External high-pressure flow cell

We have developed several new measurement techniques ideally suited to such conditions. The first of these techniques is a High Pressure Sampling Mass Spectrometric method for the spatial and temporal analysis of flames containing inorganic additives (6, 7). The second method, known as Transpiration Mass Spectrometry (TMS) (8), allows for the analysis of bulk heterogeneous systems over a wide range of temperature, pressure and controlled gas composition. In addition, the now classical technique of Knudsen Effusion Mass Spectrometry (KMS) has been modified to allow external control of ambient gases in the reaction cell (9). Supplementary to these methods are the application, in our laboratory, of classical and novel optical spectroscopic methods for in situ measurement of temperature, flow and certain simple species concentration profiles (7). In combination, these measurement tools allow for a detailed fundamental examination of the vaporization and transport mechanisms of coal mineral components in a coal conversion or combustion environment. 

This method of obtaining spectra is truly in situ spectroscopy. It is superior to the previously described high pressure method in that the reaction mixture need not be transferred to a separate cell, thus allowing cooling and undesirable reactions to occur. However, the external sampling technique offered by the flow reactor described above may be more applicable to large scale industrial use. 

Depending on the mean cell sizes and strut thicknesses, foam packings exhibit bed porosities between 75 and 95%. Pressure drop, when compared between fixed beds of the same specific external surface area, is somewhat greater over foams than over honeycombs, but considerably lower than over particle beds. The low pressure drop together with the excellent mass and, in particular, heat-transfer properties of foam packings render them particularly useful for rapid reactions of high exo- or endothermicity, when the realization of high fluid flow, efficient mass transfer, and/or efficient heat removal or supply, respectively, is mandatory [30, 31]. 

The cell is machined using a corrosion-resistant alloy and has four ports into which different components can be sealed for use at high pressures and temperatures. The components include a flowthrough external Ag/AgCl reference electrode, a flow-through Pt(H2) indicator electrode, a flow-through YSZ(Hg/HgO)... 

Pressure was generated with a diamond anvil cell (DAC) employing beveled anvils with central flats ranging from 20 to 100 jim and flat diamonds with 200-500 pm culets. Two types of DAC were used modified (to match a continuous flow He cryostat) Mao-Bell cell for operations at room and low temperatures [41] and a Mao-Bell high-T external heating cell [42]. The latter one is equipped with two heaters and thermocouples. Four experiments were performed at RT aiming to highest pressure and the final pressures varied from 180 to 268 GPa. For low-temperature measurements we used a continuous-flow He cryostat, which allowed infrared and in situ Raman/ fluorescence measurements. More details about our IR/Raman/fluorescence setup at the NSLS are published elsewhere [41]. 

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