Numerical and experimental evaluation for density-related thermal insulation capability of entangled porous metallic wire material

Entangled porous metallic wire material(EPMWM)has the potential as a thermal insulation material in defence and engineering.In order to optimize its thermophysical properties at the design stage,it is of great significance to reveal the thermal response mechanism of EPMWM based on its complex structural effects.In the present work,virtual manufacturing technology(VMT)was developed to restore the physics-based 3D model of EPMWM.On this basis,the transient thermal analysis is carried out to explore the contact-relevant thermal behavior of EPMWM,and then the spiral unit containing unique structural information are further extracted and counted.In particular,the thermal resistance network is numerically constructed based on the spiral unit through the thermoelectric analogy method to accurately predict the effective thermal conductivity(ETC)of EPMWM.Finally,the thermal diffusivity and specific heat of the samples were obtained by the laser thermal analyzer to calculate the ETC and thermal insulation factor of interest.The results show that the ETC of EPMWM increases with increasing temperature or reducing density under the experimental conditions.The numerical prediction is consistent with the experimental result and the average error is less than 4%.

Preparation and Characterization of Sandwich Structured Materials with Interesting Insulation and Fire Resistance

A cellular material in the form of 3-layered sandwich structure material was prepared via sole use of mechanical stirring without any use of a foaming agent,while Tween-80 was employed as a foam stabilizer via a developed in-situ mold casting.The resulting structure displayed a good appearance with no visual defects.The 3-layered composition of the sandwish structure,“nonporous resin layer-porous foam layer-nonporous resin layer”,was examined in terms of the microstructure,density&density distribution,pulverization ratio,mechanical strength,insulation and flame retardant performance.It was indicated from the results that the bonding between the resin layer and foam layer was tight,while the tensile rupture always occurred in the porous layer.Also,the density of the sandwich structure material was symmetrical with“saddle”distribution,and a uniform density for any given layer.The increase in the density at the interface layer provided a good interpretation for the tensile rupture never occurred at the interface.The brittleness resistance of the developed material was significantly improved,and the pulverization ratio was sharply decreased from 9.93%to 0.31%.The material acquired a thermal conductivity and limiting oxygen index(LOI)of 0.0241 W/m⋅K and 29.92%,respectively,indicating potential use of such materials broadly in fields of insulation and flame retardancy.

Investigations on Tracking and Erosion Resistance of Nano Silicone Composite for High Voltage Outdoor Insulation

In recent times, silicone rubber insulating material is used for power transmission line and substation insulation applications. In the present work, tracking and erosion resistance of the micro size filled and nano size filled silicone rubber material has been studied under the AC voltage, with ammonium chloride as a contaminant, as per IEC 60587 test procedures. The characteristic changes in the tracking resistance of the micro size and nano size filled specimens are analyzed through leakage current measurement. Comparative Tracking Index （CTI） is also evaluated in order to understand the relative behavior of solid electrical insulating material with regard to their susceptibility to surface tracking. Trend followed by the fundamental, third harmonic and fifth harmonic components of the leakage current during the tracking study are analyzed using moving average current technique. It is observed that the harmonic components of leakage current show good correlation with the tracking and erosion resistance of the material. It is noticed that 5 % wt ofnano size filler gives similar performance to that of 30 % wt of micro size filler in silicone composites.

Preparation and properties of thermal insulation coatings with a sodium stearate-modified shell powder as a filler

Waste shell stacking with odor and toxicity is a serious hazard to our living environment. To make effective use of the natural resources, the shell powder was applied as a filler of outdoor thermal insulation coatings. Sodium stearate(SS) was used to modify the properties of shell powder to reduce its agglomeration and to increase its compatibility with the emulsion. The oil absorption rate and the spectrum reflectance of the shell powder show that the optimized content of SS as a modifier is 1.5wt%. The total spectrum reflectance of the coating made with the shell powder that is modified at this optimum SS content is 9.33% higher than that without any modification. At the optimum SS content of 1.5wt%, the thermal insulation of the coatings is improved by 1.0℃ for the cement mortar board and 1.6℃ for the steel plate, respectively. The scouring resistance of the coating with the 1.5wt% SS-modified shell powder is three times that of the coating without modification.

Performance study of a complex thermal barrier functional coating with an electro-spark deposited burn-resistant layer

It is necessary to develop burn-resistant and thermal barrier complex functional coatings on the titanium alloys surface due to the poor high temperature performance for titanium materials and the problem of“titanium fire”which is easily happened.MTU Aero Engines GmbH has developed a complex functional coating which has great performance of burn resistant and sealing,the coatings has already been applied on compressor blades and casing for aero-engines and showed great performance.In this study,the complex functional coating which is composed of an electro-spark deposited amorphous Ti40Zr25Ni3 burn-resistant layer and a high-energy plasma spraying prepared YSZ thermal barrier layer was prepared on titanium alloys surface.Then the heat insulation ability,burn resistant performance and the bonding strength were investigated.The experimental results showed that the interface between the coating and the matrix was typical metallurgical bonded,and the average bonding strength was 36.335 MPa;when the temperature of the flame on the one side of the specimen reached 600℃,the average insulated temperature of the coating samples was 70.67℃;when the flame temperature was 350℃,the titanium samples without the complex functional coatings were burned,while the samples with the coating showed great performance of burn resistant even when the temperature was 750℃.This indicates that the new functional coating has good heat-insulating and burn-resistant performance.

Performance improvement of Fe-6.5Si soft magnetic composites with hybrid phosphate-silica insulation coatings

Fe-6.5Si soft magnetic composites(SMCs)with hybrid phosphate-silica insulation coatings have been designed to improve their comprehensive property via chemical coating combining sol-gel method in this work.The microstructure and magnetic performance of the Fe-6.5Si SMCs with hybrid phosphate-silica insulation coatings were investigated.The hybrid phosphate-silica coatings with high heat resistance and high withstand pressure,formed on the surface of the Fe-6.5Si ferromagnetic powders,were found stable in the composites.Compared with Fe-6.5Si SMCs coated by single phosphate or single silica,Fe-6.5Si SMCs with hybrid phosphate-silica show much higher permeability and lower core loss.The work provides a new way to optimize the magnetic performance of soft magnetic composites.

DC Insulation Parameter Characteristics of XLPE in the Course of Its Aging

This paper deals with the experimental study on the correlation betweeninsulation resistance (R) and direct current (DC) component (i_(de)) and corresponding aging degreeof insulation in the course of the aging within cross linked polyethylene (XLPE) insulation. Theaging tests were performed on a section of 10 kV transmission XLPE cable by means of water needlemethod, and _R was measured by DC voltage superimposed method, R and i_(de) were found to besignificantly dependent on the correspondingaging degree of insulation in the course of aging ofXLPE, and different kind of aging stage has different characteristics. Beside, there are generallysimilar regularity but different amplitude in the course of aging of XLPE insulation in differentelectrolyte, and the various electrochemical tree were found on the surface of aging XLPE cableimmersed in CuSO_4, solution. Therefore, according to the changing regularity of the DCcharacteristic parameters i. e. R and i_(de) within XLPE insulation judging the aging degree of XLPEinsulation will be an effective method.

Thermal insulating and fire-retardant Si_(3)N_(4) nanowire membranes resistant to high temperatures up to 1300℃

Superior thermal insulating and fire-retardant ceramic membranes are urgently demanded in the aerospace,construction,and chemical engineering industries.However,the generic characteristics of ceramic membranes,such as brittleness,structural collapse,and crystallization-induced pulverization behavior,present a great plague to their practical applications.Herein,we report a highly flexible,mechanically stable,fire-retardant,and high-temperature-resistant ceramic membrane based on the interlocked Si_(3)N_(4) nanowires formed by the precursor pyrolysis method.The Si_(3)N_(4) nanowire membrane(SNM)has excellent high-temperature resistance under alcohol lamps and butane spray lance.The thermal insulation with a thermal conductivity as low as 0.056 W m^(-1)K^(-1)can be attributed to the high porosity of SNM,which makes it a desirable candidate for heat insulators under harsh conditions.More importantly,SNM exhibits thermal stability and robust mechanical properties in the range of 25 to 1300℃.The high-temperature resistance of SNM up to 1300℃is achieved by the four stages:Si3 N4 nanowires,Si_(3)N_(4)@SiO_(2) nanowires,SiO_(2) nanowires,and bead-like SiO_(2) nanowires.After heat-treated at 1300℃,the macroscopic size of SNM does not change significantly,and the interlocked structure is still maintained.Furthermore,SNM still maintains excellent mechanical properties,with tensile strength as high as 0.26 MPa.This work provides a facile method for fabricating excellent thermal insulating and fire-retardant ceramic membranes,showing prospective application prospects in the era of thermal insulating materials.

Substrate bias effects on collector resistance in SiGe heterojunction bipolar transistors on thin film silicon-on-insulator

An analytical expression for the co/lector resistance of a novel vertical SiGe heterojunction bipolar transistor （HBT） on thin film silicon-on-insulator （SOI） is obtained with the substrate bias effects being considered. The resistance is found to decrease slowly and then quickly and to have kinks with the increase of the substrate-collector bias, which is quite different from that of a conventional bulk HBT. The model is consistent with the simulation result and the reported data and is useful to the frequency characteristic design of 0.13 μtm millimeter-wave SiGe SOI BiCMOS devices.

Investigation on Thermal Insulation and Mechanical Strength of Lightweight Aggregate Concrete and Porous Mortar in Cold Regions

Thermal insulation is an important indicator to evaluate the construction material in cold region engineering.As we know,adding the industrial waste as lightweight aggregate or creating the pore inside the cement-based composite could make the texture loose,and the thermal insulating capacity of the material would be improved with this texture.Using these methods,the industrial by-product and engineering waste could be cycled in an efficient way.Moreover,after service the fragmented cement composites paste could be used as aggregate in the thermal insulating concrete again.While the porous texture is not favorable for the mechanical strength and long-term durability in a cold environment.To balance the above three requirements from two opposite directions,different processing methods were applied to create the thermal insulation concrete/mortar.Firstly,the organic/inorganic lightweight aggregate,including the Expanded Polystyrene(EPS),Expanded Perlite(EP),and Ceramsite(CRMST)particles,were applied to create the Lightweight Aggregate Concrete(LWAC).As the comparative tests,the expanded Superabsorbent Polymer(SAP)hydrogel and Air-Entraining Agent(AEA)were also introduced to create the porous mortar.The above concrete/mortar was tested in the normal state and under the Freeze-Thaw cycle to explore the engineering performance in cold regions.During the experimenting process,the thermal insulation,mechanical strength,and frost resistance of these cement-based composites were investigated,and an optimal thermal insulation concrete/mortar was determined.

Effect of Moisture on the Insulation Condition of Twisted Coils

Method IEEE 841 is used to test endurance of insulation system of stators to 100% humidity at 40 ℃ for168 h. Insulation resistance after this test between phases or between phase and frame has not been lover as 5 × 10^6 Ohm. Some producers of motors use this method for determining quality of impregation resin. On such test insulation resistance between phases was lover as between phase and frame. Because between phases is only wire insulation impregnating resins on insulation resistance of insulation system an impregnating resin we observe influence of type of wires and after humidity test. With diagnostic of insulation, the state is dealt. We compare our impregnation resin with competitive impregnation resin. We made test on twisted coils prepared after STN IEC from two parallel wires. In this test, we succeed in demonstrating that the main influence on insulation resistance of insulation system wire and impregnation resin has insulation of wire. Impregnation resin has influenced on data dispersion.

菌丝体-杨木颗粒多孔复合材料的制备及保温阻燃性能研究

石油基高分子多孔材料的大量使用导致了严重的塑料污染(“白色污染”)。在这项工作中,采用了一种绿色可持续的合成策略,通过在杨木颗粒上接种培养真菌菌丝体,使其生长贯穿整个颗粒,最终制备出了一种菌丝体-杨木颗粒多孔复合材料。结果表明,多孔复合材料具有较低的密度(0.165 g·cm^(-3))、较高的孔隙率(82.7%)和疏水性(接触角:131.8°),并展示出优异的力学性能(压缩强度2.39 MPa;杨氏模量9.79 MPa)。另外,多孔复合材料还具有较低的导热系数(0.066 W/mK)和优异的阻燃性能(氧指数为28.4%)。这项研究工作展示了一种简捷和清洁环保的菌丝体-杨木颗粒多孔复合材料制备方法,对农林生物质高值化利用具有重要的参考价值。

550kV气体绝缘母线大电流工况下温升特性分析

探究气体绝缘母线在超高压大电流工况下的温升特性对设备的正常运行以及监测维护意义重大。然而,在长期大电流负荷运行下,因接触异常等原因导致母线在较小封闭空间内产生大量热量,极易造成局部过热严重威胁设备安全运行。针对这一问题,本文以550kV气体绝缘母线为研究对象,构建了考虑接触电阻的3维电磁-温度-流体多场耦合模型,计算其在1.1倍额定电流(8800A)、气压0.3MPa条件下的母线温度分布,并搭建了大电流温升试验平台进行验证,试验测量结果与仿真结果吻合度高。基于验证后的可靠模型,进一步探究了通流水平、SF_(6)气压及接触状态对母线温度分布的影响规律。结果表明:母线最高温度位于盆子凹面处电接触部位顶部(约为54℃),该端触头上方SF_(6)温度比导杆上方高近15℃,凹面处触头径向温度梯度明显低于凸面处触头径向温度梯度;在非等温自然对流的情况下,母线温度整体呈径向上高下低、轴向端部高中间低的规律分布;母线温度随通流水平提高呈非线性上升、随SF_(6)气压增大呈近似线性下降,可在一定范围内提高设备绝缘气体压强以降低设备运行温度;异常电接触处温度随阻值增大近似线性增加,而电接触异常往往是母线过热的主要风险点。研究结果可为超高压大电流气体绝缘设备产品设计及状态监测提供参考。

膨胀型防火涂层“新-老”涂层体系的热阻

在既有老化涂层上涂覆新涂层形成“新-老”复合涂层体系,复合涂层的热阻并非既有涂层热阻与补涂涂层热阻的简单叠加.基于隔热性能试验的温度测量结果,计算复合涂层体系的等效热阻常数,通过对不同试件等效热阻常数的对比分析,考察补涂涂层对既有涂层和复合涂层热阻的影响规律.结果表明:既有涂层热阻随补涂涂层厚度增加而降低,当补涂涂层厚度大于1.0 mm时,既有涂层热阻的贡献率不超过20%,计算复合涂层热阻时可忽略不计;当补涂涂层厚度较薄(0.5 mm)且既有涂层老化时间较短(≤21循环),或既有涂层有面漆时,建议考虑既有涂层热阻的贡献(贡献率>20%).当补涂涂层与既有涂层类型不同时,复合涂层体系的热阻更大,隔热性能更好.

TiO_(2)含量对Al_(2)O_(3)基绝缘涂层综合性能的影响

在GCr15轴承钢的基体材料上制备了不同TiO_(2)含量的Al_(2)O_(3)基绝缘涂层,研究了TiO_(2)含量对Al_(2)O_(3)基绝缘涂层性能的影响,结果表明:孔隙率基本随着TiO_(2)含量的增加而增大;结合力随着TiO_(2)含量的增加先增大后基本不变,TiO_(2)含量为1.5%左右达到峰值;TiO_(2)含量越高,耐冲击性能越好;随着TiO_(2)含量的增加,高温、常湿和常温、高湿环境下涂层绝缘电阻均呈先升高后降低的趋势,TiO_(2)含量为1.5%左右达到峰值。对绝缘涂层进行封孔处理,试验结果表明,封孔处理可以显著提高涂层的结合力、环境适应性、抗冲击性能。TiO_(2)含量为1.5%~3.0%时的涂层在未封孔和封孔后均具备较好的综合性能。

低品位蓝晶石制备锂离子电池窑炉用莫来石轻质隔热材料

为实现对低品位蓝晶石的综合利用,以低品位蓝晶石、α-Al_(2)O_(3)微粉和黏土为主要原料,在10 MPa下机压成型,分别经1450和1500℃保温3 h热处理,通过燃尽物法制备了莫来石轻质隔热材料。研究了黏土加入量(加入质量分数分别为5%、10%、15%、20%)和热处理温度(1450、1500℃)对试样体积密度、显气孔率、常温耐压强度、热导率以及抗锂离子电池正极材料侵蚀性能和显微结构的影响。结果表明:黏土的引入促进了试样的致密化和莫来石化反应,提高了试样体积密度、热导率和强度,添加20%(w)黏土的试样经1450℃烧后物理性能最佳,其体积密度为0.88 g·cm^(-3),常温耐压强度为21.0 MPa,热导率为0.25 W·(m·K)^(-1);当热处理温度为1450℃,黏土加入量为10%(w)时,试样具有较好的抗锂离子电池正极材料侵蚀性能。

铝酸盐体系中氧化时间对碳化硅颗粒增强铝基复合材料微弧氧化膜层的影响

[目的]探究氧化时间对碳化硅颗粒增强铝基(SiC_(p)/Al)复合材料微弧氧化膜层的影响。[方法]选用铝酸盐体系作为电解液,对SiC_(p)/Al复合材料进行微弧氧化处理,分析氧化时间对膜层组织结构、物相、厚度、粗糙度、结合力、电绝缘性及耐蚀性的影响。[结果]随着氧化时间延长,膜层逐渐变得连续均匀,厚度增加。若氧化时间过长,膜层会出现层叠现象,形成大尺寸微孔及裂纹,且生长速率越来越低。膜层结合力随氧化时间延长先增大后减小,在60 min时最大,达到39.85 N。氧化时间为10 min时,膜层的电绝缘性及耐蚀性最优,100 V和500 V电压下的绝缘电阻分别达到3.11×10^(12)Ω和1.41×10^(12)Ω,腐蚀电位为-0.6298 V,腐蚀电流密度为1.332×10^(-7)A/cm^(2)。[结论]SiC_(p)/Al复合材料表面微弧氧化膜层的连续性、均匀性及生长速率均与氧化时间有关。需选择合适的氧化时间,才能制备出连续、均匀且综合性能优异的膜层。

轨道交通牵引电机用耐电晕聚酰亚胺材料的制备及性能研究

普通聚酰亚胺应用于轨道交通牵引电机绝缘结构中,容易引发电晕击穿失效,严重影响电机长期运行的可靠性和安全性。本文以4,4′-二氨基二苯醚(ODA)为二胺,均苯四甲酸二酐(PMDA)为二酐,以不同硅烷偶联剂表面处理的纳米氧化铝为无机填料制备了3种耐电晕聚酰亚胺材料。探讨了不同偶联剂对耐电晕聚酰亚胺的表面形貌、力学性能、耐电晕寿命、电击穿性能的影响。结果表明:硅烷偶联剂表面处理使得氧化铝在聚酰亚胺基体中的分散性得到改善,降低了纳米氧化铝的团聚程度,提高了聚酰亚胺材料的耐电晕特性,同时保持了其优异的力学性能。其中采用双氨基的硅烷偶联剂表面处理后的纳米氧化铝在DMAc中的分散稳定性最佳,所制备的耐电晕聚酰亚胺材料表面形貌及综合性能也为最佳,在试验电压为3kV和2kV下的耐电晕时间分别为25min和120min,拉伸强度达167MPa,断裂伸长率为29.5%。

埃洛石-二氧化锆改性聚磷腈橡胶基复合材料高温烧蚀行为和原位陶瓷化反应

聚磷腈橡胶(PDPP)具有优异的阻燃性、热稳定性和高残炭率,是一种潜在的制备耐烧蚀绝热层的橡胶基体。为提高PDPP复合材料的耐烧蚀性,以埃洛石(HAL)和二氧化锆(ZrO_(2))为陶瓷化填料制备了HAL-ZrO_(2)-PDPP基复合材料,研究了这种混合陶瓷化体系对复合材料力学性能、热稳定性和烧蚀性能的影响。结果表明,HAL和ZrO_(2)陶瓷化填料对PDPP复合材料的拉伸力学性能和热稳定性无明显影响;含5 phr HAL和15 phr ZrO_(2)的PDPP复合材料拉伸强度为4.57 MPa,断裂伸长率为104.4%,经氧乙炔烧蚀后的线烧蚀率为0.060 mm/s,相较于单独使用HAL和ZrO_(2)分别提高了43.4%和33.2%。XPD和XPS结果表明,PDPP橡胶基体热解后的残炭分别与SiO_(2)和ZrO_(2)发生了生成SiC和ZrC的原位陶瓷化反应。在烧蚀过程中,低熔点陶瓷化填料熔融将基体热解形成的炭层与高熔点陶瓷粘结,使之成为含陶瓷-玻璃-热解炭复相结构的致密且具有一定强度的类陶瓷层,对提高复合材料的耐烧蚀性有积极作用。

高熵碳化物材料研究进展

高熵陶瓷是近年来得到快速发展的新型材料,吸引了许多研究者的关注,具有的高熵效应赋予了其优异的性能。其中高熵碳化物具有优异的硬度、断裂韧性、隔热性能与抗腐蚀性能,在环境障涂层、热障涂层等领域具有广阔的应用前景。本文详细介绍了高熵碳化物的预测理论、合成方法,同时对其抗氧化性能、力学性能、耐腐蚀性能以及隔热性能等方面进行了综述,指出了高熵碳化物在制备应用方面面临的问题,最后展望了高熵碳化物的发展方向。