复杂铝热反应的平衡热力学分析

利用最小自由能原理对复杂铝热反应(Fe₂O₃+Cr₂O₃+CrO₃+NiO+O₂+N₂+TiO₂+C+S+CaO+Al)过程进行了平衡热力学分析,计算了铝热剂成分、预热温度、惰性添加剂对平衡产物成分、反应热和绝热温度的影响。结果表明,平衡产物中除了Al₂O₃,Fe,Cr,Ni等产物外,还有可能生成TiC, Cr₇C₃, CrN, AlNi,Ni₃Al,FeAl₂O₄,CaS,TiN等物质。随着铝热剂中Al含量的增加,平衡产物中生成铝镍金属间化合物的倾向增加。CaO有除S的作用,此外,CaO还使体系的绝热温度降低。提高预热温度,体系的绝热温度升高。     

热爆反应合成钒铝碳材料

以V、Al和C粉体为原料,采用热爆合成技术制备V2AlC材料,并对V-Al-C体系进行了热力学分析,利用X射线衍射和扫描电镜对合成产物进行了相组成和产物形貌分析,探讨了热爆反应合成V2AlC材料的反应机制。结果表明,V-Al-C体系的绝热燃烧温度达2767K;2V/Al/C粉体热爆合成产物的主相为V2AlC,并含有少量的VCx和AlV3;原料中添加过量的Al,可消除AlV3副产物,并显著地促进V2AlC反应合成;2V/1.3Al/C热爆产物中V2AlC呈片状和板条状两种晶体形貌,长度大约为10μm;热爆反应合成V2AlC的机制为VC与V-Al共晶液相反应合成V2AlC。     

超重力场反应连接制备TiB_2-TiC/1Cr18Ni9Ti和TiB_2-TiC/Ti-6Al-4V梯度复合材料

以1Cr18Ni9Ti、Ti-6Al-4V为金属基底,通过在B4C+Ti体系中引入CrO_3+Al铝热剂,调整反应体系绝热温度依次为3 193、3 282、3 290及3 473K,采用超重力场反应连接制备TiB_2-TiC/1Cr18Ni9Ti和TiB_2-TiC/Ti-6Al-4V梯度复合材料,发现随着反应绝热温度升高,陶瓷/金属界面区厚度不仅因金属熔深增加而增大,并且残存于界面上的Al_2O_3夹杂也随之增多。分别对B4C+Al体系与CrO_3+Al铝热剂进行配制、球磨活化、压制成坯并依次填料入坩埚后,发现残存于界面上的Al_2O_3夹杂完全消除,同时发现在TiB_2-TiC/1Cr18Ni9Ti界面上生成三维网络陶瓷/金属梯度复合结构,而在TiB_2-TiC/Ti-6Al-4V界面上形成跨尺度多层次梯度复合结构。     

CuO/Al反应自生复合材料的热力学研究

在CuO Al体系的热力学试验和理论分析的基础上 ,对体系反应的热力学进行探讨 ,论证了CuO Al低温合成反应在热力学上是可行的。建立了体系的绝热温度的一般表达式 ,并且从理论上探讨了Al粉含量和反应温度对反应绝热温度的影响。计算了CuO Al体系在不同温度下的热效应值。     

TiC/NiCrMoAlTi金属陶瓷烧结过程研究

用DTA方法研究了TiC/NiCrMoAlTi金属陶瓷复合材料体系烧结过程,结果表明：温度升高到590－665℃,Al与Ni发生反应,生成NiAl3,Ni2Al3,NiAl和Ni3Al,继续升温到体系出现液相时,除NiAl外的其它产物均以[Al]和[Ni]形式溶于液相中,在随后冷却阶段,在粘结相基体中沉淀析出金属间化合物Ni3Al。该金属陶瓷体系真空烧结液相出现温度约为1330℃。     

CuO／Al反应自生复合材料的热力学研究

在CuO/Al体系的热力学试验和理论分析的基础上，对体系反应的热力学进行，论证了CuO/Al低温合成反应在热力学上是可行的，建立了体系的绝热温度的一般表达式，并且从理论上探讨了Al粉含量和反应温度对反应绝热温度的影响，计算了CuO/Al体系在不同温度下的热效应值。     

稀释剂Al2O3对NiO／Al体系燃烧速度的影响及其表观反应激活能计算

研究了Al2O3稀释剂添加量对NiO／Al体系燃烧速度及体系产物形貌的影响,结合绝热温度的计算结果,基于Merzhanov等提出的燃烧波速公式,根据体系In（v／Tnd）-1／Ld的Arrhenius图,测定了添加Al2O3后NiO／Al体系的反应激活能。研究结果表明：对于NiO／Al体系,在一定范围内（0～5％,25...     

熔融Ni与固态多晶α型Al2O3的润湿现象

采用座滴法观察了熔融Ni与固态多晶α型Al2O3间的润湿行为,测定了1773 K、1823 K和1873 K温度下的接触角,分析了接触角变化规律,评价了二者间的润湿性.结果表明,在1773～1873 K温度范围内,温度对初始接触角的影响不大,约为115°;熔融Ni与固态多晶α型Al2O3间发生反应,在界面生成45%Al-12%Ni-43%O物质,接触角随着时间的延长而下降,由此判定熔融Ni与固态多晶α型Al2O3间的润湿行为为反应润湿;1873 K温度下,当界面反应达到平衡时,还原气氛中的熔融镍的表面张力增加将导致接触角升高.     

TiC-Al2O3/Fe3Al复合粉末的燃烧合成

以天然钛铁矿为主要原料,采用燃烧合成技术制备了TiC-Al2O3/Fe3Al金属间化合物/陶瓷基复合材料.研究了预热时间和热处理对燃烧合成过程及产物的影响.研究结果表明:随着预热时间的延长,燃烧温度和燃烧波速率都增加,产物晶胞参数增大,合成更为完全,无序固溶相进行有序化转变的程度增大.当预热5min时,Fe3Al有序金属间化合物的量明显高于无序固溶相,但继续延长预热时间很难将无序相消除;在750℃下进行热处理,可以制备出以Fe3Al金属间化合物为主要成分的复合粉体.     

Ni 含量对SHS 法合成TiC-Ni 基金属陶瓷的影响

利用SHS 结合准热等静压(PH IP) 技术制备了TiC-Ni 基金属陶瓷, 理论分析和实验显示, 绝热温度T_ad和燃烧温度T c 随Ni 含量的增加而降低, 反应温度影响产物的组织形貌,Ni 含量的增加使合成的TiC 颗粒尺寸变小, 并且逐渐趋向于规则的球形。最后的产物均由TiC 和Ni 两相组成。产物的致密度随Ni 含量的增加逐渐提高, 硬度值随Ni 含量的变化而变化, 两种因素的作用使硬度值在Ni 含量为20% 时达到最大。     

Self-propagating high-temperature synthesis of Al2O3-TiC-Al composites by aluminothermic reactions

Al₂O₃-TiC-Al composites were fabricated by self-propagating high-temperature synthesis process using aluminothermic reactions with titania, aluminum, and graphite powders. As the molar ratio x of the excessive aluminum in the reactants increases, the adiabatic temperature of the reaction and the melting rate of alumina in the products obviously decrease according to thermodynamics. This reaction is theoretically presumed to be ignited at preheat temperature of 900 K even though x is up to 13 mole. The experimental results revealed that the critical molar ratio of excessive Al, which the combustion reaction can self-sustain, is 7.66 mole with a preheat temperature of 400–500 K. The excessive aluminum favors to fill in the pores of the products, and a cylindrical Al₂O₃-TiC-Al composite with a relative density of 70% can be obtained, and its tensile strength is higher ten times than that of the Al₂O₃-TiC composite. Moreover, TiC and Al₂O₃ grains in the composites are fined as the excessive aluminum increases. Although the excessive aluminum does not take part in the combustion reaction, it strongly affects combustion process and microstructures of the products.     

Interaction between liquid aluminum and NiO single crystals

The wetting behavior of NiO single crystal by liquid aluminum has been studied by the sessile drop method under vacuum at 973–1273 K for 2 h. Optical microscopy, SEM, EDS and X-ray analysis were applied to characterize the structure and chemistry of solidified cross-sectioned sessile drop couples. Under tested conditions, molten Al wets and reacts with NiO to form Al₂O₃ and Ni. This leads to alloying of the initially pure Al drop with Ni to the hypereutectic composition and to the formation of a thick reaction product region inside the NiO substrate, whose structure presents interpenetrated networks of fine alumina precipitates and an Al–Ni matrix. After solidification the Al–Ni matrix and the drop have the same phase composition, which is in agreement with Al–Ni phase diagram, showing the formation of Al₃Ni at T < 1128 K and Al₃Ni₂ at 1128 K < T < 1406 K. The strong reactivity of Al/NiO couples, accompanied with the drop deformation, fragmentation of the reaction product region and development of a crater under the drop, contributes to the perturbation of the triple line and to the formation of apparent contact angles at 1073–1273 K. This leads to unusual changes of measured contact angles with temperature, decreasing from 84^° at 973 K to 36^° at 1073 K, and then increasing to 75^° at 1273 K, while structural analysis suggests complete wetting at 1073 K.     

Synthesis of Al2O3 matrix composites by reactive infiltration

Reactive infiltration of a NiO-base blended powder with molten aluminium was attempted at 1673 K in order to obtain Al2O3 matrix composites containing a dispersion of Al3Ni, AlNi and/or AlNi3. The NiO powder was barely infiltrated by the molten aluminium after a 3600 s holding time at 1673 K. A continuous layer of Al2O3 was observed to exist at the infiltration front, which prevented any further infiltration. TiB2 particles were added to the NiO powder in order to absorb the heat of reaction between NiO and aluminium. When the TiB2 particle content in the [NiO+TiB2] powder blend was greater than 20 vol%, spontaneous infiltration occurred completely. Thus, it was shown that the addition of the TiB2 particles assisted in the spontaneous infiltration. The specimens produced by the in situ reaction consisted of Al2O3, TiB2 and Al3Ni. Al3Ni was mainly located between the TiB2 and Al2O3. The effect of the TiB2 addition on the infiltration kinetics was to decrease the maximum attainable temperature caused by the exothermic reaction. This in turn prevented the formation of a continuous Al2O3 film at the infiltration front. This resulted in the production of pathways for the infiltration of the molten aluminium and made possible the complete infiltration. This revised version was published online in November 2006 with corrections to the Cover Date.     

铝电解用NiFe2O4-10NiO基陶瓷铁元素优先腐蚀研究

在高温熔盐电解质78.07%Na3AlF6-9.5%AlF3-5.0%CaF2-7.43%Al2O3中对NiFe2O4-10NiO基陶瓷进行了电解腐蚀性能研究,结果发现烧结后的陶瓷NiFe2O4相中的Fe/Ni比为2.211～2.89,且NiO相的Fe/Ni比为0.136～0.34,而电解腐蚀后NiFe2O4相中的Fe/Ni比为2.07～2.335,且NiO相中Fe/Ni比为0.120～0.195,说明在电解腐蚀过程中Fe元素发生了优先腐蚀。铁元素在电解过程中发生优先腐蚀的原因可能是化学腐蚀和电化学腐蚀共同作用的结果。     

磁性多层膜的X射线光电子能谱研究

用射频 /直流磁控溅射法制备了NiOx/Ni81Fe19和Co/AlOx/Co磁性薄膜。利用X射线光电子能谱研究了NiOx 对Ni81Fe19耦合交换场Hex与NiOx 化学状态的关系以及Co/AlOx/Co磁性薄膜中AlOx 对Co膜的覆盖状况。结果表明 :Hex的大小只与 2价镍有关 ,单质镍和 3价镍对Hex没什么作用 ;在Co/AlOx/Co磁性薄膜中 ,Al层将Co膜完全覆盖所需要的最小厚度为 2 .0nm ,用角分辨XPS测出的Al氧化厚度为 1 15nm     

Al-TiO2-C-Ti-Fe体系的燃烧模式研究

采用与计算机相连的快速图像采集系统对Al-TiO2-C-Ti-Fe体系的燃烧模式进行研究。结果表明，燃烧波蔓延模式随着Fe含量的增中即绝热温度的降低，由稳定的平面燃烧逐渐转化为非稳定的多点波动燃烧，然而随着Fe含量进一步增加，燃烧模式又转化为稳定的平面燃烧。     

溅射Ni11Co26Cr6Al0.5Y涂层对镍基合金在1000 ℃氧化行为的影响

通过对有/无Ni11Co26Cr6Al0.5Y涂层镍基合金在1000℃进行氧化动力学曲线测定,及组织结构观察,研究了Ni11Co26Cr6Al0.5Y涂层对镍基合金高温氧化行为的影响。结果表明:高温氧化期间,合金发生外氧化和内氧化,外氧化层由NiO、NiCrO_4、CoWO_4构成,中间氧化物由TiO_2、Al_2O_3、NiWO_4构成,中间层氧化物层抑制了基体中Al元素向外扩散,形成平直连续的Al_2O_3内氧化物层;合金氧化动力学曲线呈现起伏波动的特征。镍基合金经溅射Ni11Co26Cr6Al0.5Y涂层,可有效改善合金的抗氧化性能;涂层的氧化动力学曲线仅在氧化初期有轻微增重而后趋于平稳,遵循抛物线规律,其形成的Al_2O_3氧化膜未发生明显剥落,仅在涂层内及近涂层/基体界面区域存在少量Al_2O_3内氧化物。