Boron nitride silicone rubber composite foam with low dielectric and high thermal conductivity

Silicone rubber(SR)is widely used in the field of electronic packaging because of its low dielectric properties.In this work,the porosity of the SR was improved,and the dielectric constant of the SR foam was reduced by adding expanded microspheres(EM).Then,the thermal conductivity of the system was improved by combining the modified boron nitride(f-BN).The results showed that after the f-BN was added,the dielectric constant and dielectric loss were much lower than those of pure SR.Micron-sized modified boron nitride(f-mBN)improved the dielectric and thermal conductivity of the SR foam better than that of nano-sized modified boron nitride(f-nBN),but f-nBN improved the volume resistivity,tensile strength,and thermal stability of the SR better than f-mBN.When the mass ratio of f-mBN and fnBN is 2:1,the thermal conductivity of the SR foam reaches the maximum value of 0.808 W·m^(-1)·K^(-1),which is 6.5 times that before the addition.The heat release rate and fire growth index are the lowest,and the improvement in flame retardancy is mainly attributed to the high thermal stability and physical barrier of f-BN.

Mechanical Properties and Dimensional Stability of Rigid PVC Foam Composites Filled with High Aspect Ratio Phlogopite Mica

High aspect ratio Phlogopite mica was used to enhance the dimensional stability and mechanical properties of extruded rigid Polyvinyl Chloride (PVC) foam. Mica was added to rigid PVC compound at different concentrations (0 - 20 wt%) and processed using a single screw profile extruder. PVC foam-Mica composites were characterized for their dimensional stability, and structural, thermal, and mechanical properties. Experimental results showed that the dimensional stability increased by 44% and heat resistance of the samples improved as the amount of mica increased in the composites. The storage modulus and tensile strength of the composites were also enhanced with the addition of mica. However, increasing the concentration of mica had no significant effect on the impact and flexural properties of the composites. SEM micrographs show good dispersion and orientation of the mica flakes along the cell walls of the PVC foam. Overall, the platy structure and physical properties of mica seemed to have played an important role in providing good interfacial bonding with the cell membranes of the foam, thus enhancing the dimensional stability of the PVC- Mica foam composites.

Bio-Based Trivalent Phytate:A Novel Strategy for Enhancing Fire Performance of Rigid Polyurethane Foam Composites

Biomass phytic acid has potential flame retardant value as the main form of phosphorus in plant seeds.In this study,phytate-based flame retardants aluminum phytate(PA-Al)and iron phytate(PA-Fe)were synthesized and characterized.Subsequently,they were introduced into rigid polyurethane foam(RPUF)as flame retardants by one-step water-blown method.The results indicated that RPUF/PA-Fe30 exhibited the highest char residue of 22.1 wt%,significantly higher than 12.4 wt%of RPUF.Cone calorimetry analysis showed that the total heat release(THR)of RPUF/PA-Al30 decreased by 17.0%and total smoke release(TSR)decreased by 22.0%compared with pure RPUF,which were the lowest,demonstrating a low fire risk and good smoke suppression.Thermogravimetric analysis-Fourier transform infrared spectrometer(TG-FTIR)implied the release intensity of flammable gases(hydrocarbons,esters)and toxic gases(isocyanate,CO,aromatic compounds,HCN)of composites was significantly reduced after the addition of PA-Fe.The analysis of char residue indicated that the RPUF composites formed a dense char layer with a high degree of graphitization after the addition of PA-Al/PA-Fe,endowing RPUF composites with excellent mass&heat transmission inhibition effect and fire resistance in the combustion process.

Microstructure of nickel foam/Mg double interpenetrating composites

The magnesium matrix double interpenetrating composites reinforced by nickel foam were fabricated by pressureless infiltration technology.Then the morphology of the nickel reinforcement and the microstructures of composites were characterized by SEM.The results show that not only is the nickel foam reinforcement reticular in three dimensions,but also the struts of foam keep the network structure,which ensures that the Ni foam/Mg composites are double interpenetrating.The interface bonding of composites between magnesium matrix and nickel foam reinforcement is good,without reaction around the interface,which is the indispensable condition that advanced composites should possess.Magnesium matrix distributes in the windows of nickel foam,the triangle center holes and microhole of nickel struts,and the composites have double interpenetrating structure,which makes the composites have unique properties.

Corrosion behavior of SiC foam ceramic reinforced Al-23Si composites in NaCl solution

SiC foam ceramic reinforced aluminum matrix composites(SFCAMCs)were prepared by squeeze casting aluminum alloy(Al-23Si)into the SiC foam ceramic with different pore sizes,and the corrosion behavior of the SFCAMCs was studied in NaCl solutions.Static immersion corrosion tests were conducted at 20°C,50°C and 80°C,respectively.Corrosion morphology and products were analyzed by scanning electron microscope,energy dispersive system and X-ray diffraction.It was found that the corrosion rate of SFCAMCs increases as the temperature rising,and the bigger pore size of SiC foam ceramic reinforcement,the better corrosion resistance of SFCAMCs.

Experimental investigation on weak shock wave mitigation characteristics of flexible polyurethane foam and polyurea

In recent years,explosion shock wave has been considered as a signature injury of the current military conflicts.Although strong shock wave is lethal to the human body,weak shock wave can cause many more lasting consequences.To investigate the protection ability and characteristics of flexible materials and structures under weak shock wave loading,the blast wave produced by TNT explosive is loaded on the polyurethane foam with the density of 200.0 kg/m3(F-200)and 400.0 kg/m3(F-400),polyurea with the density of 1100.0 kg/m^(3)(P-1100)and structures composed of the two materials,which are intended for individual protection.Experimental results indicate that the shock wave is attenuated to weak pressure disturbance after interacting with the flexible materials which are not damaged.The shock wave protective capability of single-layer materials is dependent on their thickness,density and microscopic characteristics.The overpressure,maximum pressure rise rate and impulse of transmitted wave decrease exponentially with increase in sample thickness.For the same thickness,F-400 provides better protective capability than F-200 while P-1100 shows the best protective capability among the three materials.In this study,as the materials are not destroyed,F-200 with a thickness more than10.0 mm,F-400 with a thickness more than 4.0 mm,and P-1100 with a thickness more than 1.0 mm can attenuate the overpressure amplitude more than 90.0%.Further,multi-layer flexible composites are designed.Different layer layouts of designed structures and layer thickness of the single-layer materials can affect the protective performance.Within the research range,the structure in which polyurea is placed on the impact side shows the optimal shock wave protective performance,and the thicknesses of polyurea and polyurethane foam are 1.0 mm and 4.0 mm respectively.The overpressure attenuation rate reached maximum value of 93.3%and impulse attenuation capacity of this structure are better than those of single-layer polyurea and polyurethane foam with higher areal density.

Protective performance of shear stiffening gel-modified foam against ballistic impact:Experimental and numerical study

As one of the most widely used personal protective equipment(PPE),body armors play an important role in protecting the human body from the high-velocity impact of bullets or projectiles.The body torso and critical organs of the wear may suffer severe behind-armor blunt trauma(BABT)even though the impactor is stopped by the body armor.A type of novel composite material through incorporating shear stiffening gel(STG)into ethylene-vinyl acetate(EVA)foam is developed and used as buffer layers to reduce BABT.In this paper,the protective performance of body armors composed of fabric bulletproof layers and a buffer layer made of foam material is investigated both experimentally and numerically.The effectiveness of STG-modified EVA in damage relief is verified by ballistic tests.In parallel with the experimental study,numerical simulations are conducted by LS-DYNA®to investigate the dynamic response of each component and capture the key mechanical parameters,which are hardly obtained from field tests.To fully describe the material behavior under the transient impact,the selected constitutive models take the failure and strain rate effect into consideration.A good agreement between the experimental observations and numerical results is achieved to prove the validity of the modelling method.The tests and simulations show that the impact-induced deformation on the human body is significantly reduced by using STG-modified EVA as the buffering material.The improvement of protective performance is attributed to better dynamic properties and more outstanding energy absorption capability of the composite foam.

Low-Velocity Impact Response of Stitched Multi-layer Foam Sandwich Composites

Low-velocity impact damage known as“imperceptible”damage usually destroys the structural integrity of the material and seriously affects the service life of the materials.To improve the low-velocity impact resistance of foam sandwich composites,an innovative concept of a stitched multi-layer sandwich structure by organically combining the discrete splitting of foam layer with full thickness stitching was proposed,and its low-velocity impact resistance obtained through drop-hammer impact tests was explored.The results showed that the multi-layer foam sandwich structure acted as a stress disperser and reduced the irreversible impact damage.The depth and area of low-velocity impact damage of multi-layer foam sandwich composites gradually decreased with increasing the number of the layers.The stitched structure would improve the integrity of the foam sandwich composites and inhibit the propagation of cracks.The maximum impact load of the stitched foam sandwich composite increased by approximately 5% compared with that of the non-stitched material.In addition,the low-velocity impact damage depth,damage area and absorbed energy of the stitched three-layer foam sandwich composite were reduced by 37.7%,34.6% and 20.7%,respectively,compared with those of the non-stitched single-layer sandwich material.

Experimental Study on Heat Storage Properties Comparison of Paraffin/Metal Foams Phase Change Material Composites

Heat storage properties of phase change materials(PCMs) are essential characteristics that perform a key role in thermal heat energy storage systems.The thermal properties of PCMs can be improved by developing metal foam/PCM composites.The addition of metal foam in PCMs has a significant effect on the thermal characteristics of PCMs.In this paper,the heat storage properties of two different metal foam/PCM composites were experimentally examined.The behavior of paraffin in metal foam(copper and iron-nickel)/paraffin composites concerning pure paraffin at a constant heat flux of 1000 W/m^(2) in three directions simultaneously(x,y,and z) was studied.Paraffin was infiltrated into copper and iron-nickel foams to develop composite materials which resulted in enhancing the thermal conductivity of the paraffin.A comparative analysis is made on the heat storage properties of paraffin in copper and iron-nickel foams/paraffin composites.Inner temperature distribution during the phase transition process is experimentally evaluated.This comparison indicates that temperature uniformity in copper foam/paraffin composite is better than in iron-nickel foam/paraffin composite and pure paraffin at the same heat flux.Experimental results show that at heat flux of 1000 W/m^(2),the heat storage time for copper foam/paraffin composite is 20.63% of that of iron-nickel foam/paraffin composite.

High Cr white cast iron/carbon steel bimetal liner by lost foam casting with liquid-liquid composite process

Liners in wet ball mill for mineral processing industry must bear abrasive wear and corrosive wear, and consequently,the service life of the liner made from traditional materials,such as Hadfield steel and alloyed steels,is typically less than ten months.Bimetal liner,made from high Cr white cast iron and carbon steel,has been successfully developed by using liquid-liquid composite lost foam casting process.The microstructure and interface of the composite were analyzed using optical microscope,SEM,EDX and XRD.Micrographs indicate that the boundary of bimetal combination regions is staggered like dogtooth,two liquid metals are not mixed,and the interface presents excellent metallurgical bonding state.After heat treatment,the composite liner specimens have shown excellent properties,including hardness>61 HRC,fracture toughnessα k >16.5 J·cm-2 and bending strength >1,600 MPa.Wear comparison was made between the bimetal composite liner and alloyed steel liner in an industrial hematite ball mill of WISCO,and the results of eight-month test in wet grinding environment have proved that the service life of the bimetal composite liner is three times as long as that of the alloyed steel liner.

Effect of Graphene Surface Functional Groups on the Mechanical Property of PMMA Microcellular Composite Foams

The functional groups on graphene sheets surface affect their dispersion and interfacial adhesion in polymer matrix. We compared the mechanical property of polymethymethacrylate (PMMA) microcellular foams reinforced with graphene oxide (GO) and reduced graphene oxide (RGO) to investigate this influence of functional groups. RGO sheets were fabricated by solvent thermal reduction in DMF medium. UV-Vis, FT-IR and XPS analyses indicate the difference of oxygen-containing groups on GO and RGO sheets surface. The observation of SEM illustrates that the addition of a smaller number of GO or RGO sheets causes a fine cellular structure of PMMA foams with a higher cell density(about 1011 cells/cm3) and smaller cell sizes (about 1 -2 jim) owing to their remarkable heterogeneous nucleation effect. Compared to GO reinforced foams, the RGO/PMMA foams own lower cell density and bigger cell size in their microstructure, and their compressive strength is lower even when the reinforcement contents are the same and the foam bulk density is higher, These results indicate that the oxygen-containing groups on GO sheets' surface are beneficial to adhere CO2 to realize a larger nucleation rate, and their strong interaction with PMMA matrix improves the mechanical property of PMMA foams.

The Effects of DOPO-g-ITA Modified Microcrystalline Cellulose on the Properites of Composite Phenolic Foams

In order to improve the comprehensive performance of phenolic foam,9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO)was grafted with itaconic acid(ITA)(DOPO-g-ITA)to modify microcrystalline cellulose(MCC).DOPO-g-ITA modified MCC(DIMMCC)was used to prepare composite phenolic foam(DCPF).The structures of DIMMCC were verified by Fourier transform infrared spectroscopy(FT-IR).The microstructure and crystalline property were characterized by scanning electron microscope(SEM)and X-ray diffraction(XRD)respectively.Compared with MCC,the crystallinity of DIMMCC was dramatically decreased,but the diffraction peak positions were unchanged.Thermal stability was decreased,and T_(i)decreased by 45.0°C.The residual carbon(600°C)was increased by 22.34%.With the dosage of DIMMCC/PR increased,compared with PF,the mechanical properties and flame retardancy of DCPF were increased.Especially,the dosage of DIMMCC/PR was 10%,the comprehensive properties of DCPF was better than others.

Stress and buckling analysis of a thick-walled micro sandwich panel with a flexible foam core and carbon nanotube reinforced composite (CNTRC) face sheets

In this paper,the stresses and buckling behaviors of a thick-walled mi-cro sandwich panel with a flexible foam core and carbon nanotube reinforced composite(CNTRC)face sheets are considered based on the high-order shear deformation theory(HSDT)and the modified couple stress theory(MCST).The governing equations of equi-librium are obtained based on the total potential energy principle.The effects of various parameters such as the aspect ratio,elastic foundation,temperature changes,and volume fraction of the canbon nanotubes(CNTs)on the critical buckling loads,normal stress,shear stress,and deflection of the thick-walled micro cylindrical sandwich panel consider-ing different distributions of CNTs are examined.The results are compared and validated with other studies,and showing an excellent compatibility.CNTs have become very use-ful and common candidates in sandwich structures,and they have been extensively used in many applications including nanotechnology,aerospace,and micro-structures.This paper also extends further applications of reinforced sandwich panels by providing the modified equations and formulae.

3D skeleton nanostructured Ni_3S_2/Ni foam@RGO composite anode for high-performance dual-ion battery

The growing global demands of safe, low-cost and high working voltage energy storage devices trigger strong interests in novel battery concepts beyond state-of-art lithium-ion battery. Herein, a dualion battery based on nanostructured Ni_3S_2/Ni foam@RGO(NSNR) composite anode is developed, utilizing graphite as cathode material and LiPF6-VC-based solvent as electrolyte. The battery operates at high working voltage of 4.2–4.5 V, with superior discharge capacity of ～90 m A h g^(-1) at 100 mA g^(-1), outstanding rate performance, and long-term cycling stability over 500 cycles with discharge capacity retention of ～85.6%. Moreover, the composite simultaneously acts as the anode material and the current collector, and the corrosion phenomenon can be greatly reduced compared to metallic Al anode. Thus, this work represents a significant step forward for practical safe, low-cost and high working voltage dual-ion batteries,showing attractive potential for future energy storage application.

Bonding effect of liquid magnesium with open-celled carbon foam in interpenetrating phase composite

The issue of bonding formation in liquid metal/open-celled carbon foam(C_(of))systems was examined,taking into account the practical aspects of the synthesis of a new type of Mg-C metal material composite.The problem is complex due to the strong oxidation and intense evaporation of liquid magnesium,as well as the 3D geometry of the carbon component,where metal transport occurred through the foam cells’windows.Laboratory experiments performed at 700℃ in ceramic crucibles showed that spontaneous carbon foam infiltration by liquid metal is impossible under the applied conditions,either in an air atmosphere coupled with flux protection or under argon protection.Comparative tests performed in a UHV chamber filled with static pure Ar by a sessile drop method,coupled with non-contact heating and capillary purification at a test temperature of 700℃ directly in the UHV chamber,showed non-wetting behavior of the Mg/C_(of)couple with a correspondingly high contact angle of about 135°.The graphite capillary was then moved down,the liquid drop being slightly pressed into the foam,but these changes did not induce effective foam penetration.Despite the short contact time for the sessile drop test under an argon atmosphere,SEM+WDS analysis of the solidified Mg/C_(of)couple revealed the formation of an MgO interlayer at the interface,with a thickness of approx.1μm.The experimentally demonstrated presence of oxygen in the carbon foam sample,both before and after its contact with magnesium,points to oxide-type bonding being established between Mg and C_(of).This observation is in a good agreement with previous reports on the interface characterization of magnesium matrix composites reinforced with glassy carbon materials and carbon fibers by stir casting and pressure infiltration.Based on the findings of this study,a general structural scheme of the bonding process between carbon foam and liquid magnesium,as an important stage in the syntheses of Mg-C composites,was proposed.

Biomass-Based Composite Foam from Tapioca Starch/Octenyl Succinate Starch Blended with Alpha-Chitin

The research study properties of the starch-based foam from mixed between tapioca starch and octenyl succinate starch (OSA starch), have addition alpha-chitin prepared by hot compression molding method. Tapioca starch with 50% OSA starch was investigated. For composite foam tapioca starch mixed by adding alpha-chitin at 5% - 30% of starch weight, it was found that water absorption was reduced. The higher alpha-chitin content in blending foam, the denser of foam structure observed which resulted in increasing of the foam density. The maximum bending stress of composite starch was decreased, but increasing the maximum bending strain.

轻钢泡沫混凝土组合墙体轴压性能研究

为获得轻钢轻质混凝土组合墙轴压性能,以试验模型为基础,采用ABAQUS软件建立墙体有限元模型,将数值模拟结果与试验结果对比,二者吻合较好。在此基础上,分析了含钢率、轻质混凝土强度对轻钢轻质混凝土组合墙轴压承载力的影响。结果表明随着含钢率的提高,其峰值荷载也随之提高,含钢率对组合墙体的轴压承载力及刚度有重要作用。随着泡沫混凝土强度的提高,组合墙体的刚度及轴压承载力显著提高,但延性系数有所降低。

密度对稻壳/聚氯乙烯发泡复合材料尺寸稳定性及力学性能的影响

针对传统木塑复合材料(wood plastic composites,WPCs)密度大、尺寸稳定性差等问题,以稻壳和聚氯乙烯(polyvinyl chloride,PVC)为原料制备三种密度的稻壳/聚氯乙烯发泡复合材料(rice husk/polyvinyl chloride foamed composites,RHPC),分别标记为RHPC-Ⅰ、RHPCⅡ、RHPC-Ⅲ,探究密度变化对RHPC性能的影响。结果显示:随着发泡程度的增加及密度的减小,RHPC的泡孔均匀程度有所降低。RHPC的线性热膨胀系数(coefficient of linear thermal expansion,CLTE)及吸水膨胀率均逐渐升高,且长度、宽度和厚度三个方向上的尺寸变化率均表现出各向异性;不同湿度和温度作用下的尺寸变化率表明湿度对RHPC尺寸的影响大于温度。RHPC-Ⅰ、RHPCⅡ、RHPC-Ⅲ的弯曲强度、弯曲模量和抗蠕变性能呈下降趋势;RHPC-Ⅱ由于均匀的泡孔结构呈现出最高的冲击强度和比冲击强度,分别为14.3 kJ/m2和19.9(k J·m^(-2))/(g·cm^(-3))。本研究为轻质高强WPCs的开发和拓宽其应用领域提供指导。

基于光谱学分析的硬质聚氨酯泡沫/钢渣/次磷酸铝复合材料阻燃机理研究

硬质聚氨酯泡沫(RPUF)的优异性能使其在各领域被广泛应用,但本身的易燃性为其在应用过程中埋下了巨大的安全隐患。钢渣(SS)作为提炼铁精矿后排放的固体废弃物,因其综合利用效率低下而造成一系列环境污染问题。为提高RPUF火灾安全性和钢渣的附加值,将SS和次磷酸铝(AHP)引入到RPUF中,采用一步全水发泡法,制备一系列阻燃RPUF(FR-RPUF)复合材料。利用射线荧光光谱分析(XRF)探究了SS的化学成分,并系统研究了SS/AHP对FR-RPUF复合材料的微观形貌、热稳定性、阻燃性能以及气相产物的影响。XRF测试表明:钢渣的化学成分主要是CaO、SiO_(2)、Al_(2)O_(3)、Fe_(2)O_(3)、SO_(3)、MgO,以上金属氧化物能够作为协效剂促进聚合物成炭,并覆盖在材料表面阻隔燃烧热,在凝聚相达到阻燃目的。扫描电镜(SEM)测试表明:SS/AHP与RPUF基体的相容性较差导致FR-RPUF的泡孔出现不同程度的破损。阻燃测试表明:RPUF-1、RPUF-4、RPUF-5的极限氧指数分别为24.2 vol%、23.4 vol%、19.7 vol%,说明SS和AHP存在一定的协效阻燃作用,且RPUF/SS/AHP复合材料全部通过UL-94 V-0级别,满足外墙保温材料使用要求。热重-红外分析(TG-FTIR)测试表明:SS/AHP并未改变RPUF的降解过程,气相产物主要为碳氢化合物、羰基化合物、氨基甲酸酯、CO_(2)、异氰酸酯化合物、芳香族化合物、氰化氢、羰基化合物和酯类。对典型挥发性产物进一步分析发现,AHP和SS的加入促进RPUF基体早期降解。拉曼测试表明:当SS/AHP加入到RPUF后,RPUF-4的D峰与G峰的峰面积比(I_(D)/I_(G))值最小,表明SS/AHP的加入提高了FR-RPUF复合材料炭渣的致密性、石墨化程度。结合上述分析提出阻燃机理:首先AHP吸热分解,降低了火焰周围的温度,其分解的PO·自由基捕获游离的HO·抑制连锁反应,分解产生的焦磷酸铝与炭渣覆盖在基体表面,抑制了火焰和可燃气体的扩散。AHP分解产生的PH3遇氧气生成酸性物质(磷酸和聚磷酸),促进了RPUF脱水成炭,并且钢渣中的矿物成分会与磷酸或聚磷酸反应,形成致密炭层,与AHP共同发挥协效阻燃作用。研究为SS和AHP复配阻燃硬质聚氨酯泡沫材料提供理论依据和实验基础。

聚氨酯复合泡沫的制备以及应用前景展望

综述了聚氨酯复合泡沫的最新发展和突破。添加高性能纳米材料是目前研究聚氨酯泡沫方向的新趋势。聚氨酯复合泡沫的纳米添加剂包括碳纳米管、碳纤维、石墨烯、纳米金属单质、纳米金属氧化物和纳米金属合金材料等。主要综述了聚氨酯复合泡沫的类型、合成方法。此外,重点介绍了聚氨酯复合泡沫在吸波屏蔽、压阻传感、阻燃和减震阻尼等领域的前沿进展。