CN109592981B

CN109592981B - Porous rare earth titanate heat insulation material and preparation method and application thereof

Info

Publication number: CN109592981B
Application number: CN201710918877.2A
Authority: CN
Inventors: 范武刚; 张兆泉; 董满江
Original assignee: Shanghai Institute of Ceramics of CAS
Current assignee: Shanghai Institute of Ceramics of CAS
Priority date: 2017-09-30
Filing date: 2017-09-30
Publication date: 2021-06-15
Anticipated expiration: 2037-09-30
Also published as: CN109592981A

Abstract

The invention relates to a porous rare earth titanate heat-insulating material, a preparation method and application thereof, wherein the porous rare earth titanate heat-insulating material has a porous structure and comprises (Re)₂O₃）_X（TiO₂）_1‑XWherein Re is at least one of Y and lanthanide, X = 0.2-0.8, preferably X = 0.4-0.7; the porosity of the porous rare earth titanate heat-insulating material is 10-90%, and the pore size is 0.1-500 microns.

Description

Porous rare earth titanate heat insulation material and preparation method and application thereof

Technical Field

The invention relates to a porous rare earth titanate heat-insulating material for high-temperature, high-humidity and nuclear reactors and a preparation method thereof, belonging to the field of materials.

Background

Nuclear power, which is the electric energy with the least greenhouse gas emission, is one of the most effective ways for human to utilize nuclear power. More than 400 nuclear power stations are currently operated in the world, and are mainly of a second-generation reactor type of a pressurized water reactor and a boiling water reactor. The advanced and safe third-generation pressurized water reactors are promoted and developed and built in all countries after the fukushima accident in 2011, and the main technical characteristic is that a passive shutdown mode is adopted, so that the shutdown can be reliably realized without depending on external power in an emergency. In addition, a hydrogen elimination device is additionally arranged aiming at the problem that the zirconium alloy cladding tube reacts with water to generate hydrogen in a high-temperature hydrothermal environment by simplifying the design of a pipeline and a valve pump. A cooling water tank which can be operated circularly by being close to gravity is arranged above a reactor, and nuclear leakage is avoided by a technology (IVR) of retaining molten material of a reactor core in a pressure vessel in the case of a serious accident. Since 2007, the AP1000 type third generation pressurized water nuclear reactor complete technology of American West House company is introduced in China, 4 sets of units are constructed for the first time, and the batch popularization is carried out after the engineering technology is verified. Meanwhile, an approach of introducing absorption re-innovation is adopted to obtain the independent intellectual property rights of the nuclear power technology and develop pressurized water reactors with higher power such as CAP1400 and the like. In recent years, a design concept of fault tolerance has been proposed, and safety of a nuclear power plant is improved by increasing a safety margin and a defense depth. The fourth generation nuclear power plant is still in verification and experiment stages at present, and the reactor type of the fourth generation nuclear reactor defined by GIF comprises a high-temperature gas-cooled fast reactor, a sodium-cooled fast reactor, a lead-cooled reactor, a molten salt reactor, a supercritical water-cooled reactor and an ultra-high temperature reactor. At present, each large nuclear power country invests huge resources in developing the four-generation heap. The Qinghua university, the nuclear and Huaneng group in China began to invest money jointly in 2012 to build a 250MW Shandong Rong Shijiwan modular high-temperature gas cooled reactor, and fuel was filled in 2017. The Shanghai applied physical institute of Chinese academy began to build the first 2MW solid molten salt reactor in 2017.

The reactor core internals of the pressurized water reactor are subjected to high temperature and irradiation influence of different degrees in the service process and are subjected to hydrothermal corrosion of about 280-350 ℃, the fourth generation nuclear reactor in the future can operate in a temperature field of 950 ℃ of 500-350 ℃, and the service life is not less than 60 years. Based on the harsh service environment, the high-efficiency and stable heat-insulating material has important significance for improving the heat efficiency and safe operation.

The thermal insulation material used in the nuclear reactor is divided into an outer core, a cavity and a core according to the installation position. The reactor cavity is mainly used for carrying out heat preservation treatment on coolant pipelines in each loop, including a hot pipe section and a cold pipe section. The thermal insulation material of the heat pipe section is usually mineral wool, calcium silicate and reflective metal parts. However, since fibrous and granular insulating materials may pass through cracks of the piping and be deposited under the core, the main trend is to use a metal reflector. Patent ZL2012205668713.4 provides a design for a bent sheet of strip steel. The cold pipe section mainly utilizes foam glass, glass fiber and various foam plastics. Most thermal modules are designed to be removable and replaceable, and the thermal insulation components of a pressurized water reactor are usually composed of tens of thousands of customized thermal insulation sheets. The outside of the pile is mainly provided with a calcium silicate heat insulation layer which accounts for more than 90 percent. It has durability and high toughness, and can suppress stress corrosion cracking of the austenitic stainless steel. Steam turbines are primarily insulated with calcium silicate or glass fiber mats.

The reactor core heat insulating materials of the pressurized water reactor and the supercritical water-cooled reactor need to reduce the temperature of a pressure vessel, a bearing part, a cladding tube and the like made of metal materials, avoid creep failure, simultaneously slow down the hydrothermal corrosion rate and prolong the service life. Oxide ceramic materials have superior high temperature stability than non-oxide ceramics, such as alumina, zirconia, magnesia alumina spinel, and the like. Among them, yttrium stabilized zirconia ceramics (YSZ) are currently most widely used. It has low thermal conductivity and good mechanical strength at normal temperature. The supercritical water-cooled reactor designed in Canada adopts a zirconia-based heat insulation material with the thickness of 10mm, so that the temperature of a pressure vessel is reduced from 650 ℃ to about 100 ℃. However, since the reactor operating temperature generally fluctuates above 300 ℃, it may cause a transition to a monoclinic phase, which may cause volume expansion and structural failure. Meanwhile, as a material used in a nuclear reactor, good radiation swelling resistance and hydrothermal corrosion resistance are required to avoid rapid corrosion when the material is in contact with a coolant (water). Researchers have found that titanate-based ceramic materials have good resistance to neutron irradiation and can withstand hydrothermal corrosion, such as Dy₂TiO₅Control rod materials have been used in russian VVER nuclear reactors.

Disclosure of Invention

In view of the above problems, an object of the present invention is to provide a rare earth titanate thermal insulation material having a porous structure, which has a certain mechanical strength while having low thermal conductivity and high stability, does not undergo phase change in a high temperature and hydrothermal medium, and can be used for a nuclear reactor thermal insulation material for a long period of time without replacement.

In one aspect, the present invention provides a porous rare earth titanate thermal insulation material having a porous structure of which composition is (Re)₂O₃)_X(TiO₂)_1-XWherein Re is at least one of Y and lanthanide, X is 0.2-0.8, preferably X is 0.4-0.7; the porous rare earth titanate heat-insulating materialThe porosity of the porous ceramic is 10-90%, and the pore size is 0.1-500 microns.

In the invention, the porosity of the porous rare earth titanate heat-insulating material is 10-90%, and the pore size is 0.1-500 microns. The porous structure enables the rare earth titanate thermal insulation material to have low thermal conductivity and high stability, has certain mechanical strength, does not generate phase change in high temperature and hydrothermal media, and can be used for the thermal insulation material of a nuclear reactor for a long time without replacement. Mainly because the titanate crystal has a stable cubic phase or tetragonal phase crystal form, but not a stable crystal structure by doping. For example, the conventional thermal insulation layer made of stable zirconium dioxide ceramics such as yttrium or cerium has structural expansion and even disintegration caused by phase change, and particularly, when the thermal insulation layer works in a working temperature region of nuclear reaction, the structural strength reduction caused by phase change is difficult to avoid due to repeated temperature rise and fall processes. The high-temperature sintered titanate compact material has low thermal conductivity (about 2W/Km) and excellent mechanical property. Moreover, the titanate crystals can resist neutron irradiation and high-temperature hydrothermal corrosion, and no phase change occurs in the use temperature range of the nuclear reactor. The invention can reduce the heat conductivity by an order of magnitude by constructing the porous structure, and the porous structure has certain strength by high-temperature sintering, thereby meeting the requirement of long-term service in the nuclear reactor. In addition, although the porosity of the porous rare earth titanate heat-insulating material prepared by the invention is 10-90%, compared with a nano or fiber material with a large specific surface area, the porous rare earth titanate heat-insulating material has lower water absorption rate. The titanate sintered at high temperature has high crystallization degree, small surface area, complete pore structure, thick pore wall and no communication between partial pores, so that the water absorption rate is lower than that of loose powder and fiber. The water absorption of the compact material is 0.2 percent at the lowest, and the porosity of 68 percent is increased to 0.6 percent.

Preferably, the Re is at least one of Y, La, neodymium, promethium, holmium, erbium, thulium, ytterbium, lutetium, and is preferably Y.

Preferably, the composition of the porous rare earth titanate thermal insulation material further comprises at least one of alumina, magnesia, chromium oxide, silicon oxide and iron oxide, and the content of the at least one of the alumina, the magnesium oxide, the chromium oxide, the silicon oxide and the iron oxide is not more than 5% of the mass of the porous rare earth titanate thermal insulation material.

In another aspect, the invention also provides a preparation method of the porous rare earth titanate thermal insulation material, which comprises the following steps: mixing a rare earth source, a titanium source and a solvent to obtain slurry;

adding a pore-forming agent into the obtained slurry, drying and molding to obtain a blank, or adding a foaming agent into the obtained slurry and directly casting and molding to obtain a blank;

and sintering the obtained blank at 1000-1500 ℃ for 2-30 hours to obtain the porous rare earth titanate heat-insulating material.

The invention adopts a solid-phase synthesis method, and prepares the rare earth titanate heat-insulating material with a porous structure by adding a pore-forming agent or adopting a foaming method and combining subsequent sintering, and the rare earth titanate heat-insulating material also has low heat conductivity, the pore size is 0.1-500 microns, and the porosity is adjustable within 10-90%. The porous rare earth titanate heat insulation material can be used as a heat insulation material (thermal insulation) of a nuclear reactor, and has low heat conductivity and high mechanical strength in a temperature range from room temperature to 800 ℃.

Preferably, the titanium source is TiO₂，Ti₂O₃And Ti, wherein the rare earth source is at least one of Re-containing rare earth oxide, hydroxide and nitrate.

Preferably, the solvent is water or a liquid organic solvent, and preferably, the solid content of the slurry is 30 to 80wt%, preferably 30 to 60 wt%.

Preferably, the slurry further comprises a sintering aid, wherein the sintering aid is at least one of aluminum oxide, magnesium oxide, chromium oxide, silicon oxide and iron oxide, and the content of the sintering aid is not more than 5wt% of the total mass of the powder.

Preferably, the pore-forming agent is at least one of PMMA, polystyrene, polyethylene spheres and ion exchange resin, and preferably, the pore-forming agent accounts for 10 to 80 volume percent of the solid raw materials in the slurry, and preferably 30 to 70 volume percent. Within the volume ratio range, the material can simultaneously meet the requirements of lower thermal conductivity, higher mechanical property and the like. Low thermal conductivity is the basic condition of heat insulating material, and mechanical properties are the necessary conditions for long-term stable operation of the material under service conditions such as pressure and temperature change.

Preferably, the foaming agent is at least one of hydrogen peroxide, azobisisobutyronitrile and sodium borohydride, and preferably, the foaming agent accounts for 10-80% by volume of the solid raw material in the slurry, and preferably 30-70% by volume of the solid raw material in the slurry.

Preferably, the blank body is subjected to rubber discharge, wherein the temperature of the rubber discharge is 300-600 ℃, and the time is 3-10 hours.

In still another aspect, the present invention also provides a use of the porous rare earth titanate thermal insulation material as described above in an environment with irradiation, high temperature and high humidity. The porous rare earth titanate heat insulation material can be used for heat preservation and heat insulation under high-temperature and high-humidity conditions; the rare earth yttrium oxide can also be used in the environment with irradiation and high-temperature water vapor corrosion inside and outside a nuclear reactor, and the rare earth used at the moment is yttrium oxide.

The thermal conductivity of the porous rare earth titanate thermal insulation material prepared by the invention is lower than that of a corresponding compact material, is equivalent to that of zirconia and alumina ceramics, does not generate phase change or pulverization in a long-term high-temperature environment, and has certain resistance to hydrothermal corrosion.

The porous titanate-based heat insulation material and the preparation method thereof have the following positive effects:

1. the ceramic material for the thermal insulation of the pressure vessel and the pipeline in the nuclear reactor provided by the invention has the advantages of low thermal conductivity and stability, good mechanical strength, hydrothermal corrosion resistance and irradiation resistance;

2. the porous structure provided by the invention can adjust the thermal conductivity and mechanical property of the heat insulation material. The porosity and the pore size can be changed by changing the proportion of the pore-forming agent, the sintering temperature and the like;

3. the rare earth titanate-based porous material provided by the invention can avoid volume expansion and structural damage caused by high-temperature circulation and phase change in a long-term service process, and can reduce the absorption of thermal neutrons due to the fact that the neutron absorption cross section of titanium and partial rare earth elements is smaller;

4. the preparation method provided by the invention is simple in process, can be used for large-scale production, and is expected to be used as a reactor core structure and a thermal insulation layer which are in service for a long time.

Drawings

FIG. 1 is a schematic structural view of a nuclear reactor equipped with porous yttrium titanate ceramic in which thermal insulation material can be placed between stainless steels to reduce the outside temperature of the steel plates;

FIG. 2 is an SEM image of the powder obtained in example 1 after mixing the titanium source and the rare earth source, and it can be seen from the SEM image that the micron-sized rare earth oxide and the nano-sized titanium dioxide are uniformly dispersed, which is beneficial to subsequent synthesis and sintering;

FIG. 3 is an SEM image of a porous rare earth titanate thermal insulation material prepared in example 1, from which it can be seen that micron-sized pores are uniformly distributed and have a regular structure;

FIG. 4 is an XRD pattern of the porous rare earth titanate thermal insulation material obtained in example 2;

FIG. 5 is a photograph of a sample of the porous yttrium titanate ceramic obtained in example 2.

Detailed Description

The present invention is further illustrated by the following examples, which are to be understood as merely illustrative and not restrictive.

The porous rare earth titanate heat-insulating material mainly comprises (R)₂O₃)_X-(TiO₂)_1-XWherein R represents Y, La or other lanthanide rare earth elements (such as one or more of neodymium, promethium, holmium, erbium, thulium, ytterbium, lutetium, etc.), and X is 0.2-0.8, more preferably 0.4-0.7. The rare earth titanate heat-insulating material with a porous structure is prepared by sintering by adopting a solid-phase synthesis method, and has low heat conductivity, the pore size is 0.1-500 microns, and the porosity is adjustable within 10-90%. In order to facilitate sintering, the composition of the porous rare earth titanate thermal insulation material may further include the above-mentioned sintering aid (e.g., alumina, magnesia, chromia, silica, iron oxide, etc.) component in an amount of not more than 5 wt%.

The porous rare earth titanate heat-insulating material is prepared by mixing a Ti-containing compound (a titanium source) and a rare earth element-containing compound (a rare earth source) serving as a precursor, adding a certain proportion of a pore-forming agent or a foaming agent, and then drying, tabletting, sintering, post-processing and the like. The following exemplarily illustrates a method for preparing the porous rare earth titanate thermal insulation material provided by the present invention.

The slurry is obtained by mixing (for example, ball milling, mixing and the like) the rare earth source, the titanium source and the solvent according to the composition of the porous rare earth titanate heat insulation material. Wherein, the ratio of Ti in the titanium source and Re in the rare earth source is selected according to the composition, for example, for Re₂Ti₂O₇Re is 0.9 to 1.1; for Re₂TiO₅And Re is 1.8: 2.2. The titanium source may be TiO₂，Ti₂O₃And Ti. The rare earth source may be at least one of a rare earth oxide, hydroxide, and nitrate containing Re. The slurry also comprises a sintering aid. The solvent may be water or a liquid organic solvent. The solids content of the slurry may be 30 to 80wt%, preferably 30 to 60 wt%. The sintering aid can be at least one of aluminum oxide, magnesium oxide, chromium oxide, silicon oxide and iron oxide, and the content of the sintering aid is not more than 5wt% of the total mass of the powder. The slurry also comprises a dispersant which can be at least one of citric acid, polyethylene glycol, polyacrylamide and potassium polyacrylate. The ratio of the addition amount of the dispersing agent to the total mass of the rare earth source and the titanium source is 1: (80-100). As an example, the material may be prepared by using powders of titanium oxide, rare earth oxide, aluminum oxide, magnesium oxide, chromium oxide, silicon oxide, iron oxide, or the like as raw material powders, or by using hydroxides or other compounds that can be converted into the above oxides by heating as raw material powders. Then, the raw material powder is mixed to prepare a biscuit (for example, the biscuit is formed by methods of dry pressing, cold isostatic pressing, casting and the like), and the biscuit is sintered to obtain a material with a certain porosity.

The porosity of the slurry can be increased by adding pore-forming agent particles of an organic polymer component to the slurry. Pore formers used include, but are not limited to, organic polymers such as polymethylmethacrylate material (PMMA), ion exchange resins, polystyrene, polyethylene spheres, and the like. The particle size of the pore-forming agent is 0.1-500 microns. The pore-forming agent accounts for 10-80% of the solid raw materials (the rare earth source and the titanium source) in the slurry by volume.

A green body is prepared by adding a foaming agent into the slurry and adopting a casting process, so that the porosity of the finally obtained porous rare earth titanate heat-insulating material is improved. Blowing agents used include, but are not limited to, hydrogen peroxide, azobisisobutyronitrile, and the like. The raw material powder is uniformly mixed according to a proportion, and the material with certain porosity is obtained by molding and sintering by methods of dry pressing, cold isostatic pressing, pouring and the like. The foaming agent accounts for 10-80% of the solid raw materials in the slurry by volume.

And drying and forming the slurry added with the pore-forming agent to obtain a blank body. The forming mode can be dry pressing forming, cold isostatic pressing forming and the like. The pressure of the dry pressing molding can be 10-200 MPa, and the pressure maintaining time can be 1-30 seconds. The pressure of the cold isostatic pressing can be 30-300 MPa, the pressure maintaining time can be 1-60 seconds, the drying temperature can be 60-100 ℃, and the drying time can be 0.5-10 hours.

And (3) carrying out glue removal and sintering on the obtained green body to obtain the porous rare earth titanate heat-insulating material. The temperature of the binder removal can be 300-600 ℃, and the time can be 3-10 hours. The sintering temperature can be 1000-1500 ℃, and the sintering time can be 2-30 hours. In the present invention, the binder removal and sintering may be performed under atmospheric conditions, including oxygen, air, inert atmosphere (e.g., argon, etc.), and the like. Wherein the sintering atmosphere is preferably an air and oxygen atmosphere. As an example, the obtained green body (biscuit) is firstly subjected to glue removal treatment at the low temperature of 300-1500 ℃, organic matters are removed, then sintering combination is carried out, the sintering temperature is between 1000-1500 ℃, the sintering holding time is 2-30 hours, and sintering can be carried out under different atmospheres, including but not limited to air, argon and oxygen atmospheres.

As an example of a method for producing a porous rare earth titanate-based ceramic heat insulating material, the composition of the porous rare earth titanate-based ceramic heat insulating material is Re₂TiO₅And Re₂Ti₂O₇,RRepresents Y and lanthanide rare earth elements, and adopts a solid-phase synthesis process, and comprises the following steps: to compounds containing titanium, including TiO₂，Ti₂O₃And mixing Ti powder and the like with rare earth oxide, hydroxide, nitrate and the like according to a certain molar ratio, and then carrying out ball milling or sand milling on the mixture by taking water or liquid organic solvent as a medium. The mixing time is 0.5-48 hours. Adding pore-forming agent with a certain proportion into the slurry, and continuously mixing for 0.5-5 hours. Drying the slurry at 60-100 deg.C or filtering in advance, drying again, sieving (80-200 meshes) to remove large particles. And tabletting the obtained powder, carrying out cold isostatic pressing treatment, and then carrying out binder removal and sintering. The debinding and sintering can be performed under atmospheric conditions, including oxygen, air, argon, and the like.

In the porous rare earth titanate thermal insulation material, the rare earth can be any one or combination of Y and lanthanide. The prepared heat insulation ceramic is a block body sintered at high temperature, and can be subjected to post-processing treatment to prepare the heat insulation ceramic into a required shape and specification.

The porous rare earth titanate thermal insulation material prepared by the invention has low water absorption, high mechanical strength, good hydrothermal corrosion resistance and certain irradiation resistance, and has good application prospect under the conditions of high temperature and high humidity and nuclear reactors. The water absorption rate (the water absorption amount and the mass percentage of the heat-insulating material) of the porous rare earth titanate heat-insulating material prepared by the invention can be 0.1-2%. The bending breaking strength of the prepared porous rare earth titanate thermal insulation material measured by a four-point bending method can be 10-200 MPa. The thermal conductivity of the prepared porous rare earth titanate thermal insulation material measured by a thermal conductivity (thermal resistance) tester of a protective heat flow meter is 0.05-2.5W/mK, preferably 0.05-1.5W/mK at 30 ℃.

The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below.

Example 1Y₂TiO₅Porous heat-insulating ceramic

Titanium dioxide powder (10g) and yttrium oxide in a molar ratio of 1: 1, mixing materials, adding citric acid (0.2g) as a dispersing agent, adding water (30g) as a ball milling medium, and ball milling for 4 hours by adopting a zirconium oxide milling ball. Adding PMMA accounting for 50% of the volume of all solid raw materials into the slurry as a pore-forming agent, continuing ball milling for 1 hour, and then drying at 80 ℃. And sieving, dry pressing and cold isostatic pressing to obtain biscuit. And carrying out degumming treatment on the biscuit at 600 ℃ for 2 hours, and then sintering the biscuit at 1200 ℃ for 10 hours under the air atmosphere condition to obtain the porous yttrium titanate ceramic heat-insulating material. The material is made into a wafer with the diameter of 50mm and the thickness of 5mm for a heat insulation test, and the thermal conductivity is 0.18W/mK at 30 ℃. The porosity of the porous yttrium titanate ceramic heat-insulating material is 50%, and the breaking strength is 50 MPa. The water absorption after 30 days of rest in air was 0.3%. At 500 ℃, the sample swelling rate is less than 0.3 percent by irradiation damage dose of 50dpa of Ne ion bombardment of 45KeV, and no crystal phase change and holes are found. Adding deoxidized deionized water into an autoclave, performing a hydrothermal corrosion resistance test at 300 ℃, taking out the autoclave after 50 hours, wherein the porous structure is basically complete and is not subjected to amorphous transformation.

Example 2Y₂Ti₂O₇Porous heat-insulating ceramic

Ti powder (50g) and yttrium oxide in a molar ratio of 2: 1, proportioning, adding polyethylene glycol (5g) as a dispersing agent, adding ethanol (50g) as a ball milling medium, and circularly mixing materials for 1 hour by adopting a sand mill. Polystyrene balls with the volume ratio of 70 percent are added into the slurry to be used as pore-forming agents, the sanding is continued for 0.5 hour, and then the drying is carried out at the temperature of 60 ℃. And sieving, dry pressing and cold isostatic pressing to obtain biscuit. Carrying out degumming treatment on the biscuit at 500 ℃ for 1 hour, and then sintering the biscuit at 1300 ℃ for 5 hours under the condition of oxygen atmosphere to obtain porous yttrium titanate (Y)₂Ti₂O₇) A ceramic thermal insulation material. The material is made into a wafer with the diameter of 50mm and the thickness of 5mm for a heat insulation test, and the thermal conductivity is 0.12W/mK at 30 ℃. The porosity of the porous yttrium titanate ceramic heat-insulating material is 68%, and the breaking strength is 60 MPa. The water absorption after 30 days of rest in air was 0.6%. At 600 ℃, the sample is bombarded by Ar ions of 45KeV at a radiation damage dose of 30dpa, the swelling rate of the sample is less than 0.2 percent, and no crystal phase change and holes are found. Adding deoxidized deionized water into an autoclave, performing a hydrothermal corrosion resistance test at 300 ℃, taking out the autoclave after 50 hours, wherein the porous structure is basically complete and is not subjected to amorphous transformation.

Example 3

Titanium dioxide powder (30g) and thulium oxide in a molar ratio of 1: 1, preparing materials, adding citric acid (0.2g) as a dispersing agent, adding water (50g) as a ball milling medium, and ball milling for 4 hours by adopting zirconia milling balls. Adding PMMA accounting for 50% of the volume of the solid raw material into the slurry as a pore-forming agent, continuing ball milling for 0.5 hour, and then drying at 80 ℃. And sieving, dry pressing and cold isostatic pressing to obtain biscuit. And carrying out degumming treatment on the biscuit at 600 ℃ for 2 hours, and then sintering the biscuit at 1300 ℃ for 5 hours under the air atmosphere condition to obtain the porous thulium titanate ceramic heat-insulating material. The material is made into a wafer with the diameter of 50mm and the thickness of 5mm for a heat insulation test, and the thermal conductivity is 0.10W/mK at 30 ℃. The obtained porous lanthanum titanate ceramic heat-insulating material has the porosity of 48 percent, the breaking strength of 90MPa and the water absorption of 0.5 percent after standing in the air for 30 days. At 300 ℃, the sample is bombarded by Ar ions of 45KeV at a radiation damage dose of 50dpa, the swelling rate of the sample is less than 0.1 percent, and no crystal phase change and holes are found. Adding deoxidized deionized water into an autoclave, performing a hydrothermal corrosion resistance test at 300 ℃, taking out the autoclave after 50 hours, wherein the porous structure is basically complete and is not subjected to amorphous transformation.

Example 4

Titanium dioxide powder (100g) and holmium oxide were mixed in a molar ratio of 1: 1, preparing materials, adding citric acid (1g) as a dispersing agent, adding water (70g) as a ball milling medium, and ball milling for 4 hours by adopting zirconia milling balls. Adding PMMA accounting for 50% of the volume of the solid raw materials into the slurry as a pore-forming agent, continuing ball milling for 1 hour, and then drying at 80 ℃. And sieving, dry pressing and cold isostatic pressing to obtain biscuit. And carrying out degumming treatment on the biscuit at 600 ℃ for 2 hours, and then sintering the biscuit at 1200 ℃ for 10 hours under the air atmosphere condition to obtain the porous holmium titanate ceramic heat-insulating material. The material is made into a wafer with the diameter of 50mm and the thickness of 5mm for a heat insulation test, and the thermal conductivity is 0.15W/mK at 30 ℃. The obtained porous holmium titanate ceramic heat-insulating material has the porosity of 52 percent, the breaking strength of 60MPa and the water absorption of 0.8 percent after standing in the air for 30 days. At 600 ℃, the sample swelling rate is less than 0.1 percent by irradiation damage dose of 30dpa of Kr ion bombardment of 100KeV, and no crystal phase change and holes are found. Adding deoxidized deionized water into an autoclave, performing a hydrothermal corrosion resistance test at 300 ℃, taking out the autoclave after 50 hours, wherein the porous structure is basically complete and is not subjected to amorphous transformation.

Example 5

Titanium dioxide powder (40g) and ytterbium oxide were mixed in a molar ratio of 1: 1, mixing materials, adding citric acid (0.3g) as a dispersing agent, adding water (60g) as a ball milling medium, and ball milling for 4 hours by adopting a zirconium oxide milling ball. Adding PMMA accounting for 60 percent of the volume of the solid raw material into the slurry as a pore-forming agent, continuing ball milling for 1 hour, and then drying at 80 ℃. And sieving, dry pressing and cold isostatic pressing to obtain biscuit. And carrying out degumming treatment on the biscuit at 600 ℃ for 2 hours, and then sintering the biscuit at 1250 ℃ for 8 hours under the air atmosphere condition to obtain the porous ytterbium titanate ceramic heat-insulating material. The material is made into a wafer with the diameter of 50mm and the thickness of 5mm for a heat insulation test, and the thermal conductivity is 0.2W/mK at 30 ℃. The porosity of the porous ytterbium titanate ceramic heat-insulating material is 60%, and the breaking strength is 80 MPa. The water absorption after 30 days of rest in air was 0.8%. At 500 ℃, the sample is bombarded by Ar ions of 45KeV at a radiation damage dose of 30dpa, the swelling rate of the sample is less than 0.3 percent, and no crystal phase change and holes are found. Adding deoxidized deionized water into an autoclave, carrying out a hydrothermal corrosion resistance test at 320 ℃, taking out the autoclave after 60 hours, wherein the porous structure is basically complete and is not subjected to amorphous transformation.

Example 6Y₂Ti₂O₇Porous heat-insulating ceramic

Ti powder (70g) withYttrium oxide is added according to a molar ratio of 2: 1, proportioning, adding polyethylene glycol (6g) as a dispersing agent, adding ethanol (50g) as a ball milling medium, and circularly mixing materials for 1 hour by adopting a sand mill. Polystyrene balls accounting for 30 percent of the volume of the solid raw materials are added into the slurry to serve as pore-forming agents, sanding is continuously carried out for 0.5 hour, and then drying is carried out at 60 ℃. And sieving, dry pressing and cold isostatic pressing to obtain biscuit. Carrying out degumming treatment on the biscuit at 500 ℃ for 1 hour, and then sintering the biscuit at 1300 ℃ for 10 hours under the condition of oxygen atmosphere to obtain porous yttrium titanate (Y)₂Ti₂O₇) A ceramic thermal insulation material. The material is made into a wafer with the diameter of 50mm and the thickness of 5mm for a heat insulation test, and the thermal conductivity is 0.5W/mK at 30 ℃. The porosity of the porous yttrium titanate ceramic heat-insulating material is 30%, and the breaking strength is 120 MPa. The water absorption after 30 days of rest in air was 0.6%. At 600 ℃, the sample is bombarded by Ar ions of 45KeV at a radiation damage dose of 30dpa, the swelling rate of the sample is less than 0.2 percent, and no crystal phase change and holes are found. Adding deoxidized deionized water into an autoclave, performing a hydrothermal corrosion resistance test at 350 ℃, taking out the autoclave after 50 hours, wherein the porous structure is basically complete and is not subjected to amorphous transformation.

Example 7Y₂Ti₂O₇Porous heat-insulating ceramic

Ti powder (30g) and yttrium oxide in a molar ratio of 2: 1, proportioning, adding polyethylene glycol (5g) as a dispersing agent, using ethanol (60g) as a ball milling medium, and circularly mixing materials for 1 hour by adopting a sand mill. Polystyrene balls accounting for 10 percent of the volume of the solid raw materials are added into the slurry to serve as pore-forming agents, sanding is continuously carried out for 0.5 hour, and then drying is carried out at 60 ℃. And sieving, dry pressing and cold isostatic pressing to obtain biscuit. Carrying out degumming treatment on the biscuit at 500 ℃ for 1 hour, and then sintering the biscuit at 1300 ℃ for 20 hours under the condition of oxygen atmosphere to obtain porous yttrium titanate (Y)₂Ti₂O₇) A ceramic thermal insulation material. The material is made into a wafer with the diameter of 50mm and the thickness of 5mm for a heat insulation test, and the thermal conductivity is 1.5W/mK at 30 ℃. The porosity of the porous yttrium titanate ceramic heat-insulating material is 12%, and the breaking strength is 180 MPa. The water absorption after 30 days of rest in air was 0.3%. Ar ion bombardment at 500 deg.C and 80KeVWhen the irradiation damage dose of 30dpa is hit, the swelling rate of the sample is less than 0.3 percent, and no crystal phase change and holes are found. Adding deoxidized deionized water into an autoclave, carrying out a hydrothermal corrosion resistance test at 320 ℃, taking out the autoclave after 50 hours, wherein the porous structure is basically complete and is not subjected to amorphous transformation.

Example 8Y₂TiO₅Porous heat-insulating ceramic

Titanium dioxide powder (60g) and yttrium oxide in a molar ratio of 1: 1, preparing materials, adding citric acid (0.3g) as a dispersing agent, adding water (40g) as a ball milling medium, and ball milling for 4 hours by adopting zirconia milling balls. Adding hydrogen peroxide with the solid raw material volume ratio of 50% into the slurry as a foaming agent, continuing ball milling for 1 hour, and then adopting slip casting. And carrying out degumming treatment on the biscuit at 600 ℃ for 2 hours, and then sintering the biscuit at 1200 ℃ for 10 hours under the air atmosphere condition to obtain the porous yttrium titanate ceramic heat-insulating material. The material is made into a wafer with the diameter of 50mm and the thickness of 5mm for a heat insulation test, and the thermal conductivity is 0.09W/mK at 30 ℃. The obtained porous yttrium titanate ceramic thermal insulation material has 70% of porosity, 68MPa of breaking strength and 0.4% of water absorption after standing in air for 30 days. At 700 ℃, the sample swelling rate is less than 0.2 percent by irradiation damage dose of 30dpa bombarded by Ar ions of 120KeV, and no crystal phase change and holes are found. Adding deoxidized deionized water into an autoclave, performing a hydrothermal corrosion resistance test at 300 ℃, and taking out a porous structure after 80 hours to be basically complete without amorphous transformation.

Comparative example 1

Titanium dioxide powder (50g) and yttrium oxide in a molar ratio of 1: 1, mixing materials, adding citric acid (0.5g) as a dispersing agent, adding water (60g) as a ball milling medium, and ball milling for 4 hours by adopting a zirconium oxide milling ball. Then dried at 80 ℃. And sieving, dry pressing and cold isostatic pressing to obtain biscuit. And carrying out degumming treatment on the biscuit at 600 ℃ for 2 hours, and then sintering the biscuit at 1350 ℃ for 20 hours under the air atmosphere condition to obtain the porous yttrium titanate ceramic heat-insulating material. The material is made into a wafer with the diameter of 50mm and the thickness of 5mm for a heat insulation test, and the thermal conductivity is 2.2W/mK at 30 ℃. The porosity of the porous yttrium titanate ceramic heat-insulating material is 0.5%, and the breaking strength is 620 MPa. The water absorption after 30 days of rest in air was 0.2%. At 600 ℃, the sample swelling rate is less than 0.2 percent by irradiation damage dose of 30dpa bombarded by Ar ions of 120KeV, and no crystal phase change and holes are found. Adding deoxidized deionized water into an autoclave, performing a hydrothermal corrosion resistance test at 350 ℃, taking out the autoclave after 50 hours, wherein the porous structure is basically complete and is not subjected to amorphous transformation.

Table 1 shows the performance parameters of the porous rare earth titanate thermal insulation materials prepared in examples 1 to 8 of the present invention and comparative example 1:

Claims

1. the preparation method of the porous rare earth titanate heat insulation material is characterized in that the porous rare earth titanate heat insulation material has a porous structure and consists of (Re)₂O₃）_X（TiO₂）_1-XWherein Re is at least one of Y and lanthanide, and X = 0.2-0.8; the porosity of the porous rare earth titanate heat-insulating material is 10-90%, and the pore size is 0.1-500 microns;

the preparation method of the porous rare earth titanate heat insulation material comprises the following steps:

mixing a rare earth source, a titanium source and a solvent to obtain slurry;

2. The method according to claim 1, wherein X = 0.4-0.7.

3. The method according to claim 1, wherein Re is at least one of Y, La, neodymium, promethium, holmium, erbium, thulium, ytterbium, and lutetium.

4. The preparation method of claim 1, wherein the porous rare earth titanate thermal insulation material further comprises at least one of alumina, magnesia, chromia, silica and iron oxide, and the content of the at least one of alumina, magnesia, chromia, silica and iron oxide is not more than 5% by mass of the porous rare earth titanate thermal insulation material.

5. The method of claim 1, wherein the titanium source is TiO₂，Ti₂O₃And Ti, wherein the rare earth source is at least one of Re-containing rare earth oxide, hydroxide and nitrate.

6. The method according to claim 1, wherein the solvent is water or a liquid organic solvent, and the slurry has a solid content of 30 to 80 wt%.

7. The preparation method according to claim 1, wherein the slurry further comprises a sintering aid, and the sintering aid is at least one of aluminum oxide, magnesium oxide, chromium oxide, silicon oxide and iron oxide, and the content of the sintering aid is not more than 5wt% of the total mass of the powder.

8. The preparation method of claim 1, wherein the pore-forming agent is an organic polymer and is at least one of PMMA, polystyrene, polyethylene spheres, ion exchange resin and starch, and the pore-forming agent accounts for 10-80% of the solid raw material in the slurry by volume.

9. The preparation method of claim 8, wherein the pore-forming agent accounts for 30-70% of the solid raw material in the slurry by volume.

10. The preparation method according to claim 1, wherein the foaming agent is at least one of hydrogen peroxide, azobisisobutyronitrile and sodium borohydride, and the foaming agent accounts for 10-80% of the solid raw material in the slurry by volume.

11. The preparation method according to claim 10, wherein the foaming agent accounts for 30-70% of the solid raw material in the slurry by volume.

12. The preparation method according to any one of claims 1 to 11, wherein the green body is subjected to binder removal before sintering, wherein the binder removal is performed at a temperature of 300 to 600 ℃ for 3 to 10 hours.

13. The porous rare earth titanate thermal insulation material prepared by the preparation method of any one of claims 1 to 12, wherein the water absorption rate of the porous rare earth titanate thermal insulation material is 0.3-2%; the bending breaking strength of the porous rare earth titanate heat-insulating material is 10-200 MPa; the thermal conductivity of the porous rare earth titanate thermal insulation material at 30 ℃ is 0.05-1.5W/mK.

14. Use of the porous rare earth titanate thermal insulation material of claim 13 in the preparation of thermal insulation material for a nuclear reactor.