DTA INVESTIGATION OF CRYSTALLIZATION BEHAVIOUR IN SrO-TiO_2-SiO_2 GLASS-CERAMICS

The crystallization process of STS glass-ce-ramics was carried out in a constant temperature. The glass-ceramics still show good piezoelectric properties. The mecha-nism of orientation crystallization was investigated bv means of DTA.

Effects of Nucleating Additives on Crystallization and Properties of CaO-B_2O_3-SiO_2 Glass-ceramics

ZrO2, TiO2 and P2O5 were doped in CaO-B2O3-SiO2 glass-ceramics as nucleating additives. Effects of different nucleating additives on the phase separation and crystalline behaviors were investigated by using gradient temperature furnace, DTA and XRD. Then, sintering process of the glass-ceramics was investigated by testing sintering shrinkage, dielectric constant and loss. The experimental results shows that the glass-ceramics doped with nucleating additives represents higher crystallization, with ZrO2 as an exceptional effective dopant to promote the precipitation of wollastonite crystal. Finally, ZrO2 containing glass-ceramics was chosen to study the influence of sintering temperature and soaking time with the help of X-ray diffraction analysis and density measurement. The glass-ceramics can be well consolidated at 850 ℃ for 10 min, with low dielectric constant （5.87） and loss （3.21×10^-4）, which is desirable for LTCC application.

Preparation and Optical Properties of Er^3+:Na2O-Al2O3-SiO2 Transparent Glass-Ceramics

Na2O-Al2O3-SiO2 glass-ceramics doped with Er^3＋ ions were synthesized by the conventional melt quenching technique at a low melting temperature.The samples were characterized by differential scanning calorimetry（DSC）,X-ray diffraction（XRD）,scanning electron microscopy（SEM）,UV-vis-NIR scanning spectrophotometry,and fluorescence spectrometry.The results show that the main crystalline phase of glass-ceramics is nepheline.The best heat-treatment process is at 520 ℃ for 2 h.Because the up-conversion luminescence and near infrared luminescence properties of glass doped with Eu^3＋ are studied in detail.

Thermal Behavior and Lithium Ion Conductivity of L_2O-Al_2O_3-TiO_2-SiO_2-P_2O_5 Glass-ceramics

A lithium ion conductive solid electrolyte, L20-AI203-TiO2-SiO2-P20s glass with NASICON- type structure have been synthesized and transformed into glass-ceramic through thermal-treatment at various temperatures from 700 to 1 000 ~C for 12 h. The differential scanning calorimetry （DSC）, X-ray diffraction （XRD）, scanning electron microscopy （SEM） and complex impedance techniques were employed to characterize the samples. The experimental results indicated that the capability of glass forming in this system is superior to that of L20-A1203-TiO2-PzO~. The glass has an amorphous structure and resultant glass-ceramic mainly consisting of LiTi2（PO4）3 phases. Impurity phases AIPO4, TiO2, TiP207 and unidentified phase were observed. With the enhanced heat-treatment temperature, grain grew gradually and lithium ion conductivity of glass-ceramics increased accordingly, the related impedance semicircles were depressed gradually and even disappeared, which could be analytically explained by the coordinate action of the ＇Constant phase element＇ （CPE） model and the ＇Concept of Mismatch and Relaxation＇ model （CMR）. When the sample is devitrified at 1 000 ~C, the maximum room temperature lithium ion conductivity comes up to 4.1 x 10-4 S/cm, which is suitable for the application as an electrolyte of all-solid-state lithium batteries.

Crystallization and Luminescence Properties of Sm3＋-Doped SrO-Al2O3-SiO2 Glass-Ceramics

The Sm^（3＋）-doped SrO-Al2O3-SiO2（SAS） glass-ceramics with excellent luminescence properties were prepared by batch melting and heat treatment. The crystallization behavior and luminescent properties of the glass-ceramics were investigated by DTA, XRD, SEM and luminescence spectroscopy. The results indicate that the crystal phase precipitated in this system is monocelsian（SrAl2Si2O） and with the increase of nucleation/crystallization temperature, the crystallite increases from 66 % to 79 %. The Sm（3＋）-doped SAS glass-ceramics emit green, orange and red lights centered at 565, 605, 650 and 715 nm under the excitation of 475 nm blue light which can be assigned to the 4 G5/2→6 Hj/2（j=5, 7, 9, 11） transitions ofSm^（3＋）, respectively. Besides, by increasing the crystallization temperature or the concentration ofSm^（3＋）, the emission lights of the samples located at 565, 605 and 650 nm are intensified significantly. The present results demonstrate that theSm^（3＋）-doped SAS glassceramics are promising luminescence materials for white LED devices by fine controlling and combining of these three green, orange and red lights in appropriate proportion.

Effect of the Cool System on Internal Stress of CaO-Al_2O_3-SiO_2 Glass-ceramic System

The samples were attained through altering the cooling system of producing glass-ceramics. The X-ray diffraction was used to test the stress value of different samples. The relation of the cooling system and internal stress were also investigated. The experimental results show that the stress of glass-ceramic had a close relation with starting cool temperature. Above 800 ~C, glass-ceramic could be accelerated cooling and did not bring stress. Temperature between 500 ℃ and 800℃ was an important temperature range of the formation of stress in glass-ceramic, in which the glass-ceramic stress would change obviously. Cool system was the key on how to control and eliminate internal stress in order to reduce the destroy of materials crated by internal stress. In addition, glass particles size increase, glass-ceramic stress increase in consequent.

Effect of Al_2O_3 Content on Residual Stress and Proper-ties of CAS Glass-ceramics

The structure and properties of the glass-ceramics were tested with X-ray diffraction testing instrument,correlative software,and other modern testing means.Then the effect of Al2O3 content on internal stresses in CaO-Al2O3-SiO2 glass-ceramics was studied deeply.In order to study the relationship of Al2O3 to the residual stress of CaO-Al2O3-SiO2 glass-ceramics,X-ray diffraction ＂sin2ψ＂ was used.The means utilized the x radial incidence produced from cathode radial tube,and took the space between crystals as measurement of strain.When the stresses produced,the space between crystals changed and the diffraction peak moved during Bragg diffraction.The magnitude of movement is related to the stresses.The experimental results show the residual stress is considerably high and Al2O3 can influence the mechanical properties of this material hugely.

Effect of Rare Earth on the Crystallization Behavior of Li_2O-Al_2O_3-SiO_2 Glass-ceramic

X-ray powder diffraction and Fourier transform infrared spectroscopy were applied for characterization of Li2O-Al2O3-SiO2 glass-ceramic powders doped with Eu2O3,Gd2O3 and Er2O3,respectively,in the conditions of different heat-treatment temperatures and with various amounts.The powders were derived from the polyacrylamide gel method.The results show that,the wet gels prepared by polyacrylamide perform a unique crystallization behavior in the process of drying,comparing with some customary preparation such as melt processing.The main crystal phase and crystallization sequence of Li2O-Al2O3-SiO2 micro-powders have no distinct with addition of Eu2O3,Gd2O3 or Er2O3,while the crystallization temperature of the β-spodumene decreased and the amount of the β-spodumene increased.

Stress Analysis of CaO-Al_2O_3-SiO_2 System Glass-ceramic with Different Thickness

In order to study the relationship between thickness and residual stress in CaO-Al2O3-SiO2 glass-ceramics.The residual stress was measured in CaO-Al2O3-SiO2 system glass-ceramic with different thickness,and the formation mechanism and characterization of residual stress in CAS system Glass-ceramic were analyzed by the X-ray diffraction analysis.The experimental results show the compressive residual stress increass with thickness of glass-ceramic increasing.

Preparation and Microstructure of Glass-ceramics and Ceramic Composite Materials

The technology and microstructure of glass-ceramics and ceramic composite materials were studied. A suitable ceramic body was chosen on the basis of the sintering temperature of CaO-Al2O3-SiO2 system glass-ceramics. According to the expansion coefficient of the ceramic body, that of CaO-Al2O3-SiO2 system glass-ceramics was adjusted, fl-wollastonite was found present as the major crystalline phase in glass- ceramic. The CaO-Al2O3-SiO2 system glass-ceramic layer and ceramic body could be sintered together by adjusting the sintering period. The compositions of glass-ceramic layer and ceramic body diffuse mutually at 1 100 ℃, resulting in an interface between them. To achieve good sintered properties of glass-ceramics and the chosen ceramic body, at least a four-hour sintering time is used.

Preparation and Characteristic of Glass-Ceramics with Super Low Thermal Expansion Coefficient

The preparation technics of glass-ceramics with super low coefficient of thermal expansion containing β-quartz solid solution as a main crystal phase based on the glass in the system Li2O-Al2O3-SiO2 was introduced. The composition of base glass, technics of melting and heat treatment effecting on characteristic of glass-ceramics was described. Specimens were prepared by melting, anneal and controlled two steps heat treatment. Crystal phase, microstructure and elementary distributing were studied by using XRD, SEM and EDS respectively. Prepared specimens show excellent transparency and super low thermal expansion coefficient of 2×10-8 ·K-1, which reaches international advanced level.

Utilization of Coal Fly Ash for the Production of Glass-ceramics With Unique Performances: A Brief Review

Coal fly ash is an industrial by-product generated during the combustion of coal for energy production. Due to the increasing annual consumption of coal power and the serious potential environmental threats of coal fly ash, a considerable amount of research on the utilization of coal fly ash has been undertaken worldwide. Vitrification seems to be one of the most promising options for reusing this industrial waste. This paper presents a short overview of the production of unique high performance glass-ceramics using coal fly ash as a raw material. A detailed description of the methodologies for the synthesis of glass-ceramics from coal fly ash and the principal crystal phases, corresponding property and possible usage of those materials are introduced. Investigations revealed that converting coal fly ash into high performance glass-ceramic materials is a promising new approach to improve the utilization of this industrial by-product. This conversion not only alleviates the problems with disposal but also converts a waste material into a high value-added marketable commodity.