Ultrasonic-assisted rapid and highly efficient liquid-phase exfoliation of α-zirconium phosphate

Journal of Materials Science - α-zirconium phosphate (α-ZrP) was liquid phase exfoliated within 10 min using diethylene glycol amine (DGA) as the exfoliator under ultrasonic...     

Derivatives of α-zirconium phosphate with two different functional groups

The syntheses of derivatives of α-zirconium phosphate having the general formula Zr(RPO₃)_x(R′PO₃)_2−x (where R and R′ are generally organic radicals, but may also indicate −H or −OH groups) have been achieved by precipitating a mixture of two phosphonic acids with a zirconium salt in the presence of hydrofluoric acid. Different mixed compounds, classified in the following three classes

• 1.(a) Zr (HPO₄)_x (R′PO₃)_2−x (R′ = −H; −C₆H₅; −CH₂CH ₂COOH)
• 2.(b) Zr (RPO₃)_x (R′PO₃)_2−x (R′ = −CH₂COOH;R′ = −CH₂OH)
• 3.(c) Zr (HPO₃)_x (R′PO₃)_2−x (R′ = −CH₆H₅; −CH₂OH; −CH₂COOH; −CH₂CH₂COOH)

were prepared and characterized with regard to their compositions, X-ray powder patterns and densities. It was found that the system is discontinuous, not all x values from 0 to 2 being possible. No single crystals for X-ray structure determination were obtained; however, some chemical evidence shows that the mixed compounds possess a layered structure similar to that of α-zirconium phosphate. Some considerations on the reciprocal disposition of the R and R′ pendent groups in the layered structure are reported. Many other derivatives are expected to be obtained easily by using other mixtures of phosphonic acids than those employed in this work. Owing to the large variety of possible combinations of R and R′ groups, the mixed compounds should exhibit a large spectrum of properties and show promise for application in the field of ion exchange, adsorption, intercalation and heterogeneous catalysis.     

Synergistic antibacterial zinc ions and cerium ions loaded α-zirconium phosphate

In order to improve the antibacterial activity of Zn²⁺, a series of Zn²⁺ or/and Ce³⁺ modified layered α-zirconium phosphate (ZrP) was prepared and characterized, and the antibacterial activity of the prepared Zn²⁺ or/and Ce³⁺ modified ZrP on Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus was investigated. The results show that the Zn²⁺ or/and Ce³⁺ is combined with ZrP, and the d₀₀₂ basal spacing of Ce³⁺ modified ZrP is not obviously changed, while the d₀₀₂ basal spacing of Zn²⁺ modified ZrP is increased. Zn²⁺ and Ce³⁺ modified ZrP displays excellent synergistic antibacterial activity, suggesting great potential application as antibacterial agents in microbial control.     

Electrical properties of vanadium pentoxide doped with lithium and sodium in the α-phase range

The electrical conductivity and Seebeck coefficients have been measured from room temperature to 500° C for polycrystalline V₂O₅ and V₂O₅ doped with lithium and sodium in the -phase range. The conductivity increases with doping and the energy of activation decreases. The Seebeck coefficient indicates that electrons are the majority carriers. The results have been discussed in terms of the two-level hopping model.     

Calcium phosphate cement: in vitro and in vivo studies of the α-tricalcium phosphate-dicalcium phosphate dibasic-tetracalcium phosphate monoxide system

In this paper, calcium phosphate cement consisting of -tricalcium phosphate (-TCP), dicalcium phosphate dibasic (DCPD) and tetracalcium phosphate monoxide (TeCP) was investigated in vitro and in vivo. Measurements of compressive strength against soaking time in simulated body fluid (SBF) showed a rapid increase of the hardness for the first 7 days. The gained strength was retained up to 1 year and the maximal mean value was 94.7 (±14.4) MPa. X-ray diffraction (XRD) and scanning electron microscopy (SEM) presented precipitates of hydroxyapatite (HA) after mixing, also after soaking in SBF and after implantation in rat subcutaneous tissues. However, the conversion to HA happened in different ways between in vitro and in vivo exposures. Histologic examinations showed that the cement causes the same reactions at the interface with surrounding soft tissues as HA. The authors consider the cement to be a promising material as a bone substitute, bone cement or dental material, however, further studies in a paste form and in bone tissue environments are necessary.     

Electrical and optical properties of µc-SiH films

Microcrystalline silicon films have been found quite useful in amorphous silicon solar cells as a contact material in n-i-p cells. Microcrystalline silicon films are obtained when amorphous silicon films are prepared by R.F. glow discharge of SiH₄ + H₂ at higher power ratings. These films possess higher conductivity as well as high transmission than amorphous silicon films. The present paper reports the preparation technique ofμc-SiH films using R.F. capacitive glow discharge of hydrogen-diluted silane. X-ray studies andtem studies of the films indicate microcrystallinity of the films. The electrical and optical properties are also reported.     

Electrical properties of undoped CoO — a Debye-Huckel approach

Thermopower and electrical conductivity data for both single crystal and polycrystalline undoped CoO are considered in terms of a defect disorder model based on doubly ionized cobalt vacancies as the predominant defects. The analysis, based on the Debye-Hückel theory for liquid electrolytes, aims at an evaluation of the interactions between defects such as doubly ionized cation vacancies. It was shown that, in the temperature range 1200–1700 K, the reciprocals of the partial pressure of oxygen p(O₂) exponent of thermopower and electrical conductivity vary between 3.6 < n < 4.2 and 3.5 < n < 3.8, respectively. About 1300 K, both n and n are higher for single crystal than for the polycrystalline specimens. It was shown that closer agreement between the defect model and experimental data can be obtained by introducing defect activities instead of concentrations.     

Electrical and optical properties of single crystalline α-Al2O3 doped with nickel

Nickel, substituting for aluminium in α-Al₂O₃ acts as an acceptor with a level ∼2.46 eV above the conduction band if a large polaron model applies, ≅ 2.57eV−H(μ _h) above the band if a small polaron model applies. It is present as Ni³⁺ at high, and as Ni²⁺ at low, oxygen pressures, the concentration of Ni³⁺ being reduced to one-half of its high value at =1 Pa. Analysis of the data provides proof that the native defect compensating the charge of Ni²⁺ (=ni _al ^′ ) is V _O ^2. , Al _i ^3. being a minority species; H _F,Al−1/2H _s=121 kJ mol⁻¹.     

Pozzolanic reaction of glass powder and its role in controlling alkali–silica reaction

It is well recognized that finely ground soda-lime glass exhibits high pozzolanic reactivity. Fine glass grains will not undergo an Alkali-silica reaction (ASR) in the presence of alkali, and can even mitigate the ASR between alkali and reactive aggregates. Influences of the pozzolanic reaction of glass powder on solid phases, pore solution in cement paste, and the ASR mitigating effect are investigated in the study. The pozzolanic reaction of glass not only consumes portlandite to form in-situ C-S-H, which appears as reaction rim around glass grains, and precipitated C-S-H, but also reduces monosulfate level. The impacts of the pozzolanic reaction on species in pore solution are characterized by increased aluminum, sulfate, sodium, and silicon concentrations and decreased calcium concentration. The increase in aluminum and sulfate concentrations results from the decrease in solid monosulfate. Glass powder controls ASR by increasing aluminum concentration in pore solution to reduce the dissolution of amorphous silica from reactive aggregates.     

Enhanced hydrated properties of α-tricalcium phosphate bone cement mediated by loading magnesium substituted octacalcium phosphate

A novel Mg-containing α-tricalcium phosphate (α-TCP) bone cement with excellent wetting compressive strength and suitable setting time has been developed in this work. Mg-substituted octacalcium phosphate (Mg-OCP) crystals with the special morphology was prepared by homogeneous precipitation method, and used to modify the α-TCP bone cement. Mg²⁺ was successfully introduced into OCP structure, and the filaments/sheet-like morphologies of OCP were obtained by changing the Mg²⁺ concentration. As added in the α-TCP cement matrix, the effects of Mg-OCP on the wetting compressive strength, setting time and microstructure of the cement system were studied. The addition of Mg-OCP shortened the setting time of cement pastes with the minimum setting time of 15 min, and enhanced the wetting compressive strength of the hydrated cement products with the highest wetting compressive strength of 36.86 MPa. This work highlights the special morphologies of Mg-OCP induced by Mg²⁺ substitution, which made an effect on the hydration reaction of α-TCP cement; Furthermore, Mg-OCP was supposed to improve the condensation capacities and mechanical properties of α-TCP cement system as a novel cement admixture.     

Na-doped β-tricalcium phosphate: physico-chemical and in vitro biological properties

Synthetic calcium phosphate ceramics as β-tricalcium phosphate (Ca₃(PO₄)₂; β-TCP) are currently successfully used in human bone surgery. The aim of this work was to evaluate the influence of the presence of sodium ion in β-TCP on its mechanical and biological properties. Five Na-doped-β-TCP [Ca_10.5−x/2Na _x (PO₄)₇, 0 ≤ x ≤ 1] microporous pellets were prepared via solid phase synthesis, and their physico-chemical data (lattice compacity, density, porosity, compressive strength, infrared spectra) denote an increase of the mechanical properties and a decrease of the solubility when the sodium content is raised. On the other hand, the in vitro study of MC3T3-E1 cell activity (morphology, MTS assay and ALP activity) shows that the incorporation of sodium does not modify the bioactivity of the β-TCP. These results strongly suggest that Na-doped-β-TCP appear to be good candidates for their use as bone substitutes.     

Synthesis and properties of bone cement materials in the calcium phosphate–calcium sulfate system

We have studied the influence of the cement liquid composition and the relationship between the components of the calcium sulfate–precipitated calcium phosphate system in a wide concentration range on the setting time, phase composition, microstructure, and mechanical properties of cement materials. The results demonstrate that the greatest promise is held by a magnesium phosphate-based cement liquid which, when mixed with powder, forms a high-strength phase, leading to a considerable increase in the strength of the cements. The addition of 20 wt % calcium sulfate to the starting mixture ensures dispersion hardening of the cements. We have obtained new cement materials offering a strength of up to 60 MPa, which are expected to find medical applications.     

Evolution properties of the complex degree of coherence of a partially coherent Laguerre–Gaussian beam in turbulent atmosphere

Evolution properties of the complex degree of coherence of a partially coherent Laguerre–Gaussian beam (LGB) on propagation in free space and turbulent atmosphere are studied comparatively with the help of the general propagation formula for such beam. It is found that the behavior of the complex degree of coherence of a partially coherent LGB on propagation in turbulent atmosphere is much different from that in free space and is closely related to the initial beam parameters and the structure constant of the turbulent atmosphere. The distribution of the modulus of the complex degree of coherence of the partially coherent LGB finally becomes of Gaussian distribution at long propagation distance in turbulent atmosphere, and it becomes of Gaussian distribution more slowly with the increase of the mode orders, beam width and wavelength. Our results will be useful in long-distance free-space optical communications.     

Electrical and optical properties of ZnO–WO<Subscript>3</Subscript> nanocomposite and its application as a solid-state humidity sensor

This study reports the humidity sensing characteristics of ZnO–WO₃ nanocomposite. Pellet samples of 0–5 weight% ZnO in WO₃ were sintered from 300 to 600 ^° C. When exposed to humidity, the resistance of the sensing samples was found to decrease with increase in relative humidity (RH). Five percent ZnO-doped WO₃ showed maximum sensitivity of 20.95 M Ω/%RH in 15–95% RH range. Sensor parameters like reproducibility, aging, hysteresis, response and recovery times were also studied. Sensing mechanism is discussed in terms of sintering temperature, composition and crystallite size of the sensing element. It was observed that sensing mechanism is strongly based on annealing temperature and percentage of doping. The sensing samples have also been investigated by X-ray diffraction, scanning electron microscope (SEM) and Raman spectroscopy. The crystalline size of the sample was identified by powder X-Ray Diffraction data. The SEM analysis was used to study the surface morphology. The structure, phase and the degree of crystallinity of the materials were examined by Raman spectroscopy.     

Thixoformability of a Mg–Gd–Y magnesium alloy and its mechanical properties

Abstract

A new magnesium alloy with composition of Mg–8·57Gd–3·72Y–0·54Zr (wt-%, GW94) amenable to semisolid forming is presented. A quantitative investigation of its thixoformability in terms of metallurgical parameters in the semisolid state is performed based on Pandat thermodynamic calculation. The optimised working window for thixoforming is from 581 to 605°C, where the volume fraction of liquid does not change significantly with temperature. The alloy is then successfully thixoformed at 600°C, and a typical thixotropic microstructure is obtained. It is shown that significant improvement of mechanical properties is achieved in the thixoformed (TF) GW94 alloy compared to its permanent mould casting counterpart. This is attributed to an obvious decrease in the amount of porosity and fine distribution of the brittle Mg₂₄(Gd,Y)₅ particles in the thixoforming process.     

Synthesis and Electrical Properties of Well-Ordered Layered α-MoO3 Nanosheets

Nano-Micro Letters - α-MoO3 ordered nanosheets have been synthesized under hydrothermal conditions using commercial MoO3 and hydroquinone as structuring agent. X-ray diffraction (XRD),...     

Effect of silicate incorporation on in vivo responses of α-tricalcium phosphate ceramics

In addition to calcium phosphate-based ceramics, glass-based materials have been utilized as bone substitutes, and silicate in these materials has been suggested to contribute to their ability to stimulate bone repair. In this study, a silicate-containing α-tricalcium phosphate (α-TCP) ceramic was prepared using a wet chemical process. Porous granules composed of silicate-containing α-TCP, for which the starting composition had a molar ratio of 0.05 for Si/(P + Si), and silicate-free α-TCP were prepared and evaluated in vivo. When implanted into bone defects that were created in rat femurs, α-TCP ceramics either with or without silicate were biodegraded, generating a hybrid tissue composed of residual ceramic granules and newly formed bone, which had a tissue architecture similar to physiological trabecular structures, and aided regeneration of the bone defects. Supplementation with silicate significantly promoted osteogenesis and delayed biodegradation of α-TCP. These results suggest that silicate-containing α-TCP is advantageous for initial skeletal fixation and wound regeneration in bone repair.     

The Principle and Architecture of a Hybrid System of a Neural Network and an Expert System in Intelligent CAD of Electrical Machines

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The controlled resorption of porous α-tricalcium phosphate using a hydroxypropylcellulose coating

Tricalcium phosphate (TCP) ceramic is known in orthopedics to be a bioresorbable bone substitute. A porous TCP ceramic body also has high potential as a drug delivery system in bony defects. Porous alpha-TCP ceramic can be easily fabricated using conventional sintering of beta-TCP, since alpha-TCP is the thermodynamically stable phase at temperatures above 1 100 degrees C. However, the solubility of alpha-TCP is much higher than that of beta-TCP. Therefore, the dissolution of porous alpha-TCP progresses at a higher rate than bone repair. In the present study, we attempted to reduce the dissolution rate of porous alpha-TCP by employing an organic polymer coating. We fabricated porous alpha-TCP ceramic with a continuous 10-50 microm diameter pore structure by sintering a body made from a beta-TCP and potato starch slurry. The porous body obtained was coated with hydroxypropylcellulose (HPC), and then subjected to heat treatment. The chemical durability and mechanical properties of the body were examined before and after coating with the HPC. The dissolution of porous alpha-TCP in buffered solutions was reduced by coating with HPC and drying at 60 degrees C. The compressive strength of the porous alpha-TCP was also improved by coating with HPC. The results of in vivo experiments showed that some parts of the porous alpha-TCP ceramic coated with HPC remained in the canal of the tibia of a rabbit four weeks after implantation, whereas no residual was observed in a non-coated alpha-TCP ceramic. Coating with HPC was found to be effective for controlling bioresorption and improving the workability of porous alpha-TCP ceramic. The prepared porous alpha-TCP ceramic is expected to be useful as a novel material for bone fillers by incorporating it with drugs or osteoinductive factors.