Synthesis Yttrium Aluminum Garnet Precursor via Homogeneous Precipitation under Microwave Irradiation

The lowly-agglomerated single-phase YAG nanopowders were synthesized for the first time by the microwave homogeneous precipitation in the presence of urea. The composition and transformations during calcination of YAG precursor were analyzed by IR, DTA/TG and XRD. The size and morphology of YAG powders were characterized by LD and TEM methods. Results show that amorphous precursor synthesized under [urea]/[metal ions] molar ratio of 15 crystallizes directly to single-phase YAG at 900degreesC. The size distribution and sinterability of YAG powders are obviously improved by adding (NH4)(2)SO4 into the reaction solution. YAG powders obtained from precursor with the (NH4)(2)SO4 content of 8% have good sinterability and are highly densified at a temperature of 1500degreesC

Structure Elucidation of Hydroxypropyl Cellulose Homogenously Prepared from NaOH/Urea Aqueous Solution

Hydroxypropyl celluloses(HPC) were homogenously synthesized by the reaction of cellulose with propylene oxide in NaOH/urea aqueous solution.Water-soluble HPC with molar degree of substitution(MSNMR) in the range of 0.52~0.78 was prepared from microcrystalline cellulose,cotton linters,and spruce sulfite pulp.The structure of the HPC samples was characterized by means of FT-IR,NMR,gas chromatography(GC),and size exclusion chromatography(SEC) analyses.Three types of cellulose samples with different molecular weights were found to dissolve well in the NaOH/urea solvent with no obvious differences in reactivity and regioselectivity.The relative reactivity of hydroxyl groups in the glycosyl unit was in the following order:O-6>O-2>O-3.In addition,the results of the study indicated that the tandem reaction during hydroxypropylation could be ignored.

Homogeneous Synthesis and Characterization of Quaternized Cellulose Derivatives in NaOH-urea Aqueous Solutions

Quaternized cellulose( QC) derivatives were synthesized by reacting cellulose with 3-chloro-2-hydroxypropyl trimethyl ammonium chloride( CHPTAC) in an aqueous solution of Na OH-urea. The chemical structures and physical properties of the obtained QC derivatives were characterized using nitrogen content analysis,Fourier transform infrared spectroscopy( FT-IR),~1H-nuclear magnetic resonance(1H-NMR),X-ray diffraction( XRD),and thermal gravity analysis( TGA). The FT-IR and ~1H-NMR results confirmed the successful introduction of cationic quaternary ammonium groups into the main chain of cellulose. A series of QC derivatives with the degree of substitution( DS) values ranging from 0. 33 to 0. 80 were derived by adjusting the molar ratio of CHPTAC to anhydroglucose unit( AGU) of cellulose,concentration of cellulose in the Na OH-urea solution,as well as reaction temperature and time. According to the DS values of the QC derivatives,the optimized synthetic conditions were as follows: 25℃ reaction temperature,3% cellulose in Na OH-urea solution,the molar ratio of etherification agent to glycosidic cellulose of 15∶ 1,and 12 h reaction time. The TGA and XRD results revealed that the crystalline structure was destroyed during etherification,and the thermal stability of the QC derivatives was lower than that of cellulose.