五硼酸钾溶液中含硼物种的研究

Boron-11 Nuclear Magnetic Resonance Study of Aqueous Potassium Pentaborate Solution

采用物种分布图与核磁共振实验研究了五硼酸钾溶液中含硼物种的类型、含量和溶液浓度间关系。研究表明五硼酸钾在稀溶液(0.05 mol/kg(H_(2)O))中几乎全部水解,主要物种为B(OH)_(3)和B(OH)_(4)^(-);在较浓溶液(0.20 mol/kg(H_(2)O))中主要物种为B(OH)_(3)和B_(3)O_(3)(OH)_(4)^(-),而B_(5)O_(6)(OH)_(4)^(-)和[B_(4)O_(5)(OH)_(4)^(2-)]的含量较小。核磁共振实验研究给出了B(OH)_(4)^(-)、B_(3)O_(3)(OH)_(4)^(-)和B_(5)O_(6)(OH)_(4)^(-)的生成常数K_(1)、K_(3),、K_(5),研究得出B_(5)O_(6)(OH)_(4)^(-)含量很少的原因是其解聚为其它类型硼酸根离子。外加离子促进五硼酸根离子的生成,而高温条件促进B_(5)O_(6)(OH)_(4)^(-)发生解聚反应。

The relationship between the type,content and solution concentration of boron-containing species in potassium pentaborate solution was studied using species distribution diagrams and NMR experiments.Studies have shown that potassium pentaborate is almost completely hydrolyzed into B(OH)_(3)and B(OH)_(4)^(-)in dilute solution(0.05 mol/kg(H_(2)O)).The main species in the concentrated solution(0.20 mol/kg(H_(2)O))are B(OH)_(3)and B_(3)O_(3)(OH)_(4)^(-),while the content of B_(5)O_(6)(OH)_(4)^(-)and[B_(4)O_(5)(OH)_(4)^(2-)]is less.The formation constants K_(1),K_(3)and K_(5)of B(OH)_(4)^(-),B_(3)O_(3)(OH)_(4)^(-)and B_(5)O_(6)(OH)_(4)^(-)were given by NMR experimental study.The reason for the low content of B_(5)O_(6)(OH)_(4)^(-)is that it depolymerizes into other borate ions.The addition of ions promoted the formation of pentaborate,while high temperature promoted the B_(5)O_(6)(OH)_(4)^(-)depolymerization.