JPH0239473B2 - ENSEKIGAISENHOSHATAIOYOBISONOSEIZOHO - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a ceramic radiator for a heater that has high far-infrared radiation efficiency. Infrared rays have a strong thermal effect, transcending space and directly reaching low-temperature objects and heating them.
It has been widely used for drying, heating, treatment, etc. since ancient times. The infrared rays that have been used up until now have mainly been near-infrared, but research on far-infrared has recently become active due to the fact that far-infrared rays have better thermal efficiency than near-infrared rays. Many heaters and the like that utilize far infrared rays have been proposed. for example,
Emitting far-infrared rays with a wavelength of 10 μm or more to the human body is said to have medical and health benefits by promoting sweating and blood circulation. Further, heating or drying using far infrared rays has many features such as high thermal efficiency, no unevenness depending on the color of the heated object, and the ability to heat the inside of the object. Various materials have been proposed for emitting such far-infrared rays, but in general, far-infrared radiators have high emissivity in the far-infrared region and low emissivity in the low wavelength region. desirable. The present inventors have found that ZrO ₂ is excellent as a material with such characteristics.
In order to put such radiant materials into practical use as heaters, various improvements are necessary, and one of them is to make them into various predetermined shapes such as planar, rod-like, lamp-like, etc. It is important to build it up. For example, in the case of a rod-shaped heater, a heating wire is placed inside a pipe (tubular body) that has at least a radiant material formed on its surface. There are two methods: one is to form the material into a shape and fire it, and the other is to form the radiation material on the surface of a metal or ceramic pipe by thermal spraying, coating and baking, or other methods. However, in the former method, it is extremely difficult to obtain a long pipe because the firing temperature is high to sinter zirconia (ZrO ₂ ) ceramics into a pipe shape, and it is difficult to obtain a long pipe with sufficient density. Not only is it difficult to obtain a product with excellent radioactivity and the excellent properties cannot be fully utilized, but there is also the problem of high costs due to the raw materials and firing conditions. On the other hand, the latter method generally has problems such as peeling of the radiation material layer due to thermal shock, insufficient hardness of the layer, and difficulty in obtaining a material with good radiation characteristics. As a result of various studies in view of these points, the present invention has succeeded in solving the above-mentioned problems and making practical use of the extremely excellent radiation characteristics possessed by zirconia. That is, the present invention is a far-infrared radiator consisting of a mullite base material and a zirconia far-infrared radiator layer that are integrated by simultaneous firing, and the gist thereof is a manufacturing method thereof. As described above, the present invention uses a raw or unsintered molded body of mullite (3Al ₂ O ₃ .2SiO ₂ ) as the base material, and integrates the formation of the zirconia layer, which becomes the radiation material layer, by simultaneously firing the two. It is characterized by the fact that By doing this, the adhesive strength of the zirconia layer to the base material was made extremely strong, and the sintered body obtained during the firing process did not peel between the two, making it resistant to thermal shock. . At the same time, the zirconia layer has a high hardness and has extremely good radioactivity, as will be described later, and since the base material is mullite, it is easy to mold and bisque (or even fire), making it a radiator with good sinterability. , even long ones of 1 m or more can be easily made. In the present invention, the mullite base material can have any arbitrary shape, and can easily have a complex shape such as a lamp shape as well as a tube shape (rod shape) and a planar shape. Because it is fired integrally with the radiation layer, it is necessary to prepare the base material as the main molded body or an unglazed molded body. This refers to the state in which the mullite base material is baked to the extent that it does not deform or crack even when processed, and in the present invention, which uses a mullite base material, it is heated at approximately 400 to 1000 degrees Celsius, depending on the raw material composition.
It is appropriate to use a product that has been treated at a temperature up to a certain temperature. In the present invention, the effect of integrating unfired materials with large firing shrinkage by simultaneous firing can be achieved because the difference in thermal expansion coefficient between the mullite base material and the zirconia radiant material is small and the firing shrinkage ratio is the same. From this point of view, it is desirable to match these as much as possible, and it is easy to do both. That is, the mullite base material has a coefficient of thermal expansion of approximately 0.7% (1000°C) in the range of 0 to 1400°C, although it contains a sintering aid in the amount normally used for sintering this type of material.
The coefficient of thermal expansion of a material with good purity is approximately 0.55% (1000°C), and a zirconia radiant material having excellent radiation characteristics is easily suitable for these values. In the present invention, this zirconia radiation material layer will be explained next. The zirconia layer is well known as a far-infrared emitting material, and it can be used as a material having radiation characteristics with particularly high heating efficiency, such as the following. That is, the wavelength is short,
For example, at a wavelength of 6 μm or less, the emissivity is low, for example, 50% or less, and at a long wavelength, for example, 8 μm or more, the emissivity is high, for example, 70% or more. Note that emissivity here is a comparison of the radiant energy of a black body (100% emissivity in all wavelength ranges) and the radiant energy of a sample for each wavelength, as is generally said, and the temperature range is This is within the commonly used measurement range of 350 to 550°C. Preferably, the zirconia-based radiation material contains rare earth elements such as Y ₂ O ₃ , CeO ₂ , La ₂ O ₃ in a predetermined amount, that is, in a range of 8% or less, specifically, from 2 to 2% by weight based on zirconia. It is partially stabilized zirconia with 8% solid solution, and the coefficient of thermal expansion at 0 to 1400°C is 1.0% or less, which is not much different from the mullite base material.
It also has excellent far-infrared radiation characteristics. In particular, among these, Y ₂ O ₃ has the advantage that its far-infrared radiation characteristics hardly change. In addition to rare earths such as Y ₂ O ₃ , MgO and CaO are also well known as solid-dissolved substances in ZrO ₂ , but there are some substances that are stabilized by these substances, those that are not stabilized at all, and those that are not stabilized at all. 10% even for rare earths
Comparing with other ceramic radiation materials such as those that are completely stabilized by solid solution, they have excellent radiation characteristics, but they are not as good as partially stabilized zirconia made of Y ₂ O ₃ etc. Since completely stabilized zirconia has a coefficient of thermal expansion exceeding 1%, the best option in the present invention is to use a partially stabilized zirconia layer made of Y ₂ O ₃ as described above. be. Here, the manufacturing method of the present invention will be explained. A zirconia unfired layer is formed on a predetermined surface of a mullite base material formed into a predetermined shape, and this can be done by any suitable method such as coating, spraying, or dipping with a zirconia composition. That's fine. The fluidity of the zirconia composition is determined by the method used, but zirconia of a desired particle size, a stabilizer (of course, zirconia that has been partially stabilized in advance may be used), and a sufficient amount are added. Other ceramic powders and binders and appropriate amounts of water are sufficient. Incidentally, as a binder, inorganic sols such as silica sol, alumina sol, titania sol, etc. seem to contribute not only to the sinterability of zirconia but also to the improvement of the adhesiveness with the base material, and are particularly suitable binders. After forming the zirconia coating layer, it is simultaneously fired together with the base material at a temperature of 1200~1200℃.
Approximately 1400℃ is appropriate. As described above, the radiator of the present invention has extremely excellent radiation characteristics and can be used repeatedly and with durability for a long time.It can also be used as a plate-shaped body simply by installing it in front of the heater. Various forms are possible, such as simply inserting a heater into the tubular body, and its practical value is great. The present invention will be further explained with examples. Example: A mullite raw tube with a length of 600 mm, an outer diameter of 12.5 mm, and a wall thickness of 2.2 mm is extruded and bisque fired at 850°C for 3 hours, and then a paste-like radiant material having the following composition is applied to the outer surface by dipping. (approximately 0.1 to 0.2 mm thick). Y ₂ O ₃ 5% added zirconia (particle size 200 mesh pass)
60 parts by weight Silica sol 5 Alumina sol 10 Water 25 Next, this was main fired at 1320° C. for 3 hours to obtain a radiator according to the present invention. The adhesive strength test results of this radiator were shown as A, along with samples B and C for comparison, and were as follows. B: A zirconia layer was coated on a pre-fired mullite tube and baked at 400℃ for 3 hours. C: A zirconia layer was formed on a stainless steel tube by plasma spraying.

[Front] is also scratched.
fleeting
Furthermore, the radiation characteristics of the obtained radiator are shown in FIG. 1 as an emissivity spectrum diagram. The emissivity spectrum shown in FIG. 1 is obtained by measuring the radiant energy of a perfect black body and a sample for each wavelength using a Hitachi infrared spectrometer 260-30, and calculating and displaying the emissivity. (Measurement temperature: 500° C.) Sample D is a conventional fired zirconia tube (ZrO ₂ 95%, CaO 5%, apparent porosity 22%).

[Brief explanation of drawings]

FIG. 1 is an emissivity spectrum diagram of far-infrared radiators of Examples and Comparative Examples of the present invention.

Claims (1)

[Claims] 1. A far-infrared radiator comprising a mullite base material and a zirconia far-infrared radiating material layer, which are integrated by simultaneous firing. 2 The zirconia layer has a thermal expansion of 1 between 0 and 1400℃.
% or less, and is a partially stabilized zirconia layer containing one or more of Y ₂ O ₃ , CeO ₂ , La ₂ O ₃ in an amount of 8% or less by weight based on zirconia, as claimed in claim 1. The far-infrared emitter described. 3. A method for producing a far-infrared radiator, which comprises forming an unfired zirconia coating material layer on the surface of a raw or unglazed mullite base material, and simultaneously firing and integrating these layers. 4. On the surface of the mullite base material, 1 of Y ₂ O ₃ , CeO ₂ , La ₂ O ₃ in an amount of 8% or less by weight based on zirconia
4. The method for producing a far-infrared radiator according to claim 3, wherein a zirconia coating layer containing a stabilizer is formed by firing the seeds and the like, and the zirconia coating layer is fired at the same time. 5. The method for producing a far-infrared radiator according to claim 3 or 4, wherein the zirconia coating layer contains an inorganic sol as a binder.