JPS61275379A - Reversible heat-sensitive material and preparation of the same - Google Patents

Abstract

PURPOSE:To obtain a reversible heat-sensitive material comprising a Bi2O3-V2O5 polycrystalline material which changes in color tint reversibly accompanying a change in temp., is thermally stable, inexpensive and nontoxic, by calcining a mixture of a Bi compd. with V2O5 at a specific temp., followed by cooling. CONSTITUTION:An oxide, nitrate or chloride of bismuth (e.g.; Bi2O3) is mixed with vanadium pentoxide in such an amount as will provide a Bi/V atomic ration in the range of 0.97/0.03-0.5/0.5. The mixture is pre-calcined and calcined at a temp. of 500-750 deg.C. The product is left to stand for cooling or gradually cooled to obtain a reversible heat-sensitive material comprising a bismuth oxide- vanadium oxide polycrystalline material. The reversible heat-sensitive material exhibits changes in color from a yellow tone to a red tone when heated at a temp. of about 120 deg.C or above and exhibits an allowable maximum temp. of about 750 deg.C. The material is suited for use in temp. displays for heating areas of heating apparatuses.

Description

[Detailed Description of the Invention] <Technical Field of the Invention> The present invention has the property that the hue changes depending on changes in temperature.
The present invention relates to a reversible temperature indicating material, which is a type of temperature control material.

<Technical background of the invention and its problems> Conventionally, there are color-changing pigments that are collectively called thermopaints. It is commercially available in the form of labels, sheets, tapes, patches, crayons, racks, etc., and is used for a variety of purposes. This material is uniformly an organic pigment, and its discoloration temperature varies, but the heat resistance limit temperature is as high as about 250°C, depending on the binder contained.

The use of this color-changing pigment is extremely wide, but in general, it is mostly used for temperature control to easily detect abnormal heat generation points in electrical substations, power distribution, control equipment, two-rotation electrical equipment, electronic components, power transmission equipment, and various manufacturing processes. Therefore, these materials do not reach very high temperatures, so the temperature limit temperature of the temperature indicating material itself is approximately 25
It is reasonable to think that around 0°C is sufficient. However, melting and welding of metal.

The above heat-resistant limit temperature is not necessarily sufficient for use around relatively high-temperature equipment such as molding. Therefore, there are many requests for a low (or high) discoloration temperature and a high (for example, 700°C) heat resistance limit temperature in manufacturing processes that involve high-temperature heating. There has not yet been a reversible temperature indicating material with such a high heat resistance limit temperature.

On the other hand, in the home appliance industry, there has long been a strong demand for temperature indicating materials to display the temperature of heating parts related to heating and cooking equipment in color, that is, to change color above a certain temperature, and various reversible materials are being used. Temperature indicating materials have been proposed. The material is a silver compound.

Composite materials of sulfide and iodide are the main materials, but at present they all have some weaknesses in terms of stability, lifespan, cost, toxicity, etc.

Next, the technical background 1 until reaching the reversible temperature indicating material according to the present invention will be explained in detail.

Conventionally, the reversible color change of vanadium pentoxide (V2O5) is a phenomenon that has been very well known for a long time, as well as that of tungsten oxide, molybdenum oxide, and the like.

The hue of V2O5 is generally yellow at room temperature, and shifts to red as the temperature rises. This change in hue is reversible with respect to temperature, and the change in hue is sufficiently visible at about 100°C. Originally, v205 has a V-6 O octahedral structure with a stack of V-O-V mesh planes, but one O is particularly far away from the center V, and the interior of the regular octahedron is greatly distorted. It has a structure that is considered to be three-sided and hermaphrodite, with numerous cavities inside. In other words, the structure has voids in which, for example, oxygen can freely diffuse.

In addition, in terms of physical properties, V2O5 basically has oxygen vacancies.
02 type semiconductor, and coupled with the above-mentioned structural specificity,
It is said that the exchange reaction of incorporation as lattice oxygen through adsorption and desorption by increasing temperature occurs easily. The mechanism of color change that occurs at relatively low temperatures, which is based on such phenomena unique to substances, is extremely interesting.

Now, as mentioned above, v20. is a compound with high oxidation activity. Therefore, it is widely used industrially as an oxidation catalyst for SO□ or as a partial oxidation catalyst for various organic compounds. Also, substances with such strong oxidizing power are generally not harmless to the human body (when inhaled, they may adhere to the mucous membranes of the organs, causing coughing and palpitations, or if inhaled in large quantities). It is said that it may lead to so-called respiratory disorders such as chest pain and difficulty breathing.It has also been pointed out that if it comes into contact with the skin, it may cause skin diseases such as rashes and pimples. This is generally caused by handling V2O5 as a powder. Taking advantage of V2O5's excellent coloring ability, it is possible to use it as a temperature indicating material by appropriately devising processing methods such as coating. Even if the substance is not designated as a poisonous or deleterious substance by law, it is wise to avoid using substances that are known to be even slightly harmful to the human body.

<Object of the Invention> The present invention has been made in view of the above-mentioned conventional points, and in particular, a reversible temperature indicator made of a material that does not contain substances harmful to the human body, is stable, has a high heat-resistant limit temperature, and is low in cost. The purpose is to provide materials.

<Examples> Examples of the reversible temperature indicating material according to the present invention will be described in detail below with reference to the drawings.

The reversible temperature indicating material according to the present invention basically consists of a bismuth oxide-vanadium oxide polycrystal obtained by firing a mixture of a bismuth compound and vanadium pentoxide. In addition, its composition is the atomization of Bi and V (B
io, 97Vo, oa) from (B iO, 50vo,
A range of (o) is appropriate.

Next, a specific manufacturing process will be explained with reference to the manufacturing process diagram shown in FIG.

Example 1 20 g of Bi and V2O5, both of reagent grade, were weighed as shown in Table 1. The atomic ratio in this case is as shown in the table.

Table 1 Samples 1 to 5 were ground and mixed separately using an automatic mortar and ball mill. Next, they were individually transferred to ceramic crucibles with lids and calcined in air at 500℃ for 24 hours.
do. Thereafter, pulverization was performed again (2), and samples 1, 2 and 3 were fired at 750°C for 7°, and samples 4 and 5 were fired at 650°C for 48 hours (2). Thereafter, it was slowly cooled to 300°C at a rate of 15°C per hour, and then allowed to cool to room temperature.

The sample after cooling was first examined for the formed phase using X-rays. For samples in which even a small amount of the V205 phase is present (in the case of a), the firing process (2) is repeated again. v205 phase does not exist (
In case b) the sample does not need to be fired again. Next, in order to examine the temperature dependence of hue using a spectrophotometer, a sample of 25μ
Adjust the particle size to 37 μm. Measurement wavelength range is 400-8
00 nm. This color tone measurement is performed from room temperature and 70℃.
Ranges at 50'Ct were performed at 70°C intervals. These results are shown in FIGS. 2 and 3. FIGS. 2 and 3 show the reflection spectra of Samples 4 and 5 at various temperatures, respectively. The temperature dependence of these hues essentially has no thermal history. The same results can be obtained by sufficiently maintaining thermal equilibrium at the measurement temperature both when the temperature is raised and when the temperature is lowered. The reflection spectra of Bi2O3 and V205, which are the basic components of the composition, measured by a spectrophotometer are shown in Figures 4 and 5, respectively. By comparison, the sample produced is not a simple mixture of its basic components (
, is found to be unique and independent.

It is also understandable that the hue changes sensitively in response to temperature changes. The color changing function of this series of substances is 750
It was confirmed that there was no damage even after repeated heat treatment at ℃.

Next, the powder of sample 5 was kneaded with a water-soluble glass coating agent at a certain concentration, and then a glass plate that had been subjected to a satin finishing process, an unglazed ceramic plate, and an asbestos plate were prepared.

Application [phase] was performed using a brush on substrates such as cement boards, matte aluminum boards, and polyimide films. In this case, for asbestos boards and cement boards, it is easier to obtain a more uniform coating film by reducing the amount of the powder mixed and applying the powder many times. drying,
The fixing method is to heat it at 150°C for 1 hour, or leave it as it is.

In the latter case, depending on the thickness of the coating film, the leaving time may be long (but I
The standard time is about 3 days before and after Opm. The color change of the coating film obtained in this way is completely unchanged from the original color tone. We also conducted various peel tests, and found that once dried and fixed, the film is extremely strong (and rarely peels off unless mechanically scratched).It is also resistant to thermal shock ( Although the glass substrate often cracks when heated or rapidly cooled, the film did not peel off even in that case.

Next, using a ceramic coating agent as a dispersant, coating was carried out in the same manner as in the above method. The ceramic coating agent used was one in which Z r 02 and AA'203 were added and dispersed in addition to the 5i02 component contained in the glass coating agent. Even in this case, a very strong film was produced. Also ZrO2, AJ? By adjusting the amount of white components such as 203, it is possible to arbitrarily select the color depth of the film. Although the color tone in this case had a slightly weak contrast, there was no problem in visual recognition.

・Example 2 Both are reagent grade B i (NO3)a・5H20, B
i C13 and v205 were weighed as shown in Table 2.

Table 2 Pre-calcination treatment (2) similar to that in Example 1 was quickly performed, and sample 6 was heated at 500°C for 48 hours, and sample 7 was initially heated at 880°C for 1 hour.
It was calcined for 2 hours, and then calcined for 48 hours at 500°C. The temperature increase rate of sample 6 was controlled at 80° C./hour. Also, in order to allow decomposition products to escape, the crucibles were not covered with lids. Next, Samples 6 and 7 were taken out, thoroughly ground again, mixed (1), and main fired (4) at 650° C. in air for 48 hours. Thereafter, cooling (2) was performed in the same manner as in Example 1 to obtain a product, which was then subjected to X-ray analysis (2). If unreacted substances remain, step (a) repeats re-baking (2). If no unreacted substances remain, re-calcination (2) is not necessary. In this case, the final product obtained is BiVO4. Here, the results of measurement (2) using a spectrophotometer were no different from those of Example 1 in which Bi2O3 was used as the starting material.

Next, the powder of sample 6 is sufficiently ground in an automatic mortar, and then made into a fine powder with a particle size of 37 μm or less using a sieve. 20% by weight of this was added to the glass frit and uniformly mixed in a ball mill to obtain a pale yellow mixed fine powder. After thoroughly mixing this with ethanol to make a paste, apply it evenly with a spatula to a thin glass plate and an unglazed ceramic plate. 480° C.) for 3 hours, and after slow cooling, it was taken out. In this case, it was difficult to obtain the same smooth surface as in Example 1, but due to the scattered light on the surface, the color tone changed neatly from pale yellow-white to pale orange as the temperature rose even from a low angle. I was able to observe it.

In addition, when directly dispersing and mixing the powder produced above into the object to be measured, uniformly mix the powder produced above into the base material, then transfer it to a mold, and press-form [phase]. good.

B i 203 v generated as above,
The composition of the o5 polycrystal is as described above (Bi
The atomic ratio of V and V ranges from (Bio, 97Vo, og) to (BiO, 50Vo, so). here(
When a compound having the composition B i O, 50Vo, so ) is fired in air at 500°C to 750°C, 13iVO4 is generated. On the other hand (Bio, 5o Juku■0.50-x)
In addition to BiVO4, formation of phases very similar to βBi2O3 and δBi20B corresponding to X is observed in the range of (ie, composition with excess Bi). However, it is not necessarily obvious, and there is a possibility of new Bi-VO compounds. On the other hand, in the range (Bio, 5o-8V0.50+x) (ie, a composition range in which V is in excess), the starting material V2O5 corresponding to X remains as is in addition to BiVO4.

It is based on this reason that the upper limit of
3) Even when 3.5H20 or BiCA'3 is used, the same formation phase as above can be obtained. Here, Bi2O3V2O5
To the best of the present inventor's knowledge, there are no known documents regarding polycrystalline polycrystals, and single 1cBi203-V205 (Q~87%)
) (D solid solution phase is Phase Diagram fo
r Ceramists (American Ceramists)
ic 5ociety).

Next, the relationship between composition range and hue will be described. First, one of the components, Bi2O3, is at room temperature.
The temperature at which changes in the γ small box phase can be visually observed is around 200°C.

On the other hand, v205 exhibits a yellow color at room temperature and changes to a rust red color when the temperature rises. The visible temperature is approximately 100°C.

In the Bi-V system, as ■ is added to Bi, the yellowish tinge at room temperature gradually increases and the red tinge increases at the time of discoloration, and the visible discoloration temperature also gradually decreases.

BiVO4 exhibits a yellow color at room temperature and an orange-red color when the temperature rises. The temperature at which a change in hue can be visually recognized is about 120°C.

Next, the heat treatment conditions after firing and the upper limit firing temperature will be described. In the above composition range, when cooling (■) after main firing (■), 75%
When rapidly cooled from 0° C., a trace amount of V2O5 tends to remain as an impurity. In addition, the obtained sintered body itself exhibits an indistinct color tone at room temperature and tends to take on a reddish-brown color even after discoloration.The origin of these phenomena is unknown. However, it can be seen that the disturbance of the crystal structure and the naturally expected increase in oxygen defects subtly affect absorption in the visible region.In any case, gentle cooling or intentional slow cooling The reason why the upper limit of the firing temperature was set at 750°C is that one of the reaction components, v205, lacks thermal stability at temperatures of 800°C or higher and is said to easily deviate from the stoichiometric composition. Depends on where you are. Basically v205-x
The X value is controlled by the function of oxygen partial pressure and temperature,
It has been demonstrated by electrical conductivity measurements that the X value is relatively large at temperatures above 800°C.

As described above, the effects of Bi-V heat treatment conditions on the generated phase and color tone are subtle, and appropriate and accurate control is required depending on the composition.

Within the above composition range, the product is stable up to about 750°C without loss of hue change. v20
5 partially dissolves in water to produce vanadic acid and exhibits a yellow color, but its aqueous composition is insoluble in cold water, hot water, and 1N caustic soda. Moreover, no deterioration is observed under ultraviolet light. In these points, v20. Much more stable and improved.

Furthermore, this polycrystalline material can be used in a wide range of applications due to its chemical, thermal, and photochemical stability unique to metal oxides and its inherent compatibility with various oxide-based materials. That is, as mentioned above, there is a method of directly mixing or dispersing it into porous glass, ceramics, asbestos, cement, plastics, etc. These materials are naturally very compatible.

Furthermore, as mentioned above, it is extremely effective to disperse the material in a solvent that can easily form a relatively porous film, such as a water-soluble glass coating agent or a ceramic coating agent, and apply it to the surface of the object to be measured. In addition, as a method of heating and fixing, a film of white, porous glass-like material can be formed by uniformly dispersing a certain amount into a glass frit and calcining it on the object to be measured at a temperature that corresponds to the glass frit. It is also possible to deposit the material.

Here, the features of the above embodiments of the temperature indicating material according to the present invention are listed below.

+1) Matters regarding temperature characteristics.

(G) Changes reversibly from yellowish to reddish in tone.

(b) The lower temperature limit at which changes can be visually recognized is approximately 120°C.

(c) Good heat followability and no thermal history.

(2) Matters related to stability and safety.

b) The heat resistance limit temperature is approximately 750°C.

(b) It is insoluble in water and does not deteriorate even under ultraviolet light.

(c) It has sufficient repeat life.

)) Contains no substances that are considered harmful to the human body.

(3) Matters regarding processing diversity and production advantages.

K) Since it is a stable metal oxide, it blends well with a wide range of materials such as glass, ceramics, asbestos, and cement.

River: It is insoluble in water and alkalis, so it can be dispersed in various solvents.

(/1) Since it is thermally stable, processing that involves heating is possible.

)) The materials themselves are relatively inexpensive and the manufacturing method is simple.

<Effects of the Invention> According to the present invention as described above, it is possible to obtain an excellent reversible temperature indicating material that is harmless to the human body, thermally stable, and whose materials are available at low cost and is rich in practicality. .

[Brief explanation of drawings]

FIG. 1 is a process diagram of the manufacturing process of an embodiment of the reversible temperature indicating material according to the present invention, and FIGS. 2 to 5 are graphs showing the temperature dependence of absorption spectra in the visible wavelength range measured by a spectrophotometer. .

Claims (1)

[Claims] 1. It consists of a bismuth oxide-vanadium oxide polycrystal obtained by firing a mixture of a bismuth compound and vanadium pentoxide, and is characterized by exhibiting different hues depending on temperature changes. A reversible temperature indicating material. 2. The bismuth compound is an oxide, a nitrate, or a chloride, and the mixing composition ratio of the bismuth compound with the vanadium pentoxide is an atomic ratio of bismuth and vanadium (Bi: 0.97, V: 0.03) to (Bi
2. The reversible temperature indicating material according to claim 1, wherein the reversible temperature indicating material is in the range of V: 0.50 and V: 0.50. 3. Calcining and main firing the mixture of the bismuth compound and vanadium pentoxide at a temperature range of 500°C to 750°C,
Next, by cooling or slow cooling, bismuth oxide
A method for producing a reversible temperature indicating material, characterized in that a vanadium oxide polycrystal is obtained.