Halogen lamp - electric lighting device, the principle of operation of the device in comparison with a simple incandescent lamp is complemented by the introduction of halides into the flask to increase the service life and preserve the product in its original form for a long time.
The history of the creation of halogen lamps
The history is closely connected with incandescent lamps, we refer readers to the corresponding review for a detailed acquaintance with the history of the invention. Here we stipulate only that the first to discover the glow of conductors on a sample of platinum wire, Sir Humphry Davy. In the basement of the Royal Institution, there was a power source of two thousand cells that managed to heat the cut to temperatures above 550 degrees Celsius, at which bodies begin to glow in terrestrial conditions. The effect did not last long, but marked the beginning of a long epic search for its use as a useful measure for the needs of mankind.
In Russian practice, the history of the creation of incandescent bulbs begin in 1872, when our countryman Lodygin created his own sample. The accomplishments of the other men of science have been prudently forgotten. The authors tend to read from 1882, when Edwin Scribner first guessed to introduce a weak chlorine atmosphere into a coal lamp instead of a vacuum. This largely blocked the blackening of the flask. In the text of the patent, the invention is given a wrong interpretation: supposedly chlorine forms a transparent film that eliminates a known defect.
In reality, the halogen compounds dissociate well, the molecules evaporated from the surface of the helix gradually return to their original place, eliminating the black deposit on the flask. Patent US254780 A is today considered the first bird to announce the arrival of halogen lamps. The idea for a long time did not find practical application. And in the atmosphere of the flask inert gases are used, for example, nitrogen in the Lodygin specimen. The merit of a scientist is to replace the vacuum, which made the construction fragile, and the manufacturing technology difficult.
Forgotten historians name - George Meikl. The text of patent US1267888 A proposes to add iodine to the inert gas medium of a lamp diode. A number of positive effects occur: parasitic voltage losses in the arc decrease to 11–12 V( usually from 16 to 20 V), work becomes constant. There is the first use of other halogens, in addition to chlorine, in the atmosphere of the lamp. Although it is a rectifier device. In addition, the vacuum lamp did not work for more than 1000 hours, the device was difficult to manufacture. Lodygin used nitrogen for practical purposes, used noble gases( argon, etc.).
The 1923 year of discovery of the regenerative cycle in the atmosphere of alkali metal halides is considered key. It is shown that tungsten molecules evaporated from the filament gradually return back. The text of the patent refers to a certain transparent film formed by halogen. It is evident that the authors relied on the ideas of Edwin Scribner. This was the starting point for the further development of halogen lamp technology. Johannes Antonius Maria van Limpnt was engaged in experiments with crystal growing. This is all the more commendable because semiconductor technology was born later, but by studying the diffusion and precipitation of impurities from gases, the scientist discovered the beneficial qualities of halogens: iodine, bromine, chlorine. With the help of these compounds, it was possible to restore tungsten( or coal) coils, spray metal with a thin layer on the surface of the parts.
The USSR patent number 7415 of January 13, 1929 deals with methods for creating durable tungsten filaments. For this purpose, from 0.1 to 3% hafnium oxide was added to the initial metal powder. Scientists went to increase the life of incandescent lamps in different ways. Similarly, Neunhoffer and Schulz obtained in 1949 a patent for an incandescent lamp filled with tungsten or rhenium halides. This contributes to the regeneration of the thread. About the patent little is known, the result of the action of halides was short-lived.
During the theoretical fabrications, it was assumed that the compounds interact in an unknown way with tungsten and other metals contained within the flask. And when the US space industry needed a powerful source of radiation imitating the Sun, the scientists had to recall the regenerative tungsten cycle and previous developments. Carbon lamps today are famous for heating not air, but objects. The reason is clear - energy is transferred predominantly by radiation. To create high power densities, the tungsten coil wriggles with a thin thread. Known designs with double thread.
Quartz Lamps: First Steps
On March 3, 1958, engineers General Electric, Friedrich Elmer and Wiley Emmett, filed a patent for a heating lamp where the coil was protected by a halide medium. The text stated that with prolonged operation, the flask of typical models was gradually covered with a dark bloom. To minimize the effect, the size of the spherical part sought to increase. Plaque is distributed over a larger area and is less noticeable. There have been other attempts to solve the problem:
- . The use of heavy vapors of krypton, xenon, mercury. In the latter case, an additional pressure above atmospheric pressure was applied.
- . Use of neutral gases: argon and nitrogen.
Measures did not correct the situation completely. Scientists propose to use for the regeneration of the thread( and cleaning the flask) a pair of iodine. As a result, the product for the space industry, blackened in 10 minutes, has already served 2,000 hours. The idea is not new, the text of the patent states that the solutions proposed earlier did not have commercial success. Such a kind of logic.
Feeling their own precarious position, the researchers continue the rationale, saying that a lamp with a diameter of 0.08 to 0.5 inches can be used for heating and lighting. At that time, there was no concept of a reflector in household appliances, the estimated distance to the wall was carefully specified in order to avoid fire. According to experimental data, iodine continues to perform a regenerative function within temperatures up to 250 degrees Celsius, the work is broken at 1200. It is better to make a flask of quartz. A Vycor material containing up to 96% silica( silica) is proposed.
The concentration of iodine is not less than 0.01 µmol per cubic centimeter. The upper limit determines the transparency of the atmosphere of the flask. Experimentally, the maximum possible partial pressure of iodine vapor was 5 mm Hg( corresponding to 1 µmol / cc).With vertical operation of a long flask, stratification of the medium is possible, but, as a rule, concentration of substances is sufficient. Some value provided comments on the inadmissibility of the use of other gases:
- Chlorine destroys thread supports and causes spikes on tungsten in extreme areas.
- Bromine is less destructive than chlorine, fluorine is not suitable at all.
- The use of mercury vapor or nitrogen contributes to the blackening of the flask.
It is recommended to maintain a partial pressure of inert gas in the region of 600 mm Hg for uniform sedimentation of tungsten on a filament. As a result, scientists obtained a device with a radiation power of 100 W / inch length at a power density of 24 W per square centimeter of the bulb. Parameters can be varied within wide limits. At a filament temperature of 2500 degrees Celsius, the efficiency of the device is 30% higher than that of standard lamps of 500 W with a similar service life of 1000 hours.
In the production of filaments, an annealing process is used on a steel mandrel. During processing, it is carefully required to control the level of iron diffusing into the helix by maintaining an appropriate temperature in the furnace. During further operation, the impurity atoms are relatively easy to evaporate and bind halogen. In addition, an indestructible raid on the walls of the flask.
Along the way, it is noted that it is desirable to minimize the number of calipers. In places of attachment the temperature is slightly lower, tungsten settles worse. In modern quartz lamps sometimes do without calipers. The owner of the convection oven will make sure if she bothers to lift the lid and look under it.
Meanwhile, the products showed a number of shortcomings: high temperature, the absence of a reflector. Metal calipers must be resistant to iodine, which means that copper is fundamentally not suitable for the required purposes - tungsten, molybdenum or platinum are needed. Similar applies to adjacent wires. They are heated to a high temperature. In modern lamps, the glass at the ends is clamped completely, only tungsten is in contact with the medium. In the patent, the inventors were able to collect the properties of the heating and lighting device. Soviet intelligence was not asleep, and in the coming 1960, the halogen lamps KI 220-1000 appeared in the USSR.
Design halogen lamps
In heating devices, a tungsten coil often touches the glass - in places. It is not curved around, but with a triangle, each coil of its own size, and only a few touch the bulb, and in a relatively small number of points. This helps to avoid excessive heating of the glass. In the convection oven the flask is constantly blown by a fan, which prevents it from warming up above 600-700 degrees. The helix works with tougher modes. With a cubic crystal lattice of refractory tungsten. The liquidus temperature is at the point of 3653 K. The operating mode does not exceed 90% of the specified value.
Such high temperatures have been achieved through the use of halogens. In vacuum, evaporation from the surface of the helix would become too strong. Quartz glass is selected for the manufacture of the flask for physical properties. The material has a wide window for transmitting radiation, therefore, the surface is heated relatively poorly. Quartz has a low coefficient of thermal expansion and excellent thermal shock holds.
Despite the fact that silicon oxide is considered the most abundant mineral on the planet( silicon by weight is 26% of the earth's crust), it almost does not occur in its pure form, but is part of agate, rauchtopaz, citrine, amethyst, jasper, rock crystal,river sand and a number of other natural formations: granite, grace, slate, various silicates. And no wonder in the patent was mentioned silica. The difficulty lies in extracting the required component from the rock. There are several stable modifications of quartz:
- Ordinary professionals bears the name of the Greek letter Beta and represents large transparent crystals. It is believed that under normal conditions is stable below the temperature of 573 degrees Celsius.
- Having overcome the specified temperature threshold, quartz turns into alpha modification. And it remains here to 870 degrees Celsius.
- With a further increase in temperature, tridymite( ternary crystals) is formed. And so to 1470 degrees Celsius.
- The next stable modification to a temperature of 1710 degrees Celsius is cristobalite.
- Higher scale silica is present in the form of a melt.
Possible technological process of cooling quartz without the formation of crystals. Amorphous form is used to create glass. The configuration of the crystals depends on:
- Crystallization rates.
- Viscosity of the liquid phase.
- The presence of impurities.
- Spatial location of the object.