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This research uses low alkali activator content and cold pressing technique for fly ash-based geopolymers formation under room temperature condition. The geopolymers were prepared using four different parameters: fly ash/alkali activator ratio, sodium hydroxide concentration, sodium silicate/sodium hydroxide ratio and pressing force. The results indicated that the compressive strength (114.2 MPa) and flexural strength (29.9 MPa) of geopolymers maximised at a fly ash/alkali activator ratio of 5.5, a 14 M sodium hydroxide concentration, a sodium silicate/sodium hydroxide ratio of 1.5 and a pressing force of 5 tons (pressing stress of 100.0 MPa and 155.7 MPa for compressive and flexural samples, respectively). The degree of reaction (40.1%) enhanced the structure compactness with minimum porosity. The improved mechanical properties confirmed that a high strength pressed geopolymer could be formed at low alkali activator content without the aid of temperature.

This paper investigates compressive strength and microstructural properties of activated cement free binder from fly ash (FA) - calcium carbide residue (CC). Different activation methods to enhance the strength of the FA-CC mixture were used including the following: 1) curing at elevated temperature of 60 °C, 2) adding 1% NaOH by weight of binder and 3) combining both 1% NaOH by weight of binder and curing at temperature of 60 °C. The compressive strengths of mortars with different activation techniques were determined at 3, 7, 28, and 90 days. Microstructural properties of activated cement free binder from the FA-CC mixture, that is, XRD patterns, SEM microscopy, EDS analysis, and degree of reaction were examined. Results from this study revealed that the activated cement free binder from FA-CC had components of Ca, Al, and Si and indicated CSH and CASH likewise the end products of pozzolanic reaction. Use of activation techniques had significantly affected on the microstructure in cementing system. The activated cement free binder from FA-CC mixture with addition of 1% NaOH and curing at 60 °C increased binder strength and promoted the formation of CSH, CASH, and some amount of NASH phase or hybrid C(N)ASH. Keywords: Fly ash, Calcium carbide residue, Compressive strength, Microstructural properties

Due to the rotor-stator interaction of Variable Nozzle Turbine (VNT), the strong excitations at the leading edge of turbine rotor can be created during engine braking down or transient acceleration. This may be a concern of high-cycle fatigue failure of VNT rotor blades. In this paper the 3-D unsteady numerical simulation of a VNT was performed to investigate the effects of nozzle vanes clearance leakage, wake and shock wave on the rotor blade pressure fluctuations, which can specify where and how these three factors influence the excitations of the turbine rotor blade. The results show that the shock wave and nozzle vanes clearance leakage are the main reasons for rotor blade surface pressure fluctuation. The shock wave only affects the suction surface at the leading edge of rotor blade because of the shape of rotor blade. When the nozzle vanes opening was closed small, the shock wave and the amplitude of the pressure fluctuations on the rotor blade surface were greatly increased compared to that for full open condition. In the regions near the hub and shroud side on the rotor blade suction surface, the magnitude of the pressure fluctuation is increased significantly by the influence of the nozzle vanes clearance leakage. Through FFT analysis of the pressure fluctuation at the rotor blade leading edge, it can be seen that the fluctuation amplitude increased significantly on the rotor passing frequency and this also implies the possibility of VNT high-cycle fatigue failure with the high-frequency excitations.

This paper assesses the effect of the use of an alternative activator based on nanosilica/MOH (M = K+ or Na+) blended solutions on the performance of alkali-activated fly ash binders. Binders produced with commercial silicate activators display a greater degree of reaction, associated with increased contents of geopolymer gel; however, mortars produced with the alternative nanosilica-based activators exhibited lower water demand and reduced permeability, independent of the alkali cation used. Na-based activators promote higher compressive strength compared with K-based activators, along with a refined pore structure, although K-activated samples exhibit reduced water demand. Zeolite type products are the major crystalline phases formed within these binders. A wider range of zeolites is formed when using commercial silicate solutions compared with the alternative activators. These results suggest that there are variations in the availability of Si in the system, and consequently in the alkalinity, depending on the silicate source in the activator, which is important in determining the nanostructure of the geopolymer gel., This study was sponsored by the Ministerio de Ciencia e Innovacion of Spain (Project GEORES MAT2010-19934 and research scholarship BES-2008-002440), European regional development fund (FEDER), and the Universitat Politecnica de Valencia (Spain). The participation of SAB and JLP was funded by the Australian Research Council (ARC), including partial funding through the Particulate Fluids Processing Centre, a Special Research Centre of the ARC. A special acknowledgement is also due to the Centre of Electron Microscopy of the Universitat Politecnica de Valencia and Pedro Garces from the Universidad de Alicante for support in some experiments.

Cement manufacture has undergone extensive change in its attempts to rise to the successive challenges posed by society. The hydration of Portland cement is a complex phenomenon that depends on both reagent characteristics and reaction conditions. It is a well-known fact that the curing temperature plays an important role on the hydration kinetics. The present study is the first to be undertaken on the effect of curing temperature on white Portland cement paste hydration over long hydration times (365 days at 20ºC and 124 days at 60 ºC). The technique used, 29Si and 27Al NMR spectroscopy, is particularly well adapted to the study of cement hydration. White cement hydration generates a C-S-H gel in which the aluminium taken up forms bridge bonds. After nine days at 60 ºC, the degree of reaction expressed in terms of the Al(IV)/Al(VI) ratio nearly doubles the value found after 90 days at 20 ºC., The Spanish Ministry of Science and Technology and the ERDF co-funded the Ramón y Cajal contract granted to SMR. The authors also thanks to the European Community for the Contract (Marie Curie) given to one of the authors.

Publicación en versión impresa: mayo de 2007, The effect of a shrinkage-reducing admixture (SRA) based on polypropylenglycol on the dimensional stability of waterglass-activated slag mortars was studied. The analysis also showed the effect of the admixture on pore structure of the mortars as well as on the mineralogical composition and microstructure of the alkali-activated slag pastes. The SRA reduced the shrinkage by up to 85 and 50% when the alkali-activated slag mortar specimens were cured at relative humidities of 99 and 50%, respectively. The mechanism primarily involved in shrinkage reduction is the decrease in the surface tension of pore water prompted by the admixture. The SRA also modified the pore structure – under both curing conditions – increasing the percentage of pores with diameters ranging from 1.0 to 0.1 μm. Capillary stress is much lower in these pores than in the smaller capillaries prevailing in mortars prepared without admixtures. Microstructurally, the SRA occasioned a slight increase in the proportion of Si units Q2 in the CSH gel and a decrease in the percentage of Al replacing the Si in the gel structure. The admixture did not, however, modify the mineralogical composition of the pastes. Finally, the SRA admixture retarded the alkaline activation of the slag, more intensely at higher admixture dosages. While the admixture did not significantly alter the degree of reaction in pastes cured for 7 days at RH=99%, the value of this parameter dropped by 7% in the presence of the admixture in pastes cured at 50% relative humidity., Funding for project MAT 2001–1490 was provided by the Spanish Ministry of Science and Technology (MCyT). The authors wish to thank A. Gil, J. L. García, I. Sobrados, J. L. Llueca and J. L. Pita for their support in the tests conducted for this study.

Publisher Summary This chapter illustrates how the different sample handling regimes influence the morphology of the surface of the sample as viewed in a scanning electron microscope. By handling samples in different ways it is possible to examine the carbonate formed at different point and therefore examine the morphology of the products formed under peak conditions and as a consequence of subsequent pore-water degassing. Under relatively low magnification the differently handled samples appear to be nearly identical. An uneven poorly crystalline reaction product is observed to form first coating grains of ordinary Portland cement exposed to supercritical CO2 at 105°C and 80bar for 24hours. The apparent abundance of crystalline reaction product on the surface of the sample is not necessarily indicative of a high degree of reaction as the bulk of the carbonate is contained in the more amorphous layer that coats the original sample grains.

Publisher Summary As a preliminary stage of an investigation into the reaction of a range of materials with carbon dioxide under supercritical conditions the effects of altering different portions of the experimental protocol were assessed using ordinary Portland cement (OPC) as the initial mineral assemblage. Ordinary Portland cement is a mixture of calcium and calcium aluminum silicates formed at high temperature and are therefore highly reactive with respect to moist carbon dioxide. The ease, with which OPC reacts, means that short duration experiments can be performed with sufficient yield to enable differentiation between the amount and nature of the product formed. In order to investigate the strength of effect and the degree to which it can affect the measured yield of any carbonation experiment a series of samples are reacted and then handled in different ways in order stop the reaction at different points. The chapter presents the experimental results. The variation in results depending upon the pressure temperature time path of the reaction shows that the full history of a sample is required if the results of subsequent analysis are to be usefully interpreted.

The kinetics of hydration of alkali-activated slag (AAS) have been studied for different temperatures. The alkaline activator used was a mix of water-glass and NaOH solution. The degree of reaction was determined by means of the heat of hydration after the induction period. The reaction mechanism determined for AAS pastes was a diffusion mechanism and their activation energy was 57.6 KJ/mol.

In order to get higher adiabatic efficieny of a cryogenic gas expasion turbine, the optimized parameters such as the degree of reaction, the velocity ratio and the blade diameter ratio are firstly selected. Then the thermodynamic calculation is made. This paper analysės various selection methods of the optimized parameters, and gives a new parameter selection method which is simpler and practical. A computer optimization model for the designing cryogenic gas expansion turbine is established. An example of a low pressure air turbine is given. And a small size air expansion turbine in medium pressure and low temperature is designed by using the model, whose adiabatic efficiency of test is about 80%.

A graphic method using Merkel diagrams to evaluate the heat performances of Chemical Heat Pumps (CHP) is presented. Such diagrams including the thermal inertia of the solid absorber reactor have been elaborated. An example of their use is given for solar ice production with CaCl2 → NH3 or CH3OH reactions and a discussion about refrigeration efficiency versus reactor thermal mass and degree of reaction completion follows.

This chapter discusses the dryway conversion processes. The process of calcination of oxides, hydrogen reduction of oxides to lower oxides, hydrofluorination, and hydrochlorination of oxides, etc., can often isbe carried out by conventional chemical engineering methods. However, the high standards of purity usually required for rare metal extraction at least necessitate novel materials of construction. A considerable development and pioneering effort has been devoted to the improvement of these techniques, particularly applied to the intermediates in the production of uranium metal and uranium trioxide, dioxide, and tetrafluoride. It is possible that the resulting processes can be more widely employed in the rare metal extraction field in the future. The early processes for interconversion of pure rare metal oxides and fluorides involved simple batch methods with static beds. The degree of reaction is dependent upon the effectiveness of the contact between gas and solid, and the rates of diffusion of reactant gas and product, gas within the solid. This can be improved by counter-current flow as this avoids the very slow reaction between a dilute reactant gas and an almost converted solid. Instead, the dilute gas is in contact with virtually unconverted solid, and the fresh feed gas with almost converted solid and the overall rate of reaction can thus be improved.

This chapter presents an overview of the Kaplan turbine. The rotor of the Kaplan turbine is a purely axial rotor, and so forms the counterpart to the axial compressor; like the rotor of the axial compressor it is decidedly a high-speed rotor. Calculation of its properties proceeds in a way completely analogous to that for an axial fan. In this case, however, the main difficulty is the necessity of avoiding cavitation; this gives an upper limit to the circumferential speed, and also has a strong influence on the design of the blade profile. Because of the guide-vanes, swirl is imparted to the water, the exact amount depending on the blade setting. Water flows through the guidevanes in the radial direction, so that to a good approximation the flow is plane and each unit of mass of water receives the same angular momentum. After the deflection into the axial direction (in front of the Kaplan rotor), the stream-tubes run at various distances from the axis. A characteristic of the Kaplan turbine is that the flow velocity relative to the blades is high and so the deflection of the relative flow direction is small.