Application of Nitramines Coated with Nitrocellulose in Minimum Signature Isocyanate‐Cured Propellants

Cyclotrimethylenetrinitramine (RDX) coated with nitrocellulose (NC‐RDX) is prepared by an internal solution method and applied in a minimum signature isocyanate‐cured propellant. It was found that RDX was coated or bonded by NC to form NC‐RDX particles; the median particle diameter (d₅₀) and specific surface area of NC‐RDX are in the range from 150 to 240 μm and 0.03 to 0.04 m²⋅g⁻¹, respectively. The NC‐RDX particles could swell in nitrate ester plasticizers with relatively low swelling rate compared with NC added directly in the plasticizers. Different types of ballistic modifiers can be effectively added to NC‐RDX. It was experimentally shown that NC‐RDX can increase the content of NC in the propellant with viscosities in the range from 371 to 394 Pa s and improve the mechanical characteristics of the propellant with maximum tensile strength (σ_m) between 0.48 MPa<σ_m<1.92 MPa, elongation at maximum tensile strength (ε_m) between 28.0%<ε_m<37.3%, and elastic modulus between 3.18 MPa<E<8.68 MPa in the temperature range from −40 to +50 °C.     

Heating and cooling of flocculated and non-flocculated slurries in tubular heat exchangers

The distinctly different turbulent heat transfer characteristics of flocculated kaolin slurries are compared with nonflocculated coal slurries via modified J-factor correlation forms for tubular exchangers. Both slurry types were statistically best-fitted with the approximate solution Bingham plastic flow model in preference to the local shear power law. In addition, the first known turbulent slurry heat transfer cooling results are presented along with the heating results. No distinction was made between heating and cooling correlation forms because of a random scatter of experimental points. Experimental results were interpreted as follows A. Flocculated kaolin slurries J_H = (h/C_pG) (C/K₁)^2;3= 0.027(DVρ/μLe^B?)^0.2 11%ω < %ω Solids < 24%ω Maximum Deviations: + 19.3%, ? 17.8% B. Non-flocculated coal slurries J_w = (h/C_pG)(C_pμLe^B?/k_w)^2/3e^?B?/4) =0.0285 (DVρ/ μLe^B?)^?0.2 13%_w > %w Solids < 33.5%. Maximum Deviations: + 17.8%, - 11.1%     

Removal of heavy‐metal ions by magnetic beads containing triazole chelating groups

The aim of this study was to prepare magnetic beads that could be used for the removal of heavy‐metal ions from synthetic solutions. Magnetic poly(ethylene glycol dimethacrylate–1‐vinyl‐1,2,4‐triazole) [m‐poly(EGDMA–VTAZ)] beads were produced by suspension polymerization in the presence of a magnetite Fe₃O₄ nanopowder. The specific surface area of the m‐poly(EGDMA–VTAZ) beads was 74.8 m²/g with a diameter range of 150–200 μm, and the swelling ratio was 84%. The average Fe₃O₄ content of the resulting m‐poly(EGDMA–VTAZ) beads was 14.8%. The maximum binding capacities of the m‐poly(EGDMA–VTAZ) beads from aquous solution were 284.3 mg/g for Hg²⁺, 193.8 mg/g for Pb²⁺, 151.5 mg/g for Cu²⁺, 128.1 mg/g for Cd²⁺, and 99.4 mg/g for Zn²⁺. The affinity order on a mass basis was Hg²⁺ > Pb²⁺ > Cu²⁺ > Cd²⁺> Zn²⁺. The binding capacities from synthetic waste water were 178.1 mg/g for Hg²⁺, 132.4 mg/g for Pb²⁺, 83.5 mg/g for Cu²⁺, 54.1 mg/g for Cd²⁺, and 32.4 mg/g for Zn²⁺. The magnetic beads could be regenerated (up to ca. 97%) by a treatment with 0.1M HNO₃. These features make m‐poly(EGDMA–VTAZ) beads potential supports for heavy‐metal removal under a magnetic field. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Nanofiltration of a German groundwater of high hardness and NOM content: performance and costs

Nanofiltration of conventionally pretreated groundwater with elevated hardness and content of NOM (Ca²⁺: 115 mg/L; Mg²⁺: 12 mg/L; DOC = 2.9 mg/L) was carried out in a German water treatment plant of the public works of Mainz. For the investigated water the employed membrane (NF200B, Filmtec/DOW) showed almost complete rejection (>95%) of NOM, determined by measuring DOC, UVA (254 nm) and AOX- and THM-formation potential. Due to the high concentration of SO₄²⁻ and presumably due to complexation of Ca²⁺ with humic substances the rejection of Ca²⁺ and Mg²⁺ was unexpectedly high (>74% and >86%, respectively) compared to a pure CaCl₂ solution (R(CaCl₂) <45%). Within an operation period of 4 weeks no significant fouling occurred (flux decline <2%). This was mainly due to the pre-treatment of the raw water (deferrization, demanganization, rapid sand filtration). The operating costs for a nanofiltration plant were calculated to about € 0.23/m³ at a permeate output of 20,000 m³/d which means an increase of the price for drinking water approximately 9%. By blending the permeate and the conventionally treated water at a ratio to yield a DOC concentration in the blend of 1 mg/L, the additional costs for nanofiltration would come to € 0.11/m³.     

State of manganese atoms in the Nd1+x Sr2−x Mn2O7−δ solid solution

The oxidation state of manganese in the Nd_2?x Sr_1+x Mn₂O_7?δ solid solution was determined by X-ray photoelectron spectroscopy and by calculating the oxygen nonstoichiometry based on the gravimetric data. As a result of the heterovalent replacement of Nd³⁺ with Sr²⁺, the change in the oxidation state of manganese occurs in different ways, i.e., it increases at x > 0 and decreases at x < 0. In the latter case, some oxygen ions acquire the oxidation state of ?1. The samples slowly cooled under oxidative conditions possess a significant positive oxygen non-stoichiometry, which tends to decrease after Nd³⁺ is replaced with Sr²⁺. An excess of oxygen stabilizes the crystal structure of Nd_1+x Sr_2?x Mn₂O_7?δ.     

Humidity,density, and inlet aspiration efficiency correction improve accuracy of a low-cost sensor during field calibration at a suburban site in the North-Western Indo-Gangetic plain (NW-IGP)

Abstract

Low-cost particulate matter (PM) sensors are now widely used by concerned citizens to monitor PM exposure despite poor validation under field conditions. Here, we report the field calibration of a modified version of the Laser Egg (LE), against Class III US EPA Federal Equivalent Method PM₁₀ and PM_2.5 β-attenuation analyzers. The calibration was performed at a site in the north-western Indo-Gangetic Plain from 27 April 2016 to 25 July 2016. At ambient PM mass loadings ranging from <1–838?µg m^?3 and <1–228?µg m^?3 for PM₁₀ and PM_2.5, respectively, measurements of PM₁₀, PM_2.5 from the LE were precise, with a Pearson correlation coefficient (r) >0.9 and a percentage coefficient of variance (CV) <12%. The original Mean Bias Error (MBE) of ～?90?µg m^?3 decreased to ?30.9?µg m^?3 (Sensor 1) and ?23.2?µg m^?3 (Sensor 2) during the summer period (27 April–15 June 2016) after correcting for particle density and aspiration losses. During the monsoon period (16 June–25 July 2016) the MBE of the PM_2.5 measurements decreased from 19.1?µg m^?3 to 8.7?µg m^?3 and from 28.3?µg m^?3 to 16.5?µg m^?3 for Sensor 1 and Sensor 2, respectively, after correcting for particle density and hygroscopic growth. The corrections reduced the overall MBE to <20?µg m^?3 for PM₁₀ and <3?µg m^?3 for PM_2.5, indicating that modified version of the LE could be used for ambient PM monitoring with appropriate correction and meteorological observations. However, users of the original product may underestimate their PM₁₀ exposure.

Copyright © 2020 American Association for Aerosol Research     

Théorie et application de la distribution normale de θ1/3 aux temps de séjour des fluides dans les réservoirs agités en régime continu

Statistical models of residence time distributions in ideal stirred tanks in series are well approximated by a normal distribution of θ^1/2, θ^1/2 or θ according as the number of tanks is > 15, > 50 and very large respectively. For one stirred tank, the normal distribution of θ^1/3 approximates well the residence time distribution for both ideal and nonideal mixing. For ideal mixing, the mean x_m and standard deviation σ of the θ^1/2 distribution assume values of 8/9 and 1/3 respectively. For nonideal mixing, x_m is < 8/9 while σ is > 1/3. At constant fluid viscosities, when the rotational speed of the agitator increases, x_m increases gradually to reach its upper limiting value of 8/9 whilst σ decreases to reach its lower limiting value of 1/3. At fixed rotational speeds, if the viscosity increases, x_m decreases whilst σ increases. A simple mixing efficiency criteria derived from the normal distribution of θ^1/3 is proposed and is compatible with Danckwerts' segregation concept.     

Quantitative relationships between intermolecular interaction and damping parameters of irganox‐1035/NBR hybrids: A combination of experiments,molecular dynamics simulations,and linear regression analyses

The damping mechanism of phenol(3,5‐bis(1,1‐dimethylethyl)‐4‐hydroxybenzenepropanoic acid thiodi‐2,1‐ethanediyl ester, abbreviated as Irganox‐1035)/nitrile‐butadiene rubber hybrids was studied by combining experiments, computer simulations, and linear regression analyses. Four important damping parameters [loss peak (tan δ_max), effective loss area (TA), glass transition temperature (T_g), and effective temperature region (ΔT)], were obtained by dynamic mechanical thermal analyses. Three intermolecular interaction parameters [the number of intermolecular hydrogen bonds (N_HBs), binding energy (E_binding), and fractional free volume (FFV)], were calculated by molecular dynamics simulations. Using linear regression analyses, the quantitative relationships between the intermolecular interaction and damping parameters were investigated. Linear and significant relationships between intermolecular interactions (N_HBs and E_binding) and damping parameters (tan δ_max and TA) (R² > 0.9; P < 0.001) were noted; FFV showed moderate linear correlations with damping parameters (R² < 0.9; P < 0.05); only E_binding showed strong correlations with T_g and ΔT (R² > 0.9; P < 0.001). Besides, after nondimensionalization, multivariate linear fitting equations based on intermolecular interaction parameters were developed to accurately predict damping parameters (R² > 0.98, P < 0.001). These studies were expected to provide the useful information in understanding the damping mechanism and to attempt a quantitative tool for designing high damping materials. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46202.     

Studies of tetrazoles as rubber chemicals. II. Reactivities and antioxidation activities of reactive antioxidants based on tetrazoles

The chemical reactivities of novel reactive antioxidants based on tetrazoles for carbon–carbon double bonds of liquid polybutadiene and their antioxidation activities toward isoprene rubber were evaluated. These antioxidants, i.e., 2-substituted phenyl-5-(3′,5′ -di-tert-butyl-4′-hydroxyphenyl)tetrazoles (PHPT), were pyrolyzed in liquid polybutadiene at 160–170°C for 30 min to attach to rubber in extents of 61–85% of the nitrileimines formed from PHPT by 1,3-dipolar addition reaction. The reactivities of PHPT followed the order p-Cl > m-Cl > H > p-CH₃ > m-CH₃, p-OC₂H₅, suggesting that PHPT reacts with diene rubber in electrophilic reaction and p-derivatives exhibit higher contents of binding than m-derivatives due to steric hindrance. From oxygen absorption data, the antioxidation activities of PHPT for isoprene rubber vulcanizates followed the order m-Cl, m-CH₃ > H, p-Cl, p-Cl, p-CH₃ > p-OC₂H₅. Isoprene rubber vulcanizates, obtained after pretreatment with PHPT by heating, were extracted with acetone, followed by aging to show that there was good retention and appreciable antioxidation activities of PHPT, especially, p-CH₃ and p-Cl substituted PHPT.     

Laser light-scattering studies of soluble high performance fluorine-containing polyimides

Two sets of soluble high performance polyimides synthesized from 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 2,2′-(trifluoromethyl)-4,4′-diaminobiphenyl diamine (PFMB), and from 2,2′-bis(trifluoromethyl)-4,4′,5,5′-biphenyl-tetracarboxylic dianhydride (HFBPDA) and 2,2′-(trifluoromethyl)-4,4′-diaminobiphenyl diamine (PFMB) have been investigated by static and dynamic laser light scattering (LLS) in tetrahydrofuran (THF) at 30°C. The calibrations, for 6FDA-PFMB: <R_g> (nm) = 3.87 × 10^?2 <M_w> ^0.568, <R_h> (nm) = 2.38 × 10^?2 <M_w>^0.560 and <D> (cm²/s) = 2.13 × 10^?4 <M_w>^?0.560; for HFBPDA-PFMB: <R_g> (nm) = 2.24 × 10^?2 <M_w>^0.626, <R_h> (nm) = 1.27 × 10^?2 <M_w>^0.621 and <D> (cm²/s) = 3.99 × 10^?4 <M_w>^?0.621, have been established, where <M₂>, <R_g>, <R_h> and <D> are the weight-average molar mass, the root mean square z-average radius of gyration, the z-average hydrodynamic radius and the z-average translational diffusion coefficient, respectively. A combination of <M_w> and the translational diffusion coefficient distribution G(D) leads to the calibrations of D (cm²/s) = 2.41 × 10^?4M^?0.564 and D (cm²/s) = 6.16 × 10^?4M^?0.656 for 6FDA-PFMB and HFBPDA-PFMB, respectively, where D and M correspond to monodisperse species. With these calibrations, we can convert a translational diffusion coefficient distribution G(D) into a corresponding molar mass distribution f_w(M). On the basis of the Kratky-Porod wormlike chain model, the persistence lengths (q) were found to be ? 3.3 nm and ? 4.5 nm, respectively, for 6FDA-PFMB and HFBPDA-PFMB, which indicates that both polyimide chains have an extended conformation. In addition, <R_g> / <R_h> ? (1.7-1.9) shows that they are in coil conformation. Therefore, we conclude that both polyimides have an extended coil conformation.     

Strong Influences of Melting Time and Tm3+ Concentration on Blue Up-Conversion Photoluminescence for Tm3+/Yb3+ Co-Doped TeO2–TlO0.5–ZnO Glass

In this study, by a conventional melt quenching method, we synthesized novel up-conversion phosphors of 60TeO₂–30TlO_0.5–(9−x)ZnO–xTm₂O₃–1Yb₂O₃ (x = 0.1–0.5) glasses, whose system was recently developed in our collaborative group, and their blue up-conversion photoluminescence (UCPL) of Tm³⁺ ions via three-step energy transfer from near-infrared (NIR) sensitizer of Yb³⁺ ions was observed. In particular, the substantial rate of the energy transfer <γ_d5> in the third step from Yb³⁺ to Tm³⁺ under excitation at 975 nm, which determined the final blue UCPL intensity, was estimated as a function of the rare-earth concentration. With an aid of analytical methods of PL lifetime and Judd–Ofelt theory, it was revealed that the highest energy transfer rate <γ_d5> was achieved to be 2.07 × 10⁻¹⁷ cm³/s for x = 0.2, and further increasing Tm₂O₃ content x in the fixed Yb₂O₃ resulted in the decrease in the energy transfer rate <γ_d5>. One of the plausible causes was concentration quenching of Yb³⁺ ions. The other was back-transfer from Tm³⁺ to Yb³⁺ ions. The influence of the condition of glass synthesis and the melting time on <γ_d5> was also discussed.     

Superabsorbent polymeric materials. I. Swelling behaviors of crosslinked poly(sodium acrylate-co-hydroxyethyl methacrylate) in aqueous salt solution

A series of crosslinked poly(sodium acrylate-co-hydroxyethyl methacrylate) based on sodium acrylate (SA), 2-hydroxyethyl methacrylate (HEMA), and N,N′-methylene-bis-acrylamide (NMBA) are prepared by inverse suspension polymerization. The resultant crosslinking polymers are xerogellants. This work investigates not only the absorbency or swelling behavior for these xerogellants composed of different ratios of HEMA/SA in water, but also the effects of various salts and pH values on the swelling properties. Experimental results indicate that the absorbency in deionized water decreases with an increase in the HEMA in copolymeric gel, which is related to the degree of expansion of the network and the strength of the hydrophilic group. The absorbency in the chloride salt solutions decreases with an increase in the salt concentration (swelling is 50 times for the IA group chloride salt solutions, but is less than 5 times for the IIA group salt solution), owing to the osmosis of water and ions between the polymeric gel and the external solution. A decrease in the extent of swelling occurs for divalent and trivalent chloride salt solutions. For the salt solutions of the same ionic strength, the swelling amount has the following tendency: LiCl(aq) = NaCl(aq) = KCl(aq), CaCl₂(aq) < SrCl₂(aq) < BaCl₂(aq), and Fe³⁺ > Ca²⁺ > Zn²⁺ > Cu²⁺. These orders are related to the complexing ability between metallic cations and the carboxylate group in the polymeric chains. Finally, the adsorption of ferric ion by these gels is also investigated. © 1996 John Wiley & Sons, Inc.     

Hydrolysis mechanism of crosslinks formed between hydroxymethylated 2-substituted 4,6-diamino-s-triazines and cotton

Hydrolysis resistance and mechanism of reaction products of hydroxymethylated 2-substituted (X) 4,6-diamino-s-triazines (MXT) with cotton fabrics has been studied. Finishing reagents used were MXT having the following substituents: X = CH₃O? (MMT), (CH₃)₂CHO? (MIPT), CH₃? (MAG), C₂H₅NH? (MEM), HOC₂H₄NH? (MHEM), and (HOC₂H₄)₂N? (MBHEM). For comparison, trimethylolmelamine (TMM), dimethylolurea (DMU), dimethylolethyleneurea (DMEU), and dimethylol-ethyltriazone (DMET) were used. Hydrolysis was carried out in buffer and NaOH solutions of various pH's for 30 min at 80°C. The order of hydrolysis resistance of crosslinked reagents was determined from the nitrogen contents retained. It was as follows: pH 1, MROT < MRNT < MRT; pH ≧ 2, MROT > MRT > MRNT; pH ≦ 13, MROT > MRNT; pH 14, MROT < MRT < MRNT, where MROT is hydroxymethylated 2-alkoxy (MMT, MIPT), MRT is hydroxymethylated 2-alkyl (MAG), and MRNT is hydroxymethylated 2-alkylamino-4,6-diamino-s-triazine (MEM, MHEM, MBHEM). This fact can be explained in terms of the basicity constant (p^K_b) of crosslinked MXT with cotton (approximately p^K_b) of 2-substituted 4,6-diamino-s-triazine (XT). The hydrolysis rates of crosslinked MMT, MAG, and MEM were determined at pH 2. The activation energies were 21.8 for MMT, 20.9 for MAG, and 21.0 kcal/mole for MEM.     

Formaldehyde and VOCs emissions from bio-particleboards

Formaldehyde and other volatile organic compounds (VOCs) emissions were determined from particleboards manufactured with natural adhesives. Thus, mimosa tannin with hexamine solution (T) and a blending of glyoxalated wheat straw lignin solution mixing with mimosa tannin and hexamine (TL) in 50/50 proportion were used as resins. These ones were compared with a traditional synthetic urea formaldehyde (UF) adhesive. Formaldehyde and other VOCs were determined and quantified with high performance liquid chromatography (HPLC) and gas chromatography–mass spectrometry (GC–MS) methods. Formaldehyde, acetaldehyde, acetone/acroleine and hexanaldehyde were the main compounds detected by HPLC. Toluene, ethylbenzene, xylene and following terpenes: α-pinene, β-pinene, 3-carene and limonene were determined by GC–MS. Results were obtained according to the EN-16000. After three days, emission results were the following: (a) formaldehyde UF: 240?>?T:66?>?TL:34?μg/m²?h; (b) acetaldehyde TL:46?>?T:40?>?UF:29?μg/m²?h; (c) acetone/acroleine TL:53.9?>?UF:39.5?>?29.3?μg/m²?h; (d) hexanaldehyde T:14.6?>?TL:13.7?>?UF:11.7?μg/m²?h; (e) toluene UF:19.4?>?TL and T: 9.4?μg/m²?h; (f) ethylbenzene UF:17.4?>?TL and T: 7.6?μg/m²?h; (g) m-xylene UF 69.11?>?TL and T 26.6?μg/m²?h; (h) o-xylene UF:16.0?>?TL and T: 5.6?μg/m²?h; and (i) terpenes were emitted with lower rate than all the other compounds. In general, higher emissions have been noticed in natural adhesives than in the UF. Thus, the main terpenes found were α-pinene: UF:8.5?<?TL:14.8?<?T:19.7; β-pinene: UF:1.8?<?TL:2.6?<?T:3.6 and 3-carene UF:3.6?<?TL and T: 4.9. Concerning limonene, no difference was observed whether the used adhesive was natural or not.     

Particle Morphology and Density Characterization by Combined Mobility and Aerodynamic Diameter Measurements. Part 2: Application to Combustion-Generated Soot Aerosols as a Function of Fuel Equivalence Ratio

Composition, shape factor, size, and fractal dimension of soot aerosol particles generated in a propane/O₂, flame were determined as a function of the fuel equivalence ratio (φ). Soot particles were first size-selected by a differential mobility analyzer (DMA) and then analyzed by an Aerodyne aerosol mass spectrometer (AMS). The DMA provides particles of known mobility diameter (d_m ). The AMS quantitatively measures the mass spectrum of the nonrefractory components of the particles and also provides the vacuum aerodynamic diam eter (d_va ) corresponding to the particles of known mobility diameter. The measured d_m, d_va , and nonrefractory composition are used in a system of equations based on the formulation presented in the companion article to estimate the particle dynamic shape factor, total mass, and black carbon (BC) content. Fractal dimension was estimated based on the mass-mobility relationship. Two types of soot particles were observed depending on the fuel equivalence ratio. Type 1: for φ < 4 (lower propane/O₂), d_va ; was nearly constant and independent of d_m . The value of d_va increased with increasing φ. Analysis of the governing equations showed that these particles were highly irregular (likely fractal aggregates), with a dynamic shape factor that increased with d_m and φ. The fractal dimension of these particles was approximately 1.7. These particles were composed mostly of BC, with the organic carbon content increasing as φ increased. At φ = 1.85, the particles were about 90% BC, 5% PAH, and 5% aliphatic hydrocarbon (particle density = 1.80 g/cm³). Type 2: for φ > 4 (high propane/O₂), d_va was linearly proportional to d_m . Analysis of the governing equations showed that these particles were nearly spherical (likely compact aggregates), with a dynamic shape factor of 1.1 (versus 1 for a sphere) and a fr actal dimension of 2.95 (3 for a sphere). These particles were composed of about 50% PAH, 45% BC, and 5% aliphatic hydrocarbons (particle density = 1.50 g/cm³). These results help interpret some measurement s obtained in recent field studies.     

Morphology control of polyoxy‐methylene/thermoplastic polyurethane blends by adjusting their viscosity ratio

Polyoxymethylene (POM) is an important plastic with very good properties. However, its poor impact strength limits its applications. Theoretical and experimental studies have confirmed that thermoplastic polyurethane (TPU) can effectively enhance the notched impact strength of POM. This paper reports that the notched impact strength of POM/TPU blends can be further improved when these blends are endowed with a fine morphology by changing the viscosity ratio of TPU to POM (P = η_TPU/η_POM) during processing. The experimental results show that the viscosity of TPU is more sensitive to temperature than that of POM, and that the viscosity ratio P decreases with increasing temperature; also for quite a wide range of shear rate, P is close to 1 when the processing temperature (T_p) is around 190 °C. Accordingly, the phase structure of POM/TPU blends changes with P. The dispersed phase of TPU shows ellipsoidal morphology when P > 1 at T_p < 190 °C, filamental morphology when P ≈ 1 at T_p ≈ 190 °C and spheroidal morphology when P < 1 at T_p > 190 °C. The results suggest that the filamental morphology endows POM/TPU (90/10) blends with the highest notched impact strength (～14 kJ m^?2). Copyright © 2006 Society of Chemical Industry     

Studies of anodic dissolution and film growth on iron in acid chloride solutions

The rate of dissolution of Armco Fe has been measured as a function of time for deaerated solutions of constant ionic strength (HCl + NaCl).For pH < 1·5, no appreciable change of the measured polarisation resistance was observed. For 1·5 < pH < 3 the polarisation resistance gave straight lines when plotted against time. The slope of the lines is represented by a = 2·0√(C_OH^?.10¹⁴ ? 45) Ωcm²/min, where C_OH^? is the concentration of the bulk.The Tafel slopes were 64–70 mV when 0 < pH < 1·2.The experimental data are explained by two very similar reaction mechanisms. The theory presented involves the formation of two surface complexes denoted by FeOH Fe·H₂O and FeO Fe·H₂O. It is suggested that the complex FeOH Fe·H₂O serves as nuclei for film formation when pH > 1·5. This would explain the change of the reaction mechanism at pH = 1·5 from a 60 mV mechanism when pH < 1·5 to a 30 mV mechanism when pH > 1·5.The theory is supported by data from the literature. It gives a reasonable explanation of the nonstationary 60 mV Tafel slopes. The mechanisms are in harmony with a hyperbolic relation between anodic current density and time. The logarithmic law of film growth may be derived from the same principles.     

Small-angle X-ray scattering from sodium hyaluronate in aqueous sodium chloride

Summary Four narrow-distribution samples of sodium hyaluronate with weight-average molecular weights M _w of 3.8 × 10³ to 1.1 × 10⁴ in 0.02 and 0.1 M aqueous NaCl at 25°C have been studied by small-angle X-ray scattering. Data for their z-average radii of gyration <S²>_z ^1/2 and particle scattering functions P(θ), together with previous <S²>_z data from light scattering for high molecular weights, are compared with relevant theories for the wormlike chain with or without excluded volume, using the parameters estimated previously from intrinsic viscosity ([η]) data. It is shown that for M _w lower than 1.1 × 10⁴, <S²>_z, P(θ), and [η] of the polysaccharide in the aqueous salts are all consistently explained by this model without excluded volume. Received: 8 December 1997/Accepted: 26 December 1997     

Superabsorbent polymeric materials. II. Swelling behavior of crosslinked poly[sodium acrylate-co-3-dimethyl(methacryloyloxyethyl) ammonium propane sulfonate] in aqueous salt solution

A series of xerogels based on sodium acrylate (SA), 3-dimethyl (methacryloyloxyethyl) ammonium propane sulfonate (DMAPS), and N,N′-methylene-bis-acrylamide (NMBA) are prepared by inverse suspension polymerization. The water absorbencies or swelling behaviors for these xerogels in water or various saline solutions respectively exhibit a value of 1435 g H₂O/g sample and 96 g H₂O/g sample of deionized water and 0.9 wt % NaCl solution at a gel containing 1.88 × 10⁻³ molar ratio of DMAPS while the extent of 1.53 × 10⁻³ molar ratio (0.25 wt % based on total monomer) of NMBA was used in the polymerization. The absorbency in the chloride salt solutions decreases with an increase in the ionic strength of salt. For the same ionic strength of various salt solutions, the swelling amount has the following tendency: Na⁺ > Fe³⁺ > A1³⁺ > Ca²⁺ for the higher ionic strength of 5 × 10⁻³ −2 × 10⁻²M and Na⁺ > Fe³⁺ > Ca²⁺ > A1³⁺ for the lower ionic strength of < 2 × 10⁻⁴M. The bound water found by DSC investigation is approximately equal to 2 g H₂O/g sample. The pH effect and thermal effect on the water absorbency for these xerogels are also investigated. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1701–1712, 1997