APPLICATIONS OF X-RAY DIFFRACTION

Because of the information it provides concerning the sub microscopic structure of any kind of material from x-ray diffraction analysis, information usually obtainable only by inference from other methods of examination, this method of crystal analysis has become very important to modern industry. The large number of industrial applications already made prove the value of these crystal structure studies, and provide a firm foundation for this branch of technology. Hence the chemist, the physicist, the metallurgist, and the engineer now have in x-ray diffraction a powerful scientific instrument for use in the quest for better methods and improved materials, and for the maintenance of required quality throughout the manufacturing processes.

APPLICATIONS TO METALLURGY AND METALLOGRAPHY

1. The Composition and Structure of Alloys.

•  Identification of alloy components and compounds.This is a special case of the general problem of chemical analysis by x-ray diffraction, and is used very frequently in many laboratories as a check on the results of other methods of examination.
• Differentiation between compound formation and solid solution.This is also a special case of chemical analysis in which a compound formed between two or more elements will give rise to a new x-ray pattern which is different from that of any of the constituents, while the solid solution will in general give the pattern of one of the elements, but with a shift in line positions which depends upon the relative amounts of the other elements present in the solution.
• Routine determination of percentage composition of solid solution phases, on the basis of measurement of line shift with varying amounts of solute present.
• Determination of the mechanism of alloy formation. This involves study of reflection and back reflection patterns of a series of alloys with various thermal treatments, and the correlation of the conclusions with chemical and microscopic data.
• Determination of miscibility limits and solid-phase boundaries of many-component alloy systems, by correlating lattice parameters with increasing percentage of alloying constituents.
• Working out and checking the details of the solidus phases of the equilibrium diagrams of binary and many-component alloy systems. X-ray diffraction analysis is the most convenient and dependable of the accepted modern methods for this purpose.
• The most rational classification of alloy types and systems has been made on the basis of x-ray crystal analysis.
• Study of the "order-disorder" phenomena in alloy systems.

2. The Effects of Rolling and Working on Metals and Alloys.

•  Determination of structural changes accompanying successive reductions of sheet and wire, as a comparison of methods of reduction .by different techniques.
• Study of the effect of initial grain size, carbon content, initial strip thickness, and of rolling variables on the final structure of rolled strip steel in determining the proper scientific methods of working and forming.
• Determination of the effects of twisting and bending strip and wire.
• Measurement of the extent of deformation and distortion by rolling, drawing, shaping, etc., as a routine check on the efficacy of the manufacturing process.
• Determination of slip planes, "fiber" structure, etc., of rolled sheet and drawn wires.
• Differentiation between surface and interior structures, or study of "zonal" structural characteristics.
• Determination of the most desirable structure of a sheet or wire to be subjected to a forming operation, and a rational method of classifying metals as to workability. This method is used in many laboratories to "grade" every production lot. In this way the sheet mill can guarantee delivery of metal best suited to the manufacturer's shaping processes,
• Furnishes an explanation of structural failures in spinning, cupping, and stamping operations. "Trouble shooting" in regard to these operations is one of the best paying uses of x-ray crystal analysis in the metallographic laboratory.
• Measurement of the depth of cold work caused by machining, drilling, punching, grinding, etc.
• Study of the mechanism of "fatigue" and other types-of metal failures, and in many cases a determination of the cause for premature or unexpected failures.

3. The Effects of Annealing and Other Thermal Treatments on Metals.

•  Establishment and routine maintenance of scientifically correct annealing techniques, and in many eases also for heat treating techniques.
• Study of recrystallization mechanism, and exact determination of recrystallization temperature.
• Study of precipitation and age hardening phenomena.
• Study of the relation of carbon content to annealing, and the relations between amount of reduction, time and temperature of anneal, and the final structure.
• Determination of quench and temper structures of spring steels, and a continuous check on hardening and tempering operations.
• Study of growth of texture in castings.
• Measurement of strain relief upon annealing.
• Determination of surface effects, such as decarburization, oxidation, excessive crystal growth, etc., as differentiated from interior structure. 

4. Miscellaneous Applications to Metals.

•  Determination of true "crystal size" as distinguished from microscopic 'grain size". This is a common and much used procedure in many factories.
• Determination of the structure of welds and the presence of strain or distortion in the neighbourhood of the weld.
• Determination of the reason for and indication of the cure for "embrittlement" of malleable iron.
• Measurement of crystal size, crystal orientation, and absence of distortion (or degree of crystal perfection) in relation to electrical and magnetic properties of transformer steels.
• Determination of the effects of thermal treatments on the "spoilage" and recovery of permanent magnet alloys.
• Determination of uniformity, depth, and mechanism of surface hardening.
• Measurement of crystal size, preferred orientation, and thickness of electrodeposited films, a routine check on the plating process.
• Determination of the chemical composition of protective films, and study of mirrors and sputtered films.
• Study of the effects of included and absorbed or adsorbed gases on the structure of metals.
• Determination of optimum crystal size and best structure for electrical contact points, and a continuous check on these during manufacture.
• Study of the effects of crystal size and crystal orientation on electrical properties.
• Aid in the study of corrosion and corrosion or thermal "fatigue" and chemical embrittlement, and determination of the chemical composition of boiler scales.
• Furnishes a scientific approach to the preparation of new alloys, and a prediction of the properties of new or untried alloys.
• Study of the transition zone between base and covering of plated or enameled metals.
• Rational determination of the effects of minute impurities upon the structure of metals.
• Identification of inclusions in metals. This is a special case of chemical analysis by x-ray diffraction.
• An absolute and non-destructive measure of residual elastic surface stresses in metals. This is used quite extensively in several countries in the study of steel structures such as bridges and building frameworks.
• Determination of particle size in the colloidal region.

APPLICATIONS IN CHEMISTRY

1. General and Physical Chemistry

• Determination of ultimate crystal structure, including lattice types, unit cell dimensions, atomic positions, ionic groupings, and crystallographic systems of substances.
• Furnishes a unique and unquestionable characterization of individual chemical compounds. This is the basis of the wide-spread use of x-ray diffraction for chemical analysis. The analysis is, of course, made in terms of chemical compounds rather than in terms of elements and ionic groupings.
• Differentiation between a mixture, solid solution or complex compound formation.
• Supplies a quantitative estimate of the relative amounts of the various compounds in a mixture. The estimate can be refined by the proper use of a recording microphotometer.
• Furnishes a certain test for the crystallinity or non-crystallinity of a material, either in the solid state or in solution.
• Determination of crystal sizes in the microscopic and sub-microscopic (colloidal) ranges.
• Study of allotropic modifications and transitions of an element or compound, and the effects of impurities on these.
• Determination of the ideal or theoretical density of a substance, giving a basis for the estimation of porosity.
• Differentiation between true and false hydrates.(Chemical analysis.)
• Discovery of unsuspected chemical reactions.
• Recognition of colloidally dispersed phases, and differentiation between true solutions and suspensions.
• Determination of crystal size and structure of colloidal so is and gels.
• Identification of adsorbed films and chemical changes involved in adsorption.
• Determination of optimum crystal sizes and orientations for maximum catalytic activity, and study of the mechanism of catalysis and "poisoning" of catalysts. This is used not only to find the best processes for preparing a catalyst but also as a routine test of production.
• Determination of molecular sizes in liquid solutions, and molecular weights of liquids.
• Determination of the mechanism and course of dry reactions and allotropic transformations in the solid state, even at extremely high or extremely low temperatures. 

2. Organic Chemistry

The list given above for General and Physical Chemistry, and in addition furnishes:

• A sure test for the identity or non-identity of synthetic and naturally occurring materials.
• Estimation of molecular weights of hydrocarbons, etc.
• Measurement of atomic sizes, interatomic distance and diameters of molecules.
• A method of following chemical reactions, as for example addition to or oxidation of a multiple bond.
• Estimation of the purity of soaps, acids, etc.
• Estimation of the positions of side chains and functional groups.
• Measurement of the thickness of oriented films.
• Determination of molecular orientation in fibers, and  molecular structure of naturally occurring fibers and membranes.
• A method of following polymerization and condensation reactions, and decomposition in breaking up long chain compounds.
• Study of lubrication and lubricants, including a routine method of quantitatively comparing efficiency of lubricants.
• Study of changes taking place in the ripening of cheese, and during other processing of dairy products.
• A rational classification of synthetic and natural plastics, and a qualitative scheme for identification of these. 

3. Analytical Chemistry.

In addition to the applications listed above, x-ray diffraction provides for:

• Identification of the chemical composition of precipitates.
• Tests for purity and identification of impurities in precipitates.
• Measurement of particle (crystal) sizes of precipitates in relation to treatment and reagent concentrations.
• Determination of the state of perfection of the crystal lattice in precipitates, particularly in regard to aging effects, etc. 

APPLICATIONS IN THE PROCESS INDUSTRIES

Since the process industries are engaged in chemical manufacture, the general applications listed under "chemistry" could be repeated here. To avoid duplication, however, only those applications of x-ray crystal analysis to some particular problems will be given.

1. Paints and Pigments.

• Structure and crystal sizes as functions of color, spreading, wetting and obscuring power, stability, gloss, and method of preparation.
• Study of the drying and setting of oils, the mechanisms of the reactions involved, etc., and their relationships to the structure and composition of pigments.
• Tests for solution of driers, and study of the mechanisms of their action.
• Routine analysis for purity of pigments. This is an important production test, particularly for those pigments which can exist in more than one crystal form, as for example titanium dioxide. 

2. Ceramics and Glass.

• Routine qualitative and quantitative analysis of materials and clay mixtures, in terms of compounds present.
• Determination of the structural and chemical changes occurring during sintering, fusing, and other thermal treatments and the mechanisms of these reactions.
• Furnishes the best and fastest method for determining and checking the solidus phases of many component systems, and for determining miscibility limits.
• Gives a definite test for incipient devitrification of glass.
• Identification of substances imparting color or opacity to glasses or enamels.
• Determination of crystal size with relation to color of pigment.
• Study of transition zones between base metal and vitreous enamel.
• Measurement of chemical reaction rates in melt or during sintering. 

3. Cement and Plaster.

• Study of reaction rates and mechanisms taking place during manufacture and use of cement.
• Routine chemical analysis of raw materials and clinker.
• Differentiation between particle size of aggregates and true crystal size.
• Method of determining and checking complex phase diagrams with certainty.
• Investigation of setting accelerators and their effects on the final structure of concrete.
• Control analysis of lime for crystal size, etc., to ensure proper plastic properties of plaster.
• Study of structure of limestone and its kiln behaviour in relation to the properties of the final product.
• Study of the dehydration of gypsum and the structural changes involved in the use and reuse of plaster of Paris molds. 

4. Storage Batteries.

• Study of physical and chemical structure of plates as related to performance.
• Study of chemical reactions occurring during charge and discharge.
• Study of the influence of the structure of grid and composition and aging of the paste upon the physical properties of the plates, and control analysis for the manufacturing process.
• Identification of deposits and sediments on plates, separators, and in cell. 

5. Rubber and Allied Products.

• Study of chemical reactions taking place during vulcanization and other processing.
• Determination of crystallinity, state of dispersions, crystal sizes of fillers, etc., and their relation to the physical characteristics of the finished products.
• Study of the basic structure of rubber and rubber-like materials. X-ray diffraction furnishes the only sure test of the fundamental relationships between natural and synthetic rubber.
• Study of fabrics and other binding materials used in the manufacture of rubber products, and routine grading of fibers as explained below. 

6. Textiles and Fibers.

• Determination of the degree'of fiberingn . A quantitative relationship between the degree of fibering and tensile strength of cotton fibers has been developed and is being used as a routine method of grading cotton.
• Furnishes a scientific method of classifying cotton, silk, wool, and other natural and synthetic fibers.
• Determination of the rate, mechanism, and completeness of mercerization, nitration, and other chemical reactions, and use in control analysis.
• Determination of the mechanism of fire-proofing fibers, and of exact amount of reagent required.
• Identification of adsorbed films and the chemical changes involved in adsorption, particularly as applied to dyeing of fibers.
• Great improvements in quality, tensile strength, and non-wrinkling properties of rayon and other synthetic fibers has been made through x-ray studies. The development of artificial wool from skim milk, peanuts, beans, etc., can be traced directly to x-ray diffraction studies of the structures of the various proteins. The development of "nylon", the new synthetic silk, has depended to a great degree on x-ray studies of its fiber characteristics by x-ray diffraction.
• X-ray diffraction studies on collagen fibers (side walls of animal intestines, tendons, etc.) have resulted in enormous improvement in the quality and wearing properties of tennis racket strings, and in the strength and controlled digestibility of surgical ligatures and sutures. 

APPLICATIONS IN MINERALOGY

1. General Mineralogy.

• Complete and unambiguous mineralogical analysis of ores, clays, and other mineral mixtures.
• Analysis of industrial dusts, and correlation with the occurrence of industrial diseases.
• Classification and evaluation of certain commercial ores.
• Identification and classification of the clay minerals and complexes making up the so-called soil-colloid.
• A scientific method of studying the changes produced in natural minerals by weathering, accelerated weathering tests, and other chemical and physical degradations.
• Specifications for asbestos, mica, and other natural insulating materials for special purposes.
• Classification of coal, charcoal, etc. 

2. Precious Stones and Gems.

• Identification, classification, and differentiation of genuine, both natural and synthetic, and imitation gems by a non-destructive test.
• Differentiation between natural and synthetic gems, nondestructively.
• Differentiation between natural and cultured pearls, non-destructively. This is a routine procedure with some of the leading jewelry manufacturers throughout the world.
• Determination of the proper orientation for a "jeweled" bearing (in watches, electric meters, etc.) to give maximum service and wearing qualities.
• Selection and classification of "black" diamonds for drills and dies, determination of causes for undue wear, and proper crystallographic orientations for optimum service.
• Determination of the proper direction of cutting quartz crystals for crystal oscillators in radio broadcasting and telephone equipment. 

APPLICATIONS IN PHYSIOLOGY, PATHOLOGY, AND BIOLOGY

1. The applications under this heading are quite recent developments and are not yet generally used. Listing of some, however, will serve to show the general trend and possibilities of x-ray diffraction research in these complex and difficult, but extremely important fields,

• Differentiation between some normal and pathological tissues.
• Study of the effects of diseases on the structures of tissues, as on bone structure changes in rickets, cancer of the bone, and other bone diseases.
• Study of structure of living tissue, as nerve and muscle, in relation to body functions.
• Identification and classification of mineral deposits in organs, such as calcifications, gall stones, siliceous deposits, etc.Much interest is evident at present in the study of the action of free quartz on lung tissue in silicosis, and of other industrial diseases and their occurrence, and many papers have been published in medicinal journals on x-ray diffractipn studies of silicotic lung tissue.
• Structure and classification of tooth enamel, dentyne, etc., and structures of the teeth in relation to diet. 

2. Papers of interest to pharmacists have appeared recently on the following subjects:

• Identification of minerals in rhubarb.
• Differentiation between natural and synthetic camphor.
• Study of the reactions between menthol and the mercuric oxides.

WEARING METALS AND THEIR RESPECTIVE PARTS IN DIESEL LOCOMOTIVE

INTRODUCTION

Lube oil analysis of Diesel locomotive by using several  analytical techniques for the condition monitoring and monetizing the engine is very important for the long life of the engine. The analytical techniques involves techniques such as elemental analysis by RDE-AES or ICP-AES , Fourier transform infrared spectroscopy, Viscosity measurement , Particle counting wear debris analysis and Karl Fischer moisture. However we had discussed about some of the above analytical techniques in earlier posts and rest of the techniques we will discuss in upcoming post. In this post we are going to discuss about the wear metals and their respective affected parts.

Elemental analysis is the most basic tests for the lube oil analysis, it is used to determine the presence of wear metals in diesel oil locomotives. There are two types of instruments which are generally used for the elemental analysis of lube oils , "RDE-AES & ICP-AES" ,which can detect more than 20 elements in lube oil. We will discuss in detail about the differences between both the instrument in the upcoming posts, however in the mean time they serve the same purpose of determination of wear metals in PPM level inside the lube oil .

During machinery in working , wear metal debris particles are produced by rubbing motion of mechanical component parts , are either normal wear or abnormal wear, these wearing metals can be detected using spectroscopy . The wear metals indicate their respective sources i.e engine parts. For every diesel engines certain limits are set for respective metals in ppm ,above which failure may occur because of the higher rate of wearing. So using spectroscopy it is much easier to monitor the condition and can take appropriate action before it will be too late and can save from bigger loss.

BELOW IS THE LIST OF THE WEAR METALS AND THEIR RESPECTIVE SOURCES:

WEAR METAL	SOURCES
Aluminium	Piston, inappropriate filtrations, Crankcases on Reciprocating Engines, Bearing Surfaces, Pumps, Thrust Washers.
Copper	Bushing, Thrust Plates.
Silicon	Inappropriate air filtrations.
Iron	Bushing, Shaft, Ring.
Chromium	Cylinder liner, Exhaust Valves.
Tin	Main bearing, Con rod, TSC bearing.
Lead	Con road, TSC bearing, Seals, Solder, Grease.
Sodium	Water coolant leakage into oil.
Boron	Water coolant Leakage.
Magnesium	Oil additives.
Nickel	Alloy from bearing metals.
Molybdenum	Piston rings.
Phosphorous	Anti-wear additive.
Potassium	Coolant Leak, Airborne Contaminant.
Silver	Bearing cages ( Silver Plating ).
Zinc	Anti-wear additive.
Calcium	Detergent Dispersant Additive.
Barium	Synthetic Oil Additive Synthetic Fluid.

TOTAL REFLECTION X-RAY FLUORESCENCE ANALYSIS

INTRODUCTION

Total reflection x-ray fluorescence (TXRF) analysis is a powerful analytical tool with respect to detectable elemental range, simplicity of quantification and detection limits. This includes the capacity to detect almost all elements of the periodic system, namely from boron to uranium. Even the highest-Z elements of the actinides can be detected. Quantitatively, the dynamic range covers several orders of magnitude, so ultra-trace element levels to major elemental concentrations can be determined. In terms of detection limits, the levels of femtogram absolute detectable masses under optimized excitation–detection conditions can be reached. Some of these features can be topped with additional properties such as rapid analysis time of a few seconds and simultaneous detection of the elements present. In some applications, non-destructiveness is of importance, e.g. while dealing with precious substances of cultural values from fine arts or also in cases of forensic investigations if only small amounts of sample are available. TXRF is an energy-dispersive XRF (EDXRF) technique, and excitation geometry with angles below the critical angle of total reflection is perfectly suited for these investigations.

The above statements emphasize the analytical power, and in addition to these arguments one can add the large number of applications that has led to the revival of x-ray fluorescence analysis for ultra-trace element analysis. The applications range from the interesting fields of medicine, techniques and environment to forensic, fine arts, extra-terrestrial samples and fundamental research. With new physical and technical ideas leading to modifications of the physical properties of the primary radiation, e.g. monoenergetic, linearly polarized, highly intense, or on the detector side high resolution, high counting capacity, large area or even arrays of detectors, new perspectives are opening up for TXRF

In Fig. 1 the experimental set-up of conventional EDXRF and TXRF is schematically shown. As TXRF is basically an energy-dispersive analytical technique, the main difference to conventional EDXRF is neither the source nor the detector but the geometry of excitation at small incidence angles below the critical angle of total reflection.

     Figure 1 Comparison between conventional (left) and total reflection mode of excitation (right).

THEORY

The theory of x-ray total reflection is based on the phenomenon that at an incident angle below the critical angle the narrow collimated primary beam is totally reflected. A beam gets reflected from a flat polished surface of any material at the same angle as the incident one and has almost the same intensity as the primary beam (total intensity is reflected), except for a small portion that is refracted and penetrates the reflecting medium. This evanescent wave loses intensity exponentially as it penetrates deeper into the medium. In Fig. 2, the fundamental formalism of x-ray total reflection is shown, based on the Fresnel formalism and the complex index of refraction for x-rays, which is given below. The index of refraction for x-rays differs only slightly from 1, which is described theoretically by the value of υ which is in the range of 10-5 . For many materials the angles involved are small, typically a few milli radians or a tenth of a degree.

      Figure 2 Sketch of the theoretical conditions for x-ray total

Applications to chemical analysis:

The incident radiation in TXRF is a fine, collimated, almost parallel beam with typical dimensions of 8 mm width and only 50 μm height. This narrow beam impinges at an angle below the critical angle of total reflection (1.8 mrad or 0.1 degrees in the case of a monoenergetic Mo K˛ radiation and Si reflector) on the surface of a flat polished material. that serves as the sample carrier. In the case of chemical analysis of different samples, such as from the environment, medicine or technical products, different procedures apply. The sample has to be transferred into the liquid form by chemical digestion procedures. A small volume of 1–20 μl of the dissolved sample is taken using a pipette. The acidic or aqueous solution is dropped at the center of the reflector and dried by infrared heating, on a hot plate or in vacuum.

Possible applications of TXRF.

Environment	Water: sea, rain, pore water, river, mineral, spring water, drinking water, chemicals and deionized water
	Air: aerosols, vapour, air dust, airborne particles, fresh air
	Soil: sewage sludge, sediments
	Plant material: Algae, fine roots, cucumber plants, pollen.
	Foodstuff: fish, flour,  fruits, crab, mussel, mushrooms, nuts, vegetables, wine, tea, soft drinks, onion
	Drinks: Coffee,  spirits and beverages, honey.
Medicine/biology	Body fluids: blood, serum, urine, amniotic fluid,  cerebrospinal fluid
	Tissue: hair, kidney, lung, liver, stomach, nails, colon
	Various enzymes, polysaccharides, glucose, proteins, cosmetics, biofilms, human bones
Industrial/technical applications	Surface analysis: Si wafer surfaces, GaAs wafer surfaces
	Implanted ions: Depth and profile variations
	Thin films: single layers, multilayers
	Oil: Crude oil,  fuel oil, grease, pure fuel oil, waste oil, petroleum, oil-shale ash, diesel
	Chemicals: Acids,  bases,salts, solvents
	Fusion/fission research: trans mutational elements in Al C Cu, iodine in water
Mineralogy	Ores, rocks, minerals, rare earth elements, quartz, mineral sands, diamond, crystals
	Geological materials, bio-mineralisation
Fine arts/archaeological/forensic	Pigments, paintings, varnish21
	Bronzes, pottery, jewellery, manuscripts, Egyptian masks
	Textile fibres, glass, cognac, dollar bills, gunshot residue, drugs, tapes, sperm, finger prints.

Sample preparation

The samples can be from many scientific disciplines and thus the physical state will be different. The best-suited samples for TXRF are in the liquid state—either in the form of aqueous or acidic solutions—so if solids or powders are to be analysed, these samples must be transferred into the liquid state. The presented procedures are typical but can of course be adapted to the sample type, and the world of chemistry is fully open to new ideas, given in detail in the respective literature. Sample preparation has been discussed by several authors and many publications deal with special methods. Even so, the complex subject leaves a lot of ideas open to get the sample prepared in a way that the elements present can be detected even if they are at the lowest concentrations. Pre-concentration methods or selective enrichment techniques by chelation or electrochemical methods can be introduced to ensure that adequate masses are present on the sample reflector in the range of absolute picograms from very low-concentration samples, e.g. sea water in which the salt extraction also is an important preparation step. Recently, the collection of fine dust and also aerosols directly on the sample carrier in a short time of a few minutes to several hours by multi-stage samplers and the direct analysis of the minute masses collected by TXRF were successfully proven in large-scale experimental series in different parts of the world at locations of interest.

INSTRUMENTATION IN TXRF

Various combinations of x-ray sources, spectral modification elements, reflector materials and detectors can be used to optimize excitation and detection conditions. Measurements can be performed in air, in a He atmosphere or in a vacuum chamber. Vacuum conditions are mandatory for the detection of light elements to avoid absorption, but it is also advantageous because the scattering of primary x-rays from air is avoided. The components of a TXRF spectrometer are shown in the below figure

        Figure 3 Components of a TXRF spectrometer

 Sources of x-rays for TXRF are mainly x-ray tubes, ranging from low power (50–75W) to high-power standing anodes of up to 3000W and finally rotating anodes up to 18 kW. The appropriate focus is a line focus with dimensions 8 or 12mm long and 40 μm wide. Everything is done to get a high flux of photons onto the sample. There is radiation from the ultimate source with best properties of having a naturally collimated beam characteristic, an extremely high flux and a linearly polarized beam—the SR. Even though it is difficult to get access to SR, the results achievable show the importance of this effective combination of the source and TXRF, from which ultimate low detection limits of a few femtogram have been achieved.

The beam from an x-ray tube is unpolarised and has a continuous spectral distribution of the characteristic radiation. In many cases, a monoenergetic excitation is the preferred one because the background is optimally low as only scattered photons of single energy are present and will appear as two lines elastically and Compton-scattered in the spectrum. The first low-cost approach to modify the spectrum was an optical flat in the beam path and taking advantage of the energy dependence of the critical angle to suppress the high-energy part of the bremsstrahlung spectrum. This leads to reduced background, in particular in the low-energy region, as the Compton edge produced by the backscattered high-energy photons disappears. Versions with two reflectors attached togetherwith a spacing of 50 mm lead to a double-reflector monochromator. Efficient monochromators are nowadays available using multilayers with reflectivities in the range of up to 80% of the characteristic radiation of the anode material of choice. Typically in use are combinations of layered structures made of W–C, Ni–C andMo–Si with a d spacing of 2–3 nm. Thus, they are adjusted to fulfill the Bragg equation and the full spectrum is modified to be monoenergetic. Using modern technology to bend these structures, it is possible to design x-ray optical components that focus the beam with a small divergence, thereby increasing the flux of photons in the focal spot which is designed to be at the sample position. The result is an increase in intensity on the sample several times more than that with the non-focussing flat multilayer. These optical components are commercially available and can be inserted in the beam path of the TXRF spectrometer to improve further detection limits. 

Quantitative TXRF

The conversion of the measured intensities into concentrations is one of the most important steps in analytical XRF. In the special case of TXRF, the complications are rather completely removed, as the approach for the thin-film sample can be applied, which leads to a simple and linear relation between the intensity, I, and concentration, C, of the element considered. The addition of an internal standard with known concentration leads to a simple quantification procedure, as follows:

• Choose or add to the multi-element standard one element as internal standard, which is the reference for calibration of the spectrometer.
• Establish the intensity vs concentration curve as the regression curve with reference to the internal standard to determine the sensitivity, Sstd/Si, from multi-element standard.
• Add the internal standard of known concentration Cstd to the unknown sample.
• Measure the intensity of element Ii and intensity of internal standard Istd.
• Determine the concentration of unknown element Ci using the relation:

Advantages of TXRF

• Double excitation by direct and reflected beams
• Almost no penetration of the primary radiation into the substrate, resulting in low background Large solid angle, as the detector can be placed close to the reflector surface 
• Large solid angle, as the detector can be placed close to the reflector surface
• The consequent improved signal/background and improved detection limits
• Very low detection limits: femtogram levels, picograms per gram concentrations, 108 atoms/cm2 of metal contamination detectable on wafer surfaces

Environment

Water:

sea, rain, pore water, river, mineral, spring water, drinking water, chemicals and deionized water

Air:

aerosols, vapour, air dust, airborne particles, fresh air

Soil:

sewage sludge, sediments

Plant material:

Algae, fine roots, cucumber plants, pollen.

Foodstuff:

fish, flour,  fruits, crab, mussel, mushrooms, nuts,

vegetables, wine, tea, soft drinks, onion

Drinks:

Coffee,  spirits and beverages, honey.

Medicine/biology

Body fluids:

blood, serum, urine, amniotic fluid,  cerebrospinal fluid

Tissue: hair, kidney, lung, liver, stomach, nails, colon

Various enzymes, polysaccharides, glucose, proteins,

cosmetics, biofilms, human bones

Industrial/technical

applications

Surface analysis:

Si wafer surfaces, GaAs wafer surfaces

Implanted ions:

Depth and profile variations

Thin films:

single layers, multilayers

Oil:

Crude oil,  fuel oil, grease, pure fuel oil, waste oil, petroleum, oil-shale ash, diesel

Chemicals:

Acids,  bases,salts, solvents

Fusion/fission research:

trans mutational elements in Al C Cu, iodine in

water

Mineralogy

Ores, rocks, minerals, rare earth elements, quartz,

mineral sands, diamond, crystals

Geological materials, bio-mineralisation

Fine

arts/archaeological/forensic

Pigments, paintings, varnish21

Bronzes, pottery, jewellery, manuscripts, Egyptian masks

Textile fibres, glass, cognac, dollar bills, gunshot residue, drugs, tapes, sperm, finger prints.