gradually decreased, and the more PCL in the coating materials, the longer effective strength-time for the suture. With the increasing of PCL in the drug-carrier, the rate of drug releasing became lower. The drug release mechanism of CPFX-PCL/PGA was a synergistic effect of drug diffusion and PCL/PGA carrier dissolution.