MORPHOLOGY AND CRYSTALLOGRAPHY OF ALUMINIUM NITRIDE WHISKERS

The AlN whiskers were composed by the Al_2O_3-C system with some CaF_2 and NH_4Cl addition under the condition of the carbothermal reduction treatment of 1450 C and 2h as well as nitrogenous atmosphere. The composed AlN whiskers were analysed and the results show that some whiskers morphology such as plate cwoed, brached corrugated were observed and the ratios of length to diameter change greatly. The composed whiskers are not even. some surface quality is not high. TEM analyse show that the fiber axes are normal to[0112] and [1101]. The mechanism of the growth of the whiskers is supposed to be VLS(Vapor-Liquid-Solid)     

Synthesis and characteristics of SiC whiskers with “rosary bead” morphology

SiC whiskers with ″rosary bead″ morphology were synthesized using suitable silicon source and carbon source through solid reaction at the temperature above 1537 K. The diameter and length of the SiC whiskers were about 0.1-1.0 μm and 20-100 μm,respectively. The largest diameter of their enlarged ends of the whiskers was about 0.2-1.0 μm, and it gradually and smoothly decreased to the size of the plain part of the whiskers. The results of X-ray diffraction analysis show that the crystalline structure of the obtained SiC whiskers is β-SiC. It is considered that the SiC whiskers grow via a vapor-solid mechanism.     

硫酸钙晶须的制备及其在聚丙烯树脂中的应用

论述晶须及硫酸钙晶须的特性.以生石膏为原料,采用水热合成法,研究反应温度、反应时间、料浆浓度、Ca/Mg摩尔比等工艺条件对晶须形态的影响.在反应温度150℃、反应时间5 h、料浆质量分数为4%、n（Ca）/n（Mg）为10条件下,制备出了直径为1-5μm、长度为30-100μm的硫酸钙晶须.X-射线衍射分析表明,产品为无水硫酸钙晶须;同时对硫酸钙晶须的应用进行初步研究.根据实验结果,当晶须的填充量为5%时,聚丙烯的力学性能最佳,拉伸强度为39.18 MPa,断裂伸长率为125.41%.     

椰壳纳米纤维素晶须的氧化法制备

椰壳纤维资源丰富,然而纳尺度化的利用较少。采用氧化法制备椰壳纳米纤维素晶须的TEM结果表明,椰壳纤维的基原纤直径为6nm~10nm,长度为0.5μm~1.5μm;其微原纤直径为20nm~40nm,长度为1μm~4.5μm。X-ray衍射结果表明椰壳纤维的结晶形式为纤维素Ⅰ型,次氯酸钠-氢氧化钠溶液能更有效地分离提取纳米纤维素晶须,且该纳米晶须的结晶度约为52%。红外显微镜结果表明纳米纤维素晶须结晶度值的提高是因为木质素、半纤维素以及杂质的减少,实验用纤维素、半纤维素和木质素的含量分别约为40.16%,39.96%和19.88%。     

AlN纳米线阵列的光学性质及第一原理计算

为了制备均匀的宏观AlN纳米线阵列,采用化学气相沉积法在二次模板上成功地合成了AlN纳米线宏观阵列.利用X射线衍射仪、扫描电子显微镜、电子能谱仪和紫外-可见光光度仪测试了AlN纳米线阵列的结构、形貌和紫外发光性能.结果表明,AlN纳米线阵列分布均匀,AlN纳米线的平均直径与平均长度分别约为41 nm和1. 8μm. AlN纳米线的分布密度约为5. 4×107mm-2,其覆盖率约为7. 1%. AlN纳米线在150～310 nm范围内具有很好的吸光性能.利用第一原理计算得到的AlN纳米线光学性质与实验结果相符.     

Preparation,Characterization, and Formation Mechanism of Calcium Sulfate Hemihydrate Whiskers

Calcium sulfate hemihydrate whiskers were synthesized successfully via one-step hydrothermal crystallization method using phosphogypsum at 130 °C for 240 min with an initial slurry mass fraction of 2.5 wt%. The phase compositions, microstructures, thermal properties and molecular structures of asprepared samples were analyzed by XRD, ESEM, EDS, TG-DTA, and FT-IR. The influence of raw materials' ball-milling time on the morphologies of whiskers was investigated. The effects of impurities on crystallization morphologies and length to diameter ratio(L/D) of calcium sulfate hemihydrate whiskers were studied. The results indicated that the calcium sulfate dihydrate crystalline could be translated directly into fibrous calcium sulfate hemihydrate whiskers. It was beneficial to form fine fiber structure when the ball-milling time of the raw material was 15 min. Aspect ratio of calcium sulfate hemihydrate whiskers decreased with increasing content of impurities. Moreover, the relative growth mechanism of whisker crystals via one-step hydrothermal crystallization method was discussed in detail.     

用电子束区熔法制备LaB_6─ZrB_2共晶自生复合材料

用电子束区熔法制备ＬａＢ_６─ＺｒＢ_２共晶自生复合材料陈昌明，周万城，张军，张立同共晶自生复合材料因具有良好的发射性能、很好的室温韧性和强度而受到重视。该材料由于共晶温度高，高温组织稳定性好，可望用于涡轮叶片的制备。乌克兰科学院［’］用高频区熔法研究...     

Preparation of mullite whiskers and their enhancement effect on ceramic matrix composites

Mullite whiskers were facilely prepared by sintering kyanite at high temperature, with the addition of AlF3·3H2O. The as-prepared whiskers have been characterized systematically in terms of phase composition, morphology, and structure. Results showed that the morphology and size of mullite whiskers were strongly depended on the content of AlF3·3H2O and sintering temperature. At temperatures in the range of 1 100 to 1 500 ℃ with 4 wt% addition of AlF3·3H2O, the well-shaped mullite whiskers were obtained. For an instance, the mullite whiskers with 5-10 μm in length and 0.1-0.2 μm in cross-section could be formed at 1 400 ℃, with 4 wt% addition of AlF3·3H2O. Moreover, results showed that the addition of mullite whiskers into ceramic matrix enhanced its fracture toughness significantly.     

燃烧合成-维纳米结构AIN及其生长机理研究

以铝粉（A1）和NH4F为主要原料,Nb为添加剂,在N2压力小于0．5MPa的条件下采用高温自蔓延燃烧法（SHS）合成了一维纳米结构的AlN粉体,并通过差热分析（TG／DSC）分析了Al—N2体系的热力学机理,运用X-射线衍射仪、场发射扫描电子显微镜（SEM）分析了所合成一维纳米结构AlN的物相组成和显微结构．结果表明,当Al：NH4F为4：1（wt％）时,在添加剂Nb的作用下,合成的产物主要为一维纳米结构六方长针状AlN,该粉体纯度高、晶体结构完整,且沿（100）存在明显择优取向;所合成的一维纳米结构AlN的生长机理属于SLS生长机理．     

含部分晶须的镍酸锂研制

以碳酸锂、氢氧化镍和硝酸为原料,采用半固相法合成了镍酸锂,并研究了合成条件和合成工艺对产物性能的影响.用DSC-TG对试样的热行为进行分析,并分别用SEM和XRD对材料的微观结构和物相组成进行表征.结果表明:烘干温度控制在250℃;以5℃/min从25℃升温至620℃;并且在620℃下煅烧9 h,此时获得的样品中有约60%的晶须存在,晶须的直径小于0.3μm,晶须的长度约为4～6μm.     

Fabrication and plasma arc thermal shock resistance of HfB2-based ultra high temperature ceramics

Two hafnium diboride based ceramic matrix composites containing 20% (volume fraction) SiC particle and with or without AlN as sintering additives were fabricated by hot-pressed sintering. The mechanical properties and microstructures of these two composites were tested and the thermal shock resistances were evaluated by plasma arc heater. The results indicate that the composite with AlN as sintering additive has a denser and finer microstructure than composite without sintering additive, and the mechanical properties, thermal shock resistance of the composite with AlN as sintering additive are also higher than those of the composite without AlN. Microstructure analysis on the cross-section of two composites after thermal shock tests indicates that a compact oxidation scale contains HfO₂ and Al₂O₃ liquid phase is found on the surface of composite with AlN, which could fill the voids and cracks of surface and improve the thermal shock resistance of composite.     

碳酸钙晶须的制备及表征

研究了碳酸钙晶须的制备方法, 探索了以MgCl₂ 为促进剂时碳酸钙晶须生长的影响因素, 通过正交实验找到了制备碳酸钙晶须的最佳条件, 即MgCl₂ 浓度为0 .50 mol/ L , 温度90 ℃, 搅拌速度为250 r/ min , CO2 流量为1 m L/ min ;采用偏光显微镜、X 射线衍射仪对碳酸钙晶须结构进行了表征, 所制备的产物中晶须质量分数在97 %以上, 长径比为20～ 30。     

Synthesis of calcium chloroborate whiskers via sedimentation and sintering process

Single crystalline calcium chloroborate(Ca_2B_5O_9Cl) whiskers with uniform diameter have been fabricated by a two-step process. The precursor was firstly prepared by the sedimentation reaction between CaCl_2, H_3BO_3 and Na OH aqueous solutions, and then sintered at different temperatures for 6 h with KCl as flux. The XRD indicates that the product synthesized at 600 °C is Orthorhombic Ca_2B_5O_9Cl. SEM and TEM results show that the Ca_2B_5O_9Cl is whisker with the diameter about 0.2-0.5 μm and the length up to 15 μm. SAED analysis shows that the whisker is single crystalline and grows along [001] direction. The possible formation process and growth mechanism were proposed.     

反应温度和反应时间对三水碳酸镁晶须长径比的影响

为了扩大其作为增强补韧剂和阻燃剂的应用,以氯化镁和碳酸氢铵为原料,通过水热法成功合成了不同长径比的三水碳酸镁晶须. 采用X射线衍射、扫描电子显微镜、透射电子显微镜对所得三水碳酸镁晶须的物相和形貌进行分析. 结果表明:当反应时间为5 h时,随着反应温度（50 ℃~80 ℃）的升高,三水碳酸镁晶须长径比减小. 当温度为50 ℃,反应时间在4 h~5 h内时,晶须处于生长阶段,长径比增大;反应时间延长至7 h,由于发生相转变,晶须开始溶解,导致长径比减小. 通过对晶须尖端的分析,证实晶须属于台阶生长机制.     

Structural and optical characteristics of Al_xGa_(1-x)N/AlN superlattice

AlN/Al0.3Ga0.7N superlattices were grown on (0001) sapphire substrate by metal-organic chemical vapor deposition (MOCVD). The superlattice period varies from 6 to 30. The layer thickness of different period stack was designed. GaN or AlGaN template was employed for growing AlN/AlGaN superlattices. Reflectivity, SEM, AFM and XRD data of the AlxGa1-xN/AlN superlattices are presented. It is found that the templates used have an intensive impact on surface roughness and interfacial properties of following AlN/AlGaN superlattices. The result of atomic force microscopy indicates that AlN/AlGaN superlattices grown on GaN template exhibit quasi-two-dimensional growth mode. The resulting superlattice has a smooth surface morphology and distinct interface. No crack is observed in the area of a 2-inch wafer.     

钨晶须制备及生长机理研究

以93W-4.9Ni-2.1Fe混合粉末为原料,采用无衬底和钼(Mo)衬底两种条件制备钨(W)晶须,并探讨其生长机理.分别采用扫描电镜、X射线能谱仪、场发射扫描电镜、透射电镜和X射线衍射仪对产物形貌、元素分布和物相等进行测试分析.研究表明,在无衬底和Mo衬底条件下均能得到表面形貌良好,无明显缺陷,直径约200~400 nm,长径比达100以上的W晶须,且Mo衬底能促进W晶须的生成,少量的Mo原子进入W晶格,可取代晶胞中的W原子,形成连续固溶体,使晶胞参数减小.     

152型碱式硫酸镁晶须疏水改性研究

以乙醇为溶剂,十七氟葵基三乙氧基硅烷(AC-FAS)为改性剂,对152型碱式硫酸镁晶须(152MHSH)的疏水改性进行了研究。采用扫描电子显微镜(SEM)、X-Ray衍射仪(XRD),傅立叶变换红外光谱仪(FT-IR)和水接触角测试仪(CAM)等测试手段对改性前后样品的形貌、结晶状况及产品组成等进行了表征。结果表明,通过疏水性处理,改性剂被成功包覆在152碱式硫酸镁晶须表面,实现了对其疏水改性的目的。当改性处理时间为1h时获得了理想的疏水表面,其水接触角达到126°。FT-IR、XRD、SEM及EDS分析均表明AC-FAS仅成功包覆在MHSH晶须的表面,并未对晶须的晶型造成影响。     

热压合成Ti_4AlN_3及其物理性能研究

以摩尔比为Ti ◇Al ◇TiN=1 1.2 2.7的混合粉为原料,采用真空热压烧结工艺在1400℃保温2 h成功合成了高纯Ti4AlN3块体材料,Ti4AlN3烧结试样结晶良好,晶粒发育完善,内部较为均匀致密,相对密度达到98.5%,具有较高的抗弯强度（384 MPa）、抗压强度（523 MPa）和断裂韧性（6.5（MPa.m1/2））,较低的维氏硬度（2.9 GPa）和抗破坏能力,具备良好的机械加工性能。Ti4AlN3常温电导率和热导率分别为4.6×105（Ω-1.m-1）和12（W.m-1.K-1）,其热导率在25～600℃范围呈上升趋势;25～1100℃的线膨胀系数为9.0×10-6K-1,良好的导热性能和高温热稳定性使其可以应用于高温领域。     

钛酸钾晶须增强尼龙

为增强聚酰胺(PA)强度,用硅烷及钛酸酯等偶联剂对钛酸钾晶须进行表面处理,并考察钛酸钾晶须对PA力学性能、工艺性等影响.研究表明,钛酸钾晶须经硅烷偶联剂处理后,可改善复合材料性能,硅烷的表面处理效果较钛酸酯的好,并比较了硅烷偶联剂改性前后晶须对PA增强性能的改变.经硅烷偶联剂KH-550表面改性的PTW能与PA基体更好地相容,达到较好的增强效果.     

反应烧结制备Ti_2AlN-TiN复合材料

采用2Ti/2Al/3TiN粉体为原料,通过反应热压烧结,以制备Ti2AlN-TiN复合材料。采用X射线衍射（XRD）、场发射扫描电镜（FE-SEM）结合能谱仪（EDS）分析试样。研究结果表明,在1350℃保温2h,压力为30MPa,可烧结得到组织细小、致密的Ti2AlN-TiN复合材料。材料中层片状Ti2AlN晶粒长约5m,TiN晶粒大小为1~2m。复合材料具有良好的机械性能,其显微硬度与弯曲强度分别达8.57GPa和450MPa。