Preparation method of nickel nanoparticle catalyst with adjustable crystal phase structure and catalyst

Abstract

The invention provides a preparation method of a nickel nanoparticle catalyst with an adjustable crystal phase structure and the catalyst, which are used for solving the technical problem that synthesis of nickel nanoparticles with different crystal phases cannot be effectively controlled in the prior art. The preparation method comprises the following steps: dissolving a nickel compound in a polyol solvent to obtain a nickel precursor solution; a protective agent and a reducing agent are evenly mixed and then heated to 180-290 DEG C, and a mixed solution is obtained; and dropwise adding the nickel precursor solution into the mixed solution, reacting for more than 10 minutes at the temperature of 180-290 DEG C, and centrifuging, washing and drying to obtain the nickel nanoparticle catalyst with the adjustable crystal phase structure, wherein the volume molar concentration of the nickel precursor solution is 0.01-1 mol / L; the nickel compound, the protective agent and the reducing agent are respectively 1 part by weight of the nickel compound, 0.1-20 parts by weight of the protective agent and 10-1000 parts by weight of the reducing agent.

Description

Technical Field

[0001] The invention relates to a method for preparing a metal nano material, in particular to a method for preparing a nickel nano particle catalyst with adjustable crystal phase structure, namely a catalyst. Background Art

[0002] Metal nanomaterials have broad applications in catalysis, biomedicine, aerospace, etc. The crystal phase of metal nanomaterials has a great influence on their physical and chemical properties and performance, because different crystal phase structures of metal materials have different spatial distributions and electronic structures.

[0003] Nickel (Ni) nanoparticles are common transition metal nanomaterials and have been widely used in industrial hydrogenation, electrocatalytic hydrogen evolution (HER), electrocatalytic oxygen evolution (OER), CO2 methanation, methane reforming and other reactions. The different crystalline phases of nickel nanoparticles have a great influence on the catalytic process. Therefore, the study of the controllable synthesis of nickel nanoparticles with different crystalline phases has far-reaching significance.

[0004] However, there are few reports on the research of controlling the synthesis of nickel nanoparticle systems with different crystalline phases and the phase control mechanism. This is because the hexagonal close-packed (hcp) phase of nickel nanoparticles is thermodynamically metastable and can easily be converted into a thermodynamically stable face-centered cubic (fcc) crystalline phase structure during the reaction process. However, there is currently no relevant literature that discloses how to effectively control the synthesis of nickel nanomaterials with specific crystalline phases. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a nickel nanoparticle catalyst with adjustable crystal phase structure and the catalyst thereof, so as to solve the technical problem that the prior art cannot effectively control the synthesis of nickel nanoparticles with different crystal phases.

[0006] To achieve the above purpose, the technical solution provided by the present invention is as follows:

[0007] A method for preparing a nickel nanoparticle catalyst with adjustable crystal phase structure is special in that it comprises the following steps:

[0008] dissolving a nickel compound in a polyol solvent to obtain a nickel precursor solution;

[0009] The protective agent and the reducing agent are mixed evenly and heated to 180-290° C. to obtain a mixed solution; wherein the protective agent is used to prevent the nanoparticles from agglomerating too large;

[0010] The nickel precursor solution is added dropwise into the mixed solution, and reacted at a temperature of 180-290° C. for more than 10 minutes, and then centrifuged, washed, and dried to obtain a nickel nanoparticle catalyst with an adjustable crystal phase structure;

[0011] Wherein, the volume molar concentration of the nickel precursor solution is 0.01 to 1 mol / L;

[0012] The nickel compound, protective agent and reducing agent are respectively calculated in parts by weight: 1 part of nickel compound, 0.1 to 20 parts of protective agent, and 10 to 1000 parts of reducing agent.

[0013] Furthermore, by using different nickel compounds, different nickel precursor solutions are obtained, and nickel nanoparticle catalysts with different crystal phase structures are prepared;

[0014] The nickel compound is any one of nickel formate dihydrate, nickel acetylacetonate, nickel acetate, nickel chloride, nickel sulfate, nickel nitrate, nickel hydroxide or nickel hydroxide.

[0015] Furthermore, by controlling the reaction temperature T, nickel nanoparticle catalysts with different crystal phase structures are prepared;

[0016] Among them, when 180≤T<210℃, a pure fcc phase nickel nanoparticle catalyst is obtained; when the reaction temperature is 210≤T<270℃, nickel nanoparticles with coexistence of fcc-hcp phases are obtained; when the reaction temperature is 270≤T≤290℃, a pure hcp phase nickel nanoparticle catalyst is obtained.

[0017] Further, the polyol solvent is selected from one of diethylene glycol, methanol, ethanol, n-propanol, isopropanol, n-butanol, pentanol, hexanol, ethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, butylene glycol, dibutylene glycol, tributylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, butylene glycol monomethyl ether, butylene glycol monoethyl ether, glycerol, diglycerol, polyglycerol, trimethylolpropane, pentaerythritol or oleylamine with a volume concentration of 50 to 100%.

[0018] Furthermore, the protective agent is one of polyvinyl pyrrolidone, polyethylene glycol, polyvinyl alcohol, polyvinyl ether, polymethacrylic acid, polymethacrylate, sodium alginate or cellulose derivatives;

[0019] The reducing agent is one of diethylene glycol, methanol, ethanol, n-propanol, isopropanol, n-butanol, pentanol, hexanol, ethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, butylene glycol, dibutylene glycol, tributylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, butylene glycol monomethyl ether, butylene glycol monoethyl ether, glycerol, diglycerol, polyglycerol, trimethylolpropane, pentaerythritol or oleylamine.

[0020] Further, the washing is performed with an organic solvent for more than 3 times, wherein the organic solvent is selected from one of acetone, methanol, ethanol, isopropanol, petroleum ether, ethyl ether, dichloromethane, n-butanol, glycerol, ethylene glycol, tetrahydrofuran, dimethyl sulfoxide, N,N-dimethylformamide, methyl acetate, ethyl acetate, propyl acetate, pentane, hexane, octane, benzene, toluene, xylene, methyl butyl ketone, methyl isobutyl ketone, cyclohexane, cyclohexanone or toluene-cyclohexanone;

[0021] The centrifugation is carried out in a centrifugal device at 5000-10000 rpm;

[0022] The drying temperature is 20-60° C., and the drying time is 2-6 hours.

[0023] In addition, the present invention also provides a nickel nanoparticle catalyst with adjustable crystal phase structure, which is special in that it includes nickel nanoparticles of fcc phase, nickel nanoparticles of coexisting fcc-hcp phases, and nickel nanoparticles of hcp phase.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The present invention adopts a synthesis method of thermally reducing a nickel precursor with a reducing agent. By using different nickel compounds and controlling the reaction temperature, nickel nanoparticle catalysts with different crystalline structures are obtained, thereby achieving continuous regulation of the crystalline phase of the nickel nanoparticles, and providing a theoretical basis and new ideas for the controllable synthesis of metal nanomaterials with different crystalline phases.

[0026] 2. The present invention prepares fcc phase, hcp phase and fcc-hcp mixed phase nickel nanoparticles by changing the nickel compound and the reaction temperature, thereby improving the application scope of the preparation method, and can prepare nickel nanoparticle catalysts with corresponding structures according to different crystal phase structure requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 XRD spectra of the nickel nanoparticle catalysts prepared in Examples 1 to 4 of the present invention;

[0028] Figure 2 XRD spectra of the nickel nanoparticle catalysts prepared in Examples 5 to 8 of the present invention;

[0029] Figure 3 is a graph showing the ratio of hcp phase nickel in the nickel nanoparticle catalysts prepared in Examples 5 to 8 of the present invention;

[0030] Figure 4 Schematic diagram of nickel atom energy conversion during the reaction process of Examples 1 to 8 of the present invention. DETAILED DESCRIPTION

[0031] In order to better illustrate the purpose, technical solution and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the catalysts not specifically described in the following embodiments are all nickel nanoparticle catalysts.

[0032] In the examples, the test methods used are conventional methods unless otherwise specified, and the materials, reagents, etc. used are all commercially available unless otherwise specified.

[0033] Example 1

[0034] S1, dissolving 0.5 mmol (64.8 mg) of nickel chloride in 10 ml of a diethylene glycol solvent having a volume concentration of 50% to prepare a nickel precursor solution.

[0035] S2, 275 mg of polyvinyl pyrrolidone and 100 ml of diethylene glycol are mixed evenly and heated to 245° C. to obtain a mixed solution.

[0036] S3, adding the nickel precursor solution dropwise to the mixed solution while stirring at a stirring speed of 400 rpm, stirring for 10 minutes to obtain a black liquid, separating the solid by a high-speed centrifuge at 9000 rpm, and then washing with 240 mL of petroleum ether for 4 times to remove the by-products, and drying at 25° C. for 3 hours to obtain a nickel nanoparticle catalyst. The XRD spectrum of the catalyst obtained by X-ray powder diffraction is as follows Figure 1 As shown by curve ① in the figure, it can be seen that the obtained catalyst is fcc phase.

[0037] Example 2

[0038] S1, dissolving 0.5 mmol (128.46 mg) of nickel acetylacetonate in 10 ml of a diethylene glycol solvent having a volume concentration of 50% to prepare a nickel precursor solution.

[0039] S2, 275 mg of polyvinyl pyrrolidone and 100 ml of diethylene glycol are mixed evenly and heated to 245° C. to obtain a mixed solution.

[0040] S3, adding nickel precursor solution dropwise to the mixed solution while stirring at a stirring speed of 400 rpm, stirring for 10 minutes to obtain a black liquid, separating the solid by a high-speed centrifuge at 9000 rpm, washing with 240 mL of petroleum ether for 4 times to remove the by-products, and drying at 25° C. for 3 hours to obtain a nickel nanoparticle catalyst. The XRD spectrum of the catalyst obtained by X-ray powder diffraction is shown as follows: Figure 1 As shown in curve ② in the figure, it can be seen that the obtained catalyst is fcc-hcp phase.

[0041] Example 3

[0042] S1, dissolving 0.5 mmol (124.4 mg) of nickel acetate in 10 ml of a diethylene glycol solvent having a volume concentration of 50% to prepare a nickel precursor solution.

[0043] S2, 275 mg of polyvinyl pyrrolidone and 100 ml of diethylene glycol are mixed evenly and heated to 245° C. to obtain a mixed solution.

[0044] S3, adding the nickel precursor solution dropwise to the mixed solution while stirring at a stirring speed of 400 rpm, stirring for 10 minutes to obtain a black liquid, separating the solid by a high-speed centrifuge at 9000 rpm, washing with 240 mL of petroleum ether for 4 times to remove the by-products, and drying at 25° C. for 3 hours to obtain a nickel nanoparticle catalyst. The XRD spectrum of the catalyst obtained by X-ray powder diffraction is shown as follows: Figure 1 As shown by curve ③ in the figure, it can be seen that the obtained catalyst is hcp phase.

[0045] Example 4

[0046] S1, dissolving 0.5 mmol (124.4 mg) of nickel formate dihydrate in 10 ml of a diethylene glycol solvent having a volume concentration of 50% to prepare a nickel precursor solution.

[0047] S2, 275 mg of polyvinyl pyrrolidone and 100 ml of diethylene glycol are mixed evenly and heated to 245° C. to obtain a mixed solution.

[0048] S3, adding the nickel precursor solution dropwise to the mixed solution while stirring at a stirring speed of 400 rpm, stirring for 10 minutes to obtain a black liquid, separating the solid by a high-speed centrifuge at 9000 rpm, washing with 240 mL of petroleum ether for 4 times to remove the by-products, and drying at 25° C. for 3 h to obtain a nickel nanoparticle catalyst. The XRD spectrum of the catalyst obtained by X-ray powder diffraction is as follows: Figure 1 As shown by curve ④ in the figure, it can be seen that the obtained catalyst is hcp phase.

[0049] Example 5

[0050] S1, dissolving 0.5 mmol (124.4 mg) of nickel acetate in 10 ml of a diethylene glycol solvent having a volume concentration of 50% to prepare a nickel precursor solution.

[0051] S2, 275 mg of polyvinyl pyrrolidone and 100 ml of diethylene glycol are mixed evenly and heated to 210° C. to obtain a mixed solution.

[0052] S3, adding the nickel precursor solution dropwise to the mixed solution while stirring at a stirring speed of 400 rpm, stirring for 10 minutes to obtain a black liquid, separating the solid by a high-speed centrifuge at 9000 rpm, washing with 240 mL of petroleum ether for 4 times to remove the by-products, and drying at 25° C. for 3 h to obtain a nickel nanoparticle catalyst. The XRD spectrum of the catalyst obtained by X-ray powder diffraction is as follows: Figure 2 As shown by curve ① in the figure, it can be seen that the obtained catalyst is fcc phase.

[0053] Example 6

[0054] S1, dissolving 0.5 mmol (124.4 mg) of nickel acetate in 10 ml of a diethylene glycol solvent having a volume concentration of 50% to prepare a nickel precursor solution.

[0055] S2, 275 mg of polyvinyl pyrrolidone and 100 ml of diethylene glycol are mixed evenly and heated to 225° C. to obtain a mixed solution.

[0056] S3, adding the nickel precursor solution dropwise to the mixed solution while stirring at a stirring speed of 400 rpm, stirring for 10 minutes to obtain a black liquid, separating the solid by a high-speed centrifuge at 9000 rpm, washing with 240 mL of petroleum ether for 4 times to remove the by-products, and drying at 25° C. for 3 h to obtain a nickel nanoparticle catalyst. The XRD spectrum of the catalyst obtained by X-ray powder diffraction is as follows: Figure 2 As shown in curve ② in the figure, it can be seen that the catalyst is a fcc-hcp phase.

[0057] Example 7

[0058] S1, dissolving 0.5 mmol (124.4 mg) of nickel acetate in 10 ml of a diethylene glycol solvent having a volume concentration of 50% to prepare a nickel precursor solution.

[0059] S2, 275 mg of polyvinyl pyrrolidone and 100 ml of diethylene glycol are mixed evenly and heated to 245° C. to obtain a mixed solution.

[0060] S3, adding the nickel precursor solution dropwise to the mixed solution while stirring at a stirring speed of 400 rpm, stirring for 10 minutes to obtain a black liquid, separating the solid by a high-speed centrifuge at 9000 rpm, washing with 240 mL of petroleum ether for 4 times to remove the by-products, and drying at 25° C. for 3 h to obtain a nickel nanoparticle catalyst. The XRD spectrum of the catalyst obtained by X-ray powder diffraction is as follows: Figure 2 As shown by curve ③ in the figure, it can be seen that the catalyst is a fcc-hcp phase.

[0061] Example 8

[0062] S1, dissolving 0.5 mmol (124.4 mg) of nickel acetate in 10 ml of a diethylene glycol solvent having a volume concentration of 60% to prepare a nickel precursor solution.

[0063] S2, 275 mg of polyvinyl pyrrolidone and 100 ml of diethylene glycol are mixed evenly and heated to 270° C. to obtain a mixed solution.

[0064] S3, adding the nickel precursor solution dropwise to the mixed solution while stirring at a stirring speed of 400 rpm, stirring for 10 minutes to obtain a black liquid, separating the solid by a high-speed centrifuge at 9000 rpm, washing with 240 mL of petroleum ether for 4 times to remove the by-products, and drying at 25° C. for 3 h to obtain a nickel nanoparticle catalyst. The XRD spectrum of the catalyst obtained by X-ray powder diffraction is as follows: Figure 2 As shown by curve ④ in the figure, it can be seen that the catalyst is hcp phase.

[0065] like Figure 1 As shown, Examples 1 to 4 respectively use X-ray powder diffraction (XRD) technology to explore the crystal phase structure of catalysts made from different nickel compounds. Different nickel compounds can produce different nickel precursor solutions, and the crystal phase structures of the nickel nanoparticle catalysts obtained by reduction are different. Among them, nickel chloride is reduced to fcc-phase nickel nanoparticles by polyols, and the nickel nanoparticles obtained by reducing nickel acetate with diethylene glycol belong to the fcc-hcp mixed phase structure, while the diffraction characteristic peaks of the catalysts obtained by reducing nickel acetylacetonate and nickel oxalate dihydrate are consistent with the diffraction characteristic peaks of standard hcp-phase nickel. The results show that by using different nickel compounds and combining the reaction conditions specified in each embodiment, the controllable synthesis of nickel nanoparticles with different crystal phases is successfully achieved.

[0066] like Figure 2 As shown, in Examples 5 to 8, the crystal structures of the catalysts prepared at different reaction temperatures using nickel acetate as a precursor were investigated using X-ray powder diffraction (XRD) technology. The results show that the crystal structures of the catalysts prepared at different reaction temperatures are different, and the reaction temperature is an effective strategy to achieve phase control of nickel nanoparticles.

[0067] like Figure 3 As shown in the figure, with the increase of reaction temperature, the proportion of hcp phase in nickel nanoparticles increases accordingly. In principle, fcc phase nickel nanoparticles are in a thermodynamically stable state. Figure 3 It can be seen that the nickel nanoparticles prepared at 210°C are of fcc phase structure; with the increase of reaction temperature, the diffraction peak of hcp phase gradually appears in the prepared catalyst, and the peak intensity gradually increases; when the reaction temperature reaches 270°C, the nickel nanoparticles prepared are of pure hcp phase.

[0068] In order to further explore the mechanism of phase control, the present invention proposes a phase control energy model to explain the above phenomenon from the energy level. Figure 4 As shown, Ni 2+ The ions are reduced to nickel atoms under the attack of polyol molecules. The energy of the reduced metal atoms is related to the precursor and the reaction temperature. The higher the reaction temperature, the greater the kinetic energy of the polyol molecules, and the higher the energy obtained by the nickel atoms. Then, the metal atoms are heated by the solvent and aggregated to form crystal nuclei. The metal atoms with high energy form the crystal nuclei of the metal metastable phase, the metal atoms with low energy form the crystal nuclei of the stable phase, and the metal atoms with medium energy form the dual-phase crystal nuclei with both metastable phase and stable term. The nickel atoms have lower energy at 210℃, forming stable fcc crystal nuclei. At 270℃, the energy of nickel atoms is higher, so the hcp crystal nuclei in the metastable state can exist. The corresponding nickel energy at 225℃ and 245℃ between the two provides mixed fcc-hcp nuclei. The crystal structure of nickel nanoparticles is determined by the corresponding crystal nuclei. For different nickel precursor solutions, the large or small steric hindrance of the ligands in the nickel compound also determines the high or low energy of nickel atoms during the formation process, forming hcp or fcc phase nuclei and growing into corresponding nickel nanoparticles. Taking nickel acetylacetonate as an example, nickel acetylacetonate has a large steric hindrance and can provide higher energy for nickel atoms. Therefore, the nickel nanoparticles prepared have a crystal structure of hcp phase, which is similar to Figure 1 The results are consistent. This model explains the phase control mechanism of nickel from an energy perspective and provides a theoretical basis for the crystal phase control of other metals. Figure 4 In the figure, Reduction is the reduction process of the metal precursor, Heating is the heating of the metal atoms in the solution, Nucleation is the formation of crystal nuclei by metal atoms, Meta-stable is the metastable state, stable is the stable state, Nucleus is the crystal nucleus, and Average energy of asreduced metal atoms is the average energy of the metal atoms that have just been reduced.

[0069] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. All equivalent structural changes made using the contents of the present invention's specification and drawings, or directly / indirectly applied in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for preparing a nickel nanoparticle catalyst with adjustable crystal phase structure, characterized in that: Includes steps: dissolving a nickel compound in a polyol solvent to obtain a nickel precursor solution; The protective agent and the reducing agent are mixed evenly and heated to 180-290° C. to obtain a mixed solution; The nickel precursor solution is added dropwise into the mixed solution, and reacted at a temperature of 180-290° C. for more than 10 minutes, and then centrifuged, washed, and dried to obtain a nickel nanoparticle catalyst with an adjustable crystal phase structure; Wherein, the volume molar concentration of the nickel precursor solution is 0.01 to 1 mol / L; The nickel compound, protective agent and reducing agent are respectively calculated in parts by weight: 1 part of nickel compound, 0.1 to 20 parts of protective agent, and 10 to 1000 parts of reducing agent.

2. The method for preparing the nickel nanoparticle catalyst with adjustable crystal phase structure according to claim 1, characterized in that: By using different nickel compounds, different nickel precursor solutions are obtained, and then nickel nanoparticle catalysts with different crystal phase structures are prepared; The nickel compound is any one of nickel formate dihydrate, nickel acetylacetonate, nickel acetate, nickel chloride, nickel sulfate, nickel nitrate, nickel hydroxide or nickel hydroxide.

3. The method for preparing the nickel nanoparticle catalyst with adjustable crystal phase structure according to claim 1 or 2, characterized in that: By controlling the reaction temperature T, nickel nanoparticle catalysts with different crystal phase structures are prepared; Among them, when 180≤T<210℃, a pure fcc phase nickel nanoparticle catalyst is obtained; when 210≤T<270℃, fcc-hcp coexisting nickel nanoparticles are obtained; when 270≤T≤290℃, a pure hcp phase nickel nanoparticle catalyst is obtained.

4. The method for preparing the nickel nanoparticle catalyst with adjustable crystal phase structure according to claim 3, characterized in that: The polyol solvent is selected from one of diethylene glycol, methanol, ethanol, n-propanol, isopropanol, n-butanol, pentanol, hexanol, ethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, butylene glycol, dibutylene glycol, tributylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, butylene glycol monomethyl ether, butylene glycol monoethyl ether, glycerol, diglycerol, polyglycerol, trimethylolpropane, pentaerythritol or oleylamine with a volume concentration of 50-100%.

5. The method for preparing the nickel nanoparticle catalyst with adjustable crystal phase structure according to claim 4, characterized in that: The protective agent is one of polyvinyl pyrrolidone, polyethylene glycol, polyvinyl alcohol, polyvinyl ether, polymethacrylic acid, polymeth)acrylate, sodium alginate or cellulose derivatives; The reducing agent is one of diethylene glycol, methanol, ethanol, n-propanol, isopropanol, n-butanol, pentanol, hexanol, ethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, butylene glycol, dibutylene glycol, tributylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, butylene glycol monomethyl ether, butylene glycol monoethyl ether, glycerol, diglycerol, polyglycerol, trimethylolpropane, pentaerythritol or oleylamine.

6. The method for preparing the nickel nanoparticle catalyst with adjustable crystal phase structure according to claim 5, characterized in that: The washing is performed with an organic solvent for more than 3 times, wherein the organic solvent is selected from one of acetone, methanol, ethanol, isopropanol, petroleum ether, ethyl ether, dichloromethane, n-butanol, glycerol, ethylene glycol, tetrahydrofuran, dimethyl sulfoxide, N,N-dimethylformamide, methyl acetate, ethyl acetate, propyl acetate, pentane, hexane, octane, benzene, toluene, xylene, methyl butyl ketone, methyl isobutyl ketone, cyclohexane, cyclohexanone or toluene cyclohexanone; The centrifugation is carried out in a centrifugal device at 5000-10000 rpm; The drying temperature is 20 to 60° C., and the drying time is 2 to 12 hours.

7. A nickel nanoparticle catalyst with adjustable crystal phase structure, prepared by the method for preparing a nickel nanoparticle catalyst with adjustable crystal phase structure according to any one of claims 1 to 6, characterized in that: It includes nickel nanoparticles in fcc phase, or nickel nanoparticles in which fcc-hcp two phases coexist, or nickel nanoparticles in hcp phase.

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