基于等离子火炬的C/C复合材料烧蚀实验及理论研究

基于等离子火炬进行了C/C复合材料烧蚀实验,获得了材料的烧蚀表面形态及烧蚀产物光谱,确定了等离子火炬务件下的典型烧蚀产物.同时基于JANAF数据,通过最小能量法计算了等离子火炬低压高焓状态的热化学烧蚀产物,与光谱检测结果基本一致.     

煤在直流电弧等离子体中的气化

实验利用由我国完全自主研制的一套直流电弧等离子体煤气化装置，以空气为等离子发生器气源，大同煤为原料，在水蒸气参与下，初步考察了工艺条件（等离子发生器功率，供煤速率和空气流量等）对等离子体煤气化过程的影响。并优化了部分工艺参数。同时发现没有液体焦油生成，并且在气相产物中没有检测到甲烷。     

三维针刺C/(SiC-TaC)复合材料的烧蚀性能及烧蚀机理

为了提高连续碳纤维增强碳化硅(SiC)复合材料的抗烧蚀性能,采用浆料浸渗结合化学气相浸渗SiC工艺制备出三维针刺碳纤维增强SiC-碳化钽(TaC)复合材料.采用氧-乙炔烧蚀试验测试复合材料烧蚀性能,用扫描电子显微镜分析烧蚀后材料表面的微观形貌,用X射线衍射、表面能谱分析对材料烧蚀后成分进行分析表征.结果表明:C/SiC-TaC)复合材料线烧蚀率为0.07mm/s,相对C/SiC复合材料而言表现出较好的抗烧蚀能力,添加TaC有助于提高C/SiC复合材料抗烧蚀性能.在中心区域,出现明显烧蚀坑,纤维与基体被致密的Ta2O5层覆盖,起到保护C纤维和基体的作用,复合材料的烧蚀以升华、氧化和机械剥蚀为主.在边缘和过渡区域,烧蚀以热化学氧化烧蚀为主.     

化学气相渗透法制备三维针刺C/SiC复合材料的烧蚀性能

用化学气相渗透法制备了三维针刺碳纤维增强碳化硅陶瓷基复合材料,复合材料的平均密度为2.15 g/cm3,气孔率为16.0%.用氧乙炔焰研究了复合材料的烧蚀性能,用扫描电镜分析了烧蚀表面的形貌,用表面能谱分析了烧蚀产物的成分.复合材料的线烧蚀率和质量烧蚀率分别为0.03mm/s和0.004 7 g/s.在烧蚀中心区,烧蚀最严重,表层只有C纤维骨架,且C纤维呈针状,复合材料的烧蚀以升华和冲刷为主.在烧蚀过渡区,垂直于烧蚀面的C纤维表现出端部锐化、根部细化的特性,平行于烧蚀面的C纤维呈针状,复合材料的烧蚀以氧化和机械剥蚀为主.烧蚀边缘烧蚀不明显,烧蚀产物和SiC基体熔融后覆盖在烧蚀表面,阻碍了复合材料的进一步烧蚀,复合材料的烧蚀以氧化为主.     

热等离子体催化耦合重整CH_4和CO_2制合成气

常压下,利用实验室制备的Ni-Ce/Al2O3催化剂,进行了热等离子单独重整与热等离子体催化耦合重整CH4和CO2制合成气的实验研究。实验中,催化剂被放置在等离子体反应区,催化剂床层由高温等离子射流气体加热。固定原料气配比V(CO2)/V(CH4)=1、等离子体工作载气流量0.8 m3/h及放电功率3.5 kW不变,考察了原料气总流量对原料转化率、产物选择性、化学能效和催化剂积碳速率的影响;并探讨了助剂Ce在重整反应中的作用。结果表明:随原料气总流量的增加,CH4和CO2转化率降低,H2和CO选择性无明显变化,C2H2选择性和催化剂积碳速率增加。热等离子催化耦合重整比热等离子单独重整具有较高的原料转化率、H2和CO选择性、化学能效值和较低的C2H2选择性。     

正戊烷介质阻挡放电等离子体转化的发射光谱研究

发射光谱是等离子体诊断的最有效方法,本实验将发射光谱应用于温压双控介质阻挡反应系统,研究正戊烷(C5)-氩气(Ar)在等离子场中的转化机制,具体分析了放电功率、温度、压力等关键影响因素下发射光谱特性、C5的转化率和产物选择性。实验结果表明:发射光谱强度以及C5转化率与放电功率呈线性增加关系,但不同放电功率下产物的选择性基本不变;随着温度升高(298～473 K)和压力(0.40～1.0 bar)的减小,光谱强度增强,C5转化率提高,但氢气的选择性基本维持在10%;发射光谱强度的变化与C5转化率的变化具有很好的吻合性,表明高能电子碰撞反应对C5的初步分解起到重要的作用。但从反应产物分析,气相短链烃和液相长链烃同时存在,且选择性基本保持不变,说明后续的自由基反应和热化学反应决定了最终的产物,且其化学反应平衡受本实验反应条件影响不大。     

C/C-SiC-ZrC复合材料抗氧化烧蚀性能研究

采用化学气相渗透(CVI-C)和液相浸渍裂解(PIP-SiC、PIP-ZrC)工艺制备了2.5D C/C-SiC-ZrC陶瓷基复合材料。通过液氧煤油超音速火焰对蘑菇头驻点试验件进行烧蚀试验,并采用扫描电子显微镜(SEM)和能谱分析仪(EDS)对材料的微观形貌及抗氧化烧蚀机理进行了初步探讨。结果表明,C/C-ZrC-SiC复合材料基体中SiC:ZrC质量比约为4:6,在2200K~2400K液氧煤油超音速火焰烧蚀试验环境下具有良好的抗烧蚀性能,100s蘑菇头驻点线烧蚀率仅为0.0054mm/s。研究发现,C/C-ZrC-SiC复合材料中合适的SiC和ZrC基体配比,高温氧化烧蚀过程中,材料表面形成了以ZrO_(2)颗粒为骨架的连续致密粘稠熔融层,有效封填材料表面的裂纹、孔洞,降低氧化性气氛向材料内部扩散的速率,对材料形成了较好的保护。     

K和Ca元素对生物质快速热解瞬态轻烃及含氧气体的影响

K、Ca元素以无机态和有机态的形式赋存于生物质内,影响着生物质热解过程中木质素、纤维素及半纤维素分子的断链及解聚过程,进而一定程度地影响着生物质热解气相产物形成与转化。热解反应过程中中间瞬态产物作为气体合成的中间产物对于热解反应最终气相产物的形成具有极为重要的研究意义。将生物质(稻壳)进行了酸洗处理,再定向负载K、Ca元素,利用Py-GC/MS在500~900℃热解温度下,对生物质原料进行了快速热解的实验研究。利用气相色谱质谱仪(GC/MS)对进样延迟时间为20 s时生物质快速热解瞬态轻烃及含氧气态组分的种类及含量进行了在线半定量分析,从而进一步表征了K和Ca元素对生物质快速热解气相组分的影响以及热解反应过程中气相中间产物的形成转化机制。研究结果表明:低温条件下(≤600℃),H-form、K-loaded和Ca-loaded生物质快速热解瞬态气体产物以CO、CO2、CH4为主,K与Ca元素促进了生物质热解CO与CO2的生成。高温条件下(≥700℃),C3H6成为20 s瞬态热解过程的主要气相产物,Ca元素对C3(C3H6)等物质的形成具有一定的促进作用,而K元素一定程度上抑制了C3H6的生成。     

SiC改性C/C复合材料的制备及其烧蚀性能

采用超声波震荡法将SiC微粉添加到二维针刺碳毡预制体中,利用热梯度化学气相浸渗工艺沉积热解碳制备了SiC改性碳纤维增强碳基(carbon fiber reinforced catbon,C/C)复合材料.借助x射线衍射与扫描电子显微镜检测和观察材料的微观结构,利用氧-乙炔烧蚀实验测试材料的抗烧蚀性能.结果表明:SiC微...     

落地原油的激光诱导击穿光谱定量分析研究

激光诱导击穿光谱作为一种新型的检测技术,它是利用样品在高温下气化电离产生的等离子体光谱对物质的成份和含量进行分析的型技术。利用Nd∶YAG脉冲激光器作为光源,以高分辨率、宽光谱段的中阶梯光栅光谱仪和ICCD为谱线分离与探测器件,在实验室自然大气环境下诱导产生土壤激光等离子体,通过等离子体原子发射光谱法定量分析了含油土壤样品中原油的含量,实验上研究了在最佳实验条件下土壤中原油的分析谱线,测定了原油的定标曲线,实验结果表明,原油浓度在50～300范围内,元素含量与光谱线强度之间呈现较好的线性关系。谱线强度随浓度的增加而增加。给出土壤中石油的定标曲线,并计算得到石油在土壤中的检测限约为45mg/L。中间点校正的相对误差最大值为8%。     

Transferred arc plasma processed mullite from coal ash and bauxite

Coal ash disposal is one of the main problems in thermal power plant unit. Currently, a number of waste management systems are being tried for effective disposal of coal ash. In this paper, coal ash from thermal power plant unit was successfully utilized for synthesis of mullite ceramic by using transferred arc plasma processing (TAP) technique. For this purpose, bauxite was added with coal ash by 0, 25, 50 and75 weight ratio. The compositions were thoroughly mixed by ball milling and were melted in the transferred arc plasma torch at 10 kW input power level for 3 min. Argon was used as plasma forming gas. The phase and microstructure formation of the melted samples were investigated by XRD and SEM images. The results show that the additions of bauxite greatly influenced the phase formation of mullite during the processes.     

热等离子体转化煤的研究进展

介绍了热等离子体裂解煤制乙炔、富勒烯、碳纳米管和炭黑,以及热等离子体煤气化制合成气的原理、研究现状、存在的主要问题及发展前景。指出热等离子煤转化是一种高效、洁净的技术,在煤化工等领域具有巨大的应用和发展空间,尤其是热等离子体裂解煤制乙炔联产氢与纳米碳材料工艺,值得重视和开发。     

A comparison of the interfacial, thermal, and ablative properties between spun and filament yarn type carbon fabric/phenolic composites

In the present paper, the interfacial, thermal, and ablative properties of phenolic composites reinforced with spun yarn type carbon fabrics (spun C/P composite) and filament yarn type carbon fabrics (filament C/P composite) heat-treated at 1100 °C have been extensively compared. The interlaminar shear strength, crack growth rate, and fracture surface were studied to evaluate the interfacial characteristics of the composites using short-beam shear test, double cantilever beam test, and scanning electron microscopy, respectively. The thermal conductivity and the coefficient of thermal expansion were also measured in the longitudinal and transverse directions, respectively. To explore the ablative characteristics of the composites in terms of insulation index, erosion rate, and microscopic pattern of ablation, an arc plasma torch was used. The interfacial properties of the spun C/P composite are significantly greater than those of the filament C/P composite, with qualitative support of fracture surface observations. It has been investigated that the presence of protruded fibers in the phenolic matrix of the spun C/P composite may play an important role in enhancing the properties due to a fiber bridging effect. The longitudinal thermal conductivity of the spun C/P composite is about 7% lower than that of the filament C/P counterpart. It has been found from the ablation test using arc plasma torch flame that the erosion rate is 14% higher than that of the filament C/P counterpart. Consequently, all the experimental results suggest that use of spun yarn type carbon fabrics heat-treated at low carbonization temperature as reinforcement in a phenolic composite may significantly contribute to improving the interfacial, thermal, and ablative properties of C/P composites.     

Acetone decomposition by water plasmas at atmospheric pressure

Decomposition of aqueous acetone was performed using a direct current (DC) plasma torch at atmospheric pressure. The torch can generate the plasma with water as the plasma-supporting gas in the absence of any additional gas supply system and cooling devices. The results indicated that 5 mol% acetone was drastically decomposed by water plasmas with energy efficiencies of 1.7×10^?7 mol J^?1. The major products in the effluent gas were H₂ (60–70%), CO₂ (5–16%), CO (6–16%), and CH₄ (0.2–0.9%). However, trace levels of formic acid (HCOOH) and formaldehyde (HCHO) were observed in the liquid effluent. Based on the experimental results and information from the literature, the following decomposition mechanism was proposed for acetone in water plasmas: first, electron dissociation in arc region generates acetyl (CH₃CO) and methyl (CH₃) radicals; then, chemical oxidation or reduction in plasma flow region forms CO and CH_x(x:1–3) radicals there. Finally, the generated intermediate species undergo complex reactions to form stable compounds such as CO in downstream region. However, if little oxygen is present, those intermediate species easily recombine with each other or are oxidized by OH to form unwanted by-products, such as HCOOH and HCHO.     

Ablation-Resistance of Combustion Synthesized TiB2–Cu Cermet

TiB₂–Cu ceramic–metal composites were prepared by combustion synthesis of elemental titanium, boron, and copper powders. The synthesized product consisted of two phases: TiB₂ and copper. The addition of copper improved the strength and fracture toughness, thermal expansion coefficient, and thermal conductivity of TiB₂. Thermal shock and ablation resistances of TiB₂–Cu composites were studied using a plasma torch arc heater. Monolithic TiB₂ failed catastrophically when the plasma arc flow reached the specimen surface. However, no cracks were found on the ablation surface of the TiB₂–Cu ceramic–metal composites. The fractional mass loss was 4.09% for a TiB₂–40Cu composite, which was close to the traditional W/Cu alloys. Volatilization of metal binder and mechanical erosion of TiB₂ were observed to be the major ablation mechanisms. An ablation process model is proposed for the TiB₂–Cu composites.     

Study of the ablation of a carbon/carbon composite at ∼25 MW/m2 with a nitrogen plasma torch

Ablation of carbon/carbon (C/C) composites was investigated in a nitrogen plasma torch with a heat flux of ∼25 MW/m². The reaction products of carbon in C/C composites and nitrogen plasma jet were calculated based on the principle of free energy minimum. The calculated results show that the thermal chemical ablation and sublimation of carbon occur and C_n(g) (n = 1–3), CN(g), C₂N(g) and C₂N₂(g) may be the major reaction products consuming carbon. Ablation is apt to begin at the interfaces, especially the fibre-matrix interface and interfaces inside the matrix. Ablation of C/C composites is mainly controlled by the thermal chemical ablation, sublimation of carbon, and mechanical breakage. The formation of needle-shaped fibres and shell-shaped matrices is attributed to both the thermal chemical ablation and sublimation of carbon, while carbon fragments and fractured fibres or matrices result from the mechanical breakage.     

Treatment of biomass tar by CO2 plasma

The tar produced in the process of biomass gasification would not only corrode the pipelines and equipment, but also reduce the efficiency of biomass gasification. Traditional methods, such as physical treatment and thermal cracking, have deficiencies which severely restrict their application. This article achieved efficient transformation (carbon yield >90%) from benzene and naphthalene, regarded as model compounds of biomass tar, to syngas using CO₂ plasma on self-designed rotating arc plasma torch, proving the feasibility of CO₂ plasma treatment of biomass tar. Further analysis on the composition of practical biomass tar and the investigation of biomass tar gasification were carried out. Water content in biomass tar could be used as gasification agent and control the H₂/CO scale (0.3—1). The above results provide new ideas for the development of biomass tar harmlessness and resource utilization technology.     

二氧化碳等离子体处理生物质焦油

生物质气化过程中副产的焦油不仅有腐蚀设备、堵塞管道等危害，而且会降低生物质气化效率，传统的物理处理与热裂解处理方法存在诸多不足。本文基于旋转弧热等离子体反应装置，以二氧化碳作为等离子介质，选取苯及苯萘混合物作为生物质焦油的模型化合物进行了气化实验，实现了向合成气的高效转化（碳收率可达到90%以上），初步显示了该路线的可行性。进一步分析了真实生物质焦油的物质组成，考察了二氧化碳等离子体对焦油的气化性能，焦油内的水分可作为气化剂，调节合成气中H₂/CO的比例（0.3~1）。上述结果为生物质焦油无害化、资源化利用技术的发展提供了新的思路。     

Impact of cathode loss on plasma characteristics,microstructures and properties of 7YSZ coatings in PS-PVD

The slight changes in geometry and mass of the cathode of O3CP plasma torch during service life caused the variety of arc motion between the cathode and anode. The voltage appeared to rise first and then fall. In this experiment, the impact of cathode loss on plasma characteristics, microstructures and properties of 7YSZ coatings was investigated. Optical emission spectroscopy (OES) was used to characterize the plasma jet characteristics such as plasma temperature and electron number density. It is found that vapor deposition is the main deposition mechanism, and the microstructures of the coatings are mainly affected by the supersaturation and subcooling of the vapor phase, which determine the nucleation and growth of crystals. At the middle of cathode service life, the plasma temperature and electron number density are the highest and the powder is completely evaporated. High crystal growth rates and surface diffusion lead to large columnar crystals with large grain size. The best thermal shock resistance. The thermal shock resistance is the best in this case. When the cathode is in the beginning and end of service life, there are columnar grains with small size produced and many solid particles in the gaps due to diffusion difficulties generated by low temperature. Shadowing enhances to manufacture fine grains and few branches. The presence of solid particles prevents the release of thermal stress and reduces thermal shock resistance of coatings. Fine grains prevent cracks propagation to improve the bonding strength of coatings.