Composition and properties of silver-containing calcium carbonate–calcium phosphate bone cement

The introduction of silver, either in the liquid phase (as silver nitrate solution: Ag(L)) or in the solid phase (as silver phosphate salt: Ag(S)) of calcium carbonate–calcium phosphate (CaCO₃–CaP) bone cement, its influence on the composition of the set cement (C-Ag(L) and C-Ag(S) cements with a Ca/Ag atomic ratio equal to 10.3) and its biological properties were investigated. The fine characterisation of the chemical setting of silver-doped and reference cements was performed using FTIR spectroscopy. We showed that the formation of apatite was enhanced from the first hours of maturation of C-Ag(L) cement in comparison with the reference cement, whereas a longer period of maturation (about 10 h) was required to observe this increase for C-Ag(S) cement, although in both cases, silver was present in the set cements mainly as silver phosphate. The role of silver nitrate on the setting chemical reaction is discussed and a chemical scheme is proposed. Antibacterial activity tests (S. aureus and S. epidermidis) and in vitro cytotoxicity tests (human bone marrow stromal cells (HBMSC)) showed that silver-loaded CaCO₃–CaP cements had antibacterial properties (anti-adhesion and anti-biofilm formation) without a toxic effect on HBMSC cells, making C-Ag(S) cement a promising candidate for the prevention of bone implant-associated infections.     

Reduced graphene oxide–nickel oxide composites with high electrochemical capacitive performance

Reduced graphene oxide (RGO)–NiO composites have been fabricated by a simple solvothermal route starting with graphite oxide (GO). The morphology, composition and microstructure of the as-obtained samples are systematically characterized by thermogravimetric (TG) analysis, X-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM). Moreover, the electrochemical performances of composites were evaluated by cyclic voltammogram (CV) and galvanostatic charge–discharge. Interestingly, it was found that the electrochemical performance of the composites could be affected by the mass ratio between RGO and NiO. The composite with the mass ratio up to 79:21 (NiO:RGO) exhibits the highest specific capacitance of 576 F g⁻¹ at 1 A g⁻¹, which is much higher than that of pure NiO (240 F g⁻¹) and pure RGO (98 F g⁻¹). In addition, the cycling measurements showed that RGO–NiO composite exhibited excellent cycling stability with no decay in the available capacity over 1100 cycles. The enhancement in specific capacitance and cycling stability may be attributed to the increased electrode conductivity owing to RGO network, the increased effective interfacial area between NiO and the electrolyte, as well as the contact area between NiO and RGO.     

Synthesis, characterization and oxide ionic conductivity of β-type solid solution in bismuth oxide doped with ytterbium oxide binary system

In this study, after doping Yb₂O₃ substance to α -Bi₂O₃ substance in the range of 1% ≤ n ≤ 8% in a series of different mole ratios, heat treatment was performed by applying a cascade temperature rise in the range of 700–790 °C for 48 and 120 h and new phases were obtained in the (Bi₂O₃)_1???x (Yb₂O₃) _x system. After 48 h of heat treatment at 750 °C and 120 h of heat treatment at 790 °C, mixtures containing 1–8% mole Yb₂O₃ formed a tetragonal phase. With the help of XRD, crystal systems and lattice parameters of the solid solutions were obtained and their characterization was carried out. Thermal measurements were made by using a simultaneous DTA/TG system. The total conductivity (σ _T) in the β-Bi₂O₃ doped with Yb₂O₃ system was measured using four-probe d.c. method.     

Mesoporous titanium dioxide@ zinc oxide–graphene oxide nanocarriers for colon-specific drug delivery

In this project, TiO₂@ZnO nanoparticles core–shell nanostructured and titanium dioxide@ mesoporous zinc oxide–graphene oxide (TiO₂@ZnO–GO) hybrid nanocomposites as controlled targeted drug delivery systems were synthesized by a facile sono-chemical method. We prepared a novel mesoporous and core–shell structure as a drug nanocarrier (NCs) for the loading and pH-responsive characteristics of the chemotherapeutic curcumin. The structure, surface charge, and surface morphology of NCs were studied using with X-ray diffraction, Fourier transform infrared spectroscopy, dynamic light scattering, brunauer–emmett–teller, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The SEM and TEM images of NCs show the uniform hexagonal mesoporous morphology with average grain size of about ～ 190 nm. The drug loading was very high about 16 and 19 for TiO₂@ZnO and TiO₂@ZnO–GO, respectively. The NCs showed pH-dependent drug release behavior. Drug release from TiO₂@ZnO–GO in neutral pH were higher than in acidic medium, due to anionic charge of GO nanosheet. MTT assay results showed that the curcumin-loaded NCs showed significant toxicity due to which cell viability reduced to below 50% at 140 μg/mL concentration, thereby confirming its anticancer effects. The goal of this study is the application of water-dispersed TiO₂@ZnO–GO with pH-dependent release properties for design a new drug delivery carrier.     

Effect of gadolinia addition on varistor characteristics of vanadium oxide–doped zinc oxide ceramics

The effect of gadolinia addition on microstructure, electrical and dielectric characteristics, and aging behavior of vanadium oxide–doped zinc oxide varistor ceramics was systematically investigated. The average grain size decreased from 5.6 to 5.2 μm with an increase in the amount of Gd₂O₃ up to 0.1 mol%, whereas a further increase caused it to increase to 5.7 μm at 0.25 mol%. The sintered densities decreased from 5.51 to 5.44 g/cm³ with an increase in the amount of Gd₂O₃. With increasing the amount of Gd₂O₃, the breakdown field increased from 4,800 to 5,365 V/cm up to 0.05 mol%, whereas a further increase decreased it to 4,781 V/cm at 0.25 mol%. The varistor ceramics modified with 0.05 mol% Gd₂O₃ exhibited excellent nonlinear properties, with 66.1 in the nonlinear coefficient, whereas a further increase caused it to decrease to 17.6 at 0.25 mol%. The gadolinium acted like a donor, based on the electron concentration increasing from 4.20 × 10¹⁷/cm³ to 7.38 × 10¹⁷/cm³ with an increase in the amount of Gd₂O₃.     

The photo-electrochemical studies of Eu doped yttrium orthovanadate–zinc oxide–reduced graphene oxide nanohybrid

A new class of nanostructured photo-electrocatalyst Eu³⁺ doped yttrium orthovanadate–zinc oxide–reduced graphene oxide (YVO₄:Eu³⁺–ZnO–RGO) nanohybrid was developed by a simple electrostatic self-assembly at room temperature, using ZnO, YVO₄:Eu³⁺ and RGO as building blocks. Interaction among YVO₄:Eu³⁺, ZnO and RGO is indicated by variation in hydrodynamic diameter (H_D) and zeta potentials of the products as compared to their individual components, thus suggesting that YVO₄:Eu³⁺–ZnO–RGO is a nanohybrid and not a physical mixture. Electrochemical response of this nanohybrid towards the redox couple of Fe(CN)₆^3−/4− was investigated before and after UV irradiation. Apart from quenching of the green emission of ZnO in photoluminescence spectrum, which serves as a probe to monitor the interfacial electron transfer from excited ZnO to RGO, degradation in electrochemical redox process provides an additional path to monitor interfacial electron transfer.     

The formation of hydroxyapatite–calcium polyacrylate composites

Tetracalcium phosphate (TetCP, Ca₄(PO₄)₂O) reacts rapidly with polyacrylic acid (PAA). Complete reaction results in the formation of hydroxyapatite (HAp) and calcium polyacrylate. Consequently, this combination of reactants can react to form a dental cement. However, reaction occurs so rapidly that it would be difficult to achieve a homogeneous mixture of reactants suitable for use in restorations. In order to explore extending the working time, the effects of prehydrating the TetCP to form surface layers of HAp on the TetCP particles was explored. Prehydration was found to be an effective means of allowing workability. Therefore, the effects of the proportions of TetCP and PAA, with and without HAp filler, on cement properties were investigated. The extents of the reactions were investigated by X-ray diffraction analysis; the extents of PAA neutralization were studied by Fourier transform infra-red spectroscopy (FTIR); pore structures were determined by mercury intrusion porosimetry; microstructures were observed by scanning microscopy, and compressive strengths were determined. After curing for 17 days at room temperature PAA neutralization was almost complete; however, residual TetCP could be detected by X-ray diffraction and PAA by FTIR. As expected, the compressive strengths of the cements showed a dependence on the liquid (water+polymer)-to-solid (TetCP+HAp filler) used. The presence of HAp filler caused a significant decrease in compressive strength and increasing the proportion of HAp filler resulted in a decrease in the compressive strength. The characteristics of the load–deflection curves showed a dependence on the presence of HAp filler. In the absence of filler, two slopes were observed in the curves whereas a linear curve, typical of a ceramic, was observed when HAp filler was present. Mercury intrusion porosimetry (MIP) indicated the majority of the porosity was present in pores larger than 0.1 m. Porosity increased with increasing liquid-to-solids ratio and with an increasing proportion of HAp filler at a constant liquid-to-solids ratio. Microstructural observations indicated the effect of HAp filler on increasing porosity was the result of porosity present in the filler itself. Thus, poorly consolidated HAp filler contributed to increased porosity and reduced compressive strength. © 1999 Kluwer Academic Publishers     

Magnetic properties and Mössbauer spectra of gamma ferric oxide and doped gamma ferric oxide

Magnetic hysteresis, Mössbauer spectra and temperature variation of initial magnetic susceptibility of thirteen samples of doped -Fe₂O₃ containing cobalt or gadolinium are determined. The samples containing more than 1.0% cobalt are found to have a multi-domain configuration, and undoped -Fe₂O₃, gadolinium-doped -Fe₂O₃ and doped -Fe₂O₃ containing less than 1.0% (except 0.3%) cobalt have a single domain configuration. Mössbauer spectra of gadoliniumdoped samples suggest that gadolinium occupies A and B sites. In cobalt-doped samples, the effective magnetic fields at A and B sites are different at room temperature and liquid nitrogen temperature. The samples which have a multi-domain configuration display an additional central doublet in Mössbauer spectra indicating that these samples contain multi-domain clusters. The saturation magnetization of gadolinium-doped -Fe₂0₃ is much lower, and the coercive force of cobalt-doped samples is much higher than of gadolinium-doped and undoped samples.     

Nanoscale epitaxial growth control of oxide thin films by laser molecular beam epitaxy—towards oxide nanoelectronics

The nanoscale growth control of oxide thin films, such as ferroelectric and magnetic materials, were explored by a novel technique based on nanoscale substrate engineering as well as atomic layer control via laser molecular beam epitaxy (laser-MBE). Atomic-scale analysis of the terminating layer of perovskite oxide films was performed by in situ coaxial impact-collision ion scattering spectroscopy. The novel heteroepitaxies that could be attained were: (1) the termination-regulated molecular layer-by-layer epitaxy of BaTiO₃ and La_0.7Sr_0.3MnO₃ thin films and (2) the step-decoration epitaxy resulting in the nanowire or nanodot structures of magnetic oxides such as (Mn, Zn) ferrite on ultrasmooth sapphire substrates with straight atomic steps.     

Rietveld refinements for calcium and yttrium containing α-sialons

The crystal structures of calcium and yttrium containing-sialons, M _x (Si, Al)₁₂(N, O)₁₆, were refined by the Rietveld analysis of their X-ray powder diffraction patterns. Rather lowR factors obtained in the refinements provide conclusive evidence for a structural model proposed by the Newcastle group. In these-sialons, the modifying cations occupy large closed interstices of the (Si, AD-(N, O) network similar structurally to that in-Si₃N₄; each cation is coordinated to seven (N, O) atoms with an average M-(N, O) length of 0.26nm. The (Si, Al)-(N, O) bonds range in distance from 0.17 to 0.18nm (average 0.176 nm). The Rietveld method has been shown to give highly accurate occupation factors for the interstitial cations.     

Effects of environment on creep behavior of two oxide/oxide ceramic–matrix composites at 1200 °C

The tensile creep behavior of two oxide/oxide ceramic–matrix composites (CMCs) was investigated at 1200 °C in laboratory air, in steam, and in argon. The composites consist of a porous oxide matrix reinforced with laminated, woven mullite/alumina (Nextel™720) fibers, have no interface between the fiber and matrix, and rely on the porous matrix for flaw tolerance. The matrix materials were alumina and aluminosilicate. The tensile stress–strain behavior was investigated and the tensile properties were measured at 1200 °C. Tensile creep behavior of both CMCs was examined for creep stresses in the 80–150 MPa range. Creep run-out defined as 100 h at creep stress was achieved in air and in argon for stress levels ≤100 MPa for both composites. The retained strength and modulus of all specimens that achieved run-out were evaluated. The presence of steam accelerated creep rates and reduced creep life of both CMCs. In the case of the composite with the aluminosilicate matrix, no-load exposure in steam at 1200 °C caused severe degradation of tensile strength. Composite microstructure, as well as damage and failure mechanisms were investigated. Poor creep performance of both composites in steam is attributed to the degradation of the fibers and densification of the matrix. Results indicate that the aluminosilicate matrix is considerably more susceptible to densification and coarsening of the porosity than the alumina matrix. The views expressed are those of the authors and do not reflect the official policy or position of the United States Air Force, Department of Defense or the U.S. Government.     

SrTiO3 glass–ceramics as oxide thermoelectrics

Glass-ceramics obtained via a true bulk glassy phase offer a possibility to obtain high-temperature stable nanostructured materials in a cost efficient way which is suitable for mass production. We apply the method of glass-ceramic manufacturing to a crystalline phase which is known for its good thermoelectric properties as an n-doped material. Nb-doped SrTiO₃ with grain sizes of several nanometers is obtained as the main crystalline phase from transparent bulk glass after applying a well-defined time–temperature profile for ceramization. The glass-ceramics show a low thermal conductivity of around 1.6 W/mK and a Seebeck coefficient around ?480 μV/K together with electronic conductivity. Thermal cycling of these glass-ceramics without degradation of the thermoelectric properties for temperatures up to 650 °C (923 K) is shown as well.     

Enhanced capacitance of composite anodic ZrO₂ films comprising high permittivity oxide nanocrystals and highly resistive amorphous oxide matrix

Anodic oxide films with nanocrystalline tetragonal ZrO(2) precipitated in an amorphous oxide matrix were formed on Zr-Si and Zr-Al alloys and had significantly enhanced capacitance in comparison with those formed on zirconium metal. The capacitance enhancement was associated with the formation of a high-temperature stable tetragonal ZrO(2) phase with high relative permittivity as well as increased ionic resistivity, which reduces the thickness of anodic oxide films at a certain formation voltage. However, there is a general empirical trend that single-phase materials with higher permittivity have lower ionic resistivity. This study presents a novel material design based on a nanocrystalline-amorphous composite anodic oxide film for capacitor applications.     

Spectral studies on CuO in sodium–calcium borophosphate glasses

Transparent borophosphate glasses doped with CuO were prepared by melt quenching technique. X-ray diffraction (XRD), optical and luminescence properties of sodium–calcium borophosphate glasses doped with CuO have been studied. The XRD results showed the amorphous nature of the sample. The introduction of CuO was favourable for the colour changes from light blue to dark bluish green colour. Direct optical energy bandgaps before and after doping with different percents of copper oxide obtained in the range 4.81–2.99 eV indicated the role of copper in the glassy matrix by ultraviolet (UV) spectra. The glasses have more than 80% transparency for emission wavelength range, and strong absorption bands due to the charge transition of the Cu⁺ and Cu²⁺ ions were observed. The emission bands observed in the UV and blue regions are attributed to 3d⁹4s–3d¹⁰ triplet transition in Cu⁺ ion.     

Hardness and fracture toughness of dense calcium–phosphate-based materials

Hardness, H, and fracture toughness, KIc, have been determined as well as fracture energy and embrittlement index, H/KIc for six calcium–phosphate ceramics differing in phase composition. These materials were produced from initial calcium–phosphate precipitates with Ca–P molar ratios ranging between 1.50 and 1.73, synthesized by wet methods. After uniaxial or isostatic moulding and thermal treatment at 1250°C, the obtained dense sinters constituted mono-, bi- or triphase ceramic materials containing hydroxyapatite (HAp), -TCP, -TCP and CaO. When comparing the investigated materials, the best parameters, i.e. relatively high hardness accompanied by high KIc, were observed in the case of a HAp–TCP composite, containing 15 wt% HAp. It has been stated that free CaO occurring on the surface of the HAp samples obtained from powders with Ca–P ratios exceeding 1.67, transforms partially to CaCO3 due to contact with the surrounding atmosphere. The well shaped calcite crystals existing on the surfaces of such sinters significantly reduce hardness and increase fracture energy of the material when comparing both with the monophase HAp and the biphase HAp–TCP ceramics. © 1998 Chapman & Hall     

The influence of zinc oxide–cerium oxide nanoparticles on the structural characteristics and electrical properties of polyvinyl alcohol films

With the objective to investigate the influence of zinc oxide–cerium oxide (ZnO–Ce₂O₃) nanoparticles on the electrical properties of polyvinyl alcohol (PVA), PVA/ZnO–Ce₂O₃ nanocomposite films were prepared by solution intercalation method with different weight percentage viz., 0.5, 1.0, and 2.0?wt% of ZnO–Ce₂O₃ nanoparticles. The fabricated nanocomposites were characterized by Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The effect of ZnO–Ce₂O₃ nanoparticles on the dielectric constant (ε′), dielectric loss (ε″), electric modulus (M′ and M″), ac conductivity (σ _ac), and dielectric loss tangent (tan δ) over a range of frequencies at room temperature of PVA nanocomposites have been studied. FT-IR, XRD, and DSC analysis indicates the nature of ZnO–Ce₂O₃ nanoparticles interaction with the PVA matrix. The morphological behavior of the nanocomposites has been performed using scanning electron microscopy (SEM). The dielectric behaviors such as dielectric constant (ε′) and dielectric loss (ε″) increases with increase in nanoparticle concentration, but decreases with increase in frequency. But, the electric modulus (M′) increases with increase in frequency. Dielectric loss tangent (tan δ) decreases with increase in filler content at lower frequency, but at higher frequencies the tan δ increases with increase in nanoparticles content. AC conductivity (σ _ac) of PVA/ZnO–Ce₂O₃ nanocomposites increases with increasing frequency following the universal dielectric response law.     

In–vitro calcium phosphate growth over functionalized cotton fibers

Biomimetic growth of calcium phosphate compound on cotton sheets treated with tetraethoxy silane and soaked in simulated body fluid solution was studied using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), micro-Fourier transform infrared spectroscopy (FTIR) and X-ray diffractometry (XRD). Micro-FTIR and EDAX results show that silicon was coupled to the cotton fiber when cotton was treated with tetra-ethoxy silane (TEOS) at 125°C for 1 h. Calcium phosphate nucleation started to occur on the surface of TEOS-treated cotton fibers upon immersion in 1.5×SBF (simulated body fluid solution) within 3 days and after 20 days, all the fiber surfaces were found covered with a thick and porous coating of calcium phosphate. The Ca and P determined by inductively coupled plasma spectroscopy (ICP) analysis revealed that the Ca/P ratio as well as the amount of calcium phosphate coating depends on the soaking time in SBF solution. © 1999 Kluwer Academic Publishers     

Electrolytic deposition of amorphous and crystalline zinc–calcium phosphates

Amorphous Zn–Ca phosphates and crystalline Zn3(PO4)2·4H2O conversion layers on cathode substrates were prepared by electrolysis of mixtures of acidic solutions saturated with metal phosphates. The solutions contained tricalcium phosphate (Ca3(PO4)2) and/or zinc phosphate dihydrate (Zn3(PO4)2·2H2O). The depositions was carried out with constant or pulsating cathode current densities in the range 20–70 mA cm-2 at 20–70 °C. The deposition of the uniform crystalline Zn3(PO4)2·4H2O was performed at a pulsating cathode current density of 70 mA cm-2 at 70 °C for periods up to 10 min. Amorphous deposits of Zn–Ca phosphates containing 20 wt% H2O with variable Zn-to-Ca ratios were deposited at a constant cathodic current of 30 mA cm-2 at 20 °C for 3 min. Surface areas of the amorphous deposits were of the order of 28 m2 g-1. X-ray diffraction, differential thermal analysis and thermogravimetry were used to investigate phase formation and transitions at increasing temperatures. The amorphous Zn–Ca phosphate deposit was after calcination at 900 °C transformed to crystalline phosphates containing the -Ca3(PO4)2 or Ca3-xZnx(PO4)2 and -CaZn2(PO4) phases. © 1998 Kluwer Academic Publishers     

Doped calcium–aluminium–phosphate cements for biomedical applications

Calcium–aluminium–phosphate cements (CAPCs) for biomedical applications, mainly intended for applications in the dental field as non-resorbable fillers, were obtained by reacting Ca-aluminates compounds, i.e. CaO·Al₂O₃ (CA) and CaO·2 Al₂O₃ (CA₂), with Al(H₂PO₄)₃ aqueous solution. Hydroxyapatite was also introduced as a bioactive dispersed phase. Suitable elements like Sr and La were used to increase the radiopacity of the set yielded pastes towards X-ray wavelength used in clinical diagnostic radiographic equipments. La and Sr doped Ca-aluminates powders have been synthesized by solid state reaction at 1,400°C from a mixture of CaCO₃, Al₂O₃, La₂O₃ and SrCO₃. The characteristics of the obtained powders were analyzed and related to the starting compositions and synthesis procedures. The microstructure, setting time, radiopacity and compressive strength of the CAPCs have been investigated and discussed.     

Cyclic and sustained loading behaviors of oxide/oxide Nextel™720/alumina composite with double edge sharp notch

This study investigated an oxide/oxide CMC consisting of Nextel?720 (meta-stable mullite) fibers in alumina matrix, N720/A, with 0°/90° fiber orientation having double edge sharp notch under sustained and cyclic loading conditions at 1200 °C in laboratory air environment. Monotonic tensile tests at 1200 °C were also conducted. Fracture surfaces were examined to analyze failure and damage mechanisms. Comparisons with counterparts from unnotched geometry showed N720/A is mildly sensitive to the sharp notch under monotonic tensile, creep and fatigue loading conditions. The ultimate tensile strength of the composite was reduced by about 15% in the presence of the sharp notch. The rupture strength of the sharp notched geometry was reduced by about 15% of unnotched geometry for a given rupture time. The fatigue strength was reduced by about 20% of unnotched geometry for a given number of cycles to failure. Deformation under cyclic loading condition had contributions both from fatigue and creep. Damage mechanisms were identical under cyclic and sustained loading conditions.