Високотемпературні термоелектричні елементи на основі багатокомпонентних безкисневих сполук

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dc.contributor.authorЦигода, Владислав Владиславович
dc.date.accessioned2020-09-29T09:48:18Z
dc.date.available2020-09-29T09:48:18Z
dc.date.issued2020
dc.description.abstractenThe thesis' main goal is determination of the influence of technological factors on the microstructure and properties of new conducting materials based on layered anisotropic composites of the «insulator-conductor» type as a part of Si3N4-carbides of transition metals, as well as the employment of these materials in thermoelectric functional elements operating at high temperatures (up to 1100 °C). It has been found that the most promising of such composites are the compositions of Si3N4-ZrC, Si3N4-HfC, in which such phases as SiC, Hf2CN and Zr2CN are formed. It has been shown that the interaction between dielectric matrixes and an additive during the process of high-temperature compression significantly influences the thermoelectric properties of the composite. The violation of stoichiometry causes the growth of the thermoelectromotive force along with the decrease of the electrical conductivity and increase of the defectiveness of n-type materials, as well as growth of the thermoelectromotive force along with an increase both in electrical conductivity and defectiveness of p-type materials. In both cases the hysteresis temperature dependence of electrical conductivity (resistivity), and the extreme temperature dependence of the temperature coefficient of resistance along with the nonlinearity of electrical conductivity in the area of small concentrations of the conductor phase, combined with the effect for the thermoelectric voltage is observed due to the inclusion of iron silicide (FeSi2) and semiconductor SiC into the percolation cluster. It has been shown that the key factor for the coefficient of thermoelectromotive force of considered composites’ increase is constituted by the in situ H2O-involving reactions flowing at certain temperatures of hot pressing (formation of Si2ON2), or in case of adding minor (0.25-1%) additives of boron nitride into the leading cluster. It has been found that the products of chemical interaction between the conductive phase, the dielectric matrix and the pressing area, such as SiC and FeSi2, shifted the reaction threshold into the area of small concentrations of the introduced conductive phase by 5 - 10% and increased the resistive cluster resistance in 102 to 105 times. For the first time, the thermoelectric properties of n-type Si3N4-ZrC, Si3N4-HfC; Si3N4-ZrC, Si3N4-WC, Si3N4-TiB2, Si3N4-TaC, Si3N4-TaN composites and p-type Si3N4-C, Si3N4-B4C composites have been researched. It has been shown that cluster percolation structures can be used as thermoelectrodes; the dependence between the thermoelectromotive force and the concentration of the thermoelectric additive is not described by the same mathematical apparatus, as the dependence between the electrical conductivity and the concentration. It has been found that in case the dispersed composite was formed in a magnetic field, under the influence of kinetic processes and the influence of a magnetic field, the particles are rearranged, and a cluster microstructure of a conductor with a high level of anisotropy is formed. The latter depends on the physical properties of the additive, namely: (i) The formation of a bulk cluster at a concentration of 8% and a high level of anisotropy (80) are observed in case of a coarse dispersed diamagnetic additive (MoSi2) using. (ii) The use of a fine-grained ferromagnetic additive in the amount of 3% already leads to the formation of a two-dimensional cluster with a low level of anisotropy. (iii) In case of the simultaneous addition of diamagnetic and ferromagnetic additives (7: 1 ratio), the 2D cluster threshold is formed at a concentration of 4.5% with an anisotropy level of 2-4. It has been proved that the functional characteristics of the thermal emf generators essentially depend on the concentration of the additive in the active layer of both the negative and positive branches of the thermoelectric converter. The highest value of Seebeck coefficient of 75 μV/h was achieved in a functional device with a positive branch of "60% Si3N4-40% B4C" composite and a negative branch of "Si3N4- (15-17)% HfC" composite. It has been shown that the linearity of the temperature dependence of thermal emf was achieved in a functional device with a positive branch of the "60% Si3N4-40% B4C" composite, and for functional devices in which graphite-containing materials were used as a positive branch, a change in the temperature dependence of the thermal emf value was observed at the temperature of about 400°C. It was shown that the coefficient of thermal conductivity of the studied materials ranges from 1.2 to 4*106 m2 /s and is characterized by a negative temperature coefficient over the entire temperature range. It was determined that the thermal conductivity of refractory oxygen-free composites is in the range of 2.1 to 5.1 W/m*K. It was found that thermoelectric sensors have decent reproducibility of results in comparison with reference thermocouples, however the ceramic thermoelectric sensors are characterized by the large inertia, and these products do not experience sharp peak temperature change. Basing on the new method, a high-temperature thermal emf generator with a maximum operating temperature of up to 2500°C and high reproducible characteristics for an aggressive environment was created. Also a high-temperature thermoelectric current generator with an operating temperature of up to 1200 ° C, and a ZT thermoelectric figure of merit of 1.2-1.6 at 600-1200°C was developed. It was shown that the newly-developed high-temperature thermoelectric current generator has different efficiency depending on the temperature difference between the hot and the cold side: within the temperature range of 150-600°C its efficiency was 4-8%; in the temperature range of 600-1000°C the generator efficiency was about 10 ± 10%. It is shown that the developed high-temperature thermoelectric current generator has different efficiency depending on the temperature difference of the hot-cold side: in the temperature range 150-600 C its efficiency was 4-8%; in the temperature range 600-1000 C the efficiency was about 10 ± 10%.uk
dc.description.abstractukДисертацію присвячено встановленню впливу технологічних факторів на мікроструктуру та властивості нових провідних матеріалів на основі шаруватих анізотропних композитів типу «ізолятор-провідник» у складі Si3N4-карбіди перехідних металів, і використання цих матеріалів в термоелектричних функціональних елементах, що працюють при високих температурах (до 1100 °С). Встановлено, що найбільш перспективними з таких композитів є композиції Si3N4- ZrC, Si3N4-HfC, в них утворюються такі фази, як SiC, Hf2CN и Zr2CN. Показано, що ключовим моментом для збільшення коефіцієнту ТЕРС композитів, що розглядаються, є реакції in situ, що протікають за участю Н2О при визначених температурах гарячого пресування (утворення Si2ON2), або незначні (0,25-1%) добавки нітриду бору в склад провідного кластеру. Встановлено, що продукти хімічної взаємодії між провідниковою фазою, діелектричною матрицею та середовищем пресування, такі як SiC та FeSi2, зсувають поріг протікання до області малих концентрацій введеної провідникової фази на 5-10% і збільшують питомий опір резистивного кластеру в 102 – 105 разів. Вперше досліджено термоелектричні властивості композитів n-типу: Si3N4-ZrC, Si3N4-HfC; Si3N4-ZrC, Si3N4-WC, Si3N4- TiB2, Si3N4-TaC, Si3N4-TaN та p-типу: Si3N4-C, Si3N4-B4C. Показано, що як термоелектроди можуть використовуватись кластерні перколяційні структури, а залежність термоелектрорушійної сили від концентрації термоелектричної добавки не описується тим самим математичним апаратом, що і залежність електропровідності від концентрації.uk
dc.format.page28 с.uk
dc.identifier.citationЦигода, В. В. Високотемпературні термоелектричні елементи на основі багатокомпонентних безкисневих сполук : автореф. дис. … канд. техн. наук. : 05.27.01 - твердотільна електроніка / Цигода Владислав Владиславович. – Київ, 2020. – 28 с.uk
dc.identifier.urihttps://ela.kpi.ua/handle/123456789/36456
dc.language.isoukuk
dc.publisherКПІ ім. Ігоря Сікорськогоuk
dc.publisher.placeКиївuk
dc.subjectтермоэлектрические свойстваuk
dc.subjectтермопары керамическиеuk
dc.subjectперколяцияuk
dc.subjectthermoelectric propertiesuk
dc.subjectceramic thermocouplesuk
dc.subjectpercolationuk
dc.subject.udc621.362:621.762.5uk
dc.titleВисокотемпературні термоелектричні елементи на основі багатокомпонентних безкисневих сполукuk
dc.typeThesisuk

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