Study of amorphous alumina coatings for next-generation nuclear reactors: High-temperature in-situ and post-mortem Raman spectroscopy and X-ray diffraction.

The present work focuses on the investigation of the thermal stability and structural integrity of amorphous alumina coatings intended for use as protective coatings on cladding tubes in Generation IV nuclear reactors, specifically in the Lead-cooled Fast Reactor (LFR) type. High-temperature Raman spectroscopy and high-temperature X-ray diffraction analyses were carried out up to 1050 °C on a 5 µm coating deposited by the pulsed laser deposition (PLD) technique on a 316L steel substrate. The experiments involved the in-situ examination of structural changes in the material under increasing temperature, along with ex-situ Raman imaging of the surface and cross-section of the coating after thermal treatments of different lengths. As it was expected, the presence of α-alumina was detected with the addition of other polymorphs, γ- and θ-Al2O3, found in the material after longer high-temperature exposure. The use of two structural analysis methods and two lasers excitation wavelengths with Raman spectroscopy allowed us to detect all the mentioned phases despite different mode activity. Alumina analysis was based on the emission spectra, while substrate oxidation products were identified through the structural bands. The experiments depicted a dependence of the phase composition of oxidation products and alumina's degree of crystallization on the length of the treatment. Nevertheless, the observed structural changes did not occur rapidly, and the coating's integrity remained intact. Moreover, oxidation signs occurred locally at temperatures exceeding the LFR reactor's working temperature, confirming the material's great potential as a protective coating in the operational conditions of LFR nuclear reactors.

Spectroscopic studies on phosphate-modified silicon oxycarbide-based amorphous materials.

Vibrational spectroscopy is the most effective, efficient and informative method of structural analysis of amorphous materials with silica matrix and, therefore, an indispensable tool for examining silicon oxycarbide-based amorphous materials (SiOC). The subject of this work is a description of the modification process of SiOC glasses with phosphate ions based on the structural examination including mainly Infrared and Raman Spectroscopy. They were obtained as polymer-derived ceramics based on ladder-like silsesquioxanes synthesised via the sol-gel method. With the high phosphate's volatility, it was decided to introduce the co-doping ions to create [AlPO4] and [BPO4] stable structural units. As a result, several samples from the SiPOC, SiPAlOC and SiPBOC systems were obtained with various quantities of the modifiers. All samples underwent a detailed structural evaluation of both polymer precursors and ceramics after high-temperature treatment with Fourier-transformed infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD) and magic angle spinning nuclear magnetic resonance (MAS-NMR). Obtained results proved the efficient preparation of desired materials that exhibit structural parameters similar to the unmodified one. They were X-ray-amorphous with no phase separation and crystallisation. Spectroscopic measurements confirmed the presence of the crucial Si-C bond and how modifying ions are incorporated into the SiOC network. It was also possible to characterise the turbostratic free carbon phase. The modification was aimed to improve the bioperformance of the materials in the context of their future application as bioactive coatings on metallic implants.

Key Properties of a Bioactive Ag-SiO2/TiO2 Coating on NiTi Shape Memory Alloy as Necessary at the Development of a New Class of Biomedical Materials.

Recent years have seen the dynamic development of methods for functionalizing the surface of implants using biomaterials that can mimic the physical and mechanical nature of native tissue, prevent the formation of bacterial biofilm, promote osteoconduction, and have the ability to sustain cell proliferation. One of the concepts for achieving this goal, which is presented in this work, is to functionalize the surface of NiTi shape memory alloy by an atypical glass-like nanocomposite that consists of SiO2-TiO2 with silver nanoparticles. However, determining the potential medical uses of bio(nano)coating prepared in this way requires an analysis of its surface roughness, tribology, or wettability, especially in the context of the commonly used reference coat-forming hydroxyapatite (HAp). According to our results, the surface roughness ranged between (112 ± 3) nm (Ag-SiO2)-(141 ± 5) nm (HAp), the water contact angle was in the range (74.8 ± 1.6)° (Ag-SiO2)-(70.6 ± 1.2)° (HAp), while the surface free energy was in the range of 45.4 mJ/m2 (Ag-SiO2)-46.8 mJ/m2 (HAp). The adhesive force and friction coefficient were determined to be 1.04 (Ag-SiO2)-1.14 (HAp) and 0.247 ± 0.012 (Ag-SiO2) and 0.397 ± 0.034 (HAp), respectively. The chemical data showed that the release of the metal, mainly Ni from the covered NiTi substrate or Ag from Ag-SiO2 coating had a negligible effect. It was revealed that the NiTi alloy that was coated with Ag-SiO2 did not favor the formation of E. coli or S. aureus biofilm compared to the HAp-coated alloy. Moreover, both approaches to surface functionalization indicated good viability of the normal human dermal fibroblast and osteoblast cells and confirmed the high osteoconductive features of the biomaterial. The similarities of both types of coat-forming materials indicate an excellent potential of the silver-silica composite as a new material for the functionalization of the surface of a biomaterial and the development of a new type of functionalized implants.