Manuel J. Ribeiro

Bio: Manuel J. Ribeiro is an academic researcher from Polytechnic Institute of Viana do Castelo. The author has contributed to research in topics: Ceramic & Crystallization. The author has an hindex of 24, co-authored 84 publications receiving 1450 citations. Previous affiliations of Manuel J. Ribeiro include Instituto Politécnico Nacional.

Non-isothermal crystallization kinetic studies on MgO–Al2O3–SiO2–TiO2 glass

Abstract: Thermal stability and crystallization kinetics of the glass 21% MgO, 21.36% Al 2 O 3 , 53.32% SiO 2 and 4.11% TiO 2 (mol%) has been studied using differential thermal analysis (DTA), dilatometry and X-ray diffraction (XRD). Glass in both bulk and frit forms were produced by melting in platinum crucible at 1600 °C for 1–2 h. From variation of DTA peak maximum temperature with heating rate, the activation energies of crystallization were calculated to be 340 kJ mol −1 and 498 kJ mol −1 for first and second crystallization exotherms, respectively. Crystallization of bulk glass was carried out at various temperatures and for different time durations in the range of 850–1000 °C. The influence of the addition of TiO 2 on the crystallization sequence of the glass was experimentally determined and discussed.

Biomass fly ash effect on fresh and hardened state properties of cement based materials

Abstract: Cement pastes and mortars were prepared by replacing ordinary Portland cement with different dosages of biomass fly ashes (0, 10, 20 and 30% BFA) whilst in dry condition The effect of BFA on the flow behaviour (spread on table and rheology), setting time, temperature of hydration and electrical resistivity was studied in this experimental research Increasing the amount of BFA in the compositions required extra dosage of water, as a result of particles fineness, tendency for agglomeration and retention/absorption of water molecules As a consequence, the relative amount of free water diminishes and the flowability is poorer The introduction of BFA also led to an increase in setting time, while the resistivity obtained from the impedance measurements tends to be lower than the reference paste (ash-free) The higher concentration of mobile species in the pore solution, namely sodium ions introduced by the ash, explains that tendency The hydration temperature of cement pastes tends to decrease with the level of cement to ash replacement Between the two tested ashes (from grate and fluidized sand bed furnaces), differences in particle size and shape, in the amount of residual organic matter and concentration of inorganic components define minor changes in the workability and setting behaviour Therefore, the introduction of biomass fly ashes affects the hardened state features but do not compromise them

Effect of Al2O3 and K2O content on structure, properties and devitrification of glasses in the Li2O–SiO2 system

Abstract: The effect of Al2O3 and K2O content on structure, sintering and devitrification behaviour of glasses in the Li2O–SiO2 system along with the properties of the resultant glass–ceramics (GCs) was investigated. Glasses containing Al2O3 and K2O and featuring SiO2/Li2O molar ratios (3.13–4.88) far beyond that of lithium disilicate (Li2Si2O5) stoichiometry were produced by conventional melt-quenching technique along with a bicomponent glass with a composition 23Li2O–77SiO2 (mol.%) (L23S77). The GCs were produced through two different methods: (a) nucleation and crystallization of monolithic bulk glass, (b) sintering and crystallization of glass powder compacts. Scanning electron microscopy (SEM) examination of as cast non-annealed monolithic glasses revealed precipitation of nanosize droplet phase in glassy matrices suggesting the occurrence of phase separation in all investigated compositions. The extent of segregation, as judged from the mean droplet diameter and the packing density of droplet phase, decreased with increasing Al2O3 and K2O content in the glasses. The crystallization of glasses richer in Al2O3 and K2O was dominated by surface nucleation leading to crystallization of lithium metasilicate (Li2SiO3) within the temperature range of 550–900 °C. On the other hand, the glass with lowest amount of Al2O3 and K2O and glass L23S77 were prone to volume nucleation and crystallization, resulting in formation of Li2Si2O5 within the temperature interval of 650–800 °C. Sintering and crystallization behaviour of glass powders was followed by hot stage microscopy (HSM) and differential thermal analysis (DTA), respectively. GCs from composition L23S77 demonstrated high fragility along with low flexural strength and density. The addition of Al2O3 and K2O to Li2O–SiO2 system resulted in improved densification and mechanical strength.

Properties Of Concrete

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