Simulation of viscous melt drop crystallization by the SPH method

Heat and mass transfer during absorption on a film of lithium bromide water solution flowing by a cooled wall in the steam atmosphere is numerically investigated in this paper. The self-similar solutions are using as the initial conditions for solving the problem beyond the entrance region. The key criteria characterizing heat and mass transfer in the film absorption with uniform velocity profile and with a constant thickness have been determined

Modification of Structure and Strength Properties of Permanent Joints Under Laser Beam Welding with Application of Nanopowder Modifiers

In the paper we present the results of experimental study of specially prepared nanosize metal-ceramic compositions impact upon structure, microhardness and mechanical properties of permanent joints produced by laser-beam welding of steel and titanium alloy plates

Parametric Generation of Second Sound by First Sound in Superfluid Helium

We report the first experimental observation of parametric generation of second sound (SS) by first sound (FS) in superfluid helium in a narrow temperature range in the vicinity of $T_\lambda$. The temperature dependence of the threshold FS amplitude is found to be in a good quantitative agreement with the theory suggested long time ago and corrected for a finite geometry. Strong amplitude fluctuations and two types of the SS spectra are observed above the bifurcation. The latter effect is quantitatively explained by the discreteness of the wave vector space and the strong temperature dependence of the SS dissipation length.Comment: 4 pages, 4 postscript figures, REVTE

Structure and properties of the layered perovskites in Sm-Ba-Co-Fe-O System

Perovskite oxide materials with the general formula of ABO3, where A is an alkali earth or rare earth metals and B is transition metals, have attracted much attention as cathodes for solid oxide fuel cells because of their high electronic conductivity and fast mobility of oxygen ions. The introduction of Ba2+ and Ln3+ ions with significantly different radii into the A-sites leads to a formation of layered perovskite-type structures which have formed due to the cations’ ordering in the alternating layers. Depending on the nature of rare earth and 3d metal, it was possible to obtain double LnBaM2O6-δ, triple LnBa2M3O9-δ, or quintuple Ln2Ba3M5O15-δ perovskites. The aim of the present work was studying the effect of Ln/Ba and Fe/Co ratio for the crystal and defect structure and properties of oxides in the Sm-Ba-Co-Fe-O system. Polycrystalline samples of SmBaCo2−xFexO6-δ and Sm2-εBa3+εFe5-yCoyO15-δ were prepared by the glycine–nitrate synthesis. Final annealing was performed at 1100°С in air during 120h with intermediate grindings, followed by slow cooling down to room temperature at a rate of about 100°/h. The structural parameters were refined by the Rietveld method using the Fullprof-2008 software. Transmission electron microscopy studies were performed using FEI Tecnai G2 30 UT microscope operated at 300kV. The changes of oxygen content in complex oxides were measured by coulometric titration method as a function of temperature and oxygen partial pressure. The absolute value of oxygen content in the samples was determined using a direct reduction in the TG cell by hydrogen flow and red-ox titration. Thermal expansion of samples was studied using Netzsch DIL 402C dilatometer within the temperature range 25 – 1100°С in air. Total conductivity and Seebeck coefficient were measured simultaneously using a 4-probe technique. The crystal structure of SmBaCo2−xFexO6-δ (0≤x≤0.5) was described by the orthorhombic ap×2ap×2ap cell (Pmmm sp. gr.), while SmBaCo2−xFexO6-δ (0.6≤x≤1.1) crystallized in the tetragonal structure, ap×ap×2ap cell (P4/mmm sp. gr.). The crystal structure of single-phase Sm2-εBa3+εFe5-yCoyO15-δ (ε = 0, y = 0.5–1.5; ε = 0.125, y = 0) determined by XRD was described as cubic (sp. gr. Pm3m). However, transmission electronic microscopy revealed that oxides possess tetragonal structure with 5-fold c parameter. The defect structure of oxides with double perovskite structure was described using the model based on the simple cubic perovskite SmMeO3 (Me = Co, Fe) as a reference state. Equilibrium constants and enthalpies of the point defects formation were refined. The concentrations of all defect species were calculated as functions of temperature and oxygen nonstoichiometry. The temperature dependencies of total conductivity for SmBaCo2−xFexO6-δ and Sm2-εBa3+εFe5-yCoyO15-δ possess maxima at approximately 300–350ºC in air. The partial substitution of iron for cobalt leads to a decrease in the conductivity value. Seebeck coefficient for all compounds reveals positive values within the entire temperature and oxygen partial pressure ranges that indicate predominant p-type conductivity. The dependencies of electrical conductivity and Seebeck coefficient versus oxygen nonstoichiometry were discussed on the basis of the defect structure models. The values of activation energy for fixed oxygen content values were calculated. This work was supported by the Russian Science Foundation (Grant № 18-73-00159

Investigations into the structure of La3Ni2−xFexO7±δ

The room-temperature (RT) 57Fe Mössbauer spectra of the La3Ni2−xFexO7±δ oxide solid solutions of Ruddlesden-Popper-type (x = 0.05, 0.10) reveal two doublets for Fe3+ ions in octahedral coordination by oxygen. The existence of two inequivalent sites for Fe at RT is at variance with the space groups Fmmm and Cmcm (Amam) which have been reported for La3Ni2O7±δ. This unexpected finding is discussed in connection with Patterson analyses and Rietveld refinements of powder XRD data for x = 0, 0.05, and 0.10. Alternative structural models have been proposed which can explain the spectroscopic findings and which are compatible with the results from X-ray diffraction

On Nanomodification of Coating Obtained by Laser Cladding of Composite Powder 12NVK-01

The results of an experimental study of the effect of nanomodifying additives on the structure and mechanical properties of a multilayer coating during laser surfacing of a composite powder with a strengthening phase are presented. As a surfacing material, nickel powder 12NVK -01 with a strengthening phase of tungsten carbide was used, and as a modifying additive was a mixture of nanosized refractory powders of titanium nitride and yttrium oxide clad with iron and chromium. It is established that the deposited coating represents a complex system of phases formed during the melting and interaction of the chemical elements of the substrate and the melted powder mixture. The main component of the coating is the combination of nickel with iron and chromium of the type Ni3(Fe,Cr). In the melting process, a partial decomposition of the strengthening phase occurs, depending on the concentration of the nanomodifier. In the case considered, the optimum amount of the modifying additive providing the maximum hardness and wear resistance increase of the composite coatings of the Ni-Cr-B-Si-Fe / WC system is 0.1% by mass of the refractory TiN+Y[2]O[3] nanopowder additive in the composite material

On Nanomodification of Coating Obtained by Laser Cladding of Composite Powder 12NVK-01

The results of an experimental study of the effect of nanomodifying additives on the structure and mechanical properties of a multilayer coating during laser surfacing of a composite powder with a strengthening phase are presented. As a surfacing material, nickel powder 12NVK -01 with a strengthening phase of tungsten carbide was used, and as a modifying additive was a mixture of nanosized refractory powders of titanium nitride and yttrium oxide clad with iron and chromium. It is established that the deposited coating represents a complex system of phases formed during the melting and interaction of the chemical elements of the substrate and the melted powder mixture. The main component of the coating is the combination of nickel with iron and chromium of the type Ni3(Fe,Cr). In the melting process, a partial decomposition of the strengthening phase occurs, depending on the concentration of the nanomodifier. In the case considered, the optimum amount of the modifying additive providing the maximum hardness and wear resistance increase of the composite coatings of the Ni-Cr-B-Si-Fe / WC system is 0.1% by mass of the refractory TiN+Y[2]O[3] nanopowder additive in the composite material

SCINTILLATION DETECTOR

FIELD: dosimetry of fast neutrons and gamma-radiation, possible use in stationary and portable radiation control devices, meant for finding radioactive materials. SUBSTANCE: scintillation detector contains at least one scintillation block sensor, including plastic scintillator in form of prism or cylinder for registration of fast neutrons, made with at least one hollow channel and fibrous scintillation light guide positioned in it, light-reflecting mirror, photodiode photo-detecting device and a block for electronic signal processing. EFFECT: increased efficiency of registration of gamma-radiation during simultaneous registration of fast neutrons with possible usage of multichannel photo-electronic multiplexers or compact photodiode devices as photo-registration means. 1 dwg.Предложенное изобретение относится к области дозиметрии быстрых нейтронов и гамма-излучения и может быть использовано в стационарных и переносных устройствах радиационного контроля, предназначенных для обнаружения радиоактивных материалов. Задачей данного изобретения является повышение эффективности регистрации гамма-излучения при одновременной регистрации быстрых нейтронов с возможностью использования в качестве фоторегистраторов многоканальных фотоэлектронных умножителей или компактных фотодиодных устройств. Сцинтилляционный детектор содержит по меньшей мере один датчик-сцинтиблок, включающий в себя пластиковый сцинтиллятор в форме призмы или цилиндра для регистрации быстрых нейтронов, выполненный, по крайней мере, с одним полым каналом и размещенным в нем волоконным сцинтилляционным световодом, светоотражающее зеркало, фотодиодное фотоприемное устройство и блок электронной обработки сигналов. При этом в качестве материала для пластикового сцинтиллятора использован дифенил-1,3,4-оксазол, а волоконные сцинтилляционные световоды выполнены из ортогерманата висмута (BGO). 1 ил

METHOD OF MANUFACTURING INFRARED LIGHT FILTER

FIELD: light engineering. SUBSTANCE: method comprises using activated LiF:U crystals as a material for the infrared filter and irradiating the crystals by neutrons. The irradiated crystals are exposed to air at a room temperature for 10-12 months and then are roasted in air at a temperature of 200-300°C for 0.5-1.5 hours. EFFECT: enhanced thermal and radiation stability. 1 dwg.Изобретение относится к области светотехники и интегральной оптики, связанной с созданием инфракрасных светофильтров отрезающего и полосового типа, поглощающих видимое излучение и пропускающих коротковолновое и длинноволновое ближнее инфракрасное излучение и предназначенных для защиты инфракрасных датчиков видеоконтрольных устройств и приборов ночного видения от паразитных помех, связанных с воздействием света видимого диапазона, а также для использования в оптических системах контроля подлинности документов, в системах охранной и пожарной сигнализации, в том числе в системах контроля и разграничения доступа и охраны периметра объектов, в видеодомофонах, видеоглазках и подобных устройствах. Суть изобретения заключается в том, что в качестве материала для ИК-светофильтра используют предварительно активированные кристаллы LiF:U и облучают их нейтронами до флюенса 1,2·10¹⁶?3·10¹⁶ см⁻². Облученные кристаллы выдерживают на воздухе при комнатной температуре в течение 10-12 месяцев, а затем подвергают их отжигу на воздухе при температуре 200-300°С в течение 0,5-1,5 часов. Технический результат: обеспечение сплошного поглощения света в видимом диапазоне и повышение термической и радиационной устойчивости. 1 ил

METHOD OF PRODUCING NANOCRYSTALLINE COATS BASED ON NANOCRYSTALS OF LITHIUM OR SODIUM FLUORIDE

FIELD: nanotechnologies. SUBSTANCE: invention aims at producing nanocrystalline coats based on lithium or sodium fluoride on various substrates. The aforesaid coats are produced by a power spraying beam representing ionic cyclotron beams of He⁺ or N³⁺ ions used to irradiate, in cyclotron target chamber in vacuum, the mother crystals of lithium or sodium fluoride arranged at the angle of 10 to 15° relative to the ion beam. The irradiation is proceeded at constant heating by means of contact platinum electrode till obtaining fluences of 5·10¹⁵t to 10⁷ ion/cm². EFFECT: production of nanocrystalline solid or insular coats based on lithium or sodium fluoride on various substrates. 4 cl, 6 dwg.Изобретение предназначено для получения нанокристаллических покрытий на основе нанокристаллов фторида лития или фторида натрия на различных подложках. Сущность изобретения: нанокристаллические покрытия на основе нанокристаллов фторида лития или фторида натрия получают с использованием энергетического распыляющего пучка, в качестве которого применяют ионные циклотронные пучки ионов гелия He⁺ или ионов азота N³⁺, которыми облучают в мишенной камере циклотрона в вакууме исходные кристаллы фторида лития или фторида натрия, которые располагают под углом 10-15° относительно пучка ионов и облучают до флюенсов 5·10¹⁵-10⁷ ион/см² при постоянном нагреве в течение всего процесса облучения с помощью контактного платинового электрода. Техническим результатом изобретения является получение нанокристаллических покрытий на основе нанокристаллов фторида лития или фторида натрия на различных подложках с высокой адгезией к подложкам и возможность создания нанокристаллических покрытий сплошного или островкового типа. 3 з.п. ф-лы, 6 ил