EDXRF analysis is conveniently split into two parts: (1) the determination of X-ray intensities and (2) the determination of elemental amounts from X-ray intensities. For the first, most EDXRF analysis has been done by some method of integrating the essentially Gaussian distribution of observed full energy pulse heights. This might be done, for example, by least-square fitting of Gaussian distributions superimposed on a straight line or a quadratic background. Recently more elaborate shapes of the energy peaks also have been considered (Kennedy, 1990). After the X-ray intensities have been determined, interelement effects between the analyte element and other elements must be corrected for in order to obtain the elemental amounts from X-ray intensities. This correction can be done either by an empirical correction procedure as in the influence coefficient method which requires measurements on a number of standard samples to determine the required coefficients, or by theoretical calculation as in the fundamental parameters method which does not require standard samples.

Gas flow proportional counters for the detection of soft X-rays were introduced about ten years ago. These detectors offered the advantages of high sensitivity, good energy discrimination qualities and the ability to handle high counting rates. Since that time they have been used for ultra-soft and harder X-rays as well, both as detectors in standard spectrographic instruments and as energy discriminating instruments themselves in various so-called nondispersive applications. Depending upon the particular instrumental application, however, their use has led to considerable complication of the associated electronic circuitry in order to realize their advantages. For the most effective use of these counters (and of sealed proportional counters as well) it is necessary to have a clear understanding of the effect of various design parameters and operating conditions on their performance. The dependence of the shape of the pulse height distribution on the operating voltage, pressure and counting rate is described as a function of the energy of the radiation detected and the nature of the gas. Stability requirements on. counter tube high voltage supplies and operating pressure are discussed. Shifts of pulse height distributions toward smaller pulse sizes with increasing counting rate are described and the dependence of these shifts on the various parameters and on wavelength are discussed. Techniques for eliminating the shifts and the implications of these techniques for the associated electronics are described.

Solid solution decomposition of several aluminumrich aluminum-zinc-silver alloys were investigated using x-ray small angle scattering, x-ray diffraction (Guinier and Dewolff camera) and transmission electron microscopy. A decomposition sequence was observed directly fay means of hot stage electron microscopy, to be:

G.P. zones were observed to exist in all of the ternary Al-Zn-Ag alloys used in this investigation. Only one type of G.P. zone was detected and evidence is given which indicated that the G.P. zone formation was governed by the existence of a metastable miscibility gap. Experimental results also indicated that the lattice of the matrix is distorted by the presence of the G.P. zone.

A transition phase, designated ɛ', was observed to nucleate on defects in the matrix and to have a hexagonal close-packed structure. The ɛ' phase is partially coherent and much more regular in spatial distribution than the equilibrium ɛ phase.

Pyroaurite and sjogrenite belong to the group of sandwiched lamellar metal hydroxides which have a fixed metallic ions MII:MIII ratio for a particular class. Their crystal structure consists of positively charged metal hydroxide blocks intercalated with negatively charged interlayers. The atomic positions for the interlayer are definite for a particular class. The exact chemical formula of the pyroaurite class is determined from crystal structure analysis to be MII6MIII2(OH)16-CO3-4.5H2O; it crystallizes in the space group Rm with a = 12.4376 Å and c = 23.4126 Å. Sjogrenite, MII6 MIII2(OH)16-CO3-4H2O crystallizes in the space group P63/mcm. The crystallogiraphy and structural relationship between these classes are discussed. Previous discussion on these compounds did not give any conclusion on the exact chemical formula and the atomic positions.

A Search/Match program using digitized X-ray powder diffraction Scans as inputs was presented in 1987 at the Denver Conference. This program has been rewritten to take full advantage of ttie newest capabilities of high end personal Computers. Software improveraents combined with the faster processing speed make it possible to search the 53,791 pattern data base in less than 16 seoonds typically (Compaq Deskpro 386/30 with 9 MB of RAM and 80387-20 numerioal processor), This can be compared to the 90 seconds one year ago. A specific program allows the user to create and, if desired, customize the searoh data base directly from the CD-ROM PDF-2, making Updates much easier. Praotiaal examples are given to illustrate the Operation of the proprietary pattern-recognition algorithm used in the search program.

Several design concepts were evaluated for on-stream X-ray analysis, chief among which were: (1) sample presentation, (2) X-ray spectrograph and (3) data handling. The sample is presented to the X-ray spectrograph through a vertical cell having a mylar window and a device to measure variations in sample density. The X-ray spectrograph is of fixed-channel, modular design, with a capacity of up to six channels, and is designed for use in industrial environments. The complete spectrograph can be translated in a horizontal plane to position itself and determine the elemental composition in a series of sample cells. The data handling uses digital circuitry to permit normal use of analog readouts or digital data logging systems. Operational data are given for on-stream analysis.

The Castel dell'Ovo on the Bay of Naples, Italy, is an important historic structure dating from the 12th century. It is composed of a soft, volcanic tuff that was employed because it was locally available and easy to quarry and work. The exposed stone of this monument shows extensive decay, principally in the form of the crumbling away of the surface, and this has progressed to the greatest extent in the lower parts of the structure. Restoration and preservative intervention are now being considered. The essential prerequisites to the formulation of a safe and effective strategy of treatment of the monument are the understanding of the nature and properties of the stone, and of the factors responsible for its decay. The present investigation was undertaken to provide that information. In the course of these studies certain novel and significant features of the crystal chemistry of one of the common zeolite minerals have been observed, and are reported here.

An active recording x-ray crystal spectrometer for extended x-ray absorption fine structure (EXAFS) has been built using a position sensitive detector of the self scanning photodiode array (SSPA) type. The SSPA detector has energy and position sensitivity for x-rays. The spectrometer was applied to the measurement for EXAFS of the several compounds in foil, powder and liquid states. The spectra can be obtained rapidly, and compare very well with other methods. We found that the SSPA detector is very useful for the measurement of EXAFS.

A versatile double-crystal X-ray spectrometer has been developed for the precise measurement of X-ray diffraction line widths to tenths of seconds. The device can be employed in either the parallel or antiparallel arrangement for rocking curve studies and can also be used in anomalous X-ray transmission experiments with nearly perfect crystals.

A detailed description of the instrument is given as well as some results concerning the Darwin theory of X-ray diffraction line widths and Borrmann effects.

Three variables in the identification of crystalline multiphase unknowns by computer search/match methods were examined: presence or absence of chemical information; varying quality of d-I diffraction data; use of a large data base vs a data base having about 10% as many entries--both contain the unknown phases. The results showed that the search/match using average quality d-I data with chemical information was quite successful, while that obtained using higher quality d-I data alone missed one of four phases. It took only half the time to obtain the average d-I data plus chemistry as it did to obtain the higher quality data. Searching the smaller data base with the higher quality data alone resulted in an identification of all phases with high reliability.

Simplified models are “being used, at the College Park Metallurgy Research Center for six popular methods for matrix correction in X-ray analysis, including Lachance-Traill, Lucas-Tooth and Pyne, and Rasberry-Heinrich procedures. A choice of models provides the broader data-handling capability required for processing information obtained by both energy-dispersive and wavelength-dispersive X-ray systems. The selection of model for each problem depends on the system and the availability of standard reference materials. Programming developed at College Park using the simplified models has been formulated for use by analytical chemists with minimal computer training. Some of the considerations involved in developing a versatile computer program for matrix correction will be presented, as well as applications of the procedures to iron-nickel-chromium alloys, aluminum alloys, and low-alloy steels.

The intensity of Compton scattering, Fe, and Ca chatacteristic radiation can be used to estimate the amount of ash in coal by Xray fluorescence spectroscopy. Mo, W, and Cr radiation were used to study a suite of New Mexico coals, and the best results were obtained with Mo and W X-ray tubes. If the actual concentrations of Fe2O3 and CaO and the mass absorption coefficient, μ*, at the Compton wavelength of scattered Mo K radiation can be determined, the regression equation:

%Ash - 24.2μ* - 6.28(%Fe2O3) - 1.96(%CaO) - 3.4

estimates the ash content with an average error of 0.5% ash at 0.71Å.

On-stream X-ray fluorescence analyzers have been available for about 20 years. They have been used with great success and they have made an effective process control possible in many concentrators. They have, however, one severe drawback. Normally the sample that ought to be measured is in slurry form and it would be difficult and expensive to prepare it into more conventional form used in ordinary laboratory practice. The main constituent of slurry is water and normally some kind of plastic film is needed to keep slurry apart from the measuring system at least when the slurry system is malfunctioning. Already these two things are sufficient to set a limit to the lightest element that can be measured with reasonable accuracy and precision. This means that minerals that contain only such low atomic number elements as e.g. Mg, Al, Si and P remain out of reach. Difficulties arise also in cases where the interesting element is not only in the solid material but also in the solution part of the slurry. In great many cases the interesting element occurs in several minerals at the same time which causes certain problems with the accuracy. Fortunately this problem does not set such a basic limitation as a too low Z does unless only one of these minerals is of interest, which may make the whole method worthless.

An X-ray small-angle scattering instrument is described which is used for recording X-ray diffraction patterns or small-angle X-ray scattering curves in an angular region very close to the direct beam. The measurement of X-ray intensity is accomplished with standard geiger or scintillation counter techniques. The instrument is designed for use with a spot-focus or vertical-line X-ray source, In essence, it is a multiple-reflection double-crystal diffractometer, based on a concept developed by Bonse and Hart, employing two grooved perfect germanium crystals arranged in the parallel position. Multiple diffraction from these crystals produces a monochromated X-ray beam which can be several millimeters wide while still exhibiting extremely high angular resolution. As a result, effective sample volumes can be employed with maximum volume-to-thickness ratios. The principal features of the instrument are discussed with emphasis on the advantages of this device over those employing complex slit systems and film-re cording techniques, Data are presented to illustrate the operation, intensity, and resolution of the unit.

We are engaged in a study of the ash produced by combustion of lignite in a 750-MW power station. The aim is to follow the transport of elements with Z> 16 from the mine, through: a) the combustion process, b) emissionto the atmosphere or c) deposition in a land fill, d) transport in the environment and e) subsequent uptake by animals and humans. The resulting data will be used to estimate potential adverse impact on human health caused by operation of the power station.

Information about the conditions and reactions in a foundry cupola is essential to understand the thermochemistry of a cupola and thus improve its efficiency. A potential source of such information is coke taken from inside an operating cupola. In the region of the cupola that extends from the melt zone to the taphole, coke is directly involved in important chemical processes such as combustion, gasification, slag formation, iron sulfurization, carbon pickup, and oxide reduction. Coke is also suspected of being involved in the transport of silicon to the liquid iron. Each of these processes produces characteristic physical and/or chemical changes in the coke, making it possible to extract information about the processes from an examination of coke pieces taken from within an operating cupola. A program to study such coke samples is in progress. To effectively interpret these data it is necessary to know the temperature history of the coke being examined, especially the maximum temperature attained by the coke piece in the cupola.

A time saving method has been applied for the determination of retained austenite.

The method involved is based on the approach of energy dispersive X-ray diffraction analysis. With this approach, polychromatic radiation from the X-ray tube is used and diffraction maxima will occur at a fixed angle 2θ in as many wavelengths or energies as “d“ values are present.

Giessen and Gordon published the first application of this method to powder diffraction analysis in 1968 for the identification of crystal structures. As the determination of retained austenite is a quantitative type of analysis, based upon identification of the crystal structure, the new approach should also be applicable in principle.

With almost 100 samples of unknown austenite content, experiments have been carried out both with the conventional and the energy dispersive X-ray diffraction technique. The results obtained are closely comparable and the retained austenite values together with the errors are shown.

For these measurements, experiments have been carried out with the energy dispersive technique to determine the relation between the known concentration of retained austenite in a number of standards and the intensity correction factors (R). The results obtained from these experiments have shown good reproducibility of the intensity correction factors.

Using this technique, a five-fold reduction in analysis time is possible over the conventional technique with no reduction in accuracy.

Various kinds of compounds containing arsenic have been used in the world as rat poisons, agricultural chemicals and so on. In the field of semiconductor materials, AsH3 is used as a doping gas on silieon-wafer substrates and GaAs is now also investigated as a wafer substrate instead of Si wafer.

As for quantitative analysis of arsenic, atomic absorption spectrometry (AAS) and inductively coupled plasma atomic-emission spectrometry (ICP-AES) have often been used. In these methods, usually, oomplioated pretreatments such as preconcentration and separation have been needed in order to obtain reproducible values for arsenic.

There is a great deal of interest by the electronics Industry in understanding the reactions occurring at the interface between a solid metal and a liquid solder or braze. This is due to the complex nature of current microelectronics Packaging, where soldering or brazing operations often involve complex metallurgies and tightly controlled furnace profiles. However, to date only a few studies have been carried out on the reaction kinetics at a liquid metal-solid metal interface. This is due in part to the difficulty in carrying out such , experiments. In the past, two main techniques have been used to obtain solid-state kinetic data. The first, quantitative metallography, is slow and tedious to perform, and generally of limited accuracy. The second technique involves measuring the change of some property, such as electrical resistivity, that is a function of the concentration of one of the phases. The main disadvantages of these techniques are that absolute values of concentration are not obtained, and that the relationships between a property and constitution are rarely available. In addition, most physical properties are sensitive to factors other than constitution, and interference from these factors can often result in erroneous data.

The use of energy dispersive analysis of x-rays (EDAX method) is now well entrenched in the electron column field(l), where more scanning electron microscopes have been fitted with EDAX instrumentation than all of the conventional (wavelength-dispersive spectrometer) microprobes ever made. The principle advantage of the EDAX approach for the SEM user is the efficiency of detection, which permits its use at the low power levels of the SEM. In addition, the simultaneous analysis of the entire spectrum and the lack of focusing restrictions that permits analysis of rough samples are important advantages.