Preparation and Spectroscopy of Aluminosilicate Films Deposited on Graphite Surfaces via an Anhydrous Sol-Gel Route

Anhydrous aluminosilicate sols with Al : Si molar ratio ranging from 1 : 10 to 1 : 5 were prepared by a two-step anhydrous sol-gel process, in which tetraethoxysilane (TEOS) is pre-hydrolysed by formic acid, followed by addition of aluminium ethoxide. Unlike the case of aqueous sol-gel routes, where the Si–O–Al network homogeneity is greatly restricted by precipitation of Al(OH)₃, this anhydrous route yields clear, homogeneous sols. The sol formation and densification processes were investigated by infrared spectroscopy and X-ray powder diffraction (XRD) techniques, and the existence of Al–O–Si linkages was confirmed. To demonstrate an application of the anhydrous sol-gel process, aluminosilicate films were deposited onto graphite surfaces by dip coating and densified at 800°C under nitrogen, and their protective effect was evaluated.     

Phase Transformation During the Heat Treatment of Sol-Gel Mullite

The mechanism of mullite formation depends upon the method of combining the silica and alumina-containing reactants. In this work, the effects of the processing variables (dilution, pH, gelling temperature and water content) on mullite formation were investigated. Monophasic gel was synthesized from aluminium nitrate nanohydrate dissolved in an absolute ethyl alcohol and silica sol mixture. The gelling was performed at room temperature and at 60°C. It was found experimentally that the temperature of mullite formation depends on the microstructure of the gel. The lowest temperature of mullite formation (970°C) was observed when the mullite gel was prepared at low pH (pH=1), low water content and high gelling temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

n-Dodecane Hydroconversion over Nickel Supported on Different Mesoporous Aluminosilicates

Introduction The hydroconversion of n-paraffins is achieved over bifunctional catalysts consisting of an acidic support and a hydrogenating/dehydrogenating metal compo-nent.1 During the reaction, the metal catalyses hydrogen transfer reactions, while isomerization and cracking oc-cur on the Br鰊sted acid sites.2,3 This reaction pathway determines that the proper ratio of metal/acid is impor-tant for the catalytic properties of the hydroconversion catalysts. The Pt, Pd or Ni promoted zeolite …     

多级复合孔硅铝材料的合成与表征

采用表面包覆聚电解质的聚苯乙烯小球为模板,制备多级复合孔硅铝材料前体。 经水热晶化处理后焙烧脱模板,获得了多级孔结构的硅铝分子筛材料。 通过X射线衍射、傅里叶红外光谱、N2吸附-脱附、扫描电子显微镜和透射电子显微镜等测试技术对水热晶化不同时间的硅铝材料进行表征。 探讨了水热晶化时间对材料孔道结构的影响。 结果表明,水热晶化时间小于22 h,样品中含有介孔-大孔双连续孔道体系。 晶化时间超过22 h,样品中含有微孔-介孔-大孔多级孔道体系。 晶化36 h的样品,大孔孔壁由纳米级ZSM-5型沸石分子筛晶体构成。     

Mullite Formation of Colloidal Matrix Hybrid Aluminosilicate Gel

A hybrid aluminosilicate gel composed of a relatively small amount of single-phase gel in a diphasic matrix forms when a diphasic gel of AlOOH and SiO₂ is heated at 700°C for 7 h. The formation of mullite from this hybrid gel is a sequential conversion process, but not of two entirely independent processes of single-phase gel and diphasic gel. The high commencement temperature (>1250°C) of mullite formation from this hybrid gel indicates that the dominant component (diphasic component) strongly affects or controls the mullite transformation behavior of the hybrid gel. The apparent activation energy for mullitization from this hybrid gel is 846 kJ/mol, which is somewhat lower than that of pure diphasic gel but much higher than that of pure single-phase gel.     

Infrared and nuclear magnetic resonance structural studies <Emphasis Type="Italic">vs</Emphasis>. thermal treatment of geopolymers/biphasic calcium phosphates

Summary In biomaterial field, the introduction of new types of composites presents a great interest for orthopaedic surgeons. In this work, geopolymers which are a family of aluminosilicates were synthesised and mixed with biphasic mixture (hydroxyapatite and of tricalcic phosphate). The optimised thermal treatment causes the reduction of pH to 7 units and favours the expansion of composites. Consequently, the increasing of porosity percentage was induced. These properties offer a good opportunity for applied composite as potential osseous biomaterial. To study the consequences of thermal treatment in the initial amorphous structure of composites some physico-chemical techniques like SEM, MAS-NMR and FTIR were employed. These methods permitted to evaluate the porosity, different links in composites and contributions of different groups of Si and Al before and after thermal treatment.     

Concentration-dependent luminescence of Tb ions in high calcium aluminosilicate glasses

This study deals with the results on the concentration-dependent fluorescence properties of Tb³⁺-doped calcium aluminosilicate (CAS) glasses of composition (100−x)(58SiO₂–23CaO–5Al₂O₃–4MgO–10NaF in mol%)-x Tb₂O₃ (x=0, 0.25, 0.5, 1, 2, 4, 8, 16, 24, 32, 40 in wt%). The FTIR reflectance spectra suggested the role of dopant ions as network modifiers in the glass network. The fluorescence spectra of low Tb³⁺-doped glasses have revealed prominent blue and green emissions from ⁵D₃ and ⁵D₄ excited levels to ⁷F_j ground state multiplet, respectively. The glass with 2 wt% of Tb₂O₃ has exhibited maximum intensity of blue emission from ⁵D₃ level, while green emission from ⁵D₄ level has increased linearly up to 24 wt% and showed reduction in the rate of increase for higher Tb₂O₃ concentrations. The concentration quenching of blue emission (⁵D₃→⁷F_j) is attributed mainly to the resonant energy transfer (RET) assisted cross-relaxation (CR) among the excited and nearest neighbour unexcited Tb³⁺ ions in the glass matrix. The decline in rate of increase of green emission (⁵D₄→⁷F_j) at higher concentrations has been explained due to a possible occurrence of cooperative energy transfers leading to 4f⁸→4f⁷5d transition interactions. The blue and green emission decay kinetics have been recorded to compute the excited level (⁵D₃ and ⁵D₄) lifetimes, which confirmed the Tb³⁺ concentration quenching of the blue emission in these glasses.     

掺钕锂铝硅玻璃陶瓷制备和发光性能研究

采用传统熔融及退火技术,引入合适的添加剂于相对低温下成功制备出掺钕锂铝硅玻璃,通过控制成核和析晶工艺制备出锂铝硅玻璃陶瓷。采用差热分析、X射线衍射、扫描电镜、紫外可见近红外分光光度计和荧光光谱仪对材料进行表征。三个发光谱带中心波长位于890 nm,1065 nm和1330 nm处,分别对应于4F3/2→4I9/2,4F3/2→4I11/2和4F3/2→4I13/2跃迁。玻璃陶瓷晶相及晶粒大小对Nd3 离子发光性能影响很大。当Nd3 离子进入晶粒尺寸为10~20 nm的β--锂霞石固溶体时,发光强度与基质玻璃相比明显增强,在1065 nm处的受激发射截面iσn达1.931×10-21cm2,比基质玻璃受激发射截面提高了约8%。当β--锂霞石固溶体晶粒尺寸接近可见光波长时钕离子发生荧光猝灭。而当β--锂霞石固溶体晶型转变为β--黝辉石固溶体时,荧光猝灭消失。     

A NOVEL ALUMINOSILICATE WITH BIMODAL MESOPORE DISTRIBUTION ?a?a SYNTHESIS AND CHARACTERIZATION

A novel aluminosilicate material (denoted as NKF-2) with well defined bimodal mesopore distribution has been hydrothermally synthesized directly using cetyltrimethylammonium chloride and tetraethylammonium hydroxide as mixed templates, in which one mesopore is distributed at around 3.8 nm and the other at 2.6 nm. The synthesized samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy, N2 adsorption, infrared spectroscopy, thermo-gravimetic analysis and solid-state 27Al and 29Si magic-angle-spinning(MAS) NMR spectroscopies to understand both the pore structures and the Local atomic arrangements of these solid products.