难溶解贵金属-硼焊料中硼的酸分解及其测定

Acidolysis and Determination of Boron in Difficultly Dissolved Precious Metal-Boron Brazing Alloys

建立了甘露醇选择性析出硼酸中与B(Ⅲ)等量的H+和pH-NaOH滴定B(Ⅲ)的新方法。系统地研究了难溶解贵金属-硼焊料中B的酸分解及其含量测定的条件。简述了H2SO4用量与Na盐量的关系及其对滴定的影响。比较了pH电极与指示剂对指示滴定终点的影响。讨论了提高测定B(Ⅲ)的准确度和精密度的条件。结果表明:采用自制简易回流装置,HNO3-H2SO4能完全分解样品中的B,并可避免B(Ⅲ)的挥发损失。于≤2.0mLH2SO4的滴定介质中,近终点NaOH微滴定和pH电极指示终点的方法,提高了滴定终点的敏锐度、分析结果的准确度和精密度。方法特点:分解完全,选择性好,准确度(测定2.00~12.00mg B,相对误差≤±0.50%)和精密度(测定4% B,相对平均误差-0.74%^+0.99%、相对标准偏差0.64%)高,操作简便,适用性强。已应用于B质量分数为1%~12%的难溶贵金属-硼焊料等样品中B的测定,结果满意。

A new method for determination of boron was established using d - mannitol as a selective reagent and pH sodium hydroxide titration H^＋ corresponding to boron quantity released from boracic acid. The conditions of acidolysis of boron in difficultly dissolved precious metal - boron brazing alloys and those of determining B were systematically studied. The relation of H2SO4 dosage and Na salt dosage and their effects on titration were also studied. The effects of pH electrode and indicator on indicating titration end -point were compared. The conditions of improving accuracy and precision for titrating boron were also discussed. Results show that boron in samples is completely decomposed without volatilization loss in a simple circumfluence device and using HNO3 -H2SO4. The acuity of titrating end -point, accuracy and precision of analytical results are improved using micro - titration of sodium hydroxide and pH electrode indicating end - point in titrating medium with ≤ 2.0mL H2SO4. The proposed method has good selectivity, high accuracy （for the determination of 2.00 - 12.00mg boron with relative error ≤ ± 50% ） and precision （for the determination of 4% boron with relative average error -0. 74% - ＋0. 99%, relative standard deviation 0. 64% tion of boron in difficultly ）, convenient operation, better applicability. It has been applied to determina-dissolved precious -boron solders and others in which the content range of boron is 1% -12% with satisfactory results.