International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

There has been growing interest in the use of the sol-gel approach to form high-quality dielectric materials. Their tailored properties allow for developing functional electronic devices in a scalable and rapid manner. According to physicochemical principles, the displacement and response behavior of charges under an applied external field can manifest in unique dielectric properties, providing useful information to improve the process, design, and quality of electronic devices. Therefore, a systematic and in-depth investigation of the fundamentals of sol-gel dielectrics is necessary. In this Research Update, we present recent advances in various sol-gel-processed dielectric materials and their applications to functional electronic devices. A brief introduction to sol-gel chemistry to form oxide dielectric films and the basis of physical mechanisms under electrical fields are discussed. Along with the dielectric properties, recent achievements of proofof-concept experiments and their various applications to functional electronic devices are introduced. It is expected that further innovations in solution-processed metal oxide dielectrics will achieve cost-effective high-performance functional electronics in the near future.

Lightweight porous ceramic has a number of advantages over the tightly sintered one depending on the field of application. As a building material with low thermal conductivity and good sound insulation properties, foam ceramic is a suitable material for the production of thermal and sound insulation panels, partition walls, as well as for layers laid under asphalt to protect road and urban square pavements from freezing. As a filling, foamed ceramic materials are also added during the production of lightweight concrete used in construction and architecture and in the manufacture of decorative and non-structural insulation elements. In the present study we consider the characteristics of marl clay, found around the village of Lovets near the town of Shumen, with coal as a foaming additive, and the technological regulation for the manufacture of foam ceramic blocks.

In this publication, the authors present an in-depth justification on the technology for the production of high-oxide ceramics. Indepth research on international markets on the supply and use of raw materials is presented. The various design developments related to the ways of pressing products are described. The physico-mechanical parameters of the synthesized corundum and boron-ceramic ceramics were also studied.

A system based on BaTiO3 – BaSnO3 (BT-BS) has been developed in search of highly efficient lead-free piezoelectric ceramics. The powder samples were mixed and homogenized in a ratio of 50%: 50% and 15%: 85%. From the compositions thus obtained, tablets with the presence of a PVA plasticizer were formed, which were further annealed in a furnace with a corundum backfill. The temperature regime is in two steps. Drying time up to 800oC with a delay of 1h 30min. and additional heating to 1150°C with one hour delay. The results were characterized by XRD analysis, the relative dielectric constant of the two samples was determined.

Due to the specifics of marl clays, research to date has shown the need to stabilize these clays with respect to their critical melting point. The research is based on a previous analysis of pure raw material from marl clay, located in the area of the village of Lovets, which is modified by various additives. On the one hand, the modification is used to stabilize the ceramic mass and on the other hand, by adding various agents, the aim is to lighten the composition and obtain the required color pattern. For the purposes of production, the experimental part includes laboratory development of a scale model of yellow paving stone. The development presents the entire process of creating instrumental equipment – model making and matrix construction, and molding of finished products – pressing process for paving stones productionfrom modified marl clay. The technological cycle that can be implemented in the real conditions for yellow paving stones production will rely on the present study.

Due to force majeure circumstances, new researches of marls from the Alexandra deposit to the village of Lovets (Shumen region) were carried out to replace the marls from the village Svetlen (Targovishte region), which are part of a plastic mass for the production of large, fine-ceramic parts (yellow paving stones) from peturgical phases. Marls are characterized in terms of mineral and chemical composition. Their properties, characterizing them as a ceramic raw material, have been determined. Three test masses with a chemical composition similar to the one with the participation of marls from the village of Svetlen were developed. The test specimens are characterized in terms of sintering and strength characteristics. It has been established that the marls can be used to repla ce the marl from the village Svetlen in the composition of the plastic fine-ceramic masses for the production of yellow pavers.

Molding of technical products with fixed thickness by casting quartz ceramics, based on pure quartz glass, requires specific technological regulations both in the preparation of the ceramic mass and in the process of molding itself. Due to the specif ic characteristics of the colloidal system such as low shrinkage and viscosity, casting in molds made only of gypsum is practically unworkable. A solution lies in developing a technology in which the dismantling of the die is supported so that the molded product can be easily removed. Proposed here is a gypsum mold developed in such a way that a silicone insert is mounted where the lower part of the cast product will be. The technological process presented here in detail includes the main stages of preparing a model according to pre-set parameters, making a gypsum mold consisting of two-parts and with a silicone insert, casting and high-temperature synthesis of the finished product made of quartz ceramics. The development is suitable for complex and large-size technical products made not only of quartz ceramics, but also of other silicate colloidal systems characterized by low and almost zero air shrinkage.

Barium titanate ceramics doped with samarium were synthesized by low temperature sol-gel method. The physicochemical characterization of the samples was carried out by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). A pure BaTiO3 cubic phase was obtained. A technological regulation has been developed for the preparation of test samples .Monitoring ofthe relative dielectric permittivity of Sm-doped BaTiO3 ceramics with temperature changes (at frequency of 10 kHz) was realized.The resulting curve is typical of ferromagnetic material. The synthesized barium titanate ceramics possesses a high dielectric constant – 17500 at a Curie temperature Tc (65oC). The obtained values for the relative dielectric permittivity and Curie temperature of Sm-doped barium titanate ceramics are much better in comparison to conventionally non-doped BaTiO3-εr = 2000 and Tc = 120°C.

Subject of the present paper is the measurement of temperature changes in the ceramic cavity walls of Dadant Blatt beehives. Using a FLIR P640 infrared camera and two different heat sources, 80 thermogramsof ceramic cavity walls were obtained. The infrared images of the studied objects are divided into rectangular zones. The results of the study are presentedtabularly and graphically.

The article presents a study of the sound and thermal insulation properties of ceramic plates with cavities, designed for beehives. The plates are obtained by the “casting” method from a water-dispersed colloidal system based on a patent-protected quartz glass-ceramic. They are composed of amorphous SiO2, mullite and cristobalite. To measure the thermal conductivity, a thermal chamber is constructed with a heater installed in it. Given that the heat flow passing through the three-layer ceramic plate for beehives is constant, the temperature difference between the two opposite sides of the plate at steady state (at constant heat flow) is measured and the thermal conductivity is calculated. A two-chamber method is used to determine the sound insulation capacity of the ceramic plates for beehives. The sound pressure of the sound waves – the incident one and of the wave which has passed through the sample –is measured in the frequency range from 100 to 3150 Hz

The research is aimed at creating a target from Sn doped barium-titanate ceramics. A technological regulation for the preparation of test bodies from a material synthesized by a low-temperature sol-gel method has been developed. The physicochemical parameters of the samples were determined and the temperature dependence of the dielectric permittivity was monitored. Physicochemical characterization of the samples was performed by X-Ray diffraction (XRD). and scanning electron microscopy (SEM). The preparation of pure BaTiO3 cubic phase was established. The dielectric permittivity of Sn doped barium-titanate possesses a maximum value of 45000 at a Curie temperature- Tc 40oC.

In recent years, interest in the application and use of materials for supercapacitors for electric vehicles has grown significantly. The advantage of capacitor ceramics over other dielectric materials for producing supercapacitors is its environmental friendliness and high economic efficiency. This paper presents the results of a study of capacitor ceramics doped with Sn at different locations of the modifier (tin) in BaSnTiO3 and BaTiSnO3 crystal lattice. The influence of modifiers in low-temperature sol-gel synthesis was studied. The samples were annealed at 1000°C. The resulting phases were identified by X-ray phase analysis. Microscopic analysis was also performed.