Sublimation chamber

Gas evaporation using Ar for the preparation of various sort of metal fine powders was first reported by Kimoto et al. in 1963 (5). The production chamber of this method is basically the same as that of a vacuum sublimation chamber. A target material is heated in this chamber with several torr inert gas atmosphere. The nanometer-sized particles are easily formed in the chamber space. However, by this method, it is difficult to get genuine nanoparticles whose sizes are several nanometers. This is because of the radiation heating in a production chamber, resulting particle coalescence on the chamber wall or particle collector, as well as the direct particle contact in the deposited particle layer (powders). Therefore the size becomes several tens to hundreds of nanometers. Several ultrafme metallic powders are now commercially available, including Cu, Ag, Al, Ni, Co, Fe, and Au, with a size of several tens of nanometers. 

For the sublimation of quantities of materials in the region of a few milligrams, the vacuum sublimation block supplied by Reichert-Jung is particularly suitable. This block is located on the hot-stage microscope (see p. 240), the sublimation chamber carefully evacuated, the temperature raised slowly, and the process of sublimation observed through the microscope. 

Nail investigated the effect of chamber pressure on heat transfer and the relative rate of sublimation. Chamber pressure has a prominent effect on product temperature. Shelf temperature is the principal influence on sublimation rate chamber pressure has a strong influence on heat transfer from the shelf to the vial and the relative difference between the vapor pressure of ice and the environment. The combined effects yield a direct impact on product temperature. The driving force of sublimation is the difference between the vapor pressure of ice in the product and the pressure of the environment. An increase in the differential increases the propensity of ice to sublime. For example, if the product temperature is 32°C with a corresponding vapor pressure of ice being 321 pHg... 

The value of the partial pressure of water vapor at the top of the dry layer is equal to the total pressure in the sublimation chamber. 

Supported Ru catalysts were also prepared by the OMCVD under static conditions. In this route, the Ru3(CO)i2 precursor is in direct contact with the Si02, i.e., the transport of the precursor from the sublimation chamber to the reactor can be avoided. Thereby, the decomposition of the precursor during transport can be avoided because Ru3(CO)i2 easily decomposes even below 423 K. The Ru content can be controlled by the initial amount of the Ru3(CO)i2 precursor. The Ru content also was affected by the used supports. When MgO, CNTs and Si02 were mixed with the same amount of the precursor and the mixtures were decomposed under the same conditions, the resulting Ru/MgO, Ru/CNTs and Ru/Si02 catalysts had a 4.37, 3.58 and 2.88 wt. % Ru content, respectively. This observation demonstrates that the support properties, such as particle size and exposed surface groups, have an important effect on the deposition of the precursor. 

Selenium(IV) oxide is purified by three successive sublimations in the apparatus illustrated in Fig. 3 (see also synthesis 33). The sublimation chamber A is maintained... 

Mixing vessel 2 Reactor 3 Hydrolysis reactor 4 Vacuum sublimation chamber Figure 11.4 Row diagram for the synthesis of quinizarin... 

Commercial sublimation adapters such as those shown in Figure 2.59 are available for microscale work. A Winston adapter is normally used with a sublimation chamber such as a 3- or 5-mL conical vial (Fig. 2.59a), whereas adjustable adapters may be used with 5- or 10-mL round-bottom flasks (Fig. 2.59b). In both cases a cold-finger that may be connected to a vacuum source is fitted to the chamber containing the substance to be sublimed, and the connection is secured with a standard-taper joint that is often accompanied by an O-ring and threaded collar (Fig. 2.59). The cold-finger can be filled with ice or dry ice. The advantage of using... 

A sublimation apparatus was set up in a chemical hood (Fig. 14.2). An Edwards E2M8 high vacuum pump with a vacuum meter to provide controllable vacuum in the sublimation chamber (trrNote 4). 

The tissue coated porous Si was attached to the bottom of the apparatus condenser in direct contact with the running cooling water. 0.3 g of CHCA or DHB was added to the bottom of the sublimation chamber see Note 5). 

Because the heat flux is not evenly distributed through the sublimation chamber, resulting principally from the relative importance of the radiative flux component coming from the shelves and from the side-walls of the freeze-dryer, each vial of the whole batch does not receive the same overall heat flux. In fact, it is well knovm that the vials located at the edges of each shelf present shorter sublimation and desorption times and higher temperature profiles. This phenomenon can be investigated by... 

Nevertheless, the main drawback of this method is that the distribution of the small ice crystals can be non-uniform along each plate of the freeze-dryer due to a complex and uncontrolled gas flow regime in the interior of the sublimation chamber. 

The influence of shelf temperature and of sublimation chamber total gas pressure on the drying curve (X(t)) and on the drying rate curve (— ) is discussed below. As observed by many authors during the drying of different types of materials, for example during the convective or infrared reactive drying of thin coating films, the... 

Although the experiments using this procedure are reproducible, the conditions of the reaction are inconsistent. The linear flow-viscosity of the solution decreases with the distance from the center if the solution is added in the center of the plate, and the linear velocity of the scraper increases with the radius. This produces different Reynolds numbers along the surface and different heat transfer conditions and, as a result, different temperatures are obtained by the strongly exothermic reaction of TMA and frozen water at the surface. To have more constant reaction conditions, a thin-film reactor was constructed [34]. A cooled and rotating steel band picks up ice by sublimation in a sublimation chamber and introduces the ice into the reaction chamber. Here, the ice reacts with a solution of TMA, producing MAO and methane. The better heat transfer on the steel band makes it possible to have more constant reaction temperatures. 

The main installation units would be sublimation and pyrolysis chambers and a cooler in the form of a slab heat converter. Adamsite will be introduced into the sublimation chamber and transformed into vapour at the temperature of 400 C. The Adamsite vapour transported by inert gas (e.g., nitrogen), will pass into the pyrolysis chamber and will be decomposed to free arsenic, hydrogen chloride, nitrogen, low molecular weight hydrocarbons and soot. Free arsenic will be precipitated in the cooler from which it will be removed after partial disassembling of this unit. Units to bind hydrogen chloride, to catch the rest of the arsenic, and to bum hydrocarbons catalytically will be further parts of the installation. It is established that the sublimation and pyrolysis chambers and the cooler will work periodically, with some down time . 

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