Determination of rate constants using microelectrodes

An understanding of the rate and the mechanism of reaction is of fundamental importance in the many facets of chemistry. Electrochemical systems are further complicated by the heterogeneous boundary, between the solution and the electrode, that the electron passes through before any electrochemical reaction can take place. This thesis concerns the development of methods for analysing electrode kinetics. One part involves the further development of the Global Analysis procedure to include electrodes with a spherical geometry which are traditionally the most popular form of electrodes. Simulated data is analysed to ascertain the accuracy of the procedure and then the known artifacts of uncompensated solution resistance and charging current are added to the simulated data so that the effects can be observed. The experimental analysis of 2-methyl-2-nitropropane is undertaken and comparisons are made with the Marcus-Hush electrochemical theories concerning electrode kinetics. A related section explores procedures for the kinetic analysis of steady state voltammetric data obtained at microdisc electrodes. A method is proposed under the name of Normalised Steady State Voltammetry and is tested using data obtained from a Fast Quasi-Explicit Finite Difference simulation of diffusion to a microdisc electrode. In a second area of work using microelectrodes, the electrochemical behaviour of compounds of the general formula M(CO)3(η3 - P2P1) where M is either Cr, Mo or W and P2P' is bis(2-diphenylphosphinoethyl)phenylphosphine) is elucidated. The development of instrumentation and mathematical procedures relevant to the measurement and quantitation of these systems is also investigated. The tungsten compound represents the first examples where the 17-electronfac+ and mer+ isomers are of comparable stability.

Effect of NbC and TiC precipitation on shape memory in an iron-based alloy

This paper examines the effects of TiC and NbC precipitation and prior cold rolling on the shape memory behaviour of an iron-based alloy. A precipitate-free alloy was used as a reference to investigate the relative contributions of prior-deformation and precipitation on shape memory. Heat treatment of the Nb- and Ti-containing alloys at 700 °C and 800 °C resulted in carbide precipitates between 120 nm and 220 nm in diameter. Bend testing of these samples showed a marginal increase in shape memory compared to the precipitate-free alloy. Under these conditions TiC precipitation exhibited slightly better shape memory than for NbC. However, this small increase was over-shadowed by the marked increase in shape memory that can be produced by subjecting the alloys to cold rolling followed by recovery annealing. When processed in this way, fine carbides are formed in the Ti- and Nb-containing alloys during the heat treatment. For particles >25 nm in diameter the shape memory is unaffected, but, it was found that small <5 nm particles have a detrimental effect on shape memory due to pinning of the martensite plates, thereby inhibiting their reversion to austenite. The optimum shape memory was observed in the precipitate-free alloy after cold rolling and recovery annealing.

Martensite/particle interactions and the shape memory effect in an Fe–Mn–Si-based alloy

The effect of carbide precipitates with a size range of 30–300 nm on the austenite to martensite transformation has been studied. Such particles are known to enhance shape memory, and it was the aim of this work to clarify how the particles exert a favourable effect on shape memory. Differential scanning calorimetry revealed that the presence of particles increases the amount of thermally induced martensite. X-ray diffraction showed that the presence of particles increases the amount of stress-induced martensite also. Surface-relief produced on a pre-polished surface by bending deformation showed that the particle-containing samples exhibited a more complex and highly tilted surface-relief indicative of the formation of a larger volume fraction of martensite. The reversion characteristics of the particle-containing and solution-treated samples were similar: both showed co-reversion of multiple variants of martensite within the same volume of microstructure. However, a higher volume fraction of martensite reverted for the particle-containing sample on recovery annealing. The increased density of nucleation sites for martensite formation and a higher volume fraction of stress-induced martensite for a given strain are therefore considered to be the main contributions of relatively coarse carbide particles to the improvement of shape memory performance.

Surface alloying of metals using fluid bed reactor

The use of fluidised bed reactors for surface alloying is reviewed. Research at Deakin has includes the use of chemical vapour deposition to form chromium rich layers on ferrous substrates, including stainless and tool steel grades. These layers can be modified to carbide or nitride if required by the end application. The deposition of aluminium and silicon has also been successfully achieved.

Evaluation of the thermal behaviour of bevelled cutting inserts using a numerical approach

The nose geometry of a hard and brittle metal cutting tool is generally modified in order to avoid the premature failure due to fracture under tensile stresses. While most research findings point to a favourable mechanical load pattern, the possible influence of the shape of the geometry on the thermal fields and the consequent changes in the stressed state of the tool seem to have attained less attention. The present work aims at establishing the thermal behaviour of bevelled tools under varying geometrical and process parameters. Data generated from statistically designed experiments and quick-stop chip samples are coupled to conduct numerical investigations using a mixed finite and boundary element solution to obtain the temperature distribution in bevelled carbide inserts. Due consideration is given to the presence of the stagnation zone and its size and shape. While the cutting forces and temperatures increased owing to the blunt shape of the tool, the possible absence of tensile stresses was found to be the likely effect of a more uniform temperature distribution resulting from a significant plastic contact on the principal flank and the consequent flank heat source. The characteristic low-temperature zones close to the nose of the conventional tool are taken over by the stagnation zone in bevelled tools. © IMechE 2007.

Machinability assessment and surface integrity characteristics of Austempered Ductile Iron (ADI) using ultra-hard cutting tools

The application of austempered ductile iron (ADI) is gaining an ever greater share of the worldwide ferrous product market, specifically centering on the aerospace, automotive and shipping industries. ADI is a heat treated cast iron, which exhibits remarkable mechanical properties and provides an attractive material for designers and engineers to displace conventional materials. Previous attempts, however, to machine ADI using carbide or ceramic cutting tools produced poor tool life characteristics due to the relatively poor machinability of the workpiece. This paper presents a research study that has applied the advanced technology of modern ultrahard cutting tools, in an attempt to achieve enhanced machinability performance. This performance was evaluated through the analysis of cutting forces, tool wear, surface finish and roundness.

Dielectrophoresis-Raman spectroscopy system for analysing suspended nanoparticles

A microfluidic dielectrophoresis platform consisting of curved microelectrodes was developed and integrated with a Raman spectroscopy system. The electrodes were patterned on a quartz substrate, which has insignificant Raman response, and integrated with a microfluidic channel that was imprinted in poly-dimethylsiloxane (PDMS). We will show that this novel integrated system can be efficiently used for the determination of suspended particle types and the direct mapping of their spatial concentrations. We will also illustrate the system's unique advantages over conventional optical systems. Nanoparticles of tungsten trioxide (WO₃) and polystyrene were used in the investigations, as they are Raman active and can be homogeneously suspended in water.

Dielectrophoresis-raman spectroscopy system for analysing suspended WO3 nanoparticles

Dielectrophoresis (DEP) utilizing a curved microelectrode pattern was developed and integrated with a Raman spectroscopy system. The electrodes were patterned on a Raman transparent quartz substrate, and integrated with a microfluidic channel in poly-dimethylsiloxane (PDMS). This integrated system can be efficiently used for the determination of suspended particles type and the direct mapping of their spatial concentrations. It will be demonstrated that the integration of Raman mapping with dielectrophoretically controlled WO3 particles can be used for studying suspended particles in situ.

Tuneable optical waveguide based on dielectrophoresis and microfluidics

In this work, an array of dielectrophoretic curved microelectrodes patterned in a microfluidic channel and integrated with a multimode rib polymeric waveguide is demonstrated. The microfluidic channel is infiltrated with suspended silica (SiO2) and tungsten trioxide (WO3) nanoparticles. The optofluidic system is found to be sensitive and responds not only to the infiltration of nanoparticle suspensions in the microfluidic channel, but also to the magnitude and frequencies of dielectrophoretic forces applied on the nanoparticles. The nanoparticles can be uniformly concentrated or repelled from the region between the curved microelectrode tips forming either a dense stream of flowing nanoparticles or a region void of nanoparticles in the evanescent sensitive region of the polymeric waveguide. The concentration and repulsion of nanoparticles from this region creates a refractive index gradient in the upper cladding of the polymeric waveguide. These conditions made it possible for light to either remain guided or be scattered as a function of dielectrophoretic settings applied on the nanoparticles. The results demonstrate that we successfully developed a novel tuneable polymeric waveguide based on dielectrophoretic assembly of nanoparticles suspended in fluids.

Wear characteristics of ultra-hard cutting tools when machining austempered ductile iron

Nodularised Ductile Cast Iron, when subjected to heat treatment processes - austenitising and austempering produces Austempered Ductile Iron (ADI). The microstructure of ADI also known as "ausferrite" consists of ferrite, austenite and graphite nodules. Machining ADI using conventional techniques is often a problematic issue due to the microstructural phase transformation from austenite to martensite during machining. This paper evaluates the wear characteristics of ultra hard cutting tools when machining ADI and its effect on machinability. Machining trials consist of turning ADI (ASTMGrade3) using two sets of PCBN tools with 90% and 50% CBN content and two sets of ceramics tools; Aluminium Oxide Titanium Carbide and Silicon Carbide - whisker reinforced Ceramic. The cutting parameters chosen are categorized as roughing and finishing conditions; the roughing condition comprises of constant cutting speed (425 m/min) and depth of cut (2mm) combined with variable feed rates of 0.1, 0.2, 0.3 and 0.4mm/rev. The finishing condition comprises of constant cutting speed (700 m/min) and depth of cut (0.5mm) combined with variable feed rates of 0.1, 0.2, 0.3 and 0.4mm/rev. The benchmark condition to evaluate the performance of the cutting tools was tool wear evaluation, surface texture analysis and cutting force analysis. The paper analyses thermal softening of the workpiece by the tool and its effect on the shearing mechanism under rough and finish machining conditions in term of lower cutting forces and enhanced surface texture of the machined part.

Effect of aluminum on the corrosion resistance of low-alloy steel in 10wt% sulfuric acid solution

The aqueous corrosion behavior of low-alloy steel with aluminum contents was examined in a 10 wt% H₂SO₄ (pH 0.13) solution using electrochemical techniques and surface analyses. The corrosion resistance of the new alloy steel was evaluated in terms of electrochemical parameters, such as passive current density, film, and charge transfer resistances. The results showed that a high Al content in the steel imparted better passivation behavior resulting in a lower corrosion rate. It related to the enrichment of iron carbonate and hydrocarbon by the dissolution of the carbide phase.

Studies of a wear resistant cast iron

 The objective of this investigation was to set down (on the base of the results obtained by the examination of white cast iron alloys with different content of the alloying elements) a correlation between chemical composition and microstructure, on one hand, and the properties relevant for this group of materials, i.e., abrasion wear resistance and fracture toughness, on the other. Experimental results indicate that the volume fracture of the carbide phase, carbide size and distribution, as well as the morphology of eutectic colonies, had an important influence on the wear resistance of white cast iron alloys under low-stress abrasion conditions, whereas fracture toughness was determined largely by the matrix microstructure.