多组元掺杂石墨微观结构及其性能的研究

制备了Si,Ti比组元和Si,Ti,B4C三组元掺杂石墨材料并研究了其结构和性能,实验结果表明,与相同条件下制得的纯石墨材料相比,掺杂石墨材料具有高密度,高强度以及极低的电阻率等特点,双组元掺杂石墨的导电性略优于三组元掺杂石墨,但其机械强度却明显低于后者,分析表明,各组元在材料中所起的作用各不相同,钛,硼添加剂对材料的机械强度有增强作用,对材料的石经具有催化作用,少量硅的添加有利于石墨材料的石墨化和蔼以及导电性能的提高,但含量较多时,由于Si的大量逸失导致气率增大,使掺杂石墨的导电极性及机械性能降低。     

天然石墨/陶瓷复合材料的制备及其性能

为了拓展天然石墨的应用领域，通过热压工艺，在天然石墨中掺杂B、Si和Zr陶瓷组元，制备了天然石墨／陶瓷复合材料，利用SEM、XRD等分析手段研究了材料微观结构，并探讨了掺杂组元以及天然石墨颗粒大小对材料性能的影响．结果表明：掺杂Zr可有效地提高石墨材料的热导率，B的加入可有效地提高石墨材料的力学性能，而Si的加入可加速Zr对石墨材料的催化石墨化；随着天然石墨粒径的增加，制得石墨材料的热导率也随之增加，其中，以粒径为13μm的天然石墨制得的材料强度和密度为最优。     

石墨化温度及掺硅组分对再结晶石墨传导性能及微观结构的影响

用煅烧石油焦作填料 ,煤沥青作粘结剂 ,分别以硅粉、碳化硅和二氧化硅 3种含硅组分作添加剂 ,采用热压工艺制备了再结晶石墨。考察了石墨化温度以及单组元掺硅组分对再结晶石墨的热导率、电阻率和抗折强度的影响及其微观结构的变化。实验结果表明 ,对于掺硅组分相同的再结晶石墨 ,材料的导电、导热性能随着石墨化温度的升高而增强 ,但其力学性能却随之降低。当掺硅粉的热压再结晶石墨再经 2 80 0℃石墨化处理后 ,材料RG Si 48沿石墨层方向的常温热导率可达 3 3 2W /(m·K) ,电阻率为 4.94μΩ·m。对于相同工艺及硅含量的不同掺硅组分再结晶石墨 ,以掺入硅粉对材料综合性能最理想 ,而掺入二氧化硅对材料的综合性能较差。XRD分析表明 ,不论掺硅组分是硅粉、碳化硅还是二氧化硅 ,硅组分最终在再结晶石墨内均以α SiC形式存在 ,甚至在石墨化温度高达 2 80 0℃时 ,再结晶石墨内仍有α SiC存在。对其微晶参数进一步分析表明 ,随着石墨化温度的升高 ,掺杂硅组分的催化作用进一步加强 ,再结晶石墨的微晶尺寸La 迅速增大 ,石墨微晶的晶面层间距d0 0 2 也迅速降低。材料RG Si 48的微晶尺寸La 以及晶面层间距d0 0 2 分别为2 5 7nm和 0 .3 3 5 77nm。     

热电材料β-Cu2-xSe热传导性能模拟研究

“声子液体”热电材料β-Cu2-xSe具有优异的热电转换效率,采用分子动力学模拟的方法研究其热传导性能,分析了类“液态”离子的扩散能力和材料导热性能的相关性,并探究了材料加工处理手段(掺杂和空位)对材料热传导性能的影响。结果表明:类“液态”离子扩散能力和导热系数存在极强的相关性,β-Cu2-xSe中Cu^+移动能力的增强会增加晶格的非简谐振动,从而强化了声子散射,导致材料导热系数的降低。掺杂和空位对“声子液体”热传导性能有不同的影响:材料内部存在空位时,Cu^+倾向于在晶格缺陷中移动,降低了与Se构成的固定亚晶格碰撞概率,造成声学支声子频率的下降,有效地降低了导热系数,提高了材料的热电转换效率;相比空位,掺杂对导热系数的影响不明显。     

含Zr多组元掺杂石墨材料的性能研究

以天然石墨为原料，通过热压工艺，制备了含Zr多组元掺杂石墨材料。研究了掺杂元素对材料性能的影响。实验结果表明：随着Zr含量增加，基体石墨的强度、导电和导热性成线性增加；但是过量的ZrO2会消耗基体炭原子，生成金属Zr蒸汽逸出基体，形成孔隙和缺陷，导致材料的性能下降，因此应控制ZrO2的加入量。另外，采用SEM、XRD等分析手段研究了材料微观结构，探讨了微观结构对其性能的影响。     

石墨材料导热性能与微晶参数关系的研究

用煅烧石油焦和煤沥青为基本原料，采用热压和石墨化工艺制备了几种纯石墨材料。考察了煤沥青的种类以及石墨化温度对石墨材料导热性能的影响。结果表明，粘结剂的种类和石墨化温度与石墨材料的导热性能有着密切的联系。石墨材料的导热性能对其石墨化度的敏感程度较大，尤其是当石墨化度较高时表现最为突出。研究结果还表明，室温时石墨材料的导热系数与其平均微晶尺寸La呈现出良好的线性关系，其直线方程为：λ=-86.66 7.26La；石墨的微晶层间距doo2与其平均微晶尺寸的倒数（1／La)也存在良好的线性关系，其直线方程为d002=0.3341 0.1664(1/La)。     

石墨和炭纤维分别改性热塑性聚酰亚胺 复合材料的导热行为

采用石墨、 炭纤维填充改善热塑性聚酰亚胺(TPI)材料的导热性能, 研究了填料物性对材料力学性能和导热行为的影响。在此基础上, 用Nielsen理论模型和有限元方法模拟了复合材料的导热行为, 进一步探讨了填料形状对材料导热系数的影响。研究表明: 炭纤维、 石墨填充TPI均能提高复合材料的导热性能; 用Nielsen理论模型预测石墨、 炭纤维填充TPI材料导热系数与实验值存在一定偏差; 采用有限元法模拟二维复合材料稳态导热行为, 能有效地预测复合材料的导热系数。基于材料内部热流分布模拟分析发现, 填料自身导热性能对复合材料导热行为的影响不明显; 与圆形填料相比, 方形填料改善材料导热性能效果显著。      

含Ti组元炭/炭复合材料微观结构和热传导/力学性能的研究

以短切炭纤维、中间相沥青和Ti粉为原料,采用模压成型、炭化、致密化、高温石墨化等一系列常规工艺,制备了含Ti组元的炭/炭复合材料.考察了Ti组元的添加对复合材料传导性能和微观结构的影响,结果表明:Ti组元的添加能增强复合材料界面、促进晶粒的完善和长大,提高材料的传导/力学性能.当Ti含量为7.3%时,2500℃高温石墨化后所制复合材料的面向热导率最高,为482W/(m·K);进一步3000℃高温处理后材料面向热导率达556W/(m·K).同时本文探讨了Ti组元的催化石墨化机理.     

超细石墨复合改性水泥石的导热性能

为提高地热的开采效率，在地热井采热段应使用具有高导热性能的固井材料。以超细石墨为提高导热性能的掺合料，选用十二烷基苯磺酸钠作为分散剂提高超细石墨在水泥浆中的分散稳定性；优选出适合的超细石墨分散液后，进一步制备超细石墨复合改性水泥石(简称为水泥石)作为固井材料；研究超细石墨掺量对水泥石的抗压强度和导热性能的影响；运用XRD、 TG、 MIP、 SEM测试和表征水泥石的物相组成、孔隙率和结构致密性，研究不同掺量的超细石墨对水泥石导热性能的影响；探讨不同石墨掺量和孔隙率条件下的水泥石导热机制。结果表明：随着超细石墨掺量的增大，水泥石的导热系数先增大后减小，当超细石墨质量分数为12%时，水泥石导热系数达到最大值，为2.45 W/(m·K);超细石墨的导热性能、孔隙率与水化产物的含量均可影响水泥石导热性能；随着超细石墨掺量的增大，水泥石的抗压强度先增大后减小；综合考虑水泥石的导热性能与力学性能，超细石墨的优选质量分数应为10%～12%。     

石墨和碳纳米管掺杂对十四醇/SiO_2复合材料相变储热及导热性能的影响

采用石墨(GP)和多壁碳纳米管(MWCNTs)为导热剂,溶胶-凝胶法和超声法制备了十四醇/SiO_2/GP、十四醇/SiO_2/MWCNTs复合相变材料,研究了不同导热剂及含量对复合相变材料的相变及导热性能的影响。结果表明,导热剂掺杂量小于3.0%(wt,质量分数,下同)时对复合材料相变焓影响不大,并且0.7%含量的MWCNTs会增加相变焓。复合相变材料的导热性随着导热剂的掺入,材料的导热系数大幅度提升;当掺杂量超过5.6%时,MWCNTs对复合材料导热系数的提高优于GP。     

双组元掺杂钛硅再结晶石墨传导性能的研究

用煅烧石油焦作填料,煤沥青作粘结剂,钛粉和硅粉作添加剂,采用热压工艺制备了一系列双组元掺杂再结晶石墨.考察了不同质量配比的添加剂对再结晶石墨的热导率、电阻率和抗弯强度的影响以及微观结构的变化.实验结果表明,与相同工艺条件下制备的纯石墨材料相比较,掺杂15wt％钛粉再结晶石墨的传导以及力学性能有较大幅度的提高.在掺杂钛粉15wt％、硅粉<2wt％时,双组元再结晶石墨的常温热导率随着硅粉的掺杂量的增加有所提高.当掺杂钛粉及硅粉分别为15wt％和2wt％时,再结晶石墨RG-TiSi-152的常温热导率可达494W/m·K.但是当掺杂钛粉15wt％、硅粉>2wt％时,随着硅粉的继续增加,再结晶石墨的常温热导率反而降低.而双组元掺杂钛硅再结晶石墨的导电以及力学性能却随着硅粉的掺杂量的增加而降低.XRD分析表明,对于双组元掺杂钛硅再结晶石墨而言,钛元素最终在材料中以碳化钛形式存在,而硅元素则大都以气态形式被逸出,XRD物相图谱中未发现硅及其碳化物的存在.材料RG-TiSi-152的微晶尺寸La以及晶面层间距d₀₀₂分别为864和0.3355nm.     

Atomistic defect structures of Co3Ti containing boron,carbon and beryllium

The lattice properties of the L1₂-type Co₃Ti alloys doped with boron, carbon and beryllium were investigated by the X-ray diffraction analysis. The solubility limits of boron, carbon and beryllium into the Co₃Ti were shown to be 3.0, 0.2, and 0.6 at%, respectively. It was shown that the doping of boron enhanced both of the lattice parameter and the atomic ordering of the alloy, while the doping of carbon or beryllium reduced both of them. Based on these experimental results and the consideration for size (difference) and energetics between the constituent atoms and the additive atoms, it was proposed that boron occupied on the octahedral interstitial site, and carbon and beryllium occupied on the substitutional sites of cobalt and titanium respectively.     

Effects of doping concentration on the microstructural and optoelectrical properties of boron doped amorphous and nanocrystalline silicon films

Boron doped hydrogenated amorphous silicon thin films were prepared by plasma-enhanced chemical vapor deposition technique at various flow rate of diborane (F_B). As-deposited samples were thermally annealed at the temperature of 800 °C to obtain the doped nanocrystalline silicon (nc-Si) films. The effect of boron concentration on the microstructural, optical and electrical properties of the films was investigated. X-ray photoelectron spectroscopy (XPS) measurements demonstrated the presence of the substitutional boron in the doped films. It was found that thermal annealing can efficiently activate the dopants in films accompanying with formation of nc-Si grains. Based on the temperature-dependent conductivity measurements, it was shown that the dark conductivity of doped amorphous samples increases monotonously with the increase of doping content. While the dark conductivity of doped nc-Si films is not only determined by the concentration of dopant but also the crystallinity of the films. As increasing the flow rate of diborane, the crystallinity of doped nc-Si films decreases, which causes the decrease of dark conductivity. Finally, the high dark conductivity of 178.68 S cm⁻¹ of the B-doped nc-Si thin films can be obtained.     

掺杂钛催化机理及其再结晶石墨导热性能的研究

用煅烧石油焦作填料、煤沥青作粘结剂、钛粉作添加剂,采用热压工艺制备了一系列不同质量配比的掺杂钛再结晶石墨.考察了不同质量配比的添加钛对再结晶石墨的热导率、抗弯强度的影响以及微观结构的变化.实验结果表明,与相同工艺条件下制备的纯石墨材料相比较,掺杂钛再结晶石墨的热导率、抗弯强度均有较大的提高.室温下,RG-15再结晶石墨的层面方向热导率可达424W/(m·k),抗弯强度可达50.2MPa.微观结构分析表明,少量的掺杂钛,即可使材料达到很高的石墨化度;过多的钛掺杂量不利于材料的热导率以及抗弯强度;原料中掺钛量为15wt％时,再结晶石墨的微晶发育以及排列程度最好,此材料的石墨化度为96.4％,微晶参数La为306nm.XRD物相分析表明,钛元素在再结晶石墨中以碳化钛的形式存在.钛对再结晶石墨制备过程的催化作用可以用液相转化机理来解释.     

Influence of chemical composition and microstructure on thermal conductivity of alloyed pearlitic flake graphite cast irons

Thermal conductivity is one of the most important properties of flake graphite cast iron, that decides the transient temperature and thermal stress distribution in the components which are subjected to elevated temperature applications. Such applications include cylinder heads, brake-drums, exhaust manifolds, ingot moulds, hot mill rolls and dies. Thermal conductivity values are experimentally measured in 23 flake graphite cast irons having an identical base iron composition. The irons selected can be classified into two groups: one with high carbon (3.93%) content and another with medium carbon (3.00%) content. The irons are alloyed with commonly used alloying elements such as molybdenum, chromium, vanadium, nickel, tin, antimony, copper and aluminium. Thermal conductivity values are determined up to the temperature range 40 to 500° C and values up to 40 to 700° C are presented by extrapolation. The present work has provided information regarding thermal conductivitiy of flake graphite cast irons which are used for thermal fatigue applications (where the temperature of the component usually reaches a maximum of 700° C). It is concluded that an increased amount of graphite carbon, an increased amount of type A graphite and an increased fineness of graphite increase thermal conductivity. Further, molybdenum increases thermal conductivity appreciably while nickel and copper increase it moderately. Aluminium and silicon considerably reduce thermal conductivity while chromium, vanadium, tin and antimony reduce it moderately.     

Borosiloxane boron diffusion for p-emitter formation on n-type silicon wafers

Thermal boron diffusion, which forms highly doped and shallow p-emitters on phosphor-doped silicon wafers, is one of the primary processes in commercial-scale production of n-type cells. Here, we report on the use of nontoxic and nonvolatile borosiloxane sols as the spin-on boron source. In comparison to the tribromide (BBr₃) boron diffusion that is applied in the production of most commercial n-type cells, borosiloxane boron diffusion may have potential advantages in terms of cost, safety, operability, etc. The borosiloxane sols studied here were formed from a cross-linking reaction between boron acid and a mixture of two types of silicon alkoxides, methyltriethoxysilane (MTEOS) and dimethyldiethoxysilane (DMDEOS). The MTEOS/DMDEOS ratio was found to be the key factor determining the synthetic period, net structure, thermal transformation property, and coating behavior of the borosiloxane sols. In combination with the spin-coating method, the performance of borosiloxane boron diffusion into phosphor-doped silicon wafers (1–3 Ω·cm) was systematically investigated by varying the borosiloxane composition (boron/silicon or MTEOS/DMDEOS ratio) and the diffusion process parameters (temperature, ambience, and period of individual sub-steps), and by relating them to the resulting sheet resistance and boron doping profile. The results show that under the diffusion conditions in conventional cell production lines, the formed p-emitters can have variable sheet resistance in the range of 35–582 Ω/□ and boron doping depth of 100–300 nm.     

硼掺杂球磨SiGe合金的热电性能

SiGe合金热电材料作为一种传统的高温热电材料一直以来受到广泛关注。本研究通过B在球磨SiGe合金中的P型掺杂,有效增加了材料的载流子浓度,优化材料的电学性能。通过球磨降低材料的晶粒尺寸,增强晶界对声子的散射,降低材料的晶格热导率。另外,B掺杂使点缺陷散射和载流子-声子散射得到增强,材料的晶格热导率进一步降低。在室温时,Si_(0.8)Ge_(0.2)B_(0.04)的晶格热导率为~4Wm~(-1) K~(-1)。由于掺杂后电导率提高,热导率降低,因此热电优值zT得到了提高。在850K时,Si_(0.8)Ge_(0.2)B_(0.04)的最大热电优值为0.42,与Si_(0.8)Ge_(0.2)B_(0.002)的样品相比,其优值提高了2.5倍左右。     

硼轻掺杂对a-Si∶H光电导层性能影响的研究

用等离子体增强化学气相沉积法制备了厚为1μm左右的B轻掺杂a-Si∶H光电导层，得到了a-Si∶H的暗电导率与淀积工艺参数和B掺杂比关系的实验曲线，利用该曲线确定了最佳工艺参数和最佳掺杂比。测量了最佳参数下淀积的a-Si∶H薄膜的电学和光学性能及其受掺杂比的影响。结果表明，当B掺杂比增大时，a-Si∶H的暗电导率先减小后增大，并可发生几个数量级的变化。光电导率减小，折射率略有降低，线性吸收系数显著增大，光学带隙减小。测量的数据表明，我们制备的B轻掺杂a-Si∶H光电导层满足投影机用液晶光阀的要求。     

Fe3+-SiO2掺杂纳米TiO2的制备及其光催化降解甲基橙的研究

以三嵌段非离子表面活性剂P123为模板,采用水热法制备了Fe3+-SiPO2掺杂纳米TiO2,通过X射线衍射(XRD)、红外光谱(FT-IR)、紫外-可见吸收光谱(UV-Vis)等手段考察了Fe3+-SiO2掺杂纳米TiO2的结构与光学特性.实验结果表明:Fe3+、SiO2掺杂进入TiO2的晶格,可获得高纯度锐钛矿相纳米TiO2.Fe3+和SiO2的加入有助于抑制金红石相的形成和晶粒长大,提高了TiO2的热稳定性.Fe3+-SiO2掺杂将TiO2的光响应范围拓宽至可见光区,提高了纳米TiO2的光催化性能.与纯纳米TiO2相比,Fe3+-SiO2掺杂纳米TiO2光催化降解甲基橙的性能显著提高.     

Low-temperature magnetothermal conductivity of pyrolytic graphite

The basal plane thermal conductivity of three highly oriented pyrolytic graphite samples was measured in the temperature region between 0.36 and 4.2 K in various magnetic fields up to 23 kG. Analysis shows that the measured thermal conductivity is simply the sum of the electronic and the lattice contributions. The lattice thermal conductivity does not depend on the external magnetic field. The phonon mean free path is limited only by the crystallite boundaries. This evidence suggests that the electron-phonon interaction is very weak. Both magnitude and temperature dependence of the lattice thermal conductivity can be explained by Komatsu's semicontinuum model. The electronic thermal conductivity has a strong magnetic field dependence and is proportional to the absolute temperature. The magnitude of the electronic thermal conductivity can be related to the electrical resistivity by the free-electron Lorenz number.