Electrical Discharge Ablation

A schematic diagram showing the general construction of an arc or spark source. Actual construction details depend partly on whether samples need to be analyzed automatically. The sample material can be placed on the cathode or can even compose the whole of the cathode. If graphite is used, the sample needs to be pressed into the shape of a cathode after admixture with the carbon. 

In operation, a spark source is normally first flushed with argon to remove loose particulate matter from any previous analysis. The argon flow is then reduced, and the cathode is preheated or conditioned with a short bum time (about 20 sec). The argon flow is then reduced once more, and the source is ran for sufficient time to build a signal from the sample. The spark is then stopped, and the process is repeated as many times as necessary to obtain a consistent series of analyses. The arc source operates continuously, and sample signal can be taken over long periods of time. 

Calibration of an arc or spark source is linear over three orders of magnitude, and detection limits are good, often within the region of a few micrograms per gram for elements such as vanadium, aluminum, silicon, and phosphorus. Furthermore, the nature of the matrix material composing the bulk of the sample appears to have little effect on the accuracy of measurement. 

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The major methods used for vaporization (ablation) include lasers, electrically heated wires, or sample holders and electrical discharges (arcs, sparks). 

The capabilities of two plasma assisted techniques (laser ablation and electrical discharge in liquids) for fabrication of nanoscale composite (Al-Cu/oxide matrix), zinc oxide and doped gadolinium oxide have been piesented. 

In conclusion, the developed techniques (based on laser ablation and electrical discharges in liquids) have been shown to be efficient for fabrication of metal and semiconductor nanoparticles of different composition and structure. 

Not only is there a need for the characterization of raw bulk materials but also the requirement for process controled industrial production introduced new demands. This was particularly the case in the metals industry, where production of steel became dependent on the speed with which the composition of the molten steel during converter processes could be controlled. After World War 11 this task was efficiently dealt with by atomic spectrometry, where the development and knowledge gained about suitable electrical discharges for this task fostered the growth of atomic spectrometry. Indeed, arcs and sparks were soon shown to be of use for analyte ablation and excitation of solid materials. The arc thus became a standard tool for the semi-quantitative analysis of powdered samples whereas spark emission spectrometry became a decisive technique for the direct analysis of metal samples. Other reduced pressure discharges, as known from atomic physics, had been shown to be powerful radiation sources and the same developments could be observed as reliable laser sources become available. Both were found to offer special advantages particularly for materials characterization. 

Flames proved to be suitable sources for the analysis of liquids, but the need for direct chemical analysis of solids soon arose, including the need for rapid analysis of more than one element in a solid sample. The development of electrical discharges fostered the growth of atomic spectrometry arc and spark sources proved useful for analyte ablation and excitation. Low-pressure discharges proved to be powerful radiation sources (a similar development has been observed more recently, with the availability of laser sources). 

Electrical discharges of various types are often used to introduce solid samples into atomizers. The discharge interacts with the surface of a solid sample and creates a plume of a particulate and vaporized sample that is then transported into the atomizer by the flow of an inert gas. This process of sample introduction is called ablation. 

The laser-ablation method can produce SWCNT under co-evaporation of metals like in the electric arc-discharge method. As metallic catalyst Fe, Co or Ni plays the important role and their combination or addition of the third element such as Y produces SWCNT in an efficient manner. But it is still difficult in the laser-ablation method to produce gram quantity of SWCNT. Nonetheless, remarkable progress in the research of physical properties has been achieved in thus synthesized SWCNT. 

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