Improved dust capture methods for crushing plant

The use of compressive crushing equipment such as gyratory crushers within minerals processing plants can potentially generate large quantities of dust. Remedies to this problem include the retrofitting of shrouds, enclosures, local exhaust ventilation (LEV) systems and water suppression systems. The single or combined application of these systems must be optimised to ensure they operate efficiently. It is desirable that the future design planning of such facilities include integrated dust suppression and/or removal systems to ensure material delivery rates are maintained and the welfare of the workforce is protected.     

Pulsed KrF laser deposited GaN/TiN/Si(111) heterostructures by sequential TiN and liquid Ga laser ablation

GaN/TiN heterostructures were deposited on 4° miscut Si(111) substrates by pulsed KrF laser ablation of TiN through vacuum, followed by reactive pulsed KrF laser ablation of liquid Ga through 70-75 mTorr of microwave-activated NH₃. Deposition temperatures of 950 °C and 1050 °C were employed for the TiN layer while 900 °C was employed for the GaN layer. The targets were positioned 5 cm from the substrate and ablated by using a reimaging beamline at a nominal energy density of 3-4 J/cm². X-ray diffraction (XRD) revealed a highly textured heterostructure with GaN(0001)//TiN(111)//Si(111) and with a rocking curve width for both GaN(0001) and TiN(111) equal to ~1.1°. The mosaic spread through the TiN(001) reflection was ~1.3°, whereas that of the GaN(101_1) was undetectable because of low S/N. Scanning electron microscopy revealed large oriented 10 7m-sized hexagonal crystallites decorating large depressions in the TiN film with many smaller pits also present. The effect of substrate processing and TiN film processing on pit formation was explored.     

Self-organized silicon microcolumn arrays generated by pulsed laser irradiation

Cumulative nanosecond pulsed excimer laser irradiation of silicon produces an array of high-aspect-ratio microcolumns that protrude well above the initial surface. The growth of these microcolumns is strongly affected by the gas environment, being enhanced in air or in other oxygen-containing atmosphere. An array of very large and complex conical structures that also protrude above the surface is formed if the irradiation is performed in sulfur hexafluoride (SF₆). Kinetics studies of microcolumn growth show that: (i) A certain number of pulses is required to initiate growth of microcolumns; (ii) column nucleation is inhomogeneous, taking place always at the edges of deep grooves or pits; (iii) growth is fast with the earlier pulses but slows down to a halt when the columns reach a certain length. These studies show that columns nucleate and grow by continuous influx of silicon with each laser pulse. It is proposed that the axial growth of microcolumns and cones is due to the deposition of atoms or clusters at their tips. The column/cone tips are melted during irradiation and act as preferred sites for deposition, resulting in a very high axial growth rate. The contribution of etching and ablation to the flux of silicon-rich vapor produced during irradiation is discussed. The mechanism of columnar growth is compared with the vapor-liquid-solid method to grow silicon whiskers.     

Resonance-enhanced multiphoton ionisation photoelectron spectroscopy of the ClO radical: the C 2 sigma- state

A (2 + 1) one-colour resonance-enhanced multiphoton ionisation study is carried out on the C 2 sigma- state of the ClO radical in the one-photon energy range 29,500-31,250 cm-1. The ClO radical is produced by one-photon photolysis of ClO2 employing 359.2 nm photons derived from a separate laser. In this way a significant concentration of vibrationally excited ClO in its spin-orbit split X 2 pi omega (omega = 3/2 or 1/2) electronic ground state is produced. In addition to mass-resolved excitation spectra, kinetic-energy resolved photoelectron spectra for the X 3 sigma-(v+)<--C 2 sigma-(v' = 3-5) transitions are measured. These transitions are not completely Frank-Condon diagonal, and indicate a decrease in bond length on removal of the Rydberg electron from the C 2 sigma- state. In addition to an unambiguous assignment of the C 2 sigma- state, valuable information is obtained on the degree of vibrational excitation with which the nascent ClO radical is formed in the photolysis of ClO2. Analysis of the photoelectron spectra is supported by Franck-Condon calculations based on potential energy curves either from experimental spectroscopic parameters, or obtained by theoretical ab initio methods.     

On dual and triple integral equations involving modified bessel functions

A generalisation of some tripe integral equations occuring in the solution of certain mixed boundary value problems involving the wave equation is investigated. It is found that the solution of the equations can be expressed in terms of the solution of a Fredholm intgral equation of the second kind and that a related pair of dual integral equations can be solved exactly     

Photoelastic determination of stresses in multiple-pin connectors

The design, fabrication, and testing of photoelastic models of double-lap, multiple-pin connectors are discussed. Interest is in the stresses in the inner laps. These stresses are determined by constructing models with photoelastic inner laps and transparent-acrylic outer laps. The connectors have two pins, in tandem, parallel to the load direction. A photoelastic-isotropic point is shown to permit the evaluation of load sharing between the two pins. A numerical scheme, utilizing the isochromatic- and isoclinic-photoelastic data and a finite-difference representation of the planestress equilibrium equations, is used to compute the stresses around the two pins. Representative stress distributions and stress-concentration factors are shown.     

Soft mode behavior in RbH2AsO4

The low frequency xy Raman spectra of RbH₂AsO₄ are reported as a function of temperature in the paraelectric phase and are fitted to a coupled damped harmonic oscillator model to yield the soft mode behavior of the ferroelectric model.     

Raman spectra of rubidium dihydrogen arsenate in its paraelectric phase1

The Raman spectra of RbH₂AsO₄, are presented as a function of temperature for the paraelectric phase and are used to investigate the molecular structure of this phase and to investigate the coupled proton—phonon mode responsible for the onset of the ferroelectric phase.