Thermal decomposition of the composite hydrotalcites of iowaite and woodallite

The thermal stability and thermal decomposition pathways for synthesized composite iowaite/woodallite have been determined using thermogravimetry analysis in conjunction with evolved gas mass spectrometry. Dehydration of the hydrotalcites occurred over a range of 56–70°C. The first dehydroxylation step occurred at around 255°C and, with the substitution of more iron(III) for chromium(III) this temperature increased to an upper limit of 312°C. This trend was observed throughout all decomposition steps. The release of carbonate ions as carbon dioxide gas initialised at just above 300°C and was always accompanied by loss of hydroxyl units as water molecules. The initial loss of the anion in this case the chloride ion was consistently observed to occur at about 450°C with final traces evolved at 535 to 780°C depending of the Fe:Cr ratio and was detected as HCl (m/z=36). Thus for this to occur, hydroxyl units must have been retained in the structure at temperatures upwards of 750°C. Experimentally it was found difficult to keep CO₂ from reacting with the compounds and in this way the synthesized iowaite-woodallite series somewhat resembled the natural minerals.     

Effects of contraction and reduction of basis set size on the He2 interaction energy components

The effect of basis set contraction and elimination of primitive Gaussian orbitals on the He₂ interaction energy components have been studied within the SCF counterpoise corrected approach supplemented by a dispersion term calculated within the variation-perturbation scheme. Despite elimination of almost half of the primitive Gaussian functions from the saturated sp basis set and complete contraction of the remaining ones, the components of interaction energy in He₂ suffer a remarkably small loss of accuracy except for the short range charge transfer contribution.     

A column packing for isothermal gas chromatographic analysis of C1−C5 paraffins and monoolefins and dimethyl ether

Summary An analytical GC method was developed which uses a single packed column consisting of three packings in series prepared with the following liquid phases: dimethyl sulfolane, propylene carbonate, and silver nitrate. This system provides satisfactory resolution of mixtures of C₁–C₅ hydrocarbons and dimethyl ether obtained when converting methanol to gasoline. Due to the high capacity of the column it is possible to inject larger sample amounts permitting trace analysis.     

Effect of strain on the thermodynamic melting temperature of polymers

X-ray diffraction, sonic velocity, and birefringence measurements were used to study the variation of the apparent melting point of strained natural rubber and polychloroprene vulcanizates with elongation ratio and crystallization temperature. The procedure of Hoffman and Weeks was employed to obtain the thermodynamic melting point, t_m, for each elongation ratio α. The parameter β relating to the distribution of fold lengths is unusually large for low elongation ratios and decreases into the usual range only at higher elongations. The observed variations of t_m with α for these two polymers are compared with the theoretical predictions of Flory and Roe and Krigbaum. Although the predictions of the Flory theory depend somewhat upon the value assigned for the number of repeating units per statistical link, and this parameter is not well known for polychloroprene, we nevertheless conclude that his treatment offers a better representation of the melting point elevation for high elongations. Due to the approximations introduced, the treatment of Flory is not valid for lower elongations. Any attempt to improve this treatment must begin by specifying the free energy of the semicrystalline system, which implies a knowledge of the distribution of crystallite orientations and how this distribution varies with strain and with the crystallization conditions.