Sintering Of Glass Research Articles

Preparation of Poriferous Glass Bodies by Useless Glasses Partial Sintering Process

The porous glass has a high chemical, thermal, and mechanical resistance, which results from a rigid and incompressible silica network. In the present manuscript, porous glasses were prepared and characterized by partial sintering of waste glasses. Polyvinyl alcohol was added as a binder to the glass powder and the mixture was uniaxially cold pressed under two different forces, followed by sintering at 850°C. The effects of thermal history, particle size of glass powder, binder content, and applied pressing forces on pore size and total porosity of fabricated porous glasses were investigated, and final products with the average porosity of 25% were prepared. The average pore size of the specimens was determined using mercury porosimetry. The morphology of the porous glasses was observed by scanning electron microscopy. The results showed that the average pore size of the samples decreased by increasing binder content due to better compaction of the mixed powder.

Evaluation of aluminosilicate glass sintering during differential scanning calorimetry

The aim of this work is to investigate a difference in heat flow observed in the differential scanning calorimetry curves when aluminosilicate glasses are analyzed. Glasses with nominal composition 56.21 SiO2 18.65 Al2O3 25.14 MgO (wt%) were produced by the conventional melting process. Glass frits were milled and sieved in the range of 45–63µm. The material was analyzed by X-ray fluorescence spectrometry, X-ray diffraction, differential scanning calorimetry (DSC), and differential thermal analyses (DTA). The particle size distribution was determined by laser diffraction technique. The microstructures of the samples were observed by scanning electron microscopy after removing them from the DSC sample holder. The density was determined by He picnometry. The difference in heat flow in the DSC curves is assigned to the sintering process occurring during the heating cycle, which was confirmed by the neck formation in the particle interface, DSC signal variation in isothermal measurements, no change in the heat flow when monolith specimen are analyzed, and in subsequent DSC analysis after cooling. The concurrent crystallization was also determined.

Radiation-induced change of OH content in Yb-doped silica glass

Yb-doped silica glasses containing low, medium, and high content of OH are prepared through nanoporous glass sintering technology. High-OH sample exhibits better X-ray irradiation resistivity than low- and medium-OH samples. After irradiation, OH content of low- and medium-OH samples increases 37.5% and 11%, respectively; in contrast, OH content of high-OH sample decreases dramatically. The different OH content changes among the samples are discussed regarding the proposed inter-conversion reactions involving Si-H and Si-OH during the irradiation.

Pressureless Sintering of Sodalite Waste-forms for the Immobilization of Pyroprocessing Wastes

ABSTRACTSodalite (Na8[AlSiO4]6Cl2), a naturally occurring Cl-containing mineral, has long been regarded as a potential immobilization matrix for the chloride salt wastes arising from pyrochemical reprocessing operations, as it allows for the conditioning of the waste salt as a whole without the need for any pre-treatment. Here the consolidation and densification of Sm-doped sodalite (as an analogue for AnCl3) has been investigated with the aim of producing fully dense (i.e. > 95 % t.d.) ceramic monoliths via conventional cold-press-and-sinter techniques at temperatures of < 1000 °C. Microstructural analysis of pressed and sintered sodalite powders under these conditions is shown to produce poorly sintered, porous, inhomogeneous pellets. However, by the addition of a sodium aluminophosphate glass sintering aid, fully dense Sm-sodalite ceramic monoliths can successfully be produced by sintering at temperatures as low as 800 °C.

Effect of minor Cu content on microstructure and mechanical property of NiTiCu bulk alloys fabricated by crystallization of metallic glass powder

Ultrafine-grained Ni50.2−xTi49.8Cux (x = 0, 2.5, 5, and 7.5) bulk shape memory alloys were fabricated by sintering of metallic glass (MG) powder and crystallization of amorphous phase. Non-isothermal crystallization kinetic analysis reveals that the crystallization mechanism of the synthesized x = 5 MG powder is typical interface-controlled two dimensional growth of nuclei followed by volume diffusion-controlled three dimensional growth of nuclei. In contrast, the crystallization mechanism of the synthesized x = 7.5 MG powder is typical volume diffusion-controlled three dimensional growth of nuclei in whole crystallization process. Correspondingly to different crystallization mechanisms, the two sintered and crystallized (SCed) bulk alloys have the same crystallized phases of bcc B2, fcc NiTi2 phases, and monoclinic B19′, but these phases display different morphologies and distributions. The SCed x = 5 bulk alloy has a microstructure of bcc B2 matrix surrounding fcc NiTi2 phase region, while the SCed x = 7.5 bulk alloy possesses discontinuous bcc B2 phase region. Consequently, the different crystallization mechanisms and microstructures causes extreme high yield strength and large plasticity for the SCed x = 5 bulk alloy and low strength and no plasticity for the SCed x = 7.5 bulk alloy. Especially, the yield strength of the SCed x = 5 bulk alloy is at least two times of that of the counterpart alloy prepared by melt solidification. The results provide a method fabricating high performance bulk alloys by tailoring crystallization mechanism using powder metallurgy.

RETRACTED ARTICLE: Application of partial sintering of waste glasses for preparation of porous glass bodies

Porous glasses were prepared by partial sintering of waste glasses. Polyvinyl alcohol was added as a binder to the glass powder and the mixture was un-axially cold pressed under two different forces, followed by sintering at 700 °C. The effects of thermal history, particle size of glass powder, binder content and applied pressing forces on pore size and total porosity of fabricated porous glasses were investigated and final products with the porosity of 15–32 % were prepared. The average pore size of the specimens was determined using mercury porosimetry. The morphology of the porous glasses was observed by scanning electron microscopy. These produced porous glasses can be used for selective and accurate filtration.

Increased surface area during sintering of calcium phosphate glass and sodium chloride mixtures

Glass scaffolds were obtained by the salt sintering method, using mixtures of calcium phosphate glass, 25.42%SiO2–10.89%P2O5–32.68%CaO–31%MgO(mol%), and salt, NaCl, pressed and sintered bellow the salt melting point, followed by leaching of the salt in water. The sintering behaviour of glass/salt powder mixtures was followed by dilatometry, BET and SEM. It was found that the specific surface area (SSA) of supports sintered between 700–750 °C and leached, can be 15–50 times higher than that of the glass precursor powder, a very surprising behaviour because it presents the opposite tendency of a typical sintering process. Dilatometric curves showed an unusual expansion from ∼450 °C until ∼700 °C, followed by shrinkage at higher temperatures. This expansion accompanies the observed increase of SSA and the microstructures showed a clear effect of reaction between the glass and the salt with remarkable wrinkling of the glass particle surfaces. This phenomenon was further investigated by using DTA, XRD and FTIR.

Magnetic Glass Ceramics by Sintering of Borosilicate Glass and Inorganic Waste.

Ceramics and glass ceramics based on industrial waste have been widely recognized as competitive products for building applications; however, there is a great potential for such materials with novel functionalities. In this paper, we discuss the development of magnetic sintered glass ceramics based on two iron-rich slags, coming from non-ferrous metallurgy and recycled borosilicate glass. The substantial viscous flow of the glass led to dense products for rapid treatments at relatively low temperatures (900–1000 °C), whereas glass/slag interactions resulted in the formation of magnetite crystals, providing ferrimagnetism. Such behavior could be exploited for applying the obtained glass ceramics as induction heating plates, according to preliminary tests (showing the rapid heating of selected samples, even above 200 °C). The chemical durability and safety of the obtained glass ceramics were assessed by both leaching tests and cytotoxicity tests.

Microwave Dielectric Properties of Ca[(Li<sub>1/3</sub>Nb<sub>2/3</sub>)<sub>0.92</sub>Zr<sub>0.08</sub>]O<sub>3</sub><sub>−δ </sub>Ceramics with Glass Addition

The effects of ZnO-B2O3-Na2O(ZBN) glass on the sinterability and microwave dielectric properties of Ca [(Li1/3Nb2/3)0.92Zr0.08]O3−δ −0.05TiO2 ceramics were investigated . ZBN glass doping can effectively reduce sintering temperatue by 100~150oC. The temperature coefficient of resonator frequency τf increased with an increase of ZBN glass content and sintering temperatue. When ZBN glass of 1.8wt% were added, the optimum microwave dielectric properties: εr=32.8, Qf =13420GHz and τf= − 4.3×10−6/oC were obtained at the sintering temperature of 1000oC.

Ytterbium-doped silica photonic crystal fiber laser fabricated by the nanoporous glass sintering technique

Based on the sintering of ytterbium-doped nanoporous glass, a nonchemical vapor deposition process aimed at fabricating a large-mode area of photonic crystal fibers has been proposed for the preparation of active silica glass. With the relatively low doping concentration and boron in the silica glass as benefits, a close refractive index between the core and the cladding was obtained. The refractive index variation indicated good homogeneity of the doped fiber core. Up to 34.8 W laser output was demonstrated with the PCF laser and the slope efficiency was 71.3%. The output laser beam quality had slightly multimode behavior, with a mean M2 of 2.42.

Effects of Sb2O3on the Mechanical Properties of the Borosilicate Foam Glasses Sintered at Low Temperature

The physical properties and microstructure of a new kind of borosilicate foam glasses with different Sb2O3doping content are comprehensively investigated. The experimental results show that appropriate addition of Sb2O3has positive impact on the bulk porosity and compressive strength of the foam glass. It is more suitable in this work to introduce 0.9 wt.% Sb2O3into the Na2O-K2O-B2O3-Al2O3-SiO2basic foam glass component and sinter at 775°C. And the obtained foam glasses present much more uniform microstructure, large pore size, and smooth cell walls, which bring them with better performance including a lower bulk density, low water absorption, and an appreciable compressive strength. The microstructure analysis indicates that, with the increase of the content of Sb2O3additives, the cell size tends to increase at first and then decreases. Larger amounts of Sb2O3do not change the crystalline phase of foam glass but increase its vitrification. It is meaningful to prepare the foam glass at a relatively low temperature for reducing the heat energy consumption.

Role of manganese on the structure, crystallization and sintering of non-stoichiometric lithium disilicate glasses

The structural role of Mn was investigated in a relatively simple non-stoichiometric lithium disilicate (Li2Si2O5) based glass composition. Glasses were prepared by partially replacing SiO2 by MnO2 from the base glass belonging to the system Li2O–K2O–Al2O3–SiO2. An overall depolymerization of the glass network was observed according to magic angle spinning nuclear magnetic resonance (MAS-NMR) and Fourier transform infrared (FTIR) spectroscopic studies, suggesting a network modifier role for Mn. However, thermal analysis, phase segregation and nucleation in the glasses suggested that Mn might also act as network former. Moreover, calculated crystal field parameters from UV-Visible spectroscopy, showing high ligand field strength (Δo) and Racah inter electronic repulsion (B) indicate the possible existence of Mn as individual molecular entities in the interstitials of the glass network. This paper discusses the implications of this structural role of Mn on the crystallization of bulk glasses and on the sintering behaviour and crystallization of glass powder compacts.

첨가제의 조성이 폐유리-점토 타일의 곡강도에 미치는 영향

Cullet-loess tile bodies are successfully fabricated using cullet, loess, hollow microspheres, and sintering additives (borosilicate glass frit, boric acid, or fumed silica) as starting materials. The effects of the additive composition and sintering temperature on the sintered density and flexural strength of the cullet-loess tile bodies are investigated. The sintered density of the cullet-loess tile bodies increases with an increase in the sintering temperature as a result of the enhanced densification of pore walls through the viscous flow of a liquid phase formed from the glass frit and sintering additives. The flexural strength of the cullet-loess tile bodies increases with increases in the sintering temperature and the cullet content in the starting composition. A maximal flexural strength of 40 MPa is obtained in cullet-loess tile bodies sintered with glass frit at 800℃ in air.

Effects of glass additions on the dielectric properties and energy storage performance of Pb0.97La0.02(Zr0.56Sn0.35Ti0.09)O3 antiferroelectric ceramics

In this work, CdO–Bi2O3–PbO–ZnO–Al2O3–B2O3–SiO2 low softening point glass powders were prepared and employed as sintering aid to improve the dielectric breakdown strength and reduce the sintering temperature of Pb0.97La0.02(Zr0.56Sn0.35Ti0.09)O3 antiferroelectric ceramics. The effects of glass content and sintering temperature on the densification, microstructure, dielectric properties and energy storage performance of Pb0.97La0.02(Zr0.56Sn0.35Ti0.09)O3 antiferroelectric ceramics have been investigated. With inclusion of glass, sintered densities comparable to those obtained by conventional sintering are achieved at only 1,050 °C. The breakdown strength of glass-added samples was notably improved due to the reduction of the grain size. The antiferroelectric to ferroelectric switching field and the ferroelectric to antiferroelectric field both increased with increasing glass content. The dielectric constant and dielectric loss decreased gradually with increasing glass content. As a result, the highest recoverable energy density of 3.3 J/cm3 with an energy efficiency of 80 % was achieved in 4 wt% glass-added sample sintered at 1,130 °C.

Solution-based approaches for making high-density sodalite waste forms to immobilize spent electrochemical salts

Three different solution-based approaches were taken to make sodalite minerals as a host for a mixed salt simulating the waste in the electrochemical separations process of nuclear fuel reprocessing. The methods used an aqueous solution of mixed chlorides (simulated waste) but the other reactants varied: (1) Al(OH)3+NaOH+CS, (2) NaAlO2+CS, and (3) Al2Si2O7+NaOH, (CS=colloidal silica). The products were dried, ground, pressed into pellets, and fired at 650–950°C. In some cases, either 5 or 10mass% of a Si–Na–B oxide glass sintering aid was introduced at different stages in the process. Method (2) proved the most successful at producing high sodalite fractions (up to 100%) with minimal sintering aid additions and showed high consolidation potential (up to 91.4% of theoretical density) at reduced firing temperatures.

Sintering and crystallization of plates prepared from coarse glass ceramic frits

The focus of this study was the development of a CAS glass-ceramic (14.0CaO·5.5Al2O3.80·5SiO2) for use in civil engineering as a decorative material. This glass-ceramic system was chosen because it can be used to produce plates with a similar appearance to those of marble and granite materials. Ceramic plates were produced by the Grain Glass Sintering process from frits with a coarse grain size (2.1 mm average particle size). Powder frit samples (5.3-μm average particle size) were prepared and characterized. The results were compared with those obtained with coarse particles. Thermal treatment was performed in one stage, with the heating rate varying from 2 to 25 °C min−1. Temperatures were defined by differential thermal analysis and heating microscopy. With these results, it was possible to establish correlations among the esthetic effects, the microstructure, and the heat treatment conditions (temperature, heating rate, and holding time). The relative density ranged from 0.92 to 0.96. The formation of wollastonite and pseudowollastonite was observed. An esthetic effect similar to that of natural marble was more apparent in those samples in which the microstructure presented a visual contrast between the bulk and the coarse frit. Lower heating rates intensified the visual contrast and reduced porosity near the surface regions.

The Effect of Isostatic Pressing on the Dielectric Properties of Screen Printed Ba0.5Sr0.5TiO3 Thick Films

Ba0.5Sr0.5TiO3 thick films with B2O3–Li2O glass sintering aid were prepared by the screen printing method on Al2O3 substrates. A 200 MPa isostatic pressure was applied to the films before sintering. After being sintered at 950 °C, lower porosity and denser microstructure was obtained compared with the films without isostatic pressing. The dielectric constant and dielectric loss were 238 and 0.0028, respectively. A tunability of 61.7% was obtained for the isostatic pressed films, a 27.8% enhancement compared to unpressurized films. These results suggest that isostatic pressing is an effective way to prepare dielectric thick films with dense microstructure, low dielectric loss, and high tunability.

Effect of CaO additive on sintering and crystallization behavior of cordierite glass–ceramic prepared by sol–gel method

In the present work, cordierite glass–ceramic was prepared via sol–gel method using TEOS, AlCl3·6H2O, MgCl2·6H2O as starting materials. Different steps of phase transformations to cordierite have been studied by DSC and XRD. Various phases have been formed at different heat-treatment temperatures. Addition of CaO led to an increase in both the formation rate and the intensity of α-cordierite. Sinterability of the samples was determined too. The results showed that high content of CaO improved sintering. Morphology of hexagonal prism for α-cordierite was displayed by SEM.

The kinetics of devitrification of amorphous alloys: The time–temperature–crystallinity diagram describing the spark plasma sintering of Fe-based metallic glasses

We present the devitrification behavior of two Fe-based amorphous alloys during spark plasma sintering. The two compositions of interest are SAM7 (Fe48Mo14Cr15Y2C15B6) and SAM2X5 (Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4), both of which have been shown to exhibit outstanding corrosion resistance. We have developed a relationship between crystallite size, time, and temperature of sintering, and propose a time–temperature–crystallinity diagram that is useful for predictive purposes and for guidance on the spark plasma sintering of amorphous metals.

Characterization of alumino-silicate glass/kaolinite composite

A novel porcelain composite of kaolin and alumino-silicate glass (ASG) as a fluxing agent was prepared. The dependence of linear shrinkage, water absorption, apparent porosity and apparent density upon glass addition and sintering temperature were investigated. X-ray diffraction study confirmed the formation of mullite at 1100 °C and existence of cristobalite phase. The glassy phase microstructure was observed using the scanning electron microscope. A self-glazed porcelain body was achieved at 25 wt% of ASG addition. The modulus of rupture (MOR) and flexural strength ( σ f ) increased with glass addition, showing maxima values at 15 wt% glass addition. Micro-hardness increased with glass addition and sintering temperature. The dielectric constant ( ε ′), dielectric loss factor ( ε ″) and dielectric loss tangent (tan δ ) are measured as a function of composition and frequency in the range (10 kHz–1 MHz). The most important property noted was an improvement of the bodies containing ASG in resistance to voltage breakdown. The results of breakdown strength exhibited a maximum value ( E br =56.60 kV/mm) for addition of 25 wt% of alumino-silicate glass sintered at 1100 °C. Owing to its lower cost it is feasible to recycle ASG waste in porcelains instead of feldspar to produce bodies having good properties.