EP0004665B1 - Corrosion inhibitor for water conduits - Google Patents

Corrosion inhibitor for water conduits Download PDF

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Publication number
EP0004665B1
EP0004665B1 EP19790101022 EP79101022A EP0004665B1 EP 0004665 B1 EP0004665 B1 EP 0004665B1 EP 19790101022 EP19790101022 EP 19790101022 EP 79101022 A EP79101022 A EP 79101022A EP 0004665 B1 EP0004665 B1 EP 0004665B1
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Prior art keywords
water
corrosion
quantities
systems
added
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EP19790101022
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German (de)
French (fr)
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EP0004665A3 (en
EP0004665A2 (en
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Manfred Dr. Dohr
Volker Dr. Wehle
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Henkel AG and Co KGaA
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Henkel AG and Co KGaA
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F11/00—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent
    • C23F11/08—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in other liquids
    • C23F11/10—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in other liquids using organic inhibitors
    • C23F11/14—Nitrogen-containing compounds
    • C23F11/147—Nitrogen-containing compounds containing a nitrogen-to-oxygen bond

Definitions

  • the invention relates to the use of tris (2-carboxyethyl) nitromethane - hereinafter abbreviated TCN - to prevent corrosion of metals in service water systems.
  • TCN tris (2-carboxyethyl) nitromethane - hereinafter abbreviated TCN -
  • TCN tris (2-carboxyethyl) nitromethane
  • the treatment of water-bearing systems such as steam generation systems, heating systems, cooling water circuits and water supply systems to protect against the corrosive attack of water, which is primarily directed against base materials such as steel, brass, aluminum, zinc or galvanized steel, has long been carried out in technology.
  • phosphorus-containing compounds such as phosphonic acids or inorganic phosphates, optionally in combination with zinc salts, has proven particularly useful.
  • TCN is used to prevent corrosion of metals in aqueous systems in the pH range from 6-9.
  • the amounts which are expediently added to the aqueous system are in the range from 0.5-100 g / m 3 , preferably 1-10 g / m 3 .
  • TCN is produced by methods known per se and is not the subject of the invention.
  • TCN extraordinarily good corrosion-inhibiting effect of TCN is surprising insofar as other similarly built compounds, such as tris (hydroxymethyl) nitromethane, do not have a corrosion protection effect which is adequate in practice.
  • the already high corrosion-inhibiting effect of the TCN without any addition is remarkable.
  • the stone protection and dispersing agents listed above are used in combination with TCN in amounts of 1-50 g / m 3 , preferably 3-10 g / m 3 .
  • non-ferrous metals such as in particular benzimidazole, benzotriazole or tolyltriazole
  • TCN benzimidazole
  • benzimidazole benzotriazole
  • tolyltriazole tolyltriazole
  • TCN can also be used in combination with zinc salts and / or compounds containing phosphorus.
  • Zinc chloride and zinc sulfate are particularly suitable as zinc salts. Quantities (calculated as zinc) of 0.5-10 g / m 3 , preferably 1-4 g / m 3 corresponding to an amount of 0.5-10 0 or 1-4 ppm are used.
  • phosphonic acids such as, for example, 1-hydroxyethane-1,1-diphosphonic acid, aminotrimethylenephosphonic acid and 2-phosphonobutane-1,2,4-tricarboxylic acid and their water-soluble salts or mixtures of these compounds, are particularly suitable as the phosphorus-containing compound. Quantities of 0.5-10 g / m 3 are used. Such a combination can significantly increase the protection against corrosion.
  • biocidal substances such as glutaraldehyde, glyoxal, pentachlorophenol sodium or alkyloligoamides, preferably in the form of a reaction product of dodecylpropylenediamine and s-caprolactam in a ratio of 1: 2.
  • a treatment agent for metal surfaces is known, which to this is intended to form a film on the treated surface.
  • Lubricants, coating materials and paints can be used as film-forming materials.
  • the anti-corrosion treatment agents contain a small amount of a fat series nitrosic acid or a derivative thereof. This is a different way of working with a different objective, whereby the use of TCN is not mentioned anywhere else. The subject of the application could therefore not be derived from this reference.
  • the corrosive behavior was determined using the method described below: A carefully cleaned test plate (75 x 12 x 1.5 mm) is placed in a 1 liter beaker filled with 1 liter water and a certain amount of the substance to be examined is immersed at room temperature for 24 hours. During the test period, the aqueous solutions are stirred at 100 revolutions per minute in a row arrangement of a total of 10 beakers. The sheets are then cleaned of corrosion products and the weight loss is determined. The corrosion protection rates of the products, based on a blank value, are determined from the mean values of three tests each.
  • test water used as the corrosive medium had the following analytical data:
  • the table below shows the reduction in the corrosive attack of a water by adding the specified agents compared to the untreated water.
  • a technical cooling system with a content of 1.2 m 3 and a circulation of 8 m 3 / h is operated with Düsseldorf city water.
  • the evaporation losses are compensated by adding fresh water to such an extent that the salt content does not exceed twice the original value.
  • an electrochemically measured corrosion rate of 0.18 mm / a occurs in the system.
  • composition according to the invention has the following composition:
  • TCN was used together with other inhibitors and the corrosion rates, expressed in mm / year, were determined using the coupon method by testing water under the same conditions through a double test section in accordance with ASTM (D 2688/70) was pumped.

Description

Gegenstand der Erfindung ist die Verwendung von Tris-(2-carboxyäthyl)-nitromethan - im folgenden abgekürzt TCN - zur Verhinderung der Korrosion von Metallen in Brauchwassersystemen. Die Behandlung von wasserführenden Anlagen wie Dampferzeugungsanlagen, Heizsystemen, Kühlwasserkreisläufen und Wasserleitungssystemen zum Schutz gegen den korrosiven Angriff des Wassers, der sich vorwiegend gegen unedle Werkstoffe, beispielsweise Stahl, Messing, Aluminium, Zink oder verzinkter Stahl richtet, wird seit langem in der Technik durchgeführt. Besonders bewährt hat sich hierbei die Verwendung von phosphorhaltigen Verbindungen, wie zum Beispiel Phosphonsäuren oder anorganische Phosphate, gegebenenfalls in Kombination mit Zinksalzen.The invention relates to the use of tris (2-carboxyethyl) nitromethane - hereinafter abbreviated TCN - to prevent corrosion of metals in service water systems. The treatment of water-bearing systems such as steam generation systems, heating systems, cooling water circuits and water supply systems to protect against the corrosive attack of water, which is primarily directed against base materials such as steel, brass, aluminum, zinc or galvanized steel, has long been carried out in technology. The use of phosphorus-containing compounds, such as phosphonic acids or inorganic phosphates, optionally in combination with zinc salts, has proven particularly useful.

Diese Kombinationen haben eine gute technische Wirksamkeit. Ihre Verwendung wird in jüngster Zeit jedoch mehr und mehr eingeschränkt durch die ökologischen und gesetzgeberischen Forderungen nach weitgehender oder absoluter Phosphor-Freiheit derartiger Produkte. Vom technischen Standpunkt haben derartige phosphathaltige Kombinationen weiter den Nachteil, daß sie häufig durch Eutrophierung des Kühlsystems zu verstärktem biologischem Wachstum führen und die zusätzliche Verwendung von Mikrobiziden erforderlich machen.These combinations have good technical effectiveness. However, their use has recently been increasingly restricted by the ecological and legislative demands for such products to be largely or completely free of phosphorus. From the technical point of view, such phosphate-containing combinations have the further disadvantage that they often lead to increased biological growth due to eutrophication of the cooling system and make the additional use of microbicides necessary.

Die Verwendung dieser phosphorhaltigen Kombinationen kann weiterhin beim Einsatz in größeren Wasserhärten zur Bildung von Apatit- oder apatitähnlichen Ablagerungen führen, die zu Betriebsstörungen führen und nur schwer zu entfernen sind. Der Einsatz dieser Kombinationen mit Zinksalzen bei höheren pH-Werten (pH > 8,0) führt im allgemeinen zu verstärkter Verschlammung des Systems durch die Ausfällung von Zinkhydroxid.The use of these phosphorus-containing combinations can furthermore lead to the formation of apatite or apatite-like deposits when used in larger water hardness levels, which lead to malfunctions and are difficult to remove. The use of these combinations with zinc salts at higher pH values (pH> 8.0) generally leads to increased silting up of the system due to the precipitation of zinc hydroxide.

Vom ökologischen Standpunkt aus ist in nicht geschlossenen Kühlsystemen die Verwendung von Zinksalzen in derartigen Kombinationsprodukten ebenfalls problematisch, da diese aufgrund der hohen Fischtoxizität zu einer starken Abwasserbelastung führen. Außerdem wird die Selbstreinigungskraft des Gewässers bereits ab 0,1 ppm Zink deutlich gehemmt.From an ecological point of view, the use of zinc salts in such combination products is also problematic in non-closed cooling systems, since these lead to a high level of wastewater pollution due to the high fish toxicity. In addition, the self-cleaning power of the water is significantly inhibited from 0.1 ppm zinc.

Es wurde nun gefunden, daß man diese Nachteile vermeiden kann, wenn man TCN zur Verhinderung der Korrosion von Metallen in wäßrigen Systemen im pH-Bereich von 6-9 verwendet.It has now been found that these disadvantages can be avoided if TCN is used to prevent corrosion of metals in aqueous systems in the pH range from 6-9.

Die Mengen, die dem wäßrigen System zweckmäßigerweise zugegeben werden, liegen im Bereich von 0,5―100 g/m3, vorzugsweise 1―10 g/m3.The amounts which are expediently added to the aqueous system are in the range from 0.5-100 g / m 3 , preferably 1-10 g / m 3 .

Die Herstellung von TCN erfolgt nach an sich bekannten Methoden und ist nicht Gegenstand der Erfindung.TCN is produced by methods known per se and is not the subject of the invention.

Die außerordentlich gute korrosionsinhibierende Wirkung von TCN ist insofern überraschend, als andere ähnlich gebaute Verbindungen, wie zum Beispiel Tris(hydroxymethyl)nitromethan, keine für die Praxis ausreichende Korrosionsschutzwirkung aufweisen. Bemerkenswert ist die bereits hohe korrosionsinhibierende Wirkung des TCN ohne jeden Zusatz.The extraordinarily good corrosion-inhibiting effect of TCN is surprising insofar as other similarly built compounds, such as tris (hydroxymethyl) nitromethane, do not have a corrosion protection effect which is adequate in practice. The already high corrosion-inhibiting effect of the TCN without any addition is remarkable.

In der Praxis spielt für das korrosive Verhalten eines Brauchwassers in hohem Maße die Anwesenheit oder Entstehung von ablagerungsbildenden Trübstoffen wie zum Beispiel Härteausfällungen, Tonsubstanzen und Eisenhydroxide eine wesentliche Rolle. Durch Verhinderung dieser Ablagerungen wird das korrosive Verhalten eines Wassers weiterhin verbessert. Daher ist es im allgemeinen vorteilhaft, dem zu behandelnden Wasser außer TCN weitere an sich bekannte Steinschutz- und Dispergiermittel zuzusetzen. Als geeignete Zusätze haben sich insbesondere Polyacrylate oder Acrylsäure-Methacrylsäurecopolymerisate mit einem Molgewicht von 500-4000 oder Äthylenoxid-Propylenoxid-Blockpolymere mit einem Molgewicht von 500-3000 und einem Äthylenoxid-Propylenoxidverhältnis von 10 90 bis 30: 70 erwiesen.In practice, the presence or formation of sediment-forming cloudy substances such as hardness precipitates, clay substances and iron hydroxides play a major role in the corrosive behavior of industrial water. Preventing these deposits further improves the corrosive behavior of water. It is therefore generally advantageous to add to the water to be treated, besides TCN, other stone protection and dispersing agents known per se. Polyacrylates or acrylic acid-methacrylic acid copolymers with a molecular weight of 500-4000 or ethylene oxide-propylene oxide block polymers with a molecular weight of 500-3000 and an ethylene oxide-propylene oxide ratio of 10 90 to 30:70 have proven to be suitable additives.

Die oben angeführten Steinschutz- und Dispergiermittel werden bei Kombination mit TCN in Mengen von 1 ― 50 g/m3, vorzugsweise 3-10 g/m3 verwendet.The stone protection and dispersing agents listed above are used in combination with TCN in amounts of 1-50 g / m 3 , preferably 3-10 g / m 3 .

Je nach den Verhältnissen in der Praxis kann es vorteilhaft sein, zusammen mit TCN spezielle Inhibitoren für Buntmetalle, wie insbesondere Benzimidazol, Benzotriazol oder Tolyltriazol, in Kombination zu verwenden. Die verwendeten Mengen liegen im Bereich von 0,1 - g/m3.Depending on the conditions in practice, it may be advantageous to use special inhibitors for non-ferrous metals, such as in particular benzimidazole, benzotriazole or tolyltriazole, in combination with TCN. The quantities used are in the range of 0.1 - g / m3.

Spielen die ökologischen Aspekte keine gravierende Rolle, wie insbesondere bei geschlossenen Kühlsystemen, so kann TCN auch mit Zinksalzen und/oder phosphorhaltigen Verbindungen kombiniert eingesetzt werden.If the ecological aspects do not play a major role, as in particular with closed cooling systems, TCN can also be used in combination with zinc salts and / or compounds containing phosphorus.

Als Zinksalze kommen insbesondere Zinkchlorid und Zinksulfat in Betracht. Dabei werden Mengen (berechnet als Zink) von 0,5 - 10 g/m3, vorzugsweise 1 -4 g/m3 entsprechend einer Menge von 0,5 - 10 0 beziehungsweise 1 -4 ppm verwendet.Zinc chloride and zinc sulfate are particularly suitable as zinc salts. Quantities (calculated as zinc) of 0.5-10 g / m 3 , preferably 1-4 g / m 3 corresponding to an amount of 0.5-10 0 or 1-4 ppm are used.

Als phosphorhaltige Verbindung kommen insbesondere komplexierende Phosphonsäuren, wie beispielsweise 1-Hydroxyäthan-1,1-diphosphonsäure, Aminotrimethylenphosphonsäure und 2-Phos- phonobutan-1,2,4-tricarbonsäure sowie deren wasserlösliche Salze oder Gemische dieser Verbindungen in Betracht. Dabei werden Mengen von 0,5-10 g/m3 verwendet. Durch derartige Kombination kann der Korrosionsschutz noch erheblich verstärkt werden.Complexing phosphonic acids, such as, for example, 1-hydroxyethane-1,1-diphosphonic acid, aminotrimethylenephosphonic acid and 2-phosphonobutane-1,2,4-tricarboxylic acid and their water-soluble salts or mixtures of these compounds, are particularly suitable as the phosphorus-containing compound. Quantities of 0.5-10 g / m 3 are used. Such a combination can significantly increase the protection against corrosion.

In bestimmten Fällen kann es auch vorteilhaft sein, weiterhin biozide Substanzen wie Glutaraldehyd, Glyoxal, Pentachlorphenolnatrium oder Alkyloligoamide, vorzugsweise in Form eines Umsetzungsproduktes von Dodecylpropylendiamin und s-Caprolactam im Verhältnis 1 : 2 zuzusetzen.In certain cases it may also be advantageous to continue adding biocidal substances such as glutaraldehyde, glyoxal, pentachlorophenol sodium or alkyloligoamides, preferably in the form of a reaction product of dodecylpropylenediamine and s-caprolactam in a ratio of 1: 2.

Aus der CH-A-262802 ist ein Behandlungsmittel für Metalloberflächen bekannt, welches dazu bestimmt ist, auf der behandelten Oberfläche einen Film zu bilden. Dabei kommen als filmbildende Materialien Schmiermittel, Überzugsmaterialien und Farbanstriche in Frage. Außer dem filmbildenden Material enthalten die Behandlungsmittel zur Korrosionsverhinderung eine geringe Menge einer Nitrosäure der Fettreihe oder eines Derivats hiervon. Es handelt sich hierbei um eine andere Arbeitsweise mit einer unterschiedlichen Zielsetzung, wobei im übrigen auch die Verwendung von TCN nirgends erwähnt ist. Der Anmeldungsgegenstand konnte daher aus dieser Literaturstelle nicht hergeleitet werden.From CH-A-262802 a treatment agent for metal surfaces is known, which to this is intended to form a film on the treated surface. Lubricants, coating materials and paints can be used as film-forming materials. In addition to the film-forming material, the anti-corrosion treatment agents contain a small amount of a fat series nitrosic acid or a derivative thereof. This is a different way of working with a different objective, whereby the use of TCN is not mentioned anywhere else. The subject of the application could therefore not be derived from this reference.

Beispiel 1example 1

Die Bestimmung des korrosiven Verhaltens erfolgte nach der nachstehend beschriebenen Methode: Je ein sorgfältig gereinigtes Testblech (75 x 12 x 1,5 mm) wird in ein 1-I-Becherglas, das mit 1 I Wasser und einer bestimmten Menge der zu untersuchenden Substanz gefüllt ist, bei Raumtemperatur 24 Stunden eingetaucht. Während der Versuchsdauer werden in einer Reihenanordnung von insgesamt 10 Bechergläsern die wäßrigen Lösungen mit 100 Umdrehungen pro Minute gerührt. Anschließend werden die Bleche von Korrosionsprodukten gereinigt und die Gewichtsverluste bestimmt. Aus den Mittelwerten von je drei Versuchen werden die Korrosionsschutzraten der Produkte, bezogen auf einen Blindwert, ermittelt.The corrosive behavior was determined using the method described below: A carefully cleaned test plate (75 x 12 x 1.5 mm) is placed in a 1 liter beaker filled with 1 liter water and a certain amount of the substance to be examined is immersed at room temperature for 24 hours. During the test period, the aqueous solutions are stirred at 100 revolutions per minute in a row arrangement of a total of 10 beakers. The sheets are then cleaned of corrosion products and the weight loss is determined. The corrosion protection rates of the products, based on a blank value, are determined from the mean values of three tests each.

Das als korrosives Medium benutzte Versuchswasser hatte folgende analytische Daten:

Figure imgb0001
The test water used as the corrosive medium had the following analytical data:
Figure imgb0001

Die nachstehende Tabelle gibt die Verringerung des korrosiven Angriffs eines Wassers bei Zusatz der im einzelnen aufgeführten Mittel gegenüber dem unbehandelten Wasser wieder.

Figure imgb0002
The table below shows the reduction in the corrosive attack of a water by adding the specified agents compared to the untreated water.
Figure imgb0002

Beispiel 2Example 2

Ein technisches Kühlsystem mit einem Inhalt von 1,2 m3 und einer Umwälzung von 8 m3/h wird mit Düsseldorfer Stadtwasser betrieben. Die Verdampfungsverluste werden durch Frischwasserzugabe soweit ausgeglichen, daß der Salzgehalt nicht den 2fachen Wert des ursprünglichen Wertes übersteigt. Ohne jede Korrosionsschutzbehandlung des Kreislaufwassers stellt sich im System eine elektrochemisch gemessene Korrosionsrate von 0,18 mm/a ein.A technical cooling system with a content of 1.2 m 3 and a circulation of 8 m 3 / h is operated with Düsseldorf city water. The evaporation losses are compensated by adding fresh water to such an extent that the salt content does not exceed twice the original value. Without any anti-corrosion treatment of the circulating water, an electrochemically measured corrosion rate of 0.18 mm / a occurs in the system.

Bei Zugabe des erfindungsgemäßen Korrosionsinhibitors in Mengen von 50 g/m3, bezogen auf das Kreislaufwasser, stellt sich eine Korrosionsrate von 0,064 mm/a ein. Dieser Wert ist als hervorragend anzusehen.When the corrosion inhibitor according to the invention is added in amounts of 50 g / m 3 , based on the circulating water, a corrosion rate of 0.064 mm / a is established. This value can be regarded as excellent.

Das erfindungsgemäße Mittel hat folgende Zusammensetzung:

Figure imgb0003
The composition according to the invention has the following composition:
Figure imgb0003

Beispiel 3Example 3

In einem Langzeitversuch über 4 Wochen wurde TCN mit anderen Inhibitoren zusammen eingesetzt und die Korrosionsraten, in mm/Jahr ausgedrückt, mittels der Coupon-Methode bestimmt, indem unter jeweils gleichen Bedingungen das Testwasser durch eine Doupon-Versuchsstrecke gemäß ASTM (D 2688/70) gepumpt wurde.In a long-term test over 4 weeks, TCN was used together with other inhibitors and the corrosion rates, expressed in mm / year, were determined using the coupon method by testing water under the same conditions through a double test section in accordance with ASTM (D 2688/70) was pumped.

Die Versuchsbedingungen waren weiterhin folgende:

Figure imgb0004
Skizze der apparativen Anordnung
Figure imgb0005
Figure imgb0006
 The test conditions were still as follows:
Figure imgb0004
 Sketch of the apparatus arrangement
Figure imgb0005
Figure imgb0006

Claims (8)

1. The use of tris-(2-carboxyethyl)-nitromethane for preventing the corrosion of metals in aqueous systems in the pH-range from 6 to 9.
2. The use claimed in Claim 1 in a quantity of from 0.5 to 100 g/m3 and preferably in a quantity of from 1 to 10 g/m3.
3. The use claimed in Claims 1 and 2 in combination with additional incrustation inhibitors and dispersants based on polyacrylates and acrylic acid-methacrylic acid copolymers or ethylene oxide-propylene oxide block polymers.
4. The use claimed in Claims 1 to 3 in combination with benzimidazole.
5. A process for preventing the corrosion of metals in industrial water systems, characterised in that tris-(2-carboxyethyl)-nitromethane is added to the water, which has a pH-value in the range from 6 to 9, in a quantity of from 0.5 to 100 g/m3 and preferably in a quantity of from 1 to 10 g/m3.
6. A process as claimed in Claim 5, characterised in that incrustation inhibitors and dispersants based on polyacrylates and acrylic acid-methacrylic acid copolymers or ethylene oxide-propylene oxide block polymers are additionally added in quantities of from 1 to 50 g/m3 and preferably in quantities of from 3 to 10 g/m3.
7. A process as claimed in Claims 5 and 6, characterised in that benzimidazole is additionally added in quantities of from 0.1 to 5 g/m3.
8. A process as claimed in Claims 5 to 7, characterised in that, in the case of closed cooling systems, zinc salts and/or complexing phosphonic acids are also added in quantities of from 0.5 to 10 g/m3.
EP19790101022 1978-04-07 1979-04-04 Corrosion inhibitor for water conduits Expired EP0004665B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE2815016 1978-04-07
DE19782815016 DE2815016C2 (en) 1978-04-07 1978-04-07 Corrosion inhibitor for domestic water systems

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EP0004665A2 EP0004665A2 (en) 1979-10-17
EP0004665A3 EP0004665A3 (en) 1979-10-31
EP0004665B1 true EP0004665B1 (en) 1981-09-02

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DE4442114A1 (en) * 1994-11-25 1996-05-30 Buna Sow Leuna Olefinverb Gmbh Nitrite, phosphate and amine free coolant and heat transfer medium

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LU28635A1 (en) * 1946-10-25
DE1221993B (en) * 1960-09-30 1966-07-28 Argentox Ges Fuer Wasserreinig Process for preventing corrosion while simultaneously preventing scale
FR1405565A (en) * 1963-08-15 1965-07-09 Commercial Solvents Corp Nitro compound and its preparation process
US4033896A (en) * 1976-06-18 1977-07-05 Monsanto Company Method of corrosion inhibition and compositions therefor

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EP0004665A2 (en) 1979-10-17
DE2815016A1 (en) 1979-10-18

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