Disclosure of Invention
The embodiment of the invention provides modified alpha-phase alumina and a preparation method thereof.
In a first aspect, an embodiment of the present invention provides a method for preparing modified α -phase alumina, including:
preparing alpha-phase alumina;
crushing alpha-phase alumina to obtain alpha-phase alumina powder material with particle size of 1-2 microns;
mixing the alpha-phase alumina powder material with an acid auxiliary agent and a binder, and dispersing and stirring to obtain mixed slurry;
spray drying the mixed slurry to obtain dried powder;
and carrying out secondary drying treatment on the dried powder to obtain the modified alpha-phase alumina.
Preferably, the preparing of the alpha phase alumina comprises:
the alpha-phase alumina is prepared by taking industrial aluminum hydroxide as a raw material and calcining the raw material in an inert atmosphere at 900-1200 ℃;
the alpha-phase alumina is in a sheet adhesion structure, the pH value is 10-11, the powder fluidity is less than or equal to 1g/s, and the powder bulk density is less than or equal to 0.3g/cm 3 。
Preferably, the acid auxiliary agent is specifically a solid acid agent, and comprises one or more of oxalic acid, citric acid, boric acid and succinic acid; the acid auxiliary agent accounts for 0.05-0.2% of the mass of the alpha-phase alumina powder material;
the binder is specifically a resin binder or carboxymethyl cellulose CMC; the binder accounts for 0.03-0.1% of the mass of the alpha-phase alumina powder material.
Further preferably, the acidic auxiliary agent is specifically citric acid.
Preferably, the spray drying is specifically spray drying by a pneumatic spray dryer;
the air pressure of the air pressure type spray dryer is 0.35-0.4 MPa; the inlet temperature is 290-300 deg.c and the outlet temperature is not lower than 120 deg.c.
Preferably, the secondary drying treatment is specifically drying treatment in an inert environment in a drying oven, wherein the drying temperature is 150-200 ℃ and the drying time is 8-12 hours.
In a second aspect, an embodiment of the present invention provides a modified α -phase alumina prepared by the method for preparing a modified α -phase alumina according to the first aspect.
Preferably, the modified alpha-phase alumina is granular, the pH value is 7-9, the powder fluidity is more than or equal to 1.5g/s, and the bulk density of the powder is more than or equal to 0.55g/cm 3 。
According to the preparation method of the modified alpha-phase alumina, the alpha-phase alumina is modified through the synergistic effect of the acid auxiliary agent and the binder, so that on one hand, the pH value of the alpha-phase alumina is reduced through the acid auxiliary agent, and the fluidity of the powder is increased, and on the other hand, the size of powder particles is increased through the addition of the binder, and the apparent density of the powder is increased. By the preparation method, the alpha-phase alumina with flaky surface morphology is converted into granular alpha-phase alumina with smooth surface and uniform morphology, and the function of increasing the fluidity of the powder is also achieved.
The preparation method provided by the invention has low preparation temperature and does not produce waste gas and waste liquid; the process is simple, is favorable for industrial production, adopts industrial aluminum hydroxide as the raw material, has low price and greatly reduces the production cost.
Detailed Description
The invention is further illustrated by the drawings and the specific examples, which are to be understood as being for the purpose of more detailed description only and are not to be construed as limiting the invention in any way, i.e. not intended to limit the scope of the invention.
The embodiment of the invention provides a preparation method of modified alpha-phase alumina, which mainly comprises the following preparation steps as shown in figure 1:
step 110, preparing alpha-phase alumina;
industrial aluminium hydroxide is used as raw material, and is passed through the process of inert atmosphere at 900-1200 deg.CCalcining for 8-12 hours to prepare alpha-phase alumina; the alpha-phase alumina is in a sheet adhesion structure, the pH value is 10-11, the powder fluidity is less than or equal to 1g/s, and the powder bulk density is less than or equal to 0.3g/cm 3 。
Because different aluminum-containing raw materials determine different alpha-phase aluminum oxide preparation methods and finally determine the production cost, the embodiment selects industrial aluminum hydroxide as the aluminum raw material, and compared with aluminum oxide and aluminum hydroxide, the aluminum hydroxide has lower price, and can effectively reduce the production cost.
120, crushing alpha-phase alumina to obtain alpha-phase alumina powder material with the particle size of 1-2 mu m;
the crushing treatment can be specifically carried out by a multistage crushing method.
For example, firstly, the alpha-phase alumina powder material with the particle size of 1-2 mu m is obtained by carrying out primary crushing by a jaw crusher, then carrying out secondary crushing by a roller mill and finally crushing the powder by an air flow mill.
The alpha-phase alumina powder material obtained by crushing has a microscopic appearance which is in a vermiform appearance of adhesion agglomeration, has poor powder fluidity and low bulk density.
Step 130, mixing alpha-phase alumina powder material with an acid auxiliary agent and a binder, and dispersing and stirring to obtain mixed slurry;
in the mixing, dispersing and stirring process of the step, the obtained alpha-phase alumina powder material is added with deionized water to prepare slurry, then the prepared slurry is added with an acid auxiliary agent and a binder in proportion, and a high-speed dispersing machine is used for stirring and dispersing to prepare mixed slurry.
The acidic auxiliary agent is specifically a solid acidic agent and comprises one or more of oxalic acid, citric acid, boric acid and succinic acid; the acid auxiliary agent accounts for 0.05 to 0.2 percent of the mass of the alpha-phase alumina powder material; the binder is specifically a resin binder or carboxymethyl cellulose (CMC); the binder accounts for 0.03-0.1% of the mass of the alpha-phase alumina powder material.
In the implementation of the invention, the acid auxiliary agent is preferably citric acid with the chemical formula of C 6 H 8 O 7 Only contains C, H, O three elements,in the subsequent sintering step involved in the industrialized application process of the modified alpha-phase alumina, the modified alpha-phase alumina can be volatilized and discharged in the form of carbon dioxide and water, and other impurities are not generated. The binder is preferably carboxymethyl cellulose (CMC).
Step 140, spray drying the mixed slurry to obtain dried powder;
the spray drying is specifically carried out by adopting a spray dryer, preferably a pneumatic spray dryer;
the air pressure of the air pressure type spray dryer is 0.35MPa-0.4MPa; the inlet temperature is 290-300 deg.c and the outlet temperature is not lower than 120 deg.c.
The fluidity and bulk density of the powder after spray drying are both increased, and the pH value of the powder is obviously reduced due to the action of the acid auxiliary agent.
And 150, performing secondary drying treatment on the dried powder to obtain the modified alpha-phase alumina.
The secondary drying treatment is specifically drying treatment in an inert environment in a drying box, wherein the drying temperature is 150-200 ℃ and the drying time is 8-12 hours.
After step 140, although the flowability and bulk density of the powder are improved, the improvement is not significant. In addition, the pH of the powder obtained in step 140 is low, so that the pH of the material can be increased by performing a small amount of volatilization of the acidic material through a secondary drying process.
The drying temperature is not too high, and the drying at the too high temperature can cause excessive acid substance loss and can not play a role in adding acid, so that the drying temperature is selected to be 150-200 ℃.
The modified alpha-phase alumina obtained by the preparation method of the invention is granular, the pH value is 7-9, the powder fluidity is more than or equal to 1.5g/s, and the bulk density of the powder is more than or equal to 0.55g/cm 3 。
According to the preparation method of the modified alpha-phase alumina, the alpha-phase alumina is modified through the synergistic effect of the acid auxiliary agent and the binder, so that on one hand, the pH value of the alpha-phase alumina is reduced through the acid auxiliary agent, and the fluidity of the powder is increased, and on the other hand, the size of powder particles is increased through the addition of the binder, and the apparent density of the powder is increased. By the preparation method, the alpha-phase alumina with flaky surface morphology is converted into granular alpha-phase alumina with smooth surface and uniform morphology, and the function of increasing the fluidity of the powder is also achieved.
In order to better understand the technical scheme provided by the invention, the following specific processes and characteristics of preparing the modified alpha-phase alumina by applying the method provided by the embodiment of the invention are respectively described in the following specific examples.
Example 1
The embodiment 1 of the invention provides a preparation method of modified alpha-phase alumina. The method comprises the following steps:
step 1, preparing alpha-phase alumina:
the industrial aluminum hydroxide was used as a raw material, and the particle size (hereinafter, referred to as the median particle size Dv 50) was 50. Mu.m.
The industrial aluminum hydroxide was calcined at 1200 ℃ for 8 hours to obtain alpha-phase alumina. Figure 2 is an XRD pattern of alpha phase alumina prepared in this step.
Step 2, crushing alpha-phase alumina:
firstly, carrying out primary crushing on alpha-phase alumina obtained by calcining in the step 1 by using a jaw crusher to obtain alpha-phase alumina powder with the particle size of about 20 mu m; then carrying out secondary crushing on the powder by a roller to obtain alumina powder with the particle size of about 15 mu m; finally, crushing the powder by air flow grinding to obtain alpha-phase alumina powder with the particle size of 1-2 mu m.
The microscopic morphology of the powder is shown in fig. 3 and 4, and the whole powder presents a worm-like morphology of adhesion agglomeration, which can lead to poor powder flowability and low bulk density. The alpha-phase alumina powder has the fluidity of 0.5g/s and the apparent density of 0.28g/cm 3 The pH was 10.42.
Step 3, mixing, dispersing and stirring the alpha-phase alumina powder material, an acid auxiliary agent and a binder:
adding deionized water into the alpha-phase alumina powder material obtained in the step 2 to prepare slurry with the solid content of 30%, stirring and dispersing the slurry for about 30min at 1000rpm by using a high-speed dispersing machine, adding an acidic auxiliary agent citric acid accounting for 0.1% of the mass of the alpha-phase alumina powder material and a binder carboxymethyl cellulose (CMC) accounting for 0.05% of the mass of the alpha-phase alumina powder material, and continuously stirring and dispersing for 1 hour to prepare the mixed slurry.
Step 4, spray drying the mixed slurry:
the air pressure type spray dryer was used at an air pressure of 0.4kg/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the The inlet temperature was 300℃and the outlet temperature was 120 ℃. The fluidity of the powder subjected to spray drying treatment is increased to 0.85g/s; bulk density 0.32g/cm 3 . The pH value of the powder is obviously reduced due to acid-base neutralization, and the measured pH value is 4.35 and is acidic.
And 5, performing secondary drying treatment on the dried powder.
And (3) drying the powder obtained by spray drying at 200 ℃ for 10 hours to obtain the modified alpha-phase alumina.
The modified alpha-phase alumina was tested to give a pH of 8.7, a flowability of 1.82g/s and a bulk density of 0.65g/cm 3 . The fluidity and bulk density of the powder are improved by 264% and 132% respectively relative to the alpha-phase alumina of step 2, and the fluidity of the powder is greatly improved.
The surface morphology of the modified alpha-phase alumina powder of the embodiment is measured by a scanning electron microscope and is shown in fig. 5 and 6. As can be seen from fig. 5 and 6, the powder has a smooth surface and no adhesion between particles. The smooth surface topography is also responsible for its strong flowability. As shown in fig. 7, the XRD pattern of the modified alpha-phase alumina powder of this example shows that all diffraction peaks correspond to the alpha-phase alumina crystal form structure of fig. 3, no impurity peak is generated, and pure alpha-phase alumina is still obtained. The results show that the amount of acidic auxiliary agent and binder added in this example is small and does not affect the crystal structure of the alumina.
Example 2
The embodiment 2 of the invention provides a preparation method of modified alpha-phase alumina. The method comprises the following steps:
step 1, preparing alpha-phase alumina:
the industrial aluminum hydroxide was used as a raw material, and the particle size (hereinafter, referred to as the median particle size Dv 50) was 48. Mu.m.
The industrial aluminum hydroxide was calcined at 1000℃for 8 hours to obtain alpha-phase alumina.
Step 2, crushing alpha-phase alumina:
firstly, carrying out primary crushing on alpha-phase alumina obtained by calcining in the step 1 by using a jaw crusher to obtain alpha-phase alumina powder with the particle size of about 20 mu m; then carrying out secondary crushing on the powder by a roller to obtain alumina powder with the particle size of about 14 mu m; finally, crushing the powder by air flow grinding to obtain alpha-phase alumina powder with the particle size of 1-2 mu m.
The alpha-phase alumina powder has the fluidity of 0.49g/s and the apparent density of 0.27g/cm 3 The pH was 10.4.
Step 3, mixing, dispersing and stirring the alpha-phase alumina powder material, an acid auxiliary agent and a binder:
adding deionized water into the alpha-phase alumina powder material obtained in the step 2 to prepare slurry with the solid content of 30%, stirring and dispersing the slurry for about 30min at 1000rpm by using a high-speed dispersing machine, adding acid additive oxalic acid accounting for 0.1% of the mass of the alpha-phase alumina powder material and binder phenolic resin accounting for 0.03% of the mass of the alpha-phase alumina powder material, and continuously stirring and dispersing for 1 hour to prepare the mixed slurry.
Step 4, spray drying the mixed slurry:
the air pressure type spray dryer was used at an air pressure of 0.35kg/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the The inlet temperature was 290℃and the outlet temperature was 130 ℃.
And 5, performing secondary drying treatment on the dried powder.
And (3) drying the powder obtained by spray drying at 150 ℃ for 12 hours to obtain the modified alpha-phase alumina.
The modified alpha-phase alumina was tested to give a pH of 8.6, a flowability of 1.76g/s and a bulk density of 0.63g/cm 3 . Fluidity and bulk density of the powder relative to the alpha-alumina fraction of step 2259% and 133% are improved respectively, and the fluidity of the powder is greatly improved.
Example 3
The embodiment 3 of the invention provides a preparation method of modified alpha-phase alumina. The method comprises the following steps:
step 1, preparing alpha-phase alumina:
the industrial aluminum hydroxide was used as a raw material, and the particle size (hereinafter, referred to as the median particle size Dv 50) was 51. Mu.m.
The industrial aluminum hydroxide was calcined at 900 ℃ for 10 hours to obtain alpha-phase alumina.
Step 2, crushing alpha-phase alumina:
firstly, carrying out primary crushing on alpha-phase alumina obtained by calcining in the step 1 by using a jaw crusher to obtain alpha-phase alumina powder with the particle size of about 22 mu m; then carrying out secondary crushing on the powder by a roller to obtain alumina powder with the particle size of about 17 mu m; finally, crushing the powder by air flow grinding to obtain alpha-phase alumina powder with the particle size of 1-2 mu m.
The alpha-phase alumina powder has the fluidity of 0.51g/s and the apparent density of 0.29g/cm 3 The pH was 10.61.
Step 3, mixing, dispersing and stirring the alpha-phase alumina powder material, an acid auxiliary agent and a binder:
adding deionized water into the alpha-phase alumina powder material obtained in the step 2 to prepare slurry with the solid content of 30%, stirring and dispersing the slurry for about 30min at 1000rpm by using a high-speed dispersing machine, adding acid auxiliary boric acid accounting for 0.2% of the mass of the alpha-phase alumina powder material and binder carboxymethyl cellulose accounting for 0.05% of the mass of the alpha-phase alumina powder material, and continuously stirring and dispersing for 1 hour to prepare the mixed slurry.
Step 4, spray drying the mixed slurry:
the air pressure type spray dryer was used at an air pressure of 0.4kg/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the The inlet temperature was 295℃and the outlet temperature was 125 ℃.
And 5, performing secondary drying treatment on the dried powder.
And (3) drying the powder obtained by spray drying at 180 ℃ for 10 hours to obtain the modified alpha-phase alumina.
The modified alpha-phase alumina was tested to give a pH of 8.2, a flowability of 1.79g/s and a bulk density of 0.67g/cm 3 . The fluidity and apparent density of the powder are improved by 251% and 131% respectively relative to the alpha-phase alumina of step 2, and the fluidity of the powder is greatly improved.
The preparation method provided by the invention has low preparation temperature and does not produce waste gas and waste liquid; the process is simple, is favorable for industrial production, adopts industrial aluminum hydroxide as the raw material, has low price and greatly reduces the production cost.
The foregoing description of the embodiments has been provided for the purpose of illustrating the general principles of the invention, and is not meant to limit the scope of the invention, but to limit the invention to the particular embodiments, and any modifications, equivalents, improvements, etc. that fall within the spirit and principles of the invention are intended to be included within the scope of the invention.