CN106018496A - Method for preparing high-sensitivity low working temperature ethanol gas sensor element - Google Patents

Abstract

The invention discloses a method for preparing a high-sensitivity low working temperature ethanol gas sensor element. LaFeO3 nanoparticles prepared through an improved sol gel method are selected as a working substance to prepare an indirectly heated ceramic tube gas sensor element. Through the adding of ethylene glycol (EG) in a precursor, the distribution uniformity of positive ions in a solution and the hole carrier concentration in particles are increased, neither heavy metal nor rare earth precious metal is added, and element resistance is reduced. Through introduction of a secondary sintering process, particle sizes and agglomeration phenomena are reduced, the content of particle surface Fe4+ions and oxygen absorption capability are improved, and thus ethanol sensitivity is improved and the working temperature is lowered. The LaFeO3 indirectly heated gas sensor element prepared through the method can have sensitivity of 46 for 200 ppm of ethanol under a working temperature of 112 DEG C, is high in sensitivity to the ethanol and low in working temperature and has the advantages of being low in cost and environmentally friendly.

Description

A kind of preparation method of high sensitivity and low working temperature ethanol gas sensor element

technical field

The invention relates to a gas sensor, in particular to a method for preparing an ethanol gas sensor element with high sensitivity and low working temperature, using _LaFeO3 nanoparticles prepared by an improved sol-gel method as a working substance.

Background technique

With the development of modern society, people pay more and more attention to health and safety issues. Ethanol is the main component of all kinds of alcohol, and it is also a flammable gas. Excessive drinking, drunk driving and leakage of ethanol have great health and safety Therefore, a highly sensitive, highly selective, stable and reliable ethanol gas sensor is of great significance to human health and life safety. At present, doped semiconductor oxides SnO ₂ , ZnO, TiO ₂ , Fe ₂ O ₃ , V ₂ O ₅ , etc. are widely used in the detection of ethanol gas. The ethanol gas reacts, thereby changing the resistance of the semiconductor material, and the detection of ethanol gas is realized by measuring the change of resistance. However, such ethanol gas sensors generally have problems such as high working temperature and low sensitivity, which are not conducive to the development of gas sensing technology.

Perovskite oxide LaFeO ₃ is a p-type semiconductor, and its resistance will increase when exposed to reducing gases such as ethanol. In recent years, the research on ethanol gas sensor elements based on LaFeO ₃ has attracted extensive attention, because this type of sensor has high stability and can achieve different selectivity and response speed by doping A and B ions. However, based on the previous research work of scientific researchers, it was found that: (1) LaFeO ₃ itself has a large resistance, which is not conducive to practical applications. Ca, Sr, Ba, Pb and other divalent elements are often doped to replace the position of trivalent La, or use Co, Mg, Ni and other elements are doped to replace the position of trivalent Fe, providing more hole carriers, thereby reducing the resistance of the material; (2) LaFeO ₃ -based ethanol gas sensor elements with high sensitivity, the best The operating temperature is still high, usually above 200°C, which is not conducive to the research of low-power devices; the LaFeO ₃ -based ethanol gas sensor element with the best operating temperature below 200°C either contains heavy metal elements such as Pb, which is not conducive to environmental protection , or contain rare earth precious metals such as Sm, and the cost is relatively high.

Contents of the invention

The purpose of the present invention is to overcome the difficulties that current _LaFeO3 -based ethanol gas sensor elements are difficult to realize high sensitivity and low working temperature, and provide _{LaFeO3nanoparticles} prepared by the improved sol-gel method as the working material, which has high sensitivity 1. Preparation method of LaFeO ₃ -based ethanol gas sensor element with side heating type ceramic tube structure with low working temperature characteristics.

The present invention is achieved through the following technical solutions:

A method for preparing a high-sensitivity low-working-temperature ethanol gas sensor element, comprising the following steps:

(1) Precursor ingredients

Accurately weigh La(NO ₃ ) ₃ 6H ₂ O and Fe(NO ₃ ) ₃ 9H ₂ O according to the stoichiometric ratio La:Fe=1:1;

(2) Preparation of xerogel

Dissolve the precursor ingredients in deionized water, add citric acid to form a mixed solution according to the molar ratio of the sum of cations and citric acid at 1:2, add ammonia water to adjust the pH to 6.5-7.5, and place the mixed solution in a 70-80°C water bath Stir in the pot, add ethylene glycol EG to form a sol according to the molar ratio of 1:2 to the sum of cations, and continue stirring until the dry gel state; the sum of cations refers to the sum of the amount of La ³⁺ ions and Fe ³⁺ ions ;

(3) Preparation of LaFeO ₃ nanopowder

Put the dry gel in a crucible to heat to produce spontaneous combustion. The obtained powder is ground and placed in a muffle furnace, and sintered at 390-410°C for 2 hours to remove residual organic matter; the obtained powder is manually ground for 30 minutes and then placed in a muffle furnace. Sintering at 590-610°C for 2 hours to obtain nano-sized LaFeO ₃ powder;

(4) Preparation of side-heated ceramic tube structure gas sensor element

Take 0.1±0.05g of LaFeO ₃ powder and place it in an agate mortar, add 0.025±0.005g of glass fiber, add 0.2-0.3ml of terpineol with a rubber dropper, and grind together until it becomes a paste; use a paint pen to It is evenly coated on the outer surface of the ceramic tube core with two ring-shaped gold electrodes and four Pt wires, dried and placed in a muffle furnace, and sintered at 590-610°C for 2h; Ni with a resistance of 35±2Ω The -Cr heating wire passes through the ceramic tube and welds the four electrode wires on the sensor base, installs the outer cover collar, and uses an aging bench to age for 24 hours at a current of 120mA to make a side-heated gas sensor element.

In the step (1), nitrate is used for batching, and the cost is low.

In the step (2), ethylene glycol EG is added as a dispersant at a molar ratio of 1:2 to the sum of cations to make the cations more uniformly dispersed.

The introduction of secondary sintering in the step (3) reduces the particle size and makes the particle size more uniform.

The LaFeO ₃ nanoparticles obtained in the step (3) have an orthorhombic perovskite structure, and the grain size is 20-25 nm.

In the step (4), the firmness of the element is increased by adding an appropriate amount of terpineol and glass fiber.

The LaFeO ₃ gas sensor element obtained in the step (4) has the characteristics of high sensitivity to ethanol and low working temperature.

The beneficial effects of the present invention are:

(1) The present invention has obvious originality in the preparation of the working substance of the LaFeO ₃ -based ethanol gas sensor element. For the first time, the LaFeO ₃ nanoparticles prepared by the improved sol-gel method are proposed as the working substance. Through the addition of ethylene glycol EG in the precursor, the uniformity of the distribution of cations in the solution and the concentration of hole carriers in the particles are increased, and no heavy metals and rare earth precious metals are added to reduce the resistance of the element; through the introduction of the secondary sintering process, Reduce particle size and agglomeration, increase the content of Fe ⁴⁺ ions on the particle surface and the ability to absorb oxygen, thereby improving the sensitivity to ethanol and reducing the working temperature.

(2) Using LaFeO ₃ nanoparticles prepared by the improved sol-gel method as the working material, the ethanol gas sensor element with a side-heated ceramic tube structure has gas-sensing characteristics of high sensitivity and low working temperature. The invention plays an important role in the development of high-performance and low-power ethanol gas sensor components, and can further improve the application range and application field of the ethanol gas sensor components.

(3) Using the sol-gel method, using nitrate as raw material, without adding heavy metals and rare earth precious metals, it has the advantages of low cost, environmental friendliness, simple process, and convenient operation.

Description of drawings

Fig. 1 is the LaFeO ₃ side-heating type gas sensor component structure schematic diagram and the physical picture prepared in embodiment 1.

FIG. 2 is a scanning electron micrograph of the LaFeO ₃ nanoparticles prepared in Example 1.

Fig. 3 is the sensitivity of the _LaFeO3 side-heated gas sensor element prepared in Example 1 to 200ppm ethanol gas at different temperatures.

Fig. 4 is the dynamic response curve of the resistance of the LaFeO ₃ side-heated gas sensor element prepared in Example 1 to 200ppm ethanol gas at 112°C.

Fig. 5 is the sensitivity of the LaFeO ₃ side-heated gas sensor element prepared in Example 1 to different concentrations of ethanol gas at 112°C.

detailed description

All raw materials of the present invention are commercially available chemically pure reagents, and the present invention will be further described in detail below in conjunction with specific examples.

Example 1

(1) Precursor ingredients

Accurately weigh 0.03mol of La(NO ₃ ) ₃ 6H ₂ O and 0.03mol of Fe(NO ₃ ) ₃ 9H ₂ O according to the stoichiometric ratio La:Fe=1:1;

(2) Preparation of xerogel

Dissolve the precursor ingredients in deionized water, add 0.12mol citric acid to make a mixed solution according to the molar ratio of the sum of cations and citric acid being 1:2, add ammonia water to adjust the pH to 7, and place the mixed solution in a water bath at 80°C Stir, add ethylene glycol EG (ethylene glycol EG: total cation = 1:2) to form a sol according to the molar ratio of 1:2 to the sum of cations, and continue stirring until the dry gel state;

(3) Preparation of LaFeO ₃ nanopowder

Put the dry gel into a crucible to heat to produce spontaneous combustion. The obtained powder is ground and placed in a muffle furnace, and sintered at 400°C for 2 hours to remove residual organic matter; the obtained powder is manually ground for 30 minutes and then placed in a muffle furnace. After sintering for 2 hours, the grain size of the obtained LaFeO ₃ powder is about 25nm;

(4) Preparation of side-heated ceramic tube structure gas sensor element

Take 0.1g of LaFeO ₃ powder and place it in an agate mortar, add 0.025g of glass fiber, add 0.2ml of terpineol with a rubber dropper, and grind together until it becomes a paste. Use a paint pen to evenly apply it to the outer surface of the ceramic die with two ring-shaped gold electrodes and four Pt wires, dry it and put it into a muffle furnace for sintering at 600°C for 2h. Pass the Ni-Cr heating wire of about 35Ω through the ceramic tube and weld the four electrode wires on the sensor base together, install the outer cover collar, and use the aging bench to age for 24h under the current of 120mA to make the side-heated gas sensor element;

The obtained LaFeO ₃ gas sensor element has an optimum working temperature of 112°C and a sensitivity of 46 for 200ppm ethanol.

The present invention adopts static gas distribution method to measure LaFeO ₃ nanoparticles are the sensitivity characteristics of the gas sensor element of the working substance to ethanol gas, the sensitivity of the gas sensor element is defined as S=Rg/Ra, wherein Rg and Ra respectively represent the element in the gas to be measured and resistance values in dry air. First, make the sensor element work at 220 ^o C for 5-10 minutes, wait for the resistance to be stable; set the target working temperature, inject the gas to be tested after the resistance is stable; exhaust the gas when the resistance is stable in the gas to be tested, wait for the resistance After reaching the stability again, change the working temperature to 220 ^o C to restore the element resistance to the working resistance at 220 ^o C before gas injection. This test method can effectively reduce the influence of incomplete gas desorption at low temperature on the sensitivity test, and make the calculated sensitivity value more accurate.

Claims (7)

1. the preparation method of a high sensitivity low operating temperature alcohol gas sensor element, it is characterised in that have following Step:

(1) presoma dispensing

Stoichiometrically La:Fe=1:1 precise La (NO₃)₃·6H₂O and Fe (NO₃)₃·9H₂O；

(2) preparation of xerogel

Presoma dispensing is dissolved in deionized water, is that 1:2 addition citric acid is made into according to cation summation and citric acid mol ratio Mixed solution, instill ammonia regulation PH to 6.5-7.5, mixed solution is placed in 70-80 DEG C of water-bath stirring, according to sun from Sub-summation mol ratio is that 1:2 adds ethylene glycol EG formation colloidal sol, continues stirring to xerogel state；Described cation summation refers both to La³⁺Ion and Fe³⁺The amount sum of ionic species；

(3) LaFeO₃The preparation of nano-powder

Xerogel is put into crucible heating and produces dieseling, put into Muffle furnace after gained powder mull, burn at 390-410 DEG C Knot 2h, removes residual organic matter；Gained powder hand lapping is put into Muffle furnace after 30 minutes, at 590-610 DEG C, sinters 2h, Obtain nanoscale LaFeO₃Powder body；

(4) preparation of heater-type earthenware formation gases sensor element

Take the LaFeO of 0.1 ± 0.05g₃Powder body is placed in agate mortar, adds 0.025 ± 0.005g glass fibre, drips with glue head Pipe adds the terpineol of 0.2-0.3ml, is ground to pasty state together；Use coating pen by its even application to two ring-type gold The ceramic die outer surface of electrode and four Pt wires, puts into Muffle furnace after drying, sinters 2h at 590-610 DEG C；By resistance It is that the Ni-Cr heater strip of 35 ± 2 Ω is welded in sensor base through earthenware together with four electrode cables, outer housing is installed The collar, utilizes agingtable aging 24h under 120mA electric current, makes heater-type gas sensor element.

2. the preparation method of a kind of high sensitivity low operating temperature alcohol gas sensor element described in claim 1, it is special Levy and be in described step (1) to utilize nitrate to carry out dispensing, with low cost.

3. the preparation method of a kind of high sensitivity low operating temperature alcohol gas sensor element described in claim 1, it is special Levy be in described step (2) according to cation summation mol ratio be 1:2 add ethylene glycol EG as dispersant, make cation Dispersion is evenly.

4. the preparation method of a kind of high sensitivity low operating temperature alcohol gas sensor element described in claim 1, it is special Levy and be in described step (3) by the introducing of double sintering, reduce particle size, make particle size more uniform.

5. the preparation method of a kind of high sensitivity low operating temperature alcohol gas sensor element described in claim 1, it is special Levy the LaFeO being that described step (3) obtains₃Nano-particle is orthogonal perovskite structure, and crystallite dimension is 20-25nm.

6. the preparation method of a kind of high sensitivity low operating temperature alcohol gas sensor element described in claim 1, it is special Levy and be in described step (4) by appropriate terpineol and adding of glass fibre increasing the fastness of element.

7. the preparation method of a kind of high sensitivity low operating temperature alcohol gas sensor element described in claim 1, it is special Levy the LaFeO being that described step (4) obtains₃Gas sensor element has high sensitivity, low operating temperature to ethanol simultaneously Feature.