机械力活化合成机制研究

用两种球磨方式活化氧化铝,用化学分析法测量氧化铝碳热还原反应后生成氮化铝的转化率,考察了球磨活化对氧化铝碳热还原反应合成氮化铝的作用,研究了机械力活化合成的机制。结果表明,氧化铝与碳粉混合球磨时对碳热还原反应的作用远小于氧化铝单元单独球磨时对反应的作用,经球磨活化后,氧化铝碳热还原的反应温度降低,两相复合结构机制不能合理地解释这一实验结果。本研究认为,球磨过程中晶粒尺寸细化至纳米级以及显微应变的存在是球磨化活化促进化学反应的主要原因。     

AlON的合成工艺

分析了合成AlON的各种方法,用模式识别结合神经网络对碳热还原氮化合成AlON工艺进行了优化,利用模式逆映射得到了理想的合成工艺参数,对AlON体系进行了热力学初步分析,计算了温度为2073K时合成AlON的热力学参数状态图,根据热力学参数状态图所确定的条件,热压合成AlON陶瓷,对所合成的AlON试样进行了X射线衍射标定及部分物理性能的测定,其密度为3．63g/cm^3,约为其其理论密度为97．8％。     

矾土碳热还原氮化合成Ca-α-Sialon及热力学研究

从热力学上分析了Ca-α-Sialon相的合成过程。研究了以高铝矾土为原料,碳热还原氮化合成Ca-α-Sialon的影响因素,包括还原剂的用量、氮化温度和时间等。结果表明:以矾土为原料,1550°C碳热还原氮化反应可以合成Ca-α-Sialon,适当过量的碳有利于Ca-α-Sialon的氮化还原合成。     

碳热还原氮化法合成MgAlON

利用重力计,比重仪,SEM,XRD,碳素分析仪,XFS和氧氮分析仪检测了不同加热条件下碳热还原氮化法合成镁阿隆(MgAlON)的密度、微观结构、相组成以及Mg,Al,O,N和C含量,讨论了碳热还原氮化法合成MgAlON的机理.结果表明,加热温度为1100℃时,原料中所有的MgO反应生成镁铝尖晶石(MgAl_2O_(4ss));当加热温度高于1300℃时,发生碳热还原氮化反应,N固溶于MgAl_2O_(4ss)生成MgAlON;由于碳热还原氮化反应不断消耗Al_2O_3,加热温度为1600℃时试样中Al_2O_3大颗粒的尺寸较加热温度为1500℃时的小;随着石墨和Al_2O_3在反应过程被完全消耗,在1650℃下加热获得了单相MgAlON.另外,碳热还原氮化反应中N原子向尖晶石结构MgAl_2O_(4ss)中固溶时导致晶格畸变而使原子间隙扩大,从而Al在MgAlON的固溶量高于其在MgAl_2O_(4ss)中的固溶量.由于碳热还原氮化反应过程产生气体及高温下Mg蒸汽分压较高,即使加热温度提高至1800℃,试样中仍然存在大量密闭气孔.     

固态氧化铝碳热还原反应研究进展

固态氧化铝碳热还原反应在陶瓷材料及铝冶金领域得到广泛的应用和研究,但其反应机理至今未能得到统一的认识。介绍氧化铝碳热还原过程形成的固态、气态产物,阐述3种主要反应机理。提出固-固相反应机理缺乏直接证据,气-固相反应机理与热力学分析及实验不符,而氧化铝分解反应机理较合理。可能的反应机理如下:氧化铝分解为含铝气体和氧气,碳与氧气反应以降低氧分压,含铝气体再次反应形成最终产物,在减压或氩气下形成碳化铝、碳氧化铝等,在氮气下形成氮化铝。并提出了系统解释固态氧化铝碳热还原反应需要继续研究的方向。     

真空下碳热还原氧化铝的二次反应

通过热力学分析和实验研究了真空条件下碳热还原氧化铝的二次反应.热力学分析表明:低温、高压有利于碳热还原氧化铝的产物Al2O、Al与CO的二次反应.分别绘制了Al2O和Al在一定分压下,与CO的二次反应平衡曲线图,给出了各二次反应的CO平衡分压与温度的关系,根据CO的分压和温度、利用二次反应平衡曲线图分析二次反应的产物.氧化铝与石墨的真空碳热还原实验研究证实:Al2O与CO降低温度首先生成Al4O4C和C,Al与CO降低温度首先生成Al4O4C和Al4C3,符合根据二次反应平衡曲线图分析得到的结论,说明二次反应平衡曲线图的合理性.     

Thermodynamic Analysis and Preparation of Composites in Zr-Si-C-N-O System

为了得到锆英石碳热还原氮化反应时产物相的稳定存在区域,用ΔfG1=A+BT法对Zr-Si-C-N-O系进行了热力学计算和分析,绘制了Zr-Si-C-N-O系优势区相图。结果表明:通过控制配碳量、反应温度、炉内的CO分压和N2分压,可以获得组成分别为ZrO2-Si2N2O、ZrN-Si2N2O或ZrN-Si3N4等的复相材料。根据热力学分析结果,以锆英石、活性炭为原料,N2(99.999%)为氮源,研究了配碳量(10%,20%,22%,30%,质量分数)对锆英石碳热还原氮化反应失重率及产物相组成的影响。结果表明:配碳量不仅显著影响锆英石碳热还原氮化反应产物的物相组成,而且配碳量的增加还会降低锆英石碳热还原氮化反应的开始温度。     

低Al2O3矾土碳热还原氮化合成复相Sialon的研究

利用低品位铝矾土经碳热还原氮化合成得到复相Sialon。采用XRD、SEM和EDS等研究了合成温度（分别为1300、1400、1500、1600℃），碳含量（分别为理论量、过量10％、过量50％和过量100％）对合成产物的影响。结果表明：以低品位铝矾土为原料，碳黑为还原剂，碳加入量为理论量，在0．9MPa流动氮气下经1600℃，3h碳热还原氮化反应合成出了α-Sialon和β-Sialon，其中α-Sialon晶体呈六方柱状结构。     

真空下碳热还原氧化铝的热力学

对真空条件下碳热还原氧化铝进行热力学研究.结果表明:在1 643～1 843 K的温度范围内,真空碳热还原氧化铝生成气体产物,该气体在温度降低时发生二次反应形成冷凝物,反应过程中体系压力保持在5～150 Pa.热力学分析表明:当体系压力为1～100 Pa时,在1 200～1 900 K的温度范围内,碳热还原氧化铝生成Al2O、Al和CO;生成Al2O的初始反应温度低于生成Al的初始反应温度,但反应温度高于一定值时,更易生成Al气体,该温度取决于体系的压力;当CO的分压分别为1、10和100 Pa时,Al2O稳定存在的温度分别高于1 462、1 560和1 674K,Al气体稳定存在的温度分别高于1 514、1635和1 777K.     

铝热还原法合成AlON粉体及其热力学分析

以微米级的Al粉和纳米级Al_2O_3粉为原料, 在N_2气氛下,通过铝热还原法,进行了AlON粉体的合成.实验表明,在1873～1923 K之间,AlON相开始形成,到2023 K时得到纯相AlON粉体.通过拟抛物线规则计算得到AlON的摩尔生成吉布斯能, 进而算得AlON相形成的转变温度为1887 K.热力学分析表明,铝热还原法合成AlON过程中,各物相易受气氛、温度的影响而表现出不同的热力学行为,进而影响合成的纯相AlON的固溶组分.实验结果与理论计算分析相符合.     

AlON粉体的合成

以α-Al_2O_3和AlN为原料,利用高温固相反应在氮气气氛下常压合成了AlON粉体.研究了成分配比、合成温度、保温时间对合成AlON粉体含量的影响,并通过热分析测试了合成过程热流和质量的变化.结果表明,当原料Al_2O_3和AlN的质量比为81:18、合成工艺为1750 ℃, 2 h时,得到AlON相的含量达到95%以上.     

Phase reaction and sintering behavior of a Al2O3–20wt%AlN–5wt%Y2O3 system

Two major problems exist in the processing of AlN. The first is the difficulty in achieving full densification even at relatively high sintering temperatures. The second is the formation of the spinel phase, AlON. Pure AlN sintered at temperatures up to 2000°C have produced no more than 90–93% densification in the former case, while AlN rich ternary systems (AlN–Al₂O₃-sintering agent) have resulted in the detrimental formation of AlON well before full densification can occur. This paper reports on the phase reaction and sintering behavior of a ternary Al₂O₃–AlN–Y₂O₃ system near the critical temperature range of 1600–1700°C, in a carbo-thermal reduction furnace in a fully nitrogen environment. Full densification (>98%) for AlN without the formation of AlON was achieved by sintering an initial Al₂O₃ rich ternary system (Al₂O₃–20wt%AlN–5wt% Y₂O₃) at a relatively low temperature of 1680°C. Formation of the AlON was delayed until 1700°C, at which a stoichiometric γ-AlON (Al₃O₃N) with spinel type structure was obtained. Thermal conductivity values for a sintered substrate obtained with low oxygen content within the AlN matrix reached 125 W m⁻¹ K⁻¹.     

Nitriding aluminum alloys by N-multicharged ions implantation: Correlation between surface strengthening and microstructure modifications

This paper deals with the surface strengthening of aluminum alloys by means of a new process allowing multi-charged nitrogen ion implantation. X-ray photoelectron spectroscopy, grazing-incidence X-ray diffraction and atomic force microscopy were used to study microstructural changes involved by implantation. This microstructural study revealed the formation of AlN and AlONγ due to the low nitrogen concentration gradient obtained with multi-charged implantation. Nanoindentation and wear tests were performed to evaluate the mechanical properties of implanted surfaces. A significant improvement of wear resistance was observed as a consequence of the nitride protective layer formation. The observed surface hardening is attributed to both AlONγ and AlN formations and to the precipitation-induced stress.     

TiN/AlN复合材料的等离子烧结

采用等离子技术,在1600℃的温度和50 MPa的压力、不同保温时间的条件下实现TiN/AlN纳米复合粉的快速烧结。随着保温时间的延长,材料致密性有所改善,在保温15 min后获得最大密度,HRA=93,ρ=4.346 g/cm~3;随后由于颗粒的长大密度有所下降。XRD分析主相为TiN,局部温度过高导致氮缺位,晶格常数增大,衍射峰较烧结前略有左偏;次相为AlN,但由于在烧结过程中存在应力,其衍射峰较烧结前略有右偏,同时在烧结过程中有轻微氧化现象生成AlON相。用SEM分析了试样断口形貌,主要呈现沿晶断裂。     

STRUCTURES OF γ Al_2O_3 AND AlON STUDIED BY ~(27)Al NMR AND QUANTUM CHEMISTRY CALCTLATIONS

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Development of Si_3N_4/Al composite by pressureless melt infiltration

1 Introduction Composites of ceramic/metal or metal/ceramic are expected to have properties superior to their constituents alone[1?4]. However, the fundamental difference in atomic bonding between metals and ceramics results in quite different physical a…     

反应磁控溅射TiN/AlON纳米多层膜的微结构与显微硬度

采用Ti靶和Al2O3靶在Ar、 N2混合气氛中进行反应磁控溅射的方法,制备了一系列不同AlON层厚度的TiN/AlON纳米多层膜,利用EDS、XRD、HRTEM和微力学探针研究了AlON的形成条件以及AlON调制层厚的改变对多层膜生长方式和显微硬度的影响.结果表明,在Ar、N2混合气氛中对Al2O3进行溅射,N原子会部分取代Al2O3中的O原子,形成非晶态的AlON化合物.在TiN/AION纳米多层膜中,由于TiN晶体层的模板效应,AlON层在厚度小于0.6 nm时被强制晶化并与TiN形成共格外延生长结构,多层膜显示出最高硬度达40.5 Gpa的超硬效应;进一步增加AlON的层厚,其生长模式由晶态向非晶态转变,破坏了多层膜的共格外延生长结构,多层膜的硬度随之降低.     

Fabrication of AlN-TiC/Al composites by gas injection processing

1. Introduction Al-based metal matrix composites (MMCs) with ceramics like SiC, Al2O3, TiC, AlN, TiN, and TiB2 as the reinforcement phase have been widely studied by some researchers. It has been reported that TiC and AlN are particularly attractive because of good wettability and high stability with molten aluminum, high hardness, and elastic modulus [1-4]. To fabricate MMCs, various techniques have been developed. Among these, the in situ technolo- gies are particularly attractive b…     

The effects of nanoparticle addition on binder removal from injection molded aluminum nitride

The effects of nanoparticle addition on the multi-step debinding of injection molded aluminum nitride (AlN) samples were studied. Experiments varying the solvent debinding conditions (time, temperature and aspect ratio) were performed on monomodal, microscale (μ) and bimodal, micro-nanoscale (μ-n) AlN samples. Variations in the solvent debinding kinetics as a result of the reduced particle size and increased powder content were examined. The bimodal μ-n AlN samples showed a slower solvent extraction of binder components compared to monomodal μ-AlN samples. The activation energy for solvent extraction estimated from diffusion coefficients (Arrhenius equation) was in close agreement with the value estimated by the master debinding curve (MDC) method. An activation value around 50 kJ/mol was estimated by both the methods for μ and μ-n AlN samples. The thermal debinding behavior of dewaxed samples was also studied and the trends correlated with the solvent debinding behavior.