Method for determining glass-ceramic nucleation time

Abstract

This invention provides a method for determining the nucleation time of a glass-ceramic, comprising: testing the differential thermal analysis (DSC) curve of a precursor glass to obtain the glass transition point Tg and the crystallization peak position Pc; selecting a nucleation temperature Tn and a crystallization temperature Tc, wherein Tn ranges from Tg to Tg+150℃ and Tc ranges from Pc-60℃ to Pc+60℃; performing DSC tests on the precursor glass at different times under heat treatment at Tc, and setting the time corresponding to the complete disappearance of the crystallization peak on the DSC curve as the crystallization time tc; preparing the glass-ceramic, wherein the precursor glass is first heated to Tn and held at that temperature, and then heated to Tc and held at that temperature for tc; testing the DSC curve of the glass-ceramic obtained in step 4, and calculating the integral area of ​​the corresponding endothermic peak on the DSC curve; gradually extending the nucleation time, repeating steps 4-5, and when the change in the integral area of ​​the endothermic peak on the DSC curve is less than a preset value, the corresponding nucleation time is the optimal nucleation time tn. This invention can quickly and accurately determine the shortest time required to reach the nucleation limit.

Description

Technical Field

[0001] This invention belongs to the technical field of glass-ceramic preparation, specifically relating to a method for determining the nucleation time of glass-ceramics. Background Technology

[0002] Glass-ceramics are materials in which uniformly distributed crystal particles are precipitated within a glass substrate through controlled crystallization. Generally, as the crystal content increases, the mechanical properties also gradually increase, such as flexural strength, Vickers hardness, and fracture toughness. Practical glass-ceramics typically require uniform grain size and distribution. To achieve this, a two-step process is generally used to prepare glass-ceramics. The first step involves nucleation at a lower temperature, precipitating uniformly dense nanoscale crystals as nuclei in the precursor glass. The second step involves raising the temperature to a higher level for crystallization, allowing the target crystal to grow uniformly based on these nuclei.

[0003] The number of crystal nuclei is the decisive factor in obtaining the crystal content in the final glass-ceramic. For a precursor glass with a specific composition, in the first step of the nucleation process, when held at a fixed temperature within the nucleation temperature range, the number of crystal nuclei increases with the extension of the holding time. However, there is a limit to the number of crystal nuclei that can be generated at that temperature. Determining the time required to reach the nucleation limit at a certain nucleation temperature is crucial for the preparation and production of glass-ceramics. Insufficient nucleation time results in the number of crystal nuclei not reaching the maximum value for the glass-ceramic composition, leading to the incomplete realization of the physical properties of the final product. Excessive nucleation time results in an ineffective nucleation period, leading to reduced production efficiency and energy waste.

[0004] X-ray diffraction (XRD) is a common method for testing the crystalline phase content in glass ceramics. However, the size of crystal nuclei is extremely small, and the X-ray diffraction peaks of glass ceramics that have only undergone the first step of nucleation treatment are very weak. Therefore, XRD cannot accurately determine the number and content of crystal nuclei, and can only perform qualitative analysis. Sequencing imaging (SEM) can also determine the number of crystal nuclei; however, it can only count the number of nuclei exposed on the sample surface. Furthermore, the sample usually needs to be etched with acid to expose the nuclei, and if the acid concentration and etching time are inappropriate, the nuclei are often etched away. Therefore, there is also a significant error when using SEM to assess the number of crystal nuclei.

[0005] CN101215077A discloses a method for determining the nucleation conditions of glass containing nucleating agents. It involves performing differential thermal analysis on pre-nucleated glass and using the magnitude of the crystallization peak temperature to determine the optimal nucleation temperature and time. However, this patent, after determining the optimal nucleation temperature, only selects a pre-nucleation time range of 0.5–2 hours to determine the optimal nucleation time. This time range is too narrow; 2 hours is far from reaching the nucleation limit of glass-ceramics. Therefore, there is an urgent need in the field for a method that can quickly and accurately determine when glass-ceramics have reached their nucleation limit. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for determining the nucleation time of glass ceramics. This method calculates and compares the endothermic peak area during the melting of precipitated crystals, thereby quickly and accurately determining the shortest time required to reach the nucleation limit.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A method for determining the nucleation time of glass-ceramics includes the following steps:

[0009] Step 1: Test the differential thermal analysis (DSC) curve of the precursor glass to obtain the glass transition point (Tg) and the position of the crystallization peak (Pc);

[0010] Step 2: Determine a nucleation temperature (Tn) and a crystallization temperature (Tc). The nucleation temperature (Tn) ranges from Tg to (Tg+150℃), and the crystallization temperature (Tc) ranges from (Pc-60℃) to (Pc+60℃).

[0011] Step 3: Heat the precursor glass for different times (Tc) and test the DSC values ​​respectively. Set the time when the crystallization peak on the DSC curve completely disappears as the crystallization time (tc).

[0012] Step 4: Prepare glass ceramics using a two-step method, including: heating the precursor glass to the nucleation temperature (Tn) and holding it at that temperature for a certain time, then continuing to heat it to the crystallization temperature (Tc) and holding it at that temperature for tc time;

[0013] Step 5: Test the differential thermal analysis (DSC) curve of the glass ceramic obtained in Step 4, and calculate the integral area of ​​the corresponding endothermic peak on the DSC curve.

[0014] Step 6: Gradually extend the nucleation time and repeat steps 4-5. When the change in the integral area of ​​the endothermic peak of the DSC curve is less than the preset value, the corresponding nucleation time is the optimal nucleation time tn required for the nucleation temperature Tn.

[0015] The method for determining the nucleation time of glass-ceramics is particularly applicable to precursor glass compositions subjected to a two-step crystallization process. The two-step crystallization process involves a first step of nucleation at a lower temperature, precipitating uniform and dense nanoscale crystals as nuclei in the precursor glass; and a second step of raising the temperature to a higher temperature for crystallization, allowing the target crystal to grow uniformly based on these nuclei.

[0016] Nucleation temperatures (Tn) typically range from Tg to Tg+150℃. In some cases, nucleation at relatively lower temperatures results in smaller and more uniform nuclei, while nucleation at relatively higher temperatures leads to larger variations in nuclei size. More uniform nuclei size is beneficial for obtaining more uniform grain size during crystal growth (crystallization). More optimal nucleation temperatures are often determined experimentally or through testing methods, such as preparing samples using combinations of nucleation temperature / nucleation time and crystallization temperature / crystallization time, and then comparing the properties of the resulting glass-ceramics to determine the optimal nucleation temperature for a specific performance characteristic.

[0017] The crystallization temperature (Tc) typically ranges from (Pc-60℃) to (Pc+60℃). In some cases, the crystallization temperature (Tc) is determined based on the performance requirements of the final product. For example, a lower Tc is chosen to obtain a transparent glass-ceramic, while a higher Tc is chosen to obtain a larger grain size. More preferred crystallization temperatures are often determined experimentally or through testing methods, such as preparing samples using combinations of nucleation temperature / nucleation time and crystallization temperature / crystallization time, and then comparing the performance of the resulting glass-ceramics to determine the optimal crystallization temperature for a specific performance characteristic.

[0018] The crystallization time (tc) can be determined by heat-treating the precursor glass for different times at Tc and performing DSC (Digital Subtraction Angiography) tests. The time at which the crystallization peak on the DSC curve completely disappears is set as the crystallization time (tc). In some cases, the precursor glass used to determine the crystallization time (tc) in step 3 may have undergone nucleation for a certain period of time. In some cases, the precursor glass used to determine the crystallization time (tc) in step 3 may have been nucleated at Tn temperature for tn time after obtaining tn through one round of testing. In some cases, the precursor glass used to determine the crystallization time (tc) in step 3 may have been nucleated at Tn temperature for tn time after obtaining tn through several rounds of testing.

[0019] In the process of determining tn as described in this invention, it is required to exclude the influence of factors other than tn variation. In some cases, apart from the change in nucleation time during the preparation of the DSC test sample, the crystallization temperature and time, as well as various parameters of the DSC test, remain unchanged during the process of determining tn, including sample composition, sample weight, sample particle size, and sample particle size range.

[0020] In some cases, the weight of the DSC test sample is 10-50 mg. If the sample weight is too small, the exothermic and endothermic peaks in the DSC test results will be too small, which is not conducive to accurately determining the location of the crystallization temperature, nor is it conducive to calculating the integral area of ​​the endothermic peak of crystal melting. If the sample weight is too large, the change of the exothermic and endothermic peaks with temperature will lag, resulting in a deviation from the actual results.

[0021] In some cases, the weight difference of DSC test samples is ≤ ±10%. Although the vertical axis of the DSC curve represents the heat released or absorbed per unit weight of sample, the sample weight deviation will lead to the deviation of the test results in the same batch of DSC tests to determine tn.

[0022] In some cases, the particle size of the DSC test sample is 0.1–5.0 mm, and different particle sizes can be selected depending on the type of crystallization in the test sample. In some cases, smaller particle sizes are selected for samples with surface crystallization, while larger particle sizes are selected for samples with overall crystallization.

[0023] In some cases, the particle size distribution of DSC test samples is ≤±10%. Different particle sizes are selected according to the crystallization type of the test sample and the particle size is limited to a certain range. When the particle size range is too large, it will lead to undesirable baseline anomalies.

[0024] In some cases, the heating rate during DSC testing is 3–30 °C / min. It is necessary to limit the heating rate to a suitable range, especially the heating rate from the nucleation temperature to the crystallization temperature. If the heating rate is too slow, nucleation changes will still occur during the heating process, leading to errors in the final determination of tc. Conversely, if the heating rate is too fast, the exothermic and endothermic peaks will lag with temperature changes, resulting in deviations from the actual results.

[0025] The crystallization time (tc) can be determined by heat-treating the precursor glass for different times at Tc and testing with DSC (Digital Subtraction Angiography), setting the time at which the crystallization peak on the DSC curve completely disappears as the crystallization time (tc). In some cases, the precursor glass used to determine the crystallization time (tc) in step 3 may have undergone nucleation for a certain period of time. In some cases, the precursor glass / nucleated glass used to determine the crystallization time (tc) in step 3 may have been nucleated at Tn temperature for tn time after obtaining tn through one round of testing. In some cases, the precursor glass / nucleated glass used to determine the crystallization time (tc) in step 3 may have been nucleated at Tn temperature for tn time after obtaining tn through several rounds of testing. In some cases, after determining tc through the above steps, the holding time at the crystallization temperature described in step 4 can be any duration ≥ tc, depending on the composition system of the glass-ceramic and the crystal growth method. For systems with epitaxial growth outside the crystal nucleus, the crystal will stop growing only after all the elements in the glass composition used for crystal growth have been consumed. Or for other systems, the crystal will stop growing only when the kinetic conditions for crystal growth are not met.

[0026] Regarding step 6, the change in the integral area of ​​the endothermic peak of the DSC curve is ≤5%, which can be the rate of change within a certain time interval, such as ≤5% / h, ≤5% / 0.5h, or ≤5% / min. This can be selected based on the accuracy of the test and the control level of the production equipment.

[0027] In some cases, the method described in this invention can also be used to compare the degree of crystallinity of glass ceramics. By testing the DSC of glass ceramics prepared under the same parameters and then comparing the integrated area of ​​their melting endothermic peaks, the degree of crystallinity between samples can be compared. However, this method cannot determine the specific crystallinity value.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] This invention provides a method for rapidly and accurately determining the optimal nucleation time of glass ceramics using DSC. By testing the DSC curves of glass ceramics prepared with different nucleation times, the nucleation time conditions under which the integral area or intensity of the crystal melting endothermic peak tends to stabilize can be obtained. This method can also be used to compare the degree of crystallization between samples, thereby selecting the best sample for subsequent experiments. Using the testing method of this invention, only a DSC device is needed to determine the optimal nucleation time of glass ceramics, without the need for complex performance tests or expensive equipment such as XRD and SEM. Attached Figure Description

[0030] Figure 1 The DSC curve of the uncrystallized precursor glass in Example 1 of the present invention;

[0031] Figure 2 The DSC curve of the glass-ceramic after crystallization treatment in Example 1 of the present invention is shown (Tn = 550℃, tn = 0.5h, Tc = 750℃, tc = 1h).

[0032] Figure 3 The DSC curve of the glass-ceramic after crystallization treatment in Example 1 of the present invention is shown (Tn = 550℃, tn = 1h, Tc = 750℃, tc = 1h).

[0033] Figure 4 The DSC curve of the glass-ceramic after crystallization treatment in Example 1 of the present invention is shown (Tn = 550℃, tn = 2h, Tc = 750℃, tc = 1h).

[0034] Figure 5 The DSC curve of the glass-ceramic after crystallization treatment in Example 1 of the present invention is shown (Tn = 550℃, tn = 3h, Tc = 750℃, tc = 1h).

[0035] Figure 6 The DSC curve of the glass-ceramic after crystallization treatment in Example 1 of the present invention is shown (Tn = 550℃, tn = 4h, Tc = 750℃, tc = 1h).

[0036] Figure 7 The DSC curve of the glass-ceramic after crystallization treatment in Example 1 of the present invention is shown (Tn = 550℃, tn = 5h, Tc = 750℃, tc = 1h). Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0038] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0039] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0040] Example 1

[0041] The raw materials for component A are taken as follows by molar percentage:

[0042] SiO2 67.0%;

[0043] Al2O3 4.3%;

[0044] Li2O 23.5%;

[0045] Na2O 1.5%;

[0046] B2O3 0.2%;

[0047] ZrO2 2.5%;

[0048] P5O2 1.0%;

[0049] After the above raw materials are mixed evenly, they are melted and shaped at 1600℃ to obtain an uncrystallized precursor glass;

[0050] The particle size of the DSC sample was 1.0±0.1 mm, the weight of the sample used for testing was 30±3 mg, the heating rate of the DSC test was 10℃ / min, the flow rate of the protective gas argon was 20 ml / min, and the flow rate of the purge gas argon was 50 ml / min.

[0051] First, the DSC curve of the uncrystallized precursor glass is tested, such as... Figure 1 As shown, the sample composition exhibits two crystallization peaks, indicating the precipitation of two or more crystal types. In this embodiment, Tn was determined to be 550°C, and to obtain the desired specific crystals, Tc was determined to be 750°C, and tc was determined to be 1 h.

[0052] Glass-ceramic samples were prepared and DSC was tested at a heating rate of 10℃ / min, with Tn set at 550℃ and tn at 0.5h, Tc set at 750℃ and tc at 1h. Figure 2 As shown, the integral area of ​​the crystal melting peak is 7.945.

[0053] Glass-ceramic samples were prepared and DSC was performed at a heating rate of 10℃ / min, with Tn = 550℃, tn = 1h, Tc = 750℃, tc = 1h, and Tn to Tc heating rate of 10℃ / min. Figure 3 As shown, the integral area of ​​the crystal melting peak is 8.430.

[0054] Glass-ceramic samples were prepared and DSC was performed at a heating rate of 10℃ / min, with Tn set at 550℃ and tn for 2 hours, Tc set at 750℃ and tc for 1 hour. Figure 4 As shown, the integral area of ​​the crystal melting peak is 9.231.

[0055] Glass-ceramic samples were prepared and DSC was performed at a heating rate of 10℃ / min, with Tn set at 550℃ and tn at 3h, and Tc set at 750℃ and tc at 1h. Figure 5 As shown, the integral area of ​​the crystal melting peak is 19.323.

[0056] Glass-ceramic samples were prepared and DSC was performed at a heating rate of 10℃ / min, with Tn set at 550℃ and tn at 4h, and Tc set at 750℃ and tc at 1h. Figure 6 As shown, the integral area of ​​the crystal melting peak is 19.536.

[0057] Glass-ceramic samples were prepared and DSC was tested at a heating rate of 10℃ / min, with Tn set at 550℃ and tn for 5 hours, Tc set at 750℃ and tc for 1 hour. Figure 7 As shown, the integral area of ​​the crystal melting peak is 19.582.

[0058] By comparing the integrated areas of the endothermic melting peaks of the crystal, the integrated area of ​​the crystal melting peak at tn = 2h was 9.231, at tn = 3h it was 19.323, and at tn = 4h it was 19.536. The crystallinity at tn = 4h increased by only 1.1% / h compared to tn = 3h, which is less than 5% / h. Therefore, tn = 3h was determined to be the optimal nucleation time.

[0059] Example 2

[0060] Take the following raw materials as a percentage of molar amount for component B:

[0061] SiO2 68.2%;

[0062] Al2O3 4.3%;

[0063] Li2O 23.5%;

[0064] Na2O 1.0%;

[0065] ZrO2 2.0%;

[0066] P5O2 1.0%;

[0067] After the above raw materials are mixed evenly, they are melted and shaped at 1600℃ to obtain an uncrystallized precursor glass;

[0068] The particle size of the DSC sample was 1.0±0.1 mm, the weight of the sample used for testing was 30±3 mg, the heating rate of the DSC test was 10℃ / min, the flow rate of the protective gas argon was 20 ml / min, and the flow rate of the purge gas argon was 50 ml / min.

[0069] First, the DSC curve of the uncrystallized precursor glass was tested. Tn was determined to be 575℃, and Tc was determined to be 770℃ and tc to be 4h in order to obtain the desired specific crystals.

[0070] Glass-ceramic samples were prepared and DSC was performed at a temperature of 575℃ for Tn, 0.5h for tn, 770℃ for Tc, 4h for tc, and a heating rate of 10℃ / min from Tn to Tc. The integral area of ​​the crystal melting peak was 8.536.

[0071] Glass-ceramic samples were prepared and DSC was performed with Tn = 575℃, tn = 1h, Tc = 770℃, tc = 4h, and the heating rate from Tn to Tc = 10℃ / min. The integral area of ​​the crystal melting peak was 9.694.

[0072] Glass-ceramic samples were prepared and DSC was performed at a temperature of 575℃ for Tn, 2h for tn, 770℃ for tc, 4h for tc, and a heating rate of 10℃ / min from Tn to Tc. The integrated area of ​​the crystal melting peak was 19.398.

[0073] Glass-ceramic samples were prepared and DSC was performed at a temperature Tn of 575℃, tn of 3h, Tc of 770℃, tc of 4h, and a heating rate from Tn to Tc of 10℃ / min. The integrated area of ​​the crystal melting peak was 19.493.

[0074] Glass-ceramic samples were prepared and DSC was performed with Tn = 575℃, tn = 4h, Tc = 770℃, tc = 4h, and the heating rate from Tn to Tc = 10℃ / min. The integral area of ​​the crystal melting peak was 19.514.

[0075] Glass-ceramic samples were prepared and DSC was performed at a temperature of 575℃ for Tn, 5h for tn, 770℃ for tc, 4h for tc, and a heating rate of 10℃ / min from Tn to Tc. The integrated area of ​​the crystal melting peak was 19.529.

[0076] By comparing the integrated areas of the endothermic melting peaks of the crystal, the integrated area of ​​the crystal melting peak at tn = 1 h was 9.694, the integrated area at tn = 2 h was 19.398, and the integrated area at tn = 3 h was 19.493. The crystallinity at tn = 3 h increased by only 0.5% / h compared to tn = 2 h, which is less than 5% / h. Therefore, tn = 2 h was determined to be the optimal nucleation time.

[0077] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A method for determining the nucleation time of glass-ceramics, characterized in that, Includes the following steps: Step 1: Test the differential thermal analysis (DSC) curve of the precursor glass to obtain the glass transition point Tg and the position of the crystallization peak Pc; Step 2: Select a nucleation temperature Tn and a crystallization temperature Tc. The nucleation temperature Tn ranges from Tg to Tg+150℃, and the crystallization temperature Tc ranges from Pc-60℃ to Pc+60℃. Step 3: Heat the precursor glass for different times (Tc) and test DSC for each time. Set the time when the crystallization peak on the DSC curve completely disappears as the crystallization time (tc). Step 4: Prepare glass ceramics. During the preparation process, the precursor glass is first heated to the nucleation temperature Tn and held at that temperature for a certain time, and then heated to the crystallization temperature Tc and held at that temperature for tc time. Step 5: Test the differential thermal analysis (DSC) curve of the glass-ceramic obtained in Step 4, and calculate the integral area of ​​the corresponding crystal melting endothermic peak on the DSC curve. Step 6: Gradually extend the nucleation time and repeat steps 4-5. When the change in the integral area of ​​the crystal melting endothermic peak in the DSC curve is less than the preset value, the corresponding nucleation time is the optimal nucleation time tn required for the nucleation temperature Tn.

2. The method for determining the nucleation time of glass-ceramics according to claim 1, characterized in that, The weight of the DSC test sample is 10 ~ 50 mg.

3. The method for determining the nucleation time of glass-ceramics according to claim 1, characterized in that, The particle size of the DSC test samples is 0.1 ~ 5.0 mm.

4. The method for determining the nucleation time of glass-ceramics according to claim 1, characterized in that, The heating rate during DSC testing is 3 ~ 30℃ / min.

5. The method for determining the nucleation time of glass-ceramics according to claim 1, characterized in that, The weight difference of each DSC test sample is ≤ ±10%.

6. The method for determining the nucleation time of glass-ceramics according to claim 1, characterized in that, The preset value in step 6 is 5%.

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