Showing papers by "National Physical Laboratory published in 1984"

AES: Energy calibration of electron spectrometers. I—an absolute, traceable energy calibration and the provision of atomic reference line energies

Abstract: Atomic standards of binding energies are presented for the calibration of X-ray photoelectron spectrometers. The binding energies are measured using a VG Scientific ESCA 3 Mk II for which the photoelectron peak positions can be established with a measurement precision standard deviation of 5 meV. The absolute calibration of the voltage scale is established with an accuracy of 11 ppm over the binding energy range 0–1250 eV, using a measurement chain traceable to the NPL primary voltage standards. The zero of energy is set to ±11 meV on the differential of the Ni Fermi edge using Mg Kα12 radiation and absolute binding energies, for the Cu 2p3/2, Cu L3MM, Cu 3p, Ag 3d5/2, Ag M4NN and Au 4f7/2 peaks, are established with errors of 0.01 to 0.02 eV. An analysis is made of literature calibrations to assess their zero setting and voltage scaling errors. Preliminary tests have been made to show that the calibrations may be reproduced on instruments outside NPL using a simple work procedure.

Modification to the JPC79 Colour–difference Formula

Abstract: The JPC79 colour–difference formula has represented a substantial improvement over earlier formulae and is being applied successfully in industrial shade passing. Modifications are described which overcome certain problems and, to some extent, simplify the formula. With available experimental data, the modified version performed even better than the original formula. Perceptibility data are fitted better by increasing the JPC79 lightness weighting by a factor of two. The new formula, designated CMC (: c), has the best overall performance of any formula so far published.

Magnesium diffusion, surface segregation and oxidation in Al-Mg alloys

Abstract: Auger electron spectroscopy (AES) has been used to follow the surface segregation behaviour of magnesium at the surface of Al-Mg alloys in the temperature range up to 600° C as a function of time The evaporation rate of magnesium from the magnesium-rich surface has also been measured The combination of the competing processes of segregation and evaporation has been treated theoretically and compared with the experimental measurements The measured equilibrium surface enrichment of magnesium fell from a factor of 24 at 100° C to 12 at 200° C At higher temperature the evaporation rate exceeded the segregation rate and the surface layer became magnesium-depleted The data also lead to a low-temperature determination of the diffusivity of magnesium in aluminium The same Al-Mg alloys have been heat-treated, within a similar time-temperature regime, in air The oxide films have been composition-depth profiled using AES with ion sputtering, and measurements of the rate of oxide growth lead to information about the diffusivity of magnesium through the oxide films

Finite amplitude distortion of the pulsed fields used in diagnostic ultrasound

Abstract: A simple theoretical model of the non-linear propagation of pulsed focused acoustic beams is described. It enables the distortion of the peak cycle of the pulse to be calculated from a few experimentally measured parameters. The model is discussed, and justified for application to the fields from medical ultrasonic diagnostic equipment. It is particularly relevant for specifying the degree of distortion present, as might be required by future written standards for diagnostic equipment performance. Preliminary experimental verification of the model is reported.

Quantitative XPS: The calibration of spectrometer intensity—energy response functions. 1—The establishment of reference procedures and instrument behaviour

Abstract: The ASTM E-42 committee round robin on XPS measurements found, in a simple survey, that the intensity-energy response of electron spectrometers was unacceptably unreliable. In this paper new, high accuracy, reference procedures are developed to define the relative intensity-energy response function of spectrometers, for the constant ΔE and ΔE/E modes, for analysts to calibrate their own instruments. Two procedures are developed, one involving the measurement of peak areas, for Cu, Ag and Au, carefully specified to reduce the effects of measurement noise, and the second, for use on well-designed spectrometers, through the measurement of the spectrum background. The measurements on Cu, Ag and Au reference foils show that intensity ratios are reproducible to within 2% standard deviation and, from preliminary tests, that the ratio of the response functions of a VG Scientific ESCALAB I and the NPL ESCA 3 Mk II is proportional to E0.094, except for the low pass energy of 20 eV in the ESCALAB I where the proportionality changes to E−0.156. Similarly the ratio of the functions for a Perkin-Elmer PHI 550 and the VG Scientific ESCA 3 Mk II is proportional to E−0.244 over the normal XPS measurement range to an accuracy of 2%.

Quantitative XPS: The calibration of spectrometer intensity—energy response functions. 2—Results of interlaboratory measurements for commercial instruments

Abstract: Deux methodes d'evaluation de la fonction reponse sont testees: la mesure de la surface des pics et les donnees de fond des spectres de feuilles de Cu, Ag et Au

An International Intercomparison of Fixed Points by Means of Sealed Cells in the Range 13.81 K–90.686 K

Abstract: An International Intercomparison of Fixed Points by Means of Sealed Cells has been conducted under the auspices of the Comite Consultatif de Thermometrie (CCT) between 1978 and 1984. Forty-one sealed cells, realizing the triple point of seven different substances, defining both primary fixed points of the IPTS-68 and secondary fixed points in the temperature range from 14 K to 90 K, were supplied by nine laboratories. They were measured in eleven national laboratories around the world, against the fixed points realized in these laboratories (both in open cryostats or in other sealed cells). Some 150 independent series of data were produced, from almost 300 melting experiments, representing some 2,300 equilibrium temperature values. The basic sets of results are presented, concerning the agreement between different cell realizations and the comparison of national IPTS-68 realizations. Data connecting the results of this intercomparison with that performed at NPL in 1975 using calibrated thermometers are also given.

Conversion of phenol formaldehyde resin to glass-like carbon

Abstract: Glass-like carbons have been produced for many years by the careful carbonization of a variety of starting materials such as cellulose, phenol formaldehyde, polyfurfuryl alcohol, acetone furfuryldehyde and other suitable thermosetting resins. A number of publications have appeared in the literature concerning their characteristics and applications. However, little is known about the preparation procedure and its influence on the development of this form of carbon. The present paper incorporates the studies on the carbonization behaviour of a suitable phenol formaldehyde resin and on the optimization of the phenol to formaldehyde molar ratio in the resin, carried out with respect to the various physical characteristics of the resins and the resulting carbons. The implications of these studies have been disucussed in detail.

Effects of surface treatment on the mechanical properties of carbon fibers

Abstract: Surface of the carbon fibers developed from PAN (polyacrylonitrile) has been modified using such methods as air oxidation, nitric acid treatment, and anodic (electrolytic) oxidation. By choosing optimum treatment parameters, the tensile strength of such fibers has been found to increase by about 60 percent over that of the untreated value. A quantitative estimation of the surface groups formed during the treatment shows an increase in number with severity of the treatment. Further, removal of these functional groups from the fiber surface during degassing at 1000°C also influences the mechanical properties of the carbon fibers considerably. Results have been discussed in detail.

Environmental, Stress-State and Section-Size Synergisms During Creep

Abstract: The time-dependent deformation and fracture characteristics of Inconel alloy X-750 have been studied at 700 $^\circ$C under uniaxial and biaxial stressing. Several unusual sets of results were obtained, which led to the discovery of synergistic interactions between the material and the environment employed during heat treatment. For example, when solid tension and thin-wall tubular torsion specimens were given the normal commercial heat treatment, lifetimes in torsion were found to lie outside the region delineated by the plane-stress isochronous rupture loci generated when fracture is controlled respectively by the maximum principal stress and the von-Mises effective stress. This is contrary to predictions of creep fracture models and at variance with published experimental work. The isochronous rupture behaviour only became `normal' when torsion life-times were compared with those obtained from tension tests on tubular specimens for which lifetimes were less than 5 % of those for solid ones. This unusually large effect of section size on lifetime was shown to be due to a corresponding change in creep resistance, rather than to a reduced fracture ductility. Detailed metallography identified the responsible micromechanism as being a very fine cavity dispersion in the near-surface region, which caused progressively more weakening as the section size was reduced. This profuse and spatially inhomogeneous cavitation was demonstrated as not being an inherent characteristic of the material but the result of some interaction with the environment-speculated as being the formation of metastable carbon dioxide gas bubbles - during heat treatment of testpieces.

AES and XPS depth profiling certified reference material

Abstract: On presente deux materiaux de reference permettant de calibrer le systeme de mesure en XPS ou AES. Il s'agit de couches minces de pentoxyde de tantale d'epaisseurs 30 et 100 nm avec des largeurs d'interface de 1,53 et 1,86 nm

Preparation, temperature and composition dependence of some physical and electrical properties of mixtures within the NiO-Mn3O4 system

Abstract: The NiO-Mn3O4 mixtures using cryochemically prepared powders have been made. Resitivity of the mixtures in the system with Ni1−xMn2+xO4 has been measured as a function of temperature and composition. Bulk densities, temperature coefficient of resistance, activation energy, bias voltage and time constant have also been determined. A fairly wide range of composition exists in the system suitable for thermistor application.

Is Ada too big? A designer answers the critics

Abstract: Many have criticized the Department of Defense's new computer language, Ada, saying it is too large, too complicated, or too difficult to use. Are they right? And are there some simplifications that could be made to Ada without destroying its usefulness?