Processing of porous glass ceramics from highly crystallisable industrial wastes

This study was carried out to gain understanding about the sintering behaviour of highly crystallisable industrial waste derived silicate mixtures under direct heating and rapid cooling conditions. The materials used in this study were plasma vitrified air pollution control waste and rejected pharmaceutical borosilicate glass. Powder compacts sintered under direct heating conditions were highly porous; compacts with particle size <?38?μm reached a maximum density of 2.74 g?cm^??3 at 850°C, whereas compacts with particles of size <?100?and <?250?μm reached maximum densities of 2.69 and 2.72 g?cm^??3 at 875 and 900°C respectively. Further increase in sintering temperature resulted in a rapid decrease in density of the glass ceramics. Image analysis results were used to link the sudden drop in density to the increase in volume of microsized pores formed in the samples during sintering. In particular, compacts made from <?38 μm particles sintered at 950°C resulted in 65 vol.-% porosity with a pore size of ～20?μm. Such materials can be used for sound and thermal insulation purposes.     

Recycling of CRT panel glass as fluxing agent in the porcelain stoneware tile production

In the present work, the feasibility to substitute feldspar raw material in a porcelain stoneware body with Panel Cathode Ray Tube (CRT) glass was investigated. A standard batch and a composition, where 35 wt.% Na-feldspar was substituted by CRT glass, were sintered at different temperatures in the range of 1000–1250 °C. The degree of the densification was studied by evaluation of the closed and total porosity, while the sintering rate was estimated by non-isothermal dilatometric measures. The variation of the crystalline phase composition was evaluated by XRD analysis. From the preliminary study other ceramic samples with different percentages of CRT glass (i.e. 2.5, 5 and 10 wt.%) were prepared and fired in industrial kiln. The sintering parameters, the microstructure and the mechanical properties were measured and compared with the standard composition.     

Effect of soda-lime glass on sintering and technological properties of porcelain stoneware tiles

The feasibility of waste glass recycling in ceramic tile production was assessed with special reference to fully vitrified products (porcelain stoneware). Soda-lime float or container glass was introduced, in replacement of sodic feldspar, in typical porcelain stoneware bodies (up to 10 wt.%) that underwent a laboratory simulation of tilemaking process, with a technological and compositional characterization of both fired and unfired tiles. Soda-lime glass had no significant effect on semi-finished products, but it influenced remarkably the firing behaviour, increasing shrinkage and closed porosity, decreasing open porosity and bulk density, and lowering mechanical and tribological performances. Waste glass promotes a more effective melting of quartz and a partial dissolution of mullite, leading to a more abundant and less viscous liquid phase, which accelerates the sintering kinetics. In conclusion, soda-lime glass can be used in small amounts (5% or less) with tolerable modifications of technological behaviour and performances of porcelain stoneware tiles.     

Characterization of basaltic tuffs and their applications for the production of ceramic and glass–ceramic materials

Alkaline basaltic tuffs, from Southern Turkey were characterized and employed to obtain ceramic and glass–ceramic materials by combined sintering and crystallization process. The chemical and mineralogical compositions were analyzed by X-ray fluorescence spectrometry and X-ray diffraction analyses, respectively. The phase formation and the sintering behaviour were investigated by DTA, differential dilatometer and hot-stage microscopy. The micro-structure and residual porosity of the sintered samples were observed by SEM and evaluated by pycnometric techniques. Ceramic material, based on 50% basaltic tuff and 50% clay, was obtained at 1150 °C with 13% total porosity and 4% water absorption. Glass–ceramic materials were synthesized directly using the milled basaltic tuff by mean of the sinter-crystallization technique, in the range 900–1150 °C. The investigation has showed that, due to the high porosity and low crystallinity, alkaline tuffs could be a suitable raw material for ceramic application.     

Novel glass ceramic foams materials based on red mud

Glass ceramic foams were prepared using red mud and fly ash with added CaCO₃ as foaming agents. The aim of the present work was to investigate the possibility of adding red mud, an alkaline leaching waste, in the raw material for the preparation of glass ceramic foams. The results of mineralogical analyses as well as the microscopic examination showed that the use of the red mud affect the mineralogical characteristics and structures of the as produced foams. The influence of amount of red mud on the bulk density and compressive strength of samples was further evaluated. The experimental results showed that relatively low bulk density foams (0.33–0.41 g/cm³) could be obtained by using low sintering temperature (760–840 °C) when the red mud/fly ash ratio does not exceed 40:60. The reduction of sintering temperature or, above all, the reduction of the holding time, was found to limit the coalescence and significantly improve the compressive strength of the foams (0.33–2.74 MPa).     

Optimization of wastes content in ceramic tiles using statistical design of mixture experiments

Mineral extraction and processing industries have been cited as sources of environmental contamination and pollution. The inclusion of wastes into productive cycles represents an alternative form of restoration, which is interesting from both environmental and economic standpoints. In this work, the development of ceramic tile formulations containing kaolin processing and granite sawing wastes was investigated using the statistical design of mixture experiments methodology. Ten formulations using the raw materials, red clay, kaolin processing and granite sawing wastes, were selected and used in the mixture design. Test specimens were fired and characterized to determine their water absorption, linear firing shrinkage and modulus of rupture. Regression models were calculated, correlating the properties with the composition. The significance and validity of the models were confirmed by statistical analysis and verification experiments. The regression models were used to optimize the waste content in ceramic compositions. The results showed that formulations containing up to 62% of waste could be used in the production of ceramic tiles.     

Recycling industrial slags in production of fired clay bricks for sustainable manufacturing

Due to the production of industrial slags in massive amounts, there is a high demand for recycling these slags and avoiding their dumping in landfills. This article aims to recycle industrial slags in brick manufacturing and investigates the performance of fired clay bricks incorporating different kinds of industrial slags such as granulated blast furnace slag (GBS), ferrochromium slag (FCS), and steel slag (STS). For this purpose, two different dosages of slags (i.e., 10 and 20 wt % of clay) and two different firing temperatures (i.e., 1000 and 1100 ^oC) were considered. Various physical, mechanical, and durability tests were performed to evaluate the properties of bricks incorporating industrial slags. Results show that the compressive strength of the bricks incorporating industrial slags are well above the minimum compressive strength limits of bricks as per different building standards. The bricks incorporating industrial slag can be classified as load-bearing bricks for structural applications in accordance with the ASTM C469 standard. An increase in the porosity of bricks is observed with the addition of STS. However, reduced porosity is observed for bricks incorporating FCS and GBS than traditional bricks. Based on the water absorption and efflorescence test results, bricks incorporating industrial slags can be used as severe weather resistant bricks following ASTM C62 standard and slight efflorescence bricks per ASTM C67 standard. The amounts of heavy metals in the leachates of bricks are observed below the specified limits of the Environment Protection Authority. SEM images and EDS analysis of bricks are also supporting the results of this study. Based on the results, utilizing industrial slags in brick manufacturing can help recycle the abundant industrial wastes and develop the fired clay bricks with desired properties.     

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.     

工业废料在耐火材料中的应用现状和进展

简单介绍了工业废料的现状,重点阐述了废料在耐火材料中的研究与应用现状,以及废弃料合成耐火原料的方法、再利用途径和发展前景。     

A new potassium-based bioactive glass: Sintering behaviour and possible applications for bioceramic scaffolds

Providing structural support while maintaining bioactivity is one of the most important goals for bioceramic scaffolds, i.e. artificial templates which guide cells to grow in a 3D pattern, facilitating the formation of functional tissues. In the last few years, 45S5 Bioglass^® has been widely investigated as scaffolding material, mainly for its ability to bond to both hard and soft tissues. However, thermal treatments to improve the relatively poor mechanical properties of 45S5 Bioglass^® turn it into a glass-ceramic, decreasing its bioactivity. Therefore, the investigation of new materials as candidates for scaffold applications is necessary. Here a novel glass composition, recently obtained by substituting the sodium oxide with potassium oxide in the 45S5 Bioglass^® formulation, is employed in a feasibility study as scaffolding material. The new glass, named BioK, has the peculiarity to sinter at a relatively low temperature and shows a reduced tendency to crystallize. In this work, BioK has been employed to realize two types of scaffolds. The obtained samples have been fully characterized from a microstructural point of view and compared to each other. Additionally, their excellent bioactivity has been established by means of in vitro tests.     

Phase evolution and photoluminescence in Er3+ doped glass ceramics containing lutetium oxyfluoride nanocrystals

Crystalline phase evolution through merely adjusting composition was achieved in silicate glass ceramics containing Lu_nO_n-1F_n+2 (n = 5–10) nanocrystals. Orthorhombic or cubic phase nanocrystals were precipitated in the aluminosilicate glass matrix after thermal treatment together with varying the Na₂O/NaF ratio. Oxyfluoride nanocrystals with quasi-spherical shape show homogenous and dense distribution in glass matrix by transmission electron microscopy measurement. Intense upconversion and mid-infrared emissions were realized in these glass ceramics compared to the precursor glass, and the emission spectral shapes, relative emission intensity and fluorescence decay curves of Er³⁺ in cubic LuOF embedded samples exhibit remarkable differences due to the crystal phase dependent effect in glass ceramics. These results indicate that the crystallization and luminescence properties of oxyfluoride glass ceramics could be modified through the alteration of glass composition, which could be used for the development of novel glass ceramics and design of luminescent properties.     

Bioactive fluorapatite-containing glass ceramics

Fluorapatite-containing glass ceramics were synthesized on the basis of the glass-forming system SiO₂–Al₂O₃–P₂O₅–CaO–CaF₂. The introduction of phosphorus and fluorine containing materials, as well as the specific regime of heat treatment of the glasses gave glass ceramic materials with crystalline phases of the apatite group—fluorapatite (Ca₁₀(PO₄)₆F₂), apatite (Ca₃(PO₄)₂), vitlokite (Ca₉P₆O₂₄), etc. The X-ray phase analysis showed that the main phase in all the glass ceramic samples was fluorapatite. The phase composition, structure and some of the basic properties of the glass ceramic samples were determined.     

Potassium based bioactive glass for bone tissue engineering

A fundamental issue for the restoration of bone defects according to a tissue engineering approach is the development of highly porous bioactive scaffolds. The polymer burning out method is widely employed to fabricate bioceramic scaffolds because of its versatility, simplicity and low cost. However, the resulting scaffolds may suffer low porosity and non-interconnected pores. In the present contribution a new fabrication method is presented. Thanks to a recently developed potassium-based bioactive glass, which has the peculiarity to be sintered at a relatively low temperature (i.e. ∼750 °C), it was possible to use sodium chloride particles as pore generating agents, which helped to maintain the shape of the struts during the entire sintering process. The salt particles can be easily removed by immersing the scaffold in water, giving place to a structure that combines high porosity (in the 70–80 vol.% range) with interconnected pores and an appreciable mechanical behaviour (Young's modulus in the 3.4–3.7 MPa range according to compression tests).     

Suppressing the effect of cullet composition on the formation and properties of foamed glass

The process of foaming glass is very dependent on the chemical composition of the glass. In this study we used a foaming-agent/oxidizing-agent couple and a crystallization inhibitor to foam cullets of flat, container and CRT-panel glass. Foamed glass with a density of 110–120?kg?m^–3, a thermal conductivity of 50–52?mW?m^–1 K^–1 and a homogeneous pore structure was obtained from a mixture of panel glass, 0.33?wt% carbon and 4.45?wt% Fe₂O₃. We also showed that it is possible to fabricate foamed glass with the same density or pore structure as mentioned above by adding up to 50?wt% container cullet or 70?wt% flat glass to the mixture. In the foamed samples with a low content of panel glass, crystals form, resulting in an increased open porosity, density and inhomogeneous pore structure. The crystallization can, however, be inhibited by adding calcium phosphate, so enabling the preparation of high-quality foamed glass from flat glass or flat/container-glass mixture. The pore gas is predominantly CO₂ and the pressure inside the pores is 0.36–0.47?bar. The reduced effect of the composition on the foaming process suggests that there is a great potential for stabilizing the production of foamed glass and ensuring the product's quality.     

A review on laser deposition-additive manufacturing of ceramics and ceramic reinforced metal matrix composites

Ceramics and ceramic reinforced metal matrix composites (MMCs) are widely used in severe working conditions and have been applied in biomedical, aerospace, electronic, and other high-end engineering industries owing to their superior properties of high wear resistance, outstanding chemical inertness, and excellent properties at elevated temperatures. These superior properties, on the other hand, make it difficult to process these materials with conventional manufacturing methods, posing problems of high cost and energy consumptions. In response to this problem, direct additive manufacturing (AM), which is equipped with a high-power-density laser beam as heat source, has been developed and extensively employed for processing ceramics and ceramic reinforced MMCs. Compared with other direct AM processes, laser deposition-additive manufacturing (LD-AM) process excels in several aspects, such as lower labor intensity, higher fabrication efficiency, and capabilities of parts remanufacturing and functionally gradient composite materials fabrication. Besides these benefits, problems of poor bonding, cracking, lowered toughness, etc. still exist in LD-AM fabricated parts. This paper reviews developments on LD-AM of ceramics and ceramic reinforced MMCs in both bulk parts fabrication and cladding. Main issues to be solved, corresponding solutions, and the trend of development are summarized and discussed.     

Preliminary experiments on metallisation of ceramic oxide superconductors

Abstract

The present paper briefly reports on preliminary experiments on two new methods for the metallisation of ceramic oxide high temperature superconductors )HTS compounds): sinter-permeate silver and chemically precipitated silver. By using well characterised HTS samples for the measurement of superconducting properties it is shown that successful metallisation and jointing were obtained. The two methods are considered to have potential for further development and application in this field.     

Glass–ceramic frits for porcelain stoneware bodies: Effects on sintering,phase composition and technological properties

In the present work, the effects of glass–ceramic frits (10 wt.%) added to a porcelain stoneware body in replacement of non-plastic raw materials were evaluated simulating the tile-making process. Each glass–ceramic frit plays its own peculiar effect on the compositional properties and only some precursors behave as real glass–ceramic materials. The positive influence of glass–ceramic precursors in promoting the sintering stands out when temperature onset densification and sintering rate are considered: both of them are improved with respect to the reference body. The presence of glass–ceramic frits allows to preserve good technological properties, complying with the latest requirements of the industrial practice.     

Electromagnetic absorption, reflection and interference shielding in X-band frequency range of low cost ceramic building bricks and sandwich type ceramic tiles using mill scale waste as an admixture

General concern for potential health effects of 24 h electromagnetic fields (EMF) exposure has increased over the recent years. This has led to the necessity of developing low cost electromagnetic interference (EMI) shielding and especially absorbing building materials. In the present study the utilization of steel mill scale waste in ceramic bricks for this purpose was investigated, while the development of an improved, regarding mainly absorption performance, building material also occurred. Both ceramic bricks and sandwich type ceramic tiles were found to have good shielding efficiency and absorption performances in the same X-band frequency range (8-12 GHz) while technological and environmental requirements as building materials were also established.     

Growth behavior,morphology and properties of lithium aluminosilicate glass ceramics with different amount of CaO,MgO and TiO2 additive

Li₂O–Al₂O₃–SiO₂ glass with CaO, MgO and TiO₂ additive were investigated. With more CaO + MgO addition, the crystallization temperature (T_p) and the value of Avrami constant (n) decreased, the activation energy (E) increased. The mechanism of crystallization of the glass ceramics changed from bulk crystallization to surface crystallization. With more TiO₂ addition, the crystallization temperature decreased, E and n had a little change. The crystallization of the glass ceramics changed from surface crystallization to two-dimensional crystallization. Plate-like, high mechanical properties spodumene-diopside glass ceramics were obtained. The mechanical properties related with crystallization and morphology of glass ceramics.     

Acoustic and thermal performances of ceramic tiles and tiling systems

Acoustic and thermal performances of floating floor and/or radiant floor can be improved by using ceramic tiles with tailored porosity and microstructure. Porcelain stonewares are still the most widespread typology of tiles, due to their high physical and mechanical performances coming from a very low level of open porosity and water absorption (≤0.5 wt%). However their closed porosity values, usually neglected, can be significantly different from one product to another. As a consequence, the properties directly dependent on the total porosity, such as thermal and acoustic ones, may be strongly diverse among commercial tiles.Several commercial porcelain stoneware tiles having different composition, microstructure and porosity, were selected for the present work. These tiles, alone or coupled with different types of resilient underlayer materials (glass fibre, cork and rubber), were studied on the basis of dynamic stiffness. Their acoustic and thermal properties were investigated in terms of thermal conductivity and walking noise reduction.