Microstructural Characteristics of Geopolymers Based on Alkali-Activated Fly Ash

Aluminosilicate geopolymers with a high silica molar ratio have been prepared by mixing Croatian coal-ash (ASTM Class F) and sodium silicate solution (water glass, technical grade). The samples were cured at 85 °C for 8 h and 24 h in different experimental conditions. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM/EDS) have been used to identify the new phases formed in geopolymeric binders, and to follow the progress of their formation. It was observed that the glassy component of fly ash used reacted with water glass. The main reaction product formed in the geopolymeric materials was amorphous alkali aluminosilicate gel that induces a shift in the T–O (T=Si or Al) asymmetric stretching band towards lower frequency (1074.58 cm–1) in relation to the ones in the original fly ash. SEM/EDS detected a highly inhomogeneous glass-like matrix, constituted mainly of Na-Si-Al phases in a bulk region, together with unreacted spheres of fly ash particles

Distribution of marine viruses in the Central and South Adriatic Sea

The seasonal distribution of marine viruses and their relationship with heterotrophic bacteria in the coastal and offshore area of the central and southern Adriatic were studied. Additionally, the percentage of high (HNA) and low (LNA) nucleic acid bacteria between the total number of bacteria and the distribution of heterotrophic nanoflagellates (HNF) as a major predator of bacteria were studied as well. The viral abundance ranged from 3.55 to 27.32 × 106 virus-like particles mL-1, and was on average 25-fold higher than bacterial abundances at all investigated stations. The highest viral abundances were found at coastal stations, especially in the area influenced by the rivers Krka and Jadro, whereas the lowest values were found in the open sea and in the coastal area of the southern Adriatic. No significant difference in relationship of viruses with HNA and LNA bacterial groups were established. The ratio between viruses and bacteria (VBR) was higher during the colder part of the year, which coincided with lower HNF abundance and vice versa during the warmer part of the year. This suggests that HNF grazing could be more important in controlling bacterial abundance during the warmer part of the year, and viral lysis during the colder part of the year

Primjena plana pokusa u optimizaciji procesa glodanja

This paper examines the influence of cutting parameters on surface roughness of steel workpiece. The experiments have been carried out in accordance with a design of experiments (DOE). Equation for the surface roughness, as a function of cutting parameters, has been obtained by means of regression analysis. To obtain the minimal value of surface roughness, the equation optimizing was performed by using partial derivations and solving system of equations. The Taguchi method, with orthogonal arrays and signal to noise ratio, has been used to analyze impact of various cutting parameters on surface roughness and to find optimal levels of the cutting parameters. The comparison of results obtained by means of the response surface method and the Taguchi method was performed.U radu je istraživana kvaliteta obrađene površine čeličnog obratka pri različitim parametrima obrade. Pokusi su izvedeni sukladno odabranom planu pokusa. Regresijskom analizom dobivena je jednadžba hrapavosti obrađene površine u ovisnosti o parametrima obrade. U cilju dobivanja minimalne hrapavosti obrađene površine obavljeno je optimiranje jednadžbe parcijalnim deriviranjem i rješavanjem sustava jednadžbi. Taguchijeva metoda s ortogonalnim nizovima i omjerom signala i šuma korištena je za analizu utjecaja parametara obrade na hrapavost površine te pronalaženje optimalne razine parametara. Na kraju su uspoređeni rezultati dobiveni metodom odzivne površine i Taguchijeve metode

Flank wear and surface roughness in end milling of hardened steel

This study examines flank wear and surface ruoghness in up and down hard end milling. After obtaining the mathematical models, it has been carried out a series of numerical simulations with variation of input parameters in order to analyze their influence on flank wear and surface roughness. Additionally, flank wear and surface roughness has been analysed in correlation with the volume of the removed material for different cutting parameters. Observed from the viewpoint of machinability, down hard milling is favorable compared to the up hard milling

GISAXS/GIXRD View of ZnO Films with Hierarchical Structural Elements

ZnO films constituted of porous sheet-like structures, formed by calcination of precursor, were examined using scanning electron microscopy and simultaneous small-angle scattering and diffraction of the synchrotron-sourced X-rays, under the grazing-incidence conditions. The presented analysis enabled insight into the complexity of the film morphology, which revealed substrate sensitivity on the microscopic and nanoscopic length scales. The average size and spatial arrangement of nanoparticles, single-crystal domains, and the average size and features of nanopores in sheet-like structures were determined for films deposited on glass, polycrystalline ZnO layer, and silicon

Primjena plana pokusa u optimizaciji procesa glodanja

This paper examines the influence of cutting parameters on surface roughness of steel workpiece. The experiments have been carried out in accordance with a design of experiments (DOE). Equation for the surface roughness, as a function of cutting parameters, has been obtained by means of regression analysis. To obtain the minimal value of surface roughness, the equation optimizing was performed by using partial derivations and solving system of equations. The Taguchi method, with orthogonal arrays and signal to noise ratio, has been used to analyze impact of various cutting parameters on surface roughness and to find optimal levels of the cutting parameters. The comparison of results obtained by means of the response surface method and the Taguchi method was performed.U radu je istraživana kvaliteta obrađene površine čeličnog obratka pri različitim parametrima obrade. Pokusi su izvedeni sukladno odabranom planu pokusa. Regresijskom analizom dobivena je jednadžba hrapavosti obrađene površine u ovisnosti o parametrima obrade. U cilju dobivanja minimalne hrapavosti obrađene površine obavljeno je optimiranje jednadžbe parcijalnim deriviranjem i rješavanjem sustava jednadžbi. Taguchijeva metoda s ortogonalnim nizovima i omjerom signala i šuma korištena je za analizu utjecaja parametara obrade na hrapavost površine te pronalaženje optimalne razine parametara. Na kraju su uspoređeni rezultati dobiveni metodom odzivne površine i Taguchijeve metode

Flank wear and surface roughness in end milling of hardened steel

This study examines flank wear and surface ruoghness in up and down hard end milling. After obtaining the mathematical models, it has been carried out a series of numerical simulations with variation of input parameters in order to analyze their influence on flank wear and surface roughness. Additionally, flank wear and surface roughness has been analysed in correlation with the volume of the removed material for different cutting parameters. Observed from the viewpoint of machinability, down hard milling is favorable compared to the up hard milling

Design of experiment’s application in the optimization of milling process

This paper examines the influence of cutting parameters on surface roughness of steel workpiece. The experiments have been carried out in accordance with a design of experiments (DOE). Equation for the surface roughness, as a function of cutting parameters, has been obtained by means of regression analysis. To obtain the minimal value of surface roughness, the equation optimizing was performed by using partial derivations and solving system of equations. The Taguchi method, with orthogonal arrays and signal to noise ratio, has been used to analyze impact of various cutting parameters on surface roughness and to find optimal levels of the cutting parameters. The comparison of results obtained by means of the response surface method and the Taguchi method was performed

Microstructural Characteristics of Geopolymers Based on Alkali-Activated Fly Ash

Aluminosilicate geopolymers with a high silica molar ratio have been prepared by mixing Croatian coal-ash (ASTM Class F) and sodium silicate solution (water glass, technical grade). The samples were cured at 85 °C for 8 h and 24 h in different experimental conditions. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM/EDS) have been used to identify the new phases formed in geopolymeric binders, and to follow the progress of their formation. It was observed that the glassy component of fly ash used reacted with water glass. The main reaction product formed in the geopolymeric materials was amorphous alkali aluminosilicate gel that induces a shift in the T–O (T=Si or Al) asymmetric stretching band towards lower frequency (1074.58 cm–1) in relation to the ones in the original fly ash. SEM/EDS detected a highly inhomogeneous glass-like matrix, constituted mainly of Na-Si-Al phases in a bulk region, together with unreacted spheres of fly ash particles