Measurement of Porosity in Ceramic Coatings by Thermogravimetric Volatilization of Liquids

A simple gravimetric method was developed to determine the open porosity in ceramic coatings. The coating's pore space was filled with a liquid and the weight loss on volatilization of the liquid was measured in a thermogravimetric analyzer. This thermogravimetric volatilization of liquids (TVL) method was used to characterize the porosity in titania coatings, alumina/aluminum phosphate coatings, and free-standing films of alumina. Several liquids were used; ethylene glycol and 1,3-propanediol gave the best results due to their low volatilities at room temperature. The measured porosities of the ceramic coatings ranged from 30% to 80% and the pore sizes (as determined by SEM and mercury porosimetry) ranged from 0.1 to 15 μm. The standard deviation of the TVL measurement was smaller for thicker coatings (e.g., ≥20 μm). Porosities determined by TVL were within typically 5-10% of those determined by mercury intrusion porosimetry on identical samples. Characterization of a series of alumina/aluminum phosphate coatings showed a decrease in porosity consistent with expectations based on density and SEM observations. TVL is nondestructive, can be used for small volumes of sample, and when combined with SEM, provides a good means to characterize coating porosity and pore structure.     

Effect of solvent exchange on the pore structure and dissolution behavior of cellulose

Effect of solvent exchange, i.e., the sequential immersion in water, acetone, and DMAc on the pore structure of cellulose and its dissolution behavior in lithium chloride/N,N‐dimethylacetamide (LiCl/DMAc) was investigated by using size exclusion liquid chromatography (SEC), dynamic light scattering (DLS), and small‐angle X‐ray scattering (SAXS). In the SEC experiment, poly(styrene)s, diethyl phthalate, and acetone were used as probe solutes and 2‐butanone was used as an eluent. Capacity factor of these solutes in the solvent‐exchanged cellulose were larger than those in the untreated one. This was remarkable when diethyl phthalate and acetone were used as solutes. Since the molecular radii of these solutes were estimated to be less than 1 nm, it was shown that the solvent exchange increases the amount of pores within cellulose with the radii of less than 1 nm. In the SAXS experiment, structural difference between the solvent exchanged and the untreated celluloses was observed when the celluloses were immersed in acetone. Values of specific inner surface and average chord length calculated from SAXS profile showed that the amount of small pores was increased in the solvent exchanged cellulose. Considering the results from SEC, DLS, and SAXS measurements, facilitated dissolution of the solvent exchanged cellulose in LiCl/DMAc was attributed to the increase in the pores with the radii of less than 1 nm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3976–3984, 2007     

Surface and pore structure of deoiled acid-and heat-treated spent bleaching clays

Samples of spent bleaching clay were deoiled by hexane, methanol, hexane-methanol, and supercritical CO₂ extractions. The deoiled clays were regenerated by acid and heat treatments. Nitrogen adsorption isotherms for these samples are type IV with hysteresis loops corresponding to type H3, indicating slit-shaped pores. Used deoiled and dried samples have smaller surface areas and pore volumes than unused clay. The surface areas and pore volumes increased after heat treatment. Acidified heat-treated deoiled samples have smaller surface areas and greater pore volumes than unused clay, except for the methanol-deoiled sample. Thus, heat and acid treatments removed substances adsorbed in the pores that were not removed by solvents or CO₂ extraction. This was confirmed from the ratios of the cumulative surface area/BET surface area, as well as analysis of the pore size distributions, which indicated an increase in mesopores with radii of between 25 and 100 Å. The t-plots showed that smaller pores with sizes between 7 and 25 Å, present originally in the unused clays, were closed by heat treatment. These pores were absent in the deoiled and the heat-treated samples except for the heat-treated sample that was deoiled by hexane followed by methanol. Smaller pores, accompanied by an increase in surface area, were also observed for all deoiled samples after acid and heat treatments.     

Unique microstructure of porous NiAl intermetallic compound prepared by combustion synthesis

Porous NiAl intermetallic compounds have been prepared by combustion synthesis from nickel and aluminum elemental powders. The synthesis process, pore structure and pore forming mechanism were studied systematically. The results show that porous intermetallic compounds are composed of single NiAl phase, which have unique feature of complex pore structure, i.e. micro-pores are distributed in the wall of macro-pores and small pores. It has been found that different pores are formed in different stages. The macro-pores are formed by the volatilization of pore-forming agent at preheating stage. Due to the kirkendall effect and molten Al to cover the surface of Ni particles by capillary force, small pores are formed during the reaction. The shape and the size of small pores depend largely on the Al particles. However, the formation of micro-pores in the unique complex pore structure mainly contributes to the liquid of Al and part of NiAl accompanied by liquid?Csolid reaction of Ni?CAl at the cooling stage, which is different from the kirkendall pores.     

Porosimetrie gequollener makroretikularer Ionenaustauscher

The relative micro and macro pore volumes and the macro pore size distribution were used to characterize the pore structure of ion exchangers. The evaluation of these from density measurements and mercury penetration measurements was described for a sulphonated macro reticular ion exchange resin in the swollen state with different contents of swelling agent. On taking up water the dry volume of the exchange resin increased (swelling) until a water content of about 33 wt.-% was reached. Additional water filled up the macro pores to a final content of 58 wt.-%. With the specific volume of the exchange resin in the swollen state in addition to the specific volume of the gel phase, the relative macro pore volume of the fully swollen state was evaluated. The results of the mercury penetration method agreed with those of the density measurements taking into account the compressibility of the mercury itself and those of the swelling agent and the matrix. Corresponding correction factors could be evaluated from measurements on micro reticular ion exchange resins. The mercury penetration measurements provided additional information on the macro pore size distribution of the swollen state. For the examined ion exchange resins a logarithmic standard distribution with an arithmetically weighed mean pore radius of about 1 100 Å was evaluated. The relative over-all pore volume of 0,65 was not identical with the value of 0,61 for the partition coefficient of ethylene glycol from dilute aqueous solutions, as only that part of the water, which is bound to the sulphonic groups (hydrated water), could be exchanged by ethylene glycol. Pure ethylene glycol substituted the hydrated water completely. The specific volume of the exchange resin thereby decreased in comparison to that of the water-swollen state.     

Preparation and membrane performance of poly(ethylene-co-vinyl alcohol) hollow fiber membrane via thermally induced phase separation

Poly(ethylene-co-vinyl alcohol) (EVOH) hollow fiber membranes with ultrafiltration performance were prepared from EVOH/glycerol systems via thermally induced phase separation (TIPS). The diluent glycerol was used as bore liquid to make a lumen of the hollow fiber for the purpose of prevention of the diluent evaporation and the larger pores formation at the inner surface of the hollow fiber. The obtained hollow fiber membranes showed asymmetric structures with skin layer near the outer surface, the larger pores just below the skin layer and the smaller pores near the inner surface. The formation of the larger pores near the outer surface was due to the enhanced pore growth by the water penetration. Some primary factors affecting the structure and performance of the membranes such as ethylene content (EC) in EVOH, cooling water bath temperature and take-up speed were studied extensively. The water permeability can be improved by increasing the water bath temperature and the take-up speed and by decreasing the EC. Both the pore size at the outer surface and the connectivity between the pores have to be considered together to understand the experimental result of the water permeability and the solute rejection.     

Effect of drying history upon the exchange of pore water with methanol and upon subsequent methanol sorption behaviour in hydrated alite paste

The counter diffusion process in which the pore water in saturated alite paste was exchanged for methanol was studied experimentally. The rate of exchange was dependent upon drying history. All of the pore water could apparently be exchanged for methanol. Length changes during the exchange process and during subsequent methanol sorption experiments were small. The methanol sorption results suggested that previous drying at intermediate relative humidities caused a partial collapse in the smaller pores and a corresponding increase in volume of the larger pores. These changes in pore structure correlated with the observed dependence upon drying history of a) the rate of methanol exchange for pore water and b) irrecoverable drying shrinkage.     

Effect of low temperatures on polymorphic structures of cotton cellulose

Effects of low temperatures upon fine structures of cotton pretreated with either liquid ammonia or caustic of mercerizing strength were investigated. Temperatures of cotton after impregnation with liquid ammonia were lowered by (1) liquid nitrogen, (2) acetone–Dry Ice, (3) acetone, or (4) simple evaporation. With alkali-impregnated fabrics, temperature was lowered by immersion in liquid nitrogen. Changes in fine structure of ammonia- and alkali-celluloses were evaluated by x-ray diffraction before and after removal of each swelling reagent. After treatment with either ammonia or caustic soda, extent of crystalline modification was increased as temperature was reduced. X-ray diffractograms taken while liquid ammonia was still present indicated that the cellulose I structure of cotton sheeting was converted to cellulose III at liquid nitrogen temperatures; extent of conversion was approximately that obtained when a looser yarn structure was treated with liquid ammonia and the ammonia was removed by evaporation. When ammonia was removed with water, the cellulose I lattice was regenerated. In the presence of 23% NaOH, diffractograms indicated a significant decrease in order after a similar drop in temperature, but patterns were not of cellulose II until the NaOH was removed with water. Conversion to cellulose III or to cellulose II was achieved instantaneously when ammonia- and alkali-impregnated fabrics were immersed in liquid nitrogen.     

Hydrophobic recovery of repeatedly plasma-treated silicone rubber. Part 2. A comparison of the hydrophobic recovery in air,water, or liquid nitrogen

Surfaces of medical grade silicone rubber (Q7-4750, Dow Corning) were modified by repeated (six times) RF plasma treatments using various discharge gases: oxygen, argon, carbon dioxide, and ammonia. The treated samples were stored for a period of 3 months in ambient air, water, or liquid nitrogen. Subsequently, the temporal behavior of the effects of the plasma treatment on the physicochemical surface properties of the silicone rubber was investigated using water contact angle measurements and X-ray photoelectron spectroscopy (XPS). Hydrophobic recovery during 3 months storage in ambient air was considerable and nearly complete for all four plasmas used. Hydrophobic recovery was almost completely suppressed during storage in liquid nitrogen, and only a minor increase of around 10° in advancing water contact angle was observed for all four plasma treatments. Also during storage of treated samples in water, hydrophobic recovery was minimal and initiated again by returning the treated samples to ambient air. XPS analyses showed that argon, carbon dioxide, and ammonia plasma-treated silicone rubber all had increased carbon percentages at the expense of oxygen and silicon after storage in water, or in liquid nitrogen, compared with after storage in ambient air. Interestingly, the carbon content of oxygen plasma-treated silicone rubber decreased during storage in water, or in liquid nitrogen, compared with storage in ambient air, while its oxygen and silicon percentages increased.     

Ice formation in hardened cement paste, Part II — drying and resaturation on room temperature cured pastes

Ice formation in partly dried and resaturated room temperature cured mature Portland cement paste has been measured. The measurements were carried out continuously in the temperature range from +20° C to −60° C.

The results demonstrate that the drying-resaturation treatment increases the volume of large pores and the continuity of the pore system. The increase in the volume of large pores occurs at the expense of small pores and necks in the pore system.

As the relative water vapor pressure at which drying takes place is decreased to 0.58, the number of continuous large pores is increased. Drying at lower relative water vapor pressures does not further increase the effect.

The present findings point out the importance of the moisture history of concrete before testing such properties as water permeability and frost resistance.     

Faserstruktur und Färbeeigenschaften von Cellulosefasern, 1. Zusammenhänge zwischen Veränderungen der Faserstruktur und der Farbstoffadsorption bei Baumwolle durch Mercerisation und Flüssigammoniak-Behandlungen

Changes of fiber structure and the adsorption of direct dyes in cotton subjected to different kinds of mercerisation and liquid ammonia treatment have been studied. Therefrom a new general relationship between dye adsorption and fiber structure of cellulosic fibres has been given as a result. The fiber structure in the water swollen state was characterized by measurements of specific pore volume, specific pore surface and pore size distribution. The dyeing behaviour of the different treated cotton was determined by adsorption isotherms. The results revealed that for equilibrium dye adsorption from aqueous solution a transitional pore region with pore diameters of 20–60 Å has a special importance. Changes of these pores by the different swelling treatments correlated directly with the dye uptake. This pore region is found in cotton between the elementary fibrils.     

Dielectric loss in porous TiO2

The dielectric loss behavior of TiO₂ was characterized on samples of variable porosity and variable pore size. Pores were formed by two methods: varying the sintering temperature and by the addition of a spherical carbon porogen. Porosities varied from 5.9% to 59.3%. Dielectric loss increased with increasing pore volume in each case. However, dielectric loss increased at a slower rate for porogen induced pores. At equivalent pore volumes, pore surface area volumes were higher than those induced using the porogen. Dielectric loss behavior was shown to vary linearly with pore surface area. Our work demonstrates that large pores reduce free surface area and decrease dielectric loss when compared to similar samples with smaller pores. A new model of porous dielectric loss is proposed that characterizes materials based on generalized free surface area instead of porosity alone. Based on this model, we show that the relative loss of porous dielectrics depends critically on the pore surface area and the loss tangent of the parent dielectric.     

In situ comparisons of ammonia volatilization from N fertilizers in Chinese loess soils

Ammonia volatilization loss from mineral N fertilizers was determined on a calcareous Chinese loess soil with a pH (CaCl₂) of 7.7. An original in situ method that required no electricity or laboratory analyses was used. By means of a bellows pump, ambient air was drawn through four conical cups placed onto the soil (total area 400 cm²) and subsequently through an NH₃-specific detector tube with direct colorimetric indication of the ammonia concentration (measuring range, 0.05–700 vol.-ppm NH₃). Duration of measurement was about 3 min. Following N fertilization to winter wheat in 1990 and to summer maize in 1991, the application methods surface broadcast, uniform incorporation into the 0–15-cm layer, and for maize, a point placement at 10 cm depth were investigated. Ammonium bicarbonate and urea were applied at rates of 100 and 200 kg N ha^–1. In the autumn of 1990, ammonia losses following NH₄HCO₃ application were more than twice as large as with urea, fertilizer incorporation reduced NH₃ losses 15-fold, and doubling the nitrogen application rate resulted in a 1.7-fold increase in the percentage of nitrogen loss. Cumulative ammonia fluxes were about 2 times higher in the summer of 1991. Comparing application methods in summer, losses were significantly (3 times) lower only with point placement. The above differences were all significant at the P<0.05 level. Due to the very low air exchange rate (0.9 volumes min^–1), actual volatilization rates were underestimated by this method. Though not yielding absolute amounts, the Dräger-Tube method proved very suitable for comparing relative differences in ammonia fluxes. The measurements clearly reflected the characteristic flux patterns for the different treatments and the effects of environmental factors on their time course.     

Preparation and characterization of poly(ethylene‐co‐vinyl alcohol) membranes via thermally induced liquid–liquid phase separation

Porous membranes were prepared through the thermally induced phase separation of poly(ethylene‐co‐vinyl alcohol) (EVOH)/glycerol mixtures. The binodal temperature and dynamic crystallization temperature were determined by optical microscopy and differential scanning calorimetry measurements, respectively. It was determined experimentally that the liquid–liquid phase boundaries were shifted to higher temperatures when the ethylene content in EVOH increased. For EVOHs with ethylene contents of 32–44 mol %, liquid–liquid phase separation occurred before crystallization. Cellular pores were formed in these membranes. However, only polymer crystallization (solid–liquid phase separation) occurred for EVOH with a 27 mol % ethylene content, and the membrane morphology was the particulate structure. Scanning electron microscopy showed that the sizes of the cellular pores and crystalline particles in the membranes depended on the ethylene content in EVOH, the polymer concentration, and the cooling rate. Furthermore, the tendency of the pore and particle sizes was examined in terms of the solution thermodynamics of the binary mixture and the crystallization kinetics. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 853–860, 2003     

Release of volatiles from large coal particles in a hot fluidized bed

Coal particles with diameters of 3–11 mm were injected into a small, hot bed of sand fluidized by nitrogen. Volatiles evolution was followed by sampling the exit gas stream and subsequent analysis by gas chromatography. Three Australian coals covering a range of volatile matter were studied and the effects of coal particle size and bed temperature were determined. The yields of gaseous components, char and tar are explained by consideration of the competitive reactions for coal hydrogen and oxygen and secondary reactions of the volatile species within the coal particle. The pore structure developed during devolatilization has a significant effect on the extent of these secondary reactions. It is concluded that heat transfer is the main process controlling the volatilization time in fluidized bed combustors. The time required for heat transfer into the coal particle, determined by calculation and experiment, agrees with the measured volatilization time. Significant factors are external heat transfer to the surface of the particle, internal conduction through the coal substance and radiation through the pores, and the counterflow of volatiles out of the coal particle. For different coals, variations in the volatilization time appear to be caused by the development of different pore structures, which affect radiant heat transfer through the pores.     

碳酸盐岩油藏近井筒区域温度场的模拟

在碳酸盐岩油藏酸化中,近井筒附近的温度场对酸化效果影响很大。通过一种双重尺度模型对这一问题进行了研究,模型考虑了孔隙中的对流传质、传热和液固表面的酸岩反应。结果表明:与实验室常温条件相比,地层高温条件下的酸岩反应速率增快,形成主蚓孔的注酸速度增大(Damköhler数减小),且当注酸速度较大时,突破体积明显下降;当模拟区与外界不发生热交换时(绝热边界),由反应放出的热量使得模拟区的温度上升,造成突破体积比等温边界时的小;若酸液在井筒中不与地层发生热交换,则注酸速度较低时不同地层温度的突破体积几乎没有差别;反之,注酸速度较低时突破体积随着地层温度的上升而增加。     

Porous polymers prepared via high internal phase emulsion polymerization for reversible CO2 capture

A series of porous polymers with different pore volumes, pore sizes, and crosslinking densities were synthesized by high internal phase emulsion (HIPE) polymerization. The crosslinked polymerized HIPEs (polyHIPEs) were formed by the copolymerization of 4-vinylbenzyl chloride and divinylbenzene using water droplets in conventional or Pickering HIPEs as the templates. These porous materials were further modified by quaternization and ion exchange to introduce quaternary ammonium hydroxide groups. The resulting polyHIPEs were utilized as sorbents for reversible CO₂ capture from air using the humidity swing. The effect of pore structure on the CO₂ adsorption and desorption processes was studied. The polyHIPEs containing large pores and interconnected porous structures showed improved swing sizes and faster adsorption/desorption kinetics of CO₂ compared to a commercial Excellion membrane with similar functional groups.     

Characterization of SiC ceramics with complex porosity by capillary infiltration: Part B – Filling by molten silicon at 1500 °C

In Part A of this study, infiltrations experiments of porous SiC samples by hexadecane with pore-size distributions comprising small and large pores were realized. Two successive stages were identified during the filling of these samples corresponding to the infiltration of the two types of pores. The experimental data were successfully treated with a new analytical function. In Part B, it was found that this function can also be applied to the analysis of the mass gain during molten silicon infiltration at 1500 °C. Prior to silicon infiltration, it was found that the operating temperature induces a shift of the pore size distributions towards larger values. A dissolution-recrystallisation mechanism can also occur during the infiltration of silicon. During the first stage, liquid silicon fills rapidly larger pores than hexadecane. The kinetics are significantly larger with liquid silicon. Consequently, the durations for the complete filling are very short with molten silicon.     

Ammonia volatilization losses from fertilizers applied to acid soil in the field

Losses of ammonia by volatilization from ammonium sulphate and urea applied to soil were studied in field conditions.Losses from ammonium sulphate generally were not large; ammonia volatilization is thus unlikely to be an important pathway of nitrogen loss from cropped soils, and does not explain the low responses to nitrogen fertilizer of wheat grown in the higher rainfall cropping areas of South-Eastern Australia.Losses of nitrogen from ammonium sulphate were not greatly affected by meteorological variables, rate of application, water applicaton or incorporation into soil.The above variables all affected losses of nitrogen from urea, by influencing the rates of solution and hydrolysis of urea, and volatilization of ammonia. Losses ranged from 4 to 50% of the applied urea-nitrogen. Losses of urea-nitrogen were large when evaporation rates were high, and large variations occurred in the rates at which urea could be hydrolyzed.Extrapolation of the results to grazing conditions suggests that ammonia volatilization may result in large losses of nitrogen from short pastures in dry conditions.     

Thermal treatment of thorium oxide gel at low temperatures

Investigations were carried out on the variation of the specific surface area of thorium oxide gel upon thermal treatment in air at temperatures between 35° and 1000° The specific surface areas and pore volumes of the parent gel and its various dehydration products were calculated from the adsorption of nitrogen at the temperature of liquid nitrogen. The results obtained were compared with those measured from the adsorption of water, methanol and cyclohexane. The adsorbates were chosen to possess different molar volumes and polarities. Water was used because of its known ability to interact with thoria, and the extent to which this interaction limited its use was tested. X-ray and thermogravimetric analyses were also investigated, and certain structural changes after thermal treatment were noticed. The gel was amorphous to X-rays at temperatures up to 300°, and then it recrystallised to the cubic ThO₂. Below 300°, the surface area decreased continuously, probably by a mechanism of diffusion and material transport from wider pores to fill fine pores ( ‘surface annealing’). This was followed at higher temperatures by a crystallisation (activation) stage, and finally, by a sintering or crystal growth stage.