IMPROVEMENT OF THE SERVICE LIFE OF CATHODE BLOCKS IN ALUMINIUM REDUCTION CELLS USING LOW-TEMPERATURE TITANIUM DIBORIDE Текст научной статьи по специальности «Электротехника, электронная техника, информационные технологии»

Original article / Оригинальная статья

DOI: http://dx.doi.org/10.21285/1814-3520-2020-4-919-930

Improvement of the service life of cathode blocks in aluminium reduction cells using low-temperature titanium diboride

Sergei N. Fedorov, Roman V. Kurtenkov, Pavel S. Palyanitsin

Saint-Petersburg Mining University, Saint-Petersburg, Russia

Abstract: The present study is aimed at elucidating the possibility of increasing the electrical conductivity of cathode blocks, comprising the reduction cell bottom in aluminium production, as well as examining the process of low-temperature synthesis of titanium diboride for subsequent cathodic application. In order to study the phase transitions of the initial and modified TiO2 obtained in different atmospheres (argon, vacuum and air), the thermogravimetric analysis method was used in combination with the X-ray diffraction method for determining the composition of the samples under study. Modification of the cathode block was carried out through the stage of preparing a carbon-graphite sample with the addition of low-temperature TiO2 in amounts up to 15% wt. The electrical conductivity of the experimental cathode block samples was measured by an installation ensuring their static fixing with an Elitech MM 300 multimeter. The carried out thermodynamic calculations of the interaction reactions between the main titanium- and boron-containing components demonstrated the theoretical possibility of obtaining TiO2. At a temperature of 1050°C and a synthesis duration of 4 h, the yield of TiO2 powder equal to 97% was established to be achieved. Under calcination at 1000-1500°C for 4 h and subsequent graphitisation (at 2200°C for 24 h), laboratory samples of cathode blocks modified by low-temperature TiO2 were obtained. When comparing the electrical conductivity of the modified and traditional cathode blocks, the samples with a content of 12.5% wt. of TiO2 were established to have 35% less electrical conductivity (32 pD^m). On the basis of laboratory studies, the maximum extraction of 97.5% under the conditions of low-temperature titanium diboride synthesis was determined to be obtained at a temperature of 1050°C and a duration of 180 min in vacuum (0.101 MPa). On the basis of the thermodynamic calculations and conducted experiments, a principal technological scheme for the low-temperature synthesis of titanium diboride is proposed. The optimal content of TiO2 in the cathode block aimed at increasing its electrical conductivity varies from 7.5 to 12.5% wt. The introduction of low-temperature TiO2 into the cathode blocks leads to reduced energy consumption of reduction cells equal to 986 kWh/t or savings of 7.5%.

Keywords: primary aluminium production, reduction cell, cathode block, titanium diboride synthesis, thermodynamics, electrical resistivity

Information about the article: Received May 14, 2020; accepted for publication July 06, 2020; available online August 31, 2020.

For citation: Fedorov SN, Kurtenkov RV, Palyanitsin PS. Improvement of the service life of cathode blocks in aluminium reduction cells using low-temperature titanium diboride. Vestnik Irkutskogo gosudarstvennogo tehnicheskogo universiteta = Proceedings of Irkutsk State Technical University. 2020;24(4):919-930. https://doi.org/10.21285/1814-3520-2020-4-919-930

УДК 669.713.7; 661.882

Повышение срока службы катодных блоков алюминиевых электролизеров при использовании низкотемпературного диборида титана

© С.Н. Федоров, Р.В. Куртенков, П.С. Паляницин

Санкт-Петербургский горный университет, г. Санкт-Петербург, Россия

Резюме: Цель - изучение возможности повышения электропроводимости катодных блоков, входящих в состав подины электролизеров производства алюминия, и процесса синтеза диборида титана низкотемпературным методом для его последующего использования в катодах. Для изучения фазовых переходов исходного и модифицированного ТЮ2, полученных в различных атмосферах (аргон, вакуум, воздух), использовали термогравиметрический метод анализа; для изучения состава изучаемых проб - рентгенофазовый метод. Модифицирование катодного блока осуществлялось через стадию подготовки навески углеграфитовой массы с добавкой низкотемпе-

ISSN 1814-3520

ВЕСТНИК ИРКУТСКОГО ГОСУДАРСТВЕННОГО ТЕХНИЧЕСКОГО УНИВЕРСИТЕТА 2020;24(4): 919-930

919

ратурного ТЮ2 до 15 масс. %. Измерение электропроводимости экспериментальных образцов катодных блоков проводилось на установке со статичным их закреплением с мультиметром Е1^ес1л ММ 300. Проведенные термодинамические расчеты реакций взаимодействия основных титан-, борсодержащих компонентов показали теоретическую возможность получения ТЮ2. Установлено, при температуре 1050°С и продолжительности синтеза 4 ч достигается выход порошка ТЮ2 97%. Получены лабораторные образцы катодных блоков, модифицированных низкотемпературным ТЮ2, при прокалке при температуре 1000—1500°С в течение 4 ч и последующей графитации (при 2200°С продолжительностью 24 ч). При сравнении электропроводимости модифицированных и традиционных катодных блоков установлено, что образцы с содержанием 12,5 масс. % ТЮ 2 имеют на 35% меньше значение электропроводимости - 32 мкОм-м. На основе проведенных лабораторных исследований установлено, что максимальное извлечение в условиях низкотемпературного синтеза диборида титана - 97,5% - достигается при температуре 1050°С и продолжительности 180 мин в вакууме (0,101 МПа). На основе термодинамических расчетов и проведенных экспериментов предложена принципиальная технологическая схема низкотемпературного синтеза диборида титана. Оптимальное содержание ТЮ 2 в катодном блоке для увеличения его электропроводимости варьируется от 7,5 до 12,5 масс. %. Внедрение низкотемпературного ТЮ 2 в катодные блоки позволяет снизить энергопотребление электролизеров до 986 кВтч/т, что составляет 7,5% экономии.

Ключевые слова: производство первичного алюминия, электролизер, катодный блок, синтез диборида титана, термодинамика, удельное электросопротивление

Информация о статье: Дата поступления 14 мая 2020 г.; дата принятия к печати 06 июля 2020 г.; дата онлайн-размещения 31 августа 2020 г.

Для цитирования: Федоров С.Н., Куртенков Р.В., Паляницин П.С. Повышение срока службы катодных блоков алюминиевых электролизеров при использовании низкотемпературного диборида титана. Вестник Иркутского государственного технического университета. 2020. Т. 24. № 4. С. 919-930. https://doi.org/10.21285/1814-3520-2020-4-919-930

1. INTRODUCTION

Due to the independent and simultaneous discoveries of Charles Martin Hall and Paul He-roult, the aluminium industry began to develop rapidly at the end of the 19th century [1, 2]. The need for the evolution process is primarily associated with the unique properties of aluminium and its alloys, now widely used in many areas of human life. Thus, the production of primary aluminium is stimulated by the high market demand. In this regard, the unresolved issues of increasing energy efficiency in aluminium production by reducing the operating voltage, as well as the aiding the disposal of spent lining using contemporary and technologically-advanced lining materials, remain relevant.

The earliest aluminium reduction cells consumed extremely high quantities of electrical power, amounting to more than 40 kWh per 1 kg of aluminium, with a current efficiency of 75-78% [3]. As a result, the global scientific community is constantly searching for ways to increase the technical and economic indicators of the process.

As can be seen from the graphic illustration (fig. 1) of the energy consumption involved in the production of primary aluminium, by the end

of the last century, an average electricity consumption of ~16 kWh/kg of aluminium had been achieved, while experimental reduction cells further reduced power consumption to 13.5 kWh/kg [3, 4].

Issues related to energy saving, including increasing the electrical conductivity of a cathode carbon-graphite lining along with its resistance in an aggressive environment of cryolite-alumina melt - and, as a consequence, an extension of the service life of aluminium production units -were raised in the studies of many Russian and foreign scientists [5-10].

The application of wettable (drained) cathodes can solve one of the most significant problems concerning the formation of bottom deposits and an excessive amount of metal in progress in the cathode shaft. Under this approach, it is possible to reduce the aluminium layer on the bottom by stabilising the technological process and improving the technical and economic indicators (TEI) due to the uniform current distribution over the main nodes of the unit, levelling the cathode surface of molten aluminium and improving the magnetohydrodynamical phenomena [11, 12]. The key point involves the reduction of specific energy consumption (Wspec). Since this technological solution can be imple -

ВЕСТНИК ИРКУТСКОГО ГОСУДАРСТВЕННОГО ТЕХНИЧЕСКОГО УНИВЕРСИТЕТА 2020;24(4):919-930

kWh/kg

50

40

30

20

10

0

1900 1920 1940 1960 1980 2000 2020 year

Fig. 1. Energy consumption for primary aluminium production in 1900-2020 Рис. 1. Энергопотребление при производстве первичного алюминия с 1900 по 2020 гг

mented in existing production facilities, capital costs involved in the construction of new reduction cells can be significantly reduced.

The defining stage of this direction evolves the development of a drained cathode presupposing the preservation of a thin aluminium layer on the wetted bottom and providing the reduced pole-to-pole distance.

By scientific and industrial research, borides and carbides of transition metals were determined to have occupied a dominant niche in the manufacture of cathode blocks, especially TiB2 due to its unique properties. However, for a number of reasons, a wide application of these modified cathode blocks in industry is not yet possible [13-20]. Although various laboratory techniques can be used to obtain TiB2, none are currently scalable for widespread use in metallurgy. Therefore, the present study is aimed at developing a method for the low-temperature synthesis of titanium diboride to facilitate its expanded possible application along with an evaluation of the technical and economic efficiency of cathode blocks modified by this material for use in electrolysis.

2. LOW-TEMPERATURE SYNTHESIS OF TITANIUM DIBORIDE

The synthesis of titanium diboride includes doping with the formation of a metatitanic acid

complex in an aqueous medium using hydrofluoric acid (a source of fluorine ions) and ammonium hydroxide (hydrolysis activator and pH regulator). With an increase in the temperature of the amorphous doped mixture in air to 300-400°C during the crystallisation of anatase, w a-ter is removed from the sediment:

TiO(OH)2F ^ a-TiO2F+ ^Of, (1)

complemented by doped anatase obtained confirmed by the carried out thermodynamic evaluation:

TiO(OH)2 + 2HF =TiOF2 + 2H2O; (2)

AH? = -175.25 kJ/mol, A S = = -17.67 kJ/K, AG? = -170.07 kJ/mol.

In order to determine the intervals of ana-tase-rutile transformation (ART), fluorine-modified titanium oxide was successively heated to 1100°C in various atmospheres (fig. 2). The maxima in the plot reflect the amount of the rutile phase after heating, exposing the undoped and doped titanium dioxide at a fixed temperature for 15 min.

Heating the modified titanium dioxide 1 in argon, as well as the initial 2 and doped 4 titanium dioxides in the vacuum, stimulates the ART.

ВЕСТНИК ИРКУТСКОГО ГОСУДАРСТВЕННОГО ТЕХНИЧЕСКОГО УНИВЕРСИТЕТА 2020;24(4): 919-930

Fig. 2. Anatase-rutile transition in various atmospheres: 1 - modified TiO2 (argon atmosphere); 2 - initial TiO2 (vacuum conditions); 3 - initial T1O2 (air atmosphere); 4 - doped titanium dioxide (vacuum conditions);

5 - doped TiO2 (air atmosphere) Рис. 2. Переход из анатаза в рутил при различных атмосферах: 1 - модифицированный T1O2 (в среде аргона); 2 - исходный T1O2 (в условиях вакуума); 3 - исходный T1O2 (в атмосфере воздуха); 4 - допированный диоксид титана (в условиях вакуума); 5 - допированный T1O2 (в атмосфере воздуха)

At the same time, the increased reactivity of ana-tase at 800-1000°C was determined to be maintained for 3 h in the air atmosphere of initial 3 and doped 5 TiO2. As a consequence, the activation of a-TiOF2 in the composition of the TiO2-B2O3-C reaction mixture assumes its reduction with the formation of a TinO2n-i oxide homologous series simultaneously with the ART process under the established conditions. Thus, it is possible to assume the interaction of the more active intermediate phase of a-TiO2 with carbon.

As can be seen from fig. 3, the results of thermogravimetric analysis (TGA) of the initial hydrated titanium dioxide demonstrate the phase formation of anatase and rutile in the range of 208.91-380.64 and 566.74-756.58°C, respectively, which is comparable with the literature data. Thermogravimetric analysis of the sample structure was carried out using an SDT Q-6O0 derivatograph (TA Instruments, USA) under heating to 1100°C at a rate of 10°C/min.

Fig. 3. Thermogravimetric analysis data of initial hydrated titanium dioxide Рис. 3. Результат термогравиметрического анализа исходного гидратированного диоксида титана

ВЕСТНИК ИРКУТСКОГО ГОСУДАРСТВЕННОГО ТЕХНИЧЕСКОГО УНИВЕРСИТЕТА 2020;24(4):919-930

Ж

The X-ray diffraction results of samples obtained using an XRD-7000s X-ray powder dif-fractometer (Shimadzu, Japan) with Cu-Ka radiation and a scanning rate of 2°/min are shown in fig. 4. Here, the presence of anatase and rutile phases after exposure at 300 (fig. 4 a) and 700°C (fig. 4 b), respectively, can be observed indicating a transition from the amorphous state of the substance to titanium dioxide with a crystal lattice.

TGA results (fig. 5) of doped titanium dioxide demonstrate the initial point of anatase formation at 450°C followed by a small part of rutile

at 750°C. Most of the titanium dioxide remained in the anatase phase (> 70% wt.) under 1000°C, therefore proving the expediency of stabilising TiO2 by doping.

The synthesis was carried out according to the reaction:

TiOF2 + 2H3BO3 + 2.5C = TiB2 + 2H2O + 2.5CO2 + 2HF, (3)

with the thermodynamic evaluation provided in tab. 1.

a b

Fig. 4. X-ray diffraction pattern of the initial hydrated titanium dioxide after exposure at 300°С (a) and 700°С (b) Рис. 4. Рентгенограмма исходного гидратированного диоксида титана после выдержки при 300°С (a) и 700°С (b)

leetOmg

ОвСН

DSC-TGA

)io«i ТЛ OAs jr

------TY \ ЯПЧ / \ V

\ 9* 1BJ* r\ 1 Ы1ЛГС / T-v Dare zrt ,J \ »UWC

mac i \ V Mir« ----

~3S

T»«i>|w«tui

MO

• ГС)

« V4 IA TA MwnMt

Fig. 5. Thermogravimetric analysis data of doped titanium dioxide Рис. 5. Результат термогравиметрического анализа допированного диоксида титана

ВЕСТНИК ИРКУТСКОГО ГОСУДАРСТВЕННОГО ТЕХНИЧЕСКОГО УНИВЕРСИТЕТА 2020;24(4): 919-930

Table 1. Thermodynamics of the titanium diboride synthesis reaction Таблица 1. Термодинамика реакции синтеза диборида титана

Reaction Temperature АН? AS AG? Log(K)

°C/K kJ/mol kJ/K kJ/mol

(3) 800/1073 1227.00 1182.772 -42.29 2.06

1050/1323 1264.56 1214.13 -341.91 13.50

As the temperature rises, the reaction shifts to the right side with an increase in the yield of the final product presented by titanium diboride. An exposure for 1 h in a vacuum at 1050°C i n-tensifies the formation of TiO monoxide. Under increased exposure time in the temperature range of 800-1070°C with the participation of TiO, two competing processes develop: the formation of TiCO oxycarbide as a result of car-bothermal reduction and the phase formation of the intermediate TiBO3 in contact with B2O3:

TiO + C ^ TiCO; (4)

TiO + B2O3 ^ TiBO3 + BO|. (5)

The overall reaction (4) and (5) is as follows:

2TiO + B2O3 + C ^ TiCO + TiBO3 + BO. (6)

In this case, the formation of titanium carbide is impossible according to the thermodynamic evaluation (T = 1323 K (1050°C),

АН? = 70.69 kJ/mol, A S = 35.55 kJ/K, AG? = 23.66 kJ/mol

Log(K) = -3.91): 2TiO + 3C = 2TiC + CO2. (7)

For further reduction of this mixture at 1050°C, it is necessary that the boron oxide and carbon content be higher than the stoichiometric coefficients:

2TiBO3 + 6C ^ TiB2 + TiCO + 5CO; (8) TiCO + B2O3 + 3C ^ TiB2 + 4CO. (9)

With a lack of boron oxide and carbon, a product containing titanium oxycarbide with an admixture of TiB2 was obtained in the experiments.

Thus, according to the research results, the multistage nature of physical and chemical transformations with the formation of titanium diboride has been proved [21]:

Ti02 ^ TiO TiCO + TiB2 ^

TiB03 ^ TiB2.

(10)

Fig. 6. X-ray diffraction pattern of the sample after synthesis in vacuum Рис. 6. Рентгенограмма образца после синтеза в вакууме

ВЕСТНИК ИРКУТСКОГО ГОСУДАРСТВЕННОГО ТЕХНИЧЕСКОГО УНИВЕРСИТЕТА 2020;24(4):919-930

Taking into account the established features of phase formation in the TiO2-B2O3-C system and the dependence of the final product yield on the composition of the initial mixture, atmosphere and temperature mode of the synthesis, experiments with an increased excess of boron oxide and carbon were carried out. Fig. 6 shows the results of experiments in vacuum with a powder of TiB2 titanium diboride obtained in a yield of 96-98% and a small amount of under-reduced titanium oxycarbide impurities.

The experiment was carried out at t = 1050°C with an exposure time of 4 h. No presence of a B2O3 phase was detected in the composition of the synthesis products, giving grounds to assume the gasification of boron oxide at t > 1000°C.

3. CATHODE BLOCK MODIFICATION BY TITANIUM DIBORIDE

Modification of the cathode carbon-graphite block by titanium diboride was carried out through the stage of composing a sample of low-temperature titanium diboride from 0 to 15% wt. with carbon-graphite mass for the manufacture of blocks / cylinders 50-60 mm in height and having a diameter of 20 mm. The prepared mixture was moulded by a laboratory hydraulic press under a pressure of 2.026 MPa to ensure

o

a sample density of 1.3-1.5 g/cm3. This was fol-

lowed by the calcination of the block at a temperature from 1000 to 1500°C for 4 h and grap h-itisation of the workpiece at a temperature of 2200°C for 24 h.

In order to evaluate the practical effectiveness of using low-temperature titanium diboride powder, it is necessary to measure the specific electrical resistivity (SER) p (pfim). For this, an installation (fig. 7) was assembled for measuring the SER of prepared cathode samples having different TiB2 content.

In the installation (see fig. 7), a sample of the cathode block 1 was statically fixed from the ends by the current-supplying plates of the springs 2 with the soldered copper plates with the ends connected to an Elitech MM 300 multimeter 3 by means of wires 4. In order to avoid leakage of the supply current, the frame of the installation is made of plastic material. The SER measurement results of the baked samples with different titanium diboride content at an electrolysis temperature of 960°C are presented in tab. 2 and in fig. 8.

A higher modifying additive content of more than 15% appears to be ineffective, failing to significantly affect a decrease in the resistivity and wettability of cathode blocks with aluminium. Thus, the optimal content of the modifying additive in the blocks for increasing the electrical conductivity is determined to be 7.5-12.5% wt.

Fig. 7. Scheme of the installation for determining the electrical resistivity of samples: 1 - cathode block; 2 - current supply spring plates; 3 - DC bridge; 4 - wires Рис. 7. Схема установки для определения электрического сопротивления образцов: 1 - катодный блок; 2 - токоподводящие пластины пружин; 3 - мост постоянного тока; 4 - провода

ВЕСТНИК ИРКУТСКОГО ГОСУДАРСТВЕННОГО ТЕХНИЧЕСКОГО УНИВЕРСИТЕТА 2020;24(4): 919-930

Fig. 8. Dynamics of a decrease in electrical resistivity with an increase in TiB2 content Рис. 8. Динамика снижения удельного электросопротивления при увеличении содержания TiB2

Table 2. Specific electrical resistivity measurement results of cathode blocks modified with low-temperature titanium diboride at 960°C baking Таблица 2. Результаты измерения удельного электрического сопротивления катодных блоков, модифицированных низкотемпературным диборидом титана, при 960°С обжига

Thus, based on the literature data and the tests carried out, a conclusion can be drawn about the optimal content of the modifying additive in the blocks in the range of 7.5-12.5% wt. aimed at increasing the electrical conductivity.

4. TECHNICAL AND ECONOMIC EFFICIENCY

CALCULATION OF MODIFIED CATHODE BLOCKS IN ALUMINIUM REDUCTION CELLS

A feasibility study of the low-temperature titanium diboride application in the cathode lining was carried out by means of an electrical calculation of the OA-300 reduction cell.

The value of Wspec depends on the value of the average voltage (Uav, V) on the reduction cell. For this purpose, an electrical calculation of the reduction cell is carried out in order to determine the voltage losses in the main nodes of

the metallurgical unit, determining the values of the heating (Uheat, V), the operating (Uoper, V) and Uav types of voltages.

In order to compile the voltage balance, design calculation data for the reduction cell, reference data and practical results of the reduction cell operation for a current strength of 300 kA with a current output of 95%1 were used.

Utent calculation was performed according to the formula:

Uheat = Ud + AUan + AUb +

+ AUel + AUae, (11)

where is the decomposition voltage of alumina, V; AUan is the voltage drop in the anode unit, V; AUb is the voltage drop in the reduction cell bottom, V; AUei is the voltage drop in the electrolyte, V; AUae is the voltage drop due to anode effects, V.

Reduction cell operating voltage is as follows:

Uoper = Uav - AUae + AUbus. (12)

Electrical calculation was carried out in accordance with the current "Norms of technological design for aluminium production"2.

TiB2 content, % wt. 0.0 2.5 5.0 7.5 10.0 12.5 15.0

p, jQ-m 53 48 42 37 34 32 31

1

Grinberg IS, Zelberg BI, Chalykh VI, Chernykh AE. Aluminium electric metallurgy: textbook. Irkutsk: Irkutsk State Technical University; 2009, 350 p. / Гринберг И.С., Зельберг Б.И., Чалых В.И., Черных А.Е. Электрометаллургия алюминия: учеб. пособ. Иркутск: Изд-во ИрГТУ, 2009. 350 с.

2VNTP 25-86 Norms of technological design for aluminium production // Mintsvetmet of the USSR; Soyuzaluminium. Leningrad: VAMI; 1986. / ВНТП 25-86 Нормы технологического проектирования алюминиевого производства // Минцветмет СССР; Союзалюминий. Л.: ВАМИ, 1986.

ВЕСТНИК ИРКУТСКОГО ГОСУДАРСТВЕННОГО ТЕХНИЧЕСКОГО УНИВЕРСИТЕТА 2020;24(4):919-930

Ж

The decomposition voltage of (Ed, V) was determined by the empirical formula:

Ep = A + 0.3 7 ■ ia, (13)

where A is the coefficient (A = 1.13).

Therefore,

Ed = 1.13 + 0.37 ■ 0.74 + 0.2 = 1.6 V,

where 0.2 is the correction factor for baked anode reduction cells.

AUan consists of a voltage drop in the carbon part of the anode, a voltage drop in the "anode -nipple" contact, a voltage drop in the nipple, a voltage drop in the "nipple - bracket - rod -support bus" section. According to calculations and practical data, AUan was 0.316 V.

The calculation of AUb was performed by calculating the voltage drop components in the following individual elements: "molten aluminium / bottom blocks" contact; "blocks"; "blocks / pour / cathode rods" contact; "cathode rods".

1. The AUAi-bi voltage drop in the "molten aluminium / bottom blocks" contact is calculated by the formula:

AÜAl-bl =

1 ■ PAlb

(14)

l- l

where I is the current in the reduction cell, A; pA--bi - contact specific resistivity, O cm; SA--bl is the contact area or area free from bottom crust,

cm

2

According to practical data, pAl-bi = 0.04 Ocm. Therefore, AUAi.bi = 0.027 V.

2. Voltage drop in blocks AUbl is determined by the formula:

AÜb, =

l

(15)

where i is the current per one bottom section (300000/40 = 7500 A); pb] is the SER of blocks, O cm; Sbl is the middle section of the block through which the current flows 40x70 cm2), l = 28 cm.

The resistivity of blocks is calculated using the following formula:

Pbi = 5.23 . 10-6 (1000 - 0.253. t), Ocm, (16)

where t is the block temperature (the arithmetic mean between the process temperature and the temperature of the corresponding section of the cathode rods).

The average section of the block through which the current flows is 40x70 cm2.

Thus, for a traditional cathode block (without adding low-temperature titanium diboride):

A и = 7500 • 5324.12 • ЦТ* • 28 = ^ y Dl 40 x 70

For a cathode block modified with low-temperature titanium diboride:

... 7500 • 3206.08 • 10-6 • 28

A Ubl = --= 0.241 V.

Dl 40 • 70

For the purposes of the calculation, we will ignore other components.

Total AUb with a traditional cathode block, i.e. without adding low-temperature titanium diboride:

AUb = AUAb + A Ub, = 0.027 + 0.399 = 0.426 V.

For a cathode block modified with low-temperature titanium diboride:

AUb = AUai-m + A UN = 0.027 + 0.241 = 0.268 V.

Calculation AUel was made according to the Forsblom-Mashovets equation1 and amounted to 1.57 V; AUae with the assumed overvoltage on the reduction cell during the anode effect of 30 V was 0.004 V.

Thus, for a traditional cathode block (without adding low-temperature titanium diboride):

Uheat = 1.6 + 0.399 + 0.426 + + 1.57 + 0.004 = 3.999 V.

For a cathode block modified with low-temperature titanium diboride:

Uheat = 1.6 + 0.241 + 0.268 + + 1.57 + 0.004 = 3.683 V.

ВЕСТНИК ИРКУТСКОГО ГОСУДАРСТВЕННОГО ТЕХНИЧЕСКОГО УНИВЕРСИТЕТА 2020;24(4): 919-930

The calculation of the average voltage is carried out according to the following formula:

Ws

3.857

spec = 0.33540.95

•103= 12105 kWh/t.

Uav = Uheat + A Ubus,

(17)

where AUbus is the voltage drop in the busbar (taking into account the general serial, according to practical data, it is equal to 0.174 V).

The average voltage of the reduction cell is determined according to the heating voltage and voltage loss in the busbar.

Thus, for a cathode block without adding low-temperature titanium diboride:

Uav= 3.999 + 0.174 = 4.173 V.

For a cathode block modified with low-temperature titanium diboride:

Uav= 3.683 + 0.174 = 3,857 V.

The calculation of the specific electricity consumption per 1 ton of aluminium is carried out according to the formula:

Wspec = — 103.

gM ■ nT

(18)

Thus, for a cathode block without adding low-temperature titanium diboride:

WSpec = J"7L-103= 13097 kWh/t.

spec 0.33540.95

For a cathode block modified with low-temperature titanium diboride:

The performed technical calculation demonstrates the possibility of introducing low-temperature titanium diboride into cathode blocks in order to reduce energy consumption. As compared to traditional bottom blocks, reduction cells equipped with a modified lining consume 986 kWh/t less electricity, equal to a saving of 7.5%.

5. CONCLUSION

As a result of the research, an effective solution was proposed for the low-temperature synthesis of titanium diboride and its use in the cathode blocks of an aluminium reduction cell. During the synthesis of a TiO2-B2O3-C mixture at 1050°C in a vacuum through the formation of intermediate phases of titanium monoxide, titanium borate and titanium oxycarbide, titanium diboride was obtained in the form of a powder under the achieved uniform formation of a finegrained structure. The results of electrical resistivity measurements of the modified cathodes showed a decrease in its values with an increase in the content of TiB2 to 15%. Thus, the optimal content of the modifying additive in the blocks for increasing the electrical conductivity is 7.5-12.5% wt.

The implementation of a cathode lining modified with low-temperature titanium diboride into the aluminium reduction cell ensures the reduction of power consumption by 940-990 kWh per ton of aluminium, equal to a saving of 7.1-7.5%.

References

1 .Grjotheim K, Welch B. Aluminium Smelter Technology. Düsseldorf: Aluminium Verlag; 1993, 260 p.

2. Alamdari H. Aluminium Production Process: Challenges and Opportunities. Metals. 2017;7(4):133. Available from: https://www.mdpi.eom/2075-4701/7/4/133 [Accessed 30th April 2020]. https://doi.org/10.3390/met7040133

3. Vasshaug K, Foosnœs T, Haarberg GM, Ratvik AP, Skybakmoen E. Formation and Dissolution of Aluminium Carbide in Cathode Blocks. Light Metals. 2009:1111-1116.

4. Evans JW. The Evolution of Technology for Light Metals over the Last 50 Years: Al, Mg and Li. JOM. 2007;59(2):30-38.

5. Sizyakov VM, Bazhin VY. Technological and Methodological Bases of Aluminum Production in High-Power

Electrolytic Baths. Saint-Petersburg: Saint-Petersburg Mining University; 2011, 130 p. (In Russ.)

6. Gorlanov ES, Bazhin VYu, Vlasov AA. Electrochemical Borating of Titanium-Containing Carbographite Materials. Russian Metallurgy (Metally). 2017;2017(6):489-493. https://doi.org/10.1134/S003602951706009X

7. Dingxiong Lu, Yungang Ban, Junman Qin, Zijin Ai. New Progress on Application of NEUI 400 kA Family High Energy Efficiency Aluminum Reduction Pot (HEEP) Technology. Light Metals. 2011:443-448.

https://doi.org/10.1007/978-3-319-48160-9_79

8. Gudbrandsen H, Sterten A, Odegerd R. Cathodic Dissolution of Carbon in Cryolitic Melts. Light Metals. 1992:521-528.

9. Mann V, Buzunov V, Pitertsev N, Chesnyak V, Polya-

ВЕСТНИК ИРКУТСКОГО ГОСУДАРСТВЕННОГО ТЕХНИЧЕСКОГО УНИВЕРСИТЕТА 2020;24(4):919-930

kov P. Reduction in Power Consumption at UC RUSAL's Smelters 2012-2014. Light Metals. 2015:757-762. https://doi.org/10.1002/9781119093435.ch128

10. Novak B, Tschöpe K, Ratvik AP, Grande T. Fundamentals of Aluminium Carbide Formation. Light Metals. 2012:1343-1348.

https://doi.org/10.1007/978-3-319-48179-1_232

11. Nemchinova NV, Radionov EY, Somov VV. Studying Working Space Form Effect on Electrolyzer MHD Parameters at Aluminum Production. Vestnik Irkutskogo gosudar-stvennogo tehnicheskogo universiteta = Proceedings of Irkutsk State Technical University. 2019;23(1 ):169-178. (In Russ.) https://doi.org/10.21285/1814-3520-2019-1-169-178

12. Joo LA, Tucker KW, McCown FE. Titanium Diboride-Graphite Composites. Patent U.S. no. 4376029; 1983.

13. Li Qing-Yu, Lai Yan-Qing, Liu Yong-Gang, Li Junlin, Yang Jian-hong, Fang Jing, et al. Laboratory Test and Industrial Application of an Ambient Temperature Cured TiB2 Cathode Coating for Aluminum Electrolysis Cells. Light Metals. 2004:327-331.

14. Ransley CE. The Application of the Refractory Carbides and Borides to Aluminum Reduction Cells. In: Tom-sett A, Johnson J. (eds.). Essential Readings in Light Metals. Cham: Springer; 2016, p. 1134-1144. https://doi.org/https://doi.org/10.1007/978-3-319-48200-2

15. Segatz M, Hop J, Reny P, Gikling H. Hydro's Cell Technology Path Towards Specific Energy Consumption Below 12 kWh/kg. Light Metals. 2016:301-305. https://doi.org/10.1007/978-3-319-48251-4_50

16. Ivanov VV, Vasilev SJ, Laurinavichjute VK, Cher-

nousov AA, Blokhina IA. Production Method of Titanium Diboride Powder for Aluminium Electrolytic Cell Wetted Cathode Material. Patent RF, no. 2498880; 2013. (In Russ.)

17. Bagdavadze J, Tsiskaridze Z, Ukleba K. Thermodynamic Analysis of the Ti-O-C System. European Chemical Bulletin. 2014;3(4): 128-129.

https://doi.org/10.17628/ecb.2014.3.319-321

18. Efimova KA, Galevsky GV, Rudneva VV. The Current Status of Titanium Diboride Production: Assessment and Determination of the Dominant Trends and Prospects. Nauchno-tekhnicheskie vedomosti SPbPU. Estestvennye i inzhenernye nauki = St. Petersburg Polytechnic University Journal of Engineering Science and Technology. 2017;23(2):144-158.

https://doi.org/10.18721/JEST.230213

19. Galevsky GV, Rudneva VV, Galevskiy SG, Ilyash-chenko DP, Kartsev DS. Nano-disperse borides and carbides: plasma technology production, specific properties, economic evaluation. In: Materials Science and Engineering: IOP Conference Series. 2016;125:012022. Available from: https://iopscience.iop.org/article/10.1088/1757-899X/125/1/012022 [Accessed 30th April 2020]. https://doi.org/10.1088/1757-899X/125/1/012022

20. Gesing AJ, Wheeler DJ. Screening and Evaluation Methods of Cathode Materials for Use in Aluminum Reduction Cells in Presence of Molten Aluminum and Cryolite up to 1000°C. Light Metals. 1987:327-334.

21. Sizyakov VM, Bazhin VY, Vilenskaya AV, Fedorov SN. Production Method of Titanium Diboride Powder. Patent RF, no. 2684381;2018. (In Russ.)

Библиографический список

1. Grjotheim K., Welch В. Aluminium smelter technology. Düsseldorf: Aluminium Verlag, 1993. 260 р.

2. Alamdari H. Aluminium production process: challenges and opportunities // Metals. 2017. Vol. 7. Issue 4. P. 133. [Электронный ресурс]. URL: https://www.mdpi.com/2075-4701/7M/133 (30.04.2020) https://doi.org/10.3390/met7040133

3. Vasshaug K., Foosn^s T., Haarberg G.M, Ratvik A.P., Skybakmoen E. Formation and dissolution of aluminium carbide in cathode blocks // Light Metals. 2009. P. 1111-1116.

4. Evans J.W. The evolution of technology for light metals over the last 50 years: Al, Mg and Li // JOM. 2007. Vol. 59. No. 2. P. 30-38.

5. Сизяков В.М., Бажин В.Ю. Технологические и методологические основы получения алюминия на мощных алюминиевых электролизерах. СПб.: Изд-во СПбГГИ (ТУ), 2011. 130 с.

6. Gorlanov E.S., Bazhin V.Yu., Vlasov A.A. Electrochemical borating of titanium-containing carbographite materials // Russian Metallurgy (Metally). 2017. Vol. 2017. No. 6. Р. 489-493. https://doi.org/10.1134/S003602951706009X

7. Dingxiong Lu, Yungang Ban, Junman Qin, Zijin Ai. New Progress on application of neui 400 ka family high energy efficiency aluminum reduction pot (HEEP) technology // Light Metals. 2011. P. 443-448. https://doi.org/10.1007/978-3-319-48160-9_79

8. Gudbrandsen H., Sterten A., Odegerd R. Cathodic dis-

solution of carbon in cryolitic melts // Light Metals. 1992. P. 521-528.

9. Mann V., Buzunov V., Pitertsev N., Chesnyak V., Poly-akov P. Reduction in power consumption at UC RUS AL's smelters 2012-2014 // Light Metals. 2015. Р. 757-762. https://doi.org/10.1002/9781119093435.ch128

10. Novak B., Tschöpe K., Ratvik A.P., Grande T. Fundamentals of aluminium carbide formation // Light Metals. 2012. P. 1343-1348.

https://doi.org/10.1007/978-3-319-48179-1_232

11. Немчинова Н.В., Радионов Е.Ю., Сомов В.В. Исследование влияния формы рабочего пространства на МГД-параметры работы электролизера производства алюминия // Вестник Иркутского государственного технического университета. 2019. Т. 23. № 1. С. 169-178. https://doi.org/10.21285/1814-3520-2019-1 -169-178

12. Pat. № 4376029 U.S., C25B 11/04, C25C 3/12. Titanium diboride-graphite composites / L.A. Joo, K.W. Tucker, F.E. McCown; assignee Great Lakes Carbon Corporation. Filed: 11.09.1980; published 08.03.1983.

13. Li Qing-Yu, Lai Yan-Qing, Liu Yong-Gang, Li Junlin, Yang Jian-hong, Fang Jing, et al. Laboratory test and industrial application of an ambient temperature cured TiB2 cathode coating for aluminum electrolysis cells // Light Metals. 2004. P. 327-331.

14. Ransley C.E. The Application of the refractory carbides and borides to aluminum reduction cells // Essential Readings in Light Metals / eds. A. Tomsett, J. Johnson.

ВЕСТНИК ИРКУТСКОГО ГОСУДАРСТВЕННОГО ТЕХНИЧЕСКОГО УНИВЕРСИТЕТА 2020;24(4): 919-930

Cham: Springer, 2016. P. 1134-1144. https://doi.org/https://doi.org/10.1007/978-3-319-48200-2

15. Segatz M., Hop J., Reny P., Gikling H. Hydro's cell technology path towards specific energy consumption below 12 kWh/kg // Light Metals. 2016. P. 301-305. https://doi.org/10.1007/978-3-319-48251-4_50

16. Пат. № 2498880, Российская Федерация, C04B 35/58. Способ получения порошка диборида титана для материала смачиваемого катода алюминиевого электролизера / В.В. Иванов, С.Ю. Васильев, В.К. Ла-уринавичюте, А.А. Черноусов, И.А. Блохина; заявитель и патентообладатель Федеральное государственное автономное образовательное учреждение высшего профессионального образования «Сибирский федеральный университет». Заявл. 13.08.2012, опубл. 20.11.2013. Бюл. № 32.

17. Bagdavadze J., Tsiskaridze Z., Ukleba K. Thermodynamic analysis of the Ti-O-C system // European Chemical Bulletin. 2014. Vol. 3. No. 4. P. 128-129. https://doi.org/10.17628/ecb.2014.3.319-321

18. Ефимова К.А., Галевский Г.В., Руднева В.В. Современное состояние производства диборида титана: оценка, определение доминирующих тенденций и перспектив // Научно-технические ведомости СПбПУ.

Authorship criteria

Fedorov S.N., Kurtenkov R.V., Palyanitsin P.S. declare equal participation in obtaining and formalization of scientific results and bear equal responsibility for plagiarism.

Естественные и инженерные науки. 2017. Т. 23. Вып. 2. 144-158. https://doi.org/10.18721/JEST.230213

19. Galevsky G.V., Rudneva V.V., Galevskiy S.G., Ilyash-chenko D.P., Kartsev D.S. Nano-Disperse Borides and Carbides: Plasma Technology Production, Specific Properties, Economic Evaluation // Materials Science and Engineering: IOP Conference Series. 2016. Vol. 125. 012022. [Электронный ресурс] URL: https://iopscience.iop.org/article/10.1088/1757-899X/125/1/012022 (30.04.2020).

https://doi.org/10.1088/1757-899X/125/1/012022

20. Gesing A.J., Wheeler D.J. Screening and evaluation methods of cathode materials for use in aluminum reduction cells in presence of molten aluminum and cryolite up to 1000°C // Light Metals. 1987. P. 327-334.

21. Пат. № 2684381, Российская Федерация, C01B 35/04, C01G 23/00, B22F 9/18. Способ получения порошка диборида титана / В.М. Сизяков, В.Ю. Бажин, А.В. Виленская, С.Н. Федоров; заявитель и патентообладатель федеральное государственное бюджетное образовательное учреждение высшего образования «Санкт-Петербургский горный университет». Заявл. 09.01.2018; опубл. 08.04.2019. Бюл. № 10.

Критерии авторства

Федоров С.Н., Куртенков Р.В., Паляницин П.С. заявляют о равном участии в получении и оформлении научных результатов и в равной мере несут ответственность за плагиат.

Conflict of interests

The authors declare that there is no conflict of interests regarding the publication of this article.

The final manuscript has been read and approved by all the co-authors.

INFORMATION ABOUT THE AUTHORS

Sergei N. Fedorov,

Head of the Metallurgy Department Laboratory, Saint-Petersburg Mining University, 2, 21st Line, St. Petersburg 199106, Russia; !"■■■"! e-mail: [email protected]

Roman V. Kurtenkov,

Cand. Sci. (Eng.),

Assistant Professor of the Metallurgy Department, Saint-Petersburg Mining University, 2, 21st Line, St. Petersburg 199106, Russia; e-mail: [email protected]

Pavel S. Palyanitsin,

Postgraduate Student, Saint-Petersburg Mining University, 2, 21st Line, St. Petersburg 199106, Russia; e-mail: [email protected]

Конфликт интересов

Авторы заявляют об отсутствии конфликта интересов.

Все авторы прочитали и одобрили окончательный вариант рукописи.

СВЕДЕНИЯ ОБ АВТОРАХ

Федоров Сергей Николаевич,

заведующий лабораторией кафедры металлургии, Санкт-Петербургский горный университет, 199106, г. Санкт-Петербург, Васильевский о-в, 21 линия, 2, Россия; !"■■■".! e-mail: [email protected]

Куртенков Роман Владимирович,

кандидат технических наук, ассистент кафедры металлургии, Санкт-Петербургский горный университет, 199106, г. Санкт-Петербург, Васильевский о-в, 21 линия, 2, Россия; e-mail: [email protected]

Паляницин Павел Сергеевич,

аспирант,

Санкт-Петербургский горный университет, 199106, г. Санкт-Петербург, Васильевский о-в, 21 линия, 2, Россия; e-mail: [email protected]

ВЕСТНИК ИРКУТСКОГО ГОСУДАРСТВЕННОГО ТЕХНИЧЕСКОГО УНИВЕРСИТЕТА 2020;24(4):919-930