Polyarylacetylene as a novel graphitizable precursor for fabricating high-density C/C composite via ultra-high pressure impregnation and carbonization

High-density carbon/carbon(C/C)composite plays a critical role in the aerospace industry owing to excellent mechanical properties and resistance to ablation.However,traditional manufacturing relies on pitch precursor and hot isostatic pressure impregnation and carbonization(HIPIC)technology,which is time-consuming and expensive.In this study,we report an innovative method utilizing polyarylacetylene(PAA)resin and ultra-high pressure impregnation and carbonization(UHPIC)technology.The extremely high char yield of PAA resin(85 wt.%)and high isotropic pressure of UHPIC(over 200 MPa)promote the densification of the composite.As a result,we achieve a high-density(1.90 g/cm^(3))C/C composite with a high degree of graphitization(81%).This composite exhibits impressive properties,including flexural strength of 146 MPa,compressive strength of 187 MPa,and thermal conductivity of 147 W/(m K).When exposed to oxyacetylene flame at 3000 K for 100 s,it displays minimal linear ablation,with a rate of 1.27×10^(-2)mm/s.This study demonstrates the exceptional graphitizable characteristic of PAA resin,setting it apart from conventional resins.Our time-saving and cost-effective approach holds significant promise for aerospace applications,particularly in harsh aerodynamic heating environments.

Dynamic Compression Behavior of Ultra-high Performance Cement-based Composite with Hybrid Steel Fiber Reinforcements

Ultra-high performance cement-based composites (UHPCC) is promising in construction of concrete structures that suffer impact and explosive loads.In this study,a reference UHPCC mixture with no fiber reinforcement and four mixtures with a single type of fiber reinforcement or hybrid fiber reinforcements of straight smooth and end hook type of steel fibers were prepared.Split Hopkinson pressure bar (SHPB) was performed to investigate the dynamic compression behavior of UHPCC and X-CT test and 3D reconstruction technology were used to indicate the failure process of UHPCC under impact loading.Results show that UHPCC with 1% straight smooth fiber and 2% end hook fiber reinforcements demonstrated the best static and dynamic mechanical properties.When the hybrid steel fiber reinforcements are added in the concrete,it may need more impact energy to break the matrix and to pull out the fiber reinforcements,thus,the mixture with hybrid steel fiber reinforcements demonstrates excellent dynamic compressive performance.

SEEPAGE ABILITY OF HIGH-PRESSURE HOT COMPOSITE FOAM IN POROUS MEDIA

The technology of hot composite foam displacement refers to the injection of high-temperature flue gas and foaming and stabilizing agent into wells with a certain concentration, and after meeting the formation water, a composite foam system is formed in the reservoir. This foam displacement technology involves thermal function and so is related to nitrogen, carbon dioxide and foam flooding characteristics. After analyzing seepage flow law of hot composite foam system, seepage flow experiment of composite foam under high pressure was conducted, and seepage flow ability of hot composite foam in porous media was investigated. In the experiment, surfactant HY-3 was chosen as the foaming agent and hot flue gas was chosen as the foaming gas, and high-pressure hot foaming apparatus was employed in experiments. The experimental results indicate that the surfactant HY-3 could form stable foam in porous media, and the foam has strong ability of plugging. It is concluded that the sealing performance of foam is improved with increasing permeability and resistance coefficient and with incresing injection rate and foam strength. After foam injection, sealing characteristics of heterogeneous cores is better than that of homogeneous cores. The foam pressure has a process of transmission in porous media. In this process, with the increase of injection volume, pressure from the inlet to the outlet increases gradually, which indicates that stable foam has been formed inside the core.

Out-of-Plane Compressive Behavior for UHMWPE/Polyurethane Composites after Hygrothermal Treatment

Quasi-static and high strain rate compressive behaviors and failure mechanisms of hygrothermal treated ultra-high molecular weight polyethylene/polyurethane(UHMWPE/PU)composites have been studied in this paper.Firstly,the UHMWPE composites were immersed in water at 70℃.The out-ofplane compression test was then performed on the dry/wet state specimens at quasi-static states(0.001-0.01 s^(-1))and high strain rate states(800-2 400 s^(-1)).The split Hopkinson pressure bar(SHPB)was adopted in the dynamic tests and waveform shapers were used to smooth and control the incident pulse.The results show that there are two platforms for the water absorption curve of UHMWPE composites.The absorption of moisture reduces the quasi-static compressive strength of the material while initially increasing,then decreasing the dynamic compressive strength.Matrix plasticization,fiber/matrix interface degradation and void expansion are the main factors affecting the irregular change of static/dynamic compressive strength of UHMWPE composites.

Dynamic damage and stress-strain relations of ultra-high performance cementitious composites subjected to repeated impact

Ultra-high performance cementitious composites (UHPCC) were prepared by replacing 60% of cement with ultra-fine industrial waste powders.The dynamic damage and compressive stress-strain relations of UHPCC were studied using split Hopkinson pressure bar (SHPB).The damage of UHPCC subjected to repeated impact was measured by the ultrasonic pulse velocity method.Results show that the dynamic damage of UHPCC increases linearly with impact times and the abilities of repeated impact resistance of UHPCC are improved with increasing fiber volume fraction.The stress waves on impact were recorded and the average stress,strain and strain rate of UHPCC were calculated based on the wave propagation theory.The effects of strain rate,fibers volume fraction and impact times on the stress-strain relations of UHPCC were studied.Results show that the peak stress and elastic modulus decrease while the strain rate and peak strain increase gradually with increasing impact times.

三重介质复合油藏压力动态特征研究

建立了三重介质复合油藏试井解释模型,采用数值方法对模型进行了求解。讨论了地层的内外渗透率比、内径的大小以、窜流系数、弹性储容比、外边界条件以及表皮系数等参数对于这种类型油藏压力响应动态的影响。表明:当油藏内外区的渗透率不同时,类似于在井的周围存在封闭边界或者定压边界;内区的大小决定着反应外区渗透率影响的压力响应出现的早晚;窜流系数影响着窜流阶段出现的早晚;弹性储容比影响着导数曲线上“凹陷”的深度和宽度;而外边界的影响则由于油藏内外区渗透率的差异而和普通的三重介质油藏不同;表皮系数对压力动态的影响与内外区域渗透率比对压力动态的影响也有着很大的差别。

高压复合热泡沫在多孔介质中的渗流能力实验

复合热泡沫驱油技术是将泡沫驱油技术和热力采油技术集成在一起，充分发挥二者优势的三次采油技术。研究所涉及的复合热泡沫体系，选择HY-3表活剂作为发泡剂，热烟道气（由85％的N2和15％的CO2组成）作为发泡气体。该体系不但具有泡沫驱油和热力采油的优点，同时又具有一定的CO2驱油和N2驱油的的作用。泡沫在地层高压条件下的稳定性和封堵能力，是泡沫体系能否取得理想驱油效果的关键。研究首次利用高压泡沫装置进行复合热泡沫高压渗流能力实验，研究了高压条件下复合热泡沫的稳定性及其在多孔介质中渗流能力的影响因素。研究结果表明：在地层高压条件下，HY-3表活剂和烟道气可以在多孔介质中形成具有较强封堵能力的稳定泡沫，且在非均质岩心中的封堵效果明显好于在均质岩心中的封堵效果；岩心渗透率越高，阻力系数越大，泡沫封堵效果越好；注入速度越高，形成泡沫强度越大，泡沫封堵能力越好；气液比越大，泡沫渗流阻力越大，气液比达到1：1后，继续增大气液比对渗流阻力影响不大，为防止气窜，建议现场实施过程中气液比采用1：1。

氧化镁对超高压复合传压介质性能的影响

为了探索氧化镁的晶粒大小和含量对超高压复合传压介质性能的影响,以高岭土、滑石、绢云母为原材料,加入6%、9%、12%、15%和18%的40nm和15μm氧化镁,以水玻璃为粘结剂,用常规烧结方面制备了超高压复合传压介质,比较了两种氧化镁晶粒尺寸的不同比例的复合传压介质的热膨胀系数、密度、抗弯强度和硬度。实验结果表明:氧化镁的晶粒尺寸和含量对传压介质的性能有很大的影响;当烧结温度为1000℃,样品外观颜色与叶腊石的比较接近;在40nm氧化镁的配方4样品,在600℃的热膨胀系数比较接近叶腊石的热膨胀系数;对于40nm氧化镁来说,氧化镁的含量越高,密度、抗弯强度和硬度值越高;对于15μm氧化镁来说,总的来说,当氧化镁含量为15%时,综合性能较好。

混合边界油藏压力分布的有限元法模拟

建立了稳定渗条件下的有限元方程,针对定边界和封闭边界混合作用下的渗流问题进行了模拟计算,给出了圆形地层和矩形地层在以上条件下的压力分布,结果表明,混合油藏外边界将产生复杂的地层压力分布,压力分布随地层方位的不同而不同,同时说明,有限元法用于求解复杂边界条件的渗流问题是方便有效的。

一种非线性复合介质不定常渗流数学模型

给出了一种新的二区非线性复合介质不定常径向渗流数学模型 ,该模型中将复合介质内区渗透率归纳为径向距离的幂函数 ,应用该模型能更好地描述近井地带介质受伤害或改善状况下的油气井不定常渗流 ,幂指数能够反映受伤害或改善地带的非均质程度 .根据Bessel函数理论得到了新模型的Laplace变换解式 ,并由Stehfest数值反演方法对解式做了分析计算 ,绘制出压力及压力导数双对数曲线 .

双孔介质复合封闭储层压力分布的求解分析

针对双孔介质复合封闭储层模型,研究了两种内边界条件(是否考虑井筒储存和表皮效应)下的变流率问题的无因次内、外区储层压力分布的Laplace空间解,在深入剖析了解的结构和相互联系的基础上,找出了它与常见的复合、双孔、均质储层压力分布间的相互关系。此项研究,无疑是对试井分析理论的一种完善,并填补了试井分析理论在此方面的空白和不足,对相应试井分析软件的研制具有深远的应用价值,对油藏工程中的数值模拟方法也具有指导意义。

超高压复合传压介质制备的研究

以高岭土、滑石、氧化镁、绢云母四种矿物为原料,设计不同配比配制四个配方,经充分研磨,压制成型和在不同的温度下进行烧结得到复合传压介质的样品。测试样品的晶体结构、热膨胀系数、密度和抗弯强度,并与叶腊石的性能进行了比较。结果表明:样品的晶体结构与天然叶腊石不同,样品的热膨胀系数和密度都小于叶腊石,在800℃烧结得到样品抗弯强度较高。

规整复合吸附剂真空变压吸附分离CH_(4)/N_(2)工艺模拟与分析

为减少甲烷排放,实现低浓度煤层气有效资源化利用,探究了使用规整复合吸附剂真空变压吸附富集低浓度煤层气的工艺。采用静态容积法测定了甲烷、氮气在规整复合吸附剂上的吸附等温线,同时建立了包括质量、热量和动量守恒在内的严格吸附床数学模型,设计了三塔连续进料的真空变压吸附工艺并进行模拟。分析了工艺达到循环稳态后吸附床层轴向温度分布和压力变化,并且探究了进料量、解吸压力、原料气中甲烷浓度和吸附压力对纯度、回收率、工艺能耗和吸附剂产率等工艺性能的影响。模拟结果表明,在进料量为100 L·min^(-1),解吸压力为0.1 bar(1 bar=0.1 MPa),原料气甲烷浓度为30%,吸附压力为3 bar时可以生产纯度为59.07%,回收率为93.64%的富CH4产品气,同时单位能耗为18.70 kJ·mol^(-1),吸附剂产率为4.56 mol·h^(-1)·kg^(-1)。表明规整吸附剂对CH4/N2具有良好的吸附分离效果,能够实现低浓度煤层气中甲烷高效富集。