Enhanced Thermal Conductivity and Bending Strength of Graphite Flakes/aluminum Composites Via Graphite Surface Modification

The effect of graphite surface modification on the thermal conductivity(TC) and bending strength of graphite flakes/Al composites(Gf/Al) prepared by gas pressure infiltration were investigated. Al3 Ni and Al4C3 phase may form at the interface in Ni-coated Gf/Al and uncoated Gf/Al composites, respectively, while the Al-Cu compound cannot be observed in Cu-coated Gf/Al composites. The Cu and Ni coatings enhance TC and the bending strength of the composites in the meantime. TC of Cu-coated Gf/Al composites reach 515 Wm^-1·K^-1 with 75 vol% Gf, which are higher than that of Ni-coated Gf/Al. Meanwhile, due to Al3 Ni at the interface, the bending strength of Ni-coated Gf/Al composites are far more than those of the uncoated and Cu-coated Gf/Al with the same content of Gf. The results indicate that metal-coated Gf can effectively improve the interfacial bonding between Gf and Al.

Preparation and characterization of ceramic materials with low thermal conductivity and high strength using high-calcium fly ash

High calcium-fly ash(HCFA)collected from the Mae Moh electricity generating plant in Thailand was utilized as a raw material for ceramic production.The main compositions of HCFA characterized by X-ray fluorescence mainly consisted of 28.55wt%SiO_(2),16.06wt%Al_(2)O_(3),23.40wt%CaO,and 17.03wt%Fe_(2)O_(3).Due to high proportion of calcareous and ferruginous contents,HCFA was used for replacing the potash feldspar in amounts of 10wt%-40wt%.The influence of substituting high-calcium fly ash(0-40wt%)and sintering temperatures(1000-1200℃)on physical,mechanical,and thermal properties of ceramic-based materials was investigated.The results showed that the in-corporation of HCFA in appropriate amounts could enhance the densification and the strength as well as reduce the thermal conductivity of ceramic samples.High proportion of calcareous and ferruginous constituents in fly ash promoted the vitrification behavior of ceramic samples.As a result,the densification was enhanced by liquid phase formation at optimum fly ash content and sintering temperature.In addition,these components also facilitated a more abundant mullite formation and consequently improved flexural strength of the ceramic samples.The op-timum ceramic properties were achieved with adding fly ash content between 10wt%-30wt%sintered at 1150-1200℃.At 1200℃,the max-imum flexural strength of ceramic-FA samples with adding fly ash 10wt%-30wt%(PSW-FA(10)-(30))was obtained in the range of 92.25-94.71 MPa when the water absorption reached almost zero(0.03%).In terms of thermal insulation materials,the increase in fly ash addi-tion had a positively effect on the thermal conductivity,due to the higher levels of porosity created by gas evolving from the inorganic decom-position reactions inside the ceramic-FA samples.The addition of 20wt%-40wt%high-calcium fly ash in ceramic samples sintered at 1150℃reduced the thermal conductivity to 14.78%-49.25%,while maintaining acceptable flexural strength values(~45.67-87.62 MPa).Based on these promising mechanical and thermal characteristics,it is feasible to utilize this high-calcium fly ash as an alternative raw material in clay compositions for manufacturing of ceramic tiles.

Fuzzy neural network analysis on gray cast iron with high tensile strength and thermal conductivity

To develop a high performance gray cast iron with high tensile strength and thermal conductivity, multivariable analysis of microstructural effects on properties of gray cast iron was performed. The concerned parameters consisted of graphite content, maximum graphite length, primary dendrite percentage and microhardness of the matrix. Under the superposed influence of various parameters, the relationships between thermal conductivity and structural characteristics become irregular, as well as the effects of graphite length on the strength. An adaptive neuro-fuzzy inference system was built to link the parameters and properties. A sensitivity test was then performed to rank the relative impact of parameters. It was found that the dominant parameter for tensile strength is graphite content, while the most relative parameter for thermal conductivity is maximum graphite length. The most effective method to simultaneously improve the tensile and thermal conductivity of gray cast iron is to reduce the carbon equivalent and increase the length of graphite flakes.

Preparation and Study of Borosilicate Foam Glass with High Thermal Insulation and Mechanical Strength

Foam glass is a kind of green building material that is widely used because of its excellent thermal insulation and mechanical properties.In this study,the borosilicate foam glass was fabricated by powder sintering method using recycled soda lime waste glass,quartz,and borax as the primary raw materials.CaCO_(3)was used as a foaming agent and Na_(2)CO_(3)as a flux agent.Results showed that as the quartz content decreases from 30 to 17.5 wt.%and borax content increases from 5 to 17.5 wt.%,the pore size,porosity,and thermal insulation of borosilicate foam glass increase significantly,while the compressive strength decreases slightly.When the content of quartz and borax are both 17.5 wt.%,borosilicate foam glass with outstanding performance can be prepared,whose pore distribution is uniform,mean pore size is 1.93 mm,total porosity is 83.44%,thermal conductivity is 0.0711W/(m⋅K),and compressive strength is 2.37 MPa.Finally,the influences of foaming agent content,flux agent content,foaming temperature,and holding time on the pore structure and various properties of borosilicate foam glass were investigated by orthogonal test.According to the results,the foaming temperature has a significant effect,and appropriate foaming agent content,flux agent content,and holding time help to form a uniform pore structure,thereby improving the thermal insulation and mechanical strength of the borosilicate foam glass.

Thermo-Physical Potential of Recycled Banana Fibers for Improving the Thermal and Mechanical Properties of Biosourced Gypsum-Based Materials

The development of bio-sourced materials is essential to ensuring sustainable construction;it is considered a locomotive of the green economy.Furthermore,it is an abundant material in our country,to which very little attention is being given.This work aims to valorize the waste of the trunks of banana trees to be used in construction.Firstly,the physicochemical properties of the fiber,such as the percentage of crystallization and its morphology,have been determined by X-ray diffraction tests and scanning electron microscopy to confirm the potential and the impact of the mode of drying on the quality of the banana fibers,with the purpose to promote the use of this material in construction.Secondly,the results obtained with the gypsum matrix allowed us to note a preponderant improvement in the composite’s thermal properties thanks to the variation of the banana fiber additive.Thirdly,the impact of the nature of the banana fiber distribution(either fiber mixed in matrix or fiber series model)on the flexural and compressive strengths of the composites was studied.The results obtained indicate that the insulation gain reaches up to 40%.It depends on the volume fraction and type of distribution of the banana fibers.However,the thermal inertia of the composites developed,represented by thermal diffusivity and thermal effusivity,was studied.Results indicate a gain of 40%and 25%,respectively,in terms of thermal diffusivity and thermal effusivity of the developed composites compared to plaster alone.Concerning the mechanical properties,the flexural strength depends on the percentage of the volume fraction of banana fibers used,and it can reach 20%more than the flexural strength of plaster;nevertheless,there is a significant loss in terms of the compressive strength of the studied composites.The results obtained are confirmed by the microstructure of the fiber banana.In fact,the morphology of the banana fibers was improved by the drying process.It reduces the amorphous area and improves the cellulosic crystalline surfaces,which assures good adhesion between the fiber and the matrix plaster.Finally,the dimensionless coefficient analysis was done to judge the optimal proportion of the banana fiber additive and to recommend its use even on false ceilings or walls.

Study on carbon matrix composite bipolar plates with balance of conductivity and flexural strength

In order to balance the conductivity and flexural strength of graphite composite bipolar plates,the influence of conductive filler on the properties of graphite composite bipolar plate was comprehensively studied by using phenolic resin as binder,natural flake graphite as conductive substrate and functional carbon materials with different structures as auxiliary filler.The results show that the particle size of conductive substrate has an important influence on the conductivity enhancement of auxiliary filler.The influence of conductive particle size on auxiliary filler electrical conductivity improvement was first investigated in this research.The effects of various auxiliary filler concentrations on improving electrical conductivity and flexural strength were then examined.This research has substantial implications for the balance of electrical conductivity and flexural strength of graphite composite bipolar plates.

钛酸铝-堇青石复相陶瓷的制备和性能研究

本研究以MgO为稳定剂,以堇青石为增强剂,通过固相反应法成功制备了钛酸铝-堇青石复相陶瓷,并系统研究了MgO和堇青石以及烧结温度对复相陶瓷物相组成、显微结构、烧结性能和热力学性能的影响。结果表明,MgO的引入促进了钛酸铝晶粒的合成和长大,降低了烧结温度,并通过形成Mg_(x)Al_(2(1-x))Ti_((1+x))O_(5)固溶体提高了钛酸铝陶瓷的热稳定性。堇青石在烧结致密化和力学性能方面起着重要作用。在1325℃烧结条件下,MgO含量为8.00%、堇青石含量为15.00%的样品表现出良好的性能,体积密度为3.49 g/cm^(3),气孔率仅为2.2%,抗弯强度达到66.8 MPa,热膨胀系数为2.6×10^(-6)K^(-1)(室温至1000℃)。研究结果为设计和制备具备优异综合性能的高温结构陶瓷提供了新的思路。

不同化学改性方法提高玉米芯骨料混凝土的性能

玉米芯具有较低的导热系数,可以作为天然的保温材料,用于混凝土砌块中。然而,由于玉米芯的多孔结构,导致玉米芯骨料混凝土的抗压强度偏低,亟需进行改性。为了推广玉米芯的规模化利用,该研究以玉米芯为原料改善混凝土砌块的性能,通过红外光谱、拉曼光谱和扫描电镜等测试手段,探讨了3种不同改性技术对玉米芯骨料混凝土水化产物化学键、分子结构、界面过渡区微观结构、抗压强度和导热系数的影响。结果表明:与环氧树脂改性相比,陶粒法改性和裹浆法改性不仅增加了玉米芯骨料混凝土界面过渡区的水化硅酸钙凝胶含量,同时也降低了界面过渡区的厚度,优化了混凝土砌块的微观结构、提高了混凝土砌块的抗压强度、降低了混凝土砌块的导热系数。其中,陶粒法改性技术的效果尤为明显。界面过渡区厚度水化硅酸钙特征峰由大到小顺序分别为陶粒法改性、裹浆法改性、环氧树脂改性。经过陶粒法改性、裹浆法改性和环氧树脂改性后,玉米芯骨料混凝土的界面过渡区分别为无明显界面过渡区、55~66 μm和93~101 μm之间。和未改性玉米芯骨料混凝土相比,掺30%陶粒法改性玉米芯骨料混凝土的抗压强度的导热系数分别降低了51.5%和32.2%。当掺入不超过15%的改性玉米芯骨料时,混凝土砌块满足国家标准GB/T8239-2014中对抗压强度的要求。为了改善玉米芯骨料混凝土砌块的综合性能,建议掺入不超过15%的陶粒法改性玉米芯骨料。研究结果为玉米芯在混凝土砌块中的大规模利用提供了依据,同时也为进一步改善混凝土砌块的相关性能提供了参考。

粉煤灰-矿渣基泡沫地聚合物微观孔隙结构与宏观性能

以粉煤灰和矿渣为主要原材料,H_(2)O_(2)为发泡剂,通过碱激发方法制备粉煤灰-矿渣基泡沫地聚合物.研究碱激发剂模数和粉煤灰掺量对泡沫地聚合物微观孔隙结构、抗压强度及导热系数的影响.基于X射线衍射仪(XRD)、光学显微镜和CT扫描分析了反应产物和孔隙结构参数对泡沫地聚合物性能影响的内在机理.同时,基于灰色关联分析得到泡沫地聚合物的孔隙结构参数与其导热系数和强度的相关关系.结果表明:泡沫地聚合物的导热系数主要由孔隙率决定,两者呈指数负相关;泡沫地聚合物的抗压强度与孔隙连通度、孔隙率、平均孔径及分级孔隙占比有关,其中孔隙连通度和孔隙率影响最显著.

水灰比对泡沫混凝土性能的影响研究

泡沫混凝土作为一种多孔材料被广泛应用于建筑中,其性能直接受内部气孔结构的影响,而水泥浆的性质是影响泡沫稳定存在的重要因素。为探究水灰比对泡沫混凝土性能的影响,该文配制了三种不同水灰比的水泥浆制备泡沫混凝土,并测量其干密度、抗压强度、导热率和吸水率,探究其性能与水灰比的关系。结果表明,随着水灰比减小,水泥含量增加,水泥粘度增加,泡沫混凝土密度逐渐增加,强度逐渐增加,导热率逐渐增大,吸水率逐渐减小。在合适的水灰比下,泡沫混凝土相比纯水泥浆密度降幅最大,达到41.76%;强度降幅最小,抗压强度达到9.8 MPa;导热率降幅达到最大,为0.212 W/m·K;吸水率达到21.5%。

聚苯乙烯颗粒泡沫混凝土保温复合材料

本文针对传统建筑保温材料高能耗等缺点,从建筑节能思想出发,以导热系数和抗压强度作为主要技术指标,综述了聚苯乙烯颗粒泡沫混凝土保温复合材料的相关研究,希望为建筑的节能设计提供一些帮助。

铁尾砂泡沫混凝土的制备及性能

以铁尾砂为细骨料,采用不同掺量的铁尾砂取代天然砂制备目标密度为900 kg/m~3的铁尾砂泡沫混凝土试件,分析铁尾砂掺量对试件干燥收缩率、吸水率、导热系数、抗压强度、劈裂抗拉强度等性能的影响;并采用扫描电镜及图象分析软件分析试件的微观形貌。结果表明:铁尾砂掺量(质量分数)在0~40%范围内,随铁尾砂掺量的增加,泡沫混凝土的干燥收缩率和吸水率下降,导热系数略有增加;泡沫混凝土的抗压强度和劈裂抗拉强度呈先增后减的趋势,铁尾砂掺量20%时抗压和劈裂抗拉强度最高;掺入适量的铁尾砂可改善泡沫混凝土的孔结构,内部孔径趋向均匀,铁尾砂质量分数超过20%时泡沫混凝土的微观结构劣化,这也是导致其力学性能开始下降的原因。

Strong,tough,and thermally conductive nacre-inspired boron nitride nanosheet/epoxy layered nanocomposites

Thermally conductive polymer nanocomposites integrated with lightweight,excellent flexural strength,and high fracture toughness(KIc)would be of great use in many fields.However,achieving all of these properties simultaneously remains a great challenge.Inspired by natural nacre,here we demonstrate a lightweight,strong,tough,and thermally conductive boron nitride nanosheet/epoxy layered(BNNEL)nanocomposite.Because of the layered structure and enhancing the interfacial interactions through hydrogen bonding and Si–O–B covalent bonding,the resulting nacre-inspired BNNEL nanocomposites show high fracture toughness of~4.22 MPa·m^(1/2),which is 7 folds as high as pure epoxy.Moreover,the BNNEL nanocomposites demonstrate sufficient flexural strength(~168.90 MPa,comparable to epoxy resin),while also being lightweight(~1.23 g/cm^(3)).Additionally,the BNNEL nanocomposites display a thermal conductivity(κ)of~0.47 W/(m·K)at low boron nitride nanosheet loading of 2.08 vol.%,which is 2.7 times higher than that of pure epoxy resin.The developed nacre-inspired strategy of layered structure design and interfacial enhancement provides an avenue for fabricating high mechanical properties and thermally conductive polymer nanocomposites.

混凝土导热系数与抗压强度的关系研究

混凝土的导热系数和抗压强度是混凝土非常重要的指标,对其影响因素的研究具有非常重要的意义。对不同水胶比和不同养护温度下混凝土导热系数和抗压强度的变化规律进行了研究,分析了各种因素与导热系数和抗压强度之间的相关性,结果表明:混凝土的导热系数与养护温度呈负相关,而抗压强度与养护温度呈正相关;混凝土导热系数和抗压强度都与水胶比呈负相关;导热系数和抗压强度之间相关性很小。

柔韧隔热纤维素基气凝胶制备与性能

纤维素基气凝胶骨架强度差、脆性强,受外力压缩后隔热性能有所下降,不利于实际应用。针对这一问题,通过引入双硅烷偶联剂1,2-二(三甲氧基硅基)乙烷(BTMSE)与纤维素纳米纤维(CNF)形成共价交联网络,借助冷冻干燥技术构筑微米级多孔柔韧的隔热纤维素气凝胶,分析了气凝胶的微观形貌、化学结构,研究了BTMSE加入量与气凝胶力学性能、导热系数之间的关系,探究了力学性能对隔热效果的影响。结果表明:气凝胶呈现典型的蜂窝状孔洞结构,具有98.15%的高孔隙率;共价交联作用使气凝胶能够承受自身500倍的重量而恢复原状,在应变为50%的情况下循环压缩200次后,应变损失仅为9.7%左右;由于低密度、交联网络和多孔结构的存在,气凝胶导热系数低至31.90 mW/(m·K);在60%压缩应变后导热系数增加量不超过1%。该改性气凝胶有望用于恶劣环境下的隔热保暖。

制备工艺参量对超大颗粒石墨/铜基复合材料基本性能的影响

添加超大石墨颗粒来提高铜的润滑性能具有制备操作简便、工艺成本低等优点。文章在研制超大粒度石墨颗粒作为功能相的铜基复合材料基础上,探讨制备工艺参量对该复合材料热导率、压缩强度和摩擦系数等基本性能的影响。研究发现,该复合制品的热导率明显大于采用等质量的较小粒度石墨原料的复合制品;石墨含量越多,颗粒越小,铜/石墨复合样品的热导率就越低。结果表明,该复合制品的规定非比例压缩强度和抗压强度均明显高于采用较小石墨颗粒的复合制品,其力学性能主要与石墨颗粒大小和添加量有关。在本工作的粒度范围(120~1500μm)和含量范围(5%~15%)内,石墨颗粒越大,含量越少,其复合制品的力学强度就越好。研究还表明:该复合制品的摩擦系数与采用等质量的较小粒度石墨原料的复合制品基本相当;对于摩擦性能,本工作中的石墨含量以10%为佳,粒度以32目即约为720μm为佳。

不同养护温度下早龄期混凝土导热系数试验研究

为了研究低温环境下的混凝土早龄期的导热系数,采用热流计法导热仪对混凝土试件进行了导热系数测试,考察了-5℃、5℃和20℃养护环境下的早龄期混凝土导热系数,同时测定了各龄期混凝土的抗压强度。采用低场核磁共振技术,研究了不同养护温度下混凝土各龄期的含水率与孔隙率。结果表明:混凝土的含水率与孔隙率随龄期增大逐渐减小,抗压强度随龄期增大逐渐增大,导热系数与龄期和养护温度呈现负相关。

基于正交试验的免蒸压加气混凝土的制备与性能优化

【目的】制备轻质高强、节能保温的免蒸压加气混凝土,寻找最优制备配合比,提高固体废弃物的利用率。【方法】基于正交试验采用极差分析和矩阵关联分析的方法确定免蒸压加气混凝土的基础最优配比,优化玻璃粉的掺入量来实现加气混凝土性能的提升。【结果】各因素对免蒸压加气混凝土的表观干密度和抗压强度的影响程度由大到小为铝粉掺量(质量分数,下同)、水泥掺量、水料比、聚丙烯纤维(PP纤维)掺量,加气混凝土的基础最优配比为水泥掺量为24%,水料比为0.44,铝粉掺量为0.13%,PP纤维掺量为0.4%;当玻璃粉质量替代率达到25%时,混凝土的综合性能达到最优。【结论】玻璃粉作为粉煤灰的替代材料,在改善免蒸压加气混凝土干密度、抗压强度、导热系数方面效果显著。

提钛尾渣基硅酸钙板的制备及性能研究

提钛尾渣作为含钛高炉渣提钛后产生的一种含氯废弃物,一直缺乏有效的规模化利用技术,对环境具有潜在的危害。本文以提钛尾渣为主要原料,制备保温隔热材料——硅酸钙板,研究了不同钙硅比、硅藻土含量、水灰比、原渣与脱氯渣配比对材料性能、物相和微观形貌的影响。研究表明,随着脱氯渣含量的增加,硅酸钙板的抗折强度呈先增大后减小的变化规律,过量的硅藻土、过高的钙硅比和水灰比均不利于样品性能的改善。当提钛尾渣质量分数为46%(原渣和脱氯渣配比为1∶1)、硅酸盐水泥质量分数为15%、硅藻土质量分数为17%、钙硅比为0.84和水灰比为0.75时,硅酸钙板样品性能最优,其体积密度为1.25 g/cm^(3),抗折强度为10.4 MPa,导热系数为0.297 W/(m·K),样品中固化的氯离子质量分数为0.36%,固氯比达56%。

功能性石墨烯/纳米纤维素复合材料研究进展

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