Oven temperature control considerations

Many commercial hplc instruments optionally provide a forced air oven which will control temperature with a stability of typically 0.1 °C from ambient temperature to 100 °C. Because of the use of flammable solvents, safety considerations are important, so the ovens are usually provided with a facility for nitrogen purging and are designed to prevent the build up of solvent vapour in the event of a leak. If temperature control is used, it is important that the sam-... 

The drying oven must be one with good air circulation and uniform temperature control drying at 120° causes the evolution of considerable amounts of free iodine. 

The water tank (4) is placed in a temperature controlled oven, separate from the column oven. Noise resulting from the formation of bubbles in the water tank (4) can be considerably reduced by use of metal frit with 10 to 20 urn porosity. The sampling port, the chromatographic column and the detector should always operate at a temperature higher than that of the water tank. In most applications a flame-ionization detector is used. 

The control of the self-cleaning procedure (pyrolysis) of especially equipped kitchen ovens is another focus of development. The underlying idea is to burn the organic residues at elevated temperatures (around 400 °C) and to detect the emerging volatile compounds. In order to minimize energy consumption, the process time should be kept as short as possible. During this process considerable amounts of CO and C02 are released. A decrease in concentration of these compounds can thus be taken is an indicator of the end of process. The most direct method would be the detection of C02 in the flue gas. The most common C02-... 

The benzene containing all solid products from the reactor and pot residue was reduced to 30 ml. volume by vacuum distillation at 50 °C. Considerable foaming was encountered, requiring careful control of the distillation. The 30 ml. of brown benzene solution was added to 300 ml. isooctane at room temperature. A yellow solid precipitated immediately and was collected by filtration. After several washings with hot methanol, the material was dried for eight hours at 70°C. in a vacuum oven. Benzene soluble polymer-Fraction 1, 2.3 grams, M.W. 4360, % C 88.32, %H 7.18, C/H 1.02. 

To prepare glazing, transparent sheets are cast in cells made of plate glass with flexible gaskets used as spacers (cf, Sandler and Karo [87], Procedure 4-2 for a detailed description of a glass casting cell). Control of the polymerization temperature used with such cells varies considerably with the thickness of the polymer sheet to be produced. For example, a sheet 3- to 5-mm thick can be prepared at 70°C with a monomer solution containing 3% of dibenzoyl peroxide over a period of 60-72 hr in a circulating air oven. After the sheet is removed from the cell, it is postcured at 115°C for an additional 2 hr. With thicker sheets, lower initial temperatures are required to permit proper dissipation of the heat of polymerization. 

Aging is carried out in thermostatically controlled ovens, which may be of the usual cabinet type or consist of a number of cells in a heated block. For plastics, relatively little consideration appears to have been given to details of the oven other than control of temperature, but for rubbers other factors that can influence results are carefully specified, and it would seem reasonable to suppose that these could be significant for plastics also. 

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