Heating method

Heating is an important laboratory technique that is used in a variety of situations. For example, many chemical reactions require heating to proceed at a reasonable rate. Heating is also used to purify liquids by distillation, to remove volatile solvents during the work-up of a reaction, and to dissolve solids when purifying solid 

Although we describe below how burners are properly used for heating purposes, the experimental procedures in this textbook focus on flameless heating devices. Burners can be substituted for such devices in most cases, but not all. Consult with your instructor if you have any questions regarding the suitability of substituting flames for other heating devices. 

Most chemistry laboratories are supplied with natural gas to fuel various types of burners. A burner provides the convenience of a rapid and reasonably inexpensive source of heat. However, many organic substances, especially solvents such as ether and hexane, are highly flammable, and you should always exercise 

You must be aware of what others are doing in the laboratory. Although you might be using a burner to perform a completely safe operation, someone nearby may be working with a very volatile, flammable solvent, some of which can creep along the bench top for several feet These vapors or others in the room may be ignited explosively by an open flame. 

Because heating mantles are constructed of nonferrous materials, they can be used in conjunction with magnetic stirring (Sec. 2.11), so simultaneous heating and stirring of a reaction mixture is possible. A variable transformer connected to an electrical outlet provides the power for heating the mantle. The cord from the mantle itself must always be plugged into a transformer, never directly into a wall outlet  

To avoid having to resort to this apparatus, the author used a different technique. This consisted of heating wastes arriving in continuous mode to the reactor. Such a method distinguishes the two processes that 1 will describe below. 

A possible sweeping of the reactor by the superheated water vapour produced by an exchanger using the lost heat of the gas burners constitutes an excellent improvement by realizing a vapo-cracking, minimizing the formation of tar and coke. 

These impurities are swept and released with the wax flowing outside the reactor. This wax is very fluid and can be easily decanted and filtered with traditional equipment, highly heat-proofed after its extrusion from the reactor without being too cooled. Therefore it is sufficiently purified to be treated in a second phase. 

The possible heavy impurities that may remain in the receiving channel of the reactor are periodically scraped by a traditional mechanical apparatus and are collected in a container prepared for the purpose of evacuating them easily. 

The uniqueness of this process results from the fact that the steam provides the total heat necessary for the primary cracking stage. It is not therefore a simple vapo-cracking. This process intervenes simultaneously while suppressing to the maximum the formation of tars and coke by dilution of steam and partial reduction of the steam pressure resulting from the heavy hydrocarbons produced. Additionally, this process is very flexible and it is suitable for the treatment of highly variable feed rates of waste. 

Thermal CVD requires high temperature, generally from 800 to 2000°C, which can be generated by resistance heating, high-frequency induction, radiant heating, hot plate heating, or any combination of these. Thermal CVD can be divided into two basic systems known as hot-wall reactor and cold-wall reactor (these can be either horizontal or vertical). 

In some cases, the parts to be coated (such as semiconductor silicon wafers) are stacked vertically. This minimizes particle contamination and considerably increases the loading capacity (as opposed to horizontal loading). 

Hot wall reactors have the advantage of close temperature control. A disadvantage is that deposition occurs everywhere, on the part as well as on the walls of the reactor, which require periodic cleaning or the use of a disposable liner. 

Cold-Wall Reactors. In a cold-wall reactor, the substrate to be coated is heated directly either by induction or by radiant heating whi 1 e th e rest of the reactor remains cool, or at least cooler. Most CVD reactions are endothermic, i.e., they absorb heat and deposition takes place preferentially on the surfaces where the temperature is the highest, in this case the substrate. The walls of the reactor, which are cooler, remain uncoated. A simple laboratory-type reactor is shown 

A more elaborate example of induct on heating is shown in Fig. 5.8, which showsareactordesignedforthedeposition of silicon epitaxy in semiconductor devices (see Ch. 13).Thepowerissuppliedby a solid-state high-frequency (20 KHz) generator. A radiation reflector, shown in Detail A, increases the efficiency and uniformity of deposition. Pressure varies from 100 mbar to 1 atm. 

Determine the optimal pH of antigen retrieval solution for each antigen. Citrate buffer (0.01 M) adjusted to pH 6.0 with HC1 is used widely. Determine the desired temperature based on the type of tissue and antigen under study. For fatty tissues, 90°C is recommended adjust the duration of heating accordingly. Place slides in plastic Coplin jars containing the 

Microwave heating for 20 min is the same as Method 1 except that the heating is employed four times for 5 min each. Total time required is 35 min. Improved immunostaining of many types of antigens can be achieved by extending the heating time. The procedure requires attention for 20 min to check the fluid level, and occurrence of hot or cold spots may complicate the procedure. 

The pressure cooker-microwave heating method is simpler than the autoclave procedure and more efficient than microwave heating alone. The pressure cooker does not require checking the level of the antigen retrieval solution during heating in the microwave oven, and a large number of slides can be loaded simultaneously. In addition, the pressure 

Place slides in Coplinjars containing antigen retrieval solution that has been previously heated at 80°C. Set the jars in the center of a stainless steel autoclave equipped with a 1,850 W heating filament. Tightly close the door of the autoclave as required by the instructions, and heat at 120°C for 10 min at 15 psi. Cool down with running tap water for 20-30 min, then rinse the sections with 0.05 M PBS at room temperature and immunostain. 

In contrast to microwave heating, steam treatment heats slides slowly to a uniform temperature. This avoids boiling the antigen retrieval fluid and minimizes section detachment from slides. Steam heat used in combination with EDTA and protease digestion has been 

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The various heating methods produce a vapor that is a mixture of gas, very small droplets, and small particles of solid matter (particulates). Before droplets or particulates can coalesce, the whole vapor is swept into the plasma flame for analysis. Clearly, the closer the heating source is... 

Both batch and continuous furnaces maybe employed. The maximum temperature that can be reached in a sintering furnace depends on the furnace and the heating methods (Table 7) (23). 

Table 7. Heating Methods and Element Material Temperature Limits ...

Air distribution methods Exhaust methods Heating methods Cooling methods... 

It the main reason for the stratification strategy is contaminant control in [he occupied zone, the same strategy should be applied in winter conditions, too. Thus, the selected hearing method has to fulfill two requirements to siip-pttrt the creation of the vertical stratification and not to create disturbing airflows into the hall. In this case one option would be the floor heating method see Fig. 8.16c. Additionally, one should consider the prevention of boundary layer flows along the outer walls using, for example, passive methods. -... 

A amimon heating method in industry is using blowers that blow heated air into the room. See Fig. 8.57, An advantage is that the installation costs are low. A possible disadvantage is that it mixes the air in the room, which may not be desirable in combination with displacement ventilation. 

Duiser, J. A. 1989. Warmteuitstraling (Radiation of heat). Method for the calculation of the physical effects of the escape of dangerous materials (liquids and gases). Report of the Committee for the Prevention of Disasters, Ministry of Social Affairs, The Netherlands, 2nd Edition. 

A modern version of the oven heating method is the Mytron FAB-1 moisture tester, in use at Waltham Abbey, Sussex, Engl, for detg moisture... 

The one-pot, three-component synthesis of a 20-membered dihydrotri-azine hbrary was also dramatically accelerated through the use of microwave irradiation [79]. Heating a subset of substituted anilines, cyanoguanidine and acetone in the presence of concentrated hydrochloric acid for 35 min at 90 °C in a single-mode microwave reactor gave the corresponding 2,2-dimethyl-1,2-dihydro-s-triazine hydrochloride 51 in comparable yield to conventional conductive heating methods but in a much shorter reaction time and increased purity (Scheme 21). 

To evaporate the source material, various heating methods are used such as resistance heating, electron beam, pulsed excimer laser, or cathodic arc (where the source is the cathode). 

The production of fatty acid-capped silver nanoparticles by a heating method has been reported [115]. Heating of the silver salts of fatty acids (tetradecanoic, stearic, and oleic) under a nitrogen atmosphere at 250°C resulted in the formation of 5-20-nm-diameter silver particles. Monolayers of the capped particles were spread from toluene and transferred onto TEM grids. An ordered two-dimensional array of particles was observed. The oleic acid-capped particle arrays had some void regions not present for the other two fatty acids. 

Ethylene oxide treatment can also be considered as an alternative to radiation sterilizahon in the commercial production of disposable medical devices (Chapter 21). These techniques do not, however, offer the same degree of sterility assuranee as heat methods and are generally reserved for temperature-sensihve items. 

We have also included R.F. (radio-frequency) current as a heating element, although it is only a heating method when employed with a suitable succeptor. Finally, one other method is listed for the sake of completeness, that of the oxy-hydrogen flame. It generates combustion products (H2O) but the RF- method can be used in any atmosphere... 

In the laser flash method, the heat is put in by laser flash instead of electric current in the stepwise heating method mentioned above. Thus this method may be classified as a stepwise heating method. A two-layered laser flash method was developed by Tada et al. " The experimental method and the data analysis, including a case involving radiative heat flow, are described in detail in the review article by Waseda and Ohta. A thin metal plate is placed at the surface of a melt. A laser pulse is irradiated onto a metal plate of thickness / having high thermal conductivity. The sample liquid under the metal plate and the inert gas above the plate are designated as the third and first layers, respectively. The temperature of the second layer becomes uniform in a short time" and the response thereafter is expressed by... 

Heat extraction from the bedrock by a heat pump system is an environmental friendly heating method where 70% of the heat is taken from the ground. This... 

Bartzanas T., Tchamitchian M., Kittas C. (2005). Influence of the heating method on greenhouse microclimate and energy consumption. Biosystems Engineering, 91(4), 487-499. 

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