The main objective of this study was to investigate the role of zirconia addition to mullite through an in-situ reaction aimed at improving both the mechanical properties and the sinterability behavior. In this work, mullite-zirconia composites were produced using a solgel technique. Different amounts of zirconia (0, 10, 15, and 20 wt.%) were added to the mullite, and the calcined gels were sintered at 1550-1700°C for 1 h. The apparent porosity and bulk density of the blank and zirconia/mullite composites were estimated in accordance with ASTM C-20. The phase composition and sample morphology were evaluated via X-ray diffraction (XRD) and scanning electron microscopy analysis (SEM), respectively. Furthermore, the mechanical properties and thermal expansion coefficient (TEC) were also evaluated. The results revealed that the apparent porosity decreased and the density of the zirconia/mullite composites increased when the sintering temperature was increased from 1550 to 1700°C. However, the mechanical properties improved with increasing zirconia content and MZ20 sintered at 1700°C exhibited the maximum bending strength. The TEC results reflected the influence of the composition on the sample TEC. Samples with higher ZrO 2 content yielded higher TEC figures than those with lower content.
The present study has been carried out to investigate the mechanisms of sol–gel reactions using TEOS as precursor in the presence of acid or base catalyst. The gels were prepared by hydrolysis of TEOS using hydrochloride acid or ammonium hydroxide catalyst. The obtained gels were also characterized by FTIR spectroscopy. The results of FTIR spectroscopy indicated the existence of silanol and siloxane bonds; due to the formation of hydrolyzed species as reactive intermediate compounds in initial stage converted by condensation reactions to gels as ultimate products. Accordingly, appropriate mechanisms have been proposed for sol – gel reaction using TEOS as precursor in the presence of acid or base catalyst. These mechanisms involve three-steps SN2 mechanisms for base catalyzed hydrolysis reaction of TEOS and SN1 mechanisms for acid catalyzed hydrolysis reaction of TEOS. Three mechanisms have been also proposed for condensation reaction as second stage in sol-gel process. These mechanisms include alcoxolation, oxolation and oltaion.
The present study is aimed to synthesize V2O5 using V(ORi)3 precursor and study its anti-microbial activity. The V(ORi)3 was prepared by reaction of VCl3 and isopropanol alcohol. The synthesized V(ORi)3 was hydrolyzed to yield black V(OH)3 gel using concentrated HCl as gelling agent. Yellow V2O5 obtained by thermal treatment of V(OH)3 gel at110oC and 380oC. All products were characterized using FT-IR Spectroscopy method. IR spectral revealed to found V(ORi)3, V(OH)3 gel and V2O5 were formed. The V2O5 has been tested in vitro against numbers of microorganisms, to assess their antimicrobial activity using disc diffusion method, according to the National Committee for Clinical Laboratory Standards Guidelines. The results showed that V2O5 is active against Staphylococcus aureus and Pseudomonas aeruginosa and partial active against Bacillus subtilis, Escherichia coli and Candida albicans. Antimicrobial Study of VO(OR)3 is required.
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