LiF对Na_3AlF_6-K_3AlF_6-AlF_3熔体初晶温度和Al_2O_3溶解度的影响

采用步冷曲线法测定Na3AlF6-K3AlF6-AlF3-LiF熔体的初晶温度,采用旋转刚玉片质量损失法测定Al2O3在Na3AlF6-K3AlF6-AlF3-LiF熔体中的溶解度。结果表明:当LiF添加量在0～4%范围内时,每添加1%LiF使Na3AlF6-K3AlF6-AlF3熔体的初晶温度降低3～4.7℃,小于Na3AlF6-AlF3熔体中添加LiF后初晶温度的影响;在0～3%的范围内,每添加1%LiF将使Al2O3在Na3AlF6-K3AlF6-AlF3熔体中的溶解度降低0.23%～0.55%。     

Influence of AlF3 and hydrothermal conditions on morphologies of α-Al2O3

Homogeneous α-Al2O3 platelets were synthesized by introducing AlF3 to alumina precursor.The effects of AlF3 additive on the phase transformation and morphology of the prepared α-Al2O3 platelets were investigated.The results show that a single phase of α-Al2O3 with an average particle size of 8μm can be obtained at 900℃ with 2% AlF3 additive.The transformation temperature decreasing IS attributed to introduction of Al3 vacancy and to the formation of intermediate compound of AlOF,which is considered to accelerate the mass transportation from transitional Al2O3 to α-Al2O3.AlF3 concentration and hydrothermal temperature can also affect the morphology of α-Al2O3.When hydrothermal temperature is 120℃,the morphology of α-Al2O3 transforms from irregular to flat hexangular platelet with increasing AlF3 concentration.As hydrothermal temperature increases,the morphology of α-Al2O3 with 2% AlF3 additive changes from polyhedron to hexangular platelet and then to vermicular.     

Influence of AlF3 and hydrothermal conditions on morphologies of α-Al2O3

Homogeneous α-Al2O3 platelets were synthesized by introducing AlF3 to alumina precursor.The effects of AlF3 additive on the phase transformation and morphology of the prepared α-Al2O3 platelets were investigated.The results show that a single phase of α-Al2O3 with an average particle size of 8μm can be obtained at 900℃ with 2% AlF3 additive.The transformation temperature decreasing IS attributed to introduction of Al3 vacancy and to the formation of intermediate compound of AlOF,which is considered to accelerate the mass transportation from transitional Al2O3 to α-Al2O3.AlF3 concentration and hydrothermal temperature can also affect the morphology of α-Al2O3.When hydrothermal temperature is 120℃,the morphology of α-Al2O3 transforms from irregular to flat hexangular platelet with increasing AlF3 concentration.As hydrothermal temperature increases,the morphology of α-Al2O3 with 2% AlF3 additive changes from polyhedron to hexangular platelet and then to vermicular.     

AlF3添加剂和焙烧温度对铝电解炭阳极过电位的影响

在实验室制备各类AlF3掺杂试验阳极，在测试其基本物理化学性能的基础上，采用“改进断电流法”进行阳极过电位测试，研究AlF3添加剂和阳极焙烧温度对阳极过电位的影响。结果表明：在一定条件下，阳极中添加AlF3既可降低阳极的空气／CO2反应活性，也可降低阳极过电位；受高温脱S等因素的影响，阳极的电化学活性及其空气／CO2反应活性并未随着焙烧温度的提高相应降低。     

添加剂对自蔓延法制备Cu-Cr合金的影响

以CuO、Cr2O3、Al为原料,采用自蔓延法制备Cu-Cr合金,考察了不同添加剂对Cu-Cr合金结构和纯度的影响。结果表明,合金由Cu、Cr相以及少量的Cr23C6相组成,熔渣由Al2O3相和Na3AlF6相以及少量的Cr相组成,熔渣中存在Cr相表明渣分离效果不理想。随着Na3AlF6配料量的增加,合金中氧化物夹杂得到有效去除,合金的微观结构变得致密均匀。随着铝粉配料量的增加,合金中氧含量降低,但铝残留量增加,合金的纯度大于97.0%。     

AlF3添加剂对氧化铝粉体微观结构的影响

在醇盐水解法制备a-Al2O3工艺过程中引入AlF3作为添加剂,通过XRD、SEM研究了AlF3加入量、水热条件、热处理温度对产物晶相及微观形貌的影响.研究结果表明:AlF3加入可使α-Al2O3相在800℃至900℃之间形成;相同水热温度下,随AlF3加入量增大,α-Al2O3的微观形貌是从不规则的板状结构向嵌入式六角板状结构发展;随水热温度升高,αa-Al2O3的微观形貌则由多面体结构向六角板状结构再到"蠕虫状"结构转变.     

铝电解质中Al_2O_3溶解度研究进展

Al2O3溶解度是铝电解用电解质熔体最重要的物理化学性质之一。本文综述了Al2O3在Na3AlF6中、Na3AlF6-AlF3体系中、在现行工业铝电解质中及钾盐中的溶解度。指出了钾盐应成为未来铝电解质的研究方向。     

酸性NaF-AlF3熔盐离子结构的Raman光谱

采用紫外激光Raman光谱,在封闭样品池中研究不同分子比的酸性NaF-AlF3熔盐的离子结构。结果表明：当电解质分子比为1时,熔盐中的铝氟离子团只以AlF4-的形式存在,而对于分子比大于1的酸性电解质,熔盐中有AlF4-和AlF63-两种铝氟离子团形式;随着温度的增加,AlF63-离子团的”寿命“越来越短,而且AlF63-特征波段峰的峰位随分子比的增加而发生红移,温度对AlF4-的”寿命“影响不大。Raman光谱的定量分析表明,在测量的熔盐配重分数区间内,温度对于熔盐中各离子摩尔分数的影响不大,而且F-含量很小,当NaF的配重摩尔分数为0.60时,AlF4-的摩尔分数在0.75左右,AlF63-的摩尔分数仅约为0.25;当NaF的配重摩尔分数增至0.71时,AlF4-的摩尔分数降为0.25左右,AlF63-增为约0.75。     

Na3AlF6-Al2O3熔盐的Raman光谱和离子结构

基于测定的熔融冰晶石的Raman光谱和对散射系数的新理解,重新分析以前研究的942～1024℃的酸性NaF-AlF3熔盐中存在的不同离子团的含量。新的定量分析结果表明：对于分子比小于2的熔盐,AlF4-是含量最高的阴离子;当分子比为1.5时,其摩尔分数约为0.70;当分子比为2时,其摩尔分数为0.50。当分子比大于2.5时,AlF6^3-相对含量更高;当分子比为2.5时,其摩尔分数为0.45。然后,采用紫外Raman光谱法研究Na3AlF6-Al2O3熔盐的离子结构。研究结果表明：熔盐中存在八面体的AlF63-和四面体的AlF4^-,基团中的F-可能被O^2-部分取代。在Al2O3的质量分数大于4%的熔盐中存在具有大散射系数的Al2O2F4^2-。光谱中的波段随温度的升高发生蓝移。     

酸性NaF-AIF3熔盐离子结构的Raman光谱

采用紫外激光Raman光谱,在封闭样品池中研究不同分子比的酸性NaF-AIF3熔盐的离子结构.结果表明:当电解质分了比为1时,熔盐中的铝氟离子团只以AlF4的形式存在,而对于分子比大于1的酸性电解质,熔盐中有AlF4和AlF6两种钳氟离子团形式;随着温度的增加,A1F6离子团的"寿命"越来越短,而且AlF6特征波段峰的峰位随分子比的增加而发生红移,温度对AlF4的"寿命"影响不大.Raman光谱的定量分析表明,在测量的熔盐配重分数区间内,温度对于熔盐中各离子摩尔分数的影响不大,而且F含量很小,当NaF的配重摩尔分数为0.60时,AlF4的摩尔分数在0.75左右,AIF6的摩尔分数仅约为0.25;当NaF的配重摩尔分数增至0.71时,AlF4的摩尔分数降为0.25左右,AlF6增为约0.75.     

Uniform AlF3 thin layer to improve rate capability of LiNi1/3Co1/3 Mn1/3O2 material for Li-ion batteries

LiNi1/3Co1/3Mn1/3O2 was coated with uniform nano-sized AlF3 layer by chemical precipitation method to improve its rate capability. The samples were characterized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), charge-discharge cycling, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Uniform coated layer with a thickness of about 3 nm was observed on the surface of LiNi1/3Co1/3Mn1/3O2 particle by TEM. At 0.5C and 2C rates, 1.5% (mass fraction) AlF3-coated LiNi1/3Co1/3Mn1/3O2/Li in 2.8-4.3 V versus Li/Li+ after 80 cycles showed less than 3% of capacity fading, while those of the bare one were 16.5% and 45.9%, respectively. At 5C rate, the capacity retention of the coated sample after 50 cycles maintained 91.4% of the initial discharge capacity, while that of the bare one decreased to 52.6%. EIS result showed that a little change of charge transfer resistance of the coated sample resulting from uniform thin AlF3 layer was proposed as the main reason why its rate capability was improved obviously. CV result further indicated a greater reversibility for the electrode processes and better electrochemical performance of AlF3-coated layer.     

论新型干法氟化铝生产工艺与主要设备

从给料酸的配制及设备,氟化氢的生成及反应炉设备,氟化氢的净化及设备,氟化铝的生成及流化床设备,紧急吸收与石膏系统等方面探讨了新型干法氟化铝生产工艺与主要设备。     

Coupled heat/mass-balance model for analyzing correlation between excess AlF3 concentration and aluminum electrolyte temperature

The influence of aluminum electrolyte component on its temperature is an important issue within the field of aluminum reduction with pre-baked cells. The characteristic correlation between excess AlF3 concentration and aluminum electrolyte temperature was explored through the modeling of heat and mass transfer processes in industrial pre-baked aluminum reduction cells. A coupled heat/mass-balance model was derived theoretically from the mass and energy balance of an electrolysis cell, and then was simplified properly into a practical expression. The model demonstrates that if environmental temperature and Al2O3 concentration keep constant, the excess AlF3 concentration decreases with the aluminum electrolyte temperature linearly and its decrease rate is dependent on the heat transfer property of aluminum electrolyte, side wall and cell shell. Secondly, experiments were conducted on site with two industrial cells in an aluminum electrolysis plant. Excess AlF3 concentration and aluminum electrolyte temperature were obtained simultaneously together with other parameters such as Al2O3, CaF2, MgF2 and LiF concentrations. Results show that the maximum absolute error between the tested value and the calculated value of excess AlF3 concentration using the proposed model is less than 2%. This reveals that the coupled heat/mass-balance model can appropriately characterize the correlation between excess AlF3 concentration and aluminum electrolyte temperature with good accuracy and practicability.     

Equivalent conductivity and its activation energy of NaF-AlF3 melts

Electrical conductivity of NaF-AlF3 melts was measured by continuously varying cell constant(CVCC) technique. Relationships between equivalent conductivity at 990-1 030 ℃ and temperature and composition, and relationship between equivalent conductivity activation energy and composition of the melts were then studied on the basis of two-step decomposition mechanism of AlF63-. According to the changes of molar fractions of different anions in NaF-AlF3 melts, courses of dependence of equivalent conductivity and its activation energy on composition were analyzed. The results show that the influence of temperature on equivalent conductivity of the melts is small in the researched temperature range, and equivalent conductivity increases with increasing the molar fraction of AlF3; there is a minimum point in the activation energy-composition curve when molar fraction of AlF3 is 0.29.     

氟铝酸铵的热分解及氟化铝的制备

采用DTA-TGA法研究了（NH4）3AlF6的热分解过程并获得了相关的热力学数据。结果表明,（NH4）3AlF6经三步分解后,固态产物为AlF3,前两步分解的固态产物分别为NH4AlF4和AlF3（NH4F）0.69,三级反应的分解温度分别为194.9,222.5和258.4℃;计算了3个反应温度下相关物质的吉布斯自由能变化,采用DSC法测量了3个反应的焓变和熵变。制备了无水氟化铝,XRD分析和失重分析表明,（NH4）3AlF6在400℃下保温3h可以得到高纯度的AlF3。     

过冷DD3单晶高温合金的净化影响因素及途径

以特制的复合熔盐作为净化剂在氩气氛保护及循环过热条件下去除DD3单晶高温合金熔体中的异质晶核 ,获得了最大 2 1 0K过冷度。详细探讨了复合熔盐净化机制 ,同时对比分析了纯循环过热和熔融玻璃净化方式对于DD3单晶高温合金获得深过冷的可行性     

铝电解质分子比的定义及分析测定

铝电解质分子比是一项重要的技术参数，然而分子比的定义表达式却多种多样。这给分子比的测定与计算带来不便。本文在电解质的物相和添加剂酸碱性研究的基础上，结合工厂实际。提出电解质分子比的定义，即电解质中总NaF的摩尔分数与总AlF3的摩尔分数的比值。并指出对含MgF2和LiF添加剂的复杂铝电解质也最好采用这一分子比定义表达式。     

氟化钾对固态铝电解质物相的影响

本文用X-射线衍射法研究了KF与冰晶石的反应及其对固态铝电解质物相的影响。研究表明:KF与Na3AlF6(冰晶石)在熔盐中能够发生化学反应,无论是在酸性还是碱性电解质中产物都有K2NaAlF6(钾冰晶石),但在酸性电解质中其反应产物同时有K2NaAl3F12和K2NaAlF6两种物相。随着KF含量的增加以及电解质酸度的增强,K2NaAl3F12的含量增加。本文还提出了K2NaAl3F12物质的生成机理以及对同时含CaF2、LiF、MgF2和KF的铝电解质的物相进行了鉴定。对分子比定义为碱性氟化物与AlF3的摩尔比进行了验证,表明只有这种定义才能够真正体现电解质的酸碱性。