JPS6218481B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing cadmium telluride (hereinafter referred to as CdTe) powder used in photovoltaic cells and the like. Conventionally, CdTe has been generally produced by reacting each element in a sealed tube and growing the melt to form a crystal. As CdTe powder is recently applied to photovoltaic cells and large-area solar cells, there is a demand for CdTe powder with high purity, fineness of several μm, and accurate stoichiometric ratio. For this purpose, we will manufacture CdTe polycrystals.
A method of heating and compressing CdTe powder by hot isostatic pressing has been studied, but at present, almost no industrial manufacturing method has been disclosed. The inventors of the present invention have conducted extensive research to provide a method that makes it possible to produce high-purity cadmium telluride powder at a high yield under the above-mentioned objective circumstances. It was discovered that the object could be achieved by firing a mixed powder in three stages, and the present invention was achieved. That is,
According to the present invention, tellurium powder is mixed with cadmium powder, and the mixed powder is heated at 320 °C in an inert gas atmosphere.
After primary firing to a temperature range of T ₁ 370°C and pulverizing the obtained primary fired powder, secondary firing is performed again to a temperature range of 550T ₂ 600°C in an inert gas atmosphere to obtain a secondary fired powder. A further 550T ₃
A method for producing cadmium telluride powder is obtained, which is characterized in that tertiary firing is performed in a temperature range of 750° C. under reduced pressure to a pressure of 10 ^-2 mmHg or less. The firing reaction in the present invention is usually carried out by installing a boat made of quartz, graphite, etc. in a reaction tube made of quartz.
It is advisable to thoroughly mix the raw materials Cd and Te powders in amounts close to equimolar in advance and transfer them to the board. The inside of the reaction tube is kept in an inert gas atmosphere such as He, Ar, _N2 , etc. If the temperature of the furnace is raised too quickly, there is a risk of rapid reaction and explosion, so the heating rate is 10°C per hour.
Care must be taken not to exceed the limit. When the temperature of the reaction zone reaches a temperature range of 320 to 370°C ( _T1 : primary calcination temperature), primary calcination is performed while maintaining at this temperature, and then gradually cooled to lower the temperature.
Return to room temperature. If the holding temperature of the primary firing is less than 320°C, the generation of CdTe will be insufficient and loss will increase in subsequent steps, and if it exceeds 370°C, each element will vaporize and the amount of loss will increase. After the temperature is lowered, the primary fired powder is taken out and lightly pulverized using a conventional pulverizing means, and then transferred to the next step. This pulverization step, along with setting the temperature range for primary calcination, is an essential condition for improving yield and achieving accurate stoichiometric ratio. As with the primary firing, the temperature for secondary firing is 550-600°C (T ₂ : secondary firing temperature) at a temperature increase rate of no more than 10°C per hour, with sufficient inert gas replacement.
However, if the secondary firing temperature is lower than 550℃, the amount of unreacted particles will increase and the loss in the next depressurization process will increase.
If the value exceeds , the loss thought to be due to the vaporization of CdTe increases. After maintaining these secondary firing temperatures for a predetermined period of time, the vacuum pump is activated to vacuum the inside of the reaction tube.
Reduce pressure to 10 ^-2 mmHg or less. At this time, increase the temperature to 550~
The temperature is raised to a temperature range of 750°C (T ₃ : tertiary firing temperature), and tertiary firing is performed. Then, when the temperature is returned to room temperature under reduced pressure, the nearly stoichiometric ratio of CdTe powder becomes 85%.
It can be obtained in high yield. In this case, if the vacuum treatment step is omitted, a small amount of Cd or Te alone remains. The CdTe powder thus obtained is different from crystals produced by the melt method, and is easily pulverized, and can be pulverized to 10 μm or less using ordinary pulverization means.According to the present invention, as described above, CdTe powder is sintered in three stages. This makes it possible to provide high-purity CdTe powder with extremely low unreacted portions and a precise stoichiometric ratio in high yield, so its industrial value is extremely large. Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. Example 1 185 g of Five Nine's sponge Cd powder and 217 g of Five Nine's tellurium metal powder, a total of 400 g, were thoroughly mixed in a mortar, the resulting product with a Cd/Te ratio of 1.05 mol was placed in a quartz port, sealed in a furnace tube, and placed in a tube furnace. Inserted. First, in order to dehydrate and degas the core samples, the pressure was reduced to 1×10 ^-3 mmHg using a vacuum pump, and preheating was performed at 150°C for 2 hours. After preheating, the atmosphere was replaced with N ₂ gas, which is an inert gas, and the temperature firing curve was set at 340°C at a heating rate of 2°C/hr to 5°C/hr using a temperature control program.
The temperature was raised to ℃. Primary firing was carried out by maintaining the temperature at 340°C for 4 hours. Next, the temperature was lowered at a rate of 20°C/hr, and the temperature was lowered for 16hr.
It was left to cool while flowing N ₂ gas until the temperature dropped to below 100°C. After cooling, the primary fired product was taken out of the furnace tube and ground in a mortar. obtained at this stage
In the X-ray diffraction chart of CdTe powder, single peaks of Cd and Te were clearly observed in addition to the CdTe peak.
390 g of this primary fired CdTe product is then placed in a furnace tube and inserted into a tubular furnace in order to produce a secondary fired product. For the secondary firing, the sample inside the furnace tube was degassed at 150℃ for 2 hours at 1×10 ^-3 mmHg as in the primary firing.
The atmosphere was replaced with _N2 gas and heated at 560℃.
Maintain the temperature for 5 hours and use a vacuum pump to reduce the temperature to 1×10 ^-2 mm.
The condition was set to Hg and maintained for 3 hours. In other words, the temperature firing curve in this case is to use a temperature control program to raise the temperature to 560°C at a temperature increase rate of 4°C/hr to 10°C/hr, perform secondary firing during that time, and after reaching 560°C, 5 hours. Hold it and continue to perform secondary firing,
Next, a reduced pressure treatment was performed at the same temperature for 3 hours, during which time a tertiary firing was performed, and then the product was allowed to cool under reduced pressure. When the CdTe tertiary fired product sample obtained in this way was taken out, crushed in a sample mill, and subjected to X-ray diffraction, no single peaks of Cd and Te were observed, and the identification results confirmed that it was CdTe. BET value
380 g of CdTe powder, which is a black powder with an area of 0.25 m ² /g and a diameter of 3.8 μm, was obtained with a high yield of 95%. The stoichiometric ratio of Cd and Te was 1.00. Example 2 An experiment was conducted in the same manner as in Example 1 by changing the raw material molar ratio and the primary, secondary, and tertiary firing temperatures, and the results shown in the following table were obtained. 【table】

Claims (1)

[Claims] 1 Mix tellurium powder with cadmium powder, and heat the mixed powder at 320T ₁ 370℃ in an inert gas atmosphere.
After primary firing to a temperature range of
It is characterized by performing secondary firing to a temperature range of T ₂ 600°C, and further performing tertiary firing by reducing the pressure to a pressure of 10 ^-2 mmHg or less in a temperature range T ₃ of 550T ₃ 750°C. A method for producing cadmium telluride powder.