CN111848133A

CN111848133A - Preparation method of high-thermal-shock-resistance magnesium oxide ceramic

Info

Publication number: CN111848133A
Application number: CN202010515974.9A
Authority: CN
Inventors: 狄玉丽
Original assignee: Xichang College
Current assignee: Xichang College
Priority date: 2020-06-09
Filing date: 2020-06-09
Publication date: 2020-10-30

Abstract

The invention belongs to the technical field of ceramic materials, and discloses a preparation method of high thermal shock resistance magnesia ceramic. The preparation method of the high thermal shock resistance magnesia ceramic comprises the following steps: micron-sized light magnesium oxide powder is used as a raw material, is subjected to ball milling and mixing with rare earth oxide and a binder, is subjected to compression molding under a hydraulic press, and is sintered to obtain the rare earth oxide, wherein the rare earth oxide is selected from rare earth cerium oxide, neodymium oxide and praseodymium oxide, more than 70% of the light magnesium oxide powder is distributed between 0.5 and 1 mu m in particle size, 90% of the light magnesium oxide powder is distributed between 0.5 and 2 mu m in particle size, the light magnesium oxide powder accounts for 91-97% by mass, and the rare earth oxide accounts for 2-8% by mass. The magnesium oxide ceramic prepared by the method has high thermal shock resistance, can prolong the service life of the magnesium oxide ceramic in a high-temperature environment, and is more suitable for being used as a crucible for smelting metal.

Description

Preparation method of high-thermal-shock-resistance magnesium oxide ceramic

Technical Field

The invention relates to the technical field of ceramic materials, in particular to a preparation method of high thermal shock resistance magnesia ceramic.

Background

The actual density of MgO is 3.58 g/cm ³Has a melting point of 2800 +/-13 ℃, is a sodium chloride type structure, belongs to a cubic crystal system, has a Mohs hardness of 6, is a good insulator, and has resistivity at room temperature>1014 omega cm, the resistivity is sharply reduced along with the temperature rise, and the crucible has better conductivity, mechanical strength and high temperature resistance and can be used as a crucible for smelting metal; in the nuclear industryThe method is also suitable for smelting high-purity uranium and thorium; can also be used as a thermocouple protective sleeve; the material can be used as radar cover and infrared radiation transmission window material. However, the magnesia ceramics have a large thermal expansion coefficient and poor resistance to thermal strain, resulting in poor sintering properties and poor thermal shock resistance.

The forming method of the magnesium oxide ceramic product comprises various methods such as dry pressing, grouting, cold isostatic pressing, gel casting, hot pressing, hot isostatic pressing and the like. The dry pressing method is widely applied due to the advantages of simple preparation process, simple operation and the like, and is a mature process. However, most of the materials of the prior magnesia products used for the ceramic crucible have poor compactness and poor shock resistance, thereby shortening the service life of the magnesia crucible. For example, patent application CN201010281144.0 discloses a method for preparing high-density magnesia ceramic, which uses nano-scale high-purity basic magnesium carbonate, and the magnesia ceramic is obtained through calcining, molding and sintering, but the method has high requirements for raw materials. Patent application CN201010563871.6 discloses a method for preparing high-density magnesia ceramic by using gel injection molding method, but the process uses more organic substances and has complicated steps. The patent application CN201611173448.9 adopts an extrusion molding method to prepare the magnesia ceramic material, but the raw materials are as many as 12, and the density and the performance of the magnesia ceramic material are not correspondingly described. The patent application CN201710793212.3 uses a hot press forming method to prepare the high-density magnesia ceramic, and the main steps comprise magnetic separation, mixing, hot press forming, sintering and the like, and the requirements on equipment are high.

Disclosure of Invention

The invention aims to overcome the defects of the background technology and provides a preparation method of magnesium oxide ceramic with high thermal shock resistance.

In order to obtain high compactness of the existing magnesia ceramic, nano magnesium carbonate powder is generally selected as a raw material, then is ball-milled and mixed with a sintering aid and additives (rare earth oxides, other ceramic powder and the like), and is sintered and molded by using methods such as vacuum sintering, hot-pressing sintering, normal-pressure sintering and the like after processes such as extrusion molding, film injection molding, hot-pressing molding, cold isostatic pressing molding and the like (the shape is determined by a mold and can be cylindrical, rectangular, square or other shapes). However, the cost, equipment requirement and process of the nano raw material powder are complex, and the cost for preparing the magnesium oxide is improved to a certain extent.

In order to achieve the purpose of the invention, the preparation method of the high thermal shock resistance magnesia ceramic comprises the following steps: micron-sized light magnesium oxide powder is used as a raw material, is subjected to ball milling and mixing with a rare earth oxide and a binder, is subjected to compression molding under a hydraulic press, and is sintered to obtain the rare earth oxide, wherein the rare earth oxide is selected from cerium oxide, neodymium oxide and praseodymium oxide, more than 70% of the light magnesium oxide powder has a particle size distribution of 0.5-1 mu m, 90% of the light magnesium oxide powder has a particle size distribution of 0.5-2 mu m, the light magnesium oxide powder accounts for 90.5-97.5% by mass, and the rare earth oxide accounts for 1.5-8.5% by mass.

Further, the purity of the light magnesium oxide powder is > 98.50%.

Furthermore, the size range of the cerium oxide is between 0.2 and 25 mu m, more than 90 percent of particles have the particle size of between 0.5 and 15 mu m, and the purity is more than or equal to 99.99 percent; preferably, the addition amount of the cerium oxide is 7.5 to 8.5 wt%.

Furthermore, the size range of the neodymium oxide is between 0.2 and 20 mu m, more than 90 percent of particles have the particle size of between 0.5 and 5 mu m, and the purity is more than or equal to 99.9 percent; preferably, the addition amount of the neodymium oxide is 3.5-4.5 wt%.

Furthermore, the size range of the praseodymium oxide is between 0.2 and 20 mu m, more than 90 percent of particles have the particle size of between 1 and 15 mu m, and the purity is more than or equal to 99.9 percent; preferably, the addition amount of the praseodymium oxide is 1.5-2.5 wt%.

Further, the binder is polyvinyl alcohol (PVC).

Preferably, the purity of the polyvinyl alcohol is more than or equal to 98.0 percent.

In the experimental process, the inventor finds that the ceramic with better earthquake-resistant performance can be obtained by adding the rare earth cerium oxide, but the addition amount is more, the cost is high, and therefore, the rare earth oxide is preferably rare earth neodymium oxide and/or praseodymium oxide.

Further, the ball milling is carried out by dry grinding and mixing in a variable frequency planetary ball mill at the rotating speed of 100-300 r/min, the size of zirconium balls is 8-12 mm of large balls phi, the size of small balls phi is 4-6 mm, and the ratio of the large balls to the small balls is 1: 4-6, ball milling for 1-3 h, taking out and drying.

Further, the sintering is performed in a muffle furnace or an electric resistance furnace.

Preferably, the sintering temperature is 1560-1600 ℃, the temperature is kept for 2-4 h after sintering, the temperature is reduced, and the finished product is taken out after furnace cooling.

More preferably, the sintering is carried out by heating to 90-110 ℃ and preserving heat for 25-35 min, then heating to 980-1020 ℃ and preserving heat for 55-65 min to remove the binder PVC, then heating to 1560-1600 ℃, wherein the heating rate in the whole sintering process is less than or equal to 5 ℃/min, and the heating rate in the last heating is less than or equal to 4 ℃/min.

Compared with the prior art, the invention has the following advantages:

(1) the invention does not need to use nano-scale magnesium carbonate as a raw material, has low requirements on the raw material, thereby reducing the cost, does not need to use methods such as hot isostatic pressing or gel film injection method and the like to prepare the magnesium oxide ceramic, has low requirements on equipment, simple operation process and few steps, and is easy to realize industrialization.

(2) The invention selects micron-sized light magnesia powder, saves cost, adds rare earth oxides (cerium oxide, neodymium oxide, praseodymium oxide and the like) to reduce the sintering temperature of magnesia, refines crystal grains, selects polyvinyl alcohol as a binder, prepares a magnesia green body by using a dry pressing method which has less process steps and is easy to operate, and can sinter and prepare the magnesia ceramic with high thermal shock resistance at lower sintering temperature (1580 ℃).

(3) The magnesium oxide ceramic prepared by the invention has high thermal shock resistance, can prolong the service life of the magnesium oxide ceramic in a high-temperature environment, and is more suitable for being used as a crucible for smelting metal.

Drawings

FIG. 1 is a graph of the particle size distribution of the feedstock of examples 1-10 of the present application.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. It is to be understood that the following description is only illustrative of the present invention and is not to be construed as limiting the present invention.

When an amount, concentration, or other value or parameter is expressed as a range, preferred range, or as a range of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted to include the ranges "1 to 4", "1 to 3", "1 to 2 and 4 to 5", "1 to 3 and 5", and the like. When a range of values is described herein, unless otherwise stated, the range is intended to include the endpoints thereof and all integers and fractions within the range.

Further, the technical features of the embodiments of the present invention may be combined with each other as long as they do not conflict with each other.

Example 1

A preparation method of high thermal shock resistance magnesia ceramic comprises the following steps:

step 1: weighing the raw materials according to the proportion shown in the example 1 in the table 1, putting the powder into a variable frequency planetary ball mill, and grinding and mixing the powder in a dry method at the rotating speed of 200r/min according to the proportion of zirconium balls (i.e. large balls phi 10mm and small balls phi 5 mm) of 1: 5, mixing, taking out after 2 hours and drying.

Table 1 raw material composition table (mass%,%)

Examples	MgO	PVC	CeO₂	Nd₂O₃	Pr₆O₁₁
						1	99	1	0	0	0
2	98	1	1	0	0
						3	97	1	2	0	0
4	91	1	8	0	0
						5	98	1	0	1	0
6	95	1	0	4	0
						7	91	1	0	8	0
8	98	1	0	0	1
						9	97	1	0	0	2
10	91	1	0	0	8

The purity and size of the raw materials are as follows: the purity of light magnesium oxide powder (more than 70 percent of particle size is distributed between 0.5 and 1 mu m, and 90 percent of particle size is distributed between 0.5 and 2 mu m) is more than 98.50 percent; the purity of the rare earth cerium oxide (the size range is between 0.2 and 15 mu m, more than 90 percent of particles have the particle size of between 0.5 and 15 mu m) is more than or equal to 99.99 percent; the purity of rare earth neodymium oxide (the size range is between 0 and 20 mu m, more than 90 percent of particles have the particle size of between 0.5 and 5 mu m) is more than or equal to 99.9 percent; the rare earth praseodymium oxide (the size range is between 0.2 and 20 mu m, more than 90 percent of particles have the particle size of between 1 and 15 mu m) has the purity of more than or equal to 99.9 percent and the adhesive polyvinyl alcohol (PVC, more than or equal to 98 percent).

Step 2: and then, carrying out dry pressing forming by adopting a powder tablet press or a hydraulic press or a pressing machine, wherein the pressing pressure is 242MPa, and the green body is formed after keeping the pressure for 3 minutes (the shape of the green body is determined according to the shape of the die).

And step 3: and (3) placing the pressed sample in an artificial intelligent box type resistance furnace (the temperature of the resistance furnace or a muffle furnace is required to be accurately controlled to be 0.1 ℃) to be sintered at 1580 ℃ for 3 hours. Wherein, the temperature is increased to 100 ℃ and kept for 30min, then the temperature is increased (the temperature increasing rate is less than or equal to 5 ℃/min) to 1000 ℃ and kept for 60min to remove the adhesive PVC, then the temperature is increased (the temperature increasing rate is less than or equal to 4 ℃/min) to 1580 ℃, the temperature is kept for 3h, then the temperature is reduced to 400 ℃, then the finished product is taken out after furnace cooling, and the temperature increasing rate of the whole sintering is less than or equal to 5 ℃/min.

Example 2

In contrast to example 1, the powders were weighed out in the proportions of the raw materials listed in table 1 and example 2 of step 1.

Example 3

In contrast to example 1, the powders were weighed out in the proportions of the raw materials described in table 1, example 3 of step 1.

Example 4

In contrast to example 1, the powders were weighed out in the proportions of the raw materials mentioned in table 1, example 4 of step 1.

Example 5

In contrast to example 1, the powders were weighed out in the proportions of the raw materials mentioned in table 1, example 5 of step 1.

Example 6

In contrast to example 1, the powders were weighed out in the proportions of the raw materials mentioned in table 1 and example 6 of step 1.

Example 7

In contrast to example 1, the powders were weighed out in the proportions of the raw materials described in table 1, example 7 of step 1.

Example 8

In contrast to example 1, the powders were weighed out in the proportions of the raw materials mentioned in table 1, example 8 of step 1.

Example 9

In contrast to example 1, the powders were weighed out in the proportions of the raw materials mentioned in table 1, example 9 of step 1.

Example 10

In contrast to example 1, the powders were weighed out in the proportions of the raw materials described in table 1, example 10 of step 1.

Effects of the embodiment

Example 1 is a comparative example, that is, the magnesia ceramics prepared by the preparation method of the present invention without adding any rare earth, while examples 2 to 10 are magnesia ceramics to which cerium oxide, neodymium oxide, and praseodymium oxide were added in different amounts of rare earth, and the thermal shock resistance times thereof were measured as shown in table 2.

The thermal shock resistance detection method comprises the following steps: and (3) putting the finished product into a 600 ℃ muffle furnace at the normal temperature of 25 ℃ for heat preservation for 20min, taking out the finished product, putting the finished product into a flowing water tank for 10min, standing for 5min, observing whether cracks appear, repeating the experiment until cracks and breakage appear, stopping the experiment, recording the thermal shock resistance times, detecting the thermal shock resistance times by using at least 3 samples, and calculating the average value.

The density detection method comprises the following steps: and testing the density of the sample by adopting a QL-102l type precise ceramic porosity volume density tester.

TABLE 2 thermal shock resistance and Density Properties of magnesium oxide

It can be seen from table 2 that the addition of rare earth oxides generally increases the thermal shock resistance of the magnesia ceramic, but the addition of each rare earth oxide has a different effect on the thermal shock resistance. The thermal shock resistance of the examples 4, 6, 9 and 10 is relatively better, but the rare earth cerium oxide in the example 4 is added in an amount of 8wt% and has a large content, and 4wt% of rare earth neodymium oxide or 2wt% of praseodymium oxide is added to save the cost.

Example 11

The difference from example 9 is that step 3 is: and (3) placing the pressed sample in an artificial intelligent box type resistance furnace (the temperature of the resistance furnace or a muffle furnace is required to be accurately controlled to be 0.1 ℃) to be sintered at 1580 ℃ for 3 hours. Wherein, the temperature is raised to 100 ℃ and kept for 30min, then raised to 1000 ℃ and kept for 60min to remove the binder PVC, then raised to 1580 ℃ at a rate of not more than 15 ℃/min, kept for 3h, cooled to 400 ℃ and cooled in a furnace, and then the finished product is taken out, the temperature rise rate of the whole sintering is not less than 10 ℃/min and not more than 15 ℃/min, the thermal shock resistance frequency of the obtained magnesia ceramic is 8, and the relative density is 90.2%.

Example 12

The difference from example 9 is that step 3 is: and (3) placing the pressed sample in an artificial intelligent box type resistance furnace (the temperature of the resistance furnace or a muffle furnace is required to be accurately controlled to be 0.1 ℃) to be sintered, wherein the sintering temperature is 1700 ℃, and the heat preservation time is 3 hours. Wherein, the temperature is raised to 100 ℃ and kept for 30min, then raised to 1000 ℃ and kept for 60min to remove the binder PVC, then raised to 1700 ℃ and kept for 3h, then cooled to 400 ℃ and taken out after furnace cooling, the temperature rise rate of the whole sintering is less than or equal to 5 ℃/min, the thermal shock resistance frequency of the obtained magnesia ceramic is 9, and the relative density is 91.5%.

Example 13

The difference from example 9 is that step 1 is: the purity of the light magnesium oxide powder (90 percent of the particle size is distributed between 2 and 5 mu m) is more than or equal to 98.0 percent; the purity of rare earth praseodymium oxide (the size range is between 10 and 30 mu m, more than 70 percent of particles have the particle size between 15 and 25 mu m) is more than or equal to 99.0 percent. The obtained magnesia ceramic has 8 thermal shock resistance times and 92.3 percent of relative density.

It will be understood by those skilled in the art that the foregoing is only exemplary of the present invention, and is not intended to limit the invention, which is intended to cover any variations, equivalents, or improvements therein, which fall within the spirit and scope of the invention.

Claims

1. A preparation method of high thermal shock resistance magnesia ceramic is characterized by comprising the following steps: micron-sized light magnesium oxide powder is used as a raw material, is subjected to ball milling and mixing with a rare earth oxide and a binder, is subjected to compression molding under a hydraulic press, and is sintered to obtain the rare earth oxide, wherein the rare earth oxide is selected from cerium oxide, neodymium oxide and praseodymium oxide, more than 70% of the light magnesium oxide powder has a particle size distribution of 0.5-1 mu m, 90% of the light magnesium oxide powder has a particle size distribution of 0.5-2 mu m, the light magnesium oxide powder accounts for 90.5-97.5% by mass, and the rare earth oxide accounts for 1.5-8.5% by mass.

2. The method for preparing the magnesium oxide ceramic with high thermal shock resistance according to claim 1, wherein the purity of the light magnesium oxide powder is more than 98.50%.

3. The preparation method of the high thermal shock resistance magnesia ceramic according to claim 2, characterized in that the size range of the ceria is between 0.2 and 15 μm, more than 90 percent of particles have the particle size between 0.5 and 15 μm, and the purity is more than or equal to 99.99 percent; preferably, the addition amount of the cerium oxide is 7.5 to 8.5 wt%.

4. The preparation method of the high thermal shock resistance magnesia ceramic according to any one of claims 1 to 3, characterized in that the size range of the neodymium oxide is between 0.2 and 20 μm, more than 90 percent of particles have the particle diameter between 0.5 and 5 μm, and the purity is more than or equal to 99.9 percent; preferably, the addition amount of the neodymium oxide is 3.5-4.5 wt%.

5. The preparation method of the high thermal shock resistance magnesia ceramic according to any one of claims 1 to 3, characterized in that the size range of the praseodymium oxide is between 0.2 and 20 μm, more than 90 percent of particles have the particle size of between 1 and 15 μm, and the purity is more than or equal to 99.9 percent; preferably, the addition amount of the praseodymium oxide is 1.5-2.5 wt%.

6. The method for preparing the magnesium oxide ceramic with high thermal shock resistance according to claim 1, wherein the binder is polyvinyl alcohol; preferably, the purity of the polyvinyl alcohol is more than or equal to 98.0 percent.

7. The preparation method of the magnesium oxide ceramic with high thermal shock resistance according to claim 1, wherein the rare earth oxide is rare earth neodymium oxide and/or praseodymium oxide.

8. The preparation method of the high thermal shock resistance magnesia ceramic according to claim 1, wherein the ball milling is dry milling and mixing in a variable frequency planetary ball mill at a rotation speed of 100-300 r/min, wherein the size of the zirconium balls is 8-12 mm in diameter of big balls, the size of the small balls is 4-6 mm in diameter of small balls, and the ratio of the big balls to the small balls is 1: 4-6, ball milling for 1-3 h, taking out and drying.

9. The method for preparing the high thermal shock resistance magnesia ceramic according to claim 1, characterized in that the sintering is carried out in a muffle furnace or a resistance furnace; preferably, the sintering temperature is 1560-1600 ℃, the temperature is kept for 2-4 h after sintering, the temperature is reduced, and the finished product is taken out after furnace cooling.

10. The preparation method of the high thermal shock resistance magnesia ceramic according to claim 1, wherein the sintering is carried out by heating to 90-110 ℃ and keeping the temperature for 25-35 min, then heating to 980-1020 ℃ and keeping the temperature for 55-65 min to remove the binder PVC, then heating to 1560-1600 ℃, wherein the heating rate in the whole sintering process is less than or equal to 5 ℃/min, and wherein the heating rate in the last heating is less than or equal to 4 ℃/min.