arbon (TC) = Total Organic Carbon (TOC) + Total Inorganic Carbo tion : ry, powdered sample in baked glass beaker with 1N HCl, @ 60 o C for 12-14 hours with de-ionized water to flush out Cl- onto a baked glass fib ed to a crucible boat for drying and elemental analysis Calcite
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Total Carbon (TC) = Total Organic Carbon (TOC) + Total Inorganic Carbon (TIC) TOC preparation: ~0.25 g dry, powdered sample acidified in baked glass beaker.
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Total Carbon (TC) = Total Organic Carbon (TOC) + Total Inorganic Carbon (TIC)
TOC preparation:
• ~0.25 g dry, powdered sample• acidified in baked glass beaker with 1N HCl, @ 60 oC for 12-14 hours• filtered with de-ionized water to flush out Cl- onto a baked glass fiber filter• transferred to a crucible boat for drying and elemental analysis
X-ray fluorescence (XRF):The emission of characteristic "secondary", or fluorescent, X-rays from a material that has been excited by bombarding with high-energy X-rays or gamma rays.
Irradiating an atom with high-energy primary X-ray photons delivers sufficient energy for an electron to be ejected completely out of the atom.
An outer shell L electron falls inward to fill the void created in the inner shell, and an X-ray characteristic of the atom's elements is emitted.
Schematic arrangement of wavelength dispersive spectrometer.
X-ray fluorescence (XRF) spectrometers
Schematic arrangement of energy dispersive spectrometer The dispersion and detection are a single operation. Proportional counters or various types of solid state detectors (PIN diode, Si(Li), Ge(Li), Silicon Drift Detector SDD) are used.
Schematic arrangement of a wavelength-dispersive (WD) X-ray fluorescence (XRF) spectrometer
B.
A.
Various types of detectors most commonly gas flow proportional and scintillation are used to measure the intensity of the emitted beam on bench top models.
Gas flow proportional counters are used mainly for detection of longer wavelengths (lighter elements). The gas is usually 90% argon, 10% methane ("P10"). The argon is ionized by incoming X-ray photons, and the electric field multiplies this charge into a measurable pulse. The methane suppresses the formation of fluorescent photons caused by recombination of the argon ions with stray electrons.
Scintillation counters consist of a scintillating crystal (typically of sodium iodide doped with thallium) attached to a photomultiplier. The crystal must be protected with a relatively thick aluminum/beryllium foil window, which limits the use of the detector to wavelengths below 0.25 nm. Typically used for heavier elements.
Scintillation - a flash of light produced in certain materials when they absorb ionizing radiation.
B.
A.
To obtain good XRF results using the pressed powder technique, control of particle size is absolutely critical.
Pressed Powder Disks/Pellets
Used primarily for trace elements and uniform samples compositions.
Lithium metaborate flux + sample in a 7:1 proportion
Fusion in Pt crucible> 750 oC
Fused glass disk from gold or brass mould
Fused Glass DiskFor Major Oxide Analysis
Sample PreparationTypical Composition of Grinding Units
MaterialMajor
ElementsMinor
ElementsHardness (Mohs)
Resistance to Abrasion Durability
Hardened Steel Fe Cr, Si, Mn, C 5.5-6 Moderate HighStainless Steel Fe, Cr Ni, Mn, S, Si 5-5.5 Moderate HighCr-free Steel Fe C, Mn, Si, Mo 5-5.5 Moderate HighTungsten Carbide W, C, Co Ta, Ti, Nb 8.5 + High Long-wearing, but brittleAlumina Ceramic Al Si, Ca, Mg 9 Very High Long-wearing, but brittle
Agate SiAl, Na, Fe, K,
Ca, Mg 8.5Extremely
High Very long-wearing, but brittle
Zirconia Zr Hf, Mg 8.5Extremely
High Very long-wearingSilicon Nitride Si Y, Al, Fe, Ca 8.5 +
Extremely High Very long-wearing
Plastic C -- 1.5 Low Low, but disposableAvailable in the Department
Major OxidesDetection limit 0.02 %:
Al2O3 CaOFe2O3 K2OP2O5 Na2OMnO MgOTiO2 SiO2
Loss On Ignition (LOI) is carried out at 1000oC. Removes volatiles including carbon, sulfur and nitrogen compounds, and structural and adsorbed water (H2O).Detection limit 0.02 %: LOI wt.% = (sample weight - residue weight) * 100 sample weight