XRF is an analytical method suitable for the fast determination of main and transition elements. It allows for the chemical analysis of materials in a wide range of concentrations (ppm to high %) for elements with an atomic number greater than 10.
X-ray fluorescence (or more specifically wave-length dispersive XRF, WDXRD as applied in the GWP labs) is based on the excitation of the substance to be analyzed and the subsequent emission of characteristic fluorescent X-rays. The radiation is a consequence of electron transition between different energetic levels of the corresponding atom and hence specific for each element. In a WDXRF machine the radiation is monochromatized by a crystal and analyzed with respect to the intensity and position (angle) of different spectral lines or regions.
Elements can be identified qualitatively (identied) by their characteristic wavelengths. The intensity of the measured signal can be used for the determination of the concentration of the element in the samples, hence a quantitative elemental analysis.
Simple sample preparation in combination with multi element analysis render XRD particularly suitable for high- and low-alloy steels, as well as aluminium and copper based alloys. XRD is widely used in metal and metal-processing industries and is generally used for the analysis of a wide range of materials, such as steel, glass, ceramics, building materials, lubricants or mineral oils.
The GWP labs are accredited for the analysis of most common alloys: steel/cast steel, aluminium, copper and cobalt/nickel alloys.
Total carbon and total sulfur content of a sample are determined simultaneously by infrared spectrometric determination of the gases carbon dioxide (CO2) and sulfur dioxide (SO2) after combustion in an oxygen stream by an induction- or resistance furnace. In this way organic carbon (TOC) and inorganic carbon (TIC) on the one hand, and sulfur in its various oxidation states on the other hand can be determined at the same time.
Due to different combustion temperatures, fractionated determination of free carbon, free sulfur, carbides and inorganic sulfates is possible.
Starting with sample weights of about 500 mg, inorganic samples (i.e. alloyed steel, cast iron, copper and copper alloys, ceramics, ores, cement, limestone, gypsum, sand, glass, minerals) and organic samples (i.e. coal, coke, wood, carbon black, rubber, municipal waste, soil, plants, mineral oils) can be analyzed in regions of 0.1% to 5% (Carbon) and 0.3% to 30% (Sulfur).
An optical emission spectrometer (OES) is a device for the chemical analysis and can hereby display the emission spectrum of chemical substances. For the analysis a spark or electric arc between the electrode and a conditioned material sample is used. By this sample material is evaporated and the released atoms and ions are stimulated by electron impact. The emitted radiation is guided through optical fiber to the optical systems, where it is divided to its single spectral components. Every element contained in the sample, is emitting in various wavelengths and can therefore be measured by photomultipliers. The so measured radiation intensity behaves proportional to the concentration of the elements in the sample.
For simultaneous determination of up to 60 chemical elements across the whole periodic system with limits of detection between 1 to 100 ppm optical emission spectrometry with inductively coupled plasma (ICP-OES) is the method of choice.
ICP-OES uses a radio frequency generated argon plasma with temperatures of up to 10.000 K. The aqueous sample usually is introduced into the plasma by a pneumatic nebulizer. Within the plasma, chemical elements in solution are thermally excited, and subsequently are emitting element-characteristic optical radiation. The concentration of the chemical element can be determined by the intensity of this radiation. ICP-OES is a valuable tool for analysis of metals and some heavy non-metals. It is frequently used for trace analysis and purity determinations.
Inert gas fusion is applied for the quantitative determination of hydrogen, oxygen and nitrogen in metal, ferrous and non-ferrous alloys as well as other inorganic materials. The method excels by its precision and short measurement times and is frequently used for the analysis of hydrogen embrittlement in steel and ferrous alloys.
The migration of hydrogen into the metal lattice can lead to crack formation, fracture and sudden failure of building elements and components. The potential effects of hydrogen embrittlement are particularly crucial for medical devices such as artificial hips or stents. For these reasons, quantitative measurement of hydrogen prior to field usage of the materials is essentially important.
In the preparation of a measurement, the sample is weighed into a tin saggar and sealed tightly. Subsequently, it is heated in a graphite crucible under a helium gas stream to 3000 °C and fused. By this procedure, the analytes are transferred quantitatively to the gas phase. The oxygen in the sample combines with carbon to form carbon monoxide (CO); this is oxidized to carbon dioxide (CO2) by a copper oxide catalyst which can be determined by infrared spectrometry. Nitrogen compounds form elementary nitrogen (N2) and are detected by a thermal conductivity detector. Hydrogen compounds transition to the gas phase as hydrogen gas (H2) which is catalytically oxidized to water and can be determined by infrared spectrometry.