Preparation method of CeO2-Co electromagnetic wave absorbing material

Abstract

The application discloses a preparation method of a CeO2-Co electromagnetic wave absorbing material. First, CeO2 nanorods with uniform sizes are prepared through a hydrothermal synthesis method; then, the CeO2-Co electromagnetic wave absorbing material is prepared through an impregnation method and a high-temperature calcination method; finally, the CeO2-Co material is uniformly mixed with carbon nanotubes and paraffin according to different filling amounts, is pressed into a ring with a thickness of about 1.5-2.5 mm under a specific mold, and electromagnetic wave absorbing performance test is carried out on the ring. Test shows that the reflection loss value of the material reaches -40 dB at 2.5 mm; the effective absorption bandwidth is 5.7 GHz (11.2-16.9 GHz), covering the entire Ku band and part of the X band.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electromagnetic wave absorbing materials, and particularly relates to a preparation method and application of a CeO2-Co electromagnetic wave absorbing material. BACKGROUND

[0002] With the continuous progress of the times, electronic and electrical equipment can be seen everywhere. The electromagnetic radiation generated by the operation of these electronic devices fills people's living space, causing serious electromagnetic pollution and destroying the good ecological environment. The large-scale use of emerging electronic devices such as household appliances, wireless base stations and military radars has exacerbated the continuous deterioration of the electromagnetic (EM) environment, posing a serious threat to human health and national security. How to solve the harm of electromagnetic radiation to humans and the environment has attracted worldwide attention. Therefore, it is still a challenge to prepare electromagnetic wave absorbing materials with wide absorption bandwidth, high absorption capacity and lightness.

[0003] Carbon-based materials such as electromagnetic absorbing materials and ferrites have been widely used on airplanes as high-performance electromagnetic wave absorbers. Ferromagnetic metal nanoparticles, including iron, cobalt, nickel and other magnetic oxides, have been explored as electromagnetic wave absorbing materials for decades due to their large saturation magnetization and high frequency range of Snoek limit. However, the effective absorption bandwidth of such electromagnetic wave absorbing materials is usually narrow, which cannot meet the requirements of high-performance electromagnetic wave absorption.

[0004] CeO2 is a representative rare earth dielectric material, which is an n-type semiconductor material like TiO2 and has been widely used in the field of electromagnetic catalysis. Due to its unique quantum size effect and the existence of a large number of oxygen vacancies inside, these oxygen vacancies can enhance the electromagnetic wave absorption capacity, which is one of the methods to obtain excellent electromagnetic wave absorption performance. For example, Meng et al. conducted a series of studies on CeO2, synthesized CeO2 with different morphologies by hydrothermal method, studied the optical properties and room temperature ferromagnetism of CeO2, and found that CeO2 showed excellent room temperature ferromagnetism. However, the electromagnetic wave absorption performance of the original CeO2 is very poor, with a minimum reflection loss value less than -10 dB.

[0005] Therefore, it is necessary to design a cobalt-doped ceria nanorod wave-absorbing material to meet the requirements of strong absorption capacity and wide effective absorption bandwidth of electromagnetic wave absorbing materials. SUMMARY

[0006] The application aims to provide a preparation method of a CeO2-Co electromagnetic wave absorbing material, which solves the defects of small effective absorption bandwidth of a cobalt-based magnetic material and poor wave absorbing performance of pure CeO2 material by regulating the content of cobalt loaded on the ceria nanorod; the composite material prepared by the method has good absorption performance and wide effective absorption bandwidth, and can be used in the field of electromagnetic wave absorption.

[0007] The technical scheme adopted by the application is a preparation method of a CeO2-Co material, which synthesizes a CeO2 nanorod by a hydrothermal method, takes CeO2 as a carrier, loads cobalt on the ceria nanorod by a method of dipping and high-temperature calcination, and prepares a CeO2-Co electromagnetic wave absorbing material; the specific operation steps are as follows:

[0008] Step 1, disperse sodium hydroxide solids in deionized water, fully stir to obtain a homogeneous solution A; disperse cerium nitrate hexahydrate solids in deionized water, fully stir to obtain a homogeneous solution B;

[0009] Step 2, slowly drop solution A in step 1 into solution B, magnetically stir at the same time, fully mix to obtain a viscous liquid C;

[0010] Step 3, transfer the viscous liquid C in step 2 to a stainless steel reaction kettle with polytetrafluoroethylene as the inner liner, heat at 100 DEG C for 24 hours, after natural cooling, separate the product by centrifugation, after washing, drying and grinding, obtain a precursor D;

[0011] Step 4, disperse cobalt nitrate hexahydrate solids in deionized water, magnetically stir for 20 min, obtain a uniformly dispersed liquid E;

[0012] Step 5, weigh the precursor D in step 3, slowly drop it into solution E in step 4, magnetically stir at 60 DEG C for 6 h, separate the product by centrifugation, after washing, drying and grinding, obtain a powder F; the mass ratio of the cobalt nitrate hexahydrate solids to the precursor D is 0.1-0.65:2;

[0013] Step 6, place the prepared powder F in a porcelain boat, and place the porcelain boat in a program-controlled temperature tube furnace, heat to 500 DEG C at a heating rate of 5 DEG C / min under an air atmosphere, keep the temperature for 3 hours, then naturally cool to room temperature, obtain a black powder G;

[0014] Step 7, mix the black powder G obtained in step 6 with carbon nanotubes and paraffin according to different filling amounts, prepare a circular ring H with a thickness of 1-2.5 mm in a specific mold, place it for standby, so as to carry out subsequent electromagnetic wave absorbing performance test.

[0015] The application also has the characteristics that,

[0016] The mass ratio of the sodium hydroxide solid to the cerium nitrate hexahydrate solid in step 1 is 5:0.8-1.2.

[0017] The magnetic stirring time in step 2 is not less than 1 hour.

[0018] The centrifugal time in step 3 is not less than 3 minutes, and the rotating speed is not less than 6000 rpm.

[0019] The cobalt nitrate hexahydrate in step 4 can be replaced by cobalt acetate and cobalt chloride.

[0020] The magnetic stirring time in step 5 is between 6-12 hours, and the temperature is between 40-80 DEG C.

[0021] The heat treatment process in step 6 is carried out in an air atmosphere, the heating temperature is not less than 500 DEG C, and the holding time is not less than 3 hours.

[0022] The synthesis principle of the key step in the application is as follows:

[0023] (1) The precursor D is prepared by hydrothermal synthesis of sodium hydroxide and cerium nitrate hexahydrate. The cerium dioxide nanorod has the characteristics of uniform size and large specific surface area. The more the specific surface area is, the more the oxygen atoms at the interface are. A large number of oxygen vacancy defects in the cerium dioxide nanorod will cause mass transfer loss and enhance electronic polarization, which is beneficial to the improvement of the wave absorption performance. The cerium dioxide nanorod as a carrier of electromagnetic wave absorbing material also provides a large number of active sites for the impregnation of cobalt nanoparticles.

[0024] (2) By impregnating the magnetic cobalt salt with the cerium dioxide nanorod, a lightweight CeO2-Co electromagnetic wave absorbing material is obtained by high temperature calcination. By controlling the loading amount of the cobalt salt, the dielectric loss and the dielectric constant of the composite material are also controlled, so that the synergistic effect is realized in a wide absorption bandwidth, which greatly improves the impedance matching of the material and enhances the electromagnetic wave absorption performance of the material.

[0025] The beneficial effects of the application are as follows:

[0026] (1) The CeO2 nanorod prepared by the hydrothermal synthesis method has the advantages of high powder purity, uniform size, easy dispersion, good crystal type, controllable size, etc. The cerium oxide has small size, large specific surface area and oxidation resistance.

[0027] (2) By simple impregnation method, cobalt ions are uniformly impregnated on the surface of cerium oxide. Only cobalt is loaded during the impregnation process, and the cobalt oxide can be uniformly dispersed on the cerium dioxide nanorod after calcination. The cerium dioxide nanorod has small size, which provides large specific surface area and more active sites for the loading of cobalt ions.

[0028] (3) The cobalt oxide is doped on the surface of cerium dioxide by calcining in air, the introduction of the magnetic material improves the dielectric loss and magnetic loss capacity of the CeO2-Co electromagnetic wave absorbing material, meanwhile, the cerium dioxide provides more active sites which will be combined with the magnetic cobalt oxide, thereby further improving the wave absorbing performance of the material.

[0029] (4) The electromagnetic wave absorbing material is cheap and easy to obtain, the preparation method is simple, and the operability is strong, so that the material is easy to synthesize in large quantities. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a preparation method flow chart of the CeO2-Co electromagnetic wave absorbing material.

[0031] Figure 2 is an XRD diagram of the CeO2-Co electromagnetic wave absorbing material.

[0032] Figure 3 is a reflection loss diagram of the CeO2-Co electromagnetic wave absorbing material under different thicknesses.

[0033] Figure 4 is a bandwidth diagram of the CeO2-Co electromagnetic wave absorbing material under different thicknesses.

[0034] Figure 5 is a real part diagram of dielectric loss of the CeO2-Co electromagnetic wave absorbing material;

[0035] Figure 6 is an imaginary part diagram of dielectric loss of the CeO2-Co electromagnetic wave absorbing material.

[0036] Figure 7 is a tangent value diagram of dielectric loss of the CeO2-Co electromagnetic wave absorbing material.

[0037] Figure 8 is a real part diagram of magnetic loss of the CeO2-Co electromagnetic wave absorbing material.

[0038] Figure 9 is an imaginary part diagram of magnetic loss of the CeO2-Co electromagnetic wave absorbing material.

[0039] Figure 10 is a tangent value diagram of magnetic loss of the CeO2-Co electromagnetic wave absorbing material. DETAILED DESCRIPTION

[0040] The preparation method of the CeO2-Co electromagnetic wave absorbing material provided by the application comprises synthesis of CeO2 nanorods, taking the CeO2 nanorods as carriers, impregnating the carriers with magnetic cobalt salt to prepare cobalt-loaded CeO2 nanorod material, and preparing the CeO2-Co electromagnetic wave absorbing material through high-temperature calcination.

[0041] The application will be further described in connection with specific examples.

[0042] Example 1

[0043] The preparation method of the CeO2-Co electromagnetic wave absorbing material of the application is shown as follows: Figure 1 The specific operation steps are as follows:

[0044] Step 1: 19.2g of sodium hydroxide solid is weighed and dispersed in deionized water, and a homogeneous solution A is obtained after sufficient stirring; 3.84g of cerium nitrate hexahydrate solid is weighed and dispersed in deionized water, and a homogeneous solution B is obtained after sufficient stirring;

[0045] Step 2: solution A in step 1 is slowly added to solution B, and magnetic stirring is performed at the same time, and a purple viscous liquid C is obtained after sufficient mixing;

[0046] Step 3: the purple viscous liquid C in step 2 is transferred to a stainless steel reaction kettle with polytetrafluoroethylene as the inner liner, heated at 100℃ for 24 hours, and after natural cooling, the product is separated by centrifugation, washed, dried, ground and obtained as yellow precursor D;

[0047] Step 4: 0.01g of cobalt nitrate hexahydrate solid is weighed and dispersed in deionized water, and a uniformly dispersed light orange liquid E is obtained after magnetic stirring for 20 minutes;

[0048] Step 5: 0.2g of yellow precursor D in step 3 is weighed and slowly added to the light orange solution E in step 4, and then magnetic stirring is performed, the product is separated by centrifugation, and after washing, drying and grinding, powder F is obtained;

[0049] Step 6: the prepared powder F is placed in a porcelain boat, and the porcelain boat is placed in a program-controlled temperature tube furnace, heated at a temperature rising rate of 5℃ / min in an air atmosphere, and then naturally cooled to room temperature to obtain black powder G;

[0050] Step 7: the black powder G obtained in step 6 is mixed with carbon nanotubes and paraffin in different filling amounts, and a circular ring H with a thickness of 1-2.5mm is prepared in a specific mold for standby to perform subsequent electromagnetic wave absorption performance test.

[0051] Example 2:

[0052] The preparation method of the CeO2-Co electromagnetic wave absorbing material is shown as follows: Figure 1 The specific operation steps are as follows:

[0053] Step 1, weigh 19.2 g of sodium hydroxide solid and disperse it in deionized water, fully stir to obtain a homogeneous solution A; weigh 3.84 g of cerium nitrate hexahydrate solid and disperse it in deionized water, fully stir to obtain a homogeneous solution B;

[0054] Step 2, slowly add solution A in step 1 to solution B, while magnetic stirring for 1.5 h, fully mix to obtain a purple viscous liquid C;

[0055] Step 3, transfer the purple viscous solution C in step 2 to a stainless steel reactor lined with polytetrafluoroethylene, heat at 100℃ for 24 hours, after natural cooling, separate the product by centrifugation, wash, dry, grind to obtain a yellow precursor D;

[0056] Step 4, weigh 0.065 g of cobalt nitrate hexahydrate solid, disperse it in deionized water, magnetic stirring for 1 h to obtain a uniformly dispersed light orange liquid E;

[0057] Step 5, weigh 0.2 g of yellow precursor D in step 3, slowly add it to the light orange solution E in step 4, magnetic stirring at 60℃ for 7 h, separate the product by centrifugation, wash, dry, grind to obtain powder F;

[0058] Step 6, place the prepared powder F in a porcelain boat, and place the porcelain boat in a program-controlled temperature tube furnace, heat to 500℃ at a rate of 5℃ / min in an air atmosphere, keep for 3 hours, then naturally cool to room temperature to obtain black powder G;

[0059] Step 7, mix the black powder G obtained in step 6 with carbon nanotubes and paraffin in different proportions according to the filling amount, prepare a circular ring H with a thickness of 1-2.5 mm in a specific mold, and place it for standby to perform subsequent electromagnetic wave absorption performance test.

[0060] Example 3:

[0061] The preparation method of the CeO2-Co electromagnetic wave absorbing material is as shown in Figure 1 , and the specific operation steps are as follows:

[0062] Step 1, weigh 19.2 g of sodium hydroxide solid and disperse it in deionized water, fully stir to obtain a homogeneous solution A; weigh 3.84 g of cerium nitrate hexahydrate solid and disperse it in deionized water, fully stir to obtain a homogeneous solution B;

[0063] Step 2, slowly add solution A in step 1 to solution B, while magnetic stirring for 2 h, fully mix to obtain a purple viscous liquid C;

[0064] Step 3, the purple viscous solution C in step 2 was transferred to a stainless steel reactor with polytetrafluoroethylene lining, heated at 100℃ for 24 hours, after natural cooling, the product was separated by centrifugation, washed, dried, ground to obtain yellow precursor D;

[0065] Step 4, 0.03g of cobalt acetate solid was weighed and dispersed in deionized water, after magnetic stirring for 20min, a uniformly dispersed light orange liquid E was obtained;

[0066] Step 5, 0.2g of yellow precursor D in step 3 was slowly added to the light orange solution E in step 4, and stirred at 60℃ for 10h, the product was separated by centrifugation, washed, dried, ground to obtain powder F;

[0067] Step 6, the prepared powder F was placed in a porcelain boat, and the porcelain boat was placed in a programmed temperature tube furnace, heated to 500℃ at a heating rate of 5℃ / min under air atmosphere, and kept for 3 hours, then naturally cooled to room temperature to obtain black powder G;

[0068] Step 7, the black powder G obtained in step 6 was mixed with carbon nanotubes and paraffin in different filling amounts, and a circular ring H with a thickness of 1-2.5mm was prepared in a specific mold for standby to test the subsequent electromagnetic wave absorption performance.

[0069] Example 4:

[0070] The preparation method of the CeO2-Co electromagnetic wave absorbing material is shown in Figure 1 , and the specific operation steps are as follows:

[0071] Step 1, 19.2g of sodium hydroxide solid was weighed and dispersed in deionized water, and a homogeneous solution A was obtained by stirring; 3.84g of cerium nitrate hexahydrate solid was weighed and dispersed in deionized water, and a homogeneous solution B was obtained after stirring;

[0072] Step 2, solution A in step 1 was slowly added to solution B, and stirred magnetically for 2h, and a purple viscous liquid C was obtained after mixing;

[0073] Step 3, the purple viscous solution C in step 2 was transferred to a stainless steel reactor with polytetrafluoroethylene lining, heated at 100℃ for 24 hours, after natural cooling, the product was separated by centrifugation, washed, dried, ground to obtain yellow precursor D;

[0074] Step 4, 0.05g of cobalt nitrate hexahydrate solid was weighed and dispersed in deionized water, and a uniformly dispersed light orange liquid E was obtained after magnetic stirring for 1h;

[0075] Step 5, take 0.2 g of yellow precursor D in step 3, slowly drop it into the light orange solution E in step 4, magnetically stir at 60℃ for 9h, separate the product by centrifugation, wash, dry, grind to obtain powder F;

[0076] Step 6, place the prepared powder F in a porcelain boat, and place the porcelain boat in a program-controlled tube furnace, heat to 500℃ at a heating rate of 5℃ / min under air atmosphere, keep for 3h, then naturally cool to room temperature, obtain black powder G;

[0077] Step 7, mix the black powder G obtained in step 6 with carbon nanotubes and paraffin in different filling amounts, prepare a circular ring H with a thickness of 1-2.5mm in a specific mold, place it for standby, so as to carry out subsequent electromagnetic wave absorption performance test.

[0078] Example 5:

[0079] The preparation method of CeO2-Co electromagnetic wave absorbing material is as shown in Figure 1 , the specific operation steps are as follows:

[0080] Step 1, take 19.2g of sodium hydroxide solid and disperse it in deionized water, stir well to obtain a homogeneous solution A; take 3.84g of cerium nitrate hexahydrate solid and disperse it in deionized water, stir well to obtain a homogeneous solution B;

[0081] Step 2, slowly drop solution A in step 1 into solution B, magnetically stir for 1h, mix well to obtain a purple viscous liquid C;

[0082] Step 3, transfer the purple viscous solution C in step 2 to a stainless steel reaction kettle with polytetrafluoroethylene lining, heat at 100℃ for 24h, naturally cool, separate the product by centrifugation, wash, dry, grind to obtain yellow precursor D;

[0083] Step 4, take 0.045g of cobalt chloride solid, disperse it in deionized water, magnetically stir for 1h to obtain a uniformly dispersed light orange liquid E;

[0084] Step 5, take 0.2 g of yellow precursor D in step 3, slowly drop it into the light orange solution E in step 4, magnetically stir at 60℃ for 8h, separate the product by centrifugation, wash, dry, grind to obtain powder F;

[0085] Step 6, place the prepared powder F in a porcelain boat, and place the porcelain boat in a program-controlled tube furnace, heat to 500℃ at a heating rate of 5℃ / min under air atmosphere, keep for 3h, then naturally cool to room temperature, obtain black powder G;

[0086] Step 7, the black powder G obtained in step 6 is mixed with carbon nanotubes and paraffin in different filling amounts, and a circular ring H with a thickness of 1-2.5 mm is prepared in a specific mold for standby to test the subsequent electromagnetic wave absorption performance. Figure 1 is a flow chart of the preparation method of the CeO2-Co electromagnetic wave absorbing material of the present application; the CeO2-Co electromagnetic wave absorbing material can be obtained by a five-step method.

[0087] Figure 2 is an XRD pattern of the CeO2-Co electromagnetic wave absorbing material of the present application; it can be seen that, after the cobalt source is impregnated, the peaks corresponding to the Co3O4 standard card appear, indicating that the cobalt is successfully loaded on the CeO2 nanorods.

[0088] Figure 3 is a reflection loss diagram of the CeO2-Co electromagnetic wave absorbing material of the present application under different thicknesses; it can be seen that, at 2.5 mm, the reflection loss value of the CeO2-Co electromagnetic wave absorbing material reaches -40 dB, showing good electromagnetic wave absorption performance.

[0089] Figure 4 is a bandwidth diagram of the CeO2-Co electromagnetic wave absorbing material of the present application under different thicknesses; the wider the effective absorption bandwidth, the better the wave absorption performance of the material. It can be seen that, at 2.5 mm, the effective absorption bandwidth ranges from 11.2 GHz to 16.9 GHz, covering the entire Ku band and part of the X band, and has good electromagnetic wave absorption performance.

[0090] Figure 5 is a real part diagram of the dielectric loss of the CeO2-Co electromagnetic wave absorbing material of the present application; the absorption value at the low band is about 11.5, and the absorption value at the high band is about 7.0, and the overall trend is downward.

[0091] Figure 6 is an imaginary part diagram of the dielectric loss of the CeO2-Co electromagnetic wave absorbing material of the present application; the absorption value at the low band is about 4.9, and the absorption value at the high band is about 2.1; the overall trend matches the downward trend of the real part of the dielectric loss.

[0092] Figure 7 is a tangent value diagram of the dielectric loss of the CeO2-Co electromagnetic wave absorbing material of the present application; it shows good dielectric loss.

[0093] Figure 8 is a real part diagram of the magnetic loss of the CeO2-Co electromagnetic wave absorbing material of the present application; the absorption value at the low band is about 1.13, and the absorption value at the high band is about 0.98.

[0094] Figure 9It is the magnetic loss imaginary part diagram of the CeO2-Co electromagnetic wave absorbing material of the application; the loss capacity increases first, then decreases and then increases with the increase of the frequency.

[0095] Figure 10 It is the magnetic loss tangent diagram of the CeO2-Co electromagnetic wave absorbing material of the application; the overall trend is basically the same as that of the magnetic loss imaginary part.

[0096] The prepared cerium dioxide nanorod is doped with cobalt chloride and calcined to form Co3O4, Co3O4 is a unique magnetic semiconductor, and due to the coexistence of dielectric loss and magnetic loss, it can be regarded as a potential EM absorbing material. Therefore, Co3O4 and CeO2 can be combined to change the loss characteristics of the material to improve the absorption performance. In addition, the magnetism of Co3O4 and the oxygen vacancy of CeO2 can also promote the electromagnetic wave absorption capacity.

Claims

1. A method for preparing CeO2-Co electromagnetic wave absorbing material, characterized in that, CeO2 nanorods were synthesized via a hydrothermal method. Using CeO2 as a support, cobalt was loaded onto the cerium dioxide nanorods through impregnation and high-temperature calcination to prepare a CeO2-Co electromagnetic wave absorbing material. The specific operational steps are as follows: Step 1: Disperse sodium hydroxide solid in deionized water and stir thoroughly to obtain homogeneous solution A; disperse cerium nitrate hexahydrate solid in deionized water and stir thoroughly to obtain homogeneous solution B; The mass ratio of the sodium hydroxide solid to the cerium nitrate hexahydrate solid is 5:0.8~1.2; Step 2: Slowly add solution A from step 1 to solution B while stirring magnetically. After thorough mixing, a viscous liquid C is obtained. Step 3: Transfer the viscous liquid C described in Step 2 to a stainless steel reactor lined with polytetrafluoroethylene, heat at 100°C for 24 hours, and after natural cooling, separate the product by centrifugation. After washing, drying, and grinding, the precursor D is obtained. Step 4: Disperse cobalt nitrate hexahydrate solid in deionized water and stir magnetically for 20 minutes to obtain a uniformly dispersed liquid E; Step 5: Weigh the precursor D from Step 3 and slowly add it dropwise to the solution E from Step 4. Stir magnetically at 60°C for 6 hours. Separate the product by centrifugation, and obtain powder F after washing, drying, and grinding. The mass ratio of the cobalt nitrate hexahydrate solid to the precursor D is 0.1~0.65:

2. The magnetic stirring time is between 6 and 12 hours, and the temperature is between 40 and 80 degrees Celsius. o Between C; Step 6: Place the prepared powder F in a porcelain boat, and then place the porcelain boat in a programmable temperature controlled tube furnace. In an air atmosphere, heat the powder at 5°C. o Heating to 500°C at a heating rate of C / min o C, keep warm for 3 hours, then cool naturally to room temperature to obtain black powder G; The heat treatment process in step 6 is carried out in an air atmosphere, and the heating temperature is not lower than 500°C. o C. The heat preservation time should not be less than 3 hours; Step 7: The black powder G obtained in Step 6 is mixed with carbon nanotubes and paraffin in different proportions to prepare a ring H with a thickness of 1-2.5 mm under a mold. The ring is then set aside for subsequent electromagnetic wave absorption performance testing.

2. The preparation method of CeO2-Co electromagnetic wave absorbing material according to claim 1, characterized in that, In step 2, the magnetic stirring time should be no less than 1 hour.

3. The preparation method of CeO2-Co electromagnetic wave absorbing material according to claim 1, characterized in that, In step 3, the centrifugation time should be no less than 3 minutes and the rotation speed should be no less than 6000 rpm.

4. The preparation method of CeO2-Co electromagnetic wave absorbing material according to claim 1, characterized in that, In step 4, cobalt nitrate hexahydrate can be replaced by cobalt acetate and cobalt chloride.

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