In vitro bioactivity evaluation of magnesium-substituted fluorapatite nanopowders

Properties of apatites, such as bioactivity, biocompatibility, solubility, and adsorption properties can be tailored over a wide range by modifying the composition via ionic substitutions. The aim of this work was preparation, characterization and in vitro bioactivity evaluation of Mg-doped fluorapatite (Mg-FA) nanopowders. Mg-FA nanopowders with different Mg contents were prepared via sol-gel method. In vitro bioactivity evaluation of powders was performed by soaking the powders in simulated body fluid (SBF). Results indicated that Mg ions entered into the fluorapatite lattice and occupied Ca²⁺ sites, and the obtained powders had crystallite size about 30-100 nm. With increasing the Mg-substitution, the solubility of powders and the adsorption of Ca²⁺ ions onto the powders surfaces increased simultaneously. It was concluded that Mg-substitution improves the bioactivity of FA.     

Mechanosynthesis of nanocomposites in TiO2–B2O3–Mg–Al quaternary system

The mechanochemical behavior of TiO₂–B₂O₃–Mg–Al quaternary system to synthesize various composite nanopowders was studied. A mixture of boron oxide and titanium dioxide powders along with different amounts of magnesium and aluminum was milled using a high-energy planetary ball mill to persuade necessary conditions for the occurrence of a mechanically induced self-sustaining reaction (MSR). Results showed that the formation of composite nanopowders was influenced strongly by the reducing agents content. In the absence of Al (100 wt% Mg), TiB₂ nanopowder was formed after 34 min of milling. In the presence of x wt% Mg–y wt% Al (x=40 and 70; y=100−x), mechanical activation was completed after 37–40 min which caused the formation of TiB₂–MgFe_0.6Al_1.4O₄ composite nanopowders. In the case of 10 wt% Mg–90 wt% Al, a ternary nanocomposite (TiB₂–MgAl₂O₄–Al₂O₃) was produced after 43 min of milling. Besides, Al₂O₃–TiB₂ nanocomposite was formed after 90 min of milling in the absence of Mg (100 wt% Al). From the SEM images, mechanochemical process reached a steady state after short milling times where the particles have become homogenized in size and shape. The reaction mechanism steps were proposed to clarify the reactions occurring during mechanochemical process.     

Fabrication and characterization of nanocrystalline Mg-substituted fluorapatite by high energy ball milling

The aim of this work was preparation and characterization of Mg-substituted nanostructured FA powders. Mg-substituted nanostructured FA powders were synthesized with a chemical composition of Ca_10?xMg_x(PO₄)₆F₂, with x=0, 0.5, 1, 1.5 and 2 by mechanical alloying method. Successful substitution of Ca²⁺ with Mg ions in the fluorapatite lattice was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). The results showed that after 12 h of milling, pure nanocrystalline Mg-substituted FA powders with different Mg contents were synthesized. The incorporation of Mg ions into the fluorapatite caused the decrease of the lattice parameters. With increasing Mg content, the crystallinity of powder decreased while the degree of agglomeration of powder increased. SEM and TEM analysis showed that the powder was agglomerated and composed of nanocrystalline particles with the average particle size of less than 100 nm.     

Diffusion bonding of alumina using interlayer of mixed hydride nano powders

In this study, mixed hydride/alanate nano powders in the Al–Mg system were used as the interlayer for low temperature diffusion bonding of dense alumina parts. Decomposition of hydride nanopowders at bonding temperatures in-situ formed metals and alloys nano particles with oxide free surfaces and high sinter-ability in the interlayer. Nano powders sintering behavior in the interlayer and formation of compounds in the reaction layer during diffusion bonding were studied. Mixture of 50–50 M ratio of AlH₃ and Mg(AlH₄)₂, as the interlayer improved bond strength of the joints. Diffusion bonding products were formed in the MgO–Al₂O₃ spinel system with different stoichiometries. Bond strength improved up to 202 MPa by induction hot pressing alumina parts at low bonding temperature of 400 °C under pressure of 20 MPa during 30 min bonding period.     

Fabrication and characterization of sol–gel derived hydroxyapatite/zirconia composite nanopowders with various yttria contents

Homogeneous composite nanopowders of hydroxyapatite/30 wt% yttria-stabilized zirconia (HA–YSZ) containing 0, 3, 5, and 8 mol% Y₂O₃ (namely; HA–0YSZ, HA–3YSZ, HA–5YSZ, and HA–8YSZ) were successfully synthesized using the sol–gel method. Simultaneous thermal analysis (STA), X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), Fourier transformed infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques were utilized to characterize the prepared nanopowders. Analyses of HA–YSZ composite nanopowders showed the successful formation of desirable phases. HA unit cell volume in the composites increased as a result of ion exchange of calcium and zirconium between HA and zirconia. Results revealed the formation of HA particles with irregular morphology (40–80 nm) and spherical yttria-stabilized zirconia particles (20–30 nm). Segregation of yttrium ions at the grain boundaries of ZrO₂ particles retarded the grain growth of zirconia particles and the presence of ZrO₂ nanoparticles among the hydroxyapatite particles resulted in grain growth inhibition of HA particles. This process can be used to synthesize HA–YSZ composite nanopowders with improved properties, which are much needed for hard tissue repair and biomedical applications.     

Synthesis,crystallization behavior and microstructure of oxynitride glass–ceramics with different modifier elements

M–Si–Al–O–N (M=Y, Ca, Mg) oxynitride glasses were prepared by melting batches at 1600 °C for 2 h under N₂ atmosphere in a Si–Mo-heated resistance furnace. The appropriate heat treatment temperatures were selected according to the information provided by the differential scanning calorimeter (DSC) measurement. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to study the crystallization behavior of the glass–ceramics with different modifier elements. The results indicate that for this glass system, heat treatment has an effect on volume fraction of the crystalline phases and the microstructure of the glass–ceramics, whereas the effect on the types of the crystalline phases precipitated is small.     

Effect of zirconia content on the mechanosynthesis and structural features of fluorapatite-based composite nanopowders

The influence of zirconia content on the mechanosynthesis of fluorapatite–zirconia composite nanopowders was investigated. The structural features of the specimens with different amounts of monoclinic zirconia (0–20 wt%) were examined after 5 h of mechanical activation. Results indicated that the formation of fluorapatite–zirconia composite was strongly influenced by the zirconia content. In the presence of 5–10 wt% monoclinic zirconia, fluorapatite–zirconia composite nanopowders were produced after 5 h of milling. With increasing zirconia content to 20 wt%, there was no trace of fluorapatite–zirconia composite. In the absence of zirconia, the average crystallite size, lattice strain and the volume fraction of grain boundary of fluorapatite were about 34 nm, 0.469% and 8.38%, respectively. These values reached 24 nm, 0.754% and 11.71% with the addition of 10 wt% monoclinic zirconia. In the presence of 10 wt% monoclinic zirconia, the fraction of crystalline phase considerably decreased after 5 h of milling. Results revealed that the lattice parameter deviations were affected by the zirconia content. Based on SEM observations, no significant differences in the size distribution and morphology of the agglomerates were observed.     

Characterization studies on plasma sprayed (AT/HA) bi-layered nano ceramics coating on biomedical commercially pure titanium dental implant

Hydroxyapatite (HA), Al₂O₃–13 wt%TiO₂ (AT) nanoparticles coated on bioactive commercially pure titanium (Cp-Ti) implant were fabricated by plasma spray coating technique. The fabricated monolayer AT, HA film of thickness 75 μm and bilayer (AT/HA) of thickness 150 μm and the coated film surface crystallinity, morphology and phases were investigated in terms of X-ray diffraction, SEM, FT-Raman spectroscopy. In this work, nanostructure AT, HA powders were plasma sprayed on the biomedical Cp-Ti implant surface improve corrosion resistance, and microhardness, surface roughness values compared to uncoated surface. Electrochemical corrosion test was carried out by simulated body fluid (SBF) with ionic concentrations comparable to that of human blood plasma and this result shows that improved corrosion resistance, for the bilayer (AT/HA) coated surface compared to a monolayer AT, HA coated surface. For Al₂O₃ addition with 13 wt%TiO₂ ceramics powder reinforced coating which can act as a barrier for the metal ion released from the implant surface. The in vitro analysis of the bilayer coated implant was good agreement with bone osteoinduction in the biological environment.     

Ca-α SiAlON hollow spheres prepared by carbothermal reduction–nitridation from different SiO2 powders

The formation process of hollow spheres composed of nanosized Ca-α SiAlON particles was investigated using SiO₂ starting powders with different characteristics in particle size, shape and crystalline state. TEM observations showed Ca-α SiAlON hollow spheres composed of a large number of nanosized particles in the products prepared at 1450 °C for 120 min in nitrogen. In all systems, the Ca-α SiAlON hollow spheres were always produced through an intermediate Si–Al–Ca–O liquid phase in the same mechanism, regardless of the characteristics of SiO₂ starting powders used. Spherical solid particles consisted of amorphous phase containing Si, Al, Ca, O and a small amount of N were generated at the initial stage of carbothermal reduction–nitridation. These spherical solid particles changed into hollow particles with the progression of the reaction from the liquid phase to the crystalline Ca-α SiAlON with increasing temperature.     

Characterization of Mg-substituted hydroxyapatite synthesized by wet chemical method

Mg-substituted hydroxyapatite made up of needle-like and plate-like particles containing different amounts of Mg (between 0.21 wt% and 2.11 wt%) were prepared via wet chemical precipitation method of a homogenous suspension of Mg(OH)₂/Ca(OH)₂ and an aqueous solution of H₃PO₄. According to the data of Brunauer–Emmett–Teller method and field emission scanning electron microscopy, high specific surface area Mg-substituted hydroxyapatite was obtained. Specific surface area of as-synthesized powders increased from 94.9 m² g⁻¹ to 104.3 m² g⁻¹ with increasing concentration of Mg up to 0.64 wt%. Fourier transform infrared spectroscopy, X-ray powder diffraction, differential thermal analysis, and heating microscopy, were used to evaluate thermal stability and sintering behavior of synthesis products. Increase in concentration of Mg in synthesis products (≥0.83 wt%) promoted decomposition of Mg-substituted hydroxyapatite to Mg-substituted β-tricalcium phosphate after thermal treatment.     

Magnetic and catalytic properties of copper ferrite nanopowders prepared by a microwave-induced combustion process

Copper ferrite nanopowders were successfully synthesized by a microwave-induced combustion process using copper nitrate, iron nitrate, and urea. The process only took a few minutes to obtain CuFe₂O₄ nanopowders. The resultant powders were investigated by XRD, SEM, VSM, and surface area measurement. The results revealed that the CuFe₂O₄ powders showed that the average particle size ranged from 300 to 600 nm. Also, it possessed a saturation magnetization of 21.16 emu/g, and an intrinsic coercive force of 600.84 Oe, whereas, upon annealing at 800 °C for 1 h. The CuFe₂O₄ powders specific surface area was 5.60 m²/g. Moreover, these copper ferrite magnetic nanopowders also acted as a catalyst for the oxidation of 2,3,6-trimethylphenol to synthesize 2,3,5-trimethylhydrogenquinone and 2,3,5-trimethyl-1,4-benzoquinone for the first time. On the basis of experimental evidence, a rational reaction mechanism is proposed to explain the results satisfactorily.     

The characteristics of Ni–Co–Mn–O precursor and Li(Ni1/3Co1/3Mn1/3)O2 cathode powders prepared by spray pyrolysis

Ni–Co–Mn–O precursor powders with spherical shape and dense structure were prepared by spray pyrolysis from a spray solution containing a drying control chemical additive (DCCA) and polymeric precursors. In contrast, the Ni–Co–Mn–O precursor powders obtained from a spray solution without additives had a hollow and porous morphology. Ni–Co–Mn–O precursor powders with a spherical shape and dense structure yielded Li(Ni_1/3Co_1/3Mn_1/3)O₂ cathode powders with a spherical shape and fine size by means of a solid-state reaction with lithium hydroxide. The mean size of the spherical cathode powder was 1.1 μm. The discharge capacity of the Li(Ni_1/3Co_1/3Mn_1/3)O₂ powders with spherical shape and filled morphology was 195 mA h g⁻¹ at a current density of 0.1 C. The discharge capacities of the cathode powders with spherical shape and filled morphology at 55 °C decreased from 183 to 154 mA h g⁻¹ by the 30th cycle at a current density of 0.5 C.     

Preparation and characterization of tetragonal-ZrO2 nanopowders by a molten hydroxides method

Pure tetragonal-ZrO₂ nanopowders are prepared by a molten hydroxides method, using hydrated zirconium nitrate as the starting material at 200 °C. X-ray diffraction analysis and transmission electron microscopy observation reveal that the nanopowders exhibit poor crystalline quality. After heat treated at 400 °C for 10 h in air, the nanopowders are crystalline with size range of ∼10–12 nm and most of them are agglomerated. The formation mechanism of the ZrO₂ nanopowders has been proposed. The heat treated nanopowders have a BET surface area of ∼27.3 m²/g due to agglomeration. The photoluminescence of the heat treated nanopowders has been investigated at room temperature.     

Synthesis and characterization of Al2O3 nanopowders by a simple chitosan-polymer complex solution route

Al₂O₃ nanopowders were synthesized by a simple chitosan-polymer complex solution route. The precursors were calcined at 800–1200 °C for 2 h in air. The prepared samples were characterized by XRD, FTIR and TEM. The results showed that for the precursors prepared with pH 3–9 γ-Al₂O₃ and δ-Al₂O₃ are the two main phases formed after calcination at 800–1000 °C. Interestingly, when the precursor prepared with pH 2 was used, α-Al₂O₃ was formed after calcination at 1000 °C, and pure α-Al₂O₃ was obtained after calcination at 1200 °C. The crystallite sizes of the prepared powders were found to be in the range of 4–49 nm, as evaluated by the XRD line broadening method. TEM investigation revealed that the Al₂O₃ nanopowders consisted of rod-like shaped particles and nanospheres with particle sizes in the range of 10–300 nm. The corresponding selected-area electron diffraction (SAED) analysis confirmed the formation of γ- and α-Al₂O₃ phases in the samples.     

Effect of the starting materials on the reaction synthesis of Ti3SiC2

Ternary carbide of titanium and silicon was produced via mechanical milling and following heat treatment. Effects of the starting materials, milling time and heat treatment temperature were studied. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were utilized to evaluate the structural and morphological evolutions of the ball-milled and annealed powders. Results showed that the ball milling of TiO–Si–C as the starting materials failed to synthesize Ti₃SiC₂. Additionally, ball milling the elemental powders for shorter milling times resulted in the activation of the powders. However, after longer milling times, Ti–TiC nanocomposite was obtained. Furthermore, during annealing the milled powders, Ti₃SiC₂–TiC nanocomposite with the mean grain size of 16 nm was synthesized. After 20 h of milling, a very fine microstructure with narrow size of distribution and spheroid particles was achieved.     

Glycothermal process for barium magnesium tantalate nanopowders synthesis

Barium magnesium tantalate Ba(Mg_1/3Ta_2/3)O₃ (BMT) nanopowders were synthesized at a low temperature of 220 °C through glycothermal reaction by using Ba(OH)₂·8H₂O, Mg(NO₃)·6H₂O, and TaCl₅ as precursors and 1,4-butanediol as solvent. It is demonstrated that higher synthesis temperatures and co-precipitation of magnesium and tantalum improve the incorporation of magnesium into BMT nanopowders under glycothermal treatment and produce a homogeneous, stoichiometric powder. The glycothermally derived BMT nanopowders are very reactive and provide a high-density sintered body with 97.1% of theoretical density at a low temperature of 1350 °C. The average grain size of the sintered ceramics was 1.2 ± 0.2 μm and relatively uniform in comparison with the ceramics sintered with powders produced from the conventional method.     

X-ray investigation of sintered cadmium doped hydroxyapatites

Pure and cadmium (Cd) doped hydroxyapatites (HA, Ca₁₀(PO₄)₆(OH)₂) were synthesized by a precipitation method from aqueous solutions of Ca(NO₃)₂4·H₂O for the former and Cd(NO₃)₂4·H₂O for the latter, by using (NH₄)₂HPO₄ as the phosphate source, while pH was kept in the range of 11–12. The effect of incorporation of Cd²⁺ ions into the structure of HA was investigated after the air sintering at 1100 °C for 1 h. The results indicate that Cd²⁺ addition into HA yields nearly fully densified products with respect to pure stoichiometric HA. The XRD patterns showed that Cd doping increases the crystallinity of HA. The 2, 4.4, and 8.8 mol% Cd doped HAs had calcium oxide (CaO) impurity phase in their lattice. The CaO phase in the HA structure gradually disappeared with increasing Cd amount, and was replaced with cadmium oxide (CdO) in the CdHA doped with 11 mol% Cd. Cd²⁺ ion incorporation decreased the a- and c-axis lattice constants and unit cell volume of HA.     

Pyrolysis synthesis of Si–B–C–N ceramics and their thermal stability

Si–B–C–N ceramics were synthesized by co-pyrolyzing hybrid polymeric precursors of polycarbosilane (PCS) and polyborazine (PBN). The pyrolysis behavior and structural evolution of the hybrid precursor, the microstructure and composition of the prepared Si–B–C–N ceramics were fully investigated. It was found that the copyrolysis of hybrid polymeric precursors in Ar led to the release of CH₄, CH₃NH₂ and CH₃CN gases at temperatures ranging from 200 to 1100 °C, and finally resulted in the formation of amorphous Si–B–C–N ceramics. In particular, the Si–B–C–N ceramics formed from the hybrid precursor with PBN/PCS mass ratio of 1 could keep amorphous state up to the annealing temperature of 1800 °C with weight change of only 2.08%. But this amorphous ceramics would decompose to form crystalline SiC, BN and Si₃N₄ at 2000 °C. Additionally, compared with PCS-derived SiC ceramics, the Si–B–C–N ceramics showed improved anti-oxidation performance up to 1300 °C due to the formation of borosilicate layers covering the ceramics.     

A novel polyborosilazane for high-temperature amorphous Si–B–N–C ceramic fibres

Polyborosilazane synthesised from BCl₃, HMeSiCl₂, and Me₃SiNHSiMe₃ is easy to cross-link for dehydrogenation of Si–H and N–H, which limits its practical applications for Si–B–N–C fibres on an industrial scale. Therefore, in this context, MeSiCl₃ was used instead of HMeSiCl₂ to synthesise a novel polyborosilazane with limited cross-linking density to fabricate Si–B–N–C fibres. The polyborosilazane synthesised from BCl₃, MeSiCl₃, and Me₃SiNHSiMe₃ exhibits good melt-processability and 1 km long polyborosilazane fibre can be obtained by melt spinning. Prior to pyrolysis, chemical curing with vapour HSiCl₃ at 80 °C was utilised to make the λ green fibres infusible. The as-cured fibres were subsequently pyrolyzed at 1200 °C in nitrogen atmospheres to provide Si–B–N–C ceramic fibres with ca. 1.5 GPa in tensile strength, ca. 160 GPa in Young's modulus, ca. 12 μm in diameter and keeping amorphous up to 1700 °C, which makes them to be promising reinforcements in ceramic matrix composites for high temperature applications.     

Carbothermal reduction–nitridation of titania-bearing blast furnace slag

The synthesis of (Ca,Mg)α′-Sialon ((Ca,Mg)_xSi_12−3xAl_3xO_xN_16−x) powders using titania-bearing blast furnace slag as a starting material by carbothermal reduction–nitridation (CRN) was reported for the first time. The reaction processes were greatly affected by initial material and reaction parameters. With the compositions shifting range from x = 0.3 up to 2.0, the amount of (Ca,Mg)α′-Sialon, TiN and AlN, the solid solubility of Ca²⁺ and Mg²⁺, the unit cell parameters of the (Ca,Mg)α′-Sialon and the amount of elongated α′-Sialon grains increased, but β′-Sialon and SiC decreased. With the increase of synthesis temperature and holding time, the formation of (Ca,Mg)α′-Sialon in the products increased and the CRN reactions accelerated. The optimum synthesis conditions of (Ca,Mg)α′-Sialon were 1480 °C for 8 h, under which the crystalline phases of the products also included AlN, TiN and a small amount of SiC and β-CaSiO₃. The volatilization of SiO resulted in a mass loss of samples, which was enhanced with the increase of synthesis temperature and holding time.