Synthesis, properties, application of nanosized powders of oxides and hydroxides. Cluster model of water state on their surface

The work is devoted to the development of the physicochemical foundations of the processes of obtaining powders of oxides and hydroxides, including aluminum, magnesium, calcium, and silicon with a given shape, size, impurity and phase composition, low thermal conductivity, etc., by methods of pyrolysis of a polymer matrix and hydrothermal treatment element-containing precursors, as well as the creation of a mechanism that allows describing the phase transformations of powders of oxides and hydroxides and reveals the role of water clusters with a low heat of vaporization in phase transformations.

Electromagnetic characteristics of materials based on ultrafine hexaferrite powders

The electromagnetic characteristics of composite materials based on nanosized powders of W-type hexaferrites are considered in the article. It is shown that not only the composition, but also the mechanical treatment affects the electromagnetic parameters. This article presents the frequency dependence of the complex magnetic and dielectric permittivity of a system of W-type hexafferites. The studies were carried out on a universal wide-band measuring complex based on the Agilent PNA-X N4257A Vector Network Analyzer. The results are presented in the frequency range from 2 to 14 GHz.

Preparation, properties and application of cerium(III) methanesulfonate

Based on the results of physicochemical analysis, IR-spectroscopy, derivatographic analysis and differential scanning calorimetry, it was established that the interaction of cerium(III) carbonate with methanesulfonic acid yields cerium(III) methanesulfonate Се(SO3CH3)34H2O. Thermolysis of complex compound Се(SO3CH3)34H2O proceeds via a complex chemical mechanism and is completed at the temperature of 540–5500C producing nanocrystalline powders of cerium(IV) oxide having cubic structure with primary particle sizes of 20–30 nm, aggregate sizes of 50–200 nm and specific surface area of 62–68 m2 g–1. A probable mechanism of thermal decomposition of cerium(III) methanesulfonate is proposed, which depends on the temperature conditions of the thermal decomposition process. At low temperatures, the thermolysis of Се(SO3CH3)34H2O proceeds by the mechanism of surface oxidation with the formation of cerium oxide. At temperatures above 4500C, thermolysis is transformed into combustion with a significant heat effect and the formation of nanosized powders of cerium(IV) oxide of the corresponding morphological structure. It was found that the solutions of cerium(III) methanesulfonate show antiviral activity in vitro.

Combustion Characteristics of Nanoaluminium-Based Composite Solid Propellants: An Overview

The nanosized powders have gained attention to produce materials exhibiting novel properties and for developing advanced technologies as well. Nanosized materials exhibit substantially favourable qualities such as improved catalytic activity, augmentation in reactivity, and reduction in melting temperature. Several researchers have pointed out the influence of ultrafine aluminium (∼100 nm) and nanoaluminium (<100 nm) on burning rates of the composite solid propellants comprising AP as the oxidizer. The inclusion of ultrafine aluminium augments the burning rate of the composite propellants by means of aluminium particle’s ignition through the leading edge flames (LEFs) anchoring above the interfaces of coarse AP/binder and the binder/fine AP matrix flames as well. The sandwiches containing 15% of nanoaluminium solid loading in the binder lamina exhibit the burning rate increment of about 20–30%. It was noticed that the burning rate increment with nanoaluminium is around 1.6–2 times with respect to the propellant compositions without aluminium for various pressure ranges and also for different micron-sized aluminium particles in the composition. The addition of nano-Al in the composite propellants washes out the plateaus in burning rate trends that are perceived from non-Al and microaluminized propellants; however, the burning rates of nanoaluminized propellants demonstrate low-pressure exponents at the higher pressure level. The contribution of catalysts towards the burning rate in the nanoaluminized propellants is reduced and is apparent only with nanosized catalysts. The near-surface nanoaluminium ignition and diffusion-limited nano-Al particle combustion contribute heat to the propellant-regressing surface that dominates the burning rate. Quench-collected nanoaluminized propellant residues display notable agglomeration, although a minor percentage of the agglomerates are in the 1–3 µm range; however, these are within 5 µm in size. Percentage of elongation and initial modulus of the propellant are decreased when the coarse AP particles are replaced by aluminium in the propellant composition.

Ceramics based on powders synthesized from ammonium hydrophosphate and acetates of calcium and magnesium

Ceramics the phase composition of which included tricalcium phosphate, calcium magnesium ortophosphate and magnesium pyrophosphate has been produced from nanosized powders synthesized by chemical deposition from 1M aqueous solutions of ammonium hydrogen phosphate and calcium and / or magnesium acetates. According to XRD analysis the phase composition of the powder synthesized from calcium acetate included calcium hydroxyapatite Ca5(PO4)3(OH), octacalcium phosphate Ca8H2(PO4)6·5H2O and brushite CaHPO4·2H2O. The phase composition of the powder synthesized from magnesium acetate included struvite MgNH4PO4·6H2O. And the phase composition of the powder synthesized from solution containing calcium and magnesium acetates at the cation ratio Са: Mg = 9: 1 included hydroxyapatite Ca5(PO4)3(OH), whitlockite Ca18Mg2H2(PO4)14, and struvite MgNH4PO4·6H2O. Ceramic materials containing the bioresorbable and biocompatible phases of calcium and / or magnesium phosphates can be used to make bone implants for treatment of bone tissue defects. Keywords: tricalcium phosphate, calcium magnesium orthophosphate, magnesium pyrophosphate, whitlockite, octacalcium phosphate, hydroxyapatite, brushite, struvite, ceramics.

Nano- and Micro-Modification of Building Reinforcing Bars of Various Types

Fiber-reinforced plastic (FRP) rebar has drawbacks that can limit its scope, such as poor heat resistance, decrease its strength over time, and under the influence of substances with an alkaline medium, as well as the drawback of a low modulus of elasticity and deformation. Thus, the aim of the article is the nano- and micro-modification of building reinforcing bars using FRP rebars made of basalt fibers, which were impregnated with a thermosetting polymer binder with micro- or nanoparticles. The research discusses the major results of the developed composite reinforcement with the addition of micro- and nanosized particles. The microstructure of FRP has been studied using scanning electron microscopy. It was revealed that dispersion-strengthened polymer composites with the inclusion of microsilica (SiO2) and nanosized aluminum oxide (Al2O3) particles have a much higher modulus of elasticity and strength when compared with the original polymer materials. In the course of the experiment, we also studied the retained plastic properties that are characterized by the absence of fragility. However, it was found that the high strength of materials was attained with a particle size of 10–500 nm, evenly distributed in the matrix, with an average distance between particles of 100–500 nm. It was also exhibited that composite reinforcement had improved the adhesion characteristics in comparison with both steel reinforcement (1.5–2 times, depending on the diameter), and with traditional unmodified FRP rebar (about 1.5 times). Thus, the use of micro-/nanosized powders increased the limit of the possible temperature range for the use and application of polymeric materials by almost two times, up to 286–320 °C, which will undoubtedly expand the range of the technological applications of products made of these materials.

BaTiO3 films for multilayer devices by tape casting

The diversity of the applicational scope of modern printed electronics relentlessly requires the improvement of operational properties simultaneously with reducing the overall dimensions of devices. One of the most effective ways to overcome this major obstacle is the reduction of functional layers thickness in respect to the size of the device. In the present article, we are discussing a simple way of practical implementation of miniaturization concept through the application of a well-known high-productive industrial method of tape casting for obtaining thin nanostructured ceramic layers based on BaTiO3 nanopowders for MLCC. Using of nanosized powders per se imply a new approach of developing suspensions with suitable rheology for tape casting. We demonstrate, that a length of polymer molecule defines the size of floccules and therefore influences the thickness and surface quality of tape casted films. A certain nanopowder/polymer ratio contributes to the formation of the tapes with the surface roughness comparable with the size of one nanoparticle (20-25 nm). Moreover, it was established that developed suspensions are extremely sensitive to temperature changes. Lowering the temperature significantly affects the flow character of suspension and thus the thickness of casted tapes. Considering this fact, we propose an effective self-developed pre-cooling method of nanopowder suspension casting, which allows obtaining extremely thin and smooth tapes with a thickness of less than 1 µm and surface roughness of 20–25 nm by tape casting method.

Material modification by high-intense pulsed ion beams

The review is devoted to the use of powerful submicrosecond ion beams for the synthesis and modification of material properties. Powerful ion beams, originally developed for the problems of inertial thermonuclear fusion, have been increasingly used over the past 30 years as a powerful pulsed heating source providing ample opportunities for modifying the surface layer of materials. By varying the key parameters of the beams, such as the composition (type of ions), the duration of the accelerating pulse (10 ns – 1 μs), the kinetic energy of the ions (0.1 – 1 MeV), the energy density transmitted by the beam to the target surface per pulse (0.1 – 50 J/cm2), the main areas of application of high-power ion beams in materials science were determined: modification of the surface layer by ultrafast quenching, melting and ultrafast recrystallization with the formation of micro- and nanostructures, pulsed implantation of ions accompanied by energetic action, deposition of thin films and synthesis of nanosized powders from ablative plasma.