CN113912125B - Calcination process for preparing high specific surface area low residual ammonia yellow tungsten oxide - Google Patents
Calcination process for preparing high specific surface area low residual ammonia yellow tungsten oxide Download PDFInfo
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Abstract
The invention discloses a calcination process for preparing high specific surface area low residual ammonia yellow tungsten oxide, which relates to the technical field of tungsten oxide preparation. According to the invention, the ammonium paratungstate is calcined at three-stage temperature, water molecules and ammonia molecules on the surface of the ammonium paratungstate are volatilized and dissociated at the first temperature, the ammonium paratungstate is calcined at the second temperature to crack, a complex intermediate product is generated, and the tungsten oxide is generated by continuously calcining at the third temperature.
Description
Technical Field
The invention relates to the technical field of tungsten oxide preparation, in particular to a calcination process for preparing yellow ammonia tungsten oxide with high specific surface area and low residual ammonia.
Background
Tungsten is an important strategic resource and is widely used because of its excellent properties such as high melting point, high hardness, high ductility, wear resistance, corrosion resistance, etc.
Tungsten oxide is an extremely important intermediate product in the field of tungsten industry, and tungsten oxide products with high specific surface areas are generally produced industrially, and are often crushed by a physical crushing method, for example, air flow crushing, ball milling and the like, by using the tungsten oxide products as raw materials. However, the method for processing the produced tungsten oxide is high in cost, and the crushing means often greatly destroy the crystal form and crystal appearance of the tungsten oxide product, so that the subsequent deep processing of the tungsten product is greatly and negatively affected. Therefore, the application field is very small and the application is very rarely performed industrially by means of physical crushing.
The yellow tungsten oxide is a finely divided yellow crystalline powder. In the process of calcining ammonium paratungstate, the temperature is strictly controlled, and bound water or water and ammonia are separated. Precise time and temperature control affects the physical properties of tungsten oxide to a great extent. In the production process of yellow tungsten oxide, the influence of the production conditions on the specific surface area and residual ammonia is contradictory, and it is generally difficult to achieve both high specific surface area and low residual ammonia, but with the increase of environmental protection requirements, the supervision of pollution factor ammonia is increasingly aggravated, and the requirement of residual ammonia in tungsten oxide is increasingly low as much as possible.
Disclosure of Invention
The invention aims to at least solve one of the technical problems in the prior art and provides a calcination process for preparing high-specific-surface-area low-residual ammonia yellow tungsten oxide.
The technical scheme of the invention is as follows:
a calcination process for preparing high specific surface area low residual ammonia yellow tungsten oxide includes dissociating ammonium paratungstate at the first temperature less than 300 ℃ and under oxidizing atmosphere to obtain ammonium tungsten compound, calcining ammonium tungsten compound at the second temperature of 300-500 ℃ and under oxidizing atmosphere, and continuously heating to the third temperature of 500-700 ℃ and calcining under oxidizing atmosphere to obtain yellow tungsten oxide.
Preferably, the first temperature is 200-285 ℃.
Preferably, the second temperature is 350-460 ℃.
Preferably, the third temperature is 550-680 ℃.
Preferably, the ammonia gas and water vapor generated during the calcination are simultaneously extracted.
Preferably, the rate of extraction is 2-3.5m 3 /min。
Preferably, the ammonium paratungstate is pretreated before calcination, and is uniformly mixed in a polymer solution.
Preferably, the polymer solution is: polyvinyl alcohol or polyvinylpyrrolidone is dissolved in distilled water to obtain a polymer solution with the mass concentration of 10-20%.
The beneficial effects of the invention are as follows:
(1) According to the calcination process for preparing the high-specific-surface-area low-residual ammonia yellow tungsten oxide, the ammonium paratungstate is calcined at the three-stage temperature, water molecules and ammonia molecules on the surface of the ammonium paratungstate are volatilized and dissociated at the first temperature, the calcination is carried out at the second temperature to crack, a complex intermediate product is generated, and the tungsten oxide is continuously calcined at the third temperature, so that compared with the primary calcination process, the particle size is greatly reduced, the residual ammonia amount is very small, and the yellow tungsten oxide with high specific surface area can be prepared.
(2) According to the calcination process for preparing the low-residual ammonia yellow tungsten oxide with high specific surface area, air extraction is started during calcination, so that the influence of the reduction atmosphere of ammonia on the tungsten oxide can be reduced, and the residual ammonia rate can be reduced.
(3) According to the calcination process for preparing the low-residual ammonia yellow tungsten oxide with high specific surface area, disclosed by the invention, the ammonium paratungstate is mixed with the polymer solution to obtain the mixed gel solution with the network-shaped template, so that the probability of coarsening the granularity of the ammonium paratungstate is possibly reduced in the low-temperature calcination process of the ammonium paratungstate, and the particle size refinement of the ammonium paratungstate is improved.
Detailed Description
A calcination process for preparing high specific surface area low residual ammonia yellow tungsten oxide includes dissociating ammonium paratungstate at the first temperature less than 300 ℃ and under oxidizing atmosphere to obtain ammonium tungsten compound, calcining ammonium tungsten compound at the second temperature of 300-500 ℃ and under oxidizing atmosphere, and continuously heating to the third temperature of 500-700 ℃ and calcining under oxidizing atmosphere to obtain yellow tungsten oxide.
Preferably, the first temperature is 200-285 ℃.
Preferably, the second temperature is 350-460 ℃.
Preferably, the third temperature is 550-680 ℃.
Preferably, the ammonia gas and water vapor generated during the calcination are simultaneously extracted.
Preferably, the rate of extraction is 2-3.5m 3 /min。
Preferably, the ammonium paratungstate is pretreated before calcination, and is uniformly mixed in a polymer solution.
Preferably, the polymer solution is: polyvinyl alcohol or polyvinylpyrrolidone is dissolved in distilled water to obtain a polymer solution with the mass concentration of 10-20%.
The invention is further illustrated by the following examples. But is not limited thereto.
Example 1
APT is placed in a feeding bin, and is fed into a rotary furnace with the relative vacuum degree of-200 Pa at the speed of 180kg/h through a screw feeder, a furnace tail observation mirror is opened to be an open system, and the temperature is controlled as follows: the first temperature control region is 200 ℃ and oxygen atmosphere, and the second temperature control region is 320 DEG CAn oxygen atmosphere; the third temperature control area is 550 ℃, the oxygen atmosphere, the furnace tube rotating speed is 2.5r/min, the ammonia gas and the water vapor generated during the calcination are pumped out at the same time, and the pumping rate is 2.5m 3 And (3) calcining in a rotary furnace, cooling and sieving to obtain the yellow tungsten oxide.
Example 2
APT is placed in a feeding bin, and is fed into a rotary furnace with the relative vacuum degree of-200 Pa at the speed of 180kg/h through a screw feeder, a furnace tail observation mirror is opened to be an open system, and the temperature is controlled as follows: the method comprises the steps of (1) a first temperature control area 180 ℃ and an oxygen atmosphere, a second temperature control area 350 ℃ and an oxygen atmosphere, a third temperature control area 600 ℃ and an oxygen atmosphere, wherein the rotating speed of a furnace tube is 2.5r/min, and ammonia gas and water vapor generated during calcination are pumped out at the same time, and the pumping rate is 3.5m 3 And (3) calcining in a rotary furnace, cooling and sieving to obtain the yellow tungsten oxide.
Example 3
APT is placed in a feeding bin, and is fed into a rotary furnace with the relative vacuum degree of-200 Pa at the speed of 180kg/h through a screw feeder, a furnace tail observation mirror is opened to be an open system, and the temperature is controlled as follows: the method comprises the steps of (1) a first temperature control area 190 ℃ and an oxygen atmosphere, a second temperature control area 380 ℃ and an oxygen atmosphere, a third temperature control area 650 ℃ and an oxygen atmosphere, wherein the rotating speed of a furnace tube is 2.5r/min, and the ammonia gas and water vapor generated during the calcination are pumped out at the same time, and the pumping rate is 3.5m 3 And (3) calcining in a rotary furnace, cooling and sieving to obtain the yellow tungsten oxide.
Example 4
Pretreating ammonium paratungstate before calcining, uniformly mixing the ammonium paratungstate and a polymer solution in a mass ratio of 1:12 in the polymer solution, uniformly stirring, and standing until bubbles completely disappear to obtain a sol-gel substance containing APT, wherein the polymer solution is: polyvinyl alcohol is dissolved in distilled water to obtain a polymer solution with the mass concentration of 10%.
Putting sol-gel substances containing APT into a feeding bin, feeding the sol-gel substances into a rotary furnace with a relative vacuum degree of-200 Pa at a speed of 180kg/h through a screw feeder, opening a furnace tail observation mirror to be an open system, and controlling the temperature to be: first temperature control zone190 ℃, oxygen atmosphere, 380 ℃, oxygen atmosphere, 650 ℃, oxygen atmosphere, 2.5r/min of furnace tube rotation speed, and extracting ammonia gas and water vapor generated during the calcination at the extraction rate of 3.5m 3 And (3) calcining in a rotary furnace, cooling and sieving to obtain the yellow tungsten oxide.
Example 5
Pretreating ammonium paratungstate before calcining, uniformly mixing the ammonium paratungstate and a high polymer solution in a mass ratio of 1:15 in the high polymer solution, uniformly stirring, and standing until bubbles completely disappear to obtain a sol-gel substance containing APT, wherein the high polymer solution is: polyvinylpyrrolidone was dissolved in distilled water to obtain a polymer solution having a mass concentration of 15%.
Putting sol-gel substances containing APT into a feeding bin, feeding the sol-gel substances into a rotary furnace with a relative vacuum degree of-200 Pa at a speed of 180kg/h through a screw feeder, opening a furnace tail observation mirror to be an open system, and controlling the temperature to be: the method comprises the steps of (1) a first temperature control area 190 ℃ and an oxygen atmosphere, a second temperature control area 380 ℃ and an oxygen atmosphere, a third temperature control area 650 ℃ and an oxygen atmosphere, wherein the rotating speed of a furnace tube is 2.5r/min, and the ammonia gas and water vapor generated during the calcination are pumped out at the same time, and the pumping rate is 3.5m 3 And (3) calcining in a rotary furnace, cooling and sieving to obtain the yellow tungsten oxide.
Comparative example 1 (one-stage calcination)
APT is placed in a feeding bin, and is fed into a rotary furnace with the relative vacuum degree of-200 Pa at the speed of 180kg/h through a screw feeder, a furnace tail observation mirror is opened to be an open system, and the temperature is controlled as follows: the temperature control area is 650 ℃, the oxygen atmosphere, the furnace tube rotating speed is 2.5r/min, the ammonia gas and the water vapor generated during the calcination are pumped out at the same time, and the pumping-out rate is 3.5m 3 And (3) calcining in a rotary furnace, cooling and sieving to obtain the yellow tungsten oxide.
Comparative example 2 (two-stage calcination)
APT is placed in a feeding bin, and is fed into a rotary furnace with the relative vacuum degree of-200 Pa at the speed of 180kg/h through a screw feeder, a furnace tail observation mirror is opened to be an open system, and the temperature is controlled as follows: first temperature control zone 380 ℃ and oxygen atmosphere, a second temperature control area 650 ℃ and oxygen atmosphere, a furnace tube rotating speed of 2.5r/min, and extraction of ammonia gas and water vapor generated during calcination at a rate of 3.5m 3 And (3) calcining in a rotary furnace, cooling and sieving to obtain the yellow tungsten oxide.
Comparative example 3
APT is placed in a feeding bin, and is fed into a rotary furnace with the relative vacuum degree of-200 Pa at the speed of 180kg/h through a screw feeder, a furnace tail observation mirror is opened to be an open system, and the temperature is controlled as follows: the method comprises the steps of (1) a first temperature control area 190 ℃ and an oxygen atmosphere, a second temperature control area 380 ℃ and an oxygen atmosphere, a third temperature control area 800 ℃ and an oxygen atmosphere, wherein the rotating speed of a furnace tube is 2.5r/min, and ammonia gas and water vapor generated during calcination are pumped out at the same time, and the pumping rate is 3.5m 3 And (3) calcining in a rotary furnace, cooling and sieving to obtain the yellow tungsten oxide.
Comparative example 4 (no bleed)
APT is placed in a feeding bin, and is fed into a rotary furnace with the relative vacuum degree of-200 Pa at the speed of 180kg/h through a screw feeder, a furnace tail observation mirror is opened to be an open system, and the temperature is controlled as follows: the method comprises the steps of calcining in a rotary furnace, cooling and sieving to obtain yellow tungsten oxide, wherein the temperature of the first temperature control region is 190 ℃, the temperature of the oxygen atmosphere, the temperature of the second temperature control region is 380 ℃, the temperature of the oxygen atmosphere, the temperature of the third temperature control region is 650 ℃, the rotating speed of a furnace tube is 2.5 r/min.
Performance particle size tests (laser particle size detector) and residual ammonia amounts (spectrophotometry) were performed on the above examples and comparative examples;
the test results are shown in Table 1.
| Sample preparation | Particle size (μm) | Residual ammonia content (%) |
| Example 1 | 11 | ＜0.01 |
| Example 2 | 10 | ＜0.01 |
| Example 3 | 9 | ＜0.01 |
| Example 4 | 6 | ＜0.01 |
| Example 5 | 5 | ＜0.01 |
| Comparative example 1 | 25 | 0.04 |
| Comparative example 2 | 18 | 0.04 |
| Comparative example 3 | 16 | 0.05 |
| Comparative example 4 | 14 | 0.08 |
From the above table, it can be seen that the particle size of the examples is small, the residual ammonia rate is low, and the main reasons are probably that the analysis of comparative examples 1 and 2 show that in the examples, the three-stage temperature is adopted to calcine the ammonium paratungstate, the water molecules and the ammonia molecules on the surface of the ammonium paratungstate are volatilized and dissociated at the first temperature, the calcination is carried out at the second temperature to crack and generate complex intermediate products, and the calcination is continued at the third temperature to generate tungsten oxide, so that compared with the one-time calcination process, the particle size is greatly reduced, the residual ammonia amount is very small, and yellow tungsten oxide with high specific surface area can be prepared. As is evident from the analysis of comparative example 3, the tungsten oxide particle size after calcination tends to be coarser at temperatures above 700℃and may be responsible for the growth of the high temperature grains. From the analysis of comparative example 4, it was found that the influence of the reducing atmosphere of nitrogen and hydrogen on tungsten oxide at the decomposition site of ammonia gas can be reduced and the residual ammonia ratio can be reduced by starting the air extraction at the time of calcination in the examples. In addition, examples 4 and 5 have smaller particle sizes mainly because ammonium paratungstate is mixed with a polymer solution to obtain a mixed gelled solution with a network-like template, and the probability of coarsening of the particle size is reduced due to the limitation of the network-like template skeleton during the calcination of the ammonium paratungstate at a low temperature section, so that the particle size refinement of the ammonium paratungstate is improved.
The above additional technical features can be freely combined and superimposed by a person skilled in the art without conflict.
The foregoing is only a preferred embodiment of the present invention, and all technical solutions for achieving the object of the present invention by substantially the same means are included in the scope of the present invention.
Claims (2)
1. A calcination process for preparing high specific surface area low residual ammonia yellow tungsten oxide is characterized in that ammonium paratungstate is dissociated under the first temperature of 200-285 ℃ and the oxidizing atmosphere to obtain an ammonium tungsten compound, the ammonium tungsten compound is calcined under the second temperature of 350-460 ℃ and the oxidizing atmosphere, and the temperature is continuously increased to the third temperature of 550-680 ℃ and the oxidizing atmosphere to obtain yellow tungsten oxide; extracting ammonia gas and water vapor generated during calcination;
the ammonium paratungstate is pretreated before calcination, and is uniformly mixed in a high polymer solution;
the polymer solution is as follows: polyvinyl alcohol or polyvinylpyrrolidone is dissolved in distilled water to obtain a polymer solution with the mass concentration of 10-20%.
2. The calcination process for preparing high specific surface area low residual ammonia yellow tungsten oxide according to claim 1, wherein the extraction rate is 2-3.5m 3 /min。
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