Thread-like Crystals Research Articles

Crystals morphology of ethylenediaminetetraacetatozincate triethylenediaminium and tetramethylethylenediaminium

Trimethylenediamine ethylenediaminetetraacetate zincate trihydrate [HN(CH2CH2)3NH]ZnL · 3H2О and tetramethylethylenediamine ethylenediaminetetraacetate zincate dihydrate [H(CH3)2NCH2CH2N(CH3)2H]ZnL · 2H2О were synthesized by reacting zinc oxide with ethylenediaminetetraacetic acid (H4L) and then with its triethylenediamine or tetramethylethylenediamine salts. The resulting compounds precipitate from aqueous or organic solvents in the form of thread-like, cubic and pyramidal crystals, which are characterized by elemental analysis, scanning electron microscopy, IR spectroscopy, thermogravimetry and differential scanning calorimetry.

V–Cd nanoparticle-formed alloys: fabrication, phase composition and structure

The results of the study of targeted sputtering and deposition of ultrafine vanadium and cadmium particles on substrates that are not heated and shifted with respect to the substrate plasma currents are revealed. As a result of the conducted studies, coatings were obtained in the range with a concentration of cadmium from 9.6 to 88.6 at.%. The critical size of vanadium particles capable of forming alloys with cadmium is 0.6 nm. The concentration limit for the presence of solid solutions of cadmium in vanadium is the cadmium content of ~37 at.%, at a higher cadmium content the film coating is represented by a mixture of cadmium phases and a solid solution of cadmium in vanadium. The dependence of the lattice parameter of α-vanadium on the content of cadmium in it corresponds to the expression: а [nm] = 8·10–4СCd + 0.3707, where СCd is the concentration of cadmium, at.%. On the surface of the sample in the region of solid solutions (31.6 at.% Cd), the presence of threadlike crystals of cadmium was found, the reason for the appearance of which is the lattice pressure of the matrix metal. Annealing of films rich in cadmium (69.5 at.%) in vacuum is accompanied by cracking of the coating and the formation of pores. The latter can be used as a method for obtaining porous vanadium.

Di-carbonyl-o-semiquinonato rhodium complexes

Two novel dicarbonyl-semiquinonato rhodium complexes were synthesized and studied. Complexes are analogues of (CO)2Rh(3,6-DBSQ) (3,6-DBSQ-3,6-di-tert-butyl-o-benzosemiquinone) which thread-like crystals can bend reversibly under light or heat activation (G.A. Abakumov, V.I. Nevodchikov, Dokl. Acad. Nauk SSSR 1982, 266, 1407–1410). Complexes differ from (CO)2Rh(3,6-DBSQ) by substituents in 3,6-positions of quinonato ring (cyclohexyl (1) and isopropyl (2) instead of tert-butyl). Single crystal structural study indicates that both complexes are the derivatives of Rh(I) with o-semiquinonato anion-radical. Molecules form pairs due the short contacts in contrast to (CO)2Rh(3,6-DBSQ) and other similar compounds which form the endless alternated chains with direct Rh-Rh bond. At that, complex 1 molecules form isolated pairs, whereas molecules of 2 can be united in the chain. Both compounds 1 and 2 have the array of intensive bands in IR spectrum in the region 1350 cm−1 which is closer to bond stretch vibrations of C–O ordinary bond but not sesquilateral. EPR of solutions of complexes indicates presence of monomeric complex molecules where the single unpaired electron is localized in o-semiquinonato ligand. The drop of EPR signal intensity with cooling of solutions of 1 and 2 evidence that the association process takes place.

Single Crystal X-ray Diffraction Studies of Two Polymorphic Modifications of the Dicarbonyl-o-Semiquinonato Rhodium Complex at Different Temperatures. Destruction Stimulated by Cooling Versus Stability.

It was found that the dicarbonyl-rhodium-o-semiquinonate complex (which thread-like crystals can bend reversibly under light/warm activation) can form two polymorphic modifications: isometric prisms (1) and sticks (2). Some thin sticks can bend as mentioned above. X-ray diffraction studies of polymorphic modifications at different temperatures were carried out. It was found that crystals 1 are destructed after cooling to 110 K as opposed to crystals 2. In turn, the reversible phase transition is detected in 2. In both polymorphic modifications, stack packaging motifs through the direct Rh–Rh bond are observed. The principal difference between packages of polymorphic modifications is that molecules 1 in the adjacent stacks are shifted relative to each other along the stack, in contrast to crystal 2. It was found that different packing of stacks leads to different anisotropic compression of crystals 1 and 2 during cooling, which is a key factor of their stability. Using the molecular invariom approach, the nature of the chemical bonds and charge distribution was investigated; the energy of the Rh–Rh bonds was estimated.

Structure and Phase Composition of V-Al-N-C Master Alloy

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Получение нитрида и оксонитрида кремния газофазным пиролизом гексаметилдисилазана

The technique was developed, the installation was done, and the conditions for the production of Si3N4 and Si2N2O by the method of gas-phase pyrolysis of hexamethyldisilazane (CH3)3-Si-NH-Si-(CH3)3 (HMDS) were experimentally studied. In the experiments, two different methods of inputting the raw material were used—the input of a vapor–gas mixture (bubbling feeder with heating to supply the HMDS vapor in a stream of carrier gases) and input as a gas-droplet stream (pneumatic nozzle). The effect of gas-dynamic synthesis conditions at temperatures up to 1100°C on the properties of silicon oxonitride and silicon nitride nanopowders was studied. The influence of the conditions of mixing the reactants, the volume ratio of nitrogen/ammonia, and the content of HMDS in the vapor–gas mixture on the yield of products was shown. The dependences of the degree of conversion of the feedstock on the gas flow rate and the concentration of ammonia in the gas phase were obtained. The optimal conditions for the pyrolysis process were found: temperature, the ratio of the components of the gas mixture, the conditions of mixing, and the contact times of the phases. X-ray amorphous Si3N4 and Si2N2O powders with particle sizes of 50–200 nm and a specific surface area of up to 15 m2/g and powders of alpha modification of silicon nitride Si3N4 in the form of threadlike crystals with a particle diameter of 50–200 nm were obtained.

Investigation on the microstructure and fracture behavior of super-eutectic ZA alloy welded joint by pulse fiber laser

In this study, we present the experimental laser welding of super-eutectic ZA alloy. Microstructures of the ZA alloy′s bond area welded by pulsed laser were investigated using an optical microscope, scanning electron microscope, energy diffraction spectrum and X-Ray diffractometer. The results showed that microstructures in the weld mainly consisted of threadlike columnar crystals, coarse dendrites and fine equiaxed grains. Secondary particles were produced in the interdendritic zones because of the composition segregation. A poor Al area was formed inside the η grain while a rich Al area takes shape outside the η grain. The occurrence of the composition segregation can increase the grain boundary cracking tendency. The existence of a large number of η phase greatly intensified the brittle of this material. The presence of many cleavage steps in the fractograph principally depended on the secondary cleavage effect between two cleavage cracks on different planes. The evolution of cracks along the twinning plane was the result of the secondary cleavage substituting for the twinning deformation in the vicinity of the crack tip.

Research of methods of obtaining continuous fibres of whiskers

The object of this research is some methods of obtaining continuous fibers of whiskers. The method of obtaining such fibers by extrusion of an organometallic colloidal solution is studied using the example of a scheme for carrying out such process. The process of obtaining fibers by the method of pyrolysis of polymeric fibers is studied using the example of another conceptual scheme. The problematic aspects of carrying out both processes and the use of such methods include the difficulty in obtaining the desired configuration and orientation of the fibers of threadlike crystals, as well as the inadequate perfection of the apparatus and installations for obtaining such fibers. When writing the work, various methods of scientific research were used, such as the method of statistical analysis, the method of analyzing the research results, the hypothetico-deductive method and the method of generalizing the results. The conducted studies show that the conditions for carrying out both processes must be strictly controlled, especially the temperature rise. It is shown that the methods used have an increased degree of danger. It is substantiated that, in spite of observance of all parameters of the conducted processes, the fact that the final fibers of the crystals will not have the necessary orientation and configuration may not be ruled out. As a result of the studies it is shown that the production of continuous fibers of whiskers by extrusion of an organometallic colloid solution is quite effective from the point of view of obtaining the final product of the desired orientation and the necessary parameters. The effectiveness of this method can be improved if the processes of doping the fibers from the gas phase are successfully used. It is shown that when carrying out studies of obtaining similar fibers by pyrolysis, it is possible to have high efficiency of the completed process, with full observance of the parameters of its conduct and sufficient perfection of the equipment. A fairly significant issue when using this particular method is the most effective conduct of the tension process of continuous fibers of whiskers during the heat treatment.

Estimates of the Elastic Characteristics of a Composite with Short Anisotropic Fibers

A composite with chaotically oriented fibers with different elongations and different anisotropy of elastic characteristics is considered. A mathematical model of interaction of such fibers and matrix particles with an isotropic elastic medium whose elastic moduli have to be found as required characteristics of the composite is constructed. The relations derived by the self-consistency method determine the moduli of the composite as functions of the volume concentration, elongations, and elastic properties of each type of fibers, and also of the elastic characteristics of the isotropic matrix. A quantitative analysis of the mathematical model is carried out, and boundaries of the domains of determining parameters within which the effect of fiber elongation is considerable are found. The relations presented allow one to estimate the elastic characteristics of a composite reinforced with various types of short fibers (in particular, high-strength and high-modulus needle-shaped and thread-like crystals, and nanostructural elements).

EELS and electron diffraction studies on possible bonaccordite crystals in pressurized water reactor fuel CRUD and in oxide films of alloy 600 material

Abstract Experimental verification of boron species in fuel CRUD (Chalk River Unidentified Deposit) would provide essential and important information about the root cause of CRUD-induced power shifts (CIPS). To date, only bonaccordite and elemental boron were reported to exist in fuel CRUD in CIPS-troubled pressurized water reactor (PWR) cores and lithium tetraborate to exist in simulated PWR fuel CRUD from some autoclave tests. We have reevaluated previous analysis of similar threadlike crystals along with examining some similar threadlike crystals from CRUD samples collected from a PWR cycle that had no indications of CIPS. These threadlike crystals have a typical [Ni]/[Fe] atomic ratio of ∼2 and similar crystal morphology as the one (bonaccordite) reported previously. In addition to electron diffraction study, we have applied electron energy loss spectroscopy to determine boron content in such a crystal and found a good agreement with that of bonaccordite. Surprisingly, such crystals seem to appear also on corroded surfaces of Alloy 600 that was exposed to simulated PWR primary water with a dissolved hydrogen level of 5 mL H 2 /kg H 2 O, but absent when exposed under 75 mL H 2 /kg H 2 O condition. It remains to be verified as to what extent and in which chemical environment this phase would be formed in PWR primary systems.

О возможности перекристаллизации дисперсного рутила, растворенного в расплаве галогенидов щелочных металлов, в нитевидные кристаллы

In the article the theoretical and experimental results of practical receipt of threadlike crystals are represented by recrystallization of dispersible rutile saluted in fusion of halide of alkaline metals. The expected kinetic parameters allow to organize a process with the set speed of flowing and necessary output of product. Possibility of recrystallization of titanium oxide is set in molten salt at blowing out by gas and gas with a repairer as the threadlike crystals with fibred form

Mechanical properties of whiskers

It is known that the structure of thread-like crystals is perfect and the limit of their strength approaches to the theoretical. However, the studies showed the ambiguity of relationship between the structure of perfect «whiskers» and their high strength. Literature review, conducted in the paper, concerning the research of such group of properties of thread-like crystals as mechanical properties, showed the presence of defects in the crystal structure of «whiskers» and the dependence of the strength of crystals on transverse and longitudinal sizes of «whiskers».The study of mechanical properties of thread-like crystals is considered in many of literature sources, in particular 12 sources were mentioned in the paper, but evaluations of the results of experimental studies are quite different and ambiguous. Based on the literature review, corresponding conclusions on some mechanical properties of thread-like crystals were considered, estimated and outlined in the paper, the influence of the changes of their characteristics on the structure of crystals and ambiguity of estimation of direct relationship between the strength of crystal and its structure was analyzed.

Narrowband spectral filters on the basis of threadlike metal Si photonic crystals

The scattering of transmitted and evanescent electromagnetic waves by threadlike photonic crystals, made of different materials, is studied theoretically. The reflection and transmission spectra of the waves, the electric vector of which is parallel to the threads, are calculated on the basis of a matrix Riccati equation. The physical reasons for the appearance of transparency peaks in the transmission spectra of threadlike photonic crystals are discussed. It is established that narrowband filters suggested previously and formed by a periodic system of Si threads about 1 μm in diameter and adjusted to a wavelength of 1.5 μm totally lose their filtering capabilities at small deviations (about 5%) from the thread diameter. However, the reflection and transmission spectra of filters containing periodically packed metallized Si threads are stable in the case of such variations in thread size. It is shown that threadlike crystals are an effective discrete mirror for radiation of the near- and mid-IR spectral range. The capabilities of threadlike crystals for filtering homogeneous and inhomogeneous waves are shown.

Changes in the structures and phases of tin-fullerite films during annealing

The patterns of change in the structure and phase composition of tin-fullerite films subjected to thermal annealing in vacuum at different temperatures (430, 450, 470, and 490 K) are studied using scanning electron microscopy, atomic-force microscopy, X-ray diffraction, and X-ray spectrum microanalysis. It is established that annealing at T = 450 K or higher leads to significant changes in the structures and phases of films; namely, new phases Sn x C60 are formed in the form of threadlike crystals with lengths of 6 μm containing 98 at % C and 2 at % Sn and ball-shaped isolations with diameters up to 12 μm consisting of 50 at % C and 50 at % Sn.

A new unprecedented method for the synthesis of 1-fluorosilatrane

We developed the simplest and the most convenient original procedure for the synthesis of fluorosilatrane. The method is shown in the following scheme: parent very viscous liquid (in contrast to other crystalline triethanolammonium halides). To this product was added an equimolar amount of tetraethoxysilane, and stirring while heating was continued with distilling off the evolved ethanol. White powder of the formed fluorosilatrane was heated in a vacuum to remove residual (EtO)4Si and EtOH (yield of the latter was 90%). The FSa formed has sublimation temperature ~300°С at the atmospheric pressure in agreement with the published data [1, 4]. Noteworthy that at the temperature above 220°С the FSa powder is transformed into threadlike crystals. IR spectrum of FSa formed (KBr pellet) contains strong adsorption bands corresponding to vibrations of Si–F (748– 785 cm ), Si–O (790–810 cm), and С–O (1075– 1150 cm) bonds. H and С NMR spectra of solution of FSa in DMSO-d6 are characterized by the following parameters: δH 2.92 and 3.69 ppm, δС 50.5 and 56.8 ppm. The IR and NMR spectra of the fluorosilatrane obtained are consistent with the published data [3, 7– 10].

The effect of degassing modes on the self-propagating reactions for the SiO 2–Al–C system in the presence of reaction promoters

The combustion synthesis process activated by organic polymers (Teflon and polystyrene) in the SiO 2/Al/C system is investigated under the counter-current and co-current degassing conditions. It is found that the combustion parameters, i.e. wave velocity and temperature, and final product microstructure are influenced by the degassing mode considered as well as the type and amount of promoters added to the starting mixture. In particular, the combustion wave results to accelerate during its propagation when adopting the forward infiltration configuration and in absence of polystyrene. In addition, under the same degassing condition, the produced gases are found to provide a specific orientation on the growth direction of thread-like SiC crystals during final product formation.

Electronic structure of simple metal whiskers

The electronic structure of thread-like cylindrical crystals (whiskers) of simple metals has been calculated within the framework of density-functional theory and the jellium model. As the whisker's radius increases, oscillations of the work function and the bandwidth are observed. They are connected with the filling of energy bands and the relation between the filling of energy bands and the shape of the electronic density and one-particle potentials is shown. The effect of dielectric surroundings on the electronic structure of metal whiskers has been studied.

Cryo-TEM of micelles and lyotropic liquid crystals in non-aqueous solvents

Surfactant molecules can form spherical micelles in water above the critical micellization concentration. At still higher concentrations, they can form thread-like micelles and liquid crystals. Cryo-transmission electron microscopy of these microstructures in water is now used successfully for studying aqueous biological and synthetic systems. The controlled environment vitrification system (CEVS) makes it possible to prepare samples accurately. Further, The on-grid processing makes specimens possible from evolving systems halted in mid-process.Despite all the successes with aqueous systems, imaging of microstructures formed in non-aqueous solvents has not been reported. The main difficulties are radiation damage, thermal drift of the specimen, and low contrast. As small a spot size and as well spread a beam as possible are needed for low magnification searching. During the image recording, the minimum dose and lowest magnification possible are desired in order to avoid the thermal drift and radiation damage while maintaining an adequate signal-to-noise ratio.

Electrodeposition of whiskers and thread-like crystals

Methods of producing metal whiskers in a two-layer bath by electrolysis are reviewed in this paper. The growth mechanism and relationship of crystal properties and conditions of their growth are discussed here. The possibility of using these whiskers for the production on metal-plastic magnets is described.

Effect of thread-like crystals on the physical properties of mullite-corundum ceramics

Effect of thread-like crystals on the physical properties of mullite-corundum ceramics