碳化钛复合材料的制备及性能研究

采用真空烧结工艺和热压烧结工艺制备了碳化钛复合材料。凭借场发射扫描电镜（SEM）对试样的表观形貌与断口形貌进行了观察,检测了其力学性能并分析了抗氧化性能。结果显示：采用不同烧结工艺制备的碳化钛复合材料的力学性能及微观结构有较大差别,热压烧结工艺制备的试样各项性能较优,且试样的断裂面显微组织细密、晶界分布明显、裂纹扩张路线多样变化且走向清晰。力学性能分别为：弯曲强度1139 MPa,断裂韧性9.8 MPa·m1/2,维氏硬度21.7 GPa,相对密度99.2%。在设定的条件氧化2 h后,900℃时热压烧结制备的试样表面生成了对基体没有保护效用的非保护性氧化膜;而1150℃时试样表面形成了一层致密的对基体具有保护效果的保护性氧化膜。     

热压烧结制备碳化钛复合材料及其性能研究

采用热压烧结工艺制备了碳化钛复合材料.选用扫描电镜(SEM)观察试样的表观形貌与断口形貌,分别检测了其力学性能,以X射线衍射仪(XRD)对复合材料的成分进行了表征并对其抗氧化性能进行了分析.结果显示,在碳化钛材料中添加WC改善了其显微结构和力学性能,WC颗粒在TiC基体材料中离散补强增韧以及金属组分的强韧化,有助于Ti...     

氮化硅加入量对碳化硅-氮化硅-莫来石复相材料氧化层的影响

以莫来石、红柱石、氮化硅、碳化硅为主要原料,在空气气氛下烧成制备碳化硅-氮化硅-莫来石复相材料,并采用XRD、SEM样品进行了表征。结果表明:碳化硅化硅-氮化硅-莫来石复合材料在烧结过程中会在试样表面形成氧化层,分为氧化膜和致密层。氧化膜的主要成分为Si O2,其主要是碳化硅和氮化硅的氧化产物,随着试样中氮化硅含量的增加,试样表面形成的Si O2逐渐增多;试样截面出现致密层,随着试样中氮化硅含量的增加,试样的致密层厚度逐渐减小。     

SiCf/SiO2复合材料的制备及界面层对其力学性能的影响

以碳化硅(SiC)纤维为增强体,采用真空浸渍法制备了2.5维连续SiC纤维增韧的SiO2基(SiCf/SiO2)复合材料,研究了SiC纤维编织体上不同的界面层对SiCf/SiO2复合材料力学性能的影响.化学气相渗透(CVI)法制备的热解碳(PyC)和PyC/SiC双层界面层分别使材料的抗弯强度由无界面层的52.2 MPa提高至67.4 MPa和180.3 MPa,但均使材料的韧性降低.用扫描电镜观察了材料的断口形貌,结果表明,PyC和PyC/SiC层不仅提高了材料的抗弯强度,而且增加了基体同纤维间的结合力,使基体有效地将载荷传递给纤维.PyC/SiC层能有效地保护SiC纤维,防止烧结过程中释放出的结晶水对纤维的损伤,有助于提高材料的力学性能.     

纤维氧化处理对SiCsf/SiC复合材料力学性能的影响

以Y2O3、Al2O3为烧结助剂,采用无压烧结法制备短碳化硅纤维(2～4mm)增强碳化硅(ShortSiCfiberreinforcedSiCcomposite,SiCsf/SiC)复合材料,研究了纤维氧化处理对SiCsf/SiC复合材料结构及力学性能的影响。采用X射线衍射(XRD)、扫描电镜(SEM)以及力学性能试验机对材料进行结构表征和力学性能测试。结果表明:纤维氧化处理后,复合材料的弯曲强度和断裂韧性均有大幅提高。当纤维含量达到5wt%时,复合材料断裂韧性为5.41MPa.m1/2,与原始纤维增强SiC样品相比,提高了6.5%;与无纤维增强SiC样品相比,提高了27%。扫描电镜显示纤维氧化处理后,纤维与基体结合紧密。     

碳化硅晶须改性反应烧结碳化硅陶瓷的显微结构及性能

以碳化硅晶须为增强体、碳化硅--碳为基体制备晶须增强反应烧结碳化硅复合材料,研究了碳化硅晶须、碳含量对复合材料显微结构与性能的影响。结果表明:碳化硅晶须经高温反应烧结后仍保持表面的竹节结构,且晶须增强体与反应烧结碳化硅基体间形成适中的界面结合强度;材料断口处有明显的晶须拔出,当碳黑含量为6%(质量分数)时,随着晶须含量的增加,材料的抗弯强度从200MPa提高到310MPa(晶须含量15%),当碳黑含量为18%时,随着晶须含量的增加,材料断裂韧性从3.3MPa·m1/2提高到4.3MPa·m1/2;碳化硅晶须含量过高时,晶须的"搭桥"效应导致材料中含有较多的游离硅,限制了材料力学性能进一步提高;微氧化处理使材料表面形成致密、均匀的氧化膜,可显著提高反应烧结碳化硅的抗弯强度和断裂韧性。     

B_4C-SiC复合材料的制备及性能研究

以碳化硼为基体,碳化硅为增强相,炭黑为烧结助剂,通过热压烧结工艺制备了B_4C-SiC复合材料。测试了其力学性能,并借助SEM对烧结体进行断口形貌观察。结果表明:在本实验条件下,当SiC添加量在9 wt%时材料力学性能最佳,体积密度为2.548 g/cm~3,相对密度为99.6%,抗弯强度为403 MPa,断裂韧性为5.26MPa·m~(1/2)。显微组织结构致密,晶粒细小、均匀。增韧机理主要为SiC颗粒弥散引起的钉扎效应和裂纹偏转。     

急冷处理对氧化烧结Si3N4/SiC复合材料强度的影响

研究了急冷处理对氧化烧结氮化硅结合碳化硅复合材料强度的影响,结果表明,经急冷(1400℃)处理制备的试样强度有明显提高。通过X射线衍射仪(XRD)对材料进行物相分析和场发射扫描电镜(FE-SEM)观察材料的断面形貌,发现经1400℃急冷处理后的试样内部有大量碳硅石(moissanite)晶相出现,并且在Si3N4晶界处,生成了很多小颗粒,这些可能是试样强度提高的原因所在。     

不同气氛下合成的SiAlON结合刚玉或碳化硅材料的研究

以刚玉细粉、碳化硅细粉、氮化硅细粉、α-Al2O3,微粉和金属Al粉为主要原料,聚乙烯醇为结合剂,经球磨、混练、困料和成型后,分别在空气裸烧(氧化气氛)、埋石墨粉(还原气氛)、埋石墨+碳化硅混合粉(还原气氛)3种气氛下进行1 600℃6 h热处理制备了SiAlON结合刚玉或碳化硅复合耐火材料,并研究了刚玉或碳化硅粉加入量(7.5%～90%,质量分数)和烧成气氛对SiAlON相的生成量、晶体形貌以及耐火制品的相组成、显微结构和性能的影响.结果表明:(1)随着刚玉粉含量的增加,3种气氛下烧后的SiAlON结合刚玉材料的致密度均增大,烧结性能增强;但氧化气氛下烧结性能好于还原气氛下的.(2)2种还原气氛下烧成的Si A10N结合刚玉试样的相组成均为刚玉、SiAlON和SiC;而在氧化气氛下烧成的试样出现了分层现象,其非氧化层主要为SiAlON、刚玉和少量的莫来石.(3)不同气氛下烧成的SiAlON结合刚玉材料中均有柱状或纤维状的SiAlON生成,但氧化气氛下的SiAlON柱状物比还原气氛下的要粗壮、完整得多,且成群生长.(4)随着SiC粉含量的增加,SiAlON结合碳化硅材料在2种还原气氛下烧后的致密度降低,烧结性能下降;而在氧化气氛下烧后严重氧化,形成了较厚的釉层.     

反应烧结制备碳化硅-氮化铝复合材料

采用硅作为熔渗剂,利用真空反应烧结的工艺,在1600℃烧结制得了结构致密、密度低的碳化硅-氮化铝(SiC/AlN)复合材料,分析测试了所制得的复合材料的物相、微观结构和力学性能.结果表明,氮化铝的添加量由2wt％增加到10wt％时,复合材料的力学性能出现先增加后减小的趋势,当AlN含量为6wt％时,得到复合材料的力学性能最高,其抗弯强度为256 MPa,显微硬度为2660 HV.加入AlN后,复合材料的孔隙率略微有点上升,烧结体的密度在2.95 ～3.01 g/cm3之间.复合材料的主要组成相为SiC、AlN和Si.     

Preparation of reaction bonded silicon carbide (RBSC) using boron carbide as an alternative source of carbon

RBSC composites are fully dense materials fabricated by infiltration of compacted mixtures of silicon carbide and carbon by molten silicon. Free carbon is usually added in the form of an organic resin that undergoes subsequent pyrolysis. The environmentally unfriendly pyrolysis process and the presence of residual silicon are serious drawbacks of this process. The study describes an alternative approach that minimizes the residual silicon fraction by making use of a multimodal particle size distribution, in order to increase the green density of the preforms prior infiltration. The addition of boron carbide provides an alternative source of carbon, thereby eliminating the need for pyrolized organic compounds. The residual silicon fraction in the RBSC composites, prepared according to the novel processing route, is significantly reduced. Their mechanical properties, in particular the specific flexural strength is by 15% higher than the value reported for RBSC composites prepared by the conventional approach.     

Decomposition of NO on Tungsten Carbide and Molybdenum Carbide Surfaces

The decomposition of ¹⁵NO on C/W(111), C/W(110), and on monolayer and bulk C/Mo/W(111) surfaces is compared based on temperature-programmed desorption (TPD) and Auger electron spectroscopy (AES) measurements. Our results indicate that the decomposition of ¹⁵NO occurs readily over all surfaces, and the only ¹⁵N-containing reaction products are ¹⁵N₂ and ¹⁵N₂O under our experimental conditions. Much higher surface reactivity for ¹⁵NO decomposition was observed over the more open-structured C/W(111) surface, with a value of 0.68 ¹⁵NO/W, in contrast to the surface reactivity of 0.24 ¹⁵NO/W over the close-packed C/W(110) surface. The selectivity of these two ¹⁵N-containing reaction products depends on the structure of the substrates as well. The more open-structured C/W(111) surface favors the production of ¹⁵N₂, with a product selectivity of ¹⁵N₂ being approximately 87%. In contrast, the selectivity to ¹⁵N₂ is only about 52% on C/W(110). In addition, we have investigated the decomposition of ¹⁵NO on C/Mo surfaces that were epitaxially grown on W(111). The selectivity of ¹⁵N₂ on C/Mo/W(111) surfaces is 88%, which is very similar to that observed on C/W(111). Finally, the general similarity between the DeNOx chemistry on carbides and on Pt-group metals will also be discussed.     

国产化干法乙炔装置运行总结

总结了国产化干法乙炔装置2次开车情况,给出了装置的实际运行指标,并详述了开车过程中发现的问题及改进办法。     

Effect of Carbon Containing Materials on Pure Carbon Reaction-bonded SiC

Petroleum coke, graphite, gas carbon and lower sulfur carbon black were used to prepare reaction-bonded silicon carbide. The influences of different carbon containing materials on properties of carbonaceous precursors, sintering process, and microstructure of the prepared SiC were researched. The results show that ： （ 1 ） With the density of carbon containing materials increasing, the porosity of carbonaceous precursors decreases and the infiltrating process of liquid silicon is more difficult. （2） The reaction between carbon containing materials and liquid silicon, the volume effect is more obvious with the density of carbon containing materials increasing. （3） As the carbon containing materials density decreasing, residual carbon in reaction bonded SiC also decreases.     

Comparison between tungsten carbide and molybdenum carbide for the hydrodenitrogenation of carbazole

The activity of molybdenum and tungsten carbides in hydrodenitrogenation (HDN) of carbazole was studied. Transition metal carbides (Mo₂C and W₂C) were synthesized using the temperature-programmed reaction of the appropriate oxide precursor (MoO₃ and WO₃) with the following gas mixture: 10 vol.% CH₄/H₂. The structure of the catalysts was characterized using X-ray diffraction, CO chemisorption, high resolution transmission electron microscopy (HRTEM) and BET surface area measurements. From the HRTEM analysis, it could be concluded that the tungsten carbide was thioresistant in our operating conditions (50 ppm of S, pressure = 6 MPa, 553 < T < 653 K, H₂/feed volumic ratio = 600). In the case of Mo₂C, molybdenum sulphide was observed as single slabs. The activity of catalysts was determined during the hydrodenitrogenation of carbazole at the wide range of temperature (553–653 K) and under a 6 MPa total pressure of H₂. The comparison of tungsten carbide and molybdenum carbide has shown higher activity of Mo₂C than W₂C at the same condition. However, W₂C leads to higher amount of isomers of main products, and have higher hydrogenation activity.     

电石法生产PVC需要注意的问题

叙述了电石法PVC的生产工艺及目前国内电石生产的现状,着重指出电石法生产PVC工艺中需要重视的要点。     

Comparison of molybdenum carbide and tungsten carbide for the hydrodesulfurization of dibenzothiophene

The molybdenum and tungsten carbides (Mo₂C and W₂C) were synthesized, characterized and tested in hydrodesulfurization (HDS) of dibenzothiophene (DBT). The phase purity of these catalysts was established by X-ray diffraction (XRD), and the surface properties were determined by N₂ BET specific surface area (Sg) measurements, CO chemisorption and high-resolution transmission electron microscopy (HRTEM). The activities of catalysts were determined during the HDS of DBT at a temperature of 613 K and under a 6 MPa total pressure. Both molybdenum and tungsten carbides were active in HDS of DBT. The reactivity studies showed that molybdenum carbide was more active than tungsten carbide related to weight. However, W₂C was shown to possess stronger hydrogenating properties.     

The effect of the third invariant on the strength and failure of boron carbide and silicon carbide

This article presents new test data to assess the effect the third invariant has on the strength and failure of two ceramic materials: boron carbide and silicon carbide. Two experimental techniques are used: the Brazilian test that produces a biaxial state of stress, and a new technique that uses a high-pressure confinement vessel to load a specially designed dumbbell specimen in triaxial extension. The dumbbell geometry provides two important advantages over the typically used cylindrical specimen: no adhesive is required to bond the specimen to the load cell because the dumbbell geometry naturally takes the specimen into tension, and any loading asymmetries are essentially eliminated due to the axisymmetric geometry. The results show that when the stress state is on the tensile meridian the equivalent stress at failure is constant, independent of the hydrostatic pressure. The average equivalent stress at failure is for boron carbide and for silicon carbide. The Brazilian test was only performed on boron carbide and failed at , much higher than when on the tensile meridian () indicating that the effect of the third invariant is significant (because of the difference in the failure strength) and must be accounted for to accurately predict when failure will occur.     

Seamless joining of silicon carbide ceramics through an sacrificial interlayer of Dy3Si2C2

A ternary carbide Dy₃Si₂C₂ coating was fabricated on the surface of SiC through a molten salt technique. Using the Dy₃Si₂C₂ coating as the joining interlayer, seamless joining of SiC ceramic was achieved at temperature as low as 1500 °C. Phase diagram calculation indicates that seamless joining was achieved by the formation of liquid phase at the interface between Dy₃Si₂C₂ and SiC, which was squeezed out under pressure and continuously consumed by the joining interlayer. This work implies the great potential of the family of ternary rare-earth metal carbide Re₃Si₂C₂ (Re = Y, La-Nd) as the sacrificial interlayer for high-quality SiC joining.     

碳化硅冶炼炉逸出气体的组成及理化性质研究

利用自行发明的多热源碳化硅冶炼炉，以煤（或焦炭）和石英砂为原料合成SiC，同时伴生大量副产品可燃性气体，研究了煤种和冶炼工艺对燃气的组成及酸碱性的影响，并对经济效益进行分析。结果表明，燃气中以CO气体为主，平均含量可达70％，CO＋H2平均含量达85％，CO＋H2＋CH4平均含量达90％，使用无烟煤、烟煤焦炭或焙烧料法可提高合成气中CO含量，若燃气用于火力发电可节约25．8％的电费成本。