Alloy material resistant to chloride molten salt corrosion and preparation method and application thereof

Abstract

The invention discloses an alloy material resistant to chloride molten salt corrosion and a preparation method and application thereof. The alloy material resistant to chloride molten salt corrosion comprises a chromium-containing alloy material matrix and a magnesium chromite-containing protective layer covering the surface of the chromium-containing alloy material matrix. The preparation method comprises the following steps: 1) mixing lithium carbonate-sodium carbonate-potassium carbonate molten salt and a magnesium source to prepare a mixture; and 2) covering the surface of a chromium-containing alloy material matrix with the mixture to carry out oxidation reaction, and then washing and drying. The surface of the alloy material is covered with the protection layer containing magnesium chromite, the preparation process of the protection layer is simple, the stability of the protection layer in a high-temperature chloride molten salt environment is good, and corrosive impurities in chloride molten salt can be effectively prevented from making contact with an alloy matrix; the corrosion of the chloride molten salt on key components such as a storage tank and a heat exchanger in the CSP system under a high-temperature condition is avoided, and the efficient, stable and safe operation of the CSP system is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of alloy anti-corrosion, and particularly relates to an alloy material resistant to chloride molten salt corrosion, a preparation method thereof, and an application thereof. Background Art

[0002] Concentrating solar power (CSP) refers to using mirrors or lenses to concentrate a large area of sunlight onto the light collection area of a generator, first converting solar energy into heat energy through photothermal conversion, and then driving a generator to generate electricity by the work of a heat engine (usually a steam turbine engine). CSP has the advantages of high efficiency and stability (higher energy conversion efficiency), environmental protection and sustainability (fully using solar energy for power generation without any carbon emissions), and flexible regulation (controlling the amount of heat energy collected by adjusting the angle and number of mirrors, thereby realizing the regulation of electricity), and has a very broad application prospect.

[0003] The energy storage system is an important part of the CSP system and is used to provide power when sunlight is insufficient. Molten salt materials have the advantages of low vapor pressure, good fluidity, high working temperature, and good heat storage performance, and have become the most commonly used heat storage medium in the solar thermal energy storage system. Chloride molten salt has the advantages of rich production, stable properties, wide working temperature, and low viscosity, and is an ideal heat storage medium. However, chloride molten salt is prone to corrode key components such as storage tanks and heat exchangers in the CSP system at high temperatures, which will not only increase the maintenance cost of the CSP system, but also easily lead to potential safety hazards.

[0004] At present, the methods for suppressing the corrosiveness of chloride molten salt mainly include the following: 1) suppressing corrosion by heat-treating the molten salt: some molten salts can be purified of residual oxygen and water vapor by heat treatment, thereby suppressing corrosion, but this method is not applicable to all component molten salts (for example: molten salt containing MgCl2 is prone to hydrolysis of MgCl2 at high temperatures); 2) suppressing corrosion by reducing the temperature: the corrosiveness of chloride molten salt to alloys will decrease at low temperatures, but the decrease range is relatively limited, and this method does not conform to the high-temperature and high-efficiency power generation requirements of the next-generation solar thermal power plants; 3) suppressing corrosion by electrochemical methods: using the method of sacrificial anode protection (for example: adding Mg to consume oxidizing impurities), but this method has a large consumption of anode materials and requires periodic replenishment, with a high maintenance cost and is difficult to be applied for a long time and on a large scale. In summary, the existing methods for suppressing the corrosiveness of chloride molten salt all have obvious defects and cannot protect alloys efficiently and at low cost, so their practical applications are greatly limited.

[0005] Therefore, it is of great significance to develop an alloy material resistant to chloride molten salt corrosion. Summary of the Invention

[0006] The object of the present invention is to provide an alloy material resistant to chloride molten salt corrosion, a preparation method thereof, and an application thereof.

[0007] The technical solution adopted by the present invention is as follows:

[0008] An alloy material resistant to chloride molten salt corrosion, the composition of which includes a chromium-containing alloy material matrix and a protective layer containing magnesium chromite (MgCr2O4) covering the surface of the chromium-containing alloy material matrix.

[0009] Preferably, the chromium-containing alloy material matrix is a nickel-based chromium-containing alloy material matrix.

[0010] More preferably, the chromium-containing alloy material matrix is one of a Hastelloy X alloy matrix, a Hastelloy B-2 alloy matrix, and a Hastelloy C-276 alloy matrix.

[0011] Preferably, the thickness of the protective layer containing magnesium chromite is 7 μm to 12 μm.

[0012] Preferably, the composition of the protective layer containing magnesium chromite further includes magnesium oxide.

[0013] A preparation method of the alloy material resistant to chloride molten salt corrosion as described above includes the following steps:

[0014] 1) Mix lithium carbonate - sodium carbonate - potassium carbonate molten salt and a magnesium source evenly to obtain a mixture;

[0015] 2) Cover the surface of the chromium-containing alloy material matrix with the mixture for an oxidation reaction, and then perform water washing and drying to obtain the alloy material resistant to chloride molten salt corrosion.

[0016] Preferably, in step 1), the mass ratio of the lithium carbonate - sodium carbonate - potassium carbonate molten salt to the magnesium source is 1:0.015 to 0.05.

[0017] Preferably, the lithium carbonate - sodium carbonate - potassium carbonate molten salt in step 1) includes the following components in mass percentages:

[0018] Lithium carbonate: 19.4% to 20.4%;

[0019] Sodium carbonate: 29.8% to 30.8%;

[0020] Potassium carbonate: 49.3% to 50.3%.

[0021] Preferably, the lithium carbonate-sodium carbonate-potassium carbonate molten salt described in step 1) is prepared by a preparation method including the following steps: Mix lithium carbonate, sodium carbonate and potassium carbonate evenly, then put them into a muffle furnace, control the heating rate to be 3°C / min to 7°C / min, and heat from room temperature (25°C ± 5°C) to 550°C to 650°C, keep warm for 3h to 5h, then take out and cool, and then grind to obtain the lithium carbonate-sodium carbonate-potassium carbonate molten salt.

[0022] Preferably, the magnesium source described in step 1) is one of magnesium oxide, magnesium carbonate, and magnesium oxide-chromium complex.

[0023] Preferably, step 1) includes the following operations: Mix the lithium carbonate-sodium carbonate-potassium carbonate molten salt and the magnesium source evenly, then put them into a muffle furnace, control the heating rate to be 3°C / min to 7°C / min, heat from room temperature to 550°C to 650°C, keep warm for 2h to 3h, then take out and cool to obtain a mixture.

[0024] Preferably, the thickness of the mixture covering the surface of the chromium-containing alloy material substrate described in step 2) is ≤ 5 mm.

[0025] Preferably, the oxidation reaction described in step 2) is carried out under the condition that the temperature is 550°C to 650°C, and the reaction time is 15 days to 25 days.

[0026] A concentrating solar power generation system includes the above alloy material resistant to chloride molten salt corrosion.

[0027] The beneficial effects of the present invention are as follows: The surface of the alloy material of the present invention is covered with a protective layer containing magnesium chromite (MgCr2O4). The preparation process of this protective layer is simple, and its stability in a high-temperature chloride molten salt environment is good. It can effectively block the contact between corrosive impurities in the chloride molten salt and the alloy substrate, avoiding the corrosion of key components such as storage tanks and heat exchangers in the CSP system by chloride molten salt at high temperatures, and ensuring the efficient, stable and safe operation of the CSP system. Description of the Drawings

[0028] Figure 1 SEM diagrams of the surfaces of the alloy materials resistant to chloride molten salt corrosion in Examples 1 to 3.

[0029] Figure 2 XRD diagram of the surface of the alloy material resistant to chloride molten salt corrosion in Example 1.

[0030] Figure 3 XRD diagram of the surface of the alloy material resistant to chloride molten salt corrosion in Example 2.

[0031] Figure 4 XRD diagram of the surface of the alloy material resistant to chloride molten salt corrosion in Example 3.

[0032] Figure 5 The corrosion mass curves of the alloy materials resistant to chloride molten salt corrosion in Examples 1 to 3 during the corrosion test.

[0033] Figure 6 The corrosion rate curves of the alloy materials resistant to chloride molten salt corrosion in Examples 1 to 3 during the corrosion test.

[0034] Figure 7 The SEM images of the surfaces of the alloy materials resistant to chloride molten salt corrosion in Examples 1 to 3 after the corrosion test.

[0035] Figure 8 The SEM images and element distribution maps of the cross-sections of the alloy materials resistant to chloride molten salt corrosion in Examples 1 to 3 after the corrosion test. Detailed implementation manners

[0036] The present invention will be further explained and illustrated below in conjunction with specific embodiments.

[0037] Note:

[0038] The Hastelloy X alloy blocks in Examples 1 to 3 were purchased from Shanghai Chenxing Metal Group Co., Ltd., and their main element compositions are Ni, Cr, Fe, Mo and other trace elements.

[0039] The Hastelloy X alloy blocks in Examples 1 to 3 were pretreated before use, and the specific operations are as follows: The Hastelloy X alloy blocks were polished smoothly with sandpaper (to remove the oxide film on the alloy surface), then ultrasonically cleaned with acetone, then cleaned with alcohol and deionized water, and then dried.

[0040] The composition of the lithium carbonate - sodium carbonate - potassium carbonate molten salt in Examples 1 to 3 is as follows (mass percentage): lithium carbonate: 19.9%; sodium carbonate 30.3%; potassium carbonate: 49.8%.

[0041] The preparation method of the lithium carbonate - sodium carbonate - potassium carbonate molten salt in Examples 1 to 3 is as follows: Lithium carbonate, sodium carbonate and potassium carbonate were mixed evenly, then placed in a muffle furnace, and the heating rate was controlled at 5 °C / min to heat from room temperature to 600 °C, held for 4 h, and then taken out and cooled and ground to obtain the lithium carbonate - sodium carbonate - potassium carbonate molten salt.

[0042] The alumina crucibles in Examples 1 to 3 were pretreated before use, and the specific operations are as follows: First, the alumina crucibles were cleaned with deionized water and alcohol, and then dried.

[0043] Example 1:

[0044] An alloy material resistant to chloride molten salt corrosion, and its preparation method is as follows:

[0045] 1) Stir and mix the lithium carbonate-sodium carbonate-potassium carbonate molten salt and magnesium oxide evenly. The mass ratio of the lithium carbonate-sodium carbonate-potassium carbonate molten salt to magnesium oxide is 1:0.015. Then put it into a muffle furnace, control the heating rate at 5 °C / min and heat from room temperature to 600 °C, keep it warm for 3 h, and then take it out and cool to obtain a mixed material;

[0046] 2) Put the Hastelloy X alloy block into a preheated alumina crucible at 80 °C, and then cover the mixed material on the surface of the Hastelloy X alloy block. The thickness of the mixed material covering the surface of the Hastelloy X alloy block is ≤5 mm. Then control the heating rate at 5 °C / min and heat from room temperature to 600 °C, keep it warm for 20 days (the reaction mechanism is as follows: 4Cr + 3O2 = 2Cr2O3; MgO + Cr2O3 = MgCr2O4), and then cool, wash with water and dry to obtain the alloy material resistant to chloride molten salt corrosion (the thickness of the protective layer containing magnesium chromite formed on the surface of the Hastelloy X alloy block is 7 μm to 9 μm).

[0047] Example 2:

[0048] An alloy material resistant to chloride molten salt corrosion, and its preparation method is as follows:

[0049] 1) Stir and mix the lithium carbonate-sodium carbonate-potassium carbonate molten salt and magnesium carbonate evenly. The mass ratio of the lithium carbonate-sodium carbonate-potassium carbonate molten salt to magnesium carbonate is 1:0.05. Then put it into a muffle furnace, control the heating rate at 5 °C / min and heat from room temperature to 600 °C, keep it warm for 3 h, and then take it out and cool to obtain a mixed material;

[0050] 2) Put the Hastelloy X alloy block into a preheated alumina crucible at 80 °C, and then cover the mixed material on the surface of the Hastelloy X alloy block. The thickness of the mixed material covering the surface of the Hastelloy X alloy block is ≤5 mm. Then control the heating rate at 5 °C / min and heat from room temperature to 600 °C, keep it warm for 20 days, and then cool, wash with water and dry to obtain the alloy material resistant to chloride molten salt corrosion (the thickness of the protective layer containing magnesium chromite formed on the surface of the Hastelloy X alloy block is 9 μm to 12 μm).

[0051] Example 3:

[0052] An alloy material resistant to chloride molten salt corrosion, and its preparation method is as follows:

[0053] 1) Stir and mix the lithium carbonate - sodium carbonate - potassium carbonate molten salt, magnesium oxide, and chromium powder evenly. The mass ratio of the lithium carbonate - sodium carbonate - potassium carbonate molten salt, magnesium oxide, and chromium powder is 1:0.015:0.01. Then put it into a muffle furnace, control the heating rate at 5 °C / min, heat from room temperature to 600 °C, keep it warm for 3 h, and then take it out and cool to obtain a mixture.

[0054] 2) Put the Hastelloy X alloy block into an alumina crucible preheated to 80 °C, and then cover the surface of the Hastelloy X alloy block with the mixture. The thickness of the mixture covering the surface of the Hastelloy X alloy block is ≤ 5 mm. Then control the heating rate at 5 °C / min, heat from room temperature to 600 °C, keep it warm for 20 days, and then carry out cooling, water washing, and drying to obtain an alloy material resistant to chloride molten salt corrosion (the thickness of the protective layer containing magnesium chromite formed on the surface of the Hastelloy X alloy block is 8 μm - 10 μm).

[0055] Performance test:

[0056] 1) The scanning electron microscope (SEM) images of the surfaces of the alloy materials resistant to chloride molten salt corrosion in Examples 1 - 3 are as Figure 1 (a1 and a2 are for Example 1, b1 and b2 are for Example 2, c1 and c2 are for Example 3) shown.

[0057] It can be seen from Figure 1 that: On the surfaces of the Hastelloy X alloy blocks in Examples 1 - 3, protective layers containing magnesium chromite and magnesium oxide are all formed, and they can all resist the corrosion of chloride molten salt; the protective layer formed in Example 2 (with magnesium carbonate as the magnesium source) is the most dense and uniform, and the effect of resisting chloride molten salt corrosion is the best.

[0058] 2) The X - ray diffraction (XRD) patterns of the surfaces of the alloy materials resistant to chloride molten salt corrosion in Examples 1 - 3 are as Figures 2 to 4 (the untreated Hastelloy X alloy block is used as a control) shown.

[0059] It can be seen from Figures 2 to 4 that: On the surfaces of the Hastelloy X alloy blocks in Examples 1 - 3, protective layers containing magnesium chromite are all formed, and they can all resist the corrosion of chloride molten salt.

[0060] 3) Weigh the alloy materials resistant to chloride molten salt corrosion in Examples 1 to 3 (i.e., Hastelloy X alloy blocks with a protective layer containing magnesium chromite on the surface) and Hastelloy X alloy blocks (untreated, as a control), then place them in an alumina crucible, and then add sodium chloride-magnesium chloride-calcium chloride molten salt (the mass percentage of each component is as follows: sodium chloride: 39.5%; magnesium chloride: 39.1%; calcium chloride: 21.4%). The addition amount is 2 / 3 of the capacity of the alumina crucible. Then control the heating rate to 5 °C / min and heat from room temperature to 600 °C, hold for 7 days, then cool, wash with water and dry, and then weigh again to calculate the corrosion mass and corrosion rate. The obtained corrosion mass curve is as Figure 5 shown, and the corrosion rate curve is as Figure 6 shown.

[0061] Note:

[0062] The formula for calculating the corrosion mass is as follows: Δm / S0 = (m f -m i ) / S0. In the formula, m f is the initial mass of the alloy sample (unit: g), m i is the mass of the alloy sample after corrosion (unit: g), and S0 is the initial surface area of the alloy sample (unit: cm 2 ).

[0063] The formula for calculating the corrosion rate is as follows: v (μm / y) = 365×10000[(m f -m i ) / (ρ×S×T)]. In the formula, m f is the initial mass of the alloy sample (unit: g), m i is the mass of the alloy sample after corrosion (unit: g), ρ is the density of the alloy sample (unit: g / cm 3 ), S is the total immersion area (unit: cm 2 ), and T is the corrosion time (calculated in days).

[0064] From Figure 5 and Figure 6 , it can be seen that: the corrosion mass and corrosion rate of the alloy material resistant to chloride molten salt corrosion in Example 2 are the smallest, and the anti-corrosion performance is the best. The reason is that magnesium carbonate can decompose into magnesium oxide at high temperature, can be more evenly dispersed on the alloy surface and react with Cr2O3 on the alloy surface to form a more uniform and dense protective layer containing MgCr2O4.

[0065] 4) The alloy materials resistant to chloride molten salt corrosion in Examples 1 to 3 and Hastelloy X alloy blocks (untreated, as a control) were corroded with sodium chloride-magnesium chloride-calcium chloride molten salt for 7 days (the method was the same as above), and then the morphology and element distribution were tested. The SEM images of the surfaces of the obtained alloy materials are as shown in Figure 7 (a represents the control group, b represents Example 1, c represents Example 2, and d represents Example 3). The SEM images and element distribution maps of the cross-sections of the alloy materials are as shown in Figure 8 (a represents the control group, b represents Example 1, c represents Example 2, and d represents Example 3).

[0066] It can be seen from Figure 7 that: severe intergranular corrosion occurred on the surface of the Hastelloy X alloy block (untreated, as a control), and many cracks were generated; there was no intergranular corrosion on the surfaces of the alloy materials resistant to chloride molten salt corrosion in Examples 1 to 3. However, the surfaces of the alloy materials resistant to chloride molten salt corrosion in Examples 1 and 3 were uneven. The reason is that the protective layers formed in Examples 1 and 3 were not uniform by themselves, and the corrosion inhibition effect was not as good as that in Example 2.

[0067] It can be seen from Figure 8 that: the Hastelloy X alloy block (untreated, as a control) consisted of an outer corrosion layer, an inner corrosion layer, and an alloy matrix from outside to inside. The outer corrosion layer was mainly composed of oxidation products, and the inner corrosion layer showed a loss of Cr element; the alloy materials resistant to chloride molten salt corrosion in Examples 1 to 3 consisted of an outer corrosion layer and an inner corrosion layer from outside to inside, and no loss of Cr element was observed inside.

[0068] The above embodiments are the preferred embodiments of the present invention. However, the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. An alloy material resistant to chloride molten salt corrosion, characterized in that: The composition comprises a chromium-containing alloy material substrate and a protective layer containing magnesium chromite and covering the surface of the chromium-containing alloy material substrate.

2. The alloy material resistant to chloride molten salt corrosion according to claim 1, characterized in that: The chromium-containing alloy material matrix is ​​a nickel-based chromium-containing alloy material matrix.

3. The alloy material resistant to chloride molten salt corrosion according to claim 1 or 2, characterized in that: The thickness of the protective layer containing magnesium chromite is 7 μm to 12 μm.

4. The alloy material resistant to chloride molten salt corrosion according to claim 1 or 2, characterized in that: The composition of the protective layer containing magnesium chromite also includes magnesium oxide.

5. A method for preparing an alloy material resistant to chloride molten salt corrosion according to any one of claims 1 to 4, characterized in that: The following steps are involved: 1) mixing lithium carbonate-sodium carbonate-potassium carbonate molten salt and a magnesium source uniformly to obtain a mixture; 2) The mixed material is covered on the surface of a chromium-containing alloy material substrate to undergo an oxidation reaction, and then washed and dried to obtain an alloy material resistant to chloride molten salt corrosion.

6. The preparation method according to claim 5, characterized in that: In step 1), the mass ratio of the lithium carbonate-sodium carbonate-potassium carbonate molten salt to the magnesium source is 1:0.015-0.

05.

7. The preparation method according to claim 5 or 6, characterized in that: Step 1) The lithium carbonate-sodium carbonate-potassium carbonate molten salt comprises the following components in percentage by mass: Lithium carbonate: 19.4% to 20.4%; Sodium carbonate: 29.8%-30.8%; Potassium carbonate: 49.3%~50.3%.

8. The preparation method according to claim 5 or 6, characterized in that: Step 1) The magnesium source is one of magnesium oxide, magnesium carbonate, and magnesium oxide-chromium complex.

9. The preparation method according to claim 5 or 6, characterized in that: Step 2) The oxidation reaction is carried out at a temperature of 550° C. to 650° C., and the reaction time is 15 to 25 days.

10. A concentrated solar thermal power generation system, characterized in that: An alloy material resistant to chloride molten salt corrosion comprising any one of claims 1 to 4.

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