简介概要

Determination of Ge in Au alloys using sodium hypophosphite and potassium iodate potentiometric titration method

来源期刊：Rare Metals2020年第12期

论文作者：Shou-Li Han Xiao-Tang He Jun-Mei Guo Zhao-Ying Ren Li-Ya Zhu Liang-Wei Chen Qing-Nan Shi Jia-Hong Yi

摘要：This paper presents a new method of determining Ge in AuGe alloys by potassium iodate（KIO₃）potentiometric titration when Ge（Ⅱ） and Au（0） are simultaneously reduced from Ge（IV） and Au（Ⅲ） by sodium hypophosphite rather than by distillation separation.The influences of such conditions as the reduction acidity,the dosage of sodium hypophosphite and the reduction time on the determination of Ge were studied.Ge in AuGe alloys such as AuGe₁₂,AuGeNi_12-2,AuAgGe_18.8-12.5,and AuAgGeNi_43.8-6-0.2 was measured with the relative standard deviation（RSD） of 0.10 %-0.31 % and the recoveries of added standard Ge in sample of 99.40 %-100.40 % under the conditions of 0.40-0.80 mol·L^-1 HCl,3.3 mol·L^-1H₃ PO₄,15 g sodium hypophosphite,and reduction time of40 min.The new method presented is of high accuracy in results,good stability and sensibility in end-point,and easy operation and strong selectivity of determination.

稀有金属(英文版) 2020,39(12),1492-1496

Determination of Ge in Au alloys using sodium hypophosphite and potassium iodate potentiometric titration method

Shou-Li Han Xiao-Tang He Jun-Mei Guo Zhao-Ying Ren Li-Ya Zhu Liang-Wei Chen Qing-Nan Shi Jia-Hong Yi

School of Materials Science and Engineering,Kunming University of Science and Technology

State Key Laboratory of Advanced Technologies for Comprehensive Utilization of Platinum Metals,Sino-Platinum Metals Resources (Yimen) Co.Ltd.

作者简介：*Liang-Wei Chen,e-mail:elegantbaby@126.com;

收稿日期：27 September 2013

基金：financially supported by the National High Technology Research and Development Program of China (Nos.2012AA063203 and 2012AA063207);

Determination of Ge in Au alloys using sodium hypophosphite and potassium iodate potentiometric titration method

Shou-Li Han Xiao-Tang He Jun-Mei Guo Zhao-Ying Ren Li-Ya Zhu Liang-Wei Chen Qing-Nan Shi Jia-Hong Yi

School of Materials Science and Engineering,Kunming University of Science and Technology

State Key Laboratory of Advanced Technologies for Comprehensive Utilization of Platinum Metals,Sino-Platinum Metals Resources (Yimen) Co.Ltd.

Abstract：

This paper presents a new method of determining Ge in AuGe alloys by potassium iodate(KIO₃)potentiometric titration when Ge(Ⅱ) and Au(0) are simultaneously reduced from Ge(IV) and Au(Ⅲ) by sodium hypophosphite rather than by distillation separation.The influences of such conditions as the reduction acidity,the dosage of sodium hypophosphite and the reduction time on the determination of Ge were studied.Ge in AuGe alloys such as AuGe₁₂,AuGeNi_12-2,AuAgGe_18.8-12.5,and AuAgGeNi_43.8-6-0.2 was measured with the relative standard deviation(RSD) of 0.10 %-0.31 % and the recoveries of added standard Ge in sample of 99.40 %-100.40 % under the conditions of 0.40-0.80 mol·L^-1 HCl,3.3 mol·L^-1H₃ PO₄,15 g sodium hypophosphite,and reduction time of40 min.The new method presented is of high accuracy in results,good stability and sensibility in end-point,and easy operation and strong selectivity of determination.

Keyword：

Ge determination; AuGe alloy; Sodium hypophosphite; Potassium iodate; Potentiometric titration;

Received： 27 September 2013

1 Introduction

Ge-containing Au alloy,characterized by low contact resistance,enc apsulation temperature,therm al expansion coefficient,good wettability,conductivity and heat conductivity,is one of the important military products because of its key roles and wide applications in the electronic encapsulation and industry [ 1] .

The inductive coupling plasma atomic emission spectrographic method (ICP-AES),with the advantages of accurate results,good selectivity,fast analysis,wide linearity range,etc.,is widely applied in the determination of Ge in base metal alloys [ 2, 3, 4, 5] .Although the method of KIO₃ starch indication titration to determine Ge has an advantage of accurate results,there are more disadvantages when the starch is used as the indicator which is interfered by oxidation reducibility and color ions.Color ions have to be separated by pre-distillation,which easily leads to the loss of Ge due to complicate operation and long process analysis [ 6, 7, 8, 9, 10] .In addition,when the titrate reaches the end-point,blue color of iodine starchy fades in 15 s.It is required that the titration speed of samples should be consistent with that of standard Ge in order to minimize the titration errors.Up to now,there are few literatures about the determination of Ge in gold alloys.

According to previous sample decomposition and electrochemical analysis [ 11, 12, 13, 14, 15] ,the authors made a study on the influences of such conditions as reduction acidity,the dosage of sodium hypophosphite,and the reduction time on the determination of Ge using the above-mentioned method.Comparison was made between the influences of end-point indication for potential method and starch method on accuracy and precision of the analyzed results,stability and sensitivity of the end-point,selectivity of method,etc.The possibility of reaction in an electrochemical way was discussed.

2 Experimental

2.1 Preparation of reagents

0.10 g Ge (purity>99.999%) was weighed with the precision of 0.00001 g and then put into a beaker with the capacity of 100 ml,and 10 ml H₂O₂ and 5%NaOH solution of 1 ml were added to the beaker,heating at about100℃until Ge was fully dissolved.The rest H₂O₂ was removed after slightly boiling of the solution,15 ml HCl was added,and then the mixture was put into the 100 ml measuring flask.Water was added to dilute up to the scale and mixed.As a result,the solution containing 1 mg·ml^-1Ge and 1.8 mol·L^-1 HCl was obtained.

0.50 g KIO₃ which was already dried at the temperature of130℃was put into the 400 ml beaker,and then 10 g KI,0.5 g NaCO₃,and 200 ml water were added into the beaker.Then,the solution was put into a 1,000 ml measuring flask,and water was added to dilute the solution up to the scale and mixed.KIO₃-KI standard titration solution was obtained.

Au(Ⅲ) solution containing 10 mg·ml^-1 Au and 0.024mol·L^-1 HCl was prepared.All reagents were analytical pure,and the water for experiment was distilled water.

2.2 Method

10 ml standard Ge solution and 9 ml Au(Ⅲ) solution were put into a 250 ml taper flask,and 15 ml HCl (1:1),45 ml H₃PO₄,15 g sodium hypophosphite,and water were added to dilute the solution up to 200 ml.The funnel containing the saturated NaHCO₃ solution was covered and heated until slightly boiling for 40 min.Then,it was put down to the ambient temperature by water cooling.

After taking off the funnel,Pt-indicating electrode was inserted,and KCl calomel reference electrode was saturated.With stirring by the magnetic mixer,KIO₃ standard titration solution was titrated to the end-point at which the potential abrupt change was the utmost.

2.3 Sample solution preparation

0.1 g alloy samples of AuGe12,AuGeNi12-2,AuAgGe18.8-12.5,AuAgGeNi43.8-6-0.2,and AuAgGe18.8-12.5,respectively,were taken to a close microwave digestion tank,and 9 ml HCl and 2 ml H2O2 solution were added to the tank and the tank was closed.The samples were dissolved at the pressure of 3,445 kPa and the temperature of 75℃,heated up for 5 min,and temperature was kept at the constant for about 9 h.The solution was taken out and cooled down,and put into a taper flask.5 ml HCl (1:1)was added to the flask,and then the operation was carried out according to Sect.2.2

2.4 Analytical results of samples and recoveries of added standard Ge in samples

Analysis was made to AuGe₁₂,AuGeNi_12-2,AuAgGe_18.8-12.5,and AuAgGeNi_43.8-6-0.2,respectively.0.2 g AuGe₁₂ and0.2 g AuGeNi_12-2 were taken to a close microwave digestion tank,respectively,and dissolved according to Sect.2.3.The solution was put into a 100 ml measuring flask,and water was added to dilute the solution up to the scale.Ge solution with a certain concentration was taken to a 250 ml taper flask,certain amount of Ge standard solution was added,and the operation was carried out according to Sect.2.2.From Table 1,it can be known that the relative standard deviation (RSD) is 0.10%-0.31%for the determination of 6%-13%Ge,and the recovery rate is99.40%-100.40%for 5-10 mg Ge.

3 Results and discussion

3.1 Selection of reduction acidity

It is well known from Fig.1a that under the acidity conditions of 2.2 mol·L^-1 H₃PO₄ and 4.0-5.0 mol·L^-1 HCl,Ge(Ⅳ) in sodium hypophosphite can be fully reduced to Ge(Ⅱ).During the process of titration,it is observed that the electric potential is stable with obvious potential abrupt change at the terminal point.However,while Au(Ⅲ) is present,the electric potential during the process of titration is unstable with small potential abrupt change at the endpoint,and the determination results are lower than the added values.It is due to that the above-mentioned acidity is not the best reduction acidity of Au(Ⅲ).There is a small amount of Au (Ⅲ) in the solution which interrupts the determination.

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Table 1 Analytical results of sample and recoveries of addition standard Ge in sample

Fig.1 Selection of reduction acidity:a 30 ml H₃PO₄ and b 45 ml H₃PO₄

It is well known from Fig.1b that at the acidity of3.3 mol·L^-1 H₃PO₄ and 0.4-0.8 mol·L^-1 HCl,Ge(Ⅳ) can be fully reduced to Ge(Ⅱ) by sodium hypophosphite in the titration system of Ge(Ⅳ) or the Ge(Ⅳ) and the Au(Ⅲ).It is observed that during the titration,the electric potential is stable with bigger electric potential abrupt change at the end-point,and the determination results accord with the added values.3.3 mol·L^-1 H₃PO₄ and 0.65 mol·L^-1 HCl were used in the experiment.

3.2 Selection of sodium hypophosphite dosage

It is well known from Fig.2 that the Ge(Ⅳ) reduction rate increases continuously with the increase of sodium hypophosphite dosage.When there is only Ge(Ⅳ),Ge(Ⅳ) can be completely reduced by about 7 g sodium hypophosphite.During the process of titration,it is observed that the electric potential is stable with bigger electric potential abrupt change at the end-point,and the determination results accord with the added values well.However,when Au(Ⅲ) and Ge(Ⅳ) coexist,it is observed that,during the process of titration by sodium hypophosphite of less than9 g,the electric potential is unstable with small potential abrupt change at the end-point,and the analytical results are lower than the added values.By sodium hypophosphite of no less than 9 g,Ge(Ⅳ) and Au(Ⅲ) can be fully reduced,and the electric potential is stable with bigger electric potential abrupt change at the end-point and the analytical results fit the added values well.15 g sodium hypophosphite was used in the experiment.

Fig.2 Selection of NaH₂PO₂ dosage

Fig.3 Selection of reduction time

3.3 Selection of reduction time

s wenownromg.aee) reduction rate increases continuously with the increase of reduction time.When the reduction time is 40-45 min,Ge(Ⅳ) and Au(Ⅲ)can be completely reduced.During the process of titration,it is observed that the electric potential is stable with bigger electric potential abrupt change at the end-point and the analytical results fit the added values well.Reduction time was 40 min in the experiment.

3.4 Influence and removal of coexistent ion

With miniaturization,the fraction of free surfaces increases,which has dominated influence on the total mechanical properties of material.It can be known from the experiments that neither color nor colorless metallic ions have any influence on the measurement as long as they have no redox[except Au(Ⅲ) and Se(Ⅵ)].When the Ge(Ⅳ) is10 mg,interferences of metallic ions to the Ge determination are as follows:Au(Ⅲ)90^*,Ag (Ⅰ)50^*,Ni(Ⅱ),Se(Ⅵ)30^*,Cd(Ⅱ),Ca(Ⅱ),Mg(Ⅱ),La(Ⅲ),Al(Ⅲ),In(Ⅲ),Zn(Ⅱ),Ba(Ⅱ),and Be(Ⅱ)10^*.In addition,Pt(Ⅳ),Pd(Ⅱ),Cu(Ⅱ),Co(Ⅲ),Cr(Ⅲ)0.5,As(V) and Sn(Ⅳ)0.1 have serious interference to the Ge determination.Electric potential has no abrupt change at the end-point.*means it is not the biggest allowable amount.

Fig.4 Curve of potentiometric titration

3.5 Potentiometric titration research and method comparison

The accuracy and precision of analytical results,stability and sensibility of end-point as well as titration speed of electric potential indication method and starch indication method were studied when the titration was carried out with KIO₃ standard titration solution Ge(Ⅱ).From Fig.4and Table 2,three aspects can be known as following paragraphs.

When electric potential indication method was used for titration,the electric potential change is 1 mV at 0.050 ml solution,about 5-10 mV at 0.050 ml solution before the end-point,about 178-200 mV at 0.025 ml solution at the end-point,and about 10 mV at 0.050 ml solution after the end-point.Retaining 60 s,after end-point,the electric potential value change is about 25 mV.When starch indication method was used for titration,blue color fades slowly before the end-point.It is light blue at the end-point and can be darker blue with 0.05 ml solution in excess,and blue color fully fades after retaining 15 s at the end-point.The electric potential indication method is better than the starch indication method in the stability and sensibility of the terminal point and the accuracy of the analytical results.

When the titration speed is 0.025-0.150 ml·s-1,the amount of Ge determined by two indication methods fits well basically and the relative errors are-0.20%to+0.10%for the electric potential indication method and-1.09%to+0.99%for the starch indication method.

With the increase or decrease of the titration speed,the electric potential indic ation method has few influences on the amount of Ge determined while the amount of Ge determined by the starch indication method relatively reduces or increases.That is to say,the former is free from the influence of the titration speed,and more precise than the latter.

When the electric potential indication method was used,color ions without redox[except Au(Ⅲ) and Se(Ⅵ)]do not have any influences on the determination;when the starch indication method was used,color ions and the oxidizing ions that are not reduced by sodium hypophosphite make the terminal point less sensitive and the blue continuously fades.That is to say,the selectivity of the electric potential indication method is better than that of the starch indication method.

3.6 Discussion in an electrochemical theoretic way

Relevant standard electrode potentials are known as follows [ 10] :

Accoramg to me reaction theory of electrocnemistry,me electrode with higher potential value was used as an oxidizing agent and that with lower potential value as a reducing agent,and there is an expression as shown in the following:

where, is the Gibbs free energy at the standard state,E is the potential value,F is the electricity of per mole of electrons (Faraday constant),n is the number of moles of electron transfer,R is the gas constant,T is thermodynamic temperature,K is the equilibrium constant.

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Table 2 Comparison of effects of titration speed on end-point indication method

△Vmax being an end-point potential abrupt value*Color of end-point disappearing in 15 s

The feasibility and degree of the reaction can be anticipated according to the following discussion.When ,and ,it is known that Ge(Ⅳ)and Au(Ⅲ) are reduced to Ge(Ⅱ) and Au(0) by sodium hypophosphite and Ge(Ⅱ) is oxidized to Ge(Ⅳ) by KIO₃.The ion reaction equations are as follows:

The calculation of the balance constant K (the degree of reaction) are as follows:

Put R=8.3144 J·K·mol^-1,F=96,500 C·mol^-1,and T=298 K into Eq.(5),it can be shown that K₁=3.4×10⁴³,K₂=1.3×10⁹⁰,and K₃=3.4×10⁵².

According to the general standard,when the balance constant K=1×10⁵,the reaction is fully undertaken rightward.Reactions (6)-(8) can be reacted and even fully reacted,which are consistent with the experimental results.

4 Conclusion

In this study,the Ge in the alloys,such as AuGe₁₂,AuGeNi_12-2,AuAgGe_18.8-12.5 and AuAgGeNi_43.8-6-0.2,etc.,was determined by KIO₃ electric potential indication titration method with RSD of 0.10%-0.31%and sample addition standard recovery rate of 99.40%-100.40%,which improves the accuracy and precision of the analytical results.

The electric end-point indication method and the starch end-point indication method basically have the same accuracy of analytical results.However,the former is better than the latter in such aspects as the precision of analytical results,the stability and sensibility of the endpoint,the titration speed,the feasibility of operation and the selectivity,etc.

In an electrochemical way,it is possible for Ge(Ⅳ) and Au(Ⅲ) to be reduced to Ge(Ⅱ) and Au(0) at the same time using sodium hypophosphite and for Ge(Ⅱ) to be oxidized to Ge(Ⅳ) using KIO₃.Chemical reaction constant was calculated,which provides a certain theoretical basis for the proposed operational method.