In order to represent the thermal motion of a hydrogen atom and a proton trapped inside a diamond lattice, trajectories of these oscillators around the trapping site were simulated using a C26H32 cluster model on the basis of the semi-empirical PM3-MO method combined with the direct molecular orbital (MO) dynamics calculation. Trapping occurs in the tetrahedral (T) interstitial site for both the hydrogen atom and the proton. With increasing temperature from 0 to 600 K the hydrogen and proton show an increase in amplitude of vibration due to the thermal activation. The hydrogen atom vibrates only around the trapping site up to 600K, which leads to a decrease in the spin density for the atom from 0.971 at 0 K to 0.963 at 600 K. On the other hand, the proton is observed to transfer to the next tetrahedral site, exceeding the potential energy barrier at 600 K. No other trapping sites can be found in this process.
The effects of operating parameters and physical properties of a dispersed phase on the volume change of a two-phase bubble formed in water as an immiscible continuous phase were experimentally investigated. The operating parameters are inner diameter of nozzle, vapor flow rate and temperature difference between water and vapor in the bubble. A larger two-phase bubble volume can be obtained by a larger nozzle inner diameter, higher flow rate, and lower temperature difference, and vice versa. The present mathematical model estimates well the two-phase bubble formation process.
In the present article, we report the flow-induced microstructure in a dilute wormlike micellar solution of cetyltrimethylammonium bromide (CTAB). The additive used here is sodium salicylate (NaSal) to enhance the supramolecular structure formation. The flow-induced microstructures in surfactant solution were reproduced by the in situ gelation of the substrate. A silicon alkoxide of tetramethylorthosilicate (TMOS) in aqueous hydrochloric acid was used as a silica precursor to capture the microstructure. The captured flow-induced structures in the wormlike micellar solution show alignment to the direction of flow under a weak flow. Meanwhile, at high shear rates, flow-induced coagulation or layer fluctuations occur. The flow-induced morphologies are dependent on the surfactant concentration, molar ratio of NaSal to CTAB, and flow intensity. SEM images taken from the direct observations through in situ gelation are consistent with the rheological responses such as shear thinning or shear thickening behavior.
The characteristics of double-diffusive convection are investigated in an initially quiescent, thermally stratified horizontal porous layer. By considering Soret effects, a new predictive model for the ionic mass transport correlation is developed in a Darcy-extended porous layer by extending the micro-turbulence model. These theoretical results are compared with the experimental results of ionic mass transfer in an electrolyte-saturated porous layer with both electrostatic fields and temperature stratification. It is observed that the present correlation of the Sherwood number represents the experimental results very well.
The influence of intracrystalline diffusivity on the selective catalytic reduction of NO with C3H8 over Co- and Cu-exchanged mordenites is examined by using mordenite samples of different crystal sizes. In the case of Co-mordenite, the intracrystalline diffusion limits the reaction and the effectiveness factor decreases with decreasing reaction temperature contrary to the usual case. In the case of Cu-mordenite, the rate of NO reduction does not depend on the crystal size of mordenite in spite of a larger reaction rate than that over Co-mordenite, which indicates that the intracrystalline diffusion in Cu-mordenite is much faster than that in Co-mordenite. These results are discussed in terms of adsorption-controlled diffusion: That is, strong adsorptive interaction of NO with Co ion, examined through TPD of NO, should be responsible for the slower diffusion rate in Co-mordenite and for the unusual temperature dependence of effectiveness factor of Co-mordenite.
CaO-C catalysts were prepared by precipitating calcium acetate with citric acid for 4 h in an aqueous solution at 80°C followed by reduction at 500-700°C. The resultant average pore radius and BET surface area of CaO-C, CaO crystallite size, and carbon content in CaO-C were about 1.5-2.5 nm, 170-200 m2/g, 11.2 nm, and 10-20%, respectively. These values suggest that the highly dispersed CaO-C catalyst forms mainly due to the residual carbon acting as a spacer. 4 wt% Ni/CaO-C reduced at 700°C was used for one step synthesis of methyl isobutyl ketone (MIBK) from acetone. 60-70% of acetone overall conversion and 70% of MIBK selectivity are obtained which are much higher than those ever reported. The diisobutyl ketone (DIBK) selectivity decreases drastically because of the remaining carbon which blocks DIBK formation sites.
A spinel-type catalyst of Cr and Co (CoCr2O4) has been prepared and tested in the oxidative decomposition of trichloroethylene (TCE). The CoCr2O4 catalyst shows a higher conversion and CO2 selectivity than the alumina-supported chromia. A rapid increase in activity of CoCr2O4 is observed with the addition of water vapor to the feed stream in contrast to the results of CrOx/γ-Al2O3 which shows a significant drop in activity when water was introduced. Water addition is also effective for the enhancement of CO2 selectivity as well in the case of CoCr2O4. The presence of water effectively suppresses the formation of tetrachloroethylene (PCE) byproduct.
Titania-pillared interlayer clays (Ti-PILCs) exhibited peculiar physicochemical characteristics as catalyst supports compared to that of titania for the reduction of NO by NH3. Korean natural bentonite (KNB) was employed as a basic component of PILC due to its high pillaring capacity. For the freeze-dried Ti-PILC, the development of needle-like crystallites revealing the formation of a “house-of-cards” structure by delamination of long-ranged layered structure of Ti-PILC has been observed. Freeze-drying creates a unique pore structure of Ti-PILC catalyst such as multi-modal pore size distribution simultaneously containing micropores and meso- or macropores in the pore network. In particular, V2O5/Ti-PILC catalyst exhibits high performance of NO removal by NH3 mainly due to the strong catalyst surface acidity and redox properties examined by NH3 TPD and TPR-TPO studies, respectively. Without the addition of the catalyst promoter, WO3 and MoO3 to the catalyst, V2O5/Ti-PILC catalyst shows competitive NO removal activity to a commercial one.
Experiments and simulations have been carried out to study the possibility of a new proposed method (MPMR) for improving the performance of a conventional porous membrane reactor system (CPMR), by which the sweep side is filled the same dehydrogenation catalyst as used in the feed side. By experiment and simulation, it is proved that MPMR can improve CPMR not only with pure feed but also with diluted feed. The reason for the improvement is because the sweep side can effectively convert reactant that permeates through the membrane. However, Vycor glass-based MPMR cannot exceed the performance of GFBR, which is a fixed bed reactor where all inert gas dilutes the reaction system. Simulation results show that partial pressures of products in the sweep side of the MPMR are much smaller than those in the feed side. Therefore permeation of reactive species from the feed side to the sweep side still occurs as observed for CPMR.
To abate NO in exhaust, a series of copper-aluminate catalysts were prepared by calcination at high temperature with high surface area support. Variables were Cu loadings and calcination temperatures. Characterization results show that a copper aluminate phase is formed with spinel type structure through high calcination temperature and copper loading. The activity and stability for NO reduction were studied in a lab. scale reactor in the presence of excess oxygen. The reducing agent was C3H6 or NH3. The catalyst, calcined at high temperature showed enhanced activity in the presence of C3H6, but copper aluminate species, formed by calcination at high temperature, have no effect on NO conversion when NH3 is used as the reducing agent. Engine dynamometer test showed that C3H6 is more effective than C2H5OH to abate nitric oxide with 10 wt.% copper loaded aluminate catalysts.
The catalytic oxidation of hydrogen sulfide in the presence of excess water and ammonia on Co3O4/SiO2 catalyst is studied with a fixed bed flow reactor. Hydrogen sulfide was successfully converted to a mixture of elemental sulfur and ammonium thiosulfate (ATS) without considerable emission of sulfur dioxide. A high concentration of hydrogen sulfide and ammonia increases the sulfur production. However, ATS increases with increasing oxygen and water vapor. From the experimental results, complex reaction paths are proposed for the production of elemental sulfur and ATS.
The reversible oxidation of barium oxide and the subsequent decomposition of barium peroxide are investigated by a volumetric measurement for the application to oxygen production. The reaction was run under isothermal and isobaric conditions at temperatures ranging between 600-950°C and oxygen pressures up to 3 atm, and the equilibrium relationship between temperature, oxygen pressure and BaO/BaO2 composition was studied. The oxygen acceptor prepared by pelletizing a mixture of barium peroxide and magnesium oxide shows a long lifetime without disintegration and loss of reactivity, and high conversions are obtained in short reaction time of several minutes in both oxidation and reduction.
LaCrO3-dispersed Cr alloy for metallic interconnector in solid oxide fuel cell has been studied as a function of LaCrO3 content in the range of 5 to 25 vol.%, and the sintering and oxidation properties of these alloys were examined. The Cr alloys were prepared from Cr and LaCrO3 powders, and were sintered at 1500°C under an Ar atmosphere with 5 vol.% H2. The LaCrO3-dispersed Cr alloys showed a relative density above 95%, and their sintering densities did not depend on LaCrO3 content. The LaCrO3 particles in the sintered alloys existed in grain boundaries of Cr particles, and the size of the Cr particles increased with decreasing LaCrO3 content. This means that LaCrO3 particles prevent grain growth of Cr particle during the sintering process. The isothermal oxidation tests of the Cr alloys were carried out for 2500 hrs at 1000°C in air. The oxidation behavior obeyed a logarithmic law probably due to ion diffusion within oxide scale. All Cr alloys show good oxidation resistance as compared with pure Cr, which is considered for LaCrO3 to increase a density of oxide scale. In particular, Cr alloys with 10 to 20 wt.% LaCrO3 are very resistant to oxidation. These results indicate that the LaCrO3-dispersed Cr alloys satisfy the sintered density and oxidation resistance requirements of interconnection material in solid oxide fuel cell.
In aqueous solutions containing basic catalysts, a wet gel was synthesized through the sol-gel process of resorcinol (R) and formaldehyde (F). The formation of RF gel is dependent on the ratio of R and catalyst (C), density of solid fraction, and temperature. The gelation proceeded quickly with low R/C ratio, high density, and high temperature. The RF organic aerogel was obtained from the wet gel by low-temperature supercritical solvent drying with carbon dioxide. The RF aerogel product shows extremely low thermal conductivity and highly specific surface area due to its ultra-porous structure. The thermal conductivity is closely related to the pore size distribution of the aerogel. The aerogel in the solid fraction ranges of near 3% (0.06 g/cm3) and the R/C ratio of 300 retains the lowest thermal conductivity.
The graft copolymerization of styrene and acrylonitrile onto natural rubber was prepared by emulsion polymerization using potassium persulfate as an initiator. The effects of initiator concentration, reaction temperature, and pressure on monomer conversion and the grafting properties of natural rubber are investigated. A high grafting yield is obtained at a temperature of 70°C, pressure of 3.1 bar, reaction time of 8 hours, and initiator concentration of 1.5 parts by weight. The copolymer composition was determined by elemental analysis. Grafted natural rubber and styrene-acrylonitrile copolymer (SAN) blends were prepared. The effect of blend composition on tensile strength, impact strength and hardness is investigated. The grafted natural rubber improves the impact toughness of SAN copolymer.
Simultaneous removal and recovery of cyanide and copper ions using a strong-base anion exchange resin are studied on the basis of formation of Cu-CN complexes at high pH in electroplating wastewater containing cyanide and copper ions. Strong-base anion exchange resin particles, of Dowex1X8-50, were contacted with synthetic aqueous solutions. For different molar ratios between cyanide and copper, ion exchange characteristics of copper-cyanide complexes were studied experimentally in a batch reactor. Treatment efficiencies of packed and fluidized beds were compared under the various conditions. Several regenerants, NaSCN, NaCN, NaOH, NaCl, and EDTA, were used to regenerate the exhausted resin. The rates of regeneration and recovery for the various regenerants were estimated and discussed. Free cyanide ion has a lower selectivity than Cu-CN complexes on the anion exchange resin. This could be explained by the size, ion pairing, and site competition of complexes. In turn, Dowex1X8-50 can exchange about three times of the equivalent capacity for cyanide as complex form under the experimental conditions of this study in a batch reactor. The degree of treatment efficiency suggested in this study is; fluidized bed > semi-fluidized bed > packed bed. NaSCN was the best regenerant among regenerants used for the regeneration of resin saturated with Cu-CN complexes.
A rigorous design procedure for a fully thermally coupled distillation column is proposed and applied to an example system of butanol isomer ternary mixture. The design procedure is composed of the calculation of limiting requirements and a rigorous simulation using material and energy balances. The result of the proposed design is compared with the design of a conventional two-column system. It is found that the fully thermally coupled distillation requires less investment and energy cost than conventional distillation, even if higher reboiler temperature is required. It is also pointed out that the dividing wall structure gives less efficient performance than the Petlyuk column having a smaller number of trays of a prefractionator than that of the mid-section of a main column.
The gas-perturbed liquid model of Zhang et al. (1995) is modified in an effort to improve its prediction of the minimum liquid velocity of fluidization, Ulmf, of a bed of solid particles in the presence of a low or moderate cocurrent flow of gas. Variants of the model are considered where the buoyancy term is based on the gas-liquid mixture, instead of the liquid alone, and with the frictional pressure gradient given by several alternative equations to the Ergun equation employed in the original gas-perturbed liquid model. All versions of the model provide similar dependence on such factors as gas velocity, particle diameter, particle density and liquid viscosity as those seen experimentally. The mixture buoyed equation with the drag based on an equation suggested by Foscolo et al. (1983) gives improved predictions over the original Zhang et al. (1995) model, but the best overall agreement is with buoyancy based on the liquid alone and the first term in the drag equation with the Carman (1937) constant of 180 instead of Ergun's 150. The predictions are sensitive to the minimum fluidization voidage, which is measured, assumed, or estimated. Further work is required to investigate minimum liquid fluidization velocities experimentally for particles of density closer to that of the liquid, and for high-viscosity liquids.
In this study, an artificial neural network (ANN) was trained to model dynamic behavior of pressure fluctuations measured in a circulating fluidized bed with a riser having an inner diameter of 0.10 m and a height of 10 m. The ability of the neural network model to approximate the dynamic behavior is examined by comparing time-averaged characteristics, power spectra, and chaotic features of time series measured and generated by the ANN. It is found that dynamic behavior of the original time series is captured well by the ANN, and that the ability of the ANN for generation improves with the number of iterations.
Fluidization of ultrafine particles with primary diameter of 7 nm is experimentally studied in a centrifugal fluidized bed (CenFB). Ultrafine particles can be fluidized without significant agglomeration of particles under high G. No bubble formation was observed in the CenFB of ultrafine particles. The entrainment of particles is suppressed by controlling G. The experimental data of pressure drop in the CenFB of ultrafine particles is larger than the estimated value. This is due to the energy dissipation required to overcome large adhesion force between ultrafine particles.
The recently developed technique of wavelet transform based on the localized wavelet functions has been applied for the analysis of nonlinear and nonstationary pressure fluctuation signals in a bubble column, because they are very complex and highly irregular as a consequence of the continual interactions among the bubble and liquid phases. The time series of pressure fluctuation signals have been expressed by means of discrete wavelet transform coefficients, multiresolution decomposition and scalogram. By this wavelet transform technique, the fluctuating pressure signals in a bubble column can be decomposed into its approximations and details at different resolutions. The energy of the details provides a measure of irregularity of the signal at various resolutions. Thus, this wavelet transform method enables us to obtain the frequency content of local complex flow behaviors in a bubble column, which are directly connected with the transport phenomena in it.
Incineration experiments are carried out to investigate the agglomeration characteristics of bed materials during fluidized bed incineration of dye sludge in a lab-scale system. With several criteria, the agglomeration potential is assessed during a 26 hr-operation. Silica sand and alumina sand are used as a bed material in the experiment. Above a temperature of 800°C, the fluidized bed of silica sand shows agglomeration behavior instantaneously resulting in serious channeling and defluidization during fluidized bed incineration of dye sludge. In the case of an alumina bed material, steady-combustion can be achieved during a 26 hr-operation.
Heat transfer characteristics in a liquid drop column (0.102 m ID×1.8 m in height) have been investigated by analyzing the temperature difference fluctuations between the immersed heater and the column proper. The temperature difference fluctuations are analyzed by resorting to chaos analysis; the fluctuations have been interpreted by means of phase space portraits as well as the Kolmogorov entropy. The effects of dispersed (kerosene) and continuous (water) liquid phase velocities on the temperature difference fluctuations and heat transfer coefficients are determined. To explain the influence of immiscible liquid flow on the heat transfer coefficient, hydrodynamics and phase holdup have also been discussed. It is found that the increase in the velocities of dispersed and continuous liquid phases results in the increase of turbulence in the column, which makes the system more complicated and irregular. The injection of gas (air) or particles (6.0 mm glass bead) into the column can increase the heat transfer coefficient considerably. However, the flow behavior of the immiscible mixture is more irregular and chaotic owing to the injection of gas, whereas the system has been more uniform and periodic by adding the solid particles into the column. The heat transfer coefficient has been correlated well in terms of operating variables.
Characteristics of gas-liquid-solid flow behavior in a riser are investigated in a three-phase circulating fluidized bed (0.102 m I.D.×3.5 m in height). Local gas holdup, solid holdup distribution, and pressure fluctuations in the riser have been measured and utilized to describe the gas-liquid-solid flow behavior more conveniently. The resultant pressure fluctuations have been analyzed by adopting the chaos method: The time series of pressure fluctuations have been interpreted by means of phase space portraits and Kolmogorov entropy. The effects of gas and liquid velocities and solid circulation rate on the local gas holdup, solid axial distribution, phase space portrait, and Kolmogorov entropy of pressure fluctuations, as well as on the flow behavior of gas-liqid-solid mixture in the riser are determined. It is found that pressure fluctuations can be a quantitative tool to characterize the flow behavior and flow regime transition of multiphases in the riser. The relations between the pressure fluctuations and the distribution of phase holdup and flow regime in the riser are also discussed.
Pressures in a circulation loop under various conditions were measured in a cold mode (a riser of 35 mm I.D.×5450 mm high and a fluidized reactor of 160 mm I.D.×1250 mm high) with particles of mean diameter of 78 μm, and bulk, and particle densities of 1.03, and 1.90 g/cm3, respectively. Solid circulation rates were measured with a load cell hopper. The particle hold-ups at various sections were analyzed from differential pressure data. The voidage in the riser reactor increases with the increase in gas velocity, even though the solid circulation rate increases with gas velocity. The solid circulation rate increases to a maximum with gas velocity at the riser, and levels off because the non-mechanical valve adopts the role of solid rate determing step in the circulation loop of the system. Particle hold-up in the riser reaction zone increases by using an underflow standpipe loopseal below the fluidized reactor instead of an overflow standpipe loopseal.
Ultra-fine titanium dioxide powders were synthesized by a thermal plasma processing. The phase compositions of powders are strongly influenced by reacting and collecting positions and the injecting method of TiCl4. Using a micro pump for injecting TiCl4, rutile contents in the powders collected for A-type reactor increases up to 95%. The powders collected at the other positions are found to be anatase of above 80%, and most of the powders are spherical. The average sizes of powders are found to be below 100 nm at lower flow rate of TiCl4 than 1.0 g/min, but they rapidly increase at flow rates of TiCl4 higher than 1.5 g/min. Using Ar-carrier gas for injecting TiCl4, the rutile content in powders increase to 60% with the flow rate of Ar-carrier gas. The average sizes of these powders are 30 nm, regardless of flow rate of Ar-carrier gas and collecting positions. The anatase-to-rutile transformation of produced powder starts at approx. 600°C and finishes at below 1000°C.
There are two types of uncertainty in mathematical representation of process models, namely model structure uncertainty and parameter uncertainty. Uncertainty in parameters was considered in most previous approaches for dynamic data reconciliation. In the present study, an efficient strategy is proposed to solve dynamic data reconciliation containing nonlinear variables and model structure uncertainty. A penalty function is introduced to address the model structure uncertainty. The problem is formulated to include the uncertainty of model structure and solved by simultaneous method. Dynamic data reconciliation was performed using nonlinear programming (NLP) with a multistep ordinary differential equation (ODE) solver. The ability of the proposed strategy is compared with that of other solution strategies: the extended Kalman filter (EKF) and a simultaneous method using high order one-step method. It is found that the proposed method shows good performance in the nonlinear region since it accelerates the computational speed without sacrificing the error reduction ability compared to one-step method. Computational load of this approach decreases to a third of the one-step method.
Refolding of reduced and denatured protein in vitro has been an important issue for both basic research and applied biotechnology. Refolding at low protein concentration requires large volumes of refolding buffer. Diafiltration method is useful to control the denaturant and red/ox reagents in the refolding solution. We constructed a refolding procedure for high concentrations of reduced and denatured lysozyme of about 10 mg/ml (700 μM) on linear reduction of urea concentration in diafiltration, 0.8 mM cystine and 8 mM cysteine under nitrogen at 2 atm. This method can obtain about 90% refolding yield at 700 μM and almost 100% in 350 μM lysozyme. The refolding yields during the diafiltration can be simulated using the competitive reaction between the refolding and aggregation. In the red/ox control with cysteine and cystine, a rate order of aggregation reaction of near 2 is obtained.
The potential of foam fractionation for intra-process recycling of surface active materials is investigated. Batch foam fractionation of poly(vinyl alcohol) (PVA) was carried out with and without external foamate reflux. The effect of PVA concentration on foam fractionation without reflux was firstly investigated. The foam fractionation of PVA without reflux is possible only at initial PVA concentrations below 200 mg/l. At initial PVA concentrations above 300 mg/l, foam fractionation is impossible because almost all the water and PVA are discharged as foamate, of which PVA mean concentration is almost equal to that of the initial solution. Effects of external foamate reflux and temperature on foam fractionation of PVA were then investigated at initial PVA concentration of 1000 mg/l. With rising temperature, the enrichment and separation factor increases, while the removal factor is almost constant. The enrichment and separation factors at 363 K are about 11 and 90, respectively. External foamate reflux is essential for foam fractionation when treating a highly foaming solution.
Hydrocarbon oils with molecular weight below 300 were obtained from automotive tire by supercritical decomposition with toluene and cyclohexane. Experiments were carried out at various temperatures (523.15, 573.15, and 623.15 K) and pressures (5, 10, and 15 MPa) for 25 g sample tires. For each solvent, the sample tire was completely decomposed within an hour at 623.15 K and 10 MPa. By measurement of the weight of residual solids and TGA analysis after each decomposition reaction, the percent decomposition and the decomposition characteristics were evaluated with respect to temperature and pressure. Also, by GC-MS analysis of decomposed oil, the major components of oil and their molecular weight were confirmed. Based on the results, the advantage and shortcomings of using each solvent are discussed.
Simultaneous removal of SO2 and NOx from simulated gas was investigated using a continuously operating fluidized bed reactor with variables of gas velocity, sorbent/catalyst feeding rate, aspect ratio (L/D), temperature, sorbent/catalyst size. NMO (natural manganese ore) was used as a sorbent and catalyst of size from 0.715 mm to 0.194 mm in diameter. Particle size, aspect ratio, and sorbent feeding rate did not affect the reduction of NOx with ammonia, and NOx removal efficiency was about 94% at 350°C, gas velocity of 0.204 m/sec, L/D=1.0. SOx removal efficiency was affected by temperature, gas velocity, sorbent/catalyst feeding rate, aspect ratio and sorbent/catalyst size and it was about 92% at 450°C, gas velocity of 0.204 m/sec, sorbent/catalyst feeding rate of 8.54 g/min, L/D=1.0.
The SiO2 concentrate after extracted of aluminum from clay from Sancheong-Hadong, Korea, was leached with NaOH at 25-100°C under atmospheric pressure. About 80% of the silicon in the concentrate was extracted at 25°C within 30 minutes. The molar SiO2/Na2O of the sodium silicate solution thus obtained ranged from 2.5 to 3.1. The silicate solution contains 0.11 wt.% of alminum and 67 ppm of iron as impurity. Out of 150 g of the concentrate charged, about 100 g was dissolved and the balance was undissolved. The filterability of the resulting slurray was studied in a pressure filter with varying pressures and temperatures. By analysis of the undissolved solid, the formation of insoluble sodium compounds during NaOH leaching is found to be negligible.
This study presents a viable method for the scouring and dyeing of polyester fibers (polyethylene terephthalate, PET) by using supercritical carbon dioxide as a mdeium. Scouring of the PET fibers was carried out at pressures ranging from 96 to 350 bar and at temperatures ranging from 313 to 393 K. The overall oil removal efficiency reached +99%. The sorption behaviors of the fibers with three single and a mixture of disperse dyes (C.I. Disperse Blue 79, Yellow 119, and Red 153) in dense CO2 were investigated at 290 bar and 393 K. The solubilities of three single dyestuffs in dense CO2 were in the weight fraction range of 10-7 to 10-4. The uptake amount of the dye at saturation fell in the range of 6.5 to 12.5 mg dye/g fiber under the dyeing conditions. The rate of dye sorption is correlated with dye solubility, and decreases in the order of Blue 79, Yellow 119, and Red 153, respectively. This dyeing approach offers superior fastness properties, which are enhanced by increasing dyeing pressure and temperature.
In this work, various silica suspensions were synthesized by a single step Stober method and by a two-step growth method using either fumed silica or colloidal silica as a seed. The synthesis proceeded through a controlled hydrolysis and condensation reactions of tetraethylorthosilicate (TEOS). After the reactions were completed, the solvent ethanol of the silica suspension was substituted by water through vacuum evaporation and ultra-centrifugation in order to obtain the aqueous silica suspension. Then, the silica suspension was stabilized by adjusting electrostatic repulsion, and by generating steric repulsion from the adsorbed polyvinyl alcohol (PVA). To elucidate the steric stabilization of colloidal silica by the polymeric surfactant of PVA, the adsorption isotherms of PVA in the aqueous silica suspension are determined. Moreover, the rheological behavior of the silica suspensions stabilized by PVA is investigated to characterize the dispersion stability of the colloidal silica suspensions. The results show that the phase stability of silica suspensions of relatively smaller particles is mainly induced by the electrostatic repulsion compared with steric stabilization contrbuted from the adsorbed layer of PVA. Meanwhile, for larger particle suspensions, the phase stability is governed predominantly by steric stabilization of the adsorbed PVA.