ΔCp, Δα and related quantities for epoxy-aromatic amine networks

Summary The parameters of glass transition in several epoxyamine polymer networks were obtained. The changes C_p (T_g) and (T_g) were proved to be correlated with the concentration of crosslinks in these systems. The difference in glass transition parameters for linear and densely crosslinked polymers was analysed in terms of Simha-Boyer (T_g) and Boyer (C_p·T_g) rules and Eyring's hole theory.     

Calorimetric and rheological studies of 12-hydroxystearic acid / digycidyl ether of bisphenol A blends

Summary Above a concentration c^* close to 0.3 wt%, blends of 12-hydroxystearic acid (HSA) with diglycidyl ether of bisphenol A (DGEBA) prepolymer mixed at 80°C give thermally reversible physical gels (organogels) on cooling.According with the literature, the turbidity of the gels indicates fibres of rectangular cross-sectional shapes. The slope of the linear melting heats versus concentration is equal to the melting heat of the pure HSA (-182 ± 4 J.g^-1).The blends are gels as the elastic modulus G is about ten times larger than the loss one G and G is practically independent of the frequency at a given concentration.The sharp variation of the temperature of the endothermic peak T_peak, of the time to reach the rubbery plateau t_r, of the exponent (G) and of the limiting strain _l of the linear viscoelastic domain below 2.5 wt%, is attributed to smaller crystallites in the blend.At a given frequency, G follows a scaling law with the concentration ( ), the scaling exponent ₁ being equal to 3.87 ± 0.02 at 1 rad.s^-1. This indicates that the gel structure is independent of the concentration.     

On the mechanism of electroless plating. I. Oxidation of formaldehyde at different electrode surfaces

To elucidate the mechanism of electroless plating solutions with formaldehyde as the reductant, the anodic oxidation of formaldehyde in alkaline medium was studied. The influence of electrode material, pH and potential was investigated. The experimental results can be explained by a mechanism in which methylene glycol anion (CH₂OHO^–) is dehydrogenated at the electrode surface, yielding adsorbed hydrogen atoms. The atomic hydrogen can either be oxidized to water or be desorbed as a gas. Kinetic rate laws for these two reactions are given. Electroless copper, platinum and palladium solutions behave according to the mechanism.Nomenclature E applied potential - E _a activation energy of adsorption - E _d activation energy of desorption (=–H+E _a) - E _eq equilibrium potential of the reversible hydrogen reaction at a given pH - F Faraday's constant - –H heat of adsorption - i ⁰ apparent exchange current density for the reversible hydrogen reaction - i ₀ exchange current density for the reversible hydrogen reaction - k rate constant for the desorption of hydrogen - L _s heat of atomization - R gas constant - T absolute temperature - ₇ rate of oxidation of hydrogen atoms - ₈ rate of desorption of hydrogen - transfer coefficient (0.5) - overpotential (=E–E _eq) - fraction of the surface covered by hydrogen atoms - _M work function of metal M - potential of the outer Helmholtz layer relative to the bulk of the electrolyte     

Unperturbed chain dimensions of polyisobutylene in different solvents and at different temperatures

Summary Intrinsic viscosity of polyisobutylene is determined in different solvents and at different temperatures. The intrinsic viscosity is found to increase with the increase in temperature. These variations are explained in terms of variation in thermodynamic quality of the solvent. From these data, the upertubed parameter (k₀) is determined. It is observed that it firstly increases with temperature and then seems to level off and is found to be different for different solvents. k₀ is also correlated with different thermodynamic parameters like H, A, and .     

Chemical determination of microstructure of diene units in 1-chloro-1,3-butadiene copolymers

A comparative study has been carried out on the electrical conductivity of PS, PMMA, and PVC before and after irradiation with -rays up to a dose of 100 MR, The obtained results are explained on the basis of electron trapping theory by making use of a formula suitable for calculating the characteristic parameter . The conclusion that the average value of is near to the theoretical value =0.5 indicates that these polymers possess long decay times and have a large number of exponentially distributed traps.     

The effect of the level of phosphate rock application on its dissolution in soil and on bicarbonate-soluble phosphorus

The effect of the level of phosphate rock application on its dissolution in a lateritic podzolic soil was investigated in laboratory incubation studies. Dissolution of phosphate rock (PR) was estimated as the increase in soil exchangeable Ca ( Ca). Concomitant increases in bicarbonate-soluble P levels ( Bic P) were estimated with the Olsen extractant. Up to 19% of PR dissolved at 200µg P g^–1 soil level of PR application whereas a ten-fold increase in the level of application resulted in the percentage dissolution decreasing to 5%. The absolute amount of dissolution however increased with the level of PR application. The amount of PR dissolved was described by the equation P = A(1 – e^–CR) where P = P dissolved from PR (µg P g^–1 soil) calculated from Ca values, A = maximum dissolution asymptote, C = curvature coefficient and R = level of PR applied expressed asµg P g^–1 soil. Values of the A coefficient increased systematically from 28 to 93µg P g^–1 soil for incubation periods from 1 to 7 days. Corresponding values of the C coefficient ranged from 0.9 – 2.1 × 10^–3. Increases in Bic P arising from the dissolution of PR were also described by an exponential equation and the asymptote values ranged from 4 to about 18µ P g^–1 soil. For Bic P the curvature coefficient values increased with incubation period due to increased P retention with increasing contact period between PR and the soil.The form of the yield response curves of plants to PR was predicted on the basis of these data and compared with response curves reported in the literature. The response curves for PR differ in shape from the Mitscherlich response curve for superphosphate and indicate that in some situations PR is unable to support the same maximum yield as soluble P fertilizers due to inadequate dissolutiuon of PR at high rates of application.     

Calorimetric,X-ray and infra-red investigations on poly(hexamethylene adipamide)

Summary In dependence on crystallization conditions three ranges with different crystal structure and heat of fusion were found by DSC,WAXS,and IR for unoriented PA 6.6 samples of densities between 1.10 and 1.17gcm^–3: Range I:_I triclinic, _c ^I =1.225 gcm^–3,H _M ^I = 235 Jg^–1. Range II:_II triclinic, _c ^II =1.165 gcm^–3, H _M ^II =185 Jg^–1. Range III:Continuous variation from _c ^I ,H _M ^I to _c ^II , H _M ^II . _a=1.095 gcm^–3 is independent of crystallization. conditions. The transition between _I and _II is probably due to changes of the chain conformation.     

Birefringence of polyamide fibres of nonround cross-sectional from

Conclusions A method of determining the birefringence n of fibres having an uncomplicated profile (pentagonal, trilobal, or double rhombus) consists of the following: Over sections of the fibre one determines the ratio of the outer-contour dimensions — the diameterl of the fibre to its thickness d — the path over which the beam acquires the difference in speed ; the values of ,l, andl/d are averaged; and the calculation of n is carried out from the equation n = .This method has been tested on specimens of polyamide fibre prepared under identical melt flow rate conditions.Translated from Khimicheskie Volokna, No. 3, pp. 42–43, May–June, 1983.     

The role of soil pH in the dissolution of phosphate rock fertilizers

The influence of soil pH on the dissolution of phosphate rock fertilizers was investigated in laboratory experiments with reactive North Carolina phosphate rock (PR) in a lateritic soil adjusted to several pH values. Increased soil pH resulted in decreased dissolution as estimated by the increase in exchangeable calcium (Ca) method. The extent of PR dissolution was related to soil pH by an equation of the form Log Ca = a–b pH, and it increased with contact period and rate of PR application. Increased plant available P, as estimated by NaHCO₃ soluble-P (BicP) was about one third of the P dissolved from PR. BicP was related to soil pH by an equation of the form Log Bic P = c–d pH. Dissolution of PR in soil can be considered as a simple chemical reaction between apatite and hydrogen ions supplied by soil constituents.     

Impact of 10 Dietary Sterols on Growth and Reproduction of Daphnia galeata

In crustaceans, cholesterol is anEssential nutrient, which they must directly obtain from their food or by bioconversion from other dietary sterols. Eukaryotic phytoplankton contain a great variety of sterols that differ from cholesterol in having additional substituents or different positions and/or number of double bonds in the side chain or in the sterol nucleus. In this study, we investigated to what extent these structural features affect the growth and reproduction of Daphnia galeata in standardized growth experiments with the cyanobacterium Synechococcus elongatus supplemented with single sterols as food source. The results indicated that ⁵ (sitosterol, stigmasterol,Desmosterol) and ^5,7 (7-dehydrocholesterol, ergosterol) sterols meet the nutritional requirements of the daphnids, while the ⁷ sterol lathosterol supports somatic growth and reproduction to a significantly lower extent than cholesterol. Dihydrocholesterol (⁰) and lanosterol (⁸) did not improve the growth of D. galeata, and growth was adversely affected by the ⁴ sterol allocholesterol. Sterols seem to differ in their allocation to somatic growth and reproduction. Thus, structural differences of dietary sterols have pronounced effects on life-history traits of D. galeata.     

Variable‐temperature IR spectroscopic studies of CO adsorbed on Na‐ZSM‐5 and Na‐Y zeolites

CO interacts with extraframework alkali metal cations (M⁺=) of zeolites to form both M⁺CO and M⁺OC species. By using variabletemperature FTIR spectroscopy, these Cbonded and Obonded species were found to be in a temperaturedependent equilibrium. For the same cation, the difference in interaction energy depends upon the zeolite framework. Thus, for the equilibrium process ZNa⁺=CO ZNa⁺OC, where Z represents the zeolite framework, H ⁰ was found to take the values 3.8 and 2.4 kJ mol^– for CO/NaZSM5 and CO/NaY, respectively. The Cbonded species show always the highest cation–CO interaction energy.     

Effect of the type of mullite and certain additives on the sintering process of mullite-zircon specimens

Conclusions The effect of the type of mullite on the sintering process of mullite-zircon specimens was studied. It was shown that using electromelted mullite as chamotte ensures optimum properties. Sintered mullite increases the porosity of the products.The optimum content of the argillaceous binder for obtaining dense and strong specimens was found to be 10%.It was shown that highly refractory oxides intensify (activate) the sintering process of the mullite-zircon products obtained using electromelted mullite and strengthen them to the maximum extent. In this case, their thermal shock resistance remains quite high.The salts of REE have a positive effect on the sintering process of the mullite-zircon specimens at 1650°C and improve their strength; however, in this case, their thermal shock resistance decreases abruptly. The oxides of REE lead to less intense sintering of the mullite-zircon specimens but these additives increase their strength significantly and impart the required thermal shock resistance.The sintering process of the mullite-zircon specimens occurs in the presence of a liquid phase and is accomplished in three stages whose kinetics can be described by the relationships (proportionalities)l/l^1,3, l/l^1/2, and l/l^1/3, respectively.Translated from Ogneupory, No. 8, pp. 12–17, August, 1988.     

Effects of crystallinity and supermolecular formations on the interfacial shear strength and adhesion in GF/PP composites

Aim of this study was to screen the morphological effects on the interfacial shear strength (i) in glass fibre (GF) reinforced isotactic polypropylene (iPP) model composites. i was determined by a modified single fibre pull-out technique. It was established that the relation between i (5–6 MPa) and the yield stress of the iPP (y30 MPa) is at about 1:6 and that the i values were not influenced by the mophological superstructure set under isothermal crystallization conditions. Increased i was only observed when specimens were produced non-isothermally, by quenching (i9 MPa). This improvement could not be related to thermal shrinkage stresses. The enhancement in i was attributed to better wetting and improved adhesion due to the enlarged amorphous PP (aPP)-phase. A schematic adhesion model considering the wetting behaviour of aPP and iPP was proposed.     

Specific features of the phase transformations occurring during the sintering process of the beta-alumina based ceramics and their properties

Conclusions During the sintering process of beta-alumina obtained using the method of plasmochemical synthesis, the structural transformation occurs and it is accompanied by the separation of the excess Na₂O and the formation of an intergranular meltlike phase that is saturated with sodium and is characterized by high dielectric properties.The quantity of the meltlike phase and the magnitude of the /( + ) ratio determine the degree of stabilization (stability) and the final resistivity of the material and depend on the initial chemical composition and the heating rate maintained during the sintering process.It was shown that when the duration of residence of the material in the hot zone of the furnace is increased or when the specimens sintered maintaining high heating rates are subjected to additional heat treatment, one observes the occurrance of the reverse structural transformation that is characterized by an increase of the phase ratio /( + ) 1, a reduction in the quantity of the meltlike phase right up to its complete disappearance, and a decrease of the electrical resistivity of the material.In the materials having a large excess quantity of sodium oxide, the process of crystallization of the intergranular NaAlO₂ phase occurs simultaneously with the second phase transformation.The best ceramic and electrophysical parameters were obtained when sintering the material contained 7.9% Na₂O.Translated from Ogneupory, No. 3, pp. 13–18, March, 1990.     

Viscous Flow and Plastic Deformation of Glasses in the Model of Excited Atoms

The critical displacement of an atom (a group of atoms) r _max, which corresponds to the interatomic interaction force at the maximum, is treated as the atomic excitation in liquids and glasses. The formation and migration of excited atoms are governed by local fluctuations of the configurational entropy. In amorphous linear polymers, the role of an excited kinetic unit is played by a small-sized macromolecular segment (an atomic group in a monomer). The atomic excitation in silicate glasses corresponds to the critical displacement of a bridging oxygen atom in the Si–O–Si bridge upon switching of adjacent bridging bonds. The activation energy _h = P _{max h} and the activation volume _h = d ²r _max of the atomic excitation are introduced. The activation energy _h is determined by the work done against the forces of the internal pressure P _max. The formation of an excited kinetic unit in polymers and glasses is a small-scale low-energy process ( _h = 10–20 kJ/mol, _h = 5–70 ų). The total activation volume of the system V _f = _h N _h is termed the fluctuation volume, and the model under consideration is referred to as the fluctuation volume model (or the model of excited atoms). The viscosity equation and other relationships of the hole theory are interpreted in the framework of the proposed model. This model is also applied to analyze the plasticity of amorphous polymers and glasses. A relationship between the glass transition condition and the Lindemann melting criterion is established.     

Sex pheromone ofGrapholita funebrana occurrence ofZ-8- andZ-10-Tetradecenyl acetate as secondary components

Z-8-Dodecenyl acetate (Z8–12Ac),E-8-dodecenyl acetate (E8–12Ac),Z-8-tetradecenyl acetate (Z8–14Ac),Z-10-tetradecenyl acetate (Z10–14Ac), andZ-8-dodecen-1-ol (Z8–12OH) were identified in the proportions 10013052 in female sex gland extracts ofGrapholita funebrana, accompanied by saturated acetates from 12 to 20 carbons with tetradecyl acetate predominating.Z10–14Ac has not previously been described as a lepidopteran sex pheromone component. Best attraction of males is obtained withZ8–12Ac in the presence of a higher proportion ofE8–12Ac than in the female. Inclusion of the 14-carbon acetates did not augmentG. funebrana catches but inhibitedG. molesta. On the other hand, addition ofZ8–12OH at the level optimal forG. molesta reduced attraction ofG. funebrana.     

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.     

An investigation of some Schiff bases as corrosion inhibitors for austenitic chromium–nickel steel in H2SO4

The corrosion inhibition of austenitic chromium–nickel steel by two Schiff bases, N-(1-toluidine)salicylaldimine and N-(2-hydroxyphenyl)salicylaldimine, was investigated in sulphuric acid medium. The effect of concentration and temperature on inhibition properties was determined. It was found that when the concentrations of inhibitor were increased the inhibition efficiencies () and surface coverage () increased. Some thermodynamic parameters such as free energy of adsorption, G _ads, and enthalpy, H, were determined for the Schiff bases. Experimental results agree with the Temkin isotherm for N-(1-toluidine)salicylaldimine, but the Langmuir isotherm is more appropriate for N-(2-hydroxyphenyl)salicylaldimine.     

Solubilization of soil organic N by alkaline-hydrolysing N fertilizers

Interactions between¹⁵N-labelled fertilizers applied at concentrations representative of the fertilizer microsite and the solubility of the nitrogenous component of soil organic matter were investigated in laboratory experiments. Soil organic N was solubilized in a-irradiated soil due to addition of NH_3(aq), and the fertilizer-induced loss of unlabelled total N in the extracted soil (TU_s) increased with increasing N fertilizer concentration and soil pH. TU_s was linearly correlated with ammoniacal-N concentration and the pH of the fertilized soil within the range of 7.5-10 (r = 0.94).Total organic N in the soil extract (OT_e) increased rapidly up to day 14 following addition of 2000 mg urea-N kg^–1 soil, but was then stable up to day 28. OT_e of a range of soils increased from between 5 and 148 to between 15 and 368 mg N kg^–1 soil after application of 1045 mg NH₃-N kg^–1 soil. While up to 25% of the organic N was solubilized by the fertilizer in nine soils, the change in total organic N in the extracts (OT_e) of three soils was not significant. The highest OT_e of 399 mg N kg^–1 soil (35.4% of soil organic N) was measured after application of 2000 mg NH₃-N kg^–1 soil.pH and OT_e decreased in the order of NH_3(aq) > urea > di-ammonium phosphate > ammonium sulphate at equivalent rates of N addition. A negative OT_e was measured following application of ammonium sulphate. OT_e was correlated with the pH of the fertilized soil but not ammoniacal-N concentration for different N fertilizer sources.     

A study of factors that control biosynthesis of the compounds which comprise the boll weevil pheromone

Biosynthesis of the four monoterpene compounds that comprise the pheromone of the male boll weevil,Anthonomus grandis Boheman, [1, (+)-cis-2-isopropenyl-1-methylcyclobutaneethanol; II, (Z)-3,3-dimethyl-^1,-cyclohexaneethanol; III, (Z)-3,3-dimethyl-^1,-cyclohexaneacetaldehyde; and IV, (E)-3,3-dimethyl-^1,-cyclohexane-acetaldehyde] was studied. More pheromone was biosynthesized in the summer months, somewhat less was produced by males in the presence of females than by isolated males, and the pheromone was concentrated in the gut and surrounding tissue of the abdomen of the males. Incubation of abdomens with the pheromone alcohols yielded related hydrocarbons, aldehydes, and alcohols, which suggested the presence of several enzyme systems. Boll weevils were able to allylically oxidize myrcene and limonene to alcohols, a capability that suggests pheromone precursors may be at least in part inhaled rather than ingested. The hemolymph may then transport the precursor to the gut or some alternative site where allylic oxidation to the pheromone occurs.Coleoptera: Curculionidae.In cooperation with the Mississippi Agricultural and Forestry Experiment Station, Mississippi State, Mississippi 39762. Received for publication.