Key Engineering Materials Vols. 336-338

Abstract: A thermal shock experiment is designed to explore the thermal shock properties of ceramic/metal gradient thermal barrier coating. The specimens are heated up by oxygen-acetylene flame and cooled by water spray. The experiment procedure includes two stages, heating the specimen from the initial temperature 30°C for 40s, and then cooling for 20s. The heat transfer and the associated thermal stresses produced during the thermal shock procedure are simulated by finite element method. Experimental results indicated that the specimen of gradient coating behaves better in thermal shock experiments, which agree with the results of simulation.

Abstract: Sodium-rich glasses of the system Na2O-SiO2 are well known to be easily soluble in water. This is not true for silica-rich compositions. We have manufactured quenched glasses with silica contents between 65 and 80 wt.% SiO2 and followed the water interaction at 100°C by measuring mass and sample dimensions in intervals. Comparing the path of edge length, mass and volume to a general shrinking core model for cuboids we conclude that only compositions between 65 and 70 wt% SiO2 can be described well by a simple dissolution process. The logarithm of the dissolution rate constant varies linearly with the SiO2 content. At higher silica contents the mechanism changes towards leaching of sodium. We propose changing glass structures to be responsible for the change in mechanism.

Abstract: Iron phosphate glasses with composition of 20Li2O-32Fe2O3-48P2O5 (in mol%) was prepared by melting, crushing and heat-treating process and the electrical properties were examined. It was found that the sample heat-treated at a temperature close to the glass transition temperature exhibit the maximum conductivity and the lowest activation energy, implying that heat-treatment may play an important role in the electrical properties of the glasses.

Abstract: The phase-separation and the crystallization of SiO2-MgO-Al2O3-K2O-Fe2O3-F glass were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe of microanalyzers (EPMA). The results reveal that the varieties and the morphology of crystalline phases formed depend sensitively on the thermal treatment schedules. During the isothermal treatments, the crystalline phases of mica, mica and iron oxide (FeFeO4), and FeFeO4 as major crystals are precipitated in the glass samples heat-treated at 900, 1000 and 1050°C respectively. However, the two-step heat treatment beginning at 900°C for 1h and subsequently followed at 1050°C for 1h leads to the precipitation of mica crystal and no any signs of FeFeO4 crystalline phase is observed. Also the morphology of sample is different from that of the isothermally treated glass at 1050°C, but is similar from that of sample at 900°C. A “worm”-shaped phase-separation is observed in the sample heated at 800°C for 0.5h, which exhibits different morphology from that of droplet- or globule-shape conventionally discerned. EPMA results show that the incorporation of Fe2O3 accelerates accumulation of fluorine element, promoting the phase-separation and the crystallization of the present glass.

Abstract: Fluorophlogopite ceramics, which possesses very good machinability, high electrical resistance and high dielectric strength, is very difficult to be sintered to fully dense state. It is usually made through glass-ceramics processing. In this paper the effects of particle size distribution and sintering agents on sintering of fluorophlogopite ceramics are investigated. The study concludes that dense fluorophlogopite ceramics can be produced through ceramic processing, including careful synthesis of fluorophlogopite powder as raw material, grinding with attrition mill, and pressureless sintering with the help of plumbum contained boron silicate glass as sintering agent in the temperature range of 1100 to 1200°C.

Abstract: Depending on surface and crack crystallization mechanism, a new type of glass-ceramics as a decorative building material has been obtained by using cracked-glass panel as precursor to replace glass grains used in conventional sintering process. In the comparative and parallel experiment, cracked-glass panels and glass grains were made from the same glass melt belonging to CaO-Al2O3-SiO2 family, and were heat-treated parallelly and transformed into two types of glass-ceramics tagged as CG-GCs and GG-GCs respectively. XRD patterns and SEM micrographs of CG-GCs demonstrate that cracked-glass can deposit β-wollastonite. Properties tests show that the compactness of CG-GCs is higher than that of GG-GCs, signifying that, in comparison to glass grains in conventional sintering process, using cracked-glass panel as precursor in this study can reduce the porosity of end products. In addition, it is of great interest that the polished surface of CG-GCs can exhibit excellent texture much different from granular one of conventional GG-GCs.

Abstract: The crystallization and sintering of the Li2O-Al2O3-SiO2 glass powder compacts were studied. Results showed the relative densities of the sintered compacts with lower crystallization temperatures were higher than those with higher crystallization temperatures. A small amount of residual glass in the crystallized compact was good for sintering and densification. Compared with the heat treatment time, the heat treatment temperature was an important factor for the crystallization and sintering of glass powder compacts. The crystallized compacts with a small amount of residual glass should be sintered at a relatively higher heating rate under the prerequisite of keeping sintered compacts from deformation.

Abstract: This process and parameters of fabricating light calcium carbonate from limestone were discussed in the paper. Raw limestone in experiment comes from Luquan city, Hebei province. The results of chemistry and XRD analysis indicate that ingredient of this limestone is mainly calcium carbonate, dolomite, silicon dioxide, which takes 83.81%, 11.03% and 1.67% separately, and a few of other impurities. The process includes calcinations, assimilation, carbonation, drying and others. It was ascertainable that the time of calcinations exceeded 5 hours at 850~ 950
and loss of calcinations was 42%. The time of assimilation was around 25 minutes at 70~90
The time of carbonation was about 30 minutes at 50~90
, and the airflow was about 160L/min and PH of latex after carbonation was 7.2~7.4. The light calcium carbonate product was obtained in experiment, whose fine sphere size was about 10 nanometer, with the agglomeration particle size 2~3μm. The degree of white improved from 42 to 76. As a result, the comprehensive properties of the produce were improved consumedly.

Abstract: Upconversion luminescence of Er3+-doped SiO2-Al2O3-CaO-NaF-CaF2 transparent glass ceramics under 980 nm excitation was investigated. XRD and TEM experiments revealed the homogeneous distribution of CaF2 nano-crystals among the glassy matrix. Intense red upconversion signal was recorded and its intensity increased with the increasing of heating temperature and Er3+-doping level at the range of 0.1 to 1.0 mol%. When Er3+ doping reached 2 mol%, the concentration quenching effect appeared. All these results could be due to the incorporation of Er3+ ions into precipitated CaF2 nano-crystals. The quadratic pump power dependence of the upconversion luminescence intensity indicated that the transition mechanism of the red emission was due to two-photon absorption processes.

Abstract: The purpose of this paper is to demonstrate sensors and structures fabricated using the LTCC technology, which has been addressed and employed increasingly as a smart packaging approach for several applications. The focus will be on inclination and cantilever force sensors and micro-fluidic structures. Motivation for selection of LTCC for these applications in addition to fabrication and structuring of the devices will be explained in details. TGA (thermo-gravimetric analysis), dilatometer analysis, SEM (scanning electron microscopy), electronic equipment for measuring sensor performance will be extensively used for explanation of the results. It will also be shown that, compared to classical thick-film technology on alumina, LTCC allows a considerable increase in sensitivity, and is therefore better suited for the sensing of minute forces and pressures.