Synthesis and Sintering

Influence of preheating temperature on splat morphology of spray deposited yttria-stabilized zirconia and lanthanum magnesium hexaaluminate in thermal barrier coatings

2025-03-06T16:06:04-04:00

The performance of thermal barrier coatings (TBCs) depends upon the morphology of individual splats and how a single particle flattens. A splat is a single unit cell of thermal barrier coatings. Its properties significantly influence the overall performance of the coating. The transition temperature of the substrate affects the splat morphology and also influences the adhesion strength of the applied coating. This study investigates the effect of substrate preheating temperature on splat morphology and the critical transition temperature for yttria-stabilized zirconia (8YSZ) and lanthanum magnesium hexaaluminate (LaMgAl₁₁O₁₉, LaMA) powders deposited via atmospheric plasma spray (APS). Using scanning electron microscopy (SEM), a critical transition temperature of 400°C was identified for both materials. At this temperature, disc-shaped splats with improved adhesion formed, while irregular shapes were observed below 400°C, and disordered morphologies appeared above it. Notably, at 400°C, 8YSZ splats exhibited surface cracks, whereas LaMA splats remained crack-free, highlighting differences in their thermo-mechanical properties. These findings emphasize the importance of optimizing preheating temperature to achieve desirable splat morphology and enhance TBC performance.

Recent developments in chitosan-based adsorbents for tetracycline removal: A mini-review

2025-03-02T13:27:12-04:00

Tetracyclines (TCs) are widely used antibiotics that have raised concerns due to their presence in the environment, posing risks to human health and ecosystems. This mini-review explores recent advancements in utilizing chitosan-based adsorbents to remove TCs from wastewater efficiently. Our review reveals that adsorption performance is highly influenced by temperature and pH, with most studies reporting effective TC removal between 25-45 °C and pH values of 2-12. The Langmuir and Freundlich isotherm models are both applicable, depending on the specific adsorbent, indicating both monolayer and heterogeneous adsorption behavior, with maximum adsorption capacities ranging from 19.32 mg/g to 940 mg/g, with the highest capacity shown for BCM Char/CS /PEI. Kinetic studies predominantly followed the pseudo-second-order model, suggesting chemisorption as a rate-limiting step, while some followed a pseudo-first-order model. High removal rates (≈ 90-99%) were reported for materials like ZIF-8-chitosan, BCM Char/CS/PEI, and CMC-modified Na-Mt. This review highlights the significant potential of chitosan-based adsorbents. At the same time, further research is needed to optimize adsorption conditions, understand the mechanisms involved, and address the diverse sources of TC pollution. Given the global impact of TCs, a comprehensive approach encompassing enhanced monitoring, stricter regulations, the development of advanced treatment technologies like chitosan-based adsorbents, and public awareness campaigns is imperative to mitigate their environmental risks effectively.

Advances in electrospinning techniques for synthesis of nanofibers loaded with herbal extracts and natural ingredients: A comprehensive review

2025-03-02T13:23:01-04:00

Electrospinning offers a versatile method for the synthesis of polymeric nanofibers integrated with natural compounds such as medicinal extracts, antibacterial agents, and antioxidants (e.g., Aloe vera, honey, curcumin). These composite fibers exhibit diverse potential applications spanning wound dressing, tissue engineering, drug delivery, and the food industry. Tailoring nanofiber morphologies and loading techniques enables modulation of release kinetics and controlled diffusion of extracts tailored to specific applications. Recent literature showcases an array of studies exploring the electrospinning of various polymers, including natural ingredients, for biomedical and industrial purposes. This article aims to compile and review methodologies for combining and encapsulating natural extracts within polymers via electrospinning synthesis method, alongside their applications. Our review presents a comprehensive analysis of electrospun nanofibers containing extracts and natural ingredients, encompassing their architectural diversity and factors influencing release kinetics. As more people become interested in natural materials, we expect to see a huge increase in research efforts in this field in the years to come.

Synthesis and characterization of mullite (3Al2O3.2SiO2) sol by sol-gel route using inorganic salts

2025-02-14T03:59:01-04:00

Mullite, also referred to as 3Al₂O₃.2SiO₂, is recognized as the only chemically stable intermediate phase in the SiO₂–Al₂O₃ system, as indicated by mineralogical studies. Several synthesis techniques can be employed to obtain mullite. In this research, the synthesis of mullite particles is aimed to be achieved via the sol-gel route using inexpensive materials, specifically silica sol and aluminum nitrate hydrate [(Al(NO₃)₃.9H₂O] as sources for silica and alumina, respectively. The article is organized into two sections which describe and discuss the systematic synthesis of the mullite sol. The first section emphasizes the influence of the stoichiometric values of Al and Si elements on the formation of the mullite phase at 1200 °C. The effects of sintering temperature on the microstructure and composition of the synthesized mullite sol, with a 3:1 alumina-to-silica ratio, are discussed in the following section. This includes pH, density, solid content, particle size distribution, thermal analysis, phase evolution with temperature, nature of bonds, and microstructural analysis. The XRD results for the mullite sol with a 3:1 alumina-to-silica ratio show strong crystalline diffraction peaks of the mullite phase and the absence of a free silica phase at 1200 °C. The solution exhibits a clear, stable, and homogeneous appearance, with a density of 1.17 g/cm³, a pH ranging from 4 to 5, and a solid content of approximately 15%, measured after heating at 1000 °C for 2 h.