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The CCQM-K148.a comparison was coordinated by the BIPM on behalf of the CCQM Organic Analysis Working Group for NMIs and DIs which provide measurement services in organic analysis under the CIPM MRA. It was undertaken as a "Track A" comparison within the OAWG strategic plan. CCQM-K148.a demonstrates capabilities for assigning the mass fraction content of a solid organic compound having moderate molecular complexity, where the compound has a molar mass in the range (75 - 500) g/mol and is non-polar (pKow < −2), when present as the primary organic component in a neat organic solid and where the mass fraction content of the primary component in the material is in excess of 950 mg/g.
Participants were required to report the mass fraction of Bisphenol A present in one supplied unit of the comparison material. Participants using a mass balance method for the assignment were also required to report their assignments of the impurity components present in the material. Methods used by the seventeen participating NMIs or DIs were predominantly based on either stand-alone mass balance (summation of impurities) or qNMR approaches, or the combination of data obtained using both methods. The results obtained using thermal methods based on freezing-point depression methods were also reported by a limited number of participants. There was excellent agreement between assignments obtained using all three approaches to assign the BPA content.
The assignment of the values for the mass fraction content of BPA consistent with the KCRV was achieved by most of the comparison participants with an associated relative standard uncertainty in the assigned value in the range (0.1 - 0.5)%.
The comparison required the assignment of the mass fraction of folic acid present as the main component in the comparison sample. Performance in the comparison is representative of a laboratory's measurement capability for the purity assignment of organic compounds of medium structural complexity [molecular weight range 300–500] and high polarity (pKOW < −2).
Methods used by the eighteen participating NMIs or DIs were based on a mass balance (summation of impurities) or qNMR approach, or the combination of data obtained using both methods. The qNMR results tended to give slightly lower values for the content of folic acid, albeit with larger associated uncertainties, compared with the results obtained by mass balance procedures. Possible reasons for this divergence are discussed in the report, without reaching a definitive conclusion as to their origin.
The comparison demonstrates that for a structurally complex polar organic compound containing a high water content and presenting a number of additional analytical challenges, the assignment of the mass fraction content property value of the main component can reasonably be achieved with an associated relative standard uncertainty in the assigned value of 0.5%
The mechanical compression of metal foam flow-field based polymer electrolyte fuel cells (PEFCs) is critical in determining the interfacial contact resistance with gas diffusion layers (GDLs), reactant flow and water management.
The distinct scale between the pore structure of metal foams and the entire flow-field warrant a multilength scale characterization that combines ex-situ tests of compressed metal foam samples and in-operando analysis of operating PEFCs using X-ray computed tomography (CT) and neutron radiography. An optimal ‘medium’ compression was found to deliver a peak power density of 853 mW/cm². The X-ray CT data indicates that the compression process significantly decreases the mean pore size and narrows the pore size distribution of metal foams. Simulation results suggest compressing metal foam increases the pressure drop and gas velocity, improving the convective liquid water removal. This is in agreement with the neutron imaging results that demonstrates an increase in the mass of accumulated liquid water with minimum compression compared to the medium and maximum compression cases. The results show that a balance between Ohmic resistance, water removal capacity and parasitic power is imperative for the optimal performance of metal foam based PEFCs.
Full penetration laser welding was carried out on a 10 mm steel plate using a 16 kW maximum power continuous wave thin disk laser. Upper surface and lower surface of molten pool were observed synchronously with two high speed CCD cameras during the welding process. The lower surface was much longer and more unstable than the upper one. A three dimensional laser deep penetration welding model in which volume of fluid (VOF) method was combined with a ray-tracing algorithm was used to simulate the dynamic coupling between keyhole and molten pool in laser full penetration welding. The calculated weld cross-section morphology and molten pool length on both upper side and lower side agree well with experimental results. Evolution of molten pool in lower side during full penetration laser welding was analyzed, periodical features of energy coupling, molten pool behavior and keyhole dynamics in laser full penetration welding were identified and discussed.
Historians and librarians are interested in watermarks and mould surface patterns in historic papers, because they represent the “fingerprints” of antique papers. However, these features are usually covered or hidden by printing, writing or other media. Different techniques have been developed to extract the watermarks in the paper while avoiding interference from media on the paper. Beta radiography provides good results, but this method cannot be widely used because of radiation safety regulations and the long exposure times required due to weak isotope sources employed. In this work, two promising methods are compared which can be used to extract digital high-resolution images for paper watermarks and these are electron radiography and low energy X-ray radiography. For electron radiography a “sandwich” of a lead sheet, the paper object, and a film in a dark cassette, is formed and it is exposed at higher X-ray potentials (> 300 kV). The photoelectrons escaping from the lead sheet penetrate the paper and expose the film. After development, the film captures the watermark and mould surface pattern Images for the paper being investigated. These images are then digitized using an X-ray film digitizer. The film employed could potentially be replaced by a special type of imaging plate with a very thin protection layer to directly generate digital Images using computed radiography (CR). For the second method, a low energy X-ray source is used with the specimen paper placed on a digital detector array (DDA). This method directly generates a low energy digital radiography (DR) image. Both methods provide high quality images without interference from the printing media, and provide the potential to generate a “fingerprint”
database for historical papers. There were nevertheless found to be differences in the images obtained using the two methods.
The second method, using a low energy X-ray source, has the potential to be integrated in a portable device with a small footprint incorporating user safety requirements. Differences obtained using the two methods are shown and discussed.
Sixteen laboratories have performed electrochemical noise (EN) measurements based on two systems. The first uses a series of dummy cells consisting of a 'star' arrangement of resistors in order to validate the EN measurement equipment and determine its baseline noise performance, while the second system, based on a previous round-robin in the literature, examines the corrosion of aluminium in three environments. All participants used the same measurement protocol and the data reporting and analysis were performed with automatic procedures to avoid errors. The measurement instruments used in the various laboratories include commercial general-purpose potentiostats and custom-built EN systems. The measurements on dummy cells have demonstrated that few systems are capable of achieving instrument noise levels comparable to the thermal noise of the resistors, because of its low level. However, it is of greater concern that some of the instruments exhibited significant artefacts in the measured data, mostly because of the absence of anti-aliasing filters in the equipment or because the way it is used. The measurements on the aluminium samples involve a much higher source noise level during pitting corrosion, and most (though not all) instruments were able to make reliable measurements. However, during passivation, the low level of noise could be measured by very few systems. The round-robin testing has clearly shown that improvements are necessary in the choice of EN measurement equipment and settings and in the way to validate EN data measured. The results emphasise the need to validate measurement systems by using dummy cells and the need to check systematically that the noise of the electrochemical cell to be measured is significantly higher than the instrument noise measured with dummy cells of similar impedance.
A pilot study for the thickness measurement of HfO2 films was performed by the Surface Analysis Working Group (SAWG) of the Consultative Committee for Amount of Substance (CCQM). The aim of this pilot study was to ensure the equivalency in the measurement capability of national metrology institutes for the thickness measurement of HfO2 films. In this pilot study, the thicknesses of six HfO2 films with nominal thickness from 1 nm to 4 nm were measured by X-ray Photoelectron Spectroscopy (XPS), X-ray Reflectometry(XRR), X-ray Fluorescence Analysis (XRF), Transmission Electron Spectroscopy (TEM), Spectroscopic Ellipsometry (SE) and Rutherford Backscattering Spectrometry (RBS). The reference thicknesses were determined by mutual calibration of a zero-offset method (Medium Energy Ion Scattering Spectroscopy (MEIS) of KRISS) and a method traceable to the length unit (the average thicknesses of three XRR data except the thinnest film). These reference thicknesses are traceable to the length unit because they are based on the traceability of XRR. For the thickness measurement by XPS, the effective attenuation length of Hf 4f electrons was determined. In the cases of XRR and TEM, the offset values were determined from a linear fitting between the reference thicknesses and the individual data by XRR and TEM. The amount of substance of HfO2, expressed as thickness of HfO2 films (in both linear and areal density units), was found to be a good subject for a CCQM key comparison.
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The final report has been peer-reviewed and approved for publication by the CCQM.
We report the results of a Versailles Project on Advanced Materials and Standards interlaboratory study on the intensity scale calibration of x-ray photoelectron spectrometers using low-density polyethylene (LDPE) as an alternative material to gold, silver, and copper. An improved set of LDPE reference spectra, corrected for different instrument geometries using a quartz-monochromated Al Kα x-ray source, was developed using data provided by participants in this study. Using
these new reference spectra, a transmission function was calculated for each dataset that participants provided. When compared to a similar calibration procedure using the NPL reference spectra for gold, the LDPE intensity calibration method achieves an absolute offset of ∼3.0% and a systematic deviation of ±6.5% on average across all participants. For spectra recorded at high pass energies (≥90 eV), values of absolute offset and systematic deviation are ∼5.8% and ±5.7%, respectively, whereas for spectra collected at lower pass energies (<90 eV), values of absolute offset and systematic deviation are ∼4.9% and ±8.8%, respectively; low pass energy spectra perform worse than the global average, in terms of systematic deviations, due to diminished count rates and signal-to-noise ratio. Differences in absolute offset are attributed to the surface roughness of the LDPE induced by sample preparation. We further assess the usability of LDPE as a secondary reference material and comment on its performance in the presence of issues such as variable dark noise, x-ray warm up times, inaccuracy at low count rates, and underlying spectrometer problems. In response to participant feedback and the results of the study, we provide an updated LDPE intensity calibration protocol to address the issues highlighted in the interlaboratory study. We also comment on the lack of implementation of a consistent and traceable intensity calibration method across the community of x-ray photoelectron spectroscopy (XPS) users and, therefore, propose a route to achieving this with the assistance of instrument manufacturers, metrology laboratories, and experts leading to an international standard for XPS intensity scale calibration.
Compared with most common construction materials, fiber reinforced cementitious materials are well known to exhibit better physical, working and mechanical properties. In this study, three fibers were selected: polypropylene fiber (PPF) and polyvinyl alcohol fiber (PVAF), which represented synthetic fibers, and sisal fiber (SF), which represented natural fibers. Effects of these fibers on the flowability, rheological properties, and adsorption behavior of the cement paste with polycarboxylate superplasticizer (PCE) were investigated. Furthermore, the above experimental results were verified by measuring the contact angle of the fiber with water and PCE solution and the apparent morphology of the fiber. Results revealed that the addition of fibers significantly reduces the fluidity of the cement paste, while the yield stress and plastic viscosity of the cement paste increase with the addition of fibers. From the contact angle and scanning electron microscope, the surface of SF was relatively rough, and the contact angle of SF with water or PCE solution was the smallest. It can be concluded that the plant fiber has a significant influence on the fluidity and rheology of cement paste.