Potential utilization of oil sludge incineration bottom ash for glass-ceramics: Crystallization kinetics,properties and toxicological evaluation

The bottom ash (OIBA) generated from the incineration of hazardous oil sludge is classified as a hazardous waste. In this work, the OIBA was applied as raw material to prepare SiO₂-Al₂O₃-CaO system glass-ceramics by melt-sintering with the addition of waste glass wool (GW). The effects of basicity (CaO/SiO₂ ratio, 0.52-1.05) and sintering temperature (900–1050 °C) on the crystallization kinetics, properties, microstructure, leaching concentrations of heavy metals and potential toxicity of glass-ceramics were investigated. The results showed that the crystallization pattern was two-dimensional crystallization, and with the decrease of basicity, the main crystalline phase evolved from gehlenite to diopside. And the glass-ceramics with basicity of 0.88 and sintering temperature of 950 °C exhibited the best comprehensive properties, including density (2.72 g/cm³), water absorption (0.06%), compressive strength (452.45 MPa) and chemical corrosion resistance. In addition, the reduction of heavy metal leaching concentration indicates that produced glass-ceramics showed excellent solidification effect on heavy metals, the low toxicity of glass-ceramics leaching solution to the wheat seeds and Artemia suggests the environmental protection characteristics of OIBA-based glass-ceramics. These findings proved that the glass-ceramics produced by OIBA and GW could be a promising method to dispose hazardous waste with preparing high value-added construction materials.     

Low temperature synthesis of anorthite based glass-ceramics via sintering and crystallization of glass-powder compacts

Anorthite based glass-ceramics were synthesized. The investigated glass compositions are located close to the anorthite-rich corner of the fluorapatite–anorthite–diopside ternary system. Glass powder compacts with mean particle size of 2 and 10 μm were prepared. Sintering behaviour, crystallization and the properties of glass-ceramics were investigated between 800 and 950 °C. In the case of specimens made from the finer particles, complete densification was achieved at a remarkably low temperature (825 °C) and the highest mechanical strength was obtained at 850 °C, but density significantly decreased at higher temperatures. The samples prepared from the larger particles exhibited higher values of density, shrinkage and bending strength within a wider temperature range (825–900 °C). Anorthite was predominantly crystallized between 850 and 950 °C, along with traces of fluorapatite. Diopside was detected only in the MgO richer compositions.     

Effect of crystallization temperature on dielectric and energy-storage properties in SrO-Na2O-Nb2O5-SiO2 glass-ceramics

The SrO-Na₂O-Nb₂O₅-SiO₂ (SNNS) glass-ceramics were prepared through the melt-quenching combined with the controlled crystallization technique. XRD results showed Sr₆Nb₁₀O₃₀, SrNb₂O₆, NaSr₂Nb₅O₁₅ with tungsten bronze structure and NaNbO₃ with the perovskite structure. With the decrease of crystallization temperature, dielectric constant firstly increased and then decreased, while breakdown strength (BDS) was increased. High BDS of the glass-ceramics is attributed to the dense and uniform microstructure at low crystallization temperature. The optimal dielectric constant of 140±7 at 900 °C and BDS of 2182±129 kV/cm at 750 °C were obtained in SNNS glass-ceramics. The theoretical energy-storage density was significantly improved up to the highest value of 15.2±1.0 J/cm³ at 800 °C, which is about 5 times than that at 950 °C. The discharged efficiency increased from 65.8% at 950 °C to 93.6% at 750 °C under the electric field of 500 kV/cm by decreasing crystallization temperature.     

Influence of the sintering temperature on the structural feature and bioactivity of sol–gel derived SiO2–CaO–P2O5 bioglass

A sol–gel method was utilized to synthesize the gel with the composition of 58 mol% SiO₂–38 mol% CaO–4 mol% P₂O₅. The thermal properties were studied using thermogravimetric and differential thermal analysis (TG/DTA). Then the gels were sintered at 700, 900, 1000 and 1200 °C. The structure features were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), in addition in vitro assays were carried out in simulated body fluid (SBF). The results revealed that at sintering temperature above 900 °C, crystallization occurred and glass-ceramics with pseudowollastonite and wollastonite were formed. Furthermore with the increase of sintering temperature, the amount of pseudowollastonite decreased while that of wollastonite increased. In vitro tests indicated that the crystallization did not inhibit the samples bioactivity. After soaking in SBF, the formation of apatite was confirmed on glass and glass-ceramics surface, and the bioactivity of the glass-ceramics was based on the formed pseudowollastonite and wollastonite.     

Preparation and characterization of alkali-free glass substrates with enhanced properties for TFT–LCDs applications

To obtain an alkali-free glass substrate with enhanced properties for thin-film transistor–liquid crystal displays (TFT–LCDs) applications, we chose a base glass composed of 3B₂O₃-15Al₂O₃-58SiO₂-22MgO-0.5SrO-1.5MgF₂ (mol%) for nucleation–crystallization. The results show that when the nucleation–crystallization processes of the base glass are 810 °C/6 h + 880 °C/6–9 h, the prepared GC/6–GC/9 glass-ceramics exhibit enhanced properties because of the precipitation of nano-sized cordierite. The transmittances in the visible range of the GC/6–GC/9 glass-ceramics exceed 85%, the densities are 2.564–2.567 g/cm³, thermal expansion coefficients are 2.934–3.059 × 10^-6/°C (25–300 °C), compressive strengths are 417–589 MPa, bending strengths are 141–259 MPa, Vickers hardnesses are 6.8–7.8 GPa, and strain points are approximately 735 °C. Considering these properties, the prepared GC/6–GC/9 glass-ceramics have good potential as candidate materials for alkali-free glass substrates. Additionally, these results demonstrate that it is feasible to improve the properties of alkali-free glass substrates by nucleation–crystallization.     

Superionic conducting Na5SmSi4O12-type glass-ceramics: Crystallization condition and ionic conductivity

Glass-ceramics of the phosphorus-containing Na₅RSi₄O₁₂ (N5)-type (R = rare earth element; Sm) Na⁺-superionic conductors (NaRPSi) were prepared by crystallization of glasses with the composition Na_3.9Sm_0.6P_0.3Si_2.7O₉. The optimum conditions for crystallization were discussed with respect to the conduction properties and the preparation of uncracked N5-type glass-ceramics. Most of the N5-type NaSmPSi compounds were obtained as uncracked glass-ceramics when the heating time for nucleation was more than 6 h. Also studied were the microstructural effects on the conduction properties, which were dependent upon the heating conditions of crystallization. Large enhancement of electrical conductivity was observed in the glass-ceramics as the grain growth was promoted with the increase of the heating time for crystallization. The ionic conductivity of the glass-ceramic Na_3.9Sm_0.6P_0.3Si_2.7O₉ heated at 900 °C for 42 h was 9.07 × 10⁻² S/cm at 300 °C.     

Synthesis of glass-ceramics in the Na2O/K2O-CaO-MgO-SiO2-P2O5-CaF2 system as candidate materials for dental applications

This study reports on the sintering behavior, crystallization process, and mechanical properties of novel glass-ceramics (CGs) produced by the glass powder compact consolidation method. Substitution of K₂O for Na₂O and MgO for CaO was attempted in the parent glasses belonging to Na₂O-CaO-MgO-SiO₂-P₂O₅-CaF₂ system. Glass powder compacts were heat treated at various temperatures between 700°C and 900°C, taking under consideration the glass transition (T_g) and the crystallization peak (T_p) temperatures, which were experimentally determined for each investigated glass by thermal analysis (dilatometry and differential scanning calorimetry). The experimental results showed that sintering always preceded crystallization, regardless of the type of substitution. In the case of MgO substitution for CaO, crystallization was advanced in the range of 800°C-850°C, resulting in the formation of an assembly of crystalline phases, such as diopside, fluorapatite, and wollastonite. The substitution of K₂O for Na₂O increased the activation energy for crystallization, shifting crystallization process to a high temperature region, with the formation of alpha-potassium magnesium silicate, instead of wollastonite. The GCs produced had values of 22-31 GPa regarding the modulus of elasticity, 5.0-6.1 GPa concerning the microhardness, and 1.4-1.9 MPa⋅m^0.5 as regard the fracture toughness, which are similar to those of the human jawbone.     

Glass-ceramics for joining oxide-based ceramic matrix composites (Al2O3f/Al2O3-ZrO2) operating under direct flame exposure

This work focuses on the joining processes of oxide-based ceramic matrix composites (Al₂O_3f /Al₂O₃-ZrO₂), which are used as radiant tube furnace components in the steel industry. These components have to operate in harsh environments, and under high temperatures, and they therefore have to resist corrosion, humidity, and combustion. Two glass-ceramics systems, which have Y₂Ti₂O₇ as their main crystalline phase, as well as specific and optimized properties to withstand severe operating conditions, including temperatures of 900 °C, are here proposed as joining materials. The adhesion of the glass-ceramics to the composite was found to be excellent after mechanical and thermal tests in which they were in direct contact with a 900 °C flame and thermal cycling of between 400 °C and 900 °C.     

Microstructural design of phlogopite glass-ceramics

Fluorophlogopite glass-ceramics in the MgO–Al₂O₃–SiO₂ glass systems were crystallized by two stages thermal treatments. Obtained glass-ceramics were characterized by DTA, X-ray diffraction and scanning electron microscopy. The heat treated samples at 705°C/3 h + 1000°C/15 min showed 2570.32 ± 98 MPa microhardness. The effect of heat treatment and preparation methods on microhardness and microstructure were studied. The microstructure of samples showed phlogopite and forsterite phases and solved or soft edge in the semi-rod like crystals was recorded which can explain the small value of microhardness. The various microhardness were determined in the range between 1591.61 to 9610 ± 147 MPa.     

Carbon nanotube/graphene oxide‐added CaO‐B2O3‐SiO2 glass/Al2O3 composite as substrate for chip‐type supercapacitor

A CaO‐B₂O₃‐SiO₂ (CBS) glass/40 wt% Al₂O₃ composite sintered at 900°C exhibited a dense microstructure with a low porosity of 0.21%. This composite contained Al₂O₃ and anorthite phases, but pure glass sintered at 900°C has small quantities of wollastonite and diopside phases. This composite was measured to have a high bending strength of 323 MPa and thermal conductivity of 3.75 W/(mK). The thermal conductivity increased when the composite was annealed at 850°C after sintering at 900°C, because of the increase in the amount of the anorthite phase. 0.25 wt% graphene oxide and 0.75 wt% multi‐wall carbon nanotubes were added to the CBS/40 wt% Al₂O₃ composite to further enhance the thermal conductivity and bending strength. The specimen sintered at 900°C and subsequently annealed at 850°C exhibited a large bending strength of 420 MPa and thermal conductivity of 5.51 W/(mK), indicating that it would be a highly effective substrate for a chip‐type supercapacitor.     

The effect of TiO2 additions on CaO–MgO–Al2O3–SiO2 (CMAS) crystallization behavior from the melt

Titania (TiO₂) was introduced into a model calcium-magnesium aluminosilicate (CMAS) glass in additions of 5-20 wt%. The crystallization behavior of the mixtures was characterized over a series of temperature profiles and compared to that of CMAS alone. X-ray diffraction, differential scanning calorimetry, light and scanning electron microscopy, and energy dispersive spectroscopy were used to characterize glass and crystalline products. Titania additions in the amount of approximately 12.5-20 wt% aided in the formation of CaTiO₃ from melts equilibrated at either 1300 or 1500°C and cooled at 10°C/min. Holding CMAS + TiO₂ (TiO₂ ≥ 10 wt%) at 900°C after cooling from 1300/1500°C resulted in the formation of additional crystalline phases including melilite, paqueite, and diopside. Implications for CMAS interactions with thermal and environmental barrier coatings are discussed.     

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。     

The influence of MgO on the crystallization behaviour and properties of SrO-rich phosphosilicate glasses

A series of glass was produced to investigate the effect of MgO/SrO replacement on the crystallization characteristics and properties of phosphosilicate glasses containing high SrO content. The glass samples were synthesized by conventional melting technique based on 5CaO-(40-X)SrO-X MgO– 43SiO₂–7P₂O₅–5CaF₂ (where; X = 10, 20, 30 and 40 mol%). The influence of MgO/SrO replacement on phase assemblages, microcrystalline structures, thermal expansion, and mechanical properties was examined as a function of basic chemical compositions and crystallization parameters. Predominant strontium meta-silicates together with strontium fluoroapatite phases are crystallized from the base glass free of magnesium. The substitution of strontium by magnesium up to 50% led to formation strontium akermanite phase Sr₂MgSi₂O₇ at the expense of SrSiO₃ phase. Whereas the increase of the MgO/SrO of more than 50%, which led to the crystallization of the clino-enstatite MgSiO₃ as a predominant phase. The results show that the α-values of the glass-ceramics are ranged in 94–125 × 10⁻⁶ K⁻¹ over the temperature range (25–500 °C). On the other hand, MgO/SrO replacements led to enhancing the microhardness of the resultant crystalline materials from 4713 Mpa to 6744 Mpa. As a result of the designed glass compositions, promising crystalline phases were obtained as well as good thermal and mechanical properties for the resultant glass-ceramics. Therefore, the designed glass-ceramics can be strongly used as biomaterials especially for bone reconstruction applications.     

Migration,transformation and solidification/stabilization mechanisms of heavy metals in glass-ceramics made from MSWI fly ash and pickling sludge

In consideration of recycling solid waste to achieve high value-added products, glass-ceramics have been fabricated from municipal solid waste incineration (MSWI) fly ash, pickling sludge (PS), and waste glass (WG) by melting at 1450 °C firstly to achieve parent glass and then crystallizing at 850 °C. Results demonstrated that heavy metals have been well solidified in the prepared glass-ceramics, and relatively/extremely low leaching concentrations of heavy metals have been detected. The synthetic toxicity index of heavy metals has been greatly reduced from 7-18 to <3.2 after crystallization treatment, and the leaching concentrations of Cr, Ni, Zn, Cu, and Pb are 0.15, 0.05, 0.26, 0.12, 0.19 mg L^-1 respectively. Chemical morphology analysis, principal component analysis, TEM and EPMA were utilized to clarify the migration, transformation, and solidification mechanism of heavy metals from the as-received solid wastes. The major heavy metals, Cr and Ni which is responsible for the most toxicity, mainly exist in form of the oxidation state and residual state in parent glass, while the residual state in the glass-ceramics. The solidification performance was mostly positively correlated with the form of residue state, which the stability of heavy metals in glass-ceramics is improved. The solidification mechanism of heavy metals in glass-ceramics could be explained by the combination of chemical solidification/stabilization and physical coating. The TEM and EPMA confirmed that Cr and Ni mainly exist in the spinel crystalline (NiCr₂O₄, Fe_0.99Ni_0.01Fe_1.97Cr_0.03O₄) by solid solution or chemical substitution, and a small amount of Cr in the diopside phase. Pb, Cu, and Zn are homogenously dispersed in the glass-ceramics, which is considered as physical coating solidification.     

Porous zirconium titanate ceramics synthesized by sol–gel process

Zirconium titanate, ZrTiO₄, was synthesized by sol–gel method from zirconium butoxide and titanium isopropoxide. Amorphous ZrTiO₄ powder was ground, calcined at 500 °C, and milled to homogenize size distribution of the powder. Milled powder was pressed into tablets and sintered at 900–1400 °C for 8 h. Differential scanning calorimetry and dilatometric studies indicated crystallization of ZrTiO₄ at 600–700 °C. Raman spectroscopy and X-ray diffraction analysis confirmed presence of crystallized ZrTiO₄ already at 900 °C, and crystallite size was determined by Scherrer equation. Scanning electron microscopy showed that ZrTiO₄ grains begin to sinter at higher temperatures, starting from 1200 °C, while preserving high porosity up to 1300 °C as confirmed by dilatometry and mercury intrusion porosimetry.     

Influence of heat treatment temperature on the properties of the lithium disilicate-fluorcanasite glass-ceramics

This study aims to investigate the influence of heat treatment temperatures on the mechanical properties and chemical solubility (CS) of lithium disilicate-fluorcanasite glass-ceramics and to develop new dental materials. The glasses and glass-ceramics were prepared using CaF₂-SiO₂-CaO-K₂O-Na₂O-Li₂O-Al₂O₃-P₂O₅-based glass system using a conventional melt quenching method followed by a two-stage crystallization process. This two-stage method involves two heating temperature steps: first at a constant temperature (T_S1) of 600°C and second step at varying temperatures (T_S2) of 650, 700, 750, and 800°C. The crystallization behavior, phase formation, microstructure, translucency characteristic, density, hardness, fracture strength, and CS were investigated. It was found that the lithium disilicate crystal acted as the main crystalline phase, and the crystalline phase of fluorcanasite occurred at the heat treatment temperatures of 750 and 800°C. In addition, it was found that density, hardness, fracture strength, and CS increased while the translucency values decreased with increasing heat treatment temperatures. Furthermore, the CS increased dramatically when the fluorcanasite phases occurred in the glass-ceramic samples. The maximum density values, Vickers hardness, fracture toughness, and flexural strength are 2.56 g/cm³, 6.73 GPa, 3.38 MPa.m^1/2, and 259 MPa, respectively. These results may offer a possibility to design a new material for dental applications based on lithium disilicate-fluorcanasite glass-ceramics.     

Preparation and crystallization of forsterite fibrous gels

Transparent forsterite fibrous gels were prepared from the hydrolysis of alkoxide precursor sols with acetic acid and water, and the crystallization process of gel fibers was studied after heat treatments up to 1500 °C. Appropriate amount of acetic acid not only promoted the formation of spinnable linear-type polymeric species, but also enhanced the chemical homogeneity and reduced the crystallization temperature of the resultant gels. On heating, fibrous gels started to crystallize into forsterite at 550 °C as investigated by infrared spectrum, X-ray diffraction and thermal analysis. Single phase forsterite fiber thus could be obtained up to 1500 °C when the amount of hydrolysis water was limited. However, fibrous gel derived from the high-water-content sol displayed a few secondary phases of the magnesia (MgO) and protoenstatite (MgSiO₃) following heating at 1000 and 1400 °C, respectively; similarly, xerogels derived from without or with insufficient amount of acetic acid also revealed the segregation of second phases on heating. The synthesized forsterite fibers displayed nanocrystalline structure up to 1100 °C. On heating to 1300 °C, fired fibers exhibited grain growth into around 0.3–0.5 μm in size, with the room temperature dielectric constants of around 6.8–7.2 (at 1 MHz).     

Synthesis of hollow forsterite by coating method and study of its dielectric properties

Wireless communication technologies are operating at higher frequencies in the current ubiquitous age, dielectrics with low dielectric constant and low dielectric loss are highly desired. A novel coating method was used for the synthesis of hollow forsterite ceramics. Here, magnesium glycolate with relatively high and high specific surface area (243.44 m²/g) and pore width (1.35 nm) is used as core material. Highly pure uniform-sized forsterite phases were obtained at a low calcination temperature of 900 °C/2 h. Scanning electron microscope, Transmission electron microscope, and X-ray diffraction were used to characterize the morphology and phase development at different calcination temperatures. The dielectric properties were measured in the range of microwave frequencies. As prepared, forsterite (Mg₂SiO₄) ceramics had shown excellent dielectric properties with ε_r = 1.85 and dielectric loss = 0.007 at 1 GHz. As wave propagation delay and attenuation depend on dielectric constant and dielectric loss. This ultra-low ε_r of 1.85 will enhance the signal speed in the microwave frequencies region which makes forsterite a promising candidate for electronics packaging applications.     

Effect of some rare-earth oxides on structure, devitrification and properties of diopside based glasses

Four diopside based glasses containing an equimolar concentration of different rare-earth oxides (La₂O₃, Nd₂O₃, Gd₂O₃ and Yb₂O₃) respectively, were obtained by melt-quenching technique. Structural and thermal behaviour of the glasses was investigated by density and molar volume, infrared spectroscopy (FTIR), dilatometry, and scanning electron microscopy (SEM). All the glasses exhibited amorphous phase separation. The crystallization behaviour of the glasses was investigated by using differential thermal analysis (DTA). Sintering, crystallization, microstructure, and properties of the glass-ceramics were investigated under non-isothermal heating conditions in the temperature range of 800–900 °C.     

Preparation of glass-ceramics from red mud in the aluminium industries

The feasibility of recycling red mud and fly ash in the aluminium industries by producing glasses and glass-ceramics has been investigated. The crystallization behavior of glass-ceramics mostly produced from red mud and fly ash was studied by DTA, XRD, optical microscopy techniques. According to DTA curve, nucleation experiments were carried out at various nucleation temperatures at the same crystallization temperature of 900 °C for 2 h, and crystallization experiments were performed at the same nucleation temperature of 697 °C for 2 h followed by crystallization at various temperatures. The nucleation results show that optimum nucleation temperature is near 697 °C, and the crystallization experiments show that the crystallization at a high temperature of over 900 °C results in denser grain size. The major crystallized phases were gehlenite (Ca₂Al₂SiO₇), and augite (Ca(Fe,Mg)Si₂O₆). The XRD results show that with the increase of crystallization temperature, the amount of gehlenite increases, and augite decreases, which is the result of augite transformation into gehlenite.