Thermal phase cleaning

Dry cleaning, also called gas-phase cleaning, is based on excitation energy such as plasma, radiation or thermal excitation. This section will concentrate on the wet processes, the area where ozone is of interest. 

Pyrolysis of 54 in the gas phase cleanly yields methyl trifluoroacetate (55), but thermal or photochemical decomposition in the liquid phase proceeds via a radical chain mechanism and gives all four possible esters (55-58). ... 

Koschmieder S. Thermal phase a new technique for stencil/PCB Cleaning. SMT. Feh. 1998. 

Crystallization is a thermal, phase-forming separation process from an amorphous phase, at least one solid crystalline phase is formed by phase transformation or by crystallization from a solution, which has one or more solids molecularly dispersed in a solvent, or by crystallization from a melt, or by desublimation out of a vapor phase. A crystalline product is produced from an initial amorphous phase, liquid or gas, with one or more components, for the purpose of forming, cleaning or mixture separation. 

Ozone can be analyzed by titrimetry, direct and colorimetric spectrometry, amperometry, oxidation—reduction potential (ORP), chemiluminescence, calorimetry, thermal conductivity, and isothermal pressure change on decomposition. The last three methods ate not frequently employed. Proper measurement of ozone in water requites an awareness of its reactivity, instabiUty, volatility, and the potential effect of interfering substances. To eliminate interferences, ozone sometimes is sparged out of solution by using an inert gas for analysis in the gas phase or on reabsorption in a clean solution. Historically, the most common analytical procedure has been the iodometric method in which gaseous ozone is absorbed by aqueous KI. 

The first phase of our efforts was the unambiguous synthesis of each model substrate. PN and PX were already well characterized materials (1) While direct synthesis of the phenyl and carbomethoxy compounds from PN and/or PX was attempted, this approach was unsuccessful due to the sluggish reactivity of the norbornenyl double bonds in these molecules (2). A successful approach to CBN and (fiBN based on N-phenyl maleimide (NPMI) trapping of the respective thermodynamically favored 1-substituted cyclopentadienes is shown in Equation 1. Similarly, kinetic trapping of 2-phenyl cyclopentadiene, from the in situ dehydration of 3-hydroxy, 3-phenyl cyclopentene, gives a clean yield of (f)VN (Equation 2). The remaining phenyl isomer (VX) and the three other carbomethoxy isomers (CBX, CVN, CVX) were all obtained by the thermal isomerization chemistry described in the next section of this paper. They were each isolated in pure form by liquid chromatography We were unable to obtain any (f)BX or any of the 7-substituted isomers by any means. 

According to the vendor, the HT-6 technology is not a destruction process but a separation process technology. The process cleans the soil and concentrates the organics into an organic oil phase. For refinery wastes, coal tar wastes, and creosote, this oil is directly suitable for commercial reuse as a refinery feedstock. The high-temperature thermal distillation technology is not currently commercially available. 

You need to decide the goal of an analysis before developing a chromatographic method. The key to successful chromatography is to have a clean sample. Solid-phase microextraction, purge and trap, and thermal desorption can isolate volatile components from complex matrices. After the sample preparation method has been chosen, the remaining decisions for method development are to select a detector, a column, and the injection method, in that order. 

SrTi03 and Ti02 crystals for gas-phase studies were polished with ly diamond paste. Pre-reduced" SrTi03 crystals were baked four hours in flowing hydrogen at 1270 K. Ti02 crystals were reduced in Vaauo. Clean surfaces were produced by Ar+ bombardment and thermal annealing. 

I. Spectroscopic Determinations. Gas-phase infrared spectra provide a useful adjunct to vapor pressure measurements in the identification of volatile materials. The cell illustrated in Fig. 9.15 allows the sample to be quantitatively returned to the vacuum line after the spectrum has been obtained, so the process is completely nondestructive. The primary problem with a gas cell is to obtain a vacuum-tight seal between the window material and the cell body this may be accomplished with Glyptal paint or with wax- If the latter is used, it is necessary to warm and cool the alkali halide windows slowly to avoid cracking them due to thermal stress. For this purpose an infrared lamp is handy. The most satisfactory method of attaching windows is O-rings because this allows the easy removal of the windows for cleaning and polishing. 

The reported gas-phase acylations with Nafion-H catalyst were generally carried out at the boiling point of the hydrocarbon to be acylated. The yield of aroylation reaction depends on the relative amount of the catalyst used. Optimum yields were obtained when 10-30% of Nafion-H was employed relative to the aroyl halide. Although this procedure allows very clean reactions with no complex formation and easy work-up procedures, it is presently limited to only aroylation. Attempted acetylation of aromatics with acetyl chloride under similar conditions led to thermal HC1 elimination from the latter to form ketene and products thereof. In the reaction of acetyl chloride by itself with Nafion-H, diketene was detected by IR and NMR... 

Thermal treatment. Heating of the material may cause desorption of weakly bound species from the surface and can therefore be used to clean surfaces. A positive side effect is that annealing reduces the number of surface defects since it increases the diffusion rates of surface and bulk atoms. There can also be some unwanted side effects surface melting and other types of phase transitions may occur well below the bulk melting point, leading to other than the desired surface structure. 

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