石墨含量对阴极炭块渗透性的影响

分别对质量分数为20%、30%和100%石墨质阴极炭块的渗透性进行研究,利用酚酞测试法测量其渗透深度,采用扫描电镜法观察电解质渗透到内部的情况。结果表明:随着石墨质阴极材料中石墨含量的增加,Na和电解质的渗透能力减弱。对于全石墨质阴极炭块经过4h的电解渗透后,阴极中有钠、氟、铝等元素,并且钠元素的含量要多于氟元素。从综合性能方面考虑,30%石墨质阴极炭块很适合在工业上推广使用。     

PENETRATION OF SODIUM INTO CATHODE CARBON BLOCKS DURING ALUMINIUM ELECTROLYSIS

用电热加压法制得的实验室铝电解槽阴极炭块试样进行了钠渗透试验,讨论了铝电解过程中钠向阴极炭块中进行渗透的机理。结果表明,钠的渗透会随着电解质分子比、电流密度的增加而增加。钠向阴极炭块中渗透有两个途径一是通过孔隙渗透,另一个是通过晶格进行扩散。     

铝电解过程中金属钠在阴极炭块中的渗透

用电热加压法制得的实验室铝电解槽阴极炭块试样进行了钠渗透试验，讨论了铝电解过程中钠向阴极炭块中进行渗透的机理。结果表明，钠的渗透会随着电解质分子比，电流密度的增加而增加。钠向阴极炭块中渗透有两个途径：一是通过孔隙渗透，另一个是通过晶格进行扩散。     

Na和铝电解质对振动成型TiB2惰性阴极的渗透

采用振动成型的TiB2和石墨分别作为Na和铝电解质渗透实验的阴极材料,在工业铝电解条件下电解5 h,考察了Na和铝电解质对其腐蚀渗透情况. XRD分析结果表明,振动成型TiB2阴极的基体中未发现Na或F的单质及化合物,而在石墨阴极中则有NaF和Na3AlF6等物质存在. SEM及EDS分析结果表明,Na, F, Al等元素渗透到TiB2阴极基体中的量极少,渗透到石墨中的量则较多. 可见振动成型TiB2阴极能够有效减缓Na和铝电解质的渗透,但并不能完全阻止.     

关于β-Al_2O_3固体电解质中钠沉积现象的研究

在电解制取金属钠和钠硫电池充电过程中,β-Al_2O_3 隔膜往往发生“钠沉积”现象。我们研究了β-Al_2O_3在发生“钠沉积”后的组成和显微结构情况,以及产生“钠沉积”的条件和原因。研究结果表明,在一般情况下“钠沉积”主要发生在晶界以及气孔、裂缝等空隙处,发生“钠沉积”的化学反应主要是钠阴极上的电化学还原反应,由“钠沉积”产生的那种黑色物质主要是钠、钾和镁等。高的槽电压和大的电解电流密度,以及β-Al_2O_3 的晶粒粗大、多孔等都是加速“钠沉积”的因素。在某些情况下发生“钠沉积”时也伴随发生“钾沉积”。     

氧化锆低温电子特征氧分压的测定

本文用从铝液和银液中抽氧的氮仑商定法测量了自制氧化钇稳定的氧化锆固体电解擀的电子特征氧分压Ｐ。结果表明，９００℃时电子特征氧分压的范围是Ｐａ自制氧化锆电解质可用于渗碳气氛压浓度的测量，而不必考虑电子电导对浓差电势的影响；用铝液能实现低温下电子特征氧分压的测量。     

国外铝和铝合金表面转化膜处理新工艺

为了装饰、防护和功能方面的需要,铝和铝合金的表面处理日益受到人们的重视,国外在处理工艺方面的进展尤其迅速。本文介绍铝和铝合金表面转化膜生成和染色的一些新工艺。通过化学反应或电化反应以及随后的一系列处理在铝表面生成稳定、耐磨、具有良好装饰作用的表面膜,是铝和铝合金的一种传统表面处理方法。近几年来英、美、法、日等国在这方面推出了不少新的方法,例如用于前处理的低磷酸抛光液、交流电解染色以及稳定的亚锡染色液、非阳极化的电解染色等等。     

炭阴极材料在操作温度下的实验室试验

深入了解阴极炭材料在实际预热、起动和电解条件下的各项性质是十分重要的。为此,我们改进了在温升下的几项试验方法,它们作为设计工具。对控制材料的质量来说非常重要。1)钠渗透引起的膨胀;2)钠渗透的速度;3)对钠的化学耐性;4)电解过程中的抗磨性;5)热膨胀/收缩;6)热导率。不同试验方法的相关性作为熔炉质量保证系统的一部分也加以讨论。     

铝合金熔化炉熔池内衬刚玉瘤成因及对策

铝合金熔化炉熔池内衬刚玉瘤的形成与扩展是熔池内衬耐火材料破损的重要原因.铝合金熔化炉熔池内衬耐火浇注料和刚玉瘤的化学分析结果显示,刚玉瘤中Al2O3的质量分数为94％,远高于原浇注料的61.0％.分析认为,铝及其合金元素与耐火材料间的化学反应,铝液液面的氧化反应,炉内温度过高是刚玉瘤形成的原因,而且冶炼过程中加入的助熔剂或清渣剂加速了对内衬耐火材料的渗透.据此提出了降低刚玉瘤形成及减轻内衬损毁的对策.     

镍—锌双盐溶液铝电解着色：用微分李沙育法的研究结果

用微分李沙育法考察了铝及铝合金阳极氧化膜在Ni-Zn盐电解着色液中的交流电解着色过程,研究了电解着色时间、电压、着色液中镍、锌盐的浓度及铝基体材料对电解着色阳极电流密度的影响.     

含LiF和KF的电解质熔体对铝电解阴极的渗透过程

研究了Na3AlF6-Al2O3-KF-LiF电解质体系中KF和LiF含量、电流密度和NaF/AlF3分子摩尔比对阴极石墨材料渗透过程的影响.结果表明,K和Na渗透到阴极碳块中形成石墨层间化合物,而Li在阴极表面生成Li2C2化合物;当钾盐含量为0～7％(ω)时,碱金属渗透深度可达28～40 mm:当锂盐含量为0～7％...     

镍铁尖晶石基金属陶瓷惰性阳极的电解腐蚀行为

采用粉末冶金法制备了10%Ag-NiFe2O4/NiO金属陶瓷惰性阳极,阳极为圆柱形,直径50 mm,高15 mm. 在960℃下进行电流密度为0.8 A/cm2的铝电解实验,电解时间为10 h. 研究了阳极在Na3AlF6-5%CaF2-5%Al2O3熔体中的腐蚀行为. 电解后的阳极外观尺寸略有变化,但没有发生阳极肿胀及阳极表面起层、剥离的现象,表现出较好的耐腐蚀性. 计算得到阳极腐蚀率为1.5′10-4 g/(cm2·h),折算为13 mm/a. 电解所得铝的纯度在92%~93%之间. 对腐蚀后阳极的表面分析发现,陶瓷相中Ni和Fe组元并不以化学计量数溶解,陶瓷组元的Fe2O3比NiO优先溶解进入电解质. 正对阴极的阳极表面和背对阴极的阳极表面氧元素的含量不同,前者中氧元素多于后者,说明在阳极正对阴极的表面发生析氧反应更剧烈一些,一部分新生态的氧与阳极表面的金属发生氧化反应生成Ag3O4. 对腐蚀后阳极断面进行分析发现,电解质渗透进入阳极内部,与陶瓷基体离解产生的Fe2O3发生反应,生成FeF3沉积在阳极的空隙中.     

Reactivity between carbon cathode materials and electrolyte based on industrial and laboratory data

Interaction between electrolyte and carbon cathodes during the electrolytic production of aluminium decreases cell life. This paper describes the interaction between carbon cathode materials and electrolyte, based on industrial and laboratory data. It also reports on the degree of expansion of semi-graphitic and graphitised materials when exposed to a sodium rich environment. Phase relations in the slow cooled bath electrolyte, spent industrial cathodes and laboratory scale cathode samples were similar: all contained Na₃AlF₆, NaF, CaF₂ and NaAl₁₁O₁₇. Al₄C₃, AlN and NaCN were only detected in the spent industrial cathodes. The inability to locate Al₄C₃ in the laboratory scale samples could be due to very low concentrations of Al₄C₃ which could not be detected by XRD, or to the limited direct contact between the produced aluminium and carbon material. X-ray diffraction analysis confirmed that sodium intercalation into graphite did not take place. Wear of the examined carbon cathodes proceeded due to penetration of electrolyte and sodium into the cathode, followed by reactions with carbon and N₂ whereby AlN and NaCN formed. Once electrolysis started the carbon cathodes expanded rapidly, but slowed down after approximately an hour. Sodium expansion decreased with degree of graphitisation of the carbon cathode material.     

An experimental study of aluminium electrowinning using a nickel-based hydrogen diffusion anode

Laboratory scale electrolysis experiments were conducted to investigate the electrowinning of aluminium using hydrogen diffusion anodes. A potassium-based electrolyte (KF–AlF₃–Al₂O₃), porous nickel alloy anode and molybdenum disk cathode were used in experiments at 750 °C. Hydrogen gas was supplied to the anode/electrolyte interface through the porous anode. Experiments were conducted in potentiostatic, galvanostatic and galvanodynamic modes. There was a measurable depolarisation of the anode potential and also anode reaction of hydrogen and oxygen ions in the bath to form water vapour was confirmed by the water vapour condensate found at the electrolysis exit gas pipe. Metallic aluminium was found on the spent cathode. The experiments conducted in the galvanodynamic mode suggested that the rate limiter for hydrogen oxidation was the availability of surface hydrogen at the anode/electrolyte interface. The anode surface corroded during electrolysis and impurities were found both in the molten bath and on the cathode.     

Investigation of the aluminium electrodeposition process in cryolite-based melts using a rotating ring-disc electrode: evidence for the existence of a subvalent intermediate species

The rotating ring-disc electrode technique has been used to investigate the reaction mechanism of the aluminium electrodeposition process in cryolite-based electrolytes. Laboratory studies using high temperature gold-molybdenum and platinum-molybdenum rotating ring-disc electrodes have provided evidence for the existence of a subvalent intermediate species (Al (I)). In a cryolite-alumina electrolyte (bath ratio: 1.5), two well separated convective-diffusion controlled oxidation processes were observed at both a gold and a platinum ring during aluminium electrodeposition at the disc. On the basis of the data presented, a reaction scheme involving reduction of A1(III) to A1(0) via A1(I), followed by chemical dissolution of A1(0) into the bulk electrolyte was proposed. The loss of current efficiency in aluminium smelting was primarily attributed to the chemical dissolution of A1(0), rather than to the formation of a subvalent intermediate species.