The Effects of Calcium‐to‐Phosphorus Ratio on the Densification and Mechanical Properties of Hydroxyapatite Ceramic

In this work, hydroxyapatite (HA) powders were synthesized using calcium hydroxide Ca(OH)₂ and orthophosphoric acid H₃PO₄ via wet chemical precipitation method in aqueous medium. Calcium‐to‐phosphorus (Ca/P) ratio was set to 1.57, 1.67, 1.87 that yield calcium‐deficient HA, stoichiometric HA, and calcium‐rich HA, respectively. These synthesized HA powders (having different Ca/P ratio) were characterized in terms of particle size and microstructural examination. Then, the densification and mechanical properties of the calcium‐deficient HA, stoichiometric HA, and calcium‐rich HA were evaluated from 1000 to 1350°C. Experimental results have shown that no decomposition of hydroxyapatite phase was observed for stoichiometric HA (Ca/P = 1.67) and calcium‐deficient HA (Ca/P = 1.57) despite sintered at high temperature of 1300°C. However, calcium oxide (CaO) was detected for calcium‐rich HA (Ca/P = 1.87) when samples sintered at the same temperature. The study revealed that the highest mechanical properties were found in stoichiometric HA samples sintered at 1100–1150°C, having relative density of ~99.8%, Young's modulus of ~120 GPa, Vickers hardness of ~7.23 GPa, and fracture toughness of ~1.22 MPam^1/2.     

Synthesis,Characterization, and In Vitro Bioactivity of Sol‐Gel‐Derived Zn,Mg, and Zn‐Mg Co‐Doped Bioactive Glasses

Bioactive glasses in the systems CaO‐SiO₂‐P₂O₅‐ZnO, CaO‐SiO₂‐P₂O₅‐MgO, and CaO‐SiO₂‐P₂O₅‐MgO‐ZnO were prepared and characterized. Bioactive glass powders were produced by the sol‐gel method. The prepared bioactive glass powders were immersed in a simulated body fluid (SBF) for periods of up to 28 days at 310 K to investigate the bioactivity of the produced samples. Inductively coupled plasma (ICP) and ultraviolet (UV) spectroscopic techniques were used to detect changes in the SBF composition. X‐Ray diffraction (XRD) was utilized to recognize and confirm the formation of a hydroxyapatite (HA) layer on the bioactive glass powders. Microstructural characterizations of the bioactive glass samples were investigated by scanning electron microscopy (SEM) techniques. Density, porosity, and surface area values of bioactive glass powders were also determined in order to characterize the textural properties of the samples. The results revealed the growth of an HA layer on the surface of the bioactive glass samples. MgO in the glass sample increases the rate of formation of an HA layer while ZnO in the glass slows it down.     

Effects of Mg‐Doping and of Reinforcing Multiwalled Carbon Nanotubes Content on the Structure and Properties of Hydroxyapatite Nanocomposite Ceramics

Surfactant‐assisted hydrothermal synthesis of magnesium‐doped hydroxyapatite (Ca_10?xMg_x(PO₄)₆(OH)₂) with 0 ≤ x ≤ 1) was realized in aqueous solution at 90°C. β‐TCP phase was formed in the Mg_0.6‐HA sample after heat treatment at 1000°C. Magnesium was found to degrade the sintering ability of Mg_x‐HA ceramics. Flexural strength (σ_f) was found to decrease as a function of Mg‐doped HA. The using of carbon nanotubes as reinforcing agents mitigated the strength loss of Mg‐HA ceramics. The flexural strength of Mg_0.6‐HA was then increased by nearly 20% from approximately 33 to 39 MPa with an optimum addition of 3 wt% of multi‐walled nanotubes.     

Electrochemical Deposition of 58SiO2‐33CaO‐9P2O5 Nanobioactive Glass Particles on Ti‐6Al‐4V Alloy for Biomedical Applications

The nanobioactive glass (58SiO₂‐33CaO‐9P₂O₅) powders were synthesized by simple sol–gel method. The prepared samples reveal amorphous nature, agglomerated spherical morphology with particle size of 100–150 nm. The specific surface area of nanobioactive glass (NBG) particle is 147 m²/g. The NBG samples were coated on titanium (Ti‐6Al‐4V) alloy through electrochemical deposition method. The particle size of the NBG‐coated surface was in the order of 200–300 nm, and it was confirmed by atomic force microscopy (AFM) analysis. In vitro and AFM studies reveal the existence of higher bioactivity and uniform coating of NBG on implants at 80 V for 1 h.     

Conductivity Studies of Silver‐, Potassium‐, and Magnesium‐Doped Hydroxyapatite

We report the electrical transport properties of silver‐, potassium‐, and magnesium‐doped hydroxyapatites (HAs). While Ag+ or K⁺ doping to HA enhances the conductivity, Mg⁺² doping lowers the conductivity when compared with undoped HA. The mechanism behind the observed differences in ionic conductivity has been discussed using the analysis of high‐temperature frequency‐dependent conductivity data, Cole–Cole plots of impedance data as well as on the basis of the frequency dependence of the imaginary part (M″) of the complex electric modulus. The f_max of modulus M″ decreased in silver‐ and potassium‐doped samples in comparison with the undoped HA.     

Development of Hydrothermally Synthesized Hydroxyapatite Coatings on Metallic Substrates and Weibull's Reliability Analysis of its Shear Strength

Hydroxyapatite (HA) and Mg‐substituted HA coatings were synthesized on Mg‐9Al‐1Zn and Ti‐6Al‐4V by the hydrothermal process. Grazing‐incidence X‐ray diffractograms showed the formation of calcium–magnesium–phosphate is resulted from the substitution of Mg²⁺‐ions into HA crystal. The chemical state of Mg²⁺‐ions in Mg‐substituted HA coatings was examined by X‐ray photoelectron spectroscopy. The shear test results showed the Mg‐substituted HA coatings deposited on Mg‐9Al‐1Zn have higher shear strength than those coatings on Ti‐6Al‐4V. The Weibull model provided a powerful statistical method for assessing failure mechanism of hydrothermal coatings, which is attributed to a wear‐out failure model with a Weibull modulus m > 3.     

Synthesis,structural characterization,and photoluminescence properties of Eu3+‐doped Mg3‐xEux(BO3)2 phosphor

Eu³⁺‐doped Mg_3‐xEu_x(BO₃)₂ (x = 0.000, 0.005, 0.010, 0.020, 0.050, and 0.100) phosphors were synthesized for the first time by solution combustion synthesis method, which is a fast synthesis method for obtaining nano‐sized borate powders. The optimization of the synthesis conditions of phosphor materials was performed by TG/DTA method. These phosphors were characterized by XRD, FTIR, SEM‐EDX, and photoluminescence, PL analysis. The XRD analysis exhibited that all of the prepared ceramic compounds have been crystallized in orthorhombic structure with space group Pnnm. Also, the influence of europium dopant ions on unit cell parameters of host material was analyzed using Jana2006 program and the crystalline size was determined by Debye‐Scherrer's formula. The luminescence properties of all Eu³⁺‐doped samples were investigated by excitation and emission spectra. The excitation spectra of Mg_3‐xEu_x(BO₃)₂ phosphors show characteristic peak at 420 nm in addition to other characteristic peaks of Eu³⁺ under emission at 613 nm. The emission spectra of Eu³⁺‐doped samples indicated most intensive red emission band dominated at 630 nm belonging to ⁵D₀→⁷F₂ magnetic dipole transition. Furthermore, the optimum or quenching concentration of Eu³⁺ ion has been determined as x = 0.010 showed the maximum emission intensity when it was excited at 394 nm.     

Hydrothermal Synthesis of Si‐doped Hydroxyapatite Nanopowders: Mechanical and Bioactivity Evaluation

Si‐doped hydroxyapatite nanoparticles (n‐Si_xHA) were prepared by hydrothermal synthesis from calcium nitrate tetrahydrate and diammonium hydrogen orthophosphate. A rod‐like morphology was obtained for all the powders irrespective of the incorporated Si‐doping level. But the crystallinity of the n‐Si_xHA powders, the density achieved upon sintering powder compacts and their mechanical properties (three‐point‐bending strength), as well as their biomineralization activity evaluated by immersing them into simulated body fluid (SBF) were found to be dependent on the Si‐doping amount.     

Non-stirred synthesis of Na- and Mg-doped,carbonated apatitic calcium phosphate

Hydroxyapatite-like (apatitic) calcium phosphate (Ap-CaP) powders are usually synthesized in stirred solutions containing the highly soluble salts of calcium, such as calcium nitrate, calcium acetate and calcium chloride as the Ca-source. The current study tested the ideas of simultaneously using (i) precipitated calcite (CaCO₃) powders as the Ca-source and (ii) non-stirred, static solutions for synthesizing carbonated, Na⁺- and Mg²⁺-doped apatitic calcium phosphate (Ap-CaP) powders. 0.5 M phosphate buffer (non-saline) solutions were used as the sole phosphate source. The synthesized Ap-CaP powders were found to consist of micron-size carnation-like crystalline particles. Samples were characterized by FE-SEM, XRD, FTIR, ICP-AES, dynamic light scattering (DLS), carbon percentage and BET surface area analyses.     

Structural and luminescence properties of silica powders and transparent glass‐ceramics containing LaF3:Eu3+ nanocrystals

In this work, silica powders and transparent glass‐ceramic materials containing LaF₃:Eu³⁺ nanocrystals were synthesized using the low‐temperature sol‐gel technique. Prepared samples were characterized by TG/DSC analysis as well as X‐ray diffraction and IR spectroscopy. The transformation from liquid sols toward bulk powders and xerogels was also examined and analyzed. The optical behavior of prepared Eu³⁺‐doped sol‐gel samples were evaluated based on photoluminescence excitation (PLE: λ_em = 611 nm) and emission (PL: λ_exc = 393 nm, λ_exc = 397 nm) spectra as well as luminescence decay analysis. The series of luminescence lines located within reddish‐orange spectral scope were registered and identified as the intra‐configurational 4f⁶‐4f⁶ transitions originated from Eu³⁺ optically active ions (⁵D₀ → ⁷F_J, J = 0‐4). Moreover, the R/O‐ratio was also calculated to estimate the symmetry in local framework around Eu³⁺ ions. The luminescence spectra and double‐exponential character of decay curves recorded for fabricated nanocrystalline sol‐gel samples (τ₁(⁵D₀) = 2.07 ms, τ₂(⁵D₀) = 8.07 ms and τ₁(⁵D₀) = 0.79 ms, τ₂(⁵D₀) = 9.76 ms for powders and glass‐ceramics, respectively) indicated the successful migration of optically active Eu³⁺ ions from amorphous silica framework to low phonon energy LaF₃ nanocrystal phase.     

A Novel Blue‐Emitting Phosphor of Eu2+‐Activated Magnesium Haloborate Mg3B7O13Cl

Eu²⁺‐doped magnesium haloborate Mg₃B₇O₁₃Cl was synthesized by the conventional high‐temperature solid‐state reaction. The phase formation was confirmed by X‐ray powder diffraction (XRD) measurements and structure refinement. The photoluminescence excitation and emission spectra, and decay curves were measured. Under the excitation of near‐UV light, Eu²⁺‐doped Mg₃B₇O₁₃Cl presents a narrow blue‐emitting band centered at 423 nm. The maximum absolute quantum efficiency (QE) of Mg₃B₇O₁₃Cl:Eu²⁺ phosphor was measured to be 80% excited at 385 nm light at 300 K. The thermal stability of the blue luminescence was evaluated by the luminescence decays as a function of temperature. The phosphor shows an excellent thermal stability on temperature quenching effects. Moreover, Mg₃B₇O₁₃Cl:Eu²⁺ phosphor shows scintillation characteristics excited by X‐ray irradiation at room temperature and presents a blue luminescence band with a fast lifetime of 600 ns.     

Preparation of Magnesium‐based Hydrogen Storage Materials and Their Effect on the Thermal Decomposition of Ammonium Perchlorate

Magnesium‐based hydrogen storage materials (MgH₂, Mg₂NiH₄, and Mg₂Cu‐H) were prepared and their structures were determined by XRD and ICP investigations. Mg₂NiH₄ has a monoclinic crystal structure and Mg₂Cu‐H is a mixture of MgCu₂ and MgH₂. The effects of magnesium‐based hydrogen storage materials on the thermal decomposition of ammonium perchlorate (AP) were studied by thermal analysis (DSC). It was found that magnesium‐based hydrogen storage materials show obvious boosting effects on the thermal decomposition of AP. The thermal decomposition peak temperature of AP was decreased, while the heat release of the decomposition of AP was increased. It was revealed that the effects of magnesium‐based hydrogen storage materials on the decomposition of AP become stronger with increasing content. The influence mechanism on the thermal decomposition of AP is suggested as follows: hydrogen released from magnesium‐based hydrogen storage materials and Mg, Ni, or Cu react with the decomposed products of AP.     

Sol–gel derived alumina–hydroxyapatite–tricalcium phosphate porous composite powders

In this study, alumina–hydroxyapatite–tricalcium phosphate (α-Al₂O₃–HA–TCP) porous composite powders were produced and characterized. At first, boehmite sol (AlOOH) was obtained via sol–gel process by using aluminium isopropoxide (Al(OC₃H₇)₃) as the starting material. Bovine hydroxyapatite (BHA) powders derived from deproteinized bovine bones were added as 10, 20, 30 and 50% weight of the starting material to each boehmite sol. Also Na-alginate was added to the boehmite sol as the dispersive agent. Subsequently, gelation for 3 h at 110 °C was applied to each sol mixture. Finally, gelated samples were heat treated for 2 h at 500, 800, 1000 and 1300 °C. DTA–TGA, XRD, FTIR and SEM-EDS analyses were used to characterize the obtained composite powders composed of α-Al₂O₃–HA–TCP phases. In order to investigate porosity properties, powders were pressed with hydraulic manual press and formed into pellets. Later these pellets were sintered for 2 h at 1300 °C. Apparent porosity and bulk density tests were applied to the pellets. The evaluation of these tests results indicate that a novel α-Al₂O₃–HA–TCP composite material with ～38–44% apparent porosity has been produced.     

Mechanical properties of 1 mol% CeO2‐10 mol% Sc2O3 co‐doped and stabilized ZrO2 synthesized through hydro/solve‐thermal method

Ultra‐fine 1 mol% CeO₂‐10 mol% Sc₂O₃ co‐doped and stabilized ZrO₂ (1Ce10ScSZ) powders with average grain size less than 10 nm in diameter were prepared by hydro/solve‐thermal method using either deionized water, ethanol, or methanol as solvent. As‐synthesized powders were characterized in terms of phase structure, particle morphology, and chemical composition by X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), high‐resolution transmission electron microscopy (HRTEM), and inductively coupled plasma‐optical emission spectroscopy (ICP‐OES), respectively. Sintering studying was conducted on pellets of 15 mm in diameter and 3 mm in thickness under uniaxial compaction using 25 MPa at either 600, 800, 1000, 1100, 1200, 1400, or 1500°C for 1 hour. Phase transitions and grain morphologies of those sintered samples were characterized by XRD and field emission scanning electron microscopy (FESEM). Mechanical properties were characterized on dense pellets sintered at 1500°C by nanoindentation. Experimental results showed that ethanol was more effective to synthesize agglomerate‐free 1Ce10ScSZ powders as compared with deionized water and methanol. Choice of solvent affected the environment of hydro/solve‐thermal solution, which led to variation of chemical compositions of powders and porosities of sintered pellets, and therefore, influenced their mechanical performance. Our study showed that solvent was important to make dense, thin, and mechanically robust 1Ce10ScSZ electrolyte for potential applications in electrochemical devices. Absolute values of hardness (H) and Young's modulus (E) measured from our samples are much higher and more consistence than those results obtained from commercial vendors reported in literatures.     

A Sucrose‐Mediated Sol–Gel Technique for the Synthesis of MgO–Y2O3 Nanocomposites

A sucrose‐mediated aqueous sol–gel procedure was developed to synthesize MgO–Y₂O₃ nanocomposite ceramics for potential optical applications. The synthesis involves the generation of a precursor foam containing Mg²⁺ and Y³⁺ cations via the chemical and thermal degradation of sucrose molecules in aqueous solution. Subsequent calcination and crushing of the foam gave MgO–Y₂O₃ nanocomposites in the form of thin mesoporous flake‐like powder particles with uniform composition and surface areas of 27–85 m² g ^{? 1}, depending on calcination conditions. The flakes exhibited a homogeneous microstructure comprising intimately mixed nanoscale grains of the cubic MgO and Y₂O₃ phases. This microstructure was resistant to grain coarsening with average grain sizes of less than 100 nm for calcination temperatures of up to 1200°C. The results indicate that the sucrose‐mediated sol–gel process is a simple effective method for making nanoscale mixed oxides.     

Development of Ce‐PSZ‐/Y‐PSZ‐Toughened Alumina Inserts for High‐Speed Machining Steel

The nanocomposite CeO₂/Y₂O₃ partially stabilized zirconia (Ce‐PSZ/Y‐PSZ)‐toughened alumina was prepared by wet chemical simultaneous coprecipitation process. The thermal stability of phases and morphology of powders were characterized by TG‐DTA, FTIR, and FESEM. The microstructure, stabilization of phases and compositional analysis with different mol% CeO₂/Y₂O₃‐doped zirconia in alumina are characterized by FESEM, XRD, and EDAX spectra. Significant improvement in fracture toughness and flexural strength has been observed in 10 vol% of partially stabilized zirconia (2.5 mol% Y₂O₃ in ZrO₂/9 mol% CeO₂ in ZrO₂)‐toughened alumina, which is suitable for high‐speed machining applications.     

The Assembly of TiO2 Nanoparticles into Micrometer‐Sized Structures,Photocatalytically Active Under UV and Vis Light

Micrometer‐sized structures consisting of TiO₂ nanoparticles were prepared using the sol–gel technique in combination with the structure‐directing agent triethanolamine (TEA). The interaction of the TEA with the hydrolyzed sol–gel products led to the formation of TEA titanate complexes, which then enabled the assembly of sol–gel‐precipitated nanosized powders. A subsequent thermal treatment of these powders resulted in the formation of micrometer‐sized structures consisting of TiO₂ anatase and rutile nanoparticles. To characterize the prepared powders, FTIR spectroscopy, XRD analysis, the Brunauer‐Emmett‐Teller method (s_BET), UV–Vis spectrometry and electron microscopy (FE‐SEM, and TEM) were employed. The photocatalytic degradation of the azo dye known as methylene blue was monitored under UV and Vis irradiation and showed that the micrometer‐sized structures consisting of TiO₂ nanoparticles exhibited a similar photocatalytic activity to submicrometer‐sized structures consisting of TiO₂ nanoparticles prepared without TEA.     

Synthesis of Cerium‐Doped Gd3(Al,Ga)5O12 Powder for Ceramic Scintillators with Ultrasonic‐Assisted Chemical Coprecipitation Method

Cerium‐doped Gd₃(Al,Ga)₅O₁₂ powders have been synthesized with ultrasonic‐assisted chemical coprecipitation method (UACC), and the traditional chemical coprecipitation method (CC) was also employed for comparison. The structure and morphology of powders were investigated by XRD, BET, and TEM. The powders were used for preparing ceramics at different temperatures. The specific surface areas of UACC and CC powders calcined at 800°C were 66 and 29 m²/g, respectively. Ceramics derived from UACC and CC powders were sintered at 1600°C, and the densities are 6.67 and 6.48 g/cm³, respectively. UACC is an attractive method for synthesizing GAGG powder for preparing ceramic scintillators.     

Synthesis of Single‐Phase Gd‐Doped Ceria Nanopowders by Radio Frequency Thermal Plasma Treatment

Gd‐doped ceria nanopowders were synthesized using Radio Frequency (RF) thermal plasma. The powders were prepared by ball‐milling Gd₂O₃ and CeO₂ powders of several tens of μm in size at the cation ratio of 8:2 and 9:1. The prepared precursors were treated by RF thermal plasma at a plate power level of ~140 kVA, and then, small‐sized powders (~50 nm) were retrieved by filtration. Transmission Electron Microscopy, Electron Energy Loss Spectroscopy, and Selected‐Area Electron‐Diffraction images of the as‐synthesized powders showed that Gd atoms were incorporated into the CeO₂ particles. In addition, no crystalline peak for Gd₂O₃ appeared in the X‐ray diffraction patterns of the as‐synthesized powders, which is attributed to the solid solution of Gd³⁺ into the CeO₂ lattices. Finally, Inductively Coupled Plasma‐Optical Emission Spectrometry analysis data revealed relatively small changes within 3 at.% in the cation composition between the ball milled powder mixtures and the nanoscale powders prepared from these mixtures.     

Effect of magnesium source on the fabrication of kotoite Mg3B2O6 ceramic

The effect of magnesium source on the fabrication of kotoite, Mg₃B₂O₆, ceramic has been investigated by high temperature solid‐state reaction route based on the calcination of different magnesium sources, containing magnesium oxide, magnesium carbonate, magnesium sulfate, and magnesium nitrate with boric acid. The X‐ray powder diffraction results showed that single‐phase kotoite, Mg₃B₂O₆, was synthesized using MgNO₃.6H₂O and 5 wt.% excess of H₃BO₃ powders as starting materials at 900°C for 48 hours. Mg₃B₂O₆ obtained, is well crystallized, in orhorhombic crystal structure with lattice parameters of a = 5.399(9), b = 8.424(6), and c = 4.506(5) Å. Jana2006 refinement of this product shows excellent fit of the experimental data with software data, GOF= 1.33. The crystallite size of the product was calculated as 40.50 nm using Debye‐Scherrer's equation. The existence of BO₃ triangles were detected by FTIR measurements of Mg₃B₂O₆. The thermal properties were studied in the temperature range of 20°C to 1400°C by TG/DTA. The results showed that thermal stability of Mg₃B₂O₆ is detected about 1380°C. Scanning electron microscopy was employed for observation of microstructure. The microstucture of obtained ceramic samples strongly depended on the magnesium source on the fabrication of Mg₃B₂O₆ ceramic.