Table of contents

The characteristics of wear debris found in the lubricant flow of a machine are reviewed along with their relationships to specific wear processes. Current wear-debris detection and analysis techniques are described with reference to systems at the research and development stage. The features of these systems are compared with those of an ideal system and an outline of a novel technique is given.

The authors have developed a simple continuous-cooling method to determine specific heat of liquids and solids in the temperature range 100-300 K. The technique employs very simple instrumentation and continuously records the sample temperature as it cools to the bath temperature through a calibrated heat link. They have obtained specific heat values which agree with the reported data to within 3% for the samples investigated. This method also facilitates easy detection of abrupt changes in specific heat, as demonstrated in the observation of glass transition in some organic glass-forming systems. The method is sensitive to the study of relaxing heat capacity in supercooled liquids.

The authors describe a new technique, frequency-resolved capacitance spectroscopy (FRCS), for observing deep-level emission rates in semiconductor diodes and determining their activation energies. The technique uses a simple swept-frequency capacitance bridge with quadrature phase-sensitive detection.

A technique has been developed for measuring magnetisation in very high magnetic fields (up to 90 T) produced by single-turn coils. The system is applied for measurements of high-field magnetisation of magnetic substances in a wide temperature range from room temperature down to 4.2 K. In a simple magnetic system, the one-dimensional Ising antiferromagnet CsCoCl₃, the magnetisation curve was successfully obtained up to 90 T including a stepwise change around 40T at 4.2 K.

Details are presented of the design of a small DC planar magnetron source and its use in a research-scale UHV getter sputter deposition system. The system has been used for depositing a range of refractory materials as well as some metal multilayer structures (single crystal, polycrystalline and amorphous). For some of these structures a relatively high sputtering pressure is required and a study has been made of the deposition rate as a function of pressure for a range of different elements. This illustrates the effect of the momentum and energy transfer of the sputtered atoms as they travel from the target to the substrate.

The authors describe a variable-pathlength cell for measuring the optical absorbance, turbidity and diffuse scattering of fluids. The cell is easily filled, demounted and cleaned. It requires a few microlites of fluid, has no moving parts and requires no delicate adjustments. Reproducible results can be obtained at pathlengths of a few micrometers. Results using the cell are given for absorbent and turbid fluids, and for diffuse scattering, large particle dispersions where the particle diameter can be larger than the smallest pathlength of the cell.

The authors describe the use of a zone plate as the dispersing element in a monochromator in which the spectrum is scanned by means of a linear axial displacement. It is considered for use as a wavelength-encoded linear displacement transducer and is shown to be both effective and simple to construct.

The design, construction and performance of a position-sensitive particle detection system for the use in experiments involving the scattering or dispersion of atoms or ions is described. The device may have applications in atomic and molecular scattering, mass spectrometry and other similar fields where the arrival in position and time of particles must be monitored. In the present realisation (designed for use in atomic collision experiments) an angular resolution of 0.1 degrees , a response time approximately 10 ns and a detection efficiency >90% have been achieved.

A microcomputer-based image processing system was constructed to acquire, process and display images of transmission electron micrographs. The system hardware consisted of a video camera, microcomputer unit, video digitiser and frame buffer boards. The software developed consisted of powerful functions for image display, saving and image manipulation. Other functions such as filtering and contrast enhancement were also included. The user is offered a friendly interactive environment, and no previous experience in image processing or computer programming is needed to operate the system. Development of an efficient program allowed many functions to be executed with the limited resources available on the microcomputer unit. Calculated theoretical images created by the system are compared with experimental images taken by the video camera. Images are displayed on the video monitor which are more meaningful to human eyes than conventional hard copy printouts. Also, the use of contrast enhancement techniques allows hidden information to be extracted from experimental images. Preliminary studies of identifying stacking faults in transmission electron microscopy using this system were very encouraging.

An automatic spectrum scanner with an automatic window selector for use with single-channel analysers has been designed and constructed. The performance of the device has been fully tested by collecting gamma-ray spectra of standard radioactive sources using the module in a spectroscopy system. The spectra obtained are in perfect agreement with those obtained using a multichannel analyser. Because of its simplicity, the module is well suited for automatic spectral data acquisition especially in teaching and small laboratories.

A new pulsed x-ray source is studied and used to preionise the discharge of a high-pressure CO₂ laser. A uniform linear x-ray beam (6 mm wide, 150 mm long, 20 keV mean energy) is obtained from runaway electrons generated in a 30 Pa pressure helium fast discharge ( approximately 20 ns FWHM) in overvoltage (60 kV) at high current (1.2 kA). Using a carbon-felt cathode and a tantalum anode with 6 mm spacing. x-ray production efficiency is 80% of that obtained in a vacuum. The electronic density measured in the ionisation chamber is 10¹³-10¹⁴ electron/m³. The laser output energy obtained in CO₂:N₂:He=1:1:8 mixture for V=35 kV at 500 kPa is 80 mJ with a 2% efficiency.

Using a curvable collimator crystal, a vertical plane of incidence, a variable camera geometry and microprocessor control this camera extends the application range of double-crystal topography to curved samples and is well suited for research and routine work. Characteristic features are short exposure times, horizontal sample arrangement and automated sample adjusting.

The Newton-Raphson method is widely used in Mossbauer spectroscopy to fit a spectrum to a number of Lorentzian-shaped lines. Although most Mossbauer spectrometers are now built around a personal computer, such computers are generally too slow for the fitting of spectra. The author discusses a concurrent version of the Newton-Raphson algorithm and its implementation on an accelerator based on a network of INMOS transputers, interfaced to a personal computer. A very significant speed-up factor is obtained with a small number of transputers; for example, the fitting time for a six-line 512-channel spectrum is 2.6 s per iteration with a four-transputer accelerator, compared with about 72 s on a Victor AT computer. Although the work has been applied to the fitting of Mossbauer spectra, the results are equally applicable to other least-squares fitting problems.

The electrical and output parameters of a high pressure pulsed CO₂ laser with plasma cathode are presented. The gain profile is also measured. The use of a sliding discharge as a pre-ionisation source and a plasma cathode permits the achievement of laser action and a high gain coefficient in helium-free mixtures at pressures of up to 8 atm (800 kPa).

A new viscometer especially designed for the high viscosity region is presented. The magnetoviscometer uses Stokes' falling sphere principle, where the gravitational force is substituted by a magnetic one. The working principle and set-up of the apparatus are described; some results obtained on technical polymers are given and special features of the magnetoviscometer (such as measurement under pressure and the use of disposable cells) are emphasised.

The influence of velocity gradients on hot-wire anemometry with an X-wire probe were investigated. Analysis showed a strong possibility that the values obtained by the usual method of measurements with an X-wire probe involve serious experimental errors caused by the velocity gradients. In order to eliminate these errors, the authors devised an entirely new method of measurement on the basis of the analysis. In this method, two X-wire probes, one of which is the mirror image of the other, are used for measuring a quality at a location. Then an ultimate value of the quantity at the location is given as an arithmetic mean of the values obtained from the two probes. The validity of the analysis was confirmed by measurements of a turbulent flow in a square duct with the present method. The results showed that the present method is very effective for the measurement of quantities such as the secondary flow velocities and the turbulent shear stresses, quantities which are very sensitive to the influences of velocity gradients.

The design, manufacturing procedures and results of testing a new pulsed-wire probe are presented. This probe is used for measuring Reynolds stresses in highly turbulent low speed air flows containing high mean shear gradients. Pulsed wire probes of the standard type suffer from measurement errors when the pulsed wire is oriented in or at 45 degrees to the main shear direction of such flows. This is due to the shearing of the thermal cloud giving the time of flight information which is used for measuring the instantaneous velocity. The new probe design proposed is designed in a fashion to avoid these 'gradient effects'; it is furthermore shown that aerodynamic interference effects have also been minimised. A detailed description of the manufacturing process is given.

A measuring set-up for the investigation of the laser blow-off process of thin metal films is described. The velocity of the blown-off plasma particles and the smearing of the flying plasma ball are measured.

A general-purpose temperature controller based entirely on the 723 integrated voltage regulator is described. It is very compact in size (20*20*30 mm³), does not create any electric disturbances during its functioning and is easy to build and install. The controller's supply can be in the range 9.5-40 V, the efficiency is close to 100%, the electronic circuit is highly reliable and cheap. With a conventional diode as a temperature sensor the temperature controller offers +or-0.03 K h^-1 stability. When necessary, improved stability can be achieved using more sensitive temperature sensors.

The theory and fabrication of an active RC frequency-to-voltage convertor (FVC) are given. Its operation is based on the principle of an active frequency-selective bridge. The convertor is studied in detail. It is shown to give an output voltage which is directly proportional to the frequency deviation delta (= Delta omega / omega ₀), over a fairly wide frequency range. The current sensitivity of the circuit is at least four times that of the popular Wien bridge. It is found to be useful in the frequency range from a few hertz to about 100 kHz with a general purpose operational amplifier. The experimental results show close conformity with theory.

A fast voltage clamp circuit is described which permits the electrical potential difference of the plasma membrane of large plant cells to be controlled in less than 1 ms. It can supply a large current.

A variable pressure infrared absorption cell of 62 mm pathlength operating at pressures up to 3 MN m^-2 and between 4 and 300 K is described. A brief account is given concerning the selection of optical windows and body materials, stress calculations and techniques for sealing the optical windows.

An inexpensive heating stage was developed for the preliminary investigation of low-temperature brazing alloys. The device fitted the standard specimen stage of the ISI Super IIIA scanning electron microscope and operated at about 600 degrees C for up to 30 min without cooling. Observations of the melting of a Cu-P-Sn alloy are reported.