Успешное развитие ряда отраслей социалистической промышленности, и в первую очередь металлургической, в значительной степени зависит от качества огнеупорных керамических изделий. Современная металлургия, применяющая кислородное дутье в доменных печах и скоростные методы выплавки стали в мартеновских печах, нуждается в новых, более высокоогнеупорных материалах, чем ныне существующие, температура плавления которых не превышает 1800— 2000°. Приведенные данные (см. статью) подчеркивают огромную актуальность проблемы новых высокоогнеупорных материалов. Основной причиной затруднений, возникающих при изыскании новых высокоогнеупоров, является отсутствие диаграмм состояния систем из окислов, входящих в состав огнеупорных масс. Число материалов, из которых обычно изготовляются огнеупорные массы, довольно ограниченно. Поэтому исследование ранее не изучавшейся диаграммы состояния системы MgO — Сг 2 О 3 — ZrО 2 (температура плавления MgO — 2800°, Сг 2 О 3 — 2110°, ZrО 2 — 2715°) может иметь не только теоретическое, но и практическое значение при изыскании новых огнеупорных материалов с более, высокими физико-химическими свойствами. Тройные смеси окиси магния, окиси хрома и двуокиси циркония, составы которых расположены в области твердых растворов, как не образующие эвтектики и не испытывающие поэтому размягчения при нагревании вплоть до температур плавления (2200—2600°), являются новыми, практически важными высокоогнеупорными материалами.
The essence of physicochemical analysis, created and formalized by Nikolai Semenovich Kurnakov into a special department of physical chemistry studying the equilibrium of various systems, consists in the application of physical methods to determine the chemical nature of substances formed in binary and multicomponent systems. The general method of physicochemical analysis consists in the quantitative study of the properties of equilibrium systems formed, depending on their composition, by two or more components. The result of the measured values is a composition-property diagram consisting of one or more lines, the positions of which determine the state of the system. The scientific works of the Kurnakov school were distinguished by their purposefulness and were mainly aimed at determining the characteristics of a chemical individual formed in binary and multicomponent systems in contrast to an ordinary solution of the same components. In other words, to determine how a substance that we can and should call a chemical individual differs from an ordinary solution of the components that form a chemical individual. The same question was posed to Proulx by Berthollet more than a hundred years ago, demanding a precise definition of both concepts. Dalton and Gay-Lussac, Wald and Ostwald were also concerned with this question.
High refractoriness (2715°), slag resistance, low thermal and electrical conductivity at high temperatures, mechanical strength and thermal stability under sharp temperature fluctuations make zirconium dioxide a very valuable source of highly refractory material, especially after it was discovered [1] that cracking during heating of products made of pure zirconium dioxide, caused by the transformation of one modification into another at a temperature of 1000°, can be eliminated by adding more than 4% magnesium or calcium oxide, which form stable solid solutions with zirconium dioxide. In the Soviet Union there are numerous deposits of zirconium ores, ensuring their industrial use. As for magnesium oxide and calcium oxide, these source materials are available in unlimited quantities. All this shows that the study of the ternary system Zr02— MgO — СаО has not only theoretical but also significant practical interest.
Among the refractory materials currently in use, chromite iron ore and magnesite deserve special attention. But, as is known, these refractories in their pure form are not stable enough and are destroyed relatively quickly, which causes frequent repairs of the internal lining of smelting furnaces. Therefore, the study of the dependence of the melting temperature on the composition of mixtures of highly refractory materials, in particular the determination of the areas of formation of solid solutions, is one of the ways to find new highly refractory materials. This prompted us to study the melting diagrams of the systems: Сr2O3 — MgO and Сr2O3 — ZrO2.
The first literary data date back to 1930, when attempts were made to study the melting diagram of the Сr2О3 — Zr02 system [1, 2]. Having discovered the significant volatility of chromium oxide, the authors abandoned further research. The results of the work are presented in Fig. 1, which shows that the data obtained cannot even be approximate. These data exhaust the literary information on the Сr2О3 — Zr02 system. Believing that the volatility of Сr2О3 in itself cannot serve as an obstacle to studying the system, since the composition of each point can be determined by chemical analysis of the fused portion of the samples, after determining the melting point, we decided to study the equilibrium diagram of this system, which is of not only theoretical but also significant practical interest.
The ternary system ZrO2—MgO—Al2O3 as a whole has not yet been studied. Literature data is available only on binary systems that limit the sides of this ternary system. A study of the fusibility temperatures was carried out along three sections in the ternary system ZrO2—MgO—AlO3 and it was found that in the direction from ZrO2 to the chemical compound MgO - Al2O3 there passes a continuous region of solid solutions, the melting point of which increases depending on the ZrO2 content from 2130° (spinel ) up to 2715 (ZrO2). The absence of eutectic, which causes premature softening of the material, makes these mixtures very important highly refractory.
With the very rapid development of automobile and aircraft construction, the question of obtaining materials that are lightweight and at the same time have sufficient mechanical properties is becoming more and more relevant. The best and, so far, unsurpassed in this regard are alloys such as duralumin, with approximate content (see article). The alloy of duralumin, as you can see, is relatively complex and therefore experiments have long been carried out in different places around the globe to obtain simpler alloys that would be not inferior to duralumin in their mechanical qualities. Of these simple alloys, the most successful, especially in America, is an alloy of aluminum and copper. The nature of this alloy has not yet been sufficiently elucidated. Therefore, in order to clarify the issue in more detail, it seemed appropriate to us to study the change in the solubility of copper in aluminum in the solid state depending on temperature, since according to available data, such a change in the solubility of various components in alloys is the main reason determining the properties of alloys such as duralumin, including property of "aging".
