Ablation mechanism of TaC coating fabricated by chemical vapor deposition on carbon-carbon composites

Ablation characteristics and mechanism at high temperature for TaC coatings on carbon-carbon composites were investigated by ablation experiments with low power laser and oxyacetylene flame. The results show that the TaC coating is decomposed at the initial stage of laser ablation in atmosphere, and free carbon diffused to the surface, then oxidized to the melt including carbon, oxygen and tantalum. With the increase of ablation time, the melt is oxidized to low valent tantalum-oxide and Ta2O5 is formed finally. During the melt cooling, needle-like crystals of Ta2O5 are precipitated. Between the melt and TaC coating, there exists a diffusion transition layer with thickness of 1-2 μm. The transition layer consists of fine crystals and pores including carbon, oxygen and tantalum. The oxyacetylene flame ablation at 2 300 ℃ results in the rapid oxidation of TaC and formation of protective liquid films of tantalum oxide on the coating surface, where the liquid film can fill up the cracks and cover the coating. In such case, the oxidation mechanism of TaC is converted to the oxygen solution and diffusion control mechanism.

A FACILE SYNTHESIS OF 2-TRIFLUOROMETHYLPYRROLE VIA 1,3-DIPOLAR CYCLOADDITION REACTION OF 2-TRIFLUOROMETHYLOXAZOLONE AND THE ACTIVATED CARBON-CARBON MULTIPLE BOND

The 1.3-dipolar cycloaddition reaction of 2-trifluoromethyl- oxazolone and the activated carbon-carbon multiple bond was studied and gave a convenient way to synthesize 2-trifluoromethylpyrrole derivatives.

Structural characteristics and formation mechanisms of crack-free multilayer TaC/SiC coatings on carbon-carbon composites

In order to improve high temperature(over 2 273 K)ablation resistance,TaC and TaC/SiC composite coatings were deposited on carbon-carbon composites by CVD method utilizing reactive TaCl5-C3H6-H2-Ar and TaCl5-C3H6-CH3SiCl3-H2-Ar systems respectively.The structure and morphology of these coatings were analyzed by XRD and SEM.The results show that the double carbide coatings have good chemical compatibility during preparation.Two distinctive composition gradients are developed and used to produce multilayer TaC/SiC coatings with low internal stress,free crack and good resistant to thermal shock.A transition layer consisting of either C-TaC or C-SiC formed between the coating and the C/C matrix can reduce the residual stress effectively. The processing parameters were optimized and the possible growth mechanisms for these coatings were proposed.A designing methodology to prepare high performance multilayer TaC/SiC composite coatings was developed.

Microstructure and isothermal oxidation of 3Al_2O_3·2SiO_2/SiC coating on high and low density carbon-carbon composites

Carbon-carbon composite (C/C) materials are prone to severe oxidation and volatilization problems. To address these issues, mullite (3Al2O3·2SiO2 )/silicon carbide (SiC) coatings were deposited on C/C composite substrates characterized into high and low densities. The coatings were applied by a two-step approach: pack cementation and silica sol based slurry coating processes. The relationship between the microstructure of 3Al2O3·2SiO2 /SiC coatings and C/C substrates during isothermal oxidation cycle at 1 500 oC was investigated using X-ray diffractometer (XRD) and scanning electron microscope (SEM) mounted with energy dispersive spectrometer (EDS). The results indicate that the density of the substrates has a marked effect on the coatings. Dense, thick and well-bonded coatings are obtained in the high density substrate. After 106 h of isothermal oxidation, the high density substrate with 3Al2O3·2SiO2 /SiC coating offers effective protection as compared to low density substrate suffering recession.

FINITE DIFFERENCE MODEL FOR SIMULATION OF DENSIFYING CARBON-CARBON COMPOSITES BY CHEMICAL VAPOR INFILTRATIONP ROCESSES

A finite difference (FD) model is proposed to simulate the chemical vapor infiltration (CVI) processes for fabrication of carbon carbon composites. With iterative operation of many discrete values, the FD based model can be used to describe and analyze the real, continuous densification processing quantitatively. Many densification characteristics of carbon carbon composites can be predicated by modeling. The prediction results can be compared with experiment value directly, which shows its good ability for practical application. Special verification experiments are designed with Iso thermal CVI processing and slender cylindroid unidirectional C/C composites are prepared to verify the accuracy of the model. The modeling curve of density versus infiltration time is in good agreement with experiment values. According to modeling analysis, the effects of infiltration temperature and fiber volume fraction on densification are also discussed preliminarily. The conclusion obtained also accords with experiment or results in other literature, further approving the accuracy of the FD based model.

Clean production of lactic acid by selective carbon-carbon bond cleavage of biomass feedstock over a novel carbon-bismuth oxychloride photocatalyst

The use of functional materials such as carbon-bismuth oxyhalides in integrated photorefineries for the clean production of fine chemicals requires restructuring.A facile biomass-assisted solvothermal fabrication of carbon/bismuth oxychloride nanocomposites(C/BiOCl)was achieved at various temperatures.Compared with BiOCl and C/BiOCl-120,C/BiOCl-180 exhibited higher crystallinity,wider visible light absorption,and a faster migration/separation rate of photoinduced carriers.For the selective C–C bond cleavage of biomass-based feedstocks photocatalyzed by C/BiOCl-180,the xylose conversion and lactic acid yield were 100%and 92.5%,respectively.C/BiOCl-180 efficiently converted different biomass-based monosaccharides to lactic acid,and the efficiency of pentoses was higher than that of hexoses.Moreover,lactic acid synthesis was favored by all active radicals including superoxide ion(·O_(2)^(−)),holes(h^(+)),hydroxyl radical(·OH),and singlet oxygen(^(1)O_(2)),with·O_(2)^(−)playing a key role.The fabricated photocatalyst was stable,economical,and recyclable.The use of biomass-derived monosaccharides for the clean production of lactic acid via the C/BiOCl-180 photocatalyst has opened new research horizons for the investigation and application of C–C bond cleavage in biomass-based feedstocks.

Weak Acetylene Adsorption Terminated Carbon-Carbon Coupling Kinetics on Silver Electrocatalysts

Owing to serious poison of downstream olefin polymerization catalysts from acetylene impurities,selective reduction of acetylene to ethylene is a pivotal process in petrochemical industry.However,during thermocatalytic and electrocatalytic acetylene semihydrogenation,acetylene C-C coupling inevitably occurs on current catalysts.The resultant oligomeric species(particularly long-chain hydrocarbons)block active sites and mass transportation,and eventually decrease catalytic activity and stability.In this work,we report Ag nanowires(NWs)as high-performance electrocatalysts for acetylene semihydrogenation,where the C-C coupling is unprecedentedly suppressed by weakening acetylene adsorption.In pure acetylene,1,3-butadiene Faradaic efficiency(FE)of Ag NWs is only 2.1%,which is far lower than 41.2%for Cu nanoparticles at−0.2 V versus reversible hydrsogen electrode.Ethylene partial current density of Ag NWs reaches 217 mA/cm^(2)at 0.85 V,which is considerably higher than those for state-of-the-art Cu-based electrocatalysts.Markedly,no 1,3-butadiene is produced on Ag NWs in a large two-electrode flow cell fed with crude ethylene containing 1 vol%acetylene,presenting thorough termination of acetylene C-C coupling.In situ electrochemical Raman spectroscopy and theoretical investigations reveal that weak acetylene adsorption on Ag surfaces is intrinsically responsible for prohibiting their oligomerization.This work will spark the rapid development of high-performance and stable electrocatalysts for reducing alkynes to olefins.

煤矿充填固碳理论基础与技术构想

在国家“双碳”目标背景下,如何减少煤炭行业的碳排放、实现碳封存已成为亟待解决的难题。煤炭行业作为高碳化石能源生产者和主体碳排放源提供者,在生产和消费过程中引发的大宗固废堆存、大型采空区形成和大量CO_(2)排放是制约煤炭可持续开发利用与绿色健康发展的瓶颈所在。为协同解决二氧化碳封存与矿山固废消纳问题,将大宗固废处置、固废高值化利用、CO_(2)封存、采空区利用有机结合,提出了二氧化碳充填的理念,从碳汇能力评估角度界定了二氧化碳充填的3种类型。具体开展工作包括:①分析了CO_(2)充填料浆输运过程和矿化反应过程涉及到的基础理论,给出了各个过程的数学方程以及碳封存量计算公式,指出了温度、湿度等因素对矿化反应机理、碳封存量和充填体强度的影响规律。②总结了现阶段CO_(2)矿化的工艺方法、主要碱性工业固废的CO_(2)封存能力和CO_(2)矿化强化措施。在此基础上提出了基于直接湿法矿化和间接矿化的2种CO_(2)充填材料制备工艺,满足矿井充填的流动性、凝固特性和强度要求。③针对CO_(2)充填过程中的CO_(2)物理封存问题,提出了窄条带式胶结充填和综采架后胶结充填2种技术路径,前者通过在弱充填条带中构筑多贯通孔隙的充填体CO_(2)物理封存,后者借助充填支架和链式自行充填挡板在长壁工作面采空区中间断构筑充填带,控制顶板垮落,形成CO_(2)物理化学封存空间。④为了评估CO_(2)充填的碳平衡效果,依据全生命周期法界定了CO_(2)充填中碳足迹及碳消纳的计算边界。然后,梳理了CO_(2)充填过程中的碳足迹及碳消纳,分别考虑了CO_(2)的来源、用量、损耗、转化等因素。给出了包括原料运输、充填料浆制备、井下注入与充填等过程中的碳足迹及碳消纳计算方法。研究成果有望降低CO_(2)封存的能耗及成本,对煤炭绿色开采及其可持续开发利用具有深远的意义。

水土保持碳汇内涵与测算方法

水土保持深刻改变着地表覆被和结构、土地利用方式和陆地生态系统结构等,是增强陆地碳汇能力的重要途径。以水土保持林草、工程和耕作措施为切入点,按照“机理阐述—模型构建—分类测算”的总体思路,阐明水土保持碳汇内涵,明确了水土保持碳汇途径,构建水土保持碳汇测算方法,估算全国水土保持碳汇量。结果表明:水土保持具有垂向碳增汇、横向保土固碳(减少侵蚀土壤横向输移导致的碳流失)与减蚀减碳(避免碳排放)的多重功能。2021年,全国现存水土保持措施垂向碳增汇总量为1.54亿t,对陆域碳汇的贡献约43.5%~56.5%,其中林草措施植被和土壤碳汇量超过95%。水土保持保土固碳作用显著,2021年全国水土保持措施保土固碳总量为3 040.86万t,且具有明显的累积效应和长效作用。总体来说,2021年水土保持碳增汇(不包括水土保持林草措施植被碳汇量和土壤碳汇量)和减碳量为5 115万~6 230万t CO_(2),约占到全国现有陆地生态系统碳中和总量的4%~6%,这一部分尚未纳入国家碳汇核算体系,其应是实现“双碳”目标的重要环节。

BIM技术在建筑碳排放计算领域研究进展

结合国内外相关文献,对BIM技术在建筑碳排放计算领域的研究进展进行综述。通过对研究进程的归纳,以及对建筑碳排放计算政策、计算方法、BIM技术适用性等影响因素的分析,总结BIM技术在建筑碳排放计算领域的研究现状。基于当前研究成果,将BIM技术在建筑碳排放计算领域的研究内容划分为理论方法、工具平台、应用价值三个层面。理论方法主要关注计算边界和计算方法的确定、BIM模型的数据提取方式以及BIM模型的参数扩展内容;工具平台主要探讨BIM建模工具、人工处理及算法程序、BIM软件插件、BIM平台系统的具体应用;应用价值主要体现基于BIM技术的建筑碳排放计算在建筑设计、物化、运营等各阶段的成果效益。三个层面虽已取得许多研究成果但也存在问题和难点。未来的研究可以在数字技术融合和信息管理完善两个方面深入发展。

“双碳”目标下的经济社会系统性变革:特征、要求与路径

实现碳达峰碳中和是一场广泛而深刻的经济社会系统性变革,强调单一目标或有限目标调控的研究范式,对碳中和目标下净零碳转型复杂性的理解存在局限性,难以有效反映与应对多重目标、多重约束下社会经济系统性、全局性深刻变革的影响。理解与研判“双碳”目标下经济社会系统性变革的主要特征、具体要求与实现路径,能够提升对“双碳”目标的认识,更好地释放系统性变革带来的红利以及规避所伴随的风险,推动实现“双碳”目标下经济社会的高质量发展,并为全球碳中和理论构建与实践探索作出贡献。

碳中和目标下矿山生态修复的制度困境与规范调适

矿山生态修复产生的碳减排与碳汇功能,对促进实现碳中和目标能够发挥重要作用。法学视角下,矿山生态修复制度研究应首先完成对相关概念的厘清,并结合碳中和要求界定法律目标。通过实践检视,发现矿山生态修复存在项目设计不科学、资金投入不到位、功能评价不全面、工作管理不严格等阻碍回应碳中和要求的因素。然而,实践上的问题表征根本归因于制度的内生困境,具体表现为矿山生态修复规划逻辑结构失调、多元激励保障失位、标准理性评判失当、监管执行监督失序等方面。因此,响应碳中和目标,应建立完善的矿山生态修复法律体系,以此为基础,优化矿山生态修复规划制度、激励机制、标准规范、监管机制等。

数字化背景下新型电力系统谐波溯源关键技术

构建以新能源为主体的新型电力系统是能源电力行业推动“双碳”战略目标的关键举措。伴随多类型电力电子设备大规模接入系统,源网荷储谐波源交互影响,谐波污染加剧且复杂多变,呈现全局化特征,影响了电力系统优质可靠供电。文中聚焦多类型谐波源交互作用下的谐波来源追溯,深度融合先进数字技术在数据资源和智能协作的优势进行主导源头辨识和谐波贡献评估。首先,围绕谐波溯源概念,分析其在数字化背景下新型电力系统面临的新挑战和新机遇。然后,阐述了谐波溯源研究现状,指出关键技术的发展新需求。基于此,利用数字电网技术架构设计了云-边-端协同溯源策略。针对数字化背景下的新型电力系统,阐述了谐波源确定在数据采集、机理分析、协同应用等方面的主要技术。最后,展望了未来数字电力系统安全、可靠、灵活发展的技术方向。

“双碳”背景下建环专业人才培养模式研究

“双碳”战略的确立,为建筑环境与能源应用工程专业的人才培养提出了新的要求。传统的人才培养模式已经不能满足“双碳”战略的需求,有必要探索适应“双碳”背景的建环专业新型人才培养模式。通过分析“双碳”背景下建环专业人才的具体要求,制订了人才培养目标,总结了课程设置及质量、教学方法以及实践教学三方面的改进措施。提出的优化建议对加强建环人才培养,推动实现“双碳”战略具有重要意义。

中国式现代化目标下构建新型能源体系之路径思考

倡导人与自然和谐共生的中国式现代化,对中国能源领域的高质量可持续发展提出了新要求、新部署,“加快规划建设新型能源体系”势在必行。为了助推中国式现代化目标下新型能源体系的构建,分析了其提出的战略背景,明确了其重要意义,阐述了其内涵特征,提出了其路径建议。研究结果表明:①新型能源体系是社会主义现代化强国建设的关键抓手,是实现碳达峰碳中和目标以及推进生态文明建设的重要支撑,是国家能源安全和国家竞争力的有力保障;②新型能源体系以促进人与自然和谐共生为根本宗旨,以保证能源安全和经济社会发展稳定为基本前提,具有理念更新、能源结构更新、技术创新、治理创新、产业革新、电力革新等内涵特征;③新型能源体系的构建路径包括加快培育绿色低碳文化、加快推动能源结构转型、加快推动产业结构升级、加快攻关关键核心技术、加快构建体制机制保障等。结论认为,立足我国能源资源禀赋,坚持“先立后破”的方式构建清洁低碳、安全高效的新型能源体系,提高能源自给率,特别是油气自给率,确保能源转型平稳有序、能源保障安全可靠,可以为当前复杂国际形势下的国家能源安全提供强有力的保障。