Influence of BFS Content in the Mechanical Properties and Acid Attack Resistance of Fly Ash Based Geopolymers

This paper analyzes the influence of an extra calcium source (added as blast furnace slag) on certain properties of fly ash based geopolymers using sodium silicate as activating solution. Geopolymers were manufactured with different fly ash/blast furnace slag (FA/BFS) ratios: 100/0, 80/20, 60/40, 40/60, and 20/80. The properties studied in the geopolymers were their compressive strength and acid attack resistance. The addition of BFS improves geopolymer compressive strength at early stages. Compressive strength increases as the proportion of BFS in the mixture increases. However, maximum compressive strength was found for a determined BFS content value in the geopolymers, so that a clear reduction of this parameter was appreciated when the BFS content increased above this value. The resistance to acid attack improves in the presence of BFS possibly due to the formation of a calcium sulphate precipitate layer that increases the compressive strength and also operates as a protective coating that hinders geopolymer deterioration.

Regular Dislocation Networks in Si. Part II: Luminescence

Regular dislocation networks formed as a result of the direct bonding of Cz-Si wafers with oxide remnants on the pre-bonding surfaces were investigated. Besides the dislocation network, oxide precipitates were detected at the bonding interface. The precipitate density across the network was ~5×1010 cm-2, except small irregularly distributed circular areas, several mm in diameter, where the density was remarkably lower (<5×108 cm-2). The dislocation network structure was not affected by the change in the precipitate density. Photoluminescence spectroscopy (PL) and light beam induced current (LBIC) mapping were applied for characterization of such dislocation networks. For the locations with high precipitate density, PL signal from dislocations and that from the band-to-band transitions were enhanced. On the other hand, the LBIC results indicated that oxide precipitates are active recombination centers and thus should suppress the observed radiative transitions. The controversy can be explained in the assumption that the D-band PL signal increases due to scattering of excitation light by the precipitates and due to related expansion of the excitation area of the dislocation network. The light reflection from the precipitate layer also enhances the detected band-to-band PL signal. The shape of PL spectra from the samples in the range of photon energies 0.75 – 1.15 eV was not influenced by the oxide precipitates.

Interlayer structure of organically modified montmorillonites: Effect of surfactant loading

The surfactant cetyltrimethylammonium ion (CTA+) was confined within the galleries of montmorillonite (MMT) to obtain a series of organo-montmorillonites (C16-MMTs) through an ion-exchange intercalation reaction. The C16-MMT formed a single precipitate layer when CTA+ loading was 18.3 wt% but stratified at high loadings. The conformational disorder increased with increasing CTA+ loading. The upper precipitate was characterized by a larger gallery height and a higher surfactant loading in comparison with lower precipitate. The confined methylene chains adopted a lateral monolayer with a small percentage of conformation freedoms at CTA+ loading of 18.3 wt%. The intercalated methylene chains were arranged either in a lateral monolayer or in a tilted interdigitated bilayer at CTA+ loading of 24.7 wt% while in either a tilted interdigitated bilayer or a lateral bilayer at high CTA+ loadings. The different arrangements of methylene chains intercalated in the MMT galleries are believed to be the reason for the stratification.

keV- and MeV- Ion Beam Synthesis of Buried SiC Layers in Silicon

Homogenous, epitaxial buried layers of 3C-SÍC have been formed in Si(100) and Si(lll) by ion beam synthesis (IBS) using 180 keV high dose C ion implantation. It is shown that an annealing temperature of 1250 °C and annealing times of 5 to 10 h are sufficient to achieve well-defined Si/SiC/Si layer systems with abrupt interfaces. The influence of dose, annealing time and temperature on the layer formation is studied. The favourable dose is observed to be dependent on the substrate orientation. IBS using 0.8 MeV C ions resulted in a buried SiC precipitate layer of variable composition.

Growth of Buried CoSi2 Layers in Si(100) by Molecular Beam Allotaxy

ABSTRACTBuried single crystalline CoSi2 layers in Si(100) have been grown using molecular beam allotaxy. In this paper, we investigated the diffusive interaction of two buried silicide precipitate layers, one with a small Co peak concentration of 10 at% and another one with 26 at%. Annealing causes first local coarsening in each layer, and then dissolution of the thinner precipitate layer. The accumulation of the Co atoms at the thicker layer is described by a simple model for the diffusional redistribution.

Concentration profiles in the electrodeposition of copper ferrocyanide by laser interferometry

The electrodeposition of cupric ferrocyanide from a solution of potassium ferrocyanide with the convection-free parallel plane horizontal electrodes with the cathode over the anode was followed by multiple beam laser interferometry as well as the conventional electrochemical instrumentation. It is considered that the cupric ion generated immediately reacts with ferrocyanide ion to form a conducting adhering precipitate layer. The initial resistance of this layer is low. Its resistance is constant with thickness until about 5 × 10−8 C mm2 has been passed probably representing ~105 molecular layers when the resistance begins to rise. A magnetic field of 0.47 T caused a slight decrease in the resistance of the cell probably due to slow rotation of the inhomogeneous paramagnetic solution. This coating may be useful as an electrode.