The 2,2',4,4',6,6'hexanitrostilbene, HNS, nucleant, used in the crystallisation of 2,4,6,trinitrotoluene, TNT, was precipitated from molten TNT and examined by differential scanning calorimetry, DSC, at several stages during purification by vacuum sublimation. During purification a broad endotherm, associated with nucleant decomposition, which could be resolved into two endotherms, depending on the sublimation temperature, was observed. Pure nucleant prepared at 70‡C showed a similar behaviour during thermal annealing for extended periods of time at >85‡C. Thus TNT, retained in the recrystallised HNS nucleant, may be migrating during the purification process or may occupy a range of lattice sites, which exhibit different activation energies for migration to the surface of the solid during thermal decomposition of the nucleant. Loss of TNT from the nucleant, during purification, could produce some free HNS. The activation energy for nucleant decomposition, which may be a two-stage processes with the initial mobility of the TNT being the limiting reaction, was estimated to be ∼210 kJ mol−. The lattice sites available for the TNT in the host HNS nucleant require elucidation and are the subject of further studies to be published at a later date.
The thermal decomposition of mercury(I) and (II) sulfates has been investigated by thermogravimetry. The solid-state decomposition products have been characterized by infrared and Raman spectroscopy, mass spectrometry and an X-ray diffraction method. It is concluded that mercury(I) sulfate decomposes in two steps, initially forming a mixture of metallic mercury and mercury(II) sulfate — the latter subsequently decomposes without forming a stable intermediate. The stoichiometry of disproportionation of mercury(I) sulfate and the thermal stability range of mercury(I) and mercury(II) sulfates have been established.
This paper deals with the examination of various types of flame resistant fabric in fire conditions, standard flammability tests and thermogravimetry. It shows how it may be possible to determine the protection afforded by a garment using very small samples and instrumental laboratory techniques. This could be important in the development of new materials where a quick assessment could be made of the protective qualities of the material.
Authors:A. Farahnaky, A. Guerrero, S. Hill and J. Mitchell
Glass transition temperature of red crayfish flour (moisture 3.56%) was determined using a phase transition analyser (Wenger
Technical Centre, USA). Due to the importance of physical ageing in functional properties of red crayfish flour (with 65%
protein) the possible occurrence of physical ageing in dry powder of crayfish flour was studied at different temperatures
below and close to the glass transition.
Endothermic peaks that corresponded to relaxation enthalpy were observed for a commercial crayfish flour with 4.5% moisture.
Enthalpy and peak temperature increased on storage of crayfish flour when it was held in the glassy-state at different temperatures
(5, 15, 25°C).
Lithium, sodium, potassium and ammonium bisulphate have been shown by detailed TG/DTA studies to have limited application as molten solvents. By contrast, the eutectic bisulphate systems, ammonium-potassium bisulphate and sodium-potassium bisulphate, appear to be excellent molten solvents in view of their low melting points, long liquid ranges and prolonged thermal stability at 200°. In contrast to previous studies, potassium pyrosulphate has been found to be an excellent molten solvent, provided rigorous preliminary drying procedures have been applied.
A thermogravimetry study of a series of cyclophane bis(sulfoxides) (1–6) has shown that thermal decomposition of these compounds occurs in two stages with a stepwise loss of the sulfoxide groups at well defined decomposition temperatures. The stepwise thermal cleavage has been rationalized in terms of the stereochemistry of the sulfoxide groups and the strain associated with the resultant elimination products.
Authors:R. Bett, J. Cuninghame, J. Hill, I. Jones, N. Taylor, J. Winter and A. Nichols
The object of this paper is to give details of a production method for123I, now in routine use at Harwell. We employ the (p, 5n) reaction, irradiating a liquid target of di-iodomethane (CH2I2) spiked with additional iodine, with 58 MeV protons. A yield of ∼9 mCi/μAh is obtained; the only detectable radionuclidic
impurity is125I, present to the extent of ∼0.15% by activity at the time of separation of Xe from I.