2014-02-17
2164
The system AI2O3-SiO2 (fig. 55) for the first time was in details investigated Н. Боуэном and Д. Грейгом, on which data in system there is only one binary connection - муллит, which structure corresponds(meets) to the formula ЗА12Оз·2 SiO2. On Н. Боуэну and Д. Грейгу, муллит плавится инконгруэнтно at 1810ЁС, being decomposed on корунд And - А12Оз and liquid of structure ~45 % (May). SiO2 and 55 % (мас). А12О3.
Later researches which have been carried out(spent) by the Soviet scientists Н. Д. Тороповым and Ф. I. Галаховым, have allowed to bring in essential changes to the diagram of a condition of system А12Оз-SiO2. Allocation корунда first of all was shown, that at плавлении
муллита (т. е. It(him) инконгруэнтное плавление) is observed only when is not accepted of measures against улетучивания кремнезема at high temperatures from расплава муллитового of structure. In conditions, when расплавы are protected from possible(probable) partial улетучивания кремнезема, муллит плавится not being decomposed, т. е. Is characterized конгруэнтным плавлением. Besides it was revealed, that муллит forms with корундом firm solutions and the area of their existence is determined.
The diagram of a condition of system А12Оз-SiO2 on Н. And. Торопову and Ф. I. Галахову is submitted in a fig. 56. According to this diagram муллит плавится конгруэнтно at 1910ЁС two also form эвтектики: one with SiO2 at 1585ЁС and second (as a firm solution) with А12О3 at 1850ЁС, appropriate to the contents 79 % (мас). А12Оз and 21 % (мас). SiO2. The area of firm solutions муллита with корундом reaches from structure муллита (3:2), appropriate to the contents 71,8 % (мас). А12О3 and 28,2 % (мас). SiO2, up to limiting structure (2: 1), appropriate to the contents ~78 % (May). А12О3 and 22 % (May). SiO2. The further researches of item. Item. Будникова, With.. Тресвятского and In. And. Кушаковского, and also With. Арамаки and Р. A plenty have confirmed basic correctness of the diagram of a condition А12Оз-SiO2, offered Н. And. Тороповым and Ф. I. Галаховым. Some specify also an opportunity of education of the limited firm solutions between муллитом and SiO2.
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Let's consider some features of system А12О3-SiO2. First of all it is necessary to pay attention that on the diagram of a condition of this system there is no maximum on a curve ликвидуса, which would correspond(meet) to connection Al2O3-SiO2 [62,9 % (мас.) А12О3 and 37,1 % (мас.) SiO2], widespread(distributed) in a nature as minerals of group силлиманита (силлиманит and his(its) version - кианит and андалузит). It is explained to that at usual pressure, at which the given diagrams are constructed, the connection А12О3·SiO2 has no area of a steady equilibrium condition. However, as show some researches, at high pressure such areas on the diagram of a condition of system Al2O3·SiO2 occur. So, for example, at pressure 2520 МПа steady binary connection in this system is any more муллит, and кианит, плавящийся инконгруэнтно
At temperature ~15000С. In a nature the minerals of group силлиманита were formed from каолинита Al2O3·2SiO2·2H2O in specific conditions under influence of high temperatures and pressure. Синтетически at usual pressure them to receive it fails, as at heating they is irreversible pass in муллит and коистобалит:
Other feature of the diagram of a condition of system А12О3-SiO2, rendering the large influence on practical application of some technical products, which structure lays in this system, consists in rather flat character curve ликвидуса in area кристаллизации муллита, laying to the left from his(its) structure. Such flat course of a curve ликвидуса causes very fast increase of the contents of a liquid phase at heating mixes containing from 5,5 % (мас). (эвтектика at 15850С) up to -72 % (мас). А12О3. From here follows, that at temperatures is higher 16000С for the structures containing the specified quantity(amount) А12О3, the contents of a liquid phase in system will depend very strongly on a parity(ratio) in samples А12О3 and SiO2.
The system А12О3-SiO2 has the especially large meaning(importance) for the "know-how" various алюмосиликатных огнеупоров both products of thin ceramics and interpretation of processes proceeding at them обжиге, and also for understanding of the phenomena occurring at interaction алюмосиликатных огнеупоров to various aggressive environments(Wednesdays).
