An investigation on the heterogeneous nature of mineral matters in Assam (India) coal by CCSEM technique

This is a very first preliminary investigation on the distribution of heterogeneous nature of mineral matter in one of the industrially important Assam (India) pulverized coal using computer-controlled scanning electron microscopy (CCSEM). The results show that clay minerals, quartz, pyrite, and pyrrhotite form the bulk of the mineral matter. Minor minerals, such as calcite, dolomite, ankerite, barite, oxidized pyrrhotite, and gypsum, are also observed in the sample. The particle size distribution (PSD) of the included minerals is generally observed to be finer than that of the excluded ones in the coal. As a consequence, the coal rich in included minerals has more small mineral particles, which may affect its reactivity. Regarding the association of individual mineral species, the proportion of included to excluded is found to be higher in major cases. With regard to the modes of occurrence of major inorganic elements, it is found that Si mostly occurs as quartz and clay minerals, while Al mostly occurs as silicate minerals. Fe is primarily present as iron sulfides, iron oxide, and Fe-Al-silicate. S is partitioned into iron sulfides and gypsum. Most Ca occurs as carbonates and gypsum, with a minor fraction associated with clay minerals. Mg is mainly present as dolomite and clay minerals, with a very minor fraction present as ankerite. The majority of alkali elements are associated with aluminosilicates. P is mostly associated with kaolinite and/or present as more complex compounds containing Al, Si, and other elements as apatite is found to be absent in the coal studied. Ti is mainly present as rutile and kaolinite.     

Liquid-phase alkylation of Assam (Baragolai) coal

Liquid paraffin which consists of a large number of alkylated aliphatics and aromatics seems to be acting as an alkyl group transfer medium to receptive complexes like coal. The alkyl group receptive spots could be created in the coal complex by treatment with molten alkalis like sodium or potassium hydroxide. By repeating extractions of fresh coal with the same volume of liquid paraffin on a laboratory scale it was found that a stage was reached when liquid paraffin became rich enough in alkyl groups to become an alkyl group donor. This suggests a method for liquid phase alkylation of coal.     

不同煤阶煤焦炭显微结构与热性质的研究

采用模拟焦炭反应性和反应后强度,研究了不同变质程度单种煤焦炭显微结构与热性质之间的关系。中等变质阶段的焦煤、肥煤和瘦煤所制焦炭有较高的各向异性,低变质程度的气煤、1/3焦煤以及高变质程度的贫煤所制焦炭各向异性程度较低。焦炭的热性质与焦炭的各向异性有很好的相关性,焦炭反应性随各向异性程度的增大而减小,反应后强度则随各向异性的增大而增大。     

Block copolyetheresters with poly(trimethylene 2,6-naphthalenedicarboxylate) segments: Effect of composition on thermal properties

Block copolyetheresters with hard segments of poly(trimethylene 2,6-naphthalenedicarboxylate) and soft segments of poly(tetramethylene oxide) were prepared by melt polycondensation of dimethyl 2,6-naphthalenedicarboxylate, 1,3-propanediol and poly(tetramethylene ether)glycol (PTMEG) of molecular weights of 650, 1000 and 2000. The block copolyetheresters were characterized by FTIR, ¹H NMR, DSC, X-ray diffraction, TSC (thermal stimulated current), DMA and TGA. It was found that the thermal transitions were dependent on the composition. As the charge molar ratio of PTMEG to dimethyl 2,6-naphthalenedicarboxylate, x, increased, the T_m and ΔH_m of the polyester segments decreased, which has been also confirmed by the X-ray diffraction data. The polyether segments of the block copolyetheresters derived from PTMEG2000 could crystallize after cooling, but those of the block copolyetheresters derived from PTMEG1000 and PTMEG650 could not crystallize. The DSC, TSC and DMA results show consistent T_g data of the polyether segments. Based on the shift in T_g of the polyether segments, the amorphous parts of the polyether segments and the amorphous parts of the polyester segments were immiscible for the block copolyetheresters derived from PTMEG2000, but became partially miscible for the block copolyetheresters derived from PTMEG1000 and PTMEG650. The TGA results indicated that composition had little effect on thermal degradation under nitrogen.     

Sol-gel processing and characterization of (RE-Y)-zirconia powders for thermal barrier coatings

The effect of doping on the structural, morphological and thermal properties of ZrO₂-XO_1.5 (X = Y, La, Sm, Er) solid solutions for thermal barrier (TBC) applications was investigated. Oxide powders of various compositions from 9.7 to 40 mol% XO_1.5 (X = Y, La, Sm, Er) were synthesised by the sol-gel route. The structural analysis of the powders was performed using X-ray diffraction analysis coupled with Rietveld refinements and the measurement of their specific surface area with the BET method. For each rare earth dopant, the morphology of the powders varies from monoliths to agglomerates of thinner particles when the doping amount increases. In order to determine the specific heat, the thermal diffusivity at room temperature and the thermal expansion coefficient of some selected compositions, DSC, laser thermal diffusivity and high-temperature dilatometry measurements were performed on samples densified by Spark Plasma Sintering. Working thermal characterisation indicated that zirconia doped with 30 mol% SmO_1.5 and ErO_1.5 have better insulation properties and a lower thermal expansion coefficient than our reference YSZ ceramic. These various compositions are very promising for the elaboration of multilayer TBCs by the sol-gel process.     

Effect of Ni substitute in off-stoichiometric Bi(Pb)-Sr-Ca-Cu(Ni)-O superconductor. Excess conductivity,XRD analysis and thermal behaviour

Two phases (2223 and 2212) are identified in Bi_1.8Pb_0.3Sr₂Ca₂(Cu_1-xNi_x)_3.3O_y superconductor system, sintered at 847?°C for 322?h, in partial nitrogen atmosphere. The volume fraction of 2223-phase is strongly dependent on Ni doping: 78.37% for x?=?0.002, 70.29% for x?=?0.005% and 51.13% for x?=?0.015. The unit cells of 2223 and 2212 phases were indexed as tetragonal structures, having different lattice constants. Plots of resistance versus temperature (four points method) on cooling to 77?K, evidenced that the critical temperature for the transition to the superconductor phase, T_c, is linearly decreasing from 106.21 to 93.47?K when the Ni content is varying from x?=?0.002 to x?=?0.03. From log-log plots of the excess-conductivity we calculated the cross-over temperatures between 3D and 2D dimensionality as well as from 2D to SWF (short wavelength fluctuation) behaviour, the coupling factor and the coherence length for all the samples. Thermal analysis of the resulting samples (after the last sintering) was performed by heating each sample from room temperature (RT) to 1000?°C at a rate of 10?K?min^?1 in dynamic air atmosphere (150?cm³ min^?1). A clear dependence on Ni content is seen by TG and DSC, but a relative thermal equilibrium between the two phases, 2223 and 2212, in RT-869?°C range, is observed. Strong endothermic effects (melting accompanied by small decomposition processes) begin at around 869?°C for all Ni doped samples. The results for the specific heat capacities, calculated from DSC plots, are also presented. Contribution of the crystal lattice to the estimated specific heat capacity was in conformity with the Einstein model, the Einstein temperature values being dependent on Ni content.     

Synthesis,crystal structure,photoluminescence of Ba3Y2(BO3)4:Er3+ and thermal expansion of Ba3Y2(BO3)4

The Ba₃Y_2–xEr_x(BO₃)₄ (х = 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) phosphors were obtained by crystallization from a melt. The Ba₃Y₂(BO₃)₄ crystal structure was refined from single crystal X-ray diffraction data to R = 0.037. Its anisotropic atomic displacement parameters for all atoms were refined for the first time. The borate crystallizes in the orthorhombic crystal system, space group Pnma with unit cell parameters a = 7.673(1), b = 16.44(1), c = 8.977(2) Å, V = 1132.3(3) ų, Z = 4. These phosphors are isotypical to those of the A₃M₂(BO₃)₄ (A = Ca, Sr, Ba, M = Ln, Y, Bi) family. The crystal structure contains the isolated BO₃ triangles, two general and a special one independent crystallographic sites for large cations, which are disordered over sites. Thermal behavior of Ba₃Y₂(BO₃)₄ was investigated by high-temperature X-ray powder diffraction and thermal expansion coefficients are calculated in a wide temperature range. An inflections of temperature dependencies of the unit cell parameters is observed in a range 600–740 °C. Luminescence spectra, excitation and kinetic curves of the Ba₃Y₂(BO₃)₄:Er³⁺ series are reported. A maximum luminescence intensity is observed for the x = 0.1 sample. According to vibrational spectroscopy data no structural changes upon activation of the Ba₃Y₂(BO₃)₄ matrix with the Er ions are observed.     

Change in crystallinity of poly(vinylidene fluoride) due to thermal evaporation

Dielectric properties are reported for thin transparent poly(vinylidene fluoride) (PVDF) films, with thickness less than 1 μm, obtained by the thermal evaporation technique. This technique had to be used with the utmost care and control over the temperature of the evaporation source to obtain transparent, undegraded films of PVDF. Capacitance and loss tangent measurements were carried out on these films in the frequency range of 20 Hz to 1 MHz and the temperature range of 25-160°C. It was found that the maximum in ϵ′-t plots at 1 kHz and tan δ-t plots at 100 Hz for these films appeared at 50 and 35°C, respectively, which are lower temperatures than those reported for solution cast PVDF films. This is attributed to the lowering of crystallinity in the thermally evaporated films. X-ray diffraction studies and IR studies also confirmed these observations. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 225–230, 1997     

Theoretical investigation of mechanical and thermal properties of MPO4 (M = Al,Ga)

Minimum lattice thermal conductivities and mechanical properties of polymorphous MPO₄ (M = Al, Ga) are investigated by first principles calculations. The theoretical minimum thermal conductivities are found to be 1.02 W (m K)^?1 for α-AlPO₄, 1.20 W (m K)^?1 for β-AlPO₄, 0.87 W (m K)^?1 for α-GaPO₄ and 0.88 W (m K)^?1 for β-GaPO₄. The lower thermal conductivities in comparison to YSZ can be attributed to the lattice phonon scattering due to the framework of heterogeneous bonds. In addition, the low shear-to-bulk modulus ratio for both β-AlPO₄ (0.38) and β-GaPO₄ (0.30) is observed. Our results suggest their applications as light-weight thermal insulator and damage-tolerant/machinable ceramics.     

Envisioning the composition effect on structural,magnetic, thermal and optical properties of mesoporous MgFe2O4-GO nanocomposites

The effect of variation in composition on the structural, magnetic, optical and photo catalytic activity of magnesium ferrite (MgFe₂O₄) -graphene oxide (GO) nanocomposites was studied. Magnetic nanocomposites of GO and MgFe₂O₄ nanoparticles (NPs) with varying w/w ratio were synthesized by facile sonication method. X-Ray diffraction patterns confirmed the presence of spinel ferrite phase in the nanocomposites with the crystalline size 8–32 nm. Fourier transformation infrared (FT-IR) spectra of the nanocomposites displayed absorption bands corresponding to GO and MgFe₂O₄ NPs along with red shift of bands corresponding to C=O, C=C and O-H stretching. Thermo gravimetric analysis confirmed higher stability of nanocomposites over pristine GO. Saturation magnetization increased from 3.63 to 11.10 emu/g with the increase in content of MgFe₂O₄ NPs in the nanocomposites. Scanning electron microscopy analysis along with energy dispersive spectroscopy (SEM-EDX) confirmed the presence of MgFe₂O₄ NPs along with GO sheets. Immobilization of clusters of MgFe₂O₄ NPs onto GO sheets was evident from transmission electron micrographs (TEM) of all the nanocomposites. BET surface area of the nanocomposites ranged from 63.04 to 165.29 m²/g and was maximum when GO:MgFe₂O₄ w/w ratio was 1:0.5. It was markedly higher than pristine GO and MgFe₂O₄ NPs. Optical studies revealed lowering of the band gap in the nanocomposites upto 2.21 eV as compared to pristine MgFe₂O₄ NPs. Photoluminescence (PL) spectra of nanocomposites displayed quenching of PL intensity with increase of GO content. Band gap also displayed similar trend. The synthesized nanocomposites were used as photocatalysts for methylene blue dye degradation under visible light irradiation. The nanocomposite with GO to MgFe₂O₄ ratio 1:0.5 displayed best activity with complete degradation of dye in 30 min. The results confirmed that the composition of GO based magnetic nanocomposites can be tailored for efficient removal of contaminants.     

Unusual thermal relaxation of viscosity-and-shear-induced strain in poly(ether-ketones) synthesized in highly viscous polyphosphoric acid/P2O5 medium

We recently described an improved method to synthesize poly(ether-ketones) or PEKs. It utilized an optimized mixture of polyphosphoric acid (PPA) and P₂O₅ that is not only milder, less corrosive and less expensive than super-acid media, but also can play the multiple roles of solvent, Friedel-Crafts catalyst and dehydrating agent. The as-prepared PEKs from such a highly viscous reaction medium displayed unexpected, thermally induced relaxation exotherms regardless of the amorphous or semi-crystalline nature of polymer. This thermal behavior was not observed for the formally identical polymers [viz. pPEK or poly(oxy-1,4-phenylenecarbonyl-1,4-phenylene] which is normally semi-crystalline) that were separately prepared in a much less viscous mixture of methanesulfonic acid and P₂O₅ (Eaton's reagent) or N-methyl-2-pyrrolidinone (NMP). Such an observation was first made when both samples of pPEKs were subjected to the same thermal history and the thermal relaxation exotherms were observed only for the pPEK sample that was prepared in PPA/P₂O₅ medium. Further confirmation of viscosity-and-shear-induced strain stored in the as-synthesized PEKs was provided by a systematic annealing study with differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) analysis and Fourier-transform infrared spectroscopy (FT-IR). Based on these data, pPEK was successfully compression-molded in the temperature range of 230-250 °C which is more than 100 °C below its melting temperature.     

聚醚砜的磺化与热性能

以浓硫酸为溶剂 ,氯磺酸为磺化剂对聚醚砜 (PES)进行了磺化 ,制备了不同磺化度的磺化聚醚砜 (SPES)。探讨了反应的影响因素 ,分析了 SPES的热稳定性。结果表明 SPES的 Tg较 PES升高 ,随着磺化度的增加 ,SPES的降解温度降低。     

Layered ceramics based on InGaO3(ZnO)2: Preparation and experimental investigation of high-temperature heat capacity and thermal conductivity

This paper reports on a method for producing ceramics from a high-purity, submicron InGaO₃(ZnO)₂ powder synthesised using a PVA-assisted gel combustion method, as well as an experimental study of the thermophysical properties of the ceramic materials obtained. The platelet-like crystallites of the InGaO₃(ZnO)₂ obtained were several microns long and up to several hundred nanometres thick. Layered ceramics obtained by sintering compacted InGaO₃(ZnO)₂ powders at temperatures of 1373–1773 K had a bulk density that was 68–96 % of the theoretical density. The temperature dependence of heat capacity in the range 306–1346 K was studied experimentally for InGaO₃(ZnO)₂ using the DSC method. It was found that, in the range 323–1173 K, layered InGaO₃(ZnO)₂ ceramics had a low thermal conductivity, which decreased from 2.0–1.3 W/(m K. The results obtained make it possible to consider this material as a promising thermal barrier coating.     

Analysis of hydrothermally-treated and weathered coals by X-ray photoelectron spectroscopy (XPS)

Analysis of hydrothermally-treated and weathered coals by X-ray photoelectron spectroscopy (XPS) was carried out, and the XPS C(1s) and N(1s) spectra obtained were curve-resolved into four peaks (C-C/CC/C-H, C-O, CO, and O-CO) and three peaks (pyridinic-N, pyrrolic-N, and quaternary-N), respectively. Upon hydrothermal treatment, the amount of carbon-oxygen forms decreased; while the ratio of pyridinic-N increased and quaternary-N decreased. On the other hand, some bituminous coals were subjected to natural weathering and laboratory oxidation, which gave opposite results compared to the hydrothermal treatment. The changes in the carbon-oxygen and organic nitrogen forms were discussed in terms of the effect of hydrothermal treatment and weathering (oxidation). Also, the XPS analysis of various kinds of coals (43 SS coals) was carried out, and the amounts of carbon-oxygen and organic nitrogen forms were discussed in terms of coal rank (carbon content).     

Influence of volatile matter and deposited carbon on coke yield from coals

The relations between coke yields and the volatile matter content of 30 individual and 30 blended coals were investigated. Coke yields and deposited carbon related to volatile matter content can be expressed in the following equations: CY (%) = 97.89?0.86 VMch+VMc; and DC (%)= ?2.24+0.16 VMch; where: CY=real coke yield; VMch = volatile matter content of charging coal; VMc=volatile matter content of coke, and in the case of <2%; DC = deposited carbon. The test results show excellent correlation with practice.     

A kinetic investigation of thermal degradation of poly(vinyl formals)

Several samples of poly(vinyl formal) having the same vinyl alcohol content (8–9%) but varying contents of vinyl acetate (6–22%) and vinyl formol (70–85%) were prepared and subjected to thermogravimetric analysis, in air and nitrogen atmospheres, employing both isothermal and dynamic methods. Kinetic parameters determined from both the isothermal and dynamic TGA data are compared. The activation energy is seen to be largely dependent on the degree of conversion, implying a complex degradation reaction. The activation energy is also much less for degradation in air than in nitrogen, which can be explained by a reaction with oxygen-producing structures favoring degradation. The activation energy is less sensitive to variation in polymer composition for degradation in air than in nitrogen. Thus, in the dynamic process, the activation energy value decreases (from 36 to 23 kcal/mole) with increasing acetate content (from 6 to 22%) in nitrogen atmosphere, while in air the activation energy value increases only moderately (from 21 to 27 kcal/mole) with increasing acetate content (from 6 to 22%). The order of reaction is nearly unity, irrespective of the composition of the polymer, both in air and nitrogen.     

Elastic and thermal parameters of lanthanide-orthophosphate (LnPO4) ceramics from atomistic simulations

We performed extensive and accurate atomistic simulations of elastic and heat transport properties of series of rare-earth orthophosphate ceramics LnPO₄ (Ln = La, …, Lu and Y) in monazite and xenotime structures. The results show clear trends in the elastic moduli along the lanthanide-series, which complement the existing experimental data on these materials. We found that the thermal conductivities of xenotimes are about two times larger than those of monazite, which is in agreement with the experimental measurements and explained by sizes of the primitive cells. Large sets of data allowed assessment of the validity of Slack's model as well as accuracy of molecular dynamics simulations of heat flow for prediction of thermal conductivity. Last, but not least, the separation of the intrinsic and extrinsic contribution to the measured thermal diffusivities allowed for a detailed analysis of the phonon mean free paths in the considered materials.     

Architecture dependence of thermal fluctuation effects on the order-disorder transition of block copolymer melts

Small-angle X-ray scattering has done to explore the difference in the strength of the thermal fluctuation effects between A-B diblock copolymer and (A/2)₂-B Y-shaped copolymer. SAXS profiles for both systems in their disordered states were analyzed with the Brazovskii-type non-mean field theory by Fredrickson and Helfand. The analyses yielded Ginzburg number characterizing the strength of thermal fluctuation effects. Ginzburg number of Y-shaped copolymer is larger than that of diblock copolymer, suggesting that the strength of the thermal fluctuation effects is affected by the architecture of copolymers.