Dysprosium selective potentiometric membrane sensor

A novel Dy(III) ion-selective PVC membrane sensor was made using a new synthesized organic compound, 3,4-diamino-N′-((pyridin-2-yl)methylene)benzohydrazide (L) as an excellent sensing element. The electrode showed a Nernstian slope of 19.8 ± 0.6 mV per decade in a wide concentration range of 1.0 × 10^? 6–1.0 × 10^? 2 mol L^? 1, a detection limit of 5.5 × 10^? 7 mol L^? 1, a short conditioning time, a fast response time (< 10 s), and high selectivity towards Dy(III) ion in contrast to other cations. The proposed sensor was successfully used as an indicator electrode in the potentiometric titration of Dy(III) ions with EDTA. The membrane sensor was also applied to the F^– ion indirect determination of some mouth washing solutions and to the Dy^3 + determination in binary mixtures.     

New potentiometric sensor for the determination of iodine species

The characteristics, performance and application of novel triiodide potentiometric sensor based on ion-pair of Rhodamine B triiodide as a membrane carrier are described. The electrode has a linear dynamic range between 1 × 10^? 6 and 1 × 10^? 1 M, with a Nernstian slope of 68 ± 1 mV pC^? 1 and detection limit of 3.9 × 10^? 7 M. Fast and stable response, good reproducibility, long-term stability, very good selectivity over a large number of common organic and inorganic anions, applicability over a pH range of 2–10 are demonstrated. The proposed sensor has been applied for potentiometric determination of some iodine species.     

Silicon nitride-based composites

The application of silicon nitride, as well as other ceramics, is limited by its tendency towards catastrophic failure and thus reduced reliability. Additional improvements in the strength and fracture toughness of these materials would considerably expand their range of application. Reinforcement of the monolithic ceramics through the introduction of fibres, particulates and whiskers offers a potential for such property improvements. Research and development work in this area, specific to silicon nitride, is reviewed with an emphasis on current developments.     

Particulate silicon nitride-based composites

In an attempt to optimize the structure and properties of silicon nitride ceramics, a variety of novel processing techniques and materials compositions have evolved over the last 15 years. Among the most important, was the development of various silicon nitride-based composites. A review of particulate, silicon nitride-based composites other than whisker- or platelets-reinforced, is presented. Materials based on silicon nitride and SiAlONs, with additions of carbides, nitrides and borides of transition metals are described. Special emphasis is placed on TiN- and TiC-containing ceramics. The manufacture of composites by hot pressing, reaction sintering, pressureless and gas-pressure sintering is discussed. The data on properties, including conductivity, density, Young's modulus, strength, fracture toughness, hardness, thermal expansion, wear, creep and oxidation resistance are presented. Analysis of actual and potential uses of the selected composites demonstrates that the particulate composites are very promising as tool, structural and electronic materials.     

Bio-functionalization of silicon nitride-based piezo-resistive microcantilevers

Methods of bio-functionalize silicon nitride involve process steps to convert it into an oxynitride via plasma implantation techniques. Such methods can potentially damage microstructures such as cantilevers. In this paper, we report successful bio-functionalization of Hotwire CVD silicon nitride-based piezo-resistive cantilevers without any oxygen plasma treatment. Process to fabricate such structures and to bio-functionalize them is discussed in detail.     

Cytotoxic evaluation of silicon nitride-based ceramics

Silicon nitride-based ceramics are potential candidates as materials for orthopedic implants due to their chemical stability associated with suitable fracture toughness and propitious tribologic characteristics. Therefore, in this work, dense silicon nitride components are investigated considering their suitability as biomaterials. Initially, two different compositions of silicon nitride were considered, using ytterbium, yttrium and aluminum oxides as sintering aids. The materials were sintered in a carbon resistance furnace under nitrogen atmosphere and were analyzed by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) in order to characterize the microstructure. Indentation method was applied in order to obtain hardness and fracture toughness measurements, and in vitro test of cytotoxicity was performed for a preliminary biological evaluation. A microstructure composed of grains of beta-silicon nitride distributed in a secondary phase was observed. The samples achieved fracture toughness values of 5 MPa m^1/2 and Vickers hardness values of 13 GPa. Since a nontoxic behavior has been observed during the cytotoxicity tests with the samples, this finding suggests that silicon nitride-based ceramic can be used as a material for clinical applications.     

A novel potentiometric hydrogen peroxide sensor based on pKa changes of vinylphenylboronic acid membranes

A potentiometric hydrogen peroxide (H₂O₂) sensing scheme was developed using arylboronic acid as the electrode modifier. It is well-known that both aliphatic and aryl boronic acid undergo electrophilic displacement reaction with H₂O₂. This reaction involves replacement of boronic acid by the hydroxyl group of peroxide resulting in a change in pK_a value that can be exploited for sensing of H₂O₂. Vinylphenylboronic acid (VPBA) ink was prepared using Nafion as the binder and it was drop cast on an electrode surface. Morphology of the modified electrode was analysed using scanning electron microscopy (SEM). The present modifier exhibited a linear relationship between the difference in electrode potential (?Ep) vs. [H₂O₂] with a Nernstian slope of 26 ± 2 mV in the concentration range of 10^? 1–10^? 5 M. Application of the VPBA modified electrode for hydrogen peroxide sensing was studied in an industrial dye-bleach effluent.     

High temperature assessment of nitride-based devices

The high temperature characterization of GaN-based devices, including high electron mobility transistors (HEMTs), p-i-n photodiodes and surface acoustic wave (SAW) filters is reported. Transmission line method (TLM) measurements reveal the reversible behaviour of both the ohmic contact resistance and the two-dimensional electron gas (2DEG) mobility. AlGaN/GaN HEMTs on sapphire and SiC substrates present a reduction of the drain current and the transconductance as temperature increases. The responsivity of InGaN/GaN photodiodes is enhanced and shifted to larger wavelengths with temperature, recovering its original value after the thermal cycle. The temperature coefficient of frequency of SAW filters on AlN epilayers on different substrates has been measured. The influence of temperature on the different surface acoustic modes is compared.     

Development of a disposable potentiometric sensor for the near patient testing of plasma thiol concentrations

The reaction of naphthoquinone with physiological thiols has been investigated as the basis of a NPT strategy for the measurement of the latter. Screen-printed carbon electrode assemblies provide an inexpensive and inherently disposable platform for the detection methodology. The key analytical parameters underpinning the selective and sensitive (0.4 uM-1 mM) determination of reduced thiol have been assessed, and the clinical efficacy of the approach has been demonstrated through its application to the analysis of human plasma. The results have been corroborated using standard techniques, and the routes through which the system can be adopted within mainstream biomedical environments are highlighted.     

Conversion mechanism of perhydropolysilazane into silicon nitride-based ceramics

The pyrolysis of perhydropolysilazane in anhydrous ammonia has been studied up to 1000 °C through the analysis of the gas phase and the characterization of the solid residue by thermogravimetric analysis, Fourier transform-infrared analysis. X-ray photoelectron spectroscopy, X-ray diffraction and ²⁹Si cross-polarization magic angle spinning-nuclear magnetic resonance. The pyrolysis mechanism involves three main steps: (1) below 400 °C, evaporation of residual solvent; (2) from 400–600 °C, reaction with ammonia leading to an increase of nitrogen content and formation of preceramic polymer-ceramics intermediate solid with a three-dimensional network; (3) from 600–1000 °C, completion of the formation of an amorphous hydrogenated solid with composition close to silicon nitride.     

A high-temperature solid-state potentiometric sensor for nitrogen based on ceramic LaAl12O18N

The nitrogen-sensing properties of LaAl12O18N are described for the first time. Positive e.m.f. measurements at high temperature across the cells -Nb (N), -Nb2N, -Al2O3, LaAl12O18NLaAl11O18 (or LaAl12O18N)LaAl12O18N, -Al2O3, -Nb2N, -Nb4N3, were in agreement with PN2(-Nb2N, -Nb4N3)>PN2(-Nb(N), -Nb2N) for the idealized stoichiometric cell reaction -Nb4N3+2-Nb(N)3-Nb2N, thus demonstrating the nitrogen-sensing property of these cells. The e.m.f. for a variety of cells with electrodes containing -V2N, -Nb2N, -Ta2N and Ti2N, were consistent with the predicted equilibrium nitrogen partial pressures.     

Properties of niobium nitride-based Josephson tunnel junctions

High T_c (16.8 K) niobium nitride thin films have been prepared by rf diode sputtering in N₂/Ar atmosphere and subsequent high temperature annealing. Josephson tunnel junctions have been made by thermal oxidation of the films. The geometry is defined by high resolution photolithography. The Josephson junctions have been characterized by magnetic field diffraction measurements and other techniques and are shown to be particularly suitable for applications especially in superconducting microwave integrated devices.     

Characterization of hot-pressed silicon nitride-based materials by microhardness measurements

The microhardness A Si₃N₄-based materials may be related to their phase and chemical compositions and to microstructural parameters such as porosity, grain size and secondary phases. By reducing the amount of intergranular phase, the microhardness may reach values up toHV ₅₀₀ = 3000 kg mm^–2. Moreover, a comparison among different materials must include the microhardness tests in a wide range of values of the applied load. The relationd ⁿ =B ₁ +B ₂ d ², obtained from those of Meyer and Kick, gives two constants:B ₁ may represent one class of materials andB ₂ is specific for each single material.     

陀螺状氮化镓基材料的制备和表征

以碳球为硬模板,通过溶剂热与NH3后处理相结合的方法合成出了具有陀螺状结构形貌的Ga0.97N0.9O0材料.通过X射线衍射(XRD)、场发射扫描电子显微镜(FE-SEM)、X射线能谱(EDS)对所制备的样品进行了表征,同时对其生长机理进行了简要的探讨.     

Gallium telluride heterojunctions

The photoelectric properties of In₂O₃-GaTe and GaTe-InSe heterojunctions were investigated. Their characteristics were described using a diffusion model of the heterojunction. Some deviation of the characteristics from ideal was observed for In₂O₃-GaTe heterojunctions as a result of the presence of a thin dielectric layer at the heteroboundary. Qualitative energy band diagrams were constructed for the heterojunction and their photosensitivity was determined in the range 0.33–1.0 μm. Pis’ma Zh. Tekh. Fiz. 25, 29–33 (January 26, 1999)     

High-temperature oxidation of silicon nitride-based ceramics by water vapour

Hot-pressed Si₃N₄, sintered Si₃N₄ and three kinds of sialon with different compositions were oxidized in dry air and wet nitrogen gas atmospheres at 1100 to 1350° C and 1.5 to 20 kPa water vapour pressure. All samples were oxidized by both dry air and water vapour at high temperature, and formed oxide films consisting of SiO₂, Y₂Si₂O₇ and Y4A1209. The oxidation rate was in the order sialon > sintered Si₃N₄ > hot-pressed Si3N4. The oxidation rate of sialon increased with increasing Y₂O₃ content, and oxidation kinetics obeyed the usual parabolic law. The oxidation rates in dry air and wet nitrogen were almost the same: the rate in wet nitrogen was unaffected by water vapour pressure above 1.5 kPa. The activation energy was about 800 kJ mol^–1.     

Lanthanide recognition: A Ho3+ potentiometric membrane sensor as a probe for determination of terazosin

In this study, complexation of N′-(1-pyridin-2-ylmethylene)-2-furohydrazide (NFH) with some metal ions was investigated by conductometry and spectroscopy. Then, a Ho³⁺ potentiometric membrane sensor was prepared based on the highly selective complexation between this ionophore and Ho³⁺. These new ionophores are more selective than the previously reported ones. In this work, for the first time, the proposed sensor was applied in indirect determination of the terazocine in its pharmaceutical formulation. The interest in constructing lanthanide sensors arises because they have similar ionic radii to calcium, but a higher charge density, which allows them to be used as probes to find the interactions between Ca²⁺ and biologically important molecules.     

Highly selective determination of perchlorate by a novel potentiometric sensor based on a synthesized complex of copper

In this paper, a highly selective poly (vinyl chloride) (PVC) membrane electrode based on (1, 9-dibenzyl-1, 3, 7, 9, 11, 15-hexaaza cyclohexa decane) copper(II) perchlorate; [Cu((benzyl)₂[16]aneN₆)](ClO₄)₂; as a synthesized ionophore, for perchlorate-selective electrode is reported. The influence of membrane composition, pH and possible interfering anions were investigated on the response properties of the electrode. The sensor responds to perchlorate ion in linear range from 1.0 × 10^? 6 to 1.0 × 10^? 1 M with a slope ? 59.4 ± 0.3 mV per decade. The limit of detection of the electrode was 4.0 × 10^? 7 M ClO₄^–. Selectivity coefficients indicate a good discriminating ability towards ClO₄^– ion in comparison to other anions. The proposed sensor has a fast response time of about 7 s and can be used for at least 2 months without any considerable divergence in potential. Due to importance of analysis of perchlorate in water samples, this selective electrode was applied as potentiometric sensor in determination of perchlorate ion in real samples.     

Conversion mechanism of polyborosilazane into silicon nitride-based ceramics

The pyrolysis of polyborosilazane in anhydrous ammonia has been studied up to 1200 °C through the analysis of the gas phase and the characterization of the solid residue by elemental analyses, thermogravimetric analysis, Fourier transform-infrared analysis, X-ray photoelectron spectroscopy, X-ray diffraction and ²⁹Si cross-polarization/magic angle spinning-nuclear magnetic resonance. The pyrolysis mechanism involves four main steps: (1) below 400 °C, an evaporation of residual solvent and reaction with ammonia leading to an increase of nitrogen content; (2) from 400–600 °C, reaction with ammonia leading to an increase of nitrogen content and formation of preceramic polymer-ceramics intermediate solid with a three-dimensional network along with evolution of gaseous species; (3) from 600–800 °C, completion of loss of C-H functionalities and progress of formation of an amorphous ceramic, accompanied by evolution of CH₄ and H₂; (4) from 800–1200 °C, completion of formation of an amorphous hydrogenated Si-B-O-N solid composed of SiN_4–x O_x(x=0,1,2,3) and BN_3–y O _y (y=0, 1), along with evolution of H₂     

Corrosion of hot pressed silicon nitride-based materials by molten copper

The behaviour of several types of silicon nitride-based materials in contact with molten copper has been evaluated. Tests were performed at a temperature of 1400 K for a holding time of 260 h in fluido-dynamic conditions.The extent of corrosion has been evaluated in terms of linear loss, weight loss, morphology and chemical composition of the surfaces remaining in contact with the molten phase, by means of SEM, EPMA and X-ray diffraction. Corrosion resistance has been found to be a function of the chemical composition, type and amount of the secondary phases. Materials produced with MgO as a sintering aid showed poor resistance whereas those with Al₂O₃ exhibited the best performance. In any case the extent of corrosion was very slight and the results revealed that all the tested ceramics may be considered suitable for use in contact with molten copper.