Slag-fly ash and slag-metakaolin binders: Part II—Properties of precursors and NMR study of poorly ordered phases

Sodium silicate-activated slag-fly ash binders (SFB) and slag-metakaolin binders (SMKB) are room-temperature hardening binders that have excellent mechanical properties and a significantly lower carbon footprint than ordinary Portland cement (OPC). The aim of this study was to use nuclear magnetic resonance (NMR) spectroscopy to study the nanostructure of poorly ordered phases in SFB by varying slag/fly ash ratio, curing time, and curing temperature. Fly ash was completely substituted with metakaolin and the effect of this substitution on the poorly ordered phases was studied. It was observed that the proportion of geopolymer was generally higher in SMKB when compared to SFB. Although C–N–A–S–H and geopolymer coexisted in SFB and SMKB, C–N–A–S–H was the major product phase formed. The mean chain length (MCL) and the structure of C–N–A–S–H gel were estimated as a function of time, temperature, and slag/fly ash ratio. The MCL was found to have a negative correlation with slag/fly ash ratio and Ca/(Si+Al) ratio, but positive correlation with curing temperature. The average Si/Al atom ratios for geopolymers were also estimated. Lastly, the increased proportion of five-coordinated aluminum (Al(V)) in metakaolin resulted in the decreased unreacted metakaolin in the hardened binder but did not increase the geopolymer content.     

Orimulsion fly ash in clay bricks—part 1: composition and thermal behaviour of ash

A bitumen-in-water emulsion (Orimulsion) is currently used as a fuel in several thermal power plants worldwide. Orimulsion combustion produces a fly ash rich in S, Mg, V and Ni, which is processed to recover metals. In order to assess the feasibility of a recycling in clay brick production, a characterization of the physico-chemical and thermal properties of ash was performed by ICP–OES, XRPD, SEM, BET and TGA–DTA techniques. Orimulsion ash resulted in fine-grained (aggregates of submicronic particles), highly hygroscopic, constituted mainly of magnesium sulphate, vanadyl sulphates and magnesium and nickel oxides, and thermally unstable in the usual brick firing conditions. These features can affect the brickmaking process, particularly the plasticity of the clay body and its drying and firing behaviour; furthermore, a mobilization of sulphates could occur, promoting the formation of efflorescence and/or the SO_x release during firing.     

Aggregate structure of “single-nano buckydiamond” in gel and dried powder by differential scanning calorimetry and nitrogen adsorption

Gels and dried powders of the single-nano buckydiamond (SNBD) have been studied by means of differential scanning calorimetry (DSC) and gas adsorption methods. Nanophase of water (NPhW) was confirmed in SNBD hydrogel by DSC, wherein the characteristic feature at 265 K was observed and attributed to melting of NPhW. No such feature was observed in commercial agglutinate samples of detonation nanodiamond. The parameters of the DSC peak were independent on the method of the material preparation and reproducible to serve as a fingerprint of SNBD material itself. The same nanophase was found in dried powders of SNBD after they were equilibrated with water vapor in isopiestic experiments. Nitrogen adsorption isotherms of the dried powder demonstrated the presence of nano voids. The characteristic size and volume of the nano voids were almost equal to those of NPhW. Gels and dried powders were easily converted back into SNBD water dispersions. Based on DSC and adsorption data it was concluded that SNBD material, though originally divided into individual diamond crystals (d = 5.2 nm) in the water dispersion, forms stable porous networks as gel and dried powder. Formation of such networks could be explained in terms of Van der Waals or Coulombic interaction between the SNBD particles.     

Epoxy reinforcement with silicate particles: Rheological and adhesive properties – Part I: Characterization of composites with natural and organically modified montmorillonites

Rheological and adhesive properties of epoxy oligomer–montmorillonite (MMT) nanocomposites containing 2 and 5 wt% of natural and organomodified clay were studied. Ultrasound treatment of epoxy–clay systems was used for their homogenization. According to rheological data, ultrasound stirring allows the development of well-dispersed systems in the case of organomodified MMT. Sonication of composites with natural clay is inefficient and leads to a poorly dispersed structure. X-ray data demonstrate increases in the interlaminar spacing for organomodified MMT (up to 2 times), which is indicative of MMT intercalation. Clay addition leads to 40–65% increase in the shear adhesion strength of the cured epoxy resin. The sonication influence on the shear adhesion strength of the system with 2 wt% of any clay is very small. Ultrasound stirring of the systems with 5 wt% of clay results in higher values of adhesion for organomodified MMT.     

Orimulsion fly ash in clay bricks—part 2: technological behaviour of clay/ash mixtures

In order to appraise the technological feasibility of the Orimulsion ash recycling in clay bricks, a laboratory simulation of the brickmaking process was carried out with various clay/ash mixtures up to 6% waste. Two different clays were selected and mixes were characterized by XRF, XRPD, TGA–DTA, TDA and PSD analyses. Plasticity, extrusion and drying behaviour, and mechanical strength, were determined on unfired mixtures, while shrinkage, water absorption, bulk density, modulus of rupture, pore size distribution, microstructure and phase composition were measured on fired bricks. Orimulsion ash caused some detrimental changes of technological properties of both unfired and fired products, concerning particularly plasticity, drying rate and drying sensitivity, porosity and colour. These effects were slightly different on the two raw materials, the carbonate-rich clay being less sensitive to the presence of ash with respect to the carbonate-free clay. In all events, drawbacks appeared to be tolerable, in technological terms, for low waste additions, approximately 1–2% ash.     

Extraction of Caprolactam with Toluene in a Pulsed Disc and Doughnut Column–Part III: Mass Transfer Characteristics

Abstract

The mass transfer characteristics of a pulsed disc and doughnut column with a 0.04 m internal diameter and 4.24 m active column length are investigated in order to evaluate its contacting efficiency for caprolactam extraction with toluene. Pilot plant experiments for both the forward and back‐extraction process were performed in order to determine the concentration profile along the column length in both the extract and raffinate phase as a function of the operating conditions. The experimental conditions covered the industrial operating range. Furthermore the dispersed phase hold‐up, average droplet diameter and operating regime were determined and compared with the results obtained for the equilibrium situation, as discussed in Part II.

In the forward extraction process a significant influence of operating conditions was observed, where an increase in the flux decreased the separation efficiency, but an increase in pulsation intensity, temperature, or the addition of ammonium sulphate increased the separation efficiency. In the back‐extraction all concentration profiles were comparable and all caprolactam was extracted after a column length of L/m=2. Compared to the equilibrium situation the drop diameter and pulsation intensity required for the transition of the mixer‐settler to the dispersion operating regime were found to increase under mass transfer conditions, while the hold‐up decreased. HETS values were determined for both the forward and back‐extraction. For the latter HETS=0.28 to 0.41, whereas in the forward extraction HETS=0.32 to 0.67.

The concentration profiles were described with the backflow model, using a constant backflow parameter for the continuous phase and a constant overall mass transfer coefficient. The interfacial area was correlated using drop diameter and hold‐up expressions derived for the equilibrium situation, taking into account the relative effect of mass transfer. Using these expressions the measured data could be correlated and described well.     

Ti(C,N)-based cermets with fine grains and uniformly dispersed binders: Effect of the Ni–Co based binders

Metallic binder is a key factor affecting the microstructure and mechanical properties of Ti(C,N)-based cermets. To optimize the overall performances, cermets with various weight ratios of Ni/(Co + Ni) ranging from 0 to 1 were fabricated by gas pressure sintering. Microstructure, phase formation, interface structure and related mechanical properties of the sintered cermets were investigated. With the increase of the Ni/(Co + Ni) ratios, the black cores became smaller and grains of Ti(C,N) dispersed uniformly. Compared to the pure Ni or Co, Ni–Co binders accelerated the formation of rim phases, and avoided the nonuniform dispersed binder pools. When the ratio was 0.5, the cermets showed fine grains, uniformly dispersed binders and small lattice misfit of the core-rim interface, exhibiting the optimal mechanical properties, i.e. satisfactory Vickers hardness of 1670 (HV30) Kgf/mm², bending strength of 1970 MPa and Fracture toughness of 8.94 MPa m^0.5. This work sheds light on constructing the relationship between the microstructure, mechanical performance of Ti(C,N)-based cermets and the Ni/Co-based binders.     

The absorption of propane and ethene in slurries of activated carbon in water—I

A gas mixture of propane and ethene was absorbed batchwise in a stirred cell in a slurry of activated carbon in water. The selectivity of the absorption process was investigated. Experiments were performed in which the influence of carbon particle size, and especially the addition of a small amount of fines, was studied. It was found that at the beginning of the experiments ethene was absorbed more readily than propane; later the adsorbed ethene was driven away from the carbon by propane. Addition of small amounts of carbon-fines resulted in an increase of the observed gas—liquid mass-transfer coefficients and also in the selectivity of the process changes. A new continuous ultrasonic gas analyser for high-resolution determination of the gas mixture composition has been developed.     

HCBS ceramic concretes in the XXI century — problems and prospects for applying technology in the field of silicate materials science. Part 1

In the technology of a number of ceramic and refractory materials, prepared on the basis of highly concentrated ceramic binder suspensions (HCBS), elements of effective nanotechnology were realized even before the present “nanoboom.” The concept has been formulated of an advance in materials technology based on HCBS both in traditional fields of their application, and in the field of structural materials science, within which for industrial introduction of existing developments it is necessary to create contemporary equipment formulation for production processes.     

Dry pressed ceramic tiles based on fly ash–clay body: Influence of fly ash granulometry and pentasodium triphosphate addition

Fly ash from brown coal (70 wt.%) and stoneware clay (30 wt.%) were used for the dry pressed ceramic tiles (according to EN 14411) raw materials mixture. The effects of fly ash milling and pentasodium triphosphate addition as a deflocculant and fluxing agent on the properties of green body (flexural strength, bulk density) and fired body (EN ISO 10545—water absorption, bulk density, true density, apparent porosity, flexural strength, frost resistance) were studied and explained as a function of the firing temperature (1000–1150 °C). Fly ash milling (corresponding to 5 wt.% residue of fly ash grains on 0.063 mm sieve) increased the sintering abilities of the fly ash–clay body. A similar effect was achieved by 1.3 wt.% pentasodium triphosphate (PST) addition with an increase in green body flexural strength and a decrease in water content of the granulate. Fly ash–clay bodies can be frost resistant with water absorption above 10% due to positive pore size distribution, which were examined using the high-pressure mercury porosimetry method.     

A GIS-based national emission inventory of major VOCs and risk assessment modeling: Part I — methodology and spatial pattern of emissions

This paper presents a method for assessing and managing the South Korean atmospheric emission inventory of volatile organic compounds (VOCs) based on a geographic information system (GIS). The use of this GIS-based assessment technique makes it possible to obtain the geographical characteristics of anthropogenic emission sources, observe spatial patterns within the emission inventory, and develop a new bottom-up method for improving the spatial accuracy of emission inventories. As a case study, we estimated the emission rates of five major VOCs (benzene, ethylbenzene, styrene, toluene, and xylene) throughout South Korea for the year 2004. The spatial pattern of emissions and relative contributions of various sources showed considerable spatial variability. A comparison of estimated emissions data and observed environmental concentration revealed a reasonable degree of accuracy for the estimated values. The proposed methodologies and information provided in this study can assist in the development of environmental policy, and can be adopted internationally to obtain a more precise emission inventory.     

Erbium-Ion-Doped Tellurite Glass Fibers and Waveguides—Devices and Future Prospective: Part II

Following on from Part I of this review article that focuses on the suitability of Er³⁺-doped tellurium oxide glass for optical amplification in fiber, this Part II article describes how the fiber gain data were then employed to engineer amplification in waveguides, which can be integrated with semiconductor pump sources. The gain characteristics and bandwidth of a phosphate modified tellurite waveguide formed on a GaAs substrate are discussed. The limiting structural compatibility of Er³⁺-doped tellurite glass with polydimethylsiloxane polymer for active–passive integration is overcome by adopting a nanoscale super-lattice approach for waveguide engineering.     

Plasticization of Fibrous Cellulose Acetate: Part I – Synthesis and Characterization

Synthesis and characterization of fibrous cellulose triacetate, CTA, are reported using an acetic acid/anhydride/perchloric acid toluene catalyzed route. The fibrous product exhibits a high degree of nano-crystallinity. An optimum concentration of the reactants for substitution and minimization of fiber degradation was studied. Chain degradation was promoted by the acetylium ion and led to a loss of fibrous structure. Heterogeneity of the material was studied by powder X-ray diffraction, optical microscopy, and solid-state ¹³C nuclear magnetic resonance. The structure formed if directly influenced by the original nano structure in the cellulose fiber.     

Electrochemical and spectroscopic studies of metal hexacyanometalate films—III. Equilibrium and kinetics studies of cupric hexacyanoferrate

The potential response of cupric hexacyanoferrate (CuHCF) thin films on glassy carbon substrate was studied by cyclic voltammetry in potassium and ammonium ions. The shift in potential with ammonium ion concentration is Nernstian with a difference of +0.70 V in 1 M NH⁺₄ with respect to 1 M K⁺. Equilibrium spectroelectrochemical studies have shown that the mole fraction of CuHCF is a reflection of film activity. Kinetic studies have indicated that the redox reaction is faster in ammonium ion than in potassium ion. Similarities and differences in the equilibrium and kinetic response of the film in both electrolytes are discussed.     

Orimulsion fly ash in clay bricks—part 3: chemical stability of ash-bearing products

The chemical stability of clay bricks containing Orimulsion ash (up to 6 wt.%) was assessed with a laboratory simulation of the brickmaking process. The development of efflorescence, the amount of water soluble salts and their elution, the fraction of S, V, Ni, Mg, Ca, Na and K immobilized in the ceramic matrix, and the amount of volatile elements potentially released during firing were determined by ICP–OES, XRPD, TGA, SEM and EMP analyses. The stabilizing mechanism acts through the capture of metals into the crystalline structure of silicates formed at high temperature. However, the firing conditions adopted in the brick industry (about 900 °C) do not permit the complete reaction of sulphates; there is considerable efflorescence and soluble salts are formed, even with 1.5% of ash added, producing a risk of sulphate attack to the mortars. On the other hand, the decompostion of sulphates during firing could bring about remarkable SO_x emissions, particularly in carbonate-free bodies. In conclusion, the disposal of Orimulsion ash in clay bricks must be practiced with caution and an amount of ash below 1 wt.% weight is strongly recommended.     

Thermogelling polysaccharides for aqueous gelcasting—part III: mechanical and microstructural characterization of green alumina bodies

The use of gelling additives, such as polysaccharides, in colloidal processing provides adequate mechanical properties to the green bodies to be handled. In this work, the green density and the mechanical behaviour (stress–strain relationships, elastic modulus, bend strength and fracture mechanism) at room temperature of gelcast alumina bodies are studied, in order to establish the influence of the type and the concentration of additive. Furthermore, the previous concentration of polysaccharide solutions is also taken into account as an important variable. Agar, agarose and carrageenan were used as gelling additives. Values of the bend strength up to 4 MPa are obtained, significantly higher than those corresponding to slip cast alumina without gelling additives, and they increase with the final concentration of polysaccharide, while Young's modulus values are mainly influenced by the concentration of additive in the precursor solution. For bodies with a large final concentration of additive, extensive plastic deformation during fracture is observed.     

The main role of silica—Based cement free binders on the microstructural evolution and mechanical behaviour of high alumina castables

One of the major innovations for monolithic refractories in the past decade has been the development of cement-free binders, no-cement castables (NCCs). NCCs with colloidal silica suspensions as binders are extended at industrial scale. Microsilica-based powder binders are valuable alternative to colloidal silica to avoid installation and transport difficulties.The success of NCCs depends on the high temperature microstructure developed. Phase equilibrium diagrams are a powerful tool for the understanding of such development.This work deals with the study of alumina castables fabricated using both silica gel technologies with the aim of establishing the main factors that determine the high temperature (1300–1400?°C, 30–300?min) microstructure and how it affects the mechanical behaviour. Deformation and fracture are determined by the formation of mullite in the matrix. Reaction kinetics is highly dependent of temperature, time and the alumina - silica relative amount at local level, determined by the composition of the binder.