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Ключевые слова: porosity

Effect of powder morphology on the structure and properties of Al2O3 based coatings obtained by detonation spraying

https://doi.org/10.58224/2618-7183-2024-7-5-7
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Аннотация
Aluminum oxide (Al2O3) remains a crucial material in the field of engineering ceramics, particularly in industrial applications. Notably, its transitional phases, in addition to the α-phase, demonstrate good properties. In this article the structure and properties of coatings obtained by detonation spraying from aluminum oxide powder with different production methods (fragmentation and spherical particle shape) and crystalline modification (α-Al2O3 and γ-Al2O3) but with similar average particle size were studied. The goal of the study was to investigate the influence of the morphology and phase composition of the powder on such properties of the coatings as microstructure, porosity, roughness and hardness. The results of the study showed that agglomerated spherical powder leads to low porosity of the coatings, while crushed fragmentation particles provide dense layers. In addition, the coating obtained using fragmentation powder showed higher hardness, and the surface had twice the roughness, compared to the coating applied using spheroidal powder. These results confirm the effect of the morphology of the original powder on the final properties and efficiency of the coatings. The study showed that the detonation spraying method allows for the efficient application of coatings from two types of Al2O3 powders with different morphology (spherical and fragmentation) and phase composition (γ-Al2O3 and α-Al2O3) but with similar particle sizes.
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Analysis of the effect of porosity on thermal conductivity with consideration of the internal structure of arbolite

https://doi.org/10.58224/2618-7183-2024-7-3-4
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Аннотация
A theoretical study of the effect of porosity and internal structure of the exterior envelope in the ANSYS and BLENDER software systems has been carried out in the paper. As an example of exterior enclosure structure, an arbolite block with porosity up to 20% and fiber structure in the direction along and across the heat flux, as well as randomly and at an angle of 45° was studied. As a result of the study, it was found that the significant effect of the heat flux dependence on the porosity of the material is the porosity of the block over 10%, which reached up to 5.92%, and with porosity up to 5% showed a difference of 1.3%. At the same time, the fiber structure also showed a significant difference from 8.16% to 15.33% depending on the fiber direction. At the same time, the analysis of the effect of porosity on the thermal conductive value also showed a difference of up to 15.33% for the same value of heat flux. At the same time, the influence of fiber structure shows an additional difference of up to 5.9%. The results of the study showed that the most thermally conductive arbolite blocks are, those in which the direction of fibers are located along (along the X axis) and at 45 ° relative to the structure of fibers across (along the Y axis) and random, the difference of which was up to 1.6%. The obtained results of this study, further excluding the costly experiments to determine the coefficient of thermal conductivity can be used to accurately estimate the coefficient of thermal conductivity of external envelopes made of arbolite blocks, considering porosity and fiber structure in the design of residential buildings.
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Evaluation of the influence of an aggressive environment on the durability of the cement stone

https://doi.org/10.58224/2618-7183-2024-7-2-4
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Аннотация
The paper proposes methods for assessing the durability of building materials and structures based on Portland cement when exposed to aggressive environments that mimic the products of the vital activity of bacteria on building materials.
To determine the main parameters of the model of degradation of building materials under the action of aggressive environments, a mathematical model has been developed in the form of integral and differential relations connecting these parameters. A technique for identifying the mechanical characteristics included in these models based on the solution of inverse biodegradation problems has been developed. The analysis of changes in the structure of the cement stone was carried out using the results of computed tomography, and the regularities of the distribution of pores in the cement stone from the time of exposure were obtained.
Based on experimental and numerical studies, it has been established that the mechanism of destruction of cement stone obtained by the traditional method and activation in the vortex layer apparatus is different. The difference lies in the greater accumulation of cement stone interaction products in the activated sample, which is confirmed by a shift in porosity to less than 0.5 mm and a lower solubility value compared to the control composition. The compressive strength of the samples as a result of exposure for 28 days decreased by 37% and 20% for the control and activated compositions. The mass of the studied samples as a result of exposure decreased by 49% and 21%, respectively.
On the basis of this mechanism, a mathematical model of the process of material degradation in an aggressive one is developed, taking into account changes in porosity and acidity concentration, and dependence of material strength reduction are obtained.
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