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.     

Optical investigation of shear- and time-dependent microstructural changes to stabilized and depletion-flocculated concentrated latex sphere suspensions

An original experimental set up was designed combining a Couette flow system and an optical sensor measuring the light flux multiple scattered from a flowing suspension. The method was used to study shear- or time-dependent microstructural changes to a concentrated suspension of monodispersed latex spheres (diameter 170 nm) for particle volume fraction ranging from 1% up to 48%. Microstructural changes were caused either by shear forces acting upon stabilized latex particles or by the addition of carboxymethylcellulose polymer chains inducing reversible depletion flocculation of latex spheres.     

Mercury porosimetry studies II. The application of mercury porosimetry to porous polymer powders

Two experimental methods are outlined for the separation of the inter- and intraparticle intrusion volumes of porous powders. The first of these relies upon the control of interparticle bed packing by mounting the particles upon a transparent adhesive substrate. The pressure at which interparticle penetration occurs (critical pressure) is measured by observing the penetration process directly in a microscope pressure cell. A mercury intrusion experiment is then run on a similarly mounted sample and the value of the critical pressure obtained previously used to define the interparticle volume.In the second method, the critical pressure is determined by running a mercury intrusion experiment on a powder sample whose intraparticle volume has been filled with a wetting liquid—dioctyl phthalate (DOP). This technique depends upon the observation made previously in Part I of this series that bed depacking rather than bed penetration is the initial step of the penetration process.Total intraparticle volumes determined by both of these methods were compared with those obtained by the uptake of a wetting oil (DOP). Although an excellent degree of correlation was observed between the two methods, the DOP uptake values were found to be high by a constant amount. This was demonstrated to be due to oil retained in the interparticle volume. The values of critical pressure determined in this study indicate that the filling of the interparticle voids in a mercury intrusion experiment may not correspond to any feature observed in the penetration curve. Thus it is necessary to determine this quantity separately.     

Particle sizing of flocculated latex particles by physisorption of nitrogen

Physisorption of nitrogen at one specific pressure is used to determine the specific surface area of a flocculated polystyrene latex by applying BET theory. Assuming that a flocculated sample of Polymer latex is composed of distinct spherical latex particles (i.e., there is no coagulation of particles), the volume–surface-average diameter can be calculated. The resulting diameters are compared to sizes obtained using a disc centrifuge sedimentometer, which fractionizes the particles by sedimentation. The diameters from both techniques were in good agreement, showing that physisorption of nitrogen, which is a simple technique, can be used to determine sizes of flocculated latex particles. This agreement also shows that the flocculation of the polystyrene latex produced separate nonporous spherical particles. When flocculation of a latex is done above its glass transition temperature, coagulation will occur. While other particle sizing techniques can produce particle size distributions, the physisorption of nitrogen only gives the volume–surface-average diameter. However, one advantage of the physisorption of nitrogen is that it covers a broad range of particle sizes compared to most other techniques. © 1994 John Wiley & Sons, Inc.     

Pore spectra from continuous scan mercury porosimetry

A method for obtaining pore spectra is described. Continuous pressure—volume data from mercury porosimetry were used to determine the volume distribution as a function of the intrusion and extrusion pressure or the pore radius for a number of porous samples.An explanation is offered for delayed intrusion of mercury into pores. Mercury vapor transfer has been postulated as a thermodynamically allowed mechanism in those few cases where pore size or constrictions prohibit liquid transfer.     

Mercury porosimeter as a means to measure mechanical properties of aerogels

It is ascertained that the mercury does not enter pores of some aerogels in experiments with mercury intrusion porosimeter. The curves obtained from mercury porosimeter represent the compaction of aerogels under isostatic pressure conditions. Thus, a novel area of research for the application of the mercury porosimeter emerges. The mercury porosimeter is proposed as a convenient tool to study the mechanical properties of aerogels based on the studies of the volume decrease/expansion of an aerogel sample under isostatic pressure deformation to selected pressures.     

Filtration Behavior of Slurries with Varying Compressibilities

Abstract

A novel filtration apparatus allows simultaneous measurements of filtrate volume, hydraulic pressure and cake thickness using slurry volumes on the order of 100 cm³ Differences in interparticle interactions were studied by varying the barium chloride concentration of 0.38-μm polystyrene latex and filtering at pressures between 2 and 100 psi. Cakes formed from these slurries are highly compressible for concentrations between 0.01M and 0.10M, moderately compressible for the 0.005M concentration, and incompressible for the 0.001M concentration. Plots of filtrate volume versus cake thickness were linear for the incompressible cakes, whereas the compressible cakes showed significant deviations, which were pressure dependent. The pressure distribution for the incompressible cake was found to be essentially linear as predicted from the resistance plots assuming constant α and ε. For the highly compressible cakes, most of the pressure drop appears to occur near the cake/medium Interface with only small changes occurring at the top of thp cakp.     

Damage to the Pore Structure of Hardened Portland Cement Paste by Mercury Intrusion

Microstructural changes due to mercury intrusion porosimetry were documented in a 6-month-old sample of ordinary portland cement paste made with a water/cement ratio of 0.5. Specimens before and after mercury intrusion were viewed at 60% relative humidity using an environmental scanning electron microscope. Specimens were intruded to a pressure just below the critical threshold pressure, removed for observation, then intruded to a pressure well above the critical threshold pressure. Significant damage caused by relatively low pressures of 10–20 MPa was found in the interior of the sample. The connectivity of pores in the 10–1 μm size range was much higher after intrusion.     

氮吸附法和压汞法测量生物质焦孔隙结构的比较

采用氮吸附法和压汞法对四种生物质焦（稻壳、树叶、玉米杆、棉花杆）的孔隙结构进行了测量,得到了两种测量方法下焦样的比表面积和孔径分布。结果表明不同测量方法得到的焦样比表面积和孔径分布有明显差别。氮吸附法主要测量焦样中微孔的孔隙结构,压汞法主要测量焦样大孔（和部分中孔）的孔隙结构。微孔对焦样的比表面积贡献最大,大孔对焦样的孔容积贡献最大。当热解温度升高时,焦样的微孔结构迅速增多,氮吸附法测得的比表面积变化大;而热解温度对大孔的影响较小,所以压汞法测得的比表面积变化不大。     

Influence of the aging time of yttria stabilized zirconia slips on the cracking behavior during drying and green properties of cast tapes

Tape-casting process was used to produce yttria stabilized zirconia (YSZ) substrates in an aqueous system using a low amount of an acrylic latex binder. Concentrated suspensions with different aging times were cast, and the influence of the slip aging time on the drying kinetics and cracking behavior of the tapes were studied. In addition, the effect of the slip aging time on the properties of the resultant green tapes was investigated. The latex particles consolidated by coalescence during the aging time of the slips and resulted in an increase in the smaller pore size of the cast tapes. The pore radius increased with increasing the slip aging time up to 14 days thereby decreasing the capillary pressure in the liquid. Aging times over 14 days did not change the pore radius and consequently the capillary pressure. The capillary tension drove the consolidation; the tapes produced from slips with lower aging times which had higher capillary pressure shrank more, had lower pore volume and consequently higher green density. Cracking was found in tapes prepared from slips with aging times shorter than 14 days; the crack area decreased with increasing the slip aging time. For slip aging time ≥14 days cracking was not observed. Aging before casting up to 14 days reduced cracking in tapes prepared with low amounts of latex; however, the lower capillary pressure resulted in low green density of the cast tapes.     

Empirical correction factors involved in mercury porosimetry

An empirical calculation method has been developed to correct the apparent porosity measured by mercury penetration porosimetry. It was found that the value of the correction depends on the geometry and volume of the sample cell, the volume of mercury in the sample cell, and the pressure applied. The effect of the compressibility of the sample was found to be negligible. Application of this correction enables valid porosity curves to be obtained even at high pressures up to 50,000 psi. Thus, by adopting Rootare and Prenzlow's method for specific surface area, appropriate results can be calculated.     

Contact angle and damage during mercury intrusion into cement paste

The operant contact angle to be used for mercury intrusion porosimetry was measured directly by intrusion into specially prepared, cylindrical pores. It was found to vary for cement pastes of different ages, and for pastes containing flyash. It also changed when the paste was previously intruded and the mercury subsequently removed. Values of the contact angle ranged from 123° to 135°. The high pressures used during intrusion were found to reduce the pore volume of cement paste with the reduction being greater in the smaller pore (higher pressure) region. Distilling mercury from a paste was also found to alter the pore structure and this effect must be considered separately before alterations due only to intrusion are discussed.     

Process model for latex film formation: Optical clarity fronts

We examined the drying behavior of latex both theoretically and experimentally. The theory extends a model for horizontal drying fronts in films with nondeformable particles to incorporate particle deformation by a capillary deformation mechanism. The pressure in the fluid, causing particle compaction, arises from flow through the packed bed to ensure evaporation from all wet areas of the film. We predicted the position of a front of volume fraction unity passing across a semi-infinite film as it dries. Experimentally, the position of the transition from a cloudy film to optical clarity was tracked visually in films comprised of either single component soft latex particles, 20°C above the glass transition, or a blend containing 35% non-deformable hard latex particles. For an initial volume fraction of 0.33, we found excellent agreement between theory and experiment. For an initial volume fraction of 0.05, the agreement is less, although still qualitative. The limitations of the model with respect to the knowledge of physical parameters and initial conditions are discussed. One major implication of the model is that deformation of soft latex particles displaces large amounts of water and, consequently, slows progression of the drying front. Harder particles and shallow initial film profiles produce more pronounced drying fronts. Dept. of Chemical Engineering, Princeton, NJ 08544. Emulsion Polymers Institute and Dept. of Chemical Engineering, Bethelhem, PA 18015.     

Impact of functionalised dispersing agents on the mechanical and viscoelastic properties of pigment coating

The effect of poly(acrylic acid) – poly(styrene sulphonic acid) (AA-SSA) and poly(acrylic acid) – poly(2-acrylamido-2-methylpropane sulphonic acid) (AA-AMPS) dispersing agents on the viscoelastic and mechanical properties of precipitated calcium carbonate-latex composites used was investigated. Four different formulations were prepared using carboxylated styrene butadiene (SBR) and styrene-acrylate (SA) latexes. Pore space was characterised using mercury porosimetry. The storage modulus and loss factor were evaluated through dynamic mechanical thermal analysis (DMTA) low frequency single cantilever bending mode. The ultimate tensile strength and the Young modulus were also measured. At low latex contents, storage modulus was found to be higher for SBR latex composites. At high latex content, the SA storage modulus was found to be higher. It is suggested that at lower latex content, the viscoelastic properties are function of physical microstructure, which at low latex is influenced by the latex glass transition temperature (Tg). Softer latex spreads more on the pigment surface providing higher stiffness, since pigments are held together by latex bridges. At higher latex content, the composite stiffness tends to be more dependent on the stiffness of the pure latex. The AA-SSA dispersant creates strong pigment–latex interfacial adhesion in dry composites, which is reflected in high elastic modulus and tensile strength. The AA-AMPS dispersant formulations had greater resistance to water. Due to the compatibility between the AMPS blocks and the SBR latex within the composite, higher storage modulus stability in water saturated composites is measured (at room temperature 56% of the storage modulus is preserved).     

聚合物改性水泥砂浆界面过渡区的交流阻抗谱研究

水泥砂浆可视为由水泥浆体、细集料和水泥浆体－－休料界面过渡区（interfacial transition zone，简称ITZ）所组成，聚合物改性水泥砂浆中，较小的聚合物颗粒有利于休料表面的紧密堆积，用交流阻抗方法研究了不同砂子粒径和不同砂子体积分数的聚合物改性砂浆在不同龄期的表现，结果表明：交流阻抗方法是研究聚合物改性砂浆界面过渡区发展变化的一种新手段，聚合物改性砂浆的阻抗谱随龄期延长出现二次明显变化，这种特征分别与聚合物在砂浆界面过渡区的聚集、凝结、形成紧密堆积的颗粒结构以及聚合物颗粒相互扩散渗透，形成具有一定力学强度的过程有关。同时，聚合物在界面过渡区的成膜情况与砂子粒径及其体积分数有关，从而在交流抗谱上可以观察到相应的响应。     

DROP SIZE DISTRIBUTION OF LITHIUM AMALGAM PRODUCED BY MERCURY JET CATHODE

The drop size distribution of the lithium amalgam produced by mercury jet cathodes was studied experimentally. Electrolysis was done in aqueous solution, 3 mole LiOH per liter, at ambient temperature. Jets were obtained by passing mercury through small orifices made in a Plexiglas plate. The orifice diameter was varied from 28 to 70 μm, the hydrostatic mercury pressure from 200 to 800mmHg, and the electrolysis voltage from 0 to 6 V. An optical method for drop size determination was carried out.

Within the limits of experimental errors, a unique distribution was obtained for all cases. The volume fraction vs. drop diameter curve resembled a Gaussian distribution having the mean diameter D¯v = 209.7 μm and the spread σ_v =39.1 μm.     

Photoabbau von PVC-folien. I. Einfluß von bestrahlungsstärke und temperature

Films from mass-PVC have been irradiated by a high pressure mercury lamp under nitrogen. The influence of variable light intensity and temperature of the sample on the dehydrochlorination reaction and changes in the absorption spectrum of the polymer were investigated.     

AN APPARATUS FOR THE DETERMINATION OF ADSORBED AIR1

Some possible ceramic applications of the Toepler mercury pump as employed in determination of gases in various materials are discussed. The procedure followed in measuring the gases given off by a clay slip at reduced pressures is described. It was found that 4.65% of gases by volume are removed from a sample of clay slip by reducing the pressure on the sample to boiling (25 mm.). An additional 0.18% of gases was cvolved between the boiling pressure and 1.8 mm. at which pressure the sample was dry.     

Viscoelasticity of porous composite materials: Experimentals and theory

The viscoelasticity of latex/PS beads composites, having the same volume content of latex and PS beads, but various porosity ratios and specific surfaces of particles has been investigated in the glass temperature range of the latex matrix. In order to give evidence for the main factors governing the viscoelastic properties, data were compared to numerical simulations based on the Christensen and Lo model and Skorokhod's approach. Such modelings were performed by considering either the latex matrix of the PS beads as the continuous phase. It was concluded that the glassy modulus is mainly governed by the volume fraction of porosity, while the rubbery modulus is controlled by both the interactions between phases and the void volume content. The location of the mechanical relaxation seems to be governed by the mechanical coupling between phases, which implies some local phase inversion. The magnitude of the mechanical relaxation depends not only on the chemical coupling induced by the interactions between phases, but also on the mechanical coupling.     

A comparison of nitrogen and mercury pore size distributions of silicas of varying pore volume

Although good correlation between the pore size distribution determined by nitrogen desorption isotherm and mercury penetration methods has been reported with low pore volume samples, large discrepancies in pore size distribution and in pore volume were found with high pore volume silicas and were shown to be a function of the pore volume of the silica. The mercury penetration method is believed-to compress these highly porous silicas and therefore reduces the pore volume and forms smaller pores.