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首页> 外文学位 >Ionic conductivity measurement in magnesium aluminate spinel and solid state galvanic cell with magnesium aluminate electrolyte.
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Ionic conductivity measurement in magnesium aluminate spinel and solid state galvanic cell with magnesium aluminate electrolyte.

机译：用铝酸镁电解质测量铝酸镁尖晶石和固态原电池中的离子电导率。

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摘要

This thesis work is about the experimental measurement of electronic and ionic conductivities in the MgAl2O4 spinel at 500∼600°C range and exploring the fundamental origin of solid-state galvanic cell behavior in the cell of Al|MgAl2O4|Mg, Al|MgAl2O 4|C, and Mg|MgAl2O4|C, in which at least one metal electrode in common with the composition of the electrolyte.; For the electronic conductivity measurement, we have used the ion-blocking Gold and Carbon electrodes which are inert with both Mg and Al ions to suppress the ionic conduction from the total conduction. DC polarization method was used to measure the conduction through Au|MgAl2O4|Au and C|MgAl2O4|C specimens. The measured electrical conductivity using Au|MgAl2O4|Au and C|MgAl2O4|C specimens showed 10-9.3 ∼ 10-8.4 (O·cm) -1 at 600∼720°C range following the Arrhenius-type relation. These conductivity data are in agreement with reported data obtained from Pt and Ag ion-blocking electrodes deposited on MgAl2O4 specimens.; For the ionic conductivity measurement, we have used the non-blocking Al and Mg electrodes for Al and Mg ionic conductivities, respectively. Ionic conductivity measurement of Al and Mg in separate manner has not been reported yet. In both Al|MgAl2O4|Al and Mg|MgAl2O 4|Mg specimens, gradual increase of conduction was observed once at the initial period before it reaches the steady state conduction. By DC method on the range of 580∼650°C, steady state Al ionic conductivity was measured from Al|MgAl2O4|Al specimen showing 10 -7.7 ∼ 10-6.8 (O·cm)-1 with the activation energy of 1.9eV in sigma = sigma0 exp-QRT formula. There was no difference in the conductivity by the change of the atmosphere from 5%H2 + 95%N2 mixed gas to pure Ar gas. So it was confirmed that the oxygen defect chemistry did not play a role. For Mg ionic conductivity Mg|MgAl2O4|Mg specimen was used and the measured conductivity shows 10-6.7 ∼ 10-4.4 (O·cm)-1 at 400∼550°C with the activation energy of 1.44eV at Ar gas atmosphere.; Higher conductivity of Mg cation than Al cation is in agreement with self-diffusion data reported in the literatures. It's also in agreement with the higher Mg ionic mobility concluded by the formation of MgO layer at the cathode as the result of reaction between Mg ions migration and surrounding oxygen decomposed by the applied voltage.; To explore the fundamental origin of the emf in the Mg|MgAl2O 4|Al galvanic cell, we set-up two postulations which are able to explain by the transportation mechanism in the MgAl2O4 with the presence of two cations in the system. The possible mechanisms are (1) Only Mg ion is involved in transportation through the MgAl2O4. Thus the emf is generated from the difference in the activity of Mg between the two electrodes. (2) Both Mg2+ and Al3+ ions are participating in transportation through the MgAl2O 4. In this case, the emf is generated from the difference in the reduction-oxidation potential between Mg and Al.; Based on the result that both Al|MgAl2O4|C and Mg|MgAl2O4|C have the emf with C positive polarity, the second suggested mechanism results in the spontaneous composition change inside MgAl2O4 in the both directions of Mg-rich and Al-rich according the electrode materials with fixed C electrode on the other side. Considering the spontaneous reaction involving the composition change of MgAl2O4 to lower free energy of the system, suggested mechanism one is more plausible.; In order to confirm that origin of the emf is determined by the activity difference on electrodes, emf measurements were carried out using different Mg activities available by using Mg-Al alloy. OCV was dependent on the difference in the Mg activity on the electrodes of Mg|MgAl2O4|Mg-Al alloy. This result supports the emf is generated by the difference in the activity of Mg ions at the both electrodes.
机译：本文的工作是关于在500-600°C范围内在MgAl2O4尖晶石中进行电子和离子电导率的实验测量，并探索Al | MgAl2O4 | Mg，Al | MgAl2O 4电池中固态原电池行为的基本起源。 | C和Mg | MgAl2O4 | C，其中至少一个金属电极与电解质的组成相同。对于电子电导率测量，我们使用了对Mg和Al离子呈惰性的离子阻挡性金和碳电极，以抑制总传导中的离子传导。使用直流极化法测量通过Au | MgAl2O4 | Au和C | MgAl2O4 | C样品的传导。使用Au | MgAl2O4 | Au和C | MgAl2O4 | C样品测得的电导率遵循阿伦尼乌斯型关系，在600〜720℃范围内显示10-9.3〜10-8.4（O·cm）-1。这些电导率数据与从沉积在MgAl2O4样品上的Pt和Ag离子阻挡电极获得的报道数据一致。对于离子电导率测量，我们分别将无阻塞的Al和Mg电极用于Al和Mg离子电导率。尚未报道以单独的方式测量Al​​和Mg的离子电导率。在Al | MgAl2O4 | Al和Mg | MgAl2O 4 | Mg样品中，在达到稳态导电之前的初始阶段，一次观察到导电逐渐增加。通过直流电法在580〜650°C的温度范围内，从Al | MgAl2O4 | Al样品中测出稳态Al离子电导率，该样品的激活能量为1.9eV，在10 -7.7〜10-6.8（O·cm）-1的条件下， sigma = sigma0 exp-QRT公式。从5％H2 + 95％N2混合气体到纯Ar气体的气氛变化，电导率没有差异。因此证实了氧缺陷化学没有起作用。对于Mg离子电导率，使用Mg | MgAl2O4 | Mg标本，测得的电导率在Ar气氛下在400〜550°C下的活化能为1.44eV，在10-6.7〜10-4.4（O·cm）-1。 Mg阳离子比Al阳离子具有更高的电导率与文献中报道的自扩散数据一致。这也与较高的Mg离子迁移率是一致的，该迁移率是由于Mg离子迁移与施加的电压分解的周围氧之间的反应而在阴极形成MgO层而得出的。为了探索Mg | MgAl2O 4 | Al电镀电池中emf的基本来源，我们建立了两个假设，它们可以通过在系统中存在两个阳离子的情况下在MgAl2O4中的传输机理来解释。可能的机理是（1）通过MgAl2O4的传输仅涉及Mg离子。因此，电动势是由两个电极之间的Mg活性差异产生的。 （2）Mg 2+和Al 3+离子都参与通过MgAl 2 O 4的传输。在这种情况下，电动势是由Mg和Al之间的氧化还原电位差产生的。基于Al | MgAl2O4 | C和Mg | MgAl2O4 | C都具有C正极性的结果，第二种建议机理导致MgAl2O4内部的自发组成沿富Mg和富Al的两个方向变化。另一侧固定C电极的电极材料。考虑到自发反应涉及改变MgAl2O4的组成以降低系统的自由能，因此建议的机理之一更为合理。为了确认电动势的起源是由电极上的活度差异决定的，使用Mg-Al合金可利用不同的Mg活度进行电动势测量。 OCV取决于Mg | MgAl2O4 | Mg-Al合金在电极上的Mg活性差异。该结果支持了通过两个电极上的Mg离子活度差异产生的电动势。

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