Deposição de recobrimentos de proteção térmica e ambiental por plasma spray utilizando precursor híbrido de SiO2+ZrO2/ Plasma spray deposition of thermal and environmental protection coatings using SiO2+ZrO2 hybrid precursor

Compósitos reforçados com fibra de carbono (C/C) são materiais amplamente utilizados em componentes estruturais, especialmente quando expostos as intensas cargas aerotermodinâmicas. Sua alta resistência e excepcional tenacidade à fratura, combinados com suas propriedades refratárias, resistência à erosão, corrosão e desgaste tornam este material ideal para aplicações em componentes estruturais, submetidos a altas temperaturas, tais como turbinas e veículos de reentrada atmosférica. Quando utilizados em atmosferas inertes ou em vácuo, os compósitos C/C mantêm suas propriedades a temperaturas superiores a 2000°C. Porém, nas condições de ambientes oxidantes e de elevadas temperaturas, os compósitos a base de fibras de carbono sofrem intensa degradação devido à elevada catalicidade de reações entre o carbono e o oxigênio, dificultando e, muitas vezes, impossibilitando seu uso em dispositivos aeroespaciais. Neste contexto, o objetivo deste trabalho é a deposição de recobrimentos de barreira ambiental (Environmental Barrier Coating, EBC), utilizando precursores híbridos de ZrO2+SiO2 visando proteção contra oxidação dos compósitos estruturais de C/C. Os recobrimentos serão depositados por meio do processo de spray a plasma de alta velocidade (High Velocity Plasma Spray, HVPS).

The Tale of al-Barrāq Son of Rawḥān and Laylā the Chaste

This book is a bilingual edition and study of a lengthy specimen of pre-modern Arabic storytelling. The tale’s origins are unknown but it probably dates from the seventeenth century. As a sustained fairy tale of the knight-in-shining-armour-rescues-damsel-in-distress variety, it reads as fiction and was probably intended as such. However, scholars in the Arab renaissance or Nahḍa received the text as history. Its pre-Islamic protagonists, ever emoting in verse, were thus celebrated as some of the earliest Arabic poets. The Arabic text featured in the monograph is sourced from five manuscripts and three published editions, and it is modelled on what I call the ‘Christian’ branch of the tale, or that version of the tale which identifies its hero as a Christian and which was promulgated by Christian scholars and literati in the nineteenth century. Two analytical chapters frame the tale: an introductory chapter which charts the evolution of the narrative and its cultural import through to the end of the twentieth century, and a concluding chapter that breaks the story down into its components and compares its structure to both the ʿUdhrī love tale and the popular epic or sīra, thereby situating the text as a hybrid precursor to the modern novel.

Preparation and structure of SiOCN fibres derived from cyclic silazane/poly-acrylic acid hybrid precursor

Ceramic matrix composite (CMC) materials have been considered a desired solution for lightweight and high-temperature applications. Simultaneously, among all different CMC reinforcements, polymer-derived ceramic (PDC) fibres have gained attention for the intrinsic thermal stability and mechanical strength with simple and cost-effective synthesis techniques. Here, carbon-rich SiOCN fibres were synthesized via hand-drawing and polymer pyrolysis of a hybrid precursor of 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasilazane (TTCSZ) and poly-acrylic acid (PAA). The type of silazane reported in this work is considered as a major precursor for SiCN; however, it is unspinnable, due to its unfavourable physical properties (low viscosity) and chemical structure (cyclic rather than linear structure). The introduction of PAA to TTCSZ to create a hybrid precursor remarkably improved the spinnability of the silazane and should be widely applicable to other unspinnable PDC pre-ceramic polymers. Investigations on the structural and compositional development of the fibres were mainly conducted via Raman spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, nuclear magnetic resonance and thermo-gravimetric analysis to determine spinnability, free carbon content, cross-linking and pyrolysis behaviour of the fibres, respectively.