Molar Ratio Of Oxidant Research Articles

Exceptional indoor carbon capture using epoxide-modified polyamine functionalized materials

In addressing concerns related to symptoms like dizziness, nausea, and reduced productivity stemming from elevated indoor CO2 levels, the primary objective of the current CO2 adsorption technology is to enhance the adsorption capacity. However, the stability and applicability of the adsorbent are of greater importance in indoor carbon capture than in other settings. This study examines the performance and stability of indoor CO2 capture using propylene oxide-modified tetraethylenepentamine supported on novel super carbon, gas-phase hydrophilic silica dioxide, and graphitic phase carbon nitride carriers. The corresponding painted films were developed to facilitate the application in indoor CO2 capture. Thermogravimetric analysis demonstrates that the propylene oxide-modified materials are more stable than the unmodified compositions. The findings indicate that an optimal adsorption capacity is achieved when water is used as the solvent and carboxymethyl cellulose sodium as a dispersant, while maintaining a carrier-to-tetraethylenepentamine mass ratio of 1:0.75. Furthermore, the painted films are stably formed by using isopropanol instead of water, and the tetraethylenepentamine-to-propylene oxide molar ratio of 1:2 for super carbon and graphitic phase carbon nitride as carriers, which exhibit notable enhancements in adsorption performance by 160.0 % and 41.8 %, respectively. The film using super carbon as supporter exhibited the highest adsorption capacity of 122.83 mg/g. This suggests that the compositions are more readily available for indoor CO2 capture by coating in everyday scenarios. Notably, even after undergoing five adsorption–desorption cycles, the desorption efficiency of the solid amine adsorbent remains consistently above 95 %.

Infusion of Fly Ash/MgO in CaO-based sorbent for high-temperature CO2 capture: Precursor selection and its effect on uptake kinetics

Calcium Looping Technology for high-temperature CO2 capture suffers from a gradual decline of uptake capacity over repeated cycles caused by the sintering-induced agglomeration of CaO particles. The latter is typically inhibited by infusing inert into the sorbent to disperse CaO grains. In this respect, current work investigates the infusion of inerts like Fly ash (FA) and Magnesium salt in CaO-based sorbent through sol-gel combustion, assessing sorbent performance under harsh conditions: carbonation at 650 °C for 30 min and calcination at 950 °C for 15 min under a CO2 (100%) atmosphere. The study includes (i) in-depth characterization of various sorbents: both unsupported and modified with inert, synthesized using inorganic (InOP) and organometallic (OMP) precursors for different fuel-to-metal oxide molar ratios (MR = 2 and 3), (ii) thermogravimetric analysis for evaluating uptake kinetics based on carbonation conversion (XCBN) and cyclic stability and (iii) kinetic modeling to evaluate rate parameters. Kinetic analysis after a single cycle revealed the highest XCBN (78%) for unsupported InOP (MR = 2 and 3) and OMP (MR = 2) among thermally pre-treated sorbents. MgO-modified InOP (MR = 2) performed better (XCBN = 66%) than its OMP counterpart, while both MgO-modified sorbents (MR = 3) performed similarly (XCBN = 66%). Cyclic stability studies conducted for 30 cycles established higher stability of FA-modified OMP with lower deterioration by 13.47% (XCBN = 22.60%) than unsupported OMP by 62.99% (XCBN = 15.06%). Overall, the results showcase FA infusion in OMP as a viable route to develop stable modified CaO-sorbents with considerable carbonation conversion.

Streamlined synthesis of iron and cobalt loaded MCM-48: High-performance heterogeneous catalysts for selective liquid-phase oxidation of toluene to benzaldehyde

Hydrothermal synthesis of MCM-48 molecular sieves featuring the incorporation of both iron and cobalt with Si/M ratios of 20, 40 and 80 (where M represents either iron or cobalt) was performed using tetraethyl orthosilicate as the silica source and cetyltrimethylammonium bromide as a template. To gain a comprehensive understanding of the synthesized materials, these were thoroughly characterized using various techniques, including XRD, XPS, UV–Vis (DRS), FT-IR, N2 adsorption-desorption analysis, SEM with EDX, TEM, TGA and NH3-TPD analysis. XRD analysis revealed the presence of well-ordered MCM-48 structure in the metal-incorporated materials, while XPS and UV–Vis DRS confirmed the successful partial incorporation of metal ions precisely in their desired tetrahedral coordination within the framework. To assess their catalytic performance, we studied the activity and selectivity of these catalysts in liquid phase oxidation of toluene using tert-butyl hydroperoxide as the oxidant. Under optimized conditions, employing a 6% (w/w) Fe-MCM-48 (40) catalyst and maintaining a toluene to oxidant molar ratio of 1:3 at 353 K in a solvent-free environment for 8 h, the oxidation reaction resulted in the formation of benzaldehyde (88.1%) as the major product and benzyl alcohol (11.9%) as the minor product.

Inorganic intumescing alkali silicate particles

New generation intumescent coatings apply self-intumescing particles to induce expansion in a controlled manner. Various studies have investigated alkali silicate-based coatings due to their inherent expansion with the release of H2O. The presented work investigated the self-intumescing concept of alkali silicates as particles. A thorough study of inorganic alkali silicate particles as potential intumescent ingredients in passive fire protection systems was carried out by applying HSDM, TGA, FTIR, XRD, and SEM. Herein, particles of lithium-, sodium-, and potassium silicates were synthesized with varying silica-to-alkali oxide molar ratios and curing humidity. Subsequently, the hydration chemistry and thermal behavior were examined. The results revealed increased expansion potential with decreasing SiO2/M2O molar ratio (M = Na, Li, or K) in the range 3.1–7.4 and increasing curing humidity in the range 35, 50, and 90% RH. Previous studies have emphasized the effect of solid-bound H2O to induce intumescence. In this study, the influence of the softening of the silicate matrix and H2O release is highlighted to allow increased expansion potential. Here, the coupling of thermal analysis with microscopy suggests an intumescence mechanism in the order of 1) initial shrinkage due to loss of free and physical bound H2O, 2) sphere formation to minimize surface energy, 3) expansion as a result of H2O evolution and viscoelastic melt formation, and 4) second shrinkage due to sintering before 5) melting. The sodium alkali silicate particles with a SiO2/M2O molar ratio of 3.4 exhibited a timely softening of the silicate matrix from about 155 °C to provide a distinct spherical particle followed by ionic H2O evolution. As a result, hereof, hollow, spherical particles with relative solid expansions of up to 550% were obtained and maintained until a second shrinkage at 650 °C with a subsequent melting at 950 °C. In comparison, the imbalance in viscoelastic melt formation and H2O release of lithium- and potassium silicate particles resulted in less expansion. Considering the expansion potential and thermal behavior of the alkali silicate particles, it is suggested as a possible, sustainable intumescence ingredient.

Synthesis of water soluble cobalt(II), copper(II) phthalocyanines and their usage as a catalyst in the photoxidation of benzyl alcohol in biphasic catalysis

In this study, we synthesized and characterized cobalt(II), copper(II) phthalocyanines (2, 3) and their water soluble derivatives (2a, 3a) bearing dimethylamino groups. Then, benzaldehyde selective photoxidation of benzyl alcohol with four different oxygen sources and catalysts (2a, 3a) was carried out by biphasic catalysis. Optimal photocatalytic reaction conditions were determined as benzyl alcohol/ oxidant molar ratio 4.0/1 amount of the catalyst 2.0 mg (9.61 × 10−7 mmol), 25 ◦C and 30 min. 92 % conversion of benzyl alcohol with 1640 turnover number for 2a and 75 % benzaldehyde selectivity for 3a are achieved under the optimal conditions. Both catalysts can be used in three times and 2a can be catalytically active after 5 cycles with giving 72 % product conversion.

Comparison of monochloramination and chlorination of 1,3-diphenylguanidine (DPG): Kinetics, transformation products, and cell-based in-vitro testing

As a widely used secondary vulcanization accelerator in the rubber industry, 1,3-diphenylguanidine (DPG) poses risks to human health and the environment. To compare and comprehend the disinfection process of DPG, this work investigates the reaction kinetics, toxicity, and transformation products (TPs) of DPG during chlorination and monochloramination. It has been revealed that the reactivity of monochloramine is significantly slower compared to chlorination of DPG, with the maximum efficiency observed at pH 7 to pH 8. Cytotoxicity assessment using HepG2 and THP-1 cells reveals that cytotoxicity hierarchy is as follows: chlorine TPs > monochloramine TPs > DPG. Moreover, oxidant-to-DPG molar ratios 10 and 20 lead to higher cytotoxicity in both chlorination and monochloramination compared to ratio 5 and 100. Additionally, cell bioenergetics experiments demonstrate that chlorine and monochloramine TPs induce mitochondrial dysfunction and enhance glycolytic function in HepG2 cells. The genotoxic response from p53 signaling further suggested genotoxic effects of certain TPs. Furthermore, analysis of TPs using high-resolution mass spectrometry (HRMS) identifies ten TPs, with chlorination yielding more TPs than monochloramination. Generally, a chlorine or monochloramine molar ratio to DPG of 10–20 results in an increased formation of TPs and heightened cytotoxicity. Notably, higher oxidant molar ratios increased the formation of monoguanidine TPs and DPG hydroxylation during chlorination, whereas monochloramination lead to DPG substitution predominantly generating chlorinated DPG due to weaker oxidation effects. These findings provide valuable information for the appropriate treatment of DPG and disinfection processes in water facilities to mitigate potential risks to human health and the ecosystem.

Prediction of the ribbon length to determine the viscosity of ladle-refining powder containing CaF2 using inclined plane test and advanced mathematical model

ABSTRACT In the present research, the inclined plane test (IPT) and an author-developed advanced mathematical model were used to determine the viscosity of ladle-refining + CaF2 powder containing 3–10% CaF2 (LRC powder). The ladle slag powder is composed of such compounds as CaO, Al2O3, SiO2 containing percentages of CaF2 to make special changes to the chemical and physical properties of the compound. The procedure for determination of the viscosity obtained by IPT method was supported using a high-temperature viscometer. The results showed that the ribbon lengths of LRC powder obtained by using the IPT method were related to an Arrhenius relationship of viscosity. Furthermore, from the advanced mathematical relationships, it was found that there is a very close relationship between the oxygen-to-silicon molar ratio (O/Si), basic/acidic oxide molar ratio (B/A), the number of non-bridging oxygen per tetrahedrally-coordinated atoms (NBO/T), and the chemical compositions of LRC powder. Hence, the advanced mathematical relationships from the software output, and Statistical Package for the Social Sciences (SPSS), were used to determine the prediction model of the viscosity of LRC powder based on its chemical composition. This model had a very good correlation with the actual values obtained.

Addition of alkaline solutions and fibers for the reinforcement of kaolinite-containing granite residual soil

Granite residual soil (GRS) contains a large amount of kaolinite, which is highly hydrophilic and thus easily disintegrated by water. These characteristics may cause severe landslides and debris flows in some hillslopes composed of GRS. This paper describes an investigation of possible solutions to this problem: the addition of fiber and/or alkaline solutions to GRS to reinforce GRS. The effects of the silica-to‑sodium oxide (SiO2-to-Na2O) molar ratios of alkaline solutions on the static mechanical properties of reinforced GRS and the effects of fiber type on the impact resistance of reinforced GRS are discussed. The reinforcement mechanism, characterized by a combination of techniques, namely X-ray powder diffraction, Fourier-transform infrared spectroscopy, microcomputed tomography, and scanning electron microscopy, is also discussed. Static load test results indicated that the alkaline solution–reinforced GRS with a SiO2-to-Na2O molar ratio of 0.5 exhibited the highest compressive strength (4550 kPa), which is attributable to this reinforced GRS having the lowest porosity (2.3%). The alkaline solution reacted with GRS to form cementitious materials, thereby improving the compressive strength of GRS. Drop weight impact testing showed that fiber-reinforced GRS had dynamic mechanical properties superior to those of pristine GRS, and that in combination with a given alkaline solution, glass fibers reinforced GRS more effectively than basalt fibers. This is because the silicon atoms on the surface of glass fibers participated in the reaction with the alkaline solution, thus forming more cementitious materials. These materials were evenly distributed on the surface of the glass fibers, and thus particles of glass fiber–reinforced GRS were more closely bound to each other than particles of basalt fiber–reinforced GRS particles. These findings suggest that waste GRS, once appropriately reinforced, could be used for the construction of high-strength foundations and embankments.

Removal of contaminants of emerging concern from secondary-effluent reverse osmosis retentates by continuous supercritical water oxidation- parametric study and conceptual design

The continuous removal of TOC and the degradation efficiency of carbamazepine and 17β-estradiol were investigated using actual secondary municipal-effluent RO-retentate solutions. A specific set of operating parameters were applied within the supercritical water oxidizing conditions: temperature range 420–480 °C, 25.1 MPa, hydraulic retention time (HRT) of 1–2 min, excess oxidant molar-ratio of 3–10 and presence of a homogenous catalyst (IPA) at 50–100 mg/L. > 99% organic carbon mineralization, along with complete degradation of model pollutants, was observed at 450 °C/1 min/OC= 5–10 and 100 mgIPA/L. The outlet estrone concentration, 1.03 ± 1.14 ng/L, representing estrogenic pollutants, dropped to the "no effect" range. A model for a SCWO plant treating secondary-municipal-effluent-RO-retentate for a city of 100,000 capita-equivalent was developed, based on a shell & tube SCWO flow reactor, showing > 75% energy-efficiency. The model yielded that for the extreme case of a zero caloric-value feed-solution, the total OPEX and CAPEX would be < $6.0 ± 2.5 per m3 of secondary effluents, i.e., two orders of magnitude lower than the reported environmental shadow-price associated with CECs (contaminants of emerging concern). Further work is required on the continuous and efficient separation of the salt-matrix, which can lead to higher overall heat transfer coefficients and enable further reduction in capital costs.

Effect of SBA-15-based immobilization of a new phosphoric triamide Ag (I) complex on its catalytic activity: Synthesis, characterization, crystallography and catalytic investigation

A new Ag (Ⅰ) complex (C) containing phosphoric triamide ligand (L) with a formula of [Ag ((C5H4NC (O) NHP (O) (NC6H12)2)2NO3] 2 was synthesized by the reaction of AgNO3 with N-nicotinyl –N′, N″-bis (hexamethylenyl) phosphoric triamide. The complex (C) was characterized by Fourier transform infrared spectroscopy (FT-IR), molar conductivity, thermal gravimetric analysis (TGA), and X-ray crystallography techniques. Results showed that complexation occurred via the nitrogen atom of the pyridine ring. The molecular structure of C, refined from single-crystal X-ray diffraction, is triclinic with a P-1 space group. The complex was immobilized on SBA-15 and the produced compound (C@SBA-15) was identified by BET, AAS, FT-IR, XRD, and TGA methods. Successful loading of the complex on SBA-15 was determined by the BET method. According to AAS findings, the amount of silver in the C@SBA-15 composition was 18%. FT-IR and XRD results showed that the complex was absorbed on the support physically and the hexagonal structure of the support was retained after immobilization. Thermal stability of C@SBA-15 was confirmed by TGA analysis. The homogeneous complex (C) and heterogeneous C@SBA-15 were used as catalysts in the oxidation reaction of aromatic aldehydes and sulfides and their catalytic properties compared. H2O2 was used as a green oxidant, some effective parameters (reaction temperature, substrate to oxidant molar ratio, catalyst amount, and solvent type) were optimized, and the conversion percentages of 70% (for C catalyst) and 50% (for C@SBA-15 catalyst) obtained. The reusability of C@SBA-15 and the generality of both catalysts were evaluated and confirmed. The results showed that when the complex was immobilized on SBA-15, its catalytic efficiency decreased, and its recoverability increased. A comparison with other published reports showed that the catalytic efficiency of the catalysts in the oxidation reaction of aldehydes and sulfides was within acceptable limits.

Analysis of a more sustainable method for recycling waste lead batteries: Surface renewal promotes desulfurization agent regeneration.

The traditional sodium desulfurization process for waste lead-acid batteries is beneficial to the environment; however, it is limited by poor economic viability as the cost of desulfurizer is much higher than the value of desulfurization by-products. This study proposes a new closed-loop pre-desulfurization process for lead paste, which consumes only lime as the indirect desulfurizer, produces sodium sulfate as a by-product, and regenerates sodium hydroxide as the direct desulfurizer. The concentration of prepared sodium hydroxide reached 2.57mol/L when the reaction was conducted at room temperature for 2.0h, with a sodium oxalate: calcium oxide molar ratio of 1:1.3, a CaO: water mass ratio of 1:6, and magnetic stirring at 600rpm. Cost estimation and economic analyses were also conducted. The cost of lead paste generated by this new pre-desulfurization process was 37.62 dollars/ton lower than traditional high-temperature smelting, and 44.42 dollars/ton lower than direct sodium pre-desulfurization. Thus, this process provides a practical and feasible clean recycling method for waste lead-acid batteries with significant environmental and economic benefits.

Preparation and properties of PANI/PI composite fabrics with conductive nanofiber network structure

Electrically conductive polyaniline (PANI)/polyimide (PI) composite fabric was prepared by in situ polymerized aniline on PI fabric in the acid solution using ammonium persulfate as the oxidant. PANI nanoflowers and nanofibers was obtained on the surface of PI fabric by controlling the molar ratio of aniline/oxidant and the acidity of the polymerization solution. Field Emission Scanning Electron Microscope (FESEM) results demonstrated that a continuous PANI nanofiber network with an average fiber diameter of 80–100 nm was successfully constructed on PI fabric when the doping acid was HNO3, the aniline to oxidant molar ratio was 4:5, and the pH value was 2.32. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis indicated that the PANI nanofibers was combined on PI fabric through hydrogen bonding. The conductivity of the composite fabric was 0.53 S/m, the contact angle of the composite fabric was increased from 50.6° to 84.7° due to the uniform nanofiber network structure, and the decomposition temperature (Td) of the composite fabrics was beyond 580.0 °C. Remarkably, the prepared PANI/PI composite fabric exhibited excellent electromagnetic wave absorption features (reflection loss of −57.99 dB), which implied it could be a good candidate for the electromagnetic wave absorbing materials.

Chemical Oxidative Condensation of Benzidine in Non-Aqueous Medium: Synthesis and Investigation of Oligomers and Polymer with Benzidine Diimine Units.

The oxidative condensation of benzidine has been carried out in acetic acid media using potassium peroxydisulfate as the oxidizing agent. Using different monomer–oxidant molar ratios, benzidine dimer, trimer, and polymer have been synthesized for the first time. It was established that the polybenzidine structure is composed from a sequence of benzidinediimine and diphenylene units with amino/amino end groups and thus proves the possibility of ammonia elimination during the oxidative polymerization of aromatic diamines. The method seems to be common for the synthesis of polymers with the sequence of aromatic diimine and arylene units. TGA analysis of the obtained trimer and polymer was investigated, and the high thermostability of both the polymer and trimer was revealed. According to the obtained data, both polymer and trimer matrix decomposition started at 300 °C, and at 600 °C, 75.94% and of 69.40% of the initial weight remained, correspondingly. Conductivities of the polymer and trimer show a semiconductor-type change from temperature and after doping show an increase in conductivity up to 10−4 Sm/cm.

Parametric Screening Analysis for the Oxidative Desulfurization of Diesel Oil

This research utilized a real raw diesel oil to be subjected in an innovative desulfurization technique. The novelty of this study is in the use of screening analysis in the ultrasonication enhancement of sulfur oxidation in actual fuel. This addresses the research gap in literature that have yet to compare and completely analyze all factors in the ultrasound-assisted oxidative desulfurization (UAOD) method. Specifically, the effects of ultrasonication via amplification and irradiation time, material usage of tetraoctylammonium bromide, hydrogen peroxide, polyoxometalate catalyst and the process parameters of fuel to oxidant molar ratio and temperature were examined. A definitive screening design (DSD) using the JMP 11.0 was utilized for a statistical screening analysis to determine the essential and non-essential parameters in the UAOD. Upon the oxidation of sulfur compounds in diesel oil, results suggested that the enhancement technique via ultrasonication, polyoxometalate catalyst and temperature were the only significant factors based on the p-value < 0.05. The aforementioned factors are essential due to being able to instigate an oxidation reaction of sulfurs into its sulfone forms. Based on the generated DSD experimental runs, sulfur conversion can range from 36.41 % to 92.69 %.

Chromium-Salophen as a Soluble or Silica-Supported Co-Catalyst for the Fixation of CO2 Onto Styrene Oxide at Low Temperatures.

Addition of a soluble or a supported CrIII-salophen complex as a co-catalyst greatly enhances the catalytic activity of Bu4NBr for the formation of styrene carbonate from styrene epoxide and CO2. Their combination with a very low co-catalyst:Bu4NBr:styrene oxide molar ratio = 1:2:112 (corresponding to 0.9 mol% of CrIII co-catalyst) led to an almost complete conversion of styrene oxide after 7 h at 80°C under an initial pressure of CO2 of 11 bar and to a selectivity in styrene carbonate of 100%. The covalent heterogenization of the complex was achieved through the formation of an amide bond with a functionalized {NH2}-SBA-15 silica support. In both conditions, the use of these CrIII catalysts allowed excellent conversion of styrene already at 50°C (69 and 47% after 24 h, respectively, in homogeneous and heterogeneous conditions). Comparison with our previous work using other metal cations from the transition metals particularly highlights the preponderant effect of the nature of the metal cation as a co-catalyst in this reaction, that may be linked to its calculated binding energy to the epoxides. Both co-catalysts were successfully reused four times without any appreciable loss of performance.

Kinetic modelling for concentration and toxicity changes during the oxidation of 4-chlorophenol by UV/H2O2

This work develops a kinetic model that allow to predict the water toxicity and the main degradation products concentration of aqueous solutions containing 4-chlorophenol oxidised by UV/H2O2. The kinetic model was developed grouping degradation products of similar toxicological nature: aromatics (hydroquinone, benzoquinone, 4-chlorocatechol and catechol), aliphatics (succinic, fumaric, maleic and malonic acids) and mineralised compounds (oxalic, acetic and formic acids). The degradation of each group versus time was described as a mathematical function of the rate constant of a second-order reaction involving the hydroxyl radical, the quantum yield of lump, the concentration of the hydroxyl radicals and the intensity of the emitted UV radiation. The photolytic and kinetic parameters characterising each lump were adjusted by experimental assays. The kinetic, mass balance and toxicity equations were solved using the Berkeley Madonna numerical calculation tool. Results showed that 4-chlorophenol would be completely removed during the first hour of the reaction, operating with oxidant molar ratios higher than R = 200 at pH 6.0 and UV = 24 W. Under these conditions, a decrease in the rate of total organic carbon (TOC) removal close to 50% from the initial value was observed. The solution colour, attributed to the presence of oxidation products as p-benzoquinone and hydroquinone, were oxidised to colourless species, that resulted in a decrease in the toxicity of the solutions (9.95 TU) and the aromaticity lost.

An efficient heterogeneous Cu(I) complex for the catalytic oxidation of alcohols and sulfides: synthesis, characterization, and investigation of the catalyst activity

A heterogeneous Cu(I) complex was synthesized by reaction of C5H4NC(O)NHP(O)[NHC(CH3)3]2 (L) with CuCl and used as a catalyst for green oxidation of aromatic alcohols and sulfides. According to the characterization results obtained from 31P NMR, UV-Vis, FT-IR, mass, XRD, elemental analysis, and molar conductivity techniques, the chemical formula of the complex (1) was suggested as [CuClL2]. Parameters on the catalytic activity (reaction temperature, the substrate to oxidant molar ratio, catalyst amount, and solvent type) were optimized, using H2O2 as a green oxidant, and excellent conversion amounts (100%) were achieved under optimal conditions. Moreover, the generality and recyclability of the catalyst were tested and confirmed. A comparison between the oxidation results of the alcohol and sulfide in the presence of 1 with other catalysts indicated that in most cases 1 showed better efficiency, in a more reasonable reaction time and conditions.

Binary alkali-activated systems obtained by the valorisation of calcined kaolin sludge and bottom ash

This paper assesses the use and valorisation of two industrial wastes generated at a large scale, which are currently disposed in landfills, as raw materials to produce geopolymers. Specifically, a kaolinitic sludge from the mining industry (CKS), and bottom ash (BA) generated during coal combustion in a thermal power station, were used as aluminosilicate precursors in geopolymer synthesis. The geopolymers were synthesised at 50°C, with a sodium oxide/aluminium oxide (Na2O/Al2O3) molar ratio of 1.0, and different silica/aluminium oxide (SiO2/Al2O3) molar ratios adjusted by manipulating the content of the soluble silicate solution used as the activator. The mechanical strength and reaction products formed during the geopolymerisation process were assessed up to 90 days of curing. The use of CKS as the main component of the precursor blend provides a geopolymer with better mechanical properties due to its higher reactivity than BA. The content of soluble silicates in the alkali activator plays an important role during geopolymerisation, improving the mechanical properties due to the formation of a more reticulated and dense structure. The mortars show a compressive strength higher than 55 MPa after 28 days and low water absorption by capillarity. This elucidates the feasibility of valorising these industrial residues as precursors for geopolymer cements.

Water absorption and compressive strength of various coal fly ash-based geopolymer pastes

This paper discusses the effects of the silicon dioxide to aluminium oxide molar ratio, sodium oxide to aluminium oxide molar ratio and concentration of sodium hydroxide on the water absorption and compressive strength of synthesised fly ash-based geopolymers. Geopolymer pastes were prepared using fly ash mixed with an alkaline activator consisting of sodium hydroxide solution and sodium silicate solution. The phase composition, microstructure and chemical bonding of the synthesised products were characterised after 7 and 28 days using X-ray diffraction, scanning electron microscopy and Fourier-transform infrared spectroscopy, respectively. The synthesised geopolymer with a silicon dioxide to aluminium oxide molar ratio of 5 and a sodium oxide to aluminium oxide molar ratio of 1.2, activated with 10 M sodium hydroxide, was found to have the highest strength and the lowest water absorption. The compressive strength was observed to increase with increasing silicon dioxide to aluminium oxide molar ratio. A high initial molar ratio of sodium oxide to aluminium oxide enhances the water absorption and decreases the strength of the geopolymer sample. The dissolution of silica and alumina from the starting materials becomes more efficient as the concentration of sodium hydroxide increases.

Lightweight and thermally insulating aluminum borate nanofibrous porous ceramics

Aluminum borate porous ceramics are excellent candidates for high-temperature insulation applications. Current research on aluminum borate-based porous ceramics mainly focuses on porous ceramics made up of aluminum borate whiskers, whose low aspect ratio leads to a relatively dense porous structure; this results in porous ceramics with low porosity and relatively high thermal conductivity. In this study, we report the manufacturing of aluminum borate nanofibrous porous ceramics by an agar-based gel casting method using electrospun nanofibers with a high aspect ratio as the three-dimensional skeleton structure. We explored the effect of the alumina/boron oxide molar ratio on the microscopic morphology and crystal phase composition of the aluminum borate nanofibers and that of the sintering temperature on the micro and macro properties of porous ceramics based on the nanofibers. The results showed that aluminum borate nanofibers with an alumina/boron oxide molar ratio of 7:2 had the densest microscopic morphology, and the corresponding porous ceramics exhibited a higher porosity (91%) and lower thermal conductivity (0.11 W m−1 K−1) after sintering at 1200 °C than aluminum borate porous ceramics with aluminum borate whiskers as the skeleton. The successful synthesis of aluminum borate nanofibrous porous ceramics provides new insights into the development of high-temperature insulators.