Different spray processes for different Al2O3 coating properties

Among the different coating technologies, a thermal spray has a leading position because of its versatility: an extremely wide variety of materials can be deposited to protect back materials from wear, corrosion, thermal flux, etc. For example, atmospheric plasma spray is a rather well-established process but some other ones, such as flame technology, can also be used with lower economical impact. After a respective optimization of the processing parameters, both plasma and wire flame thermal processes were tested to form Al₂O₃ coatings. For each process, in-flight particle conditions, coating cross-section micro-structures and coating properties were successively determined. The experimental parameters were correlated to in-flight particle characteristics and to coating micro-structure and compared to resulting coating features. The evolution of particle velocity and temperature showed well-marked trends and the mean values were dependent on the spray process. The results emphasized the difference of spray system in terms of kinetic and thermal transfers to the particles. Then, the differences observed on in-flight particle characteristics can be used to explain the differences observed in coating properties, such as porosity content and hardness.     

3ω法加热/测温膜中温度波解析及其在微/纳米薄膜导热系数测量中的应用

给出了3ω法测试系统中描述薄膜表面加热/测温膜中温度波动的级数形式解，并将复数温度波动的实部和虚部分开表示.利用该解分析了交流加热频率、加热膜宽度和材料热物性的组合参数对加热膜温度波动幅度的影响.并根据此解对测量原理的数学模型进行了修正，建立了相应的3ω测试系统，首先测定了厚度为500 nm SiO₂薄膜的导热系数，验证了实验系统的合理性.加大了测试频率，利用级数模型在高频段直接得到SiO₂薄膜的导热系数，结合低频段的数据同时确定了Si基体的导热系数.利用级数解分析测试了激光晶体Nd:YAG〈111〉面上多层ZrO₂/SiO₂增透膜的导热系数，测试的ZrO₂薄膜的导热系数比体材料小.进行了不确定度分析.结果表明，提出的分析方法可以有效研究微器件表面薄膜结构的导热性能. 关键词： ω法')" href="#">3ω法 微/纳米薄膜 导热系数 微尺度加热膜     

Thermal degradation of a palladium coating on hydrogen-tight niobium membranes

The thermal stability of palladium-covered niobium, a composite used in hydrogen-tight membranes, is studied. Palladium is applied by the method of plasma sputtering. The thermal degradation of the coating is judged from a decrease in its ability to prevent niobium oxidation. It is found that the degree of oxidation of the samples heated in air at 693 K drops when the thickness of the coating increases in the range 2.5–1000.0 nm. The reason is heating-induced destructive modifications of the coating morphology, which are observed under a scanning electron microscope. The thicker the coating, the higher the temperature of onset of destruction. At temperatures above 873 K, the initially smooth continuous coating becomes highly porous and this porous layer does not change upon subsequent heating (up to 1273 K). Critical factors and possible mechanisms of thermal degradation of palladium coatings on hydrogen-tight composite membranes are discussed.     

相变材料蓄能式低温热水采暖地板热性能模拟

提出了一种采用定形相变材料蓄能的低温热水采暖地板形式。为了研究定形相变材料蓄能式低温热水采暖地板的传热性能,建立了该地板的传热分析模型。分析了相变材料的相变温度对地板表面平均热流密度和蓄能比的影响;比较了相变材料潜热蓄能地板与混凝土显热蓄能地板的热性能差异。结果表明:定形相变材料地板停止加热后仍可以在较长时间内保持稳定的热流密度。同时定形相变材料地板具有较大的蓄能比,使其夜间蓄存的热量可被更多地用于日间供热。     

Z箍缩驱动混合堆第一壁热-力学瞬态响应分析

利用ANSYS程序对Z箍缩驱动聚变-裂变混合堆(Z-FFR)第一壁在瞬态热流加载下的热-力学响应进行了模拟计算,分析了第一壁温度、应力随时间和深度的分布。结果表明,周期性脉冲加载不会导致第一壁产生温度累积效应,第一壁温度峰值409 ℃,出现在钨层表面,钨层最大应力140 MPa,锆合金基底最大应力33 MPa。     

Evaluation of paint coating thickness variations based on pulsed Infrared thermography laser technique

In this paper, a pulsed Infrared thermography technique using a homogeneous heat provided by a laser source is used for the non-destructive evaluation of paint coating thickness variations. Firstly, numerical simulations of the thermal response of a paint coated sample are performed. By analyzing the thermal responses as a function of thermal properties and thickness of both coating and substrate layers, optimal excitation parameters of the heating source are determined. Two characteristic parameters were studied with respect to the paint coating layer thickness variations. Results obtained using an experimental test bench based on the pulsed Infrared thermography laser technique are compared with those given by a classical Eddy current technique for paint coating variations from 5 to 130 μm. These results demonstrate the efficiency of this approach and suggest that the pulsed Infrared thermography technique presents good perspectives to characterize the heterogeneity of paint coating on large scale samples with other heating sources.     

氢化非晶硅薄膜的热导率研究

采用铂电极为加热电阻,研究了厚度为300—370nm等离子体化学气相沉积(PECVD)工艺制备的氢化非晶硅(a-Si：H)薄膜的热导率随衬底温度的变化规律.用光谱式椭偏仪拟合测量薄膜的厚度,得到了沉积速率随衬底温度变化规律,傅里叶红外(FTIR)表征了在KBr晶片衬底上制备的a-Si：H薄膜的红外光谱特性,SiH原子团键合模的震动对热量的吸收降低了薄膜热导率.从动力学角度分析了薄膜热导率随平均温度升高而增大的原因,并比较了声子传播和自由电子移动在a-Si：H薄膜热导率变化上的作用差异. 关键词： 非晶硅 热导率 薄膜 热能     

Analytical investigation into laser pulse heating and thermal stresses

Laser pulse heating of metallic surfaces results in rapid rise of temperature in the region irradiated by the laser beam. This in turn results in high temperature gradient in this region. The irradiated substrate material expands as a response to the temperature gradient. Consequently, high thermal stress levels are developed in the region of the high temperature gradient. In the present study, closed form solutions for temperature and stress fields due to a laser pulse decaying exponentially in time are presented. A Laplace transformation method is employed in the analysis. The resulting equations are non-dimensionalized with the appropriate parameters. It is found that temperature rises rapidly during the early heating period in the surface region. In this case, internal energy gain dominates the conduction losses from the surface vicinity. The thermal stress levels attain high values in the surface region. The stress wave developed is compressive and it propagates with a wave speed c₁ inside the substrate.     

Studies on the electrical conductivity, optical absorption and x-ray diffraction in bismuth thin film

Spectroscopically pure bismuth is evaporated onto glass substrates at different substrate temperature using a Hind Hivac coating plant. The electrical conductivity of bismuth thin films, prepared at different substrate temperatures is measured and thermal activation energy is evaluated. From the recorded optical absorption spectrum in the ultraviolet and visible regions optical band gapE _g is determined. X-ray diffractograms are recorded and lattice parameters are determined.     

Stress analysis at the interface between Ni-P coating and SiCp/Al substrate of space mirror

This paper investigates the mechanical properties at the interface of the coating-substrate system, which comprises the electroless nickel-phosphorus (Ni-P) coating and the aluminum matrix composite substrate reinforced by the silicon carbide particles (SiC_p/Al), and is used for the space mirror. To estimate the adhesion of Ni-P coating on SiC_p/Al substrate, the scratch adhesion testing has been performed by drawing a spherically tipped diamond indenter with a radius of 200 μm over the coated surface. The influence of the coating thickness on the interfacial stress induced by the inertial accelerations, temperature gradients and thermal soaks has been evaluated by simulation analysis based on the finite element method. The results of the scratch testing indicate that the adhesion strength of Ni-P coating to SiC_p/Al composite is more than 3.0 GPa. Compared the maximum value of the interfacial stress obtained by simulation analysis with results of the scratch testing, it is can be seen that the mirror has enough safety margin. Furthermore, the most significant conclusion that can be drawn from this work is that the coating thickness should not exceed 45 μm in order to ensure the performance and reliability of Ni-P coating and SiC_p/Al substrate system for space applications.     

Responsivity of infrared antenna-coupled microbolometers for air-side and substrate-side illumination

The response of an antenna-coupled microbolometer fabricated on a Si wafer coated on both sides with thin films of SiO₂ was measured for two types of illumination: through the substrate and from the air side. The measurement was performed in the spectral range from 9.22 to 10.84 μm. Both cases are modeled by using the transmission, reflection, and absorption properties of the three-layer wafer. The spectral characteristics of the SiO₂ thin film play a major role in the response of the detector. The responses of the sensor to the parallel and perpendicular polarizations are modeled by using two main contributions: the heating by absorption in the SiO₂ layer and the coupling of incident flux on the bolometer. Fitting this model to the experimental data allows us to conclude that the antenna response is the result of the incident flux coming from the substrate side. When the device is illuminated from the air side, the antenna signal results from the flux reflected at the film/substrate interface. The efficiencies of the contributions to the antenna signal coming from the substrate or from the air side have been obtained from the data fitted with the model. The substrate-side contribution is 50 times larger than the air-side contribution, confirming the theory of lithographic antenna on a dielectric substrate.     

Near-field radiative heat transfer between two plane surfaces with one having a dielectric coating

The effect of a dielectric coating on the near-field radiative heat transfer between two plane surfaces is numerically studied in the framework of the fluctuational electrodynamics. The dielectric coating is assumed to be a SiC or SiO₂ film, which is on top of the emitter. The results show that the near-field radiative flux between the plane surfaces can be either diminished or enhanced by the dielectric coating, depending on the thermal radiative properties of the emitter and the receiver. Furthermore, the dielectric coating effect on the near-field radiative flux can be very different from that on the far-field radiative flux. Detailed analysis on the variations of the TE- and TM-wave components of the radiative flux by adding the dielectric coating is provided, along with the physical mechanisms that account for these changes. Dielectric coatings such as SiC and SiO₂ films are widely seen in microelectronic structures and nanofabrication devices. The results obtained in this work should be valuable for further study and nanotechnological applications of near-field radiative heat transfer.     

Substrate heating effects on the propagation dynamics of laser produced plume during pulsed laser deposition of oxides

We report on the expansion dynamics of laser-produced plasma plumes of complex oxides in an oxygen atmosphere. In particular, we have studied the combined effects of background gas pressure and substrate heating on the plume propagation in typical pressure and temperature regimes of oxides thin film deposition by pulsed laser deposition. Our results evidence a reduced resistance of the background gas to the plume propagation as the substrate temperature increases. The experimental data are analyzed in the frame of a model describing the plume propagation into the background gas. Our experimental findings clearly indicate that the deposition temperature might influence film growth, not only through its direct thermal effect on the surface kinetics of adatoms, but also by affecting the energetic properties of the precursors in the gas phase.     

激光辐射致热单层薄膜温度响应

用热传导方程计算了在脉宽10ns、波长1.06μm的激光辐射下,TiO_2单层膜的温度场分布.结果表明:膜层的热参数增大,其峰值温度明显降低,而基板热参数变化对膜层温度响应影响很小,温度场分布由电场分布决定,1/4波长薄膜的峰值温度低于半波长薄膜的峰值温度.     

Experimental studies of the thermal properties of thin films by a probe technique with periodic heating

The thermal properties of SrTiO₃ thin films are investigated experimentally by recording the amplitude and phase of the temperature oscillations of a flat probe with the heat flux perpendicular to the plane of the film. Results are given from measurements of the specific heat and thermal conductivity of a leucosapphire substrate and the thermal conductivity of a SrTiO₃ film of thickness 2 μm. Fiz. Tverd. Tela (St. Petersburg) 39, 1299–1302 (July 1997)     

Anti-reflective effect of transparent polymer by plasma treatment with end-hall ion source and optical coating

The surface of poly(methyl methacrylate) (PMMA) was treated by plasma with an end-Hall ion source in vacuum in order to enhance its anti-reflectivity. The cone-shaped bumps induced by the plasma etching have shown an antireflective effect. Moreover, PMMA has poor thermal durability due to its low melting point; therefore, the etched PMMA was further coated by a 5 nm thick SiO₂ film after 900 and 1300 s plasma etching. Samples after SiO₂ coating were thermally annealed at temperature of 70°C for 1 h. Experiments show that transmittance was increased after 5 nm thick SiO₂ coating. The of transmittance of PMMA after both sides treated by 900 s plasma etching and 5 nm SiO₂ coating was not changed after thermal annealing. However, without SiO₂ coating the transmission was reduced 1% after annealing. Atomic force microscope (AFM) demonstrated that the nano-structures of cone-shaped bumps were formed on the PMMA after plasma etching and a smoother nano-structured pattern preserved the transmittance of the PMMA after both sides treated by 900 s plasma etching and 5 nm SiO₂ coating. Three dimensional photonic crystal formed by uniformly distributed cone-shaped bumps was assumed to result in the reduction of the anti-reflectivity of treated PMMA.     

Finite element simulation of stress distribution and development in 8YSZ and double-ceramic-layer La2Zr2O7/8YSZ thermal barrier coatings during thermal shock

In this paper, the thermal stress of the double-ceramic-layer (DCL) La₂Zr₂O₇/8YSZ thermal barrier coatings (TBCs) fabricated by atmospheric plasma spraying (APS) during thermal shock has been calculated. The residual stress of the coating after being sprayed has been regarded as the initial condition of the first thermal cycle. The characteristic of the stress development during the thermal cycle has been discussed, and the influence of the defects on the failure mode during the thermal cycle has also been discussed systematically. Finite element simulation results show that there exist higher radial thermal shock stresses on the ceramic layer surface of these two coatings. There also exist higher thermal stress gradient at the interface between the ceramic layer and the metallic layer. Higher thermal stress in 8YSZ/NiCoCrAlY coating lead to the decrease of thermal shock property as compared to that of LZ/8YSZ/NiCoCrAlY coating. The addition of LZ ceramic layer can increase the insulation temperature, impede the oxygen transferring to the bond coating and can also reduce the thermal stress. Considering from the aspects of thermal insulation ability and the thermal shock resistance ability, DCL type LZ/8YSZ TBCs is a more promising coating material compared with the single-ceramic-layer (SCL) type 8YSZ TBCs for the application.     

Tungsten and iridium multilayered structure by DGP as ablation-resistance coatings for graphite

Oxidation protection of carbon material under ultra-high temperature is a serious problem. In this paper, a newly designed multilayer coating of W/Ir was produced onto the graphite substrate by double glow plasma. As comparison, the Ir single-layer coating on the graphite was also prepared. The ablation property and thermal stability of the coatings were studied at 2000 °C in an oxyacetylene torch flame. Ablation tests showed that the coated graphite substrates were protected more effectively by W/Ir multilayer coating than Ir single-layer coating. Ir single-layer coating after ablation kept the integrality, although there was a poor adhesion of the Ir coating to the graphite substrate because of the thermal expansion mismatch and the non-wetting of the carbon by Ir coating. The mass loss rate of the W/Ir-coated specimen after ablation was about 1.62%. The interface of W/Ir multilayer coating and the graphite substrate exhibited good adherence no evidence of delamination after ablation. W/Ir multilayer coating could be useful for protecting graphite in high-temperature application for a short time.     

在Bohm模式下氘氚燃烧的等离子体温度分布

在一定的等离子体密度分布下,从电子和离子能量输运方程出发,研究了氘氚燃烧下的等离子体温度分布.研究中采用了JET适用的Bohm模式下的热传导系数,考虑了α粒子的反常扩散效应,动态反馈加热.研究结果表明,Bohm模式下的热传导率从等离子体中心到边缘逐渐增加;为了维持氘氚燃烧,必须有动态反馈加热,否则,燃烧将熄灭;α粒子的反常扩散,使得加热效率因子η_α在中心区域小于1,在外层大于1;α粒子的反常扩散越强烈,中心离子温度越高,是由于中心区域的热传导小,电子温度低,反馈加热功率增加的结果;B 关键词：     

Effect of the substrate temperature and deposition rate on the initial growth of thin lithium niobate-tantalate films deposited from a thermal plasma

Thin lithium niobate-tantalate (LiNb_0.5Ta_0.5O₃) films are studied at the initial stage of deposition from a thermal plasma. The effect of two deposition parameters (the substrate temperature and the deposition rate) on the film morphology, the film crystallinity, and the density of nuclei growing on a (0001) sapphire substrate are investigated. It is shown that the crystalline structure and roughness of a film are determined, for the most part, in the initial growth stage and therefore depend directly on both parameters. At the optimum temperatures and growth rates for obtaining good characteristics of (0006) texture, crystallinity, and surface roughness of the films, the film nuclei on the substrate have a high density and good epitaxial orientation to it. If the growth conditions are not optimum, the islands are either amorphous or have a low density on the substrate surface. The nucleation activation energy is observed to decrease as the deposition rate increases, which supports the assumption that the species that are active in film deposition are “hot” clusters forming in an oxygen-argon plasma in the immediate vicinity of the substrate.