română MIHAI EFTIMIE, CARMEN UDREA, ALINA MELINESCU, ANA FILIP
Abstract
Borosilicate glass samples were prepared by doping a main composition with CoO and NiO, respectively, to study the influence of these ions on the optical, structural, thermal, and chemical properties. Two compositions were prepared from analytically pure reagents, melted in alumina crucibles at 1250°C, cast into graphite molds, and annealed to remove internal stresses. The glasses were characterized using hydrolytic stability tests, dilatometry, UV-Vis spectroscopy, viscosity measurements, and FTIR spectroscopy. The results show that both Co2+ and Ni2+ change the vitreous network and optical behavior even at low concentrations (0.5 wt.%). The Ni2+-containing glass exhibits better hydrolytic stability and a lower coefficient of thermal expansion, while the Co2+-containing glass has a shorter working range due to a more rapid variation of viscosity with temperature. The UV-Vis spectra confirm the characteristic absorption bands of Co2+ and Ni2+ ions, indicating tetrahedral coordination for Co2+ and a combination of tetrahedral and distorted octahedral coordination for Ni2+. FTIR analysis indicates structural rearrangements of the Si-O-(NBO) and [BO3]3-/[BO4]5- units induced by the dopants. The study demonstrates that the addition of CoO and NiO allows for the modulation of the processing behavior of borosilicate glasses, a relevant aspect for functional applications.
Keywords
borosilicate glass, cobalt oxide, nickel oxide, colored glass, optical properties, FTIR spectroscopy
SUDARSONO, PRINOB AKSAR, ABDUL KHOIRI AL-LATIF, MUHAMMAD RIFKY
Abstract
Geopolymer concrete is an innovative environmentally friendlier material in terms of being a replacement material for Portland cement by using silicate and aluminium materials like fly ash to replace both natural stone and powder aggregates. In this study, we investigate the effect of adding fiberglass fibers to the physical and mechanical properties of fly ash-based geopolymer with porous structures. In terms of geopolymers we use alkali activators (sodium hydroxide NaOH and sodium silicate Na2SiO3) and foaming agent to prepare lightweight concrete. Fly ash is combined with fiberglass fibers in the weight percentages of 0.00, 0.25 and 0.50 The tests, include density, porosity and compressive strength along with microstructural analysis using Scanning Electron Microscope (SEM). The findings indicated an increase in the porosity value from 32.83% to (44.90%) with decreasing density value from 1.1953 to 1.0042 g/cm3 ranging of fiber content addition respectively On the other hand, while porosity was increased its value in compressive strength significantly increased from 3.41 MPa up to 9.29 MPa. Results of microstructural analyzes showed that in the case of the sample devoid of fibers, a loose pore structure was observed, consisting of unevenly distributed and partially unstable pores while addition of fibers led to a more uniform pore system. A more connected pore network was obtained at higher fiber content. The improved mechanical performance was attributed to the reinforcing effect of the additions of fiberglass fibers that increased pore stability, permitted efficient stress distribution and acted as crack intermediary mechanism in the geopolymer matrix. A balance point between mechanical strength and lightweight was reached at 0.25 fiber percentage. This evidence demonstrates that applying fiberglass reinforcement develops high-performance lightweight geopolymer composite materials suitable for structural applications.
Keywords
fly ash, foamed geopolymer, fiberglass fiber, compressive strength, porosity, microstructure