John Dollimore

SURFACE COMPLEXES ON CARBON. I. A PRELIMINARY INVESTIGATION OF SURFACE OXYGEN COMPLEX ON A NON-GRAPHITIC CARBON.

Abstract A preliminary investigation has been made into the behaviour of the surface oxygen complex during its formation and thermal desorption from the cleaned surface of a non-graphitic carbon (a rapidly pyrolised 720°C polyvinylidene chloride carbon). Using a direct sampling mass spectrometric technique a reasonable agreement was obtained between the amount of oxygen chemisorbed as surface oxide (by material balance of oxygen) and that obtained from analysis of the thermal desorption products CO and CO 2 . The extent of the surface oxygen complex coverage was shown to be of the order of 3 per cent of the total surface. The thermal desorption products CO and CO 2 were found to obey separately the Elovich equation for desorption in the temperature range 400°–900°C. As a consequence of the mechanism by which thermal desorption occurred, a linear plot of increasing activation energy of desorption of CO vs. decreasing coverage θ of the active sites was obtained. A comparison is made between the observed behaviour of surface oxide on a non-graphitic carbon and that obtained by other workers on graphitic carbons.

Kinetic study on the thermal decomposition of copper(II) oxalate

The thermal decomposition of copper(II) oxalate has been studied under vacuum using a constant-volume apparatus and a microbalance; and under dynamic atmospheres of air, nitrogen and oxygen using thermogravimetry and differential scanning calorimetry. The decomposition was found to proceed to copper metal under an inert atmosphere and vacuum; while in air and oxygen, copper(II) oxide was found to be the decomposition product. In each case the decomposition was found to be exothermic with an enthalpy change of –9 ± 2 kJ mol–1 in nitrogen and –134 ± 5 kJ mol–1 in air. Isothermal kinetic analysis showed the data to fit an Avrami–Erofeev relationship with n= 3 in each case. Arrhenius parameters are reported for each decomposition atmosphere and are compared to those of other transition-metal oxalates which appear in the literature.The presence of a preparation effect is noted, as seen with other oxysalts; however, no evidence for the formation of copper(I) oxlate has been found which has previously been speculated to be an intermediate in the decomposition.

The use of partial-pressure mass spectrometry in the thermal analysis study of carbons and graphite

Abstract A versatile partial-pressure mass spectrometer system is described for measuring gaseous species thermally desorbed from solid surfaces. The system evaluates not only the ratio of masses present in the gaseous phase but also the specific mass (mg/g of solid) desorbed or decomposed during thermal treatment. The extension of the method to oxidation studies is also described. A study has been made of the evolution of gases from graphitic and nongraphitic carbons. These range in properties from a non-graphitic carbon, a PVDC charcoal of molecular sieve type, through a ground graphite of specific surface 102 m 2 /g to a nuclear type graphite of 0.6 m 2 /g. The formation of surface oxide on a clean surface at pressures of the order 0.2 mm Hg is evaluated along with the subsequent thermal decomposition of the surface oxide. The data from this paper together with other published work on graphites is used to illustrate the application of the thermal-desorption results to oxidation studies on carbons and graphites.

Energetic nature of catalyst surfaces: I. Supported cobalt on rutile

Abstract A system for investigating the energetic nature of catalyst surfaces has been developed from thermal desorption experiments. By applying an incremental isothermal heating program to the studies, the desorption kinetics have been analyzed to yield the variation in activation energy of desorption with coverage. The technique has been used to study a supported cobalt catalyst and, by following the desorption of hydrogen, the nature of the surface has been studied during reduction, and after a series of hydrogenolysis reactions had been conducted on the surface.

Precursor states for the graphitization of naphthalene, anthracene, phenanthrene and chrysene

Abstract During carbonization, graphitizable aromatic organic compounds such as naphthalene, anthracene, phenanthrene and chrysene pass through a liquid or plastic-state mesophase of optical anisotropy, the lifetime of which is limited by its hardening to a semi-coke. Reflected polarized-light micrography, using cross polarizers with a gypsum plate, has been employed to characterize the carbonaceous mesophases of the different samples.

The correlation of the strength of magnesium hydroxide compacts with heat treatment

Abstract The thermal decomposition of magnesium hydroxide is correlated with the effect of the temperature treatment on the strength of compacted discs of the material. The alteradon in the strength of the magnesium hydroxide which had been subjected to various temperatures between 450° and 800°C was obtained as well as by altering degassing conditions between ambient and 300°C. Up to twenty samples were broken at each of these conditions and the results show a skewed distribution of data points. The experiments on powders heat treated up to 800°C showed an increase in strength beyond 400°C. The TG data showed decomposition in the range 350°C to 500°C although farther weight loss was shown to be due to the presence of about 2–3% carbonate. The most useful correlation between the heat treatment and the strength is seen in the linear relationship between the surface area and the modules of rupture.

The Simultaneous Use of Mass Spectrometer and Microbalance Techniques for the Carbon-Oxygen System

The initial degassing of a high-surface-area graphite is characterized using mass spectrometric and thermogravimetric weight-loss measurements. It will be indicated how far the combination of these allied techniques can be used to define the graphitic nature of the material in terms of the extent of the basal and edge planes of the graphite crystallite. The active surface area of the graphite was measured by the formation of surface oxide during low-pressure oxygen chemisorption onto the clean surface of the material. By subsequent thermal desorption of surface oxide an additional value for the active surface area was obtained from the weight-loss data and the known ratios of the desorbed gaseous species CO and CO2. The utility of a mass spectrometer — microbalance system for the study of gas — surface reactions is discussed.