CN107884259B - Device and method for realizing high-speed cooling of trace materials by using droplet cooling - Google Patents

Abstract

The present invention discloses a device for realizing high-speed cooling of trace materials by droplet cooling, comprising: a syringe connected to an injection driver for dripping volatile cooling liquid; a temperature sensor placed directly below the syringe; a data collector for collecting thermopile signals and heating resistor signals of the temperature sensor; a gas purge device for completing the sample purge device after cooling; and a control center, wherein the syringe, the temperature sensor, the data collector and the gas purge device are all connected to the control center. The device described in the present application can achieve a cooling rate higher than that of general gas cooling by contacting the sample with a refrigerant droplet and quickly responding to shutting down the heater by program control; at the same time, the cooling rate and the possible phase transition of the sample can be tracked by collecting thermopile signals or heating resistor signals; using volatile liquids, the next step of heat treatment or morphological characterization can be carried out in situ after removing the cooling droplets by gas purge.

Description

Device and method for realizing high-speed cooling of trace materials by using droplet cooling

Technical Field

The invention relates to the technical field of obtaining and analyzing material microstructures, and in particular to a device and method for realizing high-speed temperature reduction by using droplet cooling.

Background technique

In industry, samples are often quenched from melt to solid at a cooling rate higher than 1000K/s (e.g., injection molding, film blowing, etc.). In such a complex process, materials with different degrees of ordered and reorganized structures can be formed, including some polymers, metals, blends, and alloys. The recent rapid development of additive technology and 3D printing technology also involves the process of rapid cooling of a small amount of melt. Therefore, it is very important to simulate industrial rapid cooling with experimental methods and understand the quenching process of trace materials (from nanograms to tens of micrograms). This can help us understand what happens in the material during the rapid cooling process involved in industry, so as to better guide future industrial production.

Metals and polymers are both very important materials that require cooling rates that cannot be achieved by traditional means. By reducing the sample size and using gas cooling, controlled high-speed cooling can be achieved. Ultrafast Scanning Calorimetry (FSC) is an outstanding technology for observing materials during high-speed heating and cooling. It can not only prepare samples with accurate thermal history, but also analyze them at very high scanning rates, capturing structural snapshots of tiny samples at different temperatures or times through ultra-high-speed scanning (usually above 100,000K/s). However, the fast scanning of FSC also has its limitations, especially the requirements for sample quality and the impact on the scanning rate when the sample temperature reaches the ambient temperature.

Since gases have excellent thermal conductivity and heat capacity, and low thermal inertia, air cooling is very effective when the sample needs to switch quickly from heating to cooling. However, also because of these gas properties, when the temperature difference between the sample and the gas approaches zero, the cooling efficiency will be significantly limited. In fact, the sensor used in FSC can only achieve a cooling rate of 10 ⁶ K/s when the temperature is 500K higher than the gas temperature, only 1000K/s when the temperature is 100K higher than the furnace temperature, and only 100K/s when it is 50K higher than the furnace temperature. When the temperature reaches below a certain value, the cooling rate drops sharply. This phenomenon is called ballistic cooling (as shown in Figure 1), especially for samples with large mass, the effect of ballistic cooling is particularly obvious. If helium is used instead of air, ballistic cooling can be significantly reduced, or ballistic cooling can be avoided at a certain temperature by lowering the gas temperature, such as conducting experiments in air or helium cooled by liquid nitrogen. However, this method is not always feasible and will be affected by the experimental platform and test conditions.

Summary of the invention

Purpose of the invention: In view of the above-mentioned defects in the prior art, the present application provides a high-speed cooling device which replaces gas cooling with liquid cooling to achieve a higher cooling rate, and provides a method for achieving high-speed cooling using the device.

Technical solution: The device described in the present invention uses droplet cooling to achieve high-speed cooling of trace materials, including: a syringe, connected to an injection driver, for dripping volatile cooling liquid; a temperature sensor placed directly below the syringe, including a thermopile cold end and a hot end, with a built-in heating resistor, and a silicon nitride film attached to the surface, and the trace material is placed on the silicon nitride film; a data acquisition device, used to collect thermopile signals and heating resistor signals of the temperature sensor; a gas purge device; a control center, and the syringe, temperature sensor, data acquisition device and gas purge device are all connected to the control center.

Among them, the device needs to control the size and flow rate of the cooling droplets through the injection driver and the syringe to ensure that the cooling droplets first contact the surface of the sample rather than the thin film of the sensor. In this case, the cooling efficiency is the highest.

The syringe used to inject the droplets can be any device that can form a stable stream or droplets of liquid, such as a medical syringe and an ordinary PE dropper. It can also be other injection devices, such as a microfluidic device. It should be noted that the diameter of the droplet needs to be larger than the diameter of the sample. The larger the diameter of the droplet, the higher the cooling efficiency. In general, a droplet with a diameter of about 2 mm can achieve high-speed cooling.

Furthermore, the cooling liquid is a liquid with a certain volatility. After the sample is cooled, it can be purged by a dry airflow to remove the cooling droplets at ambient temperature without changing the thermal history of the sample. Due to the Leidenfrost effect, if the liquid evaporates too quickly, it will boil on the hot sensor, thereby affecting the cooling efficiency and even interrupting the cooling; in addition, when the sensor test area is different, the boiling of the cooling droplets is also different, so it is necessary to select cooling liquids with different properties according to sensors of different areas.

Preferably, the cooling liquid is cold ethanol, and the temperature ranges from -50°C to 0°C, preferably -20°C.

Any sample that does not dissolve or absorb the cooling liquid can be used in the device, and the diameter of the sample can range from a few microns to hundreds of microns, depending on the heating area of the temperature sensor used.

The temperature sensor is any currently available commercial vacuum gauge thin film sensor (XENSOR.NL), such as XI394, XI395 and XI400, etc. Further, the XI394 measurement area used in this application is 8×6μm ² , the XI395 measurement area is 60×60μm ² , and the XI400 measurement area diameter is 500μm.

The heating resistor on the sensor can preheat the sample to a specified temperature before cooling down as needed. Due to the voltage required for heating and the limitations of the heating resistor material on the sensor, the heating range of the sample on the gold sensor is 0-1300K and the heating range on the aluminum sensor is 0-800K.

The purge gas flow of the gas purge device can be dry nitrogen, air, argon, etc., depending on the use environment and the test sample, so as to remove the cooling droplets without changing the sample temperature.

The entire cooling process using this device has a cooling rate of more than 10 ⁶ K/s, so the entire cooling process from droplet approach to complete cooling can be completed within 10ms.

An improved rapid scanning calorimeter is integrated with the above-mentioned device for realizing high-speed temperature reduction of trace materials by using droplet cooling.

Furthermore, the device for achieving high-speed cooling of trace materials using droplet cooling is attached to the sample chamber of the rapid scanning calorimeter, including but not limited to an open platform at room temperature, a hot and cold stage, a vacuum tube, etc., and effectively achieves a further increase in the cooling rate without affecting further rapid thermal analysis and structural analysis.

The rapid scanning calorimeter may be a currently available FSC device, for example, accessories may be added for an open room temperature system, a hot and cold table type closed system, and a Tube-dewar type.

A method for realizing high-speed cooling of trace materials using the above device comprises the following steps:

(1) Sample preheating: Place the sample on the silicon nitride film of the temperature sensor and use the heating resistor on the temperature sensor to preheat the sample to the specified temperature;

(2) High-speed cooling and data acquisition: cooling liquid is dripped or sprayed onto the sample surface preheated in step (1) in the form of droplets through a syringe, and the data acquisition device tracks the change of the thermopile signal during the approach of the droplets. When the droplets approach the sample, the temperature of the sample begins to decrease, and the thermopile signal used to track the sample temperature deviates from the specified temperature set in step (1). When the temperature difference ΔT of the sample is greater than the preset trigger value ΔT _trigger , the heating resistor is triggered to turn off. At the same time, the sample temperature is continuously monitored with microsecond accuracy to monitor the cooling rate and possible phase transitions of the sample, and data is collected for subsequent data analysis.

(3) Sample drying: After the cooling is completed according to the collected data of step (2), the control center starts the gas purge equipment to remove the cooling droplets. The sample without residual droplets can be used for rapid thermal analysis or structural analysis of the sample material in situ to complete the high-speed cooling.

The specified temperature in step (1) needs to be set according to the experimental requirements. The maximum range of the specified temperature of the sample is generally 100K-800K. When a gold sensor is used, the maximum temperature range of the sample can be 100K-1300K.

In step (2), the internal triggering process controlled by the data acquisition device can be realized within microseconds, and the approaching process of the droplet can be tracked before the droplet touches the sample, and the temperature control system (i.e., the heating resistor) for the sample can be turned off when necessary to achieve the best cooling rate. Turning off the heating resistor too early or too late will affect the cooling rate. During the cooling process, the temperature of the sample is continuously monitored with microsecond accuracy, and the temperature signal can show the cooling rate and possible phase transitions of the sample.

Since the reference temperature of the cold end is the ambient temperature, when the reference temperature (cold end) of the thermopile signal is unreliable, for example when the droplet temperature is much lower than the sensor temperature, the existing heating resistor on the sensor can be used for temperature measurement and correction.

Since the temperature of the cooling droplets is lower than the preheated sample temperature, coupled with the contact of the droplets and the turning off of the heater, the sample can be cooled down quickly.

In step (1), any sample that does not dissolve or absorb cooling liquid can be used in the device. Depending on the heating area of the temperature sensor used, the diameter of the sample can range from a few microns to several hundred microns.

In step (2), the cooling liquid is cold ethanol, and the temperature range is -50°C to 0°C, preferably -20°C.

In step (3), after the sample is cooled, it needs to be purged with a dry gas flow to remove the cooling droplets at ambient temperature without changing the thermal history of the sample. The gas purge gas flow rate is 0-10L/min, and the purge time can be freely set. For ethanol, 1L/min purge for 30s can be selected. After rapid cooling, the sample can be subjected to rapid thermal analysis in situ, including reheating to analyze the structure of the sample after cooling, or further heat treatment, such as isothermal or non-isothermal experiments; other morphological characterization or mechanical characterization can also be performed without the need to transfer to other equipment.

Beneficial effects: The high-speed cooling device described in this application can achieve a cooling rate higher than general gas cooling by contacting the sample with the refrigerant droplets and quickly responding to shutting down the heater through program control; at the same time, by collecting thermopile signals or heating resistor signals, the cooling rate and possible phase changes of the sample can be tracked; using volatile liquids, the next step of heat treatment or morphological characterization can be carried out in situ after removing the cooling droplets through gas purging. The high-speed cooling method described in this application can be used to obtain special phases of sample materials, and can be combined with existing ultrafast scanning calorimetry technology to expand the rate of high-speed cooling of trace samples, realize simulation of industrial quenching process, and perform in situ thermal analysis and microstructural characterization of the materials obtained by high-speed cooling.

For example, for some industrial-grade resins that crystallize very quickly (such as homogeneously nucleated polyethylene PE or polytetrafluoroethylene PTFE), even using gas to cool a very small sample mass cannot meet the cooling rate requirements, while metal materials crystallize faster. In this case, additional liquid cooling will be of great help. This method of using droplet cooling to achieve high-speed cooling can be combined with existing rapid scanning calorimeters to achieve high-speed cooling and subsequent calorimetric characterization and other microstructural characterizations according to the cooling rate requirements, the use environment, and the instrument coupling conditions. Obtaining this complementary information can help to more comprehensively explain the effects of rapid cooling and the performance of plastic or metal alloy products obtained after rapid cooling. Using liquid for additional cooling can greatly expand the limitations of traditional FSC, and also make it a very industrially attractive instrument.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic diagram of ballistic cooling;

FIG2 is a schematic diagram of the basic structure of a device for achieving high-speed cooling of trace materials using droplet cooling;

FIG3 is a schematic diagram of the structure of the device of the present application;

FIG4 is a detailed schematic diagram of the cooling process;

FIG5 is a schematic diagram of the working principle of liquid cooling;

FIG6 is a schematic diagram of the process of triggering the closing of the heating resistor in step 2 of the present application;

FIG7 is a schematic diagram showing the principle of combining a liquid cooling device with an existing fast scanning calorimeter FSC;

FIG8 is a schematic diagram showing a comparison of a tube-dewar type gas-cooled FSC device and a combination of a liquid-cooled device and a tube-dewar type FSC device;

FIG9 is a comparison diagram of the liquid cooling effect of the present application and the traditional gas cooling effect;

FIG10 is a comparison chart of the cooling effect using cold ethanol as the cooling liquid on sensors of different sizes. The smaller the sensor area, the less the liquid boils, and the higher the cooling rate that can be achieved.

Detailed ways

The present application is described in detail below in conjunction with specific embodiments.

Example 1

As shown in Figures 2 and 3, the device for achieving high-speed cooling of trace materials using droplet cooling includes: a syringe, which is connected to an injection driver and is used to drop volatile cooling liquid; a temperature sensor placed directly below the syringe, including a thermopile cold end and a hot end, a built-in heating resistor, and a silicon nitride film attached to the surface, and the trace material is placed on the silicon nitride film; a data acquisition device, which is used to collect the thermopile signal and the heating resistor signal of the temperature sensor; a gas purge device, which is used to complete the purge of the cooled sample; and a control center, the syringe, temperature sensor, data acquisition device and gas purge device are all electrically connected to the control center.

Example 2

The method for realizing high-speed cooling of trace materials using the device described in Example 1, as shown in FIG4 , comprises the following steps:

(1) Sample preheating: Place the sample on the silicon nitride film of the temperature sensor and use the heating resistor on the temperature sensor to preheat the sample to the specified temperature;

(2) High-speed cooling and data acquisition: The cooling liquid is dripped or sprayed onto the sample surface preheated in step (1) in the form of droplets through a syringe, and the data acquisition device tracks the changes in the thermopile signal during the approach of the droplets. As shown in FIG5 and FIG6 , when the droplets approach the sample, the temperature of the sample begins to decrease, and the thermopile signal used to track the sample temperature deviates from the specified temperature set in step (1). When the temperature difference ΔT of the sample decreases is greater than the preset trigger value ΔT _trigger , the heating resistor is triggered to turn off. At the same time, the sample temperature is continuously monitored with microsecond accuracy to monitor the cooling rate and possible phase transitions of the sample, and data is collected for subsequent data analysis.

(3) Sample drying: After the cooling is completed according to the collected data of step (2), the control center starts the gas purge equipment to remove the cooling droplets at the ambient temperature. The sample without residual droplets can be used for rapid thermal analysis or structural analysis of the sample material in situ to complete the high-speed cooling.

Wherein, in step (2), the cooling liquid is cold ethanol with a temperature range of -20°C; in step (1), the specified temperature range is 100K-800K, and when a gold sensor is used, the maximum temperature range of the sample can be 100K-1300K.; in step (3), the purge gas flow rate of the gas purge device is 1L/min for 30s.

Comparative Example 1

The cooling operation was performed under the same conditions using the device shown in Example 1 and the existing traditional gas cooling device. The results are shown in Figure 9. It can be seen from the figure that the cooling rate performance of droplet cooling (black solid line) is significantly better than that of atmosphere cooling (gray dotted line). Linear coordinate-a, double logarithmic coordinate-b.

Comparative Example 2

We used the device shown in Example 1 to conduct a comparative experiment on the performance of droplet cooling and gas cooling on several sensors of different specifications, including XI394 (measurement area 8x6μm ² ), XI395 (measurement area 60x60μm ² ) and XI400 (measurement area diameter 500μm). The test results are shown in Figure 10 and the comparative data are shown in the following table. It can be seen that the boiling of cold ethanol on the XI400 sensor (UHC-1Flash DSC sensor, diameter 500μm, 2μm thickness) reduces the performance of liquid cooling (gray curve), but it is still much better than the original slow cooling (black curve). The gray curve is the result of liquid cooling (gray dotted line) or traditional cooling (black dotted line) on the XI395 sensor (60x80μm ² , 1μm thickness) at the same temperature. It can be seen that the sensor area has a great influence on the cooling effect. The larger the sensor area, the more serious the boiling phenomenon of the cooling liquid and the lower the cooling rate. But even for the largest XI400 sensor tested, the cooling rate achieved with additional droplet cooling is much better than with conventional gas cooling.

Example 3

As shown in FIG8 , a Tube-dewar type fast scanning calorimeter FSC integrated with the device described in Example 1 is shown. The sample chamber of the device of Example 1 is placed in the vacuum tube in the dewar tank. Its basic principle diagram is shown in FIG7 . Since the furnace equipped with the sensor can maintain a very low temperature (about 80K), its available temperature range and scanning rate can be greatly improved. With the addition of an additional droplet cooling device, the fastest cooling rate of the current fast scanning calorimeter can be achieved.

Claims (7)

1. A device for achieving high-speed cooling of trace materials by using droplet cooling, characterized in that the cooling rate of the high-speed cooling is above 10 ⁶ K/s, and the device comprises: A syringe, connected to the injection driver, for dripping the volatile cooling liquid; The temperature sensor placed directly below the syringe includes a thermopile cold end and a hot end, a built-in heating resistor, and a silicon nitride film attached to the surface, on which the trace material is placed; A data collector, used for collecting thermopile signals and heating resistor signals of the temperature sensor; Gas purge equipment, used to purge the sample after cooling to remove cooling droplets; A trigger, used for triggering the closing of the heating resistor; The control center, the injector, the temperature sensor, the data acquisition device and the gas purge device are all electrically connected to the control center. 2. An improved rapid scanning calorimeter, characterized in that it is integrated with the device for achieving high-speed cooling of trace materials by using droplet cooling as described in claim 1. 3. The improved rapid scanning calorimeter according to claim 2 is characterized in that the device for achieving high-speed cooling of trace materials using droplet cooling is integrated into the sample chamber of the rapid scanning calorimeter. 4. A method for achieving high-speed cooling of trace materials using the device of claim 1, characterized in that it comprises the following steps: (1) Sample preheating: Place the sample on the silicon nitride film of the temperature sensor and use the heating resistor on the temperature sensor to preheat the sample to the specified temperature; (2) High-speed cooling and data acquisition: The cooling liquid is dripped or sprayed onto the sample surface preheated in step (1) in the form of droplets through a syringe, and the data acquisition device tracks the change of the thermopile signal during the approach of the droplets. When the droplets approach the sample, the temperature of the sample begins to decrease, and the thermopile signal used to track the sample temperature deviates from the specified temperature set in step (1). When the temperature difference ΔT of the sample is greater than the preset trigger value ΔT _trigger , the heating resistor is triggered to turn off. At the same time, the sample temperature is continuously monitored with microsecond accuracy to monitor the cooling rate and possible phase transitions of the sample, and data is collected for subsequent data analysis. (3) Sample drying: After the cooling is completed according to the collected data of step (2), the control center starts the gas purge equipment to remove the cooling droplets at ambient temperature. The sample without residual droplets can be subjected to rapid thermal analysis or structural analysis of the sample material in situ to complete the cooling. 5. The method according to claim 4, characterized in that in step (2), the cooling liquid is cold ethanol with a temperature range of -50°C to 0°C. 6. The method according to claim 4, characterized in that in step (1), the specified temperature range is 100K-800K. 7. The method according to claim 4, characterized in that in step (3), the gas purge gas flow rate is 0-10 L/min.