Authors:R. Bellajrou, M. Cohen-Adad, R. Cohen-Adad, N. Pillet, and M. El Hadek
Monomethylhydrazine (MMH) (CH3)NHNH2 is currently used as fuel for spacecraft engine combustion chambers. The Aestus engine of the upper stage of Ariane 5 is
fed with MMH under pressure of 16 bars. The propellant, initially at room temperature, is about 393 K when introduced into
the combustion chamber, due to heating up through the regenerative circuit. As MMH is unstable above 373 K, it has been necessary
to check its decomposition rate and vapor pressure under such conditions.
The vapor pressure of this propellant has been measured in a pressure vessel and the thermal decomposition rate was determined
with the same device up to 500 K.
Authors:M. Odlyha, N. Cohen, R. Campana, and G. Foster
This paper describes the results and conclusions of research directed towards the development and evaluation of a chemical
sensor which would provide information on the quality of indoor environments surrounding cultural objects. In our case these
objects were paintings housed in major European galleries and the main objective is their preservation through an improved
understanding of their microenvironment. The concept was to prepare and expose test tempera paintings which would behave as
dosimeters and integrate the environmental response at these locations. Artificial ageing of similar samples was performed
to provide a means of calibrating the test paintings. Samples from the test paintings were compared with artificially aged
samples and this enabled the sites to be ranked in terms of their suitability for exposure of cultural objects.
Additionally, novel methodology involving piezoelectric sensors was designed for monitoring the relative humidity and temperature
of the microenvironment of paintings. Dielectric techniques were also used for measuring the effect of relative humidity fluctuations
on artists' materials and novel non-invasive dielectric techniques in the microwave region were used for the determination
of their moisture content.
Authors:N. Cohen, M. Odlyha, D. Ucko, and Q. Pankhurst
Mechanical alloying is a versatile technique for the solid state synthesis of many materials, including alloys such as iron-copper
where the elements are immiscible under equilibrium conditions. The structural and magnetic state of these alloys, and their
thermal stability, have been investigated by means of thermomagnetometry, DSC, X-ray diffraction and Mssbauer spectroscopy.
Comparison of the thermomagnetometry curves for the various alloys together with analysis of intermediate reaction products
enabled the individual thermal processes to be identified. The Curie temperature of the alloys was measured, and it was found
that on heating the metastable alloys underwent phase segregation between 300-400C.
Authors:M. Odlyha, G. Foster, N. Cohen, and R. Larsen
A description is given how the dielectric coaxial technique measuring in the microwave region has been used for monitoring drying processes in leather samples. It is also shown how the coupling of this technique together with dynamic mechanical analysis enables the simultaneous recording of changes inthe dielectric properties, related to the moisture content of the material, together with the mechanical properties as a function of time or temperature. The samples studied include unaged and artificially aged goat and calf leathers. Measurements using the dynamic mechanical analyser are presented over a range of temperature which includes the shrinkage temperature. During the drying process, values of mechanical modulus or displacement and dielectric permittivity are recorded as a function of time or temperature which includes the temperature range of leather shrinkage, and from previous research report of Larsen  this has been associated with the chemical state of the leather samples.
Authors:D. Carr, M. Odlyha, N. Cohen, A. Phenix, and R. Hibberd
The thermal degradation of new, and artificially aged fine Ulster linen and archival linen specimens from 19th century paintings
were compared using thermogravimetric analysis and differential scanning calorimetry. Thermal degradation data from new and
artificially aged linen were found to be similar in nature. Archival specimens showed a decreased major degradation temperature,
an increase in char remaining at the end of the experiment and some evidence of a depressed glass transition temperature.
These indicate natural ageing through chain scission. Evidence of a two-stage degradation process was observed in some archival
specimens suggesting that an unknown additive was present.
Authors:M. Odlyha, N. Cohen, G. Foster, A. Aliev, E. Verdonck, and D. Grandy
DMA and solid state 13C NMR techniques were used to measure historical parchment samples within the framework of the project (MAP) Micro Analysis
of Parchment (EC contract No. SMT4-96-2101) in collaboration with the School of Conservation in Copenhagen. DMA was used in
both thermal scan and creep modes. Thermal scans provided information on the transitions associated with the collagen polymer.
Microthermal analysis was also used to obtain information on the topography and thermal conductivity of sample areas of 100
μm. Localised heating enabled measurements of softening transitions in the sample. This behaviour is influenced by the chemical
composition of parchment. 13C NMR provided information on the carbon atoms associated with the polypeptide chains of the collagen
in parchment. The behaviour of samples immersed in water and measured in DMA creep mode was used to measure the shrinkage
behaviour of the parchment samples. The different but complementary techniques provided a means for characterising the physicochemical
state of parchment samples.
Authors:E. L. Dorval, M. A. Arribére, S. Ribeiro Guevara, I. M. Cohen, A. J. Kestelman, R. A. Ohaco, M. S. Segovia, A. N. Yunes, and M. Arrondo
We have measured the cross sections, averaged over a 235U fission neutron spectrum, for the two high threshold reactions: 75As(n,p)75mGe and 75As(n,2n)74As. The measured averaged cross sections are 0.292±0.022 mb, referred to the 3.95±0.20 mb standard for the 27Al(n,p)27Mg averaged cross section, and 0.371±0.032 mb referred to the 111±3 mb standard for the 58Ni(n,p)58m+gCo averaged cross section, respectively. The measured averaged cross sections were also evaluated semi-empirically by numerically
integrating experimental differential cross section data extracted for both reactions from the current literature. The calculations
were performed for four different representations of the thermal-neutron-induced 235U fission neutron spectrum. The calculated cross sections, though depending on analytical representation of the flux, agree
with the measured values within the estimated uncertainties.