The initial activation energy at zero conversionEo of thermooxidative decomposition has been taken as a measure of thermal stability of polycarbonates (PC) andEo has been correlated with the relative hydrolysis raterh as a measure of their hydrolyse resistance. It is suggested that both decomposition processes are initiated by the same mechanism,
the attack of hydrolytic agent onto ester C−O bonds. The following values ofEo have been found:
187 (PC-M)>87 (PC-A)>43 (PC-C) kJ/mol, and they are correlated with values ofrh being 0.01 (PC-M)<1 (PC-A)<4.4 (PC-C). It has been found, using a computer modeling technique, that bothEo andrh depend on the minimized energy of conformations.
using the blends of sulfoaluminate ferrite belite (SAFB) clinkers and ordinary
Portland cement (OPC) in mass ratio 85:15 with Al2O3,
and starch, polyphosphate (poly-P) or butylacrylate/acrylonitrile were subjected
to moist atmospheres (ambient, 52 and 100% relative humidity (RH)) to investigate
their moisture resistance. Their chemical, thermal, electron microscopic and
magnetic properties were also studied before and after moisture attack. Butylacrylate/acrylonitrile
(BA/AN) copolymer was found to be the most suitable for MDF cement synthesis
since the sample containing BA/AN showed the best moisture resistant. There
are significant differences in scanning electron microscopy (SEM) of MDF cements
before and after moisture attack and with different polymers. New data on
the paramagnetic nonhysteresis magnetization curves for all the samples are
observed. The MDF cements synthesized from SAFB clinker with dissolved poly-P
give the best signal/noise (S/N) ratio. Three main temperature regions on TG curves
of both series of MDF cements are observed. In the inter-phase section of
MDF cements, the content of classical cement hydrates decomposing by 250C
is increased. Combustion of organic material took place by 550C. In the
temperature range 550-800C, the decomposition of CaCO3
The stability behaviour of a thin-film superconductor under a localized release of thermal disturbance is investigated. Two-dimensional conjugate film/substrate conduction equation with anisotropic thermal conductivity of the film, and Joule heat are employed to investigate effects of substrate and thermal properties on the intrinsic stability and quenching recovery. To consider the thermal boundary resistance between film and substrate, an interfacial-layer model (ILM) with very low diffusivity and an acoustic mismatch model (AMM) are employed. Results show that the thermal boundary resistance influences strongly the intrinsic stability. Thermal boundary resistance increases intrinsic stability if the thermal conductivity of the substrate or the disturbance energy is large. Higher Biot numbers and thermal conductivity ratios of film to substrate in longitudinal direction influence stability favorably. We demonstrate also that operation of a film/substrate system, such as YBCO/MgO, is either intrinsically stable or irrecoverably unstable.
The resistance against radiation of the tertiary pyridine resins synthesized for the treatment of spent nuclear fuels and high level radioactive waste was evaluated. After irradiation at 10 MGy, only approximately 10% or less of the exchange groups were lost in HCl solutions regardless of their concentrations, while 3040% were lost in HNO3. The pyridine resin has shown remarkable resistance against radiation particularly in HCl solution. It has been revealed that the decomposition of pyridine type resins results from the scission of the principal chains. An irradiation study was conducted also on the quaternary ammonium resins. Quatemization ratio was found to be reduced in HNO3 solutions at 10 MGy irradiation.
Sulphate resistance and passivation ability of the mortars made from pozzolan cement of CEM IV/A (P) type according to European
Standard EN 197-1 (zeolite blended cement with 60.82 mass% of PC clinker, 35.09 mass% of zeolite and 4.09 mass% of gypsum
abbreviated as ZBC) and ordinary Portland cement (abbreviated as PC) are introduced. Resistance tests were performed in water
and 5% sodium sulphate solution (both 20°C) for 720 days. The increased sulphate resistance of pozzolan cement relative to
that of PC was found. The key quantitative insight into the hydrate phase behaviour is given by thermal analysis. This is
due to pozzolanic reaction of zeolite with PC resulting in reduction of the formed Ca(OH)2 opposite to the reference PC. Ability of pozzolan cements with 15 to 50 mass% of zeolite to protect steel against corrosion
was verified in 20°C/85% RH-wet air within 180-day cure. Steel was not corroded in the mortars made with pozzolan cement containing
up to 35 mass% of zeolite. Pozzolan cement of CEM IV/A (P) type containing 35 mass% of zeolite is a suitable cementitious
material for concrete structures exposed to sulphate attack. Steel is protected against corrosion by this pozzolan cement
in the same measure as the reference PC.
Gamma-induced intermediates stabilized in “kriptofix-21”, “kriptofix-22”, “kriptand-222” and 18-ane-S6 have been studied by ESR spectroscopy at 77–300 K. Apparently, radicals with H-atom abstraction from methylene group are
the main paramagnetic products in diazocrown ethers while formation of both cyclic and uncyclic species is observed in 18-ane-S6 at 77 K. Heating γ-irradiated thiacrown ether up to room temperature mainly results in the cleavage of macrocyclic C−S following
by stabilization of uncyclic radicals. 18-ane-S6 has a higher radiation resistance by comparison with oxygen- and aza-containing crown ethers at low temperature γ-radiolysis.
Authors:T. Nishida, H. Kamezawa, T. Hara and Y. Matsumoto
Fiber of Japanese food natto (Bacillus subtilis) is known to be superabsorbent poly(-glutamic acid) (PGA). NaCl particles precipitate in FeCl2-absorbed crosslinked PGA when heated at crystallization temperature of 320 °C for 10 to 60 min. After heat treatment the Mössbauer spectrum of FeCl2-crosslinked PGA consists of a quadrupole doublet due to FeCl2·2H2O. The Mössbauer spectrum of anhydrous FeCl2 reagent heated under the same condition shows an intense sextet due to -Fe2O3 . These results prove that the superabsorbent polymer, crosslinked PGA, has higher heat resistance.
A phenomenological approach, in the parent phase of Cu-Zn-Al shape memory alloy, establishes a predictable model (or mathematical
equations) relating the dependence of Ms with the temperature over a long period of time (i.e. seasonal or yearly room temperature). High-resolution resistance and
temperature measurements vs. time are used. The long time Ms tracks the external room temperature via two temperature dependent time constants. In steady state, the changes in Ms approach17 per cent of the ‘room’ temperature change. The detailed analysis shows the puzzling disappearance of the after
Chitin and chitosan were irradiated in acidic solutions containing a decontaminating soap. It has been shown that these powders
suspended in aqueous media do not undergo radiolysis, as their I.R. spectra are not altered, and there is no radiolysis product
in the solution, except for the case of nitric acid at lowpH where some chitosan is present in dissolved form. These polymers therefore exhibit very good radiation resistance, in spite
of the fact that the monomers undergo very rapid radiolysis.60Co radiations up to 50 000 krad were used. Under these conditions, chitosan does not lose its collection capacity for most
of the metal ions of interest in the nuclear field, including cobalt, that can be collected from decontaminating soap solutions
with a volume reduction of 10.
The temperature-dependence of the electrical resistance of Al-Zn 78 wt.% was measured during linear cooling of the samples in the range of eutectoidal decomposition. The resulting resistancevs. temperature curves were analysed by:deriving the temperature-dependence of the volume fractionx(T) of theη precipitate;fitting the theoretical functionx(T)=xh(T)+xc(T) following from numerical integration of the reaction rate equations for the simultaneously occurring homogeneous (H) and cellular (C) precipitation processes.