NANOCRYSTALLINE MATERIAL BASED ON STAINLESS STEEL SURFACE, AND PREPARATION METHOD THEREFOR
20190256982 ยท 2019-08-22
Inventors
Cpc classification
C25D3/08
CHEMISTRY; METALLURGY
C23C22/43
CHEMISTRY; METALLURGY
C23F17/00
CHEMISTRY; METALLURGY
International classification
Abstract
A nanocrystalline material based on a stainless steel surface. In percentage by weight, the nanocrystalline material comprises: 0 to 3% of carbon, 20% to 35% of oxygen, 40% to 53% of chromium, 10% to 35% of ferrum, 0 to 4% of molybdenum, 1% to 4% of nickel, 0 to 2.5% of silicon, 0 to 2% of calcium, and the balance of impurity elements. Also disclosed is a preparation method for the nanocrystalline material, and the nanocrystalline material that is based on a stainless steel surface and that is prepared by using the preparation method.
Claims
1. A nanocrystalline material based on stainless steel surface, characterized in that the nanocrystalline contains, expressed in percentage by weight, 0-3% of carbon, 20-35% of oxygen, 40-53% of chromium, 10-35% of iron, 1-4% of molybdenum, 1-4% of nickel, 0-2.5% of silicon, 0-2% of calcium with the balance being impurity elements.
2. The nanocrystalline material according to claim 1, characterized in that the amount of the impurity elements is <1%; preferably, the nanocrystalline material contains, expressed in percentage by weight, 0.83% of carbon, 32.81% of oxygen, 44.28% of chromium, 14.47% of iron, 1.0% of molybdenum, 3.06% of nickel, 2.43% of silicon, 1.11% of calcium with the balance being impurity elements.
3. The nanocrystalline material according to claim 1, characterized in that the friction coefficient of the nanocrystalline material is 0.07-0.098, preferably 0.092.
4. A method for preparing the nanocrystalline material according to claim 1, characterized in that the method comprises the following steps: (1) chemically degreasing and etching with alkali a stainless steel surface using a sodium hydroxide solution and a solution containing an alkali etching active agent, followed by washing with water; (2) oxidizing the stainless steel surface treated in the step (1) by an oxidizing solution, followed by washing with water; (3) immersing the stainless steel surface treated in the step (2) as a cathode in an electrolyte to electrolyze, followed by washing with water; (4) placing the stainless steel surface treated in the step (3) at a temperature of 50-60 C. and a humidity of 60-70% for hardening.
5. The method according to claim 4, characterized in that, in the step (1), the temperature of the sodium hydroxide solution and the solution containing the alkali etching active agent is 80-85 C.; preferably, the concentration of the sodium hydroxide solution is 6.5-8%; preferably, the concentration of the solution containing the akali etching active agent is 0.3-0.5%; preferably, the alkali etching active agent is ethoxy modified polytrisiloxane; preferably, the chemically degreasing and etching with alkali is carried out for 10-15 minutes; preferably, the washing with water is performed by using water with a temperature of 80-85 C. for 3-5 minutes.
6. The method according to claim 4, characterized in that, in the step (2), the oxidizing solution contains 200-300 g/L of CrO.sub.3 and 100-150 g/L of Na.sub.2MoO.sub.4; preferably, the temperature of the oxidizing solution is 75-90 C.; preferably, the pH of the oxidizing solution is 0.4-1.5; preferably, the pH of the oxidizing solution is adjusted to 0.4-1.5 by adding a H.sub.2SO.sub.4 solution into the oxidizing solution; preferably, the concentration of the H.sub.2SO.sub.4 solution is 98%; preferably, the time for oxidizing is 15-35 minutes; preferably, the washing with water in the step (2) is performed cyclically by using water at 25-40 C. for 3-5 minutes; preferably, the pH of the water is >3.
7. The method according to claim 4, characterized in that, in the step (3), the electrolyte contains 100-150 g/L of CrO.sub.3, 100-150 g/L of Na.sub.2MoO.sub.4, 200-250 g/L of H.sub.3PO.sub.4, 50-60 g/L of Na.sub.2SiO.sub.3; preferably, the temperature of the electrolyte is 40-52 C.; preferably, the pH of the electrolyte is 0.5-1.5; preferably, the pH of the electrolyte is adjusted to 0.5-1.5 by adding a H.sub.2SO.sub.4 solution into the electrolyte; preferably, the concentration of the H.sub.2SO.sub.4 solution is 98%; preferably, the current for electrolyzing is direct current; preferably, the intensity of the current is 42-5 A/m.sup.2; preferably, the initial current intensity is 40 A/m.sup.2, and then the current intensity is gradually reduced to 5 A/m.sup.2 according to the formula i=3+A/t, wherein i is current Intensity, t is time, and A is parameter of 20-30; preferably, the time for electrolyzing is 25-55 minutes; preferably, the electrolysis comprises electrolyzing for 10-25 minutes at an initial current intensity of 40 A/m.sup.2, and then gradually reducing the current intensity to 5 A/m.sup.2 during 15-30 minutes while electrolysis; preferably, the washing with water is performed cyclically by using water at 25-40 C. for 3-5 minutes; preferably, the pH of the water is >3.
8. The method according to claim 4, characterized in that, in the step (4), the performed time for hardening treatment is 3-4 hours.
9. A nanocrystalline material based on the stainless steel surface prepared by the method according to claim 4.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0061] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, wherein
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DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0084] Further described the present invention in detail in conjunction with specific embodiments below, the examples are given only for illustrating the present invention and are not intended to limit the scope of the invention.
[0085] The experimental methods in the following examples are conventional methods unless otherwise specified. The raw materials, reagent materials, etc., in the following examples are commercially available products unless otherwise specified.
Example 1: The Test on Current Control of the Method According to the Present Invention
[0086] In the method of the present invention, the change in current during electrolysis has a large influence on the atomic packing factor of the nanocrystalline material surface. It can be found from the standard ferric chloride corrosion test that the atomic packing factor of the nanocrystalline material surface has a great influence on the corrosion results. The change in the coefficient of friction (according to GB/T12444-2006 test standard, with a silicon carbide ball of 6, with a loading force of 200 g, a rotating speed of 120 rpm, for 3 min) and the change in the corrosion resistance of the nanocrystalline material surface were observed by various changes in the electrolysis current, and the results shown that the smaller the coefficient of friction was, the better the corrosion resistance was.
[0087] As shown in
[0088] Scheme 1: As shown in
[0089] Scheme 2: As shown in
[0090] Scheme 3 (the current was controlled according to the method of the present invention): As shown in
[0091] The results were shown in Tables 3 and 4:
TABLE-US-00003 TABLE 3 friction coefficients and corrosion rate of the nanocrystalline material based on 304 stainless steel substrate (2B cold rolled stainless steel - NO. 1) Friction coefficient (being tested according Corrosion rate of to GB/T12444-2006 standard ferric Schemes standard) chloride g/m.sup.2h 304 stainless steel 0.131-0.155 17.68-22.05 substrate (without the nanocrystalline material) Scheme 1 0.997-0.105 2.01-2.32 Scheme 2 0.108-125 4.36-5.02 Scheme 3 0.086-0.092 0.91-1.12 (the current was controlled according to the method of the present invention)
[0092] Conclusion: Different ways of changing the current lead to different atomic packing factor of stainless steel nano-surfaces. As can be seen from the Table 3, the smaller the friction coefficient gi was, the smoother the nano-surface film layer was, and the higher the atomic packing factor of the nano-crystal surface was, his will result in good corrosion resistance.
[0093] According to the test of changing the current, it was found that when the change of current was subjected to the hyperbolic function i=3+A/t (i is current intensity A/m.sup.2, t is duration time, A (parameter) is 20-30), the atomic packing factor of the nanocrystalline materials surface was the highest. Thus, the friction coefficients of various materials in which the change of current was subjected to the hyperbolic function were tested. The result was shown in Table 4.
TABLE-US-00004 TABLE 4 friction coefficients of the nanocrystalline material based on different various stainless steel substrates (2B cold rolled stainless steel - NO. 1) Materials (2B cold rolled stainless steel - NO. 1), the initial current was 40 A/m.sup.2, the current intensity was subjected to i = 3 + A/t (i is current intensity A/m.sup.2, t is duration time, A (parameter) is 20-30), the friction coefficients (was tested according to the GB/T12444-2006 standard) Average Friction Materials Friction reduction Mate- coeffi- of coeffi- percentage rials cients nanosurface cients % 304 0.131-0.155 304 nanosurface 0.086-0.092 37.76% 304Ti 0.133-0.158 304Ti nanosurface 0.086-0.095 37.80% 316L 0.115-0.137 316L nanosurface 0.078-0.086 34.92% 317L 0.095-0.115 317L nanosurface 0.07-0.079 29.05% 410S 0.142-0.168 410S nanosurface 0.092-0.102 37.42% 2205 0.108-0.129 2205 nanosurface 0.073-0.085 33.33% 201 0.138-0.162 201 nanosurface 0.091-0.098 37.00%
[0094] Conclusion: The most common available stainless steel 2B cold rolled stainless steelNO. 1 was tested, and the change of current was subjected to the hyperbolic function, the atomic packing factor was the highest, the friction coefficient was the least, when compared with other various stainless steel substrates, the friction coefficient of the nanocrystalline surface is reduced by 29-38%.
Example 2: Surface Hardening Test of the Nanocrystalline Material According to the Present Invention
[0095] The hardening on the nanocrystalline material based on the stainless steel surface has a great influence on the corrosion resistance. At present, the hardening of the stainless steel surface is usually dried at room temperature.
[0096] In the present invention, the inventors evaluated the corrosion resistance of the nanocrystalline material surface using anti-flowing corrosion effect under different temperature, humidity and time to screen the most suitable surface hardening conditions.
[0097] The effect of the hardening temperature on the nano surface was tested by a 3D optical profilometer. According to the ASME B46.1-2009 standard, the roughness depth of the nanocrystalline surface was tested at a temperature of 203 C. and a relative humidity of 40-80%, the vibration velocity of air-floating seismic isolation system was <2.28 m/s, the air pressure was 0.275-0.55 Mpa, the voice was <60 dB-A, the voltage was 85-264 VAC and 47-63 Hz. The testing results of more than 20 the deepest points on the hardened surface were taken to calculate the average roughness depth. The testing results were shown in
[0098] Meanwhile, the standard ferric chloride corrosion test on the nanocrystalline surface was carried out under constant temperature and humidity conditions in a flowing corrosive environment. The corrosion resistance environment of the nanocrystalline material surface based on 304 substrate (2B cold rolled stainless steelNO. 1) was shown in Tables 5-7. It can be seen from the
TABLE-US-00005 TABLE 5 Effect of hardening temperature on the resistance of the nanocrystalline material surface to corrosion Effect of hardening temperature on corrosion resistance of the nanocrystalline material surface (the humidity was controlled at 60%, the hardening time was 4 h) Corrosion rate of Hardening Surface average flowing (with a flow temperature roughness rate of 1 m/s) Nos. C. depth (um) ferric chloride g/m.sup.2h 1 Room Temperature- 22.2522-25.7840 8.68-2.35 Uncertain Humidity 2 30 19.9217 4.09 3 40 17.1534 2.87 4 50 11.9166 1.55 5 60 15.6419 2.41 6 70 28.9225 6.22 7 80 67.7151 10.84
[0099] It can be seen from Table 5 and
TABLE-US-00006 TABLE 6 Effect of hardening humidity on the resistance of the nanocrystalline material surface to corrosion Effect of hardening humidity on the resistance of the nanocrystalline material surface to corrosion (the temperature was controlled at 50 C., the hardening time was 4 h) Corrosion rate of flowing (with a flow Hardening rate of 1 m/s) Nos. Humidity % ferric chloride g/m.sup.2h 1 <2 11.27 2 20 6.58 3 30 4.61 4 40 2.23 5 50 1.78 6 60 1.55 7 70 1.62 8 80 1.76 9 95 1.82
[0100] Conclusion: the effect of hardening humidity on the softness/hardness of the nano-film layer was similar to that of the hardening temperature. The hardening humidity was low, the surface of the nano-film layer had cracks, the humidity was high, the nano-film layer was soft and easy to fall off. It can be seen from the corrosion results of the flowing ferric chloride that, in present invention, the suitable hardening humidity can improve the corrosion resistance to liquid. The suitable humidity was 6070%.
TABLE-US-00007 TABLE 7 Effect of hardening time on the resistance of the nanocrystalline material surface to corrosion Effect of hardening time on the resistance of the nanocrystalline material surface to corrosion (the temperature was controlled at 50 C., the humidity was 60%) Corrosion rate of Hardening flowing (Flow rate 1 m/s) Nos. time h ferric chloride g/m.sup.2h 1 0.5 3.51 2 1 2.42 3 2 1.88 4 3 1.56 5 4 1.55 6 6 1.53 7 12 1.49 8 24 1.45
[0101] Conclusion: It can be seen from the table 7, the longer the hardening time was, the better the effect was. The longer the time was, the higher the stability of the nano-film layer was. However, considering the processing time, in the present invention, the best time was 3-4 h.
Example 3: Ni Element Content Test on the Nanocrystalline Material Surface According to the Present Invention
[0102] Ni is an important auxiliary element in austenitic stainless steel, which can stabilize the structure of austenitic stainless steel and enhance the corrosion resistance and toughness of weld metals. Its general content is 7-12%. When the Ni content is less than 7%, the toughness of the austenitic stainless steel is insufficient, and when the Ni content is >12%, the strength of the austenitic stainless steel is decreased. In the present invention, the inventors have performed a large number of tests, controlled the Ni content in the surface layer (i.e., the repair conversion layer) of the nanocrystalline material by adjusting the oxidation time, pH value, electrolysis time, pH value, the concentration of the electrolyte, and formulation, etc.
[0103] In particular, the inventors performed the following tests to test the anticorrosion effect of the nanocrystalline material surface containing different content of Ni, thereby screening the best Ni content: the standard ferric chloride corrosion test (according to the GB/T17897-1999 standard, the temperature was 50 C.), 1 m/s mobile chloride ion corrosion test (the corrosion solution was formulated according to the GB/T17897-1999 standard, the testing time was 24 h, the flow rate of the corrosion solution in the test pipe was controlled at 1 m/s by using a flow pump, the testing sample was placed along the flowing direction of the corrosion solution, the testing temperature was 35 C., the corrosion effect of the flowing corrosive medium on the nanocrystalline layer surface was observed), 10% hydrochloric acid corrosion test (according to the GB/T17897-1999 standard, 10% hydrochloric acid solution was formulated, the testing temperature was 50 C.), 1.5 m/s flowing hydrochloric acid corrosion test (according to GB/T17897-1999 standard, 10% hydrochloric acid corrosion solution was formulated, the time was 24 h, the flow rate of the corrosion solution in the test pipe was controlled at 1 m/s by using a flow pump, the testing sample was placed along the flowing direction of the corrosion solution, the testing temperature was 35 C., the corrosion effect of the flowing corrosive medium on the nanocrystalline layer surface was observed) and nanoindentation hardness test (according to the GB/T21838.1-2008 standard of).
[0104] 304 substrate was taken as an example, the content of Ni in the 304 substrate was 8%, when the Ni content in surface nanolayer was <7%, the Ni element in the substrate can be used directly; when the Ni content was >7%, the Ni element needs to be supplemented by adding additional nickel sulfate into electrolyte, the Ni content of the nanolayer can be controlled by adjusting the concentration.
[0105] 1. The standard ferric chloride corrosion test was carried out in a constant temperature, static and corrosive environment, and the corrosive environment of the surface of the nanocrystalline material based on the 304 substrate was shown in Table 8.
TABLE-US-00008 TABLE 8 Effect of Ni content in the nanocrystalline surface based on 304 substrate on the resistance to corrosion Effect of Ni content in the nanocrystalline surface based on 304 substrate on the resistance to corrosion (the oxidizing time was 20 min, the hardening time was 4 hours, the nano Ni content was controlled by controlling the electrolysis time and concentration) Corrosion rate of Ni content in the standard ferric chloride nanocrystalline layer g/m.sup.2h (according to (11 nm layers was GB/T17897-1999 standard, Nos. detected by XPS) the testing temperature was 50 C.) 1 0 1.02 2 0.02 0.91 3 0.51 0.87 4 1.2 0.83 5 2.35 0.81 6 3.57 0.80 7 5.74 0.83 8 6.48 0.85 9 7.25 0.87 10 9.21 0.95 11 10.53 1.15
[0106] 2. 10% hydrochloric acid corrosion test was carried out in a constant temperature, static and corrosive environment, and the corrosive environment of the surface of the nanocrystalline material based on the 304 substrate was shown in Table 9.
TABLE-US-00009 TABLE 9 Effect of Ni content in the nanocrystalline surface based on 304 substrate on the resistance to corrosion Effect of Ni content in the nanocrystalline surface based on 304 substrate on the resistance to corrosion (the oxidizing time was 20 min, the hardening time was 4 hours, the nano Ni content was controlled by controlling the electrolysis time and concentration) Ni content in the Corrosion rate of 10% nanocrystalline layer hydrochloric acid g/m.sup.2h (11 nm layers was (the testing temperature Nos. detected by XPS) was 50 C.) 1 0 1.74 2 0.01 1.66 3 0.52 1.57 4 1.51 1.21 5 2.61 1.12 6 3.41 1.05 7 5.74 1.01 8 6.81 1.13 9 7.42 1.22 10 8.94 1.35 11 11.05 1.54
[0107] Conclusion: For the static and corrosive environment, when the corrosion was made by ferric chloride and hydrochloric acid, the Ni content in the surface of the nanocrystalline layer has no obvious effect on the corrosion, but the result shows that the optimal Ni content range is 2-5%.
[0108] 3. The ferric chloride corrosion test under flowing environment was carried out in a constant temperature, flowing and corrosive environment to simulate the erosion corrosion environment in industrial devices, and the corrosive environment of the surface of the nanocrystalline material based on the 304 substrate was shown in Table 10.
TABLE-US-00010 TABLE 10 Effect of Ni content in the nanocrystalline surface based on 304 substrate on the resistance to erosion and corrosion Effect of Ni content in the nanocrystalline surface based on 304 substrate on the resistance to corrosion (the oxidizing time was 20 min, the hardening time was 4 hours, the nano Ni content was controlled by controlling the electrolysis time and concentration) Ni content in the Corrosion rate of nanocrystalline layer flowing (with a flow (11 nm layers was rate of 1 m/s) Nos. detected by XPS) ferric chloride g/m.sup.2h 1 0 3.52 2 0.01 2.23 3 0.47 1.88 4 1.1 1.62 5 2.24 1.58 6 3.51 1.52 7 5.51 2.24 8 6.87 4.35 9 7.51 7.88 10 9.88 12.66 11 11.23 18.53
[0109] 4. A double test of hydrochloric acid erosion corrosion under flowing environment was carried out in a constant temperature, flowing and corrosive environment to simulate the erosion corrosion environment in industrial devices, and the corrosive environment of the surface of the nanocrystalline material based on the 304 substrate was shown in Table 11.
TABLE-US-00011 TABLE 11 Effect of Ni content in the nanocrystalline surface based on 304 substrate on the resistance to erosion and corrosion Effect of Ni content in the nanocrystalline surface based on 304 substrate on the resistance to corrosion (the oxidizing time was 20 min, the hardening time was 4 hours, the nano Ni content was controlled by controlling the electrolysis time and concentration) Ni content in the Corrosion rate of nanocrystalline layer 10% flowing (with a flow (11 nm layers was rate of 1.5 m/s) Nos. detected by XPS) hydrochloric acid g/m.sup.2h 1 0 6.02 2 0.01 5.88 3 0.49 2.51 4 1.21 1.94 5 2.58 1.82 6 3.78 2.02 7 5.46 4.52 8 6.51 6.87 9 7.89 9.51 10 9.81 15.78 11 11.55 22.31
[0110] Conclusion: For industrially similar flowing corrosive environments, the corrosion of ferric chloride and hydrochloric acid was taken, and the Ni content in the surface of the nanocrystalline layer has a significant effect on the corrosion, and the added Ni content is significantly different from the inherent Ni content of the substrate, which has an influence on the strength of the skeleton of the nanocrystalline layer. At the same time, the increase of the added Ni content leads to a decrease of anti-corrosion of Cr correspondingly, therefore a high content of Ni may cause a decrease in the corrosion resistance effect. Through the tests of flowing corrosion resistant environment with different content of Ni, the Ni content of the nanocrystalline layer in the present invention is 1-4%.
[0111] 5. The change of the Ni content in the surface of the nanocrystalline layer also lead to a change in hardness of the surface. Theoretically, the harder the hardness of the surface was, the stronger the erosion resistance was. The corrosive environment of the surface of the nanocrystalline material based on the 304 substrate was shown in Table 12.
TABLE-US-00012 TABLE 12 Effect of Ni content in the nanocrystalline surface based on 304 substrate on the resistance to erosion and corrosion Effect of Ni content in the nanocrystalline surface based on 304 substrate on the resistance to corrosion (the oxidizing time was 20 min, the hardening time was 4 hours, the nano Ni content was controlled by controlling the electrolysis time and concentration) Ni content in the nanocrystalline layer Nanoindentation (11 nm layers was hardness Nos. detected by XPS) (GPa) 1 0 3.61 2 0.02 3.88 3 0.51 4.35 4 1.2 6.08 5 2.35 6.4 6 3.57 7.05 7 5.74 5.88 8 6.48 5.87 9 7.25 5.48 10 9.21 5.2 11 10.53 5.19
[0112] It can be seen from Table 12 that the test results of nanoindentation hardness are consistent with the erosion resistance of Tables 10-11. The hardness of the nanosurface has positive effect on the erosion corrosion in some extent. From the testing results, it can be seen that the area with a hardest hardness is the area with a best erosion resistance. In the present invention, the optimal Ni content is 1-4%.
[0113] 6. The effect of Ni content in the nanocrystalline surface based on 304 substrate on the resistance to erosion, corrosion and hardness was shown in
[0114] It can be seen from
Example 4: Screening of the Alkali Etching Active Agent According to the Present Invention
[0115] The cleaning of the surface of stainless steel by chemical degreasing and etching with alkali has influence on the corrosion resistance of the nanocrystalline layer in some extent. The alkali etching active agent was screened in the present invention. 304 substrate was taken as an example, a potential scanning at room temperature was performed on the nanocrystalline materials with different kinds and different amounts of alkali etching active agents, and different self-corrosion potential was obtained. The self-corrosion potential caused by the alkali etching active agent to nanocrystalline material based on 304 substrate is shown in Table 13.
TABLE-US-00013 TABLE 13 Self-corrosion potential caused by the alkali etching active agent to nanocrystalline material based on 304 substrate Self-corrosion potential caused by the alkali etching active agent to nanocrystalline material based on 304 substrate (the oxidizing time was 20 min, the electrolysis was performed for 15 + 20 min, the harden time was 4 hours) 3% NaCl self-corrosion potential Etching active agents (with a scanning speed of 1 mV/s, (respective optimal a polarization range of 200 mV~200 Nos. ratio wt %) mV relative to open circuit potential) 1 Without additives 0.1354 2 HDW-1050(0.3~0.5%) 0.1127 3 Phosphate salt (3~4%) 0.0347 4 Ethoxylated polytrisiloxane 0.1868 (0.3~0.5%) 5 Polyethoxylated fatty 0.0794 alcohol (0.7~0.9%) 6 OP-10(4~5%) 0.0255 7 PRO22(1.1~1.3%) 0.1534
[0116] Conclusion: compared with stainless steels, the self-corrosion potential of the nanocrystalline material based on stainless steels will produce positive shift. The more positive the self-corrosion potential was, the stronger the resistance to electrochemical corrosion was. As for each etching active agents, different ratios of tests with a range of 0.3-5% were performed. Table 12 shows the highest self-corrosion potential after adding each etching active agents in 3% NaCl, as well as the corresponding adding ratios.
[0117] It can be seen from Table 13, the best alkali etching active agents in the present invention is ethoxylated polytrisiloxane, and the resistance the nanocrystalline material based on stainless steel to electrochemical corrosion is the best after etching with such alkali with a concentration of 0.3-0.5%.
Example 5: Preparation of the Nanocrystalline Material Based on Stainless Steel (304 Substrate) According to the Present Invention
[0118] (1) A sodium hydroxide solution with a concentration of 7% and a solution containing 0.5% of ethoxylated polytrisiloxane alkali etching active agent was used to chemically degrease and etch with alkali a stainless steel surface (a 304 substrate). The total amount of the entire solution was subjected to immerse the whole stainless steel surface. The temperature of the solution was controlled at 80 C. The operation was performed for 15 min. After that, water with a temperature of 80 C. was used for washing for 3 min.
[0119] (2) The composition of the used oxidizing solution contained 300 g/L of CrO.sub.3 and 140 g/L of Na.sub.2MoO.sub.4. At 78 C., H.sub.2SO.sub.4 solution with a concentration of 98% was used to adjust the pH value to 1.3, the time for oxidizing was 15 min, after that, water under normal temperature was used for washing for 3 min.
[0120] (3) The composition of the used electrolytic solution contained 100 g/L of CrO.sub.3, 100 g/L of Na.sub.2MoO.sub.4, 200 g/L of H.sub.3PO.sub.4, 55 g/L of Na.sub.2SiO.sub.3. H.sub.2SO.sub.4 solution with a concentration of 98% was used to adjust the pH value to 1.3. The temperature was controlled at 40 C. The stainless steel (304 substrate) was used as cathode, based on the surface area of the stainless steel, the electrolysis was performed at the current intensity of 40 A/m.sup.2 for 10 min, then was performed at a gradually reduced current intensity according to the formula i=3+30/t (i is current intensity A/m.sup.2, t is duration time) for 15 min, and then the electrolyte on the surface of the stainless steel piece was washed water at room temperature.
[0121] (4) The stainless steel piece (304 substrate) was placed into an environment with a temperature of 55 C. and a humidity of 60% to harden for 3 hours. Thus, an anti-coking nanomaterial based on the stainless steel surface (304 substrate) was obtained.
[0122] The testing results of the anti-coking nanomaterial based on 304 stainless steel of the present invention were as follows: the nanocrystalline material contained 0.83% of carbon, 32.81% of oxygen, 44.28% of chromium, 14.47% of iron, 1.0% of molybdenum, 3.06% of nickel, 2.43% of silicon, 1.11% of calcium, and with the balance being remaining amount of impurity elements.
Example 6
[0123] An acid water stripping unit reflux system from Ningxia Coal Industry Group Co., Ltd. was seriously corroded, especially, the top reflux pipe, the return pump, the return tank and the condenser at the top of the tower had severe corrosion and serious leakage. The replacement of the equipment in the reflux system was short, which affected the acid water treatment of the equipment.
TABLE-US-00014 TABLE 14 Water analysis data after washing acids Items Acid water stripping unit Ammonia nitrogen in incoming water 3900 (mg/L) Sulfide in incoming water (mg/L) 72 Petroleum in incoming water (mg/L) Not detected COD in outer delivery water (mg/L) did not cause excessive COD Ammonia nitrogen in outer delivery 5-30 water (mg/L) Sulfide in outer delivery water (mg/L) Not detected Petroleum in outer delivery water Not detected (mg/L) PH in reflux 8.6-10 Iron ion in reflux (mg/L) Total iron 39.6 Cl in reflux (mg/L) Detected maximum was 11000 Non-condensable gas H.sub.2S content (%) <2 Non-condensable gas NH.sub.4.sup.+ content Total nitrogen 50 (%) Non-condensable gas CO.sub.2(%) 50
[0124] Due to high content and fast flow rate of Cl.sup. in the reflux of the acid water stripping unit reflux system and the caused washing and corrosion on the filter hanger piece was fast. When the filter hanger made of 304 stainless steel was tested, the result showed that there was visible corrosion to the naked eye after being placed for one week, as shown in
[0125] After treating the 304 stainless steel by the nanocrystalline material according to the present invention, as shown in
Example 7
[0126] A branch company of China Petroleum & Chemical Corporation designed high-sulfur and high-acid crude oil as the crude oil in an atmospheric and vacuum distillation device of a crude oil deterioration reconstruction project. A 304 filter and a 304 filter containing a nano surface layer were placed at the bottom of the third section of a packed vacuum tower. Specific temperature was shown as Table 9:
TABLE-US-00015 TABLE 9 Minus three lines Carbon residue temperature ( C.) Sulfur content Acid value content 213~331.2 0.77 m % 1.06 2.26%
[0127] After being operated for 1247 days, it can be seen from the scene that the 304 substrate was corroded, become thin, and severely embrittled. While after being treated by the method according to the present invention, the stainless steel 304 showed no significant corrosion, as shown in
Example 8
[0128] A branch company of China National Offshore Oil Corporation designed low-sulfur and high-acid crude oil as the crude oil in an atmospheric and vacuum distillation device. The temperature of the fifth section of the vacuum tower was 400 C., the sulfur content was 0.35%, the acid value was 2.65-3.09 and the filter substrate was 317L. After being operated for 3 years, it was seen from the scene that the 317L substrate had obvious corrosion, as shown in