RESUMEN
This work is aimed at the development and investigation of the oxidation behavior of ferritic stainless-steel grade AISI 441 and polymer-derived ceramic (PDC) protective coatings. Double-layer coatings of a PDC bond coat below a PDC top coat with glass and ceramic passive fillers' oxidative resistance were studied at temperatures up to 1000 °C in a flow-through atmosphere of synthetic air and in air saturated with water vapor. Investigation of the oxide products formed at the surface of the samples in synthetic air and water vapor atmospheres, at different temperatures (900, 950, 1000 °C) and exposure times (24, 96 h) was carried out on both uncoated steel and steel coated with selected coatings by scanning electron microscopy (SEM) and X-Ray diffraction (XRD). The Fe, Cr2O3, TiO2, and spinel (Mn,Cr)3O4 phases were identified by XRD on oxidized steel substrates in both atmospheres. In the cases of the coated samples, m- ZrO2, c- ZrO2, YAG, and crystalline phases (Ba(AlSiO4)2-hexacelsian, celsian) were identified. Scratch tests performed on both coating compositions revealed strong adhesion after pyrolysis as well as after oxidation tests in both atmospheres. After testing in the water vapor atmosphere, Cr ions diffused through the bond coat, but no delamination of the coatings was observed.
RESUMEN
Attempts to synthesize ZnY2O4 are made via a solid-state reaction in a high-temperature X-ray powder diffraction chamber as well as analyzing Y2O3 sinter ceramics pressure infiltrated by ZnO in a scanning electron microscope using energy-dispersive X-ray spectroscopy and electron backscatter diffraction (EBSD). The microstructure of the sinter ceramic is composed of ZnO grains dispersed in an Y2O3 matrix. Superimposed EBSD patterns of Y2O3 are misindexed as ZnY2O4 during the EBSD scan. The literature concerning ZnY2O4 is critically discussed.
RESUMEN
The crystallization of glass microspheres in the Y2O3-Al2O3-system produced from precursor powders of four different nominal compositions via flame synthesis is analyzed in detail by electron microscopy with a focus on electron backscatter diffraction (EBSD). Growth models are formulated for individual microspheres crystallized during flame synthesis as well as after an additional heat treatment step. 16 different types of crystallized bodies are cataloged for future reference. They are presented without regard for their relative occurrence; some are extremely rare but illustrate the possibilities of flame synthesis in the analyzed system. All three phases in the binary Y2O3-Al2O3-phase diagram (Y3Al5O12, YAlO3 and Y4Al2O9) and α-alumina are located by EBSD. Energy dispersive X-ray spectrometry results obtained from these microspheres show that their chemical composition can deviate from the nominal composition of the precursor powder. The multitude of differing microsphere types showing polygon and dendritic crystal growth as well as phase separation indicate that flame synthesis can lead to a wide variety of parameters during microsphere production, e.g. via irregular flight paths through the flame, contaminants or irregular cooling rates.
RESUMEN
Many elements, such as copper, cobalt (Co), strontium, magnesium and boron (B) have been used for single or multiple doping of bioactive glasses to promote angiogenesis during bone regeneration. However, few works have focused on promoting angiogenesis through stimulating several different signalling pathways which can be called a multi-target approach. In this study, 45S5 bioactive glass (BG) co-doped with B and Co was prepared by conventional melt quenching method. The synergistic effect of the two co-doping elements on angiogenesis promotion was expected. ATR-Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy and inductively coupled plasma-optical emission spectrometry were used to characterize the composition, element distribution and ion release of the samples, respectively. Results showed that the compositions of all samples were consistent with the design compositions and all elements were homogeneously distributed in the bulk glass. Different contents of B and Co led to different release rates of these elements. All samples showed bioactivity after immersion in simulated body fluid, regardless of the amount of doped B and Co. The 1% and 0.1% extracts of all samples did not show any cytotoxicity to MG-63 and ST-2 cells. Compared with single B or Co doping, the B and Co dual doped sample led to a stronger increase of the secretion of vascular endothelial growth factor from ST-2 cells, which supports and confirms the synergistic effect on angiogenesis of B and Co as co-doping elements in 45S5 BG.
Asunto(s)
Materiales Biocompatibles/química , Boro/química , Cerámica/química , Cobalto/química , Vidrio/química , Animales , Materiales Biocompatibles/farmacología , Regeneración Ósea/efectos de los fármacos , Línea Celular , Supervivencia Celular/efectos de los fármacos , Ratones , Neovascularización Fisiológica/efectos de los fármacos , Espectroscopía Infrarroja por Transformada de Fourier , Factor A de Crecimiento Endotelial Vascular/metabolismoRESUMEN
In this work, the influence of different cleaning procedures on adhesion of composite coatings containing passive ceramic and commercial glasses was investigated. Two compositions (C2c, D2-PP) of double-layer polymer-derived ceramic (PDC) coating systems, composed from bond coat and a top coat, were developed. In order to obtain adherent coatings, stainless steel substrates were cleaned by four different cleaning procedures. The coatings were then deposited onto the steel substrate via spray coating. Pretreatment by subsequent ultrasonic cleaning in acetone, ethanol and deionised water (procedure U) was found to be the most effective, and the resultant C2c and D2-PP coatings, pyrolysed at 850 °C, indicated strong adhesion without delamination or cracks, propagating at the interface steel/bond coat. In the substrate treated by sandblasting and chemical etching, small cracks in the bond coat were observed under the same pyrolysis conditions. After oxidation tests, all coatings, except for those subjected to the U-treated substrates, showed significant cracking in the bond coat. The D2-PP coatings were denser than C2c, indicating better protection of the substrate.