JP2015156314A - Filament, light source employing the same, and heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filament which improves efficiency in converting electric power into visible light or near infrared light.

SOLUTION: The filament includes a substrate formed from a metal and on a surface layer of the substrate, a predetermined impurity element is doped in the metal. The metal has such a cross point that reflectance is not changed even if a temperature is changed. The impurity element is such an element that, if doped in the metal, reflectance closer to a short wavelength than the cross point of the metal is reduced more greatly than reflectance closer to a long wavelength.

COPYRIGHT: (C)2015,JPO&INPIT

Description

  The present invention relates to a filament with improved energy utilization efficiency.

  Incandescent light bulbs are widely used in which a current is passed through a tungsten filament or the like to heat the filament to form a light bulb. An incandescent light bulb has a radiation spectrum excellent in color rendering similar to sunlight, and the conversion efficiency from the power of the incandescent light bulb to light is 95% or more, but the wavelength component of the emitted light is as shown in FIG. The infrared radiation component is 90% or more (in the case of 3000K in FIG. 1). For this reason, the conversion efficiency from the electric power of the incandescent light bulb to visible light is as low as about 15 lm / W. On the other hand, the fluorescent lamp has a conversion efficiency from electric power to visible light of about 90 lm / W, which is larger than the incandescent lamp. For this reason, incandescent bulbs are excellent in color rendering, but have a problem of a large environmental load.

  Various proposals have been made as attempts to increase the efficiency, brightness, and life of incandescent bulbs. For example, Patent Documents 1 and 2 have a configuration in which an inert gas or a halogen gas is sealed inside a light bulb, whereby the evaporated filament material is halogenated and returned to the filament (halogen cycle) to increase the filament temperature. Proposed. These are generally called halogen lamps. Thereby, the effect of the increase in the power conversion efficiency to visible light and the extension of a filament lifetime is acquired. In this configuration, it is important to control the components of the sealed gas and the pressure in order to increase the efficiency and extend the life.

  Patent Documents 3 to 5 disclose a configuration in which an infrared reflection coating is applied to the surface of a bulb glass so that infrared light emitted from the filament is reflected, returned to the filament, and absorbed. As a result, infrared light is used for reheating the filament to increase efficiency.

  Patent Documents 6 to 9 propose a configuration in which a fine structure is produced on the filament itself, and infrared radiation is suppressed and the ratio of visible light radiation is increased by the physical effect of the fine structure.

JP-A-60-253146 Japanese Patent Laid-Open No. 62-10854 JP 59-58752 A JP-T 62-501109 JP 2000-123795 A JP 2001-519079 JP-A-6-5263 JP-A-6-2167 JP 2006-205332 A

F. Kusunoki et al., Jpn. J. Appl. Phys. 43, 8A, 5253 (2004).

  However, the technologies using the halogen cycle as described in Patent Documents 1 and 2 can achieve a life extension effect, but it is difficult to greatly improve the conversion efficiency, and the current efficiency is about 20 lm / W. is there.

  In addition, as in Patent Documents 3 to 5, the technique of reflecting infrared radiation with an infrared reflecting coat and reabsorbing the filament to the filament has high efficiency of reabsorption because the reflectance of infrared light by the filament is as high as 70%. It does n’t happen well. Further, the infrared light reflected by the infrared reflective coating is absorbed by other parts other than the filament, such as the filament holding part and the base, and is not used for heating the filament. For this reason, it is difficult to greatly improve the conversion efficiency by this technology. Currently, the efficiency is about 20 lm / W.

  As described in Patent Documents 6 to 9, a technique for suppressing the infrared radiation by the fine structure is a report showing the radiation enhancement and the suppression effect for the wavelength of the extreme part of the infrared radiation spectrum as in Non-Patent Document 1. However, it is very difficult to suppress infrared radiation over a wide range of infrared light. This is because when one wavelength is suppressed, another wavelength is enhanced. For this reason, it is considered difficult to achieve significant efficiency improvements using this technology. In addition, since a fine structure such as electron beam lithography is used for manufacturing a fine structure, a light source using this is very expensive. Furthermore, even if a microstructure is formed on the W substrate, which is a high-temperature heat-resistant member, the W substrate surface particles are recrystallized and crystal grains grow at a heating temperature of about 1000 ° C., and the microstructure portion is destroyed due to this recrystallization. There is also the problem of being done.

  An object of the present invention is to provide a filament having high efficiency for converting electric power into visible light or near infrared light.

  In order to achieve the above object, the present invention provides a filament having a base formed of a metal and having a surface layer of the base doped with a predetermined impurity element. This metal has a cross point where the reflectance does not change even if the temperature changes. As the impurity element, an element that reduces the reflectance on the short wavelength side from the cross point of the metal when the metal is doped is selected.

  ADVANTAGE OF THE INVENTION According to this invention, the filament with high efficiency which converts electric power into visible light or near-infrared light can be provided.

The graph which shows a black body radiation spectrum. The graph which shows the reflectance and cross point of W. (A) The graph which shows the energy level of W which doped P of this invention, (b) The graph which shows the energy level of W which doped K of this invention. (A) The graph which shows the energy level of W which doped Sm of this invention, (b) The graph which shows the energy level of W which doped Lu of this invention. The graph which shows the reflectance and emissivity of W of 2500K. The graph which shows the reflectance and emissivity of W of 3000K. The graph which shows the reflectance and emissivity of W (Lu dope) of 2500K. The graph which shows the reflectance and emissivity of 3000K W (Lu dope). The graph which shows the luminous efficiency of a W (Lu dope) filament. Explanatory drawing which shows the metal (W) by which the impurity element was doped in the crystal grain. (A) Explanatory drawing which shows the metal (W) doped so that impurity elements may not adjoin each other in crystal grains, (b) Metal (W) doped so that impurity elements may not adjoin each other in crystal grains ) Is a graph showing the energy level. (A) An explanatory view showing a metal (W) doped with an impurity element (adjacent) in crystal grains, (b) a metal (W) doped with an impurity element (adjacent) in crystal grains ) Is a graph showing the energy level.

ただし、α＝３．７４７×１０^８ Ｗμｍ^４／ｍ^２，β＝１．４３８７×１０^４ μｍＫ，である。 It is known that the spectrum E (l) that is thermally radiated by heating the filament generally depends on the emissivity ε (λ) of the object and is expressed by the equation (1). If the filament is a black body, the emissivity ε (λ) takes a maximum value of 1 over all emission wavelengths. The black body radiation spectrum is shown in FIG.

However, α = 3.747 × 10 ⁸ W μm ⁴ / m ² and β = 1.4387 × 10 ⁴ μmK.

The emissivity ε (λ) is related to the reflectivity R (λ) by the equation (2) according to Kirchhoff's law. As shown in FIG. Become.
(Equation 2)
ε (λ) = 1−R (λ), (2)

  In the present invention, in the black body radiation spectrum of FIG. 1, the reflectance of visible light and near-infrared light is reduced by adding an impurity element, thereby increasing the emissivity of visible light and near-infrared light. Improve infrared radiation efficiency.

  By the way, in general, when an impurity element is added to a base metal, electrons are scattered by the impurity and the electric resistance and thus the reflectance of the base metal are reduced.

  On the other hand, some refractory metal elements such as W, Ta, and Mo are known to have a wavelength whose reflectance does not depend on temperature as shown in FIG. 2 (about 1.5 μm in FIG. 2). This wavelength is called a cross point or X point. For example, W. E. Forsythe and A. G. Worthing, “The Properties of tungsten and the characteristics of tungsten lamps,” Astrophysical Journal 61, 146-185 (1925).

  The inventor reduces the reflectance on the short wavelength side from the cross point at a higher rate than the reflectance on the long wavelength side by doping the refractory metal element having the cross point with a predetermined impurity element. Thus, by utilizing this effect, it has been found that the emissivity of visible and near-infrared light of a refractory metal filament can be increased compared to the prior art, and the present invention has been achieved.

  That is, according to the simulations of the inventors, the cross point exists in the vicinity of 1300 to 1600 nm for W, 700 to 900 nm for Ta, and 1100 to 1400 nm for Mo. Therefore, by doping the impurity element, the reflectance on the short wavelength side from the cross point is reduced at a higher rate than the reflectance on the long wavelength side, thereby suppressing the emission of infrared light, visible light or near red The radiation efficiency of external light can be increased.

  Specifically, the filament of the present invention has a base formed of metal, and the surface layer of the base is doped with a predetermined impurity element. The metal has a cross point where the reflectance does not change even if the temperature changes. As the impurity element, an element that, when doped into a metal, reduces the reflectance on the shorter wavelength side than the cross point of the metal to a greater extent than the reflectance on the longer wavelength side is selected and used.

  As the impurity element, an element that decreases the extinction coefficient of the metal is used.

  The impurity element is preferably contained in the metal crystal and forms an energy level together with the metal element. For example, the impurity element desirably replaces a lattice point of a metal crystal lattice. On the other hand, it is desirable that the impurity element does not replace both adjacent lattice points of the metal crystal lattice. The reason for this is that when the impurity elements are adjacent to each other in a metal crystal lattice, the adjacent impurity elements form a molecular state, and the energy level of this molecular state is longer than the cross point (infrared light side). This is because it becomes difficult to improve the radiation efficiency of visible light and near infrared light.

  The concentration of the impurity element with respect to the metal is desirably 0.1 mol% or more and 50 mol% or less.

  The metal constituting the substrate includes any of W, Ta, Mo, Os, Re, Ir, Ti, Pt, Cr, Pd, Hf, Rh, Nb, Zr, Ni, Co, Fe, and V. Use. These are refractory metals with cross points.

  The impurity element is selected in consideration of the energy level produced by the metal substrate and the added impurity. In the following, energy levels shown when an element below K or a lanthanoid is added to W metal are shown. The reflectivity at this energy level decreases (the emissivity increases), and the radiation intensity at this energy level increases compared to before the addition of impurities.

  For example, K and P can be suitably used as the impurity element having an atomic weight of K or less. As an example, when P is added as an impurity element to W, as shown in FIG. 3A, the energy levels near 900 nm and 1600 nm can be increased at a temperature of 3000 K. Radiation efficiency can be increased. Further, when K is added as an impurity element to W, the energy level in the vicinity of a wavelength of 1200 nm can be increased at a temperature of 3000 K as shown in FIG. be able to.

  Further, as the lanthanoid impurity element, one containing either Sm or Lu can be used. For example, when Sm is added as an impurity element to W, the energy level in the vicinity of a wavelength of 400 to 800 nm can be increased at a temperature of 3000 K as shown in FIG. Can do. Further, when Lu is added as an impurity element to W, the energy level in the vicinity of a wavelength of 400 to 800 nm can be increased at a temperature of 3000 K as shown in FIG. be able to.

  Further, as the impurity element, it is possible to use an element containing any of Na, Ca, V, Cr, Mn, Fe, Mo, Tc, Ru, Rh, Pd, Cd, Ta, Ir, and Re. is there.

  The reason why the reflectance of the metal can be reduced at a larger ratio on the short wavelength side than the cross point by adding a predetermined impurity element will be described below.

  The reflectance R from the metal surface is generally expressed by the following formula (3). However, the direction of reflection is the 0 ° direction (perpendicular to the metal surface).

R = ((n ₀ −n) ² + k ² ) / ((n ₀ + n) ² + k ² ), (3)
Here, n ₀ is the refractive index of vacuum and n ₀ = 1. n and k are the refractive index and extinction coefficient of the metal at a certain temperature.

  In the present invention, an impurity element having a small extinction coefficient k at a specific energy level formed by adding an impurity to a metal substrate is used. The effect of impurity addition is evaluated below on the long wavelength side and the short wavelength side from the cross point.

  The refractive index and extinction coefficient at a temperature of 2500 K are obtained by simulation using 3000 nm as a representative wavelength on the longer wavelength side than the cross point of W and 800 nm as a representative wavelength on the short wavelength side.

  The refractive index n of W at 2500 K at a wavelength of 3000 nm determined by this simulation is n = 1.35, and the extinction coefficient k is k = 6. The refractive index n of W at 2500 K at a wavelength of 800 nm is n = 3.3, and the extinction coefficient k is k = 4.

  Assuming that the value of k is reduced by about 1 by the addition of impurities, the extinction coefficient k is k = 5 at a wavelength of 3000 nm and a temperature of 2500 K, and k = 4 at a wavelength of 800 nm and a temperature of 2500 K. Further, since the amount of the impurity element added is very small, the refractive index hardly changes. At this time, in order to reduce the value of k at a wavelength of 3000 nm by about 1, 0.1 mol% of impurities such as K and Sb, and in order to reduce the value of k at a wavelength of 800 nm by about 1, The simulation was performed assuming that 0.1 mol% of impurities were added.

  When the extinction coefficient and the refractive index are substituted into the equation (3) and the reflectance R before and after the addition of the impurity at each temperature is obtained by calculation, Table 1 is obtained.

  From Table 1, W decreases the reflectance by 16% on the shorter wavelength side than the cross point by reducing the extinction coefficient k by about 1 (1−0.52 / 0.62). On the other hand, it can be seen that the reflectance is reduced only by about 9% (1−0.82 / 0.87) on the longer wavelength side than the cross point. As described above, one of the major reasons that the degree of decrease in reflectance across the cross point is different is that the extinction coefficient is generally large on the longer wavelength side than the cross point. The coefficient decreases only at a small rate and the effect of decreasing the reflectivity is small. On the other hand, the extinction coefficient is small on the shorter wavelength side than the cross point. Is reduced at a large rate, and the reflectance is also decreased at a large rate.

  Therefore, the present invention has obtained an impurity element that reduces the extinction coefficient at a shorter wavelength side than the cross point and at a larger rate than the long wavelength side by simulation. In the simulation, the energy level formed by the atomic transition in which the impurity element replaces the metal crystal lattice was obtained, and the extinction coefficient was obtained from the energy level. That is, the atomic spectrum created by the impurity element present in the metal substrate is reflected in the extinction coefficient and thus the reflectance. Specific impurity elements selected by simulation are as described above.

  Next, as comparative examples, the results of obtaining the reflectance, radiation spectrum, and visible light radiation efficiency of 2500 K and 3000 K by simulation for W filaments without added impurities are shown in FIGS. 5 and 6, respectively. As shown in FIGS. 5 and 6, the luminous efficiency of visible light is 12.2 lm / W at a temperature of 2500K, and 29.3 lm / W at a temperature of 3000K.

  On the other hand, the reflectance, radiation spectrum, and visible light radiation efficiency of the W base material doped with the impurity element Lu at a concentration of 1.0 mol% are obtained by simulation for 2500K and 3000K, respectively. As shown in FIGS. 7 and 8, by adding an impurity element, the luminous efficiency of visible light is 28.8 1 m / W at a temperature of 2500 K, and 64.0 lm / W at a temperature of 3000 K, which is almost double that of the comparative example. Efficiency is obtained.

  As described above, the impurity element is preferably added at a concentration of 0.1 to 50 mol 1% with respect to the filament base material. The reason is that if the amount of impurities added is larger than this, an alloy is formed. In the alloy, the above-described concept of atomic transition does not hold, and since the energy band of the alloy starts to be formed, the energy spreads and the sharp reflectance in the visible light region as shown in FIGS. 7 and 8 is reduced. Can not do. That is, if the concentration is too high, the effect of reducing the reflectance to a desired wavelength cannot be achieved. On the other hand, if the added amount of impurities is less than the concentration shown in this range, the reduction range of the extinction coefficient becomes small, and sufficient reflectance reduction cannot be achieved. For this reason, it becomes difficult to obtain radiation controllability by adding impurities.

  Further, the thickness of the surface layer of the base material to which the impurity element is added is preferably within 100 nm from the base material surface. This is because even if impurities are added deeper than this, radiation from the impurities is reabsorbed by the base material, so that the effect of adding impurities existing deeper than 100 nm does not affect the radiation characteristics of the surface. It is.

  FIG. 9 is a graph in which the radiation efficiency of the W filament doped with the impurity element Lu of 1.0 mol% according to the present invention is plotted against the filament heating temperature. As shown in FIG. 9, at 1500 K or higher, radiation efficiency about twice that of the W filament without impurities added in the comparative example is obtained.

  Next, a method for producing a filament doped with an impurity element according to the present invention will be described. First, the metal substrate is pre-sintered to complete crystal grain growth. For example, in W metal, crystal grains can be grown by sintering at a temperature of about 1500 to 2000K. Thereafter, an impurity element layer is formed on the surface of the substrate. For example, a vapor phase growth method such as vapor deposition can be used. Thereafter, the substrate is reheated and the impurity element is doped into the surface layer of the metal substrate. The reheating temperature is about 100-500K lower than the crystal grain growth temperature. Thereby, a filament in which the impurity element is uniformly doped inside the crystal grains of the surface layer of the metal substrate can be manufactured.

  FIG. 10 schematically shows a state in which the impurity element 10 is doped inside the metal crystal grains 11. As described above, the impurity element preferably replaces the metal element at the crystal lattice point of the crystal grain 11.

  In FIG. 11A, the impurity element 10 (for example, K) that replaces the W crystal lattice point is not aligned with the other impurity element (K) (it is adjacent to the W crystal lattice point). (Not shown) In this case, when the energy level of the filament to which the impurity element is added is obtained by simulation, it increases in the vicinity of a wavelength of 1200 nm as shown in FIG.

  On the other hand, in FIG. 12A, the impurity element 10 (for example, K) replacing the W crystal lattice point is aligned with another impurity element 10 (K) (adjacent at the W crystal lattice point). Is schematically shown. In this case, the position where the energy level of the filament to which the impurity element is added increases is shifted to the long wavelength side (near the wavelength of 3000 nm) as shown in FIG. For this reason, it becomes difficult to increase the radiation intensity of visible light and near-infrared light, and to suppress the radiation intensity of infrared light.

  Therefore, in the present invention, it is desirable that the impurity element is doped so as not to be located at the adjacent crystal lattice point of the metal. This can be realized by adjusting the heating temperature at the time of impurity doping during manufacturing, and the doping element and concentration of the impurity element.

  As described above, according to the present invention, a filament having high radiation efficiency of visible light and near infrared light can be provided by adding an impurity element. By increasing the radiation efficiency in the near infrared region, a heater light source capable of performing efficient heating can be configured, and by increasing the radiation efficiency in the visible region, a highly efficient illumination light source can be configured. I can do it. Therefore, it can be used as an illumination light source, an automobile light bulb, a projector light source, a liquid crystal backlight light source, and a near infrared heater.

10 ... impurity element, 11 ... crystal grain

Claims (13)

Having a substrate formed of metal;
The surface layer of the substrate is doped with a predetermined impurity element,
The metal has a cross point where the reflectance does not change even if the temperature changes,
The filament characterized in that the impurity element is an element that, when doped into the metal, reduces the reflectance on the short wavelength side from the cross point of the metal to a greater degree than the reflectance on the long wavelength side.   2. The filament according to claim 1, wherein the impurity element is an element that reduces an extinction coefficient of the metal by doping.   3. The filament according to claim 1, wherein the impurity element is contained in a crystal of the metal and forms an energy level together with the metal element.   4. The filament according to claim 1, wherein the impurity element replaces a lattice point of the crystal lattice of the metal. 5.   5. The filament according to claim 4, wherein the impurity element does not replace both adjacent lattice points of the crystal lattice of the metal.   6. The filament according to claim 1, wherein a concentration of the impurity element with respect to the metal is 0.1 mol% or more and 50 mol% or less.   The filament according to any one of claims 1 to 6, wherein the metal includes W, Ta, Mo, Os, Re, Ir, Ti, Pt, Cr, Pd, Hf, Rh, Nb, Zr, A filament comprising any one of Ni, Co, Fe, and V.   The filament according to any one of claims 1 to 7, wherein the impurity element is an element having an atomic weight of K or less, or a lanthanoid.   The filament according to claim 8, wherein the impurity element includes any one of K, P, Sm, and Lu.   8. The filament according to claim 1, wherein the impurity element is Na, Ca, V, Cr, Mn, Fe, Mo, Tc, Ru, Rh, Pd, Cd, Ta, or Ir. , And any one of Re.   11. The filament according to claim 1, wherein the surface layer of the base body doped with the impurity element has a thickness of 100 nm or less.   A light source using the filament according to claim 1.   An infrared heater using the filament according to any one of claims 1 to 11.

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