Ceric Ion Concentration Research Articles

Feedback control strategies for a cerium‐catalyzed Belousov–Zhabotinsky chemical reaction system

A number of control schemes including nonlinear feedback, dislocated feedback, and speed feedback have been proposed and assessed for a bromate‐malonic acid‐cerium Belousov–Zhabotinsky batch reaction process. The tuning parameters of the Oregonator model were firstly adjusted based on a UV‐vis spectrophotometric analysis in the experimental part of the research. The adjusted Oregonator model successfully reproduced the innate induction time and periodicity of the BZ‐batch system. Subsequently, the controllers were implemented and numerical simulations were carried out by employing the multi‐stage Adomian decomposition method. The nominal analysis method was used to study the linear stability of each design. All the controlled systems were found to be linearly stable for certain continuous regions of controller gain. The performance of the proposed control laws was assessed and the dislocated feedback control strategy was shown to be able to drive the system states toward desired setpoints quickly. Furthermore, the validity of the dislocated feedback control design was doubly ensured by the sliding mode control theory. It was found that those feedback schemes which manipulate cerium ion concentration can be practically realized by means of electrochemical oxidation or oxygen aeration. Our results were confirmed by the Simulink software package and the block diagram representations are included in the paper.

Adsorption of Phosphorus by Ce-Modified Lithium Silica Fume

This is a study about using cerium ions solution to modify lithium silica fume and the phosphorus adsorption by the modified material. The way to modify lithium silica fume and adsorption conditions has been researched. It was found that capacity of adsorption have been improved after modification by the cerium nitrate. In the adsorption test, we studied the effects of the concentration of cerium ions, the calcination temperature, the dosage, initial pH value, reaction temperature and other factors on the adsorption. The results indicated that after modifications by 3% cerium ions , calcinations at 573k, the adsorption of phosphorus can get more than 90% when modified lithium silica fume dosage is 9.6g.l-1 and the concentration of phosphorus solution is 4 mg.l-1. In addition, the Freundlich adsorption isotherm is fit for the description of the phosphorus adsorption. The phosphorus adsorption process was in accord with pseudo-second-order kinetic model.

Synthesis and thermal characterization of xylan-graft-polyacrylonitrile

In this study emulsion polymerization of acrylonitrile using xylan from agricultural waste material (corn cob) and cerium ammonium nitrate was investigated in terms of catalyst acid. Stock ceric solutions were prepared using either nitric or perchloric acid as catalyst. Optimum conditions were determined using different parameters such as reaction time, temperature, and component concentrations. Nitric acid catalyzed reactions resulted in maximum conversion ratio (96%) at 50°C, 1h where ceric ion, acrylonitrile, xylan, and catalyst concentrations were 21.7mmoll−1, 0.5moll−1, 0.2% (w/v), and 0.1moll−1, respectively. However, 83% conversion was obtained with perchloric acid catalysis at 27°C, 1h where concentrations were 5.4mmoll−1, 0.8moll−1, 0.5% (w/v), and 0.2moll−1, respectively. Copolymer synthesis using perchloric acid was realized at milder conditions than using nitric acid. Thermal analyses of obtained polymers were conducted to characterize copolymers. Results showed that calculated activation energy, maximum degradation temperature, and heat of thermal decomposition changed relying mainly on molecular weight.

Synthesis and properties of high corrosion resistant Ni–cerium oxide nano‐composite coating

AbstractThe effect of cerium ion on the formation, morphology, composition, and corrosion behavior of Ni–cerium oxide coatings was investigated by SEM, FESEM, XRD, EDS, XPS, EIS, and potentiodynamic polarization. The extremely highest corrosion resistant coating was obtained when the cerium ion concentration in the plating bath was 16 mM. It has been observed that the presence of cerium ion in the plating bath led to changes in the morphology of the coating from pyramid nodular structure to coaxial structure. By adding cerium ion to the plating bath, a considerable grain refinement in the nanometer region was observed.

Stepwise synthesis of fine crystalline Ce-doped yttrium aluminum garnet in water medium in subcritical and supercritical conditions

was carried out in water medium in two stages: first in subcritical conditions and then in an atmosphere of supercritical water fluid. The stoichiometric mixture of yttrium oxide and aluminum hydroxide in a water solution of cerium nitrate was maintained the certain time at 280°C and under vapor water pressure 6.3 MPa. Then temperature and pressure were risen up to a supercritical condition (T = 392–400°C, = 22 MPa). The concentration of cerium ions in reaction medium was changed in the interval 0.012–0.706 wt %. The

Corrosion behavior study of AZ91 magnesium alloy coated with methyltriethoxysilane doped with cerium ions

The present work aims to investigate the corrosion behavior of AZ91 magnesium alloy treated with a 4% (v/v) methyltriethoxysilane (MTES) alcohol solution, with and without an alkaline pretreatment. The corrosion resistance was assessed by electrochemical impedance spectroscopy (EIS) and current densities were monitored by potentiodynamic polarization curves during immersion in a 0.1M Na2SO4 solution. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to perform a surface analysis. The electrochemical results showed an improvement of anticorrosion properties of AZ91. Furthermore, alkaline pretreatment enhances adhesion between silane film and substrate surface. This can be attributed to a surface enrichment in hydroxyl groups after the alkaline step, which increases formation of Si–O–Mg covalent bonds. The addition of Ce(NO3)3 to the MTES bath was evaluated, and it was found that the electrochemical response depends on the cerium ions concentration used. It was shown that the addition of 6.0×10−5M of Ce(NO3)3 to a MTES bath improves corrosion resistance. Higher concentration of cerium ions lead to destabilizing the siloxane network, decreasing the efficiency of the silane coatings.

Optimisation of Graft Copolymerisation of Fibres from Banana Trunk

Sheets from banana trunks were opened out and dried for several weeks in air. Pulp was obtained by the nitric acid process with a yield of 37.7% while fibres were obtained according to the modified standard Japanese method for cellulose in wood for pulp (JIS 8007) with a yield of 65% with respect to oven dried plant material. Single fibre obtained by the JIS method had an average diameter of 11.0 μm and Young′s modulus, tensile strength and strain at break‐off 7.05 GPa, 81.7 MPa and 5.2% respectively. Modification of the fibres was carried out by grafting ethyl acrylate in the presence of ammonium nitrate cerium(IV). Optimisation of the copolymerisation reaction conditions was studied by measuring the rate of conversion, the rate of grafting and the grafting efficiency. The results showed that at low values of ceric ion concentration (0.04 M), at ambient temperature, after three hours and at a concentration of 0.2 M ethyl acrylate, maximum values of the parameters cited were obtained.

Graft Copolymerization of Acrylonitrile and Ethyl Methacrylate on Dextrin

Graft copolymers of Acrylonitrile and ethyl methcrylate on dextrin were prepared by the use of ceric ion initiator in aqueous medium at 290C. The molecular weight of grafted poly(ethyl methacrylate) chains were higher than for polyacrylonitrile grafts; but the latter were more frequently grafted on the backbone polymer. The dependence of the molecular weight of the grafted chains on ceric ion concentration suggests that interaction of growing graft polymer chains with ceric ion is important in the termination process of graft copolymerisation. Graft copolymeriation of ethyl methacrylate onto dextrin in the presence of various amounts of acrylonitrile was studied. The compositions of the copolymer samples, calculated from their nitrogen content, showed that in the presence of ethyl acrylate, relatively small amounts of acrylonitrile monomer was grafted onto dextrin. Nigerian Journal of Chemical Research Vol. 11 2006: pp. 22-27

Synthesis and characterization of butyl acrylate graft sodium salt of partially carboxymethylated starch

AbstractGraft copolymers were synthesized by graft copolymerization of butyl acrylate (BA) onto sodium salt of partially carboxymethylated starch (Na‐PCMS). Ceric ammonium nitrate (CAN), a redox initiator, was used for initiation of graft copolymerization reaction. All the experiments were run with Na‐PCMS having degree of substitution, DS = 0.35. The grafting reaction was characterized by parameters such as % total conversion (%Ct), % grafting (%G), % grafting efficiency (%GE), and % add‐on. Graft copolymers were characterized by infrared spectral analysis and scanning electron microscopy. Variables affecting graft copolymerization reaction such as nitric acid concentration, reaction time, reaction temperature, and ceric ion concentration were investigated. The results revealed that 0.3M CAN as initiator, 0.3M HNO3, with reaction time 4–4.5 h at 25–30°C were found as suitable parameters for maximum yield of graft copolymerization reaction. © 2006 Wiley Periodicals, Inc. JAppl Polym Sci 102: 3334–3340, 2006

Graft copolymerization of acrylamide onto cellulose in presence of comonomer using ceric ammonium nitrate as initiator

AbstractThe graft copolymerization of acrylamide (AAm) and ethylmethacrylate (EMA) monomers onto cellulose has been carried out using ceric ammonium nitrate (CAN) as initiator in presence of nitric acid at (25 ± 1)°C and varying feed molarity from 7.5 × 10−2 mol dm−3 to 60.0 × 10−2 mol dm−3 at fixed feed composition (fAAm = 0.6). The graft yield (%GY) has shown a linear increasing trend upto a feed molarity of 37.5 × 10−2 mol dm−3. The composition of grafted copolymer chains was found to be constant (FAAm = 0.56) during feed molarity variation but shown variations with feed composition (fAAm) and reaction temperature. The grafting parameters have shown increasing trends up to 7.5 × 10−3 mol dm−3 concentration of ceric (IV) ions and decreased on further increasing the concentration of ceric (IV) ions beyond 7.5 × 10−3 mol dm−3. The IR and elemental analysis data were used to determine the composition of grafted chains (FAAm) and reactivity ratio of acrylamide (r1) and ethylmethacrylate (r2) comonomers. The reactivity ratio for acrylamide (r1) and ethylmethacrylate (r2) has been found to be 0.7 and 1.0 respectively, which suggested for an alternate arrangement of average sequence length of acrylamide (mM̄1) and ethylmethacrylate (mM̄2) in grafted chains. The rate of graft copolymerization of comonomers onto cellulose was found to be proportional to square concentration of comonomers and square root to the concentration of ceric (IV) ions. The energy of activation (ΔEa) of graft copolymerization was found to be 9.57 kJ mol−1 within the temperature range of 20–50°C. On the basis of experimental findings, suitable reaction steps have been proposed for graft copolymerization of selected comonomers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2546–2558, 2006

Graft copolymerization of methacrylonitrile on caesarweed fibers by ceric ion/isopropanol redox pair

AbstractThe graft copolymerization of methacrylonitrile to caesarweed fiber and its sodium derivative by ceric ions in the presence of isopropanol was investigated in aqueous media. The percentage graft yield decreased initially and then increased with the concentration of isopropanol, but the graft levels of sodium caesarweed fibers were much lower. The graft reaction in the presence of isopropanol was characterized by the high frequency of grafting, up to 2.81 × 102 Ng/104 anhydroglucose units, and the low molecular weight of the grafted polymer, not higher than 0.94 × 103. The molecular weight of the grafted polymer showed a negative dependence on the concentration of isopropanol, suggesting the involvement of the latter in the transfer reactions with growing grafted polymer chains, which permitted calculation of the transfer constant, kA/kp, for the process: 7.91 × 10−2. The graft yield percent was found to be negatively dependent on the concentration of ceric ions for grafting of methacrylonitrile on sodium caesarweed fibers, but the molecular weight of the grafted polymer showed no clear‐cut trend with ceric ion concentration. The graft yield percent increased with temperature in the range of 30°C–50°C and decreased markedly at 70°C. The calculated activation energy of the graft reaction was 10.5 kcal/mol. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 353–358, 2006

Ceric(IV) ion‐induced graft copolymerization of acrylamide and ethyl acrylate onto cellulose

AbstractGraft copolymerization of acrylamide (AAm) and ethyl acrylate (EA) onto cellulose has been carried out from their binary mixtures using ceric ammonium nitrate (CAN) as an initiator in the presence of nitric acid at 25 ± 1 °C. The extent of acrylamide grafting increased in the presence of the EA comonomer. The composition of the grafted chains (FAAm = 0.52) was found to be constant during the feed molarity variation from 7.5 × 10−2 to 60.0 × 10−2 mol L−1, whereas the composition of the grafted chains (FAAm) was found to be dependent on feed composition (fAAm) and reaction temperature. The effects of ceric(IV) ion concentration, reaction time and temperature on the grafting parameters have been studied. The grafting parameters showed an increasing trend up to 6.0 × 10−3 mol L−1 concentration of CAN at a feed molarity of 30.0 × 10−2 mol L−1 and showed a decreasing trend on further increasing the concentration of CAN (>6.0 × 10−3 mol L−1) at a constant concentration of nitric acid (5.0 × 10−2 mol L−1). The composition of the grafted chains (FAAm) was determined by IR spectroscopy and nitrogen content and the data obtained then used to determine the reactivity ratios of the acrylamide (r1) and ethyl acrylate (r2) comonomers by using a Mayo and Lewis plot. The reactivity ratios of acrylamide and ethyl acrylate were found to be r1 = 0.54 and r2 = 1.10, respectively, and hence the sequence lengths of acrylamide (m̄M1) and ethyl acrylate (m̄M2) in the grafted chains are arranged in an alternating form, as the product of the reactivity ratios of acrylamide and ethyl acrylate (r1 × r2) is less than unity. The rate of graft copolymerization of the comonomers onto cellulose was found to be dependant on the ‘squares’ of the concentrations of the comonomers and on the ‘square root’ of the concentration of ceric ammonium nitrate. The energy of activation (ΔEa) of graft copolymerzation was found to be 5.57 kJ mol−1 within the temperature range from 15 to 50 °C. On the basis of the results, suitable reaction steps have been proposed for the graft copolymerzation of acrylamide and ethyl acrylate comonomers from their mixtures. Copyright © 2005 Society of Chemical Industry

Aqueous polymerization of ethyl acrylate initiated by ceric ion-reducing agent system in sulphuric acid medium

Kinetic study of aqueous polymerization of ethyl acrylate (EA) is carried out at 30 °C in dilute sulphuric acid medium by employing ammonium ceric sulphate–methyl ethyl ketone (MEK) as redox initiator system. The ceric ion consumption is found to be first order with respect to ceric ion and half order with respect to reducing agent concentrations. No complex formation between ceric ion and reducing agent is observed. The orders with respect to ceric ion, reducing agent and monomer concentrations are evaluated for the aqueous polymerization of EA by Ce(IV)–MEK redox initiator system, and are found to be 0.5, 0.5 and 1.4, respectively . The overall activation energy, E overall, for aqueous polymerization of EA in the temperature region of 27–40°C is found to be 20.27 kJ/mol. A kinetic scheme for the aqueous polymerization of EA initiated by Ce(IV)–MEK redox initiator system is presented.

Synthesis and characterization of guar gum‐graft‐polyacrylonitrile

AbstractCerium(IV) mediated grafting of polyacrylonitrile on to guar gum was studied. Grafting parameters were studied gravimetrically, as a function of temperature, initiator concentration and Guar to acrylonitrile ratio. Higher temperatures resulted in higher monomer conversion and homopolymer formation. Both monomer conversion and extent of grafting increased with increase in cerium ion concentration in the range studied (0.91–9.12 mmol/l). Similar results were obtained with increase in monomer to guar gum ratio from 1 to 5. Grafting with this initiator was found to be generally good with high grafting efficiencies and low homopolymer formation for most experiments. The copolymers obtained were subjected to alkaline hydrolysis to convert nitrile groups in to carboxylic acid groups and the water absorbency of the resulting anionic guar gum was studied. Materials with water absorption up to 300 g/g could be obtained from this study. Copyright © 2003 John Wiley & Sons, Ltd.

Surface modification of nanocolloidal silica for use as polishing abrasive particles

A new type of abrasive particle for polishing the dielectric layer on silicon wafers has been synthesized by modifying colloidal silica with cerium ions. Cerium ions in active silicic acid were titrated into a basic solution at 100 °C to modify the surface of the colloidal silica. The new abrasive particles are easily suspended in an aqueous medium. The removal rate of the dielectric film was higher when the modified colloidal silica was used for polishing than when the original colloidal silica was used as a polishing slurry. The effects of cerium-ion concentration [Ce 4+] and seed concentration on the mean particle size of modified colloidal silica and the polishing performance of colloidal silica were investigated in the present study.

Optimization of reaction parameters to prepare HPMA- g -Na-PCMS using can as an initiator

Sodium salts of partially carboxymethylated starch-g-poly(hydroxypropyl methacrylate)(Na-PCMS-g-PHPMA) copolymer containing 35-45% PHPMA were prepared using ceric ammonium nitrate (CAN) as an initiator. All the experiments were run with Na-PCMS (DS-1.10). Graft copolymers were characterized with respect to % PHPMA, % total conversion, % grafting, % grafting efficiency and confirmation of grafting was done by infrared spectral analysis. Variables investigated in the graft copolymerization reaction were nitric acid concentration, reaction time, reaction temperature and ceric ion concentration. The results are discussed with illustration.

Graft copolymerization of acrylic acid on methylcellulose by ceric ion/p‐xylene redox pair

AbstractThe graft copolymerization of acrylic acid onto methylcellulose by ceric ion/p‐xylene redox pair was investigated in aqueous media under homogeneous conditions. The graft yield dependency on p‐xylene concentration in the range 1.8–45.0 × 10−5M showed a minimum and an enhanced yield when the methylcellulose interacted with ceric ion and p‐xylene for an initial period of 10 min (preoxidation time) prior to addition of monomer to the reaction medium. This was attributed to the presence of two kinetically controlled reactions initiated by p‐xylyl radical and diradical species. At prolonged preoxidation times of 30 and 60 min, the graft yield dependency on p‐xylene concentration was normal and suggested the presence of only one initiating species. The effect of ceric ion on the graft reaction in the concentration range of 8.33–83.3 × 10−3M was optimal at 131% graft yield for ceric ion concentration of 16.7 × 10−3M and was reduced significantly by as much as 75% at the highest concentration of the latter. The temperature dependency of graft yield was negative in the region 30–50°C. At 50°C the initial rate of graft was only 37% of the value at 30°C. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 500–504, 2002; DOI 10.1002/app.10200

Optimization of Reaction Parameter to Prepare 2-HEMA-g-NaPCMS Using CAN as an Initiator

Sodium Salt of partially carboxymethylated starch -g-poly(hydroxyethyl methacrylate) (Na-PCMS-g-PHEMA) copolymers containing 40-50% PHEMA were prepared with ceric ammonium nitrate initiation. All the experiments were run with Na-PCMS(DS=1.10). Graft copolymers were characterized with respect to % PHEMA, % total conversion, % grafting, %grafting efficiency and confirmation of grafting was done by Infrared Spectral Analysis. Variables investigated in the graft copolymerization reaction were nitric acid concentration, reaction time, reaction temperature, and ceric ion concentration. The results are discussed with illustrations.

Aqueous polymerization of ethyl acrylate initiated by ceric ion‐reducing agent systems in nitric acid medium

AbstractKinetic study of aqueous polymerization of ethyl acrylate (EA) was carried out at 30 °C in dilute nitric acid medium by employing ammonium ceric nitrate (ACN)–methyl cellosolve (MC) and ACN–ethyl cellosolve (EC) as redox initiator systems. The ceric ion consumption was found to be first order with respect to ceric ion concentration with both initiator systems. The formation of complexes between Ce(IV) and reducing agents (RA) was observed. The order with respect to Ce(IV), reducing agents and monomer was evaluated for aqueous polymerization of EA by Ce(IV)–MC and Ce(IV)–EC redox initiator systems. The overall activation energy, Eoverall, for aqueous polymerization of EA was evaluated in the temperature region of 27–40 °C with both initiator systems. A kinetic mechanism for aqueous polymerization of EA initiated by redox initiator systems is presented.© 2001 Society of Chemical Industry

Graft copolymerization of acrylonitrile and ethyl methacrylate comonomers on cellulose using ceric ions.

The graft copolymerization of acrylonitrile and ethyl methacrylate from their binary mixtures onto cellulose has been carried out in the presence of Ce(IV) ions in acidic media at 30 +/- 0.1 degrees C. The graft copolymerization has shown an increasing trend on increasing the feed molarity of the comonomers and on increasing the reaction time. The analysis of grafted cellulose prepared with different feed compositions (f(AN)) has clearly indicated the existence of the synergistic effect of ethyl methacrylate on acrylonitrile which normally shows poor affinity for grafting on cellulose while used individually. The elemental analysis and IR data were used to determine the composition of grafted copolymers and reactivity ratios (r(1), r(2)) of the monomers using the Mayo and Lewis method. The reactivity ratios for acrylontrile and ethyl methacrylate have been found to be 0.68 and 1.15, respectively, which supported the alternate arrangement of the monomer blocks of individual monomers in the grafted chains. The rate of grafting has shown a square dependence on the concentration of the comonomers within the studied range of feed molarity from 0.5 to 2.5 mol dm(-3). The grafting data were used to calculate the number of grafted chains (N(g)), frequency of grafting (G(F)) per molecule of the cellulose and efficiency of grafting (G(E)). The variation in these parameters as a function of feed molarity, feed composition, and ceric ion concentration has been determined. The rate of ceric ion disappearance as a function of feed molarity and reaction time has provided strong support to consider the participation of ceric ions in the formation of free radicals at the backbone of the cellulose. On the basis of the experimental observations, reaction steps for grafting of monomers on cellulose have been proposed.