JP3353043B2 - Manufacturing method of low order titanium oxide ceramics - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-order titanium oxide ceramic and a method for producing the same, and more particularly to a heat-generating element having excellent NTC characteristics, low voltage, large current, and low resistance. The present invention relates to a low-order titanium oxide having electrical characteristics and an efficient production method thereof.

[0002]

2. Description of the Related Art The use of conductive ceramics as a heating element has been widely used in the past, for example, building-related equipment such as panel heating equipment, wood drying system equipment, floor heating equipment, wall heating equipment, and the like. Housing-related such as bathtub, instant water heater, various dryers, hot plate, coffee maker, rice cooker, toaster, range and other home appliances, industrial equipment-related, other environmental equipment, hospital heating equipment, thermal supporter, medical use It has already been used in fields such as medical equipment such as bathtubs for preventing icing under limited power supply, snow melting on road surfaces where low-temperature heat is effective, and snow-melting tiles.

[0003] The heating element has an electrical characteristic of N
It is preferable to have characteristics such as TC characteristics, low voltage, large current, and low resistance. Conventionally, conductive ceramics that can be used as such a highly efficient heating element include:
Research and development of low titanium oxide ceramics obtained by reducing calcined titanium dioxide containing titanium dioxide as a main component has been continued.

[0004] As a method for obtaining low-order titanium oxide ceramics, a titanium dioxide powder or an inorganic binder such as an organic binder or a clay is added to the titanium dioxide powder, followed by molding and drying. Is fired by re-heating the fired titanium dioxide containing titanium dioxide as a main component in a vacuum, non-oxidizing atmosphere or reducing atmosphere (mainly in hydrogen gas). A method of reducing titanium dioxide into a low-order titanium oxide ceramic has generally been adopted. However, this method industrially requires enormous equipment and atmosphere control technology, and has low productivity and high cost. The low-order titanium oxide ceramics obtained in this manner has a high proportion of oxygen in the composition as the low-order oxide (the value of x of TiOx is large), and when used as a heating element, it has a sufficient electrical conductivity. It was hard to say that it had characteristics.

[0005] Therefore, when these problems are solved and a heat generating element is used, it has NTC characteristics, low voltage, large current,
Low-order titanium oxide ceramics having excellent electrical properties such as low resistance and a low proportion of oxygen in the composition (small x value of TiOx) and low-order titanium oxides in which such low-order titanium oxide can be obtained by a simple operation A method for producing titanium oxide ceramics has been desired.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made from the above-mentioned viewpoints, and when used as a heating element, NTC
Has a characteristic, low voltage, high current, have excellent electrical properties such as low resistance, the proportion of oxygen in the composition is small (smaller values of TiOx of x) simple production method of the low-order titanium oxide ceramics The task is to provide

[0007]

Means for Solving the Problems The present inventor has conducted intensive studies to solve the above-mentioned problems, and as a result, calcined titanium dioxide containing titanium dioxide as a main component obtained by a conventional method has been replaced with metallic titanium and titanium. By placing it in a muffle filled with a filling powder mainly composed of carbon powder and firing it in an air atmosphere furnace, the fired titanium dioxide is reduced uniformly and the proportion of oxygen in the composition is reduced (x of TiOx Is small)
The present inventors have found that low-order titanium oxide ceramics can be obtained, and that the low-order titanium oxide ceramics have NTC characteristics, and have completed the present invention.

That is, the present invention relates to a low-order titanium oxide ceramic obtained by reducing and firing calcined titanium dioxide containing titanium dioxide as a main component. A sintering aid and / or a binder are added in accordance with the first sintering to obtain a sintering titanium dioxide containing titanium dioxide as a main component,
This is a method for producing a low-order titanium oxide ceramics in which this calcined titanium dioxide is placed in a muffle placed in an air atmosphere furnace and filled with an embedding powder mainly composed of metal titanium and carbon powder, and reduced and calcined.

Hereinafter, the present invention will be described in detail. Of the present invention
The low order titanium oxide ceramics obtained by the manufacturing method is a low order titanium oxide ceramics obtained by reducing and firing calcined titanium dioxide containing titanium dioxide as a main component (hereinafter simply referred to as calcined titanium dioxide), and has NTC characteristics. Low-order titanium oxide ceramics.

[0010] In general, when calcined titanium dioxide is reduced and calcined, the density of the calcined body is reduced while almost no shrinkage of the calcined body and generation of pores in the calcined body are observed. A vacancy that captures electrons is generated at the departure point of this, and in the lower titanium oxide ceramics obtained by reducing calcined titanium dioxide, a large number of vacancies that capture the electrons are present. Is believed to be Also, electrons trapped in such vacancies can contribute to electrical conduction by a predetermined excitation voltage due to weak binding force, and low-order titanium oxide ceramics having a large amount of vacancies capturing electrons, that is, oxygen The lower the titanium oxide ceramics from which a large amount of carbon dioxide has been removed, the better the electrical conductivity.

[0011] The low titanium oxide ceramics of the present invention comprises:
The x in the composition formula TiOx of titanium oxide is close to 1, and it has a large amount of vacancies that have released oxygen in a larger amount than calcined titanium dioxide and have captured electrons. In such low order titanium oxide ceramics of the present invention, the number of electrons trapped in the vacancy is smaller in quantity than free electrons in metal,
When activated by heat, it becomes easier to move, and the electric resistance decreases due to a rise in temperature, that is, NTC characteristics (Negative).
Temperature Coefficient).

Further, when several low-order titanium oxide ceramics of the present invention are used at the same time, if the electrical properties of the ceramics are not uniform in their initial specific resistance values, they can be rated by applying heat and heating. Further, according to the purpose, the low order titanium oxide ceramics of the present invention may be self-heated by energization, or may be energized under heating by another heat source to shift the initial resistance value to a further lower resistance value and to be rated. be able to.

The method for producing the low-order titanium oxide ceramics of the present invention is described below. If necessary, a sintering aid and / or a binder is added to titanium dioxide to perform a primary sintering to obtain a sintering titanium dioxide containing titanium dioxide as a main component. A low-order titanium oxide ceramic is manufactured by placing it in a muffle filled with a filling powder mainly composed of carbon powder and performing reduction firing.

The titanium dioxide used as a raw material is preferably a high-purity titanium dioxide powder having a purity of 99.8% or more. If the amount of impurities contained in the raw material titanium dioxide is 0.2% or more, the electronic structure at the interface of the titanium dioxide may be changed, thereby deteriorating the conductivity of the resulting low-order titanium oxide ceramics and adversely affecting the electrical characteristics. May be given.

As raw materials for the calcined titanium dioxide, in addition to the above-mentioned high-purity titanium dioxide powder, La ₂ O ₃ , Ce and Ce may be used, if necessary, in a proportion of about 0.1 to 0.3 mol% as a calcining aid.
O ₂ , Y ₂ O ₃ , salts of alkaline earth metals and the like can be blended. In the case of firing after forming titanium dioxide, it is also possible to add an inorganic binder such as an organic binder and / or clay from which residual components have been removed to the above-mentioned fired titanium dioxide raw material for forming. After thorough mixing, molding, drying, and primary firing, a fired titanium dioxide molded article is obtained.

The primary firing of the raw material mixture or molded article containing titanium dioxide as a main component may be carried out in the same manner as in the usual production method of calcined titanium dioxide. For example, the raw material mixture or the molded article is processed at 1350 ° C. to 1430 ° C. In the temperature range of
By calcining for 1 to 3 hours, calcined titanium dioxide can be obtained.

In the production method of the present invention, the calcined titanium dioxide obtained in this manner is put into a muffle, which is placed in an air atmosphere furnace and filled with an embedding powder mainly composed of metallic titanium and carbon powder. And reduction firing.

The muffle used for such reduction firing is not particularly limited, and a muffle usually used for firing ceramics can be used, for example, a heat-resistant metal or a dense refractory metal. A container etc. can be mentioned preferably. In such a muffle, the calcined titanium dioxide obtained above is buried together with the filling powder, and this is placed in an air atmosphere furnace to perform reduction calcination. In the present invention, metallic titanium and carbon powder are used as the filling powder. Filling powder as the main component is used.

The metal titanium in the filling powder used in the present invention acts as a reducing agent, and the carbon powder acts as a hermetic filler.
The mixing ratio between the titanium metal and the carbon powder was 1: 1 by weight.
４4: 1 is preferred. In addition to the above-mentioned metal titanium and carbon powder, for example, tar of 5% or less by weight relative to carbon powder is added to the filling powder for the purpose of filling the powder voids. It is also possible to mix. The weight ratio of such embedded powder to calcined titanium dioxide in the muffle is 2: 1 to 5: 1.
It is preferable that

The concentration of the reducing atmosphere in the muffle is determined by the amount of the titanium metal mixed therein, and the degree of reduction of the titanium dioxide is regulated by this. Therefore, if the amount of the titanium metal with respect to the carbon powder is smaller than the above range, or If the amount of the embedded powder relative to the calcined titanium dioxide is out of the above range, the calcined titanium dioxide may not be sufficiently reduced. Also, even if the amount of metallic titanium with respect to the carbon powder is increased beyond the above range, or the amount of embedded powder with respect to the calcined titanium dioxide is greater than the above range, the degree of reduction of the calcined titanium dioxide reaches a plateau, and Disadvantageous.

In such a reduction firing process, the mixing ratio of titanium metal and carbon powder in the filling powder is
Since the compounding ratio of the embedded powder and the calcined titanium dioxide is related to the degree of reduction of the calcined titanium dioxide, by adjusting this compounding ratio, the x of the titanium oxide TiOx in the obtained lower order titanium oxide ceramics is adjusted. Can be controlled.

Various forms such as powder and chips can be used as the form of the metal titanium used in the production method of the present invention. In the present invention, the powder is preferably used in consideration of the contact area and the like. Also, from the same viewpoint, a powder having a large bulk specific gravity is preferably used for the carbon powder.
The various raw materials constituting such an embedded powder are mixed well and packed into the muffle as an embedded powder. In the production method of the present invention, the fired titanium dioxide molded article or the like obtained as described above is buried in the filling powder thus filled in the muffle.

Next, the reduction firing of the present invention may be carried out in the same manner as in a normal reduction firing using a muffle kiln except that the above-mentioned filling powder is used. It is preferable that a muffle filled with baked titanium dioxide and filling powder is installed and baked at 950 to 1500 ° C. for about 1 to 3 hours. If the firing temperature is set to 950 ° C. or higher, the titanium metal exhibits a remarkable activity and its activity becomes higher than that of the titanium dioxide, so that the titanium metal can easily extract oxygen from the fired titanium dioxide. This makes it possible to reduce the value of x in the titanium oxide TiOx of the resulting low order titanium oxide ceramics. That is, at the firing temperature of 950 ° C. or lower, the reduction of the fired titanium dioxide may not be sufficiently performed. Also, 1
Even at 500 ° C. or more, the degree of reduction of the calcined titanium dioxide reaches a plateau, which is not preferable in terms of productivity.

[0024]

The low order titanium oxide ceramic of the present invention is a low order titanium oxide ceramic obtained by reducing and firing calcined titanium dioxide containing titanium dioxide as a main component.
It is a low-order titanium oxide ceramic having C characteristics. In addition, in order to obtain such a low titanium oxide ceramic, in the present invention, a reduction firing using a muffle, which has been performed in various fields for a long time, is applied, and metallic titanium (reducing agent) is used as a filling powder in the muffle. And carbon powder (closed filler).

The low titanium oxide ceramics of the present invention obtained in this way has conductivity, in contrast to the fact that ceramics generally do not have conductivity. This is because, in ordinary ceramics, electrons are confined to atoms or atomic groups and their movement is difficult, whereas in the lower titanium oxide ceramics of the present invention, electrons are captured by vacancies created in the manufacturing process. This is because the electron has a weak binding force and contributes to electric conduction by a predetermined excitation voltage. The operation of the low order titanium oxide ceramics of the present invention will be described below as an operation when a heating element is used by utilizing its conductivity.

Generally, electrons or ions can be mentioned as a medium of electric conduction in the heating element. In the heating element using the low-order titanium oxide ceramics of the present invention, the heating element is trapped in the vacancy formed during the manufacturing process. Electrons are thought to play this role. The electrons trapped in the vacancies of the low order titanium oxide ceramics of the present invention are quantitatively less than free electrons in the metal, so that they are easily moved if activated by heat, and have an electric resistance value due to a temperature rise. , Ie, NTC. However, when the temperature rises to 400 ° C. or higher, diffusion of oxygen into the crystal starts to occur, and the reduction of vacancy concentration due to intrusion of oxygen, that is, the restraint of electrons due to ionization of oxygen proceeds, leading to a decrease in electric conductivity. .

That is, in the heating element using the low-order titanium oxide ceramics of the present invention, electricity can be supplied from a relatively low voltage as compared with other heating elements, and the heating element can be a low voltage and high efficiency heating element. Further, the current density increases due to the decrease in the electric resistance value with the rise in temperature.
It can be said that the stability as a heating element at the following temperatures is excellent.

[0028]

Embodiments of the present invention will be described below. To 99.5 g of titanium dioxide (purity 99.8%) as a raw material, 0.5 g of CaCO ₃ was added as a firing aid, and ₃ g of microwax was added as an organic binder, and 3 × 0.4 × 12 c
m into a plate shape and put it in a firing furnace at 100 ° C / hr.
After the temperature was raised to 1400 ° C., this temperature was maintained for 2 hours, and then allowed to cool to obtain calcined titanium dioxide. With the same raw material composition (weight% of each raw material is the same), 2.8 × 0.4 × 1
A plate-shaped calcined titanium dioxide having a size of 8.5 cm was produced. In this way, several pieces of calcined titanium dioxide of each size were produced.

Next, 2 kg of embedded powder obtained by mixing titanium powder (46 mesh) and clay-like graphite powder (325 mesh) at a weight ratio of 1: 1 into the silicon carbide-based muffle was charged into the plate-shaped muffle. After 1 kg of the calcined titanium dioxide molded article of Example 1 was embedded and sealed in a closed state at 1300 ° C. for 3 hours, it was allowed to cool to 1000 ° C. Thereafter, the muffle was pulled out of the furnace and rapidly cooled to take out the obtained low order titanium oxide ceramics of the present invention.

<Evaluation of Low Titanium Oxide Ceramics of the Present Invention> Using the low titanium oxide ceramics obtained as described above as a heating element, an energization test as described below was performed.
The electrical characteristics were evaluated.

(Test 1) Flat low-order titanium oxide ceramics (3 × 0.4 × 12 cm) obtained in the above example
Was used as a heating element. First, a silver paste was applied to both ends of the heating element, and a pure aluminum mesh net was wound thereon, and this was used as an electrode. A thermometer was set on the heating element, connected to a power supply together with an ammeter and a voltmeter, and changes in surface temperature, current, and voltage of the heating element when a DC voltage of 6 V was applied were measured over time. Also current,
The resistance was determined from the measured voltage. The test uses a variable DC constant voltage / constant current power supply (Kikusui Electronics Corporation)
, PAD 35-10L), the ammeter was a digital multimeter (Yokogawa Instruments Co., Ltd., 753701), and the voltmeter was a digital multimeter (Iwasaki Communication Equipment Co., Ltd., SC
-7405) and an infrared radiation thermometer (IT2-50, manufactured by Keyence Corporation) was used as the thermometer. The surface temperature is an indicated value when the emissivity of the infrared radiation thermometer is set to 0.98.

The results are shown in the relationship between the conduction time and the surface temperature of the heating element (FIG. 1), the relationship between the conduction time and the resistance value of the heating element (FIG. 2), and the relationship between the conduction time and the current value flowing through the heating element (FIG. 1). 3). From these results, when the low order titanium oxide ceramics of the present invention was used for a heating element,
The temperature rises with the energization time, and the electrical resistance value decreases with the rise. This indicates that the low-order titanium oxide ceramics of the present invention has excellent NTC characteristics that contribute to the efficiency of the heating element.

(Test 2) Flat low-order titanium oxide ceramics (28 × 4 × 185 mm) obtained in the above example.
A heating element (28 × 4 × 550 mm) connecting three flat low-order titanium oxide ceramics obtained in the above example and a nichrome wire type ceramic heater (ceramic) for comparison Box (300x
Nichrome wire (L = 300) specially treated within 200 mm
mm) A test was conducted using three types of heating elements, a heater incorporating one heating element, CMH-210, manufactured by Noritake.

An electrode was manufactured in the same manner as in Test 1 above, except that one piece of the above-mentioned plate-shaped low-order titanium oxide ceramics was used as a heating element. Further, in the case where the above-mentioned three low-order titanium oxide ceramics were connected to form a heating element, a silver paste was applied to both ends of all three heating elements, and the first right end (silver paste portion) and the second The left end (silver paste part) is overlapped and fastened with a brass screw. Similarly, the second right end and the third left end are overlapped and fastened with a brass screw and connected. The first left end and the third right end A pure aluminum mesh net was wound from above the silver paste portion to form an electrode. The nichrome wire type ceramic heater of the comparative example was used as it was.

A thermometer is set on each of the thus obtained electrodes, connected to a power supply together with an ammeter and a voltmeter, the power supply is turned on, and the surface when a current flows through the heating element is turned on. Changes in temperature, current, and voltage were measured over time. All the instruments used in the test were the same as in Test 1, except that a general household outlet was used as the AC power supply in addition to the above as the power supply. Further, the resistance value was determined from the measured values of the current and the voltage. Table 1 shows the results.

[0036]

[Table 1]

From these results, it was found that when the low-order titanium oxide ceramics of the present invention was used as a heating element, the NTC characteristics were excellent as in the above-mentioned Test 1, and that the low-voltage titanium oxide ceramic had a lower voltage than the heating element of the comparative example. It can be seen that there are advantages such as low power consumption due to low resistance.

[0038]

The low order titanium oxide ceramics of the present invention has a small proportion of oxygen in the composition (the value of x in TiOx is small) and has NTC characteristics when used as a heating element.
It has excellent electrical properties such as low voltage, large current and low resistance.
Further, according to the production method of the present invention, the low-order titanium oxide ceramics can be produced simply and efficiently.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the energization time and the surface temperature of a heating element of a low-order titanium oxide ceramic of an example.

FIG. 2 is a diagram showing the relationship between the energization time and the resistance value of the heating element of the lower titanium oxide ceramics of the example.

FIG. 3 is a diagram showing a relationship between an energization time and a current value flowing through a heating element made of a low-order titanium oxide ceramics of an example.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiro Fukuda 785-1 Kokuso-cho, Kamiso-cho, Kakogawa-shi, Hyogo (56) References JP-A-60-79691 (JP, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) C04B 35/42-35/50 H05B 3/14

Claims (8)

(57) [Claims] 1. A firing aid and / or a binder, if necessary, is added to titanium dioxide to perform a primary firing to obtain a fired titanium dioxide containing titanium dioxide as a main component, and the fired titanium dioxide is placed in an air atmosphere furnace. Further, a method for producing a low-order titanium oxide ceramic, which is placed in a muffle filled with a filling powder mainly composed of titanium metal and carbon powder and reduced and fired. 2. The method according to claim 1 , wherein the purity of the titanium dioxide is 99.8% or more. 3. A process according to claim 1 or 2 the temperature of the reduction firing is 950 to 1,500 ° C.. 4. The compounding ratio of titanium metal and carbon powder in the filling powder is 1: 1 to 4: 1 by weight, and the weight ratio of the filling powder to calcined titanium dioxide is 2: 1 to 5: 1. Claims 1-3
The production method according to any one of the above. 5. A sintering aid, if necessary, for titanium dioxide.
After adding and / or forming a binder, primary baking
The fired titanium dioxide containing titanium as the main component
Titanium dioxide was placed in a metal tube installed in an air atmosphere furnace.
Filled with a filling powder mainly composed of tin and carbon powder
A low-order titanium oxide ceramic that is placed in a full and reduced and fired
A method for manufacturing a heating element made of silicon. 6. The titanium dioxide having a purity of 99.8% or more.
The method according to claim 5. 7. The reduction firing temperature is from 950 to 1500 ° C.
The production method according to claim 5 or 6, wherein 8. Mixing of titanium metal and carbon powder in filling powder
The ratio is 1: 1 to 4: 1 by weight, and the embedded powder and the calcined diacid
The weight ratio of titanium oxide is 2: 1 to 5: 1.
The production method according to any one of the above.