New iron-doped multilayer ceramic scaffold with noncontinuous bioactive behavior

New multilayer porous ceramic scaffolds, constituted by a core covered with external layers, are proposed as future bone tissue implants. The core with composition SiO₂ - 25P₂O₅ – 68CaO–6Li₂O (mol%) provided suitable compressive strength (0.9–1.6 MPa) to act as an initial support during bone tissue regeneration. The external layers with composition 29SiO₂ - 3P₂O₅ - (68-x) CaO - xFe₂O₃ (mol%) (x = 0.3 and 1) (samples C/EL-1Fe and C/EL-3Fe, respectively) conferred a bioactive character to scaffolds. The surfaces of both samples showed apatite precipitates after coming into contact with simulated body fluid (SBF). Sample C/EL-1Fe exhibited noncontinuous bioactive behavior, with precipitates of apatite that precipitated and dissolved between days 1 and 28. Sample C/EL-3Fe showed precipitates after 8 days that remained until the end of the study time. This variation in material, achieved by modifying the amounts of iron in external layers, represents an important advance in the ability to control an implant's bioactivity in line with requirements of future applications.     

Phosphate content affects structure and bioactivity of sol-gel silicate bioactive glasses

Bioactive glasses can heal bone defects and bond with bone through formation of hydroxyl carbonate apatite (HCA) surface layer. Sol-gel derived bioactive glasses are thought to have potential for improving bone regeneration rates over melt-derived compositions. The 58S sol-gel composition (60 mol% SiO₂, 36 mol% CaO, and 4 mol% P₂O₅) has appeared in commercial products. Here, hydroxyapatite (HA) was found to form within the 58S glass during sol-gel synthesis after thermal stabilization. The preformed HA may lead to rapid release of calcium orthophosphate, or nanocrystals of HA, on exposure to body fluid, rather than the release of separate the calcium and phosphate species. Increasing the P₂O₅ to CaO ratio in the glass composition reduced preformed HA formation, as observed by XRD and solid-state NMR. Instead, above 12 mol% phosphate, a phosphate glass network (polyphosphate) formed, creating co-networks of phosphate and silica. Nanopore diameter of the glass and rate of HCA layer formation in simulated body fluid (SBF) decreased when the phosphate content increased.     

Titania doped bioactive ceramics prepared by solid state sintering method

A bioactive ceramic in (48−x) SiO₂–36CaO–4P₂O₅–12Na₂O–xTiO₂ (where x= 0, 3.5, 7, 10.5 and 14 mol%) system was prepared by solid state sintering method. The in vitro bioactive properties of bodies were evaluated using stimulated body fluid under static condition at 37 °C. The formation of hydroxyl-carbonated apatite layer on the surface of samples was examined by XRD, FTIR, SEM and AAS. It was found that partial substitution of SiO₂ with TiO₂ produced a positive impact on the bioactivity of the specimens. Addition of TiO₂≤10.5 mol% to the system not only enhanced the bioactive properties but also accelerates the apatite forming process.     

Gel-derived SiO2–CaO–P2O5 bioactive glasses and glass-ceramics modified by SrO addition

The effect of SrO substitution for CaO in two sol–gel glasses with different chemical compositions (mol%) A2Sr: (54−x)CaO–xSrO–6P₂O₅–40SiO₂ and S2Sr: (16−x)CaO–xSrO–4P₂O₅–80SiO₂ (x=0, 1, 3 and 5) stabilized at 700 °C on their structure (XRD, FTIR) and bioactive properties (SBF test) was investigated. Preliminary in vitro tests using human articular chondrocytes of selected A2Sr glass were also conducted. Moreover, the subject of this study was to detect the changes on material properties after heat treatment at 1300 °C. The results show that the effect of strontium substitution on structure, bioactivity and crystallization after treatment at both the above temperatures strongly depends on CaO/SiO₂ molar ratio. The presence of 3–5 mol% of strontium ions creates more expanded glass structure but does not markedly affect crystallization ability after low temperature treatment. Sintering at 1300 °C of A2 type glasses results in crystallization of pseudowollastonite, hydroxyapatite and also Sr-substituted hydroxyapatite for 3–5 mol% of SrO substitution. The increase of strontium concentration in silica-rich materials after sintering leads to appearance of calcium strontium phosphate instead of calcium phosphate. Bioactivity evaluation indicates that substitution of Sr for Ca delays calcium phosphate formation on the materials surface only in the case of silica-rich glasses treated at 700 °C. Calcium-rich glasses, after both temperature treatments, reveals high bioactivity, while crystal size of hydroxyapatite decreases with increasing Sr content. High temperature treatment of high-silica glasses inhibits their bioactivity. Preliminary in vitro tests shows Sr addition to have a positive effects on human articular chondrocytes proliferation and to inhibit cell matrix biomineralization.     

Dispersity of the ferriferous chrome spinelid and composition of the filler as factors affecting the formation of structure in refractories

Physicomechanical properties of periclase-spinelid ceramics, in particular, the softening temperature under load and compressive strength, are shown to be controlled by the granular composition of the native ferriferous chrome spinelid. At relatively low concentration of CaO (0.51–0.88 wt.%), SiO₂ (0.53–1.33 wt.%), and ratio CaO/SiO₂ = 0.38–1.36, the incipient deformation temperature under load does not exceed 1700°C.Translated from Novye Ogneupory, No. 7, July, 2004, pp. 37–40.     

An approach to monitor the real-time deformation during heat treatment of 3D-printed glass

This study suggests a tool for a better control on the sintering/crystallization of 3D-printed bioactive glass-ceramics bodies. A small cantilever in form of a bar with square cross section attached to a base and inclined 34° with the horizon, was used to monitor the viscous flow and sintering/crystallization headway of a glass-ceramic systems. 3D printing and sintering of bioactive glass-ceramics is of great interest for medical care applications. Viscous flow ensures sufficient densification of the typically low density printed green bodies, while crystallization prevents the structure from collapsing under the gravitational load. As a model system, a bioactive glass called BP1 (48.4 SiO₂, 1 B₂O₃, 2 P₂O₅, 36.6 CaO, 6.6 K₂O, 5.6 Na₂O (mol%)), which has a chemical composition based on that of ICIE16, was employed in this work. In addition, ICIE16 was used as a reference glass. The results show that the suggested design is a very promising tool to track the real-time deformation of 3D printed glass-ceramic specimens and gives a good indication for the onset of crystallization as well.     

Physical and structural characteristics of sol–gel derived CaO–B2O3–SiO2 glass-ceramics and their dielectric properties in the 5G millimeter-wave bands

In this study, sol–gel derived CaO–B₂O₃–SiO₂ glass-ceramics with a set B₂O₃ content of 22.2 mol% and CaO/SiO₂ ratios ranging between 0.15 and 0.27 were used for low-temperature cofired ceramic applications in the 5G millimeter-wave bands. X-ray diffraction analysis, scanning electron microscopy, Fourier-transform infrared spectroscopy, and Raman spectroscopy data indicated that, unlike the typical CaO–B₂O₃–SiO₂ glass-ceramics prepared via melting resulted in the presence of calcium silicates, the CaO–B₂O₃–SiO₂ glass-ceramics in this study comprised only an amorphous phase containing different amounts of CaB₂O₄ crystallites depending on the CaO/SiO₂ ratio. Among the formulations evaluated, the 14.5CaO?22.2B₂O₃?63.3SiO₂ glass-ceramic sintered at 950 °C exhibited a dielectric constant of 4.33 and a dielectric loss of 0.0012 at 60 GHz, which conferred its low signal propagation delay and low signal attenuation in applications. In addition, the electrical resistivity, breakdown strength, thermal conductivity, and coefficient of thermal expansion of the 14.5CaO?22.2B₂O₃?63.3SiO₂ glass-ceramic were 1.72 × 10¹² Ω cm, 15.49 kV/mm, 1.70 W/mK, and 4.1 ppm/°C, respectively. The 14.5CaO?22.2B₂O₃?63.3SiO₂ glass-ceramic exhibited excellent insulating properties, facilitating its use as substrate material; moreover, its thermal properties matched those of Si and GaAs.     

Influence of triethanolamine on the hydration characteristics of tricalcium silicate

The hydration characteristics of 3CaO.SiO₂ or β2CaO.SiO₂ are studied by an addition of 0.0, 0.1, 0.5 or 1.0% triethanolamine. The amount of Ca(OH)₂ found at 1, 3, 7 or 28 days was in the order C₃S + 0% TEA > C₃S +0.1% TEA > C₃S + 0.5% TEA > C₃S+1.0% TEA, irrespective of whether lime was estimated by X-ray, DTA, TGA or chemical analysis. The rate of hydration, in terms of the disappearance of 3CaO.SiO₂, showed that hydration proceeded faster in the presence of TEA after 1 day. Additions of TEA increase the induction period, promote the formation of a C-S-H with higher CaO/SiO₂ ratio, increase the formation of non-crystalline Ca(OH)₂ and enhance the surface area of the hydrated silicate product.     

Mass Spectrometric Study of the Thermodynamic Properties of Melts in the CaO–TiO2–SiO2 System

The composition of the vapor over melts in the CaO–TiO₂–SiO₂ system, activities of the melt components, and Gibbs energies of formation are determined by high-temperature mass spectrometry upon evaporation from tungsten cells in the temperature range 1800–2200 K. It is demonstrated that the positive deviation of the SiO₂ activity from ideal behavior in melts of the CaO–TiO₂–SiO₂ system at constant mole fraction ratios CaO/TiO₂ equal to 2.33 and 1.5 is caused by the presence of titanium dioxide. The SiO₂ activity decreases in the case when CaO is added to SiO₂ and increases when TiO₂ is introduced into the system under investigation.     

Effect of CaO/SiO2 ratio on phase transformation and properties of anorthite-based ceramics from coal fly ash and steel slag

Anorthite-based ceramics were produced entirely from coal fly ash and steel slag. The effect of the CaO/SiO₂ ratio (0.12–0.8) on the phase transitions was examined by adding steel slag to coal fly ash in the range of 10–50 wt%, and a temperature range of 900–1200 °C. The influence of CaO/SiO₂ and sintering temperatures on the technological properties were assessed by response surface methodology (RSM) and correlated with the phase changes. The results revealed that anorthite was the main phase for the CaO/SiO₂ ratio ranging from 0.12 to 0.56, while at 1200 °C, a ratio of 0.8 involved a high content of gehlenite. RSM showed that the CaO/SiO₂ ratio was the main influencing factor on the density, while the variation of apparent porosity and compressive strength were more affected by sintering temperature. The crystallisation of the anorthite phase significantly enhanced the properties of the obtained ceramics, whereas the appearance of gehlenite reduced the mechanical strength. The optimum conditions to fabricate anorthite-based ceramics with suitable properties were found to be a CaO/SiO₂ ratio of 0.46 and a temperature of 1188 °C. The optimised anorthite-based ceramic exhibited a low thermal conductivity (0.39 W/m.K) and a dielectric constant of 6.03 at 1 MHz, along with a compressive strength of 41 MPa, which makes this sample a potential candidate for insulator applications.     

Influence of FeO/SiO2 and CaO/SiO2 Ratios in Iron‐Saturated ZnO‐Rich Fayalite Slags on the Corrosion of MgO

The corrosion behavior of MgO in iron‐saturated ZnO‐rich fayalite (ZFS) slags having various FeO/SiO₂ ratio and CaO/SiO₂ ratio was investigated using MgO crucible tests for 12 h at 1200°C. The FeO/SiO₂ and CaO/SiO₂ ratios in the ZFS slags were varied from 1.0 to 2.2, and from 0.04 to 0.32, respectively. In all of the tests, it was observed that MgO dissolves into ZFS slags and that (Zn,Fe,Mg)₂SiO₄ olivine and (Zn,Fe,Mg)O solid solution are formed at the crucible/slag interface. The MgO dissolution decreased with the FeO/SiO₂ ratio up to a value of 1.7 and then slightly increased, whereas it continuously increased with the CaO/SiO₂ ratio. There is no obvious relationship between the amount of olivine and the FeO/SiO₂ ratio or CaO/SiO₂ ratio. In comparison, the formation of (Zn,Fe,Mg)O solid solution is enhanced by increasing the FeO/SiO₂ ratio or CaO/SiO₂ ratio in ZFS slags. The results suggest that MgO corrosion is the lowest for FeO/SiO₂ and CaO/SiO₂ ratios around 1.7 and 0, respectively.     

Eco-friendly preparation and structural characterization of calcium silicates derived from eggshell and silica gel

In this work, the preparation of calcium–silicate-based composites consisting of natural waste from calcium source as eggshell and silica gel from a desiccator as a silicon source both presenting alternative materials for cheap preparation of eco-friendly calcium–silicate bioceramics has been investigated. The effect of the CaO/SiO₂ ratio on microstructural properties has also been studied. The pseudowollastonite formation has been observed in the case of 40 wt.% CaO and 60 wt.% SiO₂ with lowest porosity and highest density 2.6 g/cm³. In the case of 50 wt.% CaO and 50 wt.% SiO₂, the phase transformation from pseudowollastonite to wollastonite was observed. Increasing the calcium content caused higher apparent porosity with 19%. It was shown that the development of novel ceramics from reused waste, eggshell, or silica can be an optimal solution for the low-cost preparation of calcium silicates with potential applications in medicine or cement, food industry.     

Characterization of bioactive glass-coated carbon nanotubes prepared by solgel process

Due to its excellent bioactivity, bioactive glass (BG) is suitable for use as bone graft substitutes in biomedical applications. In this study, carbon nanotubes (CNT-COOH) served as templates for depositing bioactive glass based on 60SiO₂–36CaO–4P₂O₅ wt.% were synthesized via the solgel process. The BG and BG/CNT-COOH composites were treated at 300, 500, 700, and 900°C; their properties were also examined by X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The experimental results showed that BG/CNT-COOH composites treated at 500 and 700°C were amorphous and contained silicate nanocrystals. By altering precursor concentration, bioactive glass of various thicknesses was successfully solgel coated on CNT-COOH. Immersion of the BG/CNT-COOH composites in simulated body fluid solution and MG-63 cell culture assessment showed the 500°C treated BG/CNT-COOH exhibits excellent bioactivity.     

Correlation between microstructure and properties of biocomposite coatings

A SiO₂–CaO–Na₂O (SCN) based bioactive glass was used to prepare glass–matrix/Ti particle composite coatings (SCNT). The coatings were obtained by vacuum plasma spray (VPS) on Ti–6Al–4V substrates. Two different deposition methods have been compared: (a) VPS of powders obtained by ball milling of sintered composites; (b) in situ plasma spray of mixed titanium and glass powders. For comparative purposes, pure SCN glass coatings were produced. The coating morphology and microstructure were observed by optical and scanning electron microscopy, compositional analyses by energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). Comparative mechanical tests were carried out by shear tests and by Vickers indentations at the interface between the substrate and the coatings. The bioactivity of glass- and composite coatings was investigated in vitro by soaking them in a simulated body fluid (SBF) with the same ion concentration of the human plasma. All the layers retain their starting composition. The composite coatings obtained by VPS of the powdered presintered composites showed a better mechanical behaviour with respect both to the composite coatings obtained by the in situ method and to the pure glass coatings. Both the glass- and the two kind of composite coatings revealed to be bioactive by the growth of a thick apatite layer after 30 days of soaking in SBF. The electrochemical behaviour of the SCNT coatings was evaluated by means of potentiodynamic anodic polarization curves and free corrosion potential measurements in Ringer solution at 25 °C. For comparative purposes the same analyses were performed on analogous bioactive glass-matrix/Ti particle composite coated samples, based on the system TiO₂–SiO₂–CaO–B₂O₃ (TSCB), and obtained both by the in situ and by presintering method as well. The results of the electrochemical tests showed a better corrosion behaviour of the samples coated by VPS of powdered sintered composites with respect to those coated by in situ VPS composites.     

Influence of SiO2 and CaO additions on the microstructure and magnetic properties of sintered Sr-hexaferrite

The effect of simultaneous addition of CaO and SiO₂ on the microstructure and magnetic properties of sintered SrO-excess Sr-hexaferrites was studied. Both additives markedly affect the grain growth behavior and the magnetic properties. CaO-additions promote densification, which results in increased remanence, but due to simultaneuous grain growth the coercivity drops to <100 kA/m. SiO₂ additions are known to suppress grain growth. Simultaneous addition of CaO and SiO₂ is shown to be very beneficial in tailoring a dense microstructure with relatively small grains. The ratio of CaO/SiO₂ was found to be optimum at about 1, and magnets with a remanence of 430 mT and a coercivity of 300 kA/m were obtained. Transmission electron microscopy (TEM) studies and investigations by energy-dispersive analysis of X-rays (EDX) in the scanning TEM (STEM) mode show that both CaO and SiO₂ are concentrated at grain boundaries and grain junctions forming an amorphous secondary phase.     

Thermodynamic analysis of calcium oxide assisted hydrogen production from biogas

This paper investigates calcium oxide assisted hydrogen production from biogas. Preliminary experiments were performed to compare the catalytic performance of combined carbon dioxide reforming and partial oxidation of biogas among four different adsorbent (CaO)/catalyst (Ni/SiO₂·MgO) arrangements; i.e. (i) Ni/SiO₂·MgO before CaO, (ii) CaO before Ni/SiO₂·MgO, (iii) Ni/SiO₂·MgO mixed with CaO, and (iv) Ni/SiO₂·MgO without CaO. The mixture of CaO and Ni/SiO₂·MgO was found to be the best arrangement, offering the highest hydrogen yield. Thermodynamic investigation of the integrated sorption-reaction systems for hydrogen production from biogas was performed. The system can be operated under thermal neutral condition when appropriate operating parameters are adjusted. Finally based on the thermal neutral operation, the effects of H₂O/CH₄ and CaO/CH₄ ratios on the required O₂/CH₄ ratio, hydrogen yield, hydrogen concentration and CO/H₂ ratio in product were determined. Obviously the use of CaO adsorbent can improve hydrogen production and there is an optimum H₂O/CH₄ ratio which offers the highest hydrogen production at each CaO/CH₄ ratio. Increasing H₂O/CH₄ ratio generally increases H₂/CO ratio but decreases hydrogen concentration in the product.     

Thermodynamic Stability of Spinel Phase at the Interface Between Alumina Refractory and CaO–CaF2–SiO2–Al2O3–MgO–MnO Slags

The interfacial reaction between alumina refractory and CaO–CaF₂–SiO₂–Al₂O₃–MgO–MnO slag was observed at 1873 K to estimate the stability of the spinel phase using computational thermodynamics under refining conditions of Mn‐containing steels. The concentration of MnO formed by the slag–steel reaction in the CaO–CaF₂–SiO₂–Al₂O₃–MgO melts generally increased by decreasing the CaO/SiO₂ ratio of the initial melts. No intermediate compounds were formed at the refractory–slag interface when the initial CaO/SiO₂ ratio was 0.5, whereas CaAl₁₂O₁₉ (CA6) and Mg(Mn)Al₂O₄ (spinel), identified from TEM analysis using EDS mapping and SAED patterns, were observed at the refractory–slag interface when the CaO/SiO₂ ratio was 1.0 or greater. The (at.%Mg)/(at.%Mn) ratio in the spinel solution increased by increasing the CaO/SiO₂ ratio, which originated from the fact that MgO activity continuously increased as the CaO/SiO₂ ratio increased. From thermodynamic analysis considering the equilibrium constant (K_SP) and activity quotient (Q_SP) of the spinel formation reaction at the slag–refractory interface and the bulk slag phase, the precipitation–dissolution behavior of the spinel phase was predicted, which exhibited good consistency with the experimental results. Hence, the dissolutive corrosion mechanism of alumina refractory into the CaO–CaF₂–SiO₂–Al₂O₃–MgO–MnO slag was proposed.     

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

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

Densification and characterization of SiO2B2O3CaOMgO glass/Al2O3 composites for LTCC application

A glass/ceramic composite using lead-free low melting glass (SiO₂B₂O₃CaOMgO glass) with Al₂O₃ fillers was investigated. X-ray diffraction analysis revealed that the anorthite and cordierite phase appeared in the sintered composites. The dilatometric analysis showed that the onset of shrinkage took place at ∼624 °C for all the samples and the onset temperature was independent on the content of glass. The low melting glass significantly promoted densification of the composites and lowered the sintering temperature to ∼875 °C. The addition of 50 wt% glass sintered at 875 °C showed ε_r of 7.3, tan δ of 1.15×10⁻³, TEC of 5.41 ppm/°C, thermal conductivity of 3.56 W/m °C, and flexural strength of 184 MPa. The results showed that the SiO₂B₂O₃CaOMgO glass/Al₂O₃ composites were strong potential candidates for low temperature cofired ceramic substrate applications.     

Solid acidities of SiO2–TiO2/montmorillonite composites synthesized under different pH conditions

SiO₂–TiO₂/montmorillonite composites were prepared under acidic, neutral and basic conditions and the solid acidity of the resulting composites were determined. All the SiO₂/TiO₂ ratio of the colloidal particles was set at 10 but the resulting SiO₂/TiO₂ ratios were significantly richer in TiO₂. The XRD patterns of the acidic composite showed expanding and broadening of the (001) reflection by intercalation of colloidal SiO₂–TiO₂ particles, but the neutral and basic composites showed only broadening of the reflections and no intercalation. The specific surface areas of the acidic, neutral and basic composites (375, 237 and 247 m²/g, respectively) were much larger than of montmorillonite (6 m²/g). The average pore sizes were about 4, 15 and 50 nm, and the amounts of solid acidic sites measured by the NH₃-TPD were 178, 95 and 86 µmol/g for the acidic, neutral and basic composites, respectively. The solid acid amount of the acidic composite was twice that of a commercial catalyst, K-10, (85 µmol/g) and much higher than the guest phase SiO₂–TiO₂ gel (16 µmol/g) or the host phase montmorillonite (6 µmol/g). The TPD peak temperatures reflect the acid strength, and were similar in all the samples, ranging from 175° to 200 °C.