A near-zero thermal expansion standard and its preparation method and application

Abstract

The application discloses a near-zero thermal expansion standard device and a preparation method and application thereof, and belongs to the technical field of metrological standard devices. The application provides a preparation method of the near-zero thermal expansion standard device, and comprises the following steps: placing PbO, TiO2 and SrO in a ball mill jar to perform first ball milling, and then performing calcination to obtain calcined powder; performing second ball milling on the obtained calcined powder, and then performing compression molding, sintering, third ball milling and secondary sintering to obtain the near-zero thermal expansion standard device. The application uses a solid phase method, adjusts and controls a perovskite lattice structure by means of A-site doped lead titanate material system, so that the thermal expansion performance is changed, meanwhile, the negative linear expansion property of the lead titanate doped with Sr is weakened, and the preparation of the near-zero expansion standard device is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of metrological standards, and in particular relates to a near-zero thermal expansion standard and a preparation method and application thereof. Background Art

[0002] Solid materials typically expand and contract with temperature changes. However, changes in material volume with temperature can reduce the structural stability and safety reliability of precision components, and even destroy the functional properties of the material. In high-tech fields such as optical instruments, microelectronics, and aerospace, there is an urgent need for materials whose shape and size do not change with temperature to ensure that their components have high dimensional stability, precision, and long service life. This has led to a demand for the research and development of near-zero expansion functional materials. The coefficient of thermal expansion (CTE) is an important parameter for characterizing the thermal expansion properties of materials. The development of near-zero expansion materials has placed high demands on the measurement and characterization of CTE. The development of near-zero thermal expansion standards is the basis for accurate measurement of thermal expansion instruments and is also a necessary support for the processing and application of near-zero expansion materials.

[0003] The instruments currently used to measure CTE mainly include thermomechanical analyzers and thermal expansion meters. Their working principle is to continuously measure the size of the sample under programmed temperature conditions and calculate the CTE value through the numerical relationship between the size and temperature. Such instruments need to be calibrated and the method confirmed using a standard instrument or standard material at the beginning of the measurement to ensure the accuracy, consistency and traceability of the results. By carrying out near-zero adjustable thermal expansion coefficient (10 -7 ~10 -8 / ℃ level) can effectively solve the daily calibration problem of thermal expansion meters and provide traceability support and technical guarantee for the subsequent application of related measuring equipment in the field of material analysis and testing.

[0004] Research on near-zero thermal expansion standards has a long history, but there are still few reports on the release of linear expansion standard materials. Overseas, only the National Institute of Standards and Technology of the United States has released a thermal expansion coefficient standard material based on borosilicate glass material. In 2024, the China National Institute of Metrology released two new thermal expansion coefficient standard materials (high-purity aluminum and polyetheretherketone). Among them, high-purity aluminum is purchased from Alfa and is easily subject to foreign trade import and export restrictions. In addition, due to the lack of core technology related to product development, the stability of subsequent products is difficult to guarantee; at the same time, the thermal expansion coefficients of these two standard materials are on the order of 10 -6 / °C, unable to meet the current domestic market demand for thermal expansion meters. Traditional low-expansion materials, such as Invar alloy, have high specific gravity and a narrow linear expansion range; while zero-expansion glass-ceramics are brittle and difficult to process. These characteristics severely limit their practical application.

[0005] Therefore, there is an urgent need for a near-zero thermal expansion standard to solve the above problems. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention proposes a near-zero thermal expansion standard and its preparation method and application.

[0007] To achieve the above objectives, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing a near-zero thermal expansion standard, comprising the following steps:

[0009] (1) PbO, TiO2, and SrO are placed in a ball mill for a first ball milling, and then calcined to obtain a calcined powder;

[0010] (2) The calcined powder obtained in step (1) is subjected to a second ball milling, and then subjected to pressing, sintering, a third ball milling and a second sintering to obtain the near-zero thermal expansion standard.

[0011] Preferably, in step (1), the molar ratio of PbO, TiO2, and SrO is 1:1:x, where x=0.05, 0.1, 0.15, or 0.2.

[0012] Preferably, in step (1), the calcination temperature is 450-600° C., and the calcination holding time is 10 h.

[0013] Preferably, in step (2), the pressing pressure is 30 MPa.

[0014] Preferably, in step (2), the sintering temperature is 1050-1200° C., and the sintering holding time is 5 hours.

[0015] Preferably, in step (2), the temperature of the secondary sintering is 1050-1200° C., and the holding time of the secondary sintering is 5 hours.

[0016] Preferably, in step (2), a polishing step is further included after sintering.

[0017] Preferably, in step (1) or (2), the grinding balls used in the first ball mill, the second ball mill and the third ball mill are all agate balls, the ball-to-material ratio is 2:1, the ball milling time is 24 hours, and the ball milling medium is all anhydrous ethanol.

[0018] The present invention provides a near-zero thermal expansion standard prepared by the preparation method described in the above technical solution, wherein the thermal expansion coefficient of the near-zero thermal expansion standard is 10 -7 ~10 -8 / ℃.

[0019] The present invention also provides the application of the near-zero thermal expansion standard described in the above technical solution in a high-precision dilatometer.

[0020] Compared with the prior art, the present invention has the following advantages and technical effects:

[0021] The present invention uses a solid-phase method to control the perovskite lattice structure by doping the A-site lead titanate material system to change the thermal expansion properties. Lead titanate has excellent properties such as a large negative linear expansion coefficient, a high Curie temperature, and a large spontaneous polarization. As an excellent ceramic oxide, it shows the potential for the development of near-zero expansion standard materials; at the same time, by using Sr to dope lead titanate, its negative linear expansion is weakened, and the preparation of a near-zero expansion standard device is achieved.

[0022] The near-zero thermal expansion standard provided by the present invention has stable thermal expansion performance within the range of 0 to 200°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0024] Figure 1 This is a thermal expansion performance curve of the near-zero thermal expansion standard prepared in Example 3;

[0025] Figure 2 A physical picture of the near-zero thermal expansion standard prepared by the present invention;

[0026] Figure 3 XRD patterns of the near-zero thermal expansion standards prepared in Examples 1 to 4;

[0027] Figure 4 These are SEM images of the near-zero thermal expansion standards prepared in Examples 1 to 4. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making creative efforts are within the scope of protection of the present invention.

[0029] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] An embodiment of the present invention provides a method for preparing a near-zero thermal expansion standard, comprising the following steps:

[0031] (1) PbO, TiO2, and SrO are placed in a ball mill for a first ball milling, and then calcined to obtain a calcined powder;

[0032] (2) The calcined powder obtained in step (1) is subjected to a second ball milling, and then subjected to pressing, sintering, a third ball milling and a second sintering to obtain the near-zero thermal expansion standard.

[0033] In a preferred embodiment, in step (1), the molar ratio of PbO, TiO2, and SrO is 1:1:x, where x = 0.05, 0.1, 0.15, or 0.2. The present invention adjusts the thermal expansion coefficient of the thermal expansion standard by controlling the amount of SrO. Too little SrO has little effect on lattice distortion, thus failing to improve thermal expansion performance. Excessive SrO may damage the original perovskite lattice structure and lose the negative expansion correction property. Using SrO as the Sr source can avoid the formation of other additional products (e.g., SrCO3 may generate complex carbides during sintering).

[0034] In a preferred embodiment, in step (1), the grinding balls used in the first ball mill are agate balls, the ball-to-material ratio is 2:1, the ball milling time is 24 hours, and the ball milling medium is anhydrous ethanol. The present invention achieves thorough mixing of the raw materials and reduces their size through the first ball milling, which facilitates a thorough reaction between the raw materials during the subsequent sintering process. The use of agate balls has the advantages of high wear resistance and no pollution, while the use of anhydrous ethanol as the ball milling medium has the advantages of being environmentally friendly, readily available, and low-toxic.

[0035] In a preferred embodiment, a heating step is further included after the first ball milling is completed; the heating step specifically comprises: pouring the slurry obtained by the first ball milling into a beaker, and then placing it on a magnetic stirrer for heating and stirring; the temperature of the heating and stirring is 50° C. The present invention volatilizes the ethanol by heating.

[0036] In a preferred embodiment, in step (1), the calcination temperature is 450-600°C, the calcination holding time is 10 hours, the calcination atmosphere is air, and the calcination equipment is a muffle furnace. The present invention activates the raw materials by calcination and performs a pre-reaction at the same time.

[0037] In a preferred embodiment, in step (2), the pressure of the press molding is 30 MPa; the diameter of the product obtained by the press molding is 10 mm and the thickness is 2 mm.

[0038] In a preferred embodiment, in step (2), the sintering temperature is 1050-1200° C., the sintering holding time is 5 hours, and the sintering atmosphere is air.

[0039] In a preferred embodiment, in step (2), the secondary sintering temperature is 1050-1200°C, the holding time is 5 hours, and the atmosphere is air. The present invention facilitates obtaining a near-zero thermal expansion standard with high uniformity and stable performance through secondary sintering.

[0040] In a preferred embodiment, in step (2), a grinding step is further included after sintering; the grinding tool is fine sandpaper. The present invention removes the surface portion of the product obtained by secondary sintering by grinding, and retains the middle layer portion to ensure the uniformity of the sample.

[0041] In a preferred embodiment, in step (2), the grinding balls of the second ball mill and the third ball mill are agate balls, the ball-to-material ratio is 2:1, the ball milling time is 24 hours, and the ball milling medium is anhydrous ethanol.

[0042] The present invention provides a near-zero thermal expansion standard prepared by the preparation method described in the above technical solution, wherein the thermal expansion coefficient of the near-zero thermal expansion standard is 10 -7 ~10 -8 / ℃.

[0043] In a preferred embodiment, the composition of the near-zero thermal expansion standard is Pb 1-x Sr x TiO3, wherein x = 0.05, 0.1, 0.15 or 0.2.

[0044] The present invention also provides the application of the near-zero thermal expansion standard described in the above technical solution in a high-precision dilatometer.

[0045] The room temperature in the embodiments of the present invention refers to "25±2°C".

[0046] Unless otherwise specified, the raw materials in the examples of the present invention were purchased from commercial sources.

[0047] Example 1

[0048] A method for preparing a near-zero thermal expansion standard, comprising the following steps:

[0049] (1) The raw materials PbO, TiO2, and SrO were placed in glassware, dried in a vacuum oven at 100°C for 24 h, and then transferred to a drying dish for use after cooling. PbO, TiO2, and SrO were weighed using an electronic balance at a molar ratio of 1:1:0.05, then placed in a polytetrafluoroethylene ball mill, milled for 24 h using anhydrous ethanol as the milling medium and agate balls as the grinding balls at a ball-to-material ratio of 2:1. The slurry obtained by ball milling was then poured into a beaker, which was placed on a magnetic stirrer and heated and stirred at 50°C. After the ethanol evaporated, a mixed powder was obtained.

[0050] (2) The mixed powder obtained in step (1) is placed in an alumina crucible, and the alumina crucible is placed in a muffle furnace and kept at 500° C. for 10 h to obtain a calcined powder.

[0051] (3) The calcined powder obtained in step (2) is placed in a planetary ball mill, using anhydrous ethanol as the ball milling medium, agate balls as the grinding balls, and a ball-to-material ratio of 2:1, and ball milling is performed for 24 hours. The slurry obtained by ball milling is then poured into a beaker, and the beaker is placed on a magnetic stirrer and heated and stirred at 50°C. After the ethanol evaporates, the powder obtained by ball milling is placed on a tablet press and pressed into a ceramic sheet with a diameter of 10 mm and a thickness of 2 mm at a pressure of 30 MPa.

[0052] (4) The ceramic sheet obtained in step (3) was sintered at 1100°C for 5 h. After cooling, the surface of the ceramic sheet was polished off with fine sandpaper, leaving the middle layer. The ceramic sheet was then ball-milled into powder using a planetary ball mill (using anhydrous ethanol as the ball milling medium, agate balls as the grinding balls, a ball-to-material ratio of 2:1, and a ball milling time of 24 h). The ceramic sheet was then sintered at 1100°C for 5 h to complete the secondary sintering and obtain a near-zero thermal expansion standard, which was recorded as 1:1:0.05.

[0053] Example 2

[0054] The difference from Example 1 is that in step (1), PbO, TiO2 and SrO are weighed according to the material ratio of 1:1:0.1, and the remaining steps are the same as Example 1, recorded as 1:1:0.1.

[0055] Example 3

[0056] The difference from Example 1 is that in step (1), PbO, TiO2 and SrO are weighed according to the material ratio of 1:1:0.15, and the remaining steps are the same as Example 1, recorded as 1:1:0.15.

[0057] Example 4

[0058] The difference from Example 1 is that in step (1), PbO, TiO2 and SrO are weighed according to the material ratio of 1:1:0.2, and the remaining steps are the same as Example 1, recorded as 1:1:0.2.

[0059] Example 5

[0060] The difference from Example 1 is that in step (4), the ceramic sheet obtained in step (3) is sintered at 1200° C. for 5 h, and the remaining steps are the same as Example 1.

[0061] Example 6

[0062] The difference from Example 1 is that in step (4), the ceramic sheet obtained in step (3) is sintered at 1180° C. for 5 h, and the remaining steps are the same as Example 1.

[0063] Example 7

[0064] The difference from Example 1 is that in step (4), the secondary sintering is completed by sintering at 1150° C. for 5 hours, and the remaining steps are the same as Example 1.

[0065] Example 8

[0066] The difference from Example 1 is that in step (4), the secondary sintering is completed by sintering at 1050° C. for 5 hours, and the remaining steps are the same as Example 1.

[0067] Example 9

[0068] The difference from Example 1 is that in step (2), the temperature is kept at 550° C. for 10 h, and the remaining steps are the same as Example 1.

[0069] Example 10

[0070] The difference from Example 1 is that in step (2), the temperature is kept at 450° C. for 10 h, and the remaining steps are the same as Example 1.

[0071] Comparative Example 1

[0072] The difference from Example 1 is that in step (1), PbO, TiO2 and SrO are weighed according to the molar ratio of 1:1:0.02, and the remaining steps are the same as Example 1.

[0073] Comparative Example 2

[0074] The difference from Example 1 is that in step (1), PbO, TiO2 and SrO are weighed according to the molar ratio of 1:1:0.25, and the remaining steps are the same as Example 1.

[0075] Comparative Example 3

[0076] The difference from Example 1 is that in step (4), the ceramic sheet obtained in step (3) is sintered at 900° C. for 5 h, and the remaining steps are the same as Example 1.

[0077] Comparative Example 4

[0078] The difference from Example 1 is that in step (4), the secondary sintering is completed by sintering at 1300° C. for 5 hours, and the remaining steps are the same as Example 1.

[0079] Comparative Example 5

[0080] The difference from Example 1 is that in step (4), the secondary sintering is completed by sintering at 1100° C. for 2 hours, and the remaining steps are the same as Example 1.

[0081] Comparative Example 6

[0082] Steps (1) to (3) are the same as in Example 1;

[0083] (4) The surface of the ceramic sheet obtained in step (3) was polished off with fine sandpaper, leaving the middle layer, and then the ceramic sheet was ball-milled into powder using a planetary ball mill (using anhydrous ethanol as the ball milling medium, agate balls as the grinding balls, a ball-to-material ratio of 2:1, and a ball milling time of 24 hours), and then sintered at 1100°C for 5 hours to obtain a near-zero thermal expansion standard.

[0084] The thermal expansion coefficients of the thermal expansion standards prepared in Examples 1 to 10 and Comparative Examples 1 to 6 were tested with reference to the thermal expansion coefficient calibration method for NIM-ZY-CD-LX-118 material. The specific testing process is as follows: using laser interferometry, the expansion or contraction of the test piece causes a change in the optical path difference, resulting in fringe movement. The fringe changes are detected, and the change in fringe length is recorded. According to the selected temperature range, the temperature value of the test piece and the laser interferometer reading are recorded at each temperature point, and the instantaneous thermal expansion coefficient of the test piece is calculated at a reference temperature of 20°C. The results are shown in Tables 1 and 2.

[0085] Table 1 Thermal expansion coefficients of thermal expansion standards prepared in Examples 1 to 10 and Comparative Examples 1 to 6 at 200°C

[0086] <![CDATA[Coefficient of thermal expansion (1×10 -8 / °C)]]> Example 1 20.53 Example 2 14.47 Example 3 9.84 Example 4 11.52 Example 5 10.11 Example 6 10.03 Example 7 9.97 Example 8 11.89 Example 9 12.37 Example 10 15.79 Comparative Example 1 60.53 Comparative Example 2 80.64 Comparative Example 3 -40.22 Comparative Example 4 110.51 Comparative Example 5 180.11 Comparative Example 6 100.74

[0087] As can be seen from Table 1, the thermal expansion coefficients of the thermal expansion standards prepared in Examples 1 to 10 of the present invention are all close to 10 at 200°C. -8 The thermal expansion coefficient of the thermal expansion standards prepared in Comparative Examples 1 to 6 reaches 10 -6 Even comparative example 3 (when the sintering temperature is too low) exhibits negative expansion.

[0088] Table 2 Thermal expansion coefficient test data of thermal expansion standard prepared in Example 3

[0089]

[0090]

[0091] Figure 1 This is a thermal expansion performance curve of the near-zero thermal expansion standard prepared in Example 3. Figure 1 As can be seen from Table 2, the CTE of the near-zero thermal expansion standard prepared in Example 3 is 10 -8 / ℃, approaching to 0; with the increase of measurement temperature, the CTE value of the standard device remains basically unchanged, indicating that the thermal expansion performance of the standard device is stable.

[0092] Figure 2 This is a physical picture of the near-zero thermal expansion standard prepared by the present invention.

[0093] Figure 3 The XRD patterns of the near-zero thermal expansion standards prepared in Examples 1 to 4 are shown below. Figure 3 It can be seen that the near-zero thermal expansion standard prepared by the present invention is made of Pb 1-x Sr x Composed of TiO3. Figure 3 The middle dotted line shows that as the Sr doping concentration increases, the characteristic peak shifts to a larger angle, indicating that the higher the doping concentration, the smaller the lattice spacing becomes, that is, Sr atoms are mainly inserted into the perovskite lattice, which is also consistent with the stoichiometric ratio of the components of the present invention.

[0094] Figure 4 The SEM images of the near-zero thermal expansion standards prepared in Examples 1 to 4 are shown below. Figure 4 It can be seen that the surface of the near-zero thermal expansion standard prepared in Example 3 is the most uniform and has almost no holes.

[0095] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for preparing a near-zero thermal expansion standard, characterized in that: The following steps are involved: (1) placing PbO, TiO2, and SrO in a ball mill for a first ball milling, and then calcining to obtain a calcined powder; the molar ratio of PbO, TiO2, and SrO is 1:1:x, where x=0.05, 0.1, 0.15, or 0.2; (2) The calcined powder obtained in step (1) is subjected to a second ball milling, and then subjected to pressing, sintering, a third ball milling and a second sintering to obtain the near-zero thermal expansion standard; the sintering temperature is 1050-1200°C, and the sintering holding time is 5 hours; the sintering step also includes a grinding step; the second sintering temperature is 1050-1200°C, and the second sintering holding time is 5 hours.

2. The preparation method according to claim 1, characterized in that In step (1), the calcination temperature is 450-600° C., and the calcination holding time is 10 hours.

3. The preparation method according to claim 1, characterized in that In step (2), the pressing pressure is 30 MPa.

4. The preparation method according to claim 1, characterized in that In step (1) or (2), the grinding balls of the first ball mill, the second ball mill and the third ball mill are all agate balls, the ball-to-material ratio is 2:1, the ball milling time is 24 hours, and the ball milling medium is all anhydrous ethanol.

5. A near-zero thermal expansion standard prepared by the preparation method according to any one of claims 1 to 4, characterized in that: The thermal expansion coefficient of the near-zero thermal expansion standard is 10 -7 ~10 -8 / ℃.

6. Use of the near-zero thermal expansion standard according to claim 5 in a high-precision dilatometer.

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