A protective slag for producing silicon-manganese spring steel and a preparation method thereof

Abstract

The invention discloses a protective slag for producing silicon-manganese spring steel and a preparation method thereof, belonging to the technical field of protective slag. The preparation method comprises the following steps: adding premelt powder, composite carbon powder and carbon black into a stirrer, stirring and mixing, then adding deionized water accounting for 65-70% of the total raw material mass and dextrin accounting for 1-1.2% of the total raw material mass, stirring at 200-300r / min for 1-1.5h, transferring the obtained mixed slurry to a spray drying tower for spray granulation, vibrating and screening, and obtaining protective slag for producing silicon-manganese spring steel with a particle size of 0.15-1mm. Rare earth components CeO2 and La2O3 are added into the protective slag, so that the protective slag can improve the absorption capacity of the protective slag for inclusions in the silicon-manganese spring steel ingot, thereby helping to improve the purity of the silicon-manganese spring steel and reduce surface cracks on the ingot, and has good application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of protective slag, and specifically relates to protective slag for producing silicon-manganese spring steel and a preparation method thereof. Background Art

[0002] Silicon manganese spring steel is a high-performance spring steel widely used in machinery manufacturing, automobile industry and railway vehicles, with excellent elasticity, strength and wear resistance. In the production process of silicon manganese spring steel, the raw materials need to be smelted in an electric furnace or converter, then continuously cast into billets, hot rolled and then quenched and tempered to optimize its performance.

[0003] Protective slag is a synthetic slag that covers the surface of molten steel during the continuous casting process. Its functions generally include the following aspects: (1) insulation and heat preservation to prevent heat dissipation; (2) isolation of air to prevent oxygen in the air from entering the molten steel and causing secondary oxidation, which affects the quality of the steel; (3) absorption and dissolution of inclusions that float from the molten steel to the slag interface to purify the molten steel; (4) a layer of slag film between the crystallizer wall and the solidified shell acts as a lubricant, reducing the resistance to billet drawing and preventing the solidified shell from sticking to the copper plate; (5) filling the air gap between the billet shell and the crystallizer to improve the heat transfer of the crystallizer.

[0004] Since the production process of silicon-manganese spring steel has extremely high requirements on steel purity, inclusion control and surface quality, these characteristics directly affect the design direction of the protective slag. Summary of the invention

[0005] The object of the present invention is to provide a protective slag for the production of silicon-manganese spring steel and a preparation method thereof, by adding a three-dimensional porous Ce0 2 The composite carbon powder can enhance the absorption capacity of the protective slag on inclusions in the silicon-manganese spring steel and improve the purity of the silicon-manganese spring steel.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A protective slag for the production of silicon-manganese spring steel, the chemical composition of which, by mass percentage, includes:

[0008] CaO: 27.10-30.77%, Si0 2 :29.30-33.84%,Al 2 O 3 :7.85-9.37%, MgO: 5.58-8.76%, Fe 2 O 3 :2.05-2.83%, Ce0 2 :3.24-3.89%, La 2 O 3: 0.33-0.45%, C: 9.28-11.52%, F: 5.17-5.72, and the balance is inevitable impurities.

[0009] A method for preparing protective slag for producing silicon-manganese spring steel comprises the following steps:

[0010] Step 1: quartz sand, limestone, cement clinker, fused magnesia, boric anhydride and cerium oxide powder are sieved through 200 mesh sieves respectively, ball-milled and mixed, and then transferred to a high-temperature electric furnace, kept warm at 1500-1600°C for 30-50 minutes, naturally cooled, crushed, ball-milled, and sieved through 200 mesh sieve to obtain pre-melted material powder.

[0011] Step 2: Add the premelt powder, composite carbon powder and carbon black into a mixer and stir and mix, then add 65-70% of the total raw material mass of deionized water and 1-1.2% of the total raw material mass of dextrin, continue stirring at 200-300r / min for 1-1.5h, transfer the mixed slurry to a spray drying tower for spray granulation, vibrate and screen, and obtain protective slag for silicon-manganese spring steel production with a particle size of 0.15-1mm. The total raw materials are premelt powder, composite carbon powder and carbon black.

[0012] Furthermore, during the spray granulation process, the inlet temperature of the spray drying tower is 640-650°C, the outlet temperature is 140-150°C, the spray gun pressure is 0.8-1MPa, the spray blade specification is 1.8mm, and the rotary blade specification is 3mm.

[0013] Furthermore, the basicity of the protective slag for silicon-manganese spring steel production is 0.8-1.05, the hemisphere point is 1070-1130℃, the melting speed at 1300℃ is 30-50s, the viscosity at 1300℃ is 0.15-0.24Pa.s, and the bulk density is 0.6-0.85g / cm 3 .

[0014] Further, the composite carbon powder is prepared by the following steps:

[0015] Step 1: Add micron graphite powder with a particle size of 20-40 μm and nitric acid solution with a mass fraction of 65% into a reactor in a mass ratio of 1:10-20, stir for 4-6 hours at 60-80°C and 200-300 r / min, filter, wash the filter cake with deionized water until the last washing liquid is neutral, and vacuum dry to obtain acidified graphite powder containing a large amount of carboxyl groups.

[0016] Step 2: Add the acidified graphite powder into a reactor and disperse it ultrasonically with deionized water, then add cerium nitrate hexahydrate into the reactor, stir at 200-300 r / min for 40-60 min, cerium ions are adsorbed on the surface and pores of the acidified graphite powder through the chelation of carboxyl groups, then dissolve 1,3,5-benzenetricarboxylic acid as an organic ligand with anhydrous ethanol and add it into the reactor, stir and react for 3-4 hours at 60-70°C and 300-500 r / min, filter, wash the filter cake with anhydrous ethanol until the last washing liquid is neutral, and vacuum dry to obtain a supported graphite powder loaded with a cerium-based metal organic framework.

[0017] Step 3: Transfer the supported graphite powder to a muffle furnace and calcine it at 300-350°C in a nitrogen atmosphere for 3-3.5 hours, and then at 550-600°C for 20-30 minutes. The organic matter in the cerium-based metal organic framework is carbonized, and the cerium is converted into a three-dimensional porous Ce0 2 The form is retained, and after natural cooling, it is passed through a 300-mesh sieve to obtain composite carbon powder.

[0018] Furthermore, the usage ratio of the acidified graphite powder, deionized water, cerium nitrate hexahydrate, 1,3,5-benzenetricarboxylic acid and anhydrous ethanol is 10 g: 300-500 mL: 17.35 g: 8.55 g: 300-500 mL.

[0019] Beneficial effects of the present invention:

[0020] The protective slag for silicon-manganese spring steel production of the present invention has a reasonable ratio of chemical components, has a suitable basicity (0.8-1.05), can effectively adjust the melting speed, viscosity and hemisphere point, and meets the requirements of the silicon-manganese spring steel continuous casting process. The protective slag contains rare earth component CeO 2 and La 2 O 3 It can improve the ability of the protective slag to absorb inclusions in the silicon-manganese spring steel ingot, thereby helping to improve the purity of the silicon-manganese spring steel and reduce surface cracks on the ingot, and has good application prospects.

[0021] In the production process of protective slag for silicon-manganese spring steel of the present invention, CeO 2 Cerium oxide is dispersed on the surface of graphite particles in the form of a porous skeleton, which can effectively prevent their agglomeration and improve CeO 2 The dispersion and stability in the mold slag improves the lubrication performance of the mold slag. 2 The precursor of the component is a cerium-based metal organic framework with a three-dimensional porous structure. Compared with directly adding CeO 2 , can provide a larger specific surface area and can more effectively adsorb inclusions in silicon-manganese spring steel. DETAILED DESCRIPTION

[0022] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] Example 1: This example provides a protective slag for the production of silicon-manganese spring steel, which is prepared by the following method:

[0024] S1: Add micron graphite powder with a particle size of 20-40 μm and nitric acid solution with a mass fraction of 65% into a reactor in a mass ratio of 1:10, stir for 6 hours at 60°C and 200 r / min, filter, wash the filter cake with deionized water until the last washing liquid is neutral, and vacuum dry to obtain acidified graphite powder.

[0025] S2: 100 kg of acidified graphite powder was added into a reactor and ultrasonically dispersed with 3000 L of deionized water. Then, 173.5 kg of cerium nitrate hexahydrate was added into the reactor and stirred at 200 r / min for 40 min. Then, 85.5 kg of 1,3,5-benzenetricarboxylic acid was dissolved with 3000 L of anhydrous ethanol and added into the reactor. The reaction was stirred at 60°C and 300 r / min for 3 h. The filter cake was washed with anhydrous ethanol until the last washing liquid was neutral. The filter cake was dried under vacuum to obtain a supported graphite powder with a cerium-based metal organic framework.

[0026] S3: The supported graphite powder was transferred to a muffle furnace, calcined at 300°C in a nitrogen atmosphere for 3 h, and then calcined at 550°C for 20 min. After natural cooling, the powder was sieved through a 300-mesh sieve to obtain a composite carbon powder.

[0027] S4: quartz sand, limestone, cement clinker, fused magnesia, boric anhydride and cerium oxide powder are sieved through 200 mesh sieves respectively, ball-milled and mixed, transferred to a high-temperature electric furnace, kept warm at 1500°C for 30 minutes, naturally cooled, crushed, ball-milled, sieved through 200 mesh sieves, and pre-melted material powder is obtained.

[0028] S5: Add the premelt powder, composite carbon powder and carbon black into a mixer and stir to mix, then add 65% of the total raw material mass of deionized water and 1% of the total raw material mass of dextrin, with dextrin as a binder, and continue stirring at 200r / min for 1h to obtain a mixed slurry, and then transfer it to a spray drying tower for spray granulation. During the spray granulation process, the inlet temperature of the spray drying tower is 640°C, the outlet temperature is 140°C, the spray gun pressure is 0.8MPa, the spray blade specification is 1.8mm, and the rotary blade specification is 3mm. The obtained powder is vibrated and sieved to obtain protective slag for silicon-manganese spring steel production with a particle size of 0.15-1mm.

[0029] The chemical composition of the mold slag includes CaO: 27.10%, Si0 2 :33.84%,Al 2 O 3 :7.85%, MgO:8.76%, Fe 2 O 3 :2.83%, Ce0 2 :3.24%, La 2 O 3 : 0.33%, C: 9.28%, F: 5.17, and the remainder are inevitable impurities.

[0030] The basicity of the protective slag is 0.8, the hemisphere point is 1070℃, the melting speed at 1300℃ is 50s, the viscosity at 1300℃ is 0.15Pa.s, and the bulk density is 0.6g / cm 3 .

[0031] The protective slag of this embodiment was tested in a domestic factory when producing 60Si2Mn spring steel ingots. During the continuous casting process, the protective slag spread smoothly in the crystallizer without crusting and slagging, the flame was moderate and melted evenly, and there were no longitudinal cracks on the surface of the ingot. The ingot was analyzed using the Zeiss EVO18 inclusion analysis system, and the number of inclusions on the surface of the ingot was 3 / mm 2 .

[0032] Example 2: This example provides a protective slag for the production of silicon-manganese spring steel, which is prepared by the following method:

[0033] S1: Add micron graphite powder with a particle size of 20-40 μm and nitric acid solution with a mass fraction of 65% into a reactor in a mass ratio of 1:15, stir for 5 hours at 70°C and 250 r / min, filter, wash the filter cake with deionized water until the last washing liquid is neutral, and vacuum dry to obtain acidified graphite powder.

[0034] S2: 100 kg of acidified graphite powder was added into a reactor and ultrasonically dispersed with 4000 L of deionized water. Then, 173.5 kg of cerium nitrate hexahydrate was added into the reactor and stirred at 250 r / min for 50 min. Then, 85.5 kg of 1,3,5-benzenetricarboxylic acid was dissolved with 4000 L of anhydrous ethanol and added into the reactor. The reaction was stirred at 65°C and 400 r / min for 3.5 h. The filter cake was washed with anhydrous ethanol until the last washing liquid was neutral. The filter cake was dried under vacuum to obtain a supported graphite powder with a cerium-based metal organic framework.

[0035] S3: The supported graphite powder was transferred to a muffle furnace, calcined at 325°C in a nitrogen atmosphere for 3.2 h, and then calcined at 580°C for 25 min. After natural cooling, the powder was sieved through a 300-mesh sieve to obtain a composite carbon powder.

[0036] S4: quartz sand, limestone, cement clinker, fused magnesia, boric anhydride and cerium oxide powder are sieved through 200 mesh sieves respectively, ball-milled and mixed, transferred to a high-temperature electric furnace, kept warm at 1550°C for 40 minutes, naturally cooled, crushed, ball-milled, sieved through 200 mesh sieve, and pre-melted material powder is obtained.

[0037] S5: Add the pre-melt powder, composite carbon powder and carbon black into a mixer and stir to mix, then add 68% of the total raw material mass of deionized water and 1.1% of the total raw material mass of dextrin, continue stirring at 250r / min for 1.2h, and transfer the mixed slurry to a spray drying tower for spray granulation. During the spray granulation process, the inlet temperature of the spray drying tower is 645℃, the outlet temperature is 145℃, the spray gun pressure is 0.9MPa, the spray blade specification is 1.8mm, and the rotary blade specification is 3mm. The obtained powder is vibrated and sieved to obtain protective slag for silicon-manganese spring steel production with a particle size of 0.15-1mm.

[0038] The chemical composition of the mold slag includes CaO: 29.55%, Si0 2 :30.45%,Al 2 O 3 :9.37%, MgO:5.58%, Fe 2 O 3 :2.35%, Ce0 2 :3.89%, La 2 O 3 : 0.45%, C: 11.52%, F: 5.45, and the remainder are inevitable impurities.

[0039] The basicity of the protective slag is 0.97, the hemisphere point is 1102℃, the melting speed at 1300℃ is 41s, the viscosity at 1300℃ is 0.21Pa.s, and the bulk density is 0.85g / cm 3 .

[0040] The protective slag of this embodiment was tested in a domestic factory when producing 60Si2Mn spring steel ingots. During the continuous casting process, the protective slag spread smoothly in the crystallizer without crusting and slagging, the flame was moderate and melted evenly, and there was no longitudinal crack on the surface of the ingot. The ingot was analyzed using the Zeiss EVO18 inclusion analysis system, and the number of inclusions on the surface of the ingot was 1 / mm 2 .

[0041] Example 3: This example provides a protective slag for the production of silicon-manganese spring steel, which is prepared by the following method:

[0042] S1: Add micron graphite powder with a particle size of 20-40 μm and nitric acid solution with a mass fraction of 65% into a reactor in a mass ratio of 1:20, stir for 4 hours at 80°C and 300 r / min, filter, wash the filter cake with deionized water until the last washing liquid is neutral, and vacuum dry to obtain acidified graphite powder.

[0043] S2: 100 kg of acidified graphite powder was added into a reactor and ultrasonically dispersed with 5000 L of deionized water. Then, 173.5 kg of cerium nitrate hexahydrate was added into the reactor and stirred at 300 r / min for 60 min. Then, 85.5 kg of 1,3,5-benzenetricarboxylic acid was dissolved with 5000 L of anhydrous ethanol and added into the reactor. The reaction was stirred at 70°C and 500 r / min for 4 h. The filter cake was washed with anhydrous ethanol until the last washing liquid was neutral. The filter cake was dried under vacuum to obtain a supported graphite powder with a cerium-based metal organic framework.

[0044] S3: The supported graphite powder was transferred to a muffle furnace, calcined at 350°C in a nitrogen atmosphere for 3.5 h, and then calcined at 600°C for 30 min. After natural cooling, the powder was sieved through a 300-mesh sieve to obtain a composite carbon powder.

[0045] S4: quartz sand, limestone, cement clinker, fused magnesia, boric anhydride and cerium oxide powder are sieved through 200 mesh sieves respectively, ball-milled and mixed, transferred to a high-temperature electric furnace, kept warm at 1600°C for 50 minutes, naturally cooled, crushed, ball-milled, sieved through 200 mesh sieve, and pre-melted material powder is obtained.

[0046] S5: Add the pre-melted material powder, composite carbon powder and carbon black into a mixer and stir to mix, then add 70% of the total raw material mass of deionized water and 1.2% of the total raw material mass of dextrin, continue stirring at 300r / min for 1.5h, and transfer the mixed slurry to a spray drying tower for spray granulation. During the spray granulation process, the inlet temperature of the spray drying tower is 650℃, the outlet temperature is 150℃, the spray gun pressure is 1MPa, the spray blade specification is 1.8mm, and the rotary blade specification is 3mm. The obtained powder is vibrated and sieved to obtain protective slag for silicon-manganese spring steel production with a particle size of 0.15-1mm.

[0047] The chemical composition of the mold slag includes CaO: 30.77%, Si0 2 :30.45%,Al 2 O 3 :9.37%, MgO:5.58%, Fe 2 O 3 :2.05%, Ce0 2 :3.53%, La 2 O 3 : 0.41%, C: 10.76%, F: 5.72, and the remainder are inevitable impurities.

[0048] The basicity of the protective slag is 1.05, the hemisphere point is 1130℃, the melting speed at 1300℃ is 30s, the viscosity at 1300℃ is 0.24Pa.s, and the bulk density is 0.78g / cm 3 .

[0049] The protective slag of this embodiment was tested in a domestic factory when producing 60Si2Mn spring steel ingots. During the continuous casting process, the protective slag spread smoothly in the crystallizer without crusting and slagging, the flame was moderate and melted evenly, and there were no longitudinal cracks on the surface of the ingot. The ingot was analyzed using the Zeiss EVO18 inclusion analysis system, and the number of inclusions on the surface of the ingot was 2 / mm 2 .

[0050] Comparative Example 1: Based on Example 2, in step S5, the composite carbon powder is replaced with micron graphite powder, and the other steps remain unchanged to prepare protective slag.

[0051] The chemical composition of the mold slag includes CaO: 31.54%, Si0 2 :31.21%,Al 2 O 3 :9.60%, MgO:5.72%, Fe 2 O 3 :2.10%, La 2 O 3: 0.42%, C: 11.03%, F: 5.86, and the remainder are inevitable impurities.

[0052] The basicity of the protective slag is 1.01, the hemisphere point is 1138℃, the melting speed at 1300℃ is 32s, the viscosity at 1300℃ is 0.21Pa.s, and the bulk density is 0.88g / cm 3 .

[0053] The protective slag of this comparative example was tested in a domestic factory when producing 60Si2Mn spring steel ingots. During the continuous casting process, the protective slag spread smoothly in the crystallizer without crusting and slagging. The flame was moderate and melted evenly, but cracks appeared on the surface of the ingot. The Zeiss EVO18 inclusion analysis system was used to analyze the ingot, and the number of inclusions on the surface of the ingot was 16 / mm. 2 .

[0054] Comparative Example 2: Based on Comparative Example 1, commercially available cerium oxide powder was added as Ce0 during the preparation of the pre-melt powder. 2 The content of each chemical component by weight was adjusted to be consistent with that in Example 2 to prepare the protective slag.

[0055] The basicity of the protective slag is 0.97, the hemisphere point is 1105℃, the melting speed at 1300℃ is 40s, the viscosity at 1300℃ is 0.21Pa.s, and the bulk density is 0.89g / cm 3 .

[0056] The protective slag of this comparative example was tested in a domestic factory when producing 60Si2Mn spring steel ingots. During the continuous casting process, the protective slag spread smoothly in the crystallizer without crusting and slagging, the flame was moderate and melted evenly, and there was no crack on the surface of the ingot. The ingot was analyzed using the Zeiss EVO18 inclusion analysis system, and the number of inclusions on the surface of the ingot was 9 / mm 2 .

[0057] It can be seen from the test results in the examples and comparative examples that the protective slag in the examples can reduce the number of inclusions in the silicon-manganese spring steel ingot and improve the purity of the silicon-manganese spring steel.

[0058] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0059] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing mold slag for silicon-manganese spring steel production, characterized in that: The preparation method comprises the following steps: The premelt powder, composite carbon powder and carbon black are added into a mixer and stirred and mixed, and then 65-70% of the total raw material weight of deionized water and 1-1.2% of the total raw material weight of dextrin are added, and stirred at 200-300r / min for 1-1.5h to obtain a mixed slurry, which is then transferred to a spray drying tower for spray granulation, and vibrated and sieved to obtain protective slag for silicon-manganese spring steel production with a particle size of 0.15-1mm; The composite carbon powder is prepared by the following steps: The acidified graphite powder is added into a reaction kettle and ultrasonically dispersed with deionized water, and then cerium nitrate hexahydrate is added into the reaction kettle, and stirred at 200-300 r / min for 40-60 min, and then 1,3,5-benzenetricarboxylic acid is dissolved with anhydrous ethanol and added into the reaction kettle, and stirred for reaction at 60-70° C. and 300-500 r / min for 3-4 h, and filtered, and the filter cake is washed with anhydrous ethanol until the last washing liquid is neutral, and vacuum dried to obtain a supported graphite powder loaded with a cerium-based metal organic framework; The supported graphite powder is transferred to a muffle furnace, calcined at 300-350° C. in a nitrogen atmosphere for 3-3.5 hours, and then calcined at 550-600° C. for 20-30 minutes. After natural cooling, the powder is sieved through a 300-mesh sieve to obtain a composite carbon powder.

2. The method for preparing mold slag for silicon-manganese spring steel production according to claim 1, characterized in that: The premelt powder is prepared by the following steps: The quartz sand, limestone, cement clinker, fused magnesia, boric anhydride and cerium oxide powders are sieved through 200 meshes respectively, ball-milled and mixed, and then transferred to a high-temperature electric furnace, kept at 1500-1600°C for 30-50 minutes, naturally cooled, crushed, ball-milled, and sieved through 200 meshes to obtain pre-melted material powder.

3. The method for preparing mold slag for silicon-manganese spring steel production according to claim 1, characterized in that: In the spray granulation process, the inlet temperature of the spray drying tower is 640-650° C., the outlet temperature is 140-150° C., the spray gun pressure is 0.8-1 MPa, the spray blade specification is 1.8 mm, and the rotary blade specification is 3 mm.

4. The method for preparing mold slag for silicon-manganese spring steel production according to claim 1, characterized in that: The dosage ratio of the acidified graphite powder, deionized water, cerium nitrate hexahydrate, 1,3,5-benzenetricarboxylic acid and anhydrous ethanol is 10g:300-500mL:17.35g:8.55g:300-500mL.

5. The method for preparing mold slag for silicon-manganese spring steel production according to claim 1, characterized in that: The acidified graphite powder is prepared by the following steps: Micron graphite powder with a particle size of 20-40 μm and nitric acid solution with a mass fraction of 65% are added into a reactor in a mass ratio of 1:10-20, stirred for 4-6 hours at 60-80°C and 200-300 r / min, filtered, washed the filter cake with deionized water until the last washing liquid is neutral, and vacuum dried to obtain acidified graphite powder.

6. A protective slag for the production of silicon-manganese spring steel, characterized in that: The invention is prepared by the method for preparing protective slag for producing silicon-manganese spring steel as described in any one of claims 1 to 5.

7. The protective slag for producing silicon-manganese spring steel according to claim 6, characterized in that: Calculated by mass percentage, its chemical composition includes: CaO: 27.10-30.77%, Si02: 29.30-33.84%, Al2O3: 7.85-9.37%, MgO: 5.58-8.76%, Fe2O3: 2.05-2.83%, Ce02: 3.24-3.89%, La2O3: 0.33-0.45%, C: 9.28-11.52%, F: 5.17-5.72, and the remainder is unavoidable impurities.

8. The protective slag for producing silicon-manganese spring steel according to claim 7, characterized in that: The protective slag for silicon-manganese spring steel production has a basicity of 0.8-1.05, a hemisphere point of 1070-1130°C, a melting speed of 30-50s at 1300°C, a viscosity of 0.15-0.24Pa.s at 1300°C, and a bulk density of 0.6-0.85g / cm 3 .