Sintering Of Glass Powders Research Articles

Large dielectric properties of niobate-titanate glass ceramics prepared by powder sintering method

Niobate-titanate glass-ceramics with large dielectric constant were prepared by the dual optimization strategy employed——glass powder sintering method and simultaneous introduction of multiple nucleating agents. The study delved into the crystallization and microstructure of the glass ceramics, with a subsequent characterization of their dielectric and ferroelectric properties. In this investigation, the crystalline phase underwent a transformation from the Pb2Nb2O7 phase of G700 glass ceramics to the coexistence of (Pb, Sr)TiO3 and (Ba, Sr, Pb)Nb2O6 phase of G1100 glass ceramics. The crystal phase content exhibited a notable increase from 29 % to 82 %. The relative density of the glass ceramics reached a high of 99.4 %. The maximum dielectric constant recorded was 1493, accompanied by a maximum energy efficiency of up to 88.0 %. These results underscore the potential of glass ceramics as a promising material for Multilayer Ceramic Capacitor (MLCC) dielectric layers.

The role of heating rate on the sintering of glass powders

AbstractIt is proposed that heating rate affects the apparent sintering temperatures of glass powders. The accumulation of thermal energy over time, or heat work (K s), is calculated over the range from the glass transition temperature to sintering temperature with the logarithm of time for heating rates from 1 to 60 K/min. The required heat work is independent of heating rate for two silicate glass powders but shows a decreasing heat work requirement for increasing heating rates for a borosilicate glass powder. Small cylindrical powder compact samples were used to minimize heat‐transfer problems and were observed thermoanalytically using a hot‐stage microscope. The densification temperature, defined as the peak in the shrinkage versus temperature curve, increases with increasing heating rate and is sensitive to the initial compact density. The use of mechanically pressed compacts with similar compact densities minimizes the contribution of initial density, allowing the comparison of sintering behavior as a function of heating rate.

Crystallization Kinetics, Properties of α-cordierite Based Glass-ceramics Prepared by Glass Powder Sintering

Crystallization Kinetics, Properties of <i>α</i>-cordierite Based Glass-ceramics Prepared by Glass Powder Sintering

Melting, sintering and wetting properties of ZnO–Bi2O3–B2O3 sealing glass

Glasses based on ZnO−Bi2O3−B2O3 system are expected to be a new kind of sealing glasses because of their low melting temperature and other properties. In order to reveal the effect of B2O3 on the rheological behavior of ZnO−Bi2O3−B2O3 system glass melt, the properties of viscosity, thermal expansion, fluxion property and wetting process between cylinder samples and stainless steel were investigated with the rotating crucible viscometer, dilatometer and high-temperature microscope. The structure of sintered glass samples was investigated with scanning electron microscope. The results show that the B2O3 content increasing in B1−B3 at the given temperature between 400 °C and 500 °C leads to the increasing of the sample viscosity. When the amount of B2O3 increases from 5.24% to 9.24% (mass fraction), the coefficients of thermal expansion of glass samples decrease smoothly from 10.94×10−6 to 10.71×10−6 and 10.38×10−6 °C−1 respectively. In the case of sealing temperature, its value increases from 453 °C to 494 °C. ZnO−Bi2O3−B2O3 system low-melting glass powder sintering was with viscous liquid to participate, which could make the densification of glass sample more effective and more efficient. With the content of B2O3 increasing, the wetting angle between the glasses samples and stainless steel could also increase, and the resulting appropriate sealing temperature range is 460−490 °C.

Influence of Al2O3 and B2O3 on Sintering and Crystallization of Lithium Silicate Glass System

This article reports on the effect of Al2O3 and B2O3 added as dopants on the preparation of glass‐ceramics (GCs) belonging to the lithium silicate glass system. The GCs are prepared by sintering route using glass powders. The reasons for the crystallization of the metastable crystalline phase lithium metasilicate (LS) are discussed and the impact of the dopants on the thermodynamics and kinetics of crystallization is investigated. The addition of dopants modifies the thermodynamic equilibrium of the system and this change is mainly entropy driven and also slowdown the kinetics of crystallization. Differential thermal analysis and hot‐stage microscopy are employed to investigate the glass‐forming ability, sintering, and crystallization behavior of the studied glasses. The crystalline phase assemblage studied under nonisothermal heating conditions in the temperature range of 800°C–900°C in air. Well sintered and dense glass‐ceramics are obtained after sintering of glass powders at 850°C–900°C for 1 h featuring crystalline phase assemblage dominated by lithium disilicate (LS2).

Influence of Kaolin on the Sintering of Glass Powder to Glass–Ceramics

Glass powder derived from a waste water flocculate was used to prepare sintered glass–ceramics. Different amounts of kaolin as a binder were mixed with the glass powder to form green bodies. The influence of the kaolin on the sintering, crystallization of the glass powder and on the microstructure of the obtained glass–ceramics has been investigated. DTA analysis suggests that the kaolin increases the crystallization temperature of the glass-kaolin mixtures. The results also show that the kaolin benefits reducing the sintering shrinkage of the green bodies. The kaolin does not lead to the change of crystalline phases in the sintered glass–ceramics. Instead, with an appropriate addition, the kaolin can provide reactive Al2O3 and SiO2 sources due to its decomposition favoring the crystal growth and improving the mechanical property of the sintered product.

Enhanced surface crystallization of glass by adding traditional oxide nucleating agents

Abstract In the preparation of glass–ceramics, bulk crystallization of glasses can be improved by adding nucleating agents. However, surface crystallization of glasses conventionally can only be enhanced by using small particles, whose surfaces provide nucleating sites. Herein, oxide nucleating agents such as TiO 2 and Cr 2 O 3 which are normally used to improve bulk crystallization were introduced into a lithium–iron-phosphate (LIP) glass. Differential thermal analysis results suggest that tendency to bulk crystallization of the LIP glass increases to some extent after addition of the nucleating agents. However, no bulk crystallization really occurred in the thermally treated samples. Instead, surface crystallization of the glass is facilitated by the nucleating agents. The samples containing nucleating agents show thicker crystallized surface layers compared with the pure LIP glass. It is proved nucleation stage to be important to increase the surface crystallization, further confirming the enhancement effect of the nucleating agents on surface crystallization. The results enrich the understanding of surface crystallization of glass and provide useful information for the preparation of glass–ceramics via glass powder sintering process which is based on surface crystallization.

Crystallization-controlled pore retention in calcium-phosphate glassceramics from powder sintering of CaO–P2O5–B2O3–Al2O3–TiO2–ZrO2 glass

The formation of a porous structure plays a key role in the synthesis of calcium-phosphate biomaterials for bone implantology and endoprosthesis, since it determines both bioactivity and mechanical strength of the final material. The results of the present investigation demonstrate the feasibility of a crystallization-controlled design of material porosity, without pore-former addition, through a low-cost glass powder sintering process. The method takes advantage of the partial crystallization of glass with molar composition 45P2O5–50СаО–5Al2O3, with added 5B2O3, 5ZrO2, and 5TiO2, for achieving controlled pore retention and mechanical strength. The investigation — comprising differential thermal analysis, X-ray diffraction, scanning electron microscopy, viscosity, density, flexural and compressive strength measurements — gives a quantitative description of how the pore retention is driven by the system viscosity and by the formation of a reinforcing framework of precipitated crystals, the latter ones preventing the collapse into a vitrified non-porous material. The final porosity turns out to be describable by a modified Frenkel's model accounting for the crystallization constraints to the liquid flow. As a result, the present study demonstrates the possibility of obtaining calcium-phosphate glassceramics with 70% of crystal fraction, flexural strength 25MPa, compressive strength 40MPa, and a final porosity of 25% with pore sizes selectable from 10 to 180μm from the starting grain size. Importantly, bioactivity tests show good bio-integration and pore filling with neogenic bone tissue and blood vessels, without toxicity, opening the way to possible applications in small-bone implantology.

The Use of High Durability Alumino-Borosilicate Glass for the Encapsulation of High Temperature Reactor (HTR) Fuel

ABSTRACTThe development of suitable waste forms for waste produced by generation IV reactors is of critical concern for future operations. To date no accepted disposal route for Tri-Structural Isotropic (TRISO) High Temperature Reactor (HTR) fuel exists. Alumino-borosilicate glass has been studied for its ability to encapsulate TRISO particle fuels. This glass was selected for its high aqueous durability. Encapsulation was achieved by cold pressing and sintering of glass powders mixed with HTR fuel. Sintering profiles capable of eliminating interconnected porosity in the composites were developed. The chemical compatibility and wetting of the glass matrix with the fuel were analysed along with the aqueous durability of the sintered glass matrix. Composites sintered under a controlled atmosphere produced unfractured monoliths with minimal chemical interaction between the glass and the TRISO particles. The Product Consistency Test (PCT) durability assessment indicated the sintered alumino-borosilicate glass was approximately an order of magnitude more durable than an equivalent R7T7 borosilicate glass. These results suggest sintered alumino-borosilicate glass-TRISO particle composites may provide a potential disposal route for spent TRISO particle fuel.

Development of a Piezoresistive Force Transmitter for Gauging Yarn's Linear Density in High-Speed Textile Machinery

A piezoresistive force transmitter has been developed for gauging the variation of yarn's linear density with the measuring range of 0-5 N and the corresponding voltage output of 0- -5 V. The transmitter simply consists of a force sensor head and a signal processing circuit unit. The sensor head consists of a sensitive silicon chip and an elastic metal element. The chip is based on piezoresistive effect of silicon and is made using microfabrication techniques. The elastic metal element is designed using finite-element method (FEM) and fabricated by electrical discharge machining (EDM). The location of the expected maximum stress of the elastic metal element is also analyzed using FEM. The sensitive silicon chip is packaged on the elastic metal by glass powder sintering process. The signal processing circuit unit is used to amplify the sensor's output to the standard voltage. According to the dynamic and static experiments, the experimental results show that the accuracy of the piezoresistive force transmitter is 0.203%FS and the response frequency is 878.5 Hz, so the transmitter is suitable for the auto leveling system for high-speed textile machinery.

Influence of strontium on structure, sintering and biodegradation behaviour of CaO–MgO–SrO–SiO 2–P 2O 5–CaF 2 glasses

The present study investigates the influence of SrO on structure, apatite-forming ability, physico-chemical degradation and sintering behaviour of melt-quenched bioactive glasses with the composition (mol.%): (36.07 − x) CaO– xSrO–19.24MgO–5.61P 2O 5–38.49SiO 2–0.59CaF 2, where x varies between 0 and 10. The detailed structural analysis of the glasses is made by infrared spectroscopy and magic angle spinning–nuclear magnetic resonance spectroscopy. Silicon is predominantly present as Q 2 (Si) species, while phosphorus is found as orthophosphate in all the investigated glasses. The apatite-forming ability of glasses is investigated by immersion of glass powders in simulated body fluid for time durations varying between 1 h and 7 days. While increasing the Sr 2+/Ca 2+ ratio in the glasses does not affect their structure significantly, their apatite-forming ability is decreased considerably. Further, physico-chemical degradation of glasses is studied in accordance with ISO 10993-14 “Biological evaluation of medical devices – Part 14: Identification and quantification of degradation products from ceramics” in Tris–HCl and citric acid buffer, and the possible implications of the ion release profiles from the glasses in different solutions are discussed. The addition of strontium to the glasses leads to a sevenfold decrease in chemical degradation of glasses in Tris–HCl. The sintering of glass powders renders glass ceramics (GCs) with varying degrees of crystallinity and good flexural strength (98–131 MPa), where the mechanical properties depend on the nature and amount of crystalline phases present in the GCs.

Effect of B2O3 and P2O5 on fluorosilicic mica glass-ceramic sintering process

To study the effect of B2O3 and P2O5 on fluorosilicic mica glass-ceramic sintering process, six sets of K2O-MgO-SiO2-F glasses were prepared by using B2O3 and P2O5 as sintering aid, respectively. Green bodies of the glass powder were formed by gel casting and sintered at 800, 850, 900, 950, 1000oC for 6 hours, resectively. The sintering and crystallization behavior were studied by thermal shrinkage , X-ray diffraction and SEM. The results showed that the shrinkage rate of the glass with 2wt% B2O3 and P2O5 was highest, while the rate of the glass with 5wt% P2O5 was lowest. An additional crystal other than fluorosilicic mica was precipitated in the glass ceramics generated by sintering of glass powder. The present results confirmed that the glass powder of pure K2O-MgO-SiO2-Fsystem had poor sinterability, while glass powder with minor addition of P2O5 and/or B2O3 showed good sinterability. This result was also verified by SEM.

Fast‐Sintered Gehlenite Glass–Ceramics from Plasma‐Vitrified Municipal Solid Waste Incinerator Fly Ashes

Plasma heating is a highly efficient industrial treatment for municipal solid waste incinerator fly ashes, converted into leach‐resistant glass. The viscous flow sintering of glass powders appears a very promising way for the subsequent conversion of the vitrified waste, not refined and available as glass flakes, into valuable glass–ceramics. Because of the particular glass composition, the densification of glass–ceramics was much hindered by the strong tendency of glass toward surface crystallization. The crystallization of glass was successfully coupled to a low porosity, thus yielding strong gehlenite‐based glass–ceramics (with a bending strength exceeding 100 MPa), by adopting a fast sintering treatment (direct insertion of glass compacts at 1050°C, with an holding time of 1 h).

Effects of glass components on crystallization and dielectric properties of BST glass–ceramics

Crystallization behavior was studied for glass powders in which some portions of AlF3 in the net composition of 60(Ba0.7Sr0.3)TiO3–25SiO2–15AlF3 were replaced with Ga2O3 or Bi2O3. The replacement with Ga2O3 resulted in a progressive increase in crystallization temperature, which effectively assisted the viscous sintering of glass powders to produce densified BST glass–ceramics at relatively lower temperatures. For the Bi2O3-replaced glass powders, an increasing amount of Bi2O3 replacement lowered the crystallization temperature and yielded less densified glass–ceramics containing a considerable amount of glassy phase. The temperature dependence of permittivity was estimated for the Ga2O3- and Bi2O3-replaced glass–ceramics as a function of sintering conditions and the amount of replacement, respectively.

RSM 법에 의한Li2O−Al2O3−SiO2(LAS) 유리의 소결 거동과 결정화에 대한 연구

This paper presents results and observations obtained from a study of sintering behavior and crystallization in Li₂O-Al₂O₃-SiO₂ (LAS) Glass by screen printing method. The variable experimental conditions were determined carefully by Thermal-Mechanical Analyzer (TMA), Differential Thermal Analyzer (DTA) for setting the optimum transparent sintering conditions in LAS glass system, 10.5Li₂O-14.7Al₂O₃-58.1SiO₂-16.7B₂O₃(wt%), such as glass-ceramics which usually have low crystallization temperatures. Crystallization glasses generated during sintering was observed from diffraction patterns by X-Ray Diffraction (XRD), transmittance by UV-Vis spectrometer. Finally, the optimum sintering condition of LAS glass and the relation between factors and results in several sintering conditions were given by using Response Surface Methodology (RSM). From this study, we confirmed that crystallization interrupted densification during glass powder sintering. Furthermore, we observed that main effect of factors in glass powder sintering with concurrent crystallization depended on experimental conditions from main effects plot by MINTAB-14.

Factor of individual error at sintering of glass powder

Factor of individual error at sintering of glass powder

Sintering of low-melting glass powders and glass-abrasive composites

Sintering of glass powders in Na2O-B2O3-SiO2 and PbO-ZnO-B2O3-SiO2 systems as well as of their mixtures has been studied. The process of sintering is shown to change because of crystallization of the glass of the PbO-ZnO-B2O3-SiO2 system. Addition of diamond or cubic boron nitride to glass powders affects shrinkage in sintering composites. Sintering of powders of lead-containing glass proceeds by the mechanism of viscous flow.

Use of the Anion Structure Coefficient in Developing Glass Ceramic Materials

Anion structure coefficients (ASC) are given for solid solutions synthesized on the basis of stoichiometric compositions with a ratio of Li2O : Al2O3 : SiO2 equal to 1 : 1 : 4 – 1 : 1 : 12. A fundamental possibility of selecting the residual vitreous phase and predicting the process of sintering of glass powders by calculating the ASC of the initial compositions and the residual vitreous phase in developing glass ceramic materials with preset properties is demonstrated.

Influence of various heating procedures on the sintered density of Sr-celsian glass-ceramic

Glass-ceramics are crystalline materials that can be formed by controlled crystallization heat treatments of proper parent glasses. Most of them have unique properties such as translucency, high strength and very low and uniform thermal expansion [1]. They also have very fine and randomly oriented crystals with a few percent of the residual glass. The recent applications of glass-ceramics are for matrix materials for ceramic fiber-reinforced composite materials, substrate materials for semiconductor packaging, heat exchangers, telescope mirrors, artificial hard tissues and cook wares. A relatively new method of glass-ceramic preparation is the sintering of glass powders, followed by a nucleation heat treatment [2–5]. This technique gives cost benefits by reducing the processing temperatures. Furthermore, the formation of complex shapes can be obtained by using equipment common to a ceramic factory. When sintering is employed for the production of a glass-ceramic, sintered density becomes a critical factor for its application. That is, its mechanical properties are highly related to the sintered density and in most cases high density is desirable. In order to obtain high sintered density, fine glass powder is required to increase the surface area that can supply the deriving force for sintering. In addition, heating procedures strongly affect the final density of a glass-ceramic. Many people use different heating procedures for sintering of glass powder and subsequent crystallization of the sintered glass body. A strontium aluminosilicate composition forming monocelsian (SrO · Al2O3 · 2SiO2 : SA2S) as a primary crystalline phase, which has been studied mainly for use as a matrix material for high-temperature ceramic composites [6, 7], were used for the present study. It shows high refractory character, low thermal coefficient of expansion (TCE) of 2.5 × 10−6 /◦C, oxidation resistance and phase stability up to its melting temperature at 1650 ◦C [6–8]. Bansal et al. [8] fabricated stoichiometric SA2S glass-ceramics by cold pressing, cold isostatic pressing and sintering. The samples, heated to 900 ◦C that is slightly above glass transition temperature (Tg: 883 ◦C) for 10 h and subsequently heated to 1300 ◦C that is the crystallization completion temperature (Tc) for 10 h, showed 94% of theoretical density. On the other hand, the samples, heated to 1100 ◦C that is between crystallization onset (To: 1086 ◦C) and crystallization

Sintering behavior of gel powder in binary glass-forming SiO2TiO2 system

Abstract Gel powders in a binary glass-forming SiO 2 TiO 2 system with compositions of 2–8 mol% TiO 2 were synthesized by hydrolysis of metal alkoxides in a sol-gel process. The sintering behavior of calcined gel powders was investigated with a dilatometer. Their sintering stage could be divided into three by two characteristic temperatures ( T sin and T cry ) on the shrinkage curve. It was found that the sintering temperature, T sin , in the second stage decreases with increase of TiO 2 content. Considering the effect of viscous flow on the sintering of glass powders, these results mean that the addition of TiO 2 into silica glass reduces the viscosity of this glass. On the basis of these results, it was concluded that the formation of [TiO 4 ] units in the SiO 2 network makes the whole glass network rather weaker than stronger. The correlation between sintering temperature and thermal expansion coefficient of these compositions was also discussed.