Dispersion of concentrated aqueous yttria-stabilized zirconia with ammonium polyacrylate

The dispersion of concentrated 0.53 μm yttria stabilized zirconia (YSZ) aqueous slip to achieve sintered compacts with high and uniform microstructure was investigated. 78 wt.% (37.5 vol%) and 83 wt.% (45.3 vol%) slips were prepared by dispersing the powder in water with ammonium polyacrylate (NH₄PA) at pH values in a range of 8–9.5. The influences of the amount of NH₄PA and pH on the rheological properties of 78 and 83 wt.% slips were studied. The minimum viscosities of 78 and 83 wt.% slips were obtained with the addition of 0.05–0.1 wt.% NH₄PA at pH 9. Increasing pH from 8 to 9.5 had no effect on the YSZ dispersion with NH₄PA. These dispersions yielded green densities of 63% of theoretical density (TD) and sintered to 98% TD at 1400 °C.     

Internal versus external surface active sites in ZSM-5 zeolite: Part 2: Toluene alkylation with methanol and 2-propanol catalyzed by modified and unmodified H3PO4/ZSM-5

Vapor-phase methylation of toluene with methanol and isopropylation of toluene with 2-propanol has been investigated in a down flow reactor under atmospheric conditions using N₂ gas carrier over a series of surface modified and unmodified ZSM-5 (Si/Al = 60–170) loaded with H₃PO₄, differing in the external surface treatment of the zeolites. The feed molar ratios of toluene/methanol and toluene/2-propanol were varied over a wide range (8–0.125), and the optimum feed ratio of toluene/alcohol was less than 0.5 in both cases. Space velocity employed in toluene methylation reported as WHSV (toluene) = 1.2 h⁻¹, and the space velocity employed in toluene isopropylation reported as WHSV (toluene) = 0.8 h⁻¹. The methylation reactions were carried out in the temperature range of 623–773 K, and the isopropylation reactions were carried out in the temperature range of 483–583 K. Atmospheric pressures was maintained in all runs. Catalysts containing 0–4.9 wt.% P were prepared using modified and unmodified ZSM-5 zeolites, and their catalytic performance for vapor-phase alkylation of toluene with methanol and 2-propanol were investigated. The optimum phosphorous content for methylation was 2.1 wt.% P which was greater than the optimum phosphorous loading for isopropylation (0.7 wt.% P).     

Influence of the chestnuts drying temperature on the rheological properties of their doughs

Chestnut flour doughs were prepared using chestnut air-dried at 45, 65, and 85 °C with constant load density (8.0 ± 0.6 kg/m²). Mixing curves of doughs using Mixolab^® device showed that chestnut flour doughs dried at 85 °C needed more water absorption to reach the target consistency, (1.1 ± 0.07 Nm). Thermorheological properties were evaluated by means of a controlled stress rheometer. All tested doughs showed shear-thinning behaviour in the steady-shear tests (0.001–1 s^?1). Oscillatory (1–100 rad s^?1 at 0.1% strain), temperature sweep (30–90 °C) and creep-recovery (loading 50 Pa for 60 s) tests showed that flour doughs from chestnuts dried at 85 °C provide interesting properties, particularly remarkable elasticity that is associated with starch gelatinisation. Experimental data were described using various rheological models.     

Template effect of single/double-chain quaternary ammonium salts on the formation of mesoporous ZrO2 nanomaterials

A double-chain quaternary ammonium salt of dioctyl dimethyl ammonium chloride (DDAC8) was first used as a low-cost template to prepare the mesostructured zirconia nanomaterials in an alcohol-thermal system. The material was calcinated to obtain pure tetragonal crystalline zirconia (t-zirconia) and thus has significantly improved original structure properties, including a narrow pore size distribution of 4–7 nm and a high surface area of 195 m²/g. The t-zirconia hierarchical nanoparticle aggregate material is different from the smooth microsphere material obtained using the single chain quaternary ammonium salt template. The characteristic rough surface morphology results from the grid distribution form of the DDAC8 micelles in the ethanol solution and caused the formation of more defect sites, which demonstrate the potential for possible catalytic applications. A formation mechanism of the mesoporous zirconia nanomaterial in the alcohol-thermal system of the surfactants is reasonably explained. The synthesis system may provide a new approach to the preparation of mesoporous nanomaterials.     

Rheology studies on highly filled nano-zirconia suspensions

The rheological properties of highly filled nano-zirconia suspensions in water and in various water–1,2-propanediol mixtures were investigated. The influence of an electrosteric (polyacrylic acid), an electrostatic (triammonium citrate) and a steric dispersant (2-(2-(2 methoxy ethoxy) ethoxy) acetic acid, TODA) on the viscosity and the elastic properties of the suspensions were also recorded. For any given water–propanediol mixture TODA was the most effective of the investigated dispersants. It resulted in the lowest slurry viscosities and the highest tan δ values, indicating best dispersing properties and the lowest elastic shear modulus, respectively. The water–propanediol proportion influenced the properties of the slurries strongly. For all dispersants the relative viscosity of the slurries decreased with increasing propanediol content. This was found to be a non-linear function in the case of TODA, where at a minimum level of 50 wt.% propanediol the properties of the slurries were the best. For the other dispersants this was a linear function, which indicates that the dispersing quality there only depended on the polarity of the dispersing medium. A screen printing paste was produced using TODA as a dispersant and a 75 wt.% propanediol–25 wt.% water mixture dispersing medium and subsequently printed. The printed layer showed 40–50 nm sized particles, indicating that the dispersing properties were also retained.     

A novel catalyst of Ni–Mn complex oxides supported on cordierite for catalytic oxidation of toluene at low temperature

The catalytic combustion of toluene over Ni–Mn mixed complex supported on industrial cordierite was investigated. The catalysts were prepared by the wet impregnation method and characterized by using the Brunauer Emmett Teller (BET), Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Transmission Electron Microscope (TEM) and X-ray fluorescence (XRF). The catalytic activity toward the complete oxidation of toluene to CO₂ and H₂O strongly depended on the molar ratio of Ni/Mn, loading amount of Ni–Mn oxides, and calcination temperature. All the results above indicated that the Ni–Mn complex oxide catalyst calcined at 400 °C with 0.5 mol ratio of Ni/Mn, 10 wt.% loading amounts, and showed the highest activity as complete oxidation of toluene.     

Direct conversion of syngas to DME as a green fuel in a high pressure microreactor: Influence of slurry solid content on characteristics and reactivity of washcoated CuO–ZnO–Al2O3/HZSM-5 nanocatalyst

Microchannels of a stainless steel microreactor were successfully washcoated with slurry of Cu–ZnO–Al₂O₃/HZSM-5 (CZAZ) nanocatalyst with different concentrations (10, 20 and 30 wt.%). The properties of nanocatalyst and the washcoated microchannels were investigated by XRD, FESEM, N₂ physisorption, FTIR, EDX-Dot mapping and EDX-Line mapping analysis. The best adherence was observed for 20 wt.% catalyst which has a uniform coating, almost no cracks and homogenous dispersion of copper and zinc. Trend of weight gain during 10 soaks in catalyst slurry was very slow for 10 wt.% but faster for 20 and 30 wt.%. Low amount of weight gain was observed for the last soaks of catalyst slurry in the case of 30 wt.% washcoating. The performance of microreactor with different slurry concentrations were evaluated in direct synthesis of DME at 200–300 °C, 60–150 cm³/min and 40 bar. Regardless of slurry concentration, the microreactor exhibited a better reactivity in comparison to fixed-bed reactor performance. Among three different slurry concentrations, 20 wt.% catalyst slurry revealed the best reactivity in direct DME synthesis. The reduction in reactor performance at higher flow rates was significant in the fixed-bed reactor while microreactor, particularly 20 wt.% washcoated channels, revealed less drastic reduction.     

Measurement and correlation of quaternary solubilities of dihydroxybenzene isomers in supercritical carbon dioxide

The equilibrium quaternary solubilities of dihydroxybenzene (resorcinol + pyrocatechol + hydroquinone + SCCO₂) isomers were experimentally determined at 308, 318 and 328 K over a pressure range of 9.8–15.7 MPa by using a saturation method. The effects of temperature, pressure and the components on each other have been thoroughly investigated. The selectivity of SCCO₂ for ternary (resorcinol + pyrocatechol + SCCO₂) and quaternary systems was discussed. A new model equation for quaternary solubilities of solids has been developed by accounting for non-idealities by combining the solution model with Wilson activity coefficient model. The model equation has five adjustable parameters and correlates the quaternary solubilities of current data along with two other quaternary data reported in the literature.     

Formation of magnesium silicate hydrate (M-S-H) cement pastes using sodium hexametaphosphate

Magnesium silicate hydrate (M-S-H) gel is formed by the reaction of brucite with amorphous silica during sulphate attack in concrete and M-S-H is therefore regarded as having limited cementing properties. The aim of this work was to form M-S-H pastes, characterise the hydration reactions and assess the resulting properties. It is shown that M-S-H pastes can be prepared by reacting magnesium oxide (MgO) and silica fume (SF) at low water to solid ratio using sodium hexametaphosphate (NaHMP) as a dispersant. Characterisation of the hydration reactions by x-ray diffraction and thermogravimetric analysis shows that brucite and M-S-H gel are formed and that for samples containing 60 wt.% SF and 40 wt.% MgO all of the brucites react with SF to form M-S-H gel. These M-S-H cement pastes were found to have compressive strengths in excess of 70 MPa.     

Enhanced production of high octane gasoline blending stock from methanol with improved catalyst life on nano-crystalline ZSM-5 catalyst

Methanol value addition reaction has been studied on lab-synthesized nano-crystalline ZSM-5, Si/Al = 13 (NZ) possessing particle size of ∼29–51 nm and a micro-crystalline ZSM-5 (MZ) of similar atomic ratio is also taken as standard for comparison studies. The NZ sample exhibited excellent catalytic activity to produce 50.7 wt.% of high octane (Research Octane Number = 137) gasoline blending stock rich in desired toluene and xylene components, while the undesired benzene is very low, suitable for fuel applications. The superior performance of NZ to MZ catalyst reflected in three fold increase in gasoline yield and considerably high time-on-stream performance.     

Relationship between surface concentration of amphiphilic quaternary ammonium biocides in electrospun polymer fibers and biocidal activity

Electrospinning was utilized to generate antimicrobial Nylon and polycarbonate fibers for potential applications including self-decontaminating fabrics, wound dressings, and filtration media. The effects of quaternary ammonium salt concentration on fiber morphology, diameter, and antimicrobial activity of the resulting fiber mats were investigated. Fibers were characterized utilizing scanning electron microscopy and X-ray photoelectron spectroscopy, while antimicrobial activity was evaluated against Staphylococcus aureus. The co-electrospinning of soluble quaternary ammonium biocides within polymeric solutions generated uniform fibers with diameters ranging from 91 to 278 nm for Nylon and 0.55–2.34 μm for polycarbonate. Fiber morphology and diameter of the resulting fibers were shown to be dependent on polymer type and biocide concentration. A positive correlation between surface concentration of quaternary ammonium salts and antimicrobial activity was observed as fibers loaded with biocides exhibited up to a 7 log reduction of viable bacteria.     

Heteroatom-doped carbon gels from phenols and heterocyclic aldehydes: Sulfur-doped carbon xerogels

Sulfur-doped carbon xerogels were obtained through carbonization of resorcinol/2-thiophenecarboxaldehyde organic gels. The acid-catalyzed sol–gel polymerization of resorcinol and 2-thiophenecarboxaldehyde leads to organic gels whose morphology and texture is dependent on the amount of catalyst used. As a result, monolithic organic gels with sulfur content of up to 19.6 wt.% and easily tailored properties can be produced. After carbonization, a substantial amount of sulfur is retained and porous carbon xerogels with S-content of up to 10 wt.% are produced (at 800 °C). Depending on the sol–gel synthesis conditions, monolithic S-doped carbon xerogels with controllable and enhanced mesoporosity, surface areas of up to 670 m²/g and enhanced mechanical integrity were obtained. Additional KOH activation of the organic or carbon xerogels enables production of micro–mesoporous carbons with surface areas of up to 2550 m²/g while retaining over 5 wt.% of sulfur. Preliminary CO₂ adsorption measurements were performed. On the basis of resorcinol/2-thiophenecarboxaldehyde gel synthesis a more general approach towards heteroatom-doped carbon gels is proposed: sol–gel polymerization of phenols and heterocyclic aldehydes. Thus a variety of heteroatom-doped porous carbon materials with a tailored pore texture and morphology are available via this procedure.     

Influence of silica fume on the microstructure of cement pastes: New insights from 1H NMR relaxometry

¹H NMR has been used to characterise white Portland cement paste incorporating 10 wt.% of silica fume. Samples were measured sealed throughout the hydration without sample drying. Paste compositions and C–S–H characteristics are calculated based on ¹H NMR signal intensities and relaxation analysis. The results are compared with a similar study of plain white cement paste. While the presence of silica fume has little influence on C–S–H densities, the chemical composition is impacted. After 28 days of sealed hydration, the Ca/(Si + Al) ratio of the C–S–H is 1.33 and the H₂O/(Si + Al) ratio is 1.10 when 10% of silica fume is added to the white cement. A densification of the C–S–H with time is observed. There are no major changes in capillary, C–S–H gel and interlayer pore sizes for the paste containing silica fume compared to the plain white cement paste. However, the gel/interlayer water ratio increases in the silica fume blend.     

Synthesis of organoclays and their application for the adsorption of phenolic compounds from aqueous solution

Organoclays were synthesized by exchanging inorganic cations between layers in Thanh Hoa bentonite using organic cations including benzylhexadecyldimethylammonium (BHDDM⁺), dimethyldioctadecylammonium (DMDOD⁺) and benzylstearyldimethylammonium (BSDM⁺). Inserting organic cations increases material interlayer distance significantly (from 15 Å to 40 Å) and simultaneously enhances affinity of materials toward organic pollutants. The results show that adsorption capacity of organics on organoclays strongly depends on affinity between organic substances and ammonium cations rather than on interlayer distance of organoclays. This means that the sorption of organoclays for organic contaminants was significantly influenced by the nature of the surfactants added to the clay.     

Graphene-supported Pd–Ru nanoparticles with superior methanol electrooxidation activity

Pd–Ru bimetallic nanoparticles dispersed on graphene nanosheets (GNS) have been obtained by a microwave-assisted polyol reduction method and investigated for methanol electrooxidation in 1 M KOH + 1 M CH₃OH at 25 °C. Structural and electrochemical characterizations of electrocatalysts are carried out by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, CO stripping voltammetry and chronoamperometry. The study shows that introduction of Ru (1–10 wt.%) into 40 wt.%Pd/GNS produces an alloy of Pd and Ru with the face centered cubic crystal structure. The electrocatalytic activity increased with increasing percentage of Ru in the Pd–Ru alloy showing maximum with 5 wt.%Ru. The electrocatalytic activity of the 40 wt.%Pd–5 wt.%Ru/GNS electrode at E = −0.10 V vs. Hg/HgO was ∼2.6 times greater than that of the base (40 wt.%Pd/GNS) electrode. Based on the methanol oxidation current, measured at 1 h during the chronoamperometry tests at E = −0.10 V vs. Hg/HgO, the active 40 wt.%Pd–5 wt.%Ru/GNS electrode exhibited ∼72% and ∼675% higher poisoning tolerance as compared to 40%Pd/GNS and 40%Pd/multiwalled carbon nanotube electrodes, respectively.     

Preparation and properties of AlN ceramic suspension for non-aqueous gel casting

A non-aqueous gel casting process based on the mixed solvent (ethanol and polyethylene glycol) and low-toxicity N,N-dimethylacrylamide (DMAA) was developed for an aluminum nitride (AlN) ceramic. In the present work, rheological properties of non-aqueous concentrated AlN suspensions were investigated in the presence of mixed solvent, dispersant, milling time, monomer and solid loading, in order to screen for the most suitable experimental conditions to obtain a good rheological behavior for gel casting. The results showed that the 50 vol% slurry with 0.2 wt% dispersant concentration, 2 h milling time, 6 wt% -monomer content, and a solvent ratio of 3:1, can meet the requirements for the casting process of AlN ceramic slurries. After being dried at 100 °C for 1 h, the optimum bulk density and maximum flexural strength of the AlN green bodies were as high as 1.97 g/cm³ and 18.68 MPa, respectively. SEM photographs revealed that the green body had a relative uniform microstructure when the solid loading was 50 vol%. The shrinkage and deformation of shaped sintered bodies prepared through gel casting were small after sintering. The sintering shrinkage, apparent porosity, bulk density and flexural strength were 14.8%, 0.22%, 3.21 g/cm³ and 310 MPa, respectively.     

Boron carbide green sheet processed by environmental friendly non-aqueous tape casting

An environmental friendly non-aqueous tape casting process for producing boron carbide green sheet has been discussed in the present paper. An ethanol-based formula was developed by using castor oil, single-oleic acid glycerol, polyvinyl butyral and di-n-butyl phthalate as the dispersant, wetting agents, binder and plasticizer, respectively. The influence of binding system on rheological behavior of the slurry was studied. In addition, the effects of drying condition, milling time and binding systems on green sheet were also investigated. The results indicate that the optimal composition of the boron carbide slurry is 47.0 wt.% boron carbide powder with particles size of 3.5 μm, 2.0 wt.% dispersant, 2.0 wt.% wetting agent, 39.0 wt.% EtOH, 5.0 wt.% binder and 5.0 wt.% plasticizer. The green sheet with high-quality can be obtained by the combination of the three-stage milling method and drying process conducted at room temperature without air convection. The density and tensile strength of the boron carbide green sheet are 1.64 ± 0.06 g/cm³ and 2.66 MPa, respectively.     

Synthesis,surface characteristics,and electrochemical capacitance of Cu-doped carbon xerogel microspheres

Small-amplitude oscillatory shear tests were used to determine the rheological properties of a copper acetate-doped resorcinol–formaldehyde mixture at between 30 and 40 °C. The apparent activation energy of the sol–gel transition was 76.6 ± 0.6 kJ/mol. Organic gel microspheres were only obtained when the sol was emulsified immediately before the gelation point and not at the gelation point itself, due to the fast gelation kinetics of the copper acetate-doped resorcinol–formaldehyde mixture. The microspherical shape was preserved after carbonization. Cu-doped carbon xerogel microspheres were steam-activated at 840 °C. All samples comprised isolated well-formed microspheres, whose size increased with higher degree of activation. The surface area and porosity varied with the activation degree. Copper was detected as CuO, which acted as gasification catalyst during activation, and its size increased with higher activation degree. Electrochemical measurements were conducted with a three-electrode cell in 1 M H₂SO₄. A very large volumetric capacitance, 146 F/cm³, was found for the 30%-activated Cu-doped activated carbon xerogel, attributable to the high particle density resulting from the very compact packing of the microspheres. This sample also showed the lowest equivalent series resistance, due to its pore texture and high surface Cu content.     

Evaluation of the role of an ionic liquid as organophilization agent into montmorillonite for NBR rubber nanocomposite production

In this work we have shown the preparation of montmorillonite (Na + Mt) co-intercalated with a quaternary ammonium salt (hexadecyltrimethylammonium — HDTMA) and an ionic liquid (IL) (1-methyl-3-octylimidazolium bis(trifluoromethanesulfonyl)imide — OMImTf₂N) using a mechanochemical process. Changes in the structure of the organophilized montmorillonite were characterized using X-ray diffraction (XRD), thermal gravimetry (TG), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The presence of both cations (HDTMA and OMIm) into the clay mineral layers was confirmed by FTIR. XRD studies support that the co-intercalation process of the IL cation is more easily established in phases in which the interlayer space is not totally packed with HDTMA and an additional order in ionic liquid phase was observed when the IL amount exceeds 15 mass%. The addition of IL induced a thermal stability gain of 90 °C in comparison with the ammonium treated montmorillonite. The incorporation of IL in the ammonium based organoclays also displayed their better compatibility with the elastomeric matrix (NBR). Morphology studies by SEM of cryofractured surfaces evidence an improved interface interaction between the clay mineral and elastomer, indicating that ionic liquid has a direct and pronounced effect on the final clay polymer nanocomposites. This result can be assigned to the covered clay mineral particles mainly for higher IL content.     

Synthesis and swelling properties of poly[acrylamide-co-(crotonic acid)] superabsorbents

Superabsorbent polymers of acrylamide (AAm)/crotonic acid (CA) were synthesized by foamed polymerization in an aqueous solution of AAm with CA as a comonomer, initiated by an initiator couple of ammonium persulfate and N,N,N′N′-tetramethylethylenediamine. A crosslinking agent N,N′-methylenebisacrylamide, a foaming agent sodium bicarbonate, and a foam stabilizer, a triblock copolymer of polyoxyethylene/polyoxypropylene/polyoxyethylene, were used in the polymerization. The influences of the relative contents of CA, crosslinking agent, and initiator, on the swelling properties of the superabsorbent polymer systems were examined. The superabsorbent polymer synthesized with an AAm/CA ratio of 98:2 by mole, 0.5 wt.% of N,N′-methylenebisacrylamide and 1 wt.% of ammonium persulfate at 250 rpm and 50 °C for 30 min of polymerization time produced the highest water absorption of 211 ± 9 times its dried weight and could absorb water up to 162 ± 4 g g⁻¹ of the dry copolymer within 10 min. The electrochemical reaction for acrylamide–crotonic acid polymerization was investigated by cyclic voltammetry. The anodic current indicated that acrylamide acting as an electron donor whereas crotonic acid performed as an electron receiver, then providing the cathodic current. The diffusion of water into the superabsorbent polymer was non-Fickian (case II and anomalous). Acrylamide–crotonic acid superabsorbents containing various crosslinker concentrations had a water swelling in the range of 79–289 g g⁻¹. The diffusion coefficients varied between 6.9 × 10⁻⁹ and 5.1 × 10⁻⁸ cm² s⁻¹. Adsorption of the basic dye by the superabsorbent was a monolayer evaluated by the Langmuir isotherm. The superabsorbents can thus be used to adsorb cationic dyes in textile industry.