NiO-silica based nanostructured materials obtained by microemulsion assisted sol-gel procedure

NiO-silica based materials have been synthesized by microemulsion assisted sol-gel procedure. The versatility of these soft nanotechnology techniques has been exploited in order to obtain different types of nanostructures, such as NiO nanoparticles, NiO silica coated nanoparticles and NiO embedded in silica matrix. These materials have been characterized by adequate structural and morphology techniques: DLS, HR-TEM/SAED, BET, AFM. Optical and semiconducting properties (band-gap values) of the synthesized materials have been quantified by means of VIS-NIR diffuse reflectance spectra, thus demonstrating their applicative potential in various electron transfer phenomena such as photocatalysis, electrochromic thin films, solid oxide fuel cells.     

Synthesis and characterization of large specific surface area nanostructured amorphous silica materials

Large specific surface area materials attract wide attention because of their applications in adsorption, catalysis, and nanotechnology. In the present study, we describe the synthesis and characterization of nanostructured amorphous silica materials. These materials were obtained by means of a modification of the Stobe-Fink-Bohn (SFB) method. The morphology and essential features of the synthesized materials have been studied using an automated surface area and pore size analyzer and scanning electron microscopy. The existence of a micro/mesoporous structure in the obtained materials has been established. It was also found that the obtained particle packing materials show large specific surface area up to 1,600 m2/g. (To our best knowledge, there is no any reported amorphous silica material with such a higher specific surface area.) The obtained materials could be useful in the manufacture of adsorbents, catalyst supports, and other nanotechnological applications.     

Nanoporous metallic templates for embedded magnetic nanostructured films

We demonstrate a metallic template assisted method for realizing out-of-plane magnetic anisotropy in electro-deposited Co and Ni films, using highly porous TiN films as templates. TiN films containing high aspect ratio sub-50 nm wide pillars were obtained by controlling film-morphology via gas pressure during sputter deposition of the films. The nanoscale separation between these pillars allowed us to electro-deposit magnetic films on the pillars resulting in high aspect ratio magnetic structures. Co and Ni films grown on such nanostructured TiN films showed a significant coercivity enhancement as compared to planar films. Angular dependence of coercive field and the remnance ratio (M_r/M_s) reveals that, in the ultrathin limit, magnetic films coated onto the nano-pillars are akin to magnetic nanotubes.     

Integrated computational chemistry system for the design of heterogeneous catalysts and nanostructured materials

The valuable catalytic and adsorptive properties of heterogeneous catalysts and the challenging area of nanostructure materials provide ample reason for establishing a firm theoretical understanding of their structure and behaviour. Computer simulation studies can contribute significantly in achieving an understanding of structure property relationships by the synthesis of current understanding and data, and by their capacity in revealing critical conceptual issues whose resolution demands additional experimentation. In the present communication I emphasize on the activity of our group in the area of computer simulation. Our group activity involves generation of new codes, better compatibility to solve the problem as well as application of the available computation technique in solving the problems generated in industry and in academics. We are concentrating on basic research as well as application using integrated computational chemistry as a tool.     

Hybrid materials design to control creep in metallic pipes

A hybrid material has been developed to improve creep performance in pressurized metallic pipes subjected to high-temperatures. Model materials were selected for an investigation of reinforcement design parameters in architectured materials. Brass pipes (65 wt.% Cu/35 wt.% Zn) with austenitic stainless steel reinforcement were pressurized and creep rupture tested at 673 K. Compared to unreinforced pipes of equal dimensions, a 47-times reduction in the effective strain rate was observed with a 50° reinforcement angle. A ‘neutral angle’ of 54.7 ± 1.5° was determined experimentally, where tangential (hoop) and longitudinal stresses on the pipe can be balanced and strains minimized. For initial angles below the neutral angle, creep strain was shown to facilitate a shift in orientation towards the neutral angle. For an initial angle of 42°, this shift towards the neutral angle resulted in instantaneous creep rate dropping from 170% of the mean creep rate to 60% of the mean creep rate over 820 h, when the final angle was measured to be 50°. A high-temperature prototype (tungsten braid oriented at 53° over a 253MA stainless steel pipe) was shown to give a creep life extension in excess of 300-times at 1313 K.     

Modification of nanostructured materials for biomedical applications

Adaptation (or incorporation) of nanostructured materials into biomedical devices and systems has been of great interest in recent years. Through the modification of existing nanostructured materials one can control and tailor the properties of such materials in a predictable manner, and impart them with biological properties and functionalities to better suit their integration with biomedical systems. These modified nanostructured materials can bring new and unique capabilities to a variety of biomedical applications ranging from implant engineering and modulated drug delivery, to clinical biosensors and diagnostics. This review describes recent advances of nanostructured materials for biomedical applications. The methods and technologies used to modify nanostructured materials are summarized briefly, while several current interests in biomedical applications for modified and functionalized nanostructured materials are emphasized.     

One dimensional nanostructured materials

The quest for materials with molecular scale properties that can satisfy the demands of the 21st century has led to the development of one dimensional nanostructures, ODNS. Nearly, every class of traditional material has an ODNS counterpart. ODNS has a profound impact in nanoelectronics, nanodevices and systems, nanocomposite materials, alternative energy resources and national security. The interface of nanoscience and technology with biological and therapeutic sciences is expected to radically improve the ability to provide efficient treatments in otherwise impossible situations. Ironically, the huge investment in the past few years across the globe is yet to bring the real benefit of nanotechnology in day to day life. While scientists and engineers are working towards this goal, concerns about the possible harmful effects of the high aspect ratio materials are increasing every day. Following is an effort to assimilate most of the aforementioned aspects including the entire gamut of ODNS, i.e., elements, ceramics, polymers and composites, with a brief discussion on CNT and toxicology. The focus of this article is mainly on the science behind the synthesis and properties of the ODNS rather than the device fabrication. However, a few challenges in the field of device fabrication are mentioned in appropriate contexts. Possible mechanisms of the ODNS evolution from various methods, such as vapor liquid solid (VLS), template based and electrochemically induced growth, have been discussed in detail. Electron microscopy analysis has received special focus in determining the unique structural features. The article concludes by discussing current research related to environment and toxicology effects and current challenges in this rapidly evolving field.     

Properties of sol-gel derived silica membranes

Silica membrane materials have been produced by sol-gel processing using tetraethyl orthosilicate as a precursor and oxyethylated fatty alcohols and alkyl phenols as templates. Using low-temperature nitrogen adsorption-desorption, we have studied the adsorption properties and microstructure of silica membranes templated around colloidal surfactant crystals. The results demonstrate that the pore structure of the membranes differs significantly from that of their bulk analogs. The silica membranes have type IV isotherms and an H1 hysteresis loop, characteristic of cylindrical mesopores. The I + IV type mixed isotherms of the bulk analogs are dominated by features of type I with an H2 or H4 hysteresis, characteristic of monodisperse bottle-shaped or slit-like mesopores, respectively.     

Novel photorefractive sol-gel materials

We have developed new photorefractive media based on hybrid organic-inorganic materials containing a charge transporting (CT) molecule either as side-chain or main-chain substituents on the silica backbone. Second order nonlinear optical (NLO) chromophores were introduced either as side chain or as guest units. These materials were prepared by the sol-gel process in the form of thin films of a few μm-thick. NLO and photorefractive properties have been evaluated using electro-optic measurements, two beam coupling experiments and photoconductivity measurements.     

A simple sol-gel technique for synthesis of nanostructured hydroxyapatite, tricalcium phosphate and biphasic powders

Hydroxyapatite (HAP), β-tricalcium phosphate (β-TCP) and biphasic calcium phosphate (BCP) nanocrystalline powders were prepared by a simple sol-gel approach. Because of the unique characteristic of the phosphorous source ((CH₃O)₃P) and the proper uses of calcic and phosphorous sources with Ca/P molar ratio between 1.4 and 1.67, three different kinds of nanostructured calcium phosphate powders were achieved by changing the ratio of calcic and phosphorous sources. For HAP and β-TCP, pure phases were prepared. For BCP, the proportion of HAP and β-TCP could be changed by thermal treatment.     

Investigations into sol-gel silica and silica hybrid coatings for dielectromagnetic soft magnetic composite applications

A series of inorganic and organic–inorganic hybrid silica coatings were synthesised by a sol-gel process from tetraethoxysilane (TEOS) and methyltrimethoxysilane (MTMS) precursors, and used to investigate their effectiveness as insulation materials in dielectromagnetic soft magnetic composites. The coating materials and coated iron powders were analysed by FTIR, electron and atomic force microscopy. Results showed that introduction of the organic phase imparted desirable hydrophobicity and flexibility to the coating, whilst still providing effective electrical insulation at temperatures up to 500 °C. The hybrid coatings covered the iron particle surface very effectively and formed continuous coatings that could remain intact even after compaction at pressures up to 900 MPa, depending on the coating amount. Initial magnetic characterisations are also encouraging. As a result, such hybrid-coated iron powders can be considered suitable candidates as heat-treatable high-performance dielectromagnetics.     

Dissipative properties of nanostructured materials

Results of studies of the effect of the size of micro-and substructure elements (grains, twin domains, etc) on the dissipative properties of materials have been generalized. It has been shown that when the size of the microstructure elements of materials decreases to nanoscale, their dissipative properties change qualitatively. This is due to a change in mechanical energy dissipation mechanism on the transition of material to nanostructured state. The possibility of creating a new class of highly damping hard coatings based on nanostructured materials is discussed. __________ Translated from Problemy Prochnosti, No. 5, pp. 96–104, September–October, 2008.     

Chemical routes to nanostructured materials

Abstract

Chemical synthesis has been used to fabricate polymerisable nanoparticles. Agglomerate free, well crystallised particles have been obtained by hydrothermal treatment and by using surface modifiers. Polymerisable liquids are used as modifiers to obtain polymerisable particles. Suspensions of these particles were used to carry out dip and spin on coating processes, either for optical applications or for superhard coatings. For optical purposes, a wet coating antireflection technology has been developed. The superhard coatings have been developed for polycarbonate plastic glazing for automobiles. These coatings are employed on top of nanocomposite (Nanomer) hard coatings and are cured by UV polymerisation. They show abrasion resistance of 1.5 haze after 1000 taber abrador cycles, a value which is similar to glass.     

Fabrication and characterization of molecular hybrid materials with lanthanides covalently bonded in silica via sol-gel process

Tetraethoxysilane (abbreviated as TEOS) and a kind of monomer (abbreviated as PMA-APES) derived from modifying phenylmalonic acid with double carboxylate groups (abbreviated as PMA) with (3-aminopropyl)triethoxysilane (abbreviated as APES) were used as the inorganic and organic compounds respectively. Coordination reaction between lanthanides and the two -CO groups of the monomer happened simultaneously. The resulting material exhibits strong red-colored fluorescence (Eu³⁺) and green-colored fluorescence (Tb³⁺), suggesting the intramolecular energy transfer caused by coordination effect of the organic counterpart. IR, NMR, UV/vis absorption, low-temperature phosphorescence and fluorescence spectroscopy were applied for characterization of the material and the above spectroscopic data revealed that the triplet state energy of organic ligand matches with the emissive energy level of europium and terbium ions and effective intramolecular energy transfer process in these molecular hybrid systems.     

Review Stability of nanostructured materials

The different aspects of nanostructured material (NM) stability such as thermal and chemical stability as well as NM behavior under deformation and radiation are characterized and analyzed in detail. Grain growth, phase transitions (including spinodal decomposition), homogenization diffusion processes, relaxation of residual stresses, and behavior of grain boundary and triple junction segregations are discussed in context of the change of nanostructure and properties. Special interest is given to the availability of NMs with ultra-fine grain size and their behavior during annealing as soon as to the possibility of development of nanostructures with high thermal stability. Some unsolved problems are emphasized.     

Preparation of silica monolith via sol-gel route

The present investigation deals with the synthesis of monolithic NiCl₂-silica gels obtained by hydrolysis and polycondensation of tetraethoxy silanes. This sol to gel formation can mainly be controlled by adjusting some variables e.g. acid content of the solution, ageing and leaching times. A minimum acid content was found necessary to prepare uncracked gel while ageing and leaching times were found to be not that sensitive for the formation of uncracked gels.     

Optical bonding using silica nanoparticle sol-gel chemistry

A simple method is described to bond optical components using silica nanoparticle sol-gel chemistry. The silica nanoparticles polymerize into highly branched networks that link the surfaces together. The nanoparticle mediated bonding has several advantages to currently used optical joining technologies. The bonding is a room-temperature process and does not require any clean room facilities. The bonded interface has a high mechanical strength and low scattering. The bonding is resistant to organic solvents on silylation with hydrophobic surface groups. This method achieves 100% successful bonding rates between soda-lime glass slides. The bond-setting time can be tailored to allow time for precision optical alignment.     

A meso-model of spalling with thermal coupling for hard metallic materials

Study and modeling of physical mechanisms of spalling observed via plate impact experiments for two industrial alloys are the subject of this paper. Because spalling is a specific kind of fracture, which is loading history dependent, the aspects of the initial microstructure and its evolution during plastic deformation are very important. In order to understand better the physical mechanisms of spall, numerous scanning electron microscopy pictures of the free surface created by spalling have been taken for two materials, a hard aluminum alloy and an armor steel. It has been confirmed that the microstructure has a direct influence on the mechanism of nucleation, growth and coalescence of micro-cavities or micro-cracks by means of distribution of nucleation sites and decohesion between the harder particles and the softer lattice. The results of measurements in the form of statistical distribution of horizontal micro-segments of fractured surfaces of targets, corresponding to quasi-brittle fracture, and vertical micro-segments, corresponding to ductile or adiabatic shear banding, all along the entire cross-section of a target, are reported for armor steel. As a result a new model has been proposed, based on the meso-scale approach. The model is in agreement with physical mechanisms which are present during spall fracture.