Issue No 1, April

Abstract

The repair of defects in sanitary ware during production entails considerable costs to the process, requiring, in most cases, a second firing of the entire piece. Thus, the development of a solution based on the localized repair of faults is very attractive to the sector. Laser technology fulfills this requirement, with a highly localized heat source allowing the repair of small defects by a fast, economical and environmentally friendly approach. This work studied the interaction between a CO₂ laser and the glaze material to be repaired, setting the basic parameters to repair defects in sanitary ware pieces. This approach could decrease repair time from the 22 hours (conventional process) to only 7 min. However, due to the high thermal stresses, several cracks appeared in the ceramic surface being necessary an additional heat source, an infra-red lamp, to overcome crack formation. This combination reduced significantly the number of cracks and their dimensions. Nevertheless, a full functional solution was not possible to develop for sanitary ware, due to persisting thermal stresses issues.

Abstract

This study compares the effect of the addition of sawdust (S), rice husk ash (RHA) and fired sand (Sa) on reaction kinetics, mechanical properties and microstructures of geopolymers for filtering application. Two kaolins were used as aluminosilicate sources. The kinetics of the formation of the Si-O-Al bond of eight final compositions were performed through in-situ FTIR spectroscopy; then their mechanical properties and microstructures were also achieved. It was found that the addition of around 1 wt% of S, 5 wt% of RHA and 10 wt% of Sa was suitable to obtain geopolymer networks within the range of geopolymer zone in Metakaolin-Silica-Alkaline solution (M-S-A) ternary diagrams. ATR-FTIR spectra shows that the Si-O-Si/Al bond shifts between 9 and 19 cm-1 with a slope between -0.06 to -0.02 cm-1/min. It was found that the addition of sawdust slightly decreases the reaction rate than silica additives (rice husk ash and fired sand). The compressive strength of MK2-based geopolymers was higher (90 and 130 MPa) than that of MK1-based geopolymers (57 to 80 MPa) even though the addition of sawdust decreased the mechanical properties of specimens than silica (RHA and Sa). From the point of view of microstructure, nanometric to micrometric networks were observed into the designed geopolymers. MK2-based geopolymers were more compact than MK1 and the porosity appeared on the matrix with sawdust which reduced simultaneously the density of specimens. The elaborated materials were lightweight with good mechanical performance, properties required in various field as filter designing.

Abstract

The paper considers the main results of the authors’ investigations in the field of the scientific backgrounds of the processes of self-propagating high-temperature synthesis (SHS) and their practical realization.
The scientific discovery of the phenomenon of solid flame dates back to 1967 (A.G. Merzhanov, I.P. Borovinskaya, V.M. Shkiro, 1967).
The first part of the paper considers the results connected with the elaboration of the methods of SHS experimental diagnostics, investigations of gasless and filtration combustion regularities, discovery of new interesting phenomena, processes, modes, and development of the process mechanism concept.
Great attention is paid to the formation of solid products in self-propagating processes (it’s the main difference of SHS from fuel combustion). The concepts of phase and structure formation mechanisms in final combustion products, equilibrium and non-equilibrium SHS products and processes are stated. The method of kinetic electrothermography as a new direction of investigations of high-temperature metal interaction with gases and  dynamic X-ray analysis for studying dynamics of phase transformations in the SHS wave are discussed.
The lecture describes the discovered phenomenon of structure non-uniqueness in binary systems and application of this phenomenon for structural regulation of combustion product characteristics, some interesting data in polymorphism of silicon nitride structure and dynamics of recrystallization in combustion products.
The second part, which is set out rather sparingly in spite of a great number of results, describes various SHS applications (chemical synthesis of inorganic compounds, elaboration of powders with particular properties, net-shape synthesis). Interesting examples of self-propagating high-temperature synthesis of yttrium-barrium cuprate (high-temperature superconductor), abrasive pastes for simultaneous grinding and polishing, complex titanium-chromium carbide possessing heat and wear resistance at high temperatures and used as an excellent material for protective coatings, unusual characteristics of multicomponent ceramics containing various combinations of nitrides, borides and sialons, etc. are given.
The paper contains brief information of alternative principles of the technology of inorganic materials, science-intensive production and various directions of material application, which are developed in the SHS field.
As the main result of their 40-year activity, the authors consider the creation of the boundary area between the combustion theory and materials science, the formation of a bridge between the combustion techniques and inorganic material technology, the spontaneous formation under the influence of the authors’ activity of the World community of the specialists who turned SHS into the advanced field of scientific and technical progress.

Abstract

In this study, a bibliometric analysis of hydroxyapatite (HA) and scaffold research using the online version of Science Citation Index (SCI) databases of the Thomson Reuters’ Web of Science Core Collection from 1991 to 2019 was performed. The stages of the study included the analysis of the author’s keywords, annual scientific production, and contributions of countries, institutions, and publication sources. Analysis of 8752 publications showed an increase in using HA-based scaffolds as a promising strategy to treat tissue defects. Global trend inclined toward the application of additive manufacturing (AM) to fabricate scaffolds. AM techniques such as Stereolithography, direct inkjet 3D printing, selective laser sintering, and fused deposition modeling seem to have more applications in production of ceramic-based scaffolds and will see further advancement in the coming years. Among 90 countries, the USA and China were countries that provided the highest number of publications during the investigated period. The most productive three institutions in this research area were located in China. Throughout the past 29 years, Journal of Biomedical Materials Research Part A, Materials Science, and Engineering: C, Journal of Materials Science: Materials in Medicine, Acta Biomaterialia and Biomaterials have the highest number of publications on HA and scaffold research.