CN1188369C - Electronic ceramic sintering process in reduction atmosphere - Google Patents

Abstract

The present invention relates to an electronic ceramic sintering process in a reduction atmosphere, which adopts N2 gas and NH3 decomposing gas as the reduction atmosphere; NH3 is decomposed into mixed gas of H2 and N2 through a decomposing device, and oxygen contents of the mixed gas of H2 and N2 are below 10 ppm; the purity of the N2 gas is above 99.995 %; the mixed gas of H2 and N2 and nitrogen are lead into a gas mixing chamber through a gas output flowmeter; pure water is filled in the mixing chamber which is also provided with heating temperature controlling equipment. By regulating water level and steam air pressure in the mixing chamber capable of controlling water temperature, the mixed gas of H2 and N2 decomposed from the NH3 is mixed with the nitrogen in the gas mixing chamber according to different mixing proportions to obtain mixed gas of H2 and N2 having the hydrogen contents from 0 to 75 vol%, and the obtained mixed gas of H2 and N2 is guided into a firing furnace. The present invention can regulate and control the ceramic semiconducting performance by regulating the contents of the H2 in the mixed gas.

Description

Electronic ceramic sintering process in reduction atmosphere

The present invention relates to the process for calcining of pottery, particularly relate to electronic ceramic sintering process in reduction atmosphere.

In the prior art, the reduction firing atmosphere that relates to the electronic ceramics semiconductor abroad mainly adopts N ₂, H ₂Gas mixture also has the CO of employing or other rare gas element in addition.Adopt N ₂, H ₂During gas mixture, H ₂Content generally should be controlled at below 10%, or even below 6%, to guarantee safety.The domestic ammonia that adopts very early decomposes the electrodes in base metal that the high temperature reduction atmosphere that produces is fired insulating ceramic, and this method began to be applied to produce SrTiO in 1996 ₃Annular voltage-sensitive resistor.

Publication number is that the middle employing ammonia degradation production that proposes of the Chinese invention patent application " semiconducting sintering method of grain boundary layer and upper layer ceramic condenser " of CN1211050A---the mixed gas of nitrogen and ammonia replaces original high pure nitrogen to add high-purity hydrogen as grain boundary layer and the required reducing atmosphere of upper layer ceramic condenser semiconductor sintering.Publication number is that the mixed atmosphere continuous and automatic in combination stove that also proposes to adopt ammonia to decompose in the Chinese patent application " process for preparing substrate of semiconductor ceramic capacitor " of CN1279489A carries out the method that the semiconductor ceramic capacitor semiconductor is handled.The formation reducing atmosphere often adopts in kiln or well heater and charges into H when as seen, burning till some semiconductive ceramic at present ₂, N ₂Mixed gas or NH ₃Decomposition gas, the former atmosphere are easy to control, but H ₂High and the safety inadequately of cost; Though the latter is easy, it contains H ₂Amount is up to 75%vol, and wayward atmosphere.Most of reducing atmospheres are burnt till or heat treated electronic ceramics, and reductibility that need be by controlled atmosphere is obtaining best electrical property, rather than reductibility is strong more good more.The atmosphere reductibility is strong excessively, and for example the liquefied ammonia branch is vented one's spleen, and can cause pottery to burn till or produces excessive oxygen room [V during thermal treatment _o], make [the V in the crystal grain _o] be uneven Gradient distribution, influence the state of crystal boundary Schottky barrier, as the inhomogeneous of potential barrier occur and have directivity.[V in a large number _o] formation and the mass transfer process of diffusion when promoting to burn till, be prone to coarse grain.

At (1-x) N ₂+ xH ₂In the atmosphere system, H in the time of 1350 ℃ ₂With O ₂The standard Gibbs free energy change Δ G of reaction ⁰=-1.57 * 10 ⁵J/mol, and N ₂Δ G ⁰Only be-1.76 * 10 ³J/mol, as seen H in this atmosphere system ₂The strong and N of reductibility ₂What for a little less than.Usually can use " redox value V _R" characteristic of sintering atmosphere described.(Lee builds the English doctorate paper " strongly reducing atmosphere of once mixing sintering SrTiO ₃The research of double functional ceramics ", instructor: Li Shengtao, solemnity)

$V_R=\underset{i=1}{\overset{m}{\mathrm{\Σ}}}\mathrm{\Δ}{G}_i^0\·\lg \left[A_I\right]$

M---the species number of reducing gas in the sintering atmosphere;

[A _i]---the absolute concentration of i kind gaseous fraction, the i.e. molecule number of unit volume.

V _RThe big more then reductibility of absolute value strong more.

Can push away thus (1-x) N ₂+ xH ₂The redox value of system

V _R＝(-1.5)×10 ⁷)[lg(x×6.02×10 ²³)+lgN]

N is the mole number of mixed gas in the stove, when N is constant, and V _RAbsolute value | V _R| with H ₂The increase of content is exponential growth, H ₂Content is less than at 10% o'clock | V _R| increase rapidly, to H ₂Content is greater than 30%|V _R| change and become slow, little to the influence of atmosphere reductibility.As seen, work as H ₂, N ₂H in the gas mixture ₂Content is 10% when following, H ₂Content adjusting is burnt till or heat treated reducing atmosphere very effective.To SrTiO ₃Semiconductor porcelain is at low H ₂Electricalresistivity when burn till in the content district is with H ₂Content increases and descends rapidly, and pressure sensitive voltage E ₁₀Also descend thereupon.

Some semiconductive ceramic need burn till in reducing atmosphere or thermal treatment, and the power of reducing atmosphere (oxygen partial pressure height) is most important to the performance of product.But,, still there is not the method for the adjustable atmosphere reductibility of ideal so far for the sintering method of electronic ceramics reducing atmosphere by as can be known aforementioned.

The electronic ceramic sintering process in reduction atmosphere that the purpose of this invention is to provide a kind of not only safety but also adjustable atmosphere reductibility.

In order to achieve the above object, the present invention adopts N ₂Gas and NH ₃Divide and vent one's spleen as reducing atmosphere NH ₃Be decomposed into H through decomposer ₂, N ₂Gas mixture, its oxygen level is lower than 10ppm, and this oxygen level is based on above-mentioned H ₂, N ₂Gas mixture, N ₂Gas purity is higher than 99.995%, the above-mentioned H that makes respectively ₂, N ₂Gas mixture and nitrogen feed custom-designed gas mixing chamber through gas output flow meter, this gas mixing chamber is arranged on the sintering oven outside, and pure water is housed in it, and is provided with the heating temperature control device, by regulate wherein water level and the water vapour air pressure in the water temperature control mixing section, above-mentioned NH ₃Decompose the H that obtains ₂, N ₂Gas mixture mixes in gas mixing chamber in varing proportions with nitrogen, obtains the H that hydrogen content is 0～75vol% ₂, N ₂Gas mixture, this gas mixture and water vapour enter sintering oven by the pneumatic outlet that is arranged on gas mixing chamber top.

Sintering method of the present invention mainly is applicable to some semiconductive ceramic, as SrTiO ₃Piezoresistor, SrTiO ₃, BaTiO ₃Grain boundary layer or upper layer semiconductor ceramic capacitor etc. also are applicable to the titanate to be dielectric medium, and base metals such as nickel or copper are the laminated ceramic capacitor of interior electrode.

The present invention compared with prior art has the following advantages: the present invention adopts N ₂Gas and NH ₃Divide and vent one's spleen as reducing atmosphere, can be by regulating H ₂-N ₂H in the gas mixture ₂Content for electronic ceramics burn till or thermal treatment provides and has difference | V _R| atmosphere, thereby can more freely regulate and control the pottery semiconducting behavior.

Below in conjunction with drawings and Examples the present invention is described in further detail.

Fig. 1 is the structural representation of the gas mixing chamber in the embodiment of the invention.

Present embodiment adopts N ₂Gas and NH ₃Divide and vent one's spleen as reducing atmosphere:

A. the preparation of decomposed ammonia

High pressure ammonia in the commercially available bottled ammonia is delivered to the vaporization of ammonia vaporizer after the reducing valve decompression, through the decompression of reducing valve group, thermal degradation obtains containing H under the effect of catalyzer in decomposer again ₂75%, contain N ₂25% mixed gas (the about 0.05Mpa of pressure, residual ammonia＜0.1%, O ₂≤ 10ppm), after the water-cooling system cooling, output to deoxygenator and purifying regenerating unit by the output flow meter, deoxidation is decomposed oxygen, residual ammonia and moisture in the mixed gas (behind the ammon residue amount＜10ppm), it is stand-by by the output flow meter an above mixed gas part to be delivered to gas mixing chamber again, and another part is delivered to the front and back door charge flow rate meter group of sintering oven.

B. the preparation of nitrogen

Nitrogen provides by commercially available bottled nitrogen or by Nitrogen plant, and the high purity nitrogen purity that present commercially available Nitrogen plant makes can reach 99.99%, as more reaching 99.9995% behind the purified device purifying.Principle is summarized as follows: (compressor can select for use oil free type or common compressor to add Al on pipeline to provide source of high pressure air by oil-free air compressor ₂O ₃Strainer), deliver to varying-voltage adsorption nitrogen machine through refrigerant type dryer and level air filter three-stage filtration, utilize molecular sieve to have " absorption " performance difference function that gaseous mixture is separated to the gas with various molecule, commonly used is carbonaceous molecular sieve, nitrogen is different in the rate of diffusion on carbonaceous molecular sieve surface with oxygen, very fast than the diffusion of the oxygen of minor diameter, the more molecular sieve solid phase that enters just can obtain the enrichment composition of nitrogen like this in the gas phase.After for some time, molecular sieve reaches balance to the absorption of oxygen, according to carbonaceous molecular sieve characteristic different to the adsorptive capacity of adsorbed gas under different pressures, reduces pressure and makes carbonaceous molecular sieve remove absorption to oxygen, and this process is called regeneration.The double tower parallel connection is adopted in transformation absorption usually, hocket pressurization absorption and decompress(ion) regeneration, thus obtaining the successive nitrogen gas stream, purity is 99.99%, this so-called transformation absorption (PSA) technology.Then through deoxygenator, condenser, strainer, water cooler and moisture eliminator nitrogen is further purified as the need purifying, purity can reach 99.9995%.Gained nitrogen is delivered to N ₂The output flow meter is input in the gas mixing chamber.

By the structural representation of gas mixing chamber shown in Figure 1 as can be known, in the gas mixing chamber 1 that the sintering oven outside is set up pure water is housed, purity nitrogen that is made by above-mentioned steps and decomposed ammonia are respectively through N ₂Input flow rate meter 2 and N ₂+ H ₂Input flow rate meter 3 is sent into gas mixing chamber 1 mistake water and is overflowed, and is sent in the sintering oven through 7 outputs of gas mixture delivery valve by the outlet on gas mixing chamber 1 top jointly with the water vapour that is produced in the gas mixing chamber 1.Water level and water temperature that above-mentioned water vapour Pneumatic pipe cleaner is crossed in the pilot-gas mixing section 1 realize that hot resistance 8 is used for the water temperature of measurement gas mixing section 1, generally should be controlled at 30～50 ℃, replenishing when water intaking valve 9 is responsible for water level decline.For the water temperature in the pilot-gas mixing section 1, be provided with heating unit 4 below gas mixing chamber 1, present embodiment adopts the mode of indirect heating, promptly earlier the water in the heating unit 4 is heated, by thermal conduction the water temperature in the gas mixing chamber 1 is improved again, to guarantee safety; Heating unit 4 adopts well heater 11 heating, and measures control water temperature by hot resistance 5.In addition, also can directly the water intaking valve in the heating unit 6 be connected to the water side of the watercooling jacket of sintering oven, adjust the water temperature of the size control hot water flow of water valve 10 with adjusting heating unit 4, and then the water temperature in the adjustments of gas mixing section 1.The effect of above-mentioned gas mixing section is: 1. realize the mixing output of nitrogen, hydrogen, water vapour; 2. because cold nitrogen (bottled nitrogen) temperature is too low, can improve gas temperature behind the water excessively, prevent that cold nitrogen from impacting furnace temperature; 3. has the anti-backfire effect.

Therefore, by regulating N ₂ Output flow meter 2 and N ₂+ H ₂The flow of output flow meter 3, can control the ratio of nitrogen and decomposed ammonia respectively, can control water vapor pressure by water temperature and water level in the adjustments of gas mixing section, according to treating that the requirement of burned product to the atmosphere reductibility mixes these three kinds of gases after burner hearth mixed admission under meter is introduced in the sintering oven, form the reduction firing atmosphere in the kiln burner hearth, described kiln can be box-type furnace, bell jar stove or continuous tunnel furnace etc.

Should be noted that during adjusting: sintering oven is provided with fiery curtain and front and back door charge flow rate meter group at front and back in-out end fire door, is to utilize fiery curtain to light the H that overflows fire door for fire door when opening ₂, prevent air admission burner hearth and H ₂Mixing is blasted.When fire door was in closing condition, malleation made H in the stove ₂Light outlet from front and back waste gas and light discharge, to guarantee safety.Burner hearth air inlet (N ₂+ H ₂+ H ₂O ↑) pressure should be much higher than before and after the door intake pressure, prevent before and after the door H at high proportion ₂Enter the ceramics sintering zone, destroy sintering atmosphere, help also guaranteeing that ceramics is in the same atmosphere simultaneously when high temperature is reduced to low temperature.

To SrTiO ₃Annular voltage-sensitive resistor, SrTiO ₃Grain-boundary layer capacitor and BaTiO ₃The production of upper layer semiconductor capacitor is by regulating N ₂And NH ₃Divide the ratio of venting one's spleen, at H ₂Be that the resistivity of the product after the semiconductor is adjusted in 0.1～5 Ω cm scope, thereby regulate the E of ring varistor ₁₀, α and electrical capacity C; Regulate C, tg δ and the insulation resistance R of grain-boundary layer capacitor and upper layer semiconductor capacitor.The differing materials prescription, different firing temperatures can be regulated by this atmosphere and obtain best electrical property.Thereby the yield rate of burning till product is increased substantially.

Claims (5)

1. electronic ceramic sintering process in reduction atmosphere is characterized in that: adopt N ₂Gas and NH ₃Divide and vent one's spleen as reducing atmosphere NH ₃Be decomposed into H through decomposer ₂, N ₂Gas mixture, its oxygen level is lower than 10ppm, and this oxygen level is based on above-mentioned H ₂, N ₂Gas mixture, N ₂Gas purity is higher than 99.995%, the above-mentioned H that makes respectively ₂, N ₂Gas mixture and nitrogen feed custom-designed gas mixing chamber through gas output flow meter, this gas mixing chamber is arranged on the sintering oven outside, and pure water is housed in it, and is provided with the heating temperature control device, by regulate wherein water level and the water vapour air pressure in the water temperature control mixing section, above-mentioned NH ₃Decompose the H that obtains ₂, N ₂Gas mixture mixes in gas mixing chamber in varing proportions with nitrogen, obtains the H that hydrogen content is 0～75vol% ₂, N ₂Gas mixture, this gas mixture and water vapour enter sintering oven by the pneumatic outlet that is arranged on gas mixing chamber top.

2. electronic ceramic sintering process in reduction atmosphere according to claim 1, it is characterized in that: described heating temperature control device is arranged on the below of mixing section, adopt the mode of indirect heating,, by thermal conduction the water temperature in the gas mixing chamber is improved again promptly earlier with the heating of the water in the heating unit.

3. electronic ceramic sintering process in reduction atmosphere according to claim 1 is characterized in that: the water temperature of described gas mixing chamber is 30～50 ℃.

4. electronic ceramic sintering process in reduction atmosphere according to claim 1 is characterized in that: described NH ₃Decompose the H that obtains ₂, N ₂The preparation of gas mixture is to deliver to the vaporization of ammonia vaporizer by the high pressure ammonia after the reducing valve decompression, and through the decompression of reducing valve group, thermal degradation obtains containing H under the effect of catalyzer in decomposer again ₂75%, contain N ₂25% mixed gas, wherein, the about 0.05Mpa of pressure, residual ammonia＜0.1%, O ₂≤ 10ppm after the water-cooling system cooling, outputs to deoxygenator and purifying regenerating unit by the output flow meter, and oxygen, residual ammonia and the moisture in the mixed gas is decomposed in deoxidation, makes its ammon residue amount＜10ppm.

5. electronic ceramic sintering process in reduction atmosphere according to claim 1 is characterized in that: described nitrogen provides by commercially available bottled nitrogen or by Nitrogen plant, and obtains behind the purified device purifying.

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