John Simpson

Bio: John Simpson is an academic researcher. The author has contributed to research in topics: Thermal decomposition & Bromate. The author has an hindex of 1, co-authored 2 publications receiving 11 citations.

Piezo X-ray Absorption Spectroscopy for the Investigation of Solid-State Transformations in the Millisecond Range

Abstract: The piezo XAFS technique in combination with an in situ cell has been used for the investigation of fast solid−solid transformations with millisecond time resolution The technique records X-ray ab

Preparation of explosive nanoparticles in a porous chromium(III) oxide matrix: a first attempt to control the reactivity of explosives.

Abstract: This paper reports the first attempt to control the combustion and the detonation properties of a high explosive through its structure. A porous chromium(III) oxide matrix produced by the combustion of ammonium dichromate was infiltrated by hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). The structure of the Cr(2)O(3) matrix was studied by both scanning and transmission electron microscopy (SEM, TEM); the Cr(2)O(3)/RDX nanocomposites were characterized by nitrogen adsorption. A mathematical model based on these techniques was used to demonstrate that the Cr(2)O(3) matrix encloses and stabilizes RDX particles at the nanoscale. The decomposition process of the nanocomposites was investigated by atomic force microscopy (AFM). The reactivity and sensitivity of the nanocomposites were studied by impact and friction tests, differential scanning calorimetry (DSC), time-resolved cinematography and detonation experiments, and were correlated with their structure. The size of RDX nanoparticles and their distribution in the Cr(2)O(3) matrix have an important influence on their reactivity. The reactive properties of nanostructured RDX differ significantly from those of classical micron-sized RDX. For instance, the melting point disappears and the decomposition temperature is significantly lowered. The quantization of the explosive particles in the Cr(2)O(3) matrix decreases the sensitivity to mechanical stress and allows controlling the decomposition mode-i.e. combustion versus detonation.

Synthesis of CrO3 intercalated multilayer graphene for rapid and reversible NH3 gas sensing

Abstract: A novel material synthesized by intercalating CrO3 in the multilayer graphene was used for the fabrication of reversible ammonia (NH3) gas sensor based on resistive transduction mechanism. Electron diffraction and X-ray diffraction revealed the formation of partial stage-2 CrO3 intercalated graphene. High resolution transmission micrographs showed the increase in the interlayer distances in graphene after intercalating CrO3 layers between graphene layers. Energy dispersive X-ray spectroscopy confirmed the presence of chromium and oxygen in the graphene layers. Current voltage studies using conducting atomic force microscopy showed the formation of junction between graphene and CrO3. Rapid and reversible sensing was observed when the CrO3-intercalated material was kept at 180°. Sensor film demonstrated sensing response of 22.5% and 54% for 20 ppm and 50 ppm of NH3 at 180 °C. It took ∼10 s for sensing NH3 gas and ∼20 s for recovery on removal of gas. Reversible charge transfer between NH3 and electron deficient graphene connected to chromium trioxide at high temperature is proposed to be responsible for high selectivity and sensitivity of the intercalated material towards ammonia gas. The intercalated material showed >8 months stability and sensing ability.

Thermal Decomposition of Irradiated Solids

Abstract: THE thermal decomposition, in vacuo, of potassium permanganate1 and silver permanganate2 crystals is markedly affected by pre-irradiation in Bepo or in a cobalt-60 hot-spot. The induction periods are shortened and the maximum velocities are increased. A mechanism has been suggested involving the growth of decomposition spikes and the accumulation of strain in the crystal over the induction period.