On the Promotion of Ag/γ-Al2O3 by Cs for the SCR of NO by C3H6

The promotion of Ag/-Al₂O₃ by adding alkali metals (Li, Na, K, Cs) for selective catalytic reduction of NO with C₃H₆ was studied in this work. The activity of NO reduction was enhanced by addition of Cs to Ag/-Al₂O₃ in the presence of excess oxygen and SO₂. The stability and growth of silver oxide particles were promoted and the dispersion of silver particles on -Al₂O₃ was improved by the addition of 0.5 wt% Cs and 1 wt% Cs to 2 wt% Ag/-Al₂O₃, respectively. The results were confirmed by H₂ TPR, UV-Vis DRS, TEM, and XPS.     

Influence of iron content on the color of the C3A–Fe2O3 system synthesized under different conditions of temperature,atmosphere and cooling

The 3CaO·Al₂O₃–Fe₂O₃ (C₃A–Fe₂O₃) system is important for the production of white clinker. In the present study this system was examined from the perspective of improving the sustainability of the production process. Microstructural evaluation was employed to explain the changes in color caused by variation of: iron content; temperature; type of atmosphere; and cooling conditions. It was found that color was more significantly affected by the iron content, temperature and type of atmosphere than by the type of cooling used. It was also observed that the utility of iron-rich raw materials could be maximized by understanding and enhancing the solubility of Fe₂O₃ in C₃A. It was found that a 2 wt.% Fe₂O₃ solid solution was stable only under kiln open to atmospheric conditions and remained clear at temperatures up to 1370 °C. However, the same 2 wt.% Fe₂O₃ solid solution suffered a significant change in color when the temperature rose to 1400 °C. Mössbauer spectroscopy showed that the oxidation state of Fe was Fe³⁺, which did not change between 1370 and 1400 °C; however, a structural change in the C₃A–Fe₂O₃ solid solution was detected as a result of the alteration of the thermal treatment. The distinction between the structures at these two temperatures was that at 1370 °C, all of the Fe³⁺ had a tetrahedral coordination, while at 1400 °C, 19 wt.% of the Fe³⁺ appeared in octahedral sites, a result that was corroborated by Rietveld analysis.     

Spontaneous nucleation of diamond in the system MgCO3–CaCO3–C at 7.7 GPa

High-pressure and high-temperature experiments were carried out to determine the minimum temperature required for spontaneous nucleation of diamond in the system comprising a carbonate mixture (60 mol% MgCO₃ and 40 mol% CaCO₃) and graphite at 7.7 GPa, for 1 h and longer reaction times up to 12.5 h, and also in the systems MgCO₃–graphite and CaCO₃–graphite for comparison. The above carbonate mixture melted at a temperature between 1600°C and 1700°C. The minimum temperature for spontaneous nucleation of diamond was 1900°C for a reaction time of 1 h; it was lowered to 1700°C for 11 h, but no diamond was formed at 1600°C for 12.5 h. These results indicate that the molten state of the solvent-catalyst and enough reaction time are necessary for diamond nucleation in the systems examined at 7.7 GPa.     

Effects of a low amount of C on the phase transformations in the AlN–Al2O3 pseudo-binary system

The effects of a low amount of C on the phase transformations in the AlN–Al₂O₃ pseudo-binary system are reported in samples having an AlN content in mol% ranging between 44 and about 0. Various complementary experimental techniques were used to determine the nature of the phase equilibria. Carbon is embedded in the components of three eutectics as a function of the average chemical composition of the sample in AlN. In two of them, a component belonging to the quaternary system Al–O–N–C and having a wide composition range was found. Its X-ray and neutron diffraction spectra are well refined with a hexagonal crystalline structure.     

Effects of Cα -Oxidation in the Fungal Metabolism of Lignin

C_α-Oxidation (benzyl alcohol oxidation) is a prominent reaction in the degradation of lignin by white-rot fungi. This study showed that such oxidation markedly retards metabolism of a nonphenolic β-O-4 model compound, 1-(3-methoxy-4-ethoxyphenyl)-2-(o-methoxyphenoxy)propane-1,3-diol, by cultures of Phanerochaete chrysosporium Burds. Surprisingly, however, selective chemical C_α -oxidation of spruce lignins enhanced their depolymerization by the cultures. Thus the decrease in intrinsic degradability of substructures is more than compensated by another effect of C_α-oxidation in lignin. One possibility is that the oxidation increases the accessibility of the lignin to enzymes by decreasing its steric complexity. This study also revealed that the β-O-4 model, like lignin in wood, is degraded in part via C_α-oxidation by P. chrysosporium. Reduction of the α-carbonyl groups thus formed does not occur. Addition of L-glutamate to ligninolytic cultures completely suppresses their competence to degrade the model compound, as it does their ability to oxidize lignin to CO₂. This result strengthens past evidence indicating that substructure models are metabolized by the same enzyme system as lignin.     

Advanced modelling of self-propagating high-temperature synthesis: the case of the Ti–C system

A novel mathematical model to simulate SHS processes is proposed. Based on the so-called enthalpy approach to properly account for phase transitions, the model describes microstructural evolution using suitable population balances. For the case of the synthesis of TiC from pure Ti and C, the model quantitatively interprets that reactants are heated up to the Ti melting point. Once Ti melting occurs, the melt is redistributed within the porous system, thus increasing the contact area between reactants and favoring graphite dissolution. TiC grains are then modelled as nucleating in the melt and then growing until the final microstructure is reached. Model reliability is tested by comparison with experimental data.     

The Hydration and Carbonation of Tricalcium Aluminate （C3 A） in the Presence of Heavy Metals

The hydration of tricalcium aluminate （ C3A ） has a significant effect on the effectiveness of cement-based systems. In addition, the carbonation of hydration products of C3A is particularly important in respect of durability performance. The present work investigates the hydration and carbonation reactions of C 3A and the changes induced by the presence of the heavy metal ions such as Zn^2＋ , Pb^2＋ , Cu^2＋ and Cr^3＋ by X-ray diffrac- tometry （ XRD ）. During hydration of C3A, gehlenite hydrate, hydrogarnet , calcium monoaluminate （ C4AHx ） and calcium carboaluminate were detected in C3A pastes except the Zn^2＋ doped paste, where hydrogarnet did not form. The examinations revealed that heavy metals coexisted with gehlenite hydrate, calcium monoaluminate （ C4AHx ） and calcium carboaluminate, inhibiting the formation of hydrogarnet. Hydrating C3A was liable to be carbonated on exposure to air and carbon dioxide, especially in the presence of heavy metals, resulting in the formation of carboaluminate and/or calcium carbonate. The presence of heavy metals in-fluenced the polymorphism of calcium carbonate, ndicating that heavy metals could co-precipitate with calcium to form a carbonate solid solution.     

Effects of the molecular weight and CC functionality of poly 1-hexene on the properties of poly 1-hexene-based high impact polystyrene

Here we are aimed to unravel the effects of CC functionality and molecular weight of the rubber on the final properties of poly1-hexene-based high impact polystyrenes (HIPS). In this regard, various HIPS samples were synthesized by free radical polymerization of styrene in the presence of different weight fractions of various poly1-hexene-based impact modifiers including: (i) high molecular weight poly1-hexene (PHex), (ii) low molecular weight poly1-hexene (Olig), and (iii) 1-hexene/1,5-hexadiene copolymer (Copolym). Results showed that by increasing CC functionality from PHex to Oligm and Copoly, the degree of grafting increases which has its influence on the mechanical, thermal and morphological perspectives of the synthesized HIPSs. Besides CC unsaturation degree, the effect of rubber molecular weight on the final HIPS properties was studied as well. According to the results, molecular weight has significant effect on the final HIPS performance, too. Finally, our obtained results suggest new HIPS/Copolym sample as the one with the highest mechanical and thermal properties which is comparable well with commercial HIPS/polybutadiene grades. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47169.     

Improving the Cyclic-Oxidation Resistance of Ti3AlC2 at 550°C and 650°C by Preoxidation at 1100°C

Preoxidation of Ti₃AlC₂ at 1100°C for 2 h was conducted to improve its cyclic-oxidation resistance at the testing temperature of 550°C and 650°C in air. The cyclic oxidation of the preoxidized Ti₃AlC₂ was found to follow a parabolic rate law rather than the linear oxidation rate for that without preoxidation. Through the X-ray diffraction and SEM analysis, the remarkable improvement of the cyclic-oxidation resistance of preoxidation Ti₃AlC₂ is suggested due to the existence of protective α-Al₂O₃ layers formed during the preoxidation treatment, which inhibits the formation of amorphous Al₂O₃, which can result in larger thermal stress and stress-induced microcracks.     

Examining the Gas Sensing Properties of the Nanocrystalline Sm2O3-WO3

In this study, nanocrystalline (NC) WO3 and Sm2O3-WO3 gas sensors have been synthesized and deposited on Al2O3 substrate by gas condensation method, then sintering to 600℃. SEM is used to observe the morphology of the surface. TEM is used to measure the particle size. The resistance of sensor is measured in different temperatures and gas concentration to evaluate the sensing properties of NC WO3 and NC Sm2O3-WO3 sensor. The results indicate that WO3 is a usability gas sensor material. After Sm2O3 is doped in WO3, it does not obviously influence CO detection; it owns better sensitivity and stability. To UV irradiation on WO3, the sensitivity of WO3 is enhanced and it maintains WO3 recovery properties in NO2 detecting. UV irradiation on Sm2O3 doped WO3 does not show enhanced well properties as UV illuminate on WO3.     

Experimental and numerical studies of the lower flammability limit of mixtures of C1–C5 hydrocarbons with air

The lower concentration limit of flammability of hydrocarbon-air mixtures has been studied experimentally and by numerical simulation. Simulation using a detailed mechanism of chemical reactions has shown that calculations results are in good agreement with experimental data on the effect of water vapor on the lean concentration limit of flammability of hydrocarbon mixtures with air. The presence of water vapor at low concentrations in the mixture does not affect the lower concentration limit of flammability, but, at the same time, significantly changes the flame propagation velocity. Key words: concentration limits of flammability, opposed-jet premixed flame, hydrocarbons.     

Effect of the addition of β-Si3N4 nuclei on the thermal conductivity of β-Si3N4 ceramics

Various microstructures of β-Si₃N₄ were fabricated, with or without the addition of β-Si₃N₄ seed particles to high-purity β-Si₃N₄ powder, using Yb₂O₃ and ZrO₂ as sintering additives, by gas-pressure sintering at 1950 °C for 16 h. The thermal conductivity of the specimen without seeds was 140 W·(m·K)⁻¹, and the specimen exhibited a bimodal microstructure with abnormally grown grains. The thermal conductivity of the specimen with 24 vol.% seed addition was 143 W·(m·K)⁻¹, and this specimen had the bimodal microstructure with finer grain size than that without the seeded material, but maintained the same amount of large grains (⩾2 μm in diameter) as in the specimen without the seeds. This finding indicates that the thermal conductivity of β-Si₃N₄ is controlled by the amount of reprecipitated large grains, rather than by the grain size of the β-Si₃N₄.     

Effect of chromium on the kinetics of the contact melting and the graphite-to-diamond transformation in the Co–Fe–C system

We have studied the effect of chromium concentration in alloys of the Co–Fe system on their interaction with graphite at p, T parameters of thermodynamic stability of diamond. It has been found that addition of chromium to the alloys stabilizes the Me₃C-type carbide, as a result, the structure of a layer of a contact melting at the alloy–graphite interface is identical to a horizontal section of the metastable phase diagram of the Fe–C system. It is shown that addition of chromium to the Co–Fe–C system lowers the eutectic melting temperature by 80–100 K. In this case, the coefficient of carbon diffusion in the melt increases by ∼20–30%. An increased surface activity of a Cr-containing melt with respect to graphite is noted, which is the reason of intensive intrusion of the melt deep into a graphite layer along the grain boundaries. As a result, the number of nucleating diamond crystals and the degree of the graphite→diamond transformation increases.     

Thermodynamic calculations on the chemical vapor deposition of Si–C–N from the SiCl4–NH3–C3H6–H2–Ar system

Based on the Gibbs free energy minimum principle and Factsage software, the thermodynamic phase diagram for the SiCl₄–NH₃–C₃H₆–H₂–Ar system was calculated. The effects of temperature, dilution ratio of H₂, total pressure on product types and distribution regions of reacted solid products were discussed. The results show that: (1) The area of SiC–Si₃N₄ increases at first, then decreases with the rising of temperature and reaches the maximum value at 1273.15 K. (2) The ratio of C/Si is the main factor for the deposition of SiC in the double phase of SiC–Si₃N₄. (3) The preferred deposition conditions of Si₃N₄ are: T=1173.15 K, H₂:SiCl₄=10:1, and P_Total=0.01 atm. Taking the deposition of SiC into consideration, the deposition of Si₃N₄ influences the formation of Si–C–N directly. (4) According to the influencing factors of depositing SiC and Si₃N₄, the suitable parameter for Si–C–N deposition can be determined. (5) Through the experimental verification, it can be demonstrated that Si–C–N can be obtained by low-pressure chemical vapor deposition (CVD), its product being amorphous and mainly constituted by Si–N and Si–C bonds. The obtained Si–C–N ceramics can transform to α-Si₃N₄ and SiC nano-crystal when heat-treated at 1773.15 K in N₂ for 2 h.     

Study on the Anti—oxidation of Al2O3—MgO—C Based Refractory

The anti-oxidation agents containing Al2O3-MgO-C refractories was developed and the properties of them were investigated after being tratd at different temperature.It was found that the anti-oxidation agents could enhance the anti-oxidation property and increase the mechanic property of the refractories,The mineral components of the oxidation film were detected with XRD method.     

The influence of B4C and MgB2 additions on the behavior of MgO–C bricks

Carbon-containing refractory materials have received great attention over the last years due to their importance in the steelmaking process. The oxidation of carbon present in refractory materials at temperatures above 500 °C is usually accompanied by the decrease of their mechanical strength and chemical resistance. Aiming to improve the oxidation resistance of carbon-oxide refractories, the use of materials known as antioxidants has been extensively studied. In this work we evaluated the performance of MgB₂ and B₄C antioxidants when incorporated into MgO–C bricks. We observed that the co-addition of metallic antioxidants and B₄C or MgB₂ leads to refractory bricks with enhanced hot modulus of rupture and resistance against oxidation and slag corrosion. However, the excessive addition of these antioxidants could impair the performance of the obtained bricks. Thus, when determining the optimum concentration of MgB₂ and B₄C to be added into MgO–C refractories, one must take into consideration this behavior.     

Correlation of the Rates of Solvolysis of Two Arenesulfonyl Chlorides and of trans-��-Styrenesulfonyl Chloride �C Precursors in the Development of New Pharmaceuticals

Additional specific rates of solvolysis have been determined, mainly in fluoroalcohol containing solvents, for benzenesulfonyl chloride (1) and p-nitrobenzene-sulfonyl chloride (2). For trans-β-styrenesulfonyl chloride (3), a study has been carried out in 43 pure and binary solvents, covering a wide range of hyroxylic solvent systems. For the specific rates of solvolyses of each of the three substrates, a good correlation was obtained over the full range of solvents when the extended Grunwald-Winstein equation was applied. The sensitivities to changes in solvent nucleophilicity and solvent ionizing power are similar to values determined earlier and an S_N2 process is proposed. For 3, kinetic solvent isotope effects of 1.46 for k_H2O/k_D2O and 1.76 for k_MeOH/k_MeOD were determined. These are also compared to literature values for other sulfonyl chlorides.     

Modification of the rate of formation and surface area of ettringite by polycarboxylate ether superplasticizers during early C3A–CaSO4 hydration

Early C₃A–CaSO₄ hydration was studied in the presence of various amounts of two polycarboxylate ether superplasticizers differing in their grafting degree. Hydration and surface area developments were investigated by in-situ NMR relaxometry coupled with BET and DSC during the first 2 h after mixing. This study enables a quantitative comparison of the amount and the specific surface area of the ettringite precipitated along the C₃A–CaSO₄ hydration with or without PCE. The main effect of PCE is to strongly increase ettringite specific area for a variable period. These effects are clearly dependent on the PCE charge and dosage and are reduced when using delayed addition. In this context the NMR relaxometry technique is of particular interest because of its high sensitivity to ettringite and furthermore this in-situ method does not need preliminary preparation likely to damage structure or modify particle arrangement.     

Unraveling the cooperative effects of acid sites and kinetics for pyrolysis of CHF3 to C2F4 and C3F6 on SO42−/ZrO2-SiO2

The treatment or upgrading of waste trifluoromethane (CHF₃, R23), which has a significant greenhouse effect, is of great importance in industry. Herein, series of SO₄²⁻/ZrO₂-SiO₂ catalysts with different Brønsted and Lewis acid site densities and ratios were prepared for pyrolysis of R23 to tetrafluoroethylene (C₂F₄, TFE) and hexafluoropropylene (C₃F₆, HFP). The effects of impregnation concentration of (NH₄)₂SO₄ on specific surface area, crystal phase, and Brønsted and Lewis acid site densities and ratios were respectively demonstrated. The Brønsted and Lewis acid sites were observed to have cooperative effects on R23 transformation and up to 94.6% selectivity of (TFE + HFP) could be achieved at 750°C. The kinetic studies revealed the decomposition of R23 into CF₂ carbene and HF was the rate-determining step, and a deactivation behavior was found due to the site coverage and pore blockage by the oligomers of TFE and HFP.