The effect of extraction condition on ‘HyperCoal’ production (1)—under room-temperature filtration

In order to produce ashless coal (HyperCoal) in a high yield, extractions with several organic solvents—tetralin, 1-methylnaphthalene, dimethylnaphthalene and light cycle oil (LCO) at 200–380 °C were conducted for various ranks of coals, and subsequent solid/solution separation was done at room temperature. LCO was found to be a useful, cost-effective solvent, since it gave similar extraction yields to three other reagent solvents. The extraction yield for Illinois No. 6 coal gradually increased over 200 °C, and a significant increase in extraction yield was observed from 350 to 360 °C. We succeeded in producing ashless coal with less than 0.1% in ash content for seven of nine coals used in this study.     

The volatilization behavior of chlorine in coal during its pyrolysis and CO2-gasification in a fluidized bed reactor

The volatilization behavior of chlorine in three Chinese bituminous coals during pyrolysis and CO₂-gasification in a fluidized bed reactor was investigated. The modes of occurrence of chlorine in raw coals and their char samples were determined using sequential chemical extraction method. The Cl volatility increases with increasing temperature. Below 600 °C the Cl volatility is different, depending on the coal type and the occurrence mode of Cl. Above 700 °C, the Cl volatilities for the three coals tested are all higher than 80%. About 41% of the chlorine in Lu-an coal and 73% of that in Yanzhou coal are organic forms, and most of them are covalently-bonded organic chlorine, which shows high volatile behavior even at low pyrolysis temperatures (below 500 °C), while the inorganic forms of chlorine in two coal samples are hardly volatilized even at low pyrolysis temperatures (below 400 °C). The restraining efficiency of addition of CaO on chlorine volatility is greatly dependent on pyrolysis temperature. The optimal restraining efficiency can be obtained at temperature range from 450 to 650 °C during pyrolysis of Lu-an coal. The volatile behavior of Cl is mainly dependent on temperature. Above 700 °C high volatility of Cl is obtained in both N₂ and CO₂ atmospheres.     

Carbon nanotube wires for high-temperature performance

We developed carbon nanotube wires (CNWs) and monitored in situ their electrical properties at high temperature conditions for the first time. The dominant type of CNTs present in the material and packing density of thereof proved to have a dominant effect on the thermal stability of CNWs. Furthermore, we showed that kinetics of CNW oxidation plays an important role and slow heating rates or prolonged heating times are essential for the proper determination of thermal stability of CNTs. To enhance the stability at high temperatures, we applied SiC coating onto the CNWs, what allowed a 300 °C improvement to the operational window, eventually reaching 700 °C in the long-haul. Correlation of the change in electrical properties with thermogravimetric response showed that the loss of electrical percolation takes place at 100 °C lower temperature than the last observed weight loss in CNTs content. Finally, we demonstrated feasibility of SiC-coated CNWs under high temperature conditions, by creating a heating device out of them. The presence of SiC layer gave rise to a significant improvement to the thermal stability of the CNT heaters, which now offer unprecedented range of operation reaching 700 °C, as compared to 400 °C when uncoated.     

Low temperature catalytic steam gasification of HyperCoal to produce H2 and synthesis gas

HyperCoal is an ultra clean coal with ash content <0.05 wt%. Catalytic steam gasification of HyperCoal was carried out with K₂CO₃ at 775–650 °C for production of H₂ rich gas and synthesis gas. The catalytic gasification of HyperCoal showed nearly four times higher gasification rate than raw coal. The major gases evolved were H₂: 63 vol%, CO: 6 vol% and CO₂: 30 vol%. Catalyst was recycled for four times without any significant rate loss. The partial pressure of steam was varied from 0.5 atm to 0.05 atm in order to investigate the effect of steam pressure on H₂/CO ratio. The H₂/CO ratio decreased from 9.5 at 0.5 atm to 1.9 at 0.05 atm. No significant decrease in gasification rate was observed due to change in partial pressure of steam. Gasification rate decreased with decreasing temperature and become very slow at 650 °C. The preliminary results showed that HyperCoal, an ash less coal, could be a potential hydrocarbon resource for H₂ and synthesis gas production at low temperature by catalytic steam gasification process.     

Effect of drying temperatures on starch-related functional and thermal properties of chestnut flours

The use of starchy flours in food systems greatly depends on the related functional properties of starch. The effect of drying temperatures on starch-related functional properties of flours obtained from fruits of the two most common Portuguese Castanea sativa varieties (Martainha and Longal) was evaluated. Flours were analysed for amylose and resistant starch contents, swelling ability, pasting properties and thermal characteristics. Drying temperature is positively correlated with amylose content, resistant starch and viscoamylographic properties, mainly the temperatures higher than 40 °C. Amylograms of fruits dried at 60 °C displayed higher peak viscosity (1370 B.U. and 2260 B.U. respectively for Longal and Martainha) when compared to the other temperatures tested (40 °C, 50 °C and 70 °C). Decreases in transition temperatures and in enthalpy evaluated by thermal analysis were observed with increasing drying temperatures, suggesting modifications in starch structure during the drying process. The effects of drying temperatures were more evident in Longal variety. The flours from the two chestnut varieties and from fruits dried at low temperatures and fruits dried at high temperature showed significant differences between the evaluated properties.     

Sintering of zirconia ceramics by intense high-energy electron beam

A comparative analysis of the efficiency of zirconia ceramics sintering by thermal method and high-energy electron beam sintering was performed for compacts prepared from commercial TZ-3Y-E grade powder. The electron energy was 1.4 MeV. The samples were sintered in the temperature range of 1200–1400 °C. Sintering of zirconia ceramics by high-energy accelerated electron beam is shown to reduce the firing temperature by about 200 °C compared to that in conventional heating technique. Ceramics sintered by accelerated electron beam at 1200 °C is of high density, microhardness and smaller grain size compared to that produced by thermal firing at 1400 °C. Electron beam sintering at higher temperature causes deterioration of ceramics properties due to radiation-induced acceleration of high-temperature recrystallization at higher temperatures.     

Linear thermal expansion coefficients of relaxor-ferroelectric 0.57Pb(Sc1/2Nb1/2)O3–0.43PbTiO3 ceramics in a wide temperature range

The objective of this work was to examine linear thermal expansion of virgin and poled 0.57Pb(Sc_1/2Nb_1/2)O₃–0.43PbTiO₃ ceramics between 30 °C and 600 °C by contact dilatometry. The thermal expansion dL/Lo of the virgin ceramic increases with increasing temperature until approximately 260 °C. The physical and technical thermal expansion coefficients were determined. At 260 °C the physical thermal coefficient is 2.08 × 10^?6 K^?1. Between 260.0 °C and 280.0 °C an anomaly in the thermal expansion vs. temperature and an endothermic peak in the differential scanning calorimetry curves correspond to the phase transition region from tetragonal to cubic phase. At temperatures from 280 °C to 600 °C the thermal expansion dL/Lo increases again.In the derivative of the dL/Lo heating curves of the poled ceramics, additionally to the anomaly at 270 °C, also the anomaly at 160 °C is observed, which is associated with the depolarization of the material during heating.     

Elucidation of hydrogen mobility in coal under reductive atmosphere using a tritium tracer method

Hydrogen exchange reaction of three Argonne coals (Illinois No. 6, Upper Freeport and Pocahontas #3) and Wandoan coal with tritiated gaseous hydrogen were performed at several temperatures. Hydrogen exchange reaction was performed in a flow reactor packed with 0.4 g of coal and 0.05 g of catalysts under the following conditions: pressure 15 kg/cm², temperature 200, 250, 300 °C, carrier gas H₂ or N₂ 5 ml/min. When a pulse of [³H]H₂ was introduced into a coal in H₂ carrier gas at several temperatures, the delay of [³H]H₂ pulse observed increased with increasing the reaction temperature and decreased with increasing coal rank. Further in the reaction of tritiated coals with gaseous hydrogen at constant temperature, the hydrogen exchange rate was estimated from the release rate of [³H]H₂. The apparent hydrogen exchange rate at 200 °C was higher than that at 250 °C. This shows that the hydrogen with low reactivity came to participate in the reaction at high temperature. When the reaction of tritiated coal with gaseous hydrogen was performed during heat treatment, one, two or three peaks of tritium concentration were observed in the outlet of the reactor depending on temperature (200, 250 or 300 °C, respectively) at which tritium was incorporated into coal initially. It was suggested that there were at least three kinds of hydrogen with different reactivity in coal.     

Preparation of carbon adsorbents from lignosulfonate by phosphoric acid activation for the adsorption of metal ions

Activated carbons were prepared from sodium lignosulfonate by phosphoric acid activation at carbonization temperatures of 400–1000 °C. The resulting materials were characterized with regard to their surface area, pore volume, pore size distribution, distribution of surface groups and ability to adsorb copper ions. Activated carbons were characterized by nitrogen adsorption, scanning electron microscopy, Fourier transform infrared spectroscopy and thermal gravimetric analyses. The results indicate that with increasing carbonization temperature, the surface area decreased from 770 m²/g at 400 °C to 180 m²/g at 700 °C and increased at higher temperatures to 1370 m²/g at 1000 °C. The phosphorus content peaked at 11% for carbon obtained by carbonization at 800 °C. Potentiometric titration revealed the acidic character of all the phosphoric acid-activated carbons, which were found to have total concentrations of surface groups of up to 3.3 mmol/g. The carbons showed a high adsorption capacity for copper ions even at pH values as low as 2.     

Thermal,optical and dielectric properties of Zn–Al layered double hydroxide

Zn–Al–NO₃–layered double hydroxide (Zn–Al–NO₃–LDH) was prepared by the co-precipitation method at a constant pH of 7 and a ratio of Zn/Al = 4. A thermal treatment was performed for LDH at various temperatures. Powder XRD patterns showed that the layered structure of the LDH samples was stable below 200 °C, which was also confirmed by thermogravimetric (TGA) and differential thermal (DTA) analyses. Infrared spectra of the samples showed the characteristic peaks of LDH, and changes of these peaks were observed when thermal treatment was performed above 150 °C. Diffuse reflectance spectroscopy of the samples showed more than one energy gap at calcination temperatures below200 °C. In samples calcined at 200 °C and above only one energy gap was observed at approximately 3.3 eV. The photocatalytic activity was found to increase with the increase of the ZnO crystal size, which can be achieved by increasing the calcination temperature of the samples. Because of the presence of water molecules and anionic NO₃⁻ in the interlayer of the LDH, the dielectric response of the calcined LDH can be described by an anomalous low frequency dispersion using the second type of Universal Power Law for calcination temperatures below 200 °C. The dielectric response of the calcined LDH above 150 °C displays the dielectric relaxation behaviour of ZnO because of the formation of a ZnO phase in the LDH within this temperature range.     

Influence of pressure on stable carbon isotope ratio and production yield of coal-derived methane

Two immature coals have been pyrolyzed in confined gold reactors from 250 to 600 °C, but at different constant heating rates (2 and 20 K/h) and under different pressures (30 and 65 Mpa). Yields of coal-derived methane show significant differences under different pressures even with the same analytical procedure. Generally speaking, increasing pressure can result in an increasing yield of methane, even though the experiment did show a slight decrease at low temperatures (≤400 °C) with high heating rates. The range of activation energies for methane generation is obviously narrower at 65 Mpa than at 30 MPa.Under high pressure conditions of 65 MPa, methane relatively depleted in ¹³C would be induced at the major stage of methane generation. However, our kinetic modeling results show that isotope-specific kinetic parameters, activation energies and frequency factors of methane at high pressure are almost the same as those at low pressure. The isotope ratios for methane precursors in two coals studied were also similar to each other but with some variances under the two different pressure circumstances. The modeled δ¹³C of cumulative methane by using two pressure-based series of kinetic parameters under geological conditions at 2 K/Myr exhibits less differences, which manifests that the effect of pressure can be regarded as being negligible. The modeled δ¹³C values of instantaneously generated methane at two different pressures under geological conditions are, however, significantly distinctive, and this is especially the case at high maturation stage of coal.     

Structural parameters and oxygen ion conductivity of Y2O3–ZrO2 and MgO–ZrO2 at high temperature

The oxygen ion conductivity of zirconia-based solid electrolytes doped with 8 mol% Y₂O₃–ZrO₂ (YSZ) and 9 mol% MgO–ZrO₂ (Mg-PSZ) at high temperature was investigated in terms of their thermal behavior and structural changes. At room temperature, YSZ showed a single phase with a fluorite cubic structure, whereas Mg-PSZ had a mixture of cubic, tetragonal and some monoclinic phases. YSZ exhibited higher ionic conductivity than Mg-PSZ at temperatures from 600 °C to 1250 °C because of the existence of the single cubic structure and low activation energy. A considerable increase in the conductivity with increasing temperature was observed in Mg-PSZ, which showed higher ionic conductivity than YSZ within the higher temperature range of 1300–1500 °C. A monoclinic-to-tetragonal phase transformation was found in Mg-PSZ and the lattice parameter of the cubic phase increased at 1200 °C. The phase transformation and the large lattice free volume contributed to the significant enhancement of the ionic conductivity of Mg-PSZ at high temperatures.     

Rheological behavior and thermal properties of pitch/poly(vinyl chloride) blends

The effect of adding poly(vinyl chloride) (PVC) and coke filler on the rheological behavior and thermal properties of a coal tar pitch was investigated with a view to developing an appropriate viscoelastic binder for the injection molding of graphite components. Dynamic mechanical analysis revealed that the pitch formed compatible blends with PVC featuring a single glass transition temperature (Tg) intermediate to the two parent Tg’s. Adding PVC to the pitch increased melt viscosity substantially and resulted in strong shear thinning behavior at high PVC addition levels. Adding coke powder as filler increased the melt viscosity even further and enhanced shear thinning trends. Pyrolysis conducted in a nitrogen atmosphere revealed interactions between the PVC and pitch degradation pathways: the blends underwent significant thermal decomposition at lower temperatures but showed enhanced carbon yields at high temperatures. Pyrolytic carbon yield at 1000 °C was further improved by a heat treatment (temperature scanned to 400 °C) in air or oxygen. However, carbon yield decreased with addition of PVC. In addition, the degree of ordering attained following a 1 h heat treatment at 2400 °C also decreased with increasing PVC content.     

Effects of heat treatment conditions on the structural and magnetic properties of MgCuZn nano ferrite

Mg_0.5Cu_0.05Zn_0.45Fe₂O₄ nanoparticles were prepared through sol–gel method using polyvinyl alcohol as a chelating agent. The as prepared sample was annealed at three different temperatures (500 °C, 700 °C and 900 °C). The phase formation, morphology and magnetic properties with respect to annealing temperature were studied using the characterisation techniques like X-ray diffraction (XRD) as well as Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM), respectively. The crystallite size and magnetisation showed increasing trend with annealing temperature. The coercivity increased up to a particular annealing temperature and decreased thereafter, indicating transition from single domain to multi domain state with increasing annealing temperature. Further, to know the suitability of the material, as a ferrite core, in multilayer chip inductors, the powder sample annealed at 500 °C was compacted in the form of torroids and sintered at three different temperatures (800 °C, 900 °C and 950 °C). The permeability showed increasing trend with the increase of sintering temperature since the permeability depends on microstructure. The frequency dispersion of permeability, for the sintered samples, demonstrated high frequency stability as well as high operating frequency. The cut-off frequency for the sintered samples 800 °C, 900 °C and 950 °C is 32 MHz, 30.8 MHz and 30.4 MHz, respectively.     

Electromagnetic characteristics and microstructure stability of Nextel 610 fiber after heat treatment

The thermal and microstructure stability of Nextel 610 fibers has great influence on high-temperature application of Nextel 610 fiber-reinforced ceramic matrix composites. In this work, Nextel 610 fibers were heat treated at 500–700 °C in vacuum and 800–1100 °C in Ar atmosphere, respectively. The sizing agent on Nextel 610 fiber surface could be decomposed into pyrolytic carbon, SiC and gaseous little molecules at lower temperatures, otherwise it was decomposed mainly in the form of gaseous little molecules at higher temperatures, so that the complex permittivity firstly increased and then decreased with the increasing of temperatures. The results showed that the annealed Nextel 610 fiber (T>900 °C) could be regarded as electromagnetic wave transparent fibers, while the tensile strength had declined by half when the temperature increased to 1100 °C. Therefore, Nextel 610 fibers after being annealed at higher temperatures could be further used as reinforcement to prepare high temperature ceramic matrix composites for electromagnetic wave absorption and transparent applications.     

Fractionation of coal by use of high temperature solvent extraction technique and characterization of the fractions

The authors have recently presented a new coal fractionation method that can separate a bituminous coal into several fractions, just like petroleum distillation, without decomposing coal. In this paper this method was applied to two bituminous coals and a brown coal. Sequential solvent extraction at different temperatures lower than 350 °C successfully separated the two bituminous coals into several fractions having different molecular mass compounds. Since all the extracted fractions are almost free from mineral matter, and some fractions were found to be fusible like a synthesized pitch when heated, the possibility of producing high performance carbon materials from the coal fractions was investigated. On the other hand, fractions obtained from the brown coal by the sequential solvent extraction were very close in both chemical composition and molecular mass, although the sequential extraction could greatly suppress the decomposition of the brown coal below 350 °C. The difference in the extraction behavior between the bituminous coals and the brown coal were attributed to the difference in their chemical structure.     

Phase transformation and morphological evolution of electrospun zirconia nanofibers during thermal annealing

Pure zirconia nanofibers were fabricated by electrospinning zirconia-polymer precursor and subsequent annealing. Fiber properties such as polymer decomposition, crystallization formation, phase transformation, surface morphologies, etc., were investigated by various techniques, including thermogravimetric analysis (TGA) and differential thermal analysis (DTA), high temperature differential scanning calorimeter (HTDSC), powder X-ray diffractometer (XRD), field emission scanning electron microscopy (FESEM), etc. It was found that the crystallization of as-spun fibers started at 450 °C and the initial crystallized zirconia phase was tetragonal (t), which began transforming to monoclinic (m) phase at 650 °C as evidenced by XRD; HTDSC showed at different thermal circles, the m-to-t transformation temperatures remained virtually unchanged while the reverse t-to-m temperatures systematically shifted from 924.9 to 978.6 °C as the progress of thermal circles; FESEM examinations revealed that fibers calcined to 1000 °C went through thermal grooving due to surface diffusion during heat treatment; fibers heated to 1370 °C formed the so-called “bamboo wires”, where volume diffusion was the dominant driving force.     

Microstructural and optical features of a Eu-monazite

The obtention of europium-phosphate nanoparticles by the precipitation method and its thermal evolution to become ceramics materials is presented. The monazite structure was obtained from the rabdophane phase after firing at 1000 °C during several hours. The powder characteristics made easy the pressing and sintering processes and it was possible to obtain high density bodies (relative density > 97%) at only 1200 °C. The fluorescence spectra and the lifetimes were investigated as a function of the heating temperature, as well, the microstructure and the residual glassy phase. It was found that higher sintering temperatures (>1500 °C) resulted in lower fluorescence emission than lower temperatures (maximum at 1200 °C) as consequence of the microstructure detrimental. The gamma irradiation up to the dose of 18 kGys did not produce any appreciable effect in the optical properties; however, the sintering temperature modified the optical absorption in the UV range.     

Safe and fast polyamidation of 5-[4-(2-phthalimidiylpropanoylamino)benzoylamino]isophthalic acid with aromatic diamines in ionic liquid under microwave irradiation

Ionic liquids are outstanding microwave-absorbing agents owing to their high ionic conductivity and polarizability, thus leading to a high heating rate and a considerably shortened reaction time. In this study, a series of novel optically active polyamides (PA)s with pendent 4-(2-phthalimidiyl-propanoylamino)benzamide units were prepared with excellent yields via a simple microwave heating method using 1,3-dipropylimidazolium bromide and triphenyl phosphite. In comparison with classical heating, microwave irradiation was demonstrated to be a more effective energy source. The resulting PAs have inherent viscosity in the range of 0.52–0.71 dL/g. All of the polymers were readily soluble in many organic solvents and showed good thermal stability associated with high glass-transition temperatures above 200 °C as measured by differential scanning calorimetry. Thermogravimetric analysis showed that the 10% weight-loss temperatures in nitrogen were 455 and 410 °C, a significant improvement in thermal stability having been observed with the increase in the side-chain length.     

Influence of ohmic heating on rheological and electrical properties of reconstituted whey solutions

Reconstituted whey solutions (in the range of 8–24% w/v solute concentrations) were heated from 20 °C to prescribed temperatures (30, 40, 50, 60, 70 or 80 °C) ohmically by applying voltage gradients of 20, 30 or 40 V/cm, and conventionally at water bath. Electrical conductivity changes with increasing temperature were linear during ohmic heating. Whey solutions have non-Newtonian characteristics since Herschel–Bulkley model satisfactorily fitted the experimental shear stress–shear rate data. “n” values were in the range of 0.520–1.503. The whey solution having 24% concentration had a yield stress of 0.006–0.024 Pa at low temperatures. Although temperature and concentration were critical factors for the consistency and the electrical conductivity changes during heating (p < 0.01), the voltage gradient was not effective statistically. The high correlation (between ?0.910 and ?0.991) was obtained between changes of electrical conductivity and consistency coefficient values during ohmic heating. Since activation energies for ohmic heating (26.34–45.79 kJ/mol) depending on solute concentration were lower than conventional heating (26.70–50.04 kJ/mol), reconstituted whey solutions were less sensible to temperature changes during ohmic heating. It was recommended that ohmic heating could be applied as a faster alternative heating method in the whey processing.