Oxidational wear of low alloy steel in gases other than air

A pin on disc wear machine has been used to study the oxidational wear of low alloy steel in a series of experiments which were carried out under dry wear sliding conditions at range of loads from 11.28 to 49.05 N and three sliding speeds of 2 m/s, 3.5 m/s and 5 m/s, in atmosphere of air, Ar, CO2, 100% O2, 20% O2-80% Ar and 2% O2-98% Ar. Also, the experiments were conducted to study frictional force, surface and contact temperatures and surface parameters of the wearing pins. The wear debris was examined using x-ray diffraction technique for the identification of compounds produced by the wear process. Scanning electron microscopy was employed to study the topographical features of worn pins and to measure the thickness of the oxide films. Microhardness tests were carried out to investigate the influence of the sub-surface microhardness in tribological conditions. Under all loads, speeds and atmospheres parabolic oxidation growth was observed on worn surfaces, although such growth is dependent on the concentration of oxygen in the atmospheres employed. These atmospheres are shown to influence wear rate and coefficient of friction with change in applied load. The nature of the atmosphere also has influence on surface and contact temperatures as determined from heat flow analysis. Unlubricated wear debris was found to be a mixture of αFe2O3, Fe3O4 and FeO oxide. A model has been proposed for tribo-oxide growth demonstrating the importance of diffusion rate and oxygen partial pressure, in the oxidation processes and thus in determination of wear rates.

Kinetic study on thermal decomposition of woods in oxidative environment

The purpose of this work is to gain knowledge on kinetics of biomass decomposition under oxidative atmospheres, mainly examining effect of heating rate on different biomass species. Two sets of experiments are carried out: the first set of experiments is thermal decomposition of four different wood particles, namely aspens, birch, oak and pine under an oxidative atmosphere and analysis with TGA; and the second set is to use large size samples of wood under different heat fluxes in a purpose-built furnace, where the temperature distribution, mass loss and ignition characteristics are recorded and analyzed by a data post-processing system. The experimental data is then used to develop a two-step reactions kinetic scheme with low and high temperature regions while the activation energy for the reactions of the species under different heating rates is calculated. It is found that the activation energy of the second stage reaction for the species with similar constituent fractions tends to converge to a similar value under the high heating rate.

Mechanistic studies of organotellurium chemistry

The oxidation of bis(p-ethoxyphenyl) ditelluride by hydrogen peroxide has been studied kinetically. The reaction monitored was an oxidation from tellurium(I) to tellurium(II). The reaction stoichiometry ratio was found to depend upon the initial reagent concentrations. The presence of dioxygen was found to retard the rate and attributed to a dioxygen-ditelluride adduct. The rate varies in the following order of different atmospheres N2> Air> > O2. The final product obtained from the oxidation has been characterised by IR, NMR and ESR spectroscopy. A mechanism for the oxidation has been suggested. The reduction of p-EtOPhTeCl3 by the hydrazinium ion has been studied kinetically. The stoichiometric measurements show that four moles p-EtOPhTeCl3 are equivalent to three moles hydrazinium ion. The kinetics were studied under pseudo first order conditions. No ammonia was detected as a nitrogen containing product. The reduction proceeds via a two-electron process which indicates that it is inner-sphere in nature. A mechanism for the reduction is suggested. The solvolysis of p-EtOPhTeCl3 by methanol in benzene/methanol media has been studied. The study shows that the solvolysis is a reversible, acid catalysed reaction. Replacement of the chlorides on tellurium by methanol is agreed to be associative and replacement of the first chloride is rate determining. The rate of solvolysis varies in the order trichloride > tribromide > triiodide. A mechanism for the solvolysis is suggested. The synthesis of some tellurium heterocyclics is reported. The synthesis and characterisation of telluranthrene is reported. The attempted synthesis of telluraxanthene was unsuccessful.

The plasma nutriding of tool and bearing steels

There is some evidence to suggest that nitriding of alloy steels, in particular high speed tool steels, under carefully controlled conditions might sharply increase rolling contact fatigue resistance. However, the subsurface shear stresses developed in aerospace bearing applications tend to occur at depths greater than the usual case depths currently produced by nitriding. Additionally, case development must be limited with certain materials due to case spalling and may not always be sufficient to achieve the current theoretical depths necessary to ensure that peak stresses occur within the case. It was the aim of' this work to establish suitable to overcome this problem by plasma nitriding. To assist this development a study has been made of prior hardening treatment, case development, residual stress and case cracking tendency. M2 in the underhardened, undertempered and fully hardened and tempered conditions all responded similarly to plasma nitriding - maximum surface hardening being achieved by plasma nitriding at 450°C. Case development varied linearly with increasing treatment temperature and also with the square root of the treatment time. Maximum surface hardness of M5O and Tl steels was achieved by plasma nitriding in 15% nitrogen/85% hydrogen and varied logarithmically with atmosphere nitrogen content. The case-cracking contact stress varied linearly with nitriding temperature for M2. Tl and M5O supported higher stresses after nitriding in low nitrogen plasma atmospheres. Unidirectional bending fatigue of M2 has been improved up to three times the strength of the fully hardened and tempered condition by plasma nitriding for 16hrs at 400°C. Fatigue strengths of Tl and M5O have been improved by up to 30% by plasma nitriding for 16hrs at 450°C in a 75% hydrogen/25% nitrogen atmosphere.

Corrosion inhibitors for the rehabilitation of reinforced concrete

Four corrosion inhibitors namely sodium nitrite, sodium monofluorophosphate, ethanolamine and an alkanolamine-based mixture were studied by immersing mild steel bars for 42 days in model electrolytes of varied pH and chloride concentration which were intended to simulate the pore solution phase present within carbonated and/or chloride-contaminated concrete. Site trials were carried out on sodium monofluorophosphate and the alkanolamine-based inhibitor to study their depth of penetration into concrete. The influence of various carbonating atmospheres on the pore solution chemistry and microstructure of hydrated cement paste was investigated. Physical realkalisation of carbonated cement paste and a calcium nitrite-based corrosion rehabilitation system for chloride-contaminated cement paste were investigated by monitoring ionic transport within the pore solution phase of laboratory specimens. The main findings were as follows: 1,Sodium nitrite, sodium monofluorophosphate, ethanolamine and the alkanolamine-based mixture all behaved as passivating anodic inhibitors of steel corrosion in air-saturated aqueous solutions of varied pH and chloride concentration. 2,Sodium monofluorophosphate failed to penetrate significantly into partially carbonated site concrete when applied as recommended by the supplier. Phosphate and fluoride penetrated 5mm into partially carbonated site concrete treated with sodium monofluorophosphate. 3,The ethanolamine component of the alkanolamine-based inhibitor was found to have penetrated significant depths into partially carbonated site concrete. 4,Carbonating hydrated cement paste over saturated solutions of sodium nitrite resulted in significant concentrations of nitrite in the pore solution of the carbonated paste. Saturated solutions of sodium chloride, ammonium nitrate, magnesium nitrate and sodium dichromate were investigated and identified as alternatives for controlling the relative humidity of the carbonating environment. 5,Hardened carbonated cement paste can by physically realkalised to a limited extent due to the diffusion of hydroxyl ions under saturated conditions. A substantial proportion of the hydroxyl ions that diffused into the carbonated cement paste however, became bound into the cement matrix. Hydroxyl ion concentrations remained below 5mmol/l within the pore solution of the realkalised cement paste. 6, Nitrite ions penetrated significant distances by diffusion within the pore solution of saturated uncarbonated hydrated cement paste.

Influence of reaction atmosphere (H2O, N2, H2, CO2, CO) on fluidized-bed fast pyrolysis of biomass using detailed tar vapor chemistry in computational fluid dynamics

Secondary pyrolysis in fluidized bed fast pyrolysis of biomass is the focus of this work. A novel computational fluid dynamics (CFD) model coupled with a comprehensive chemistry scheme (134 species and 4169 reactions, in CHEMKIN format) has been developed to investigate this complex phenomenon. Previous results from a transient three-dimensional model of primary pyrolysis were used for the source terms of primary products in this model. A parametric study of reaction atmospheres (H2O, N2, H2, CO2, CO) has been performed. For the N2 and H2O atmosphere, results of the model compared favorably to experimentally obtained yields after the temperature was adjusted to a value higher than that used in experiments. One notable deviation versus experiments is pyrolytic water yield and yield of higher hydrocarbons. The model suggests a not overly strong impact of the reaction atmosphere. However, both chemical and physical effects were observed. Most notably, effects could be seen on the yield of various compounds, temperature profile throughout the reactor system, residence time, radical concentration, and turbulent intensity. At the investigated temperature (873 K), turbulent intensity appeared to have the strongest influence on liquid yield. With the aid of acceleration techniques, most importantly dimension reduction, chemistry agglomeration, and in-situ tabulation, a converged solution could be obtained within a reasonable time (∼30 h). As such, a new potentially useful method has been suggested for numerical analysis of fast pyrolysis.