Synthesis and characterization of calcium aluminate compounds from gehlenite by high-temperature solid-state reaction

The mineral transition mechanism and self-pulverization property of the sintered products in the Ca₂Al₂SiO₇-CaO system were systematically studied using pre-synthesized gehlenite determined by XRD, SEM, FTIR and particle size analyses. The minerals of Ca₁₂Al₁₄O₃₃, CaAl₂O₄, Ca₃SiO₅ and Ca₂SiO₄ are formed by the direct reactions of Ca₂Al₂SiO₇ with CaO. CaAl₂O₄ reacts with CaO to form Ca₁₂Al₁₄O₃₃ or Ca₃Al₂O₆, while Ca₃SiO₅ reacts with Ca₂Al₂SiO₇ to form Ca₂SiO₄ and calcium aluminate compounds. The sintered products mainly contain CaAl₂O₄, Ca₁₂Al₁₄O₃₃ and Ca₂SiO₄ at 1350?°C or above 1500?°C when the molar ratio of CaO to Al₂O₃ is 1.0. Increasing the sintering duration or the CaO consumption promotes the transition of Ca₂Al₂SiO₇ to Ca₂SiO₄ and calcium aluminate compounds when sintered at 1350?°C, which accordingly improves the self-pulverization property of the sintered products. The formed minerals of Ca₁₂Al₁₄O₃₃, CaAl₂O₄ and Ca₂SiO₄ transform into Ca₂Al₂SiO₇ again when the sintering temperature is between 1400?°C and 1450?°C, and the corresponding self-pulverization property of the sintered products deteriorates sharply.     

Al2O3-MgO refractory castables with enhanced explosion resistance due to in situ formation of phases with lamellar structure

This work evaluated an alternative route (formic acid addition and in situ generation of hydrotalcite phases) to reduce the explosion trend of dense MgO-bonded refractory castables during their drying step. Aqueous suspensions containing different magnesia sources (caustic or dead-burnt) and hydratable alumina were firstly analyzed in order to identify the likelihood of generating these in situ compounds with a lamellar structure in mixtures prepared with and without formic acid (hydrating agent). After that, high-alumina vibratable castables containing MgO and this carboxylic acid were evaluated and the following experimental tests were carried out: thermogravimetry, mechanical strength evaluation, apparent porosity and hot elastic modulus measurements. According to the obtained results, the thermal decomposition of the formed hydrotalcite-like phases led to samples’ mass loss over a broader temperature range, preventing their explosion even when a critical heating rate (20?°C?min^?1) was applied during the tests. Besides that, no deleterious effect to the refractories’ mechanical properties were observed during firing (i.e. softening at high temperatures). Thus, the addition of formic acid and the in situ formation of hydrotalcite-like phases is suggested as an alternative route to the conventional incorporation of amorphous silica or polymeric fibers into the castable dry-mixes to prevent the explosion of MgO-bonded refractories.     

Synthesis and microstructural characterization of nano-size calcium phosphates with different stoichiometry

Calcium phosphates with Ca/P molar ratios of 0.5, 0.75, 1.33, 1.5, 1.55, 1.67, 2.0, and 2.5 were synthesized by a wet chemistry precipitation method and sintered at 500 °C, 700 °C, 900 °C, 1100 °C and 1300 °C for 2 h. Presence of phases and microstructures of calcium phosphates were determined by X-ray diffraction and scanning electron microscopy. In all different Ca/P ratios, the precipitated phase was always hydroxyapatite with very small size and/or partial disorderness regardless of the Ca/P ratios in the starting precipitating medium. For samples with 0.5 and 0.75 Ca/P ratios in starting solution, tricalcium phosphate and calcium pyrophosphate phases were observed. In contrast, for samples with 1.0 and 1.33 Ca/P ratios, the only stable phase was tricalcium phosphate. For the samples with Ca/P ratio of 1.5, the tricalcium phosphate phase was dominant. However, small amounts of hydroxyapatite started to appear. For samples with Ca/P ratio of 1.67, the hydroxyapatite phase was dominant. Lastly, for samples with the Ca/P ratios of 2.0 and 2.5, the CaO phase started to appear in addition to the hydroxyapatite phase which was the dominant phase. Moreover, the average grain size, porosity (%) and the average pore size decreased with increasing the Ca/P ratios.     

Manganese oxide hollow structures with different phases: Synthesis, characterization and catalytic application

Manganese oxide hollow structures with different phases were synthesized by calcination using a γ-MnO₂ hollow structure as a precursor. Our results revealed that the as-synthesized β-MnO₂ and Mn₂O₃ still maintained the morphology of the precursor. Compared with the MnO₂ reported and conventional MnO₂, both the γ-MnO₂ and β-MnO₂ hollow structures showed a higher catalytic activity and an excellent selectivity in the aerobic oxidation of cinnamyl alcohol to cinnamyl aldehyde. The TPR experiments demonstrated that the reduced size of crystallite, hollow nature and higher BET specific surface area were responsible for their higher catalytic activity.     

Synthesis and characterization of the atomic laminate Mn2AlB2

Herein, we synthesize dense, predominantly single-phase polycrystalline samples of the Mn₂AlB₂ ternary compound, using reactive hot-pressing of manganese, aluminum, and boron powder mixtures under vacuum. With a Vickers hardness of 8.7?GPa, Mn₂AlB₂ is relatively soft for a transition metal boride and lacked dominant cracks at the corners of the indentations. With Young’s and shear moduli of 243?GPa and 102?GPa at 300?K, respectively, it is reasonably stiff. The Poisson’s ratio is calculated to be 0.19. With compressive strengths of 1.24?±?0.1?GPa, the samples were quite strong considering the grain size (1–15?μm). The electrical resistivity at 300?K was ～5 μΩm and decreased linearly upon cooling. At 0.0036?K^?1, the temperature coefficient of resistivity was relatively high compared to MoAlB. The average linear thermal expansion coefficient was also found to be relatively high at 18.6?×?10^-6?K^?1 from 298 to 1173?K. Mn₂AlB₂ was not thermally stable above ～1379?K. While Mn₂AlB₂ was not machinable with conventional tooling, intriguingly, high-speed carbide tools bits readily penetrate the surface – with no cracking or chipping for a few millimeters – before stopping.     

Synthesis and characterization of polyelectrolyte hydrogels with controlled swelling behaviour

Copolymerization of sulfopropyl methacrylate potassium salt (K‐SPMA) and 2‐acrylamido‐2‐methyl propane sulfonic acid (AMPS) has been studied in the range 10–90% K‐SPMA in the feedstock. The reactivity ratios have been determined for K‐SPMA/AMPS copolymers. The copolymer compositions, utilized for determining the reactivity ratio, have been determined from nitrogen content. Crosslinked poly(AMPS) and K‐SPMA/AMPS copolymers were prepared in water in the presence of potassium persulfate as initiator and N,N‐methylene bisacrylamide (MBA) as tetrafunctional crosslinker. Irradiation of K‐SPMA and AMPS with an electron‐beam was carried out at 50 wt% aqueous solution with low pH and irradiation dose 40–120 kGy. The swelling behaviour of highly crosslinked K‐SPMA/AMPS copolymer polyelectrolyte gels in aqueous medium was studied in the presence of different types of salts. The crosslink density, the average molecular weight between the crosslinks and the dissociation constant (pK_a) of the crosslinked polymer were determined from stress–strain measurements. © 2001 Society of Chemical Industry     

Synthesis and characterization of polyethylene-like polyurethanes derived from long-chain, aliphatic α,ω-diols

Long-chain aliphatic α,ω-diols containing up to 32 consecutive methylene groups were synthesized by several methods and characterized. 1,22-Docosanediol HO-(CH₂)₂₂-OH and 1,32-dotriacontanediol HO-(CH₂)₃₂-OH both exhibited a solid-solid phase transition before melting. The α,ω-diols HO-(CH₂)_m-OH, where m=12, 22, or 32, were reacted in the melt with much shorter aliphatic α,ω-diisocyanates OCN-(CH₂)_n-NCO, where n=4, 6, 8, or 12, producing a series of linear, aliphatic, and increasingly polyethylene-like m,n-polyurethanes. Characterization (by DSC, TGA, and SAXS) of the m,n-polyurethane series showed that when the aliphatic segments were increased, and the hydrogen-bonding densities thus decreased, the polymers displayed physical and thermal properties (for example, solubility and melting temperature) typical of polyethylene.     

Synthesis and physical properties of (Zr1−x,Tix)3AlC2 MAX phases

MAX phase solid solutions physical and mechanical properties may be tuned via changes in composition, giving them a range of possible technical applications. In the present study, we extend the MAX phase family by synthesizing (Zr_1?xTi_x)₃AlC₂ quaternary MAX phases and investigating their mechanical properties using density functional theory (DFT). The experimentally determined lattice parameters are in good agreement with the lattice parameters derived by DFT and deviate <0.5% from Vegard's law. Ti₃AlC₂ has a higher Vickers hardness as compared to Zr₃AlC₂, in agreement with the available experimental data.     

Synthesis, characterization and photocross-linking of copolymers of furan and aliphatic hydroxyethylesters prepared by transesterification

Mild experimental conditions were applied to the synthesis of furan-aliphatic photoreactive copolymers by bulk transesterification, which called upon potassium carbonate as the catalyst, reaction times of about 30 h and temperatures ranging from 95 to 120 °C. The ensuing copolymers contained 3-10% of furan photoreactive monomer units, which absorbed at 308 nm, and had molecular weights of about 8000. They were semi-crystalline materials with glass transition temperatures of −51 to −62 °C and were stable up to 225 °C. The irradiation in the near-UV of concentrated solutions or thin films of these copolymers resulted in their cross-linking and suggested their possible use as photoresists, particularly in offset printing plates.     

Synthesis and characterization of hyperbranched polyethylenes containing cross-linking structures by chain walking copolymerization of ethylene with diacrylate comonomer

We report the synthesis of higher-molecular-weight hyperbranched polyethylenes containing cross-linking structures via chain walking copolymerization of ethylene with a diacrylate cross-linker, 1,4-butanediol diacrylate, using a Pd-diimine catalyst, [(ArNC(Me)-(Me)CNAr)Pd(CH₃)(NCMe)]SbF₆ (Ar = 2,6-(iPr)₂C₆H₃). The hyperbranched chain topology of these polymers was achieved through the chain walking mechanism of the Pd-diimine catalyst. By controlling the diacrylate feed concentration in the polymerization system, three sets of hyperbranched polyethylenes having various cross-linking levels (including both intermolecular and intramolecular cross-linking) but without macrogelation were synthesized at three different temperatures, 15, 25, and 35 °C, respectively. The diacrylate content and cross-linking density in the copolymers were found to increase with the enhancements of diacrylate feed concentration and polymerization temperature. Triple-detection gel permeation chromatography (GPC) measurements confirmed the significant enhancement of polymer average molecular weight and broadening in molecular weight distribution with an increase of diacrylate feed concentration as a result of intermolecular cross-linking. The chain topology of the copolymers becomes more compact, compared to homopolymers, due to the presence of intermolecular cross-linking. Rheological studies show that the copolymers possess characteristic rheological properties typically found in polymers containing intermolecular cross-linking. Our results also indicate qualitatively the presence of intramolecular cross-linking in these hyperbranched copolymers, particularly in those synthesized at 35 °C, probably due to their highly compact chain topologies. This work demonstrates the capability of chain walking polymerization for synthesis of hyperbranched polyethylenes of enhanced molecular weights with the simple use of diacrylate as a cross-linker.     

Synthesis, characterization and electrocatalytic behaviour of non-alloyed PtCr methanol tolerant nanoelectrocatalysts for the oxygen reduction reaction (ORR)

In order to point out the effect of the second metal in platinum-based catalysts, a synthesis method by colloidal route derived from that of Bönnemann was used to prepare non-alloyed Pt_1−xCr_x/C electrocatalysts active towards the oxygen reduction reaction (ORR). The non-alloyed character of the catalysts was showed by XRD analysis. The Pt/Cr electrocatalyst having an nominal atomic ratio, as determined by EDX then corresponding to bulk composition and not surface composition, close to (0.8:0.2) showed higher activity for ORR in methanol-free oxygen saturated electrolyte, whereas the catalyst having an atomic ratio of (0.7:0.3) displayed higher activity for ORR at low overpotentials in saturated oxygen electrolyte containing 0.1 M methanol.Correlation of XRD and electrochemical results allows us to point out the effect of electronic interactions in catalyst activity towards ORR. It was also shown that adding chromium to platinum does not alter the reaction mechanism of oxygen reduction, and that in presence of low methanol concentration, the ORR occurs via the four-electron process according to the same mechanism as in methanol-free solution.     

Synthesis,characterization and in-vitro biocompatibility of electrophoretic deposited europium-doped calcium silicate on titanium substrate

Europium (Eu) has attracted attention to be incorporated as biologically active ions to achieve different biological and functional properties of biomaterials. In this study, calcium silicate (CS) coatings doped with different amount of Eu (up to 10 mol%) were successfully formed on titanium substrates via electrophoretic deposition. A low amount of Eu (2.5 mol%) gave a relatively denser coating and improved coating adhesion strength (～3.3 N). All Eu–CS coatings provided good apatite forming ability, yet lower degradation rate, as compared to CS coating. Moreover, it was observed that the human fetal osteoblast (hFOB) cells could attach and proliferate on all Eu–CS coatings, suggesting their biocompatible nature. Eu2.5CS not only showed comparable cell proliferation with CS, but also enhanced the osteogenic activity of the CS coating. All results suggested that Eu2.5CS coatings are promising coating materials for biomedical implants, particularly bone tissue engineering applications.     

Study of hydrated phases present in a MK-lime system cured at 60 °C and 60 months of reaction

This research presents the experimental results of a study carried out to determine the effect of curing temperature on the reaction kinetics in a metakaolin/lime mixture cured at 60 °C and after 60 months of hydration. The stabilities of hydrated phases formed during the pozzolanic reaction in these working conditions were evaluated. The results obtained in current paper showed that metastable hexagonal phases (C₂ASH₈ and probably C₄AH₁₃) coexist with stable cubic phase (hydrogarnet) in the absence of lime. Also, there is evidence of the possible presence of a calcium aluminum silicate hydroxide hydrate (vertumnite).     

Synthesis, characterization and hydrolysis of an aliphatic polycarbonate by terpolymerization of carbon dioxide, propylene oxide and maleic anhydride

Terpolymerization of propylene oxide (PO), carbon dioxide (CO₂) and maleic anhydride (MA) was carried out by using a polymer-supported bimetallic complex (PBM) as a catalyst. A degradable aliphatic poly(propylene carbonate maleate) (PPCM) was synthesized, and determined by FT-IR, ¹H NMR, ¹³C NMR, DSC, TGA and WAXD measurements. The influences of various reaction conditions such as molar ratio of the monomers, reaction time and reaction temperature on the terpolymerization progress were investigated. The results showed that MA was inserted into the backbone of CO₂–PO successfully. The viscosity, glass transition temperature and decomposition temperature of the terpolymers were much higher than those of poly(propylene carbonate) (PPC). Because of the existence of the MA ester unit, PPCM had stronger degradability than PPC in a pH 7.4 phosphate-buffered solution. MA offered an ester structural unit that gave the terpolymers remarkable degradability. And the degradation rate of the backbone increased with the insertion of MA into the terpolymers.     

Synthesis and characterization of polyesteramides having short Nylon-6 segments in the main chains through polycondensation and chain extension

A Nylon-6 oligomer (PrePA) was synthesized by ring-opening polymerization from ε-caprolactam with 2-amino-ethanol under the catalysis of H₃PO₃. Polyesteramide prepolymers (PrePEAs) having amide content from 10 to 60 mol% were prepared through melt polycondensation from adipic acid, 1,4-butanediol and the PrePA. Chain extension of PrePEAs was carried out at 200 °C using 2,2′-(1,4-phenylene)-bis(2-oxazoline) and carbonylbiscaprolactamate as combined chain extenders. The chain-extended polyesteramides (ExtPEAs) with intrinsic viscosity up to 0.61 dL/g were synthesized. The ExtPEAs were characterized by FT-IR and ¹H NMR spectra, differential scanning calorimetry, wide angle X-ray scattering, thermogravimetric analysis and tensile test. The results showed that the ExtPEAs mainly crystallized in the Nylon-6 crystallites. ExtPEAs had T_g from −46.71 to 4.28 °C, T_m from 106.69 to 139.92 °C, thermal stability with initial decomposition temperature over 339 °C, tensile strength up to 30.89 MPa and stain at break higher than 797.1%. These ExtPEAs were strong, thermally stable and tough thermoplastic polymers.     

Synthesis of Y(Al,Cr)O3 red pigments by co-precipitation method and their interactions with glazes

New red pigment based on the system YAl_1−yCr_yO₃ (y = 0.01–0.1) was synthesized by co-precipitation method. The precipitant was attained by mixing solutions of yttrium, aluminum and chromium nitrates, respectively, and addition of ammonia as the precipitator. The effects of chromium as dopant and glaze composition on the color shade of resulting pigments were studied. EDX analysis of the prepared pigment particles, which was embedded in glaze, showed the occurrence of reactions between some glaze constituents and pigment particles. Accordingly, a glaze which was enriched in Al₂O₃ and poor in ZnO was more suitable in point of achieving a reddish shade. The resulting pigments were characterized by using X-ray diffraction (XRD), SEM and UV–vis spectrophotometer.     

Synthesis of Magnesium Aluminate Spinel-corundum Composite with Waste Slide Plate and Magnesia Carbon Brick

Magnesium aluminate spinel-corundum composite was prepared with waste slide plate and magnesia carbon brick. Microstructure and sintering ability of as-prepared magnesium aluminate spinel-corundum composite were investigated with XRD, SEM, and DSC/TG. With the addition of waste slide plate increasing or synthesis temperature rising, the bulk density of the specimen increases and the apparent porosity decreases, but the crystallinity of the specimen decreases and the magnesium aluminate spinel phase increase...     

Gluconate action in the hydration of calcium aluminate cements: Theoretical study,processing of aqueous suspensions and hydration reactivation

Considering the production of stable CAC aqueous suspensions, this work addressed the action of gluconate anion as a Ca²⁺ complexing agent and retarder of CAC hydration. Using quantum simulations, the complexation energy of gluconate complexes was calculated. The pH range of stability for the complexes was estimated and aqueous suspensions containing CAC and sodium gluconate (NaG), stable up to 4 days at room temperature, were prepared. Afterwards, their hydration reactions were reactivated by adjusting the systems’ pH. Results of solidification kinetics and mineralogical characterisation highlighted that, after reactivation, calcium aluminate hydrates were formed. Thermodynamics simulations indicated that using NaG up to 1 wt% would not be deleterious to the systems refractoriness up to 1700 °C. These systems could be applied in less explored processing routes for CAC-based refractory compositions (e.g. slip casting, direct foaming and additive manufacturing), resulting in innovations to produce advanced refractory ceramics.     

Synthesis,Surface and Interfacial Properties of Dodecyl Diphenyl Oxide Disulfonate with Different Counterions

Dodecyl diphenyl oxide disulfonate with different counterions (C₁₂MADS‐M, M = Na, Mg, Ca) were synthesized using dodecyl alcohol, diphenyl oxide and SO₃ as reagents through alkylation–sulfonation–neutralization. The structure of the product was characterized by infrared spectroscopy and electrospray ionization‐mass spectrometry. The surface and interfacial prosperities were investigated. The critical micelle concentration (CMC) of C₁₂MADS‐Na, C₁₂MADS‐Mg and C₁₂MADS‐Ca was 1.23 × 10^?3, 5.25 × 10^?4 and 5.37 × 10^?4 mol/L, respectively. The surface tension at CMC (γ_CMC) of C₁₂MADS‐Na, C₁₂MADS‐Mg and C₁₂MADS‐Ca was 43.2, 37.1 and 36.6 mN/m, respectively. Interfacial tensions between crude oil and C₁₂MADS‐M aqueous solution gave only a small change in the calcium chloride concentrations ranging from 50 to 10,000 mg/L.     

Synthesis and characterization of amphiphilic functional polyesters by ring-opening polymerization and click reaction

During this work we have prepared novel amphiphilic graft-block (PαN₃CL-g-alkyne)-b-PCL functional polyesters, comprising poly(α-azido-ε-caprolactone-graft-alkyne) (PαN₃CL-g-alkyne) as the hydrophilic segment and poly(ε-caprolactone) (PCL) as the hydrophobic segment, by ring-opening polymerization of ε-caprolactone (ε-CL) with hydroxyl-terminated macroinitiator PαClCL, substituting pendent chloride with sodium azide. The copolymers were subsequently used for grafting of 2-propynyl-terminal alkyne moieties by the Cu(I)-catalyzed Huisgen’s 1,3-dipolar cycloaddition, thus producing a “click” reaction. ¹H NMR, FT-IR, GPC, and differential scanning calorimetry (DSC) examined the characteristics of the copolymers. Grafting of PMEs or PMPEGs onto the PαN₃CL-b-PCL caused these amphiphilic copolymers to self-assemble into micelles in the aqueous phase. Fluorescence, dynamic light scattering (DLS) and transmission electron microscopy (TEM) then examined these micelles. The critical micelle concentration (CMC) ranged from 8.2 mg L⁻¹ to 39.8 mg L⁻¹ at 25 °C and the average micelle size ranged from 140 to 230 nm. The hydrophilicity and length of the hydrophilic segment influenced micelle stability. The current study describes the drug entrapment efficiency and drug loading content of the micelles, dependent on the composition of graft-block polymers. The results from in vitro cell viability assays indicated that (PαN₃CL-g-alkyne)-b-PCL shows low cytotoxicity.