The influence of the binder on the properties of sintered glass-ceramics produced from industrial wastes

Sintered glass-ceramics were produced from coal fly ashes, red mud from aluminum production and silica fume. The capabilities of Tunçbilek fly ash and a mixture of Orhaneli fly ash, red mud and silica fume to be vitrified and devitrified by sintering process were investigated by means of scanning electron microscopy and X-ray diffraction analysis. To determine the effect of binder in the sintering technique, glass powders were pressed without or with the addition of polyvinyl alcohol. Owing to microstructural observations, density and hardness measurements, it can be said that physical properties and the hardness of the produced samples strongly depended on the crystallization degree of the samples. Toxicity characteristic leaching procedure test results showed that glass-ceramic samples produced by using sintering technique could be considered as non-hazardous materials. Chemical durability of the sintered glass-ceramic samples was also good. Microstructural investigations, hardness and physical properties of the samples indicated that the addition of polyvinyl alcohol improved the properties of sintered glass-ceramics obtained from Orhaneli fly ash, red mud and silica fume.     

反应析晶烧结法制备硅灰石玻璃陶瓷

本文提出了一种直接利用废玻璃制备硅灰石玻璃陶瓷的新工艺:反应析晶烧结法。将高岭土和碳酸钙为主要原料合成的析晶促进剂加入到废玻璃粉末中烧结,通过两者间的反应析出硅灰石。研究了析晶促进剂含量和烧结温度对硅灰石玻璃陶瓷的组织、烧结和性能的影响,结果表明:随着析晶促进剂含量的增加,玻璃陶瓷的体密度和开孔隙率增加,强度先增后降。提高烧结温度促进反应析晶,并导致玻璃陶瓷的体密度、开孔隙率和强度降低。析晶促进剂含量为15%,烧结温度为850℃时,制得的硅灰石玻璃陶瓷的力学性能最佳。     

Production of ceramics from coal furnace bottom ash

Furnace bottom ash (FBA) is generated in significant quantities from coal fired power stations and is a problem when commercially viable reuse applications do not exist locally. Representative samples of FBA from the Kilroot power station in Northern Ireland have been milled, pressed and sintered at a range of temperatures to form new ceramic materials. The effect of adding recycled glass to the mix has been investigated. The optimum FBA ceramics were produced by sintering at 960 °C and these had a density of 2.388 g/cm³, zero water adsorption indicating minimal open porosity, and a Vickers hardness comparable to commercially available glass-ceramics. The addition of 20% by weight of glass reduced shrinkage during sintering, while the samples maintained high density and hardness. This glass addition allows greater dimensional control during sintering to form FBA ceramic tiles. The research demonstrates that FBA can be processed into ceramics for use in higher value products compared to conventional use as lightweight aggregate. Further research is required to optimize processing and fully characterize material properties. This novel approach to managing FBA has potential to transform a problematic waste in Northern Ireland into a valuable resource.     

Crystallization pathways in glass-ceramics by sintering cathode ray tube (CRT) glass with kaolin-based precursors

The crystallization mechanisms for the formation of glass-ceramics by sintering CRT glass with kaolin-based precursors were investigated by quantitatively determining the crystalline and amorphous phases in the products. Amorphization of sintered products was observed in CRT/kaolinite and CRT/mullite glass-ceramics systems at 700–900?°C. With the increase of temperature, the crystallochemical formation of lead feldspar and orthoclase was detected. Orthoclase was found to be the major crystalline phase in both CRT/kaolinite and CRT/mullite systems at 1000–1100?°C. When the temperature increased to 1000–1100?°C, lead feldspar was formed as the only crystalline phase to host Pb. The leaching tests suggested that the glass-ceramic product sintered by CRT/kaolin-based precursors has stronger resistance against acid attack because of the incorporation of lead into lead feldspar crystal protected by glass matrix. The incorporation of CRT glass into glass-ceramics provides a promising strategy for reducing the environmental hazard of CRT glass.     

Sintering and reactive crystal growth of diopside-albite glass-ceramics from waste glass

Diopside-albite glass-ceramics were fabricated by sintering the powder mixtures of crystallization promoters and waste glass. Two kinds of promoters were synthesized using kaolin clay, talc and chemical reagents. The crystalline phases were formed by a reactive crystallization between promoters and glass during sintering. The effect of promoter components, additions and sintering temperatures on the crystallizing and densifying behavior, microstructures and mechanical properties of glass-ceramics was investigated. The results showed that the higher densities and better mechanical properties were obtained for the glass-ceramics with 12-15% crystallization promoters sintered at 950 °C for 2 h.     

透辉石玻璃陶瓷的制备及其析晶特性研究

以废玻璃粉为原料,采用反应析晶烧结法制备了透辉石玻璃陶瓷。采用差热分析、X射线衍射分析、扫描电镜、能谱、高分辨透射电镜等方法研究了顽辉石-堇青石粉和废玻璃粉混合样品等温烧结过程中顽辉石-堇青石向透辉石转变的演变过程。结果表明:顽辉石-堇青石与玻璃粉在815°C下即可发生反应析晶;900°C保温2 h可获得透辉石为主晶相的玻璃陶瓷。在保温过程中,顽辉石的Mg~(2+)和O~(2-)向玻璃中扩散,玻璃中的Si~(4+)和Ca~(2+)向顽辉石中移动,使顽辉石晶体在b轴方向交替排列的两条链沿c轴方向断开,转变成单链,由Mg~(2+)和Ca~(2+)连接生成透辉石。保温0 h时,由于堇青石[MgO_6]八面体膨胀较小,玻璃中的Si~(4+)、Ca~(2+)、Na~+向堇青石中移动,反应析晶生成钠长石与透辉石;当保温时间延长至2 h时,堇青石[MgO_6]八面体骨架进一步扭曲,生成主晶相为透辉石的玻璃陶瓷。     

LZS/Al2O3 nanostructured composites obtained by colloidal processing and spark plasma sintering

Li₂O-SiO₂-ZrO₂ (LZS) glass-ceramics have high mechanical strength, hardness, resistance to abrasion and chemical attack, but also a high coefficient of thermal expansion (CTE), which can be reduced adding alumina nanoparticles. The conventional glass-ceramic production is relatively complex and energy consuming, since it requires the melting of the raw materials to form a glass frit and a two-step milling process to obtain particle sizes adequate for compaction. This study describes the preparation of LZS glass-ceramics through a colloidal processing approach from mixtures of SiO₂ and ZrO₂ nanopowders and a Li precursor (lithium acetate obtained by reaction of the carbonate with acetic acid). Concentrated suspensions were freeze-dried to obtain homogeneous mixtures of powders that were pressed (100 MPa) and sintered conventionally and by spark plasma sintering. The effect of the alumina nanoparticles additions on suspensions rheology, sintering behavior and properties such as thermal expansion, thermal conductivity, hardness and Young’s modulus were evaluated.     

Rapid synthesis of Gd2Zr2O7 glass-ceramics using spark plasma sintering

Glass-ceramics are possible host matrix for high level waste immobilization. The Gd₂Zr₂O₇ glass-ceramic matrix was successfully synthesized using spark plasma sintering (SPS) method in 5 minutes. The phase transition with sintering temperature was studied using X-ray diffraction, Raman and transmission electron microscopy. It revealed that samples kept a main defected fluorite phase as being sintered below 1800°C. Glass phase increased rapidly beyond 1850°C. The amorphous structure became the main body at 1900°C, with nanoscale crystal scattered in the bulk. With the increase of glass phase, the grain boundary became almost indistinguishable. The relationship between the final phase of Gd₂Zr₂O₇ with its synthetic temperature range and corresponding technology was reviewed. Gd₂Zr₂O₇ glass-ceramics could be acquired by extending the sintering temperature beyond 1850°C using SPS method.     

Recycling of Iron Sintered Wastes Into Nanoparticles Barium Hexaferrite and Zinc-Ferrite Glass-Ceramics

About 25 % of iron oxides in the sintering process are wastes. In this paper, sintered waste (SW) was used as a source of iron oxides to prepare both hard and soft magnetic glass-ceramics via a melting-quenching technique. About 71 % by wt. of sintered waste was used for preparing soft magnetic glass-ceramics, while ～46 % was used for preparing hard magnetic glass-ceramics. The comparison between ferrimagnetic glass-ceramics prepared from pure chemicals and that from sintered waste before and after heat treatment was studied. X-ray diffraction shows crystallization of both hematite and Zn-ferrite phases in sintered waste while pure Zn-ferrite or Ba-hexaferrite phases were crystallized in soft magnetic and hard magnetic glass-ceramics, prepared from sintered waste, respectively. Transmission electron microscopy determined the crystalliza- tion of nano-particles ～20 nm and <15 nm for soft and hard magnetic glass-ceramics respectively. Vibrating scanning magnetometry revealed a significant increase in saturation magnetization from ～26 emu/g for sintered waste to ～44 emu/g in soft magnetic glass ceramics while it decreased to ～12 emu/g for hard magnetic glass-ceramics.     

传统陶瓷工艺制备玻璃陶瓷/SiC晶须复合材料

针对传统陶瓷工艺难以直接用于制备玻璃陶瓷/SiC晶须复合材料问题,本文以白云鄂博尾矿基透辉石系玻璃粉和商用SiC晶须为主要原料,在石墨粉包埋条件下,采用传统陶瓷工艺成功制备出透辉石玻璃陶瓷/SiC晶须复合材料.在此基础上,研究了填加0～40wt％SiC晶须对所制备复合样品显微结构及性能的影响.结果证明了所制备复合材料样...     

Technological properties of glass-ceramic tiles obtained using rice husk ash as silica precursor

This paper reports the results of a study focused on the obtainment of glass-ceramic by using rice husk ash (RHA) as silica precursor. RHA is a by-product generated in biomass plants using rice husk as fuel for kilns or in the rice mills to generate steam for the parboiling process. Worldwide, it is annually produced about 132 Mt of rice husk, which gives rise to a production of 33 Mt/year of RHA. Glass-ceramic tiles were produced by a sinter-crystallization process using a glassy frit formulated in the MgO–Al₂O₃-SiO₂ composition system. The realized glass-ceramics were studied according to ISO rules for sintering and technological properties (water absorption, apparent density, bending strength, Young's modulus, deep abrasion, Mohs hardness). To complete the investigation crystalline phase formation and microstructural characterization of the glass-ceramic materials was carried out using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Finally, chemical durability tests on parent glass and derived glass-ceramics were performed. The results obtained showed that it is possible to use RHA to produce glass-ceramic tiles by a sinter-crystallization process, obtaining nepheline (Na₂O*Al₂O₃*SiO₂) as main crystalline phase and forsterite (2MgO*SiO₂) at 900 °C. Regarding technological features, the sintered materials showed bending strength values and Mohs hardness higher with respect to commercial glass-ceramics like NeopariesR. Other properties as water absorption (0.5%) allowed to classify these materials into the Group BIa characteristic of high sintered ceramic tiles according to European Standard rule.     

Effect of microwave sintering on the microstructure and mechanical properties of AA7075/B4C/ZrC hybrid nano composite fabricated by powder metallurgy techniques

AA7075 + 6%B4C+3%ZrC nano hybrid composite was successfully fabricated, with nano reinforcements composition in AA7075 alloy selected based on previous investigation, to achieve better mechanical performance. Two different sintering techniques, namely conventional and microwave, were implemented to determine the effect on microstructural and mechanical properties. Microstructural investigation was performed with the help of W-SEM. Tensile, compression, and hardness were measured with the help of UTM and Vickers microhardness machine. Porosity was calculated by using Archimedes principle. It was observed that the added nano ZrC particles formed agglomerates and the B₄C particles were distributed homogenously. Composites processed by microwave sintering showed excellent mechanical properties compared to the conventionally sintered composites. No intermetallic compounds were detected in microwave sintered composites through XRD analysis, indicating strong and clean interface bonds between matrix and reinforcement particles. High strain to fracture value of 12.24% was noted in microwave sintered nano hybrid composite, while it was 6.12% for conventional sintered one. Fractography revealed no peeling action of reinforcements from the matrix material, and the mode of failure was brittle. It was concluded that, while fabricating nano range hybrid composites, the implementation of advanced sintering technique (microwave sintering) with low sintering temperatures and low sintering times with internal heat generations, helps in eliminating defects that may develop because of high surface energies of nano range reinforcements.     

Preparation and properties of the glass-ceramics from low Ti-bearing blast furnace slag and waste glass

Ti-bearing blast furnace slag is a typical silicate material, which can be an important component for the preparation of silicate-based glass-ceramics. Quartz-based waste glass is commonly used as an additive to adjust the basicity of slag-based glass-ceramics. In this study, the quartz-based waste glasses were added to the Ti-bearing blast furnace slag to prepare the mixed solid waste glass-ceramics. The effects of waste glass content and heat treatment temperatures on the crystallization and performances of the prepared glass-ceramics were investigated. The results showed that as the waste glass content increased, the crystallization ability of the glass was weakened. Fassaite and nepheline were identified as the dominant crystalline phases in the prepared glass-ceramics and mainly featured a combination of both massive and dendritic forms. With increasing the heat treatment temperatures, the size of dendritic crystals first increased and then decreased. The optimal experimental conditions were identified as a waste glass content of 45%, a crystallization temperature of 900°C, and a nucleation temperature of 730°C. Under these conditions, the prepared glass-ceramics exhibited good crystalline phase distribution and excellent mechanical properties, including a Vickers hardness of 991.67 MPa and a flexural strength of 89.81 MPa. All the prepared solid waste-based glass-ceramics exhibited excellent chemical durabilities.     

Sinterability,microstructure and compressive strength of porous glass-ceramics from metallurgical silicon slag and waste glass

Porous glass-ceramics have been prepared by the direct sintering of powder mixtures of metallurgical silicon slag and waste glass. The thermal behavior of silicon slag was examined by differential thermal analysis and thermogravimetry to clarify the foaming mechanism of porous glass-ceramics. The mass loss of silicon slag below 700 °C was attributed to the oxidation of amorphous carbon from residual metallurgical coke in the silicon slag, and the mass gain above 800 °C to the passive oxidation of silicon carbide. The porosity of sintered glass-ceramics was characterized in terms of the apparent density and pore size. By simply adjusting the content of waste glass and sintering parameters (i.e. temperature, time and heating rate), the apparent density changed from 0.4 g/cm³ to 0.5 g/cm³, and the pore size from 0.7 mm to 1.4 mm. In addition to the existing crystalline phases in the silicon slag, the gehlenite phase appeared in the sintered glass-ceramics. The compressive strength of porous glass-ceramics firstly increased and then decreased with the sintering temperature, reaching a maximal value of 1.8 MPa at 750 °C. The mechanical strength was primarily influenced by the crystallinity of glass-ceramics and the interfaces between the crystalline phases and the glassy matrix. These sintered porous glass-ceramics exhibit superior properties such as light-weight, heat-insulation and sound-absorption, and could found their potential applications in the construction decoration.     

Sintering Behavior and Properties of Iron-Rich Glass-Ceramics

Iron-rich glass-ceramics were obtained by the sintering of two glass powders, labeled G1 and G2, at heating rates of 5° and 20°C/min followed by an isothermal step in the 850°–1050°C temperature interval. The sintering process was evaluated by the linear shrinkage; the closed porosity was estimated by density measurements; the structure and the morphology of the glass ceramics were observed by scanning electron microscopy. The bending strength, the Young modulus, and Vickers hardness of the glass-ceramics materials were evaluated. The results showed that the sintering process and morphology of the glass-ceramics depends on the amount of magnetite and pyroxene formed. With a low percentage of crystal phase formed (25%–30% typical of G1) the structure is characterized by closed porosity; at higher crystallization (45%–50% typical of G2) open porosity is mainly formed. The properties of the glass-ceramics were not influenced by the heating rate but improved with an increase in the degree of crystallization.     

Ultra-low temperature preparation of mullite glass-ceramics with high transparency sintered from EMT-type zeolite

Nanocrystalline mullite glass-ceramics have been regarded as an ideal optical window material due to its excellent thermal shock resistance, low dielectric constant, and perfect high-temperature strength. However, the fabrication of high-purity mullite glass-ceramics at a low temperature still faces great challenges. Herein, highly transparent mullite glass-ceramics have been prepared at an ultra-low temperature (~800°C) via the spark plasma sintering (SPS) of EMT-type zeolite. Unlike the mullite glass-ceramics made by the conventional sintering process, the one obtained in this study present high transparency both in the visible and infrared regions. The sintering activity and linear thermal shrinkage behavior of sample during the SPS process has been thoroughly investigated. Benefitted from the existence of ultra-small mullite nanocrystals, the derived glass-ceramics g-950 possess a high Vickers hardness (7.0 GPa), Young's modulus (86.6 GPa), and MSP strength (123.2 MPa), which show more excellent mechanical properties than conventional aluminasilicate or silica glass.     

Microstructural development and electrical behavior during crystalization of iron-rich glass-ceramics obtained from mill scale

Mill scale is one of the most hazardous waste generated from the steelmaking industry. In 2014, around 16.4–32.8 million t of mill scale was generated all over the world. In this paper, we present recent results about the effect of the structure and microstructure of iron-rich glass-ceramics obtained from mill scale on their electrical behavior. Five iron-rich glass compositions were investigated. The crystalline phases of the crystallized (glass-ceramic) materials were identified by X-ray diffractometry, and phase content quantifications were performed by the Rietveld method. The crystallinity and porosity were also related to the electrical behavior of the glass-ceramics, which was determined by impedance spectroscopy, and the hardness, measured by the Vickers indentation method. Albite, andradite, anorthite, clinopyroxene, franklinite, nepheline, and spinel were shown to be the main crystalline phases present in the investigated compositions. The conductivity showed an increasing trend with the degree of crystallinity. This behavior was attributed to a decrease in porosity, an increase in the concentration of charge carriers in the glass phase (iron, Li⁺, and Na⁺), and an increase in the number of conduction paths through the glassy phase/crystalline phase interfaces. The relationship between hardness and crystallinity could not be verified due to the structural complexity of the glass-ceramics studied. However, a nearly linear relationship was found between the effect of porosity and hardness. The G2Z composition exhibited a hardness of 6.1 ± 0.5 GPa at 850 °C, which is a value in very good agreement with other iron-rich glass-ceramics studied.     

Preparation and characterization of fully waste-based glass-ceramics from incineration fly ash,waste glass and coal fly ash

Municipal solid waste incineration (MSWI) fly ash (FA) is a typical hazardous waste due to its high contents of toxic heavy metals, and hence its disposal has attracted global concern. In this work, it was recycled into environmental-friendly CaO–Al₂O₃–SiO₂ system glass-ceramics via adding coal fly ash (CFA) and waste glass (WG). The effects of CaO/SiO₂ ratios and sintering temperatures on the crystalline phases, morphologies, mechanical and chemical properties, heavy metals leaching and potential ecological risks of glass-ceramics were investigated. The results showed that wollastonite (CaSiO₃), anorthite (CaAl₂Si₂O₈) and gehlenite (Ca₂Al₂SiO₇) were the dominant crystals in the glass-ceramics, which were not affected by CaO/SiO₂ ratio and sintering temperature. The compressive strength increased, while the Vickers hardness and microhardness decreased as increasing the sintering temperatures from 850 to 1050 °C, which reached their maximum values of 660.69 MPa, 6.14 GPa, and 7.43 GPa, respectively. However, the increase of CaO/SiO₂ ratio resulted into the reduction of the three mechanical parameters. As varying CaO/SiO₂ ratio from 0.48 to 0.86, the maximum compressive strength, Vickers hardness and microhardness were 611.80 MPa, 5.43 GPa, and 6.56 GPa, respectively. Besides, all the glass-ceramics exhibited high alkali resistance of >97%. The extremely low heavy metals leaching concentrations and low potential ecological risk of glass-ceramics further revealed its environmentally friendly property and potential application feasibility.     

Effect of microwave sintering on the properties of copper oxide doped Y-TZP ceramics

The effect of various amounts of copper oxide (CuO) up to 1?wt% on the densification behaviour and mechanical properties of 3?mol% yttria-tetragonal zirconia polycrystal (Y-TZP) were studied by using microwave (MW) sintering method. The MW sintering was performed at temperatures between 1100?°C and 1400?°C, with a heating rate of 30?°C/min. and holding time of 5?min. The beneficial effect of MW in enhancing densification was also compared for the undoped and 0.2?wt% CuO-doped Y-TZP when subjected to conventional sintering (CS) method. The results showed that significant enhancement in the relative density and Vickers hardness were observed for the undoped Y-TZP when MW-sintered between 1100?°C and 1250?°C. It was revealed that the 0.2?wt% CuO-doped Y-TZP and MW sintered at 1250–1300?°C could attain ≥?99.8% of theoretical density, Vickers hardness of about 14.4?GPa, fracture toughness of 7.8 MPam^1/2 and exhibited fine equiaxed tetragonal grain size of below 0.25?µm. In contrast, the addition of 1?wt% CuO was detrimental and the samples exhibited about 50% monoclinic phase upon sintering coupled with poor bulk density and mechanical properties. The study also revealed that the addition of 0.2?wt% CuO and subjected to conventional sintering produced similar densification as that obtained for microwave sintering, thus indicating that the dopant played a more significant role than the sintering method.     

Magnetic properties of magnetite-based nano-glass-ceramics obtained from a Fe-rich scale and borosilicate glass wastes

Magnetite-based glass-ceramic is a special composite material composed by magnetic nanocrystals embedded in a vitreous matrix. In this work, it was developed magnetic glass-ceramics based on borosilicate glass wastes and, for the first time, by using iron-rich scale (a waste from the metallurgical industry). Different compositions were established with increasing scale contents (20, 30, 45?wt%). Raw materials were melted (1550?°C/4?h) and later cast in a preheated steel mold at 400?°C. Then, the obtained samples were heat-treated at 700?°C/ 30?min. The sample with 45?wt% scale also was heated at 800?°C and 900?°C/ 30?min, in order to promote more crystallization. The obtained glass-ceramics properties were investigated using X-ray diffraction (XRD), Raman spectroscopy, vibrating-sample magnetometer (VSM), Mössbauer spectroscopy and transmission electron microscopy (TEM). Magnetite nanocrystals (average size in the 40–64?nm range) in the glass-ceramics were evidenced by TEM images and Mössbauer spectrum. VSM analysis revealed that the obtained ferrimagnetic glass–ceramic with composition of 45?wt% scale annealed at 800?°C/ 30?min, improved the magnetic saturation (Ms), reaching 42?emu/g. Results indicated a great potential of this magnetic-based glass-ceramics for being applied in many applications, such as the biomedical engineering field, in magnetic devices, magnetic resonance imaging contrast agents, hyperthermia, waste sorbent, and microwave devices.