Showing papers by "National Physical Laboratory published in 1999"

Viscosities of ironmaking and steelmaking slags

Abstract: A model based on the optical basicity corrected for the cations required for the charge balance of AlO5-4 is investigated. This model has the advantage of being generally applicable and not limited to slags of a certain composition. The calculated results were in reasonable agreement with traceable experimental data for a range of synthetic slags and industrial iron- and steelmaking slags. The latter included mould fluxes and blast furnace, steelmaking and coal slags. For most slag compositions here, the viscosities predicted with the present model were in better agreement with the measured values than those predicted by the Riboud and Urbain models; coal slags were the only exception. In the case of CaF2 containing slags, the results indicate that an optical basicity of CaF2 of 1·2 provided the best fit to the viscosity data.

Analysis of the instrumental line shape of high-resolution fourier transform IR spectrometers with gas cell measurements and new retrieval software.

Abstract: The instrumental line shape (ILS) of two commercial high-resolution Fourier transform IR spectrometers has been analysed with gas cell measurements and a new ILS retrieval software LINEFIT. The instruments are used for atmospheric remote sounding, and the compatibility of the ILS deduced from laboratory gas cell measurements with the ILS in the atmospheric measurement itself is examined.

Review of naphthenic acid corrosion in oilrefining

Abstract: Naphthenic acid corrosion is a major concern for the oil refinery business. While much is now known about the phenomenon, it is still not completely understood because of the complex influences on corrosion of the type of acid and other constituents in the crude oil and the effects of both temperature and fluid flow. A review of this form of corrosion has been undertaken with respect to the role of crude oil composition, temperature, fluid velocity, physical state (vapour or liquid), pressure, and materials of construction. Simple measures of corrosivity based on the total acid or neutralisation number are insufficient. The sulphur content of the crude is important but the extent to which the various sulphur containing compounds act as inhibitors or corrodents is not understood. There is little knowledge also of the nature of films formed on the steel surfaces under operating conditions and the role of natural inhibitors that may be present in crudes requires more attention.

Design for a compact high-accuracy CMM

Abstract: The trend towards miniaturisation in manufacturing has led to a requirement for a coordinate measuring machine (CMM) capable of measuring tiny features on small components. A compact CMM has been designed and built which has a working volume of a cube of side 50 mm, and a measurement uncertainty estimated to be 50 nm. The machine utilises a self-calibrated solid cube to provide a geometrical reference that is transferred into the CMM by means of a combination of three, mutually orthogonal, mirrors, six laser interferometers and three dual axis autocollimators. In situ measurement of the mirrors' flatness and orthogonality and redundancy of measurement are used to minimise systematic uncertainties. This paper describes the design of the CMM and an overview of the theoretical uncertainty analysis.

Comparison of test configurations for determination of mode II interlaminar fracture toughness results from international collaborative test programme

Abstract: This paper presents a summary of the tests performed within a Versailles Project on Advanced Materials and Standards collaborative test programme to examine the measurement of mode II interlaminar fracture toughness using four different test methods based on end notched flexure, stabilised end notched flexure, end loaded split, and four point end notched flexure carbon fibre reinforced epoxy specimens. Tests were performed by members of the European Structural Integrity Society, the Japan Industrial Standards group, and the American Society for Testing and Materials.

Imaging properties of the Gabor superlens

Abstract: A superlens is an optical system consisting of a pair of microlens arrays in which there is a slight difference in pitch. The relative displacement of one lens with respect to its partner causes the bundle of light passing through a pair of lenses to be deviated in such a way that all bundles converge to a common point and the system behaves like a lens. The focal properties are very different from those of a conventional lens and were originally described by Gabor in 1940. We have extended his analysis and have taken advantage of modern technology to assemble superlenses and confirm their properties experimentally.

Characteristics of aqueous polycarbazole batteries

Abstract: The characteristics of electrochemically prepared polycarbazole (PCARB) as the cathode active material for secondary batteries are studied in aqueous electrolytes The cell of the type Zn/Zn(ClO 4 ) 2 /PCARB has a specific capacity of 30 Ah/kg and an energy density of 46 Wh/kg The coulombic efficiency is about 80-90% and is dependent on the thickness of PCARB films Cole-Cole plots for PCARB electrodes by impedance measurements have been obtained at different oxidation potentials as a function of doping

Experimental studies of viscosities of some CaO–CaF2–SiO2 slags

Abstract: In the present work, the viscosities of some CaO–CaF2–SiO2 slags were measured using the rotating cylinder method. The effects of various volatile fluorine compounds on the change in slag composition are discussed on the basis of thermodynamic calculations. The kinetic factors concerning the escape of the volatile fluorides under the experimental conditions were also examined. It was found that the formation of gaseous species SiF4 was the main source for compositional changes during the viscosity measurements. In the case of CaO–CaF2–SiO2slags, the formation of SiF4 would be somewhat limited owing to the existence of CaO. The composition change during the measurements was only about ±1 wt-% for all components in most cases. Viscosity measurements are reported for slags, based on the post-measurement compositions. It was found that the addition of CaF2 causes a significant decrease in viscosity.

Extending the frequency range of the National Physical Laboratory primary standard laser interferometer for hydrophone calibrations to 80 MHz

Abstract: A method for the primary calibration of hydrophones in the frequency range up to 60 MHz is described. The current National Physical Laboratory (NPL) primary standard method of calibrating ultrasonic hydrophones from 500 kHz to 20 MHz is based on optical interferometry. The acoustic field produced by a transducer is detected by an acoustically transparent but optically reflecting pellicle. Optical interferometric measurements of pellicle displacement at discrete frequencies in tone-burst fields are converted to acoustic pressure, and the hydrophone for calibration is substituted at the same point, allowing sensitivity in volts per pascal to be obtained directly. For calibrations up to 60 MHz, the interferometer is capable of measuring the displacement of the pellicle as a function of frequency in a harmonically rich nonlinear field up to and including the 12th harmonic of the shocked field generated by a 5 MHz focusing transducer, allowing hydrophones to be calibrated by substitution in the same field. Sources of uncertainty in the new method have been investigated. Best combined random and systematic uncertainties at the 95% confidence level for the new method are 7% at 20 MHz, 11% at 40 MHz, and 16% at 60 MHz.

Influence of pitting on the fatigue life of a turbine blade steel

Abstract: The role of pits as stress raisers and their influence on fatigue life has been investigated for a 12Cr turbine blade material. A particular feature of this work was the establishment of an electrochemical procedure for generating pits with ‘controlled’ pit depth and low density. Pits grown under laboratory conditions were partially spherical in shape and simulated, in general appearance, those observed in service. In terms of the threshold stress intensity factor, the results supported the concept of pits acting as effective cracks of the same depth, provided that a short crack model based on an effective crack length is used.

Proposed standard thermal test object for medical ultrasound.

Abstract: A general design for a thermal test object (TTO) is proposed. A number of novel features make the design particularly suitable for use as a standardised device for assessing the heating capability of diagnostic ultrasound beams. To assess performance, soft-tissue TTOs have been made containing thin-film thermocouples sandwiched between discs of tissue-mimicking gel. Installed in an appropriate measurement system, these TTOs exhibit excellent thermal and spatial resolution, allowing the ultrasound beam to be located rapidly and reproducibly. The measured temperature rise after 3 minutes of heating has been compared with theoretical predictions based on measured pressure distributions, and agreement is within 10%. Other studies have shown that soft-tissue– and bone-mimicking TTOs can be used to evaluate a wide range of ultrasound fields and that different physical tissue models can be simulated. It is concluded that this design would be suitable for providing reference assessments of the thermal hazard posed by diagnostic ultrasound under standardised conditions.Crown copyright. Reproduced by permission of the Controller of HMSO.

Understanding limitations of through thickness test methods

Abstract: Through thickness properties are increasingly important for the detailed analysis of complex composite structures. Recent papers and research have proposed a variety of test method solutions for the determination of through thickness properties. A comprehensive experimental evaluation has led to the drafting of standards for through thickness tension, compression, and shear test methods. A detailed comparison of the mechanical test methods, data, and failure modes is presented. An assessment is made of their utility, applicability, and limitations, highlighting sensible test precautions. In selected cases, comparisons with elastic constant data obtained using ultrasonic techniques are provided. Despite a number of difficulties, tension and compression specimens are relatively easy to design, provided the test material is of sufficient thickness (e.g. 20 mm). Shear test methods are not so easily defined, such that none is applicable to all materials or all directions, and failure modes may be neither initiated nor dominated by shear.

A comparison of grain imaging and measurement using horizontal orientation and colour orientation contrast imaging, electron backscatter pattern and optical methods

Abstract: The problems associated with the definition of a grain, grain size measurement, and the issues associated with making one- and two-dimensional measurements on a three-dimensional structure are discussed. The relatively new scanning electron microscope (SEM)-based techniques of colour orientation contrast imaging (COCI) and automated electron backscatter pattern (EBSP) are explained and examples given. Comparisons with conventional (horizontal) orientation contrast imaging (HOCI) in the SEM are made. A direct comparison is made between conventional metallographic methods and these new techniques on precisely the same region of an interstitial free iron specimen. Both optical imaging and HOCI were found to miss a large number of grain boundaries (7 and 12%, respectively), and to create boundaries (≈ 2%). COCI was found to be reliable, with only 3% of boundaries missed. EBSP was taken to be the standard against which the others were compared, as it unambiguously measured changes in crystallographic orientation. Errors in the number of grain boundaries that are detected have a considerable effect on grain size measurements, e.g. mean linear intercept, and a follow-on effect on the modelling of mechanical properties. New methods for increasing the acquisition speed of orientation maps are discussed, along with examples. The combination of COCI (for grain location) and EBSP (for orientation measurement) is promising, but requires improvements in either imaging or image analysis to be totally reliable.

Biaxial disc flexure – modulus and strength testing

Abstract: There is widespread use of biaxial testing of ceramics, but relatively little information concerning the accuracy of testing, and the pitfalls that can arise unless the test is carefully prescribed. The present paper reviews recent work in measuring elastic moduli using a biaxial natural frequency method, and in investigating some of the potential sources of error in strength testing.

Measurement of the s-2(1/2)-d-2(5/2) clock transition in a single yb-171(+) ion

Abstract: Spectroscopy of the 411-nm transition in 171Yb+ has been performed and the feasibility of its use as an optical frequency standard has been demonstrated. The 2S1/2(F=0, mF=0)-2D5/2(F=2, mF=0) frequency, at zero-magnetic field, has been measured to be 729 487 779 566(153) kHz. This transition is free from the first-order Zeeman shift and has a measured second-order shift of +0.38(8) Hz/(μT)2. In addition, the hyperfine structure of the 2D5/2 level has been deduced by driving the other hyperfine components of the 411-nm transition, showing it to be inverted. The 2D5/2 hyperfine splitting, measured to be -191(2) MHz, implies an A factor of -63.6(7) MHz. These data taken in conjunction with previous work yield an isotope shift of ν171-ν172=+1317.1(1.3)MHz for this transition between the 171 and 172 isotopes.

Electrical Properties of Sol-Gel Processed Amorphous BaTiO3 Thin Films

Abstract: BaTiO3 thin films were prepared on single crystal silicon (1 0 0) and platinum substrates by sol-gel technique. Amorphous films with thickness uniformity were obtained by spinning the solution at 3000 rpm for 30 s and by post-deposition annealing at 400°C. The films exhibited good dielectric and insulating properties. The dielectric constant and dissipation factor at a frequency of 100 kHz were 17 and 0.20, respectively, for 1400 A thick film on platinum substrate (MIM). The corresponding values were 16 and 0.015 for films on Si (MIS). Dielectric properties were also studied as functions of frequency and voltage. The C-V curve for MIS structure exhibited a hysteresis. The density of interface states recharged during the bias cycle in hysteresis measurement was estimated to be of the order of 2.10 × 1011 cm−2 and total oxide charge density was about 4.28 × 1011 cm−2. I-V measurements were performed on films of different thicknesses. The leakage current densities at 5 V for the films having thicknesses 1400 and 2800 A were 0.86 and 0.11 μA/cm2 respectively. The conduction mechanism is found to be Poole-Frenkel and Schottky mechanisms at low and high fields, respectively.

Subkilohertz comparison of the single-ion optical-clock 2 S 1/2 - 2 D 5/2 transition in two 88 Sr + traps

Abstract: A simultaneous observation of the optical-clock ${}^{2}{S}_{1/2}{\ensuremath{-}}^{2}{D}_{5/2}$ transition at 674 nm, in two separately trapped single ${}^{88}{\mathrm{Sr}}^{+}$ ions, is reported. Two nominally identical miniature rf Paul traps were used together with a 674-nm sideband-injection-locked extended-cavity diode laser. This ``slave'' laser was optically phase locked about 650 MHz away from a ``master'' diode laser, which was itself locked to a high-finesse, ultra-low-expansion (ULE) cavity. The ULE cavity was temperature-stabilized and suspended in an evacuated enclosure, and provided an ``optical flywheel'' reference standard with a relative drift rate of better than 1 part in ${10}^{11}$ per hour. The difference between center frequencies of the single ${}^{88}{\mathrm{Sr}}^{+}$-ion 674-nm (445-THz) transition multiplet in two traps was 120(90) Hz (one standard uncertainty). Thus the two trap center frequencies agree to 3 parts in ${10}^{13}.$