Investigation into polishing process of CVD diamond films

A new technique used for polishing chemical vapor deposition (CVD) diamond films has been investigated, by which rough polishing of the CVD diamond films can be achieved efficiently. A CVD diamond film is coated with a thin layer of electrically conductive material in advance, and then electro-discharge machining (EDM) is used to machine the coated surface. As a result, peaks on the surface of the diamond film are removed rapidly. During machining, graphitization of diamond enables the EDM process to continue. The single pulse discharge shows that the material of the coated layer evidently affects removal behavior of the CVD diamond films. Compared with the machining of ordinary metal materials, the process of EDM CVD diamond films possesses a quite different characteristic. The removal mechanism of the CVD diamond films is discussed.     

以不同PAN系炭纤维布制备燃料电池气体扩散层之研究

采用石墨化PAN系炭纤维布制备了高分子电解质燃料电池气体扩散层。通过电学实验、X-ray绕射与元素分析考察了所制气体扩散层的性能。结果表明：随热处理温度的升高，气体扩散层的电阻率降低，L2增加，d（x）2减小。高温处理后的炭纤维布作为高分子电解质燃料电池气体扩散层显示了较高的电池效能。     

Carbonization and graphitization

A review is made of recent electron microscope observations relating to the carbonization and graphitization of a variety of carbonaceous precursors. The different behaviors of graphitizing and non-graphitizing carbons are elucidated, and the effect of sulphur as a cross-linker is determined. The resulting processes are shown to apply to a wide variety of materials ranging from cokes to carbon fibers.     

Bi、Cu对大断面可锻铸铁的影响

研究Bi Cu复合孕育对大断面可锻铸铁的形成和力学性能的影响 ;结果表明 ,制作大断面可锻铸铁 ,铋含量必须达到0 .0 3 % ;Cu含量达到 0 .3 0 %可明显缩短大断面可锻铸铁第一和第二阶段石墨化时间 ,并且可使组织细密 ,石墨形态好     

Thermal and Electrical Conductivity of Amorphous and Graphitized Carbide‐Derived Carbon Monoliths

The influence of graphitization and composition of carbide‐derived carbon (CDC) monoliths on the electrical and thermal conductivity was investigated. Carbon monoliths with varying porosities were synthesized employing biomorphous macroporous TiC and SiC as precursors. Graphitization was carried out in situ during high‐temperature chlorination with and without addition of nickel, iron, and cobalt chloride to the carbide. The graphitized monoliths showed improved properties. The results demonstrate that despite graphitic carbon also glass‐like carbon, stemming from the carbide synthesis, increases the thermal and electrical conductivity significantly.     

Amorphization and graphitization of single-crystal diamond — A transmission electron microscopy study

The amorphization and graphitization of single-crystal diamond by ion implantation were explored using transmission electron microscopy (TEM). The effect of ion implantation and annealing on the microstructure was studied in (100) diamond substrates Si⁺ implanted at 1 MeV. At a dose of 1 × 10¹⁵ cm^− 2, implants done at 77 K showed a damage layer that evolves into amorphous pockets upon annealing at 1350 °C for 24 h whereas room temperature implants (303 K) recovered to the original defect free state upon annealing. Increasing the dose to 7 × 10¹⁵ Si⁺/cm² at 303 K created an amorphous-carbon layer 570 ± 20 nm thick. Using a buried marker layer, it was possible to determine that the swelling associated with the amorphization process was 150 nm. From this it was calculated that the layer while obviously less dense than crystalline diamond was still 15% more dense than graphite. Electron diffraction is consistent with the as-implanted structure consisting of amorphous carbon. Upon annealing, further swelling occurs, and full graphitization is achieved between 1 and 24 h at 1350 °C as determined by both the density and electron diffraction analysis. No solid phase epitaxial recrystallization of diamond is observed. The graphite showed a preferred crystal orientation with the (002)g//(022)d. Comparison with Monte Carlo simulations suggests the critical displacement threshold for amorphization of diamond is approximately 6 ± 2 × 10²² vacancies/cm³.     

铸铁钢锭模铸态残留应力初探

通过对合格的铸铁钢锭模的铸态残留应力的实际检测,发现当钢锭模内表层有“额外”石墨化时残留铸造应力呈不利状态;而无额外石墨化时残留铸造应力呈“拉内压外”的有利状态、无需时效热处理,并从而推荐了合理化学成分。通过实际检测还发现,沿用工艺铸得的锭模的弹性模数及泊松比值较低,且具有软的力学特性。     

利用感应加热技术进行炭纤维连续石墨化

采用感应加热技术研制出炭纤维连续高温热处理专用设备石墨化炉，最高使用温度3000℃。对PAN基炭纤维T300进行了连续石墨化处理，热处理温度为2000℃～3000℃，制备出力学性能相当于日本东丽公司M40的石墨纤维，验证了该设备的技术可行性。考察了热处理温度对炭纤维力学性能、密度和直径的影响，用SEM观察了石墨化前后炭纤维表面微观形态的变化。结果表明：随热处理温度的提高，炭纤维的密度增大、直径减小，弹性模量升高，而抗拉强度下降。经3000℃高温热处理后，纤维的弹性模量高达450GPa。