The hydration of slag,part 1: reaction models for alkali-activated slag

Reaction models are proposed to quantify the hydration products and to determine the composition of C–S–H from alkali-activated slags (AAS). Products of the slag hydration are first summarized from observations in literature. The main hydration products include C–S–H, hydrotalcite, hydrogarnet, AFm phases (C₄AH₁₃ and C₂ASH₈) and ettringite. Then, three stoichiometric reaction models are established correlating the mineral composition of slag (the glass part) with the hydration products. Using the proposed models, quantities of hydration products and composition of C–S–H are determined. The models are validated with a number of experimental investigations reported in literature, yielding good agreement, i.e., these models can successfully predict the hydration reaction of AAS. The models are furthermore applied to calculate the retained water in the hydration products of AAS in different hydration states and a general hydration equation of AAS is derived. As an illustration to one of the model applications, chemical shrinkage of the AAS cement paste in different hydration states are predicted. The chemical shrinkage of AAS is shown to be remarkably higher than OPC. Furthermore, phase distribution in the hardened AAS paste and the porosity are calculated.     

Factors affecting prior austenite grain size in low alloy steel

The effect of varying normalising and hardening temperatures on the prior austenite grain size in a low alloy Cr–Mo–Ni–V steel has been examined. An initial relative insensitivity of grain size to increasing austenitising temperature was observed followed by a sudden growth of grains at approximately 1000 °C. A detailed study of the precipitates in the steel showed the presence of a bimodal size distribution of vanadium carbides. The grain size increase is attributed to a decrease in volume fraction and an increase in size of V₄C₃ particles with increasing temperature.     

Identification of microstructural zones and thermal cycles in a weldment of modified 9Cr-1Mo steel

This paper presents the results of a study on the microstructural and microchemical variations in a multipass Gas Tungsten Arc weld (GTAW) of modified 9Cr-1Mo steel. The changes brought about in the steel due to the heating and cooling cycles during welding and the subsequent effects due to reheating effects during multipass welding are described. Detailed analytical transmission electron microscopy has been carried to study the type and composition of the primary and secondary phases in this steel. The systematic changes in microstructural parameters such as Prior Austenite Grain Size, martensite lath size, number density, size and microchemistry of carbides, have been understood based on the different transformations that the steel undergoes during the heating and cooling process. Based on the observed microstructure, an attempt has been made to identify distinct microstructural zones and possible thermal cycles experienced by different regions of the weldment.     

Effect of copper additions in directly quenched titanium–boron steels

The present study concerns the effect of copper additions on the microstructural evolution and mechanical properties of directly quenched Ti–B steels. Ti and B are added as microalloying elements with an aim of achieving adequate austenite hardenability and Cu is added to retard the austenite (γ) → ferrite (α) transformation. Therefore, the microalloying and Cu additions together allow the transformation of austenite to occur at a lower temperature, resulting in a finer microstructure containing martensitic constituents. The direct-quenching route is adopted with an aim of facilitating the nucleation of the constituent phases from the deformed austenite. In order to circumvent the hot-shortness due to the Cu addition, 0.79 wt% Ni has been added to one of the 1.5 wt% Cu microalloyed steels. The present study has demonstrated that the Ni-containing 1.5Cu–Ti–B steel is capable of providing an attractive combination of strength and ductility comparable to the high strength varieties of HSLA steels in directly quenched condition.     

Review on the fracture processes in nanocrystalline materials

An overview of experimental study, computer simulations and theoretical models of fracture of nanocrystalline materials is presented. The key experimentally detected facts on ductile and brittle fracture processes are discussed. Special attention is paid to computer simulations and theoretical models of nucleation and growth of nanocracks and nanopores in deformed nanocrystalline materials. Also, we discuss mechanisms for fracture suppression in such materials showing good ductility or superplasticity.     

Magnetostriction of binary and ternary Fe–Ga alloys

This article will review the development of the Fe–Ga (Galfenol) alloy system for magnetostriction applications including work on substitutional ternary alloying additions for magnetic property enhancement. A majority of the alloying addition research has focused on substitutional ternary elements in Bridgman grown single crystals with the intent of improving the magnetostrictive capability of the Galfenol system. Single crystals provide the ideal vehicle to assess the effectiveness of the addition on the magnetostrictive properties by eliminating grain boundary effects, orientation variations, and grain-to-grain interactions that occur when polycrystals respond to applied magnetic fields. In almost all cases, ternary additions of transition metal elements have decreased the magnetostriction values from the binary Fe–Ga alloy. Most of the ternary additions are known to stabilize the D0₃ chemical order and could be a primary contribution to the observed reduction in magnetostriction. In contrast, both Sn and Al are found to substitute chemically for Ga. For Sn additions, whose solubility is limited, no reduction in magnetostriction strains are observed when compared to the equivalent binary alloy composition. Aluminum additions, whose effect on the magnetoelastic coupling on Fe is similar to Ga, result in a rule of mixture relationship. The reviewed research suggests that phase stabilization of the disordered bcc structure is a key component to increase the magnetostriction of Fe–Ga alloys.     

Effect of preparation technique on the properties of Mo-containing Al-MCM-41

The Al-MCM-41 has been used as support to prepare Mo-containing catalysts. The 12- molybdophosphoric heteropoly acid (HPMo) is used as initial compound. The catalysts are synthesized by two different methods: incipient impregnation with aqueous solution of the acid and mechanochemical synthesis. The samples were tested in the reaction of the thiophene hydrodesulfurization after activation with mixture H₂ + H₂S. The effect of the preparation method of the catalysts on their physicochemical and catalytic properties has been studied. A partial destruction of the loaded compound is observed in mechanochemically treated sample whereas the aggregates are formed from the particles of different size in the impregnated sample. The specific surface area of the sample prepared by mechanical–chemical treatment decreases 2–3 times, while the total pore volume is about four times lower. The HDS activity is higher on the impregnated sample than on the mechanochemically treated one.     

On structural and high temperature electrochemical properties of ZrO2 thin film coating on Zr metal produced by carbonate melt

Melt of NaCO₃ can favor oxidation of Zr to form ZrO₂ thin film on Zr surface, which is used to make Zr/ZrO₂ oxidation/reduction electrode of pH sensor for testing elevated temperature aqueous solutions. Using SEM, EPMA, XPS, EXAFS and HRTEM, we found that ZrO₂ film is tightness and solid with 20 μm thickness composed by nanometer-sized monoclinic crystals. Zr/ZrO₂ interface is characterized of zoning structure according to topography and chemical composition in five zones: oxygen-rich ZrO₂, ZrO₂, oxygen-rich Zr metal, oxygen-bearing Zr and Zr from outmost to center. Melt oxidation process of Zr involved oxidation time, air and temperature. The air is important effect on structural and electrochemical properties of ZrO₂ thin film for making elevate temperature electrochemical sensor. If oxygen air largely presented in carbonate melting process, ZrO₂ thin film is not tightness and not for oxidation/reduction electrode.     

Study of the hydrolysis and condensation of γ-Aminopropyltriethoxysilane by FT-IR spectroscopy

The hydrolysis and condensation reactions of γ-APS have been studied in different acid content aqueous solution by using Fourier Transform infrared (FT-IR) spectroscopy. The hydrolysis of γ-APS under the studied conditions can be followed by the increase of the ethanol band located at 882 cm⁻¹ and the decrease of the band due to the ρ(CH₃) of γ-APS molecules located at 959 cm⁻¹. Hydrolysis reaction is faster by increasing both H₂O and acid concentrations, and it is completed when 3 moles of H₂O per mole of γ-APS are used. The increase of the vibrational band located at 1146 cm⁻¹ shows that condensation of the hydrolysed γ-APS molecules take place forming linear chains in poorly cross-linked structures. Besides, both 8-membered cyclic siloxane formations and poorly cross-linked structures are formed and increase as the water and acid content are increased. On the other hand, highly connected cross-linked structures do not appear due to the steric hindrance of the non-hydrolysable aminopropyl group. The silanol band shows that hydrolysis is faster than condensation except for samples with the lowest H₂O content.     

Optimized hydrogen positions for aluminium and iron containing hydroxide minerals

The structures of a number of hydroxide and oxyhydroxide minerals have previously been reported without the hydrogen positions explicitly defined. Here we use two atomic scale computer simulation techniques, one based on classical ionic potentials, the other on density functional theory (DFT), to predict these positions. The aim is not only to provide data that can be used as the basis for future experimental structure optimizations but also model parameters that can be used to predict complex hydroxide structures. The efficacy of the approach is demonstrated through the comparison of predicted and experimental data for minerals whose hydrogen positions are known.