Effect of the Retarder on Initial Hydration and Mechanical Properties of the"one-step"Alkaliactivated Composite Cementitious Materials

This paper studied the effects of different retarders on the performance of the"one-step"alkali-activated composite cementitious material(ACCM)which is composed of ground granulated blast slag(GGBS)and fly ash(FA),and analyzed its mechanical properties,hydration mechanism,and retardation mechanism.The effects of retarders on the hydration products,mechanical properties,and hydration kinetics of ACCM were investigated using XRD,SEM,FTIR,EDS,and thermoactive microcalorimetry.The results showed that Na_(2)B_(4)O_(7)·10H_(2)O(B)delayed the exotherm during the alkali activation process and could effectively delay the setting time of ACCM,but the mechanical properties were slightly decreased.The setting time of ACCM increased with the increase in SG content,but the mechanical properties of ACCM decreased with the increase in SG content.C1_(2)H_(22)O_(11)(CHO)could effectively delay the hydration reaction of ACCM and weakly enhanced the compressive strength.H_(3)PO_(4)(HP)at a concentration of 0.05 mol/L had a certain effect on ACCM retardation,but HP at a concentration of 0.07 and 0.09 mol/L had an effect of promoting the setting and hardening time of ACCM.

Wear behavior of SiC/PyC composite materials prepared by electromagnetic-field-assisted CVI

Silicon carbide/pyrolytic carbon (SiC/PyC) composite materials with excellent performance of self-lubrication and wear resistance were prepared on SiC substrates by electromagnetic-field-assisted chemical vapor infiltration (CVI). The composition and microstructure of the SiC/PyC materials were investigated in detail by XRD, SEM and EDS, etc. The effects of the deposition temperature on the section features and wear resistance of the SiC/PyC were studied. The results show that the PyC layers were deposited onto SiC substrates spontaneously at a lower deposition temperature. The SiC substrates deposited with PyC can significantly reduce the wear rate of the self-dual composite materials under dry sliding condition. The wear tests suggest that the SiC/PyC composite materials own a better wear resistance property when the deposition temperature is 800 °C, and the wear rate is about 64.6% of that without the deposition of PyC.

Preparation of Ni-Cr/BN self-lubricating composites by active sintering process

A Ni-Cr/BN composite was produced by a active sintering process. The powder of nickel carbonyl,Cr2O3 and C were used as the original materials,and a hexagonal BN(h-BN) powder was added as a solid lubricant. The influence of sintering temperature,heating rate and holding time on the properties of Ni-Cr/BN were studied. The composition and microstructure of Ni-Cr/BN were analysed by X-ray diffraction(XRD) and the optical microscopy(OM). The frictional behavior and hardness were measured with ring-block friction testing machine and Brinell hardness tester respectively. The results show that Ni-Cr is the matrix and a low-melting eutectic compound is the bonding phase in the composite. The porosity reaches 48% and the value of hardness reaches HB18 when the composite is fabricated at 1 100 ℃ for 1 h. Its wear rate is 7.44×10-5 g/min,and the average friction coefficient is 0.266. These properties make such composite suitable for use as self-lubricating material.

Synthesis of steel slag ceramics: chemical composition and crystalline phases of raw materials

Two types of porcelain tiles with steel slag as the main raw material （steel slag ceramics） were synthesized based on the CaO-A1203-SiO2 and CaO--MgO-SiO2 systems, and their bending strengths up to 53.47 MPa and 99.84 MPa, respectively, were obtained. The presence of anorthite, a-quartz, magnetite, and pyroxene crystals （augite and diopside） in the steel slag ceramics were very different from the composition of traditional ceramics. X-ray diffraction （XRD） and electron probe X-ray microanalysis （EPMA） results illustrated that the addition of steel slag reduced the temperature of extensive liquid generation and further decreased the firing temperature. The considerable contents of glass-modifying oxide liquids with rather low viscosities at high temperature in the steel slag ceramic adobes promoted element diffusion and crystallization. The results of this study demonstrated a new approach for extensive and effective recycling of steel slag.

Tungsten combustion in impact initiated W-Al composite based on W(Al) super-saturated solid solution

Element W can effectively improve the density of energetic structural materials. However, W is an inert element and does not combust in air. To change the reaction characteristics of W, 60 at.% Al was introduced into W through mechanical alloying. XRD analysis shows that after 50 h of ball milling, the diffraction peak of Al completely disappears and W(Al60) super-saturated solid solution powder is obtained. Further observation by HAADF and HRTEM reveals that the W(Al60) super-saturated solid solution powder is a mixture of solid solution and amorphous phase. Based on the good thermal stability of W(Al60) alloy powder below 1000℃, W(Al60)-Al composite was synthesized by hot pressing process.Impact initiation experiments suggest that the W(Al60)-Al composite has excellent reaction characteristics, and multiple types of tungsten oxides are detected in the reaction products, showing that the modified W is combustible in air. Due to the combustion of tungsten, the energy release rate of the W(Al60)-Al composite at speed of 1362 m/s reaches 2.71 kJ/g.

La_(0.75)Sr_(0.25)Cr_(0.5)Mn_(0.5)O_(3)-δ−Ce_(0.8)Gd_(0.2)O_(1.9) composite electrodes as anodes in LaGaO_(3)-based direct carbon solid oxide fuel cells

Direct carbon solid oxide fuel cells(DC-SOFCs)are promising,green,and efficient power-generating devices that are fueled by solid carbons and comprise all-solid-state structures.Developing suitable anode materials for DC-SOFCs is a substantial scientific challenge.Herein we investigated the use of La_(0.75)Sr_(0.25)Cr_(0.5)Mn_(0.5)O_(3)-δ−Ce_(0.8)Gd_(0.2)O_(1.9)(LSCM−GDC)composite electrodes as anodes for La_(0.9)Sr_(0.1)Ga_(0.8)Mg_(0.2)O_(3)-δelectrolyte-based DC-SOFCs,with Camellia oleifera shell char as the carbon fuel.The LSCM−GDC-anode DC-SOFC delivered a maximum power density of 221 mW/cm^(2) at 800℃ and it significantly improved to 425 mW/cm^(2) after Ni nanoparticles were introduced into the LSCM−GDC anode through wet impregnation.The microstructures of the prepared anodes were characterized,and the stability of the anode in a DC-SOFC and the influence of catalytic activity on open circuit voltage were studied.The above results indicate that LSCM–GDC anode is promising to be applied in DC-SOFCs.

Recent progress and challenges in silicon-based anode materials for lithium-ion batteries

Anode materials for Li-ion batteries(LIBs)utilized in electric vehicles,portable electronics,and other devices are mainly graphite(Gr)and its derivatives.However,the limited energy density of Gr-based anodes promotes the exploration of alternative anode materials such as silicon(Si)-based materials because of their abundance in nature and low cost.Specifically,Si can store 10 times more energy than Gr and also has the potential to enhance the energy density of LIBs.Despite the many advantages of Si-based anodes,such as high theoretical capacity and low price,their widespread use is hindered by two major issues:charge-induced volume expansion and unreliable solid electrolyte interphase(SEI)propagation.In this detailed review,we highlight the key issues,current advances,and prospects in the rational design of Si-based electrodes for practical applications.We first explain the fundamental electrochemistry of Si and the importance of Si-based anodes in LIBs.The excessive volume increase,relatively low charge efficiency,and inadequate areal capacity of Si-based anodes are discussed to identify the barriers in enhancing their performance in LIBs.Subsequently,the use of binders(e.g.,linear polymer binders,branched polymer binders,cross-linked polymer binders,and conjugated conductive polymer binders),material-based anode composites(such as carbon and its derivatives,metal oxides,and MXenes),and liquid electrolyte construction techniques are highlighted to overcome the identified barriers.Further,tailoring Si-based materials and reshaping their surfaces and interfaces,including improving binders and electrolytes,are shown to be viable approaches to address their drawbacks,such as volume expansion,low charge efficiency,and poor areal capacity.Finally,we highlight that research and development on Si-based anodes are indispensable for their use in commercial applications.

Phase Representation and Property Determination of Raw Materials of Solid Lubricant

The composition, microstructure, mechanical and frictional properties of PTFE and its fillers were represented and analyzed by XRD, SEM, DSC, XPS and large-scale polarizing microscope. The results show that PTFE has a flocculent structure with high melt temperature and decomposition temperature, big contact angle and crystallinity, and low surface hardness, compression strength, friction coefficient, wearing capacity and surface energy. Cooling rate influenced the friction coefficient and wear resistance. Graphite and molybdenum disulfide have a flake structure, and molybdenum disulfide has a big contact angle and low surface energy. Copper powder has a globular structure and its chief component is Cu-Pb alloy, and there is a loose layer on the surface. Carbon fiber has a rod structure and there are C=O and C-O-C polar groups on the skeleton surface. The decreasing order of water absorption capacity is graphite, carbon fiber, molybdenum disulfide, PTFE and copper powder.

Partial Replacement of Cement by Solid Wastes as New Materials for Green Sustainable Construction Applications

The manufacturing of ordinary Portland cement is an energy-intensive process that results in pollution and CO2 emissions,among other issues.There is a need for an environmentally friendly green concrete substitute.Waste products from a variety of sectors can be recycled and used as a green concrete substitute.This decreases the environmental effects of concrete manufacturing as well as energy consumption.The use of solid waste materials for green building is extremely important now and in the future.Green concrete is also in its infancy in terms of manufacturing and application.Academics must intervene by encouraging business implementation.The aim of this review paper is to raise awareness about the importance of repurposing recycled materials and to highlight new technologies for producing green,sustainable concrete.

Influence of sulfides on the tribological properties of composites produced by pulse electric current sintering

Self-lubricating A1203-15wt% ZrO2 composites with sulfides, such as molybdenum disulfide （MoS2） and tungsten disulfide （WSz） serving as solid lubricants, were fabricated by using the pulse electric current sintering （PECS） technique. The coefficient of friction （COF） of the A1203-15wt% ZrO2 composite without/with sulfides was in the range of 0.37-0.48 and 0.27-0.49, respectively. As the amoant of sul- fides increased, the COF and the wear rate decreased. The reduction in COF and wear rate of the sulfide-containing composite is caused by a reduction in shear stresses between the specimen and the tribological medium due to the formation of a lubricating film resulting from the lamellar structure of sulfides located on the worn surface.

Microstructure of fly ash cenosphere/AZ91D composite during solution treatment at 380-420℃

The fly ash cenosphere/AZ91D (FAC/AZ91D) composites containing 5 wt.% and 100 μm in size of fly-ash cenosphere particles were fabricated by means of the compcasting method.The microstructures of the as-cast samples and the effect of the solution treatment at 380℃,400℃,and 420℃ for 16 h on the microstructures of the samples were investigated by using of OM,SEM,XRD and EDS.The results showed that the cenospheres distributed homogeneously in the Mg alloy,and were almost filled with Mg alloy.The main interfacial phase between the cenospheres and AZ91D Mg alloy was identified as MgAl2O4 according to XRD,EDS and thermodynamic analysis.Mg2Si particles tended to be spheroidized via the solution treatment and the β phase (Mg17Al12) dissolved completely at 400℃.

Toward Analytical Homogenized Relaxation Modulus for Fibrous Composite Material with Reduced Order Homogenization Method

In this manuscript,we propose an analytical equivalent linear viscoelastic constitutive model for fiber-reinforced composites,bypassing general computational homogenization.The method is based on the reduced-order homogenization(ROH)approach.The ROH method typically involves solving multiple finite element problems under periodic conditions to evaluate elastic strain and eigenstrain influence functions in an‘off-line’stage,which offers substantial cost savings compared to direct computational homogenization methods.Due to the unique structure of the fibrous unit cell,“off-line”stage calculation can be eliminated by influence functions obtained analytically.Introducing the standard solid model to the ROH method enables the creation of a comprehensive analytical homogeneous viscoelastic constitutive model.This method treats fibrous composite materials as homogeneous,anisotropic viscoelastic materials,significantly reducing computational time due to its analytical nature.This approach also enables precise determination of a homogenized anisotropic relaxation modulus and accurate capture of various viscoelastic responses under different loading conditions.Three sets of numerical examples,including unit cell tests,three-point beam bending tests,and torsion tests,are given to demonstrate the predictive performance of the homogenized viscoelastic model.Furthermore,the model is validated against experimental measurements,confirming its accuracy and reliability.

Numerical simulation of the transient multiphase field during plasma deposition manufacturing composite materials

A solid/liquid/gas unified model has been developed to investigate the gradient composition formation during the plasma deposition manufacturing(PDM) composite materials process. In this model,an enthalpy porosity model was applied to deal with the melting and solidification of the deposited layer,and a level-set approach was introduced to track the evolution of the free surface of the molten pool and the deposited layer. Moreover,complicated physical phenomena occurring at the liquid/gas interface,including forced convection heat loss,heat emission and plasma heat source,have been incorporated into the governing equations by source terms. In this study,the numerical experiment of nickel base alloy powder deposited on the medium steel substrate by PDM technique was implemented based on the staggered grid and SIMPLEC algorithm. Concentration gradient distribution of the solute material at the composite material interface,fluid flow and temperature distribution in the molten pool and the deposited layer have been investigated in detail.

Formation Kinetics of Unsaturated (Ti, W)C Solid Solution

The effects of temperature (1650-2250°C), time (20-180 min), particle size of WC (1-13 μm) and that of TiO2 (1-7 μm) on the formation process of solid solution Ti0.5W0.5C have been investigated by X-ray diffraction, optical microscopy, SEM and EPMA methods. It is found that the formation of (Ti, W)C is controlled by diffusion process between WC and disequilibrium (Ti, W)C. According to Jander and Arrhenius equation, the apparent activation energy was calculated to be 318-380 kJ/mol (for T<1850°C) and 100-117 kJ/mol (for T≥1850°C). The diffusion model for different temperature interval was proposed. An X-ray diffraction calculating index H was also developed to examine the micro-inhomogeneity of (Ti, W)C. The H value variation agrees well with the experimental results.

兰炭灰固碳对复合相变储热材料性能的影响

为推动“双碳”战略,促进工业固废兰炭灰的低成本消纳,开发新型绿色低碳复合材料,提出在已有的兰炭灰/硝酸钠复合相变储热材料基础上,利用兰炭灰进行碳捕捉。对固碳前、后兰炭灰及复合相变储热材料的性能进行研究。结果表明:兰炭灰碳捕集的最佳条件为气体组分20%CO_(2)/80%N_(2)、通气时间40 min、加热温度650℃;在最佳实验条件下,兰炭灰的固碳率达到29.27%,所制得的复合相变储热材料固碳兰炭灰/NaNO_(3)的最佳质量比为5:5,在100~380℃储热密度达到288.65 J/g,拥有更好的机械性能、热稳定性及化学相容性。固碳兰炭灰作为骨架材料制备复合相变储热材料具有较好的可行性,为工业固废兰炭灰的资源化利用和碳排放处理提供了新的途径。

含氟高分子材料包覆铝核壳材料研究进展

金属铝(Al)具有高燃烧热值、高密度、低耗氧量等优异性能,是固体复合推进剂领域最受青睐的金属添加剂。为了提高固体复合推进剂的性能,有必要采取措施对Al进行包覆改性。近年来含氟高分子包覆Al因其优异的综合性能而受到广泛关注。介绍了不同种类的含氟高分子包覆金属Al核壳材料、不同包覆方法、Al核壳材料的性能以及含氟高分子与Al的作用机理,总结发现通过Al核壳结构设计、含氟高分子引入和Al颗粒表面的自活化策略等途径,含氟高分子与氧化铝层之间的表面发生剧烈的氧化过程,增强Al核壳材料点火和燃烧性能,显著改善推进剂的燃烧团聚和燃烧效率。但目前含氟高分子包覆Al核壳材料研究过程仍存在许多不足,如缺乏新型多元含氟高分子包覆Al的能量性能的研究;缺乏Al颗粒与包覆层在高升温速率下作用机理的认识;包覆效率和批量制备能力低,阻碍了其实际应用等。未来可从进一步增强朝着研发新型含氟聚合物、研究对反应历程中产物的实时捕捉和开发工业化生产制造技术等方向发展。

陶瓷增强铝合金互渗相复合材料的半固态设计和成形

目的开发一种针对金属-陶瓷互渗相复合材料生产的高效方法,以提升该类材料在高温高负荷环境中的使用寿命和工作可靠性。方法采用数值扫描技术研究了半固态成形过程,以铝合金为金属成分、氧化铝开孔体为陶瓷成分,制备了复合材料。通过模拟2种腔体(开放式和封闭式)的金属陶瓷压铸成形过程模拟不同的模腔设计,详细分析了腔体内的压力水平及其分布情况,探讨了压铸温度、金属液相体积分数等参数对材料成形质量的影响。结果封闭模腔能够在成形过程中产生更加均匀的压力分布,有助于减少如气孔、未渗透区域等材料缺陷,并提高金属与陶瓷之间的互渗质量。与封闭模腔相比,开放模腔在控制材料均匀流动和确保渗透效果方面效果较差。结论采用封闭模腔的半固态成形工艺能显著提升金属-陶瓷互渗相复合材料的整体质量和性能,有效减少成形缺陷,为高性能金属-陶瓷复合材料的制备提供了一种有效路径。

原位合成Si/(SiO+Ag)复合负极材料及其电化学性能

将微米Si和纳米Ag_(2)O进行机械球磨,通过原位固相反应合成了Si基复合材料[Si/(SiO+Ag)],以沥青为碳源采用高温煅烧法制备了碳包覆Si基复合材料[Si/(SiO+Ag)-C]。采用XRD、XPS、SEM、TEM对复合材料进行了表征,测试了其电化学性能。结果表明,微米Si和纳米Ag_(2)O在球磨破碎过程中原位形成Si O和Ag颗粒,并附着在基体Si上,两种复合材料都展现出良好的倍率性能,在低电流密度(0.12 A/g)下Si/(SiO+Ag)和Si/(SiO+Ag)-C循环5次后分别表现出1422和1039 mA·h/g的可逆比容量,而在高电流密度(2.40 A/g)下仍能获得672和393 mA·h/g的可逆比容量;当电流密度再次恢复到0.12 A/g时,可逆比容量可恢复到1329和961m A·h/g,Si/(SiO+Ag)-C表现出更好的循环稳定性,经80次循环后可逆比容量仍稳定在943 m A·h/g,其突出的倍率性能归因于微米Si的颗粒细化以及球磨过程中原位反应形成纳米Ag颗粒导电特性,而循环稳定性的提高与原位形成Si O和包覆碳构成的双相缓冲结构有关。

典型硫酸盐固废复合胶凝材料制备与微观特性研究

硫酸盐类工业固废造成的环境污染和资源浪费问题引起了国内外学者的广泛关注,当前中国两种典型的硫酸盐类固废(电解锰渣和磷石膏)堆存量巨大,造成严重的环境污染,其无害化与资源化利用刻不容缓。依据电解锰渣、磷石膏两种固体废弃物的特性,利用电解锰渣和磷石膏结合矿渣制备复合胶凝材料,探究了磷石膏和水泥不同掺量对复合胶凝材料硬化体力学性能的影响。通过XRD、SEM和EDS分析了硬化体的物相组成和微观形貌变化特征,同时对硬化体进行毒性浸出测试。结果表明:硬化体各龄期强度随着水泥掺量增加而增大,硬化体各龄期强度随着磷石膏掺量增加而减小。复合胶凝材料较优配合比(质量分数)为电解锰渣为50%、磷石膏为20%、矿渣为30%,水泥外掺12%的硬化体28 d抗压强度为27.1 MPa,硫酸盐固废复合胶凝材料的水化产物主要为水化硅酸钙(C-S-H)凝胶和钙矾石(AFt)。养护至28 d的硬化体浸出液中可溶性Mn^(2+)、NH_(4)^(+)-N、PO_(4)^(3-)和重金属离子浓度稳定后满足GB 8978—1996《污水综合排放标准》的排放要求。

复合固体推进剂药浆浇铸工艺仿真及优化

为了研究HTPB复合固体推进剂药浆浇铸的最佳工艺参数,采用实验与理论模拟相结合的方法,基于HTPB复合固体推进剂药浆流变性能建立了推进剂药浆流动过程的本构模型;利用有限元软件对HTPB复合推进剂药浆浇铸工艺进行仿真,通过实验验证了仿真结果的可靠性;并对该推进剂药浆浇铸工艺进行了优化,获得了最佳浇铸工艺参数。结果表明,HTPB推进剂是典型的假塑性流体,其黏度随剪切速率增大而降低;实验与仿真对比后的气孔率及浇铸时间误差分别为12.5%和11.25%;其中,温度对浇铸时间的影响最明显,真空度对气孔率影响最明显。