Ceramic–metal and ceramic–polymer composites prepared by a biomimetic process

A biomimetic process was developed to prepare apatite–metal and apatite–polymer composites. A variety of metals and organic polymers incorporated surface functional groups such as Si–OH, Ti–OH or Ta–OH to induce formation of a biologically active bonelike apatite by chemical treatment or physical adsorption. Subsequent immersion in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma or 1.5 SBF led to the formation of a dense and uniform bonelike apatite layer on the surface. Apatite–metal and apatite–polymer composites prepared in this way are believed to be very useful as artificial bone substitutes.     

Nanostructured SiC ceramics prepared by a new process—Crystallization of interfacial glass

Large bulk and fully dense SiC based nanoceramics with average grain size of 50 nm and 20–30 wt.% nanometer sized α-Sialon, Al_xSi_{3 − x}O₆ and α-SiO₂ interfacial phases were prepared by a new process, crystallization of interfacial glass, using LMAS glass-coated SiC powder as starting material. The process involves two major steps: densification by hot pressing, and crystallization of interfacial glass by annealing treatment. The densification was controlled by interfacial glass content, hot pressing temperature, and hot pressing pressure; density 99.8% theoretical being reached for SiC/30 wt. % glass nanoceramics hot-pressed at 1520 °C and 22 MPa for 30 min. The crystallization was complete and nearly all the interfacial glass was transformed into nanocrystalline phases after 800 °C and 900 °C for 5 h annealing treatments. Plastic flow and rearrangement of particles and interfacial glass infiltration are densification mechanisms. A large number of nanometer sized SiC powder particles serve as nucleating agents, e.g. hetero-nucleation, and are responsible for interfacial glass crystallization. A characteristic of the present process is that there is no SiC grain growth during densification and interfacial glass crystallization.     

Production and characterization of synthetic aragonite prepared from dolomite by eco-friendly leaching–carbonation process

Dolomite is an alternative material for producing precipitated calcium carbonate (PCC) particles, which have widespread industrial applications depending on their morphology and particle sizes. These properties are readily controlled by the production conditions such as reaction time, temperature, stirring speed, and CO₂ flow rate. In this paper, we investigate the influences of these experimental conditions on the production of synthetic aragonite crystals from dolomite using a leaching carbonation process. The proposed process is believed so be more eco-friendly than other methods suggested in the literature because the CO₂ released from the dolomite during the leaching stage is stored for use in the carbonation stage. The experimental results indicate that the morphology of the produced PCC is influenced not only by the reaction time and temperature, but also the stirring speed and CO₂ flow rate. The required reaction time decreases with an increase in the CO₂ flow rates. However, calcite forms along with the aragonite crystals at higher CO₂ flow rates. We successfully synthesized pure aragonite crystals in the reaction temperature range of 40–70 °C at a fixed CO₂ flow rate of 3.00 l/min, and at a stirring speed of 750 rpm. The d₉₀ values of the aragonite crystals at various temperatures ranged from 18.47 to 25.99 μm. We fit the experimental results by a single-term exponential model.Additionally, we obtained a Mg-rich solution and CO₂ gas as by-products, which are in high demand.     

Reciprocating wear resistance of Al–SiC nano-composite fabricated by accumulative roll bonding process

In this work the wear behaviour of Al–SiC nano-composite, produced by accumulative roll bonding process was characterized using a pin-on-flat wear-testing machine. Hence various tests such as micro-hardness and reciprocating wear test were carried out. Morphology of the worn surfaces of this nano-composite was examined using scanning electron microscope. Experimental results have been revealed that the wear resistance of this nano-composite increased by increasing the cycle number due to SiC particles act as a solid lubricant. Also by increasing the cycle’s number the size of SiC particle becomes less than 100 nm and nano-composite was formed.     

Bioresorbable and bioactive composite materials based on polylactide foams filled with and coated by Bioglass® particles for tissue engineering applications

Poly(DL-lactide) (PDLLA) foams and bioactive glass (Bioglass®) particles were used to form bioresorbable and bioactive composite scaffolds for applications in bone tissue engineering. A thermally induced phase separation process was applied to prepare highly porous PDLLA foams filled with 10 wt % Bioglass® particles. Stable and homogeneous layers of Bioglass® particles on the surface of the PDLLA/Bioglass® composite foams as well as infiltration of Bioglass® particles throughout the porous network were achieved using a slurry-dipping technique. The quality of the bioactive glass coatings was reproducible in terms of thickness and microstructure. In vitro studies in simulated body fluid (SBF) were performed to study the formation of hydroxyapatite (HA) on the surface of the PDLLA/Bioglass® composites, as an indication of the bioactivity of the materials. Formation of the HA layer after immersion in SBF was confirmed by X-ray diffraction and Raman spectroscopy measurements. The rate of HA formation in Bioglass®-coated samples was higher than that observed in non-coated samples. SEM analysis showed that the HA layer thickness rapidly increased with increasing time in SBF in the Bioglass®-coated samples. The high bioactivity of the developed composites suggests that the materials are attractive for use as bioactive, resorbable scaffolds in bone tissue engineering.     

A comparative study of Ni–Ti and Ni–Ti–Cu shape memory alloy processed by plasma melting and injection molding

Shape memory alloys (SMA) are smart materials that present potential applications in such diverse areas as aeronautics, automotive, electronics, biomedicine and others. This work aimed at comparing some physical and functional properties of a Ni–Ti–Cu and equiatomic Ni–Ti SMA. Therefore, Ni–50Ti and Ni–50Ti–5Cu (at.%) were manufactured using plasma melting followed by injection in metallic mold, named Plasma Skull Push–Pull (PSPP) process. Afterwards, samples of both Ni–Ti based SMA were annealed at 1113 K during 2400 s and water quenched. The obtained specimens were analyzed by optical microscopy, microhardness, differential scanning calorimetry, electrical resistance as a function of temperature, and force generation tests. The results showed that Ni–Ti alloy presented higher levels of hardness and lower generated recover forces during heating when compared to the Ni–Ti–Cu SMA. Moreover, the Ni–Ti alloy holds hysteresis larger than the Ni–Ti–Cu SMA as a result of the presence of the R-phase transformation. There was also a better stability under thermal cycling of NiTiCu SMA compared with the equiatomic NiTi.     

Comparison between the process–structure–property relationships of silica foams prepared through two different processing routes

Cellular silica with improved framework, crosslinking, and stability properties are desirable for applications in thermal insulation. A process for the preparation of cellular silica foam with interconnected cells with tailored porosity and pore size distribution has been attempted. The silica foams have been prepared through two different methods; surfactant- and particle-based stabilization. The silica foams prepared through two different processes namely surfactant-stabilized foams (SSF) and particle-stabilized foams (PSF) have exhibited a wide range of differences in their structure which in turn have shown to affect the final properties of the foam. The cell size distributions in SSF (89 vol% porosity) and PSF (85 vol% porosity) have been found in the range of 50–250 μm (monomodal) and 4–10 μm and 50–100 μm (bimodal), respectively, whereas the cell counts of both have been found in close proximity. The microstructure of both the sintered SSF as well as PSF samples foams have shown an open and interconnected porosity with the permeability of both in the region of ~10⁻⁸ m². The mechanical (compressive) strength and Young’s modulus of the PSF are a third of that in SSF. The structure–property relationship of both the SSF and PSF and their comparison have been discussed.     

Compressive behaviour of open cell Al–Al2O3 composite foams fabricated by sintering and dissolution process

Abstract

The sintering and dissolution process (SDP) was used to produce the fine open cell Al–Al₂O₃ composite and pure Al foams with the relative density of 0·25–0·40 and the pore size of 112–400 μm. The composite foam exhibited much higher yield strength and Young's modulus than the pure Al foam, and thus had an elevated plateau stress. Moreover, the composite foam showed a unique dependence of the compression stress on the pore size, i.e. it increased with increasing pore size, which was quite different from that for the common metal foams.     

Structural,morphological and optical properties of undoped and Co-doped ZnO thin films prepared by sol–gel process

Undoped and Co-doped ZnO thin films with different amounts of Co have been deposited onto glass substrates by sol–gel spin coating method. Zinc acetate dihydrate, cobalt acetate tetrahydrate, isopropanol and monoethanolamine (MEA) were used as a precursor, doping source, solvent and stabilizer, respectively. The molar ratio of MEA to metal ions was maintained at 1.0 and a concentration of metal ions is 0.6 mol L^?1. The Co dopant level was defined by the Co/(Co + Zn) ratio it varied from 0 to 7 % mol. The structure, morphology and optical properties of the thin films thus obtained were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDX), scanning electron microscopy (SEM), ultraviolet–visible (UV–Vis), photoluminescence (PL) and Raman. The XRD results showed that all films crystallized under hexagonal wurtzite structure and presented a preferential orientation along the c-axis with the maximum crystallite size was found is 23.5 nm for undoped film. The results of SEM indicate that the undoped ZnO thin film has smooth and uniform surface with small ZnO grains, and the doped ZnO films shows irregular fiber-like stripes and wrinkle network structure. The average transmittance of all films is about 72–97 % in the visible range and the band gap energy decreased from 3.28 to 3.02 eV with increase of Co concentration. DRX, EDX and optical transmission confirm the substitution of Co²⁺ for Zn²⁺ at the tetrahedral sites of ZnO. In addition to the vibrational modes from ZnO, the Raman spectra show prominent mode representative of Zn_yCo_3?yO₄ secondary phase at larger values of Co concentration. PL of the films showed a UV and defect related visible emissions like violet, blue and green, and indicated that cobalt doping resulted in red shifting of UV emission and the reduction in the UV and visible emissions intensity.     

Fine SrTiO3 and Sr(Mg0.4Ti0.6)O3–δperovskite ceramic powders prepared by a sol-precipitation process

Fine and Sr(Mg_0.4Ti_0.6)O_3– powders were prepared by a sol-precipitation method. Tetraisopropyl titanate was used as a starting material, which firstly chelated with the acetic acid to form a water-soluble titanyl precursor. This precursor was then precipitated in a strong NaOH solution, to which, a nitrate solution of the required ratio of was also added. By properly controlling reaction conditions, high crystalline undoped and Mg-doped strontium titanates with the dominating perovskite structures could be obtained directly at 80 °C. Owing to the chelating reaction of tetraisopropyl titanate with the acetic acid, the problem of the premature hydrolysis of titanium precursor was circumvented. The rates of the hydrolysis and condensation of titanyl acylate were also diminished. The final powder obtained had a uniform particle size of 40–60 nm. The formation mechanisms of and Sr(Mg_0.4Ti_0.6)O_3– were also discussed. This study indicated that in the entire sol-precipitation process, the mixing of cations was homogeneous and the diffusion of alkaline earth cations into titanium particles occurred all at atomic level, which allowed the realization of the optimized solid-solubility in the complex oxide system. This method could be exploited for the preparation of other doped titanates.     

Degradation behavior of novel Fe/ß-TCP composites produced by powder injection molding for cortical bone replacement

When it comes to bone replacement in load-bearing areas, there are currently no adequate biodegradable implants available. Several non-degradable metallic materials fulfill the requirements of biocompatibility and mechanical strength. However, besides magnesium, only iron is a degradable metallic material. The aim of this long-term degradation study was to investigate the effects of iron beta-tricalcium phosphate interpenetrating phase composite on degradation rate and strength in comparison to pure iron. Cylindrical samples with 0–50 vol% beta-tricalcium phosphate (ß-TCP) were prepared by powder injection molding. In addition to dense samples, porous iron samples with a porosity of 60.3 % were produced with polyoxymethylene as a placeholder. Dense and porous samples were immersed in 0.9 % sodium chloride solution (NaCl) or in phosphate buffered saline solution (PBS) for 56 days. Following immersion, the degradation rate, compressive yield strength, and ion release were determined. A maximum degradation rate of 196 µm/year was observed after 56 days for iron with 40 vol% ß-TCP. This was found to be 28 % higher than for pure iron. After immersion, the compressive yield strength of pure iron decreased by 44 % (NaCl) and 48 % (PBS). In comparison, iron with 40 % ß-TCP samples lost <1 % (NaCl) and 9 % (PBS) of strength following immersion. It was demonstrated that the solubility of calcium phosphate enhanced the corrosion processes and led to an increase in degradation, thus showing that the addition of ß-TCP to pure iron can be a promising route for a novel degradable bone substitute material, particularly for load-bearing areas due to the increased strength.     

Thermal stability and nonisothermal kinetics of Folnak® degradation process

Aim: The purpose of this article is to investigate the thermal stability and nonisothermal kinetics of Folnak® drug degradation process using different thermoanalytical techniques. Methods: The nonisothermal degradation of Folnak® powder samples was investigated by simultaneous thermogravimetry–differential thermal analysis, in the temperature range from ambient to 810°C. Results: It was found that the degradation proceeds through five reaction stages, which include the dehydration, the melting process of excipients, the decomposition of folic acid, corn starch, and saccharose. The presence of compounds such as excipients increases the thermal stability of the drug and some kind of solid–solid and/or solid–gas interaction occurs. Conclusion: It was concluded that the main degradation stage of Folnak® sample represents the decomposition of folic acid. It was established that the folic acid decomposition cannot be explained by simple reaction order model (n = 1) but with the complex reaction mechanism that includes higher reaction orders (n > 1). The isothermal predictions of the folic acid decomposition at four different temperatures (T_iso = 180°C, 200°C, 220°C, and 260°C) were established. It was concluded that the shapes of conversion curves at lower temperatures (180–200°C) were similar, whereas they became more complex with further temperature increase because of the complexity of the decomposition reaction.     

Characteristics of Eu-doped Ca-α-SiAlON phosphor powders prepared by spray pyrolysis process

Eu²⁺-doped Ca-α-SiAlON phosphor powders with fine size and regular morphology were prepared by combining spray pyrolysis and the carbothermal reduction and nitridation processes. The precursor powders were prepared by spray pyrolysis from the spray solution with ethylenediaminetetraacetic acid, citric acid, and sucrose; they had large sizes, were hollow, and had thin wall structures. The precursor powders containing a carbon component turned into Ca-α-SiAlON phosphor powders after firing at 1450 °C under a H₂/N₂ mixture gas. The mean size of the phosphor powders was 5.1 μm. The phosphor powders had a broad excitation spectra range of 250-500 nm; this consisted of two broadbands centered at 305 and 400 nm. When excited by a 455-nm blue light, the emission spectra of the phosphor powders displayed a broadband in the range of 500-700 nm, which resulted in a yellow emission. The wavelength of the emission spectrum showing the maximum intensity was 576 nm.     

Titanium diboride–nickel graded materials prepared by field-activated, pressure-assisted synthesis process

The formation of four-layered functionally graded material (FGM) samples of TiB₂–Ni/TiB₂–Ni₃A + Ni/Ni₃Al/Ni by field-activated, pressure-assisted synthesis process (FAPAS) was investigated. The microstructure, phase composition of the interfaces, and mechanical properties of the graded material were characterized. Elemental concentration profiles across interfaces between layers showed significant interdiffusion, indicative of formation of good bonds. The measured microhardness values of the sample increased monotonically from the nickel substrate to the surface layer (TiB₂–Ni). The values ranged from about 360 to over 3500 HK over a distance of 2 mm. The results of this investigation demonstrate the feasibility of the FAPAS process for rapid formation of FGMs with good diffusion bonds.     

Structural properties and visible emission of Eu3+-activated SiO2–ZnO–TiO2 powders prepared by a soft chemical process

In this work, the structural and optical properties of the 60SiO₂–20ZnO–20TiO₂ system (in mol%) doped with 1 mol% of Eu³⁺ were evaluated. Stable and transparent sols, homogeneous gels, and powders were prepared by a soft chemical process followed by annealing from 700 to 1100 °C. Visible emission was observed in the photoluminescence (PL) spectra from 570 to 700 nm owing to the Eu³⁺ ions, with the most intense emission peaks at 614 and 590 nm related to the ⁵D₀ → ⁷F₂ and ⁵D₀ → ⁷F₁ transitions, corresponding to red (R) and orange (O) colors, respectively. The R/O intensity ratios between 3.16 and 3.73 were observed and correlated to the structural properties of the host. X-ray diffraction patterns indicated that the reduction of PL at 614 nm and changes in the R/O values were due to the crystallization process. In addition, the FTIR spectra showed a gradual decrease of the hydroxyl absorption bands around 3436 and 1640 cm⁻¹ and an increase of the bands related to Ti–O–Ti and Si–O–Si linkages, indicating polymerization and densification process of the host was achieved above 700 °C. Moreover, increasing the annealing temperature resulted in the formation of ZnTiO₃ and Zn₂TiO₄ crystalline phases, as well as rutile TiO₂. Finally, intensity parameters (Ω_λ), and quantum efficiency were calculated by applying Judd–Ofelt theory to Eu³⁺ ions, which showed that the Eu³⁺-doped samples can be used in displays and LEDs.     

Apatite–organic polymer composites prepared by a biomimetic process: improvement in adhesion of the apatite layer to the substrate by ultraviolet irradiation

A dense and uniform layer of highly bioactive apatite can be formed in arbitrary thickness on any kind and shape of organic polymer substrates by the following biomimetic process. The substrate is first placed in contact with granular particles of CaO, SiO2-based glass soaked in a simulated body fluid with ion concentrations nearly equal to those of human blood plasma for forming apatite nuclei, and then soaked in another fluid highly supersaturated with respect to the apatite for making the apatite nuclei grow. In the present study, the polymer substrates were pretreated with ultraviolet (UV) light, and then subjected to the biomimetic process described above. By UV irradiation, the induction period for the apatite nucleation of poly(ethylene terephthalate) (PET), poly-ether sulphone (PESF), polyethylene (PE), poly(methyl methacrylate) (PMMA) and polyamide 6 (N6) substrates were reduced form 24 h to 10 h. The adhesive strengths of the apatite layer to the substrates increased from 2.5–3.2 MPa to 4.5–6.0 MPa for PET, PESF and PMMA, and from about 1.0 MPa to 4.0–6.5 MPa for PE and N6 substrates. These results have been explained by assuming that silicate ions, which induce apatite nucleation, are easily adsorbed on the substrates due to the formation of polar groups, with an improved hydrophilic nature, on the polymer surfaces by UV irradiation. © 1998 Chapman & Hall     

Diffuse phase transition and leakage current characteristics of (Pb0.25Sr0.75)TiO3 thin films prepared by a sol–gel process

Nanocrystalline (Pb_0.25Sr_0.75)TiO₃ (PSrT25) thin films were grown on Pt/Ti/SiO₂/Si substrates by using a sol–gel process. The dielectric constant and loss tanδ of Au/PSrT/Pt thin-films capacitor were 345 and 0.016 at 100 kHz, respectively. The dielectric constant of PSrT film changes significantly with applied dc bias field and has a tunability of 22.7 % under an applied field of 150 kV/cm. Phase transition of the PSrT25 film has shown the diffuse-type phase transition behavior. The leakage current varied depending on the voltage polarity. At low electrical field and with Au electrode biased negatively, the Au/PSrT interface exhibits a Schottky emission characteristic, while at higher fields, Poole–Frenkel dominated the electronic conduction.