Synthesis and tribological properties of hexagonal titanium silicon carbide crystals

Hexagonal titanium silicon carbide (Ti₃SiC₂) crystals were prepared by vacuum sintering of Ti, Si, and C powders at 1300 °C. The microstructure and grain deformations of Ti₃SiC₂ were examined by scanning electron microscopy and transmission electron microscopy. The tribological properties of hexagonal Ti₃SiC₂ crystals as lubrication additive in HVI500 base oil were investigated by a UMT‐2 ball‐on‐plate friction and wear tester. The Ti₃SiC₂ additives exhibited good friction reduction. Under determinate conditions, the friction coefficient of base oil containing Ti₃SiC₂ crystals is lower than that of pure base oil. The base oil with 3.0 wt.% hexagonal Ti₃SiC₂ crystals presented good anti‐wear capability. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,characterization, and tribological properties of two‐dimensional Ti3C2

We report on the preparation of two‐dimensional (2D) Ti₃C₂ and its friction and wear properties. Laminated Ti₃AlC₂ was synthesized by pressureless sintering using Ti, Al, and graphite, followed by HF exfoliation and sonication treatment to form 2D‐layered Ti₃C₂, which exhibited individual layer or stack of several layers. Analysis of microstructure and composition was used to confirm the successful exfoliation of laminated Ti₃AlC₂. The tribological behaviors of the as‐prepared 2D Ti₃C₂ as a lubrication additive in base oil were investigated. Results indicate that 2D‐layered Ti₃C₂ can greatly enhance the friction‐reducing and anti‐friction properties of base oil, especially with 1.0 wt% Ti₃C₂. This novel 2D‐layered Ti₃C₂ would be a good candidate for lubricating materials to meet emerging needs in practical applications.     

机械合金化-低温烧结Ti3SiC2导电陶瓷材料

采用化学计量比为3Ti/Si/2C的单质粉体为反应原料,通过机械合金化工艺和热处理制备高纯度的Ti3SiC2陶瓷粉体,研究了热处理温度对提高机械合金化混合粉体中Ti3SiC2纯度的影响.研究表明:在球磨转速400 r/min,球磨时间10 h的条件下,合成以Ti3SiC2为主相的混合粉体,其中Ti3SiC2含量为75.5vol;,同时出现表面灰黑色且坚硬的不规则块体,成分与球磨粉体相似.在热处理温度为850～1000℃范围内,混合粉体中Ti3SiC2的含量随着热处理温度的升高而提高,当热处理温度为1000℃时,计算粉体中Ti3SiC2的含量高达98.5vol;..     

Synthesis and tribological properties of NbSe3 nanofibers and NbSe2 microsheets

NbSe₃ nanofibers and NbSe₂ sheets were prepared by solid state reaction. The as‐prepared products are characterized by powder X‐ray diffraction (XRD), and scanning electron microscopy (SEM). The results showed that the obtained NbSe₃ nanofibers have a diameter in the range of 100–300 nm and length about 10 μm, while the NbSe₂ sheets have a hexagon structure. The tribological properties of the as‐prepared NbSe_x powders as additives in HVI500 base oil were investigated on UMT‐2 multispecimen tribo‐tester. The wear scars were measured by VEECO WYKO NT1100 non‐contact optical profile testing instrument. It is found that the addition of both NbSe_x nanofibers/sheets improves the tribological properties of base oil. Furthermore, NbSe₂ sheets exhibit better friction reduction and wear resistance properties than NbSe₃ nanofibers in HVI500 base oil. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of MoSe2/Reduced graphene oxide composites with improved tribological properties for oil‐based additives

In this work, we developed a facile and effective hydrothermal method synthesis of MoSe₂ nanoflowers on reduced graphene oxide (RGO) sheets. The as‐prepared MoSe₂/reduced graphene oxide (MoSe₂/RGO) composites are characterized by X‐ray diffractometer (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicated that MoSe₂ nanoflowers were successfully deposited on RGO nanosheets to form a well interconnected hybrid structure. The tribological properties of MoSe₂/RGO composites as lubricating oil additive were investigated by a UMT‐2 ball‐on‐plate friction and wear tester. By the addition of MoSe₂/RGO composites in paraffin oil, the antiwear ability was improved and the friction coefficient was decreased. The based oil with MoSe₂/RGO composites showed better tribological properties than the oil with MoSe₂ and pure oil. The good friction and wear properties of MoSe₂/RGO composites as additives were attributed to the formation of a thin physical tribofilm on the substrate.     

Synthesis and tribological properties of Mo‐doped WSe2 Nanolamellars

The Mo‐doped WSe₂ nanolamellars have been successfully prepared via solid‐state thermal (750 °C) reaction between micro‐sized W, Mo with Se powders under inert atmosphere in a closed reactor and characterized by X‐ray diffractometer (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that the morphologies of the as‐prepared products changed from microplates to nanolamellars to aggregations composed of nanoparticles with the doping of Mo powders. And the sizes of crystallites evidently reduced while the contents of dopant increased within a certain limit (1 wt.%–7 wt.%). The tribological properties of the as‐prepared products as additives in HVI750 base oil were investigated by UMT‐2 multispecimen tribotester. The friction coefficient of the base oil containing Mo‐doped WSe₂ nanolamellars was lower and more stable than that of WSe₂ nanolamellars. A combination of rolling friction, sliding friction, and stable tribofilm on the rubbing surface could further explain the good friction and wear properties of Mo‐WSe₂ nanoparticles as additives than that of WSe₂.     

钙钛矿型层状化合物K2Pr2Ti3O10的合成及XRD研究

在K2CO3-镧系元素氧化物(Pr2O3)-TiO2三元体系中,用固相反应法合成K2Pr2Ti3O10,利用X射线粉晶衍射仪对K2Pr2Ti3O10进行扫描测定,获得X射线衍射数据,进行指标化,得到其晶胞参数。XRD分析结果表明,K2Pr2Ti3O10为四方晶系,空间群I4/mmm。     

Synthesis and tribological properties of copper matrix solid self‐lubricant composites reinforced with NbSe2 nanoparticles

Copper matrix solid self‐lubricant composites were prepared by powder metallurgy route using copper powders and NbSe₂ nanofiber or sheet. The tribological properties of the as‐prepared materials were estimated by a ball‐on‐disc on UMT‐2 multi‐function friction and wear tester under dry conditions in a normal laboratory atmosphere (55‐70% relative humidity, 15‐25 °C). The NbSe₂ nanofiber or sheet was very effective in improving the tribological properties of the composites. It is found that the composites with 15 wt.% NbSe₂ nanofibers showed a very low coefficient of friction of 0.1487. Furthermore, the value levels of electrical resistivity for the composites with different contents of NbSe₂ nanofiber reached to 10^‐6 Ω.cm. When the NbSe₂ content was high enough, a continuous supply of NbSe₂ nanofiber to the tribo‐surface is an important precondition and the benefit of its anti‐friction properties for the copper matrix composites. This behavior is related that little NbSe₂ is reacted with the Cu‐base in the sintering process, although there needs enough NbSe₂ nanofibers as solid lubricants; too much NbSe₂ nanofibers will decrease the intensity of the composites, reducing the wear resistance. So adding the appropriate contents of NbSe₂ nanofiber to the composites play an important role in anti‐friction and wear resistance. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

钛宝石晶体的泡生法生长和闪烁发光性能

采用泡生法生长了115 kg级大尺寸钛宝石(Ti:Al2 O3)晶体,晶体外形完整无开裂,制备了口径达?300 mm的高质量大口径钛宝石单晶样品.在X射线和α粒子激发下测试了晶体的闪烁发光性能.结果表明,Ti:Al2 O3晶体的闪烁发光包含近红外和近紫外发光.近红外发光来源于Ti3+特征发射,效率较高,衰减时间慢.近紫...     

二维晶体Ti3C2的制备及其对有机染料的吸附性能研究

采用49;的氢氟酸刻蚀Ti3AlC2成功制备了层状二维晶体Ti3C2,并研究了其作为吸附剂对有机染料罗丹明B(RhB)、亚甲基橙(MO)和亚甲基蓝(MB)的吸附性能.利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、气体吸附分析仪、紫外可见分光光度计等对样品物相、晶体结构和孔隙结构及比表面积进行了表征,考察了温度和染料浓度对Ti3C2吸附效果的影响.结果表明,二维晶体Ti3C2对有机染料具有较好的吸附性能,随着温度的升高吸附速率有明显的提高;Ti3C2对RhB和MB的吸附效果随着温度的升高均有明显的提高,但对100 mg/L的MO,在25℃时吸附效果最好.45℃时,Ti3C2对浓度为50 mg/L的染料的吸附速率RhB＞ MB＞ MO.     

Large‐scale synthesis of SiC nanowires from polysiloxane and wood powder composites

Large‐scale SiC nanowires were prepared by directly annealing polysiloxane and wood powder composites without catalyst assistant at 1420 °C under argon atmosphere. SiC nanowires are up to tens of micrometers in length and the diameters are in the range of 30–150 nm. Most nanowires are smooth and straight in morphology. High‐resolution TEM image shows that SiC nanowires grow along the [111] direction. The vapor–solid mechanism was proposed to explain the growth procedure of SiC nanowires. The present work provides an efficient and simple strategy for large‐scale production of SiC nanowires.     

Na3La2(BO3)3晶体生长及光谱特性

本文以起始摩尔比为1:1的Na2CO3:H3BO3,并添加5;质量分数的NaF为助熔剂,用顶部籽晶法生长出φ35mm×5mm的透明Na3La2(BO3)3单晶.该晶体属正交晶系,空间群:Amm2,晶胞参数为a=0.51580(10)nm,b=1.1350(2)nm,c=0.73230(15)nm,α=β=γ=90°.测量了Na3La2(BO3)3晶体在室温下的透过光谱,紫外截止波长约为200nm.该晶体常温下稳定,不吸潮,但却易溶于稀酸.     

煅烧制度对Lu2Ti2O7粉体生长形貌的影响

采用熔盐法制备Lu2Ti2O7粉体,研究了不同煅烧工艺对粉体形貌的影响,确定了适用于Lu2Ti2O7粉体合成的工艺条件,并在利用XRD、SEM等方法分析表征样品的基础上,提出了初步的粉体形貌生长转变机制。实验结果表明:形核速率和生长速率对粉体的颗粒尺寸和形状影响很大,过快的形核速率和生长速率有利于多面棱柱状晶粒的生长,反之则有利于八面体形状的晶粒生长。     

Facile synthesis of ultrathin NbTe2 nanosheets for enhanced tribological properties as a lubricant additive

Graphite‐like bulk NbTe₂ powders were prepared by a facile solid phase synthesis process and ultrathin NbTe₂ nanosheets were obtained by using wet ball milling induced delamination. The X‐ray diffraction analysis illustrated that the reduction of particle size was mainly along the stacking direction of the basal planes without great influence on the short range order of NbTe₂ crystals. Scanning electron microscopy, transmission electron microscopy, and atomic force microscope observations revealed that the longitudinal dimension of NbTe₂ samples changed into the nanoscale from the larger micron level after mechanical exfoliation. The exfoliated NbTe₂ nanosheets had better long‐term dispersion stability in paraffin oil than bulk NbTe₂. The tribological properties were determined on an UMT‐2 ball‐on‐disk friction and wear tester. The results indicated that the paraffin oil with NbTe₂ nanosheets exhibited better lubricating behaviors with the lower friction coefficient and wear rate in comparison with the bulk NbTe₂. It was demonstrated that NbTe₂ nanosheets could easily enter into a point of friction contact, and form an available tribofilm to prevent the direct contact between counterparts during the friction process. Furthermore, this work shows the potential applications of ultrathin NbTe₂ nanosheets in the field of tribology.     

Synthesis and properties of PbGeO3 nanostructures

PbGeO₃ nanostructures including nanofibers and nanobelts, have been synthesized via a facile hydrothermal method by the reaction between GeO₂ and Pb(CH₃COO)₂·3H₂O in the absence of any surfactant. The influences of synthetic parameters, such as reaction time, reaction temperature, and the concentration of ethylenediamine, on the morphologies and sizes of PbGeO₃ nanostructures have been investigated. It is found that an evolution of PbGeO₃ nanostructures from nanobelts to nanofibers is observed for the first time with the reaction time increased from 1 h to 6 h. The diameters of PbGeO₃ nanofibers can be controled from 300–900 nm to 80–120 nm by adjusting the concentration of ethylenediamine. Under similar conditions, PbGeO₃: Eu³⁺ nanofibers with rough surfaces can also be obtained. The photoluminescent spectra of PbGeO₃: Eu³⁺ nanofibers exhibits two fluorescence emission peaks centered at around 591 and 614 nm as the excitation wavelength is 395 nm. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of γ‐irradiation on spectral properties of undoped Y2SiO5 crystals

The absorption spectra of undoped Y₂SiO₅ crystals were studied before and after γ‐irradiation. After γ‐irradiation, the additional absorption peaks at 260‐270 and 320nm were observed in as‐grown and H₂‐annealed Y₂SiO₅ crystal, but it did not occur in air‐annealed Y₂SiO₅ crystal. These absorption peaks were attributed to F color centers and O^– hole centers, respectively. Owing to more oxygen vacancies and color centers in H₂‐annealed Y₂SiO₅ crystal than that in as‐grown Y₂SiO₅ crystal after γ‐irradiation, the additional absorption peaks were more intense in the former than that in the latter. With the irradiation dose increasing from 20 to 220kGy, the intensity of additional absorption peaks increased. © 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Na3Sm2(BO3)3的晶体生长及热学和光谱性质

以Na2CO3-H3BO3为助溶剂,用顶部籽晶法生长了14mm×8mm×2mm的Na3Sm2(BO3)3晶体.差热分析(DTA)表明Na3Sm2(BO3)3非同成分熔融,熔点为1089.1℃.该晶体易溶于酸,在空气条件下能稳定存在,不易潮解.测量了室温下晶体在200～2500nm范围内的吸收光谱,并对跃迁能级进行了初步指认.     

Influence of photonic excitations on the electrical parameters of TlInS2 crystals

The photo‐excitation effect on the current transport mechanism in TlInS₂ crystals has been studied by means of dark and illuminated conductivity measurements. The temperature‐dependent electrical conductivity analysis in the temperature region of 110‐340 K revealed the domination of the thermionic emission and the thermally assisted variable range hopping (VRH) of charge carriers above and below 160 K, respectively. Above 160 K, the conductivity activation energies in the dark are found to be 0.28 and 0.15 eV in the temperature regions of 340‐240 K and 230‐160 K, respectively. In the temperature region of 110‐150 K, the dark variable range hopping analysis revealed a density of localized states of 1.99×10²² cm^–3eV^–1, an average hopping distance of 0.53 nm and an average hopping energy of 79.65 meV. When the sample was photo‐excited, the values of the conductivity activation energies, the density of localized states near the Fermi level and the average hopping energy were observed to decrease sharply with increasing illumination intensity. On the other hand, the average hopping distance increased with rising illumination intensity. Such behaviours were attributed to the Fermi level shift and/or trap density reduction by electron‐hole recombination. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Laser‐induced crystal growth of nonlinear optical Ba3Ti3O6(BO3)2 on glass surface

Nonlinear optical Ba₃Ti₃O₆(BO₃)₂ crystals were patterned on the surface of CuO (1 mol%)‐doped 40BaO‐40TiO₂‐20B₂O₃ glass by irradiations of continuous‐wave Nd:YAG (wavelength: λ=1064 nm) and Yb:YVO₄ (λ=1080 nm) lasers. Laser energies absorbed by Cu²⁺ ions were transferred to the lattice system through a nonradiative relaxation process, consequently heating the glass and inducing local crystallizations. For the lines patterned by Yb:YVO₄ laser irradiations with a power of 1 W and a scanning speed of 20 μm/s, a c‐axis orientation of Ba₃Ti₃O₆(BO₃)₂ crystals along the laser scanning direction is proposed from measurements of X‐ray diffraction analyses, polarized optical photographs, polarized micro‐Raman scattering spectra, and azimuthal dependence of second harmonic generations. The laser‐induced crystallization technique is found to be applied successfully for the spatially selective patterning of nonlinear optical Ba₃Ti₃O₆(BO₃)₂ crystals in glass. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

AlN-Y2O3配比对SiC耐磨材料结构和性能的影响

在AlN-Y2O3添加量为6wt;的前提下,将摩尔比分别为10∶90、20∶80、30∶70和40∶60的AlN、Y2O3引入SiC耐磨材料中,于氧化气氛下经1600℃保温3h烧成,研究了AlN、Y2O3配比对SiC耐磨材料结构和性能的影响.结果表明:AlN、Y2O3配比对SiC耐磨材料的性能影响较大,当其为30∶70时,SiC耐磨材料的性能较优,其体积密度和显气孔率分别为2.66 g/cm3和3.95;,磨损量为0.11 g/min,硬度和抗折强度分别为2774 HV和185 MPa.SiC耐磨材料较优异的烧结性能和力学性能可归因于新生成的Y2Si2O7和3Al2O3·2SiO2充填于SiC颗粒间所起的强化作用.