Conventional and electric field-assisted ion exchange on glass-ceramics for dental applications

Ion exchange can be used to mechanically reinforce dental glass-ceramics to reduce the problems associated to the flaws created upon various processing steps and handling. This work introduces a novel ion exchange method to the field of dental glass-ceramic to increase the possibilities of preparing highly reliable glass-ceramic restorations. The aim of the study was to compare Electric Field-Assisted Ion Exchange with conventional method, for newly developed nepheline based dental glass-ceramic. Multicomponent glass system was synthesized using melt-quench method and then prepared into glass-ceramic specimens via powder sinter-crystallisation route. The prepared glass-ceramic specimens were tested for bi-axial flexural strength before and after ion exchange according to the dental ceramics ISO 6872:2015. Ion exchange process was carried out in molten potassium nitride and the potassium penetration depth determined by EDXS was found greater and occurring in a matter of minutes within the nepheline crystal structure during electrical field assisted ion exchange compared with several hours of conventional treatment. The newly developed nepheline glass-ceramic system and the results achieved by electrical field assisted ion exchange may renew the ion exchange concept for dental application.     

Microstructure,cytocompatibility, and chemical durability of chemically strengthened LAS (Li2O-Al2O3-SiO2) glass-ceramic materials

The K⁺-Na⁺ ion exchange was used to strengthen LAS glass-ceramic materials prepared by hot-pressing sintering. The microstructure, cytocompatibility, and chemical durability of the chemically strengthened LAS glass-ceramics were characterized. The XRD results showed that the K⁺-Na⁺ ion exchange mainly occurred between the glass phase of the LAS glass-ceramics and molten salt baths. The ion-exchange process was mainly responsible for the improved chemical durability of the LAS glass-ceramics. The dissolution in acetic acid was significantly reduced from 72 to 15 μg·cm^?2 after the ion-exchange treatment, which was attributed to residual compressive stress and increased contents of Q³ and Q⁴ structural units in the surface region of the LAS glass-ceramics. In addition, the chemically strengthened LAS glass-ceramic samples exhibited good biocompatibility determined by the CCK-8 process using the L929 cell line, having a promising potential as dental restorative materials.     

Effect of addition of titanium on structural,mechanical and biological properties of 45S5 glass-ceramic

The purpose of the present study was to evaluate the effect of addition of titanium on the structural, mechanical, and biological properties of sol-gel derived 45S5 bioactive glass-ceramic. For the synthesis of 45S5 glass ceramics, 5 and 10?mol% titanium were added to replace calcium named as Ti5 and Ti10, respectively. The structure of glass-ceramic was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), and energy dispersive X-ray spectroscopy (EDS). The ability of glass-ceramics to form hydroxyapatite (HA) was also evaluated using XRD, FTIR and FE-SEM/EDS following immersion in the simulated body fluid (SBF) for 1, 7 and 14 days. The ion release potential was also evaluated during the afore-mentioned immersion periods. Furthermore, the cell viability and alkaline phosphatase (ALP) activity of osteoblast-like cells exposed to the dissolved products of glass-ceramics were evaluated. The effect of addition of titanium on the mechanical properties was evaluated by measuring the compressive strength. Despite the slower rate of HA formation in Ti-containing groups during the first day of immersion, all groups showed similar results after 14 days. The addition of titanium to 45S5 bioactive glass-ceramic decreased the silicon and sodium ion release. Ti5 showed the highest level of cell viability and ALP activity. The compressive strength of 45S5 glass-ceramic significantly increased following addition of titanium, and Ti10 showed the highest value. In conclusion, the findings of this study support the synthesis of 45S5 glass-ceramic modified by addition of 5?mol% titanium ions due to improved mechanical and biological properties along with the ability to control solubility and ion release profile.     

可加工硅碱钙石微晶玻璃/金属铜功能梯度材料

采用粉末冶金法经1000℃烧结制备了可加工硅碱钙石微晶玻璃/金属铜功能梯度复合材料(functionally gradient materials,FGM),其中金属含量(质量分数)为0,20%,40%,60%,80%和100%,呈非对称梯度变化.通过金相显微镜、扫描电镜、X射线电子能谱等分析了材料的微观结构和微区元素含量,用万能材料试验机测试了复合材料的弯曲强度.结果表明:硅碱钙石微晶玻璃/金属FGM的结构呈宏观不均匀且微观连续变化,微晶玻璃相与金属粉末相结合紧密,两相均相对独立,两者之间没有发生化学反应;随着金属粉末含量的增加,硅碱钙石微晶玻璃/金属功能梯度复合材料中各梯度层的热膨胀系数和力学性能逐渐变化.     

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.     

Synergistic effect of glass fibre and Al powder on the mechanical properties of glass-ceramics

To explore the synergistic effect of glass fibre and Al powder on the mechanical properties of glass-ceramics, blast furnace slag was chosen as the main material, and glass fibre and Al powder as reinforcement materials. The phase compositions, microstructures, compressive properties, and apparent density of the glass-ceramics with varying quantities of glass fibre and Al powder were investigated. The experimental results indicated that Al powder could exist as a simple substance in glass-ceramics and form a dense net coating on the surface of blast furnace slag to improve the plasticity of the glass-ceramic. The glass fibre had better reinforcement effect than Al powder because of its extremely high mechanical strength. The plasticity of glass-ceramics, however, severely decreased; the glass-ceramics exhibited brittle failure during compression. A slight increase in the content of CaSi₂ and SiO₂ in the glass-ceramics was closely related to the addition of glass fibre. Considering safety and economy, glass-ceramics with 6% Al and 14% glass fibre (S4) have the best mechanical properties. The compressive strength, strain at maximum force, and apparent density were 40?MPa, 19% and 1.974?g/cm³, respectively.     

Nucleating role of P2O5 in nepheline-based transparent glass-ceramics

The nepheline-based transparent glass-ceramics are promising candidates for cover glass applications in electronic displays owing to their superior mechanical properties (than glasses) and ability to be chemically strengthened. However, our poor understanding about the kinetic and thermodynamic drivers controlling their crystallization processes usually results in their opacification and development of large internal stresses. The present work focuses on the development of nepheline-based nanocrystalline transparent glass-ceramic designed in the Na₂O–Al₂O₃–SiO₂ ternary system nucleated with P₂O₅. The temporal evolution of the phosphate and nepheline nanocrystal formation has been followed using X-ray diffraction, scanning/transmission electron microscopy, and energy-dispersive spectroscopy. The incorporation of P₂O₅ in the glass structure leads to the phase separation resulting in the crystallization of nanocrystalline Na₃PO₄ as an intermediate phase; thus, acting as a nucleating site for volume crystallization of nepheline. The optimization of nucleation and growth profile in the designed composition results in the formation of a transparent glass-ceramic with high optical transmittance (91.5 ± 0.1%).     

Mechanical properties of solid oxide fuel cell glass-ceramic sealants in the system BaO/SrO-MgO-B2O3-SiO2

Planar solid oxide fuel cells (p-SOFCs) require materials that can satisfy the high mechanical demands related to their utilization in stationary and, especially, in mobile applications. Two suitable glass-ceramic sealants based on the system BaO/SrO-MgO-B₂O₃-SiO₂ have been characterized with respect to their mechanical properties such as hardness, Young’s modulus, flexural strength at room and elevated temperature, fracture toughness as well as creep behavior at relevant operation temperatures (800 °C). Fracture toughness was calculated from crack opening displacements (COD) and the results were compared with fracture toughness measured by bending tests of notched bar samples. The mechanical behavior has been discussed regarding different thermal aging times of the glass-ceramics and their microstructural evolution. The glass-ceramics containing SrO revealed a better mechanical behavior than glass-ceramics with BaO. In particular, several superior properties were found in comparison to previously reported materials for this application.     

Microstructure,residual stresses,and mechanical performance of surface crystallized translucent glass-ceramics

Mechanical properties of glasses can be significantly increased by inducing surface crystallization of a low coefficient of thermal expansion phase. In this work, we produced surface crystallized lithia-alumina-silica glass-ceramics with different crystallized layer thicknesses and analysed the resulting residual stresses and their effect on mechanical properties. The residual stress magnitude was estimated by analytical and experimental methods, as well as numerical modeling. The surface compressive stress reached 390 MPa and 490 MPa, as given by the analytical and experimental determination, respectively. These stresses prevented radial cracking in microhardness and scratch tests. The best glass-ceramic achieved a Vickers hardness of 7.5 GPa and fracture strength of 680 ± 50 MPa in a ball-on-three-ball test. These glass-ceramics are translucent, providing 50–60% transmittance over the visible wavelength spectrum (1.3 mm-thick-sample). This study unveiled the causes of improved mechanical properties and validates the concept that surface crystallization is a valuable technique for developing high strength glass-ceramics.     

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.     

Crystallization behavior and mechanical properties of high strength mica-containing glass-ceramics from granite wastes

The high-strength mica-containing glass-ceramics were prepared from granite wastes by bulk crystallization. The influences of SiO₂/Al₂O₃ molar ratio (S/A = 7.72, 9.62, 12.58, 17.82 and 29.67) on the crystallization behavior, microstructure, mechanical properties and machinability of glass-ceramics were investigated. The results demonstrated that the polymerization degree of the glass network decreased with the S/A ratio increasing, which further caused the decrease in glass transition temperature and crystallization temperatures. The increase in the S/A ratio promoted the precipitation of diopside, hectorite, kalsilite and tainiolite in glass-ceramics when the samples were heated at 750 °C, while inhibiting the precipitation of forsterite. For the glass-ceramics crystallized at 800 and 900 °C, the main crystalline phases transformed from diopside, forsterite, and nepheline to diopside, kalsilite, and tainiolite, with the S/A ratio increasing. As the SiO₂ gradually replaced Al₂O₃, the morphology of crystals changed from lamellar to granular, while the mean size of crystals reduced. The Vickers-Hardness values of glass-ceramics crystallized at 800 and 900 °C ascended with S/A ratio rising, and the values were above 6.30 GPa. The bending strength of most glass-ceramics is stable between 90 and 140 MPa, among which the maximum bending strength is 133.28 ± 14.81 MPa. The fracture toughness of the glass-ceramic crystallized at 800 and 900 °C declined, while that at 700 °C increased with a larger S/A ratio. Glass-ceramics after heat-treated at 900 °C with S/A ratio of 9.62 had the largest fracture toughness of 3.28 ± 0.15 MPa m^1/2. In preliminary tests of machinability, glass-ceramic after heat-treated at 900 °C with S/A ratio of 9.62 showed better results.     

Controlling the microstructure and properties of lithium disilicate glass-ceramics by adjusting the content of MgO

In order to obtain lithium disilicate glass-ceramics for dental restoration with both high strength and high translucency, lithium disilicate glass-ceramics with different MgO contents were prepared by melt-casting and heat treatment method. The effects of MgO content on the crystallization temperature, microstructure and flexural strength of lithium disilicate glass-ceramics were investigated. The results indicate that Mg²⁺ exists in the form of [MgO₄] in the network of lithium disilicate glass-ceramics when the MgO content is 0.56 mol% (M0.56), which is beneficial to increasing the homogeneity and thermal stability of the glass system, and short rod-like lithium disilicate crystals can be formed after heat treatment at 840°C. Thus, the obtained lithium disilicate glass-ceramics exhibit excellent comprehensive performance, with the flexural strength being 312 ± 23 MPa, and the average transmittance of visible light being 37.3% (d = 1.62 mm). Especially, the glass-ceramic sample shows better translucency than the commercially available products. The research results are of great significance for developing high performance lithium disilicate glass ceramics and promoting its broad application in the field of dental restoration.     

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.     

LAS微晶玻璃在离子交换后的去结晶相变化及机械性能表征

Li₂O-Al₂O₃-SiO₂(LAS)系微晶玻璃是一种高性能的实用微晶玻璃体系,以Li₂O、Al₂O₃和SiO₂作为主要原料,采用整体析晶法制备了以透锂长石(LiAlSi₄O₁₀)为主晶相的微晶玻璃,并采用低温离子交换单元盐浴的方法,对其进行化学强化。利用X射线衍射仪、扫描电子显微镜等设备研究了LAS系微晶玻璃化学强化后的表面形貌和机械性能。结果表明,化学强化后此体系微晶玻璃表面出现去结晶相,维氏硬度显著降低,但抗弯强度显著提高,强化10 h时,表面出现约740 nm的非晶相层,抗弯强度达到最大值472 MPa。     

Surface strengthening of lithium disilicate glass-ceramic by ion-exchange using Rb,Cs nitrates

In order to further improve the flexural strength of lithium disilicate glass-ceramic, surface strengthening by ion exchange using Rb, Cs nitrates has been studied for the first time. The influences of ion exchange using rubidium and cesium salts on the flexural strength and corrosion resistance have been investigated. It was found that the mechanical properties of the lithium disilicate glass-ceramic could be increased greatly by the ion exchange in rubidium nitrate (RbNO₃) salt. After ion exchange for 4?h in RbNO₃ salt, the flexural strength and microhardness increased from 169?MPa and 587?kgf?mm^?2 (5.75?Gpa) of the original lithium disilicate glass-ceramic to 493?MPa and 654?kgf?mm^?2 (6.4?Gpa), respectively. Moreover, the corrosion resistance of the lithium disilicate glass-ceramic was further improved by ion exchange in rubidium and cesium nitrate salts. Furthermore, the maximum thickness of the ion exchange layer using RbNO₃ and CsNO₃ was only 4.3?µm and 0.45?µm respectively. Such a thin exchange layer, which will only require very low Rb⁺, Cs⁺ ions exchange amount, indicates that the molten salts of RbNO₃ and CsNO₃ can be reused for many times. So it is suggested that surface strengthening of lithium disilicate glass-ceramic by ion exchange using Rb, Cs nitrates is cost-efficient and very suitable for the actual production and applications.     

Effects of glass-ceramic spray deposition manipulation on the surface characteristics of zirconia dental restorations

A novel glass-ceramic spray deposition (GCSD) method was developed to modify the yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) surface and to enhance the bond strength between Y-TZP and resin cement. Five different experimental groups were characterized, non-treatment (NT), airborne particle abrasion (AB), GCSD without etching (GS), GCSD with 5% HF etching (GSE5), and GCSD with 9.5% HF etching (GSE9), to determine the optimal method for improving the bond strength. Scanning electron microscopy and an argon ion milling system were used to investigate the surface and cross-sectional microstructures. The changes in the surface characteristics of Y-TZP were analyzed via contact angle analysis, atomic force microscopy, X-ray diffraction, and energy-dispersive X-ray spectrometry. The bond strengths were determined using shear bond strength test. The results revealed that GCSD could produce a dense and uniform lithium disilicate glass-ceramic coating layer and infiltrate the Y-TZP surface. This coating resulted in superior micromechanical interlocking and increased hydrophilicity, thereby enhancing the bond strength between Y-TZP and resin cement (P < 0.05). The study findings indicated that GCSD accompanied by 5% HF etching for 100 s is optimal for strengthening the Y-TZP/resin cement bond, thereby providing a novel solution for dental bonding systems.     

Improving sealing performance of borosilicate glass-ceramics for solid oxide fuel cell applications: Effect of AlN

Glass and glass-ceramic are one of the key sealing materials for solid oxide fuel cells (SOFCs) and they need to meet stringent requirements for long-term operation at high temperatures. Here, we report for the first time the incorporation of aluminum nitride (AlN) dopant into borosilicate glasses and glass-ceramics so as to tailor their basic properties and sealing performance. The results show the AlN-doped glass-ceramics exhibit remarkably enhanced thermal stability and chemical compatibility when adhering to Y₂O₃-ZrO₂ electrolyte. The electrical conductivity is also significantly reduced by the AlN doping, and the conductivity of 15 wt.% AlN-doped glass-ceramic is nearly two orders of magnitude lower than that of the undoped glass-ceramic. This work indicates that AlN doping is an effective strategy to obtain a reliable borosilicate glass-ceramics for SOFCs.     

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.     

结合中国专利申请分析微晶玻璃制造技术的发展和应用

微晶玻璃,是由玻璃经受控热处理得到的多晶固体,具有机械强度高、热膨胀系数可调、热稳定性好、化学稳定性好、低介电损耗、电绝缘性好的特点。依据1985年至今的微晶玻璃相关中国专利申请,分析了微晶玻璃制造技术在建筑材料、化学工业、机械工业、电子工业以及生物医学领域的发展和应用情况。     

Double-layer waste-derived glass-ceramics prepared by low temperature sintering/sinter-crystallisation

Lightweight glass-ceramics with a dense surface layer were produced by a novel sintering approach. The surface porosity of a glass-ceramic body from the direct sintering of an engineered mixture of fly ash from thermal power plants, recycled soda-lime glass and boron waste (residues of the mining and purification of valuable boron containing minerals) was sealed by a glaze, deriving from the sinter-crystallisation of glass powders produced from the same mixture. The use of boron waste, providing B₂O₃, allowed a substantial viscous flow, for the substrate, even at the relatively low temperature (850–950°C) adopted for a single firing treatment (simultaneous sintering of substrate and sinter-crystallisation of glaze). The dense sinter-crystallised layer, besides imparting improvements in the mechanical properties, was found to feature an enhanced chemical stability.