Kinetics and mechanism during mechanical/thermal dewatering of lignite

In order to increase the efficiency of lignite fired power stations the mechanical/thermal dewatering (German abbreviation: MTE, Mechanisch/Thermische Entwässerung, also used for ‘mechanical/thermal expression’) was developed at the University of Dortmund as an energy efficient process for the reduction of the water content of lignite prior to combustion [1-3], [Patentschrift DE 44 34 447 A1, 1994; Patent EP 0 784 660 B1; WO 96/10064, 1996; VDI-Berichte 1280 (1996) 165]. While a 25 t/h demonstration plant has been constructed at the Niederaußem power station of RWE in Germany and came into operation in 2001 [4], [Proceedings of the VGB/EPRI Conference, 2001] additional detailed research has been done on the process fundamentals at the University of Dortmund. Experiments for three different lignites from Germany, Greece and Australia are presented in this paper and it is shown, that the dewatering kinetics depending on time, temperature and pressure can be described by a new model derived from soil-mechanical fundamentals and rate-process-theory [5], [Mechanismen und Kinetik der Mechanisch/Thermischen Entwässerung von Braunkohle, 2001]. Due to differences in lignite composition the experimental determination of some model parameters for each coal is necessary. From the activation energy which is determined from experiments concerning dewatering kinetics it can be deduced, that even during secondary consolidation (creep) the drainage of water is the dominating process. The experiments also provide a clear distinction between the effect of the so-called ‘thermal dewatering’ due to heating of the lignite and the subsequent mechanical expression.     

Mechanical/thermal dewatering of lignite. Part 3: Physical properties and pore structure of MTE product coals

The mechanical thermal dewatering (MTE) process has been shown to effectively dewater high moisture content low rank coals via the application of mechanical force at elevated temperatures.Using mercury intrusion porosimetry (MIP) as an investigative tool, this study examines how MTE processing conditions, such as temperature and pressure, affect the compressibility, pore size distribution, apparent (skeletal) density and shrinkage behaviour of three low rank coals sourced from Australia, Greece and Germany. As both pore filling and sample compression occurred at high mercury intrusion pressures, all MIP data were corrected for compression effects by using compressibility values derived from mercury extrusion data.The MTE process is shown to produce a low porosity coal, which, depending upon the processing conditions used, undergoes further shrinkage upon oven drying at 105 °C. An increase in MTE temperature (above about 85 °C) led to an increase in mesopore volume, which is caused by a hardening of the coal structure, leading to pore volume retention and a consequent reduction in percent shrinkage on oven drying. The increase in measured mesopore volume is also associated with an increase in measured surface area.The reverse trend is seen with increasing MTE pressure, where both the macro and mesopore volume decrease with pressure, causing the percent shrinkage to increase accordingly. This effect may be due to an increase in capillary forces caused by a decrease in the average pore diameter. The percent shrinkage increased up to a pore volume of about 0.1 cm³/g, beyond which no further reduction in pore volume was achieved. The decrease in mesopore volume is also associated with a decrease in measured surface area.Compressibility values derived from mercury extrusion data show that the MTE process has little impact on the network strength of the skeletal network structure of all three coals investigated. Likewise, the skeletal density remained relatively unchanged.The reduction in water content, pore volume and the changes in shrinkage behaviour under increasingly severe MTE conditions are suggestive of the physical changes that accompany increased coalification (rank) within the lignitic range.     

Rheological properties of hot melt pressure-sensitive adhesives based on styrene--isoprene copolymers. Part 1: A rheological model for [sis-si] formulations

The viscoelastic properties of hot melt pressure-sensitive adhesives (HMPSA) based on formulations of block copolymers and tackifying resins have been studied in detail, through the variation of the complex shear modulus, G*, as a function of frequency, y . In this first article, we analyze the individual behavior of the components of HMPSA blends: (1) the two copolymers, styrene-isoprene (SI) diblock copolymer and styrene-isoprene-styrene (SIS) triblock copolymer and (2) two tackifying resins. The viscoelastic behavior of the overall formulation is also presented. We have mainly studied the effects of (1) the molecular characteristics of the SI and SIS copolymers and (2) the composition of the blends (mainly the effect of SI content, S content in SIS and SI, resin content) on the viscoelastic properties. A theoretical approach based on concepts of molecular dynamics leads to a model which describes reasonably well the linear viscoelastic properties of individual components and their formulations. Our systematic study can be used to design new copolymer molecules which can mimic the rheological behavior and end-user properties of regular formulations at room temperature.     

Design of 7 wt.% Y2O3–ZrO2/mullite plasma-sprayed composite coatings for increased creep resistance

Plasma-sprayed stand-alone coatings of 7 wt.% Y₂O₃–ZrO₂ (YSZ), nominally 74 wt.% Al₂O₃–26 wt.% SiO₂ mullite, and a 46:54 volume ratio composite of YSZ to mullite were examined using X-ray diffraction, dilatometry, and compression creep. X-ray diffraction and dilatometer results showed that the as-sprayed predominantly amorphous mullite crystallized at 970 °C. Creep tests were conducted on all three coating types in the as-sprayed condition at stresses from 40 to 80 MPa and temperatures of 1000–1200 °C. The primary deformation mechanism in coatings made from all three materials was stress-assisted densification of the porous coating. While the creep behavior of YSZ/mullite composite specimens was between that of pure YSZ and pure mullite specimens for all combinations of temperature and stress tested, the creep response of the composite was more similar to that of pure mullite for all cases tested, consistent with mullite being the continuous phase in the composite.     

Effect of Rubber Content of ABS on Properties of PC/ABS Blends. I. Rheological,Mechanical, and Thermal Properties

ABSTRACT

The effect of rubber content of poly (acrylonitrile butadiene styrene) (ABS) on compatibility and properties of polycarbonate (PC)/ABS blend systems has been investigated. The rheological, mechanical, physical, and thermal properties of PC/ABS blend systems containing ABS of different rubber content were studied. The reduced torque data on Torque Rheocord indicated improved processability of PC by addition of ABS, however, in ABS-rich compositions, higher rubber content reduces the extent of improvement. The tensile strength of PC decreased with addition of ABS to it but PC-rich compositions have a nearly additive response. The deviation form additivity for blends having higher rubber ABS was more pronounced. However, the impact strength of blends having higher rubber ABS were higher than other types and showed a positive deviation from additivity with variation in compositions. The blends containing ABS with lower rubber content showed a single glass-transition temperature (Tg) in differential scanning calorimetry studies (DSC) in the whole composition range indicating miscibility. Although two Tgs, one associated with PC phase and one with ABS phase, were observed for blends containing high rubber ABS, the shift in Tgs with respect to pure component values indicates partial miscibility. The decrease in the extent of shift with increase of ABS in these blends indicates undesirable phase separation due to poor adhesion of higher level of rubber content.     

Mechanical properties and thermal shock resistance of Si2BC3N ceramics with ternary Al4SiC4 additive

Dense Si₂BC₃N ceramics were prepared through SPS sintering the amorphous Si₂BC₃N and Al₄SiC₄ powders obtained from mechanical alloying. The phase compositions, microstructures, and mechanical properties, as well as the thermal shock resistance were investigated. In addition, evaluations of oxidation and the ablation resistance were also preceded. The results show that Al₄SiC₄ phase can be detected at 1200 and 1400?°C under pressureless sintering. However, Al₄SiC₄ can be decomposed to AlN and SiC phases under higher temperatures. As for the bulk Si₂BC₃N ceramics, the Al₄SiC₄ additive induce the development of turbostratic BN(C) plates and improve the relative density consequently. Besides, the Al₄SiC₄ plates are embedded in the matrix of ceramics. Therefore, the mechanical properties and thermal shock resistance are improved apparently with the addition of additive. Meanwhile, the additive containing composites have superior ablation resistance than the pristine Si₂BC₃N ceramics due to their higher relative density.     

Effect of thermal residual stress on the tensile properties and damage process of C/SiC composites at high temperatures

Due to the mismatch of the thermal expansion coefficients between the matrix and yarns, thermal residual stress will appear in C/SiC composites. In this paper, a progressive damage model was used to predict the thermal-mechanical behavior of C/SiC composites and reveal the failure mechanism. Firstly, the properties of the composites under tensile load were tested at three different temperatures in vacuum. Then, the elastic-plastic progressive damage constitutive laws were used and implemented by a user-defined subroutine UMAT in ABAQUS. The thermal residual stress evolution in the cooling and heating processes was characterized. Finally, the stress-strain curves of the composites under tensile load at different temperatures were studied. The effects of thermal residual stress on the tensile properties and progressive damage process of C/SiC composites were revealed sequentially. This work can give design guidance for strengthening of C/SiC composites.     

ZrB2-MoSi2 ceramics: A comprehensive overview of microstructure and properties relationships. Part II: Mechanical properties

The mechanical behavior of ZrB₂-MoSi₂ ceramics made of ZrB₂ powder with three different particle sizes and MoSi₂ additions from 5 to 70 vol% was characterized up to 1500 °C. Microhardness (12–17 GPa), Young’s modulus (450–540 GPa) and shear modulus (190–240 GPa) decreased with both increasing MoSi₂ content and with decreasing ZrB₂ grain size. Room temperature fracture toughness was unaffected by grain size or silicide content, whilst at 1500 °C in air it increased with MoSi₂ and ZrB₂ grain size, from 4.1 to 8.7 MPa m^½. Room temperature strength did not trend with MoSi₂ content, but increased with decreasing ZrB₂ grain size from 440 to 590 MPa for the largest starting particle size to 700–800 MPa for the finest due to the decreasing size of surface grain pullout. At 1500 °C, flexure strength for ZrB₂ with MoSi₂ contents above 25 vol% were roughly constant, 400–450 MPa, whilst for lower content strength was controlled by oxidation damages. Strength for compositions made using fine and medium ZrB₂ powders increased with increasing MoSi₂ content, 250–450 MPa. Ceramics made with coarse ZrB₂ displayed the highest strengths, which decreased with increasing MoSi₂ content from 600 to 450 MPa.     

Crystal structure,mechanical and thermal properties of Yb4Al2O9: A combination of experimental and theoretical investigations

The key requirements for a successful thermal and environmental barrier coating (T/EBC) material include stability in high temperature water vapor, low Young's modulus, close thermal expansion coefficient (TEC) with mullite, low thermal conductivity and weak mechanical anisotropy. The current prime candidates for top coat are ytterbium silicates (Yb₂SiO₅ and Yb₂Si₂O₇). A major weakness of these two silicates is the severe anisotropy in mechanical properties and thermal expansion that would lead to cracking of the coating. Thus, searching for new materials with weak mechanical and thermal anisotropy is of signification. In this work, the crystal structure, mechanical and thermal properties of a promising T/EBC candidate, Yb₄Al₂O₉, are investigated theoretically and experimentally. Good ductility, low shear deformation resistance, low Young's modulus (151 GPa) and low thermal conductivity (0.78 W m⁻¹ K⁻¹) is underpinned by heterogeneous bonding characteristic and distortion of the structure. Close TEC (6.27 × 10⁻⁶ K⁻¹) with mullite and weak mechanical anisotropy highlight the suitability of Yb₄Al₂O₉ as a prospective T/EBC.     

Fine-grained and electrically conductive NdB6/SiO2: A promising electromagnetic interference shielding material with good thermal and mechanical properties

Searching for thermal conductive materials with high electromagnetic interference (EMI) shielding effectiveness (SE) is the key to protect electronic equipment against electromagnetic pollution and excess heat emission. Herein, NdB₆/SiO₂ bulks with high EMI SE and thermal conductivity which also exhibit good mechanical properties were prepared by liquid phase sintering (LPS). The NdB₆/SiO₂ bulk prepared by LPS at 1550 °C has fine grain-size, which is beneficial to improving mechanical property and EMI shielding performance. It exhibits high conductivity of 1.47 × 10⁴ S/cm, high EMI SE of 55.1 dB in K band, and high thermal conductivity of 37.9 W/m K. It also possesses flexural strength of 266 MPa and Vickers hardness of 14.8 GPa. Thus, NdB₆/SiO₂ composite ceramics are promising candidates for EMI shielding with good heat dissipation and mechanical load-bearing capabilities.     

The effect of thermal annealing on Fe/TiO2 coatings deposited with the help of RF PECVD method. Part II. Optical and photocatalytic properties

In this work, morphology, optical properties, photowetting effect, and bactericidal behavior of titanium dioxide coatings, both plain and iron doped within the range of 0.52 and 4.76 at%, are presented. The coatings were synthesized with the help of radio frequency plasma enhanced chemical vapor deposition technique followed by thermal annealing at 500 °C under normal atmospheric conditions. Atomic force microscopy examination of the film morphology reveal roughness differences depending on the concentration of iron. Measurements of optical properties, carried out with the UV–VIS absorption spectrometry, show high transmittance in the visible range. Optical gap values, determined with the help of the Tauc equation, exhibit a decreasing tendency with an increasing iron content, but only up to the concentration of 2.5 at%, with thermally annealed coatings characterized by higher E_g values than those of the non-annealed materials. Results of variable angle spectroscopic ellipsometry measurements indicate that both iron doping and thermal annealing have the effect of increasing refractive index of the films. An analysis of the coatings surface wettability, performed under conditions of an alternative exposure either to daylight or to the UV-B radiation, show the most important parameter to be the time of water contact angle return to its initial value under darkroom conditions. Finally, bactericidity studies of the UV-B irradiated samples, performed with the Escherichia coli DH5α bacteria, reveal the most extensive bactericidal effect observed for low iron concentrations, equally for both non-annealed and thermally annealed materials.     

The effect of thermal annealing on Fe/TiO2 coatings deposited with the help of RF PECVD method. Part I. Chemical and phase composition

Results of the studies on chemical structure and phase composition of both non-annealed and thermally annealed iron doped TiO₂ coatings are presented. The coatings were synthesized with the help of radio frequency plasma enhanced chemical vapor deposition (RF PECVD) and characterized by iron content in the range of 0–4.76 at%. In these studies, an analysis of both elemental composition and chemical bonding was performed with the help of X-ray photoelectron spectroscopy (XPS). X-ray diffraction (XRD) was applied to determine phase composition and Fourier transform infrared spectroscopy (FTIR) was used as a supplementary source of information. The obtained elemental composition data show that, apart from titanium, oxygen and iron, traces of chlorine as well as substantial amounts of carbon are present in the coatings. While chlorine has originated from plasma decomposition of TiCl_4, used as a source of titanium, a presence of carbon is associated with a surface contamination resulting from photocatalytic reactions of TiO₂ with the adsorbed carbon dioxide. The results of XPS and FTIR indicate that thermal annealing not only modifies phase composition of these materials, but also affects chemical bonding. Finally, XRD analysis shows that iron content has an effect on the size of coherent diffraction domains present in the films.     

A simple and efficient method for the preparation of SiO2/PI/AF aerogel composite fabrics and their thermal insulation performance

As a new type of insulation material, aerogels are characterized by a high specific surface area, high porosity, low density and low thermal conductivity, which makes them a new alternative to the use of traditional insulation materials. In this paper, a simple method for preparing aerogel insulation materials is proposed. Specifically, SiO₂/PI/AF (aramid fiber) aerogel composite fabrics were successfully obtained by combining coating technology and finishing processes to use tetraethoxysilane (TEOS) as the precursor, polyimide (PI) powder as the reinforcing agent, and nonwoven AF as the substrate. These composite fabrics were characterized using field-emission scanning electron microscopy (FESEM), tensile testing with an Instron 5967, Fourier transform infrared spectroscopy (FT-IR) and thermal infrared imaging. The results show that the composite fabrics exhibited excellent performance and could effectively block heat transfer. Moreover, the thermal conductivity of the front decreased from 4.08 to 3.91 (W/cm·°C) × 10^-4. This work provides a novel method for the structural design of thermal insulation clothing.     

Organoclay/thermotropic liquid crystalline polymer nanocomposites. Part VI: Effects of intercalated organoclay on nanocomposite morphology,thermal and rheological properties

A study of a typical intercalated structure of a thermotropic liquid crystalline polymer (TLCP) with organoclay was performed to elucidate the influence of intercalated organoclay on the TLCP molecules, especially on their liquid crystallinity, thermal and rheological properties. The intercalated structures were confirmed in TLCP and organoclay formed molecular interactions with TLCP molecules in the system. Such intercalated structures caused the glass transition temperature of the nanocomposite to become invisible in thermal measurement and also caused loss of liquid crystallinity. The TLCP molecules inside the organoclay galleries showed higher thermal stability and transition temperatures, but the orderly structure of the TLCP molecules outside the galleries was destroyed by the organoclay, causing the TLCP to display lower thermal stability and transition temperatures than pristine TLCP. At 185°C, where TLCP is in the nematic phase, the nanocomposite had three orders of magnitude higher viscosity in the linear viscoelastic region than that of TLCP, with chain mobility and relaxation time slowed due to the intercalated effects in the nanocomposite. Steady shear altered the domain sizes and oriented the highly anisotropic organoclay layers or tactoids along the shear direction.     

A Study of Chemical Interactions at the Stainless Steel/Polymer Interface by Infrared Spectroscopy. Part 2: Mechanical Properties and Study of the Interphase

The interaction of a thermoplastic ethylene-maleic anhydride copolymer with stainless steel has been studied by infrared spectroscopic techniques (FTIR). The aim was to improve understanding of the reaction processes at the steel/polymer interface in order to optimize the quality of assemblies in terms of adhesion and durability under the conditions which will subsequently be those of normal operation.

Steel/polymer associations have been tested after being submitted to several different conditions of treatment and aging in order to understand the various phenomena which occur at the steel/polymer interphase.

Mechanical behavior improves after heat treatment, and similar conclusions can be transposed to the structure after use, such as in domestic equipment. Modifications in interactions between stainless steel and polymer are caused first by the chemical reactivity of anhydride functions, and second by the mobility of organic chains which reorganize at the interphase.

Analysis of failure surfaces shows several correlations between the mechanical behavior and the chemical nature of residual polymer on the metal substrate. Localization of failure depends on aging conditions and can be explained by minimization of interfaical energy between the polar structure of the metal surface and the organic chains.     

Structural, thermal and mechanical properties of transparent Yb:(Y0.97Zr0.03)2O3 ceramic

Yb doped (Y_0.97Zr_0.03)₂O₃ transparent ceramics were fabricated by solid state reaction and vacuum sintering. The microstructure, thermal and mechanical properties of Y₂O₃ ceramic, as well as the effect of Yb doping concentration on these properties were investigated in detail. The lattice parameter and unit cell volume decrease with the increasing of Yb content, whereas thermal expansive coefficient increases. With Yb content increasing from 0 to 8 at.%, the mean grain size increases from 15.82 μm to 26.54 μm, and the thermal conductivity at room temperature (RT) decreases from 11.97 to 6.39 W/m/K. The microhardness decreases with Yb content, and the microhardness and fracture toughness of (Y_0.97Zr_0.03)₂O₃ transparent ceramic is 11.11 GPa and 1.29 MPa m^1/2, respectively.     

Poly 2-ethyl-2-oxazoline/microcrystalline cellulose composites for cultural heritage conservation: Mechanical characterization in dry and wet state and application as lining adhesives of canvas

The aim of this work is the investigation of the stabilizing effect of microcrystalline cellulose powder (MCC) on the mechanical performance of two commercial thermoplastic resins (Aquazol® 200 and Aquazol® 500) used as adhesives in the conservation of artworks. The two polymers, having different molecular weights, were melt-compounded and compression molded with various amounts of MCC (5–30 wt%). The mechanical response of the microcomposites under dry and wet (equilibrium at 23 °C and a R.H. 55%) conditions, was investigated. DMTA analysis showed an increase of the dynamic moduli and the glass transition temperature with the microfiller content more pronounced for conditioned samples over the dried ones, and a concurrent decrease of the thermal expansion coefficient. Creep tests showed that MCC caused an improvement of the creep stability (i.e. a reduction of the creep compliance) for both dried and conditioned samples. For wet samples, the simultaneous enhancement of the elastic modulus and the stress at break limited the embrittling effect detected for dried composites. These materials were applied as lining adhesive for oil paintings between two kinds of canvas an English linen and a woven polyester under environmental conditions at temperature of 23 °C and a relative humidity of 55%. Single-lap shear tests both in quasi-static and creep conditions confirmed the improvement of the dimensional stability provided by MCC with a reduction of the joint displacement and an increase of the adhesive strength as the filler content increases. Additionally, post-fracture optical microscope observations of the cross-sections of the adhesive area proved how MCC introduction did not change the fracture behavior of the neat adhesives.     

Pd/Ce0.6Zr0.4O2/Al2O3 as advanced materials for three-way catalysts: Part 1. Catalyst characterisation, thermal stability and catalytic activity in the reduction of NO by CO

Pd-loaded Ce_0.6Zr_0.4O₂ solid solutions supported on Al₂O₃ are investigated as catalysts for the reduction of NO by CO. The attention is focused on the role of the Ce_0.6Zr_0.4O₂ and of the Pd dispersion on the catalytic activity. The system shows a very high activity below 500 K, which is almost independent on the Pd dispersion. The high activity is attributed to a promoting effect of the Ce_0.6Zr_0.4O₂ on the NO conversion. Investigation of the influence of high temperature treatments disclosed a thermal stabilisation of both Ce_0.6Zr_0.4O₂ and Al₂O₃ in the Ce_0.6Zr_0.4O₂/Al₂O₃ system.