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Surface thermodynamics
Published in Nils O. Petersen, Foundations for Nanoscience and Nanotechnology, 2017
Small bubbles of vapor are therefore inherently unstable, and in the limit, it requires a very high vapor pressure to form the first tiny bubble with just a few molecules in it. This can only happen if the temperature is increased significantly above the phase transition temperature and leads to super heating of the liquid and a sudden violent boiling of the liquid. However, in many cases there are small imperfections in the walls of the container that can form sites of nucleation of the bubbles. Alternatively, there are small impurities in the liquid (such as dust) which allows bubbles to form around them. In most laboratory settings we add highly porous materials (boiling chips or wood fibers) to act as nucleation sites to avoid super heating.
Assessment and comparison of PHCs removal from three types of soils (sand, silt loam and clay) using supercritical fluid extraction
Published in Environmental Technology, 2019
Mahmoud Meskar, Majid Sartaj, Julio Angel Infante Sedano
The 500-mL evaporation flask was connected to the concentrator tube (10 mL graduated glass tube) by a clamp. The liquid extract which was collected in the silica gel column, was transferred to the K-D with an additional 20 mL of solvent, a mixture of acetone and hexanes with a ratio of 1:1. One or two boiling chips were added to the flask [33]. Boiling chips with approximately 10–40 mesh from VWR Scientific, Inc. (ON, Canada) were used. Boiling chips are added to liquids to make them boil more calmly and prevent bumping [34]. The (3-ball macro) Snyder column were joined to the flask with a clamp. Approximately 1 mL of solvent (acetone/hexane with a ratio of 1:1) was used to moisten the column. The whole K-D set-up was placed in a hot water bath in a fume hood. The flask was positioned at a level such that the lower surface of the flask could be bathed in steam. The temperature of water bath was adjusted to approximately 85°C so that it could vaporize solvents. Around 1 mL of exchange solvent (toluene) was added to the flask by removing the Snyder column instantly [33]. Toluene (C6H5CH3) was purchased from Fisher Scientific (ON, Canada) at an Optima-grade and also met the ACS specifications. The concentration rate can be modified with the water’s temperature compared with the boiling point of solvents. The final volume of extract around 2 mL can be reached after a few hours [28]. At the end, the K-D device should be removed from the water bath to be cooled down before collection of the final extract.