Effect of processing parameters on the morphology of hydrothermally synthesized calcium borate powders

The present study aimed to examine the effect of pH and time on the final morphology of calcium borate powders. Primarily, aqueous solutions that mainly consisted of borax and calcium chloride were prepared with five different pH values varying between 2 and 15. Hydrothermal synthesis temperature was determined as 200°C, and four different times from 30 min to 24 h were selected. Phase formation and powder morphology were examined via an X-ray diffractometer and scanning electron microscopy. Fourier transform infrared spectroscopy was used to identify the type of borate groups. Results revealed that pH directly determines the growth mechanism of calcium borate crystals. Lower pH induced nonclassical growth by forming self-assembled nano-plates. Individual, rodlike particles were observed for alkali solution. At weak basic conditions, priceite (4CaO·5B₂O₃·7H₂O) and alkali condition parasibirskite (2CaO·B₂O₃·H₂O) phases were obtained.     

Kinetics models for polyacrylamide-graphene oxide composites as antifoulant

Antifouling paints are used to protect the surface against these organisms such as algae, sea squirts, and barnacles. According to previous research, fish and seaweeds do not adhere to submerged surfaces using wet and soft hydrogels. The aim of this study is to investigate the temperature effect on the performance of antifouling composites to develop new useful antifouling composites for shipping sector. In this swelling experiment, the behavior of hydrogels produced from polyacrylamide (PAAm) and graphene oxide (GO) was investigated at different temperatures. Free-radical cross-linking copolymerization formed composite, using acrylamide, ammonium persulfate, N, N′-methylenebisacrylamide (BIS, Merck), and graphene oxide with various contents. The steady-state fluorescence technique was used for studying the swelling of PAAm-GO composites at various temperatures in pure water. When pyranine fluorescence intensity, I was measured, it decreased until swelling equilibrium was achieved. After the swelling experiment was started, the fluorescence emission (I_em) and scattering light intensities, I_sc from different GO content hydrogels were observed by real-time monitoring at various temperatures. Li-Tanaka and Fickian models were used to determine the diffusion coefficients for the swelling experiments in distilled and Marmara Sea Water for 8 and 50 μl of GO content hydrogels, respectively. According to literature, PAAm is utilized as a surface coating material to reduce biofouling, for this reason, this research will show a way to be able to use PAAm inside antifouling paints material for the marine industry.