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.     

Formation and transition of calcium aluminate and calcium silicate compounds from pre-synthesized mullite in low-calcium system by solid-state reaction

The formation and transition of calcium aluminate and calcium silicate compounds from pre-synthesized mullite in low-calcium system were systematically studied by solid-state reaction at 1350–1500 °C using XRF, XRD, FTIR, SEM and PSD methods. Ca₃Al₂O₆, Ca₁₂Al₁₄O₃₃, CaAl₂O₄, Ca₂SiO₄ and Ca₂Al₂SiO₇ can form via direct reaction of mullite with CaO at the beginning of the reactions, then Ca₁₂Al₁₄O₃₃ and Ca₃Al₂O₆ react with mullite to form CaAl₂O₄ and Ca₂SiO₄, and finally Ca₂Al₂SiO₇ reacts with CaO to generate Ca₂SiO₄ and calcium aluminate compounds as the sintering process proceeds. Elevating the sintering temperature is in favor of the formation of Ca₁₂Al₁₄O₃₃, Ca₃Al₂O₆ and Ca₂Al₂SiO₇ at the initial reaction stage, but Ca₂Al₂SiO₇ cannot totally transform to calcium silicate and calcium aluminate compounds in the low-calcium system, which deteriorates the pulverization performance of the final products. Increasing the calcium dosage accelerates the transformation of Ca₂Al₂SiO₇ to Ca₁₂Al₁₄O₃₃, CaAl₂O₄ and Ca₂SiO₄, which enhances the pulverization performance. If the CaO/Al₂O₃ molar ratio exceeds 1.4, Ca₃Al₂O₆ will generate by the reactions of pre-formed CaAl₂O₄ and Ca₁₂Al₁₄O₃₃ with excessive CaO.     

Synthesis,characterization, and properties of PCDL aliphatic hyperbranched polyurethane coatings

The isocyanate‐terminated polyurethane pre‐polymer (PPU) was synthesized via the step‐growth polymerization approach by using polycarbonate diol (PCDL, Mn = 2000) and isophorone disocyanate (IPDI) as monomers, dibutyltin dilaurate (DBTDL) as the catalyst. Subsequently, the hyperbranched polyurethane (HBPU) was synthesized by graft copolymerization using PPU, hyperbranched poly(amide–ester) polyol (HPAE) and 1,4‐butanediol (BDO). The molecular structure of HBPU was characterized by means of FTIR, ¹H‐NMR, and ¹³C‐NMR. It was observed that HBPU was synthesized as anticipated. The thermal and mechanical properties, the microstructure, and morphologies of the filmed HBPU and LPU (linear polyurethane) were tested, respectively. The filmed HBPU, revealed better thermal stability, and higher T_g accompanied with lower viscosity than those of filmed LPU. Additionally, the mechanical experiment showed that the filmed HBPU exhibited enhanced mechanical properties because it contained certain amounts of HPAE. Compared with its linear analog (LPU) specimen, the tensile strength of the filmed HBPU containing 10 wt % HPAE increased by 1.9 times (up to 28.15 MPa), and its elongation at break increased by 1.5 times (up to 543.8%), resulting from the dual effects of the hydrogen bonding and the crosslinking density in the HBPU system. The morphologies of filmed HBPU were characterized by means of WAXD and SEM, which indicated that increasing the content of HPAE lowers the crystallinity of HBPU. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2671–2679, 2013     

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.     

Influence of sodium silicate amount on the setting time and EXO temperature of a complex binder consisting of high-aluminate cement, liquid glass and metallurgical slag

The influence of sodium silicate amount on the setting time and EXO temperature of a complex binder (CB) consisting of high-aluminate cement (HAC), liquid glass and metallurgical slag (MS) has been investigated. Two maximums were observed on exothermal curves during the hydration process of CB, in which sodium silicate quantity was >4%. The first maximum of exothermic temperature occurred due to the reaction proceeding between sodium silicate and the slag. The second maximum of the exothermal effect was observed after the final set in the already hardened CB, and it was accompanied by the hydration of HAC, the degree of which depended on the sodium silicate amount in CB.     

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 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.     

Reactions of fly ash with calcium aluminate cement and calcium sulphate

The hydration processes in the ternary system fly ash/calcium aluminate cement/calcium sulphate (FA/CAC/C$) at 20 °C were investigated; six compositions from the ternary system FA/CAC/C$ were selected for this study. The nature of the reaction products in these pastes were analysed by X-ray diffraction (XRD) and infrared spectroscopy (FTIR). At four days reaction time, the main hydration reaction product in these pastes was ettringite and the samples with major initial CAC presented minor ettringite but calcium aluminates hydrates. The amount of ettringite developed in the systems has no direct relation with the initial components.     

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 and characterization of biodegradable aliphatic copolyesters with poly(tetramethylene oxide) soft segments

A series of aliphatic poly(ether–ester)s based on flexible poly(tetramethylene oxide) (PTMO) and hard poly (butylene succinate) (PBS) segments were synthesized by the catalyzed two‐step transesterification reaction of dimethyl succinate, 1,4‐butanediol, and α,ω‐hydroxy‐terminated PTMO (M_n = 1000 g/mol) in the bulk. The content of soft PTMO segments in the polymer chains was varied from 10 to 50 mass %. The effect of the introduction of the soft segments on the structure, thermal, and physical properties, as well as on the biodegradation properties was investigated. The composition and structure of the aliphatic segmented copolyesters were determined by ¹H NMR spectroscopy. The molecular weights of the polyesters were verified by viscometry of dilute solutions and polymer melts. The thermal properties were investigated using DSC. The degree of crystallinity was determined by means of DSC and WAXS. Biodegradation of the synthesized copolyesters, estimated in enzymatic degradation tests on polymer films in phosphate buffer solution with Candida rugosa lipase at 37°C, was compared with hydrolytic degradation in the buffer solution. Viscosity measurements confirmed that there was no change in molecular weight of the copolyesters leading to the conclusion that the degradation mechanism of poly(ester–ether)s based on PTMO segments occurs through the surface erosion. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Synthesis and characterization of novel borosiloxane‐containing aromatic copolyimides with excellent thermal stability and low coefficient of thermal expansion

The properties of borosiloxane‐containing copolyimides with borosiloxane in the main chain and in the side chain were studied. Two series of borosiloxane‐containing copolyimides were synthesized by the reaction of 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (s‐BPDA ) and 2,3′,3,4′‐biphenyltetracarboxylic dianhydride (a‐BPDA ) with p ‐phenylenediamine (PDA ), 4,4′‐oxydialinine (4,4′‐ODA ) and different borosiloxane diamine monomers (BSiAs ). The synthesized borosiloxane‐containing copolyimides exhibited better solubility than borosiloxane‐free copolyimides and showed high glass transition temperatures (320–360 °C), excellent thermal stability (570–620 °C for T ₁₀), great elongation at break (10% ? 14%) and a low coefficient of thermal expansion (14–24 ppm °C^?1). More specifically, the copolyimides containing BSiA‐2 formed nano‐scale protrusions and the copolyimides containing BSiA‐1 formed micro‐scale protrusions. The contact angles of the copolyimides increased from 72° for neat copolyimide to 96° for 5% of borosiloxane in the main chain of the copolymer up to 107° for 10% of borosiloxane in the side chain of the copolymer. © 2017 Society of Chemical Industry     

Synthesis and crystal structure solution of potassium dawsonite: An intermediate compound in the alkaline hydrolysis of calcium aluminate cements

Potassium dawsonite is formed as an intermediate compound during the alkaline hydrolysis (AH) in calcium aluminate cements (CACs). A synthesis method of potassium dawsonite has been developed. The crystal structure of potassium dawsonite KAl(CO₃)(OH)₂ has been solved by direct methods from X-ray powder diffraction data and refined with the Rietveld method. It crystallises in the orthorhombic Cmcm space group with unit cells parameters a=6.3021(3) Å, b=11.9626(5) Å, c=5.6456(3) Å and Z=4. The structure consists of carboaluminate chains, formed by the basic unit [Al₂(OH)₄(CO₃)₂]²⁻ arranged along the c axis. The carbonate groups are placed in an alternate manner at both sides of the carboaluminate chains. The carboaluminate chains are also held together by the K⁺ cations that are located in the middle of three such chains. Finally, the chemical reactions explaining the AH process in CACs are postulated.     

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.     

Lightweight bricks made of diatomaceous earth,lime and gypsum

Diatomaceous earth from Lampang Province in the north of Thailand composes of diatom, kaolinite, montmorillonite and illite, and has porous cellular structure. In this work, the diatomite, hydrated lime and gypsum are the main ingredients in making autoclaved lightweight bricks. Water content, pre-curing period, lime content, gypsum content and calcined temperature are the factors investigated. Mechanical and thermal properties are used to indicate their quality. The nature of hydration products and morphological characteristics of the lightweight bricks are also investigated.