Теоретичні основи технології периклазошпінельних вогнетривів на основі композиції MgO – Al₂O₃ – FeO – TiO₂ для футерівки цементних печей

Abstract

Дисертація на здобуття наукового ступеня доктора технічних наук за спе-ціальністю 05.17.11 − технологія тугоплавких неметалічних матеріалів. – Наці-ональний технічний університет «Харківський політехнічний інститут», Харків, 2022 р. Дисертацію присвячено створенню фізико-хімічних засад одержання периклазошпінельних матеріалів на основі системи MgO – Al₂O₃ – FeO – TiO₂ з заданою термопластичною матрицею, яка має підвищену адаптивну здатність зберігати цілісність матеріалу та експлуатаційну надійність вогнетривів в умовах знакозмінних та високоградієнтних термічних навантажень. Досліджено субсолідусну будову трикомпонентних систем MgO – FeO – Al₂O₃, MgO – FeO – TiO₂, МgO – Al₂O₃ – ТiO₂, FeO – TiO₂ – Al₂O₃ та чотирико-мпонентної системи MgO – Al₂O₃ – FeO – TiO₂. Аналіз отриманих результатів розрахунків геометро-топологічних характеристик трикомпонентних систем та чотирикомпонентної системи дозволяють цілеспрямовано планувати склади нових композиційних матеріалів, а саме периклазошпінельних вогнетривів, з заданим фазовим складом та заданими властивостями. Розроблено склади периклазошпінельних вогнетривів на основі системи MgO – Al₂O₃ – FeO – TiO₂ для обертових цементних печей шляхом апробації технологічного підходу введення до складу сировинної шихти модифікатора у вигляді заздалегідь синтезованого продукту, який містить кристалічні фази систем Al₂O₃ – TiO₂ – FeO, MgO – FeO – TiO₂ та MgO – Al₂O₃ – FeO – TiO₂, що забезпечує покращення експлуатаційних характеристик периклазошпінельних матеріалів, а саме підвищує здатність адаптувати фазовий склад та мікроструктуру матеріалу до змін експлуатаційних параметрів, що спрямовано на знижен-ня собівартості цементного клінкеру та збереження енергоресурсів за рахунок збільшення строку експлуатації футерівки.Thesis for obtaining the scientific degree of Doctor of Technical Sciences in the field 05.17.11 – Technology of refractory non-metallic materials. – National Technical University «Kharkiv Polytechnic Institute», Kharkiv, 2022. The thesis is devoted to the development of the physico-chemical basics of the creation of periclase-spinel materials using compositions of the MgO – Al₂O₃ – FeO – ТіО₂ system with a given thermoplastic matrix, which has an increased adaptive ability to preserve the integrity of the material and the operational reliability of re-fractories under sign-changing conditions and high-gradient thermal loads. The subsolidus structure of the three-component systems MgO – FeO – Al₂O₃, MgO – FeO – TiO₂, МgO – Al₂O₃ – ТiO₂, FeO – TiO₂ – Al₂O₃ and the four-component system MgO – Al₂O₃ – FeO – ТіО₂ was studied. It was established that the division of systems into elementary triangles undergoes changes in different tem-perature intervals: for MgO – FeO – Al₂O₃ – in two, MgO – FeO – TiO₂ and МgO – Al₂O₃ – ТiO₂ – in three, FeO – TiO₂ – Al₂O₃ – in five. The analysis of the obtained results of the calculations of the geometrical and topological characteristics of three-component systems allows purposeful planning of compositions of new composite materials with a given phase composition and given properties. It was established that the four-component system MgO – Al₂O₃ – FeO – ТіО₂ has a complex structure that varies in six temperature intervals: I – 800 – 1141 K, II – 1141 – 1413 K, III – 1413 – 1537 K, IV – 1537 – 1630 K, V – 1630 – 2076 K, VI – above 2076 K. The obtained calculated data above the temperature of 2076 K are of a recommendatory nature, since the existence of the Al4TiO8 compound has not been proven, and therefore requires further theoretical and practical research. Above the temperature of 1141 K, four elementary tetrahedra remain unchanged: MgO – FeO – Mg₂TiO₄ – MgAl₂O₄, FeAl₂O₄ – Mg₂TiO₄ – FeO – Fe₂TiO₄, FeAl₂O4 – Mg₂TiO₄ – MgAl₂O₄ – FeO и FeAl₂O₄ – MgTiO₃ – MgAl₂O₄ – Al₂O₃, which have relatively large volumes, so these areas have higher reliability of predicting the phase composi-tion of materials without special technological techniques for obtaining periclase-spinel and spinel-containing materials. An analysis of the temperatures and compositions of eutectics of multicompo-nent intersections of the MgO – Al₂O₃ – FeO – TiO₂ system was carried out, which confirmed the possibility of synthesizing periclase-spinel refractories with high oper-ational characteristics in this system and provided the necessary technical information for targeted control of the «composition – structure – properties» relationship during their obtaining. A thermodynamic analysis of the coexistence of different types of spinels was carried out: MgAl₂O₄ (aluminomagnesian), FeAl₂O₄ (hercynite), Fe₂TiO₄ (ulvospinel) and Mg₂TiO₄ (quandilite). The compositions of periclase spinel refractories based on the MgO – Al₂O₃ – FeO – TiO₂ system for rotary cement kilns were optimized by testing the technological approach of introducing a modifier into the composition of the raw charge in the form of a presynthesized product containing the crystalline phases of the Al₂O₃ – TiO₂ – FeO, MgO – FeO – TiO₂ systems and MgO – Al₂O₃ – FeO – TiO₂. The influence of volume changes that occur during the firing and operation of peri-clase-spinel materials on the physical, mechanical and operational characteristics of re-fractories, which must be taken into account when predicting the phase composition and which in its turn depend on the type and amount of raw materials, was studied. The main points of the concept of increasing the heat resistance of periclase-spinel materials based on the MgO – Al₂O₃ – FeO – TiO₂ system have been defined, which include both known mechanisms of excess energy absorption by cracks that develop as a result of thermal shock, and new mechanisms of structural and phase ad-aptation while preserving the integrity of periclase-spinel refractories. The processes of phase formation of periclase spinel materials based on the MgO – Al₂O₃ – FeO – TiO₂ system were studied using electron microscopic studies and it was established that the formation of a specific dissipative microstructure of the material and combinations of phases capable of rational interaction under critical load parameters and compensation of excess energy influence, which contributes pre-serving the integrity of the material and increasing the adaptability of the material to thermomechanical and corrosive loads of operational environments, as well as a set of ledge-coating. The basic regularities of obtaining periclase-spinel materials with a thermo-plastic matrix were revealed. It has been established that the introduction of a SAI modifier based on sintered alumina and ilmenite concentrate (85 % and 15%, respec-tively) into the charge increases the adaptability of the material to the thermomechan-ical and corrosive loads of operational environments. Also, the presence of ilmenite concentrate in the composition of the modifier contributes to the compaction of the material as a result of firing and increases its corrosion resistance due to the presence of Fe (II)-containing phases in it, which are responsible for the set of ledge-coating, which provides resistance to the action of mechanical impact and abrasive loads. In the process of firing and operation, the components of the periclase-spinel charge en-ter into a complex physico-chemical interaction, forming new solid solutions with the periclase, which fill the cracks of the product formed during their performance and increase the resistance of the refractory to corrosion. The combination of the listed factors improves the performance characteristics of periclase-spinel refractories, namely, increases the ability to adapt the phase composition and microstructure of the material to changes in operational parameters, which is aimed at reducing the cost of cement clinker and saving energy resources by increasing the life of the lining of ro-tary kilns for firing cement clinker. Technology for obtaining periclase-spinel refractories with a «thermoplastic ma-trix» has been developed. The results of the development were successfully tested in the conditions of Druzhkiv Refractory Plant LLC and accepted for implementation. Specialists of «Service center «Refractory Service»» LLC performed work on lining the firing zone of the short rotary kiln with periclase-spinel brick, which undergo successful approval. The results of the thesis work are implemented in the education-al process of the Department of Technology of Ceramics, Refractories, Glass and Enamels of NTU «KhPI».