Grain-Boundary Effect in Ceria Doped with Trivalent Cations: II, Microstructure and Microanalysis

Various samples studied for their electrical behavior in the previous paper are here examined in detail by microstructural and microanalytical techniques. While several microstructural features are observed, the presence of "thick boundaries" (an amorphous silica-rich phase that surrounds grain boundaries and forms a continuous network) appears to be the principal feature responsible for the grain-boundary effect. Such features are absent from samples prepared with nearly silicon-free materials, for which the grain-boundary effect is also virtually absent.     

Grain-Boundary Effect in Ceria Doped with Trivalent Cations: I, Electrical Measurements

The "grain-boundary effect," which leads to a greatly reduced dc ionic conductivity due to the presence of a blocking layer in the vicinity of the grain boundaries, is studied in detail for ceria ceramics doped with various trivalent dopants (particularly Y³⁺, Gd³⁺, and La³⁺). The effects of porosity, of sintering time, and of dopant size and dopant concentration are investigated. Finally, it is shown that the grain-boundary effect virtually disappears when nearly silicon-free starting materials are used.     

Electrochemistry of Organic Cations. VI. Investigations about the Cathodic Cleavage of Some Pyridinium and Triazolium Ions

The electrochemical reduction of some N-acylamino-, N-amino-, N-benzyl- and N-phenacyl-substituted pyridinium and triazolium ions is investigated in acetonitrile by voltammetric methods and potentiostatic electrolyses. The acylaminopyridinium ions 1 and the arylaminopyridinium ions 3 are cathodically cleaved into the pyridine derivative and the carboxylic amide or the aromatic amine. In the case of the 1-benzyl-4-acylaminotriazolium ions 5 the reductive formation of hydrogen from the acidic N-acylamino group is preferred and the corresponding ylide is formed, which reacts at more negative potential by splitting off the benzyl group. The reduction of the N-phenacylpyridinium ion 7d occurs with splitting off the phenacyl radical, which dimerizes to 1,2-dibenzoylethane in a good yield. In the case of N-benzyl- and N-p-cyanobenzylpyridinium ions the cathodic dimerization to the corresponding bisdihydropyridines was found, whereas the electrolysis of the N-nitrobenzylpyridinium ions occurs with cleavage of the N-substituent-bond, which is initiated by the primary formation of the nitrophenyl anion radical. It follows from electrogenerated chemiluminescence experiments that the cleavage of the cations 1 and 5 occurs with the uptake of one electron.     

溴化氢的冰乙酸溶液脱除苯磺酰基的研究

采用溴化氢的冰乙酸溶液与苯酚的混合物快速脱除N-苯磺酰基-4-乙酰基哌啶-4-羧酸乙酯中的苯磺酰基,避免了酸解法脱除苯磺酰基引起反应物的脱羧反应,得到了目标产物4-乙酰基哌啶-4-羧酸乙酯,产率和纯度高。通过对脱除反应液的分析,表明溴化氢的冰乙酸溶液与苯酚的混合物对苯磺酰基的脱除可能是一个氧化-还原过程,苯酚在其中起了消除溴并防止脱除产物溴化的作用。     

Mechanical properties of BaTiO3 open-porosity foams

Barium titanate (BaTiO₃) foams synthesized via direct foaming method using silicon-free, rigid polyurethane systems (PU), commercially purchased and lab developed, are being engineered for piezocomposites in sonar applications. The mechanical properties of these foams were measured using confined compression testing to evaluate the suitability of these foams for the intended application. Compressive modulus and collapse strain determined from the experimental data increased with increasing density. Additionally, the foams fabricated using the lab developed PU (LPU) showed a higher mechanical strength due to a higher average density than the foams developed using commercial PU (CPU) system. The data was then fit with a phenomenological model to verify the values of the compressive properties extracted from the experimental data and also to extract additional properties such as tensile strength. Based on these findings, it is proposed that these foams can be successfully incorporated into piezocomposites by infiltrating the foams with polymer.     

Polymeric structure of coal. 2. Structure and thermoplasticity of sulphur-rich Raša lignite

The methods of reduction and reductive alkylation with potassium in tetrahydrofuran and sodium in liquid ammonia have been applied to sulphur-rich, highly fluid (in carbonization) Ra?a lignite. The results indicate that solubilization of coal by alkylation of the coal anion formed in liquid ammonia is a clean and defined process. It is concluded that the highly thermoplastic properties of Ra?a coal result mainly from cleavage of CSC(COC) bridges, low contents of OH and lack of SH groups. In contrast to ‘normal’ bituminous coals investigated until now and characterized by wide distribution of the molecular weight of clusters formed on cleavage of ether bridges, about 80% (w/w) of Ra?a lignite is built of units of almost uniform molecular weight (MW 500).     

Corrosion of alumina and mullite hot gas filter candles in gasification environment

Reliable fuel gas cleaning is required to meet environmental regulations as well as to prevent corrosion and erosion of downstream components. The aggressive process environment in biomass-gasification power generation systems or in biofuels production systems causes corrosion in the ceramic hot gas filter candles used to clean the fuel gas. Therefore, in order to improve the reliability and durability of filters, the influence of steam, ash, hydrogen sulfide, and alkaline metals on the corrosion processes was studied for alumina and mullite filter candles fabricated by Pall Schumacher. Exposure to these contaminants effects the chemical composition of the binder phases resulting in exchange of alkaline metals and alkaline earth metals. Analyses by energy dispersive X-ray spectroscopy demonstrate the negative effect of silicon containing binder phases. These effects are discussed and it is shown that the usage of silicon-free binder phases in hot gas filter candles for gasification processes is promising.     

Ozone treatment of water-soluble polymers. III. Ozone degradation of polyacrylamide in water

Polyacrylamide (MW 350,000) was ozonized at pH 2 and pH 10 buffer solution. There was little ozonization at pH 2, but at pH 10 the COD and the viscosity of the solution decreased upon ozonization, and a linear relationship existed between the ozone consumed and the number of breaks calculated from the viscosity. This relationship apparently indicated that 45 molecules ozone were consumed for one cleavage of the polymer chain. Such random cleavage was confirmed also by the observation of molecular weight distribution by means of gel filtration chromatography. The amide group decreased scarcely by the ozonization, while a small amount of aldehyde was observed in the ozonized solution. No remarkable change was observed in the IR spectra of the ozonized sample, except for a weak absorption band at 1725 cm^?1 which arose from the carbonyl of aldehyde or ketone. Although no variation was observed in the ¹³C NMR spectra either, a strong absorption peak at 266 nm appeared in the UV spectra of the ozonized solution and increased with the ozonization time. This phenomenon was presumed to be due to the formation of a certain ring structure between the amide group and the small amount of ketone produced in the main chain. However, the details of the ozonization mechanism could not be ascertained.     

Catalytic hydrogenolysis of saccharides. II. Formation of glycerol

The selectivity of the formation of glycerol from saccharides and hexitols by catalytic hydrogenolysis is determined by a number of reaction variables. Evaluation of the results of variations in operating conditions was effected by the use of the parameters: cleavage selectivity, hydrogenation selectivity, and cleavage percentage. There were strong indications that the cleavage selectivity was controlled by the molecular structure of the saccharide used, being considerably higher for a fructofuranose structure than for a pyranose one. The main reactions were cracking, isomerisation, acid formation, hydrogenation, dehydrogenation, and dehydration. Of these, cracking and hydrogenation reactions had the greatest influence on the glycerol yield. The choice of the catalyst is difficult, because of the conflicting demands for maximum hydrogenation selectivity and maximum cleavage percentage.     

Novel silicon-contained lignin-based carbon fibers derived from bamboo pulping black liquor with improved electrochemical performance for supercapacitors

Carbon fibers (CFs) are a promising candidate as electrode materials for flexible supercapacitors given its light weight and moderate cost. In this study, the lignin used was partially separated from kraft bamboo pulping black liquor and the higher molecular weight fraction, unavoidably contains a small amount of silicon compounds, so named silicon-contained lignin. Novel CFs were prepared using commercial polyacrylonitrile (PAN) and the lignin by electrospinning and further carbonization. Even in the presence of silicon compounds, the fibrous morphology of precursor fibers was significantly good, and the CFs with uniform fiber diameter and high specific surface area up to 182 m²/g were obtained with an increase in silicon-contained lignin. The CFs fabricated from silicon-contained lignin and commercial PAN had higher specific capacitance (22.20 mF/cm² at 10 mA/cm²) and superb cycling stability (94.21%) than that from silicon-free lignin or pure PAN separately.     

Electrochemical reactions of halohydrins. I. Attempt at reductive coupling

The electrochemical reductive coupling of 2-chloroethanol and 2-bromoethanol to 1,4-butanediol was attempted. The electrochemical cleavage of the carbon-halogen bond leads to intermediates which are either unstable and decompose to ethylene and OH^–, or undergo chemical reactions leading to ether formation. The presence of the hydroxyl group in halohydrins seems to be responsible for the observed reaction paths. When the alcohol group was protected by esterification, coupled products were observed. Coupling of bromoethyl acetate to 1,4-butanediol diacetate thus appears technically feasible, but is a commercially less attractive route to 1,4-butanediol.     

Basic gel-permeation chromatography studies. I. Polymer degradation

Polymer degradation has been studied by using gel-permeation chromatography (GPC) to measure the product distribution. The method is rapid and has a good accuracy that permits one to see most of the degradation products, as they elute at a point different from the starting material. In the cases studied, polystyrene cleavage has the result of random cleavage, as judged by the product distribution. A GPC curve to be expected from random cleavage has been put together to aid in the evaluation. Both wide and narrow molecular weight distribution polystyrenes have been studied after degradation. The narrow distribution products were degraded by peroxides, irradiation, and weathering. With the latter, the combination of simple fragments to form the starting portions of cromslinking were measured in small amounts. In none of the cases studied did degradation in solution produce crosslinked products. Kinetic rate studies were made that concerned the action of peroxides and inhibitors.     

Polymeric structure of coal. 3. Re-examination of the role of ether bonds in reduction of molecular weight of a low-rank vitrinite treated with hydrogen donor

Although available literature does not unequivocally establish the presence of open ether bonds (ROR) in low-rank bituminous coals, formation of low-molecular-weight products on reacting such coals with hydrogen donors is usually interpreted in terms of scission of ether bridges. This lack of consistency could be justified by supposing that ethereal and hydroxyl functions in low-rank coals exist in phenoxyphenol-type structures. Ethers of this type have never been cleaved on treatment with sodium in liquid ammonia but, contrary to expectations based on extant literature, can be split by certain hydrogen donors. The results presented here indicate, however, that phenoxyphenol-type ethers do not exist in low-rank vitrinite and/or their cleavage does not result in lowering the molecular weight of the vitrinite. It is concluded that, unless non-reactive oxygen exists in low-rank vitrinite in dialkyl ether structures, formation of low-molecular-weight products on hydrogen donor treatment should be attributed mainly to CC bond cleavage.     

Photochemie von Aminoketonen. V. Diastereoselektive Synthese von 3-Aryl-azetidin-3-olen durch Photocyclisierung von Aryl-α-amidoalkyl-ketonen

Photochemistry of Aminoketones. V. Diastereoselective Synthesis of 3-Aryl-azetidin-3-ols via Photocyclization of Aryl-α-amidoalkyl-ketones N-Acyl-azetidin-3-ols 3 and 4 are formed by diastereoselective cyclization of n,π*-excited N-benzyl-N-phenacyl-amides 1 and 2 in ether solution. Dependent on the nature of the p-and α-substituents of the phenacyl part and especially of the N-acylgroups in the amides 1 and 2 competing reactions occur, particularly the NORRISH II cleavage and an oxydative cleavage of the intermediate hydroxybiradicals A . N-Acylgroups with low energy barrier ΔG^≠ of internal rotation favour the diastereoselective photocyclization by intramolecular interaction between the amide oxygen atom and the n,π*-CO-group in 1 *, 2 * and the OH group in the biradicals A , respectively. An intramolecular hydrogen bonding enables the N-tosyl-azetidinols 3 to rearrange to the N-tosylamino-methyl-benzhydryl-ketones 6 by 1 -sensitized photoreaction.     

Controlled atmosphere electron microscopy studies of graphite gasification—I. The catalytic influence of zinc

The catalytic activity of zinc in the gasification of single crystals of graphite has been studied by a controlled atmosphere electron microscopy technique. Continuous observation showed that catalyst particles are only active when in contact with steps on the cleavage surface of the graphite crystal and cut channels into the steps. Quantitative estimates of channel propagation rates as a function of oxygen pressure and temperature have been obtained. It is suggested that the catalyst composition is close to ZnO.     

Reversible crosslinking in epoxy resins. I. Feasibility studies

The objective of the research is to investigate epoxy resins where crosslinks formed in curing reactions can be cleaved and reformed without significant sacrifice in resin properties. In this phase of the investigation, experimental disulfide-containing crosslinking agents have been studied, including dihydrazides of dithiodicarboxylic acids(aliphatic and aromatic) and dithio-aromatic diamines. Conditions for curing reactions and for subsequent cleavage of crosslinks by reduction have been determined in model systems and confirmed for a prototype epoxy resin. A preliminary comparative evaluation of cure kinetics and of crosslink density and thermal and mechanical properties has been carried out for this resin cured with aromatic curing agents (4,4′-dithiodianiline and methylene dianiline) and with aliphatic compounds (3,3′-dithiopropionic acid dihydrazide and hexamethylene diamine). It has been shown that in a resin fully cured with disulfide-containing crosslinking agents, crosslinks could be ruptured by reduction, and reestablished by oxidation under mild conditions.     

Formation of anomalous structures in PVC and their influence on the thermal stability: 3. Internal chloroallylic groups

Internal double bonds were determined by oxidative cleavage in fractions of a commercial suspension PVC (S-PVC) and experimental PVC samples obtained at subsaturation conditions (U-PVC). The changes in molecular weight were measured by g.p.c. and viscometry. The oxidation was performed by ozonolysis in tetrachloroethane solution at ?20°C. Oxidation by potassium permanganate in dimethylacetamide solution at ?10° to +50°C was also studied. However, this method was found to give erratic results. With increasing monomer starvation the number of internal double bonds increased. In the original S-PVC sample the internal double bond content was $\text{0.2}\text{1000}\text{VC}$. The formation of double bonds is assumed to be the result of an increased tendency, by chlorine atoms, to attack on the methylene groups in the chain. Hydrolytic cleavage and ¹H n.m.r. measurements did not give any evidence of ketoallylic groups. With increasing chloroallylic group content the U-PVC samples showed an increased rate of dehydrochlorination at 190°C in nitrogen. The S-PVC fractions, however, showed a decreased rate. However, the thermal stability in both series of samples could be related to the tertiary chlorine content. Butyl and long chain points with tertiary chlorine are more frequent than the internal chloroallylic groups. It was assumed that tertiary chlorine is the most important labile structure not only in U-PVC but also in ordinary PVC.     

Macromolecular structure of coals. IV. Equilibrium swelling studies of coal networks subjected to various treatments

The macromolecular network structure of the organic phase of bituminous coals was investigated with equilibrium swelling experiments at 35° and 60°C. It was determined that an oxygen-methylation technique led to cleavage of hydrogen bonds and significant increase of swelling. Pyridine preextraction led to significant differences in swelling due to partial incorporation in the network structure.     

Highly Sensitive RNA-Cleaving DNAzyme Sensors from Surface-to-Surface Product Enrichment

The engineering of easy-to-use biosensors with ultra-low detection sensitivity remains a major challenge. Herein, we report a simple approach for creating such sensors through the use of an RNA-cleaving DNAzyme (RcD) and a strategy designed to concentrate its cleavage product significantly. The assay uses micron-sized beads loaded with a target-responsive RcD and a paper strip containing a microzone covered with a DNA oligonucleotide capable of capturing the cleavage product of the RcD through Watson–Crick hybridization. Placing the beads and the paper strip in a target-containing test sample allows the bead-bound RcD molecules to undergo target-induced RNA cleavage, releasing a DNA fragment that is captured by the paper strip. This strategy, though simple, is very effective in achieving high levels of detection sensitivity, being able to enrich the concentration of the cleavage product by three orders of magnitude. It is also compatible with both fluorescence-based and colorimetric reporting mechanisms. This work provides a simple platform for developing ultrasensitive biosensors that take advantage of the widely available RcDs as molecular recognition elements.     

Photooxidation von Leukofarbstoffen. XII. Kurzzeitspektroskopische Untersuchungen zur Photooxidation von Bis-schwefelsäuremonoestern der Leukoformen von Thioindigoverbindungen

Photooxidation of Leuco Dyes. XII. Time Resolved Investigations on the Photooxidation of Bis-sulfuric Acid Monoesters of Leucothioindigoid Compounds The photooxidation of 4, 4′-dimethyl-6, 6′-dichlorothioindigosol ( 1 ) was studied by means of laser and conventional flash photolysis. Three transients were detected and assigned to a radical R generated by homolytic splitting of one O S-bond of the parent compound and to two further radicals which are formed from R by hydrolytic cleavage of the second ester group. The latter two radicals are in a protolytic equilibrium with each other and react, depending on the nature of the solvent by H-atom abstraction, or by disproportionation forming the leuco-thioindigoid dye or both dye and leuco dye. A mechanistic scheme is proposed.