Issue No 3, December

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.
 

Abstract

High temperature superconductors (HTS) are progressing rapidly to commercial use in a variety of applications, particularly in the electric power sector. The most advanced applications are underground cables for the power grid, where multiple cables are in service today on a beta-site test basis. A highlight is the recent energization of the world’s first transmission-level voltage cable at a LIPA site in Long Island, New York. Fault current limiters, generators, transformers, and magnetic energy storage are also all being developed.  HTS technology is expected to have a significant impact in upgrading the world’s power grid, making it more efficient and stable, and addressing significant power bottlenecks.