The leaching of chlorine from hard coal: Part I. Relationship between the process parameters and its effectivity

In the study the research potential offered by the Scanning Electron Microscope to investigate into the surface of hard coal for mineral substances, especially of chlorine, was utilized. The identification of such substances - basing upon the resulting X-ray spectra and photographs - allowed one to corroborate the usefulness of further investigation step - viz. leaching. Variable parameters in those investigations were: grain size, leaching temperature, time and leaching cycles. Of great importance for the efficiency of the leaching process is granulation. The smaller the grain of coal, the more chlorine was removed because the opening of pores closed in the process of fragmentation increases the carbon surface available for water molecules.     

Simultaneous removal of asphaltenes and water from water-in-bitumen emulsion: I. Fundamental development

Simultaneous removal of asphaltenes and water from a water-in-bitumen emulsion by adding light paraffinic solvents was investigated with a bench-scale unit. Asphaltene precipitation in bitumen, emulsion breaking, and phase separation were found to be largely dependent on solvency and temperature. Increasing temperature facilitated the precipitation of asphaltenes in bitumen, and accelerated the separation of the light deasphalting oil (DAO)/solvent phase and the heavy asphaltenes/water phase. The removal of 98 +% asphaltenes and 99.9 +% water from the emulsion was achieved with the n-pentane/bitumen volumetric ratio of 3.0 in temperature range of 423–453 K. The interaction between asphaltene particles and water droplets is actually beneficial to the removal process. For process design and optimization, the operation pathway including two-step solvent injections at different temperature, the supercritical recovery of solvent from DAO stream and the solidification of asphaltenes by depressurization, as well as other important issues have been addressed.     

Microstructural characterization of leaching effects in cement pastes due to neutralisation of their alkaline nature: Part I: Portland cement pastes

When concrete is exposed to the elements, its underlying microstructure can be attacked by a variety of aggressive agents; for example, rainwater and groundwater. The knowledge of concrete resistance to long term water aggression is necessary for predictions of their performance in different environments. This study aims to analyse the effects of leaching on the microstructure of Portland cement binders. Leaching of cement pastes was performed by an accelerated extraction leaching test that produces significant degradation and helps to achieve equilibrium or near-equilibrium conditions between the leachant medium and cement paste. FTIR spectroscopy, TG-DTA thermal analysis, low temperature nitrogen gas sorption, and geochemical modelling were used to characterize the microstructural changes produced in cement pastes at different equilibrium pHs reached during the leaching process.     

Contribution of acoustic emission technique for monitoring damage of rubber coating on metallic surfaces: Comparison with electrochemical measurements

Chlorobutyl coatings are industrially applied on metallic inner walls of HCl storage tanks, in order to protect steel against corrosion. Rubber coating constitutes an efficient barrier against HCl penetration up to metallic surface; yet, traces of monochlorobenzene (MCB) into HCl solutions can locally damage the coating and induce both acid infiltration and rapid corrosion of steel under the coating. Acoustic emission (AE) technique, due to its non-intrusive feature and its sensitivity, is a potential technique for the detection of polymer coating damage as well as metallic corrosion under the coating. In that context, this technique was coupled and compared to electrochemical measurements at least for metal damage evaluation. AE signals produced by corrosion of bare metal in HCl solution were first characterized, and then AE and electrochemical results obtained during metal and/or coating damage were compared, in the case of physical or chemical deteriorations of the coating, in an HCl solution containing traces of monochlorobenzene. In case of physical coating damaging, AE and polarisation resistance measurements are in good correlation as soon as metallic corrosion starts. When polymer coating suffers a solvent impregnation, previously to HCl solution contact, acoustic activity increases as soon as corrosion under the coating occurs, whereas polarisation resistance measurements do not allow detecting corrosion of steel.     

Silicone-containing polymer matrices as protective coatings: Properties and applications

The paper addresses the technologically important problem of porous building materials protection, e.g. sandstone, limestone, marble against soiling. Protective coatings applied to the surface of porous building material should be characterized by very efficient water vapour permeability and self-cleaning properties.     

Simultaneous removal of asphaltenes and water from water-in-bitumen emulsion: II. Application feasibility

Application feasibility of the accelerated deasphaltening process for simultaneous removal of asphaltenes and water from a water-in-bitumen emulsion has been examined with a pilot plant having capacity of 1.590 m3/day. The solvent (n-pentane) was injected into the emulsion from three locations with progressively increasing temperature from 423 K. The first solvent injection precipitated the asphaltenes in bitumen, the second broke the emulsion and facilitated the phase separation, and the third extracted the oil that remained in heavy asphaltenes/water phase. The effects of operation parameters such as temperature, solvent/bitumen ratio, feed rate and feedstock composition on the quality of DAO (Deasphaltening oil) were investigated. The DAO with the yield of ~ 80 wt.% and asphaltene content of < 0.5 wt.% was produced under optimal operating conditions, and the residual product was a porous solids containing 38% sulfur, 47% nitrogen, 64% MCR, and 85% metals (nickel and vanadium) of the bitumen. For a real application in oil industry, other important aspects including energy efficiency, solvent recovery and water purification have been discussed.     

Film formation from monodisperse acrylic lattices: Part 3: Drying and ageing of acrylic latex films

The influence of drying/ageing on the structure and properties of acrylic latex films was investigated using turbidity measurements in combination with gravimetry, scanning electron microscopy (SEM), atomic force microscopy (AFM) and water vapour permeability. Ageing above the minimum film formation temperature (MFFT) leads to marked changes in a dried latex film, whereas, after ageing below the MFFT, changes are hardly found. Above the MFFT there is a continuous change in the film properties with time. This becomes obvious from the decreases in the regenerated interference minimum, water vapour permeability and corrugation height. The influence of ageing on the water absorption of the films is less straight forward. It was expected that films with a more compact structure would absorb less water. This is correct for short drying times only, from 0.5 to 3 h. Ageing of better-dried films, however, yields the opposite result: by increase of the ageing time from 3 to 150 h the water uptake increases. There are various reasons for this increase; they are discussed briefly.     

Coal liquefaction by hydrogen produced from methanol: 3. Examination of reaction conditions

Coals were liquefied in a 50 ml autoclave using hydrogen produced from methanol with decomposition and hydrogenation catalysts under various conditions. The conversion increased with increasing reaction temperature and time. This reaction is more suitable for the liquefaction of lower-rank coals. The hydrogen pressure had little effect on the conversion in the range of the ratio of methanol to coal of 2 g/g. The use of a solvent is very effective in increasing the liquefaction, especially at short times.     

Experimental investigation and numerical modeling of carbonation process in reinforced concrete structures: Part I: Theoretical formulation

In this work, the mathematical-numerical model of carbonation process in reinforced concrete (RC) structures, which has been developed by the authors, is applied to different cases of study to take into account the probabilistic nature of durability assessment procedure even if within the framework of a rough and ready approach. In particular, the aim of this Part I of the work is to study how the variability of the parameters defining the differential equations in the model influence the assessment of the corrosion initiation time of RC structure. Comparison with experimental results and numerical simulations are undertaken in Part II of this work.     

Sweet aqueous solution for electrochemical synthesis of polypyrrole: Part 2. On ferrous metals

The electrochemical synthesis of polypyrrole on iron has been fruitfully achieved in aqueous medium of sodium saccharinate and pyrrole. The obtained coating under these conditions has been reached with cyclic voltammetry and chronomethods. The applied current density has a great effect on the thickness of PPy electrodeposited on iron electrodes. The characterization techniques show a good homogeneity of the PPy coating. The corrosion behaviour of PPy/Fe was investigated in sodium chloride by linear polarization, electrochemical impedance spectroscopy, and weight loss. The results show that PPy coating electrodeposited could provide a good protection against corrosion.     

Ash chemistry and mineralogy of an Indonesian coal during combustion: Part 1 Drop-tube observations

The paper reports a systematic and comprehensive laboratory investigation into the ash chemistry and mineralogical changes undergone by a low-rank Indonesian coal during combustion. Combustion experiments conducted in a drop-tube furnace included ash formation experiments (using cyclone and filter arrangement) under closely controlled conditions in the range of 1200–1400 °C and deposition experiments at a probe temperature of 750 °C. Tests conducted with raw coal, coal/additive mixtures and washed coal indicated significant changes in ash characteristics. Of the ash formation and deposit samples examined, the raw coal + bauxite showed the lowest glass content and high contents of corundum indicating low ash deposition propensities. When compared to the ash formation samples, the deposit samples showed even significantly lower glass contents and were enriched in quartz. With the exception of the raw coal + bauxite sample, all are characterized by high silica and iron and moderate aluminium contents. In contrast, the raw coal + bauxite sample have low silica and much higher alumina contents which is in agreement with XRD observations. QEMSCAN™ results showed that the ash particles are sparsely distributed suggesting lack of a deposit initiation layer. Experimental observations suggest that the use of raw coal with bauxite would appear to offer the best performance with respect to handling ash-related issues. Present findings are of practical significance to power utilities employing Indonesian coal as there is no comprehensive work reported in the literature on ash chemistry and mineralogy of such coals.     

Semiconducting photocathodes for the reduction of dioxygen: Part I. Characterisation of crystalline and amorphous p-Si

As a first step toward the development of photocathodes for use in water-purification reactors, we have investigated the behaviour of p-type Si(1 0 0)-oriented single crystals and glow-discharge a-Si:H layers as photocathodes for the reduction of dissolved dioxygen. The electrode surfaces were prepared by HF rinsing and were characterised by cyclic voltammetry in the dark and under tungsten-halogen lamp illumination. This study has been performed in dilute-buffered fluoride medium, in dilute sulphuric acid, and lastly in three buffered phosphate media at pH 2, 7 and 12. A study using a rotating-disk electrode (RDE) arrangement permits to distinguish the contribution from dioxygen reduction (mass-transport dependent) and that from hydrogen evolution (kinetically limited). Crystalline Si and a-Si:H appear to exhibit rather similar behaviours. The Si surface acquires catalytic properties for dioxygen reduction upon negative pre-polarisation. However, these catalytic properties do not appear usable in practice for efficient operation, which calls for chemical modifications of the silicon surface.     

Development of an environmentally friendly protective coating for the depleted uranium-0.75 wt.% titanium alloy: Part V. Electrochemical impedance spectroscopy of the coating

Molybdenum oxide based conversion coatings have been formed on the surface of the depleted uranium-0.75 wt.% titanium alloy. Electrochemical impedance spectroscopy (EIS) measurements have been performed on the as-made and aged coatings and compared with the untreated depleted uranium (DU) alloy. The Nyquist and Bode plots of the as-made coating were similar to the untreated samples and contained capacitive and inductive loops. The aged coating exhibits significantly different behavior from the as-made coating and has been modeled with a four element equivalent circuit that contains a constant phase element (CPE).     

Alternative calcium sulfate-bearing materials as cement retarders: Part I. Anhydrite

The hydration process of cement pastes is of great importance to the physicomechanical properties of the hardened material. Thus, substances that regulate the setting of cement, such as natural anhydrite, have attracted significant scientific interest during the past years. This paper briefly describes the results of utilization of natural anhydrite in cement pastes of CEM-I and CEM-II types. The aim of the study has been to inquire the extent of natural gypsum replacement by natural anhydrite. The result of the hydration process has been expressed by the setting time and the compressive strength development, with respect to the SO₃⁻² content of each mixture. The experimental data conclude that natural anhydrite can be a very efficient retarder of the setting of cement, with no significant change in the physicomechanical properties of the hardened pastes.     

Non-structural cracking in RC walls: Part I. Finite element formulation

In this paper, a three-dimensional finite element model for the analysis of non-structural cracks occurring in reinforced concrete (RC) walls is introduced. The numerical model could take into account both time-dependent temperature variations due to hydration heat and non-uniform moisture distribution during drying, and the coupling effect between the heat transfer and the moisture diffusion. Calculation of the temperature and internal relative humidity variations of RC walls is followed by determination of stresses due to thermal gradients, differential drying shrinkage, and average drying shrinkage. The mechanical properties of early age concrete, determined from numerous experimental studies, are taken into consideration to improve the accuracy of the numerical results, and a discrete steel element derived using the equivalent nodal force concept is also used to simulate reinforcing steels embedded in a concrete matrix. The validity of the proposed procedure is verified by comparing the measured experimental data with the analytical results for RC walls.     

Sweet aqueous solution for electrochemical synthesis of polypyrrole: Part 1-A. On non-ferrous metals

The electrosynthesis of polypyrrole (PPy) has been achieved on aluminum electrode in aqueous medium of 0.1 M saccharin sodium salt and 0.5 M pyrrole. Scanning electron microscopy shows that the PPy coating obtained in galvanostatic and potentiostatic modes starts with small islands at weak applied potentials or current densities. Moreover, energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) reveal a good homogeneity of the film achieved in cyclic voltammetry during 10 cycles. The electrochemical impedance spectroscopy (EIS) results show that the coating decreases the polarization resistance of the aluminum electrode. The open circuit potential (OCP) and dc polarization measurements achieved in HCl and NaCl solutions displayed a large positive displacement of corrosion potential and a reduction of corrosion current in the case of PPy coating electrode in comparison with electrode bare.     

Inhibition of mild steel corrosion in hydrochloric acid solution by triazole derivatives: Part I. Polarization and EIS studies

A comparative study of 5-amino-1,2,4-triazole (5-ATA), 5-amino-3-mercapto-1,2,4-triazole (5-AMT), 5-amino-3-methylthio-1,2,4-triazole (5-AMeTT) and 1-amino-3-methylthio-1,2,4-triazole (1-AMeTT) as inhibitors for mild steel corrosion in 0.1 M HCl solution at 20 °C was carried out. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were applied to study the metal corrosion behaviour in the absence and presence of different concentrations of these inhibitors under the influence of various experimental conditions. Measurements of open circuit potential (OCP) as a function of time till reaching the steady-state potentials (E_st) were also established. The studies have shown that 5-AMT was the most efficient inhibitor reaching values of inhibition efficiency (IE%) up to 96% at a concentration of 10⁻³ M. Polarization curves showed that the four studied compounds act as mixed inhibitors. The potential of zero charge (PZC) of mild steel was determined in 0.1 M HCl in the absence and presence of the studied inhibitors. The effect of chemical structure of the four tested inhibitors was discussed. Results obtained from OCP versus time, polarization and impedance measurements are in good agreement.     

Electrochemical impedance spectroscopy in the presence of non-linear distortions and non-stationary behaviour: Part I: theory and validation

In order to investigate non-linear and non-stationary electrochemical systems, this series of two papers describes a new measurement method for electrochemical impedance spectroscopy (EIS), using specially designed broadband excitation signals. During one single experiment, the impedance, the level of the disturbing noise, the level of the non-linear distortions, and the level of the non-stationary behaviour are simultaneously measured.Part I of the paper presents the measurement strategy and validates it on a linear and a non-linear electrical circuit.In part II the described measurement strategy is applied to the pitting corrosion of aluminium (99.5 wt.%) immersed in an aerated sodium chloride solution.     

Experimental investigation and numerical modeling of carbonation process in reinforced concrete structures: Part II. Practical applications

The mathematical-numerical method developed by the authors to predict the corrosion initiation time of reinforced concrete structures due to carbonation process, recalled in Part I of this work, is here applied to some real cases. The final aim is to develop and test a practical method for determining the durability characteristics of existing buildings liable to carbonation, as well as estimating the corrosion initiation time of a building at the design stage. Two industrial sheds with different ages and located in different areas have been analyzed performing both experimental tests and numerical analyses. Finally, a case of carbonation-induced failure in a prestressed r.c. beam is presented.     

Characterization of mercury- and zinc-doped alkali-activated slag matrix: Part I. Mercury

The physical properties, pore structure, hydration process and hydration products of mercury-doped (Hg-doped) alkali-activated slag (AAS) matrixes have been evaluated by examination of physical properties, pore structure analysis and XRD, TG-DTG, FTIR and TCLP methods. Low concentrations of Hg²⁺ ions had little effect on the compressive strength, pore structure and degree of hydration of AAS matrixes. The addition of 2% Hg²⁺ ions into the AAS matrix brought out an evident retardation on early hydration and reduction of early compressive strength, but no negative effects were noticed after hydration for 28 days. The results also show that up to 2% of Hg²⁺ ions can be effectively immobilized in the AAS matrix, with the leaching meeting the TCLP mercury limit. Two mechanisms, physical encapsulation and chemical fixation, are assumed to be responsible for the immobilization of mercury in the AAS matrix.