Original Synthesis Method Research Articles

Reaction of acetyl- and alkylideneglycosylamines with diphenylphosphinous acid

An original method of synthesis of optically active α-aminophosphoryl compounds containing a carbohydrate residue is proposed.

Sequential Grafting of Dielectric Phosphates onto Silicon Oxide

This work explores the growth of high-k oxide films deposited onto silicon by original synthesis methods based on wet chemistry, either aqueous or organic. Zirconium and titanium phosphate layers have been deposited by alternate dipping sequences in diluted solutions of monomeric Ti or Zr alkoxides (M) and phosphoric acid (P). The films have been characterized by dynamic contact angle measurements with water, infrared spectroscopy, X-ray reflectometry, HRTEM microscopy, and Rutherford backscattering spectroscopy. The composition of the zirconium phosphate films corresponds to a P/Zr = 1 ratio, induced by the dipping sequence, and not to that defined by thermodynamic conditions that would precipitate a P/Zr = 2 composition. The growth rate shows that, in optimized conditions, dense monolayers can be deposited during each cycle. The dielectric properties indicate a high dielectric constant that decreases p Z, upon dehydration at 300 degrees C. The static dielectric constant measured at 1 kHz in capacitance-voltage geometry is around 40 for the films heat-treated at 300 degrees C in air.

Application of neuro‐fuzzy techniques to robust speed control of PMSM

PurposeThe purpose of the paper is to find a simple structure of speed controller robust against drive parameter variations. Application of neuro‐fuzzy technique in the controller of PI type creates proper nonlinear characteristics, which ensures controller robustness.Design/methodology/approachThe robustness of the controller is based on its nonlinear characteristic introduced by neuro‐fuzzy technique. The paper proposes a novel approach to neural controller synthesis to be performed in two stages. The first stage consists in training the neuro‐fuzzy system to form the proper shape of the control surface, which represents the nonlinear characteristic of the controller. At the second stage, the PI controller settings are adjusted by means of the random weight change procedure, which optimises the control quality index formulated in the paper. The synthesis is performed using simulation techniques and subsequently the behavior of a laboratory speed control system is validated in the experimental setup. The control algorithms of the system are performed by a microprocessor floating point DSP control system.FindingsThe proposed controller structure with proper control surface created by the neuro‐fuzzy technique guarantees expected robustness.Research limitations/implicationsThe proposed controller was tested on a single machine under well defined conditions. Further investigations are required before any industrial applications can be made.Practical implicationsThe proposed controller synthesis and its results may be very helpful in the robotic system where changing of system parameters is characteristic for many industrial robots and manipulators.Originality/valueThe original method of robust controller synthesis was proposed and validated by simulation and experimental investigations.

Characterization of mesoporous alumina prepared by surface alumination of SBA-15

Mesoporous aluminas of controlled pore sizes were synthesized by multiple grafting of Al isopropoxide in organic solvents on mesoporous silica SBA-15. These materials were characterized by N 2 physisorption, TEM, XRD, 27Al NMR and their surface chemical properties were probed by DRIFT, cumene cracking and MoO 3 thermal spreading. The results show that the chemical nature of the Al-grafted materials varies continuously with the number of grafting from pure silica to pure alumina. Typically, after three graftings, this original method of synthesis allows one to prepare ordered mesoporous aluminas with specific surface areas above 300 m 2 g −1 and a narrow pore size distribution centered on ca. 60 Å. In addition to the characterizations, different models were developed to understand the evolution of the specific surface area and to discard a possible pore blocking.

Application of Artificial Neural Network to Robust Speed Control of Servodrive

This paper deals with the problem of robust speed control of electrical servodrives. A robust speed controller is developed using an artificial neural network (ANN), which creates a nonlinear characteristic of controller. An original method of neural controller synthesis is presented. The synthesis procedure is performed in two stages. The first stage consists in training the ANN and at the second stage controller settings are adjusted. The use of the proposed controller synthesis procedure ensures robust speed control against the variations of moment of inertia and stator magnetic flux. Simulations and laboratory results validate the robustness of the servodrive with permanent magnet synchronous motor

Artificial neural network based robust speed control of permanent magnet synchronous motors

PurposeThe aim of the paper is to find a simple structure of speed controller robust against drive parameters variations. Application of artificial neural network (ANN) in the controller of PI type creates proper non‐linear characteristics, which ensures controller robustness.Design/methodology/approachThe robustness of the controller is based on its non‐linear characteristic introduced by ANN. The paper proposes a novel approach to neural controller synthesis to be performed in two stages. The first stage consists in training the ANN to form the proper shape of the control surface, which represents the non‐linear characteristic of the controller. At the second stage, the PI controller settings are adjusted by means of the random weight change (RWC) procedure, which optimises the control quality index formulated in the paper. The synthesis is performed using simulation techniques and subsequently the behaviour of a laboratory speed control system is validated in the experimental set‐up. The control algorithms of the system are performed by a microprocessor floating point DSP control system.FindingsThe proposed controller structure with proper control surface created by ANN guarantees expected robustness.Originality/valueThe original method of robust controller synthesis was proposed and validated by simulation and experimental investigations.

Quasi-planar transversal band-pass filters for Ka-band applications

A quasi-planar technology is applied to the design of transversal multiple pole filters for space applications. To define the optimal dimensions of the filter, an original synthesis method is developed to yield the transversal equivalent electrical circuit. In this article, a 2nd-order and a 4th-order transversal filters are designed, built, and tested. These filters are centered around 28.5 GHz and exhibit a 3-dB bandwidth of 1.75% and 4.2%, respectively. © 2004 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005.

Elaboration of mixed tantalum and niobium carbides from tantalite mineral (Fe,Mn)(Ta1−xNbx)2O6

This paper presents an original method of synthesis of mixed tantalum and niobium carbides from an oxalic precursor elaborated from the tantalite mineral (Fe,Mn)(Ta1−xNb x )2O6. The process of elaboration consists initially in melting the ore with potassium pyrosulphate, then performing a lixiviation with a concentrated hydrochloric acid solution. During the latter reaction, iron and manganese oxides are converted into water-soluble chlorides while the fused mass containing potassium, niobium and tantalum is not dissolved. Traces of chlorides are eliminated by filtration with boiling aqueous solution. Then, the solid is dissolved slowly in hot concentrated sulphuric acid solution. Adding ammonium hydroxide up to a pH of 8 completes the precipitation of niobium and tantalum hydroxides. The precipitate (Ta1−xNb x )(OH)5 is washed and submitted to a reaction of complexation with oxalate ions in an aqueous environment. This reaction involves the formation of a water-soluble oxalic complex containing tantalum and niobium. The excess of water is eliminated by evaporation at 333 K. The tantalum and niobium carbides are obtained by submitting the oxalic complex of chemical formula (NH4)3(Ta1−xNb x )O(C2O4)3·nH2O to a gas-solid reaction in a methane-hydrogen atmosphere at 1273 K. The oxalic precursor and their resultant mixed carbides are characterized by atomic absorption and Infra-Red spectroscopies, thermogravimetric-differential thermal analysis coupled, laser granulometry, X-ray diffraction and transmission electronic microscopy.

Heat-resistant coreless silicon carbide fibres for composite materials with ceramic and metallic matrices

An original method of synthesis of fibre-forming polycarbosilane was developed. A study of the physicochemical properties of samples of Japanese and our polycarbosilane demonstrated their identity. Manufacture of coreless silicon carbide fibres was investigated. The conditions were developed and samples of fibres with a strength of up to 2.5 and a modulus of elasticity of 180 GPa were made. It was found that the physicomechanical properties of our fibres are on the level of mass-produced Japanese fibres and their structural and thermal characteristics are identical.

Inorganic membranes and solid state sciences

Abstract The latest developments in inorganic membranes are closely related to recent advances in solid state science. Sol–gel processing, plasma-enhanced chemical vapor deposition and hydrothermal synthesis are methods that can be used for inorganic membrane preparation. Innovative concepts from material science (templating effect, nanophase materials, growing of continuous zeolite layers, hybrid organic–inorganic materials) have been applied by our group to the preparation of inorganic membrane materials. Sol–gel-derived nanophase ceramic membranes are presented with current applications in nanofiltration and catalytic membrane reactors. Silica membranes with an ordered porosity, due to liquid crystal phase templating effect, are described with potential application in pervaporation. Defect-free and thermally stable zeolite membranes can be obtained through an original synthesis method, in which zeolite crystals are grown inside the pores of a support. Hybrid organic–inorganic materials with permselective properties for gas separation and facilitated transport of solutes in liquid media, have been successfully adapted to membrane applications. Potential membrane developments offered by CVD deposition techniques are also illustrated through several examples related to the preparation of purely inorganic and hybrid organic–inorganic membrane materials.

Cobalt stabilized layered lithium-nickel oxides, cathodes in lithium rechargeable cells

In the present paper the effect of cobalt, as substituent, on the stabilization of layered lithium-nickel oxides has been shown. Using an original method of synthesis, the series LiCo 1− x Ni x O 2 (O< x<1), has been obtained and analysed by X-ray powder diffraction. The electrochemical characteristics has been obtained in a three-electrode glass cell using standard electrolyte of 1 M LiClO 4 in propylene carbonate:dimethyoxyethene. It has been demonstrated by cyclic voltammetry that the reversibility in the ternary LiNiCoO system increases with the Co content due to the enhanced stability and structural order of materials.

Synthesis of mechanically activated YBa 2Cu 3O x samples. Microstructure evolution during grain growth process

The original method of synthesis of bulk YBa 2Cu 3O x ceramics based on preliminary mechanical activation of initial oxide mixture is presented. The microstructure of the samples obtained under different temperature conditions were carried out by X-Ray, SEM and TEM analysis.

Activation energies in chemical vapour deposition kinetics of SiO 2 films using TEOS chemistry

The film boiling chemical vapor process is an original and rapid synthesis method for ceramic coatings and composites. This work reports the deposition of silica coating from tetraethyl orthosilicate (TEOS) by film boiling chemical vapor process. Experiments were carried out under atmospheric pressure between 900 °C and 1100 °C. Several modifications of the experimental setup were made in order to allow a better thermal monitoring. Silica coatings were fast synthetized: several microns per minute. An activation energy of 209 kJ/mol ± 20 was deduced. The structure and microstructure of the oxide coating were characterized by Optical Microscopy, Scanning Electron Microscopy, Energy Dispersive Spectroscopy, Electron Probe MicroAnalyzer, Fourier-Transform InfraRed spectrometery and X-ray diffraction.