纳米TiO2晶粒生长动力学研究

研究了纳米ＴｉＯ２粒子热处理过程的晶粒生长,结果表明:低于８２３Ｋ锐钛矿晶粒的长大速率较小,８２３Ｋ后锐钛矿晶粒的长大速率显著增加．锐钛矿晶粒的生长动力学符合五次方方程,表观生长活化能由于纳米尺寸和相变效应的影响在高温区和低温区表现不同,高于８２３Ｋ时为(２０１．５５±５．６２)ｋＪ/ｍｏｌ,低于８２３Ｋ时为(３８．６７±６．３７)ｋＪ/ｍｏｌ;金红石晶粒的生长符合二次方方程,表观生长活化能为(１０８．７２±５．０６)ｋＪ/ｍｏｌ．     

多元纳米复合氧化锌压敏陶瓷的晶粒生长

研究了多元纳米复合ZnO电压敏粉体在高温下的烧结行为.应用晶粒生长的动力学方程Gn-G0=K0texp(-Q/RT),确定了晶粒生长的动力学指数n和激活能Q.实验结果表明,随着烧结温度的提高和保温时间的延长,ZnO压敏陶瓷的晶粒不断长大,其动力学指数n=3.2,激活能Q=(185±28)kJ/mol.     

纳米Y-TZP材料烧结过程晶粒生长的分析

分析了无压烧结、热压烧结及SPS烧结过程中晶粒生长的行为及表现活化能．结果表明：在1100～1300℃之间,纳米Y-TZP材料在以上几种烧结条件下的晶粒生长行为不同．无压烧结时晶粒生长较慢,而热压烧结和SPS烧结时晶粒生长较快．对晶粒生长的活化能分析可在一定程度上解释以上现象．分析结果显示：无压烧结的表观活化能为281kJ／mol与纳米Y－TZP材料的晶界扩散活化能相近;热压烧结过程中,由于外压对扩散的促进作用,活化能比无压烧结时略有降低;在SPS烧结过程中,由于外加的脉冲电流能使晶粒表面大大活化,所以活化能与无压烧结相比大幅度下降．     

微波烧结氧化锌压敏电阻的致密化和晶粒生长

研究了微波烧结的ZnO压敏电阻的致密化和生长动力学, 微波烧结温度从900～1200℃, 保温时间从20min～2h. 研究表明, 微波烧结ZnO压敏电阻的物相组成和传统烧结的样品没有区别; 微波烧结有助于样品的致密化, 并降低致密化温度. 随着烧结温度的升高, 致密化和反致密化作用共同影响样品的密度, 其中Bi的挥发是主要影响因素. 微波烧结ZnO压敏电阻的晶粒生长动力学指数为2.9～3.4, 生长激活能为225kJ/mol, 传统烧结的ZnO压敏电阻的晶粒生长动力学指数为3.6～4.2, 生长激活能为363kJ/mol. 液相Bi₂O₃、尖晶石相和微波的“非热效应”是影响微波烧结ZnO压敏电阻陶瓷晶粒生长的主要因素.     

氧化锌纳米晶体的生长及生长机理分析

采用沉淀法生长了不同粒径且性能良好的氧化锌纳米晶体,探讨了晶粒尺寸与煅烧温度的变化关系,研究了ZnO纳米晶体的生长机理.通过实验验证了在中间产物Zn(OH)2中加入NH4HCO3后,ZnO纳米晶体实现了局域生长,很好地阻碍了晶核的过度生长,从而使生成的ZnO纳米晶体保持很小的粒径.煅烧温度较低时,ZnO纳米晶体的生长模式为正常扩散生长,煅烧温度在800℃时,发生了竞争生长现象.     

活性炭载体对TiO2/活性炭中二氧化钛晶粒生长及相变的影响

以活性炭为载体,采用溶胶-凝胶法制备了TiO2/活性炭(TiO2/AC)复合体,并利用SEM和XRD手段对复合体进行表征,通过Dt2=ktnexp(-E/RT)方程的计算,分析,研究活性炭对复合体中TiO2晶粒生长及其相变的影响.结果表明TiO2/AC复合体晶粒粒径增长的时间比TiO2本体短;TiO2/AC复合体纳米粒子平均尺寸为50nm比TiO2本体小;锐钛矿向金红石转变的相变温度和晶粒生长最快温度TiO2/AC复合体比TiO2本体高.锐钛矿和金红石晶粒生长的表观活化能TiO2/AC复合体分别为6.21±1.27和46.54±1.56kJ/mol,TiO2本体分别为5.764±1.02和36.4±1.14kJ/mol.在锐钛矿阶段和金红石阶段TiO2/AC复合体反应指数分别为0.19和0.35,而TiO2本体分别为0.13和0.26.原因是活性炭的强吸附力和非晶相层对TiO2晶粒生长的阻遏作用.     

纳米Cu粉末的SPS烧结与晶粒长大行为的研究

为了研究金属材料在放电等离子烧结(SPS)过程中晶粒的长大行为和激活能的变化情况,利用SEM、FESEM、TEM等技术分析测定了纳米Cu粉坯体在SPS过程中组织形貌和晶粒尺寸的变化情况.研究表明:特定的工艺和烧结制度下,应用SPS技术可以得到均匀、致密的组织;脉冲电流的作用使晶粒表面大大活化,晶粒长大激活能大大降低,材料在迅速烧结的同时,晶粒也迅速长大.     

氧化硅对二氧化钛纳米晶相变和晶粒生长的抑制作用

通过让正硅酸乙酯先水解，用溶胶－凝胶法制备了织构均匀的二氧化硅／二氧化钛复合粉体。用紫外－可见吸收光谱、傅里叶红外，透射电镜、X射线衍射和比表面仪对复合粉体进行了表征，发现添加少量的二氧化硅有效地抑最二氧化钛晶粒生长和锐钛矿向金红石的相变，选择性溶解能除去复合粉体中90％以上的氧化硅，得到高比表面积，骨架为锐钛矿相的介孔二氧化钛，复合粉体中二氧化硅主要形成了连通的网络结构，这种网络结构在800℃仍有很好的稳定性。     

一维纳米氧化锌的制备及应用

过去10年,一维(1D)ZnO纳米结构材料因其在当前和未来的各种应用潜力受到越来越多的关注。对气相和液相方法合成1DZnO纳米结构方面所取得的进展进行分类总结。总结1DZnO纳米结构在催化、传感、能量采集设备和电子、光学、光电子等领域的功能特性。     

蒙特卡罗方法模拟陶瓷晶粒生长研究进展

概述了蒙特卡罗模拟方法的基本原理和思想,介绍了陶瓷烧结过程中,蒙特卡罗分别模拟单相系统和二相系统中晶粒生长的模型,综述了国内外蒙特卡罗方法模拟陶瓷烧结过程中晶粒生长的研究进展,指出了当前该研究领域中存在的问题,提出了今后发展的主要方向:将模型与具体材料和实际工艺联系起来,模拟定量化,并向三维模拟发展,以解决实际问题.     

半导体ZnO单晶生长的技术进展

ZnO单晶是一种具有半导体、发光、压电、电光、闪烁等性能的多功能晶体材料。近年来,它在紫外光电器件和GaN衬底材料等方面的应用前景而使其成为新的研究热点。本文综述了ZnO单晶助熔剂法、水热法、气相法等生长技术的研究进展,结合ZnO单晶的化学结构,探讨了该晶体的结晶习性及生长技术发展方向。     

Grain growth of ZnO in binary ZnO-V2O5 ceramics

Grain growth of ZnO during liquid-phase sintering of binary ZnO-V₂O₅ ceramics has been studied for V₂O₅ contents from 0.5 to 4 mol% and sintering from 900°C to 1200°C. The results are discussed and compared with previous studies in terms of the phenomenological kinetic grain growth expression: G ⁿ – G _o ⁿ = K _o t exp(–Q/RT).Addition of V₂O₅ is found to decrease the ZnO grain growth exponent, n, as well as the apparent activation energy, Q. The activation analysis also reveals a change in the rate-controlling mechanism for ZnO grain growth. Following a low-V₂O₅-content (2 mol%) of nearly constant Q values of about 88 kJ/mol, further V₂O₅ additions cause an increase of the Q value to about 115 kJ/mol. Consistent with accepted models of liquid-phase sintering, it is concluded that the rate-controlling mechanism of ZnO grain growth during liquid-phase sintering in the presence of V₂O₅ changes from one of a phase-boundary reaction at low V₂O₅ levels to one of diffusion through the liquid phase at more than 2 mol% V₂O₅ levels.     

ZnO宽带隙半导体及其基本特性

ZnO半导体是宽带隙半导体领域中继GaN和SiC之后的研究热点.同时,作为一种氧化物半导体,ZnO半导体在能带结构、晶格缺陷、抗辐照特性以及电学性质等方面具有特殊性,已有的研究中还存在一些不同的认识.本工作在阐述ZnO的晶体结构和基本性质基础之上,对其能带结构和缺陷特征、电子输运以及P型掺杂等主要的半导体特性研究现状进行了较为全面综述和分析.由于ZnO半导体具有高的激子束缚能、优良的电子输运性质、强抗辐照特性以及低成本和环境友好等显著特征,它是未来半导体光电子领域极具应用潜力的新一代宽带隙半导体材料,但是到目前为止,p型掺杂技术仍然是ZnO半导体器件面临的最大挑战.     

配位均匀共沉淀法制备Ag/ZnO纳米复合材料的研究

采用配位均匀共沉淀法成功制备出了粒径20～50nm的Ag/ZnO纳米复合材料,用TG-DTA、XRD、IR及TEM等技术对前驱物及不同温度下焙烧前驱物所得的产品进行了表征分析.结果表明,当前驱物的焙烧温度为300℃时,粒子呈球形,粒径小,且其粒径随前驱物焙烧温度的升高而增大.对Ag/ZnO晶粒生长动力学的研究发现,在较低温度范围内,晶粒生长速度较快,其晶粒生长动力学指数为1.32.     

Preparation of nano-sized flower-like ZnO bunches by a direct precipitation method

In this work, nano-sized ZnO particles were prepared by a direct precipitation method with Zn(NO₃)₂·6H₂O and NH₃·H₂O as raw materials, and the impact of the synthesis process was studied. The optimal thermal calcined temperature of precursor precipitates of ZnO was obtained from the differential thermal analysis (DTA) and the thermal gravimetric analysis (TGA) curves. The purity, microstructure, morphology of the calcined ZnO powders were studied by X-ray diffraction (XRD), energy dispersive X-ray spectrum (EDS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The synthesized ZnO powders had a wurtzite structure with high purity. The final products were of flower-like shape and the nanorods which consisted of the flower-like ZnO bunches were 20–100 nm in diameter and 0.5–1 μm in length. The effect of process conditions on the morphology of ZnO was discussed.     

Inhomogeneity of Grain Boundaries of ZnO Varistor

The zinc oxide varistor with a low threshold voltage and large grain size was derived with ZnO crystalline seeds from a molten salt process The chemical composition and I-V characteristics of single grains and single grain boundaries were determined by means of energy dispersive spectrum (EDS) and microcontact measurement respectively. Temperatu re dependence of dielectric loss at various frequencies and voltage dependence of capacitance were carefully measured. Based on these experimental data. the barrier heights of giain boundaries are estimated to be 0.2. 0.5 and 0.6 eV respectively corresponding to thick, th in and direct contact grain boundaries. In addition. a computerized electrical circuit simufation is employed in simulating I-V characteristics of single grain boundary within ZnO varistor. By adjustjng parameters of resistor and diode, a general agreement between the measured data and simulated curves is achieved     

Grain growth

Abstract

The processes and mechanisms controlling grain growth in crystalline solids are reviewed. The driving forces governing the overall process are considered, and a distinction is made between normal and anomalous grain growth. The influence of solutes and dispersions (soluble and insoluble, coherent and incoherent) is discussed. Recent experimental studies of grain growth in model and commercial materials are surveyed.

MST/1297     

Spin injection from ferromagnetic semiconductor CoZnO into ZnO

2x （FeNi/CoZnO）/ZnO/（CoZnO/Co） x2 spin-inJection devices were prepared by sputtering and photo-lithography. In the devices, two composite magnetic layers 2x（FeNi/CoZnO） and （CoZnO/Co）x2 with different coercivities were used to fabricate the ZnO-based semiconductor spin valve. Since the CoZnO ferromagnetic semiconductor layers touched the ZnO space layer directly, the significant spin injection from CoZnO into ZnO was observed by measuring the magnetoresistance of the spin-injection devices. The magnetoresistance reduced linearly with increasing temperature, from 1.12% at 90 K to 0.35% at room temperature.     

溶剂热法制备铝掺杂纳米ZnO及其气敏性能

采用溶剂热法合成了铝掺杂的纳米ZnO气敏材料,运用XRD和BET等手段对产物进行了表征并进行了相应的气敏性能测试.结果表明,掺杂1.5%Al后的ZnO比表面最大,粒径最小;材料对乙醛、90#汽油、90#乙醇汽油、硫化氢、二氧化氮响应较高.掺杂量为1.5%Al的元件对90#汽油在浓度为50ppm时灵敏度接近120.