Nano-sized Na A zeolite was successfully synthesized via the sol-gel process and microwave techniques. The synthesis parameters, such as hydroxide ion concentration, seed amount, as well as heating time and temperature, were studied to obtain the most uniform and very small sized NaA zeolite using the composition of SiO 2 :Al 2 O 3 : xNa 2 O:410H 2 O; 3 ≤ x ≤ 6. It was found that hydroxide ion concentration affects the crystal size and heating time, whereas a higher amount of seed provides smaller sized NaA zeolite. The zeolite product can be synthesized using a higher temperature for a shorter time or lower temperature for a longer time. The best conditions for synthesizing the smallest size, 0.1-0.2 µm, and the most homogeneous NaA zeolite is to use the composition of SiO 2 :Al 2 O 3 :3Na 2 O:410H 2 O and 3 wt% crystal seed at 80 • C microwave heating for 6 h. The synthesized NaA zeolite was characterized using XRD and SEM.
Activated carbons were prepared by chemical activation from scrap tire with two chemical reagents, NaOH and KOH. The activation consisted of different impregnation of a reagent followed by carbonization in nitrogen at 700°C. The resultant activated carbons were characterized in terms of BET surface area, methylene blue adsorption and iodine number. The influence of each parameter of the synthesis on the properties of the activated carbons was discussed, and the action of each hydroxide was methodically compared. It is the first time that preparation parameters and pore texture characteristics are simultaneously considered for two closely related activating agents of the same char precursor. Whatever the preparation conditions, it was shown that KOH led to the most microporous materials, having surface areas and adsorption properties (methylene blue adsorption and iodine number) higher than those obtained with NaOH, which was in agreement with some early works. However, the surface areas, methylene blue adsorption and iodine number obtained in the present study were much higher than in previous studies, up to 951 m2/g, 510 mg/g and 752 mg/g, respectively, using scrap tire waste char:KOH equal to 1:1. The thorough study of the way each preparation parameter influenced the properties of the final materials bought insight into the activation mechanisms. Each time it was possible; the results of scrap tire waste chemically activated with hydroxides were compared with those obtained with anthracites; explanations of similarities and differences were systematically looked for.
Mullite-zirconia composites were prepared by adding various zirconia contents in the mullite ranging from 0 to 30 wt-% and sintering at 1400-1600uC for 2 h. The phase composition examined by X-ray diffraction showed that mullite was the major phase combined with developed t-ZrO 2 and m-ZrO 2 phase as a function of zirconia content, especially at 1600uC, wherein m-ZrO 2 predominated. Density increased when the zirconia content and sintering temperature were increased ranging from 2?2 to 3?53 g cm 23 . The morphology of mullite grain showed elongated grains, whereas dispersed zirconia showed equiaxed and intergranular grains. Flexural strength was continuously improved by adding zirconia during the sintering temperature ranging from 1400 to 1500uC, whereas flexural strength was initially improved up to 5 wt-% of zirconia addition and deteriorated with more than 5 wt-% of zirconia content during sintering between 1550 and 1600uC. The maximum strength, 190 MPa, was obtained when sintering mullite with 30 wt-% of zirconia content at 1500uC. The degradation of strength at high sintering temperature may be a result from more occurrence of m-ZrO 2 phase. Thermal expansion of sintered specimens indicated linear change and hysteresis loop change. The hysteresis loop obtained with increased zirconia content resulted in the t-m phase transformation. Martensitic start temperature M s was determined to be 530uC for 15 wt-% zirconia sintered at 1500uC, implying that the t-m phase transformation occurred.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.