High temperature lithium/sulphur batteries: a preliminary investigation of a zeolite—sulphur cathode

A reversible lithium/sulphur high temperature cell is described in which the cathode consists of elemental sulphur absorbed in a zeolite 4A matrix. A lithium—aluminium alloy is used for the anode and the electrolyte is a molten ionic salt consisting of a LiI-KI eutectic (m.p. 260°). The cell was operated at 300° and underwent more than 70 continuous charge/discharge cycles (800 h) without significant loss in efficiency. The coulombic efficiency was more than 90% and the energy density 404 Wh/kg (based on the masses of active electrode materials, viz lithium metal and zeolite 4A—sulphur). The cell showed an open circuit voltage of 1.80 V, a short-circuit cd of about 1.1 A/cm² and a maximum power of about 0.5 W/cm². The internal resistance was 0.54 Ω (cathode surface area ～ 3 cm²).     

Gases evolved and possible reactions during low-temperature oxidation of coal

Preliminary experiments have been made by pace-heating three coals from about ?40 °C to 120 °C at a rate of 0.5 °C/min in various concentrations of oxygen and analysing the effluent gases. Carbon monoxide was always the predominant gas produced. At the lower temperatures its production appeared to be more dependent on temperature than on atmospheric oxygen content. However, there is evidence of a critical temperature — about 70 °C — above which, provided that sufficient oxygen is available, spontaneous combustion of coal becomes inevitable. If the exothermic reactions could be controlled to prevent coal exceeding the critical temperature, incipient heating might be prevented. Even below 70 °C traces of certain gases were formed, some doubtless components of ‘gobstink’, the smell characteristic of spontaneous combustion, but in quantities too small to be reliably measured. Chemical mechanisms are suggested and tested in part, and determinations of carbon monoxide and acetaldehyde concentrations in a working colliery have provided some confirmation of them.     

Surface temperature of decomposing construction materials studied by laser‐induced phosphorescence

Measurements of surface temperature and mass loss of decomposing construction materials during rapid pyrolysis are presented. Experiments have been performed with samples of low‐density fiberboard, medium‐density fiberboard, particleboard and poly(methyl methacrylate) in a single particle reactor at temperatures between 300° and 600°C. Ultraviolet laser light was used to excite micrometer‐sized thermographic phosphor particles that were deposited on the investigated materials, and the temperature was obtained from temporally resolved measurements of the laser‐induced emission. The wood‐based materials show a similar behavior, with small differences being attributed to differences in material properties. The surface temperature rapidly increases to about 400°C when a particle is introduced to the hot reactor. The initial phase is followed by rapid decomposition during which the surface temperature is 380°–540°C. The heating rate is slowed down during the rapid pyrolysis, and again increases as the remaining char is heated to the reactor temperature. The poly (methyl methacrylate), however, melts and at high temperatures can be characterized as a liquid with a boiling point of about 400°C. Thermographic phosphors are concluded to be suitable for high precision remote measurements of the surface temperature of decomposing construction materials, and possibilities for further studies and developments of the technique are discussed. Copyright © 2004 John Wiley & Sons, Ltd.     

Confectionery fats. I. Preparation by interesterification and fractionation of pilot-plant scale

A cocoa butter-like fat has been prepared on a pilot plant scale by the interesterification of hydrogenated cottonseed oil and a triolein product or olive oil followed by fractional crystallization from acetone at two different temperatures. The coproducts—a fraction which consists primarily of trisaturates and is obtained by fractionation at 20 to 28°C., and a fraction which is primarily di- and triunsaturates and is obtained from the low temperature (0°C.) filtrate—are reused in the process. In five of the six pilot plant runs conducted, 100 pounds of 70∶30 or 75∶25 mixtures of the hard fat and liquid oil were used as starting materials. In the sixth run, 140 pounds were used. Yields varied from 25 to 35%. Characteristics of the cocoa butter-like fat products are discussed. Variations in the products were made by changing the ratio of starting materials to 75∶25 and by lowering the first crystallization temperature from about 28° to about 19°C. Operational data obtained show that the process has commerical feasibility. Solvent-to-fat ratio was only 4 to 1. Filtration rates based on production of dry solids were 9 to 44 pounds per hour per square foot of filter area, respectively, for the first and second crystallizations. Although time to attain crystallization temperature was about 4 hours in the pilot plant oeprations, laboratory data indicate that comparable products can be obtained for crystallization times as low as one-half hour. The shorter crystallization time would be more applicable for commercial consideration. The steps in the process are considered conventional in commercial processing.     

An aliphatic amine cured rubber modified epoxide adhesive: 1. Preparation and preliminary evaluation using a room temperature cure

Methods of preparing epoxy resins capable of being cured at room temperature to yield adhesives of high shear and peel strengths are examined. The preferred formulation consists of reacting the diglycidyl ether of bisphenol A with a dicarboxy-terminated butadiene—acrylonitrile (CTBN) rubber (10–15 phr) at 150°C for a minimum period of 2 h. These materials may be cured with diethyleneglycol bis-propylamine at room temperature for 3 days to yield adhesives which have shear and peel strengths of about 32 MN/m² and 5 kN/m respectively at 10 phr CTBN and about 26 MN/m² and 8 kN/m at 15 phr CTBN.     

Hydrogen production via solar‐aided water splitting thermochemical cycles with nickel ferrite: Experiments and modeling

Water splitting — thermal reduction cyclic studies with NiFe₂O₄ redox materials were performed in a differential fixed‐bed laboratory reactor in the temperature range 700–1,400^°C to quantify the effects of operation temperatures and steam mole fraction on hydrogen and oxygen yields. Hydrogen yield increased drastically by an increase of the water splitting temperature from 800 to 1,000^°C reaching a plateau at 1,100^°C. In parallel, a simple mathematical model was formulated describing the water splitting process via the heterogeneous surface reactions of water vapor with the redox powder material, from which, in conjunction to the aforementioned experiments, the kinetic parameters of the water splitting and thermal reduction reactions were extracted. The water splitting kinetic constants exhibited weak temperature dependence between 700 and 1,100^°C suggesting the existence on the redox material of more than one type of oxygen storage sites with respect to ease of exposure and accessibility to the gas phase. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1213–1225, 2013     

Thermal diffusivity and thermal conductivity of pyrolytic graphite from 300 to 2700° K

The thermal diffusivity and thermal conductivity of as-deposited, annealed, and stress-annealed pyrolytic graphite have been measured at room temperature and over the range 1500–2700°K. Values of the thermal conductivity parallel to the plane of deposition compare reasonably well with published results on similar materials, as do the values in the perpendicular direction at room temperature. The conductivity in the perpendicular direction for the annealed and stress-annealed materials is the first reported for such highly oriented materials at temperatures above 900°K, and they follow approximately a T^?n dependence with $\text{n ?}\text{1}\text{2}$ over the temperature range 1500–2700°K, where the conductivity is two-to-three times larger than expected from a T^?1 extrapolation from room temperature.     

Annealing-induced morphological changes in segmented elastomers

Thermal analysis has been used to study annealing-induced ordering in segmented elastomers. Twelve segmented elastomers were studied each having approximately 50% by wt hard segment content. Seven general classes of materials were examined including polyether and polyester polyurethanes, polyether polyurethane-urea, and polyether-polyester. Materials were slow cooled (?10°C min^?1) from the melt to an annealing temperature (?10°, 20°, 60°, 90° or 120°C) where they were annealed (16, 12, 8, 6 or 4 days, respectively). Annealing was followed by slow cooling (?10°C min^?1) to ?120°C after which a d.s.c. experiment was run. In general, annealing resulted in an endothermic peak at a temperature 20°–50°C above that of the temperature of annealing. This phenomenon was observed in both semicrystalline and amorphous materials. The closer the annealing endotherm was to a crystalline endotherm without exceeding it in temperature, the larger its size. Annealing endotherms resulted from hard or soft segment ordering. Only one annealing endotherm was observed for a given annealing history, even though in some materials hard and soft segments could exhibit annealing-induced morphological changes. Hard segment homopolymers were studied yielding results similar to the block polymers containing shorter sequences of the same material. This suggests that annealing-induced ordering is an intradomain phenomenon not associated with the interphase between domains, or necessarily dependent on the chain architecture of segmented elastomers.     

The effect of drawing temperature on multi-stage drawn ultra-high molecular weight polyethylene

The effect of drawing temperature on multi-stage drawn ultra-high molecular weight polyethylene (UHMWE) fiber, produced by gel spinning, has been studied. Drawing at higher temperature generally gives higher crystal orientation, as expected. The activation energy of drawing increased with the draw ratio and raw 4sequence. It varied at a given draw ratio and draw stage between two temperature ranges, 85 to 115°C and 115 to 135°C. Thus, for the first draw stage, the activation energy is ～ 19—35 KJ/Moe in the range of 85 to 115°C, and ～ 60—99 KJ/mole in the range of 115 to 135°C. In the second stage, the activation energy is 40 KJ/mole in the range of 105 to 115°C and 70—99 KJ/mole in the range of 115 to 135°C. In the third stage, the activation energy is ～ 92—100 KJ/mole in the range of 115 to 135°C.     

Beeinflussung des mechanisch-dynamischen Verhaltens von Polyamid 12 durch Wasser und Weichmacher

Similar to other polyamides, dry polyamide-12 shows two typical relaxation processes in the temperature range between—196°C and 150°C. The relaxation process at 50°C (γ-process, frequency 1 sec^-1) is related to a freezing process of the main chain mobility within the amorphous regions. The character of the molecular motions responsible for this process seems not to be influenced by water or plasticizer. The relaxation behaviour of the γ-process (approx. —150°C, freq. 1 sec^–1) in the presence of water or plasticizer indicates that the rotation of the methylene groups depends on the mobility of the carbonamide groups. A third relaxation process (γ′-process) appears between the β and γ region by adding water. This process is interpreted in a different manner as reported in the literature. Comparing the activation energy of the diffusion of water in polyamide-12 with that of the γ′-process it seems reasonable that above this transition temperature the water molecules are diffusing inter-or intramolecular between the carbonamide groups. At the temperature of the γ′-process, this diffusion process of the water molecules freezes in.     

Effect of γ-radiation on the thermal conductivity of polypropylene

The effect of ⁶⁰Co γ-radiation on the thermal conductivity of polypropylene (PP) has been studied over the temperature range 0–160°C. for radiation doses of 600 and 1800 Mrad. The conductivity of unirradiated specimens rises from 4.5 × 10^?4 cgs units (cal./cm.-sec.-°C.) at 0°C. to 4.8 × 10^?4cgs units at 80°C. and subsequently decreases with temperature to a value of about 3.1 × 10^?4cgs units at 160°C. Upon irradiation to 600 Mrad the thermal conductivity is lowered over the 0–150°C. temperature range. Above 90°C. the conductivity decreases with temperature and becomes relatively constant at 3.4 × 10^?4 cgs units from 120 to 160°C. Differential scanning calorimeter (DCS) measurements from 30 to 200°C. show that irradiation to 600 Mrad lowers the energy associated with crystalline melting and shifts the endotherm melting peak from about 160 to 105°C. Irradiation to 1800 Mrad results in additional lowering of the thermal conductivity over the 50–160°C. range, a further decrease in area of the endothermic peak and a shift of its maximum peak position to about 75°C. The effects of radiation on the thermal conductivity of polypropylene are compared and correlated with the observed effects of radiation on the dynamic mechanical behavior.     

Novel combustion synthesis of La3+-substituted MnFe2O4

La³⁺-substituted MnFe₂O₄ compounds have been prepared by using a novel combustion synthesis method. This process was found to yield homogeneous, finely crystalline powders without intermediate decomposition and/or calcination steps. Combustion-synthesized powders were sintered at 1000°C, and structural features of thus prepared materials were characterized by XRD analysis and FT-IR spectroscopy. The dc electrical conductivity of synthesized materials has been measured as a function of temperature up to 1000°C. The materials have shown semiconducting behavior at elevated temperatures. The ac electrical conductivity of synthesized samples was found to increase with increasing applied frequency. The dielectric constant and dielectric loss tangent have also been characterized. The article is published in the original.     

Preparation of new microporous titanium pillared kenyaite materials active for the photodegradation of methyl orange

In recent years, layered silicates have extensively been used to design new nanomaterials through functionalization. In this work, the lamellar sodium silicates magadiite and kenyaite have been hydrothermally synthesized in presence of ethanol as organic co-solvent. Materials of high purity and high crystallinity were obtained after only 24 h of crystallization at a temperature of 180 °C for kenyaite and a temperature of 150 °C for magadiite. It appears that the presence of ethanol in the synthesis medium tends not only to increase the crystallization rate, but also to stabilize the formation of magadiite.The as-synthesized Na-kenyaite was used as precursor for the preparation of titanium pillared clay materials. The resulting microporous titanium oxide pillared kenyaite materials exhibit large specific surface areas up to 180 m² g^?1 with a Ti contents up to 24 wt% and are active for the photocatalytic degradation under UV light irradiation of the organic dye methyl orange in water.     

Thermischer Abbau von Polyacrylnitril unter Luft

Hydrogen cyanide is the most important product during thermal degradation of polyacrylonitrile (PAN) under air at temperatures below 250°C. The amount of HCN evolved is temperature dependent; up to 250°C 17 mol-% and above 250°C only 10 mol-% HCN with regard to all nitrile groups in PAN were found. The energy of activation of this reaction was calculated to 15 kcal mol^?1 between 250 and 300°C. By means of DTA and IR-spectroscopy it could be shown, that a cyclization of the nitrile groups competes with the evolution of HCN. The energy of activation of the cyclization was found to be 29 kcal mol^?1. The decomposition of PAN preferentially starts—as indicated by thermogravimetric measurements—at the isolated double bonds originating from the elimination of HCN. In account of IR-spectra and elemental analysis—great amounts of bonded oxygen in degraded PAN were found—a suggestion for the structure of PAN degraded under air was made.     

Kinetics of reduction of solid copper sulphate by hydrogen and carbon monoxide

Cupric sulphate is reduced to metallic copper by H₂ at 225° to 400° with formation of Cu₂SO₄ as an intermediate product. Under the present experimental conditions, the reduction followered the equation k = 1 — (1 — R)^1/3, where R is the fraction reacted at time t and k is the velocity constant. The activation energy of the overall process in this temperature range lies between 15 and 17 Kcal/mole. Reduction by CO takes place at 400° to 650°C with formation of Cu₂SO₄ and Cu₂O and the activation energy in this temperature range lies between 24 and 29 Kcal/mole. Reduction in both cases is exothermic.     

Studies on ion—solvent interactions through viscosity measurements—potassium iodide in N,N-dimethylformamide—water mixtures

The viscosities of DMF—water mixtures and of KI solutions in these mixed solvents have been measured at 25°, 30°, 35° and 40° C, covering the whole range of solvent composition. The Jones—Dole B-Coefficient, after passing through a minimum in water-rich solvent composition region, increases with the increase in DMF content in the solvent mixture. The variation of viscosity of the solvent mixture and of B-coefficient with solvent composition and temperature have been discussed in terms of solvent—solvent and ion—solvent interactions.     

Thermal Conductivity: X,Data for Several Pure Oxide Materials Corrected to Zero Porosity

The thermal conductivities of several oxide ceramics have been measured. Data for fifteen pure oxides of theoretical density have been calculated. A table and plots of thermal conductivity from 100° to 1800°C. are included. The conductivity of the polycrystalline oxide materials measured varies from a factor of more than 100:1 at room temperature to about 10:1 above 1000°C.     

Compression creep behaviour of precursor-derived SiCN Ceramics

The creep behaviour of SiCN materials derived from polyvinylsilazane (PVS) and polyhydridomethylsilazane (PHMS) precursors was investigated in the temperature range between 1200 and 1550°C at compressive stresses between 30 and 250 MPa in air. Both materials show very similar creep behaviour. Decreasing strain rates with time were observed. Even after 4×10⁶ s creep deformation, stationary creep was not observed. Temperature dependence of the creep behaviour of such materials is very low. Dense passivating oxide layers were found on the surface of creep specimens tested in the temperature range up to 1500°C. At 1550°C active oxidation was observed.     

Towards new environmentally friendly fluoroelastomers: from facile chemical degradation to efficient photo‐crosslinkable reaction

Our objective is to develop a versatile and facile method that allows the synthesis of novel primary fluorinated co‐oligomers as precursors of photo‐crosslinkable networks. Transparent carboxyl‐terminated fluorinated co‐oligomers with molecular weights ranging between 2000 and 10 400 g mol^?1 were synthesized via facile degradation. The structural changes of fluorinated backbone were investigated using various analysis techniques. Then two major approaches, namely esterification and ring opening, were applied to obtain photochemical diacrylates (HEMA‐ and GMA‐IEM‐terminated co‐oligomers). These two precursors can be cured in 60 s under UV radiation without high temperature, high pressure or toxic solvent. The glass transition temperatures of HEMA‐ and GMA‐IEM‐terminated fluoropolymers at about ?20 °C, assessed from differential scanning calorimetry, showed an increase after crosslinking, and the glass transitions at 20 °C were no longer observed. These two crosslinked films were found to have higher decomposition temperatures, when compared to starting precursors. The contact angles on the surface of the two elastomer materials were only about 74° and 78°, which increased to 105° and 110° after UV irradiation. The tensile strength of the two cured fluoroelastomers can still reach 1.3 MPa at 200 °C. © 2019 Society of Chemical Industry     

Oxidation behavior and protection of carbon/carbon composites

The oxidation behavior of C/C composite sheet materials in air has been studied over a wide range of temperature. Gasification was detectable at around 500°C and above about 900°C, under the flow conditions used in the experiments, the overall rates of gasification were controlled by gas phase diffusion. The presence of catalysts reduced the temperature for the onset of gasification but had no effect on the kinetics in the diffusion-controlled region. Borate-based coatings containing refractory particulates and silicon carbide coatings sealed with borates have been found capable of protecting C/C composites against air oxidation for extended periods to temperatures of at least 1200°C.