JPS6225751B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to aqueous compositions for forming insulating glass coatings directly on oriented silicon steel strip and sheet stock and methods for stabilizing the viscosity of such aqueous compositions. More specifically, the composition includes a highly concentrated aqueous magnesia slurry stabilized by the addition of a thermally decomposable phosphate-containing compound to achieve a stable low viscosity. In the production of cube-on-edge oriented silicon steel, cold rolled decarburized strip and sheet stock are coated with an aqueous slurry of magnesia and dried at low heat. The coated stock then undergoes a final high temperature annealing at approximately 1095-1260°C during which the magnesia in the coating reacts with the silicon in the surface of the stock to form a glass film and create a cube-on-edge orientation. develops through secondary reconsolidation. 200 to cause a reaction between magnesia and the iron silicate (huayarite) surface layer.
Activated magnesia with a citric acid activity (defined below) of less than 2 seconds is used. Such magnesia becomes hydrated, resulting in increased viscosity. However, the viscosity of the slurry must be kept within a range that allows a coating of uniform thickness to be applied by dipping, spraying, or metering rolls. Although additives to magnesia slurries have been proposed to improve the properties of the glass film and/or to accelerate the reaction of magnesia phaayalite, to the best of the applicant's knowledge no additives have been proposed to reduce and stabilize the viscosity of aqueous magnesia slurries. There are no additives developed in It is known to add degradable phosphates to magnesia annealing separator compositions to improve glass film properties and magnetic properties of silicon steel substrates. Evans (JDEvans and DW
Taylor, US Pat. No. 3,615,918, which discloses magnesia compositions containing degradable phosphates. During the final high temperature anneal which develops the cube-on-edge orientation by secondary recrystallization, 1-25% by weight of phosphate calculated as _P2O5 is reduced to elemental phosphorus, which is transferred from the coating to the silicon steel _. Diffuse inside. Phosphate-based coatings that may be applied directly to metal surfaces or as a secondary coating over a mill glass magnesia basecoat are known in the art. Phosphate and magnesia containing coatings suitable for application directly or as a secondary coating to oriented silicon steel surfaces are disclosed in JDEvans US Pat. Nos. 3,840,378 and 3,948,876. The main source of difficulty with using activated magnesia (with less than 200 seconds of citric acid activity) in an aqueous slurry is the gradual increase in viscosity over time due to hydration. This increase in hydration rate causes variations in the quality of the glass film and also requires a lower viscosity magnesia, which gives the desired lower initial viscosity but removes large amounts of water when drying the coating on the stock surface. Difficulty arises in doing so. The main object of the present invention is to stabilize the viscosity of an aqueous magnesia slurry and provide a method for forming an insulating glass film on a silicon steel plate using an enriched composition. Another object of the present invention is to provide an annealing separator composition as a low stable viscosity aqueous slurry having a substantially higher magnesia concentration than previously used. According to the present invention, in preparing the composition, magnesia has a citric acid activity of less than 200 seconds,
The magnesia as well as calcium phosphate, water-soluble ammonium polyphosphate, aluminum phosphate,
A method is provided for stabilizing the viscosity and increasing the consistency of an aqueous magnesia slurry comprising mixing with water a degradable phosphate compound selected from the group consisting of magnesium phosphate and phosphoric acid, the method comprising: mixing a degradable phosphate compound selected from the group consisting of magnesium phosphate and phosphoric acid with water, the method comprising: mixing a degradable phosphate compound selected from the group consisting of magnesium phosphate ^and phosphoric acid;
Sufficient said magnesia is added to provide 0.1 to 0.24 g and said phosphate compound is based on the weight _of magnesia and calculated as _P2O5 .
Sufficient amount is added to provide 0.5 to about 25% by weight. The present invention further provides a degradable slurry selected from the group consisting of an aqueous slurry of magnesium oxide, calcium phosphate, water-soluble ammonium polyphosphate, aluminum phosphate, magnesium phosphate, phosphoric acid, and mixtures thereof, having a citric acid activity of less than 200 seconds. A composition is provided for forming an insulating glass film on the surface of silicon steel strips and sheets containing a phosphate-containing compound, wherein the phosphate-containing compound is calculated as P ₂ O ₅ based on the weight of magnesia. 0.5~
25% by weight and the concentration of magnesia is in the range of 0.1 to about 0.24 g/cm ³ of the slurry, the viscosity of the slurry being virtually constant over a longer period of time. Preferred phosphoric acid compounds are monocalcium phosphate monohydrate and water-soluble ammonium polyphosphate. When using ammonium polyphosphate, it has been found that the addition of about 2 to 4 weight percent chromic oxide, based on the weight of magnesia, provides optimal glass film properties. When monocalcium phosphate monohydrate is used, addition of dichromic oxide is not necessary to improve glass film properties. Citric acid activity is a standard for the rate of hydration of magnesium oxide, determined by measuring the time required for a given amount of magnesia to provide enough hydroxyl ions to neutralize a given amount of citric acid. be done. The test is similar to that described in U.S. Pat. No. 3,841,925, namely: 1. 100 ml of 0.400N aqueous citric acid containing 2 ml of 1% phenolphthalein indicator brought to 30°C in an 8 oz jar. . The bottle is fitted with a screw cap and a magnetic stirring bar. 2.Pour 200g of magnesia into the bottle and start the stopwatch at the same time. 3 Immediately after adding the magnesia sample, cap the jar. Shake bottle and contents vigorously at 5 seconds. Stop shaking at 10 seconds. 4 Place the sample on the magnetic stirrer at 10 seconds.
Mechanical agitation should create a vortex approximately 2 cm deep at the center when the inner diameter of the bottle is 6 cm. 5. When the suspension turns light pink, stop the stopwatch and record the time. The number of seconds of this time is the citric acid activity. Cold rolled decarburized silicon steel strip and sheet stock may be produced by conventional methods of casting a suitable melt in ingot form or continuous casting in slab form. If cast into ingots, the steel is conventionally bloomed into slabs and the slabs are hot rolled to medium thickness, preferably at a temperature of about 1200 to 1400°C, and preferably annealed after hot rolling. do. The hot mill scale is then removed and the material is cold rolled in one or more stages to final gauge and then decarburized in a hydrogen atmosphere. If the steel is continuously cast in slab form, Littmann (M.
It is preferred to follow the method disclosed in US Pat. No. 3,764,406 to F. Littmann. A coating of magnesia slurry is then applied to the surface of the decarburized stock by dipping, spraying, metering roll, or other conventional methods. The coating is then dried by heating to a temperature sufficient to evaporate the water and leave a dry coating on the surface. The coverage should be about 6-20 g/m ² , preferably about 11 g/m ² . The coated stock is then subjected to a final high temperature anneal at about 1095-1260°C in a reducing atmosphere. It may be a box annealing or an open coil annealing. During this annealing, magnesia reacts with the silicon steel surface to form a glass film, and secondary recrystallization results in cube-on
Edge orientation is achieved. Magnesia suitable for the practice of this invention has the following specifications: Cl ^- (like NaCl): 0.02% Maximum CaO: 0.020% Maximum loss on ignition (1000°C): 1.5-3.0% Citric acid activity: less than 200 seconds
(Preferably 25-40 seconds) Sieve analysis: 200 meshes passing minimum 99.9% 325 meshes passing minimum 99.5%. The composition of the silicon steel and the method of processing it into final strip and sheet form do not form the scope of this invention. Oriented silicon steels of standard or high permeability grades that utilize magnesia coatings may be treated in accordance with the present invention. Non-limiting examples of compositions and methods in which the present invention finds utility include U.S. Pat.
No. 3905843, No. 3932234, No. 3957546 and No.
4000015 is included.
With the exception of No. 3932234, these patents relate to the production of high permeability materials (relative permeability greater than 1850 at 796 A/m) by adding boron and nitrogen to steel. Manganese and sulfur [and/or selenium] may also be present. For conventional grain-oriented silicon steels in which manganese and sulfur [and/or selenium] are present as grain growth inhibitors, a typical but non-limiting composition for cold-rolled, decarburized stock is contains about 2-4% silicon and about 0.01-4% manganese by weight.
0.4%, sulfur approx. 0.01~0.03%, carbon approx. 0.002~0.005
%, up to about 0.065% (total) aluminum, and the balance iron and associated elements. As described above, after applying a uniform coating of magnesia slurry to the steel surface, e.g. by a metering groove roll, low heating, e.g.
Dry for up to 5 minutes. The coating includes magnesium oxide, magnesium hydroxide, and a degradable phosphate compound, which decomposes during the subsequent elevated temperature portion of the final anneal. The phosphates are reduced to form elemental phosphorus, which diffuses harmlessly into the steel, while at the same time the silicon in the steel surface layer is further oxidized and therefore reacts with magnesia as the annealing temperature increases. seems to be encouraged. In conventional aqueous magnesia rallies using magnesia of the above specification, the concentration of magnesia usually does not exceed about 0.08 g/cm ³ to obtain a viscosity that allows coating by conventional methods. In contrast, in the practice of the present invention, ^{approximately}
A magnesia concentration of 0.1 to 0.24 g can be used at a viscosity suitable for application in conventional methods, and it is stable for long periods of time, up to at least 1 hour. Degradable phosphate compounds that can be used to reduce and stabilize the viscosity of magnesia in aqueous slurries include monocalcium phosphate monohydrate, dibasic calcium phosphate, tribasic calcium phosphate, water-soluble ammonium polyphosphate, Included are aluminum acids, magnesium phosphates, or phosphoric acids or mixtures thereof. Excellent results were obtained from an aqueous solution of ammonium polyphosphate (allied chemical company under the trademark "Arcadian PolyN").
Granular monocalcium phosphate monohydrate (sold under the name "12" by Stauffer Chemical Corporation) and granulated monocalcium phosphate monohydrate
Company). In the case of an aqueous solution of ammonium polyphosphate, it is added to the water of the aqueous slurry before or after mixing with magnesia. In the case of monocalcium phosphate monohydrate, it is in granular form and the material can be dry blended with magnesia before forming an aqueous slurry, or mixed into water before, during or after mixing with magnesia. . Therefore, the method and steps of charging the phosphate compound into the slurry do not constitute the scope of the practice of this invention. The amount of phosphate compound is preferably about 0.5 to ₁₀ , calculated as _P2O5 based on the weight of magnesia.
Weight%. A minimum addition of 0.5% calculated as P ₂ O ₅ was found to be critical, but the upper limit is determined by the detrimental effect on the appearance of the glass membrane. Addition of more than about 15% by weight calculated as P ₂ O ₅ is undesirable because iron globules tend to develop in the glass film. A magnesia slurry was tested using magnesia that fell within the specifications and had a citric acid activity value of about 30-50 seconds. Varying amounts of ammonium polyphosphate and various magnesia concentrations were tested for viscosity change over time and the results are summarized in the table. In the table, control samples 1 and 2, which did not contain ammonium polyphosphate, significantly increased in viscosity to 4700 and 4070 centipoise, respectively, after 45 minutes. In contrast, samples 3-9, representing slurries of the present invention, exhibited low and stable viscosities after 45 minutes.
In some cases the viscosity was lower than in the mixed state after 45 minutes. Although not shown in the table, Samples 6 and 7 were held for an additional period of up to 80 minutes and their respective viscosities increased to 45
It was acknowledged that the value remained virtually the same as the minute value. Silicon steel specimens having the compositions listed above were then coated with the series of slurries shown in the table after 45 minutes of hydration using a metered groove roll. The coverage was varied from about 10 to 21 g/m ² . After drying the specimens, they were annealed in hydrogen at 1205°C with soaking for 22 hours. Iron loss and permeability, and U.S. Pat.
The adhesion of secondary coatings of the type disclosed in US Pat. No. 3,948,876 was measured and is shown in the table. It is clear that improved iron loss was obtained with increasing phosphate content _up to 4.4% _P2O5 . Furthermore, it was also observed that the addition of phosphate improved the oxidation resistance of the glass membrane. No coating problems were encountered with any of the phosphate-containing slurries. Additional tests were conducted using monocalcium phosphate monohydrate, which was mixed in granular form with the same type of magnesia used in the sample. Slurries with varying concentrations were prepared. All contain 2.5% _P2O5 based on the weight _of magnesia. The viscosity measurements of these series of slurries are shown in the table. Additional examples tested ignition loss on samples of 0 to 7.5% _P2O5 based on the weight _of magnesia. It is a standard for the degree of hydration, samples of which are also shown in the table. Again, a stabilization of the viscosity and a significant reduction in hydration are evident as a result of the addition of monocalcium phosphate monohydrate.

【table】

【table】

Further tests were conducted with varying concentrations of monocalcium phosphate monohydrate and magnesia, and viscosity measurements were made for longer hydration times up to 2 hours. The magnesia source and type of phosphate compound were the same as those of samples 10-18. The results are shown in the table. All calcium phosphate additions in slurries having a magnesia concentration of 0.144 g/c.c. of slurry lowered and stabilized the viscosity of the slurry.
In fact, after 120 minutes, the phosphate-containing slurries have virtually equal viscosities, so viscosity is independent of phosphate percentage above the minimum amount of phosphate required for stabilization for a given magnesia concentration. It is shown that Magnesia 0.192g/cc, 5% phosphate (P ₂ O ₅
Phosphate 5% had only a slight effect on the viscosity after 120 minutes of hydration at a concentration of
The addition of clearly stabilized the viscosity during the 60 min hydration time. Addition of 10% and 20% phosphate reduced the viscosity at 120 minutes. Other degradable phosphate-containing compounds have been tested and found to work similarly to those described above. CaHPO ₄ 2H ₂ O using the same activated magnesia as above in the table.
(dibasic calcium phosphate) and 3Ca ₃ (PO ₄ ) ₂・Ca
The viscosity measurements of magnesia slurry prepared by adding (OH) ₂ (tertiary calcium phosphate) are shown. It should be noted that monocalcium phosphate monohydrate is water soluble, dibasic calcium phosphate is only slightly water soluble, and tribasic calcium phosphate is insoluble in water. Since all three compounds can be used in the compositions and methods of the present invention, the solubility of these calcium phosphates is not critical as far as operation is concerned. On the other hand, ammonium polyphosphate, which is insoluble in water, was found to be ineffective. Furthermore, the tricalcium phosphate content, calculated as P ₂ O ₅ , was insufficient to stabilize the viscosity for more than 30 minutes at the magnesia concentration of the slurry.

【table】

【table】

Claims (1)

[Claims] 1. A decomposable phosphate selected from the group consisting of magnesia and calcium phosphate, water-soluble ammonium polyphosphate, aluminum phosphate, magnesium phosphate, phosphoric acid, and mixtures thereof, having a citric acid activity of 1200 sec or less. In a method of forming an insulating glass film on the surface of a silicon steel strip or sheet using a composition comprising an aqueous slurry with a compound, in preparing the composition, the magnesia is added to 1 cm ³ of the slurry. and 0.5 to 25% by weight of said phosphate compound calculated as P ₂ O ₅ based on the weight of magnesia. A method of using an aqueous slurry composition of magnesia characterized by: 2. The method according to claim 1, wherein the phosphate-containing compound is ammonium polyphosphate. 3. The method of claim 1, wherein the phosphate-containing compound is monocalcium phosphate monohydrate. 4. The method of claim 1, wherein the amount of phosphate-containing compound is sufficient to provide from 0.5 to ₁₀ % by weight calculated as _P2O5 based on the weight of magnesia. 5 The amount of ammonium polyphosphate is 0.5 to 4.5 calculated as P ₂ O ₅ based on the weight of magnesia.
3. A method according to claim 2, wherein the method is sufficient to give % by weight. 6. The method of claim 2 including the step of adding 2 to 4% by weight of chromic oxide based on the weight of magnesia. 7. An aqueous slurry of magnesia having a citric acid activity of 200 seconds or less and a decomposable phosphate compound selected from the group consisting of calcium phosphate, water-soluble ammonium polyphosphate, aluminum phosphate, magnesium phosphate, phosphoric acid, and mixtures thereof. A composition for forming an insulating glass film on the surface of silicon steel strips and sheets comprising, on a weight basis of magnesia, said phosphate-containing compound;
0.5-25% by weight calculated as _P2O5 is present and the concentration of magnesia is _0.1-25 % by weight per ^cm3 of slurry.
0.24 g and wherein the viscosity of the slurry is substantially constant over an extended period of time. 8. The composition according to claim 7, wherein the phosphate-containing compound is ammonium polyphosphate. 9. The composition of claim 7, wherein the phosphate-containing compound is monocalcium phosphate monohydrate. 10 The phosphate-containing compound is 0.5 to 10% by weight calculated as P ₂ O ₅ based on the weight of magnesia.
A composition according to claim 7 within the scope of claim 7. 11. The composition of claim 8, wherein said ammonium polyphosphate is in the range of 0.5 to _4.5 % by weight calculated as _P2O5 based on the weight of magnesia. 12. The composition according to claim 8, containing 2 to 4% by weight of chromic oxide based on the weight of magnesia.