Porous mullite ceramics through diphasic gels of large boehmite and small silica particles

Mullite formation process has been studied in stoichiometric mullite (3Al₂O₃·2SiO₂) diphasic gel containing large boehmite (1 m) and small silica (10 nm) particles. It has been found that initial mullitization did not take place inside the silica phase (cristobalite), but took place in the defect -alumina phase. -alumina was stabilized by silica when the temperature was below 1350°C. At temperatures above 1350°C, mullite crystallized directly. It was suggested that silica diffused into the pores (<1.8 nm) of -alumina and prevented the collapse of -alumina pore structure. On the other hand, when silica was not present, the pore structure of -alumina collapsed and -alumina crystallized at 1100°C. Porous mullite ceramics were obtained by using special diphasic gels containing large boehmite and small silica particles.     

Differentiation between conformational transitions of polymers and the transition observed near the theta conditions

Summary The differentiation between the conformational transitions of polymers and the transition observed near the conditions has been investigated. The conformational transitions are related with side-group effects and vanish under the influence of an appropriate amount of a polar solvent. In the contrary, the transition observed in the vicinity of the temperature is related with chain-backbone effects. The addition of a polar solvent shifts this transition to a different temperature in accordance with the resulted change of the temperature of the system.     

Liquid-phase mass transfer enhancement by gas evolution at inclined plates

The limiting current technique has been employed to determine mass transfer coefficients at vertical and inclined plates with stirring by coplanar electrochemical oxygen evolution. Orientation of the plate has been varied from –45 (down-facing inclined position) to +45 (up-facing inclined position) at ten intervals. At a constant oxygen evolution rate, maximum mass transfer enhancement was achieved at down-facing inclined orientations where (the angle from vertical) is small. The inclination angle at which mass transfer attained its highest value depended on the oxygen evolution rate and is given by _max =a + 10.96 logI _g whereI _g (mA) is the electrochemical current for the oxygen evolution.For the range of the inclination angle, 0 _max, the relationship between the mass transfer coefficient and can be represented byK =K _o +aK _o(sin )^0.3 whereK _o is the mass transfer coefficient at the vertical plate.     

Adsorption and corrosion inhibition properties of thymol

On the basis of electrocapillary and differential capacitance measurements it was established that thymol from acid solutions was adsorbed on a mercury electrode. The shape of the thymol adsorption isotherm, the positive value of the attraction constanta and the position of the minimum of the Inc/ vs dependence (wherec is thymol concentration and is electrode coverage) indicated the applicability of the Frumkin equation.The characteristics of thymol as a corrosion inhibitor were studied by observing the dissolution of aluminium and zinc in hydrochloric acid with and without thymol addition. The values of the reaction numbers (RN) plotted against thymol concentration were compared with the adsorption curves. The analysis of the results, i.e. the comparison of theRN(c) and(c) curves for the liquid and solid metal electrodes and the difference between theRN(c) curves for aluminium and zinc, indicated a different adsorption mechanism and also a different corrosion inhibition efficiency by thymol for aluminium and zinc.     

Relationship between preferential adsorption coefficient and intrinsic viscosity in ternary systems

Summary The relation proposed between the preferential adsorption coefficient, , and the intrinsic viscosity, ¦¦ ¦¦=¦¦+AK has been applied in this paper to previously published data. This equation is found to be valid in theta condi tions and far away from them. The obtained results are compared to the ones calculated with the Dondos-Benoit equation.     

Comparison of some 4- and 4,4′-substituted derivatives of stilbene for their reactivities towards the benzoyloxy radical

Summary 4-Fluoro- and 4,4-difluorostilbene are similar in their reactivities towards the benzoyloxy radical; a similar conclusion has been reached in respect of 4-chloro- with 4,4-dichlorostilbene and 4-phenyl-with 4,4-diphenylstilbene. These results have been obtained by consideration of the numbers of benzoate and phenyl end-groups in poly (methyl methacrylate) made using benzoyl peroxide in the presence of the appropriate derivative of stilbene.     

Miscibility of poly(α-methyl styrene-co-methacrylic acid) with alkyl methacrylate-co-4-vinylpyridine copolymers

Summary The miscibility of blends of poly(-methyl styrene-co-methacrylic acid) (PMSMA) with various alkyl methacrylate polymers or poly(alkyl methacrylate-co-4-vinylpyridine) was studied by differential scanning calorimetry and Fourier transform infra red spectroscopy. PMSMA is immiscible with poly(methyl methacrylate), poly(ethyl methacrylate) and poly(n-butyl methacrylate). The introduction of 4-vinylpyridine by random free radical copolymerization within these alkyl methacrylate polymer chains enhanced the miscibility of these copolymers with PMSMA as a result of specific interactions that occurred between the carboxylic and pyridine groups, evidenced from the significant changes observed by FTIR in the carboxyl and pyridine ring regions. The density of interacting groups required for miscible blends depends on the size of the pendant group.     

Thermodynamics of complex formation of polyacrylic acid with poly(N-vinyl-2-pyrrolidone) and chitosan

Summary Interpolymer complexing of poly(acrylic acid) (PAA) with poly(N-vinyl-2-pyrrolidone) (PVP) as well as with chitosans (CHI) of various chain lengths was studied at different temperatures by pH measurements. The degree of conversion (), the complex stability constant, K, and the thermodynamic parameters of these reactions were evaluated. Complexing proceeds cooperatively in both systems and values of near unity are obtained for the higher molecular weight samples. The variation of K with for the PAA-CHI system indicates that this complex comprises long sequences of bound pairs of monomer units.     

Oxidation of carbon monoxide and deuterium on a Pd(100) film

For Pd/MgO(100) pre-exposed to oxygen, the catalytic oxidation of CO and D₂, respectively, has been studied in the temperature range 100–300°C. At temperatures 200°C, the CO₂ desorption rate is independent of oxygen coverage, _O, and the reactive sticking coefficient for CO is close to unity. The D₂O desorption rate is strongly dependent on _O. D₂ adsorption is blocked by adsorbed oxygen and the maximum D₂O desorption rate is reached when almost all oxygen has been consumed (<0.03). The formation of an oxygen c(2×2) structure, coexisting with the initial p(2×2) phase, is reflected in the oxidation rates.     

Synthesis of new metal-containing side-chain monomers and polymers

New metal-containing vinyl monomers, hexyl-6-oxy-{4-[4-(4-carboxy cyclopentadienyl manganese tricarbonyl phenyl)phenyl]benzoyloxy}methacrylate and hexyl-6-oxy-{4-[4-(4-ferrocenoyl phenyl)phenyl]benzoyloxy}methacrylate, and the corresponding homopolymers and random copolymers with hydroxy monomer hexyl-6-oxy-{4-[4-(4-hydroxyphenyl)phenyl]benzoyloxy}methacrylate were synthesized. The compounds were characterized by¹H NMR; their thermal behavior was investigated by means of differential scanning calorimetry. Monomers and polymers containing the ferrocene unit melt at lower temperatures than those derived from the cyclopentadienyl managanese tricarbonyl moiety. The melting temperatures of the monomers and polymers ranged from 399 to about 515 K, Both monomers and polymers failed to exhibit mesogenic behavior. Values ofM _n,M _w,M _w/M _n, and degree of polymerization were obtained by gel permeation chromatography. TheM _n ranged from 16,500 for the copolymer containing hexyl-6-oxy-{4-[4-(4-ferrocenoyl phenyl)phenyl] benzoyloxy}methacrylate and hydroxy monomer hexyl-6-oxy-{4-[4-(4-hydroxyphenyl)phenyl]benzoyloxy}methacrylate at a 1:3 ratio to 26,000 for the copolymer containing hexyl-6-oxy-{4-[4-(4-carboxy cyclopentadienyl manganese tricarbonyl phenyl)phenyl]benzoyloxy}methacrylate and hydroxy monomer hexyl-6-oxy-{4-[4-(4-hydroxyphenyl)phenyl]benzoyloxy}methacrylate at a 1:3 ratio.M _w/M _n ranged from 1.6 in the case of the copolymer containing hexyl-6-oxy-{4-[4-(4-carboxy cyclopentadienyl manganese tricarbonyl phenyl)phenyl]benzoyloxy}methacrylate and hydroxy monomer hexyl-6-oxy-{4-[4-(4-hydroxyphenyl)phenyl]benzoyloxy}methacrylate at a 1:3 ratio to 2.2 in the case of poly(hexyl-6-oxy{4-[4-(4-carboxy cyclopentadienyl manganese tricarbonyl phenyl)phenyl]benzoyloxy}methacrylate).     

Critical solution point and chain dimension of branched-polystyrene solutions

Summary Critical solution point and chain dimension were measured for branched polystyrene(BPS) in solution as a function of molecular weight(M) and compared with those for linear polystyrene(LPS). The critical concentration _c of BPS was quite different from that of LPS at a fixed M, but the same at a fixed overlap-concentration ^*, i.e., plots of _c vs. ^* fall on a single straight line for both BPS and LPS (gf_c ^*). Reduced critical temperature _c defined by gt_c=(–T_c)/ [T_c: critical temperature, : the -temperature] was related to _c as _{c c} ² for BPS, whereas _{c c} for LPS.     

Excluded volume and hydrodynamic properties of polystyrene in non-ideal solvents

At 298 K, intrinsic viscosity [], has been measured for fifteen polystyrene, PS, samples of different relative molar masses M in pure toluene T, and seven different binary solvents. These solvents were toluene / methanol (MeOH) mixtures having different volume fractions of MeOH. The -composition for the binary solvent system was found to be 77% T / 23% MeOH at 298 K. The dependance of excluded volume of polymer molecules on M and the solvation power was demonstrated. A constant value of 0.633 nm for the effective unit length, b, was obtained under -condition. Meanwhile a non-constancy of b, obtained in case of thermodynamically good solvents, was attributed to the neglect of excluded volume effect.     

Plasma-induced polymerization

Summary Investigations carried out in plasma-induced polymerization (copolymerization) led to the idea of the existence of living macroradicals. Their presence in both homogeneous and heterogeneous media was experimentally proved and theoretically explained and their use as macromolecular initiators in polymerization processes is exemplified.Dedicated to Prof. Dr. Dragutin Fle at the Occasion of his 60th Anniversary     

Evaluation of the Form Birefringence and Other Structural Parameters Due to Thermal Annealing for Nylon 6 Fibers

In the present work nylon 6 fibers were annealed at 155±1C at different times and allowed to cool down in the oven to room temperature (27±1C). A Pluta polarizing interference microscope was used for measuring the changes in the optical parameters. From the optical and density parameters the optical orientation values of F ₂(), F ₄(), F ₆() and F _av were calculated. Also, the dielectric constant, dielectric susceptibility, molar refractivity, segment anisotropy, optical stress coefficient, optical configuration and the form birefringence were evaluated. The segment anisotropy and deformational thermal stress was evaluated. Relationships between the measured and calculated parameters are given for illustration. The mechanism of structural variations for nylon 6 fiber due to the annealing process is discussed, and structural details for opto thermal parameters are explained. The present study throws light on the changes due to thermal annealing conditions for nylon 6 fibers. Microinterferograms and curves are given for illustration.     

Effect of branched alkyl groups on physical properties in poly(ethylene-co-branched alkyl methacrylate)s

Summary Poly(ethylene-co-5.4 mol% n-alkyl/branched alkyl methacrylate)s (PEM) were prepared by a dehydrogenchloride reaction of poly(ethylene-co-5.4 mol% alkyl methacrylic chloride) with the corresponding alkyl alcohol to investigate effect of branching structure and length of alkyl ester on a few physical properties of PEM [glass transition temperature (T_g), degree of crystallinity in polyethylene region (X_c) and dielectric molecular motion], where the alkyl groups used here are n-propyl, n-butyl, n-hexyl, n-decyl, 2-ethylhexyl, 3,5,5-trimethylhexyl and 2-(1,3,3-trimethylbutyl)-5,7,7-trimethyloctyl. In the n-alkyl methacrylate copolymers, T_g and X_c were almost unchanged with the presence of alkyl ester, but T_g increased and X_c decreased in the highly branched alkyl methacrylate copolymers even at the low methacrylate content of 5.4 mol%.     

Functional polymers

N-Acryl-N,N-dicyclohexylurea and N-methacryl-N,N-dicyclohexylurea have been synthesized. N-Acryl-N,N-dicyclohexylurea was polymerized with azobisisobutyronitrile as the initiator and the copolymerization of these two monomers with styrene and methyl methacrylate was also accomplished. Monomers, polymers, and copolymers were characterized.Part XXXV: O. Vogl, Polimery, in press.     

The mechanism of CO oxidation over Cu(110): Effect of CO gas energy

The effect of the temperature of gas phase CO upon the kinetics of the oxygen titration reaction: CO_g +O_a CO_2,g, has been studied. It is found that the reaction's rate is independant of CO gas temperature between 300 and 623 K. The activation energy (6.5 kcal/mole), dependence upon CO pressure (first-order), and independence upon oxygen coverage for 0.1 _o 0.4 are all independant of the CO gas phase temperature. This result rules out any Eley-Rideal type mechanism whereby CO reacts directly from the gas phase with an oxygen adatom without first being accommodated to the surface temperature in an absorbed state. The result is instead interpretable in terms of a Langmuir-Hinshelwood mechanism.Camille and Henry Dreyfus Foundation Teacher-Scholar Fellowship.     

The electrochemical properties of polyaniline derivatives: poly(4,4′-diphenylamine methylenes) and poly(4,4′-diphenylimine methines)

Summary The electrochemical properties of poly(4,4-diphenylamine methylenes) and poly(4,4-diphenylimine methines) were investigated by cyclic voltammetry. A dehydrogenation reaction occured when poly(4,4-diphenylamine methylenes) underwent a electrochemical reaction and transformed to poly(4,4-diphenylimine methines). The fully oxidized poly(4,4-diphenylimine methines) had the electrochemical band gaps of 1.60–1.72 eV, which were found to significantly smaller than those of the fully reduced poly(4,4-diphenylamine methylenes).     

Activation of Ni/A12O3 catalysts through modification of the Al2O3 support

The effect of alumina pretreatment on the performance of alumina supported nickel catalysts was demonstrated in gas phase hydrogenation of toluene to methylcyclohexane. The state of the alumina was changed from pure to pure phase through various heat treatments in air. The catalysts were prepared from vapor phase by saturating the accessible binding sites on the pretreated alumina with the nickel precursor. The highest number of active sites for hydrogenation was observed for catalysts prepared on alumina having an incomplete phase transition and a / alumina phase ratio between 0.5 and 10. Results from temperature programmed desorption (TPD) studies revealed that a maximum in weakly chemisorbed hydrogen as well as in total amount of desorbed hydrogen was found for the same catalysts. By hydrogen chemisorption studies the total hydrogen uptake was found to correlate with the observed hydrogenation maximum. It is suggested that both the chemical and physical properties of the alumina influence the activity. An optimal metal-support interaction and structural defects on the alumina due to the phase transition can explain the observed maximum in the number of active sites and in hydrogen uptake.     

Synthesis of poly(tetrahydrofuran-b-ε-caprolactone) macromonomer via the Sml2-induced transformation

Summary A novel well-defined macromonomer consisting of different types of monomers in polymerization mechanisms was synthesized for the first time through the SmI₂-induced transformation. The macromonomer, -methacryloylpoly-(tetrahydrofuran-b--caprolactone), was prepared by the reaction of methacryloyl chloride with living poly(tetrahydrofuran-b--caprolactone) [poly(THF-b-CL)] which was obtained by the two-electron reduction of the cationic growing center of poly(THF) by samarium iodide (SmI₂) followed by the polymerization of CL. ¹H NMR analysis indicated the quantitative introduction of the methacryloyl group onto the polymer end. The molecular weight distribution of the macromonomer was relatively narrow, and the unit ratio of THF to CL could be controlled by both polymerization time of THF and the amount of CL, resulting from the living nature of both CL- and THF-polymerizations. Radical copolymerization of the produced macromonomers with methyl methacrylate in the presence of AIBN resulted in a polymethacrylate backbone grafted with poly(THF-b-CL) block copolymers.