Processing and properties of transparent hydroxyapatite and β tricalcium phosphate obtained by HIP process

Stoichiometric β-tricalcium phosphate (β-TCP) and hydroxyapatite (HA) powders were synthesized by chemical precipitation of aqueous solutions of diammonium phosphate and calcium nitrate. After a calcination treatment and a milling step, the powders were shaped by slip casting. The sintering temperature effect on the relative density and the average grain size was investigated. By natural sintering at 1200 and 1120 °C, densities of 98% and 99% were obtained for HA and TCP, respectively. After determination of minimum temperatures to obtain only closed porosity and a pre-sintering at these temperatures, hot isostatic pressing (HIP) treatment was carried out. Transparent or translucent samples were obtained, indicating a relative density very close to the theoretical value (>99.9%). Mechanical properties (three-point bending strength, fracture toughness, Young's modulus and Vickers hardness) were measured on both materials with similar grain size (～ 1 μm). Bending strengths of 181 and 105 MPa were measured for TCP and HA, respectively.     

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.     

Corrosion behaviour of silicon carbide–diamond composite materials in aqueous solutions

The corrosion behaviour of the relatively new silicon carbide bonded diamond materials (ScD) was investigated in NaOH, H₂SO₄ and hydrothermal conditions and compared with that of conventional SSiC and SiSiC-materials. The corrosion resistance increases with decreasing diamond grain size. In H₂SO₄ all investigated materials show a very high corrosion resistance, whereas in NaOH and under hydrothermal conditions above 100 °C some leaching of residual silicon takes place. Nevertheless the fine grained ScD material exhibits a residual strength of 400 MPa after 200 h corrosion in NaOH at 90 °C. Under the same conditions the strength of the SiSiC-material reduces to 50 MPa. The silicon carbide-diamond composites demonstrate corrosion resistance superior to SiSiC and wear properties analogous to that of conventional superhard materials. This material would therefore be suitable for use in demanding corrosive wear applications.     

Adsorption of γ -UPS silane onto E-glass fibers from aqueous solutions

The deposition of γ-ureidopropyltrimethoxysilane (γ-UPS) from aqueous solutions onto plasma-treated E-glass fibers was investigated over a wide range of concentrations and pH values. At low concentrations for all the deposition pHs chosen, the silane was shown to form a surface consisting of silanols. At high concentrations, the silane was shown to form a different surface, consisting of condensed Si–O–Si groups. The ureidosilane thus produced a hydrophobic surface at high concentrations. Osterholtz and Pohl demonstrated that condensation of γ-APTES (γ-aminopropyltriethoxysilane) increased rapidly between pH 6 and 7, and that the hydrolysis was slow. This pH range corresponds to the most extensive adsorption of γ-UPS onto the E-glass surface, as judged from water contact angle, mass loss, and SEM results. The silane was deposited as patches onto the E-glass fibers. At the higher solution concentrations, an outer surface or 'skin' was formed over these patches, giving the appearance of completely siloxane polymer-coated fibers. The structure under the outer surface was open and porous.     

Synthesis,characterization and controlled release behaviour of adducts from chloroacetylated cellulose and α-naphthylacetic acid

Celluloses partially functionalized with chloroacetate groups were obtained by reaction of cellulose with chloroacetyl chloride using pyridine as catalyst and the dimethylacetamide/LiCl system as solvent. ¹³C NMR spectra at 75.4 MHz of partially modified cellulose with chloroacetate groups were studied in order to evaluate the selectivity of the reaction of cellulose with chloroacetyl chloride in the homogeneous phase. Analysis of the spectra of ring carbons in the anhydroglucose units shows that the reactivity of the individual hydroxyl groups decreases in the order C-6>C-3>C-2. The coupling of α-naphthylacetic acid to cellulose functionalized with chloroacetate groups was carried out by reaction with their potassium salts or directly in the presence of 1.8-diazabicyclo[5.4.0]-7-undecene. High degrees of modification were obtained by both methods. However, the esterification reaction is somewhat more efficient in the case of the potassium salt. The kinetic results were consistent with a second-order reaction. The hydrolysis in the heterogeneous phase of cellulose–α-naphthylacetic acid adducts showed that the release of the bioactive compound is dependent on the hydrophilic character of the adduct as well as on the pH value of the medium.     

Porous organic and carbon xerogels derived from alkaline aqueous phenol–formaldehyde solutions

Porous carbons were synthesized from the low cost precursors phenol and formaldehyde in aqueous solution, catalysed with NaOH. The xerogels were ambient pressure dried without prior solvent exchange. For an excess of formaldehyde, the resulting carbon xerogels show porosities up to 90%, with a predominant fraction of macroporosity, specific surface areas up to 768?m²/g and mesopore volumes up to 0.59?cm³/g. Small-angle X-ray scattering reveals fractal behaviour for many samples. Relevant sodium impurities up to 3?C4?wt% in the organic and carbon samples cannot be avoided, even by washing of the samples. As possible reason for the high sodium content, the formation of crown ether like calix [6] arene is assumed. Overall, the sodium impurities detected confine the use of this system to applications, where higher ash contents are uncritical.     

Morphologies and thermal properties of flame-retardant polystyrene/α-zirconium phosphate nanocomposites

The phosphorus- and nitrogen-containing monomer, acryloxyethyl phenoxy phosphorodiethyl amidate (AEPPA), was synthesized and characterized. Poly(St-co-AEPPA)/α-zirconium phosphate (α-ZrP) nanocomposites with different amounts of α-ZrP were then prepared by in situ radical bulk copolymerization. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results showed that the α-ZrP layers were exfoliated in the polymer matrix. Improvements in thermal stability and char residues of the copolymer and nanocomposites were observed by thermogravimetric analysis (TGA). The incorporation of AEPPA can reduce the flammability of polystyrene (PS). Moreover, further reductions were observed when α-ZrP was added. The reduction in flammability was attributed to a lower maximum mass loss rate and more char residues of the nanocomposites involved in thermal degradation.     

Removal of chromium (Ⅵ) from aqueous solutions using quaternized chitosan microspheres

In this study, quaternized chitosan microspheres(QCMS) were prepared and its Cr(VI) removal potential was investigated. Batch experiments were conducted to examine kinetics, adsorption isotherm, p H effect,and thermodynamic parameters. Equilibrium was attained within 50 min and maximum removal of 97.34%was achieved under the optimum conditions at p H 5. Adsorption data for Cr(VI) uptake by the QCMS were analyzed according to Langmuir, Freundlich, and Temkin adsorption models. The maximum uptake of Cr(VI)was 39.1 mg·g~(-1). Thermodynamic parameters for the adsorption system were determinated at 293 K, 303 K,313 K and 323 K.(ΔH° = 16.08 k J·mol~(-1);ΔG° =- 5.84 to- 8.08 k J·mol~(-1)and ΔS° = 74.81 J·K~(-1)·mol~(-1)).So the positive values of both ΔH° and ΔS° suggest an endothermic reaction and increase in randomness at the solid–liquid interface during the adsorption. ΔG° values obtained were negative indicating a spontaneous adsorption process. The kinetic process was described by a pseudo-second-order rate equation very well. The results of the present study indicated that the QCMS could be considered as a potential adsorbent for Cr(VI) in aqueous solutions.     

Effect of pH on separation of Pb (II) and NO3− from aqueous solutions using electrodialysis

Pb²⁺ and NO₃^? are major water pollutants with severe environmental effects. Several methods were used for treating them, but most of the intended solutions failed to treat these ions simultaneously. Electrodialysis (ED) may be able to treat them, particularly after the recent progress in membrane manufacture that has led to significant improvements in the performance. In this paper, we investigated the effect of pH on ED separation of Pb²⁺ and NO₃^? in terms of concentration ratio (CR), concentration polarization (i_lim), current efficiency (η), and energy consumption (EC). The results showed that, pH between 3 and 5 was the most effective for removal of these ions. Additionally, the distribution of ions among the charged sites on the membrane surfaces was governed by pH. At low electric potentials (< 10 V), ion exchange/adsorption was the prevalent phenomenon occurring on the membrane surfaces, while at voltages over 25 V the membranes were regenerated. Consequently, cation and anion exchange membranes could be used for water treatment at low voltages, then regenerated at higher voltages.     

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.     

Adsorption of thiourea at the polycrystalline silver electrode from aqueous KF solutions—I

Differential capacity of polycrystalline silver electrode in aqueous KF solutions containing thiourea (TU) of concentrations from 0.001 to 0.25 mol dm⁻³ has been measured by the previously described potentiostatic method [M. Brzowstowska-Smolska et al., J. electroanal. Chem.89, 389 (1978)]. The TU adsorption is discussed on the basis of differential capacity results and the potential shift caused by TU concentration changes. Furthermore, the surface pressure has been obtained by integration of the ΔE_σM vs σ_M curves for a number of TU concentrations.     

Fracture behaviour of magnesia and magnesia–spinel composites before and after thermal shock

Microstructural changes, as a consequence of the thermal expansion mismatch between magnesia and spinel phases, and fracture behaviour of magnesia and spinel composites have been investigated as a function of spinel content (10, 20, 30 wt.%). Fracture surfaces of magnesia showed mostly transgranular fracture; for the composites, however, the amount of intergranular fracture increased with increasing spinel content. This change in fracture behaviour is thought to be the main reason for the increase in the work of fracture, γ_WOF. The 30% spinel composite was found to exhibit both the greatest resistance to crack propagation, and the greatest resistance to thermal shock damage, with the highest retained strength after quenching.     

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.     

Location of Mn in MnAPO‐11: influence of synthesis from aqueous and non‐aqueous media

MnAPO11 samples were synthesized from aqueous (MnAPO11(A)) and ethylene glycol (MnAPO11(NA)) media. The crystallinity of the samples was more when the synthesis was carried out in ethylene glycol. Chemical and thermogravimetric analyses reveal greater incorporation of Mn in the framework of MnAPO11(NA) than in MnAPO11(A). At least five different types of Mn(II) species are detected in the samples by ESR. The studies suggest that Mn is more homogeneously distributed in MnAPO11(NA) than in MnAPO11(A).     

Application of ZnO–NiO greenly synthesized nanocomposite adsorbent on the elimination of organic dye from aqueous solutions: Kinetics and equilibrium

Organic dyes are discharged into aquatic systems from several industries causing severe environmental problems and toxicity to aquatic life. Therefore, it should be removed from water with a suitable process. Among several treatment processes, adsorption is one of the most attractive because of its simplicity, efficiency, and low operating cost. Moreover, adsorption supports environmental sustainability if a suitable adsorbent is used. In this work, a green route was followed to prepare ZnO: NiO nanocomposites using the Neem leaf extract as a stabilizing agent instead of harmful chemicals. Four different samples with three different ZnO:NiO ratios were prepared, namely: 3Z:1 N, 1Z:1 N, 1Z:3 N and 1Z:1 N without extract. The samples were characterized by XRD, TEM, SEM, IR, and UV, which all confirmed the successful synthesis of the nanocomposites. The nanocomposites were used for the adsorption of methyl orange (MO) from aqueous solutions. The four nanocomposites prepared with the aid of the extract showed a high sensitivity with 100% removal of MO from 6.25 ppm solutions. Furthermore, all the samples have a relatively fast kinetic with an equilibrium time less than 1 h. Also, the three samples maintained 100% removal efficiency after 5 adsorption-desorption cycles. The difference in particle size distribution obtained for the 1Z:1 N prepared with and without the extract confirms the important rule of the extract as a capping agent with an average size of 18 nm for the sample with the extract and 88 nm for the sample prepared without the extract. This difference in the particle sizes has been reflected on the adsorption performance of the two samples with a maximum adsorption capacity of 33 mg/g for the sample prepared with the extract compared to 6 mg/g for the sample without the extract.     

High-temperature mechanical and thermal properties of Ca1−xSrxZrO3 solid solutions

Perovskite oxides are promising thermal barrier coatings (TBCs) materials but their thermophysical properties still need to be further improved before commercial applications. In this work, mechanical/thermal properties of calcium-strontium zirconate solid solutions (Ca_1−xSr_xZrO₃) are investigated. Comparing to the end-compounds CaZrO₃ and SrZrO₃, the solid solutions achieve the enhanced thermal expansion coefficient, decreased thermal conductivity as well as good high-temperature mechanical properties. The experimental thermal conductivities of Ca_1−xSr_xZrO₃ (x = 0.2, 0.4, 0.6, 0.8) are in the range of 1.76-1.94 W·(m·K)⁻¹ at 1073 K, being lower than that of the yttria-stabilized zirconia (YSZ). At the same time, their thermal expansion coefficients (10.75 × 10⁻⁶-11.23 × 10⁻⁶/K at 1473 K) are comparable to that of YSZ. Moreover, the Young's moduli of Ca_0.8Sr_0.2ZrO₃, Ca_0.6Sr_0.4ZrO₃, Ca_0.4Sr_0.6ZrO₃, and Ca_0.2Sr_0.8ZrO₃ at 1473 K are 70.7%, 69.4%, 68.8%, and 71.1% of the corresponding values at room temperature, respectively. The good high-temperature mechanical and thermal properties ensure the potential applications of Ca_1−xSr_xZrO₃ solid solutions as high-temperature thermal insulation materials including TBCs.     

An erbium–organic framework as an adsorbent for the fast and selective adsorption of methylene blue from aqueous solutions

The applicability of erbium–metal–organic framework (Er-MOF) in the adsorption and removal of methylene blue from aqueous solution has been studied. Er-MOF was synthesized by hydrothermal method and characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray powder diffraction. The high thermal stability, water stability and accessible nano-sized aperture for the Er-MOF could endow it with a very high potential in adsorption of dye pollutant. The adsorption isotherm, kinetic and thermodynamic investigations confirm that the adsorption behavior is based on Langmuir isotherm with an exothermic mechanism and enthalpy-driven process. The speed adsorption process (30 min), low cost, high efficiency, big surface area, selectivity and very high and rapid reusability are the main advantages of the proposed compound as a sorbent.