CN102608168B - Air-sensitive resistance material and preparation method thereof - Google Patents

Abstract

The invention provides a gas sensitive resistance material and a preparation method thereof. The material is a compound of the following general formula: RFe ₂ O ₄ (RFeO ₃ ) _n , wherein R is Y, Dy, Ho, Er, Tm, Yb, Lu or In, n is equal to 0 or 1. The invention uses the above material as a detection resistance wire, which has corrosion resistance, high temperature resistance, fast response time (on the order of seconds), simple preparation process and wide working temperature range (-50°C to 200°C).

Description

Gas sensitive resistor material and preparation method thereof

technical field

The invention belongs to the field of atmosphere detection, in particular to a gas sensitive resistance material and a preparation method thereof.

Background technique

For some materials, the resistance value changes with the change of the external atmosphere. The resistance has different mechanisms in response to the atmosphere. For example, the oxidation-reduction reaction between the sample surface and the atmosphere gas in different atmospheres leads to changes in the energy band structure of the sample surface, which affects the electrical transport properties of the sample, or due to the different thermal conductivity of different gases, resulting in The temperature of the resistance wire is detected in the atmosphere. By measuring the resistance, the gas environment and the pressure of the sample can be calculated.

A common component for detecting gas vacuum is the Pirani resistance gauge. This resistance gauge generally uses metal wire, which has poor corrosion resistance and high temperature resistance. Therefore, the Pirani resistance gauge has a narrow working temperature range and is only used It is used to detect the vacuum degree of a given gas. The rest of the gas sensing elements, such as SnO ₂ gas sensing elements, can calibrate the components of the detected gas according to the different resistance values of SnO ₂ in different atmospheres, but their working response temperature is relatively high, and only at high temperatures can they react with the atmosphere to cause chemical resistance of the element. Change to achieve the purpose of detecting the atmosphere.

Contents of the invention

Therefore, the object of the present invention is to solve at least one problem of the above prior art, and provide a new gas-sensitive resistor detection material.

Above-mentioned purpose of the present invention is achieved through the following technical solutions:

According to one aspect of the present invention, a gas sensitive resistor material is provided, which is a compound of the following general formula: RFe ₂ O ₄ (RFeO ₃ ) _n , wherein R is Y, Dy, Ho, Er, Tm, Yb, Lu Or In, n is equal to 0 or 1.

In the gas-sensitive resistor material mentioned above, the material is single crystal or polycrystalline.

According to another aspect of _the present invention, there is provided a method for preparing gas-sensitive resistance material _RFe2O4 , comprising the following steps:

Step 1): Mix R ₂ O ₃ and Fe ₂ O ₃ thoroughly according to the molar ratio of 1:2, sinter in the atmosphere of CO ₂ and H ₂ at a temperature of 1000°C to 1300°C, and then cool to room temperature to obtain RFe ₂ O ₄ powder; wherein R is Y, Dy, Ho, Er, Tm, Yb, Lu or In;

Step 2): The obtained polycrystalline powder is placed in a platinum crucible and heated to 1500°C-1700°C, the solid is melted, and then cooled to 900°C.

In the above method, step 1) includes sintering at 1200° C. and then cooling to room temperature with the furnace.

In the above method, step 2) includes heating to 1620°C.

In the above method, step 2) includes cooling to 900°C at a rate of 1°C/min.

According to another aspect of _the present invention, there is provided a method for preparing gas-sensitive resistance material _RFe3O7 , comprising the following steps:

Step 1): Fully mix R ₂ O ₃ and Fe ₂ O ₃ according to the molar ratio of 2:3, mix evenly, press into tablets, put them into a tube furnace, and sinter in a mixed atmosphere of CO ₂ and H ₂ ;

Step 2): When the temperature of the product obtained in step 1) drops to 900° C., put the product into an ice-water mixture to quench.

In the above method, the sintering time in step 1) is 48 hours.

In the above method, the sintering temperature in step 1) is 1200°C.

Compared with the prior art, the present invention has the advantages of:

The invention uses an oxide ceramic material as a detection resistance wire, which is corrosion-resistant, high-temperature-resistant, has a fast response time (the response time is on the order of seconds), has a simple preparation process, and has a very wide working temperature range (-50°C to 200°C). . In the temperature range from room temperature to 400K, it can produce resistive response to different atmospheres (including vacuum), so as to achieve the purpose of detecting the atmosphere. The gas sensitive resistance detection material of the invention can not only be used to detect the degree of vacuum to prepare a vacuum gauge, but also can be prepared into a gas sensitive element by utilizing the property of being sensitive to the atmosphere at normal temperature.

Description of drawings

Embodiments of the present invention will be further described below with reference to the accompanying drawings, wherein:

Fig. 1 shows the current-voltage relationship of LuFe ₂ O ₄ obtained under different atmospheres;

Figure 2 shows the response range of _LuFe2O4 resistance at different _temperatures when the gas environment changes gradually;

_Figure 3 shows the periodic change of _LuFe2O4 resistance in oxygen and vacuum;

Fig. 4 has shown YbFe ₂ O The change curve _of resistance in vacuum, argon and oxygen successively;

Fig. 5 shows the change curve of Yb ₂ Fe ₃ O ₇ resistance in vacuum, argon and oxygen successively;

Fig. 6 shows the variation curves of the resistance of InFe ₂ O ₄ in vacuum, argon and oxygen in sequence.

Detailed ways

The properties and preparation methods of several typical materials in the RFe ₂ O ₄ (RFeO ₃ ) _n (n=0, 1) system of the present invention will be specifically described below through examples.

Embodiment 1: Preparation of LuFe ₂ O ₄ samples

The LuFe ₂ O ₄ polycrystalline samples used in the experiment were synthesized by the traditional solid-state sintering method. High-purity lutetium oxide Lu ₂ O ₃ (99.99%) and Fe ₂ O ₃ (99.9%) were fully mixed according to the molar (mol) ratio of 1:2, put into a tube furnace, and used different CO ₂ and H ₂ Volume ratio (for example, 1.9~7) to control different redox atmospheres, sintered at 1200°C, and then cooled to room temperature with the furnace. The obtained polycrystalline LuFe ₂ O ₄ powder was placed in a platinum crucible and heated to 1620 °C, the solid was melted, and then cooled to 900 °C at a rate of 1 °C/min. The typical size of the grown single crystal is 1×2×0.5 mm ³ .

_Figure 1 shows the current-voltage relationship of _LuFe2O4 under different atmospheres. As shown in Figure 1, under different detection currents, the voltage drop of the sample LuFe ₂ O ₄ in different atmospheres is different, that is, the sample resistance is different in different atmospheres. It can be seen that the gas sensitive resistance meter can be made by using the corresponding relationship between resistance and atmosphere.

Figure 2 shows the response range of the resistance of LuFe ₂ O ₄ at different temperatures when the gas environment changes gradually. As shown in the figure, when the gas environment of the sample LuFe ₂ O ₄ changes (from argon to vacuum), its resistance response ranges from room temperature to 350K. It also has the same properties in other different gases.

Figure 3 shows the periodic change of _LuFe2O4 resistance in _oxygen and vacuum. It can be seen that the gas-sensing characteristics of the sample have good repeatability and sensitivity, and the resistance of the sample decreases with the increase of the vacuum degree.

Embodiment 2: Preparation of Lu ₂ Fe ₃ O ₇ samples

High-purity lutetium oxide Lu ₂ O ₃ (99.99%) and Fe ₂ O ₃ (99.9%) were thoroughly mixed according to the molar ratio of 2:3, and after mixing evenly, they were pressed into tablets, and put into a tube furnace under CO ₂ and H ₂ Control the oxygen partial pressure in a mixed atmosphere, in which the volume ratio of CO ₂ : H ₂ can be adjusted (for example, 1.9~7), sinter at 1200°C for 48 hours, and put the sample into the ice-water mixture when the temperature of the sample drops to about 900°C Quenching in medium to prepare Lu ₂ Fe ₃ O ₇ polycrystalline samples.

Experiments have shown that when the gas environment of the sample LuFe ₂ O ₄ changes (from argon to vacuum), its resistance response ranges from room temperature to 370K, and it also has the same properties in other different gases.

Embodiment 3: Preparation of YbFe ₂ O ₄ samples

The YbFe ₂ O ₄ polycrystalline samples used in the experiment were synthesized by the traditional solid-state sintering method. High-purity yttrium oxide Yb ₂ O ₃ (99.99%) and Fe ₂ O ₃ (99.9%) are fully mixed according to the molar (mol) ratio of 1:2, put into a tube furnace, and use different CO ₂ and H ₂ Volume ratio (for example, 1.9~7) to control different redox atmospheres, sintered at 1200°C, and then cooled to room temperature with the furnace. The obtained polycrystalline YbFe ₂ O ₄ powder was placed in a platinum crucible and heated to 1620 °C, the solid was melted, and then cooled to 900 °C at a rate of 1 °C/min. The volume ratio of CO ₂ : H ₂ in the mixed atmosphere can be adjusted throughout the process. The typical size of the grown single crystal is 1×2×0.5 mm ³ .

Figure 4 shows the change curves of the resistance of YbFe ₂ O ₄ in vacuum, argon and oxygen in sequence. It can be seen from the figure that in different atmospheres, the sample resistance is quite different.

Embodiment 4: Preparation of Yb ₂ Fe ₃ O ₇ samples

High-purity lutetium oxide Yb ₂ O ₃ (99.99%) and Fe ₂ O ₃ (99.9%) were thoroughly mixed according to the molar ratio of 2:3, and after mixing evenly, they were pressed into tablets, and placed in a tube furnace under CO ₂ and H ₂ Control the oxygen partial pressure in a mixed atmosphere, in which the volume ratio of CO ₂ : H ₂ can be adjusted (for example, 1.9~7), sinter at 1200°C for 48 hours, and put the sample into the ice-water mixture when the temperature of the sample drops to about 900°C Quenching in middle to prepare Yb ₂ Fe ₃ O ₇ polycrystalline samples.

Fig. 5 shows the change curve of Yb ₂ Fe ₃ O ₇ resistance in vacuum, argon and oxygen in sequence. It can be seen from the figure that in different atmospheres, the sample resistance is quite different.

Embodiment 5: Preparation of InFe ₂ O ₄ samples

The InFe ₂ O ₄ polycrystalline samples used in the experiment were synthesized by the traditional solid-state sintering method. High-purity indium oxide In ₂ O ₃ (99.99%) and Fe ₂ O ₃ (99.9%) are fully mixed according to the molar (mol) ratio of 1:2, put into a tube furnace, and different CO ₂ and H ₂ The ratio is used to control different redox atmospheres, sintered at 1200 ° C, and then cooled to room temperature with the furnace. The obtained polycrystalline InFe ₂ O ₄ powder was placed in a platinum crucible and heated to 1620 °C, the solid was melted, and then cooled to 900 °C at a rate of 1 °C/min. The volume ratio of CO ₂ : H ₂ in the mixed atmosphere can be adjusted throughout the process. The typical size of the grown single crystal is 1×2×0.5 mm ³ .

Fig. 6 shows the variation curves of the resistance of InFe ₂ O ₄ in vacuum, argon and oxygen in sequence. It can be seen from the figure that in different atmospheres, the sample resistance is quite different.

Embodiment 6～10:

According to the process steps and conditions _described in Example ₁ , _YFe2O4 , _DyFe2O4 , HoFe ₂ O ₄ , ErFe ₂ O ₄ , and TmFe ₂ O ₄ . Tests have shown that under different detection currents, the pressure drop of samples in different atmospheres is significantly different; when the gas environment of these products changes (from argon to vacuum), the resistance response ranges from room temperature to 400K.

Embodiment 11～15:

According to the process steps and conditions described in Example 2, YFe ₃ O ₇ , DyFe ₃ O ₇ , HoFe ₃ O ₇ , ErFe ₃ O ₇ and TmFe ₃ O ₇ . After testing, when the gas environment of these products changes (from argon to vacuum), the resistance response ranges from room temperature to 400K.

_It can be seen from the above _{examples that} due to the _{polycrystalline} or single The following phenomenon is found in crystal materials: at room temperature, the resistivity of the material is significantly different in different gas atmospheres and vacuum (<10 ^-2 Pa), so the present invention uses RFe ₂ O ₄ (RFeO ₃ ) _n (n = 0, 1) polycrystalline or single crystal ceramic material as a gas sensitive resistance detection element.

In the RFe ₂ O ₄ (RFeO ₃ ) _n system of the present invention, it has the following characteristics: taking the resistivity standard in air at room temperature, in an oxidizing atmosphere, such as oxygen, the sample resistivity will increase (change rate > 10 %), in vacuum (<10 ^-2 Pa), the resistivity of the sample becomes smaller (change rate>10%). And as the current density through the sample increases, the change in resistivity under different atmospheres (including vacuum) increases. For a typical LuFe ₂ O ₄ sample, when the current density is 2.5mA/cm ² , the resistivity of the sample changes by 30% relative to the vacuum in an oxygen atmosphere. When the current density is 5.0 mA/cm ² , the variation increases to 70%. In addition, it can produce resistive response to different atmospheres (including vacuum) in the temperature range from room temperature to 400K, so as to achieve the purpose of detecting the atmosphere.

It should be noted that the above examples are for illustrative purposes only, and in other examples of preparing RFe ₂ O ₄ of the present invention, the sintering temperature may also be between 1000°C and 1300°C, and cooling may be performed by means of a cold water bath or the like. The heating temperature after obtaining RFe ₂ O ₄ powder can be between 1500°C and 1700°C, because if the temperature is not enough, the material cannot be fully melted and the required compound cannot be prepared, but if the temperature is too high, the rare earth elements will be accelerated. Volatile, so between 1500°C and 1700°C is the preferred process condition. In addition, the cooling rate may vary according to the specific cooling method, and those skilled in the art can determine it according to the cooling device and method. In other embodiments of the present invention for preparing RFe ₃ O ₇ , the sintering temperature may also be between 1000° C. and 1300° C., because the two compounds are more fully mixed within this temperature range.

Although the present invention has been specifically described with reference to the above-mentioned embodiments, those of ordinary skill in the art should understand that modifications or improvements can be made based on the disclosure of the present invention, and these modifications and improvements are all within the spirit of the present invention and within the range.

Claims (2)

1. A compound whose general formula is RFe ₂ O ₄ (RFeO ₃ ) _n is used as a gas-sensitive resistance material, wherein R is Y, Dy, Ho, Er, Tm, Yb, Lu or In, and n is equal to 0 or 1 . 2. The use according to claim 1, characterized in that the gas-sensitive resistor material is single crystal or polycrystalline.