Densification and crystallisation of celsian glass derived from alkoxide gel

High density (98% of theoretical) was achieved at 900°C for an all-alkoxide derived bulk celsian gel prior to crystallisation. TEM indicated that crystallisation was dominated by volume nucleation and growth of hexagonal disc shaped hexacelsian. Kinetic studies using SEM indicate a maximum nucleation rate at 980°C and an activation energy for crystal growth of 566 KJ/mol. The high rates of densification and of nucleation are attributed to the high OH content in the gel-derived glass.     

The sintering of silica aerogels studied by thermoporometry

The evolution of the texture of silica aerogels during sintering is studied by thermoporometry for both neutral and base catalysed materials.During the densification the macroporous volume drops and the analysis of the mesopore size distribution evolution shows that the collapse of the smallest mesopores is responsible for the macropore volume transformation. However, corrections of the measured volumes are necessary to characterize the most compliant materials.     

Sol-Gel Processing of Transparent PLZT((Pb,La)(Zr,Ti)O3) Fibers

PLZT((Pb,La)(Zr,Ti)O₃) ceramic fibers were prepared by the sol-gel method from a solution of lead acetate trihydrate, lanthanum isopropoxide, zirconium n-propoxide and titanium isopropoxide containing 2-methoxyethanol as the solvent. The as-drawn gel fibers were pretreated in an autoclave and preheated in flowing H₂O vapor prior to the heat-treatment for crystallization. The effects of autoclaving and preheating in flowing H₂O vapor on the structure and composition of the resultant fibers were investigated. Optically transparent single phase perovskite PLZT fibers of 5–15 m in thickness and 5 cm in length were successfully prepared when the autoclave-treatment and the preheating in flowing H₂O vapor were conducted prior to crystallization. These treatments are thought to promote hydrolysis of the organic groups and polycondensation reaction in the gel fibers, leading to the successful formation of dense, crack-free transparent PLZT fibers.     

Emanation thermal analysis study of a sol-gel precursor for silica-titania waveguides

Emanation Thermal Analysis (ETA) was demonstrated as a tool for the characterization of microstructure changes of a sol-gel precursor for silica-titania layers deposited on the glass plate to be used as planar waveguides. Temperature ranges of 280-330 and 380-500°C, respectively, in which the densification of the layers took place, were determined by ETA under in situ conditions of the sample heating. Results of thermogravimetry were compared with the ETA data. This revised version was published online in August 2006 with corrections to the Cover Date.     

Application of Hot Press Sintering to Na2O-B2O3-SiO2 Gels Containing Quantum Dots for Lowering of Densification Temperature

Na₂O-B₂O₃-SiO₂ (NBS) gels containing a large amount of CdS quantum-dots (10 wt%) were densified using the hot press (HP) sintering method. By HP treatment, full-densification temperature could be lowered by about 40°C than that of the normal non-pressing (NP) heat treatment. Exciton absorption of CdS quantum-dots in HP-sample showed a large blue shift compared with that in the NP sample, and the size-distribution of CdS dots remained very sharp, with a mean particle diameter d = 3.66 nm and a standard deviation of = 0.72. HP pressure had a large effect on the reduction of sintering temperature and time, resulting in the suppression of the aggregation and growth of CdS quantum-dots in NBS glasses.     

Influence of PbO and Ta2O5 on Some Physical Properties of MgCuZn Ferrites

Two series of MgCuZn ferrites are prepared by addition of Ta⁵⁺ and Pb²⁺ ions, separately. The variations of the sintered density, initial permeability, saturation magnetization, Curie temperature and electrical resistivity with the dopant concentration have been studied. The sintered density was found to increase when PbO content is 0.6 wt% or larger. Samples doped with PbO exhibit an appreciable higher resistivity compared to Ta‐doped and undoped samples as a result of the insulating layers on the grain boundaries. The temperature dependence of the electrical resistivity shows a change in slope in the neighbourhood of Curie temperature for all samples and this has been attributed to the influence of the magnetic ordering on the conduction mechanism. Also PbO addition improves the temperature dependence of the initial permeability. The origin of the beneficial effect of PbO compared to Ta₂O₅ is believed to be attributed to the melting of PbO and formation of liquid phase at grain boundaries.     

掺杂烧结金刚石聚晶致密化试验

 实验表明，钛、硅－硼结合剂比镍、硅－硼结合剂聚晶致密化程度高，细粒度金刚石比粗粒度金刚石聚晶德致密化程度高。而且，钛、硅－硼结合剂和细粒度金刚石聚晶的耐磨性亦好。     

Dynamical processes in sol-gel derived rare-earth doped glasses

We have investigated the dynamical processes of rare-earth photoluminescence in silica glasses produced by the sol-gel method. Generally, static spectroscopic properties are used as a tool to probe the local structure near dopants as well as for the study of glass formation. Rare earth ions are preferred structural probes, especially the Eu³⁺ ion for its sensitivity to local structural modifications and its spectroscopic simplicity. By an analysis of the decaying emission that follows a pulsed laser excitation, we have studied several dynamical processes. Importance of a distribution of different environments for the dopant is clearly seen even for the wet gels. The evolution of the lifetimes allow to study the densification process.     

Oxygen transport as a solid‐state structure probe for polymeric materials: A review

In the quest to elucidate the solid‐state structures of polymers, insight into the amorphous phase is particularly elusive. Although the permeability of small molecules is often measured as an important performance property, numerous researchers have found that a deeper analysis of the transport characteristics provides insight into polymer morphology, especially if used in combination with more usual characterization techniques. The transport of small gas molecules senses the permeable amorphous structure and probes the nature of the free volume. In recent years, our interest in the gas barrier of polyesters has resulted in an unusual opportunity to investigate the nature of the free volume in the polymer glassy state. This effort has been aided by access to aromatic polyesters with designed variations in their chemical structure. This review focuses on oxygen transport, supplemented with other methods of physical analysis, as a probe of the excess‐hole free volume. The review addresses the profound effects of orientation and crystallization on the free volume of the glassy state. The discussion also presents a simple odel for the gas permeability of the isotropic glass based on lattice concepts and tests more sophisticated models for the gas permeability of semicrystalline polymers. The final section addresses other opportunities for fruitful applications of oxygen transport as a solid‐state structure probe. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1047–1063, 2005