Mathematical modelling of thermal microexplosion in a catalyst granule with point sources of heat release

A mathematical model of heat and mass transfer in a spherical catalyst granule is proposed. Exothermic synthesis reactions are carried out on point active centres located inside a porous ceramic granule. From the surface of the granule the heat of catalytic reactions is removed into liquid synthesis products. The rate of a chemical reaction is modelled by a modified Arrhenius law. In contrast to the homogeneous model of a catalytic granule methods for calculating heat transfer processes in a system of point, active centres do not develop. An iterative procedure is suggested to calculate the unknown temperature and concentration of the reagent at the active centre. It is shown that the temperature of the active centres is significantly higher than in the volume of the granule. The results of modelling a thermal explosion with increasing granule size and reactor temperature are presented.

The use of ceramics as an internal curing agent in high performance concrete with variable temperature curing to improve mechanical characteristics

Concrete curing is one of the most significant factors in the development of compressive strength, and a high temperature difference during curing may reduce strength. The microcracks created in the concrete as a result of the constant temperature change cause this exudation. Internal curing has become popular for decreasing the risk of early-age cracking in high-performance concrete by limiting autogenous shrinkage (HPC). This study looks at the effectiveness of internal wet curing offered by a new kind of aggregate called “recycled waste porous ceramic fine aggregates”. The evolution of measured mechanical characteristics is examined on three distinct HPCs, both with and without internal curing materials. Ceramic fine aggregates were used to replace two different quantities of regular weight fine aggregate. Ceramic fine aggregates were shown to be quite beneficial for internal cure. It has been discovered that incorporating 20% ceramic fine aggregates into HPC improves the properties of the material, resulting in low internal stress and a large improvement in compressive strength. It should be emphasized that, unlike some traditional lightweight aggregates, no loss in compressive strength has been seen for the various quantities of ceramic fine aggregates introduced at either early or later ages.

Porous Ceramic Sternal Prosthesis Implantation in a 13-Year-Old Patient Presenting with Metastatic Ewing's Sarcoma

Ewing's sarcoma is the second most frequent primary malignant bone tumor in adolescents and young adults. Locations on the thoracic wall represent up to 20% of primary and secondary locations. We present the case of a 13-year-old patient treated with the use of a radiolucency porous bioceramic prosthesis as a sternal replacement for a wide tumor resection in an oncologic context. Focal radiation therapy was not possible due to the high risk of severe myocardial injuries caused by the sternal location of the tumor. The sternum CERAMIL® (I.CERAM, Limoges, France), in porous alumina (Al2O3) has already been implanted into adults in sternal replacement during its invasion by a tumor or its infectious destruction. There were no complication concerning the surgery. The last follow-up at 2 years postoperatively reveals a satisfactory clinical situation with any functional thoracic complaint and nor any functional respiratory symptoms. The porous alumina sternal prosthesis offers a reliable alternative for sternal replacement indications for children in an oncologic context.

DEVELOPMENT OF RESOURCE-SAVING TECHNOLOGY OF POROUS-HOLLOW CERAMIC STONES

A resource-saving technology of porous ceramic materials using low-quality non-sintering sandy loam as a basic raw material has been developed. Based on the analysis of the plastic properties of two- and three-component ceramic masses, including sandy loam, expanded clay and fuel slag in various ratios, it was found that the required level of their plasticity provides the content of the main raw material in the following range (wt%): fuel slag – 15 – 20; sandy loam – 50 – 65; expanded clay – 20 – 30. By the method of planning the experiment, the rational composition of the three-component ceramic mass was substantiated. This which contains: 62.5 wt. % sandy loam, 20 wt. % medium-sintering plastic clay as a plasticizer and 17.5 wt. % fuel slag of TPP as a porous agent. For the developed mass, the main technological properties were investigated, which made it possible to recommend the drying mode of the raw material – 60 hours, the optimal firing temperature – 950 °С. Such conditions ensure that samples are obtained without drying cracks and signs of deformation. Оn the results of dilatometric analysis of mass the rational mode of firing high-hollow semifinished products was designed. The firing mode provides for a 44-hour firing and a decrease in the heating rates in the areas of dehydration of clay minerals, direct quartz transition and intensive sintering of the mass, as well as a decrease in the cooling rate in the area of the reverse quartz transition. The proposed firing mode provides the degree of sintering and their properties necessary for ceramic materials. Based on the developed mass under the recommended drying and firing modes, porous ceramic materials with an apparent density of 1.48 g/cm3, a compressive strength of 18.2 MPa and frost resistance of 30 cycles were obtained. The developed materials belong to the group of conditionally effective, and if 50% of the voids are organized, they can be classified as effective.

Heat-insulating porous material based on glauconite-containing sands and aleurites of the Novodvorskoye deposit of the Republic of Belarus

The results on the research of heat-insulating porous ceramic materials produced using overburden rocks of the Novodvorsk deposit of Pinsk district of the Brest region as the main component of raw materials are presented in the study and the use of bulk rock consisting of glauconite sands and aleurites is recommended. Low-melting clay, basalt and a blowing agent are used as additional components, rational combination of which would ensure the forming ability of ceramic masses and the required set of the physicochemical properties of the material. The dependence of the bulk density, swelling coefficient, coefficient of thermal conductivity on the chemical and mineral composition of the used and raw materials is established, wich is the criteria for choosing composition with the maximum use of overburden and the necessary plasticity of the ceramic mass required for the molding process of raw granules. The obtained results can serve as a basis for the large-scale use of not only the minerals of the Novodvorsk deposit (basalts and tuffs), but also associated – glauconite-containing overburden. This will make a significant contribution to the expanding the mineral resource base of the Republic of Belarus.

Influence of gas permeability of abrasive tools on their structural and mechanical parameters

Quality assurance and processing capacity are essential performance parameters of abrasive tools. It is of prime importance for grinding wheels operating at a speed of 35–60 m/s. In this case, the opportunities to increase the high-rate grinding efficiency without burns are associated with using high-porosity and low-hardness wheels. Artificial pore-forming agents are used to manufacture tools. Introduction of pore-forming agents decreases grinding forces and increases the maximum grinding depth without burns. The porosity of filled compound materials can be attributed to the conception of gas permeability. The gas permeability parameter describes the openness degree of such structures and the velocity of the air volumes passing through porous materials. The porosity and gas-permeability degrees of the material of high-porous ceramic-bond abrasive tools with various parameters, depending on the abrasive material type, porogen grain size and content, and the composite structure number have been studied. It appeared that the porosity degree of high-porous abrasive tools, made both of fused alumina and silicon carbide increases as the structure number, grain size, and content of burning porogens increases. Besides, the increase degree of fused alumina is a little higher than that of silicon carbide. The gas permeability degree depends on the factors mentioned above in nearly the same way. Compared to porosity, the effect of gas permeability increases due to an altered structure, grain size, and content of porogens is much higher, up to 6 times. In this case, the gas permeability value is primarily characteristic of the pore size; in other words, the speed and volume of the air or lubrication and cooling fluid penetrating the material structure increase correspondingly at nearly the same increase of the pore size by several times and at the same volume porosity degree. The gas permeability degree can be used for quantitative and qualitative description of the material structure of high-porous abrasive tools, as well as their structural and mechanical parameters. The operating parameters of tools can depend on the gas permeability level of their materials. Thus, the results of abrasive processing can be foreseen.