Sintering and mechanical properties of tricalcium phosphate–fluorapatite composites

Tricalcium phosphate and synthesized fluorapatite powder were mixed in order to elaborate biphasic ceramics composites. The effect of fluorapatite addition on the densification and the mechanical properties of tricalcium phosphate were measured with the change in composition and microstructure of the bioceramic. The Brazilian test was used to measure the mechanical resistance of the tricalcium phosphate–26.52 wt% fluorapatite composites. The densification and rupture strength increase versus sintering temperature. The composites have a good sinterability and rupture strength in temperature ranging between 1300 and 1400 °C. Thus, the densification ultimate was obtained at 1350 °C and the mechanical resistance optimum reached 9.6 MPa at 1400 °C. Above 1400 °C, the densification and the mechanical properties were hindered by the allotropic transformation of tricalcium phosphate, grain growth and the formation of both intragranular porosity and many cracks. The ³¹P magic angle spinning nuclear magnetic resonance analysis of composites reveals the presence of tetrahedral P sites.     

Synthesis and thermal behaviour of β tricalcium phosphate precipitated from aqueous solutions

Abstract

In the present study, β tricalcium phosphate (β-TCP) was prepared by precipitation from aqueous solutions. Calcium nitrate tetrahydrate Ca(NO₃)₂.4H₂O and diammonium hydrogen phosphate (NH₄)₂HPO₄ salts with an initial Ca/P molar ratio of 1·5 were dissolved in distilled water and mixed at 20°C and pH 10. Phase evolution of the as received precipitate was studied by X-ray diffraction and infrared spectroscopy before and after calcination in a dry air atmosphere at temperatures in the range 200-1400°C for 1 h. Thermal behaviour was investigated by simultaneous thermal analysis (DTA-TG). Calcium and phosphorus contents of the as received precipitate were determined by the inductively coupled plasma technique, and a Ca/P molar ratio of 1·49 ± 0·01 was found. The densities of the as received precipitate and of powder calcined at 800°C were determined by picnometery to be 2·43 and 3·01 ± 0·05 g cm^-3 respectively. The experimental data suggest the formation of an amorphous phase corresponding to a TCP-like composition, which is calcium deficient and contains a very small amount of HPO₄^2- groups.     

Synthesis and properties of Zn and Zn–Mg-doped tricalcium phosphates obtained by Spark Plasma Sintering

β-tricalcium phosphate (Ca₃(PO₄)₂ or TCP) are essential biomaterials because of the chemical composition, high biocompatibility and osseointegration. However, their limited mechanical properties restrict their use to areas where high mechanical performances are not required. Spark Plasma Sintering (SPS) was selected out of the unconventional sintering methods in order to obtain high-density doped-TCP bioceramic materials. The main advantages of SPS are a high heating rate, low sintering temperatures and short residence times, producing bioceramics with full density and fine-grain microstructure. The main purpose was to design, obtain by SPS and characterize undoped β-TCP, 1ZnO-doped β-TCP and 1ZnO-1MgO codoped β-TCP (wt. %) bioceramics. All the obtained samples were visually semitransparent and mainly β-TCP was detected by X-ray analysis. Densification behavior was determined by Archimedes' method and microstructural features of the sintered specimens were analyzed by Field Emission Scanning Electron Microscopy (FE-SEM-EDX). The undoped and doped β-TCP bioceramics were mechanically characterized, specifically the modulus of elasticity and Vickers microhardness. The results are compared with equivalent samples obtained by conventional solid-state sintering (CS) reaction. A first study of biological behavior was carried out, specifically direct cell adhesion of MG-63 human osteoblast-like cells on the polished surfaces of β-TCP, 1ZnO-β-TCP and 1ZnO–1MgO-β-TCP dense samples were determined. The present study concludes that the SPS process together with the doping effect enhanced sinterability, mechanical and biological properties of Zn-TCP and Zn–Mg-TCP based materials.     

Processing and mechanical properties of hydroxyapatite–polysulfone laminated composites

Designing biocomposites that mimic bone with specific mechanical properties of toughness and elastic modulus is a long-standing challenge in the biomaterials field. Traditional biocomposites comprise polymer matrices reinforced with ceramic particles. Laminated composites are structures also found in nature that can offer improved mechanical properties such as strength, elastic modulus and toughness. Hydroxyapatite/polysulfone laminated composites were fabricated to develop biologically compatible, toughened composites that would match the elastic modulus of bone. Multilayered composites were successfully designed with improved toughness measured by the work of fracture. Toughness measurements were more than an order of magnitude greater than monolithic hydroxyapatite. The toughness and modulus values of hydroxyapatite/polysulfone were within the range of cortical bone.     

Fabrication of interconnected porous calcium-deficient hydroxyapatite using the setting reaction of α tricalcium phosphate spherical granules

Interconnected porous calcium-deficient hydroxyapatite (cdHAp) blocks may be an ideal biomaterial to repair bone defects because of their greater similarity to human bone than that of sintered hydroxyapatite (HAp) with respect to calcium content and crystallinity. In particular, the interconnected pores in cdHAp may provide pathways for cell migration and tissue ingrowth. In this study, the feasibility of fabricating interconnected porous cdHAp blocks through the setting reaction of alpha-tricalcium phosphate (αTCP) spherical granules was investigated. It was found that regulation of cdHAp formation was important to fabricate interconnected porous cdHAp blocks. That is, cdHAp needed to precipitate preferentially at the contacting areas between αTCP spherical granules. Exposure of αTCP spherical granules to steam under appropriate pressure was effective for this purpose. When αTCP spherical granules were immersed in water at 100 °C, the setting reaction resulted in dense cdHAp blocks because of the free crystal growth of cdHAp in water. Therefore, steam was used to localize the water at the contacting areas between αTCP spherical granules, which was driven by the surface tension of the water. Without an applied load, no setting reaction was observed when αTCP spherical granules were exposed to steam at 100 °C for 12 h. In contrast, under a load of 20 MPa, cdHAp precipitated to bridge spherical granules, providing an interconnected porous cdHAp block. The porosity and diametral tensile strength of this block were approximately 63% and 1.5 MPa, respectively.     

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.     

Preparation of transparent ultrahydrophobic silica film by sol�Cgel process

Transparent ultrahydrophobic films were synthesized by sol–gel process with organic silicones modified into silica sol and cured under UV irradiation. The effects of hydrolysis temperature, hydrolysis time, molar ratio of organic silicone to silica sol, and surface morphology on the hydrophobicity of the films were discussed in detail using FTIR spectroscopy, scanning electron microscopy (SEM), AFM, optical transmission, and contact angle measurement, respectively. The AFM and SEM images indicated that the surface roughness enhanced the hydrophobicity of the films. The results revealed that methyl-trimethoxysilane (MTMS)-modified silica film prepared at 50°C for 2 h with an MTMS/silica sol molar ratio of 1:10 had a very high contact angle (130°). However, the higher hydrolysis temperature and longer reaction time might have accelerated the self-condensation of silanol and decreased the contact angle of the films.     

Microstructural and electrical properties of AlN–CoCrFeMnNi cermet obtained by hot pressing

AlN and equimolar ratio of gas atomized CoCrFeMnNi HEA powders were used to prepare AlN–CoCrFeMnNi cermets by ball milling followed by hot pressing sintering at 1240 °C for 2 h. The microstructure characteristics and electrical properties of the cermets were investigated. The sintered cermet bulks were composed of a FCC-structured CoCrFeMnNi solid solution binder phase, AlN phase, and a small amount of Cr₇C₃ type carbide. No obvious interfacial reaction occurred between AlN and CoCrFeMnNi HEA. The resistivity of AlN–CoCrFeMnNi cermets nonlinearly increased with increasing AlN content and temperature. A conductivity model of AlN–CoCrFeMnNi cermets at room temperature and 600 ^oC was established based on the generalized effective medium (GEM) equation. Results indicated that AlN–CoCrFeMnNi cermets had a typical percolation threshold phenomenon, which allowed to continuously regulate their resistivity between 10² μΩ cm to 10³ μΩ cm as AlN was in the range of 10–50 wt% under room temperature. Therefore, the AlN–CoCrFeMnNi cermets are promising materials for applications in the e-cigarette field.     

Microstructural,electrophysical and gas-sensing properties of CeO2–Y2O3 thin films obtained by the sol-gel process

Nanopowders and thin films of (СeO₂)_1-x(Y₂O₃)_x composition (x = 0.10, 0.15 and 0.20) were obtained by the sol-gel process, using hydrolytically active complexes of the metal alkoxoacetylacetonate class [M(C₅H₇O₂)_3-y(C₅H₁₁Oⁱ)_y] (M = Ce³⁺ and Y³⁺) as precursors. The impact of the chemical composition and crystallization conditions on the microstructure, electrophysical and chemosensory characteristics of the obtained planar-type solid electrolytes was studied. The prospects of the thin-film nanostructures obtained as receptor components of resistive oxygen sensors, as well as of electrolytes of planar-type intermediate-temperature solid oxide fuel cells (SOFC) have been shown. It has been found that (CeO₂)_0.90(Y₂O₃)_0.10 thin films demonstrate the maximum values of electrical conductivity (550 °C) and the highest sensory response when detecting oxygen (concentration range 1–20%, operating temperature range 300–450 °C).     

Fabrication and dielectric properties of transparent PZN–BT ceramic

Transparent ceramic of 0.85Pb(Mg_1/3Nb_2/3)O₃–0.15BaTiO₃ has been successfully prepared by a two-stage sintering method using conventional raw materials. The ceramics exhibited an excellent crystallinity, high density and clean grain boundary. The transmittance keeps about4 0% from visible to near infrared regions. The frequency dependence of T_m and relaxor behavior has also been investigated using Vogel–Fulcher model and Power model.     

Synthesis and characterization of hydroxyapatite/β-tricalcium phosphate nanocomposites using microwave irradiation

Microwave assisted synthesis method is a relatively new approach employed to decrease synthesis time and form a more homogenous structure in biphasic calcium phosphate bioceramics. In this study, nanocrystalline HA/β-TCP composites were prepared by microwave assisted synthesis method and, for comparison reason, by conventional wet chemical methods. The chemical and phase composition, morphology and particle size of powders were characterized by FTIR, XRD and SEM, respectively. The use of microwave irradiation resulted in improved crystallinity. The amount of hydroxyapatite phase in BCP ranged from 5% to 17%. The assessment of bioactivity was done by soaking of powder compacts in simulated body fluid (SBF). The decreasing pH of the solution in the presence of β-TCP indicated its biodegradable behavior. Rod-like hydroxyapatite particles were newly formed during the treatment in SBF for microwave assisted substrate synthesis. In contrast, globular particles precipitate under same conditions if BCP substrates were synthesized using conventional wet chemical methods.     

Preparation and luminescent properties of Eu-doped transparent mica glass–ceramics

Eu-doped transparent mica glass–ceramics were prepared, the influence of Eu-doping on the crystallization of the parent glasses was investigated and the luminescent properties of the parent glasses and the glass–ceramics were estimated. A small additive amount of Eu element was very effective in preparing transparent mica glass–ceramics. However, the excess addition led to the coarsening of phase separation in the glass phase and the separation of unidentified crystal phases and β-eucryptite during heating of the parent glasses, which caused white opaque at lower heating temperatures. When mica crystals were separated, Eu ions entered the interlayers of mica crystals. The observed emission and excitation spectra showed that parts of Eu³⁺ ions which were added as Eu₂O₃ were reduced to Eu²⁺ ions during melting of the starting materials and heating the parent glasses in air and the energy transfer from Eu²⁺ to Eu³⁺ ions occurred.     

Preparation，properties and applications of hydroxyapatite/synthetic polymer composites

随着生物医用材料的需求量日趋增大,磷灰石与人工合成高分子的复合材料成为组织修复和替代材料的研究热点。以不同单体分类,综述了磷灰石与合成的非降解高分子、可降解高分子复合材料的研究进展;对羟基磷灰石/合成高分子复合材料的制备方法、性能及其应用等方面进行研究,并对此复合材料存在的问题和发展前景进行讨论。说明从分子水平设计出具有良好力学性能、生物活性和生物相容性的医学材料,具有十分重要的意义。     

Physicochemical and catalytic properties of iron‐promoted Raney‐nickel catalysts obtained by mechanical alloying

Raney‐type catalysts were prepared by means of a two‐step procedure: (i) mechanical alloying of the metals and (ii) alkaline aluminum leaching. Mechanical alloying is a novel alternative related to the synthesis of skeletal Ni catalysts. Catalysts characterization was performed by atomic absorption, X‐ray diffraction, electron microscopy, and Mössbauer spectroscopies. Textural studies were also carried out. Binary Al–Ni and ternary Al–Ni–Fe alloys were produced by mechanical alloying from pure metallic powders; in particular, the intermetallic α‐(AlNi) phase was formed with a fine microstructure as a non‐equilibrium phase; then, aluminum was selectively removed. After aluminum leaching the α‐(AlNi) phase was transformed into the more stable nickel fcc structure. The effect of iron addition to the Ni–Al catalysts depends on iron concentration and reduction temperature; both parameters determine catalysts composition and activity. This work reports physicochemical properties and benzene hydrogenation activity of these materials, compared with conventional catalysts obtained by melting and leaching.     

Microstructure and property of porous mullites with a whiskers framework obtained by a sol–gel process

Porous mullites with a whiskers framework and high porosities were fabricated by the reaction sintering (1100 to 1600 °C, 1 h, in an airtight container) of an aerogel block shaped by the sol–gel transition of a mullite precursor composed of SiO₂ sol, Al₂O₃ and AlF₃ powders (as reaction catalyst). The effect of heating temperatures on porosity, whisker formation, microstructure feature and compressive strength of the porous mullites was determined by XRD, SEM and compressive test. The results indicate that after heating at temperatures from 1100 to 1600 °C, the porosities of the mullites varied within the range of 84.1–80.2%. The whiskers in the framework well lap-jointed each other to form the large space and became elongated and smooth at high temperatures due to the accelerated vapor–solid reaction rate. A maximum compressive strength of 16.1 MPa was obtained for the whiskers framework heated at 1600 °C; this strength was attributed to the strong bonding among the smooth whiskers.     

Surface properties and moisture behaviour of pine and heat-treated spruce modified with alkoxysilanes by sol–gel process

The surface morphology and moisture behaviour of pine (Pinus sylvestris) sapwood and heat-treated spruce (Picea abies) deposited with two types of silane-based sol–gel coatings were studied by atomic force microscopy (AFM) and water contact angle measurement. The chemical composition and distribution of sol–gel coatings on wood surfaces were investigated by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The AFM images revealed that the sol–gel coatings applied by spreading covered the fine structure of the wood substrates. The surface roughness analysis of the AFM topographical images indicated that the sol–gel coatings, especially the one with short aliphatic chain, had a tendency to smooth the wood surface. The XPS results confirmed that the sol–gel coatings had successfully deposited onto pine sapwood and heat-treated spruce changing their surface chemistries. ToF-SIMS images showing Si ion distribution on treated surfaces revealed that the coatings fully covered pine sapwood surfaces. The thin coating layers formed on heat-treated spruce surfaces followed the original wood surface structure. The contact angle measurements indicated that the water repellent properties of both pine and heat-treated spruce were improved to certain extent by the sol–gel coatings.     

The hydrolysis process of γ-AlON powder and preparation of highly transparent ceramics with aqueous gel-casting

The untreated γ-AlON powders were proposed to prepare highly transparent γ-AlON ceramics by aqueous gel-casting technique and two-step sintering process. The related mechanism of hydrolysis of γ-AlON powders was discussed. The surface of the synthesized γ-AlON powders is covered with a layer of aluminum hydroxides compound. As the period of hydrolysis extends, the surface layer dissolved, and the boehmite and bayerite gradually formed, which is characterized by various techniques including XRD, FT-IR, XPS and TEM. The low viscosity slurry with high solids loading (53 vol%) was obtained by γ-AlON powders without any surface modification treatments as a result of the slow hydrolysis process. In addition, compared with the dry pressed sample, the sample (4.12 mm in thickness) prepared by aqueous gel-casting exhibits superior in-line transmittance of 81–83% in the visible region, which could be ascribed to the more homogenous and denser microstructure of the green body. Finally, the Weibull modulus and characteristic strength of γ-AlON transparent ceramic were determined to be 4.85 and 295 MPa, respectively.     

Wear properties of α- and α/β-SiAlON ceramics obtained by gas pressure sintering and spark plasma sintering

In this study, α- and α/β-SiAlON materials, doped with Y₂O₃ and Nd₂O₃, were sintered using two different sintering processes: spark plasma sintering (SPS) and gas pressure sintering (GPS). The wear and mechanical properties of the samples were compared related to the composition, additives and sintering processes. The results show that the hardness was not affected by the processing type whereas the toughness values were lower for spark plasma sintered materials than gas pressure sintered materials. This can be explained by the changed microstructure of the two different types of material. Additionally, α/β-SiAlON materials, sintered using gas pressure sintering, showed a lower wear than the spark plasma sintered materials. The results of the wear test were compared with β-Si₃N₄ materials and it was observed that α/β-SiAlON, sintered by GPS, has better wear properties than the tested β-Si₃N₄ materials.     

Effect of TiN concentration on microstructure and properties of Ni/W–TiN composites obtained by pulse current electrodeposition

In this study, Ni/W–TiN composites were fabricated by the pulse current electrodeposition (PCE) method. The effects of TiN concentration on the microstructure, microhardness, and wear properties of the resulting composites were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), microhardness tester, and friction wear testing. Among the four obtained composites, Ni/W–TiN composite prepared at 8 g/L showed the densest and finest surface structure. The TiN contents in obtained Ni/W–TiN composites at 8 and 16 g/L were estimated to 8.1 and 5.4 wt%, respectively. The average Ni/W grain diameter in Ni/W–TiN composite obtained at 8 g/L TiN was recorded as 84.7 nm. The protrusion and depression heights of the composite deposited at 8 g/L were 81.8 and 45.4 nm, respectively. This composite also processed an average microhardness of 897.6 HV, with only a few shallow and narrow scratches on its worn surface, demonstrating its prominent wear resistance when compared to the other three composites.     

Processing and mechanical properties of hot-pressed zirconium diboride – zirconium carbide ceramics

ZrB₂ was mixed with 0.5 wt% carbon and up to 10 vol% ZrC and densified by hot-pressing at 2000 °C. All compositions were > 99.8% dense following hot-pressing. The dense ceramics contained 1–1.5 vol% less ZrC than the nominal ZrC addition and had between 0.5 and 1 vol% residual carbon. Grain sizes for the ZrB₂ phase decreased from 10.1 µm for 2.5 vol% ZrC to 4.2 µm for 10 vol% ZrC, while the ZrC cluster size increased from 1.3 µm to 2.2 µm over the same composition range. Elastic modulus was ~505 GPa and toughness was ~2.6 MPa·m^½ for all compositions. Vickers hardness increased from 14.1 to 15.3 GPa as ZrC increased from 2.5 to 10 vol%. Flexure strength increased from 395 MPa for 2.5 vol% ZrC to 615 MPa for 10 vol% ZrC. Griffith-type analysis suggests ZrB₂ grain pullout from machining as the strength limiting flaw for all compositions.