CA1166804A - Stable slurry of inactive magnesia and method therefor - Google Patents
Stable slurry of inactive magnesia and method thereforInfo
- Publication number
- CA1166804A CA1166804A CA000402189A CA402189A CA1166804A CA 1166804 A CA1166804 A CA 1166804A CA 000402189 A CA000402189 A CA 000402189A CA 402189 A CA402189 A CA 402189A CA 1166804 A CA1166804 A CA 1166804A
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- Prior art keywords
- magnesia
- weight
- phosphate
- seconds
- slurry
- Prior art date
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C8/00—Enamels; Glazes; Fusion seal compositions being frit compositions having non-frit additions
- C03C8/02—Frit compositions, i.e. in a powdered or comminuted form
- C03C8/08—Frit compositions, i.e. in a powdered or comminuted form containing phosphorus
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/68—Temporary coatings or embedding materials applied before or during heat treatment
- C21D1/70—Temporary coatings or embedding materials applied before or during heat treatment while heating or quenching
-
- 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
- C23D—ENAMELLING OF, OR APPLYING A VITREOUS LAYER TO, METALS
- C23D5/00—Coating with enamels or vitreous layers
- C23D5/10—Coating with enamels or vitreous layers with refractory materials
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
- H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
- H01F1/147—Alloys characterised by their composition
- H01F1/14766—Fe-Si based alloys
- H01F1/14775—Fe-Si based alloys in the form of sheets
- H01F1/14783—Fe-Si based alloys in the form of sheets with insulating coating
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Organic Chemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Physics & Mathematics (AREA)
- Mechanical Engineering (AREA)
- Dispersion Chemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Electromagnetism (AREA)
- Thermal Sciences (AREA)
- Power Engineering (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Crystallography & Structural Chemistry (AREA)
- Geochemistry & Mineralogy (AREA)
- Chemical Treatment Of Metals (AREA)
- Paints Or Removers (AREA)
- Manufacturing Of Steel Electrode Plates (AREA)
- Heat Treatment Of Sheet Steel (AREA)
- Laminated Bodies (AREA)
- Lubricants (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An aqueous magnesia slurry for forming an insulative glass coating on silicon steel, wherein a substantial portion of the magnesia is inactive (a citric acid activity greater than 200 seconds), a decomposable phosphate compound is present within the range of 2% to 25% by weight calculated as P2O5, based on the dry weight of magnesia, and the magnesia concentration is at least 0.24 grams per cubic centimeter of slurry. The slurry is stable against settling for up to 10 hours and has a desirable viscosity for coating application by conventional means. From 10% to 100% inactive magnesia may be used with the remainder an active magnesia (citric acid activity of 20 to 40 seconds). Preferred phosphate compounds include monocalcium phosphate monohydrate, water soluble ammonium polyphosphate and dicalcium phosphate dihydrate.
An aqueous magnesia slurry for forming an insulative glass coating on silicon steel, wherein a substantial portion of the magnesia is inactive (a citric acid activity greater than 200 seconds), a decomposable phosphate compound is present within the range of 2% to 25% by weight calculated as P2O5, based on the dry weight of magnesia, and the magnesia concentration is at least 0.24 grams per cubic centimeter of slurry. The slurry is stable against settling for up to 10 hours and has a desirable viscosity for coating application by conventional means. From 10% to 100% inactive magnesia may be used with the remainder an active magnesia (citric acid activity of 20 to 40 seconds). Preferred phosphate compounds include monocalcium phosphate monohydrate, water soluble ammonium polyphosphate and dicalcium phosphate dihydrate.
Description
1 1 66~0~
This invention relates to an aqueous composition for forming an insulative glass coating directly on silicon steel strip and sheet stock, and more particularly to an aqueous magnesia slurry of high concentration wherein a substantial portion o the magnesia (magnesium oxide) is an inactive magnesia (having a citric acid activity, as hereinafter de~ined, of greater than 200 seconds), and wherein a thermally decomposable phosphate containing compound is present as a stabilizing agent which keeps the inactive magnesia in suspension and increases the viscosity of the slurry. The invention further relates ~o a method o suspending an inactive magnesia in water to produce a stable slurry which can be readily applied to silicon steel surfaces to form a dried layer which will react with the steel to form a glass film during a subsequent hlgh temperature anneal.
In the production of oriented silicon ste~l decarburized strip and sheet stock is conventionally coated with an aq~eous slurry of magnesia which is dried at 1GW
heat. During decarburization a layer of fayalite (an iron silicate) if formed on the silicon steel stock surfaces.
The stocX which is coated with a dried layer of magnesia is then subjected to a finalt high temperature anneal at about 1095 to about 1260C, during which the magnesia in the coating reacts with the fayalite layer to form a glass film, and the cube-on-edge orientation is deveLoped by secondary recrystallization, as is well known in the art.
Heretofore, it has been considered nece3sary to use an active maynesia having a citric acid activity of less than ~00 seconds, in order to provide an aqueous 1 3 ~)6~ 0 ~
slurry from which the magnesia would not settle out rapidly and in order to obtain reaction between the magnesia and the fayalite surface layex. An active magnesia of the type conventionally used hydrates, with consequent increase in viscosity of the magnesia - water slurry, and thi~ creates a problem since the viscosity of the slurry must be kept within a range which will permit application of a coating of uniform thickness by dipping, spraying, metering rolls, or the like.
Inactive magnesias have never previously been considered suitable for forming an insulative glass ilm on oriented silicon steel strip and sheet stock ~ecause the dense particles could not be kept in suspension resulting in the formation of a slurry with very low viscosity. The dense inactive particles also would not react with the fayalite surface layer, at least within the time limits imposed by commercial production rates.
However, since inactive magnesias are available at much lower cost than the active magnesias, substitution of inactive magnesia in an annealing separator composition offers the prospect of very ~ubstantial economies in the processing of cube-on-edge oriented silicon steel.
Although additives to magnesia slurries have been proposed Xor the purpose of improving glass film properties and/or to facilitate the magnesia-fayalite reaction, to the best of applicant's knowledge no additives have been developed which are successful in stabilizing an aqueous slurry o an inactive magnesia and increasing the viscosity thereof.
The addition of phosphates to an active magnesia I ~ 66~0~
slurry is known, in order to i~prove the glass ilm properties and magnetic properties o the silicon steel base stock. Reference may be made to United Sta~es Patent 3,615,918, issued to J. D~ Evans and D. W. Taylor, wherein a magnesia composition containing a decomposable phosphate compound is disclosed. According to this patent, the phosphate, which ranges between 1~ and 25% by weight calculated as P2O5 is reduced to elemental phosphorus during the final high temperature anneal which diffuses inwardly from ~he coating into the silicon steel.
Pho~phate base coatings which may be applied directly to metallic surfaces, or as secondary coatings over a mill glass magnesia-base coatiny, are known in the art. Pho~phate and magnesia-containing coatings suitable for application to oriented silicon steel surfaces, either directly or as a secondary coatings, are disclosed in United States Patents 3,840,378 and 3,948,876, issued to J. D. Evans.
As indicated above, to the best o~ applicant's knowledge, the prior art has never suggested the use of inactive magnesia for annealing separator composition on oriented silicon steel strip and sheet ~tock, nor have additives been proposed which would remedy the problems inherent in using an inactive magnesia for this purpose.
It is a principal object of the present invention to provide an aqueous magnesia slurry of high concentration containing a substantial portion of an inactive magnesia having a citric acid activity greater than 200 seconds which is stable against settling, which has a viscosity suitable for application by conventional means and which o ~
will react with the Eayalite layer on the stock surfaces to form a uniform insulating glass filrn o~
satisfactory quality.
It is a further object of the invention to provide a method of suspending an inactive magnas.ia in wa-ter to produce a stable slurry which can be readily applied to silicon steel surfaces and which will react to form an insulating glass film during a subsequent high temperature anneal.
According to the invention there is provided a composition for forming an insulative glass film on oriented silicon steel strip and sheet surfaces, com-prising an aqueous slurry of magnesia, at least 25% by weight oE said magnesia having a citric acid activity greater than 200 seconds, a phosphate-containing com~
pound chosen from the group consisting of calcium phos-phates, water soluble ammonium polyphosphate, aluminum phosphate, magnesium phosphates, phosphoric acid, and mixtures thereof, said compound being present within the range Oe 2% to 25~ by weight calculated as P205, based on the weight of magnesia, and balance essenti-ally water, the magnesia concentration being up to 006 gram per cubic centimeter of slurry, said slurry being stable against settling for periods of time up to 10 hours.
The present invention further provides a method of suspending in water a magnesia at least 25% of which consists of magnesia having a citric acid activity greater than 200 seconds to produce a slurry having increased viscosity and stability against settling, which comprises the step of providing in said slurry a - t ~ ~6~
phosphate-containing compound within the range o~ 2~ to 25% by weight calculated as P20s, based on the weight of magnesia, said phosphate-containing compound being chosen from the group consisting of calcium phosphates, water soluble ammonium polyphosphate, aluminum phos-phate, magnesium phosphates, phosphoric acid and mixtures thereof.
It has been found that the invention can be practiced successfully with inactive magnesia from a commercial source having a citric acid activity greater than 200 seconds, a Cl- level of 0.02~ maximum and a S04-- level of 0.02% maximum. Tests have been conducted on such a magnesia having a citric acid activity ranging from about 1500 to about 3000 secondsr wherein the inactive magnesia comprised 100% of the total magnesia content of the slurry. Blends of 50% by weight inactive magnesia with 50~ by weight active magnesia have also been tested and have been found -to provide optimum adherence of -the dried coating to the stock and improved glass film quality. It is evident that lower proportions of inactive magnesia with an active magnesia can also be used, down to 10% inactive magnesia and 90% active magnesia for improved glass film quality, although the economic advantage o the inactive magnesia is thereby lost. At the other extreme, satisfactory results have been obtained with slurries in which 100% of the magnesia had a citric acid value greater than 200 seconds. The principal disadvantage in use of a composition in which all the magnesia is inactive arises from the fact that the ~ ~ ~6~30~
adherence of the dried coating is only fair, ~o that care must be exercised in handling the coated coils in order to prevent removal of hte magnesia coating. Where the inactive magnesia constitutes 25~ to 75% of the ~otal magnesia content, this problem is minimized. Thi~ range is thus preferred. The active magnesia preferably wiLl have a citric acid activity of about 20 to 40 seconds.
The phosphate addition not only stabilizes the inactive magnesia slurry against settling but also increases the viscosity to a range desirable for application by conventional means such as dipping, spraying, metering rolls and the like. Moreover, the magnesia concentration can be highsr t~an that o the prior art slurries containing only active magnesia. Such high concentrations are advantageous in that drying can be effected with less heat and in a shorter period of time, and in that ignition 105s can be maintained below 1~. With such low ignition losses the glass film quality has been ~ound to remain very uni~orm along both the length and the width of a coil.
Pre~erred phosphate compounds are monocalcium phosphate monohydrate, dicalcium phosphate dihydrate and water soluble ammonium polyphosphate. Preferably rom ~.5~
to 10~ by weight calculat~d as P205, based on the weight of magnesia, is added. When adding monocalcium phosphate monohydrate or dicalcium phosphate dihydrate, which are particulate, the material can be dry blended with the magnesia prior to forming an aqueous slurry, or can be added to the water before, during or after mixing the magnesia therewith. Accordingly the manner in which and stage at which the pho~phate compound is introduced into the slurry do not constitute a limitation on 6 ~3 V ~
the practi~e of the invention. In the case of water soluble a~monium polyphosphate, which is available as an aqueou~
solution only, ~he addition is made to the water of the aqueous slurry either before or after mixing the magnesia therewith.
~ The high calcining tem~eratures used in the production of inactive maynesia result in sintering and/or agglomeration of the magnesia producing a dense particle which requires grinding to obtain the de~ired particle size distribution, This grinding produces magnesia particles with an active surface. Although not intending to be bound by theory, it is belieYed that the phosphate compound added in accordance with the present invention reacts with the magnesia particles forming a thin~phosphate layer on the surface of the particles. This thin phosphate layer ~P205 ) giv~s the particles a net negative char~e preventing agglomeration and settling from occurring. ?his is believed to be the theoretical basis for the markedly improved stability against settling out which ha~ been observed. Additionally, the stable suspension of su¢h magnesia particles also increases the viscosity of the slurry to a desixable range.
It has been foun~ that concentratio~s up to 0.6 grams per cubic centimeter (5 pounds per gallon) can be used without settling and without increasing the viscosity to an objectionable extent when the magnesia component is lO0~ inactive magnesia. When using a mixture of 50~ inactive and 50% active magnesia, co~cen~rations ranging from about 0.24 grams per cubic centimeter to about 0.36 grams per centimeter (3 pounds per gallon) can be used. Dried coating weights of about 7.5 to about 1 11 6680~
15 grams per square meter were obtained within the above concentrations ranges when applied in conventional manner with metering rolls.
The amount of phosphate containing compound which may be added depends u~on the decarburizing and final annealing conditions, with a relatively low phosphate level for highly oxidizing decarburizing conditions, and a relatively high phosphate level for less oxidi~ing conditions.
Comparision of a 100% inactive magnesia slurry conta1nin~ a phosphate compound in accordance with~ the present invention with a control slurry containing 100~ of the same inactive magnesia slurry but with no additive indicated that there was no appreciable settling of the slurry of the invention after lO hours, whereas the slurry lS with no additive settled out completely within one hour leaving a substantially clear supernatant liquid layer.i By way of background, it is pointed out that a cold reduced decarburi2ed silicon steel strip and sheet stoc~ may be prepared by conventional procedures wherein a suitable melt is cast in the form of ingots or continuously cast into slab form. If cast into ingots the steel is bloomed and slabbed in conventional manner and the slabs are hot rolled to intermediate thickness from a temperature of about 1200 to about 1400C with annealing a~ter hot rolling. The hot mill scale is removed, and the material is then cold rolled to final guage in one or more stages, followed by decarburixation preferably in a wet hydrogen-containing atmosphere. If the steel is continuously cast into slab form, the method disclosed in United 5tates Patent 3,764,406, to ~O F Littman is ~ 1 ~6~3(3~
preferably ~ollowed.
A magnesia coating is then applied to the surfaces of the decarburized stock by dipping, spraying, metering rolls, or other conventional means. Th~ coati~g is then dried by heating to a temperature sufficient to ~evaporate the water. The dried coating weigh~ should preferably range between about 6 and 20 grams per square metsr.
The coated stock is then subjected to a final high temper-ature anneaL at about 1095 to about l260C, which may be a box annaal or an open coil anneal, in a reducing atmosphere. During this anneal the magnesia reacts to form an insulative glass film, and the cube-on-edge orientation is obtained by secondary recrystallization.
The composition and method of processing the silcion s~eel to final strip and sheet form do not constitute a limitation on the present invention. Any of the regular or high permeability grades of oriented silicon steel on which a magnesia coating is utilized may be treated in the practice of the present invention. By way of non-limiting example, compositions and methods in which the present invention finds utility include thosedisclosed in United States Patents 3,287,183; 3f873,381; 3,90S,842; 3,905,B43; 3,932,~234;
3,957,546,and 4,000,015. Except for No. 3,932,234, these ~atents relate to the production of high permeability _ material (relative permeability greater than 1850 at 796 A/m) by means of boron and nitrogen additions to the steel.
Manganese and sulfur (and/or selenium) may also be presen~.
For a reguIar g~ain oriented silicon steel wherein manganese and sulfur (and/or selenium) are present as grain qrowth inhibitors, a typical but non~limiting 1 ~ ~)6~0~
composition fox the cold rolled and decarburized stock may comprise, in weight percent, about 2% to about 4%
silcion, about 0.01~ to about 0~4% manganese, about 0.01%
to about 0.03% sulfur, about 0.002~ ~o about 0.005% carbon, up to about 0.065% (total) aluminum, and balance iron plus incidental impurities.
Two series of laboratory tests were conducted which demonstrated the effectiv~ess of phosphate addition to an aqueous slurry of an inactive magnesia. In both series of tests the mag,nesia was from a commercial souxce and had a citric acid activity of about 2000 seconds. ,The phosphate compound used was monocalc~um phosphate monohydrate (sold by S-tauffer Chemlcal Company under the designation "12 XX" and sold by Monsanto Corporation under the designation "MC.P~"). Both source~ were in particulate form.
- In the first serias aqueous slurries wPre ,prepared each containing 0.6 grams per cubic centimeter of magnesia, the first slurry containin~ no additive, and the remaining slurries containing 2.5~, 5~, 7.5% and lOg respectively - of the calcium phosphate calculated as P205, ba~ed on the weight of magnesia. D~carburized silicon steel stoc~ of 14 mil thickness was coated with each of the slurries~
The slurry-containing no additive and the slurry containing -
This invention relates to an aqueous composition for forming an insulative glass coating directly on silicon steel strip and sheet stock, and more particularly to an aqueous magnesia slurry of high concentration wherein a substantial portion o the magnesia (magnesium oxide) is an inactive magnesia (having a citric acid activity, as hereinafter de~ined, of greater than 200 seconds), and wherein a thermally decomposable phosphate containing compound is present as a stabilizing agent which keeps the inactive magnesia in suspension and increases the viscosity of the slurry. The invention further relates ~o a method o suspending an inactive magnesia in water to produce a stable slurry which can be readily applied to silicon steel surfaces to form a dried layer which will react with the steel to form a glass film during a subsequent hlgh temperature anneal.
In the production of oriented silicon ste~l decarburized strip and sheet stock is conventionally coated with an aq~eous slurry of magnesia which is dried at 1GW
heat. During decarburization a layer of fayalite (an iron silicate) if formed on the silicon steel stock surfaces.
The stocX which is coated with a dried layer of magnesia is then subjected to a finalt high temperature anneal at about 1095 to about 1260C, during which the magnesia in the coating reacts with the fayalite layer to form a glass film, and the cube-on-edge orientation is deveLoped by secondary recrystallization, as is well known in the art.
Heretofore, it has been considered nece3sary to use an active maynesia having a citric acid activity of less than ~00 seconds, in order to provide an aqueous 1 3 ~)6~ 0 ~
slurry from which the magnesia would not settle out rapidly and in order to obtain reaction between the magnesia and the fayalite surface layex. An active magnesia of the type conventionally used hydrates, with consequent increase in viscosity of the magnesia - water slurry, and thi~ creates a problem since the viscosity of the slurry must be kept within a range which will permit application of a coating of uniform thickness by dipping, spraying, metering rolls, or the like.
Inactive magnesias have never previously been considered suitable for forming an insulative glass ilm on oriented silicon steel strip and sheet stock ~ecause the dense particles could not be kept in suspension resulting in the formation of a slurry with very low viscosity. The dense inactive particles also would not react with the fayalite surface layer, at least within the time limits imposed by commercial production rates.
However, since inactive magnesias are available at much lower cost than the active magnesias, substitution of inactive magnesia in an annealing separator composition offers the prospect of very ~ubstantial economies in the processing of cube-on-edge oriented silicon steel.
Although additives to magnesia slurries have been proposed Xor the purpose of improving glass film properties and/or to facilitate the magnesia-fayalite reaction, to the best of applicant's knowledge no additives have been developed which are successful in stabilizing an aqueous slurry o an inactive magnesia and increasing the viscosity thereof.
The addition of phosphates to an active magnesia I ~ 66~0~
slurry is known, in order to i~prove the glass ilm properties and magnetic properties o the silicon steel base stock. Reference may be made to United Sta~es Patent 3,615,918, issued to J. D~ Evans and D. W. Taylor, wherein a magnesia composition containing a decomposable phosphate compound is disclosed. According to this patent, the phosphate, which ranges between 1~ and 25% by weight calculated as P2O5 is reduced to elemental phosphorus during the final high temperature anneal which diffuses inwardly from ~he coating into the silicon steel.
Pho~phate base coatings which may be applied directly to metallic surfaces, or as secondary coatings over a mill glass magnesia-base coatiny, are known in the art. Pho~phate and magnesia-containing coatings suitable for application to oriented silicon steel surfaces, either directly or as a secondary coatings, are disclosed in United States Patents 3,840,378 and 3,948,876, issued to J. D. Evans.
As indicated above, to the best o~ applicant's knowledge, the prior art has never suggested the use of inactive magnesia for annealing separator composition on oriented silicon steel strip and sheet ~tock, nor have additives been proposed which would remedy the problems inherent in using an inactive magnesia for this purpose.
It is a principal object of the present invention to provide an aqueous magnesia slurry of high concentration containing a substantial portion of an inactive magnesia having a citric acid activity greater than 200 seconds which is stable against settling, which has a viscosity suitable for application by conventional means and which o ~
will react with the Eayalite layer on the stock surfaces to form a uniform insulating glass filrn o~
satisfactory quality.
It is a further object of the invention to provide a method of suspending an inactive magnas.ia in wa-ter to produce a stable slurry which can be readily applied to silicon steel surfaces and which will react to form an insulating glass film during a subsequent high temperature anneal.
According to the invention there is provided a composition for forming an insulative glass film on oriented silicon steel strip and sheet surfaces, com-prising an aqueous slurry of magnesia, at least 25% by weight oE said magnesia having a citric acid activity greater than 200 seconds, a phosphate-containing com~
pound chosen from the group consisting of calcium phos-phates, water soluble ammonium polyphosphate, aluminum phosphate, magnesium phosphates, phosphoric acid, and mixtures thereof, said compound being present within the range Oe 2% to 25~ by weight calculated as P205, based on the weight of magnesia, and balance essenti-ally water, the magnesia concentration being up to 006 gram per cubic centimeter of slurry, said slurry being stable against settling for periods of time up to 10 hours.
The present invention further provides a method of suspending in water a magnesia at least 25% of which consists of magnesia having a citric acid activity greater than 200 seconds to produce a slurry having increased viscosity and stability against settling, which comprises the step of providing in said slurry a - t ~ ~6~
phosphate-containing compound within the range o~ 2~ to 25% by weight calculated as P20s, based on the weight of magnesia, said phosphate-containing compound being chosen from the group consisting of calcium phosphates, water soluble ammonium polyphosphate, aluminum phos-phate, magnesium phosphates, phosphoric acid and mixtures thereof.
It has been found that the invention can be practiced successfully with inactive magnesia from a commercial source having a citric acid activity greater than 200 seconds, a Cl- level of 0.02~ maximum and a S04-- level of 0.02% maximum. Tests have been conducted on such a magnesia having a citric acid activity ranging from about 1500 to about 3000 secondsr wherein the inactive magnesia comprised 100% of the total magnesia content of the slurry. Blends of 50% by weight inactive magnesia with 50~ by weight active magnesia have also been tested and have been found -to provide optimum adherence of -the dried coating to the stock and improved glass film quality. It is evident that lower proportions of inactive magnesia with an active magnesia can also be used, down to 10% inactive magnesia and 90% active magnesia for improved glass film quality, although the economic advantage o the inactive magnesia is thereby lost. At the other extreme, satisfactory results have been obtained with slurries in which 100% of the magnesia had a citric acid value greater than 200 seconds. The principal disadvantage in use of a composition in which all the magnesia is inactive arises from the fact that the ~ ~ ~6~30~
adherence of the dried coating is only fair, ~o that care must be exercised in handling the coated coils in order to prevent removal of hte magnesia coating. Where the inactive magnesia constitutes 25~ to 75% of the ~otal magnesia content, this problem is minimized. Thi~ range is thus preferred. The active magnesia preferably wiLl have a citric acid activity of about 20 to 40 seconds.
The phosphate addition not only stabilizes the inactive magnesia slurry against settling but also increases the viscosity to a range desirable for application by conventional means such as dipping, spraying, metering rolls and the like. Moreover, the magnesia concentration can be highsr t~an that o the prior art slurries containing only active magnesia. Such high concentrations are advantageous in that drying can be effected with less heat and in a shorter period of time, and in that ignition 105s can be maintained below 1~. With such low ignition losses the glass film quality has been ~ound to remain very uni~orm along both the length and the width of a coil.
Pre~erred phosphate compounds are monocalcium phosphate monohydrate, dicalcium phosphate dihydrate and water soluble ammonium polyphosphate. Preferably rom ~.5~
to 10~ by weight calculat~d as P205, based on the weight of magnesia, is added. When adding monocalcium phosphate monohydrate or dicalcium phosphate dihydrate, which are particulate, the material can be dry blended with the magnesia prior to forming an aqueous slurry, or can be added to the water before, during or after mixing the magnesia therewith. Accordingly the manner in which and stage at which the pho~phate compound is introduced into the slurry do not constitute a limitation on 6 ~3 V ~
the practi~e of the invention. In the case of water soluble a~monium polyphosphate, which is available as an aqueou~
solution only, ~he addition is made to the water of the aqueous slurry either before or after mixing the magnesia therewith.
~ The high calcining tem~eratures used in the production of inactive maynesia result in sintering and/or agglomeration of the magnesia producing a dense particle which requires grinding to obtain the de~ired particle size distribution, This grinding produces magnesia particles with an active surface. Although not intending to be bound by theory, it is belieYed that the phosphate compound added in accordance with the present invention reacts with the magnesia particles forming a thin~phosphate layer on the surface of the particles. This thin phosphate layer ~P205 ) giv~s the particles a net negative char~e preventing agglomeration and settling from occurring. ?his is believed to be the theoretical basis for the markedly improved stability against settling out which ha~ been observed. Additionally, the stable suspension of su¢h magnesia particles also increases the viscosity of the slurry to a desixable range.
It has been foun~ that concentratio~s up to 0.6 grams per cubic centimeter (5 pounds per gallon) can be used without settling and without increasing the viscosity to an objectionable extent when the magnesia component is lO0~ inactive magnesia. When using a mixture of 50~ inactive and 50% active magnesia, co~cen~rations ranging from about 0.24 grams per cubic centimeter to about 0.36 grams per centimeter (3 pounds per gallon) can be used. Dried coating weights of about 7.5 to about 1 11 6680~
15 grams per square meter were obtained within the above concentrations ranges when applied in conventional manner with metering rolls.
The amount of phosphate containing compound which may be added depends u~on the decarburizing and final annealing conditions, with a relatively low phosphate level for highly oxidizing decarburizing conditions, and a relatively high phosphate level for less oxidi~ing conditions.
Comparision of a 100% inactive magnesia slurry conta1nin~ a phosphate compound in accordance with~ the present invention with a control slurry containing 100~ of the same inactive magnesia slurry but with no additive indicated that there was no appreciable settling of the slurry of the invention after lO hours, whereas the slurry lS with no additive settled out completely within one hour leaving a substantially clear supernatant liquid layer.i By way of background, it is pointed out that a cold reduced decarburi2ed silicon steel strip and sheet stoc~ may be prepared by conventional procedures wherein a suitable melt is cast in the form of ingots or continuously cast into slab form. If cast into ingots the steel is bloomed and slabbed in conventional manner and the slabs are hot rolled to intermediate thickness from a temperature of about 1200 to about 1400C with annealing a~ter hot rolling. The hot mill scale is removed, and the material is then cold rolled to final guage in one or more stages, followed by decarburixation preferably in a wet hydrogen-containing atmosphere. If the steel is continuously cast into slab form, the method disclosed in United 5tates Patent 3,764,406, to ~O F Littman is ~ 1 ~6~3(3~
preferably ~ollowed.
A magnesia coating is then applied to the surfaces of the decarburized stock by dipping, spraying, metering rolls, or other conventional means. Th~ coati~g is then dried by heating to a temperature sufficient to ~evaporate the water. The dried coating weigh~ should preferably range between about 6 and 20 grams per square metsr.
The coated stock is then subjected to a final high temper-ature anneaL at about 1095 to about l260C, which may be a box annaal or an open coil anneal, in a reducing atmosphere. During this anneal the magnesia reacts to form an insulative glass film, and the cube-on-edge orientation is obtained by secondary recrystallization.
The composition and method of processing the silcion s~eel to final strip and sheet form do not constitute a limitation on the present invention. Any of the regular or high permeability grades of oriented silicon steel on which a magnesia coating is utilized may be treated in the practice of the present invention. By way of non-limiting example, compositions and methods in which the present invention finds utility include thosedisclosed in United States Patents 3,287,183; 3f873,381; 3,90S,842; 3,905,B43; 3,932,~234;
3,957,546,and 4,000,015. Except for No. 3,932,234, these ~atents relate to the production of high permeability _ material (relative permeability greater than 1850 at 796 A/m) by means of boron and nitrogen additions to the steel.
Manganese and sulfur (and/or selenium) may also be presen~.
For a reguIar g~ain oriented silicon steel wherein manganese and sulfur (and/or selenium) are present as grain qrowth inhibitors, a typical but non~limiting 1 ~ ~)6~0~
composition fox the cold rolled and decarburized stock may comprise, in weight percent, about 2% to about 4%
silcion, about 0.01~ to about 0~4% manganese, about 0.01%
to about 0.03% sulfur, about 0.002~ ~o about 0.005% carbon, up to about 0.065% (total) aluminum, and balance iron plus incidental impurities.
Two series of laboratory tests were conducted which demonstrated the effectiv~ess of phosphate addition to an aqueous slurry of an inactive magnesia. In both series of tests the mag,nesia was from a commercial souxce and had a citric acid activity of about 2000 seconds. ,The phosphate compound used was monocalc~um phosphate monohydrate (sold by S-tauffer Chemlcal Company under the designation "12 XX" and sold by Monsanto Corporation under the designation "MC.P~"). Both source~ were in particulate form.
- In the first serias aqueous slurries wPre ,prepared each containing 0.6 grams per cubic centimeter of magnesia, the first slurry containin~ no additive, and the remaining slurries containing 2.5~, 5~, 7.5% and lOg respectively - of the calcium phosphate calculated as P205, ba~ed on the weight of magnesia. D~carburized silicon steel stoc~ of 14 mil thickness was coated with each of the slurries~
The slurry-containing no additive and the slurry containing -
2.5% phosphate did not wet the stock well and without 25_ agitation the magnesia tended to settle out rapidly. No problems were encountered wi~h coating with the remaining slurries.
After a final high temperature anneal at 1200C, examination of the glass film developed on each sample indicated.
that they ranged from a thin rainbow glass for the composition containing no additive to a light gray continuous film for .
I ~ 66~0~
the slurries containing more than 5% phosphate. A progressive .
improvement in the physical appearance of the glass f~m was noted for each higher amount of phosphate additive.
The second series involved preparation of slurries containing 100~ i~active magnesia with 0~, nominal 5~, 7.5%
and 10% additions o calciunl phosphate calculated as P205i 50~ inactive magnesia by we~ight with 50~ active magnesia by weight having a citric acid activity of about 30 seconds with 0%, nominal 2.5% and 5% calcium phosphate calculated as P2~5, and 50~ by weight inactive magnesia with 50~ active magnesia from another source having citric acid activity of 30 seconds with 0%, nominal 2.5~ and 5% calcium phosphate, calculated as P205. A control composition was also prepared contàining 50~ each by weight of the active magnesias.from the two sources with 2.5% by weight addition of calcium phos-phate calculated as P205.
The active magnesias which were used had the following s~ecifications:
. F-: less than 500 ppm Cl-: less than 200 ppm Na l: less than 200 ppm Ignition loss at 100C: 1.5-13.0%
Citric acid activity: 20 to 40 seconds Particle size: 99.9% through 200 mesh 25_ 99.5% throu~h 325 mesh These Specifications should be observed in the practice of the invention, although the citric acid activity may range up to less than 200 seconds, as indicated previously.
- The slurries in which all the magnesia was inactive weFe prepared with a concentration of 0.60 grams l?
1 J ~i6~04 per cc, whereas the slurries containing 50% inactive and 50% active magnesias were prepared with concentrati~n ~or 0.36 grams per cc. The control slurry was prepared with a concentration of 0.144 grams per cc.
Decarburized silicon steel sheets of 11 mil thic~ness were-coa~ed with each of the above slurries and were subjected to a box anneal in a reducing atmosphere at about 120QC. No coating problems were encountered with any of the.slurries except the one containing only inactive }o magnesia with no addition of calci~n phosphate. All the remaining slurries remained in suspension and wet the stock well.
Evalua~on of the glass:films formed by the various s}urries indicated the following:
The inactive magnesia with no calcium phosphate addition formed a thin, discon~inuous glass filmO
The slurries of 100% inactive magnesia with additions of 5% and 7.5% calcium phosphate calculated as P205, formed a thin, rough, light gray glass film~ The slurry con~aining lOn% inactive magnesia and 10~ by weight calcium phosphate resulted in a rough, re~dish gray poor quality glass film.
. The mixtures of 50% inactive magnasia and 50%
.
active magnesia formed ~lass films with improved ph~sical appearance. The slurries containing no calcium phosphate additions to these mixtures exhibited a continuous gray glass film with a slightly rough texture. ThP calcium , . . .
1 3 t~6~0'1 phosphate additions of 2.5~ and 5% calculated as P2O5 re-sulted in the forrnation of a smoother, lighter gray glass film.
All -the slurries containing 100~ inactive magnesia had poor oxidation resistance regardless of the calcium phosphate additions.
~ the slurries containing 50~ inactive magnesia and 50% active magnesia with no calcium phosphate addition also exhibited poor oxidation resistance. Slurries containing 2.5% calcium phosphate calculated ag P205 exhibited somewhat improved oxidation resistance. The best oxidation resistance was exhibited by slurries containing 50% inaçtive and 50% active magnesias with 5~ calcium phosphate calculated as PzO5. By way of comparison the control sample containing equal parts of the two active magnesias with 2.5% calcium phosphate addition, had poor oxidatio~ resistance.
Secondary coatings of the type disclosed in the above-mentioned United States Patents 3,840,378 and 3,948,876 (containing magnesia, phosphate and alurninum) were applied to all samples, and tested for adherence. The adherence of the secondary coatings followed the same trend as oxidation resistance. Glass films which demonstrated good oxidation resistance had good adherence of the secondary coating while those which had poor oxidation resistance exhibited poor adherence of the secondary coatings. The best adherence was exhibited by ~ixtures of 50% active and 50% inactive magnesias with 5% calcium phosphate calculated as P205.
Various magnetic properties of the samples of the second series were determined at 60Hz and are summarized in Ta~le I. It will be noted that of the compositions containing
After a final high temperature anneal at 1200C, examination of the glass film developed on each sample indicated.
that they ranged from a thin rainbow glass for the composition containing no additive to a light gray continuous film for .
I ~ 66~0~
the slurries containing more than 5% phosphate. A progressive .
improvement in the physical appearance of the glass f~m was noted for each higher amount of phosphate additive.
The second series involved preparation of slurries containing 100~ i~active magnesia with 0~, nominal 5~, 7.5%
and 10% additions o calciunl phosphate calculated as P205i 50~ inactive magnesia by we~ight with 50~ active magnesia by weight having a citric acid activity of about 30 seconds with 0%, nominal 2.5% and 5% calcium phosphate calculated as P2~5, and 50~ by weight inactive magnesia with 50~ active magnesia from another source having citric acid activity of 30 seconds with 0%, nominal 2.5~ and 5% calcium phosphate, calculated as P205. A control composition was also prepared contàining 50~ each by weight of the active magnesias.from the two sources with 2.5% by weight addition of calcium phos-phate calculated as P205.
The active magnesias which were used had the following s~ecifications:
. F-: less than 500 ppm Cl-: less than 200 ppm Na l: less than 200 ppm Ignition loss at 100C: 1.5-13.0%
Citric acid activity: 20 to 40 seconds Particle size: 99.9% through 200 mesh 25_ 99.5% throu~h 325 mesh These Specifications should be observed in the practice of the invention, although the citric acid activity may range up to less than 200 seconds, as indicated previously.
- The slurries in which all the magnesia was inactive weFe prepared with a concentration of 0.60 grams l?
1 J ~i6~04 per cc, whereas the slurries containing 50% inactive and 50% active magnesias were prepared with concentrati~n ~or 0.36 grams per cc. The control slurry was prepared with a concentration of 0.144 grams per cc.
Decarburized silicon steel sheets of 11 mil thic~ness were-coa~ed with each of the above slurries and were subjected to a box anneal in a reducing atmosphere at about 120QC. No coating problems were encountered with any of the.slurries except the one containing only inactive }o magnesia with no addition of calci~n phosphate. All the remaining slurries remained in suspension and wet the stock well.
Evalua~on of the glass:films formed by the various s}urries indicated the following:
The inactive magnesia with no calcium phosphate addition formed a thin, discon~inuous glass filmO
The slurries of 100% inactive magnesia with additions of 5% and 7.5% calcium phosphate calculated as P205, formed a thin, rough, light gray glass film~ The slurry con~aining lOn% inactive magnesia and 10~ by weight calcium phosphate resulted in a rough, re~dish gray poor quality glass film.
. The mixtures of 50% inactive magnasia and 50%
.
active magnesia formed ~lass films with improved ph~sical appearance. The slurries containing no calcium phosphate additions to these mixtures exhibited a continuous gray glass film with a slightly rough texture. ThP calcium , . . .
1 3 t~6~0'1 phosphate additions of 2.5~ and 5% calculated as P2O5 re-sulted in the forrnation of a smoother, lighter gray glass film.
All -the slurries containing 100~ inactive magnesia had poor oxidation resistance regardless of the calcium phosphate additions.
~ the slurries containing 50~ inactive magnesia and 50% active magnesia with no calcium phosphate addition also exhibited poor oxidation resistance. Slurries containing 2.5% calcium phosphate calculated ag P205 exhibited somewhat improved oxidation resistance. The best oxidation resistance was exhibited by slurries containing 50% inaçtive and 50% active magnesias with 5~ calcium phosphate calculated as PzO5. By way of comparison the control sample containing equal parts of the two active magnesias with 2.5% calcium phosphate addition, had poor oxidatio~ resistance.
Secondary coatings of the type disclosed in the above-mentioned United States Patents 3,840,378 and 3,948,876 (containing magnesia, phosphate and alurninum) were applied to all samples, and tested for adherence. The adherence of the secondary coatings followed the same trend as oxidation resistance. Glass films which demonstrated good oxidation resistance had good adherence of the secondary coating while those which had poor oxidation resistance exhibited poor adherence of the secondary coatings. The best adherence was exhibited by ~ixtures of 50% active and 50% inactive magnesias with 5% calcium phosphate calculated as P205.
Various magnetic properties of the samples of the second series were determined at 60Hz and are summarized in Ta~le I. It will be noted that of the compositions containing
3 0 4 100% inactive magnesia the be5t magnetic quality was eY.hibited by the sample containing a nominal 5% calcium phosphate additio~
calculated as P205. Additions of nomlnal 7.5% and 10% ~;
calcium phosphate resulted in a decrease in magnetic quality.
The magnetic quality,of samples containing 50% inactive and 50% active magnesia~ exhibiting a sux-pr-ising improvement, particularly with calcium phosphate additions. With no calcium phosphate addition the magnetic quality was co~parable to that of the control sample. With calcium phosphate additions of nominal 2.5 and 5% calculated as P205, all samples exhi,bited a significant improvement in magnetic quality as compared to the control sample.
Plant trials wexe next conducted using decarburized silicon steel coils of 11 mil thickness within the conventional steel composition ranges set forth above, and coils were coated with the following'composition:' ' 5~% by weight inactive magnesia CAA 2000 seconds 50% active magnesia CAA 30 seconds 5% mo,nocalcium phosphate monohydrate calculated as P2s balance water Slurry concen-trations and coating weights,of the dried coatings are set forth in Table II. No coating problems were encountered. The slurry wet the strip very well producing smooth, uniform coatings; the as dried adherence _- was air. No appreciable settling was observed in the coating pan.
7 ~
It was found tha~ the coatings dried much more rapidly than conventlonal coatings containing only ac ~ve magnesia. Consequently coatings containing inactive magnesia can be dried at lower temperature, thus reducing the amount of energy required.
The coated coils were box annealed in a reducing atmosphere at about 1150C in conventional manner for 24 hours. The coils formed an excellent ylass film which was light gray:, smooth, continuous and devoid of any oxide o~
; rainbow. Moreover the coil front end to coil back end variation in physical appearance o~ the ylass film whlch , normally occurs with conventional active ma~nesias, was not ! present in any of these coils.
Magnetic properties of the above coils are reported in Table III together with magnetic properties o~ control coils from the same heat coated witp a mixture of 50%
active magnesia CAA 30 seconds fxom a first source and 5Q~
acti~e magnesia CAA 30 seconds from a second source. It is evident that the magnetic quality of coils coated with the composition of the invention was good and e~ual to or better than-those of ~he control coils~
Further tests have been conducted showing that the composition and me~hod of the present invention are applicable to the production of very high pe~meability silicon steel conkaining boron and nitrogen in accordance with the teachings of United States Patent 3,873,381, and wherein boron and titanium dioxide are added to the magnesia composition. Prior art magnesia compositions to which boron and titanium dicxide addit~ons are made have always contained only an active magnesia having a citric acid 1 1 ~6~0~
activity ranging from, e.g., about 20 to about 80 seconds.
The boron addition may be in the form of a boron compound such as boric acid, sodium tetraborate, and the liXe.
In these tests a mixture of 50% by weiyht of an inactive magnesia from a domestic source having a CAA of about 2000 seconds, and 50% by weight of an active magnesia from a domestic source ha~ing a CAA of about 30 seconds, was used as the base composition. An active magnesia from a Japanese source having a CAA of about 30.
seconds was used as a control since this had produced optimum glass film properties and magnetic quality in th0 production of very high permeability material by prior art methods. This contained 0.08% boron as supplied.
. The base composition was mixed with water to form a slurry having a concent~ation of 0.36 gm per cc.
Various combinatlons of additives were mixed with slurry samples, based on the total dry magnesia weight, as follows:
% monocalcium phosphate mono- % .
hydrate as P205. Boron _2_ S O O
, 0 0 .12 0 .12 0 -. .12 0 .12 0 S' O ' S
. ln o ~ 15 0 5 S o 10 8 0 ~
.12 5 .12 5.
.12 5 .L2 ~ 5 .12 10 ~, lS 12 . 10 .12 lQ
The control composition was mixed with water to form a slurry of 0.147 gm per cc concentxation, and 5%
titanium dioxide (based on the weight of magnesia) was a~ded.
Coatings were applied to decarburized blanks of very high permeability silicon steel of 11 mil thi.ckness r and coating weights as-dried ranged from 10 to 12 gm per m2.
The coated blanks were then subjected to a final anneal,in a reducing atmosphere which included holding at 1190C
in pure hydrogen for 24 hours..
Evaluation of the various coated and annealed blanks showed the following results:
The samples with 5%, 10%, 15% and 20% calcium phosphate with and without boron additions plus titanium dioxide, developed smooth, light gray glass films.
Titanium dioxide additions made the glass film rougher and ~arker gray. At 5% calcium phosphate and 5% and 10% t.itanium dioxide the physical appearance was similar to that of the control sample (containing 5~ titanium dioxide). At 10%, 15~ and 20% calcium phosphate levels the glass film was progressively rougher and darker in color.
Secondary coatings of the type disclosed in the above mentioned United States Patent 3,840,378 were . 18 / o ~
applied. Samples containing 5~ and 10~ calcium phosphate plus 5~ and 10% titanium dioxide had the best appe ~ance.
In samples containing no titanium dioxid~ the secondary coating adherence was poor. The titanium dioxide-containing samples had improved adherence. The samplecontaining 5% calcium phosphate and S% titanium dioxide had adherance similar to that of the control sample, while the adherence of the sample containing 10% calcium phosphate and 5% titanium dioxide was superior to that of the control sample.
With respect to magnetic quality, samples containing 5%, 10% and 15~ calcium phosphate (with no boron and titanium dioxide additions) had simiLar properties, i.e., core loss at 1.7T and 60 Hz of 1.675watts/kg, and relative 15 permeability of 1875 at 796 A/m.
In the samples containing 0.12~ boron and no titanium dioxide, the magnetic quality was inferior to that of samples above containing no boron and no titanium dioxide.
Samples containing titanium dioxide and no - boron exhibited inferior magnetic quality.
Samples containing boron and titanium dioxide exhibited improved magnetic quality, the best being obtained with 5% calcium phosphate, 0.12~ boron and 5% titanium dioxide.
25 The core loss for the best sample was 1.679 wat~.s/kg at 1.7T
and 60~z, and relative permeability was1880 at 796 ~/m, as com pared to 0.763 and 1905 for the control sample.
. ' 19 ..
~ ' t3V~
. It was further observed that boron additions increased the final grain size significantly, and tha~
calcium phosphate additions greater than 5% (wi~h boron and titanium dioxide) were detrimental to magnetic quality.
It is thereforeevident that in the production ~of very high permeability material a best combination of properties is obtained with 5% to 10X phosphate compound calculated as ~205,about 0.10% to about 0~15% bor~n, and about 5~ to about 10% titanium dioxide, based on the weight of magnesia~ These ranges are applicable to a magnesia composition wherein about 25% to about 75~ is an inactive magnesia having a CAA of about 1500 to about 3000 seconds and the remainder is an active magnesia having a CAA of about 20 to 40 seconds.
The above data show that calcium phosphate additions significantly change the reactions which occur and the composition of the glass ilm during the f.inal high temperature anneal. The phosphate oxidizes the silicon and iron on the stock surface increasing the amount of fayalite at the surface. The phosphorus is thus reduced, - . and most of lt diffuses harmlessly into the steel, as described in the above-mentioned United States Patent 3,615,918. On the other hand, calcium, in the form of calcium oxide, acts as a ~uxing agent causing liquid formation at a lower temperature. The calcium oxide reacts with the fayalite on the silicon steel suxfaces to form wollastonite, which is a magnesium and calcium oxide~silicon dioxide complex. Wollastonite melts about 200C lower than fayalite, and this incxeased amount of . 30 liquid phase formation is thus able ~o take th~ magnesia 2n I ~ 6680~
into solu~ion more readily to complete the glass ilm formation.
The citric acid activity is a measure of the hydration rate of magnesium oxide and is determined by measuring the time required for a given weight of a magnesia to provide hydroxyl ions sufficient to neutralize a given weight of citric acid. The test is the same as that reported in United States Patent 3,841,925, viz.;
1. 100 ml of 0.400 normal aqueous citric acid containing 2 ml of 1~ phenolphthalein indicator is brought to 30C in an 8 oun¢e wide mouth jar. The jar is fitted with a screw cap and a magnetic stirrer bar.
2. Magnesia weighins 2.00g is admitted to the jar, and a stop watch is started at the same instant.
3. As soon as the magnesia sample is added the lid is screwed on the ja~. At the 5 second point the jar and contents are vigorously shaken. Shaking is terminated at ~he 10 second point.
calculated as P205. Additions of nomlnal 7.5% and 10% ~;
calcium phosphate resulted in a decrease in magnetic quality.
The magnetic quality,of samples containing 50% inactive and 50% active magnesia~ exhibiting a sux-pr-ising improvement, particularly with calcium phosphate additions. With no calcium phosphate addition the magnetic quality was co~parable to that of the control sample. With calcium phosphate additions of nominal 2.5 and 5% calculated as P205, all samples exhi,bited a significant improvement in magnetic quality as compared to the control sample.
Plant trials wexe next conducted using decarburized silicon steel coils of 11 mil thickness within the conventional steel composition ranges set forth above, and coils were coated with the following'composition:' ' 5~% by weight inactive magnesia CAA 2000 seconds 50% active magnesia CAA 30 seconds 5% mo,nocalcium phosphate monohydrate calculated as P2s balance water Slurry concen-trations and coating weights,of the dried coatings are set forth in Table II. No coating problems were encountered. The slurry wet the strip very well producing smooth, uniform coatings; the as dried adherence _- was air. No appreciable settling was observed in the coating pan.
7 ~
It was found tha~ the coatings dried much more rapidly than conventlonal coatings containing only ac ~ve magnesia. Consequently coatings containing inactive magnesia can be dried at lower temperature, thus reducing the amount of energy required.
The coated coils were box annealed in a reducing atmosphere at about 1150C in conventional manner for 24 hours. The coils formed an excellent ylass film which was light gray:, smooth, continuous and devoid of any oxide o~
; rainbow. Moreover the coil front end to coil back end variation in physical appearance o~ the ylass film whlch , normally occurs with conventional active ma~nesias, was not ! present in any of these coils.
Magnetic properties of the above coils are reported in Table III together with magnetic properties o~ control coils from the same heat coated witp a mixture of 50%
active magnesia CAA 30 seconds fxom a first source and 5Q~
acti~e magnesia CAA 30 seconds from a second source. It is evident that the magnetic quality of coils coated with the composition of the invention was good and e~ual to or better than-those of ~he control coils~
Further tests have been conducted showing that the composition and me~hod of the present invention are applicable to the production of very high pe~meability silicon steel conkaining boron and nitrogen in accordance with the teachings of United States Patent 3,873,381, and wherein boron and titanium dioxide are added to the magnesia composition. Prior art magnesia compositions to which boron and titanium dicxide addit~ons are made have always contained only an active magnesia having a citric acid 1 1 ~6~0~
activity ranging from, e.g., about 20 to about 80 seconds.
The boron addition may be in the form of a boron compound such as boric acid, sodium tetraborate, and the liXe.
In these tests a mixture of 50% by weiyht of an inactive magnesia from a domestic source having a CAA of about 2000 seconds, and 50% by weight of an active magnesia from a domestic source ha~ing a CAA of about 30 seconds, was used as the base composition. An active magnesia from a Japanese source having a CAA of about 30.
seconds was used as a control since this had produced optimum glass film properties and magnetic quality in th0 production of very high permeability material by prior art methods. This contained 0.08% boron as supplied.
. The base composition was mixed with water to form a slurry having a concent~ation of 0.36 gm per cc.
Various combinatlons of additives were mixed with slurry samples, based on the total dry magnesia weight, as follows:
% monocalcium phosphate mono- % .
hydrate as P205. Boron _2_ S O O
, 0 0 .12 0 .12 0 -. .12 0 .12 0 S' O ' S
. ln o ~ 15 0 5 S o 10 8 0 ~
.12 5 .12 5.
.12 5 .L2 ~ 5 .12 10 ~, lS 12 . 10 .12 lQ
The control composition was mixed with water to form a slurry of 0.147 gm per cc concentxation, and 5%
titanium dioxide (based on the weight of magnesia) was a~ded.
Coatings were applied to decarburized blanks of very high permeability silicon steel of 11 mil thi.ckness r and coating weights as-dried ranged from 10 to 12 gm per m2.
The coated blanks were then subjected to a final anneal,in a reducing atmosphere which included holding at 1190C
in pure hydrogen for 24 hours..
Evaluation of the various coated and annealed blanks showed the following results:
The samples with 5%, 10%, 15% and 20% calcium phosphate with and without boron additions plus titanium dioxide, developed smooth, light gray glass films.
Titanium dioxide additions made the glass film rougher and ~arker gray. At 5% calcium phosphate and 5% and 10% t.itanium dioxide the physical appearance was similar to that of the control sample (containing 5~ titanium dioxide). At 10%, 15~ and 20% calcium phosphate levels the glass film was progressively rougher and darker in color.
Secondary coatings of the type disclosed in the above mentioned United States Patent 3,840,378 were . 18 / o ~
applied. Samples containing 5~ and 10~ calcium phosphate plus 5~ and 10% titanium dioxide had the best appe ~ance.
In samples containing no titanium dioxid~ the secondary coating adherence was poor. The titanium dioxide-containing samples had improved adherence. The samplecontaining 5% calcium phosphate and S% titanium dioxide had adherance similar to that of the control sample, while the adherence of the sample containing 10% calcium phosphate and 5% titanium dioxide was superior to that of the control sample.
With respect to magnetic quality, samples containing 5%, 10% and 15~ calcium phosphate (with no boron and titanium dioxide additions) had simiLar properties, i.e., core loss at 1.7T and 60 Hz of 1.675watts/kg, and relative 15 permeability of 1875 at 796 A/m.
In the samples containing 0.12~ boron and no titanium dioxide, the magnetic quality was inferior to that of samples above containing no boron and no titanium dioxide.
Samples containing titanium dioxide and no - boron exhibited inferior magnetic quality.
Samples containing boron and titanium dioxide exhibited improved magnetic quality, the best being obtained with 5% calcium phosphate, 0.12~ boron and 5% titanium dioxide.
25 The core loss for the best sample was 1.679 wat~.s/kg at 1.7T
and 60~z, and relative permeability was1880 at 796 ~/m, as com pared to 0.763 and 1905 for the control sample.
. ' 19 ..
~ ' t3V~
. It was further observed that boron additions increased the final grain size significantly, and tha~
calcium phosphate additions greater than 5% (wi~h boron and titanium dioxide) were detrimental to magnetic quality.
It is thereforeevident that in the production ~of very high permeability material a best combination of properties is obtained with 5% to 10X phosphate compound calculated as ~205,about 0.10% to about 0~15% bor~n, and about 5~ to about 10% titanium dioxide, based on the weight of magnesia~ These ranges are applicable to a magnesia composition wherein about 25% to about 75~ is an inactive magnesia having a CAA of about 1500 to about 3000 seconds and the remainder is an active magnesia having a CAA of about 20 to 40 seconds.
The above data show that calcium phosphate additions significantly change the reactions which occur and the composition of the glass ilm during the f.inal high temperature anneal. The phosphate oxidizes the silicon and iron on the stock surface increasing the amount of fayalite at the surface. The phosphorus is thus reduced, - . and most of lt diffuses harmlessly into the steel, as described in the above-mentioned United States Patent 3,615,918. On the other hand, calcium, in the form of calcium oxide, acts as a ~uxing agent causing liquid formation at a lower temperature. The calcium oxide reacts with the fayalite on the silicon steel suxfaces to form wollastonite, which is a magnesium and calcium oxide~silicon dioxide complex. Wollastonite melts about 200C lower than fayalite, and this incxeased amount of . 30 liquid phase formation is thus able ~o take th~ magnesia 2n I ~ 6680~
into solu~ion more readily to complete the glass ilm formation.
The citric acid activity is a measure of the hydration rate of magnesium oxide and is determined by measuring the time required for a given weight of a magnesia to provide hydroxyl ions sufficient to neutralize a given weight of citric acid. The test is the same as that reported in United States Patent 3,841,925, viz.;
1. 100 ml of 0.400 normal aqueous citric acid containing 2 ml of 1~ phenolphthalein indicator is brought to 30C in an 8 oun¢e wide mouth jar. The jar is fitted with a screw cap and a magnetic stirrer bar.
2. Magnesia weighins 2.00g is admitted to the jar, and a stop watch is started at the same instant.
3. As soon as the magnesia sample is added the lid is screwed on the ja~. At the 5 second point the jar and contents are vigorously shaken. Shaking is terminated at ~he 10 second point.
4. At the 10 second point the sample is placed on a magnetic stirrer assembly. Mechanical stirring should produce a vortex abou~ 2 cm deep at the center when the inside diameter of the jar is 6 cm.
5~ The stop watch is stopped at the lnstant the suspension turns pink, and ~he time i5 noted~ This time - 25 in seconds is the citric acid activity.
~ 3 ~6~30~
T~BL~ I
Magnetic Properties Ca (H2P4) ~2n Core Loss Relative perm nominal wt. percent Watts/kg at 6011z eability at Magnesia 2 5 1.5 T 1~7 T- ?96_A/m 100% inactive (CA~ 2000 secs.) O 1.065 1.583 1840 100% i~active 5 1O054 1.526 1840 100% inactiye 7.5. 1.116 }.662 1823 100% inactive 10 1.111 1.638 1824 50% inactive.+
50% acti~e CAA 3Q sec. 0 1.056 1.563 1834 , 50% inactive +
50~ active CAA 30 sec. 2.5 1.038 1.519 1835 50~ inactive +
50~ active CAA 30 sec. 5 1.038 1.493 1844 50% inactive +
50~ active CA~ 30 sec. 0 1.052 1.55Z 1836 50% inactive +
50~ active CAA 30 sec. 2.5 1.038 1.515 1837 50% inactive +
50~ active CAA 3n sec. 5 1.042 1.506 1842 50% active CA~ 30lsec.
50% active C~A 30 ~ec. 2.5 1.060 1.559 1837 T~B1E II
, Coating Conditions Sample . Concentration Coating Weight /cc =,~
(Coil 1) 0.1~5 11.34 (Coil 2) . 0.248 15.12 (Coil 3) 0.225 . 11~34 ~ ~2 \
3 ~) ~
X . .
~D
a) ~ a~
~ ~ o o . ~ .
. ~
.
a~
.,,.,, ~_,~ o ,~
~ ,a ~D 0~ C~
t~ ~ a) r~
~ .
, .
o ~ . `
X
tn ~ u~ u~
..
~ I~ ~
~
3-1 .
. -' ~ .
O ~ . . r~
H ~ ~ U~ Ul 1--~. Ll~
H ~ ~`` ~O . ;
t.) 1:4 l¢ O O
~ b a) ~
~ ~ ~ o o .,, ~ co ,Q ~ .,.
a) ~ a~
o P; ~`
N
' ~O
a . ,_ ~D
. ~ a In U~
,~
~ I~
~: ~t , a~
a.) a o ~
~ U~ ~ ~
~ l ~
3 ~o o~o
~ 3 ~6~30~
T~BL~ I
Magnetic Properties Ca (H2P4) ~2n Core Loss Relative perm nominal wt. percent Watts/kg at 6011z eability at Magnesia 2 5 1.5 T 1~7 T- ?96_A/m 100% inactive (CA~ 2000 secs.) O 1.065 1.583 1840 100% i~active 5 1O054 1.526 1840 100% inactiye 7.5. 1.116 }.662 1823 100% inactive 10 1.111 1.638 1824 50% inactive.+
50% acti~e CAA 3Q sec. 0 1.056 1.563 1834 , 50% inactive +
50~ active CAA 30 sec. 2.5 1.038 1.519 1835 50~ inactive +
50~ active CAA 30 sec. 5 1.038 1.493 1844 50% inactive +
50~ active CA~ 30 sec. 0 1.052 1.55Z 1836 50% inactive +
50~ active CAA 30 sec. 2.5 1.038 1.515 1837 50% inactive +
50~ active CAA 3n sec. 5 1.042 1.506 1842 50% active CA~ 30lsec.
50% active C~A 30 ~ec. 2.5 1.060 1.559 1837 T~B1E II
, Coating Conditions Sample . Concentration Coating Weight /cc =,~
(Coil 1) 0.1~5 11.34 (Coil 2) . 0.248 15.12 (Coil 3) 0.225 . 11~34 ~ ~2 \
3 ~) ~
X . .
~D
a) ~ a~
~ ~ o o . ~ .
. ~
.
a~
.,,.,, ~_,~ o ,~
~ ,a ~D 0~ C~
t~ ~ a) r~
~ .
, .
o ~ . `
X
tn ~ u~ u~
..
~ I~ ~
~
3-1 .
. -' ~ .
O ~ . . r~
H ~ ~ U~ Ul 1--~. Ll~
H ~ ~`` ~O . ;
t.) 1:4 l¢ O O
~ b a) ~
~ ~ ~ o o .,, ~ co ,Q ~ .,.
a) ~ a~
o P; ~`
N
' ~O
a . ,_ ~D
. ~ a In U~
,~
~ I~
~: ~t , a~
a.) a o ~
~ U~ ~ ~
~ l ~
3 ~o o~o
Claims (14)
1. A composition for forming an insulative glass film on oriented silicon steel strip and sheet surfaces, comprising an aqueous slurry of magnesia, at least 25% by weight of said magnesia having a citric acid activity greater than 200 seconds, a phosphate-containing compound chosen from the group consisting of calcium phosphates, water soluble ammonium polyphosphate, aluminum phosphate, magnesium phosphates, phosphoric acid, and mixtures thereof, said compound being present within the range of 2% to 25% by weight calculated as P2O5, based on the weight of magnesia, and balance essentially water, the magnesia concentration being up to 0.6 gram per cubic centimeter of slurry, said slurry being stable against settling for periods of time up to 10 hours.
2. The composition claimed in claim 1, wherein said magnesia comprises about 50% by weight of a magnesia having a citric acid activity of 1500 to 3000 seconds and about 50%
by weight of a magnesia having a citric acid activity of 20 to 40 seconds.
by weight of a magnesia having a citric acid activity of 20 to 40 seconds.
3. The composition claimed in claim 1, wherein said phosphate-containing compound is present within the range of 2.5% to 10% by weight calculated as P2O5, based on the weight of magnesia.
4. The composition claimed in claim 1, wherein said magnesia comprises 25% to 75% by weight magnesia having a citric acid activity of 1500 to 3000 seconds and the remainder a magnesia having a citric acid activity of 20 to 40 seconds, and wherein said phosphate-containing compound is within the range of 2.5% to 10% by weight calculated as P2O5, based on the weight of magnesia.
5. The composition claimed in claim 1, wherein said magnesia comprises about 50% by weight of magnesia having a citric acid activity of 1500 to 3000 seconds and about 50%
by weight of magnesia having a citric acid activity of about 30 seconds, and wherein said phosphate-containing compound is present within the range of 2.5% to 10% by weight calculated as P2O5, based on the weight of magnesia.
by weight of magnesia having a citric acid activity of about 30 seconds, and wherein said phosphate-containing compound is present within the range of 2.5% to 10% by weight calculated as P2O5, based on the weight of magnesia.
6. The composition claimed in claim 1, wherein said phos-phate-containing compound is monocalcium phosphate monohydrate, dicalcium phosphate dihydrate, or water soluble ammonium polyphosphate.
7. The composition claimed in claim 2, wherein the magnesia concentration is at least 0.24 gram per cubic centimeter of slurry.
8. The composition claimed in claim 4, wherein said silicon steel has very high permeability, wherein said phosphatecontaining compound is within the range of 5% to 10% by weight calculated as P2O5, and including 0.10% to 0.15% boron and 5% to 10% titanium dioxide, based on the weight of magnesia.
9. A method of suspending in water a magnesia at least 25% of which consists of magnesia having a citric acid activity greater than 200 seconds to produce a slurry having increased viscosity and stability against settling, which comprises the step of providing in said slurry a phosphate-containing compound within the range of 2% to 25%
by weight calculated as P2O5, based on the weight of magnesia, said phosphate-containing compound being chosen from the group consisting of calcium phosphates, water soluble ammonium polyphosphate, aluminum phosphate, magnesium phosphates, phosphoric acid and mixtures thereof.
by weight calculated as P2O5, based on the weight of magnesia, said phosphate-containing compound being chosen from the group consisting of calcium phosphates, water soluble ammonium polyphosphate, aluminum phosphate, magnesium phosphates, phosphoric acid and mixtures thereof.
10. Method according to claim 9, wherein said magnesia comprises 25% to 75% by weight of a magnesia having a citric acid activity of 1500 to 3000 seconds and the remainder a magnesia having a citric acid activity of 20 to 40 seconds.
11. Method according to claim 9 or 10, wherein said magnesia comprises about 50% by weight of a magnesia having a citric acid activity of 1500 to 3000 seconds and about 50%
by weight of magnesia having acitric acid activity of 20 to 40 seconds.
by weight of magnesia having acitric acid activity of 20 to 40 seconds.
12. Method according to claim 9 or 10, wherein said phosphate-containing compound is monocalcium phosphate monohydrate or dicalcium phosphate dihydrate and is present within the range of 2.5% to 10% by weight calculated as P2O5, based on the weight of magnesia.
13. Method according to claim 9 or 10, including the step of adding to said slurry from 0.10% to 0.15% boron and from 5% to 10% titanium dioxide, based on the weight of magnesia.
14. Method according to claim 10, wherein the magnesia concentration of said slurry is at least 0.24 gram and ranges up to 0.6 gram per cubic centimeter of slurry.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8213163A GB2120645B (en) | 1982-05-06 | 1982-05-06 | Stable slurry of inactive magnesia for coating silicon steel |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1166804A true CA1166804A (en) | 1984-05-08 |
Family
ID=10530209
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000402189A Expired CA1166804A (en) | 1982-05-06 | 1982-05-04 | Stable slurry of inactive magnesia and method therefor |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS6017027B2 (en) |
| BE (1) | BE893342A (en) |
| CA (1) | CA1166804A (en) |
| DE (1) | DE3218821C2 (en) |
| FR (1) | FR2527198B1 (en) |
| GB (1) | GB2120645B (en) |
| SE (1) | SE450496B (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS62151080A (en) * | 1985-12-25 | 1987-07-06 | Matsushita Electric Ind Co Ltd | Receiver |
| JPS62156226A (en) * | 1985-12-27 | 1987-07-11 | Nippon Steel Corp | Production of grain oriented electrical steel sheet having uniform glass film and excellent magnetic characteristic |
| FR2718129B1 (en) * | 1994-04-05 | 1996-06-21 | Europ Propulsion | Process for the protection against oxidation of a porous material containing carbon, and material obtained. |
| CN102253166A (en) * | 2011-06-07 | 2011-11-23 | 首钢总公司 | Method for determining activity degree curve of magnesium oxide citric acid for electrical steel |
| DE102013102301A1 (en) * | 2013-03-08 | 2014-09-11 | Chemische Fabrik Budenheim Kg | Coating system based on a combination of monoaluminum phosphate with magnesium oxide |
| CN104831267B (en) * | 2015-04-23 | 2017-12-12 | 包头市威丰稀土电磁材料股份有限公司 | Cold-rolled orientation silicon steel magnesium oxide coating production technology |
| JP7151350B2 (en) | 2017-10-19 | 2022-10-12 | 株式会社デンソー | spark plug for internal combustion engine |
| CN107740079A (en) * | 2017-10-20 | 2018-02-27 | 德清县康祺化学品有限公司 | Can low temperature phosphor metal surface conditioner and preparation method thereof |
Family Cites Families (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2385332A (en) * | 1941-04-23 | 1945-09-25 | American Rolling Mill Co | Production of silicon steel sheet stock having insulative surfaces |
| US3287183A (en) * | 1964-06-22 | 1966-11-22 | Yawata Iron & Steel Co | Process for producing single-oriented silicon steel sheets having a high magnetic induction |
| US3615918A (en) * | 1969-03-28 | 1971-10-26 | Armco Steel Corp | Method of annealing with a magnesia separator containing a decomposable phosphate |
| US3840378A (en) * | 1970-05-22 | 1974-10-08 | Armco Steel Corp | Insulative coatings for electrical steels |
| JPS5113469B2 (en) * | 1972-10-13 | 1976-04-28 | ||
| US3873381A (en) * | 1973-03-01 | 1975-03-25 | Armco Steel Corp | High permeability cube-on-edge oriented silicon steel and method of making it |
| US3841925A (en) * | 1973-09-12 | 1974-10-15 | Morton Norwich Products Inc | Magnesium oxide steel coating composition and process |
| US3905843A (en) * | 1974-01-02 | 1975-09-16 | Gen Electric | Method of producing silicon-iron sheet material with boron addition and product |
| US3905842A (en) * | 1974-01-07 | 1975-09-16 | Gen Electric | Method of producing silicon-iron sheet material with boron addition and product |
| US3957546A (en) * | 1974-09-16 | 1976-05-18 | General Electric Company | Method of producing oriented silicon-iron sheet material with boron and nitrogen additions |
| US3948786A (en) * | 1974-10-11 | 1976-04-06 | Armco Steel Corporation | Insulative coating for electrical steels |
| US4000015A (en) * | 1975-05-15 | 1976-12-28 | Allegheny Ludlum Industries, Inc. | Processing for cube-on-edge oriented silicon steel using hydrogen of controlled dew point |
| GB1597656A (en) * | 1977-05-20 | 1981-09-09 | Armco Inc | Process of producing an electrically insulative glass film on silicon steel |
| BR7804962A (en) * | 1977-08-04 | 1979-05-08 | Armco Inc | PROCESS TO STABILIZE VISCOSITY AND INCREASE THE CONCENTRATION OF Aqueous MAGNESIA PASTE |
| JPS5558331A (en) * | 1978-10-25 | 1980-05-01 | Kawasaki Steel Corp | Forming method for forsterite insulation film of anisotropic silicon steel plate |
| IT1127263B (en) * | 1978-11-28 | 1986-05-21 | Nippon Steel Corp | SEPARATION SUBSTANCE TO BE USED IN THE ANNEALING PHASE OF ORIENTED GRAINS OF SILICON STEEL |
-
1982
- 1982-05-04 CA CA000402189A patent/CA1166804A/en not_active Expired
- 1982-05-06 SE SE8202847A patent/SE450496B/en not_active IP Right Cessation
- 1982-05-06 GB GB8213163A patent/GB2120645B/en not_active Expired
- 1982-05-18 DE DE19823218821 patent/DE3218821C2/en not_active Expired - Fee Related
- 1982-05-19 FR FR8208814A patent/FR2527198B1/en not_active Expired
- 1982-05-26 JP JP8812782A patent/JPS6017027B2/en not_active Expired
- 1982-05-28 BE BE0/208209A patent/BE893342A/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| GB2120645A (en) | 1983-12-07 |
| BE893342A (en) | 1982-11-29 |
| DE3218821C2 (en) | 1994-01-20 |
| SE8202847L (en) | 1983-12-14 |
| DE3218821A1 (en) | 1983-11-24 |
| JPS6017027B2 (en) | 1985-04-30 |
| FR2527198B1 (en) | 1986-04-11 |
| FR2527198A1 (en) | 1983-11-25 |
| JPS58210171A (en) | 1983-12-07 |
| SE450496B (en) | 1987-06-29 |
| GB2120645B (en) | 1987-02-25 |
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