Rare earth silicate environmental barrier coatings for SiC/SiC composites and Si3N4 ceramics

Rare earth silicates have been investigated to evaluate their potential as an advanced environmental barrier coating (EBC) having higher temperature capability than current EBCs. Volatility data in high steam environments indicate that rare earth monosilicates (RE₂SiO₅; RE: rare earth element) have lower volatility than the current barium strontium aluminum silicate (BSAS) EBC top coat in combustion environments. Rare earth silicates also exhibit superior chemical compatibility compared to BSAS. The superior chemical compatibility and low volatility are key attributes to achieve higher temperature capability. The chemical compatibility is especially critical for EBCs on Si₃N₄ because of the high chemical reactivity of some of the oxide additives in Si₃N₄. In simulated combustion environments, EBCs with a rare earth monosilicate top coat exhibit superior temperature capability and durability compared to the current state-of-the art EBCs with a BSAS top coat.     

The NO and N2O formation mechanism under circulating fluidized bed combustor conditions: From the single particle to the pilot-scale

The NO and N₂O formation mechanism is studied starting from a single fuel particle burning under well-defined conditions up to a pilot-scale circulating fluidized bed combustor (CFBC). The fuel, petroleum coke, was the same in all tests and care has been taken to obtain chemical similarity between the different units: a formation rate unit, a laboratory-scale and a pilot-scale CFBC. A detailed single particle NO/N₂O formation model has been developed and incorporated in a CFBC NO/N₂O emission model. To thoroughly test the modeled NO/N₂O mechanism, the iodine addition method has been used in all units.     

Application of the Indium-containing mesoporous silicas catalysts in the alkylation of aromatics reaction

The benzylation of benzene and substituted benzenes reaction employing benzyl chloride as the alkylating agent over a series of Indium-containing mesoporous silicas with different In contents has been investigated. These materials (In-HMS-n) have been characterized by chemical analysis, N₂ adsorption/desorption isotherm, X-ray diffraction (XRD) and FTIR spectroscopy. The mesoporous Indium-containing materials showed both high activity and high selectivity for benzylation of benzene. The activity of these catalysts for the benzylation of different aromatic compounds is in the following order: benzene > toluene > p-xylene > anisole. More interesting is the observation that these catalysts are always active and selective for large molecules like naphthenic compounds such as methoxynaphthalene. Kinetics of the benzene benzylation over these catalysts have also been investigated.     

The influence of some new 2,5-disubstituted 1,3,4-thiadiazoles on the corrosion behaviour of mild steel in 1 M HCl solution: AC impedance study and theoretical approach

The new 2,5-disubstituted 1,3,4-thiadiazoles were investigated as corrosion inhibitors of mild steel in 1 M HCl using AC impedance technique. Four of these compounds exhibit good inhibition properties, while two of them, 2,5-bis(4-nitrophenyl)-1,3,4-thiadiazole and 2,5-bis(4-chlorophenyl)-1,3,4-thiadiazole, stimulate the corrosion process especially at low concentrations. The experimental data obtained from this method show a frequency distribution and therefore a modelling element with frequency dispersion behaviour, a constant phase element (CPE) has been used. Possible correlations between experimental inhibition efficiencies and quantum chemical parameters such as dipole moment (μ), highest occupied (E_HOMO) and lowest unoccupied (E_LUMO) molecular orbitals were investigated. The models of the inhibitors were optimised with the Density Functional Theory formalism (DFT) using hybrid B3LYP/6-31G (2d,2p) as a higher level of theory. The Quantitative Structure Activity Relationship (QSAR) approach has been used and composite index of some quantum chemical parameters were constructed in order to characterize the inhibition performance of the tested molecules.     

N-(1,3,4-Oxadiazol-2-yl)Benzamides as Antibacterial Agents against Neisseria gonorrhoeae

The Centers for Disease Control and Prevention (CDC) recognizes Neisseria gonorrhoeae as an urgent-threat Gram-negative bacterial pathogen. Additionally, resistance to frontline treatment (dual therapy with azithromycin and ceftriaxone) has led to the emergence of multidrug-resistant N. gonorrhoeae, which has caused a global health crisis. The drug pipeline for N. gonorrhoeae has been severely lacking as new antibacterial agents have not been approved by the FDA in the last twenty years. Thus, there is a need for new chemical entities active against drug-resistant N. gonorrhoeae. Trifluoromethylsulfonyl (SO₂CF₃), trifluoromethylthio (SCF₃), and pentafluorosulfanyl (SF₅) containing N-(1,3,4-oxadiazol-2-yl)benzamides are novel compounds with potent activities against Gram-positive bacterial pathogens. Here, we report the discovery of new N-(1,3,4-oxadiazol-2-yl)benzamides (HSGN-237 and -238) with highly potent activity against N. gonorrhoeae. Additionally, these new compounds were shown to have activity against clinically important Gram-positive bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), and Listeria monocytogenes (minimum inhibitory concentrations (MICs) as low as 0.25 µg/mL). Both compounds were highly tolerable to human cell lines. Moreover, HSGN-238 showed an outstanding ability to permeate across the gastrointestinal tract, indicating it would have a high systemic absorption if used as an anti-gonococcal therapeutic.     

Synthesis,Surface Activities and Toluene Solubilization by Amine-oxide Gemini Surfactants

A series of amine-oxide gemini surfactants featuring amide groups [N, N’-dimethyl-N, N’-bis(2-alkylamideethyl)-ethylenediamine oxide (alkyl = C₁₁H₂₃, C₁₃H₂₇, C₁₅H₃₁, C₁₇H₃₅)] have been synthesized via a three-step synthetic route, and their chemical structures were confirmed by mass spectra, FTIR and ¹H-NMR spectra. The surface activities of these compounds have been measured. The results show that these synthesized amine-oxide gemini surfactants reduced the surface tension of water to a minimum value of approximately 26.91 mN m^?1 at a concentration of 2.92 × 10^?5mol L^?1. Furthermore, their critical micelle concentration (CMC) values and solubilization of toluene decrease with an increase of the hydrophobic chain length from 12 to 18. Isoelectric point measurements revealed that their pI values range from 4.0 to 10.5.     

Preparation and properties of fully esterified erythritol

Pure tetraesters of erythritol with C₁₀, C₁₂, C₁₄, C₁₆, C₁₈ saturated, and C_18:1 unsaturated (oleoyl) fatty acyl chains have been prepared for the first time and characterized using the acylating systems fatty acid/N,N′‐dicyclohexylcarbodiimide/4‐dimethylaminopyridine (DMAP), fatty acid anhydride/DMAP, fatty acyl chloride/pyridine, and fatty acyl chloride/boron trifluoride etherate. For the first three systems the yields were in the range of 80–90% while the fatty acyl chloride/pyridine system has the advantage of lower cost. The fatty acyl chloride/boron trifluoride etherate system gave lower (ca 70%) yields of the tetraesters. The tetraesters of erythritol may have applications analogues to those of triglycerides. In addition, new applications can be envisaged for these compounds, as a result of their differences in physical, chemical, and biochemical properties compared to triglycerides. Practical applications: The tetraesters of erythritol with saturated fatty acyl chains may have applications analogous to those of saturated triglycerides. However, tetraesters with unsaturated fatty acid chains may have greater prospects of having industrial uses after doing chemistry on the carbon–carbon double bonds.     

Temperature and Composition‐Induced Structural Transitions in Bi1−xLa(Pr)xFeO3 Ceramics

Bi_1?xLa_xFeO₃ and Bi_1?xPr_xFeO₃ ceramics of the compositions near the morphotropic phase boundary have been studied by X‐ray and neutron diffraction techniques and differential thermal analysis. The structural phases characterized by the long‐range polar, antipolar, and nonpolar ordering as well as the phase coexistence regions have been identified using the diffraction data depending on the dopant concentration and temperature. As a result of these studies the three phase region has been observed for the Pr‐doped compounds and the phase diagrams have been constructed. The detailed evolution of the structural parameters permitted to itemize the factors affecting the structural phase transitions and clarify the origin of the enhanced electromechanical properties in these materials. The performed structural analysis disclosed different character of the chemical bonds in the La‐ and Pr‐doped BiFeO₃ compounds. Further, the role of the rare‐earth ions in the covalency of the chemical bonds is discussed.     

Chemiluminescence of indole and its derivatives induced by electrogenerated superoxide ion in acetonitrile solutions

Electrochemical behavior of the dioxygen (O₂)/superoxide ion (O₂ ⁻) redox couple in acetonitrile (AN) solutions containing indole compounds and no proton acceptor, and their chemiluminescence have been examined using spectroelectrochemical techniques. In AN solutions, in the presence of indole compounds having a substituent at the N-position (e.g. 1-methylindole and 1,2-dimethylindole), these indole compounds did not work as a proton donor to electrogenerated O₂ ⁻, and did not affect the redox reaction of the O₂/O₂ ⁻ couple. On the other hand, the indole compounds bearing a hydrogen at the N-position (e.g. indole, 3-methylindole (3-MI), tryptamine (TP), 3-indolemethanol and 3-indoleacetic acid) acted as a proton donor to O₂ ⁻. In addition, chemiluminescence was observed for some of the indole compounds having a hydrogen at the N-position and an electron-releasing group at the 3-position (i.e. TP, 2,3-dimethylindole, 2-(3-indole)-ethanol and 3-MI). The intensity of chemiluminescence of 3-MI was by far the strongest among those of the above four compounds. The chemiluminescent reaction of the indole compounds seemed to have close connection with electrogeneration of O₂ ⁻, which functioned as a proton acceptor to the indole compounds, and the chemical stability of a radical species (i.e. a one-electron oxidized form of conjugate base of indole compounds) due to the substituent which is present at the 3-position. The chemiluminescence was considered to occur via the formation of 1,2-dioxetane-like intermediates. The reaction mechanisms of chemiluminescence based on the electrogenerated O₂ ⁻ were briefly discussed.     

Design and synthesis of novel dual-action compounds targeting the adenosine A(2A) receptor and adenosine transporter for neuroprotection

A novel compound, N⁶‐(4‐hydroxybenzyl)adenosine, isolated from Gastrodia elata and which has been shown to be a potential therapeutic agent for preventing and treating neurodegenerative disease, was found to target both the adenosine A_2A receptor (A_2AR) and the equilibrative nucleoside transporter 1 (ENT1). As A_2AR and ENT1 are proximal in the synaptic crevice of striatum, where the mutant huntingtin aggregate is located, the dual‐action compounds that concomitantly target these two membrane proteins may be beneficial for the therapy of Huntington’s disease. To design the desired dual‐action compounds, pharmacophore models of the A_2AR agonists and the ENT1 inhibitors were constructed. Accordingly, potentially active compounds were designed and synthesized by chemical modification of adenosine, particularly at the N⁶ and C^5’ positions, if the predicted activity was within an acceptable range. Indeed, some of the designed compounds exhibit significant dual‐action properties toward both A_2AR and ENT1. Both pharmacophore models exhibit good statistical correlation between predicted and measured activities. In agreement with competitive ligand binding assay results, these compounds also prevent apoptosis in serum‐deprived PC12 cells, rendering a crucial function in neuroprotection and potential utility in the treatment of neurodegenerative diseases.     

Preparation of mesoporous and macroporous materials from rubber of tyre wastes

From residual rubber (RR) separated from tyre wastes, adsorbent materials were prepared by applying thermal, chemical and combined (thermal and chemical or vice versa) methods. In the preparation of samples, RR was heated at 200–900 °C for 2 h in N₂ atmosphere. The material was also contacted with H₂SO₄, HNO₃, and H₂SO₄/HNO₃ solutions for 24 h. Finally, RR was first heated at 400 °C for 2 h in N₂ and the resultant product was then treated chemically with an H₂SO₄/HNO₃ solution for 24 h, or vice versa. Both RR and the products derived from it were characterised texturally by gas adsorption (N₂, 77 K), mercury porosimetry, and helium and mercury density measurements. Usually, the yield is lower for the heat treatments than for the single chemical treatments (e.g., the smallest yield values are 33.0 and 60.5 wt.%). For the combined treatments, as compared to the single treatments, the yield is higher. RR is a nonporous solid. The treatments of RR as a rule result in a great porosity development mainly in the mesopore and macropore ranges for the heat and chemical treatments, respectively. The presence of HNO₃ in the acid solution used in the treatments of RR has proved to be an essential factor for the development of the porosity made up of large pores. When RR is subjected to combined treatments, the predominant effect on the porosity development is that of the treatment effected first. By successive heat and chemical treatments, a product containing the same volumes of mesopores and macropores is obtained. The micropore content is low for all products, but especially for those prepared chemically.     

Preparation,Characterization and Properties of Novel Cationic Gemini Surfactants with Rigid Amido Spacer Groups

A series of novel cationic gemini surfactants with rigid amido groups inserted as the spacers, named C ₁₂ ‐PPDA‐C ₁₂ , C ₁₄ ‐PPDA‐C ₁₄ and C ₁₆ ‐PPDA‐C ₁₆ , were synthesized by a two‐step reaction with dimethyl terephthalate, N,N‐dimethyl propylene diamine and alkyl bromide as raw materials. The chemical structures of the prepared compounds were confirmed by IR, ¹H and ¹³C NMR and element analysis. Surface activity properties of the synthesized compounds were investigated by surface tension, electrical conductivity and fluorescence. Increasing the number of carbon atoms in the hydrophobic alkyl chain, decreased the critical micelle concentration (CMC), surface tension at the CMC and the minimum surface area. Other relevant properties including foaming ability and emulsion stability were investigated. The results indicated that the synthesized gemini surfactants possess good surface properties, emulsifying properties and steady foam properties.     

The fate of organic nitrogen in photocatalysis: an overview

Photocatalytic processes taking place on TiO₂ have been widely employed and investigated. However, nitrogen-containing substances have not received the same attention as other substrates. Mineralization of such compounds is expected to lead to the formation of N₂ gas, ammonium and/or nitrate ions through photooxidative and/or photoreductive pathways. Herein, we will focus the attention on how the chemical structure may influence both the ratio and the extent of formation of the inorganic nitrogen. This review will consider heteroaromatic compounds, containing two or three-nitrogen in the ring, and small molecules, that could be formed as intermediate during the degradation of more complex substrates (i.e. pesticides), such as amino-alcohols, and molecules containing amide groups and nitriles. The fate final of the nitrogen in all these structures has been rationalized on the basis of the nature of N–N and C–N bonds in which the organic nitrogen is involved.     

Competitive adsorption of sulfolane and thiolane on clay materials

Groundwater samples directly beneath a waste disposal site have been shown to contain a higher concentration of sulfolane and a relatively low concentration of thiolane. The sulfolane is a source compound of thiolane, a reduced form of sulfolane. In subsequent analyses of groundwater samples, these compounds have been detected from all of the monitoring wells in the study area. Since these compounds are present together in an aquifer, a possible competition, that can happen in such a system, has been investigated. Thiolane is a nonpolar heterocyclic organic compound whereas sulfolane is a weakly acidic dipolar solvent. As expected, thiolane adsorbs more strongly onto clay than sulfolane in a single solute system. For regression of bisolute system using Matlab to obtain Q (maximum number of moles of solute adsorbed per unit weight of adsorbent), k₁ (constants related to the energy of adsorption for sulfolane), and k₂ (constants related to the energy of adsorption for thiolane), the k₁ value (sulfolane) is smaller than the k₂ value (thiolane) which reflects that thiolane is more strongly adsorbed than sulfolane. This is strongly consistent with the result obtained from single solute system. The Q for the sulfolane and combined data is the same that indicates that the sulfolane data is dominantly fitted because the concentrations of sulfolane are much greater than those of thiolane in the experiments. In combined data regression, the suppression of sulfolane adsorption on clay was also observed by the presence of thiolane.     

Measurement and prediction of the emission of pollutants from the combustion of coal and biomass in a fixed bed furnace

The effect of co-combustion of coal and biomass has been studied for a fixed bed appliance originally designed for coal and in widespread use in many parts of the world especially Eastern Europe. Organic, inorganic and gaseous emissions have been measured. Organic compounds have been determined for a range of fuel combinations. These include polycyclic aromatic hydrocarbons PAH, alkyl PAH, a range of oxygenated compounds (including phenols, aldehydes and ketones, oxygenated polycyclic aromatic compounds (O-PAC) and dioxins), polycyclic aromatic sulphur hydrocarbons (PASH), nitrogenated polycyclic aromatic compounds (N-PAC) and common volatile organic compounds (VOC). Inorganic species include trace heavy metals, as well as the gases, CO, CO₂, SO_x and NO_x. The concentration of the trace metals in the ash and fly ash have been compared to equilibrium calculations of the emission profiles during co-combustion.     

Paper derived SiC–Si3N4 ceramics for high temperature applications

Biomorphic Si₃N₄–SiC ceramics have been produced by chemical vapour infiltration and reaction technique (CVI-R) using paper preforms as template. The paper consisting mainly of cellulose fibres was first carbonized by pyrolysis in inert atmosphere to obtain carbon bio-template, which was infiltrated with methyltrichlorosilane (MTS) in excess of hydrogen depositing a silicon rich silicon carbide (Si/SiC) layer onto the carbon fibres. Finally, after thermal treatment of this Si/SiC precursor ceramic in nitrogen-containing atmosphere (N₂ or N₂/H₂), in the temperature range of 1300–1450 °C SiC–Si₃N₄ ceramics were obtained by reaction bonding silicon nitride (RBSN) process. They were mainly composed of SiC containing α-Si₃N₄ and/or β-Si₃N₄ phases depending on the nitridation conditions. The SiC–Si₃N₄ ceramics have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and Raman spectroscopy. Thermal gravimetric analysis (TGA) was applied for the determination of the residual carbon as well as for the evaluation of the oxidation behaviour of the ceramics under cyclic conditions. The bending strength of the biomorphic ceramics was related to their different microstructures depending on the nitridation conditions.     

Preparation and characterization of carbon membranes made from poly(phthalazinone ether sulfone ketone)

Carbon membranes were prepared from a novel polymeric precursor of poly(phthalazinone ether sulfone ketone) (PPESK), of which the changes of microstructure and chemical compositions during pyrolysis from 500 °C to 950 °C were monitored by thermal gravimetric analysis, X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. It has been found that the weight loss of the PPESK precursor up to 800 °C is about 43.0 wt%. After the heat treatment, the typical chemical structure of the PPESK precursor disappears, at the same time a graphite-like structure with more aromatic rings is formed. The interlayer spacing (i.e., d value) decreases from 0.471 nm to 0.365 nm as the pyrolysis temperature increases. The gas permeation performance of carbon membranes has been tested using pure single gases including H₂, CO₂, O₂ and N₂. For the carbon membrane obtained by carbonizing the PPESK precursor at 800 °C, the maximum ideal permselectivities for H₂/N₂, CO₂/N₂ and O₂/N₂ gas pairs could reach 278.5, 213.8 and 27.5, respectively.     

13C- and 15N-NMR spectra of phenylazoacetoacetamides and similar compounds

The ¹³C- and ¹⁵N-NMR spectra of phenylazoacetoacetamides (1) and similar compounds and their ¹⁵N-isotopomers have been measured and the carbon and nitrogen signals have been assigned. The compounds exist in their hydrazone forms. Based on the stereospecific behaviour of the coupling constants ²J(¹⁵N¹³C) a strong predominance of (Z)-isomer has been found for the compounds 1 in C²HCl₃ or in [²H₆DMSO solutions. In some cases (E)-isomers (⩽5%) have been observed.     

<Emphasis Type="Italic">N</Emphasis>-bromohexamethyldisilazane: Investigation of properties and thermodynamic simulation of precipitation of thin-layer structures from the vapor phase

N-Bromohexamethyldisilazane has been characterized using an elemental analysis and IR, UV, ¹H NMR, ¹³C NMR, and ²⁹Si NMR spectroscopy. The spectral characteristics of the compound have been determined and the saturated vapor pressure has been measured. The thermodynamic simulation of the chemical vapor deposition (CVD) of silicon carbonitride films in the Si-C-N-Br-H system has been performed at low pressures (13.30 and 1.33 Pa) over a wide temperature range (from 400 to 1200 K) with the use of initial gas mixtures of N-bromohexamethyldisilazane with hydrogen and ammonia. The possibility of preparing films of different compositions has been demonstrated and the optimum conditions for deposition of silicon carbonitride coatings of the general composition SiC _x N _y have been established.     

Morphology control of a silicon nitride thick film derived from polysilazane precursor using UV curing and IR heat treatment

Silicon nitride (Si₃N₄) has excellent thermo-mechanical properties, and can be used as heat dissipation substrate for various devices. Si₃N₄ thin films are generally synthesised by chemical vapour deposition (CVD) or plasma-enhanced CVD. The use of polysilazanes (PSZs) as a precursor to the synthesis of Si₃N₄ has attracted significant attention because of their high mouldability and processability. In this study, Si₃N₄ thick films were prepared on silicon wafers or aluminium substrates by a spin- or dip-coating liquid PSZ, followed by UV curing and IR heat treatment under various conditions. The effects of the heat treatment conditions on the Si₃N₄ thick film surface were analysed by optical microscopy, X-ray diffraction, and scanning electron microscopy. An almost single phase of Si₃N₄ was synthesised successfully on the single crystalline silicon with UV curing at 400°C for 30 min and IR heating at 800°C in N₂ atmosphere.