Heating object

Stable at room temp powerful explosive. If some dry crystals are scattered loosely on a piece of cardboard and one of the crystals touched with a flame or heated object (rod etc), the material will detonate with such brisance that each crystal will puncture the cardboard Refs 1) Beil 26, (123-24) 2) K.A. Hofmann H. Hock, Ber 44, 2953 (1911) 3) F.R. Benson, Chem Revs 41, 9 (1947) 4) Karrer (1950. ed) p 803 (under Tetrazole)... 

Duration of burning The incendiary materials must not only impart high temperatures but also maintain heat generation without replenishment of fuel. The heat must continue to radiate for an appreciable time and when the heated object is ready to bum, the fire must be present to ignite it. In fact two factors viz. intensity of heat and duration of burning are complementary to each other and must satisfy the purpose of incendiary materials. 

In fluidized bed coating, a product to be coated is heated and then immersed in a dense-phase air fluidized bed of powdered plastic the plastic adheres to the heated object and subsequent heating provides a smooth, pinhole-free coating. 

Heating the target material and immersing it in a thick suspension of the coating material, a partially cured fluid resin, or even a thick solution of the resin, so the resin would migrate to the heated object and gel on the hot surface, then be further baked or ambient cured in place. This is still a favored method of applying vinyl plastisols. (Plas-tisols are, however, more frequently applied by airless spray.)... 

Spectroscope A device for studying the light produced by a heated object. 

One of the most powerful instruments for studying chemical elements is the spectroscope. The spectroscope is a device for smdying the light produced by a heated object. For example, a lump of sodium metal will burn with a yellow flame. The flame looks quite different, however, when viewed through a spectroscope. 

Lead enamels are still used for coating small cast iron objects the enamel coat is formed by dipping the heated object in powdered enamel. 

These photos illustrate the phenomenon of heated objects emitting different frequencies of light. Matter, regardless of its form, can gain or lose energy only in small "quantized" amounts. 

The emissivity is a property of the material. The Umiting value is 1 (blackbody) shiny surfaces have a low value of emissivity. The view factor is a fractional value that depends on the geometric orientation of the source with respect to the heating object. 

Resolved the ultraviolet catastrophe of classical physics, which predicted intense ultraviolet radiation for all heated objects (7 > 0)... 

Incandescence is light emission from a heated object, such as the filament in a lamp or the... 

Always allow heated objects to return to room temperature before you attempt to weigh them. 

When placing a heated object in a desiccator, the increase in pressure as the enclosed air is warmed may be sufficient to break the seal between lid and base. Conversely, if the seal is not broken, the cooling of heated objects can cause a partial vacuum to develop. Both of these conditions can cause the contents of the desiccator to be physically lost or contaminated. Although it defeats the purpose of the desiccator somewhat, allow some cooling to occur before the lid is seated. It is also... 

Never place a heated object on the benchtop instead, place it on a wire gauze or a heat-resistant ceramic plate. 

Keep the tongs and forceps used to handle heated objects scrupulously clean. In particular, do not allow the tips to touch the benchtop. 

The intensity of the radiation is a function of the fourth power of the temperature of the heated object. This means that a radiant heat source operating at several hundred degrees will have a high rate of heat transfer toward a substrate at temperatures up to a few hundred degrees, providing the substrate is not highly reflective or transparent toward the emitted infrared. In practice, a filament is heated by gas or electricity and the radiant energy is directed toward the substrate by means of reflectors. 

Aerosols can experience external influences induced by forces other than electrical or gravitational fields. For example, more than a century ago it was observed by side illumination that next to a heated object there is a layer containing practically no aerosol particles. The thickness of this layer was found to increase with the temperature of the object. In our discussion so far, we have assumed that the fluid in which our particles are suspended is homogeneous without temperature or gas concentration gradients, and so on. Under these conditions there is no preferential direction for the bombardment of the particle by fluid molecules. However, when there are gradients in the fluid temperature, concentration, and so on, there are differences in momentum imparted to a particle by molecules coming from different directions, producing a directional preference in the Brownian diffusion. 

O Reading Check Explain why the color of heated objects changes with their temperature. 

Another method of measuring flow that has had biomedical application is the measurement of cooling of a heated object by convection. The object is usually a thermistor (see Section 2.2.6.2) placed either in a blood vessel or in tissue, and the thermistor serves as both the heating element and the temperature sensor. In one mode of operation, the amount of power required to maintain the thermistor at a temperature slightly above that of the blood upstream is measured. As the flow around the thermistor increases more heat is removed from the thermistor by convection, and so more power is required to keep it at a constant temperature. Relative flow is then measured by determining the amount of power supplied to the thermistor. 

Kirchhoff, Gustav Robert (1824-1887) German physicist in Berlin, Breslau and Heidelberg, who contributed to the fundamental understanding of electrical circuits, spectroscopy, and the emission of black-body radiation by heated objects. 

Hot surfaces If an explosible atmosphere has contact with heated surfaces (hot pipework, boilers, hot spots in stored material), ignition can occur. The temperature at which ignition takes place depends on the size and geometry of the heated object, on the concentration gradient near the wall and to some extent on the wall material. Monitoring of surface temperatures... 

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