Authors:L. Barral, J. Cano, A. J. López, J. López, P. Nogueira, and C. Ramírez
The diffusive and dynamic mechanical behavior of the DGEBA/1,3-BAC epoxy resin system was studied during water absorption. The diffusion of water was investigated at 100% relative humidity, by immersion of specimens in water at 60, 80 and 100°C. In all absorption experiments, water diffusion followed Fick's law. Diffusion coefficients and saturated water concentrations are given for these temperatures. The activation energy for diffusion was determined from the relationship between the diffusion coefficient and the reciprocal of the absolute temperature. The value obtained was 31.2 kJ mol−1. Dynamic mechanical analysis of samples immersed in 100°C water and with various water contents showed both a shift of Tg, defined by thetanδ peak, to lower temperatures and a slight decrease in the dynamic modulus in the presence of water. These effects are probably a result of plasticization.
A method is proposed which, through the monitoring and modeling of the diurnal variation of α-radioactivity in the air near
the ground, appears with a potential in enhancing the measurement of low radioactivity unexpected peaks over the natural background.
Portable field instrumentation was used for the monitoring which further included the total γ-radiation at ground level, the
relative humidity and temperature. The variation of the α-radioactivity follows a periodic form with peaks in the morning
and in the afternoon. The applicability of a mathematical model to describe this variation of the α-radioactivity in terms
of the meteorological variables and the γ-radiation was tested positive. This could reduce the difference between the measured
and modeled periodic variation to an almost flat one, above which sudden unexpected peaks of radioactivity from possible undeclared
nuclear activities could be easier identified.
Airborne concentration levels of222Rn and its progeny, and220Rn progeny were measured in an underground U mine. In addition, concurrent measurements of several meteorological variables such as temperature, relative humidity, barometric pressure and airflow rate were also carried out. Mining operations and mining activities during the measurements were carefully noted. The data collected show great variability. Although not particularly strong, some definite correlations could be found between airborne radioactivity concentration levels, meteorological variables, and mining operations (and mining activities). The difficulty in obtaining stronger correlations between the above variables is attributed to the great and simultaneous variability of most of the variables measured. The data presented here are typical of active U–Th mining environments, i.e., of Ontario (Canada) underground U mines. Measurements extended for a period of a full calendar year and involved several thousand independent measurements.
Authors:A. Kumar, Y. Gautam, V. Kumar, K. Rao, S. Sharma, A. Sharma, and A. Hegde
Knowledge of the dynamics of HTO in leafy plant–soil system is required to verify models, such as the NORMTRI code, which
predict environmental tritium following its release. Tritium concentrations in plants has been evaluated using the code NORMTRI
and experimentally by collection of samples of different plants and their soils samples. In the present study, major seasonal
crop plants i.e. wheat, mustard, sugar cane, coriander, spinach, potato, were collected beyond Narora Atomic Power Station
site boundary and gular, arandi, neem, ashok, amaltas, csuarina leaf samples within NAPS site boundary for analysis of HTO
content. Data analysis indicated that HTO in leaf is strongly influenced by atmospheric relative humidity and type of the
Differential scanning calorimetry (DSC) has been used to probe ordered structures and glassing behaviour for a range of agars containing < 25% w/w water. Most commercial agars are supplied in an ordered (double-helical) state, show an endothermic helix-to-coil transition above 100‡C at low-moisture, and require 90–100‡C for solubilisation in excess water. Agars dried from the coil (single-chain) state show no corresponding endothermic transitions and only require a minimum of 45‡C for aqueous dissolution. Evidence from helix-to-coil transition enthalpies, equilibrium water content as a function of relative humidity, and solid-state13C NMR spectroscopy suggests that water molecules are associated enthalpically with double-helical agar. Single-chain agar is apparently not obtained in a glassy state by direct drying from solution, but in common with double-helical forms, exhibits rubber/glass transition behaviour following heating (in a DSC pan) to 180‡C.
Authors:R. Filho, P. Franco, E. Conceição, and M. Leles
A new formulation of nifedipine tablets was prepared. The tablets were conditioned in amber-colored glass containers and placed
in a climatized room at 40 °C and relative humidity of 75% for 180 days. Differential scanning calorimetry (DSC) and Thermogravimetry
(TG) were used in order to evaluate the thermal properties of nifedipine, the excipients and two well-known nifedipine degradation
products. There is no evidence of interaction between nifedipine and excipients or degradation products. High performance
liquid chromatography (HPLC) was used in the dosage of nifedipine tablets before and after acclimatized exposure. Results
show that DSC and TG offer important data for a more detailed assessment of the stability of a pharmaceutical formulation.
The isothermal heat of hydration of MgSO4 hydrates was studied by humidity controlled calorimetry. Two hydrates, starkeyite (MgSO4·4H2O) and a mixture of MgSO4 hydrates with summary 1.3 mol H2O were investigated. The solid-gas reactions were initiated at 30°C and 85% relative humidity. The heat of hydration was determined
in a circulation cell in the calorimeter C80 (Setaram). The crystal phases formed after the hydration process were analyzed
by thermogravimetry (TG) and X-ray powder diffraction (XRD).
Starkeyite reacted with the water vapour to the thermodynamic stable epsomite and the MgSO4 hydrate mixture with 1.3 mol water to hexahydrite. The hydration heats of starkeyite and the mixture were determined to be
−169±3 and −257±5 kJmol−1, respectively.
Authors:A. Bigi, M. Borghi, G. Cojazzi, A. Fichera, S. Panzavolta, and N. Roveri
Differential scanning calorimetry and high angle X-ray diffraction analyses were performed on gelatin films, air dried at
different values of constant elongation, crosslinked with glutaraldehyde and examined at constant relative humidity of 75%.
Drawing induces a preferential orientation of the chain segments of gelatin parallel to the stretching direction,and a linear
increase of the renaturation level, calculated as the ratio between the denaturationenthalpy of gelatin films and that of
tendon collagen. The comparison with the results previously obtained on the mechanical properties of the films, puts into
evidence the different contributions of orientation and renaturation on the improvement of the mechanical parameters on drawing.
The results offer important information on the role of glutaraldehyde (GTA) crosslinking on the stability of collagenous materials.
Authors:M. Odlyha, Q. Wang, G. M. Foster, J. de Groot, M. Horton, and L. Bozec
Dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC) and thermogravimetry (TG) have been used
to characterise model tapestries, especially woven for the EC-funded project (MODHT) and to historic tapestries in royal palaces
and museums. Modulus values of woollen threads from model tapestries are reported and the effects of traditional dyeing and
mordanting processes quantified. TG, particularly of black woollen threads showed alterations in thermal stability. Tests
of creep on immersion in water and subsequent heating to 90C and on exposure to a controlled relative humidity programme
were also used to rank these effects. Modulus values of historic woollen samples were also obtained and DSC studies of model
and historic silk samples are reported together with preliminary atomic force microscopy (AFM) images of silk fibres.
The stability of Supersulphated Cement (SSC) is investigated at 95°C when subjected to relative humidities of 100, 53 and
11% of water vapour. Previously  investigations at 25, 50, 75°C under the same conditions of humidity reported the stability
of ettringite, one of the initial hydration products. At 95°C, decomposition of ettringite, is found at all humidities and
is rapid at 100% relative humidity. The hydration products of cement pastes at a water cement ratio of 0.27 were determined
by thermogravimetry (TG) and X-ray diffraction (XRD).
The formation of the hydragarnet, plazolite is recorded during the decomposition/dehydration process enhanced by possible
carbonation. Rehydration studies on the products after storage for up to 9 months were carried out using distilled water and
the samples tested for ettringite content. It is concluded that ettringite in SSC is inherently unstable at 95°C.