Density of softwood bark and softwood char: procedural calibration and measurement by water soaking and kerosene immersion method

Particle density plays an important role in the design and operation of thermoconversion reactors fed with bed of particles such as softwood bark (SB). Little information is available on the single particle density of SB and charcoal derived. As SB and softwood char (SC) particles are highly irregular in shape and size, conventional methods of particle density measurement cannot be applied. A method known as the water soaking and kerosene immersion procedure, used for density measurement of sugarcane bagasse, has been tested and adapted to the density measurement of individual particles of softwood (SW), SB and SC. The particle density has been determined to be 360, 482 and 299 kg m⁻³ for SW, SB and SC, respectively. The average particle density of a typical SB feedstock sample comprised of ca. 30% SW and 70% SB was calculated to be 438 kg m⁻³.     

Effect of dehydroxylation on the specific heat of simple clay mixtures

Specific heats of four clays (standard reference kaolins, commercial kaolin and montmorillonite) before and after dehydroxylation have been measured. The results were compared with handbook data for the thermal chemical properties of solids. Good agreement has been obtained for the reference kaolin before any thermal treatment. Then, following thermal treatments at 500 °C, 600 °C and 700 °C, dehydroxylation leads to a progressive decrease of heat capacity per unit mass. After dehydroxylation, heat capacity values for all the studied materials are rather similar and agree closely with those estimated by the rule of mixtures. Finally, an empirical relation describing the specific heat capacity (C) in J kg⁻¹ K⁻¹ of dehydroxylated kaolin from 40 °C to 1100 °C is proposed: C = 1128 + 0.102T − 36 × 10⁶T⁻² where T is in K.     

Thermal conductivity and permeability of consolidated expanded natural graphite treated with sulphuric acid

The thermal conductivity and permeability of consolidated expanded natural graphite treated with sulphuric acid (ENG-TSA) were measured both parallel and perpendicular to the direction of compression used to produce the samples. Results showed that the thermal conductivity and permeability were highly anisotropic. The thermal conductivity perpendicular to the direction of compression was 50 times higher than that parallel to the direction of compression and the permeability was 200 times higher. The maximum thermal conductivity measured was 337 W m⁻¹K⁻¹ at a bulk density of 831 kg m⁻³. The permeability perpendicular to the direction of compression varied in the range of 10⁻¹¹ to 10⁻¹⁶ m² as the density increased from 111 to 539 kg m⁻³. The specific heat was measured, and the average value is 0.89 kJ kg⁻¹K⁻¹ in the temperature range 30–150 °C. As a type of heat transfer matrix the thermal diffusivity was about five times higher than that of, for example, pure aluminium due to the combination of improved thermal conductivity with comparatively low density and reasonable specific heat.     

Thermal conductivity studies on ceramic floor tiles

Thermal diffusivity, thermal conductivity and specific heat of several materials used as floor tiles have been measured using the laser flash method. Natural stones, particularly granite, porcelain stoneware and red stoneware materials of low water absorption, are more effective thermal conductors than white stoneware and vinyl, which have thermal conductivities below 1 W m⁻¹ K⁻¹. Therefore, last two should not be recommended for radiant floor heating applications. Enhancement of thermal conductivity of red and porcelain stoneware has been achieved by adding Al₂O₃ of certain characteristics to the ceramic paste. In this way, thermal diffusivity increases of up to 50% have been obtained by adding 20 wt.% of Al₂O₃ particles.     

Thermal conductivity and microstructure of Ti-doped graphite

Ti doped and Si-Ti doped graphites have been developed. The influence of the dopants on the properties and microstructure of doped graphites was analyzed. Test results reveal that Ti doped graphite has excellent bending strength and high thermal conductivity, with highest values reaching 50.2 MPa and 424 W m⁻¹ K⁻¹ for a Ti concentration of 15 wt% in the raw materials. Si added simultaneously with Ti promotes the growth of graphite crystals resulting in an increased thermal conductivity. A kind of Si-Ti doped graphite has been developed with thermal conductivity as high as 494 W m⁻¹ K⁻¹ by optimizing the compositions. Correlation between the content of dopant and the properties and microstructure of doped graphites was studied, and catalytic graphitization mechanism of dopants is also discussed.     

Thermal conductivity in mullite/ZrO2 composite coatings

Mullite-based multilayered structures have been suggested as promising environmental barrier coatings for Si₃N₄ and SiC ceramics. Mullite has been used as bottom layer because its thermal expansion coefficient closely matches those of the Si-based substrates, whereas Y–ZrO₂ has been tried as top layer due to its stability in combustion environments. In addition, mullite/ZrO₂ compositions may work as middle layers to reduce the thermal expansion coefficient mismatch between the ZrO₂ and mullite layers. Present work studies the thermal behaviour of a flame sprayed mullite/ZrO₂ (75/25, v/v) composite coating. The changes in crystallinity, microstructure and thermal conductivity of free-standing coatings heat treated at two different temperatures (1000 and 1300 °C) are comparatively discussed. The as-sprayed and 1000 °C treated coatings showed an almost constant thermal conductivity (K) of 1.5 W m⁻¹ K⁻¹. The K of the 1300 °C treated specimen increased up to twice due to the extensive mullite crystallization without any cracking.     

Hydrogenated hydroxy-functionalized polyisoprene (H-HTPI) and isocyanurate of isophorone diisocyanates (I-IPDI): reaction kinetics study using FTIR spectroscopy

The reaction between a hydrogenated hydroxyl-functionalized polyisoprene (H-HTPI) and isophorone diisocyanate isocyanurate (I-IPDI) is followed by using direct FTIR spectroscopy. The reaction kinetics is studied using a simple model taking into consideration the I-IPDI structure. The rates of individual isocyanate groups are described by a second order equation. Influence of dibutyltin dilaurate (DBTL) concentration and temperature on selectivity, defined as the ratio between the rate constant of secondary isocyanate group and the rate constant of the primary isocyanate group, is investigated. It is observed that selectivity decreases when temperature or DBTL concentration increases. Eyring parameters are determined for the catalyzed [ΔH^*=77/35 (kJ mol⁻¹), ΔS^*=12/−100 (J mol⁻¹ K⁻¹)] and uncatalyzed reactions [ΔH^*=48/43 (kJ mol⁻¹), ΔS^*=−179/−167 (J mol⁻¹ K⁻¹)] primary and secondary isocyanate groups being differentiated.     

Transverse and longitudinal coefficient of thermal expansion of carbon fibers at high temperatures (300-2500 K)

The transverse and longitudinal coefficients of thermal expansion (CTE) of carbon fibers are important parameters in C/C composites behaviour. In this study, the measurements of CTE are presented at very high temperatures (up to 2500 K). Experimental validations are first realised on isotropic metallic (tungsten) fiber. Then, measurements are performed on four carbon fibers (rayon-based, PAN-based and pitch-based). The results show that the mean transverse CTE varies from 5 × 10⁻⁶ K⁻¹ to 10 × 10⁻⁶ K⁻¹ and the longitudinal one from 1.6 × 10⁻⁶ K⁻¹ to 2.1 × 10⁻⁶ K⁻¹ depending on the fiber structural properties. For that, the relationships between the structural properties and the heat treatment temperature of the carbon fibers are discussed in relation to thermal expansion behaviour. A calculation of the ratio between the transverse and the longitudinal measured CTE as a function of the temperature allows us to classify fibers from the most isotropic to the most anisotropic in relation with the structural properties measured at room temperature.     

Thermal and electrical conductivity of tall, vertically aligned carbon nanotube arrays

Vertically aligned multi-walled carbon nanotube (MWCNT) arrays up to ∼6 mm high with an array density of 0.06 g cm⁻³ have been grown by chemical vapor deposition. Thermal conductivities (κ) and electrical conductivities (σ) were determined from 5 K to 390 K. The range for κ at 300 K is 0.5-1.2 W m⁻¹ K⁻¹ along the tube growth direction, with the shortest array having the highest κ, and an order of magnitude lower in the direction perpendicular to the tubes. The same trends also were evident for electrical conductivity, i.e., decreasing values with increasing array height and conductivity an order of magnitude lower in the perpendicular direction. Values of σ ranged from 7 to 14 S cm⁻¹ along the array at 300 K. The Seebeck coefficient is ∼20 μV K⁻¹ at 300 K. The effective Lorentz number indicates that thermal conductivity in the carbon nanotube arrays is phonon dominated over the full temperature range.     

Microstructural and mechanical characterization of fly ash cenosphere/metakaolin-based geopolymeric composites

Novel fly ash cenosphere (FAC)/metakaolin (MK)-based geopolymeric composites were prepared by adding FAC to the MK-based geopolymeric slurry. Microstructure, mechanical property, thermal conductivity, and bulk density of the FAC/MK-based geopolymeric composites were investigated. It was confirmed by the scanning electron microscope (SEM) and transmission electron microscopy (TEM) that the FAC did not dissolve in alkaline condition, but element diffusion took place around the interface between geopolymeric matrix and FAC. The compressive strength, thermal conductivity and bulk density of FAC/MK-based geopolymeric composites decreased monotonically with the increase of the FAC content from 15 vol.% to 40 vol.%, and the minimum values for the 40 vol.% FAC/MK-based geopolymeric composite reached 36.5 MPa, 0.173 W m⁻¹ K⁻¹ and 0.82 g cm⁻³, respectively, in the range of FAC content from 15 vol.% to 40 vol.%. The results showed that the FAC could lower thermal conductivity effectively and bulk density of FAC/MK-based geopolymeric composites at a cost of slight decrease of mechanical properties. The 40 vol.% FAC/MK-based geopolymeric composite was a promising candidate material for intermediate-temperature thermal insulation applications due to its low thermal conductivity and low density.     

LaBaCuFeO5+δ-Ce0.8Sm0.2O1.9 as composite cathode for solid oxide fuel cells

The performance of the LaBaCuFeO_5+δ-Ce_0.8Sm_0.2O_1.9 (LBCF-SDC) composite cathodes was studied in this paper. Electrical conductivity, thermal expansion and electrochemical properties were investigated by four probing DC technique, dilatometry, AC impedance and polarization techniques, respectively. The thermal expansion coefficients of the LBCF-SDC were between (16.3 and 13.4) × 10⁻⁶ K⁻¹ from 30 to 850 °C, which was lower value than LBCF (17.0 × 10⁻⁶ K⁻¹). AC Impedance spectroscopy measurements of LBCF-SDC/SDC/LBCF-SDC test cell were carried out. Polarization resistance values for the LBCF-SDC10 cathode was as low as 0.097 Ω cm² at 750 °C.     

Thermal conductivity and dielectric property of hot-pressing sintered AlN–BN ceramic composites

A study was conducted of the effects of sintering temperature and CaF₂ additives on densification, microstructure, dielectric property and thermal conductivity of AlN–BN composites. Increasing sintering temperature and CaF₂ contents help to improve the densification, thermal conductivity, and purification of the grain boundaries. Thermal conductivity value reached 110 W m⁻¹ K⁻¹ for AlN–BN composites with 3 wt.% CaF₂ and sintered at 1850 °C. Increasing sintering temperature decreases relative dielectric constant and tan δ. The increase in CaF₂ content increases relative dielectric constant and decreases tan δ. Relative dielectric constants values were between 7.29 and 7.64 and dielectric loss tangent values ranged from 6.36 to 7.83 × 10⁻⁴ at 1 MHz.     

Synthesis and transport properties in La2−xAxMo2O9−δ (A = Ca, Sr, Ba, K) series

The La_2−xA_xMo₂O_9−δ (A = Ca²⁺, Sr²⁺, Ba²⁺ and K⁺) series has been synthesised as nanocrystalline materials via a modification of the freeze-drying method. The resulting materials have been characterised by X-ray diffraction (XRD), thermal analysis (TG/DTA, DSC), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The high-temperature β-polymorph is stabilised for dopant content x > 0.01. The nanocrystalline powders were used to obtain dense ceramic materials with optimised microstructure and relative density >95%. The overall conductivity determined by impedance spectroscopy depends on both the ionic radius and dopant content. The conductivity decreases slightly as the dopant content increases in addition a maximum conductivity value was found for Sr²⁺ substitution, which show an ionic radii slightly higher than La³⁺ (e.g. 0.08 S cm⁻¹ for La₂Mo₂O₉ and 0.06 S cm⁻¹ for La_1.9Sr_0.1Mo₂O_9−δ at 973 K). The creation of extrinsic vacancies upon substitution results in a wider stability range under reducing conditions and prevents amorphisation, although the stability is not enhanced significantly when compared to samples with higher tungsten content. These materials present high thermal expansion coefficients in the range of (13-16) × 10⁻⁶ K⁻¹ between room temperature and 753 K and (18-20) × 10⁻⁶ K⁻¹ above 823 K. The ionic transport numbers determined by a modified emf method remain above 0.98 under an oxygen partial pressure gradient of O₂/air and decreases substantially under wet 5% H₂-Ar/air when approaching to the degradation temperature above 973 K due to an increase of the electronic contribution to the overall conductivity.     

Effect of LiAlSiO4 particle size on the properties of LAS/SiC porous ceramics with near zero thermal expansion

Near zero thermal expansion porous ceramics were fabricated by using SiC and LiAlSiO₄ as positive and negative thermal expansion materials, respectively, bonded by glassy material. The microstructure, mechanical properties, and thermal expansion behavior of LAS/SiC porous ceramics with different particle sizes of LiAlSiO₄ were investigated. The results indicated that the coefficient of thermal expansion of the LAS/SiC porous ceramics decreased from 0.5206×10⁻⁶ to −1.1053×10⁻⁶ K⁻¹ with increasing the LiAlSiO₄ particle size from ~45 µm to ~125 μm. It was attributed to the reduction in the reaction between LiAlSiO₄ and SiO₂ as the particle size of LiAlSiO₄ increased. Young’s modulus increased from 36 MPa to 54 MPa as the sintering temperature increased from 850 °C to 950 °C because of the good bonding between the SiC grains and the glass materials.     

Impregnation of vitamin E acetate on silica mesoporous phases using supercritical carbon dioxide

Impregnation of a drug model (α-tocopheryl acetate) into mesoporous host matrices has been carried out using supercritical carbon dioxide (SC CO₂) as impregnation solvent at 15 MPa and 313 K with a flow rate of 500 g h⁻¹. The operating conditions were defined following the solute concentration in the fluid phase as a function of pressure and carbon dioxide flow rate. Solubility measurements of α-tocopheryl acetate were first performed at 313 K for pressures ranging 10-20 MPa. High values of solubility in SC CO₂ were measured: 6 wt% at 10 MPa and 14 wt% at 20 MPa. Measurements of the concentration of the solute in SC CO₂ in the experimental conditions of impregnation in dynamic mode showed than it was ten times lower than the solubility. The variations of this concentration have been studied at 313 K, for a pressure varying from 8 to 15 MPa, and for a carbon dioxide flow rate varying from 120 to 600 g h⁻¹. Two different host matrices were used: a commercial chromatographic silica support and a MCM-41-type mesoporous organized silica synthetized at the laboratory. This latter showed the best drug loading of 1.14 g per gram of adsorbent. The drug loadings obtained in supercritical media were similar to the ones obtained in liquid media using hexane as impregnation solvent. Nevertheless, the maximum loading was obtained after 1 h of impregnation in SC media while 4 h were needed in liquid media.     

Porous mullite templated from hard mullite beads

Porous mullite bodies were developed by spark plasma sintering (SPS) amorphous mullite beads of about ∼30 μm in diameter at two temperatures, 950 and 1300 °C. Materials showed a close random stacking of solid spheres that retained their original packing but slightly flattened at the contacts in some cases. Depending on the thermal history, the beads were partially or fully crystallized. The thermal conductivity of the different porous mullite materials was analyzed as a function of the microstructure. Owing to the particular porous network, high gas permeability and very low thermal conductivities (1-2 W m⁻¹ K⁻¹) were achieved, among the lowest reported for sintered mullite materials.     

Kinetics of catalytic steam gasification of bitumen coke

The catalytic steam gasification of coke from Athabasca bitumen was investigated by thermogravimetric analysis using K₂CO₃ and Na₂CO₃ as catalysts, both of which reduced the activation energy of the reaction considerably to 1.2 × 10⁵ J mol⁻¹ and 1.3 × 10⁵ J mol⁻¹, respectively, down from 2.1 × 10⁵ J mol⁻¹ for the uncatalyzed reaction. The reaction rates varied with the partial pressure of steam between 60 kPa and 85 kPa consistent with a Langmuir-Hinshelwood model, but a first order equation was also sufficient given the low partial pressures. The initial rate of gasification of the coke particles correlated linearly with the estimated external surface area of the particles, as expected from a surface reaction involving a non-porous solid. The initial reaction rate increased with increasing the catalyst loading up to 2.4 (mol potassium)/kg. A portion of the catalyst penetrated into the coke, as confirmed by secondary ion mass spectroscopy analysis, where it could not promote the reaction with steam. This result was consistent with a small increase observed in the reaction rate at low catalyst loading. The shrinking core model was successful in predicting the rates at higher conversions from the initial rate data, despite increases in BET surface area with conversion.     

Microbial desulphurization of coal containing pyritic sulphur in a continuously operated bench scale coal slurry reactor

Pre-combustion microbial desulphurization of coal containing total sulphur (3.90%) and pyritic sulphur (2.80%) has been evaluated in a coal slurry reactor. The coal slurry reactor operated at hydraulic retention time (HRT) of 96 h with a coal pulp density of 15 percent and remove 79 percent of pyritic sulphur and 76 percent of ash with an increase in the calorific value of coal from 4400 to 6800 kcal kg⁻¹ at a pyritic load of 1.9 kg pyritic sulphur kg⁻¹ MLSS d⁻¹. The treated coal yield is 72 percent. The biochemical kinetic coefficients, viz. yield coefficient (Y) and decay coefficient (K_d) in the coal slurry reactor system are 0.178 and 0.007 d⁻¹, respectively, while maximum growth rate (μ_max) and half saturation rate constant (K_s) are 0.025 h⁻¹ and 0.220 g l⁻¹ as pyrite, respectively.     

A 1-D non-isothermal dynamic model for the thermal decomposition of a gibbsite particle

A 1-D mathematical model describing the thermal decomposition, or calcination, of a single gibbsite particle to alumina has been developed and validated against literature data. A dynamic, spatially distributed, mass and energy balance model enables the prediction of the evolution of chemical composition and temperature as a function of radial position inside a particle. In the thermal decomposition of gibbsite, water vapour is formed and the internal water vapour pressure plays a significant role in determining the rate of gibbsite dehydration. A thermal decomposition rate equation, developed by closely matching experimental data reported previously in the literature, assumes a reaction order of 1 with respect to gibbsite concentration, and an order of −1 with respect to water vapour pressure. Estimated values of the transformation kinetic parameters were k₀ = 2.5 × 10¹³ mol/(m³ s) for the pre-exponential factor, and E_a = 131 kJ/mol for the activation energy. Using these kinetic parameters, the gibbsite particle model is solved numerically to predict the evolution of the internal water vapour pressure, temperature and gibbsite concentration. The model prediction was shown to be very sensitive to the values of heat transfer coefficient, effective diffusivity, particle size and external pressure, but relatively less sensitive to the mass transfer coefficient and particle thermal conductivity. The predicted profile of the water vapour pressure inside the particle helps explain some phenomena observed in practice, including particle breakage and formation of a boehmite phase.     

Polyfurfuryl alcohol derived activated carbons for high power electrical double layer capacitors

Polyfurfuryl alcohol (PFA) derived activated carbons were prepared by the acid catalysed polymerization of furfuryl alcohol, followed by potassium hydroxide activation. Activated carbons with apparent BET surface areas ranging from 1070 to 2600 m² g⁻¹, and corresponding average micropore sizes between 0.6 and 1.6 nm were obtained. The porosity of these carbons can be carefully controlled during activation and their performance as electrode materials in electric double layer capacitors (EDLCs) in a non-aqueous electrolyte (1 M Et₄NBF₄/ACN) is investigated.Carbon materials with a low average pore size (<∼0.6 nm) exhibited electrolyte accessibility issues and an associated decrease in capacitance at high charging rates. PFA carbons with larger average pore sizes exhibited greatly improved performance, with specific electrode capacitances of 150 F g⁻¹ at an operating voltage window of 0-2.5 V; which corresponds to 32 Wh kg⁻¹ and 38 kW kg⁻¹ on an active material basis. These carbons also displayed an outstanding performance at high current densities delivering up to 100 F g⁻¹ at current densities as high as 250 A g⁻¹. The exceptionally high capacitance and power of this electrode material is attributed to its good electronic conductivity and a highly effective combination of micro- and fine mesoporosity.