Sulfonation of PEEK-WC polymer via chloro-sulfonic acid for potential PEM fuel cell applications

The preparation and characterization of thin dense sulfonated poly-ether-ether-ketone with cardo group (PEEK-WC) membranes for proton exchange membrane fuel cell (PEMFC) applications are described. The sulfonation of PEEK-WC polymer was realized via chloro-sulfonic acid and different kinds of membrane samples were prepared with a sulfonation degree ranging from 67 to 99%. The degree of sulfonation, homogeneity and thickness significantly affect both the membrane transport properties and the electrochemical performances. The dense character of the membranes was confirmed by SEM analysis. Proton conductivity measurements were carried out in a temperature range from 30 to 80 °C and at 100% of relative humidity, reaching 5.40×10⁻³ S/cm⁻¹ as best value at 80 °C and with a sulfonation degree (DS) of 99%. At the same conditions, a water uptake of 17% was achieved. DSC and TGA characterizations were used in order to determine the thermal stability of the membranes, confirming a T_g ranging between 206 and 216 °C depending on the DS, whereas FT-IR yielded indication about intermolecular interactions and water uptake at various sulfonation degrees.     

A finite element method for neutron transport—III. Two-dimensional one-group test problems

The even-parity transport equation for an isotropic scattering medium is applied using a maximum principle to determine the angular flux in a square lattice cell with a cylindrical fuel element, a square isotropic source in a corner of an absorbing shield and a dog-leg duct through an absorbing shield. The finite element solutions obtained are compared with an exact solution for the cell, and benchmark results for the square source and duct problem. The accuracies achieved for the fluxes in the cell problem are everywhere better than 0.75% and high accuracy is achieved for the other test problems. The linear elements, used for the spatial dependence of the angular flux in conjunction with a spherical harmonic expansion for the angular dependence, provide a flexible means of treating awkward geometries. At present the equations are assembled and solved using the UNCLE code, which uses direct Gaussian elimination. This process limits the speed of the finite element method to about 1/3 of the Fletcher finite difference spherical harmonics method for the square source problem. This latter method is, however, limited to systems with geometries defined by co-ordinate surfaces, whereas the finite element method can be used for any region that can be triangulated.     

Determination of deuterium in dead-sea water by nuclear methods

By using the D(d, p)³H nuclear reaction combined with the Rutherford-backscattering method, the amount of D₂O in relation to H₂O in water from the Dead Sea is measured. The amount of deuterium in the samples is determined from the integrated yield of the D(d, p)³H reaction in relation to the ¹⁶O(d, p₀)¹⁷O or ¹⁶O(d, p₁)¹⁷O reaction. For the low deuteron energies used (E 0.63 MeV), the differential cross section of the ¹⁶O(d, p₀)¹⁷O reaction was determined experimentally. No significant change of deuterium concentration in Dead-Sea water down to a depth of 36 m could be detected.     

Increase in cast density in production of silicon nitride articles of irregular shape

The effect of modifying organic additives on the tenacity of ethyl silicate binders and the strength of castings based on Si₂N₃ ultradisperse powder is studied. The effect of the modified Si₃N₄ powder together with the combined sol-gel composition on the density and strength of the castings is demonstrated.     

N,N-bis (2-hydroxyethyl) fatty amide as novel environmentally friendly crosslinking agent for acid functional acrylic copolymer resin

N,N-bis (2-hydroxyethyl) fatty amide (HAFA) derived from dehydrated castor oil (DCO) has been employed as a curing agent for a carboxylic acid functional acrylic resin (AAR). Coating compositions with a varying AAR/HAFA ratio have been prepared and their various film properties have been studied and compared with the conventional butylated melamine formaldehyde (MF) based systems. The study reveals that HAFA can be used successfully as a crosslinking agent for AAR in baking systems. In addition to other technical advantages, the use of HAFA is environmentally friendly as no toxic volatiles are evolved during curing reaction, unlike in MF-cured systems. Department of Industrial Chemistry, Vallabh Vidyanagar, Gujarat 388 120 India. Hyderabad, India.     

Characteristics of phase transitions in poly[bis(trifluoroethoxy)phosphazene]

The data on phase transitions in bis(trifluoroethoxy)phosphazene were examined and generalized. Their nature was determined and the mechanism of the transitions was described. Schemes were proposed for the phase transitions that take into account the conditions of fabrication and thermal history of the samples. Translated from Khimicheskie Volokna, No. 5, pp. 24–27, September–October, 1998.