CN1064452C - Composite electrode for on-line measurement of pH value - Google Patents
Composite electrode for on-line measurement of pH value Download PDFInfo
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- CN1064452C CN1064452C CN 96106474 CN96106474A CN1064452C CN 1064452 C CN1064452 C CN 1064452C CN 96106474 CN96106474 CN 96106474 CN 96106474 A CN96106474 A CN 96106474A CN 1064452 C CN1064452 C CN 1064452C
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Abstract
A composite electrode for on-line pH measurement. The electrode is composed of a metal electrode, an auxiliary electrode and a reference electrode, wherein the metal electrode is melted by a region and protected by a cathode, and the reference electrode is of a full-sealing structure and takes a polymer as a base material. The composite electrode has the advantages of small and exquisite structure, reliable sealing, convenient operation and the like, can be used for the online measurement of the pH value of the fermentation process, and can also be used for the online measurement of the pH value in other high-temperature environments.
Description
The present invention relates to the measuring electrode of pH, specifically relate to the high temperature resistant combination electrode of pH on-line measurement.
Prior art is: in technological process, often run into the problem of on-line measurement pH under hot conditions, or on-line measurement need stand the problem of high temperature test with the pH electrode.The former example is the pH on-line measurement of power plant's high-temperature boiler water, and the latter's example is a zymotechnique pH on-line measurement electrode.
In microbiotic, monosodium glutamate, ascorbic zymotechnique,, the operation of high-temperature sterilization in early stage is arranged all until in all bionic zymotechniques.At this moment, the temperature of steam or liquid between 120-150 ℃, for the time 20 minutes to 2 hours.For the glass pH electrode of common usefulness,, can cause electrode failure mainly due to the destruction of high temperature lower-glass surface gel layer.Other special glass electrode costs are high, and, in order to avoid the influence of high temperature, usually when high-temperature sterilization, electrode body is moved back in the storage chamber in the fermentation tank, not only the Operation and Maintenance inconvenience also easily causes microbiological contamination.
In order to remedy the weak point of glass pH electrode, various replacement schemes have been proposed, as zirconia ceramics electrode, ion-sensitive field effect transistor electrode, exchange membrane electrode, tempered glass electrode, modified electrode, charcoal paste electrode etc.They have the characteristics of himself, but have in the pH on-line measurement of pyroprocess in this class of zymotechnique, do not enter the practical stage yet so far.
Metal electrode is antimony, bismuth, iridium, platinum, palladium, tungsten, molybdenum, tantalum, titanium, stainless steel electrode etc. for example, is known by people for a long time.It has simple in structure, be easy to advantages such as processing and forming, internal resistance be low, high temperature resistant, be suitable for the pH on-line measurement of technological process.But the very easy generation oxide film of surface of metal electrode, this is disadvantageous as a rule.Oxide film makes the electrode surface state labile, causes the drift and the fluctuation of electrode potential, pH is measured can't carry out at all.In order in time to remove the oxide film of electrode surface, often adopt mechanical ablution, make squeegee material exactly, for example oilstone, fiberglass etc. are pressed close to surface of metal electrode.By motor-driven or liquid flow, scraping blade is rotated with respect to metal electrode, thereby bring in constant renewal in electrode surface, as described in USSR (Union of Soviet Socialist Republics) patent SU-418784 and Chinese patent 85204611.The shortcoming of this cleaning device, except cleanup action not exclusively, also exist complex structure, bulky, safeguard disadvantage such as inconvenience.
The scheme of another kind of improvement metal electrode comprises metal electrode and the employing monocrystalline that adopts high-purity (＞99.999%) and makes the method for single crystal face as potential electrode, as described in U.S. Pat 4338175 and US4119498.But their preparation method is more complicated, and cost is very high, and does the time spent for a long time in technology, still can not eliminate the intrinsic shortcoming of metal electrode fully.
The objective of the invention is to propose a kind of stable performance, simple in structure, volume is small and exquisite, sealing is reliable, safeguard combination electrode easy to use.
Technical scheme of the present invention:
Combination electrode of the present invention has been to use the technology of zone-melting, and the metal electrode that the pH sensitivity characteristic is arranged is carried out recrystallization.
Combination electrode of the present invention is to have used an auxiliary electrode, so that there is the metal electrode of pH sensitivity characteristic to be under the condition of cathodic protection.
Combination electrode of the present invention is to have used fully enclosed solid-state reference electrode, and it constitutes conductive liquid network portion based on polymeric material, the seepage of reference liquid in stoping.
Combination electrode of the present invention also is to reduce metal electrode as far as possible on the structural design, the volume of auxiliary electrode and contrast electrode, and making them be placed in one compactly is in the electrode shell of matrix with the polymkeric substance, is beneficial to maintenance, airtight and installation.
Range of application of the present invention comprises metal electrodes such as antimony, bismuth, palladium, molybdenum, stainless steel, in order to narrate conveniently, below only is that example is illustrated with the antimony electrode.In addition, understanding for essence of the present invention being had more in depth, will be representative with the antimony electrode also, and the principle of its pH response is briefly illustrated.
For a long time, it is believed that antimony is based on reaction to the response mechanism of pH:
The pass of deriving antimony electrode electromotive force Esb and pH value of solution according to thermodynamic principles is thus:
In the following formula, E
θ SbBe the standard electrode potential of antimony, R is a gas law constant, and F is a Faraday constant, and T is an absolute temperature.
But in actual applications, the electromotive force drift often takes place in antimony electrode, the potential pH slope of a curve is lower than theoretical value, electromotive force is subjected to the influence of solution stirring speed and air content etc., more tangible phenomenon is, electrode surface tarnishes, forms black film very soon, and these all are difficult to explain with theory of thermodynamics.By more deep research, can think that now it is the corroding electrode of conjugation cathode reaction (or title " oxygen depolarization ") that antimony electrode is actually with the dissolved oxygen DO.The antimony that we measured is actually under this pH system the electrode potential of pH response, the corrosion potential that the oxidation of antimony and dissolved oxygen DO reduction are constituted.
The present invention has following accompanying drawing:
Fig. 1 is the potential pH sketch of antimony
Fig. 2 is an antimony potential change synoptic diagram
Fig. 3 is the metal electrode sketch
Fig. 4 is metal electrode principle of cathodic protection figure
Fig. 5 is solid state reference electrode figure
Fig. 6 is the pH combination electrode
Fig. 7 is pH combination electrode on-line measurement figure as a result
Fig. 1 is the potential pH sketch of antimony.Its center line a and b are respectively the balanced lines of hydrogen and oxygen.Line C is Sb/Sb
2O
3Balanced line.Hatched area below the line C is antimony " exempting from rotten district ", when the antimony electrode electromotive force is in this scope, can eliminate the possibility that the antimony galvanic corrosion takes place.As can be seen from Figure 1, in broad pH (0-12) scope, Sb and Sb
2O
3Keep good linear relationship, this has beaten the basis for the pH sensitivity characteristic of antimony electrode, but the position of line C also just means the tendency that the following redox reaction of generation is arranged under line b:
Fig. 2 has made further instruction to this phenomenon.It is Sb and dissolved oxygen DO in certain pH system, when redox reaction takes place, the synoptic diagram of potential change, for brevity, all polarization curves all replace with straight line.Ordinate among Fig. 2 is electromotive force E, and horizontal ordinate is the absolute value of corrosion current | I|.When corrosion current was 0, when also promptly being in thermodynamic equilibrium state, (pHC), the equilibrium potential that oxygen and antimony are corresponding respectively was E for pHA, pHB according to different pH systems
P O, A ', E
P O, B 'E
P O, CAnd E
P Sb, A 'And E
P, E
P Sb, B 'E
P Sb, CPass between this equilibrium potential and the pH value ties up to and meets following thermodynamics expression formula under 25 ℃
EO
2／H
2O=1．23-0．059pH+0．151gPO
2 (5)
ESb/Sb
2O
3=0.15-0.059pH (antimony cubic system) (6)
But under the situation that above-mentioned reaction (3) and (4) takes place, just under the situation that produces the macro etch electric current, balance is destroyed, has produced polarization as shown in Figure 2.The intersection point of their polarization curve is respectively E
A', E
B', and E
C', this is the corrosion potential that we can practical measurement.Also keeping certain corresponding relation between its numerical value and the system pH.But this corresponding relation is unsettled, and is uncertain.When solution stirring speed and oxygen level change, must influence the polarization curve of oxygen, thereby influence the value of corrosion potential.Even stirring rate and oxygen level are constant,, changing anodic site (area and the ratio of react (4) and cathodic area ((3) react) because the antimony surface is constantly corroded.On the whole, the anodic site constantly diminishes, and the cathodic area constantly increases, thereby anode polarization is increased, and cathodic polarization reduces.Be in original pHA system shown in two dotted lines among Fig. 2, because the variation of polarization curve makes corrosion potential become E
A".Can illustrate qualitatively that thus antimony electrode reappears and fundamental cause accurately the response of PH is not enough.This shows, for make with the antimony electrode be the electromotive force of numerous metal electrodes of representative can stablize, accurately, pH value of reaction system linearly, key is to suppress the corrosion process of electrode surface.
Measure in order to finish pH, except the pH sensitive electrode, the stable and reproduction of contrast electrode electromotive force is vital.Especially under hot conditions, the volatilization and the seepage of reference solution more have practical significance in stoping.This also is one of the present invention's problem of trying hard to solve.
Below in conjunction with accompanying drawing, invention is further elaborated.
Fig. 3 is the sketch for preparing metal electrode according to the present invention by zone melting method.Before this, metal electrode 5 has been cast in the heatproof quartz-ceramics pipe 4 and has been condensed into the bulk metal piece.Pipe 4 bottom is placed among the high-frequency induction coil 1.After the energized, make the temperature in the high-frequency induction coil 1 exceed 3-5 ℃ than the fusing point of metal electrode all the time.For example, the fusing point of antimony is 630 ℃, then the temperature in the high-frequency induction coil 1 should be controlled at 633-635 ℃.After this, by a cover reducing gear (not shown), the speed constant speed of pipe 4 with 2-3mm/h descended, in the temperature range of high-frequency induction coil 1 control, metal becomes molten state 2, and a small amount of bubble 3 discharges that will mix, after metal breaks away from this temperature controlled region, cohesion forms crystal again, and has characteristics such as particle is thick, marshalling, compact structure, bubble minimizing, temperature raising.On macroscopic view, step through above-mentioned zone fusion and recrystallization, the surface of metal electrode 5 is bright luster, flawless, pit, pore and alloy, so just, guarantee the galvanochemistry homogeneity of electrode surface and stability, the reappearance creation good prerequisite of electrode potential for suppressing corrosion of metal.
Fig. 4 is according to metal electrode principle of cathodic protection figure of the invention process.Constant-current supply 9 output Constant Direct Currents or through the electric current of half-wave rectification, its anode is connected with auxiliary electrode 6 by lead 8, negative terminal passes through lead 8 and is connected with metal electrode 5.Solution 11 in container 12 makes electrode constitute electric loop.Metal electrode 5 can adopt materials such as antimony, bismuth, tungsten, molybdenum, tantalum, stainless steel to make, and 6 of auxiliary electrodes can adopt the material of platinum, gold, iridium, graphite or other electrochemical corrosion resistant to make.No matter be that metal electrode 5 is in the measurement state, or be not in measurement state (for example high-temperature sterilization), constant-current supply 9 is connected all the time, and metal electrode 5 is under the cathodic protection.The electromotive force of metal electrode 5 is among " exempting from rotten district " shown in Figure 1.The numerical value of constant current, because of the material of metal electrode different.Current density is too small, can weaken the protection effect, and current density is crossed conference and caused the non-linear skew of measured value, disturbs that precipitated cationic and hydrogen are separated out etc.Cathodic protection current density is controlled at 0-3mA/cm
2Be advisable.The potential value of metal electrode 5 and contrast electrode 7 links through lead 8 and the pH meter 10 with high input impedance.
Fig. 5 is according to solid state reference electrode schematic diagram of the invention process, is that with traditional contrast electrode difference it is a kind of fully closed structure.Polymkeric substance is a matrix, evenly sneak into and have chemically inert silicate powder 19, it is in the lower end of contrast electrode 7, constitute conductive diaphragm 20 with polymkeric substance, play a part liquid network portion, the top of electrode shell 17 still is common polymeric material, and interior Sheng NaCl or KCl saturated solution 16 are as interior reference solution.And there is the crystal 18 of part NaCl or KCl to separate out.The middle Ag/AgCl electrode 15 that inserts, the upper end is with capping 14 and tackifier 13 sealings.This polymeric material can be selected thermostability engineering plastics such as teflon, polysulfones, polypropylene, polyoxymethylene for use, and the galvanochemistry inert silicate powder 19 of sneaking into can be porcelain earth, euthalite, sodalite, smectite, sepiolite, zeyssatite, bentonitic clay etc.Powder particle needs to sieve through 200 order to 400 orders, and content is the 5-15% of polymer body.Contrast electrode through this method is made does not need the additonal pressure chamber, and reference solution in need not refilling or replenishing is particularly suitable for the on-line measurement under the hot conditions.
Fig. 6 is the pH combination electrode of making according to the present invention 21, its matrix 23 can be made by thermostability engineering plastics such as teflon, polysulfones, polypropylene, polyoxymethylene, metal electrode 5, auxiliary electrode 6 and contrast electrode 7 all are embedded within the matrix 23, three kinds of electrodes are connected with extraneous by lead 22 separately, be anti-stop signal bypass and enhanced leaktightness, all gaps are all with high-temperature resistance adhesive 13 sealings.In the lower end of contrast electrode is conductive diaphragm 20, and its moulding process has been seen above-mentioned.The physical size of combination electrode 21 is diameter 25mm, and overall height is 120mm, and it self flange 24 just can play the effect of sealing gasket.Combination electrode 21 can be fixed on the sidewall of container easily by flange and nut like this, problems such as unlikely generation leakage of oil, microbiological contamination.
Fig. 7 utilizes above-mentioned combination electrode to carry out the actual result that the online pH of the zymotechnique of streptomysin measures in certain pharmaceutical factory at home.Wherein ordinate is electromotive force (mV) signal that combination electrode provides, horizontal ordinate is the pH value that contrasts in the laboratory hand sampling simultaneously, can see, in the pH scope of being surveyed, basic and the pH maintenance rectilinearity variation of electrode signal, maximum error is equivalent to 0.1pH less than 5mV, can satisfy the requirement of technology.
In sum, pH combination electrode of the present invention has adopted multiple technologies to make, and its advantage can be summarized as follows:
1. adopt the zone-melting technology of metal electrode, so that metal electrode itself forms marshalling, the thick crystal of particle, effectively suppressed the corrosion of electrode surface.
2. adopt the cathode protection technology of metal electrode, so that the electromotive force of metal electrode is in E-pH figure's in " exempt from rotten district ", stoped the corrosion of electrode.
3. adopted by polymer and mixed the technology of making conductive diaphragm with the inert silicate powder, made reference electrode be hermetically sealed property, be convenient to maintenance and operation.
4. metal electrode, auxiliary electrode and reference electrode are formed combination electrode compactly, so that the structure of electrode is small and exquisite, sealing is reliable, and is easy to operate, prevented the appearance of leakage and microbiological contamination.
The present invention mainly is zymotechnique pH on-line measurement service, but also can be applicable in other online pH measurement. For example, GEOTHERMAL WATER, high-temperature boiler water, high purity water, waste water etc. can be obtained good result equally.
Claims (8)
1. a high temperature resistant online pH measures and uses combination electrode; comprise metal electrode (5), auxiliary electrode (6) and contrast electrode (7); it is characterized in that metal electrode (5) being carried out cathodic protection by auxiliary electrode (6) and constant-current supply (9); metal electrode (5) links to each other with the negative pole of constant-current supply (9); auxiliary electrode (6) links to each other with the positive pole of constant-current supply (9); constitute electric loop by solution (11), the current density on metal electrode during cathodic protection (5) surface is 0-3mA/cm
2
2. combination electrode according to claim 1, the material that it is characterized in that metal electrode (5) is antimony, bismuth, tungsten, molybdenum, tantalum and stainless steel.
3. combination electrode according to claim 1 and 2 is characterized in that using the technology of zone-melting, and metal electrode (5) is carried out recrystallization, and the temperature of zone-melting control exceeds 3-5 ℃ than the fusing point of this metal electrode (5).
4. combination electrode according to claim 1, the material that it is characterized in that auxiliary electrode (6) is conductive materials such as platinum, gold, iridium or graphite.
5. combination electrode according to claim 3, the material that it is characterized in that auxiliary electrode (6) is conductive materials such as platinum, gold, iridium or graphite.
6. combination electrode according to claim 1 or 5 is characterized in that contrast electrode (7) is a full-enclosed structure, and it is matrix with the polymkeric substance, evenly sneaks into galvanochemistry inert silicate powder (19), constitutes conductive diaphragm (20).
7. combination electrode according to claim 6, it is characterized in that the galvanochemistry inert silicate powder (19) of sneaking into can be porcelain earth, euthalite, sodalite, smectite, sepiolite, zeyssatite, bentonitic clay etc., powder particle needs to sieve through 200 order to 400 orders, and content is the 5-15% of polymer body.
8. according to claim 1 or 7 described combination electrodes, it is characterized in that metal electrode (5), auxiliary electrode (6) and contrast electrode (7) all are embedded within the matrix (23), and matrix (23) is made by thermostability engineering plastics such as teflon, polysulfones, polypropylene, polyoxymethylene.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN 96106474 CN1064452C (en) | 1996-08-14 | 1996-08-14 | Composite electrode for on-line measurement of pH value |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN 96106474 CN1064452C (en) | 1996-08-14 | 1996-08-14 | Composite electrode for on-line measurement of pH value |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN1155660A CN1155660A (en) | 1997-07-30 |
| CN1064452C true CN1064452C (en) | 2001-04-11 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN 96106474 Expired - Fee Related CN1064452C (en) | 1996-08-14 | 1996-08-14 | Composite electrode for on-line measurement of pH value |
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| CN (1) | CN1064452C (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN100419416C (en) * | 2005-03-21 | 2008-09-17 | 张荣华 | Zr/ZrO2 electrode and producing method thereof and integrated high temperature high-pressure chemical sensor composed by the same |
| CN102087202B (en) * | 2010-11-17 | 2012-08-22 | 哈尔滨工业大学 | Preparation method of all solid state reference electrode for monitoring reinforcement corrosion |
| CN109342519A (en) * | 2018-09-29 | 2019-02-15 | 中国科学院长春应用化学研究所 | A kind of measuring device and preparation method thereof avoiding pollution pH combination electrode |
| CN109342520B (en) * | 2018-09-29 | 2019-10-18 | 中国科学院长春应用化学研究所 | A kind of all-solid-state pH combination electrode device and preparation method thereof |
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1996
- 1996-08-14 CN CN 96106474 patent/CN1064452C/en not_active Expired - Fee Related
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| Publication number | Publication date |
|---|---|
| CN1155660A (en) | 1997-07-30 |
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