The scientific and practical issues of the development of core mixtures for foundry, based on phosphate binding materials, are considered. The binder presented in this article differ from those previously known by the fact that scarce prepared metal phosphate binding components and powder solidifiers are not used to produce them. As a result, all developed binders are different forms of aluminum phosphates. It is shown that to obtain them it is possible to use combinations of orthophosphoric acid with aluminum-containing materials of different chemical nature.The formation of high-strength phosphate binders in the interaction of phosphoric acid with aluminosilicates and sludge wastes of aluminum production has been established. They are rationally used for processes of thermal strengthening of cores in the temperature range of 200…300 °C.The formation of binders in the interaction of orthophosphoric acid with inorganic aluminum salts are theoretically proved and practically confirmed. The results are confirmed by thermodynamic calculations, as well as by X-ray phase analysis.The compositions of the developed core mixtures and examples of their application for obtaining high-quality castings from iron and steel are presented.
Purpose. Creation of binder based on orthophosphoric acid and aluminum sulfate, study on its structure and physicochemical patterns of formation, determination of the properties of structured mixtures for the needs of foundry. Methodology. In the work, X-ray qualitative and quantitative analysis was performed on the Rigaku Ultima IV unit, and differential thermal analysis was performed on the STA 449 C Jupiter synchronous thermal analyzer. Orthophosphoric acid, technical thermal, of 85% concentration, 18-hydrous sulfate of aluminum Al2(SO4)3 18H2O and quartz sand of brand 3K5O3025 were used. The strength of core mixtures was determined on the US-700 unit on standard cylindrical samples with a diameter and height of 50mm. The roughness of the cast surfaces was determined on a profilometer model 107622 with computer processing of the obtained data and construction of profilograms. To determine the propensity of the core mixtures to form caking, a hexagon sample was used according to the method by M.Fedorov. Breakability was determined on standard cylindrical samples with a diameter and height of 50 mm according to the original method described in the text of the article. Findings. For the first time, the mechanism of formation of aluminum phosphates with binding properties during the interaction of aluminum hydrate crystal sulfate Al2(SO4)3 18H2O with orthophosphoric acid in the temperature range of 100200 has been investigated. The formation is proved of an intermediate phase during heating aluminum hydroxide Al(OH)3, which, in contrast to its sulfate, according to the results of thermodynamic analysis is able to interact with acid. Formation of aluminum in the system of ortho- and metaphosphates, which features binding properties and ensures high strength of samples based on quartz filler, has been established. The thermal transformations of the obtained binder, which consists of a combination of aluminum phosphates with its residual sulfate, are studied. Stages of gradual disintegration of crystal hydrates, formation of new aluminum phosphates and thermal decomposition of residual sulfate are recorded. The tendency to burn and knockout of the developed core mixtures was determined. Originality. For the first time, a description has been developed of the mechanism of formation of aluminum phosphates with binding properties during the interaction of its sulfate crystal hydrate Al2(SO4)3 18H2O with orthophosphoric acid in the temperature range of 100200. Practical value. A new inorganic binder from orthophosphoric acid and 18-aqueous aluminum sulfate has been obtained for foundry production. The scheme of its preparation involves preliminary mixing and heating of the specified reagents with the resulting formation of a dry powder material which consists of phosphates and residual aluminum sulfate, and therefore it is called phosphosulfate. The binding has a long shelf life and is introduced into the mixture in a ready-made form while the technology of its production is less energy-intensive and long-lasting compared to the preparation of traditional metal phosphate binding.
The technology of synthesis of inorganic binder material based on sodium tripolyphosphate Na5P3O10 and orthophosphoric acid has been developed. The sequence of physicochemical transformations in this system, as well as the optimal mass ratio of orthophosphoric acid and sodium tripolyphosphate are established. The research uses methods of quantitative and qualitative X-ray phase analysis, differential thermal analysis, standard methods of testing samples for compressive strength. The ratios of the atomic radii of the cation (Na) and the anion (P2O7), as well as the presence of hydrogen bonds, provide a significant increase in the binding potential compared to other sodium phosphates. It was found that the strengthening of mixtures with 2…8 mass parts including sodium pyrophosphate, the filler of which is quartz-based sand, occurs as intensely as possible when heated to 150°C. A further increase in temperature above 250 °C leads to the conversion of sodium pyrophosphate to ordinary (non-polymeric) metaphosphate NaPO3, which exists without changes in chemical structure up to 1000°C. The developed binder material, given the global trends of decarbonization and resource conservation, is a competitive alternative to widely used synthetic resins and other organic materials. It does not contain harmful substances and does not emit dangerous products when heated.
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