POROSITY AND RESIDUAL EQUILIBRIUM SATURATION OF SINTERED SPHERES OF GLASS BEADS

Sintered spheres(made of glass beads) were simply produced with a definite diameter, with a precision of ±0·5 mm in diameter, for a wide range of sintered angles (0–27°). The experimental values of the porosity of the sintered spheres were consistent with the calculated results for the coordination number N ≠ 8. The residual equilibrium saturation, as one of the basic physical properties of sintered glass beads was investigated experimentally and theoretically, resulting in the presence of a distribution in the angle of pendular ring.     

SUPERHEATED STEAM DRYING OF SINTERED SPHERES OF GLASS BEADS UNDER VACUUM

Drying of sintered spheres of coarse glass beads with a wide sintering range in superheated steam under vacuum was studied.

In samples with sintered angles of 7.5° -27°, the experimental normalized drying rates in superheated steam at pressures of 7.3-7.9mmHg were smaller than those for 56.0-767.6 mmHg in the vicinity of the critical moisture cotents for 56.0-767.6GmmHg. As reported in an earlier paper, there were     

STEAM DRYING OF SINTERED SPHERES OF GLASS BEADS

Superheated steam drying of sintered spheres of glass beads with different diameters is investigated to reveal the effects of the gravitational force on drying rates. In a previous study, the drying rate curves of small samples with coarse glass beads in which the frictional resistance to flow of water and the effect of the gravitational force are negligible, were predicted by an evaporation zone model.In the present investigation, the drying rate curves of sintered spheres of glass beads with diameters ranging from 1.53×10^-2m to 4.99×lO^-2m are experimentally and theoretically obtained, and also the capillary pressure curves are measured by use of Haines' apparatus. The drying rate curves of large samples in which the effect of the gravitational force can not be negligible, are compared with those for small samples and the difference among these curves is discussed in terms of the moisture distributions which are estimated from the evaporation zone model with the observed capillary pressure curves.     

STEAM DRYING OF SINTERED SPHERES OF GLASS BEADS

ABSTRACT

Superheated steam drying of sintered spheres of glass beads with different diameters is investigated to reveal the effects of the gravitational force on drying rates. In a previous study, the drying rate curves of small samples with coarse glass beads in which the frictional resistance to flow of water and the effect of the gravitational force are negligible, were predicted by an evaporation zone model.In the present investigation, the drying rate curves of sintered spheres of glass beads with diameters ranging from 1.53×10^-2m to 4.99×lO^-2m are experimentally and theoretically obtained, and also the capillary pressure curves are measured by use of Haines' apparatus. The drying rate curves of large samples in which the effect of the gravitational force can not be negligible, are compared with those for small samples and the difference among these curves is discussed in terms of the moisture distributions which are estimated from the evaporation zone model with the observed capillary pressure curves.     

SUPERHEATED STEAM DRYING OF SINTERED SPHERES OF GLASS BEADS UNDER VACUUM

Drying of sintered spheres of coarse glass beads with a wide sintering range in superheated steam under vacuum was studied.

In samples with sintered angles of 7.5° –27°, the experimental normalized drying rates in superheated steam at pressures of 7.3-7.9mmHg were smaller than those for 56.0-767.6 mmHg in the vicinity of the critical moisture cotents for 56.0-767.6GmmHg. As reported in an earlier paper, there were     

Paste Residence Time in a Spouted Bed Dryer. II: Effect of Spout Operational Conditions

Residence time distributions for an aqueous solution of 10% sodium chloride in a spouted bed dryer of inert particles were determined using the stimulus-response technique. Glass and polyethylene beads with diameters 2.6 and 3.4 mm were used as inert bodies in a cylindrical column of 14.0 cm diameter and 60° conical base. The effects of inert bodies load, air, and paste flow rates on the mean residence times and RTD were determined following 2³ factorial designs. The RTD could be correlated to the perfect mixing cell model with R² varying from 0.8684 to 0.9815. The mean residence times in CSBD varied from 10.8 to 13.9 and 10.7 to 13.3 min for glass and polyethylene beads, respectively. For both inert particles, mean residence times increased with bed height and decreased with paste feed rates. Also, terms of interaction among the factors were significant in some cases, showing a complex behavior of paste residence times. Equations obtained by response surface regression could predict mean residence times on glass and polyethylene beads with deviations lower than ±10%.     

Vacuum Drying of Porous Solids under Supercooling

Vacuum drying of sintered glass beads, cemented glass balloons, and baked clay was investigated under supercooling. Glass beads and glass balloons, which were made of a common glass material, were used for comparison. Concerning sintered glass beads, there was no effect of supercooling on drying rates at a pressure of 0.93 kPa. In cemented glass balloons as well as in baked clay, however, a prominent peak of drying rates emerged in drying rate curves and at the same time, a stepwise increase in the surface temperature appeared under supercooling at a pressure of 1.19 kPa; no peak of drying rates emerged in drying rate curves of sintered glass beads. The total amount of latent heat of vaporization and sensible heat generated at the peak of drying rates was 39-59% of the latent heat of solidification. A part of the latent heat of solidification evaporated the water in the sample, producing a peak of drying rates as well as a stepwise increase in the surface temperature of the sample.     

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.     

Comparison of Drying Rate Curves of Porous Solids in Superheated Steam to Those in Air

Drying of porous solids was experimentally investigated in superheated steam as well as in air. Drying rate curves, including critical moisture contents, in steam at subatmospheric pressure, were compared to those for air at atmospheric pressure; moreover, they were compared to those for steam at atmospheric pressure as well. The former comparison was carried out under conditions of sample temperatures of 41.8-42.5°C (which were nearly equal to saturation temperatures of 42.1-42.2°C at pressures of 8.23-8.30 kPa) for the constant rate period in steam and the corresponding sample temperatures of 42.0-45.0°C (which were close to the wet-bulb temperatures) for the constant rate period in air. There were distinct differences between normalized drying rate curves, including critical moisture contents in steam and in air at the above similar sample temperatures for materials of baked clay, firebrick, and cemented glass balloons over the minimum value of 8.3 × 10^-3 µm and up to the maximum value of 1.2 × 10² µm in cumulative pore-size distributions: longer constant rate periods and lower critical moisture contents in steam than in air, and higher drying rates in steam than in air for the falling rate period. Moreover, the latter comparison of the drying rates in steam at subatmospheric pressure to those in steam at atmospheric pressure revealed that the differences in normalized drying rates between subatmospheric pressure and atmospheric pressure were small for both materials under mild external conditions. These findings were common to the baked clay, firebrick, and cemented glass balloons over a wide range of pore-size distributions studied in the present work, as well as sintered coarse glass beads as previously reported.     

Liquid-phase viscosities of the binary systems carbon dioxide-oleic acid, carbon dioxide-methyl myristate, and carbon dioxide-methyl palmitate at high pressures

Liquid-phase viscosities of the binary systems carbon dioxide-oleic acid, carbon dioxide-methyl myristate, and carbon dioxide-methyl palmitate were determined at 40 °C, 50 °C, and 60 °C and at different pressures up to 126 bar. The change of viscosity with pressure was also recorded for the pure liquids. Experiments were performed by visually observing the motion of small saturated gas bubbles and of glass beads in the liquid within a high-pressure view cell. Viscosities were determined by applying an appropriate law describing flow resistance to the motion of the bubbles and beads for which size and velocity were recorded. All numerical results are given in full detail.     

Drying Rate Curves of Porous Solids in Steam and in Air under Low-Pressure Conditions

Drying of porous solids such as sintered glass beads, baked clay, and cemented glass balloons in both steam and air streams was investigated under low-pressure conditions. There was no significant difference between the normalized observed drying rate curves in air at low pressures of 0.71-1.19 kPa and those in steam at low pressures of 0.97-0.99 kPa. However, lower critical moisture contents and higher drying rates in superheated steam at subatmospheric pressures of 8.27-8.33 kPa were observed compared to those in steam at pressures in the range of 0.97-0.99 kPa. Moreover, two models were validated for the prediction of drying rate curves of sintered glass beads at subatmospheric and low pressures. The patterns of the drying rate curves, which depend on the drying medium and its pressure, were common to these materials.     

Microstructural evolution in nanocrystalline Y–TZP containing a silicate glass

Nanocrystalline yttria stabilized tetragonal zirconia polycrystal (NC–Y–TZP) powders were coated with a sodium strontium silicate glass using the sol-gel technique. The compact powders were sintered at 1400°C for 1 h resulting in dense nanocrystalline pellets with 5, 10 and 15 vol.% glass. Short pre-sintering heat treatment at 800°C caused the full stabilization of the tetragonal phase while long treatments led to the devitrification of the glassy phase. The mean grain size decreased from 196 nm in the glass-free specimen to 140, 110 and 100 nm in the specimens containing 5, 10 and 15 vol.% glass, respectively. The grain size distribution width also decreased with increase in the glass content. TEM revealed the morphological changes of the highly facetted polyhedral grains in the glass-free specimens into the round-shape grains with increase in the glass content. The effect of the glass on the phase formation, densification and microstructure have been discussed.     

Vacuum Drying of Porous Solids under Supercooling

Vacuum drying of sintered glass beads, cemented glass balloons, and baked clay was investigated under supercooling. Glass beads and glass balloons, which were made of a common glass material, were used for comparison. Concerning sintered glass beads, there was no effect of supercooling on drying rates at a pressure of 0.93 kPa. In cemented glass balloons as well as in baked clay, however, a prominent peak of drying rates emerged in drying rate curves and at the same time, a stepwise increase in the surface temperature appeared under supercooling at a pressure of 1.19 kPa; no peak of drying rates emerged in drying rate curves of sintered glass beads. The total amount of latent heat of vaporization and sensible heat generated at the peak of drying rates was 39–59% of the latent heat of solidification. A part of the latent heat of solidification evaporated the water in the sample, producing a peak of drying rates as well as a stepwise increase in the surface temperature of the sample.     

Corrosion effects of glass on YSZ electrolytes

This work reports on the microstructure and electrical properties of different yttria stabilized zirconia (YSZ) based cells using: (i) intimate mixtures of YSZ and a commercial soda-lime glass (up to 20 wt%), sintered at different temperatures; (ii) YSZ disks covered with a layer of glass on one side and fired in a clean laboratory furnace for two hours at different temperatures (1250–1350 °C); (iii) YSZ pellets exposed to the exhaust gases of one (industrial) glass melting furnace, at temperatures around 1300 °C. Microstructural observations and impedance spectroscopy measurements were used to demonstrate the potential of the latter technique in monitoring the electrolyte corrosion. The high-and intermediate-frequency impedance arcs showed a significant and coherent dependence on the progress of corrosion, due to the formation of glass–ceramic composites with large glass/ceramic interfaces. Similar results were obtained with laboratory scale and industrial experiments. EDS analysis showed an higher concentration of Y₂O₃ in the intergrain region and a corresponding concentration decrease in the electrolyte grains.     

New low-density ceramic material for packing fractional distillation columns

This paper presents a general comparison between glass beads and new low-density ceramic spheres as packing materials for fractional distillation columns. The light-weight ceramic spheres have higher through-puts, lower pressure drops, better separating power and higher wettability than glass beads.     

Oxidation of pressureless sintered Si2N2O materials

The oxidation behaviour of pressureless sintered Si₂N₂O materials prepared from both amorphous and crystalline starting powders has been examined. The materials exhibited excellent oxidation resistance at temperatures of up to 1350°C. Thin protective oxide scales formed which had a duplex morphology after long exposures to air at high temperatures. Substantial crystallisation of the intergranular glass phase with formation of Y₂Si₂O₇ occurred during oxidation at 1200°C and 1350°C. Catastrophic oxidation occurred at temperatures ≥ 1400°C. This behaviour is enhanced by an oxidation-induced shift in the composition of the material to a liquid-forming region in the Y-Si-Al-O-N system.     

GENERALIZED EQUATION OF PRESSURE LOSSES IN DISPERSED POWDER FLOW THROUGH VERTICAL PIPES

The results of the experimental investigation of pressure losses in a vertical co-current flow of a two phase solid particles-air system are given for the transient character of flow of the continuous phase. The dispersed phase was formed by 6 fractions of polypropylene particles and 5 fractions of glass ballotini of 90 · 10^-6-370 · 10^-6 m and 60 · 10^-6-200 · 10^-6 m equivalent diameter, respectively. The relative mass fraction of solid particles varied over the interval 0-1 dilute. On the basis of experimental data the generalized equation for the computation of pressure losses for the vertical transport was derived. The pressure losses calculated on the basis of this equation were compared with data published by 9 authors.     

COMPARISON OF GLASS TRANSITION TEMPERATURE AND STICKY POINT TEMPERATURE FOR SKIM MILK POWDER

Wall deposition of particles in spray dryers is a key processing problem, and information about the glass transition temperature of the amorphous material that arises from spray drying can be used to guide the selection of operating conditions that may minimise wall deposition. The glass transition temperatures for skim milk powder with various moisture contents were determined using Differential Scanning Calorimetry (DSC), and a repeatable glass transition temperature diagram was established from these results. The glass transition temperature decreased as the moisture content increased, as expected (low moisture content 1.65 g/100 g of dry powder, glass transition temperature 87.7°C; high moisture content 4.52 g/100 g of dry powder, glass transition temperature 46.7°C). The glass transition temperature was found to be virtually the same as the sticky-point temperature measured using a thermo-mechanical test. The difference is essentially due to the difference between doing a mechanical test for viscosity (sticky-point) and a phase transition measurement (DSC).     

Predictive radiation field modeling for fluidized bed photocatalytic reactors

A predictive model of the radiation distribution for fluidized bed photocatalytic reactors was proposed and solved by means of the Monte Carlo approach coupled with the ray tracing technique. This model considers the interaction between the photocatalytic TiO₂-coated spheres and the photons, taking into account the shadowing effect of the beads, the reflection on the surface of the spheres, and the absorption in the TiO₂ films. This radiation model is completely predictive and does not use any adjustable parameter. Modeling results indicate a strong influence of the bed expansion on the radiation distribution, with the shadowing effect of the beads being the main cause for this dependence. Increasing the bed expansion improves the uniformity of the radiation distribution in the reactor. Nevertheless, an excessively expanded bed would reduce the efficiency of the reactor because the transmittance of the bed increases and a fraction of photons leave the reactor without being absorbed by the TiO₂-coated spheres. The radiation model was evaluated in a laboratory-scale fluidized bed photocatalytic reactor that was designed and built for the elimination of organic pollutants from water streams. TiO₂-coated glass spheres with a diameter of 1.18 mm were used as photocatalyst. The model was validated by comparing the predicted values of the effective transmittance of the bed with experimental results measured under different bed expansions. The performance of the reactor was also assessed experimentally, showing a good efficiency for the photocatalytic degradation of formic acid as a model compound.     

A novel method for immobilization of chitosan onto nonporous glass beads through a 1,3-thiazolidine linker

A new method for the surface modification of nonporous glass beads (average diameter, 6 μm), which characterized by formation of a 1,3-thiazolidine ring between l-cysteine linkers on the glass bead and reducing ends of chitosan, has been developed. γ-Aminopropyltriethoxysilane (APES)-treated glass bead was first subjected to condensation with an l-cysteine derivative, l-4-carboxy-3-formyl-2,2-dimethylthiazolidine (CFMT), in the presence of water-soluble carbodiimide hydrochloride (WSC) and HOBt. After deprotection by diluted hydrochloric acid, the glass beads with activated cysteine linkers on the surface were treated with reducing chitosan in aqueous acetic acid solution at room temperature. The maximum content of chitosan immobilized on the glass beads estimated by acid-hydrolysis and subsequent glucosamine analysis by Svennerholm method after was 0.73% (w/w). This was obtained by using chitosan having an average molecular weight of 14 kD. Model reactions of the cysteine derivatives with reducing chitosan were also performed and the product was examined by IR and NMR spectroscopy to verify the linkage between cysteine and chitosan.