Preparation of highly porous Al2O3 aerogel by one-step solvent-exchange and ambient-pressure drying

This work presents the preparation of alumina aerogel via sol-gel route utilizing ambient-pressure drying. A novel and efficient solvent-exchange process has been utilized as an alternative to conventional solvent-exchange processes by directly boiling the hydro-gel in solvent. High emphasis has been given in the selection of solvent based on polarity, boiling point, and specific gravity compared with water to facilitate efficient solvent-exchange and reuse of the solvent. The ambient-pressure-dried alumina aerogel was thermally treated at temperature from 300°C-1200°C to study the change in density, porosity, specific surface area, and microstructure along with crystalline properties. The ambient-pressure-dried alumina aerogel showed lower tapped density 0.108 g/cm³, specific surface area 519 m²/g, and total weight loss of 36.94% at 900°C. The degree of crystalline structure from amorphous was observed to increase with increase in thermal treatment temperature above 300°C, dominant above 700°C, whereas the transformation of bayerite γ-Al(OH)₃ to boehmite γ-AlO₂H was observed at 150°C-300°C and to γ-Al₂O₃ phase was observed at temperature of 300°C-1200°C.     

1H n.m.r. study of tars from flash pyrolysis of three Australian coals

The structure and composition of tars from the flash pyrolysis of one brown and two bituminous Australian coals were investigated by ¹H n.m.r. spectroscopy. Reaction times in a fluidized bed were about 1 s. For each tar the aromatic hydrogen content increases slightly with pyrolysis temperature up to ≈650 °C and then rapidly up to 900 °C. The aromatic carbon content increases rectilinearly with temperature. The yield of aromatic carbon reaches a maximum at 600–700 °C, and then decreases; the yield of aromatic hydrogen is independent of temperature. The proportion of aromatic material with condensed ring structures increases with temperature. Three temperature zones of reactivity can be recognized. Polymethylene chains and aromatic groups are stable up to 600 °C. Between 600 and 700 °C aliphatic substituents, other than α groups, decompose; between 700 and 900 °C α-aliphatic and aromatic groups also decompose, resulting in lower yields of tar.     

Low-cost,green synthesis and adsorption properties for dyes of novel porous gangue/palygorskite composite microspheres

In this work, gangue/palygorskite composite microspheres were fabricated through spray drying process and activated by calcination treatment. Its microstructure and adsorption capacity for the removal of dye (MB) were also studied, systematically. Results showed that kaolinite, α-quartz and palygorskite were the major phases in microspheres after proper calcination (lower than 900°C). BET-specific surface area of the microspheres reached the maximum value of 62.23 m²/g at 700°C, and then decreased with further increasing the heating temperature. In general, composite microspheres showed the largest adsorption capacity of MB after heat-treated at 700°C. The q_max of MB onto microspheres was 29.9-51.9 mg/g. The adsorption process of MB onto microspheres was well described by both the pseudo-second-order kinetic and Langmuir isotherm model. The composite microspheres also had extraordinary recyclability. This novel microsphere could be employed as a candidate for novel absorbent and filter medium in the practical application for dye treatment in industrial applications.     

Analysis of volatiles evolved during high-temperature treatment of thermally stable polymers. II. Polybutadiyne

Polybutadiyne samples were heated at 20°C/min up to 1200°C in a pyroprobe attached to a gas chromatograph/mass spectrometer (GC/MS). Analysis of the volatiles evolved during heating identified carbon dioxide (adsorbed on polymer surface), methane, ethylene, benzene, toluene, and traces of higher aromatics. Correlations have been made between sample temperature and evolution (onset, maximum, and end temperatures) of each of the five listed volatiles. Average polybutadiyne weight loss at 1200°C was 14 ± 2%. Two cure studies were performed in the pyroprobe, and it was shown that both weight loss and volatile evolution were affected. The results were consistent with a higher degree of polymer cross-linking as cure time and temperature increased. © 1996 John Wiley & Sons, Inc.     

Integration of High‐Frequency M‐Type Hexagonal Ferrite Inductors in LTCC Multilayer Modules

Monolithic hexagonal BaCo_1,3Ti_1,3Fe_9,4O₁₉ ferrite multilayers sintered at 900°C exhibit a fine‐grained microstructure with permeability of μ′ = 16 and a resonance frequency f_r ≥ 1GHz. Co‐firing of hetero‐laminates of ferrite with CT700 glass–ceramic LTCC tapes and with polycrystalline zinc titanate (ZT) LTCC tapes was studied. Co‐firing at 900°C of ferrite/CT700 leads to multilayers with cracks caused by substantial thermal expansion mismatch. Co‐fired ferrite/ZT multilayer laminates exhibit a permeability of μ′ = 16 and do not show any defects. Hexagonal ferrite multilayer inductor elements were integrated into ZT‐based multilayer LTCC modules and co‐fired at 900°C with Ag metallization.     

Pyrolysis of scrap tyres

Cross-section samples (2–3 cm wide), representative of a whole car tyre, have been pyrolysed under nitrogen in a 3.5 dm³ autoclave at 300°C, 400°C, 500°C, 600°C and 700°C. The whole solid, liquid and gaseous products generated during each pyrolysis were collected and characterised. No significant influence of temperature on the amount and characteristics of pyrolysis products was observed over 500°C. Tyre-pyrolysis liquids are a complex mixture of C₅–C₂₀ organic compounds, with a great proportion of aromatics. They have high gross calorific values, GCV (∼42 MJ kg⁻¹) and N and S contents (0.4% and 1.2%, respectively) within those specified for certain heating fuels. About 30 wt.% of such liquids is an easily distillable fraction with boiling points (70–210°C) in the range of commercial petrol, and about 60 wt.% of them have the boiling point range (150–370°C) typical of diesel oil. Pyrolysis gases are composed of hydrocarbons of which C₁ and C₄ are predominant, together with some CO, CO₂ and SH₂; they have very high gross calorific values (68–84 MJ m⁻³). Tyre-pyrolysis residues have equal dimensions as the original tyre portion and are easily disintegrable into black powder and steel cords. The black powder has surface areas comparable to those of commercial carbon blacks, but it has a great proportion of ash and impurities (∼12 wt.%), which are the inorganic fillers added to tyre rubber; it may have a potential use as semireinforcing or nonreinforcing carbon black.     

The effect of temperature on the properties of calcined red iron oxide pigments

The effect of calcination temperature on the properties of red iron oxide pigments obtained from FeSO₄, 7H₂O by calcination at constant temperatures over the range from 700 to 900 °C, has been investigated. It was found that the particle diameter increased from 0.065 μm at 700 °C to 0.25 μm at 900 °C; the increase was gradual up to 800 °C and abrupt at 850 and 900 °C. The colour changed from red with decreasing yellowish hue between 700 and 750 °C, to red with increasing bluish hue between 750 and 900 °C; the dominant wavelength increased from 599 nm at 700 °C to 610 nm at 900 °C. The tinting strength was found to vary irregularly with temperature, and to pass through a maximum at 750 °C. The oil absorption was found to decrease with temperature and to be a linear function of the specific surface area.     

Thermoelectric Properties of Reduced Polycrystalline Sr0.5Ba0.5Nb2O6 Fabricated Via Solution Combustion Synthesis

The thermoelectric properties of bulk polycrystalline Sr_0.5Ba_0.5Nb₂O₆ (SBN50) fabricated via solution combustion synthesis (SCS) and reduced at temperatures of 900°C–1150°C were explored. The Seebeck coefficient (S) of all samples increased over the entire range of testing temperatures; a peak S value of ?281 μV/K was obtained at 930 K for the sample reduced at 900°C. A metal‐insulator transition was observed in the electrical conductivity (σ) of samples reduced at 1000°C–1150°C, whereas only semiconducting electrical behavior was observed for the sample reduced at 900°C. An optimal balance between S and σ was achieved for the pellet reduced at 1000°C, which exhibited a maximum power factor of 1.78 μW/cm·K² at 930 K. Over a temperature range of 300–930 K, the thermal conductivity (κ) of as‐processed and reduced (1000°C) SBN50 was found to be 1.03–1.4 and 1.46–1.84 W/m·K, respectively. A maximum figure of merit (ZT) of 0.09 was obtained at 930 K for the 1000°C‐reduced sample. X‐ray photoelectron spectroscopy revealed that the Nb²⁺ peak intensity increased at higher reduction temperatures, which could possibly lead to a distortion of NbO₆ octahedra and a decrease in the Seebeck coefficient.     

Preserving Nanomorphology in YSZ Scaffolds at High Temperatures via In Situ Carbon Templating of Hybrid Materials

Yttria‐stabilized zirconia (YSZ, 8 mol% Y₂O₃) scaffolds, with surface areas up to 68 m²/g, were prepared by sintering hybrid inorganic‐organic propylene oxide (PO) gels in an argon atmosphere between 1050°C and 1350°C. During sintering, a hard carbon template forms in situ that preserves the scaffold nanomorphology. The carbon template is completely removed postsinter by heating in air to 700°C. Surface areas of 24, 14, 3.2, and 2.4 m²/g were achieved for argon sintering temperatures of 1050°C, 1150°C, 1250°C, and 1350°C, respectively. By adding glucose to the gel formulation, the amount of carbon template increases from 4 to 59 wt% and the surface area increases from 14 to 68 m²/g. Remarkably, the surface area only decreases to 59 m²/g upon heating to 900°C in air. This in situ carbon templating approach offers a flexible platform to create and preserve highly desirable surface areas and nanomorphologies while sintering at high temperatures. The utility of this approach to improve low‐temperature solid oxide fuel cell electrode performance is discussed.     

Influence of Crystallization Temperature on Ferroelectric Properties of Na0.9K0.1NbO3 Glass‐Ceramics

The correlation between the crystallization temperature and ferroelectric properties is studied by the measurements of impedance spectroscopy, activation energy, dielectric breakdown strength and dielectric constant in Na_0.9K_0.1NbO₃ glass‐ceramics, while different nucleating agents are added to optimize performance. It is found that the glass‐ceramics crystallized at the temperatures of the second exothermic peak (about 900°C) have higher crystal degree, lager interface numbers and larger amount of bulk charges accumulated at the interfaces. However, the higher crystal degree of ferroelectric phase results in a lower value of resistivity and E_a which represent better charge spreading behavior. The better charge spreading behavior and drastic increase in the accumulation of bulk charge also result in low breakdown strength. The results show that the glass‐ceramics heated at the temperature of first exothermic peak (about 700°C) with a reasonable crystal degree obtain higher energy storage density which is 1.94 J/cm³.     

SYNTHESIS OF ACTIVATED CARBON FROM JATROPHA SEED COAT AND APPLICATION TO ADSORPTION OF IODINE AND METHYLENE BLUE

This article provides evidence that jatropha seed coat residues can be used as a carbon source for preparing activated carbons that have good adsorption properties for iodine and methylene blue. Activated carbons were prepared using three different methods of activation, physical, chemical, and physico-chemical, for a range of activation temperatures (600°, 700°, 800°, and 900°C) and activation hold times (1, 2, and 3 h). The highest BET surface area (1479 m² g^?1) and the highest iodine adsorption (1511 mg g^?1) were obtained with physico-chemical activation at a temperature of 900°C and a hold time of 2 h. This activated carbon gave higher BET surface area and iodine adsorption than commercial activated carbon (1169.1 m² g^?1 and 1076 mg g^?1). The activated carbons prepared by physico-chemical activation at 900°C and 2 h were then tested for adsorption of methylene blue at a range of concentrations of methylene blue (100, 200, 300, 400, and 500 mg L^?1). It was found that a Langmuir isotherm gave a better fit (R ² = 0.999) to the observed adsorptions than a Freundlich isotherm (R ² = 0.884). For the adsorption kinetics, a pseudo-second-order model gave a better fit (R ² > 0.998, Δq _e  = 3.7%) than a pseudo-first-order model (R ² ≈ 0.95, Δq _e  = 85.6%). These results suggest that chemisorption is the rate-controlling step for the adsorption of methylene blue. The experimental results show that jatropha seed coat is a lignocellulosic waste precursor for preparation of activated carbon that is an alternative source for preparation of commercial-grade activated carbons.     

Measurement of the silica glass fatigue limit

The static fatigue limit, or the threshold stress intensity factor, K_o, for first subcritical crack growth has been measured directly in silica glass for T ≥ 600°C using the double cantilever beam (DCB) crack growth technique. Values measured ranged from 0.48 to 0.61 MPa·m^1/2 for a temperature range of 600°C-850°C, respectively. Cracks growing near the static fatigue limit had a time-dependence, where the crack growth decreased and appeared to stop at K ≈ K_o. Slow crack growth curves (K-v) have been measured from room temperature, 50% RH, up to 850°C with subcritical crack growth not measurable for T > 900°C. Increasing temperature was found to first increase, and then decrease the slope of Region I, and a peak in fatigue resistance was found around 150°C-300°C. At T > 600°C subcritical crack growth was observed for K higher than previously measured K_IC values. This observation and the static fatigue limit in silica are explained by a water-assisted stress relaxation mechanism at the crack tip.     

Evaluation of adhesion and mechanical properties of plasma sprayed NiCrAl/Al2O3-13wt.%TiO2 coatings

Plasma sprayed NiCrAl/Al₂O₃-13wt.%TiO₂ coating was fabricated and annealed at 300–900 °C in air atmosphere. The Elastic modulus (E), micro-hardness (H_V) and fracture toughness (K_ca) were evaluated by Vickers Indentation Fracture technique. The microstructure was studied by scanning electron microscopy. It can be concluded that with the increasing of annealing temperature, E and H_V at the interface of Substrate/Bond layer (S/B) are firstly increased and retain the highest value at 600 °C then decreased with higher annealing temperatures due to the phase transformation. E of the ceramic coating rised initially with annealing temperature increasing, reached the highest value at 400 °C, and then decreased with the further increasing of the temperature. The K_ca of the S/B interface firstly increased as the heating temperature increasing, confirming the crack initiation resistance increasing after annealing with the temperature below 700 °C. However, the K_ca decreased for further annealing temperature, even lower than that of the as-sprayed coating. Thereby, a proper annealing temperature can improve the mechanical properties of the coating since the coating becomes denser, ceramic lamellar structure becomes ambiguous and cracks are partially healed.     

The influence of EB-crosslinking on barrier properties of HDPE–mica composites

High-density polyethylene (HDPE) was compounded with untreated and surface-treated mica (10, 20, 40 wt %) and composites were injection-molded. The composites were radiation crosslinked (100, 300, 700 kGy) and hydrocarbon permeability, tensile impact strength, and tensile strength at 25 and 80°C of the composites were examined. The permeability of HDPE decreased from 7 to 3.6 g/(d × m²) by compounding the polymer with 20 wt % mica, and the permeability was additionally reduced to 1.3 g/(d × m²) by irradiation of the compounds (700 kGy). When surface-treated mica was used, the permeability of the composite furthermore decreased to about 1.0 g/(d × m²). Upon irradiation, the E modulus measured at 25°C increased 5% when the dose was 300 kGy. At 80°C, the corresponding increase was 40%. The tensile impact strength of an unfilled polymer increased more than three times by an irradiation dose of 700 kGy, and for a polymer with 10 wt % mica, the tensile impact strength was twice the level of an unirradiated composite. © 1996 John Wiley & Sons, Inc.     

A study of the Influence of the Synthesis Conditions upon the Catalytic Properties of LaMnO3.15 in Methane Combustion in the Absence and Presence of H2S

We report here on the activity and stability of LaMnO_3.15 for the methane combustion, in the absence and presence of H₂S, in a temperature interval of 250–750 °C. Two powders with different specific surface area were prepared by coprecipitation method using ammonia. Precursors calcined at high temperature, in air, for 10 h have led to LaMn-C solid with S_BET = 11 m²/g, while those previously aged in solution (hydrothermal treatment at 200 °C under 20 atm. for 24 h) then calcined at high temperature led to LaMn-HydC with S_BET = 31 m²/g. Temperature programmed reduction (TPR) profile of both samples showed two main peaks; surface and weakly bound oxygen named α-oxygen species and lattice oxygen β-oxygen species. While for LaMn-C the maximum reduction temperature peak corresponding to α-oxygen species was found to be ca. 600 °C, for LaMn-HydC samples this peak was shifted to lower temperature ca. 430 °C. Indeed, LaMn-HydC samples showed higher depletion of surface and weakly bound oxygen species compared to LaMn-C. The superior catalytic performance of LaMn-HydC in methane combustion was attributed to its high BET surface area and to both the high amount of α-oxygen species and their mobility. In the presence of 100 ppm H₂S in the feed this catalyst showed a higher propensity to poisoning by sulphur compounds than LaMn-C. This was attributed to the rapid formation of stable sulphate/sulphite species, the decomposition of which occurs above 800 °C.     

Effects of Ca-based additives on desulfurization during coal pyrolysis

The effects of different Ca-based additives on the sulfur removal of coals during pyrolysis up to 900 °C have been studied in a fixed-bed reactor. It was found that Ca(OH)₂ and CaO were quite effective to capture the sulfur-containing gases, 95% of the sulfur evolved from untreated coal was retained in the char by the use of additives. Both the tar yield and the sulfur content of the tar decreased with addition of Ca-based additives. The effect of Ca(OH)₂ was better than that of CaO due to its higher activity, but CaCO₃ had little effect because of its higher decomposition temperature (−900 °C) than the peak temperature range (400–500 °C) of sulfur-containing gases emission. There is remarkable sulfur retention effect with Ca(OH)₂ prepared by impregnation and ultrasonic treatment due to the higher dispersion in coal particles than by simple mechanical mixing. The ultrasonic treatment is the best method with regard to the lowest SO₂ release during the char combustion. XRD results showed that the sulfur captured by Ca-based additives during pyrolysis turned into CaS. FeS detected in pyrolysis char without additives disappeared in chars with additives, which indicated that CaO could react with FeS through solid-solid reaction. When the chars with calcium-additives were burned in fixed bed reactor, they gave out less SO₂ than the raw coal added with same additives. The best total desulfurization efficiency could reach to about 85%.     

Synthesis and Thermal Properties of Boron-Nitrogen Containing Phenol Formaldehyde Resin/MMT Nanocomposites

The nanocomposites of boron-nitrogen containing phenol formaldehyde resin (BNPFR) and organic-montmorillonite (O-MMT) (BNPFR/MMT) were synthesized from phenol, formaldehyde, boric acid, ammonia water and montmorillonite. The thermal properties of nanocomposites were characterized. The results show that the remaining weight fraction of BNPFR is 68.82% at 750°C, but the hybrid nanocomposite (BNPFR/MMT) is 75.51%. At 900°C, the remaining weight fraction of 7% O-MMT containing nanocomposites is 72.89%, which is 11.46% higher than BNPFR. The mechanical loss peak temperature T _p of BNPFR/MMT nanocomposites is 194.6°C, which is higher 7.3°C than that of BNPFR.     

Phase development in ZnO varistors

Based on a typical ZnO varistor composition (97·0 mol.-% ZnO, 1·0 mol.-% Bi₂O₃, 1·0 mol.-% Sb₂O₃, 0·5 mol.-% MnO and 0·5 mol.-% Co₃O₄), phase development of the ZnO varistor during sintering has been investigated using in situ high temperature X-ray diffraction up to 900°C, and conventional ambient X-ray diffraction for samples sintered at 900°C to 1250°C. The results indicate that α-Bi₂O₃ can be detected until 700°C; the pyrochlore phase can be detected in the samples heat treated at 700°C and up to 1250°C; the spinel phase is present at and >900°C. However, the main phases in the varistor are established by 950°C. By this temperature, the essential microstructure features are formed, and the varistors exhibit non-linear electrical properties, with a non-linear coefficient α of 35 and breakdown field of 8000 V cm^?1. With increasing sintering temperature, both the α value and breakdown field decrease.     

Effects of cultivar and tempering procedures on crude soybean oil volatiles

The effects of soybean cultivar and tempering procedures on crude soybean oil volatiles were investigated by gas chromatography/mass spectrometry (GC/MS). Varietal differences in volatiles were not obvious. Trends in volatile contents due to tempering were noted primarily when comparing mean peak areas of these compounds in oils stored 16 days at 60°C. Differences in volatiles in response to tempering were not apparent in oils that had not been stored. Equilibration of beans with water resulted in oils with higher volatile contents than those from untempered beans. Steaming lowered volatiles from equilibrated values, and pressure steaming had an even more dramatic lowering effect.     

Stabilizer Reaction is Cast Double Base Rocket Propellants. Part VIII: Characterization of propellant gassing properties during simulated aging

The decomposition process of two cast double base (CDB) propellant compositions was measured in vacuum. The process of gas evolution during heating of propellant compositions in vacuum has been studied using Vacuum Stability Test (VST) and Gas chromatography/ Mass Spectrometry (GC-MS) techniques. The results for the two different compositions aged at different storage temperatures for different periods of time were compared. VST has been used to quantify the amount of gases evolved during heating of propellant (aged and unaged) compositions at 100°C in vacuum, while quantitative GC-MS has been used to identify and quantify the evolved gases when the same propellant compositions were heated at 60 °C and 70 °C at low free volume. The results have shown that the amount and type of gases evolved depend on the composition of propellant, percentage of stabilizer etc. Composition 1 evolved CO₂, CO, N₂, NO and N₂O and produced the greater total gas volume, while Composition 2 evolved C0₂, CO and N₂ only. In each case C0₂ was the predominant gas and Composition 1 produced more COz but less CO than Composition 2. It is suggested that these differences in gas evolution profiles are due to the presence of different ballistic modifiers in the two propellant compositions. Gas evolution assessment using VST technique cannot be the strict measure of double base propellants stability.