Key Engineering Materials Vols. 336-338

Abstract: This paper reports a novel route to synthesize nano particles of YAG:Ce3+ luminescent materials via polymer gel precursor. In an aqueous solution containing Y(NO3)3, Ce(NO3)3 and Al(NO3)3, citric acid was added to improve the stability of the solution. Then, acrylamide and N,N`-methylenebis- acrylamide were added. The polymerization of mixture solution was initiated by adding (NH4)2S2O8. By heating the solution at 80oC for 3 h, a transparent gel was obtained. The gel was firstly transformed into active carbon by soaking it at 700oC in ultrahigh pure N2 atmosphere. Carbon in as-received mixture was then removed when the atmosphere was changed from nitrogen to air at the same heating temperature. Well dispersive nano powders of single phase YAG:Ce3+ were thus obtained. XRD, SEM and BET were used to study the characteristics of as-prepared nano YAG:Ce3+ powders.

Abstract: This paper reports a novel non-aqueous solvent chemical process to prepare nano ZrO2 powders. ZrOCl2•6H2O and urea were directly dissolved into an organic solvent of glycol. After this solution was put into an oven and reacted at 950C for 2 h, a transparent gel was obtained. As-received gel was heated at 2100C for 5 hrs to remove glycol, and dry powders were obtained. Then the powders were calcined at 7500C, and monoclinic phase of ZrO2 was obtained. With different concentration of ZrOCl2, a range of nano ZrO2 powders were obtained. Furthermore, a surfactant of polyglycol was added into the solution to improve the dispersion of nano-particles in the gel. XRD analysis confirmed the monoclinic phase of ZrO2. SEM imaging showed the characteristics of nanoparticles. BET analysis was employed to test the aggregation of as-received nano ZrO2 particles. Considering the effects of both the concentration of ZrOCl2 and the surfactant, the optimized synthesis process of nano ZrO2 particles was formed.

Abstract: The main chemistry ingredients of the shale in Baoding, China, are SiO2 and Al2O3, and the mineral components are quartz, feldspar and mica. The shale was sintered to produce pottery at 1000 ~ 1300°C and its deposit density and expansion ratio were measured. The compressive strength, apparent density, water absorption, etc, of some sintered samples with expansion ratio more than 1.5 were measured according to GB/T17431.2-1998. When sintered at 1150°C for 15 min, the expansion ratio of the shale is 1.96. When sintered at 1200°C for 10 min, the expansion ratio is 2.00. The performances of the prepared pottery accord with GB/T17431.2-1998: the compressive strength is 3.8MPa with the expansion ratio 1.96, the compressive strength is 4.2MPa with the expansion ratio 2.00. The water absorption is 4.9~5.8%, according with GB/T17431.2-1998.

Abstract: Pr-CeO2 nano-crystalline red lanthanide pigments were prepared from cerium (III) nitrate hexahydrate and praseodymium oxide by low-temperature combustion synthesis. Its ignited temperature was approximately 250°C. The prepared pigments were characterized by DSC, XRD, SEM and XPS. The results showed that the crystallite size decreases with increasing Pr mol concentration. The valence of praseodymium in the pigments and its coloring mechanism were also investigated. The trivalent Pr entered into CeO2 crystal lattice and formed Pr-CeO2 solid solution, which was based on the fluorite structure. It substituted trivalent Pr for tetravalent Ce in CeO2 crystal and was compensated by oxygen vacancies, which caused the distortion and the defection of the crystal lattice. Therefore the pigments can absorb the light with the wavelength of approximate 600nm and present the red tonality.

Abstract: The highly pure nanocrystalline Mg,Al-hydrotalcite with Zn2+ doping was synthesized by the one-step liquid reaction method at atmospheric pressure. And the preparation of the Zn2+-doped Mg,Al-hydrotalcite nanocrystalline was investigated according to the results of XRD, TEM, IR and DSC. Moreover, based on the DSC test results, the thermal mechanism functions of the Mg,Al-hydrotalcite with Zn2+ doping are studied in detail after calculation and comparison.

Abstract: In the present work, we investigate the photoluminescence (PL) and structural properties of Si nanoparticles embedded in SiO2 matrix. Si-rich silicon oxide (SRSO) films with Si concentration of 39% were synthesized by reactive RF magnetron sputtering. Annealing was performed at temperatures between 600°C and 1100°C in N2 ambient for 2h to precipitate Si nanoparticles from oxide matrix. Near infrared photoluminescence around 750nm can be clearly observed even in the as-deposited films, which indicates the existence of Si nanoparticles in films. The structural properties were analyzed by infrared absorption and Raman spectra. It is found that the structural properties strongly affect the PL properties of Si nanoparticles embedded in SiO2 matrix.

Abstract: β-SiC nanometer whiskers were prepared in a double heating furnace that is composed of the interior and exterior heating systems. The SiO2 nanometer powder and char pyrolyzed from phenol formaldehyde resin were used as starting materials. The effects of sintering temperature and holding time on β-SiC nanometer whiskers were investigated and the synthetic mechanism was studied. It was revealed that the β-SiC nanometer whiskers, with the diameter of 50-80nm and the aspect ratio of 50-300, can be prepared at 1300°C for 60 min. The purity of the β-SiC nanometer whiskers is about 99%.

Abstract: Xerogel was prepared by the sol-gel method using butyl titanate, alcohol, carbamide and glucose as raw materials. The precursor powders were obtained after xerogel was solvothermally treated at 220oC for 2 h. The IR analysis suggests that the precursor with 10% excess glucose gave an absorption peak at 1084.37cm-1, which was assigned to Ti-OH bond, while no such a peak can be observed for that with 30% excess glucose. The prepared precursor powders were then sintered at 1400oC in nitrogen atmosphere. XRD and SEM results indicated that the sintering time and the contents of glucose had great effects on synthesizing titanium nitride powders. The titanium nitride powders with a high purity and a mean grain size of about 35 nm could be prepared by heating the precursor with 10% excess glucose at 1400oC for 6.5 h.