Uptake of various cations by amorphous BaAl2Si2O8 prepared by solid-state reaction of kaolin with BaCO3

The uptake of various ions by amorphous and crystalline BaAl₂Si₂O₈ was investigated. The BaAl₂Si₂O₈ samples were prepared by solid-state reaction of kaolin ground with BaCO₃ for periods from 1 to 24 h followed by firing at temperatures of 800–1200 °C for 24 h. Uptake experiments were performed at room temperature (25 °C) using a solid/solution ratio of 0.1 g/50 ml, with a cation concentration of 10⁻³ M and reaction time of 24 h. The cations used for the uptake experiments were alkaline earth ions (Mg²⁺, Ca²⁺ and Sr²⁺) and transition metal ions (Ni²⁺, Co²⁺, Cu²⁺ and Zn²⁺). The uptake of alkaline earth ions was low in all the samples while the transition metal ion uptakes were higher in the amorphous BaAl₂Si₂O₈ sample than crystalline BaAl₂Si₂O₈ samples. The high uptake of transition metal ions by the amorphous sample was further enhanced by prolonging the grinding time. Since the amorphous sample appears from the ²⁹Si and ²⁷Al NMR spectra to have a similar local structure to crystalline hexacelsian (double-layered structure consisted of alternatively corner shared AlO₄ and SiO₄ tetrahedra), the uptake of transition metal ions is suggested to occur by release of interlayer Ba ions in the vicinity of edge sites with the adsorption of transition metal ions from the solution.     

Formulation and characterization of glass–ceramics based on Na2Ca2Si3O9–Ca5(PO4)3F–Mg2SiO4-system in relation to their biological activity

Glasses having a chemical composition based on combeite [Na₂Ca₂Si₃O₉]–fluoroapatite [Ca₅(PO₄)₃F] and forsterite [Mg₂SiO₄] system were crystallized through controlled heat-treatment. Two forms of sodium calcium silicate e.g. combeite Na₂Ca₂Si₃O₉ and pectolite Na₂CaSi₃O₈, were formed together with diopside (CaMgSi₂O₆) and monticellite (CaMgSiO₄) in addition to fluoroapatite (Ca₅(PO₄)₃F) phases by thermal treatment of the glasses. Selected glass–ceramics were exposed to a simulated body fluid solution (SBF) which is close to human plasma for 3 weeks. Energy dispersive X-ray analysis (EDX) and inductive coupled plasma (ICP) analysis confirmed the formation of an apatite layer which indicate bioactivity in the all crystallized sample. A decreasing of surface bioactivity with increasing Mg₂SiO₄/Na₂Ca₂Si₃O₉ replacement was observed as indicated by the decrease in the amount of apatite layer on the surface of the crystallized specimens. The Vicker’s microhardness of the studied glass–ceramic materials are between 5,047 and 6,781 MPa.     

Synthesis of Al-substituted 11 Å tobermorite from newsprint recycling residue: a feasibility study

Newsprint recycling is responsible for significant volumes of secondary waste material for which further reprocessing and market development would be beneficial. In response to this problem, a layer lattice, ion exchange material, Al-substituted 11 Å tobermorite, has been synthesised from newsprint recycling residue comprising gehlenite (Ca₂Al₂SiO₇), akermanite (Ca₂MgSi₂O₇), β-dicalcium silicate (Ca₂SiO₄) and anorthite (CaAl₂Si₂O₈) under hydrothermal conditions at 100 °C in the presence of NaOH. The hydrogarnet phase, katoite (Ca₃Al₂SiO₁₂H₈), was also formed. Similar treatment regimes in the presence of LiOH and KOH did not yield significant quantities of Al-substituted 11 Å tobermorite. A batch sorption study confirmed that the Al-substituted 11 Å tobermorite-bearing product was effective in the exclusion of Cd²⁺, Pb²⁺ and Zn²⁺ from acidified aqueous media. The potential to enhance the yield of Al-substituted 11 Å tobermorite relative to that of katoite and thus optimise the ion exchange efficiency of the product is discussed with respect to its application to heavy metal-contaminated wastewater treatment.     

Study on the emission properties of Sr2MgSi2O7:Eu,Dy for luminous fiber application

Rare earth long afterglow phosphors Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ was synthesized by a modified solid-state reaction using H₃BO₃ as auxiliary reagents. In order to promote the emission properties of Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺, samples of Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ were prepared and the effect of manufacturing elements including the concentration of H₃BO₃ and environmental factor of calcining temperature, concentration of Eu²⁺ and Dy³⁺ ions, external environmental factors of applications such as fiber-forming polymer as well as the addition of Ca²⁺ ion on its emission property were investigated through evaluating their emission spectra. The results showed that the molar ratio of the Eu²⁺ ions and Dy³⁺ ions, the amount of doping H₃BO₃, calcining temperature and fiber-forming polymer had little effect on the position of the emission peak and the shape in the luminescence, but greatly influenced the emission intensity of luminescent materials. The effect of Ca²⁺ ion doping was further studied. Ca²⁺ influenced not only the intensity but also the wavelength of emission and spectra of the emission peak shifted to longer wavelength as the concentration of Ca²⁺ increased.     

Sol-gel synthesis of single-phase Ca5MgSi3O12: Eu, Mn phosphors for white-light emitting diodes

A novel Ca₅MgSi₃O₁₂: Eu²⁺, Mn²⁺ phosphor has been prepared by a sol-gel method. X-ray diffractometer, spectrofluorometer were used to characterize structural and optical properties of the samples. The results indicate that Ca₅MgSi₃O₁₂: Eu²⁺, Mn²⁺ phosphors show two emission bands excited by ultraviolet light. Blue (around 450 nm) and green (around 502 nm) emissions originate from Mn²⁺ and Eu²⁺, respectively. With appropriate tuning the concentration ratios of Eu²⁺ to Mn²⁺, Ca₅MgSi₃O₁₂: Eu²⁺, Mn²⁺ phosphors exhibit different hues and relative color temperatures, which have potential to act as a single-phase phosphor for white-light emitting diode.     

Influence of samarium doping on the phase stability and optical properties of calcium silicates derived from agro-food wastes

Calcium silicates are very stable and good hosts for luminescent materials. These calcium silicates are synthesized using cost-effective agro-food wastes such as rice husk ash and eggshell powder along with doping of samarium oxide [Ca_3?xSi₂O₇:xSm³⁺(x(%)?=?0.25, 0.50, 0.75, and 1.00)] via solid-state reaction method. X-ray diffraction confirms that the Ca₃Si₂O₇ phase co-exists with the monoclinic-Ca₂SiO₄ phase. An increase in doping concentration of Sm³⁺ enhances the Ca₂SiO₄ phase content. Two types of morphology can be seen in the SEM micrographs confirming the presence of two phases. Photoluminescence emission spectra contain peaks in the visible region. Characteristic emission peaks of Sm³⁺ are present along with strong peaks due to the titanium ions present in agro-food wastes. Commission International de'Eclairage (CIE) co-ordinates correspond to the green region, which is significantly different from the CIE co-ordinates of Sm³⁺ doped samples derived from mineral oxides. This study presents an alternate use of agro-food wastes for synthesizing visible light-emitting phosphors and presents a mechanism for stabilizing Ca₂SiO₄ in waste-derived samples.

     

Phase Relations in the LiOH–TiO2–SiO2–H2O System at 500°C and 0.1 GPa

The compounds crystallizing in the LiOH–TiO₂–SiO₂–H₂O system at 500°C and 0.1 GPa are Li₂SiO₃, Li₂Si₂O₅, and Li₂SiO₃. At a TiO₂ : SiO₂ molar ratio of 6.4 : 1, the dominant phase is Li₂TiSiO₅. The crystallization fields of Si-containing phases at TiO₂ : SiO₂ ratios from 1 : 1 to 1 : 4 are (in order of increasing LiOH concentration) SiO₂ (quartz), Li₂Ti^[5]Si^[4]O₅ + Li₂Si₂O₅, and Li₂Ti^[5]Si^[4]O₅ + Li₂Si₂O₅ + Li₂Si^[4]O₃. The observed crystallization behaviors of Li₂TiSiO₅, Li₂Si₂O₅, and Li₂SiO₃ are interpreted in terms of the matrix assembly of the structure from cyclic subpolyhedral structural components.     

Nanostructure effects on the bioactivity of forsterite bioceramic

Recently, forsterite (Mg₂SiO₄) has been introduced as a possible bioceramics due to its good biocompatibility. It has a better bending strength and fracture toughness than those of commercially available hydroxyapatite ceramics. In this study, nanostructure effects on the bioactivity of forsterite powder were investigated. For synthesizing forsterite powder, talc and magnesium carbonate powders were mechanically activated for various times. Then, the prepared powders were mixed with ammonium chloride (as a catalyst) and annealed at different temperatures. For bioactivity evaluation, the obtained forsterite powders were pressed in the form of tablets and then immersed in simulated body fluid (SBF). The results showed that nanostructure forsterite powder with crystallite size of about 31 nm, unlike micrometer-sized forsterite, possessed apatite formation ability and its bioactivity, biocompatibility, and good mechanical properties make it a suitable candidate for load bearing application in bone implant materials and open new horizons in tissue engineering.     

Black Bioceramics: Combining Regeneration with Therapy

Bioceramics have been developed from bioinert to bioactive or biodegradable materials in the past few decades. However, at present, traditional bioceramics are still mainly used in bone tissue regeneration and dental restoration. In this work, a new generation of “black bioceramics,” extending the applications from tissue regeneration to disease therapy, is presented. Black bioceramics, through magnesium thermal reduction of traditional white ceramics, including silicate-based (e.g., CaSiO₃, MgSiO₃) and phosphate-based (e.g., Ca₃(PO₄)₂, Ca₅(PO₄)₃(OH)), are successfully synthesized. Due to the presence of oxygen vacancies and structural defects, the black bioceramics possess photothermal functionality while maintaining their initial high bioactivity and regenerative capacity. These black bioceramics show excellent photothermal antitumor effects for both skin and bone tumors. At the same time, they have significantly improved bioactivity for skin/bone tissue repair in vitro and in vivo. These fascinating properties award the black bioceramics with profound applications in both tumor therapy and tissue regeneration, which should greatly promote the scientific relevance and clinical application of bioceramics, representing a promising new direction of cell-instructive biomaterials.     

Luminescent properties of Ca2MgSi2O7 phosphor activated by Eu2+, Dy3+ and Nd3+

Long lasting alkaline earth silicates, Ca₂MgSi₂O₇:Eu,Dy,Nd was prepared under a reduction atmosphere through solid state reaction. The obtained phosphor was characterized by means of X-ray diffraction (XRD) and photoluminescence spectrum (PLS). The crystal structure of Ca₂MgSi₂O₇:Eu,Dy,Nd phosphor was refined by Rietveld analysis. The obtained Ca₂MgSi₂O₇:Eu,Dy,Nd phosphor showed a yellow–green emission peaking at 518 nm, which is ascribed to the luminescent emission of the Eu²⁺ that occupied the octa-coordinated Ca²⁺ sites in the Ca₂MgSi₂O₇ host. The electron affinity (ea) value for Eu²⁺ in [EuO₈] was calculated to 1.9 eV. The decay profile and the emission spectrum indicated that when the value of Dy/Eu is increasing, there is a concentration quenching of Eu²⁺.     

Photoluminescence properties of Eu2+-activated Ca2Y2Si2O9 phosphor

Eu²⁺-activated Ca₂Y₂Si₂O₉ phosphors with different Eu²⁺ concentrations have been prepared by a solid-state reaction method at high temperature and their photoluminescence (PL) properties were investigated. Photoluminescence results show that Eu²⁺-doped Ca₂Y₂Si₂O₉ can be efficiently excited by UV–visible light from 300 to 425 nm. Ca₂Y₂Si₂O₉: Eu²⁺ exhibits broad band emission in the wavelength range of 425–700 nm, due to the 4f⁶5d¹ → 4f⁷5d⁰ transition of the Eu²⁺ ions located at two different sites ((Ca/Y)1 and (Ca/Y)2) in Ca₂Y₂Si₂O₉. The effect of the Eu²⁺ concentration in Ca₂Y₂Si₂O₉ on the PL properties was investigated in detail. The results showed that the relative PL intensity reaches a maximum at 1 mol% of Eu²⁺, and a red-shift of the emission bands from these two different sites was observed with increasing Eu²⁺ concentration. Also there exists energy transfer between these two Eu²⁺ sites. The potential applications of Ca₂Y₂Si₂O₉: Eu²⁺ have been pointed out.     

Synthesis and photoluminescence of new phosphors M2(Mg, Zn)Si2O7:Mn (M = Ca, Sr, Ba)

New phosphors M₂(Mg, Zn)Si₂O₇:Mn²⁺ (M = Ca, Sr, Ba) were prepared by sol-gel process, and their luminescent properties in ultraviolet and vacuum ultraviolet region were investigated. The results showed that the (Ca, Sr, Ba)₂MgSi₂O₇:Mn²⁺ samples did not emit any visible light; the Sr₂ZnSi₂O₇:Mn²⁺ and Ca₂ZnSi₂O₇:Mn²⁺ samples showed green light. The Ba₂ZnSi₂O₇:Mn²⁺ sample mainly showed green light under 254 nm excitation and red light under 147 nm excitation. The different emission was due to the Mn²⁺ ions occupied different sites, which were excited selectively. Among the three phosphors Sr₂ZnSi₂O₇:Mn²⁺ showed the highest green emission intensity, and its decay time was shorter than that of Zn₂SiO₄:Mn²⁺ under 147 nm excitation.     

Extracting hydroxyapatite and its precursors from natural resources

Healing of segmental bone defects remain a difficult problem in orthopedic and trauma surgery. One reason for this difficulty is the limited availability of bone material to fill the defect and promote bone growth. Hydroxyapatite (HA) is a synthetic biomaterial, which is chemically similar to the mineral component of bones and hard tissues in mammals and, therefore, it can be used as a filler to replace damaged bone or as a coating on implants to promote bone in-growth into prosthetic implants when used in orthopedic, dental, and maxillofacial applications. HA is a stoichiometric material with a chemical composition of Ca₁₀(PO₄)₆(OH)₂, while a mineral component of bone is a non-stoichiometric HA with trace amounts of ions such as Na⁺, Zn²⁺, Mg²⁺, K⁺, Si²⁺, Ba²⁺, F^?, CO₃ ^2?, etc. This review looks at the progress being made to extract HA and its precursors containing trace amount of beneficial ions from biological resources like animal bones, eggshells, wood, algae, etc. Properties, such as particle size, morphology, stoichiometry, thermal stability, and the presence of trace ions are studied with respect to the starting material and recovery method used. This review also highlights the importance of extracting HA from natural resources and gives future directions to the researcher so that HA extracted from biological resources can be used clinically as a valuable biomaterial.     

Synthesis,tunable luminescence and thermal stability of Mg<Subscript>2</Subscript>Al<Subscript>4</Subscript>Si<Subscript>5</Subscript>O<Subscript>18</Subscript>:Ce<Superscript>3+</Superscript>/Mn<Superscript>2+</Superscript> phosphors

Ce³⁺/Mn²⁺ singly doped and codoped Mg₂Al₄Si₅O₁₈ phosphors were synthesized by a solid state reaction. The phase, luminescent properties and thermal stability of the synthesized phosphors were investigated. Ce³⁺ and Mn²⁺ singly doped Mg₂Al₄Si₅O₁₈ phosphors show emission bands locating in blue and yellow–red regions, respectively. In Ce³⁺ and Mn²⁺ codoped Mg₂Al₄Si₅O₁₈, tunable luminescence was obtained because of the energy transfer from Ce³⁺ to Mn²⁺. In Mg₂Al₄Si₅O₁₈:Ce³⁺/Mn²⁺ phosphors with a fixed Ce³⁺ concentration, energy transfer efficiency increases with the increasing Mn²⁺ concentration, which is confirmed by the continually decreasing intensity and shortening decay time of Ce³⁺ emission. Moreover, the luminescent properties and thermal stability provide a great significance on the applications in the field of light emitting diodes.     

Binary, ternary and quaternary silicates of CaO, BaO and ZnO in high thermal expansion seals for solid oxide fuel cells studied by high-temperature X-ray diffraction (HT-XRD)

Gas-tight seals based on glasses suitable for joining of materials with high thermal expansion coefficients are for example required for solid-oxide fuel cells. If these seals are to be used at high temperatures, they can only be fabricated from glasses which enable the crystallization of phases with high thermal expansion coefficients. This paper reports on some components from systems suitable for high thermal expansion seals: binary calcium silicates, CaSiO₃, Ca₃Si₂O₇ and Ca₂SiO₄ zinc silicates, Zn₂SiO₄, ternary silicates of BaO, CaO and ZnO, BaCa₂Si₃O₉, Ca₂ZnSi₂O₇, and one quaternary silicate, Ba₂CaZn₂Si₆O_17, studied by high-temperature X-ray diffraction. Only CaSiO₃, Ca₃Si₂O₇ and BaCa₂Si₃O₉ exhibit thermal expansion coefficients in the range suitable for high thermal expansion seals of 11.2-11.8 × 10⁻⁶ K⁻¹ (100-800 °C). The thermal expansions strongly depend on the respective crystallographic axis. The coefficient of thermal expansion of a sealing glass is not only affected by the thermal expansions of the crystalline phases, but also by that of the residual glassy phase as well as by the elastic properties. The phase formation should carefully be controlled also with respect to aging.     

A novel red phosphor Na2Ca4Mg2Si4O15:Eu3+ for plasma display panels

A novel red emitting phosphor, Eu³⁺-doped Na₂Ca₄Mg₂Si₄O₁₅, was prepared by the solid-state reaction. X-ray powder diffraction (XRD) analysis confirmed the formation of Na₂Ca₄Mg₂Si₄O₁₅:Eu³⁺. Field-emission scanning electron-microscopy (FE-SEM) observation indicated a narrow size-distribution of about 300 nm for the particles with spherical shape. Upon excitation with vacuum ultraviolet (VUV) and near UV light, the phosphor showed strong red-emission lines at around 611 and 617 nm, respectively, corresponding to the forced electric dipole ⁵D₀ → ⁷F₂ transition of Eu³⁺, and the highest PL intensity at 617 nm was found at a content of about 8 mol% Eu³⁺. The optical properties study suggests that it is a potential candidate for plasma display panels (PDPs) application.     

Photoluminescence properties and charge compensation investigations of novel orange-emitting Eu<Superscript>3+</Superscript> doped Na<Subscript>4</Subscript>Ca<Subscript>4</Subscript>(Si<Subscript>6</Subscript>O<Subscript>18</Subscript>) phosphors

A series of polycrystalline Na₄Ca₄(Si₆O₁₈):Eu³⁺ orange emitting phosphors were synthesized by a conventional high-temperature solid-state reaction. The phase formation was confirmed by X-ray power diffraction analysis. The excitation spectra show a strong host absorption indicating an efficient energy transfer process from O^2? to Eu³⁺ ions. Upon NUV radiation, the phosphors showed strong red emission around 610 nm (⁵D₀ → ⁷F₂) and orange emission around 591 nm (⁵D₀ → ⁷F₁), but the ⁵D_1,2,3 emission nearly can not be seen. Compared with the luminescence properties of Li⁺, Na⁺, and K⁺ co-doped samples, we deduced that Na⁺ ions probably prefer to dope into the intrinsic Na vacancies rather than Ca²⁺ ions vacancies in Na₄Ca₄(Si₆O₁₈) crystal. Thermal stability properties, quantum efficiency and chromaticity coordinates of the phosphors have been investigated for the potential application in white LEDs.     

Nanostructured Titanate with Different Metal Ions on the Surface of Metallic Titanium: A Facile Approach for Regulation of rBMSCs Fate on Titanium Implants

Titanium (Ti) is widely used for load‐bearing bio‐implants, however, it is bio‐inert and exhibits poor osteo‐inductive properties. Calcium and magnesium ions are considered to be involved in bone metabolism and play a physiological role in the angiogenesis, growth, and mineralization of bone tissue. In this study, a facile synthesis approach to the in situ construction of a nanostructure enriched with Ca²⁺ and Mg²⁺ on the surface of titanium foil is proposed by inserting Ca²⁺ and Mg²⁺ into the interlayers of sodium titanate nanostructures through an ion‐substitution process. The characteriz 0.67, and 0.73 nm ation results validate that cations can be inserted into the interlayer regions of the layered nanostructure without any obvious change of morphology. The cation content is positively correlated to the concentration of the solutions employed. The biological assessments indicate that the type and the amount of cations in the titanate nanostructure can alter the bioactivity of titanium implants. Compared with a Na⁺ filled titanate nanostructure, the incorporation of divalent ions (Mg²⁺, Ca²⁺) can effectively enhance protein adsorption, and thus also enhance the adhesion and differentiation ability of rat bone‐marrow stem cells (rBMSCs). The Mg²⁺/Ca²⁺‐titanate nanostructure is a promising implantable material that will be widely applicable in artificial bones, joints, and dental implants.     

Enhanced red-emitting phosphor Na<Subscript>2</Subscript>Ca<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>8</Subscript>:Eu<Superscript>3+</Superscript> by charge compensation

A series of novel red-emitting Na₂Ca_3???x Si₂O₈:xEu³⁺ phosphors were synthesized by solid state reactions. The phosphors can strongly absorb 395 nm light, and show red emission with a good color purity. The excitation and emission spectra properties of Na₂Ca₃Si₂O₈:Eu³⁺ were characterized. Na₂Ca₃Si₂O₈:Eu³⁺ with self-compensated and alkali metal ions charge compensated approaches (2Ca²⁺→Eu³⁺ + M⁺, M?=?Li⁺, Na⁺, K⁺) have investigated, which found that the red emission of luminescent intensity can be greatly enhanced, and shows superior luminescent property to the commercial Y₂0₃S:Eu³⁺. The present work implies that the efficient charge compensated phosphors are promising candidates as red-emitting phosphor for w-LEDs.     

Sintering and devitrification of glass-powder compacts in the akermanite–gehlenite system

The sintering and devitrification behavior of glass-powder compacts with four compositions, Ca₂Mg_0.5Al_1.0Si_1.5O₇, Ca₂Mg_0.6Al_0.8Si_1.6O₇, Ca₂Mg_0.7Al_0.6Si_1.7O₇, and Ca₂Mg_0.8Al_0.4Si_1.8O₇, corresponding to akermanite–gehlenite ratios (mol%) of 50/50, 60/40, 70/30, and 80/20 were investigated. Glass frits were prepared by the classical melt quenching technique in water. The structure of the glasses was investigated using FTIR and NMR, whereas the sintering behavior was studied by DTA and HSM. Sintering precedes crystallization only in Ca₂Mg_0.5Al_1.0Si_1.5O₇ glass while in the remaining glass compositions maximum densification was achieved slight after the onset of crystallization. However, the ratios of final area/initial area (A/A ₀) of the glass-powder compact ranging from 0.63 to 0.66 imply towards good densification levels (95–98 %) achieved in the investigated glasses. Qualitative and quantitative XRD analyzes were performed in glass-powder compacts heat treated at 900 and 1000 °C. Merwinite was found to crystallize first followed by decomposition at higher temperatures to form akermanite-like phase.