Non-dispersive X-ray Analysis Research Articles

Observations of surface structures and reaction products for materials exposed in space in low-earth orbit

A preliminary study of materials exposed in space in low-earth orbit for nearly six years (in the NASA Long-Duration Exposure Facility (LDEF)) has revealed a range of micrometeorite and microparticle impact craters and blisters of unknown origin on aluminum alloy 6061-T6 samples on the leading edge of the satellite. In addition these samples were covered with an enormous range of reaction products which included crystals and polycrystalline aggregates which originated in part from other reactions and atomic oxygen degradation taking place in systems proximate to the alloy samples.A replication-type lift-off techniques was developed to remove reaction products (crystals and polycrystals, etc.) and debris from the specimen surfaces in order to isolate them from the background substrate without creating microchemical or microstructural artifacts. This technique culminates in extracted surface features resting on a carbon support film which is virtually “invisible” to observation by electron microscopy and non-dispersive x-ray analysis.

Effects of space environment on structural materials: A preliminary study and development of materials characterization protocols

A preliminary study of materials exposed in space in a low-earth orbit for nearly 6 years (in the NASA Long-Duration Exposure Facility) has revealed a wide range of micrometeorite or microparticle impact craters ranging in size from 1–100 μm diameter, debris particles from adjacent and distant materials systems, reaction products and other growth features on the specimen surfaces, and related phenomena. The exposed-surface features included finegrained and nearly amorphous materials as well as single-crystal particles. A replication-type, lift-off technique was developed to remove reaction products and debris from the specimen surfaces in order to isolate them from the background substrate without creating microchemical or microstructural artefacts or alterations. This resulted in surface features resting on a carbon support film which was virtually invisible to observation by electron microscopy and non-dispersive X-ray analysis. Characterization of these surface features involved observations by optical metallography, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray analysis; including an analytical transmission electron microscope with a STEM attachment. The results illustrate a wide variety of materials phenomena which must be addressed in the evaluation of materials exposure in space, and the formidable materials characterization effort which will be necessary to understand these features.

Observations on diagenesis in North Sea reservoir sandstones

Pressure solution If there were a grain-boundary solution phenomenon due solely to pressure it would be a function of depth of burial and have important consequences for the prediction of porosity reduction trends in hydrocarbon reservoirs. However, many of the interpenetrant grain contacts that have been illustrated by speakers at this meeting and termed 'pressure solution' require additional explanation. From our own work on both outcrop and core materials we have been unable to find any convincing correlation between burial depth and 'pressure solution'—for a variety of facies. Furthermore, Hancock (1978) does not claim to have seen pressure-solution phenomena although his sediments were recovered from a greater depth than any others described at this meeting. We suspect that the nature of the pore fluids flushing through the sediment is very important, particularly where grain-boundary reactions have been catalysed by surfactant coatings such as clays and micas. Reservoir sandstones did not become 'closed systems' until hydrocarbon emplacement was completed. Before this occurred pore-fluid evolution was probably continuous. Fibrous illite In our own studies on offshore core material from probable Old Red Sandstone in the Buchan Field, we have found fibrous outgrowths on clays and micas (Pl 1, fig. 1) in fractures. In this case, therefore, the fibres post-dated fracture development. We are not convinced that the fibres are simple illites (as has been proposed by several speakers) for the following reasons: 1. Using non-dispersive X-ray analysis it may be possible to show that the fibres are composed mainly of K 2 O,

Scanning electron microscopy: applications and implications in developmental neurobiology.

With explosively rapid technological advances in the fields of electronics and solid-state physics has emerged a new generation of biomedical instrumentation. In the forefront of these advances is the science and application of scanning electron microscopy (SEM). Despite its relatively recent emergence as a tool for both physical and biological investigations (Thornton, 1 1968; Carr, 2 1971; and Scott et al, 3 1974), conceptually the ideatum behind its evolution as an instrument of practical application can be traced back to the pioneering efforts of Oatly et al 4 in Cambridge in 1965. Unlike optical or transmission electron microscopy (TEM), SEM is restricted to the evaluation of surface structures. However, the sample size available for such analysis exceeds that for TEM by an order of magnitude of greater than 500:1. Furthermore, SEM easily interfaces with TEM and other sophisticated techniques, such as nondispersive x-ray analysis, allowing the investigator a considerably broader

Auger Electron Spectroscopy, SEM and Non-Dispersive X-Ray Analysis Techniques for Examination of Ag-CdO Contact Materials

A new examination method is described by which the contact surface microstructure and composition may be related to effects caused by electrical arcing. Auger Electron Spectroscopy (AES) and Non-Dispersive X-ray Analysis surface-study techniques are used to examine the anode surface composition of powder metallurgy Ag-CdO contact materials. The microstructure and morphology changes which take place on the anode surface as a result of electrical arcing were observed using the Scanning Electron Microscope. Technical differences between the AES technique and the Non-Dispersive X-ray method are discussed in general; specific application to Ag-CdO contact material is included, The chemicai composition of two different contact materials that were studied is the same. However, electrical tests show that one material is more susceptible to welding than the other. The results show that, for both materials, the CdO concentration on the anode surface after electrical arcing is much larger than before. The amount and distribution of CdO in the arc spot area differs between the two materials. One material shows higher concentration of CdO in the periphery of the arc spot, the other material shows higher concentration in the central region. For the same arc energy, differences exist in the quantity of CdO found in the arced area.

Cinétique de durcissement de l'alliage de titane TA 6V 6E 2. Analyse de l'évolution structurale au cours du revenu

The kinetics of the structural hardening of TA 6V 6E 2 alloy during annealing, subsequent to a water quench from the ( α + β) field, have been studied both by changes of hardness and resistivity. Thermal treatments were carried out at temperatures between 200 °C and 550 °C and for annealing times ranging from 5 min to 3 weeks. The experimental curves may be interpreted on the basis of the Johnson-Mehl equation. In order to characterise the structural changes in the alloy studied, various other complementary methods have been used such as X-ray diffraction, differential thermal analysis, optical microscopy and scanning microscopy combined with non-dispersive X-ray analysis of the constituents of each of the phases observed. By means of these observations, a possible interpretation of the successive transformations which occur with increasing temperature has been advanced; the results, in general, indicate that the different processes which occur are essentially controlled by the diffusion of vanadium.

A Programmable and Automated System for Gamma and X-Ray Analysis

A programmable, automatic system was developed to analyze multiple samples by either neutron activation analysis or nondispersive X-ray analysis. The system incorporates a Nuclear Data Series 2200 multichannel analyzer and a NOVA 800 minicomputer. An analyzer-computer interface, a sample changer, and computer software were designed and developed. The completed system was tested to illustrate its usefulness.

An Automatic X-Ray Analytical Instrument for the Chemical Laboratory

Although isotope excited non-dispersive X-ray analysis has shown considerable promise for use in portable instruments and in on-line control applications, its use as a general analytical tool in the chemical laboratory has not developed as well as expected. Much of this is thought to be due to lack of flexibility in the instruments available and to difficulties with their use by unskilled operators. Wide element coverage is essential and many analytical problems arise at the light element end of the periodic table. While developing on-line techniques for light elements it was found that a measuring head using a very compact source-sample-detector geometry was well suited to a number of routine analytical laboratory problems, and enabled high precision to be obtained with minimum sample preparation for rapid single element analysis. Sensitivities in a light matrix from 100. p.p.m. for silicon to 10 p.p.m. for heavy elements were attainable. An instrument specifically for chemical laboratory use was therefore designed to accept solid, liquid and powder samples for single element analysis of silicon and all heavier elements. The instrument can give direct numerical readout of concentration and achieves high stability and precision. In its basic form it is equipped with a range of isotope excitation sources but will also accept a small X-ray tube which has been specially developed for it to provide higher sensitivity and precision. The measuring head may be removed for remote use, and multiple sample changing facilities with printout of results can be added, permitting unattended automatic routine analysis.

The enhancement effect in non-dispersive X-ray analysis

A theoretical model of the enhancement effect in non-dispersive X-ray analysis is proposed. The considerations relate to a point source and detector localized in the same place (which is an approximation of the conditions of compact geometry). The results obtained in this work are different from those of other authors. Possibilities are suggested for the elimination of the influence of the enhancement effect on the results in non-dispersive X-ray fluorescence analyses.

Theoretical discussion of methods of elimination of matrix effects in non-dispersive X-ray analysis

Theoretical consideration concerning some possibilities for the elimination of matrix effects in non-dispersive X-ray fluorescence and absorption analysis are discussed. The theoretical treatment is concerned with the following methods: (a) double-channel absorption edge analysis, (b) concentration increase and dilution method in fluorescence analysis, (c) fluorescence-absorption method, (d) emission-transmission method, (e) fluorescence-Compton scattering method, (f) method of multicomponent analysis.

A selective non-dispersive X-ray fluorescence analyser without balanced filters

Filters for non-dispersive X-ray analysis require painstaking balancing and are in some cases unstable under adverse conditions. A modification to an onstream X-ray analyser, using two different secondary X-ray targets to obtain selectivity of the same order as that found with balanced filters, is described.