Sintering oxide ceramics based on AI[2]O[3] and ZrO[2], activated by MgO, TiO[2] and SiO[2] additives

The positive effect of the addition of MgO and TiO[2] in an amount of no more than 1 wt. % on sintering and physico-mechanical properties of alumina ceramics is established. Addition of 5% of SiO[2] to A1[2]O[3] provides the mechanism of liquid phase sintering of ceramics, which leads to increase in its density and strength up to 480 MPa. In ceramic system A1[2]O[3] - ZrO[2] - Y[2]O[3] highest level of physical and mechanical properties of the composition had a hypereutectic composition 16.6% A1[2]O[3] - 76% Z1O[2] - 7.4% Y[2]O[3]. In this composition two mechanisms of hardening are realized simultaneously, such as transformational hardening by t-m -ZrO[2] transition and dispersion strengthening with high-modulus particles of [alpha]- A1[2]O[3]

Extraordinary Burial of the Great Migration Period from Karban-I Necropolis (Northern Altai)

The article presents the results of the materials study from kurgan 11 of the Karban-I site, excavated in 1989 by the expedition of the Barnaul State Pedagogical Institute. This archaeological complex is located on the left bank of the Katun river, 1.7 km northwest of the Kuyus village of Chemal district of the Altai Republic. The key characteristics of the fixed structures (mound with an oval-shaped crepe-laying; a shallow grave pit, a burial chamber in the form of a stone box) and the method of inhumation (single position of the corpse on the back; orientation of the deceased with his head to the western sector of the horizon; the absence of an accompanying burial of a horse) indicate that that this object belongs to the Karban tradition of ritual practice of the population of Altai of the 2nd century BC – 5th century AD. Analysis of the discovered inventory (horn onlays for a bow, combat knife, typesetting belt, bone arrowheads, awl, pendants and braids made of non-ferrous metal, beads) and its comparison with materials from synchronous complexes in adjacent territories became the basis for determining the chronology of the burial within the Early Xianbei period (2nd – early 3nd centuries AD). It was established that the set of objects included items that were typical for both female and male “standard” rite of the Altai nomads of this period. It is concluded that the buried individual, most likely a male, was a representative of the prosperous stratum of the ordinary population. Judging by the availability of means of long-range and close combat including numerous equipment, he was part of a group of professional warriors. At the same time, the deceased during his lifetime occupied a rather high position in a small group of pastoralists who left the Karban-I necropolis

Activation of consolidation processes of alumina ceramics

The methods for activating sintering ceramics based on Al[2]O[3] by mechanical activation in the planetary mill, by adding in the mixture of nanopowders (NP) Al, Al[2]O[3], and submicron powder TiO[2], and by applying the technology of spark plasma sintering (SPS) are developed. It has been shown that adding the nanopowder up to 20 wt. % Al2O3 in a coarse powder [alpha]-Al[2]O[3] activates the sintering process resulting in increased density and hardness of the sintered alumina ceramics. Substantial effect of increasing density of alumina ceramics due to adding the submicron powder TiO[2] in the compound of initial powder mixtures has been established

Properties of nickel-phosphorous coatings codeposited by the electroless and electrochemical plating process

At present, despite numerous studies and practical application, the process of chemical nickel plating remains imperfect. The low nickel deposition rate, the high consumption of the solution components, and the complexity of the deposition process do not contribute to the widespread use of chemical nickel plating. At the same time, chemically deposited coatings are significantly different from the electrochemical: they possess valuable properties. In the paper, the intensification method of chemical nickel plating considered through the use of the co-deposition process with chemical and electrochemical methods. The co-deposition was carried out in an acidic electrolyte solution on an aluminum plate with the stationary potential shift from - 0.01 to - 0.25 V with the use of three electrode system. The presented technique of intensification due to the combination of nickel deposition processes by chemical and electrochemical methods is able to increase the deposition rate of the coatings, and also allows influencing their composition and mechanical properties

Activated sintering of ceramics on the basis of Al[2]O[3]

Ceramic sintering on the basis of Al2O3 activated by nanopowder additives Al[2]O[3] and Al has been studied. The given paper shows that adding nanopowder Al[2]O[3] in the amount of up to 20 wt. % into the coarse powder [alpha]-Al[2]O[3] activates the sintering process and, as a result, leads to the increase in density and microhardness of sintered alumina ceramics. The study has revealed a significant effect of alumina ceramic density growth which is due to introducing the submicron powder TiO[2] to the initial blends composition

New Data on Female Burials of Rouran Period from the Northern Altai (based on the materials from the Choburak-I complex)

The article presents the results of the analysis, cultural-chronological and ethnic-social interpretation of one of the female burials (barrow No. 32a), excavated at a small necropolis of the Bulan-Koby culture as part of the Choburak-I site. This complex, studied by the archaeological expedition of the Altai State University, is located in the Chemal district of the Altai Republic. The key characteristics of this female burial are a small stone mound with an oval revetment; a shallow, narrow and long pit; the corpse is stretched on the back with the head, oriented to the west, as well as the accompanying burial of a horse at the “legs” of a dead. A considerable inventory was found in the burial, including jewelry, costume details, tools and harness. Analysis of the finds made it possible to determine the dating of this object within the middle – second half of the IV century AD. The recorded features of inhumation with a riding horse demonstrate that this burial belongs to the Dyalyan tradition of the ritual practice of the Bulan-Koby culture nomads. Judging by the qualitative composition of the items, woman, buried in barrow No. 32a, had a high social status in the local community, that left the Choburak-I necropolis

Low temperature sintering of corundum powders

Relevance of the research is caused by the necessity of profound processing of raw mineral and perfection of technology of obtaining alumoxide ceramic. The main aim of the research is to develop the activation methods of ceramic sintering based on corundum Al2O3 by mechanic treatment of powders in a planetary mill, additions of Al, Al2O3 nanopowder and TiO2 submicrom powder in a mixture, application of spark plasma sintering method. The methods: sieve analysis of a large-scale powder dispersion using the analyzer A20, x-ray phase analysis of the studied samples, hydrostatic weighting for determining a conditional density of the sintered samples, measuring microhardness of the sintered samples using microhardness tester PMT-3, measuring HRA hardness by the Rockwell hardness tester. The results. Addition of Al2O3 nanopowder in GK-5 corundum contributed to increase of sintering ceramic density and microhardness. Such activation effect is explained by the increase of interparticle contact area, which is related to Al2O3 nanopowder addition. Sintering activation is caused by high structural activity and surface energy of Al2O3 nanopowder, which are determined by crystal structure deficiency and particle small size. The most significant rise in density was observed for ceramic, containing 5…20 wt. % of Al2O3 nanowpoder. Additional activation of Al2O3 nanopowder sintering when adding aluminum nanopowder: its porosity decreased, was proved by the experiment. Sintering activation by adding Al nonopowder is explained by aluminum oxidation and phase transformation (Hedvall effect). TiO2 nanopowder additive in Al2O3 powder had the maximum activation effect: the density of sintering ceramic, containing 1,5 wt. % TiO2, achieved 3,48 g/cm3

Medium-term forecasting of power generation by hydropower plants in isolated power systems under climate change

Reliable operation of power systems (PS), including those with a significant share of hydropower plants (HPPs) in the energy balance, largely depends on the accuracy of forecasting power generation. The importance of power generation forecasts increases with the development of renewable power generation, which is stochastic by nature. Those kinds of tasks are complicated by the lack of reliable information on metrological data and estimated energy consumption, which is also stochastic. In the medium-term forecasting (MTF) of power generation by HPPs, the seasonality of changes in flow and inflow of water should be taken into account, which significantly affects the reserves and regulatory capabilities of the power system as a whole. This work discusses the problem of constructing a model for MTF of power generation HPP in isolated power systems (IPS), taking into account such atmospheric parameters as air temperature, wind speed and humidity. To address constant climatic changes, this paper suggests implementing machine learning models. The proposed approach is characterized by a high degree of autonomy and learning automation. The paper provides a comparative study of the machine learning models such as polynomial model with Tikhonov’s regularization (LR), k-nearest neighbors (kNN), multilayer perceptron (MLP), ensembles of decision trees, adaptive boosting of linear models (ABLR), etc. Computational experiments have shown that the machine learning approach yields the results of sufficient quality, which allows to use them for forecasting of power generation HPP in isolated power systems under conditions of climate change. The Adaptive Boosting Linear Regression model is the simplest and most reliable machine learning model that has proven itself well in the tasks with a relatively small amount of training samples

Low temperature sintering of corundum powders

Актуальность работы обусловлена необходимостью глубокой переработки минерального сырья и совершенствования технологии получения алюмооксидной керамики. Цель исследования: разработка методов активирования спекания керамики на основе Al2O3 путем механической обработки порошков в планетарной мельнице, добавления в шихту нанопорошков Al, Al2O3 и субмикронного порошка TiO2, применения метода искрового плазменного спекания. Методы исследования: ситовый анализ крупнодисперсных порошков с использованием анализатора А20, рентгенофазовый анализ исследуемых образцов, гидростатическое взвешивание для определения кажущейся плотности спеченных образцов, измерение микротвердости спеченных образцов с использованием микротвердомера ПМТ-3, измерение твердости HRA с помощью твердомера Роквелла. Результаты. Добавка нанопорошка Al2O3 в порошок корунда марки ГК-5 способствовала повышению плотности и микротвердости спеченной керамики. Такое активирующее влияние объясняется увеличением площади межчастичных контактов, которое связано с добавлением нанопорошка Al2O3. Механизм активирования спекания обусловлен повышенной структурной активностью и энергией поверхности нанопорошка Al2O3, которые определяются дефектностью кристаллического строения и малыми размерами частиц. Наиболее существенный прирост плотности наблюдался у керамики, содержащей 5…20 мас. % добавки нанопорошка Al2O3. Экспериментально подтверждено дополнительное активирование спекания нанопорошка Al2O3 при добавлении нанопорошка алюминия: наблюдалось снижение его пористости. Активирование спекания добавлением нанопорошка Al объясняется окислением алюминия и фазовыми переходами (эффект Хедвалла). Наибольшим активирующим эффектом обладала добавка нанопорошка TiO2 в порошок Al2O3: плотность спеченной керамики, содержащей 1,5 мас. % TiO2, достигала 3,48 г/см3.Relevance of the research is caused by the necessity of profound processing of raw mineral and perfection of technology of obtaining alumoxide ceramic. The main aim of the research is to develop the activation methods of ceramic sintering based on corundum Al2O3 by mechanic treatment of powders in a planetary mill, additions of Al, Al2O3 nanopowder and TiO2 submicrom powder in a mixture, application of spark plasma sintering method. The methods: sieve analysis of a large-scale powder dispersion using the analyzer A20, x-ray phase analysis of the studied samples, hydrostatic weighting for determining a conditional density of the sintered samples, measuring microhardness of the sintered samples using microhardness tester PMT-3, measuring HRA hardness by the Rockwell hardness tester. The results. Addition of Al2O3 nanopowder in GK-5 corundum contributed to increase of sintering ceramic density and microhardness. Such activation effect is explained by the increase of interparticle contact area, which is related to Al2O3 nanopowder addition. Sintering activation is caused by high structural activity and surface energy of Al2O3 nanopowder, which are determined by crystal structure deficiency and particle small size. The most significant rise in density was observed for ceramic, containing 5…20 wt. % of Al2O3 nanowpoder. Additional activation of Al2O3 nanopowder sintering when adding aluminum nanopowder: its porosity decreased, was proved by the experiment. Sintering activation by adding Al nonopowder is explained by aluminum oxidation and phase transformation (Hedvall effect). TiO2 nanopowder additive in Al2O3 powder had the maximum activation effect: the density of sintering ceramic, containing 1,5 wt. % TiO2, achieved 3,48 g/cm3