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用热重法结合化学分析及X射线等固相鉴定的方法研究了LaB_6和CeB_6与CO_2在500—1000℃范围内的化学作用,实验表明六硼化物于700℃以下在CO_2中比较稳定,而700℃以上作用就渐为显著.在所研究的温度范围内,主要的反应可以式(1)表示: 2LnB_6+21CO_2→Ln_2O_3·3B_2O_3+3B_2O_3+21CO (1) 其中Ln=La或Ce;少量的反应按式(2)进行 4LnBe_6+21CO_2→2Ln_2O_3·3B_2O_3+6B_2O_3+21C (2) 根据试样在反应过程中的增重按主要反应式(1)估算了各温度下的反应速度.计算结果表明,当作用量不太大时(即温度不高、或温度虽高而在反应初始阶段),作用分数R与时间t符合于式(3): 1-(1-R)~(1/3)=k_1t (3) 而在较高温度反应进行一定时间后,R与t则有下列关系: [1-(1-R)~(1/3)]~3=k_2t (4) 其中k_1及K_2在不同温度下为不同的常数.对上述结果提出了解释.
The chemical reaction of LaB_6 and CeB_6 with CO_2 in the range of 500-1000 ℃ was studied by thermogravimetry combined with chemical analysis and X-ray solid phase identification. The experimental results showed that hexaboride was stable in CO_2 at 700 ℃ Above 700 ℃, the effect becomes obvious gradually. The main reaction in the studied temperature range can be expressed as (1): 2LnB_6 + 21CO_2 → Ln_2O_3 · 3B_2O_3 + 3B_2O_3 + 21CO (1) where Ln = La or Ce; The reaction is carried out according to the formula (2) 4LnBe_6 + 21CO_2 → 2Ln_2O_3 · 3B_2O_3 + 6B_2O_3 + 21C (2) According to the weight gain of the sample during the reaction, the reaction rate at each temperature is estimated according to the main reaction formula , When the amount is not too large (ie, the temperature is not high, or the temperature is high at the initial stage of the reaction), the role of the score R and time t in accordance with the formula (3): 1- (1-R) ) = k_1t (3) However, after the reaction at a higher temperature for a certain period of time, R and t have the following relationship: where k_1 and K_2 are different constants at different temperatures, and the above results are explained.