Year 2020, Volume 2

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.

Abstract

Phosphatic porcelain (PP), commonly known as bone china, constitutes approximately 50 wt% bone ash, 25 wt% kaolin, and 25 wt% feldspar, and its primary characteristics are high translucency and a high impact resistance. However, the low plasticity of these ceramic raw materials makes its moulding difficult owing to the plastic deformation due to the throwing wheel. Plasticizers or plasticity-promoting additives, such as sodium bentonite and methyl hydroxyethyl cellulose, modify the rheological behavior to pseudoplastic with a yield stress. Ceramic raw materials with plasticizers were prepared and characterized using helium pycnometry density, X-ray fluorescence, X-ray diffraction, and particle size distribution. In addition, characterization analysis was performed in commercial porcelain P905 for comparison purposes. The squeeze flow technique (compression of a cylindrical sample between two parallel plates) was employed to assess and compare the rheological behavior of the PP compositions with and without additives with the behavior of the commercial material. Results show that the addition of 4 wt% bentonite in the PP introduced a plasticity similar to that of the commercial porcelain, easing the shaping process using a throwing wheel. Plasticity index (PI) from the Atterberg test is useful; however, it is not sufficiently detailed to predict conformation performance of the ceramic raw materials in the throwing wheel as per the rheological information provided by the squeeze flow test.

Abstract

The aim of this study is to valorise clays from the Fez region in Morocco as aluminosilicate precursors for geopolymer synthesis. In addition to the clays, the use of calcite and dolomite as mineral additives was also investigated. At first, the Moroccan clays were thermally activated by calcining at 700 °C, and then, a potassium alkaline silicate solution was used for alkali activation. Samples were synthetized by combining clay, metakaolin and mineral additive in several ratios. Consolidated materials were successfully obtained, and geopolymerization reaction was monitored by in situ Fourier transform infrared spectroscopy (FTIR), which revealed several networks. The results demonstrated that composite geopolymers with a mechanical resistance range from 8 to 50 MPa could be obtained from Moroccan clays.

Abstract

In 1975, the SiC fiber was made from polycarbosilane by Prof. Yajima, for the first time. We started to develop the industrial production of the SiC fiber and succeeded in development of manufacturing technology for the multi-filament continuous Si-C-O fiber (Nicalon) in 1978. Nicalon fiber has high tensile strength and modulus, and heat resistance at high temperature in air atmosphere. Nicalon fibers have been used for the reinforcements of composite materials such as Polymer Matrix Composite (PMC), Ceramic Matrix Composite (CMC). In recent years, it has been increasing demand for high performance CMC for high temperature applications. We have improved fiber properties by reducing oxygen content and excess carbon in chemical composition of the SiC fibers. In 1988, low-oxygen-content Si-C fibers (Hi-Nicalon) with 0.5wt% oxygen were prepared from polycarbosilane with electron beam irradiation curing and pyrolysis. The thermal stability of Hi-Nicalon fibers was significantly improved compared to Si-C-O fiber (Nicalon) with 12wt% oxygen. However, creep deformation occurred in the Hi-Nicalon fiber at high temperature, caused by SiC micro crystals and amorphous carbon. Then, stoichiometric and highly crystalline SiC fiber (Hi-Nicalon Type S) was prepared from EB irradiation cured fiber by pyrolysis in a hydrogen gas flow in 1994. Type S fibers had high tensile modulus, excellent thermal stability, and creep resistance at high temperature. Hi-Nicalon and Type S fibers appear to be the best candidates for the reinforcement of ceramic matrix composites. Hi-Nicalon and Type S fiber reinforced SiC composites are being developed as the components of gas turbines for aerospace and power generation.

Abstract

Growing demands for energy in the modern world require increased efficiency in the use of resources to generate power. This paper identifies the opportunity for technology development in this space, and the requirements for a solution to this issue. Solid oxide fuel cells (SOFCs) at megawatt scale offer a potential solution at high (60+%) efficiency and benefit from a fuel flexibility not enjoyed by other types of fuel cell. This paper presents the Rolls-Royce Fuel Cell Systems Limited (RRFCS) technology to deliver a SOFC system at this scale and address the inherent challenges.

Abstract

The present energy paradigms have to undergo significant changes for reaching the ultimate goal of a real sustainable energy future. Key point is the transition from a fossil fuel based chemical energy to a physical energy essentially based on electricity from renewable sources. Valuable technologies for an efficient exploitation of solar power, wind power, biomass conversion etc. are already available. So the transition will proceed more smoothly if all Society players will move in the same direction.

Abstract

We present and discuss the effects in sanitary-ware ceramic mixtures induced by partial replacement of raw materials with alumina, or andalusite, on i) phase composition, ii) Gibbs energy of formation (∆G), iii) microstructures and iv) some reference technological properties. Measurements were carried out by X-ray powder diffraction, scanning electron microscopy, synchrotron X-ray computed micro-tomography, linear dilatometry, water absorption and mechanical testing. The results show that the introduction of alumina affects phase composition of the ceramic output as a function of the replacement scheme, leading to a mullite-ceramic glass quasi-equilibrium whose ∆G ranges from -32 to -14 kJ·mol-1. Although alumina modestly participates in the ceramic reactions, it yet influences surface microstructures, giving relevant whiteness, and some reference technological properties, providing low deformation and high flexural strength. The resulting ceramic material exhibits performances that lie in between those from fireclay and vitreous technologies, providing aesthetic improvements and high shape stability.

Abstract

Geopolymer materials are synthetized by the activation of an aluminosilicate source with an alkaline solution. Their properties strongly depend on the polycondensation reaction that is influenced by the raw materials used. Thus, this work aims at studying the influence of reactive or unreactive aluminosilicate sources with different layered structures (T-O-T or T-O) on the geopolymer’s working properties. To this end, six formulations with differences in the metakaolin content and in the addition of mica fillers were synthetized. The structure and the particle’s surface charge of the raw materials were identified and then, the consolidated materials were observed with SEM and characterized by compression testing. The results show that the increase in metakaolin content leads to a decrease in the porosity rate of the geopolymer (from 47 to 40%) and therefore to the improvement of its mechanical properties from 31 to 45 MPa. Besides, the addition of mica provides different microstructure, defined by a growth in the pore size, which modifies the mechanical properties. Finally, a connection between the particle’s surface charge and the specific compressive strength is outlined. As an example, a zeta potential corrected by the reactive volume (ζ*) inferior to -20 leads to a decrease in the geopolymer’s mechanical properties.

Abstract

The antibacterial and antifungal activities of distinct sets of titania and zinc oxide nanopowders against gram-positive bacteria (S. Aureus and S. Pyogenus), gram-negative bacteria (E. Coli and P. Aeruginosa) and fungi (C. Albicans, A. Niger, and A. Clavatus) were tested and compared with standard drugs. The changes in structural and microstructural characteristics are discussed in detail. The as-received and microwave-assisted samples of TiO₂ possess pure anatase phase, soft-chemically synthesized TiO₂ retain the pure rutile phase while TiO₂ powders high energy ball mill for 10 hrs and 20 hrs have coexistence of anatase, rutile and brookite phases. The minimal inhibition concentration (MIC) of 10 hrs milled sample of TiO₂ for E. Coli is comparable or much smaller than standard drugs, Chloramphenicol, and Ampicillin. The as-received and microwave-assisted samples bactericide D. Aureus with MIC 250 µg/ml, the value matches well with MIC of Ampicillin. Not a single set of TiO₂ nanoparticulates found responsive to P. Aeruginosa and S. Pyogenus. The MIC of as-received and 10 hrs milled samples of ZnO for S. Aureus is much lower than the Ampicillin while MIC of as-received ZnO nanopowders to bactericide S. Pyognus is comparable with MIC of Ampicillin. C. Albicans can be fungicide by as-received, chemically synthesized and 10 hrs milled samples of TiO₂ with MIC comparable with Greseofulvin while MIC of the as-received sample of ZnO is 250 µg/ml, much smaller and for 10 hrs milled sample of ZnO, MIC is comparable with MIC of standard drug Greseofulvin. It is found that the MIC of gram-positive bacteria is much higher than gram-negative bacteria.