Electrothermal Flow

Hawkins BG, Kirby BJ (2010) Electrothermal flow effects in insulating (electrodeless) dielectrophoresis systems. Electrophoresis 31 3622-3633... 

This implies that the electrothermal flow velocity increases in propordcMi to the electrical conductivity of the medium. Not only that, the dielectrophoretic force also dominates near the electrode edges (r —> 0). On the other hand, the influence of the electrothermal forces becomes progressively stronger for larger particles. 

Although electrothermal flows have been extensively studied in the literature, significant work is yet to be done to examine the interactimis between AC electroosmosis and electrothermal flows. Significant research effort also needs to be devoted to investigate the electrothermal flows from a stochastic viewpoint, primarily because of the uncertainties in the various factors that eventually dictate the magnitude and directirm of the net body force that acts on the fluid under these conditions. 

Ferrophosphoms is produced as a by-product in the electrothermal manufacture of elemental phosphoms, in which iron is present as an impurity in the phosphate rock raw material. The commercial product contains ca 23—29% P and is composed primarily of Fe2P [1310-43-6] and Fe P [12023-53-9] along with impurities such as Cr and V. Ferrophosphoms is used in metallurgical processes for the addition of phosphoms content. Low concentrations (up to - 0.1%) of phosphoms in wrought and cast iron and steel not only increases the strength, hardness, and wear resistance but also improves the flow properties. In large stmctural members and plates, it is desirable to use a type of steel that does not need to be quenched or tempered, and thus does not exhibit weld-hardening. This property is afforded by the incorporation of a small quantity of phosphoms in steel. Ferrophosphoms from western U.S. phosphoms production is used as a raw material for the recovery of vanadium (see Vanadiumand vanadiumalloys). 

Figure 4.1 Flow scheme of a plant comprising an electrothermal tubing-based micro reactor configured for ethylene polymerization [1],...

A typical measurement was performed as follows. The feeder was lowered into the crucible and the sample solution (seawater) was allowed to flow under an inert atmosphere with the suction on. A constant current was applied for a predetermined time. When the pre-electrolysis was over, the flow was changed from the sample to the ammonium acetate washing solution, while the deposited metals were maintained under cathodic protection. Ammonium acetate was selected for its low decomposition temperature, and a 0.2 ml 1 1 concentration was used to ensure sufficient conductivity. At this point the feeder tip was raised to the highest position and the usual steps for an electrothermal atomic absorption spectrometry measurement were followed drying for 30 s at 900 C, ashing for 30 s at 700 °C, and atomization for 8 s at 1700 °C, with measurement at 283.3 nm. The baseline increases smoothly with time as a consequence of an upward lift of the crucible caused by thermal expansion of the material. 

There are several sample introduction methods that are used in conjunction with ICP, including nebulization, electrothermal evaporation, gas chromatography, hydride generation, and laser ablation [30]. Laser ablation combined with ICP (LA-ICP) is useful for analysis of solids. In such a source the sample is positioned in a chamber prior to the ICP source, the ablation cell. Argon gas at atmosperic pressure flows through the cell towards the ICP source. The sample is irradiated by a laser beam and... 

Fig. 5.17 Gas flow arrangement preferred for linking an electrothermal vaporizer to ICP/MS.

To optimize the applicability of the electrothermal vaporization technique, the most critical requirement is the design of the sample transport mechanism. The sample must be fully vaporized without any decomposition, after desolvation and matrix degradation, and transferred into the plasma. Condensation on the vessel walls or tubing must be avoided and the flow must be slow enough for elements to be atomized efficiently in the plasma itself. A commercial electrothermal vaporizer should provide flexibility and allow the necessary sample pretreatment to introduce a clean sample into the plasma. Several commercial systems are now available, primarily for the newer technique of inductively coupled plasma mass spectroscopy. These are often extremely expensive, so home built or cheaper systems may initially seem attractive. However, the cost of any software and hardware interfacing to couple to the existing instrument should not be underestimated. 

Because of its capability for rapid multielement analysis, ICP-MS is particularly suited to sample introduction methods which give rise to transient signals. For example, electrothermal vaporization, flow injection and chromatographic methods can be interfaced and many elements monitored in a single run (see Chapter 7). 

S. Ch. Nielsen, S. Sturup, H. Spliid and E. H. Hansen, Selective flow injection analysis of ultra-trace amounts of Cr(VI), preconcentration of it by solvent extraction and determination by electrothermal atomic absorption spectrometry (ETAAS), Talanta, 49(5), 1999, 1027-1044. 

Copper, Manganese, Nickel Plants — Flow injection on-line sorption preconcentration in a reactor, electrothermal [84]... 

Bio, G., Contado, C., Fagioli, F., Bollain Rodgiguez, M. H., and Dondi, F. (1995). Analysis of kaolin by sedimentation field-flow fractionation and electrothermal atomic absorption spectrometry detection. Chromatographia 41,715-721. 

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