Effects of Sintering Temperature on Crystallization Behavior and Performance of Glass-Ceramics From Coal Fly Ash

The glass-ceramics was prepared from coal fly ash, limestone and Na2CO3 by sintering processes. Effects of the crystallization temperature (850–1100 ℃) on crystallization behavior, microstructure, sintering character and chemical stability of the glass-ceramics samples were analyzed by means of DTA, XRD, SEM and other analytical methods. The results show that the main crystalline phase of as-prepared glass-ceramics after crystallization treatment is gehlenite (Ca2Al2SiO7). The species of crystalline phases keep the same, however, the main crystalline intensity, line shrinkage rate and bulk density increase first then decrease with the increasing of heat treatment temperature. Water absorption of the samples was reduced as the heat treatment temperature rising. The glass-ceramics display high performance crystallization properties and chemical stability. The optimized glass-ceramics with desired sintering character and chemical stability was obtained by crystallized at 1050 ℃.

Influence of ZrO_2 on sintering and crystallization of CaO-Al_2O_3-SiO_2 glass-ceramics

ZrO2 was added into CaO-Al2O3-SiO2 glass-ceramics and the effect of ZrO2 on sintering and crystallization of CaO-Al2O3-SiO2 glass ceramics was investigated. The results show that the sintering shrinkage ratio of glass particles decreases with the increase of the content of ZrO2. ZrO2 has an unfavourable effect on sintering shrinkage ratio of glass particles. The sintering shrinkage ratio of glass particles increases with the increase of sintering temperature. The increase of sintering temperature favors the decrease of the liquid phase viscosity of glass particles. ZrO2 has little effect on crystallization of main crystalline phase （β-wollastonite）. However, it promotes the crystallization at relatively low temperature.

Effect of sintering temperature on the microstructure and properties of foamed glass-ceramics prepared from high-titanium blast furnace slag and waste glass

Foamed glass-ceramics were prepared via a single-step sintering method using high-titanium blast furnace slag and waste glass as the main raw materials The influence of sintering temperature(900–1060℃) on the microstructure and properties of foamed glass-ceramics was studied. The results show that the crystal shape changed from grainy to rod-shaped and finally turned to multiple shapes as the sintering temperature was increased from 900 to 1060℃. With increasing sintering temperature, the average pore size of the foamed glass-ceramics increased and subsequently decreased. By contrast, the compressive strength and the bulk density decreased and subsequently increased. An excessively high temperature, however, induced the coalescence of pores and decreased the compressive strength. The optimal properties, including the highest compressive strength(16.64 MPa) among the investigated samples and a relatively low bulk density(0.83 g/cm^3), were attained in the case of the foamed glass-ceramics sintered at 1000℃.

Preparation and crystallization action of SiO_2 -Al_2O_3 -CaO-ZnO-R_2O porous glass-ceramics

Using powder-sintering method,SiO2-Al2O3-CaO-ZnO-R2O porous glass-ceramics were produced for analysis. Five samples with different SiO2 /CaO ratios were used in the research. The mechanical properties, microstructures and textures of porous glass-ceramics are investigated by using differential thermogravimetric analysis/differential thermal analysis ( TGA/SDTA) ,X-ray diffraction ( XRD) ,and scanning electron microsco- py ( SEM) . The activity energy of crystallization ( E) and crystallization kinetics parameter ( k) were calculated based on the modified JMA equation. The Avrami parameter n was obtained according to Augis-Bennett function. The results show that the k value of No. 1 sample ( SiO2 /CaO = 61∶ 18) is the largest among all samples, which tends to crystallize more easily,and crystallization processes of all samples are observed bulk crystallization. The main crystal phase observed is parawollastonite ( clinorhombic system) with puncheon shape. Poreforming agents decomposed at 100 - 500 ℃ form a large number of closed pores with micron dimension and several semi-open pores distribute uniformly in the glass-ceramics matrix. This work may be expected to be favorable for industrial scale applications of porous glass-ceramics in the field of building thermal insulation.

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.

Influence of aluminium nitride as a foaming agent on the preparation of foam glass-ceramics from high-titanium blast furnace slag

To effectively reuse high-titanium blast furnace slag （TS）, foam glass-ceramics were successfully prepared by powder sintering at 1000℃. TS and waste glass were used as the main raw materials, aluminium nitride （AIN） as the foaming agent, and borax as the fluxing agent. The influence of the amount of A1N added （lwt%-5wt%） on the crystalline phases, microstructure, and properties of the produced foam glass-ceramics was studied. The results showed that the main crystal phases were perovskite, diopside, and augite. With increasing A1N content, a transformation from diopside to augite occurred and the crystallinity of the pyroxene phases slightly decreased. Initially, the aver- age pore size and porosity of the foam glass-ceramics increased and subsequently decreased; similarly, their bulk density and compressive strength decreased and subsequently increased. The optimal properties were obtained when the foam glass-ceramics were prepared by adding 4wt% AIN.

Influence of CeO_2 addition on the preparation of foamed glass-ceramics from high-titanium blast furnace slag

Foamed glass-ceramics doped with cerium oxide（CeO_2）were successfully prepared from high-titanium blast furnace slag by one-step sintering.The influence of CeO_2 addition（1.5wt%–3.5wt%）on the crystalline phases,microstructure,and properties of foamed glass-ceramics was studied.Results show that CeO_2 improves the stability of the glass phase and changes the two-dimensional crystallization mechanism into three-dimensional one.XRD analysis indicates the presence of Ca（Mg,Fe）Si_2O_6 and Ca（Ti,Mg,Al）（Si,Al）_2O_（6 ）in all sintered samples.Added with CeO_2,Ti CeO_4 precipitates,and crystallinity increases,leading to increased thickness of pore walls and uniform pores.The comprehensive properties of foamed glass-ceramics are better than that of samples without CeO_2.In particular,the sample added with a suitable amount of CeO_2（2.5wt%）exhibits bulk density that is similar to and compressive strength（14.9 MPa）that is more than twice of foamed glass-ceramics without CeO_2.

RESEARCH AND PRODUCTION OF GLASS-CERAMIC DECORATED MATERIAL CONTAINING CHROMIUM

In this paper, the influences of catch-color agent content on glass-ceramic decorated material in the system of CaO-Al2O3-SiO2 were studied. By ladder temperature furnace and sintering shrinkage curve measurement . the influence of catch-color agent content on sintering and crystallization temperature was discussed. By means of XRD, three point bending strength and density measurement, the properties of the decorated material were investigated.

不同析晶促进剂对红色玻璃陶瓷析晶及力学性能的影响

以废玻璃粉为主要原料,采用反应析晶烧结法,改变不同颜料的添加量(10wt.%、15wt.%、20wt.%),添加不同析晶促进剂(氟云母、钙铝黄长石、顽辉石),制备出红色玻璃陶瓷。使用X射线衍射、扫描电子显微镜与抗折仪对红色玻璃陶瓷的物相、形貌、力学性能进行表征。实验结果表明:未添加析晶促进剂时,获得主晶相为硅酸钙钠与石英;当添加氟云母时,主要析出枪晶石;当添加钙铝黄长石时,主要析出硅灰石;当添加顽辉石时,主要析出透辉石。添加20wt.%颜料时,基质上出现大量的孔洞;而添加15wt.%颜料时,可获得析出晶体与基质紧密结合的玻璃陶瓷。加入三种析晶促进剂均可提高红色玻璃陶瓷的断裂模数。其中:未添加析晶促进剂,红色玻璃陶瓷断裂模数为35.92 MPa;添加氟云母,红色玻璃陶瓷断裂模数为40.50 MPa;添加顽辉石,红色玻璃陶瓷断裂模数为42.42 MPa;而添加钙铝黄长石,红色玻璃陶瓷的断裂模数最高,达到55.01 MPa。

Some recent studies on glass/glass-ceramics for use as sealants with special emphasis for high temperature applications

Glass-ceramics owing to a combination of useful properties such as tuneable thermal expansion coefficient(TEC),good mechanical durability and chemical inertness find widespread uses in a variety of applications including seals and coatings.Glass-ceramic-to-metal seals have been fabricated with various silicate,phosphate and borate based oxide glasses depending upon the intended application.In this article,we review our studies on various glass and glass-ceramics materials development with a view to understand bonding behaviour with metals/alloys at ambient and high temperatures through a comprehensive structure property correlation investigations.Detail studies on BaO-CaO-Al2O3-B2O3-SiO2(BCABS),barium strontium alumino-silicate,and strontium alumino-silicate with different additives(like Nd2O3,La2O3,NiO,TiO2,V2O5,ZrO2,Cr2O3,and P2O5)and barium/strontiun zinc silicate(B/SZS)glass-ceramics for high temperature sealing.We shall illustrate the role of various thermo-physical and structural characterization techniques that allowed optimum selection of materials and processing parameters.We particularly highlight the complementary role of NMR and XRD in studying the material at the short range and long range length scales.

Na_2O和K_2O对CaO-Al_2O_3-SiO_2-R_2O-ZnO红色微晶玻璃若干性能的影响

研究了碱金属Ｎａ２Ｏ和Ｋ２Ｏ对ＣａＯ－Ａｌ２Ｏ３－ＳｉＯ２－Ｒ２Ｏ－ＺｎＯ红色微晶玻璃着色及烧结和析晶的影响及作用，以及微晶玻璃烧结和析晶随热处理温度变化的规律。

碱金属对CaO-Al_2O_3-SiO_2-R_2O-ZnO红色微晶玻璃的影响

研究了碱金属Ｎａ２Ｏ和Ｋ２Ｏ对ＣａＯ－Ａｌ２Ｏ３－ＳｉＯ２－Ｒ２Ｏ－ＺｎＯ红色微晶玻璃着色、烧结和析晶的影响与作用，以及微晶玻璃烧结和析晶随热处理温度变化的规律。

烧结法制备赤泥质微晶玻璃及其结构分析

以赤泥为主要原料,采用烧结法成功地制备了表面光滑平整,有漂亮析晶花纹的装饰用微晶玻璃板材。样品中赤泥质量含量高达50%。利用XRD、SEM、EPMAI、R等现代分析测试手段分析了烧结法赤泥微晶玻璃理化性能和微观结构。结果表明:赤泥质量含量为50%时,最佳热处理制度为:核化温度860℃,时间1 h;晶化温度1 060℃,时间2—3 h。赤泥微晶玻璃样品体积密度为2.79 g/cm3,平均显微硬度为572.6 Hv,抗折强度为36.14 MPa;其主晶相是锌黄长石(Ca2ZnSi2O7),次晶相有硅灰石(CaSiO3)、镁黄长石(Ca2MgSi2O7)、铁黄长石(Ca2FeSi2O7)等。