氧化镓晶体不同晶面的纳米力学性能

为了分析易解理的脆性氧化镓晶体的精密加工过程中材料去除机理,采用金刚石压头、G200型纳米压痕仪,分别对氧化镓晶体的(100)和(010) 2个主要晶面的纳米力学性能进行了试验研究。纳米压痕试验发现:2个晶面都有"pop-in"现象,首次出现pop-in的载荷分别为:4.31 m N和5.42 m N。通过变载荷纳米划痕试验和VK-X110激光显微系统观测,发现2个晶面都有"pile-up"现象,刻划过程中期均出现了塑性域加工特征,(100)和(010)晶面的塑性域加工切削深度范围分别是96.5～576.8 nm和84.6～421.6 nm。     

水热法制备羟基氧化镓纳米晶体

提供一种以氧化镓为原料,140℃下用水热法制得不同长径比的羟基氧化镓纳米棒和纳米粒子的新工艺。研究了溶液的pH、水热时间及水热温度对纳米羟基氧化镓晶体粒子形态及尺寸的影响。采用X射线衍射（XRD）,透射电镜（TEM）等方法对制备的纳米羟基氧化镓形貌进行了表征。结果表明,溶液的pH增大,羟基氧化镓纳米棒的长径比增大,pH=12时,得到单分散性纳米粒子;延长水热时间,酸性条件下样品形貌基本不变,碱性条件下纳米棒长度及长径比变大;水热温度为180℃时,形成由纳米线组成的骨状纳米棒样品。     

压痕法确定纤维复合材料界面影响区蠕变特性的数值模拟法

研究由平头压痕蠕变试验来确定纤维复合材料界面影响区蠕变性能参数的可行性。利用有限元蠕变分析确定在定压痕应力下的压痕蠕变率，重点放在稳定压痕蠕变率和复合材料材料界面影响区的蠕变性能参数的关系上。计算结果表明，界面影响区的剪应力沿纤维轴向在蠕变的主要过程中均匀分布，并且保持不变；详细地研究了压头大小对压痕蠕变响应的影响：提出两种方法由压痕蠕变试验来确定界面影响区蠕变性能参数，并给出了算例。这些结果也有利于准确认识平头压痕蠕变试验从而拓宽其应用范围。     

添加剂对纳米晶铜膜微观结构及纳米压痕性能的影响

采用电刷镀技术制备不同晶粒尺寸的纳米晶铜膜。利用透射电子显微镜分析电刷镀纳米晶铜膜的微观结构,计算晶粒尺寸范围;利用UNMT-1型纳米力学综合测试系统对电刷镀纳米晶铜膜进行室温纳米压痕实验。由实验可知,添加剂对纳米晶铜膜的晶粒尺寸和压痕硬度均有较大的影响。在添加剂45g/L条件下,平均晶粒尺寸最小为32nm左右,压痕硬度为3.26GPa;在添加剂1g/L条件下,平均晶粒尺寸增大到150nm左右,压痕硬度减小为1.72GPa。     

基于压痕功法对单晶硅压痕硬度的测量

在对材料的微/纳米级表层压痕硬度测试中,压痕周围出现的凸起对硬度的计算结果有很大的影响.采用压痕功法,通过载荷-压深曲线直接得到压痕过程中所作的功,利用原子力显微镜和Matlab软件,精确得到压痕中产生的塑性变形体积,并计算得到材料的硬度值.用压痕功法对单晶硅的压痕硬度进行了实验研究,并与其它方法进行了比较分析.结果表明:压痕功法得到的结果更稳定,凸起对结果影响较小.     

氮化铝纳米粉末的氧化特性研究

采用直流电弧等离子体蒸发－凝聚法制备了高纯氮化铝（ＡＩＮ）纳米粉末。粉末的平均晶粒度为５０ｎｍ，纯度大于９８％。借助Ｘ射线光电子能谱、化学分析和差热失重等测试手段，探索了ＡＩＮ纳米粉末的表面化学组成和氧化特性。研究结果表明，ＡＩＮ纳米粉末易吸湿氧化，大大降低了其纯度。ＡＩＮ纳米粉末表面的氧是以两种状态即物理吸附态和化合态存在。     

纳米压痕法研究金刚石薄膜的力学性能

用热丝化学气相沉积法在硅基体上制备了大面积硼掺杂金刚石薄膜,硼的浓度大约为2×10~(20)/cm3。利用纳米压痕仪及其附件研究了薄膜和纳米划擦有关的力学性能。结果表明:薄膜具有较高的硬度,平均硬度约为30GPa,弹性模量约为419GPa;薄膜与基体的结合强度较高,薄膜发生剥落的第一次破坏力大约是4N。比较而言,薄膜中心区域的硬度高于边缘,结合强度则相反。     

准静态纳米压痕的理论基础与数据分析

纳米压痕技术已经被广泛地用于在纳米尺度上评价材料的力学性能,而建立于1992年的经典Oliver-Pharr (OP)方法则是分析纳米压痕实验数据的最常用方法.本文详细介绍了OP方法的理论基础及其数据处理技术,并结合纳米压痕技术在陶瓷材料弹性模量及硬度测试中的应用,对影响OP方法测试精度及测试可靠性的各种可能因素进行了...     

纳米镓/聚甲基丙烯酸甲酯复合材料的原位超声合成与表征

超声作用于低熔点金属镓,使其超细化为纳米级的镓粒子,并采用无引发剂的乳液聚合方法制备出GA/聚甲基丙烯酸甲酯(PMMA)纳米复合粒子,并分析了其微观结构。结果表明纳米镓的形态和结构因有无表面改性剂而不同;乳液聚合得到的纳米镓复合粒子是核壳结构型,粒子大小为50~80 NM,内核金属镓粒径为30~50 NM,与聚合物存在一定的化学作用。     

镁质耐火材料高温蠕变特性的研究现状

介绍了镁质材料高温蠕变特性的研究现状，并对镁质耐火材料的高温蠕变特性的理论进行了阐述，同时指出了将镁质蓄热材料用在高炉热风炉上的可行性。     

Low-Stress Creep of Single-Crystalline Calcium Oxide

The creep behavior of single-crystalline CaO compressed along the 〈100〉 direction has been investigated over the temperature range 1350° to 1450°C at stresses between 5 to 15 MPa. Creep strains greater than 0.10 were required to achieve a steady-state creep rate. Power-law creep was exhibited over the entire stress range with a stress exponent equal to 4.4 and an apparent activation energy for creep of 345 kJ·mol⁻¹.     

Dehydrogenation of Propane Over a Silica-Supported Gallium Oxide Catalyst

The dehydrogenation of propane over a silica-supported gallium oxide catalyst was investigated at temperatures ranging from 793 to 853K under atmospheric pressure. The catalyst was found to be moderately active and highly selective to propene in the dehydrogenation of propane. The amount of carbonaceous deposits on the catalyst in the dehydrogenation was around 1/10th of that on a silica-supported chromium oxide catalyst. Lower reaction temperatures and lower concentrations of propane in the feed would be favorable for selective production of propene.     

自组装ANFs/GO复合薄膜的结构与纳米压痕力学性能

将氧化石墨烯(GO)在氢氧化钾/二甲基亚砜中分散并与对位芳纶聚对苯二甲酰对苯二胺(PPTA)聚阴离子分散液混合得到稳定分散的复合分散液,将该复合分散液通过去离子水处理并利用自组装方法制备由直径为40 nm左右的高长径比芳纶纳米纤维(ANFs)和表面无羧基、羟基含量相对增多的部分脱氧GO(DGO)组成的复合薄膜。对系列复合薄膜进行电子显微镜观察和光谱学分析发现ANFs与DGO间通过氢键和π–π堆叠相互作用紧密结合形成多层结构。采用纳米压痕技术测试旋涂自组装方法制备的薄膜的微观力学性能,发现薄膜弹性模量和纳米硬度在GO用量为PPTA质量的1.5%时,分别达到了32 GPa和1.5 GPa,较未加GO的ANFs提升了104%和87.5%,表明ANFs与GO形成的DGO之间具有较强的协同增强作用。这种具有高硬度、高弹性模量的新型复合材料有望在个体防护、船壳材料、航空航天等领域发挥重要作用。     

Harper–Dorn and Power-Law Creep in Single-Crystalline Magnesium Oxide

The creep behavior of single-crystalline MgO tested in the 〈100〉 direction is reviewed in the temperature range 1300° to 1800°C. At low stresses, the stress exponent is equal to about unity, and the deformation process is attributed to Harper–Dorn creep. At high stresses, the stress exponent is equal to approximately 5 and the deformation process is attributed to dislocation glide controlled by climb. The creep behavior in both regions is successfully predicted by an internal stress model for Harper–Dorn creep.     

Grain-Size Effect on Compressive Creep of Silicon-Carbide-Whisker-Reinforced Aluminum Oxide

The steady-state compressive creep of Al₂O₃ with 10 vol% SiC whiskers having grain sizes of 1.2, 2.3, and 4.0 μm has been measured at 1400°C in argon. The creep rate is related to the free volume within the whisker network, not the nominal grain size. The results are consistent with diffusional-controlled creep with different contributions from grain-boundary sliding. Under low stresses, only Liftshitz sliding is possible and the diffusional process controls deformation, while at stresses over a threshold, Rachinger sliding is the mechanism controlling deformation. The evolution between Liftshitz and Rachinger sliding is marked by a significant increase in the value of the stress exponent.     

Synthesis of Gallium Oxide Hydroxide Crystals in Aqueous Solutions with or without Urea and Their Calcination Behavior

Gallium oxide hydroxide (GaOOH· x H₂O) single crystals were synthesized in aqueous solutions by using two different precipitation techniques: homogeneous decomposition of urea and forced hydrolysis in pure water. Precipitation of crystals started at exactly the same pH value (i.e., 2.05 at 85°C) in both cases. The morphology of crystals turned out to be quite different (zeppelin-like with urea, rodlike without urea) in each of the above methods. Calcination of these gallium oxide hydroxide crystals in air at temperatures ≥500°C transformed them into Ga₂O₃. Characterization of the samples was performed by X-ray diffractometry, scanning electron microscopy, thermogravimetry/differential thermal analysis, Fourier transform infrared spectroscopy, and ICP, carbon, and nitrogen analyses.     

纳米压痕技术对比研究DNAN和TNT晶体的微观力学性能

通过溶剂挥发法制备了DNAN和TNT晶体;利用纳米压痕技术研究了DNAN和TNT晶体的微观力学性能(硬度和弹性模量);通过原位扫描探针成像技术(SPM)研究了DNAN和TNT晶体的压痕形貌随时间的变化差异。结果表明,DNAN晶体的平均硬度和弹性模量分别为7.82GPa和0.22GPa,TNT晶体的平均硬度和弹性模量分别为12.19GPa和0.48GPa,表明TNT抵抗变形的能力优于DNAN;随着压痕深度由118nm增至856nm,DNAN的硬度从0.61GPa降至0.22GPa;随着压痕深度由27nm增至481nm,TNT的硬度从2.9GPa降至0.48GPa,表明DNAN和TNT均存在尺寸效应。随着时间由0增至50.4min,DNAN的压痕深度由-270.99nm减至-44.28nm,TNT的压痕深度由-415.12nm减至-369.21nm,表明DNAN晶体比TNT晶体具有更明显的慢回弹性,DNAN具有更强的冲击能量吸收能力。     

Effect of Creep Damage on the Tensile Creep Behavior of a Siliconized Silicon Carbide

The tensile creep behavior of a siliconized silicon carbide was investigated in air, under applied stresses of 103 to 172 MPa for the temperature range of 1100° to 1200°C. At 1100°C, the steady-state stress exponent for creep was approximately 4 under applied stresses less than the threshold for creep damage (132 MPa). At applied stresses greater than the threshold stress for creep damage, the stress exponent increased to approximately 10. The activation energy for steady-state creep at 103 MPa was approximately 175 kJ/mol for the temperature range of 1100° to 1200°C. Under applied stresses of 137 and 172 MPa, the activation energy for creep increased to 210 and 350 kJ/mol, respectively, for the same temperature range. Creep deformation in the siliconized silicon carbide below the threshold stress for creep damage was determined to be controlled by dislocation processes in the silicon phase. At applied stresses above the threshold stress for creep damage, creep damage enhanced the rate of deformation, resulting in an increased stress exponent and activation energy for creep. The contribution of creep damage to the deformation process was shown to increase the stress exponent from 4 to 10.     

氧化物杂质对Al2O3陶瓷力学性能与抗蠕变性的影响

采用无压烧结成型工艺,研究了氧化物杂质(碱金属、碱土金属氧化物及SiO2)对Al2O3陶瓷力学性能与抗蠕变性的影响,并利用扫描电子显微镜以及万能试验机表征样品的微观结构和力学性能;提出一种恒压试样的方法评价材料的蠕变性,测试恒压后标准试样的弯曲程度.结果表明:氧化物杂质对Al2O3陶瓷常温力学性能和高温蠕变性影响存在很大差异,常温力学性能方面,除MgO外,所研究的其它氧化物杂质均使材料抗弯强度和断裂韧性有不同程度降低,而MgO能明显提高陶瓷力学性能;另一方面,高温蠕变性受氧化物杂质影响则表现相反,MgO会导致材料抗蠕变性下降,其它氧化物杂质或多或少地提高抗蠕变性能,其中含量为1 mol％ SiO2的Al2O3陶瓷抗蠕变性能明显提高.     

Low-Temperature Creep of Nanocrystalline Titanium(IV) Oxide

Nanocrystalline TiO₂ with densities higher than 99% of rutile has been deformed in compression without fracture at temperatures between 600° and 800°C. The total strains exceed 0.6 at strain rates as high as 10⁻³ s⁻¹. The original average grain size of 40 nm increases during the creep deformation to final values in the range of 120 to 1000 nm depending on the temperature and total deformation. The stress exponent of the strain rate, n , is approximately 3 and the grain size dependence is d ^{− q} with q in the range of 1 to 1.5. It is concluded that the creep deformation occurs by an interface reaction controlled mechanism.