KR20010064094A - Sintered zirconia partly stabilized by magnesia - Google Patents

Abstract

PURPOSE: A zirconia sintering compact partially stabilizing magnesia is provided which has superior physical properties such as heat impact property, response property and change of electromotive force by adding constituents having superior properties sensing oxygen in molten steel to a magnesia zirconia solid electrolyte composition. CONSTITUTION: The zirconia sintering compact partially stabilizing magnesia comprises 0.05 to 0.2 wt.% of alumina for the total amount of sintering compact, 0.1 to 0.2 wt.% of silicon oxide for the total amount of sintering compact, 0.02 to 0.05 wt.% of iron oxide for the total amount of sintering compact, 0.02 to 0.05 wt.% of titanium oxide for the total amount of sintering compact, 0.005 to 0.01 wt.% of calcium oxide for the total amount of sintering compact, 0.005 to 0.01 wt.% of calcium carbonate for the total amount of sintering compact, 0.001 to 0.002 wt.% of lithium carbonate for the total amount of sintering compact, and 0.001 to 0.002 wt.% of yttrium oxide for the total amount of sintering compact.

Description

Magnesia partially stabilized zirconia sintered body {Sintered zirconia partly stabilized by magnesia}

The present invention relates to a magnesia partially stabilized zirconia sintered body, and more particularly, to a magnesia partially stabilized zirconia sintered body having improved thermal shock resistance including components having excellent molten steel oxygen sensor properties.

[Prior art]

Controlling the oxygen concentration in molten steel during steelworks, especially during steelmaking, is an important task in determining the quality of hiss. Oxygen concentration in molten steel is measured by immersing a measuring device using a zirconia-based solid electrolyte in the water and measuring the electromotive force generated by the difference in oxygen concentration. The solid electrolyte used at this time is generally in the form of a tube as shown in FIG. 1 and a disposable consumable.

The zirconia-based solid electrolyte device used to measure the oxygen concentration in molten steel must be deposited in molten steel with a temperature of 1650 ° C. or higher and maintained for several seconds until the output of electromotive force is stabilized. Not only do they have to withstand and fail, they must also have good responsiveness and small deviations in electromotive force values. For this reason, magnesia-added zirconia partially stabilized sintered compact has been used as a solid electrolyte for molten steel oxygen sensors.

Solid electrolytes for molten steel oxygen sensors having such excellent physical properties are disclosed in Japanese Patent Application Laid-Open No. Hei 6-256,060. The disclosed technique discloses a zirconia sintered body containing 0.1 wt% or less of silicon oxide, 0.05 wt% or less of titanium oxide, and 0.05 wt% of iron oxide, and 2.5 wt% of magnesium oxide (MgO) as a stabilizer. Although electromotive force characteristics, responsiveness, and thermal shock resistance are good, there is a problem in that the thermal shock resistance is partially lowered.

The present invention is to solve the above problems, an object of the present invention is to add a component of excellent molten steel oxygen sensor properties to the magnesia zirconia solid electrolyte composition magnesia partial stabilization excellent physical properties such as thermal shock characteristics, responsiveness, electromotive force variation It is to provide a zirconia sintered body.

1 is an apparatus for measuring oxygen concentration in molten steel using the magnesia partially stabilized zirconia sintered compact of the present invention.

Explanation of symbols on the main parts of the drawings

1: electromotive force measurement 2: molten steel contact electrode

3: solid electrolyte 4: molten steel

5: temperature measurement 6: platinum wire

7: platinum-rhodium wire 8: standard electrode

In order to achieve the above object, the present invention

0.05 to 0.2% by weight of alumina relative to the total amount of sintered compacts, 0.1 to 0.2% by weight of silicon oxide relative to the total sintered compact, 0.02 to 0.05% by weight relative to the total amount of sintered compact, 0.02 to 0.05% by weight of titanium oxide relative to the total sintered compact, 0.005% to 0.01% by weight of calcium oxide, 0.005% to 0.01% by weight of calcium carbonate, 0.001% to 0.002% by weight of lithium carbonate and 0.001% to 0.002% by weight of yttrium oxide, And a magnesia partially stabilized zirconia sintered body having a specific gravity of 5.4 to 5.5, monoclinic 54 to 72 wt%, and grain size of 35 to 53 μm.

Hereinafter, the present invention will be described in more detail.

In order to prepare a magnesia partially stabilized zirconia sintered body having excellent physical properties according to the present invention, first, alumina (Al ₂ O ₃ ), silicon oxide (SiO ₂ ), iron oxide (Fe) as an additive to a binder (ZrO ₂ -MgO) in zirconia and magnesia ₂ O ₃ ), titanium oxide (TiO ₂ ), calcium oxide (CaO), calcium carbonate (CaCO ₃ ), lithium carbonate (Li ₂ CO ₃ ) and yttrium oxide (Y ₂ O ₃ ) are added and mixed uniformly One solid mixture is prepared.

The additives are used to improve the characteristics such as electromotive force value, response speed, thermal shock breakage, etc. caused by the difference in oxygen concentration when the sintered body is immersed in the molten steel for several seconds to measure the oxygen concentration in the molten steel having a temperature of about 1650 ° C. or more. Is added.

Among the additives, alumina is added to increase the density of the sintered compact and to improve the thermal shock resistance. The amount of the alumina is preferably 0.05 to 0.2 wt% based on the total amount of the sintered compact, and when the addition amount is less than 0.05 wt%, the thermal shock resistance characteristics are poor. There is a problem of deterioration and if the amount of addition exceeds 0.2% by weight, there is a problem of deterioration in response.

Among the additives, silicon oxide is added to the sintered compact of the present invention in order to reduce thermal conductivity and stabilize thermal shock resistance, but the amount of silicon oxide is preferably added in an amount of 0.1 to 0.2 wt% based on the total amount of sintered compact, and the amount is less than 0.1 wt%. If the thermal shock resistance is not improved and the amount added exceeds 0.2% by weight, there is a problem that the thermal shock resistance and responsiveness are lowered.

Among the additives, iron oxide is added to the sintered body in order to facilitate kneading of the sintered body component mixture. The addition amount of the iron oxide is preferably 0.02 to 0.05% by weight based on the total amount of the sintered body, and the addition amount is less than 0.02% by weight. Mixing of the mixture is not easy and if the addition amount exceeds 0.05% by weight, the color of the sintered body is changed to yellow color due to the impurity effect, there is a problem in usability.

Among the additives, titanium oxide is also added to the sintered compact of the present invention for the same purpose as the iron oxide, and the amount of the titanium oxide is preferably 0.02 to 0.05 wt% based on the total amount of the sintered compact, and when the added amount is less than 0.02 wt%, the sintered compact mixture Kneading is not easy and there is a problem that the responsiveness is lowered when the added amount exceeds 0.05% by weight.

Calcium oxide in the additive is added to synthesize beta-wollastonite (β-wollastonite, CaSiO ₃ ) by reacting with the additive silicon oxide, but the beta-walostonite is low in thermal conductivity to the thermal shock stability of the sintered body Helped. The addition amount of the calcium oxide is preferably 0.005 to 0.01% by weight based on the total amount of the sintered body, and when the addition amount is less than 0.005% by weight, the thermal shock resistance of the sintered body does not appear to be improved. There is a problem that the thermal shock resistance and responsiveness of is lowered.

Among the additives, calcium carbonate is added for the same purpose as the calcium oxide, and the amount of added calcium carbonate is preferably 0.005 to 0.01% by weight based on the total amount of the sintered body.

Lithium carbonate in the additive is added to form beta-spodumene (β-spodumene, LiAlSi ₂ O ₆ ) in reaction with the added alumina, silicon oxide, etc., wherein the beta-spodum is used to improve the thermal shock resistance of the sintered body. do. The addition amount of the lithium carbonate is preferably 0.001 to 0.002% by weight based on the total amount of the sintered body, and if the addition amount is less than 0.001% by weight, there is no improvement in thermal shock resistance of the sintered body, and when the addition amount exceeds 0.002% by weight, the thermal shock resistance and responsiveness decrease. There is a problem.

Among the additives, yttrium oxide is added to form garnet (Y ₃ Al ₅ O ₁₂ ) for improving the corrosion resistance of the sintered body in molten steel. The addition amount of yttrium oxide is preferably 0.001 to 0.002% by weight based on the total amount of the sintered compact, and if the added amount is less than 0.001% by weight, there is a problem that corrosion resistance of the sintered compact in molten steel does not improve. There is a problem of deterioration.

After adding a binder, a plasticizer and water to the solid mixture prepared by adding additives to the zirconia-magnesia oxide binder and extruding to prepare a molding, the molding is dried and sintered to partially stabilize the magnesia, which is a solid electrolyte in the form of a tube. A zirconia sintered body is manufactured.

The binder is added to increase the bonding strength of the sintered components of the present invention. Methyl cellulose, polyvinyl alcohol (polyvinylalcohol, PVA), and the like may be used as the binder, and preferably methyl cellulose is used. As for the addition amount of the said binder, 1-3 weight% is preferable with respect to the total amount of sintered compacts.

The said plasticizer is added in order to improve the moldability of the sintered compact of this invention. As the plasticizer, it is preferable to use glycerin. As for the addition amount of the said plasticizer, 1 to 2 weight% is preferable with respect to the total amount of sintered compacts.

It is preferable to add 24 to 25 weight% of said water | moisture content with respect to the total amount of sintered compacts in kneading, shaping | molding, etc. of a sintered compact.

After extruding the mixture of the sintered compact component of the present invention in the form of a tube, it is dried at a temperature of 100 to 200 캜, preferably 150 캜 and sintered at a temperature of 1400 to 1800 캜 to prepare a solid electrolyte as the sintered compact of the present invention.

The sintered body of the present invention prepared by the above method preferably has an oxygen sensor characteristic required by the present invention to have a specific gravity of 5.4 to 5.5, monoclinic 54 to 72 wt%, and grain size of 35 to 53 μm.

The molten steel oxygen sensor characteristics are measured by using the solid electrolyte in the form of the tube of the present invention prepared above. The method for measuring the characteristics of the molten steel oxygen sensor using the solid electrolyte of the present invention is performed by constructing the apparatus shown in FIG. 1, wherein the standard electrode (8), which is an internal electrode of the solid electrolyte (3) manufactured according to the present invention, is used as Cr +. When CrO ₂ is used and molybdenum is used as the molten steel contact electrode (2), the molten steel is immersed in the molten steel to generate an electromotive force due to the difference in oxygen concentration between the inside of the water and the standard electrode due to the characteristics of the solid electrolyte (1). The oxygen concentration is measured. In addition, the oxygen sensor characteristic of the molten steel 4 is measured by measuring temperature 5 using the platinum wire 6 and the platinum-rhodium wire inside the molten steel. These characteristics are described in the examples.

EXAMPLE

The following presents preferred examples and comparative examples to aid in understanding the invention. However, the following examples are provided only to more easily understand the present invention and do not limit the present invention.

(Example 1)

The sintered compact components are uniformly mixed so that the sintered compact is formed in the weight shown in the following Table 1 by the weight of the components shown in Table 1, and 2 weight percent methylcellulose, 1 weight percent glycerin and 24 weight percent based on the total amount of the sintered compact component added thereto. Water was added and extruded in the form of a tube. The molded article was dried at a temperature of about 150 ° C. and sintered at a temperature of about 1700 ° C. to prepare a solid electrolyte (inner diameter 3mm, outer diameter 4.5 length 43mm). Physical properties such as monoclinic amount, average particle diameter, and the like of the prepared sintered body were measured by a conventional method and shown in Table 1 below. In addition, by using the prepared solid electrolyte, the device shown in FIG. 1 was constructed and oxygen sensor characteristics in molten steel at a temperature of 1700 ° C. were measured. At this time, molybdenum wire was used as an electrode contacting the molten steel, and the solid electrolyte internal electrode was used. Cr + CrO ₂ was used. When the solid electrolyte was immersed in the molten steel to measure the oxygen sensor characteristics, the response speed was 5 seconds and the electromotive force was 170 mV. The measurement results for the oxygen sensor characteristics are shown in Table 1 below.

(Examples 2 to 9)

To prepare a sintered compact having the components shown in Table 1 in the amounts shown in Table 1 below, a solid electrolyte was prepared in the same manner as in Example 1, and then the physical properties of the sintered compact were measured in the same manner as in Example 1. Oxygen sensor characteristics of the solid electrolyte were measured in the same manner as in Example 1, and the results are shown in Table 1 below.

(Comparative Example)

After preparing a solid electrolyte in the same manner as in Example 1 using the components and contents of the conventional sintered compact to have a content of the solid electrolyte, the physical properties of the sintered compact were measured in the same manner as in Example 1, and also in Example 1 Oxygen sensor characteristics of the solid electrolyte were measured by the same method as described above, and the results are shown in Table 1 below.

Sintered body characteristics (ZrO ₂ -MgO (8 mol%)) Molten Oxygen Sensor Additive amount (% by weight) importance Monoclinic weight (wt%) Average Sintered Particle Size (㎛) damage Electromotive force performance Al ₂ O ₃ SiO ₂ Fe ₂ O ₃ TiO ₂ CaO CaCO ₃ LiCO ₃ Y ₂ O ₃ Responsiveness Deviation Example One 0.05 0.15 0.05 0.05 0.01 - 0.005 0.001 5.35 54 45 Good 102 101 2 0.1 0.15 0.02 0.02 0.01 - 0.005 0.002 5.4 58 53 Good 102 102 3 0.2 0.1 0.02 0.02 - 0.01 0.002 0.002 5.35 64 38 Good 103 97 4 0.15 0.1 0.05 0.05 - 0.01 - - 5.35 68 47 Good 103 96 5 0.15 0.15 0.05 0.05 - 0.01 0.005 0.005 5.4 78 62 damage - - 6 0.05 0.2 0.02 0.02 0.005 0.005 0.002 0.002 5.5 72 45 Great 98 99 7 0.1 0.15 0.02 0.02 0.005 0.005 0.002 0.002 5.5 69 49 Great 99 100 8 0.2 0.1 0.05 0.05 0.005 0.005 0.001 - 5.45 65 41 Great 100 101 9 0.15 0.2 0.02 0.02 0.005 0.005 0.002 0.001 5.5 59 38 Great 98 99 Comparative example 0.1 0.02 0.01 < 0.01 < - - - - 5.3 60 35 Good 100 100

As shown in Table 1, it can be seen that the sintered body to which the additive of the present invention is added has superior thermal shock resistance as the thermal shock performance is improved as compared with the conventional sintered body.

The magnesia partially stabilized zirconia sintered body of the present invention is alumina (Al ₂ O ₃ ), silicon oxide (SiO ₂ ), iron oxide (Fe ₂ O ₃ ), titanium oxide (TiO ₂ ), calcium oxide (CaO), calcium carbonate (CaCO ₃ ), By including additives of lithium carbonate (Li ₂ CO ₃ ) and yttrium oxide (Y ₂ O ₃ ), it has excellent molten steel oxygen sensor characteristics and can accurately measure oxygen concentration inside molten steel.

Claims (2)

0.05 to 0.2% by weight of alumina relative to the total amount of sintered compacts, 0.1 to 0.2% by weight of silicon oxide relative to the total sintered compact, 0.02 to 0.05% by weight relative to the total amount of sintered compact, 0.02 to 0.05% by weight of titanium oxide relative to the total sintered compact, 0.005% to 0.01% by weight of calcium oxide, 0.005% to 0.01% by weight of calcium carbonate, 0.001% to 0.002% by weight of lithium carbonate and 0.001% to 0.002% by weight of yttrium oxide, Magnesia partially stabilized zirconia sintered compact. The method of claim 1, The magnesia partially stabilized zirconia sintered compact having a specific gravity of sintered compact of 5.4 to 5.5, monoclinic 54 to 72 wt%, and grain size of 35 to 53 µm.