Formation Of Primary Structures Research Articles

Influence of hydrogen on formation of primary structures of tin and aluminium bronze

It is shown that hydrogen is a demodifying element of primary structures of tin and aluminum bronzes during their crystallization. The mechanism of influence of hydrogen on the formation of primary structures of tin and aluminum bronzes can be explained from the position of nanostructured crystallization of casting alloys. Hydrogen atoms adsorbed on elementary nanocrystals in melts prevent the combination of nanocrystals into nuclei of crystallization of microcrystals α‑phases of tin and aluminum bronzes. The result is castings with unmodified primary structures. The modifiers reduce the concentration of adsorbed hydrogen in the melts of tin and aluminum bronzes. This results in the milling of the primary phase microcrystals in the castings as they solidify.

The [S ii] Spectral Images of the Planetary Nebula NGC 7009. II. Major Axis

We derived position–velocity density distribution diagrams along the major (PA = 77°) axis of the elliptical planetary nebula NGC 7009 with the Keck HIRES [S ii] 6716/6731 Å doublet spectral images. The average densities of the main shell and knots of NGC 7009 derived from the [S ii] 6716/6731 Å fluxes integrated over the line of sight indicate a density range of N e = 103.4 to 103.9 cm−3, while the local densities from the volume fraction resolved in radial velocities along the line of sight show a considerably large range of about 102.8–104.7 cm−3. The derived projection angle of the major axis of the main shell is ψ ∼ 18.3° (±2°). Assuming that the main shell is an ellipsoidal shell with a ≃ 16″ and b ≃ 6″, we found the range of the expansion velocity, radius, and latitude of four knots and a hot bubble. The four knots at points in symmetrical positions are roughly aligned with the same axis of expansion of latitudes ϕ ∼ ±34.5° (±0.6°): one pair expands at about 35 km s−1 close to the main ellipsoidal shell, and the other expands rapidly at about 60 km s−1 at a distance of r ∼ 16″. In the latitude range ϕ = 65°–75°, the hot bubble of a relatively large structure expands rapidly with a velocity of 130–150 km s−1. The four knots and hot bubble points, which expand faster than the main shell, appear to have been formed by two to three eruptions at a different epoch from the primary structure formation.

In situ synchrotron research of phase formation in mechanically activated 3Ti + Al powder composition during high-temperature synthesis under the condition of heating with high-frequency electromagnetic fields.

An in situ synchrotron study of the specific features of the phase formation dynamics in mechanically activated 16 wt% Al + Ti powder composition is described, the high-temperature synthesis being carried out under the condition of high volume inflammation by means of inductive heating. The kinetics of the phase formation were registered with an experimental complex, especially designed, constructed and adjusted for the method of dynamic diffraction analysis in synchrotron radiation beams. It has been experimentally in situ shown that increasing the time of mechanical activation of the initial powder mixture reduces the temperature at which components start to react and the time of realization of the high-temperature synthesis. With the latter set at 1 min of mechanical activation, the temperature of the reaction in the mixture is T = 603°C; at 3 min of mechanical activation, T = 442°C; and at 7 min, T = 359°C. The maximum burning temperatures are: for 1 min of mechanical activation, Tmax = 1080°C; for 3 min, Tmax = 1003°C; and for 7 min, Tmax = 820°C. It was found that formation of both stable compounds Ti3Al, TiAl3, TiAl2, TiAl and metastable phases Ti9Al23, Ti5Al11, Ti2Al5, Ti3Al5 occurs at the stage of primary structure formation, before the system goes to thermal explosion. High-temperature synthesis of a mixture of the studied composition takes place without formation of a liquid phase, in the solid-phase combustion mode. It was found that the increase in the time of mechanical activation of the initial powder mixture contributes to the formation of a product with a dominant content of intermetallic compound Ti3Al. By synthesis of the powder mixture of composition 16 wt% Al + Ti, mechanically activated for 7 min, the content of Ti3Al in the final product was found to be 68%.

Multivalent, multiflavored droplets by design

Nature self-assembles functional materials by programming flexible linear arrangements of molecules and then folding them to make 2D and 3D objects. To understand and emulate this process, we have made emulsion droplets with specific recognition and controlled valence. Uniquely monovalent droplets form dimers: divalent lead to polymer-like chains, trivalent allow for branching, and programmed mixtures of different valences enable a variety of designed architectures and the ability to subsequently close and open structures. Our functional building blocks are a hybrid of micrometer-scale emulsion droplets and nanoscale DNA origami technologies. Functional DNA origami rafts are first added to droplets and then herded into a patch using specifically designated "shepherding" rafts. Additional patches with the same or different specificities can be formed on the same droplet, programming multiflavored, multivalence droplets. The mobile patch can bind to a patch on another droplet containing complementary functional rafts, leading to primary structure formation. Further binding of nonneighbor droplets can produce secondary structures, a third step in hierarchical self-assembly. The use of mobile patches rather than uniform DNA coverage has the advantage of valence control at the expense of slow kinetics. Droplets with controlled flavors and valences enable a host of different material and device architectures.

Расчетная и экспериментальная оценка формирования первичной структуры металла шва с тугоплавкими инокулянтами

Расчетная и экспериментальная оценка формирования первичной структуры металла шва с тугоплавкими инокулянтами

Computation and experimental evaluation of formation of primary structure in weld metal with refractory inoculants

Computation and experimental evaluation of formation of primary structure in weld metal with refractory inoculants

Effect of modifying tungsten additions on formation of primary structure of R6M5-type high-speed steel

The effect of modifying additions of powder and compact (in the form of chips) tungsten on the formation of the primary structure of the R6M5-type tungsten-molybdenum high-speed steel has been investigated. The results of metallographic and electron microprobe analyses of base and modified steels have been discussed. It has been shown that the modification of the R6M5 steel with tungsten brings about considerable qualitative and quantitative changes in the microstructure of the matrix and carbide component of eutectic origin.

Special features of microstructure of W– Mo high-speed steel modified with titanium diboride

The effect of a modifying additive of titanium diboride on formation of primary structure in tungsten-molybdenum high-speed steel of type R6M5 is investigated. Results of metallographic, x-ray diffraction, and microscopic x-ray spectrum analyses of the base and modified steels are discussed. It is shown that modifying of steel R6M5 with titanium diboride causes qualitative and quantitative changes in the microstructure of the matrix and of the carbide component.

Secondarily-induced gravitational wave background in modified gravity

We explore the effect of structure formation on gravitational wave background in dark energy cosmology. Second-order tensor perturbations induced by first-order scalar mode are considered in a modified gravity dark energy model. We present explicitly the procedure for an approximate estimation of the second-order tensor perturbations caused by primary structure formation.

Characteristic properties of combustion and structure formation in the Ti-Ta-C system

Macrokinetic characteristics of the combustion of mixtures in the (100% − X)(Ti + 0.5C) + X(Ta + C) system with a variable mixing parameter X and initial temperature T0 of charge heating are considered. For compositions with X = 10 and 30%, an abrupt increase in the velocity Uc and temperature Tc of combustion as a result of passing two parallel chemical reactions of titanium and tantalum carbide formation is established. The Uc (T0) and Tc (T0) dependencies are linear for the mixture with X = 50%. By hardening the combustion wave, it is revealed that the primary structure formation in the combustion region starts from the selection of submicron grains of nonstoichiometric titanium carbide from the supersaturated titanium melt. In the investigated range of parameter X, synthetic products are single-phase and represent titanium-tantalum carbide. An increase in X results in a decrease in the size and microhardness of (Ti, Ta) C grains and a reduction of the relative density of compact synthetic products. The kinetics of high-temperature oxidation of alloys on the basis of carbide (Ti, Ta) C is studied. Ceramics produced at X = 10% are most heat-resistant.

Study of Solutions of Heterocyclic Para-Copolyamide

Polycondensation copolyamide solutions are homogeneous systems according to spectroturbidimetric evaluation. Solutions of reprecipitated copolyamide are heterogeneous. The heterogeneity could be caused by relatively strong supramolecular formations that are not decomposed by the solvent. The use of turbidimetric titration curves for assessing the molecular-weight distribution of copolyamide is problematic, since irregular distribution of the units, the acidity of the medium, and primary structure formation, together with the molecular weight, can affect separation of copolyamide from a solution of the copolymer by the precipitant. The extreme character of the dependence of the intrinsic viscosity of copolyamide on the acidity of the solution suggests that in certain conditions, the copolyamide can exhibit polyelectrolytic properties.

Crystallization behaviour of poly(N-methyldodecano-12-lactam) Part 1. Isothermal crystallization

Differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS) and Raman spectroscopy have revealed a complex melting/crystallization behaviour of poly(N-methyldodecano-12-lactam), MPA. After cooling from the melt to crystallization temperature Tc of 250–280K, primary lamellar structure is formed which melts at about 324K. During later stages of isothermal crystallization, imperfect “fringed” crystallites melting at about Tc+10K are formed in the interlamellar space of the primary structure. On heating, additional crystallization of the primary lamellae takes place with an optimum temperature at about 300K. In the case of isothermal crystallization at Tc=290K and higher, the two steps of the primary structure formation combine in a single isothermal step. Under certain conditions an additional endotherm, possibly corresponding to some less-defected “fringed” lamellae, was detected. On further heating, the primary crystallites undergo recrystallization with an optimum temperature at about 327K. The final higher-ordered structure melts at about 335K. Melting temperature of the imperfect crystallites shows a strong dependence while that of the highest-melting structure a negligible dependence on Tc. Within 24h at 300K, the MPA sample reaches crystallinity of about 34%.

Computer Modeling of Primary Structure Formation in Ductile Iron

Computer Modeling of Primary Structure Formation in Ductile Iron

Particulate processes in freshly prepared silver iodide hydrosols Part IV. The concept of metaphase and its experimental verification

Experimental data on stable silver iodide hydrosols have been compared with the corresponding values calculated on the basis of the existing models of silver iodide hydrosols. Comparison shows the existence of a new structural form of silver iodide and yields information on its physico-chemical properties. The properties of the new structural form indicate that the formation of primary particles of silver iodide hydrosols proceeds through a specific mechanism. In order to explain the formation of primary structures from water solutions of silver and iodide ions, possible states of the system appearing during the extremely short time of primary particles formation have been analysed. The analysis is based on the known properties of ionic solutions and their interactions and on the experimentally determined properties of the newly formed product. The resulting structure whose properties correspond to the predicted properties of the new structural form of silver iodide, is called the metaphase. A theoretical model involving primary silver iodide particle formation and metaphase—phase transition during the ageing process (aggregation of primary particles to the secondary ones) is proposed. It is based on the experimentally defined mechanism of the interactions between sol particles and on the knowledge of their structural properties. Evaluation of the proposed model has been made by comparison between the theoretical predictions and experimental data.