GB1559289A

GB1559289A - And others glass electrodes

Info

Publication number: GB1559289A
Application number: GB4264476A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1976-10-14
Filing date: 1976-10-14
Publication date: 1980-01-16

Description

(54) IMPROVEMENTS IN OR RELATING TO GLASS ELECTRODES (71) We, MIKHAIL MIKHAILOVICH SHULTS, prospekt Engelsa 63, Korpus 3, kv 51, Leningrad, ANATOLY ALEXANDROVICH BELJUSTIN, naberezhnaya kanala Griboedova 156, kv 2, Leningrad, ALEXANDR MOISEEVICH PISAREVSKY, Kronverskaya ulitsa 29/37, kv 109, Leningrad, LJUDMILA VASILtEvNA AVRAMENKO, ulitsa Timurovskaya 6, korpus 3, kv 76, Leningrad, SERGEI EGOROVICH VOLKOV, ulitsa Matrosa Zhehleznyaka 29, kv 8, Leningrad, VERA NIKONOROVNA LAKHTIKOVA, ulitsa Lenina 6, kv 9, Chelyabinsk, VLADIMIR ALEXANDROVICH DOLIDZE, ulitsa Zakariadze 10, kv 10, Tbilisi, and VALENTINA MIKHAILOVNA TARASOVA, prospekt Plekhanova 148, kv 19, Tbilisi, all of U.S.S.R.

and all citizens of the Union of Soviet Socialist Republics, do hereby declare the invention, for which we pray that a patent may be granted us, and the method by which it is to be performed, to be particularly described in and by the following statement: - This invention relates to glass electrodes for measuring the oxidation potentials of liquid media.

According to the present invention there is provided a glass electrode for measuring the oxidation potential of a liquid medium, the electrode comprising a tubular casing of high resistance glass having one end thereof sealed to a sensing element which is rigidly connected to a current lead disposed within the tubular cas ing, the sensing element being of an electron conductive glass and consisting of 32-45% by weight of SiO2, 7.0-26% by weight of Me2O, wherein Me is Li, Na, and/or K, 16.0-40% by weight of TiO2, 0.8-4.2% by weight of Ti2O3, and 2.0-32% by weight of one or each of Nb2O5 andTa2O5.

Electrodes in accordance with the invention can be used as sensing elements for the continuous control and monitoring of processes in the chemical, pulp- and paper-making, textile, pharmaceutical and microbiological industries, as well as in hydrometallurgy.

The fact that the sensing element is made of electrically-conductive glass containing oxides of tri- and tetravalent titanium, which increases considerably the chemical stability of the glass, enables oxidation potentials to be measured in liquid media having a pH below 3.

Relatively large amounts of titanium oxides in the glass and a pre-determined ratio between their two different valency states namely: Ti 0.08 to (I!!) Ti (III) + Ti(IV) = 0.08 to 0.20 provides the glass with a required level of electrical conduction.

If less than 16% by weight of titanium oxides are present in the glass, its resistivity exceeds 108 ohmcm, and it is unsuitable for redox measurements by reason of only small exchange currents at the glass-solution interface.

Excessive concentrations of titanium oxides (above 44.2% by weight) may result in complete crystallization of the glass during manufacture, rendering it unfit for use as an electrode.

It is, however, possible to improve the stability of electrode readings and to prolong the service life of this type of electrode in liquid media having a pH below 3.

The presence of Nb2O5 and/or Ta2O5 in the glass for electrodes in accordance with the invention renders the glass structure more compact, so that its chemical stability is increased.

Introducing less than 2% by weight of Nb2O5 into the glass has no positive effect on the properties of the glass, while amounts of Nb2Os above 32% be weight result in crystallization of the glass.

The mechanism of action of Ta2O5 in the glass is similar to that of Nb2Os. Excessive con centrations result in a loss in the mechanical strength of the glass.

Oxides of pentavalent niobium and/or tantalum enable the range of potentiometric measurements with glass electrodes to be ex tended towards high positive values of oxidation potentials (up to 1.5 V in relation to a conventional hydrogen electrode), in strongly acid media, at temperatures in excess of 60"C, and in the presence of dissolved oxygen, hydrogen and catalyst poisons.

The sensing element of the glass electrode is preferably of a glass which exhibits electrical conduction and contains the following components in % by weight: SiO2 - 32.0 to 37.4 Li2O - Oto 1.8 Na2O - 5.0 to 8.3 K2O - 2.2 to 10.7 TiO2 - 26 to 40 Ti203 - 0.8 to 1.7 Nb2Os - 4.0 to 25.0 The use of such a sensing element for a glass electrode significantly simplifies electrode production.

The sensing element of the glass electrode is preferably of a glass which exhibits electrical conduction, and contains the following components in % by weight: SiO2 - 37.1 to 45 Na2O - 5.0 to 8.0 K2O - 6.3 to 17.4 Li2O - 1.8 to 3.1 TiO2 - 16 to 31.8 Ti203 - 1.7 to 4.2 Nb2Os - 10.7 to 21.2 Ta2O5 - 2.0 to 32.0 High concentrations of trivalent titanium make it possible to manufacture sensing elements by casting the molten glass into a mould.

The sensing elements thus produced are characterised by a pre-determined Ti(III) to Ti(IV) ratio and offer reproducible electrical parameters.

The herein proposed electrode enables oxidation potentials to be measured from 700 to 1250 mV relative to the conventional hydrogen electrode, in solutions having a pH from 0.5 to 14, at temperatures between 0 C and 150"C, and in the presence of dissolved oxygen, hydrogen and catalyst poisons.

A glass electrode in accordance with the invention will now be described, by way of example, with reference to the accompanying drawing which is a single figure showing a longitudinal sectional view of the glass electrode.

The illustrated glass electrode has a cylindrical tube 1 which serves as a casing. Tube 1 is of a high-resistance glass, i.e. a glass whose electrical resistance is substantially higher, for example by a factor of 103, than that of a sensing element 2. The sensing element 2, secured by soldering to one end of the tube 1, is made of an electron - conductive glass consisting of 32 to 45% by weight of SiO2, 7.0 to 26.0% by weight of Me2 0, wherein Me is Li, Na, and/or K, 16.0 to 40% by weight of TiO2, 0.8 to 4.2% by weight of Ti203 and 2.0 to 32.0% by weight of Nb2 0s and/or Ta2 0s The sensing element 2 is connected to a metal current lead 3 within the cylindrical tube 1, and it is led out of the tube 1 as a cable 5 through the top of said tube protected by a cap 4 which hermetically seals the inner cavity of the electrode.

The glass electrode and a reference electrode,, for instance, a silver chloride electrode, are immersed in a solution containing a redox system. A potential arises between the electrodes at the interface between the glass of the sensing element and the solution. The potential of the glass electrode depends on the redox state of the solution, whereas that of the reference electrode remains constant. The electrodes are connected to a measuring instrument, e.g. a high-resistance millivoltmeter, which registers the potential difference between the electrodes and determines the ratio of the oxidized to reduced forms of elements in the solution being analysed, according to the Nernst equation.

Electrodes can be formed in accordance with the invention to measure oxidation potentials from -700 to 1250 mV at pH values from 0.5 to 14. The electrodes can be operated at temperatures from 0 to +1500C, at an electrical resistance of 610 Mohm.

Hereinafter are examples of specific glass compositions which can be used for the manufacture of electrodes in accordance with the invention.

The compositions of these glasses were selected from a study of the electrical and electrode properties of solutions of redox systems from indifference boundaries determined by the charging curves methed, as well as from a study of processing characteristics.

Two types of production processes for manufacturing electrodes in accordance with the invention have been developed, depending on the different valency forms of titanium in the glass compositions.

First production process.

Titanium is introduced into a charge both in the form of TiO2 and as Ti2 03 . A quartz crucible containing the charge is placed into a furnace pre-heated to a temperature of 1200 C; the temperature is further increased to 1400-15500C, and the crucible with the charge is maintained at this temperature for some 2.5 to 5 hours. Glass melting is carried out with continuous blowing of an inert gas. On completion of the melting, molten glass is poured into a mould to form glass rods.

Electrodes are manufactured by melting glass in the flame of a gas-oxygen burner. The glass melt is transferred to the open end of a cylindrical glass tube 1, heated and blown out to form a hemisphere. Prior to introducing the current lead 3 into the inner cavity of the cylindrical tube 1, a thin layer of glass is removed from the outer and inner surfaces of the resultant hemisphere, since the composition and structure of the glass undergoes changes during connecting a sensing element to the elec TABLE Glass1 Glass2 Glass3 Glass4 Glass5 Glass6 Glass7 Glass8 Oxides percent by percent by percent by percent by percent by percent by percent by percent by weight weight weight weight weight weight weight weight Na2O 5.3 5.4 8.3 5.0 6.5 8.6 8.3 7.7 K2O 2.2 6.4 10.7 3.2 - 17.4 6.3 5.8 Li2O - - - 1.8 3.1 - - TiO2 26.5 23.4 40.0 16.0 21.1 31.8 27.0 24.7 Ti2O3 3.4 0.8 4.2 4.1 3.8 2.9 3.2 4.2 Nb2O5 25.2 11.4 4.0 21.2 8.7 5.3 10.7 19.4 Ta2O5 - 20.6 - 10.3 11.8 - - SiO2 37.4 32.0 32.8 38.4 45 34 44.5 38.1 trode casing in the gas-oxygen burner flame.

Second production process.

Glass is produced according to the first production process, at a temperature of 1450 to 16000C, in an inert gas atmosphere. The molten glass is cast in special moulds having refractory metal filaments therein, these filaments serving as current leads for the electrodes.

The resultant sensing elements are transferred to a muffle furnace and are heated to a temperature of 450 to 5000C, where they are annealed for 10 hours. The sensing elements are then secured in tubes made of a material with high insulating properties. The glass compositions are set forth in the Table.

In the hereinafter described solutions containing redox systems, the proposed electrodes exhibited definite oxidation potentials.

The following Examples are given by way of illustration only.

EXAMPLE 1 A glass electrode was immersed in 200 ml of a buffer solution having a pH of 6.86 and containing 5.795g K3 Fe(CN)6 and 1.208g K4 Fe(CN)6 3H2O. The sensing element of this glass electrode can be manufactured from any of the glass compositions set forth in the Table below. The oxidation potential measured for the glass electrode in the solution relative to a saturated silver chloride electrode was +294 t 10 mV at a temperature of 25 C.

EXAMPLE 2 A glass electrode was immersed in 200 ml of 1 N-solution of sulphuric acid containing 0.511 g of Fe2(SO4)3 9H2O and 6.63g at FeSO4 7H2O. The sensing element of the glass electrode can be manufactured from any glass composition set forth in the Table below. The oxidation potential of the glass electrode measured in the solution relative to a saturated silver chloride electrode was +405 + 10 mV at a temperature of 250C.

EXAMPLE 3 A glass electrode was immersed in 200 ml of N-solution of sulphuric acid containing 4.213g of Fe2(SO4)3 -9H2O and 1.38g of FeSO4 7H2O. The sensing element of this glass electrode can be manufactured from any glass composition set forth in the Table. The oxidation potential of the glass electrode measured in the solution relative to a saturated silver chloride electrode was +496+10 mV at a temperature of 250C.

EXAMPLE 4 A glass electrode was immersed in 200 ml of a buffer solution which contained 4.28g of KIO3 and 10 ml of a 10%-solution of I2 in alcohol. The sensing element of this glass electrode can be manufactured from any glass composition set forth in the Table. The oxidation potential of the glass electrode measured in the solution relative to a saturated silver chloride was 720 + 10 mV at a temperature of 25 C.

EXAMPLE 5 A glass electrode was immersed in 1 litre of a 0.5 N-solution of sulphuric acid containing 3.56g of Ce(SO4)2 4H2O and 4.3g of Ce(NO3)3 - 6H2O. Any glass composition set forth in the Table can be used for the manufacture of the sensing element of the glass electrode. The oxidation potential of the glass electrode measured in the solution relative to a saturated silver chloride electrode was +1235 + 10 mV at a temperature of 25 C.

EXAMPLE 6 A glass electrode was immersed in 250 ml of a 0.1 N-solution of hydrochloric acid containing 0.97g Eu2O3 -H2O. Any glass compostion set forth in the Table can be used for the manufacture of the sensing element of this glass electrode. Electrolysis was then effected at a current of 8-10-3 A, for 1 hour, in a protective atmosphere provided by an inert gas. The oxidation potential of the glass electrode in the solution relative to a saturated silver chloride electrode was -700 + 10 mV at a temperature of 250C.

WHAT WE CLAIM IS: 1. A glass electrode for measuring the oxidation potential of a liquid medium, the electrode comprising a tubular casing of highresistance glass having one end thereof sealed to a sensing element which is rigidly connected to a current lead disposed within the tubular casing, the sensing element being of an electron - conductive glass and consisting of 32-45% by weight of SiO2, 7.0-26% by weight of Me2O, wherein Me is Li, Na, and/or K, 16.040% by weight of TiO2, 0.8-4.2% by weight of Ti203, and 2.0-32% by weight of one or each of Nb2os and Ta2O5.

2. A glass electrode according to claim 1, wherein the glass of the sensing element consists of 32.0-37.4% by weight of SiO2 , 0-1.8% by weight of Li2O,5.0-8.3% by weight of Na2O, 2.2-10.7% by weight of K2O,26.0-40% by weight of TiO2, 0.8-1.7% by weight of Ti203, and 4.0-25% by weight of Nb2O5.

3. A glass electrode according to claim 1, wherein the sensing element is of a glass consisting of 37.1-45% by weight of SiO2 5.0-8.0% by weight of Na2O, 6.3-17.4% by weight of K2O, 1.8-3.1% by weight of Li2O, 16.0-31.8% by weight of TiO2,1.7-4.2% by weight of Ti203, 10.7-21.2% by weight of Nb2O5 ,and 2.0-32.0% by weight of Ta2O5.

4. A glass electrode substantially as herein described with reference to, and as shown, in the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. trode casing in the gas-oxygen burner flame. Second production process. Glass is produced according to the first production process, at a temperature of 1450 to 16000C, in an inert gas atmosphere. The molten glass is cast in special moulds having refractory metal filaments therein, these filaments serving as current leads for the electrodes. The resultant sensing elements are transferred to a muffle furnace and are heated to a temperature of 450 to 5000C, where they are annealed for 10 hours. The sensing elements are then secured in tubes made of a material with high insulating properties. The glass compositions are set forth in the Table. In the hereinafter described solutions containing redox systems, the proposed electrodes exhibited definite oxidation potentials. The following Examples are given by way of illustration only. EXAMPLE 1 A glass electrode was immersed in 200 ml of a buffer solution having a pH of 6.86 and containing 5.795g K3 Fe(CN)6 and 1.208g K4 Fe(CN)6 3H2O. The sensing element of this glass electrode can be manufactured from any of the glass compositions set forth in the Table below. The oxidation potential measured for the glass electrode in the solution relative to a saturated silver chloride electrode was +294 t 10 mV at a temperature of 25 C. EXAMPLE 2 A glass electrode was immersed in 200 ml of 1 N-solution of sulphuric acid containing 0.511 g of Fe2(SO4)3 9H2O and 6.63g at FeSO4 7H2O. The sensing element of the glass electrode can be manufactured from any glass composition set forth in the Table below. The oxidation potential of the glass electrode measured in the solution relative to a saturated silver chloride electrode was +405 + 10 mV at a temperature of 250C. EXAMPLE 3 A glass electrode was immersed in 200 ml of N-solution of sulphuric acid containing 4.213g of Fe2(SO4)3 -9H2O and 1.38g of FeSO4 7H2O. The sensing element of this glass electrode can be manufactured from any glass composition set forth in the Table. The oxidation potential of the glass electrode measured in the solution relative to a saturated silver chloride electrode was +496+10 mV at a temperature of 250C. EXAMPLE 4 A glass electrode was immersed in 200 ml of a buffer solution which contained 4.28g of KIO3 and 10 ml of a 10%-solution of I2 in alcohol. The sensing element of this glass electrode can be manufactured from any glass composition set forth in the Table. The oxidation potential of the glass electrode measured in the solution relative to a saturated silver chloride was 720 + 10 mV at a temperature of 25 C. EXAMPLE 5 A glass electrode was immersed in 1 litre of a 0.5 N-solution of sulphuric acid containing 3.56g of Ce(SO4)2 4H2O and 4.3g of Ce(NO3)3 - 6H2O. Any glass composition set forth in the Table can be used for the manufacture of the sensing element of the glass electrode. The oxidation potential of the glass electrode measured in the solution relative to a saturated silver chloride electrode was +1235 + 10 mV at a temperature of 25 C. EXAMPLE 6 A glass electrode was immersed in 250 ml of a 0.1 N-solution of hydrochloric acid containing 0.97g Eu2O3 -H2O. Any glass compostion set forth in the Table can be used for the manufacture of the sensing element of this glass electrode. Electrolysis was then effected at a current of 8-10-3 A, for 1 hour, in a protective atmosphere provided by an inert gas. The oxidation potential of the glass electrode in the solution relative to a saturated silver chloride electrode was -700 + 10 mV at a temperature of 250C. WHAT WE CLAIM IS:

1. A glass electrode for measuring the oxidation potential of a liquid medium, the electrode comprising a tubular casing of highresistance glass having one end thereof sealed to a sensing element which is rigidly connected to a current lead disposed within the tubular casing, the sensing element being of an electron - conductive glass and consisting of 32-45% by weight of SiO2, 7.0-26% by weight of Me2O, wherein Me is Li, Na, and/or K, 16.040% by weight of TiO2, 0.8-4.2% by weight of Ti203, and 2.0-32% by weight of one or each of Nb2os and Ta2O5.