Novel ion-exchangeable nepheline glass-ceramics for dental application

Ion exchange of a glass-ceramic system with a specific crystalline phase can lead to materials with superior chemical, physical and mechanical properties. The aim of this study is to characterize newly synthesised nepheline glass-ceramics for dental restorative applications. Four novel experimental glasses based on the nepheline composition were ground into fine powders and then sinter-crystallized into monolithic glass-ceramics. The developed glass-ceramics were characterized before and after ion exchange in a potassium nitrate bath using X-ray diffraction, EDX-SEM, and biaxial flexural strength, hardness and solubility testing in accordance with ISO-6872. The ion exchange process of nepheline containing glass-ceramic Al20 increased the characteristic strength by more than 163 % compared to the starting value. The experimental glass-ceramics increased in strength after ion exchange compared to their as-sintered values by 139 %, 24 % and 123 %. The strength scatter decreased after ion exchange for the nepheline-containing glass-ceramics by 10 %. The characterised glass-ceramics in this work require further investigation and have the potential to be developed into layered glass powders, which can be ion exchanged after sinter-crystallization to produce dental restorations with superior mechanical and chemical properties.     

霞石微晶玻璃热膨胀系数的研究

霞石微晶玻璃热膨胀系数的研究刘小波（湘潭矿业学院４１１２０１）ＳｔｕｄｙｏｎＴｈｅｒｍａｌＥｘｐａｎｓｉｏｎＣｏｅｆｆｉｃｉｅｎｔｏｆＮｅｐｈｅｌｉｎｅＧｌａｓｓ－Ｃｅｒａｍｉｃｓ￥ＬｉｕＸｉａｏｂｏ（ＸｉａｎｇｔａｎＭｉｎｉｎｇＩｎｓｔｉｔｕｔｅ）...     

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.     

Preparation and characterization of immobilized ion exchange polyurethanes (IEPU) and their applications for continuous electrodeionization (CEDI)

Immobilized ion-exchange polyurethanes (IEPU) were prepared as ion conducting spacers in continuous electrodeionization (CEDI) for the treatment of a synthetic primary coolant. Ion exchange resins were immobilized by using allophanate/biuret cross-linking in preparation of polyurethane. Synthesized IEPU was characterized in terms of mechanical strength, ion exchange capacity (TEC), electrical conductivity and the porous plug model, which schematically represents the transport pattern through the IEPU. CEDI was carried out in a laboratory scale with an effective area of 20 cm². The CEDI operation with a layered bed configuration showed the main removal mechanism of cobalt ion was dependent on the active surface area between ion conducting materials. The performance of the CEDI operation showed over 98% removal of cobalt ions, suggesting the feasibility of IEPU as ion conducting spacers in a CEDI system.     

应用ISEP系统回收氯化铵废液

ＩＳＥＰ系统是一种连续型离子交换系统，能彻底解决氯化铵废液的污染问题，并能减少树脂用量，降低碳酸钾的生产成本，有巨大的经济效益     

Continuous ion exchange using magnetic shell resins. I. Dealkalisation—laboratory scale

A completely novel technique of continuous ion exchange has been developed, which uses ion exchangers prepared by grafting an active shell onto a magnetic polymeric core. In the magnetised form, the ion exchange resin beads clump together in the form of large flocs, with sedimentation velocities many times those of the individual beads. Small beads may then be used in fluidised or semi-fluidised beds, at liquid flow rates equal to or greater than conventional ion exchange systems, but with the advantage of rapid reaction rates and attainment of equilibrium. A major practical advantage is that even as a settled bed the magnetised ion exchange resin remains semifluid, and can be pumped with practically no attrition. Utilising these properties, a truly continuous ion exchange system has been built for the process of dealkalisation, comprising a single stage fluidised adsorber and a compact moving bed regenerator which develops multistage contact. Transfer of ion exchanger between each vessel is effected by means of two peristaltic pumps. This paper summarises the results obtained in a laboratory sized apparatus, treating a hard, alkaline water at a superficial velocity of 30 m h^?1, and demonstrates the potential for a system utilising a fraction of the volume of ion exchange resin employed in a conventional system, in a simple robust plant with no valves, no screens, no pressure vessels and only one electrical level control.     

Properties of grafted polymer metal complexes as ion exchangers and its electrical conductivity

A polyelectrolyte has been prepared, as a potential proton exchange polymer, by grafting acrylic acid/acrylamide (AAc/AAm) and acrylic acid/acrylonitrile (AAc/AN) comonomers onto a low‐density polyethylene film via gamma irradiation. The developed polymers were characterized by evaluating their physico‐chemical properties such as ion exchange capacity (IEC) and electrical conductivity as functions of grafting yield. The grafted film at different compositions was characterized by Fourier transform infrared, thermogravimetric analysis, and scanning electron microscopy. IEC of the grafted film at grafting % 191 and monomer concentration ratio 50:50 for (LDPE‐g‐AAc/AAm) was found to be more than that for (LDPE‐g‐AAc/AN). The electrical conductivity was found to be greatly affected by the comonomer composition, were it increased as the degree of grafting increased for all grafted films. After alkaline treatment with 3% KOH (3% potassium hydroxide), the electrical conductivity of the grafted films found to be increased. The presence of potassium as counter ion maximized the electrical conductivity of the grafted films. The electrical conductivity of Cu‐membrane complexes was higher than that of both Co (cobalt) and Ni (Nickel) complexes. It has been indicated that, the electrical conductivity increased by increasing both Cu ion content and temperature. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers.     

Mechanism of the Adsorption of Ammonium Ions from Aqueous Solution by a Chinese Natural Zeolite

Abstract

The adsorption of ammonium ions onto a Chinese natural zeolite in an agitated batch adsorber was studied. A trial‐and‐error non‐linear method was developed to examine two widely used isotherms, the Langmuir and Freundlich. The data gained from the adsorption system fitted the Freundlich isotherm better. An ion exchange model, describing the relationship among the total metal ions in the solution, NH₄ ⁺ removed from the solution, and ions initially released from the zeolite, was developed for the adsorption system. In addition, a parameter of the ion exchange potential was defined to describe the adsorption mechanism. Ion exchange was the main mechanism that accounted for the adsorption of ammonium ions onto the Chinese natural zeolite.     

离子色谱法在碱性离子液体合成中的应用

利用离子色谱法对阴离子为乙酸根的碱性离子液体合成过程进行跟踪,探讨了离子液体前驱体、溶剂种类及所用的交换试剂等对交换过程的影响。结果发现,以甲醇为溶剂,利用乙酸钾与烷基咪唑氯化物离子液体前驱体进行离子交换,可获得目标阴离子含量为96mol％（摩尔分数）的产物。     

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.     

Crystallisation and microstructure of nepheline–forsterite glass-ceramics

This work presents the results of a study focused on the development of forsterite–nepheline glass-ceramic with the use of rice husk ash (RHA) as a silica source. The glass-ceramics were produced by a sintering process of a glassy frit formulated in the MgO–Al₂O₃–SiO₂ base system with the addition of B₂O₃ and Na₂O to facilitate the melting and pouring processes. The crystallisation study was carried out by depicting the TTT curve (Time–Temperature–Transformation). The mineralogical characterisation of the glass-ceramic materials was carried out using the X-ray diffraction (XRD). The crystallisation activation energies were calculated by the Kissinger method. The results obtained show that devitrification of the RHA glass leads to a glass-ceramic material composed of nepheline (Na₂O·Al₂O₃·2SiO₂) and forsterite (2MgO·SiO₂). A study of the microstructure by scanning electron microscopy (SEM) allowed to establish the morphological evolution in both the shape and spatial arrangement of the nepheline and forsterite crystals on heating.     

Photocatalytic dye degradation using lithium borate-bismuth tungstate glass-ceramics

The disposal of wastewater contaminated with dyes is a prevalent global concern that necessitates the implementation of diverse remediation strategies. There are several methods available for the treatment of wastewater, one of which is photocatalytic treatment. The primary objective of this study is to assess the efficacy of a lithium borate-bismuth tungstate glass-ceramic material (0.7Li₂B₄O₇ - 0.3Bi₂WO₆) in the degradation of methylene blue dye through photocatalysis under visible light irradiation conditions. The glass under consideration was prepared using the conventional melt-quench technique. The characterization of the glass was conducted using X-ray diffraction technique and Raman spectroscopy. Additionally, the glass obtained was subjected to various heat treatments in order to achieve crystallization, as assisted by differential scanning calorimetry as reported. The elemental analysis and morphology of the glass ceramics that were prepared were examined using X-ray photoemission spectroscopy (XPS) and field emission scanning electron microscopy (FE-SEM). The glass-ceramic sample exhibited a dye degradation efficiency of 73% within a time span of 240 min. The evaluation of the active species involved in degradation is also conducted through the utilisation of a scavenger test. The experiments were conducted multiple times to verify the effectiveness of the prepared glass-ceramic material for water purification purposes.     

A bioreactor with an internal contactor for primary recovery of bovine serum albumin from yeast suspension

In this paper the internal contactor is a newly developed device for the primary recovery of protein from crude feedstock. Ion exchanges (DEAE-Streamline) are confined inside the internal contactor in a stirred tank. Interactions between the ion exchange in the internal contactor and protein (BSA) in yeast suspension have been studied. For better performance, two strategies are considered: to determine the ion conductivity of a simulated yeast suspension, and to select the optimum process time for adsorption. In this system, advantages of both batch adsorption and expanded bed adsorption were obtained. Furthermore, in denser cell concentration (50 g/L) where EBA cannot be operated, the primary recovery was carried out in 1–2 hr. The efficiency of yield is higher than 80% in this condition.     

Growth of ZnO Nanorods by the Chemical Solution Method with Assisted Electrical Field

Zinc oxide (ZnO) nanorod arrays on the ZnO-coated seed substrates were prepared by the solution chemical method from Zn(NO₃)₂/NaOH under an assisted electrical field. The influence of the electrical field on ZnO nanorod growth was primarily explored, and the positive effects of the electrical field were demonstrated by adding polyethylene glycol in growth solution. It has been proved that the electrical field enhances ion adsorption to the substrate and lowers the nucleation energy barrier by increasing charge intensity; meanwhile, it produces H⁺ through oxidation of OH⁻ and increases properly the degree of solution supersaturation near the substrate surface. XRD results show that the nanorods grown under the electrical field primarily have a zincite structure. With increasing precursor concentration, the average diameter and length of ZnO nanorods increase. The maximum rod growth rate at a given concentration of Zn²⁺ ion occurs at a specific temperature.     

Crystallization and Chemical Strengthening of Nepheline Glass-Ceramics

Electron micrographic and X-ray diffraction techniques were used to study the nucleation and growth of titania-nucleated nepheline in glass. On heating, the glasses phase-separated as a prelude to the crystallization sequence. The first crystalline phase identified was the metastable phase, carnegieite. With time, the equilibrium phase, nepheline, crystallized and the titania crystallized to anatase. The resulting materials were nonporous and largely crystalline. These nepheline glass-ceramics were chemically strengthened by treatments in molten potassium salts. A K⁺→ Na⁺ exchange took place and effected transformation of nepheline to kalsilite. This transformation was a function not only of the exchange treatment, but of the composition of the initial nepheline crystals. Confining the kalsilite surface against a volume increase during the phase transformation created a surface compressive stress. Glass-ceramics containing nepheline crystals with an appropriate structure were chemically strengthened in this manner to yield bulk, abraded modulus of rupture values above 200,000 psi.     

Eu2+-doped oxyfluoride glass-ceramic with nepheline as an efficient 400 nm UV-LED color converter

SiO₂-Na₂O-Al₂O₃-LaF₃ glass-ceramics doped with Eu²⁺ were synthesized as an efficient inorganic color converter for 400 nm UV-LED. When Eu²⁺ formed within the glass matrix, the obtained glass showed cyan emission under 400 nm excitation, but its emission peak drastically shifted to greenish yellow upon heat treatment. With heat treatment the glass-ceramic also showed highly increased emission intensity, and the color coordinate of the glass-ceramic shifted to yellow. When it was mounted on top of a 400 nm UV-LED, it demonstrated high color conversion efficiency and practical feasibility as an UV-LED color converter. To vary the color coordination the heat-treatment conditions and the thickness of the glass-ceramic were adjusted. The resulting ceramic showed a high quantum yield of up to 78%, which is comparable to conventional ceramic phosphors. The spectral change in the glass-ceramic is attributed to the formation of nepheline and LaF₃ crystalline phases. X-ray diffractometer (XRD), transmission electron microscope with energy dispervise spectroscopy (TEM-EDS) and cathode luminescence (CL) were used to investigate the mechanism of Eu²⁺-doped nepheline crystal formation, and its effect on the spectral change with heat treatment.     

Effect of ZrO2 crystallization on ion exchange properties in aluminosilicate glass

Ion exchange has the potential to improve the mechanical properties of glass ceramics. In this work, ZrO₂ nanocrystals embedded transparent glass ceramics were prepared and effect of the crystallization on ion-exchange properties was investigated. The crystallization of ZrO₂ did not affect the transmittance and Vickers hardness due to the small nanocrystal size and the low crystallinity, but significantly enhanced the ion exchange depth of layer (DOL). X-ray diffraction, high resolution transmission electron microscope, Raman spectra and nuclear magnetic resonance analysis demonstrated that with the crystallization of ZrO₂, the charge compensator (Na⁺) was released, which promoted the transformation of highly coordinated Al into [AlO₄]⁻ tetrahedral units and the formation of Na⁺ balanced non-bridging oxygens. These changes in structure of glass made the Na⁺ more mobile and increased the DOL upon the crystallization. Results reported here may be useful for the development of glass-ceramic materials suitable for chemical strengthening.     

Electrodialysis processes using ion exchange resins between membranes

Ion exchange resins were introduced between permselective membranes in a laboratory scale electrodialysis unit. It was found that by this method polarization is substantially decreased, and high electrical efficiency can be obtained even when working on highi/c values (1000–5000) and at low linear velocity of solution (1–2 cm/sec) in the cell. Different ion exchange resins were introduced in the diluate and brine cells and the boundary conditions of such a stack were determined.     

Synthesis and electrical properties of NaSS–MAA–MMA cation exchange membranes for membrane capacitive deionization (MCDI)

We present a novel synthetic ion exchange membrane that is composed of 4-styrenesulfonic acid sodium salt hydrate (NaSS), methacrylic acid (MAA) and methyl methacrylate (MMA), which was synthesized with various monomer ratios using solution polymerization. The ion exchange membrane was prepared by heat cross-linking and esterification reactions. The chemical structure of the membrane was characterized using Fourier-transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy. Several membrane properties were measured, including water uptake, ion exchange capacity (IEC), ion transport number and electrical properties. The morphology analysis of the membrane was also obtained by scanning electron microscope (SEM). Increasing the NaSS concentration simultaneously increased the IEC and the electrical conductivity due to the increased presence of ionic groups. Compared with conventional membranes, the pattern of cyclic charge and discharge currents in the synthetic membrane indicated that it possessed more efficient electrosorption and desorption properties.     

Mechanical properties,in vitro and in vivo bioactivity assessment of Na2O-CaO-P2O5-B2O3-SiO2 glass-ceramics

Glasses having chemical composition based on Na₂O-CaO-P₂O₅-SiO₂ system were crystallized. Then, the resultant crystallized phases were examined by X-ray diffraction technique. Furthermore, density, microhardness and fracture toughness were measured. In order to investigate the biological responses of these glass-ceramic samples, in vitro and in vivo experiments were performed. In vitro test was performed by soaking the prepared samples in simulated body fluid (SBF) for different time intervals and then, specimens were examined by Fourier transform infrared spectroscopy. Moreover, the conversion kinetics of these samples to hydroxyapatite (HA) were determined by measuring the weight loss of glass-ceramic grains, pH values of SBF solution and recording the ionic concentrations of Si, B, P and Ca using inductive coupled plasma-atomic emission spectroscopy. The results pointed out that the prepared samples possessed fair in vitro bioactivity. However, after six weeks of implantation, the prepared glass-ceramics, on the contrary to the parent glasses, did not exhibit any bioactivity suggesting that they may need longer time. On the other hand, the crystallization process caused significant increases of microhardness and density values. From these results, we can conclude that the prepared glasses and glass-ceramics had suitable properties for bone grafts and dental applications, respectively.