Kristalline und flüssigkristalline copolyester substituierter und unsubstituierter 4-hydroxybenzoesären

Three synthetic strategies were explored to lower the melting point of poly(4-hydroxybenzoate) below 400°C. Binary copolyesters of 4-hydroxybenzoic acid and 3-substituted 4-hydroxybenzoic acid were highly crystalline, regardless of composition, and did not melt below 400°C. In contrast ternary and quartenary copolyesters containing 3-bromo-4-hydroxybenzoic acid may possess melting points below 360°C. Binary copolyesters of 4-mercaptobenzoic acid and 3-substituted 4-hydroxybenzoic acids melt in the range of 360–400°C. Random copolyesters of 3-(4-hydrophenyl) propionic acid and 4-hydroxybenzoic acid are mainly amorphous with glass-transition temperatures between 50 and 15°C. They contain liquid-crystalline domains, which in the case of the 1:1 copolyester are stable over a range of ca. 400°C. The heat-distortion temperatures are low (60–80°C) due to the predominant influence of the amorphous matrix.     

Preparation and characterization of low overvoltage transition metal alloy electrocatalysts for hydrogen evolution in alkaline solutions

Transition metal electrocatalysts for hydrogen evolution were prepared by thermal decomposition of solutions containing nickel or cobalt and molybdenum, tungsten or vanadium on a metallic substrate and curing the oxide coated substrate under an atmosphere of hydrogen at elevated temperatures.The most active and stable hydrogen evolving cathode, based on a nickel and molybdenum combination, exhibited overvoltages of about 60 mV for over 11,000 h of continuous electrolysis in 30 w/o KOH at 500 mA cm^?2 and 70°C. The cathode was prepared by high temperature (ca. 400°C) treatment of a nickel substrate, coated with an aqueous solution containing nickel and molybdenum salts in the atomic ratio 60:40 followed by reduction of the resulting oxides at about 500°C in atmosphere of hydrogen.X-ray diffraction, and thermogravimetric and ESCA measurements, were employed to identify the active component of the nickel-molybdenum system responsible for its electrocatalytic activity. The results indicated that the electrocatalyst is a face centred cubic nickel-molybdenum alloy in which the molybdenum is randomly substituted at the nickel lattice.The electrochemical properties of a number of nickel-molybdenum electrocatalysts (NiMo = 60:40) were determined in the temperature range 20–80°C. Steady state measurements at different temperatures in 30 w/o KOH showed that the electrodes had low apparent activation energies (ca. 5 kcal mol^?1) and revealed the presence of two Tafel regions with transfer coefficients of 1.13 and 0.63. The corresponding exchange current densities at 70°C, based on the electrodes geometric areas, were 52 and 150 mA cm^?2 respectively. Results of potentiodynamic measurements and preliminary work on hydrogen oxidation are also presented.     

Analyse der potentiellen Explosionswirkung von kurzzeitig in die Atmosphäre freigesetzten Brenngasmengen. Teil I: Gesetze der Wolkenausbreitung und -deflagration aus Berstversuchen an Modellbehältern

Explosion hazard analysis of inflammable gas released spontaneously into the atmosphere . The processes of flash evaporation, atmospheric vapour cloud formation ignition and explosion after the bursting of vessels containing liquefied gas have been studied by model experiments with propylene heated up to 70°C and pressurized to 60 bar. The experiments have shown that a blast wave with considerable peak pressure in the vicinity of the vessel is produced already by flash expansion of the propylene. The experimentally determined decrease of peak pressure with growing distance could be scaled up to vessels of arbitrary size and different propylene temperatures. Scaling laws could be established as well for the calculation of peak pressure and positive pressure duration of the deflagration wave as functions of released mass and distance. The experiments have not revealed any evidence of a detonation process even when the cloud was ignited by an explosive charge.     

Rhenium,tungsten and molybdenum as substitutes for plantinum in aromatics hydrogenation catalysts

Three metal substitutes for platinum on alumina-supported catalysts have been investigated. These metals are rhenium, tungsten and molybdenum. In the absence of platinum, these metals are catalytically inactive. At high hydrogenation temperatures (≥100°C) rhenium, tungsten and molybdenum appear to substitute platinum up to at least 66.7, 50 and 33.3% of the platinum atoms, respectively, providing almost the same conversion as platinum. At low hydrogenation temperatures (～50°C), the catalyst containing 0.6 wt% Pt is more active than those containing metallic combinations. At low reaction temperatures, in particular for high platinum substitution ratios, tungsten appears functionless whereas molybdenum may act as an inhibitor for platinum.     

Explosionskenngrößen von Ethylenoxid und Ethylenoxid/Propylenoxid‐Gemischen

Gas phases of ethylene oxide and propylene oxide, commonly used for technical alcoxylation reactions, can decompose explosively with an enormous temperature and pressure rise even without the presence of air. For the estimation of consequences of such reactions explosion pressures and rates of pressure rise of EO and certain mixtures of ethylene oxide and propylene oxide at temperatures between 100 °C and 200 °C and pressures between 1 bar and 10 bar were determined experimentally using vessels with volumes of 3 dm³ and 100 dm³.     

Selektive Härtung von Fetten und Fettsäuren mit Sulfiden der Übergangsmetalle als Katalysatoren

Selective Hydrogenation of Fats and Fatty Acids with Sulfides of Transition Metals as Catalysts Sulfides of some transition metals are suitable as catalysts for the selective hydrogenation of fats and fatty acids. Ni₃S₂, a stoichiometrically, thermally and crystallographically defined compound is especially active. Also mixed catalysts containing tungsten sulfide and molybdenum sulfide besides Ni₃S₂ are sufficiently active. The same is true for cobalt sulfide catalysts, whereas molybdenum sulfide and tungsten sulfide exhibit considerably lower activities. The conditions of hydrogenation are essentially the same as customary: temperature range 180° to 210°C for fats, 200° to 220°C for fatty acids, hydrogen pressure 2–25 kg/cm², catalyst concentration 0.05 to 2 parts by weight of metal sulfide per 100 parts of fat or 0.5–5 parts by weight of metal sulfide per 100 parts of fatty acids. Using the above catalysts, the selectivity of S₃₁ or S₂₁ attained in the steps triene (polyene → monoene or diene → monoene is over 75. The remaining double bonds in the hydrogenated product possess almost exclusively the trans configuration. The above catalysts are resistant to sulfur compounds and they exhibit exceptional longevity. The regeneration can be performed with ease. Consequently, the pretreatment of the material to be hydrogenated can be limited to washing and drying.     

High Temperature Cyclic Oxidation Resistance of Iron Chromium Base Alloys

The cyclic oxidation behavior of an experimental stainless ferritic steel, without molybdenum and with copper‐aluminum‐titanium‐lanthanum additions, developed for solid oxide fuel cell applications, was evaluated and compared with the oxidation behavior of commercial austenitic and ferritic stainless steels. For the cyclic oxidation tests, the steel samples were tested at temperatures ranging from 600 to 800 °C. The experimental ferritic stainless steel showed the highest cyclic oxidation behavior among the studied steels at 700 °C and 800 °C, presenting a parabolic and logarithmic kinetics, respectively.     

Herstellung modifizierter Carbonsäuren aus α-Olefinen durch Hydroxycarbonylierung

Preparation of Modified Carboxylic Acids from α-Olefins by Hydroxycarbonylation The hydroxycarbonylation of α-olefins to carboxylic acids was investigated. Yields around 95% were achieved using NiJ₂ as catalyst at temperatures of ca. 200°C and carbon monoxide pressure of 30 atm. and higher for 3–7 hrs. The acids are composed mainly of isomers having 2-methyl branching as well as the normal ones and the 2-ethyl acids. Ca. 95% of the NiJ₂ is recovered from the reaction product by washing with water.     

Adsorption of chromium(VI) and nickel(II) ions on acid- and heat-activated deoiled spent bleaching clay

De-oiled spent bleaching clay was activated either by acid treatment followed by heat activation or by heat activation alone at temperatures between 200 and 800°C. The surface area of the heat-activated clay attained a maximal value of ≈120 m² g⁻¹ at temperatures between 400 and 500°C while the acid-heat-treated clay attained maximal surface area of ≈140 m² g⁻¹. The adsorption capacities of chromium [Cr(VI)] for both series studied increased as the activation temperature increased until 300°C and decreased again at higher temperatures. At lower pH, more than 95% of the Cr(VI) was absorbed in a solution with initial concentration of 1 mg L⁻¹ per gram of adsorbent activated at 300°C. The adsorption patterns followed Freudlich's isotherms. Two maximal values of adsorption capacities of nickel [Ni(II)] were observed at activation temperatures of 200 and 500°C for acid-treated samples, whereas these were at 200 and 700°C for the nonacid-treated samples. The amount of Ni(II) adsorbed increased with the pH of the solution for all samples studied. The maximal adsorption capacities of the adsorbents in solution containing initial Ni(II) concentration of 5 mg L⁻¹ per 0.5 g of adsorbent and at pH 6 were found to be 44 and 42%, respectively, for the acid-treated sample activated at 500°C and for the nonacid-treated sample activated at 700°C. They all obeyed both the Langmuir's and Freundlich's isotherms.     

On chemical and diffusional interactions between PCBN and superalloy Inconel 718: Imitational experiments

During a metal cutting process, chemical wear can become the dominant mechanism of tool degradation under the high temperatures and contact pressures that arise between the tool and the metal workpiece. This study focuses on the chemical and diffusional interactions between superalloy Inconel 718 and cubic boron nitride (cBN) tool material with and without TiC binder. It covers thermodynamic modeling and experimental tests in the pressure range of 0.1 Pa to 2.5 GPa at temperatures up to 1600 °C. The methods used include diffusion couples under both vacuum and high pressure, transmission electron microscopy (TEM) analysis and in-situ synchrotron observations. It is shown that cBN is prone to diffusional dissolution in the metal and to reactions with niobium, molybdenum, and chromium from Inconel 718. Adding TiC binder changes the overall degradation process because it is less susceptible to these interaction mechanisms.     

Structure and properties of iron containing glassy carbons

Glassy carbons containing iron were prepared from copolymers of furfuryl alcohol and ferrocene derivatives at heat-treatment temperatures from 500°C to 2500°C. The copolymerization produced a highly dispersed state of iron in carbonaceous matrices at least in the early stage of pyrolysis. Above 500°C, the homogeneously dispersed iron separated into irregularly spaced domains consisting of cementite, pure iron and iron compounds of unknown composition. Addition of iron resulted in a local graphitization of the glassy carbon at heat-treatment temperatures above 1000°C. At heat-treatment temperatures between 500°C and 800°C, electrical resistivities of the iron-doped carbons were much smaller than those of unmodified polyfurfuryl alcohol carbons but followed more or less the behavior of the latter for heat-treatment temperatures above 800°C.Measurements of mechanical properties indicated a remarkable increase in tensile strength of the low temperature carbons (500°C) with increasing iron content but the strength of the iron containing carbons decreased at higher carbonization temperatures.     

Preparation and Xylene‐Sensing Properties of Co3O4 Nanofibers

Co₃O₄ nanofibers were prepared by an electrospinning method and characterized by differential thermal and thermal gravimetric analyzer (DTA‐TGA), X‐ray diffraction (XRD), Fourier Transform Infrared Spectrometer (FT‐IR), and scanning electron microscopy (SEM). Xylene‐sensing properties of the as‐prepared nanofibers were also investigated in detail. The results showed that the morphology of the as‐prepared fibers was largely influenced by the calcination temperature. The Co₃O₄ nanofibers calcined at 500°C exhibited the highest response to xylene in a wide concentration range. Moreover, Co₃O₄ nanofibers calcined at 500°C also exhibited good selectivity, fast response (15 s) and recovery (22 s) rate at a low operating temperatures of 255°C. These properties make the fabricated nanofibers good candidates for xylene detection.     

Autoxidationsverhalten von Tritetradecylglycerinäther im Vergleich zu Trimyristin und Kokosöl

Autoxidation Behaviour of Tritetradecyl Glycerol Ether in Comparison with Glyceryl Myristate and Coconut Oil Tritetradecyl glycerol ether is considerably less stable towards atmospheric oxygen than glyceryl myristate and coconut oil: During the storage of tritetradecyl glycerol ether at 60°C up to 96 hours, the peroxide value increases continuously after an incubation time. Under the same conditions, the peroxide value of a reference sample containing 500 ppm of α-tocopherol did not increase. Upon heating to 180°C the tritetradecyl glycerol ether is degraded much more rapidly than glyceryl myristate and coconut oil. Chiefly polar reaction products are being formed, according to liquid and gel permeation chromatography presumably mono- and dialkyl glycerol ethers, tetradecanal, tetradecanol and further compounds not yet identified. The reaction products, in part, possess a higher molecular weight than the original compound. The resolution of the reaction products by liquid chromatography is described.     

Application of Halogens as Catalysts of CH4 Esterification

The aim of our work was to examine halogens as the catalysts of methane esterification in oleum. The experiments were performed at 160 °C in oleum containing 25 wt% SO₃, at methane pressure of 4.27 MPa. A mathematical model including the impact of the catalyst concentration on the initial reaction rate was proposed. The solubility of elemental iodine in 25 wt% oleum at 160 °C was found to be ca. 17 mmol/dm³.     

Compressive strength of fly‐ash‐based geopolymer concrete at elevated temperatures

This paper presents the compressive strength of fly‐ash‐based geopolymer concretes at elevated temperatures of 200, 400, 600 and 800 °C. The source material used in the geopolymer concrete in this study is low‐calcium fly ash according to ASTM C618 class F classification and is activated by sodium silicate (Na₂SiO₃) and sodium hydroxide (NaOH) solutions. The effects of molarities of NaOH, coarse aggregate sizes, duration of steam curing and extra added water on the compressive strength of geopolymer concrete at elevated temperatures are also presented. The results show that the fly‐ash‐based geopolymer concretes exhibited steady loss of its original compressive strength at all elevated temperatures up to 400 °C regardless of molarities and coarse aggregate sizes. At 600 °C, all geopolymer concretes exhibited increase of compressive strength relative to 400 °C. However, it is lower than that measured at ambient temperature. Similar behaviour is also observed at 800 °C, where the compressive strength of all geopolymer concretes are lower than that at ambient temperature, with only exception of geopolymer concrete containing 10 m NaOH. The compressive strength in the latter increased at 600 and 800 °C. The geopolymer concretes containing higher molarity of NaOH solution (e.g. 13 and 16 m ) exhibit greater loss of compressive strength at 800 °C than that of 10 m NaOH. The geopolymer concrete containing smaller size coarse aggregate retains most of the original compressive strength of geopolymer concrete at elevated temperatures. The addition of extra water adversely affects the compressive strength of geopolymer concretes at all elevated temperatures. However, the extended steam curing improves the compressive strength at elevated temperatures. The Eurocode EN1994:2005 to predict the compressive strength of fly‐ash‐based geopolymer concretes at elevated temperatures agrees well with the measured values up to 400 °C. Copyright © 2014 John Wiley & Sons, Ltd.     

Korrosionsschutzanstriche leichtlegierter Baustähle

Corrosion Protective Coatings for Light Alloy Constructional Steels A number of suggested processes are discussed. Customarily speaking, weatherproof constructional steels are light alloy steel varieties that can be employed without corrosion protection, since they form a stable layer of rust in the atmosphere. The low content of alloying components, such as ca. 0.5% copper, ca. 0.8% chromium, ca. 0.5% nickel, and in some cases 0.1% phosphorous impart stability against weathering influences. Discussions are made on whether at all or under what circumstances it is necessary to apply coatings; thereby conversion primers are considered, that are applied for temporary protection.     

ABSRACTERS

Steel containing sufficient titanium to combine with all of the carbon does not react with vitreous enamels like ordinary low-carbon steel or ingot iron so that white cover-coat enamels, without a ground coat, can be fused on it without blistering or black specking. The titanium content must be more than 4.5 times the carbon content. This steel has been made commercially by the basic open-hearth process, and the requirements for successful manufacture are explained. It is of excellent quality for deep-drawing and does not have a definite yield point even when normalized or annealed so that stretcher strains cannot occur in it. It is not subject to strain aging of any kind, even when strained as much as 17% and aged at 450°F. It is resistant to caustic embrittlement, and to attack by hydrogen at high temperatures and pressures, and it also resists sagging at enameling temperatures better than regular enameling steel or iron. The yield strength of this steel at room temperature as now manufactured commercially is low, but titanium steels of higher strength containing manganese, nickel, and copper are described, which have the same favorable enameling quality. These stronger steels have excellent ductility and toughness, fair weldability, good resistance to strain-aging embrittlement, and better resistance to grain growth at high temperature than the regular titanium enameling steel. Their properties, however, still remain to be checked on commercial heats.     

Sintering‐induced aromatization during n‐heptane reforming on Pt/Al2O3 catalysts

A platinum/alumina catalyst was sintered in oxygen and hydrogen atmospheres using two metal loadings of the catalyst: 0.3% Pt and 0.6% Pt. After sintering, the aromatization selectivity was investigated with the reforming of n‐heptane as the model reaction at a temperature of 500 °C and a pressure of 391.8 kPa. The primary products of n‐heptane reforming on the fresh platinum catalysts were methane and toluene, with subsequent conversion of benzene from toluene demethylation. To induce sintering, the catalysts were treated with oxygen at a flow rate of 60 mL min^?1, pressure of 195.9 kPa and temperatures between 500 and 800 °C. The 0.3% Pt/Al₂O₃ catalyst exhibited enhanced aromatization selectivity at various sintering temperatures while the 0.6% Pt/Al₂O₃ catalyst was inherently hydrogenolytic. The fact that aromatization was absent on the 0.6% Pt/Al₂O₃ catalyst was attributed to the presence of surface structures with dimensionality between two and three as opposed to essentially 2‐D structures on the 0.3% Pt/Al₂O₃ catalyst surface. On the 0.3% Pt/Al₂O₃ catalyst, the reaction product ranged from only toluene at a 500 °C sintering temperature to predominantly cracked product at a sintering temperature of 650 °C and no reaction at 800 °C. For sintering at about 650 °C, subsequent conversion of n‐heptane was complete and dropped thereafter. The turnover number was observed to change from 0.07 to 2.26 s^?1 as the dispersion changed from 0.33 to 0.09. The Koros–Nowark (K–N) test was used to check for the presence of internal diffusional incursions and Boudart's criterion was used for structural sensitivity determination. The K–N test indicated the absence of diffusional resistances while n‐heptane reforming was found to be structure sensitive on the Pt/Al₂O₃ catalyst. Copyright © 2006 Society of Chemical Industry     

XPS Characterization of reduced LaCoO3 perovskite

Three samples of LaCoO₃ were prepared by two different methods and calcined at 800 or 1000 °C. They had BET areas of 1, 12, and 16 m²/g and all of them showed pure perovskite X-ray diffraction patterns with identical unit cell dimensions. In a series of experiments the oxide, having larger surface area, was stepwise reduced in hydrogen at temperatures between 60 and 500 °C. The XPS spectra, taken at room temperature after evacuation at 400 °C at each reduction level, showed that the surface concentration of Co° was very low up to 300 °C but increased sharply between 300 and 350 °C (9–75%). This concentration further increased to 100% after 10 min reduction at 450 °C, but upon heating in hydrogen for an additional 10 min at 500 °C it decreased again to 75%. In another series of experiments the mixed oxide was reoxidized after each reduction. A fresh sample was reduced to 350 and 400 °C by contacting with hydrogen for 1 hr and evacuated at temperatures between 400 and 500 °C. Both high evacuation temperatures and reduction at 400 °C during 1 hr produced a sharp decrease in Co° surface concentration. These results are consistent with the catalytic behavior of this perovskite reported earlier by E. A. Lombardo et al. (4–7). A model is proposed to interpret the reduction of LaCoO₃.