Heating Materials

A number of methods are used to supply heat in the laboratory depending upon the intensity of heat required, the duration of heat required, the stability of temperature required, and whether or not a flame can be used because of the absence or presence of flammable solvents. 

Hot tap water. If only gentle warming of a sample is required, it 

Bunsen burner. A Bunsen burner, shown in FIGURE D.l.a, is designed 

If a flame of intermediate heat intensity is required, the flame can be adjusted between the extremes of the luminous flame and the nonluminous flame by proper rotation of the collar regulating the air supply. Practice these adjustments before using the Bunsen burner in an experiment. 

Fisher burner. A Fisher burner (or Meker burner), shown in FIGURE D.3.a, attains slightly higher temperatures (about 1200°C) than a Bunsen burner and can provide up to twice the heat output of a Bunsen burner. A 

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Advanced Structural and Heating Materials. Molybdenum siHcide [12136-78-6] and composites of MoSi2 and siHcon carbide, SiC, have properties that allow use as high temperature stmctural materials that are stable in oxidizing environments (see Composite materials Metal-matrix composites). Molybdenum disiHcide also finds use in resistance heating elements (87,88). 

Vapor Toxicity. Laboratory exposure data indicate that vapor inhalation of alkan olamines presents low hazards at ordinary temperatures (generally, alkan olamines have low vapor pressures). Heated material may cause generation of sufficient vapors to cause adverse effects, including eye and nose irritation. If inhalation exposure is likely, approved respirators are suggested. Monoethan olamine and diethanolamine have OSHA TLVs of 3 ppm. 

Reactivity. Bromine is nonflammable but may ignite combustibles, such as dry grass, on contact. Handling bromine in a wet atmosphere, extreme heat, and temperatures low enough to cause bromine to soHdify (—6° C) should be avoided. Bromine should be stored in a cool, dry area away from heat. Materials that should not be permitted to contact bromine include combustibles, Hquid ammonia, aluminum, titanium, mercury, sodium, potassium, and magnesium. Bromine attacks some forms of plastics, mbber, and coatings (62). 

Primary chemical processes. The external heat source may supply free radicals which accelerate combustion. The heating material might also be activated by autocatalytic or autoignition mechanisms. 

Autoclave Vessel for heating materials under high steam pressure. Used for sterilization and other applications. 

As applied to molded plastics, the process of heating material to a specified temperature and slowly cooling it to relieve stresses. 

Thermal Sensitivity. At 375—90° it decomps with burning in 6-8secs (Ref 2). In a 20mm tube combstn is difficult. It melts and boils before burning and only the heated material burns without propagation to unheated material. When unconfined it melts and boils without burning (Ref 1)... 

Lane, G.A., 1983. Solar Heat Storage Latent Heat Material, Volume I Background and Scientific Principles, CRC Press, FL. 

From Fig. 3.12, we see that at fixed (low) temperature, the specific heat of various solids range over many orders of magnitude. Low specific heat materials (high Debye temperature) are for example very important in the realization of detectors (see Chapter 15). High specific heat materials are essential as regenerators in cryocoolers (see Chapter 5 and Fig. 3.13). 

Figure 4 shows the results. Above 200"C, the dashed line reflects heats of pyrolysis according to Equation 2 and Figure 3, while the more realistic, full line is based on heats which approach zero at 300 C. According to the figure, heat release peaks between 130 and 230 C. Since heat dissipates out of self-heating materials in proportion to temperatures above ambient, and at 230"C the dissipation should exceed the dissipation at 130 C by a factor of two, the most rapid pyrolytic self-heating can be expected between 120 and 170 C. 

Self-Heating Materials. Universitat, Arbeitsgem. Feuerschutz, Forschungsber. 24 Rarlsruhe, Fed. Rep. 

This is identical with our result for the ignition time at a high heat flux in the thermally thin ignition of a solid. It can be generalized to say that flame speed - thermally driven -can be represented as the ratio of the flame extension length to the time needed to ignite this heated material, originally at 7). 

Thomas, P. H., "On the Thermal Conduction Equation for Self-Heating Materials with Surface Cooling," Trans. Faraday Soc., 54,60 (1958). 

Spontaneously Combustible and Pyrophoric Substances Spontaneously combustible substances will readily react with the oxygen in the atmosphere, igniting and burning even without an ignition source. Ignition may be immediate, or may result from a self-heating process that may take minutes or hours (hence, some spontaneously combustible substances are known as self-heating materials). 

Molybdenum co-factor (Moco), 77 33 Molybdenum complexes, 26 927-929, 949 Molybdenum(III) complexes, 17 26-27 Molybdenum compounds, 17 19-43 in advanced structural and heating materials, 17 38-39 in anticorrosion agents, 17 39 biological aspects of, 17 31-34 biological uses for, 17 39-40 biomedical uses for, 17 40 catalytic applications of, 17 38 chemistry of, 17 29-31... 

Ideally, all components of interest (including such entities as common cleaning materials, air, water, heat, materials of construction, additives, catalysts, other utility services, etc.) are listed on both the x and y axes of the grid. The intersections of the cells in the matrix represent the consequences of each mixed pair. Presentation of the data in chart form allows for quick use, especially during a process upset (i.e., emergency) situation. 

Materials that readily undergo violent chemical change at elevated temperatures and pressures Materials that exhibit an exotherm at temperatures less than 200° C and materials that polymerize vigorously and evolve heat Materials that react violently with water or form potentially explosive mixtures with water heat of mixing less than 600 but greater than 100 cal/g Less than 100 but greater than 10 W/mL... 

Fontaine et al. [81] concluded that the increase in crystallinity by further heating material, crystallized at 200 °C, to 215 °C involves a crystal (lamellae) thickening process which is probably due to crystal perfection at the boundary layers. Further annealing of this material at temperatures above 215 °C led to a melting temperature increase that was attributed to crystal perfection alone and not to crystal thickening. 

Avoid handling heated materials until they have cooled. 

CNTs can enhance the thermal properties of CNT-polymer nanocomposites. The reinforcing function is closely associated with the amount and alignment of CNTs in the composites. Well-dispersed and long-term stable carbon nanotubes/ polymer composites own higher modulus and better thermal property as well as better electronic conductivity (Valter et al., 2002 Biercuk et al., 2002). Both SWNT and MWNT can improve the thermal stability and thermal conductivity of polymer, the polymer-CNT composites can be used for fabricating resistant-heat materials. 

TABLE 2. Bonding Strength of Selected Thermoplastic Polyimides after Exposing Surfaces to Plasma Treatment or Heating Material to 380°C... 

Hazard Class 4 - Division 4.2. Spontaneously Combustible Materials (These include pyrophoric materials and self-heating materials) ... 

A major challenge that remains is to link the structural insight provided by HRTEM to simultaneous measurements of the catalytic activity and selectivity at ambient pressures or higher. At the moment, this seems to be a daunting task, as the amount of catalyst used for TEM imaging is significantly smaller than the amount of heated material in contact with the gas within a microscope. One way to... 

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