Evaluation of thermal spike due to exothermic reaction in curing process of carbon fiber-reinforced plastic pressure accumulators for hydrogen stations

In the curing process of fiber-reinforced plastic accumulators, a thermal spike appears due to the exothermic reaction of the resin. It is necessary to accurately evaluate this thermal spike to guarantee quality and avoid using a trial and error approach to control the temperature. Thus, we developed a curing process simulator that is able to accurately evaluate the thermal spike of the thermosetting resin. A simplified mesoscale finite element model with the definite separation of fiber and resin is used in the simulation. In this study, the newly developed simulation system was examined by comparing its results with the experimental results from the curing process of fiber-reinforced plastic accumulators.     

Microstructure and oxidation resistance of porous NbAl3 intermetallic prepared by thermal explosion reaction

Porous Nb–Al intermetallic was prepared by thermal explosion (TE) of combustion synthesis (CS). The temperature profile, phase composition, open porosity and oxidation resistance of Nb–Al compact were investigated. The results showed that the significant exothermic reaction occurred, which means that an obvious TE appeared during heating. The volume expansion of 190% was observed, and the prepared sample exhibited interconnected pores with an open porosity of 65.7%. The porous NbAl₃ intermetallic showed ‘pest’ oxidation in the temperature range of 500–600°C, and followed the parabolic oxidation law at 400°C. Moreover, due to the highly porous structure, this material had great potential for application to separation and heat insulation at a temperature range of room temperature to 400°C.     

Effect of heating rate on porous TiAl-based intermetallics synthesized by thermal explosion

TiAl-based porous materials were synthesized by a novel process of thermal explosion (TE) reaction. The effects of heating rate on the expansion behavior of powder assemblies, phase compositions, and pore structures were investigated. Results showed that the actual temperature of specimen increased rapidly from 655 to 661°C (furnace temperature) to 1018–1136°C (combustion temperature) in a short time interval of 25–55?s, indicating that an obvious TE reaction occurred at different heating rates (1, 2, 5, and 10°C min^?1). TE reaction in Ti/Al powder assemblies resulted in the formation of open-celled TiAl-based intermetallics. When the heating rate was set at 5°C min^?1, the maximum open porosity of 59% was obtained in Ti-Al bodies, which experienced the highest combustion temperature (1136°C) and underwent maximum volume expansion (48%). The pore size distribution was uniform and pores were interconnected in TE products.     

Adhesion failures on hard coatings induced by interface anomalies

In this work, the lack of adhesion occurred during the up-scaling of the deposition of tribological coatings in a semi-industrial apparatus is interpreted. The adhesion problems were detected for both hard and self-lubricant coatings from W-Ti-N and W:C systems, respectively, when they were deposited in a 4 cathodes TEER^® chamber by reactive unbalanced magnetron sputtering. In spite of cleaning the substrates surface by ion bombardment prior to deposition, by establishing a discharge close to the substrate, insufficient adhesion critical load values were measured by scratch-testing.A powerful set of complementary techniques was used to the detailed analysis of the interfaces in order to understand and overcome the adhesion problems: RBS gave some insights on the nature of the problem by detecting composition anomalies in the substrate/coating interface; Auger spectroscopy was used for identifying the underneath chemical composition close to the interface; cross section TEM gave the final evidence of the presence of a contamination layer attributed to malfunctioning of the ion cleaning process, which was the cause of the lack of adhesion.     

Observation of exothermic reaction during laser-assisted iron oxide coating on aluminum alloy

Aluminum and Fe₃O₄ reacts readily in what is known as thermite reaction to produce large amount of heat. Attempts were made to coat Fe-oxide on A319 cast aluminum alloy employing a high power laser to exploit this reaction. High-speed, high-resolution infrared thermography was employed to study the thermal conditions during the laser treatment. Parallel experiment using a less exothermic oxide (FeO) and the same substrate further emphasized development of higher temperature during highly exothermic reaction. The cooling rate calculated via both steady state and non-steady state relations were one order of magnitude different, which was supported by microstructural observations. Transmission electron microscopy revealed formation of aluminides as a result of reaction between iron oxide and aluminum alloys.     

Flow induced by a standing thermal wave

We consider the flow induced on a heated horizontal boundary. The boundary temperature varies spatially in a sinusoidal manner, which is itself sufficient to generate a flow parallel to the boundary. A harmonic modulation in time is superposed upon this such that in addition to the fluctuating flow a time-independent, or steady streaming, flow develops which provides the main focus for this investigation.     

Synthesis of TiC-TiB2-Ni cermets by thermal explosion under pressure

TiC/TiB₂-based cermets were fabricated in situ by means of the thermal explosion under pressure technique starting from Ti-B₄C powders with the addition of varying contents of Ni metal binder to achieve near-net-shape bulks. The combustion reaction was ignited in a graphite die heated by current. Full conversion of the reactants was obtained by thermal explosion and the process yielded TiC-TiB₂-Ni materials characterised by a fine microstructure. Appreciable differences in terms of microstructure, hardness and fracture toughness by indentation were observed between core and external surface of the products due to fast cooling caused by heat transfer to the die walls. Cermets with a high content of Ni showing high hardness and fracture toughness were obtained, with values of HV₅ = 2182 and K_Ic = 8.8 MPa m^1/2 for 30 wt.% Ni and of HV₅ = 1684 and K_Ic = 12.7 MPa m^1/2 for 47 wt.% Ni.     

Effect of nanostructures on the exothermic reaction and ignition of Al/CuOx based energetic materials

Al/CuOx based micro- and nanoenergetic materials (EMs) have been made by the thermal oxidation of Cu thin films deposited onto silicon substrates followed by Al integration through thermal evaporation. The micro- and nano-EMs are then characterized by scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, differential thermal analysis, and differential scanning calorimetry. By comparing the thermite reactions and ignition properties of Al with micro-CuOx and Al with nano-CuOx, we show experimentally that one-dimensional nanostructures (CuO nanowires) and nano-Al affect greatly the exothermic behaviors and ignition properties of the Al/CuOx based EMs. The higher surface energy associated with the CuO nanowires and the deposited nano-Al is believed to be a possible factor contributing to the enhanced exothermic reactions that occur below the melting point of Al and the smaller ignition delay and lower ignition energy.     

Whisker taper induced by heterogeneous chemical reaction

Experimental data are presented on the taper of silicon whiskers grown in an open chloride system. The whisker taper is shown to depend on the crystal growth rate, whisker radius and length, and process parameters. The experimental data are analyzed under the assumption that the size of the liquid droplet on the whisker tip decreases because of the heterogeneous chemical reaction responsible for the etching of the metallic component of the alloy. The influence of the crystal radius and vapor phase composition on the flux that leads to a decrease in the size of the liquid droplet. A model is proposed for whisker tapering as a result of the heterogeneous chemical reaction responsible for the etching of the metal on the surface of the liquid phase, and conditions for the growth of zero-taper whiskers are discussed.     

Negative thermal expansion induced by intermetallic charge transfer

Suppression of thermal expansion is of great importance for industry. Negative thermal expansion (NTE) materials which shrink on heating and expand on cooling are therefore attracting keen attention. Here we provide a brief overview of NTE induced by intermetallic charge transfer in A-site ordered double perovskites SaCu₃Fe₄O₁₂ and LaCu₃Fe_4−xMn_xO₁₂, as well as in Bi or Ni substituted BiNiO₃. The last compound shows a colossal dilatometric linear thermal expansion coefficient exceeding −70 × 10⁻⁶ K⁻¹ near room temperature, in the temperature range which can be controlled by substitution.     

强激光作用下生物组织热损伤问题的研究

详细阐述了强激光对生物组织的影响以及热损伤原理 .讨论了如何建立合理的生物组织热损伤换热模型 ,并根据数值模拟解与热损伤实验数据的比较 ,再进行模型识别 .理论与实验相结合的方法去解决热损伤问题     

Negative thermal expansion induced by intermetallic charge transfer

Abstract

Suppression of thermal expansion is of great importance for industry. Negative thermal expansion (NTE) materials which shrink on heating and expand on cooling are therefore attracting keen attention. Here we provide a brief overview of NTE induced by intermetallic charge transfer in A-site ordered double perovskites SaCu₃Fe₄O₁₂ and LaCu₃Fe_4?xMn_xO₁₂, as well as in Bi or Ni substituted BiNiO₃. The last compound shows a colossal dilatometric linear thermal expansion coefficient exceeding ?70 × 10^?6 K^?1 near room temperature, in the temperature range which can be controlled by substitution.     

Estimation of the critical rate of temperature rise for thermal explosion of first-order autocatalytic decomposition reaction systems using non-isothermal DSC

A method of estimating the critical rate of temperature rise for thermal explosion of first-order autocatalytic decomposition reaction systems using non-isothermal DSC is presented. Information is obtained on the increasing rate of temperature in highly nitrated nitrocellulose containing 14.14% of nitrogen when the first-order autocatalytic decomposition converts into thermal explosion.     

Time-resolved explosion dynamics of H2O droplets induced by femtosecond laser pulses

Series of time-resolved still images of the explosion dynamics of micrometer-sized water droplets after femtosecond laser-pulse irradiation were obtained for different laser-pulse intensities. Amplified pulses centered around a wavelength of 805 nm with 1-mJ energy and 60-fs duration were focused onto the droplet to initiate the dynamics. Several effects, such as forward and backward plumes, jets, water films, and shock waves, were investigated. Additionally, the influence of different pulse durations produced by chirping the laser pulses was observed.     

感应加热聚晶金刚石热损伤机理的研究

为了研究聚晶金刚石(PCD)在空气中的氧化方式,以及感应加热造成热损伤的形式和机理,分析了其在空气中的DTA和TG曲线,并对不同加热条件下的试件进行了XRD检测和SEM形貌观察.结果表明:PCD受热时,主要是金刚石和金属钴与氧气发生放热反应;PCD热损伤的形式有4种:金刚石表面的微裂纹、金刚石表面的"皱纹"、球状凸起、微孔洞;PCD热损伤机理为:受热时,金刚石氧化成CO和CO2逸掉,热应力致使金刚石表面产生微裂纹和皱纹;随着金刚石的减少,钴氧化物的生成量渐增,导致凸起和微孔洞的形成.     

Efficient relaxation of strained-SiGe layers induced by thermal oxidation

The new route to fabricate compositionally graded and highly-relaxed Si_1-xGe_x layers using thermal oxidation at high temperatures is investigated. Ge atoms behavior during thermal oxidation of Si_1-xGe_x layers is strongly dependent on the oxidation temperature. For low temperature oxidation processes Ge is incorporated as GeO₂ in the grown oxide layer, while for higher temperatures it accumulates below the grown oxide into a layer with a higher concentration than the initial Si_1-xGe_x. However, Si_1-xGe_x layers oxidized at 1000 °C did not show such an accumulation layer because Ge diffusion efficiently occurred, resulting in the formation of a compositionally graded and relaxed Si_1-xGe_x layer. Such layers could be used as virtual substrates for the strained-Si and relaxed-SiGe applications.     

Low-temperature interface reaction in aluminium-silicon carbide particulate composites produced by mechanical alloying

An experimental investigation has been carried out on the reaction that takes place between 3 and 20 μm SiC particles and the aluminium alloy 1050 matrix of composite materials prepared by a mechanical alloying process. The work is different from that undertaken by other researchers in that the SiC-Al interface reaction has been studied in the temperature range 853–933 K, i.e., with the matrix initially in the solid state. Differential thermal analysis, X-ray diffraction and scanning electron microscopy all show that the SiC-Al reaction initiates in the solid state at temperatures as low as 883 K. The reaction produces Al4C3 and Si, the latter entering into solid solution in the aluminium matrix. At temperatures exceeding 903 K, the reaction produces a liquid phase and at this stage the speed of the interface reaction increases significantly. The results are discussed in terms of Al-Si-C metastable equilibrium and the kinetics of the reaction. This revised version was published online in November 2006 with corrections to the Cover Date.     

Bounds on the effective thermal conductivity of composites with imperfect interface

A new model is developed to bound the effective thermal conductivity of composites with thermal contact resistance between spherical inclusions and matrix. To construct the trial temperature and heat flux fields which satisfy the necessary interface conditions, the transition layer for each spherical inclusion is introduced. For the upper bound, the trial temperature field needs to satisfy the thermal contact resistance conditions between spherical inclusions and transition layers and the continuous interface conditions between transition layers and remnant matrix. For the lower bound, the trial heat flux field needs to satisfy the continuous interface conditions between different regions. It should be pointed out that the continuous interface conditions mentioned above are absolutely necessary for the application of variational principles, and the thermal contact resistance conditions between spherical inclusions and transition layers are suggested by the author. According to the principles of minimum potential energy and minimum complementary energy, the bounds of the effective thermal conductivity of composites with imperfect interfaces are rigorously derived. The effects of the size and distribution of spherical inclusions on the bounds of the effective thermal conductivity of composites are analyzed. It should be shown that the present method is simple and does not need to calculate the complex integrals of multi-point correlation functions. Meanwhile, the present method provides an entirely different way to bound the effective thermal conductivity of composites with imperfect interface, which can be developed to obtain a series of bounds by taking different trial temperature and heat flux fields. In addition, the present upper and lower bounds are finite when the thermal conductivity of spherical inclusions tends to ∞ and 0, respectively.