Strain Hardening Behavior of Engineered Geopolymer Composites: Effects of the Activator Combination

Fly ash-based engineered geopolymer composites (EGCs) exhibiting strain hardening behavior under uni-axial tension were developed employing two different sodium-based (Na-based) and potassium-based (K-based) activator combinations. The relatively brittle low calcium (Class F) fly ash-based geopolymer matrix was reinforced with randomly oriented short poly vinyl alcohol (PVA) fibers (2% v/v). Na-based activator combination was composed of 8.0 M NaOH solution (28.6% w/w) and Na2SiO3 solution (71.4% w/w) with a SiO2/Na2O ratio of 2.0; whereas, Kbased activator combination was composed of 8.0 M KOH solution (28.6% w/w) and K2SiO3 solution (71.4% w/w) with a SiO2/K2O ratio of 2.23. The matrix and composite properties of the developed fly ash-based EGCs including workability of the fresh matrix, density, compressive strength and uni-axial tensile behavior were evaluated. The experimental results revealed that the sodium-based EGC (EGC-Na) exhibited superior tensile strain capacity, compressive and uni-axial tensile strengths with significantly enhanced ductility

Transparent and conducting boron doped ZnO thin films grown by aerosol assisted chemical vapor deposition

Boron doped zinc oxide thin films via aerosol assisted chemical vapor deposition with resisitivities as low as 5.1 × 10−3 Ω cm

Compressive strength of tungsten mine waste- and metakaolinbased geopolymers

Neuro-fuzzy approach has been successfully applied to a wide range of civil engineering problems so far. However, this is limited for geopolymeric specimens. In the present study, compressive strength of different types of geopolymers has been modeled by adaptive neuro-fuzzy interfacial systems (ANFIS). The model was constructed by 395 experimental data collected from the literature and divided into 80% and 20% for training and testing phases, respectively. Curing time, Ca(OH)2 content, NaOH concentration, mold type, aluminosilicate source and H2O/Na2O molar ratio were independent input parameters in the proposed model. Absolute fraction of variance, absolute percentage error and root mean square error of 0.94, 11.52 and 14.48, respectively in training phase and 0.92, 15.89 and 23.69, respectively in testing phase of the model were achieved showing the relatively high accuracy of the proposed ANFIS model. By the obtained results, a comparative study was performed to show the interaction of some selected factors on the compressive strength of the considered geopolymers. The discussions findings were in accordance to the experimental studies and those results presented in the literature

Geopolymer as well cement and variation of its mechanical properties under different curing temperature and curing mediums

Geo sequestration of carbon dioxide (CO2) has been found to be one of the best solutions to reduce anthropogenic amount of greenhouse gases to the environment. Well integrity of sequestration wells should be maintained for the success of any sequestration projects. Well cement plays a vital role in well integrity for any sequestration projects, and ordinary Portland cement (OPC) based well cement has been used in underground wells. There are many problems, such as cement degradation, chemical attacks, durability issues, leakage, etc., associated with OPC based well cement. One of the best replacements for OPC based well cement would be the use of geopolymer cement, as it is economical in production, sustainable in reducing waste products, consumes less energy, doesn‟t undergo chemical attacks, durable, resistive in acidic environments and possess higher strength compared to OPC. This paper will review suitability of geopolymer as well cement under downhole conditions, and analyse the advantages of using geopolymer over OPC-based well cement. Moreover, well cement will be exposed to range of temperatures, pressures and fluid medium from the ground surface to sequestration depths of more than 1 km. Therefore, this paper aims to study the mechanical behaviour of geopolymer under different curing temperatures (from 23 ºC to 80 ºC) and curing mediums (brine, water and CO2 saturated brine). It has been found that optimum curing temperature for higher strength is 60 ºC and geopolymer exhibits high strength compared to class G cement above ambient temperature. In addition, water saturated samples showed higher strength reduction compared to brine saturated geopolymer samples

Previsão da resistência de geopolímeros monofásicos

The discovery of one-part geopolymers is considered a key event on the evolution of geopolymer technology because emulates one of the most important properties of Portland cement, the just add water concept. This materials are not associated with the known problems of two part geopolymers, namely the use of caustic solutions that have poor workability and make the handling and application of geopolymers difficult and the fact that alkaline or soluble silicates are not consumed during geopolymerization leading to severe efflorescence phenomena. However, so far very few investigations were published on this field and some report low mechanical strength. This paper discloses results regarding the numerical modelling of one part-geopolymers compressive strength.A descoberta dos geopolímeros monofásicos é considerado um importante acontecimento no âmbito da tecnologia dos geopolímeros porque mimetizam uma das mais importantes propriedades do cimento Portland, o conceito relativo à simples adição de água. Estes materiais não estão associados aos conhecidos problemas dos geopolímeros correntes nomeadamente a utilização de soluções cáusticas, baixa trabalhabilidade que dificultam a sua colocação e o facto das espécies alcalinas e silicatos solúveis não reagirem na sua totalidade durante a reacção de geopolímerização originando o aparecimento de elevada quantidade de eflorescências. Contudo muito poucas investigações foram publicadas neste domínio e algumas apresentam baixa resistência mecânica. Este artigo apresenta resultados relativos à modelação numérica da resistência à compressão de geopolímeros monofásicos.info:eu-repo/semantics/publishedVersio

1,8-Bis(4-meth­oxy-3-nitro­phen­yl)naphthalene

Mol­ecules of the title compound, C24H18N2O6, are located on a twofold rotation axis passing through through the central C—C bond of the naphthalene ring system. The mol­ecular conformation is characterized by a roughly coplanar arrangement of the two substituted phenyl rings [dihedral angle 18.53 (5)°]. These two aryl rings are each twisted by 65.40 (5)° from the plane of the naphthyl unit

Visible-Light-Active Iodide-Doped BiOBr Coatings for Sustainable Infrastructure

The search for efficient materials for sustainable infrastructure is an urgent challenge toward potential negative emission technologies and the global environmental crisis. Pleasant, efficient sunlight-activated coatings for applications in self-cleaning windows are sought in the glass industry, particularly those produced from scalable technologies. The current work presents visible-light-active iodide-doped BiOBr thin films fabricated using aerosol-assisted chemical vapor deposition. The impact of dopant concentration on the structural, morphological, and optical properties was studied systematically. The photocatalytic properties of the parent materials and as-deposited doped films were evaluated using the smart ink test. An optimized material was identified as containing 2.7 atom % iodide dopant. Insight into the photocatalytic behavior of these coatings was gathered from photoluminescence and photoelectrochemical studies. The optimum photocatalytic performance could be explained from a balance between photon absorption, charge generation, carrier separation, and charge transport properties under 450 nm irradiation. This optimized iodide-doped BiOBr coating is an excellent candidate for the photodegradation of volatile organic pollutants, with potential applications in self-cleaning windows and other surfaces

Di-tert-butyl N,N′-(octa­hydro­penta­lene-2,5-di­yl)dicarbamate

In the molecule of the title compound, C18H32N2O4, the central bicyclo­[3.3.0]octane (octa­hydro­penta­lene) has a rigid ring junction. Both rings of the bicyclo­[3.3.0]octane unit adopt an envelope conformation, and the flexible tert-butyl­carbamoyl side chains each have an extended conformation. Such a constrained bicyclo­[3.3.0]octane aliphatic template is of inter­est with respect to the design of novel self-assembling motifs. Mol­ecules related by c-glide symmetry are linked via inter­molecular N—H⋯O hydrogen bonds, forming a two-dimensional layer structure. Neighboring layers are weakly associated along the a axis due to the close approach of the tert-butyl­carbamoyl groups (2.55 Å)

Enhanced Photoacoustic Visualisation of Clinical Needles by Combining Interstitial and Extracorporeal Illumination of Elastomeric Nanocomposite Coatings

Ultrasound (US) image guidance is widely used for minimally invasive procedures, but the invasive medical devices (such as metallic needles), especially their tips, can be poorly visualised in US images, leading to significant complications. Photoacoustic (PA) imaging is promising for visualising invasive devices and peripheral tissue targets. Light-emitting diodes (LEDs) acting as PA excitation sources facilitate the clinical translation of PA imaging, but the image quality is degraded due to the low pulse energy leading to insufficient contrast with needles at deep locations. In this paper, photoacoustic visualisation of clinical needles was enhanced by elastomeric nanocomposite coatings with superficial and interstitial illumination. Candle soot nanoparticle-polydimethylsiloxane (CSNP-PDMS) composites with high optical absorption and large thermal expansion coefficients were applied onto the needle exterior and the end-face of an optical fibre placed in the needle lumen. The excitation light was delivered at the surface by LED arrays and through the embedded optical fibre by a pulsed diode laser to improve the visibility of the needle tip. The performance was validated using an ex-vivo tissue model. An LED-based PA/US imaging system was used for imaging the needle out-of-plane and in-plane insertions over approach angles of 20 deg to 55 deg. The CSNP-PDMS composite conferred substantial visual enhancements on both the needle shaft and the tip, with an average of 1.7- and 1.6-fold improvements in signal-to-noise ratios (SNRs), respectively. With the extended light field involving extracorporeal and interstitial illumination and the highly absorbing coatings, enhanced visualisation of the needle shaft and needle tip was achieved with PA imaging, which could be helpful in current US-guided minimally invasive surgeries