Correction of Edge Effect in AC Calorimetric Method for Measuring Thermal Diffusivity of CVD Diamond Films1

In the thermal diffusivity measurement of a CVD diamond film using an ac calorimetric method, the reflection of an ac temperature wave at the edge of the film sample should be considered due to the limited length of the sample and its high thermal diffusivity, i.e., the edge effect. In this case, the measured thermal diffusivity is given as a function of frequency. The relation between the measured thermal diffusivity and the frequency is represented as an analytical expression. The real thermal diffusivity is obtained by correcting the edge effect by two means. One is an iterative method using the directly measured edge length of the sample to fit the analytical expression. The other is a parameter estimation method by which a simplex method is used to estimate the edge length and the real thermal diffusivity. Thermal diffusivities of two diamond films were measured, and data were analyzed using the above methods. The result shows that the parameter estimation method is relatively accurate and convenient in processing test data.     

Preparation and mechanical properties of exfoliated mica-polyamide 6 nanocomposites using sericite mica

A new mica/polyamide 6 (PA6) nanocomposite was formed by exfoliation of a mica, potassium sericite (K⁺-SE). The powder sample was separated through an air-classifier into D₅₀:6.0 μm (median particle diameter), D₁₀:3.5 μm, and D₉₀:9.5 μm. The K⁺-SE was modified with a dodecylammonium salt (DDA) by ion exchange at 70 °C for four days. The resulting organically modified SE was melt-kneaded with PA6 in a twin-screw kneader at 260 °C. In order to characterize the nanocomposite morphology, X-ray diffraction and transmission electron microscopy were used. Differential scanning calorimetry and mechanical property measurements were also carried out. The morphology of the nanocomposite revealed mica nanolayers with very high aspect ratios; that is, at levels about two times greater than that of conventional exfoliated clay-polymer nanocomposites. A small amount of organically modified SE with 2.1 mass% silicate was sufficient to improve the flexural properties and heat distortion temperature of the nanocomposite. However, overall mechanical properties were not completely improved, because the shearing stress induced during exfoliation of the silicate layers resulted in inhomogenous dispersion of silicate platelets in the matrix. The present study indicates that three factors, degree of exfoliation, aspect ratio and dispersion homogeneity of silicate platelets, play an important role for the development of high performance nanocomposites.     

Comparison of out-of-plane tensile strengths of aligned CFRP obtained by 3-point bending and direct loading tests

In order to propose a simple and effective test method for the out-of-plane tensile strength of laminated carbon fiber reinforced plastics (CFRPs), 3-point bending tests using an aligned CFRP with the span direction coinciding with through-the-thickness direction were performed, and the results were compared with those obtained by the direct loading test proposed by the authors. Weibull statistics were applied to evaluate the size and stress distribution effects on both results. The out-of-plane tensile strengths obtained by both tests were found to be consistent. Thus the 3-point bending test was recommended as a standard test method to evaluate the out-of-plane tensile strength of CFRPs from the perspectives of ease of preparation of the specimen and the simple procedure to derive the strength.     

Nanowhiskers formation by radio frequency Ar/O2 plasma etching of aluminum coated diamond films

Diamond nanowhiskers were fabricated by etching as-grown and aluminum coated diamond films in radio frequency (RF) Ar/O₂ plasma. It was found that diamond nanowhiskers could be obtained by anisotropic etching of both kinds of films. For the as-grown diamond film, the whiskers randomly formed on the diamond surface with higher etching rate. However, for the Al-coated diamond film, an energy dispersive X-ray spectroscopy measurement revealed that the distribution of the whiskers was the same as that of the coated Al particles. During the etching process, Al particles served as masks contributing to restraining the etching of the film underneath. It was found that the distribution of the whiskers was significantly influenced by the Al coating. The whiskers (1 μm in height and 50 nm in diameter) could be obtained under the optimum etching condition. In addition, the dependence of the distribution of the whiskers on Al coating time was demonstrated.     

An analysis of film boiling phenomena of subcooled water spreading radially on a hot steel plate

The film boiling phenomena on a hot steel plate are experimentally and theoretically analyzed in due consideration of the interaction between the cooling water and the plate surface temperatures, when a relatively hot water bar impinges on the plate surface.     

Thermal Diffusivity by Modified ac Calorimetry Using a Modulated Laser Beam Energy Source

Modified ac calorimetry, a variation of the Angstrom method, has been shown to be a precise tool for measuring the in-plane thermal diffusivity of thin films (thickness less than 300 m) of a wide variety of materials and layered composites. The property is determined from an analysis of the decay curve of the ac temperature waves generated by irradiation of a specimen using uniform chopped light (at frequencies from 1 to 20 Hz) from a halogen lamp source. To address certain limiting factors, especially to improve the signal-to-noise ratio and to eliminate heat losses, an improved form of measurement instrument has been developed. It is based on the use of a modulated laser beam heating to provide a higher intensity energy source plus a special optical system to ensure that one-dimensional ac temperature wave propagation is obtained. Measurements can now be made using frequencies in the range of 0.01 to 10 Hz, i.e., 10 times lower than in the traditional method. The performance of the improved measurement instrument will be illustrated by results on various materials of known thermal properties such as nickel and stainless steel, proposed reference materials such as a glassy carbon and alumina, plus a comparison of results obtained on CVD diamond films used in an international round-robin series with those obtained by the traditional technique.     

Prediction of forming limit in deep drawing of Fe/Al laminated composite sheets using ductile fracture criterion

Axisymmetric deep drawing processes of laminates composed of mild steel and various aluminium alloy sheets are simulated by FEM. From the calculated stress and strain histories of elements in each layer, the fracture initiation site and the forming limit are predicted by using the ductile fracture criterion. The predictions so obtained are compared with experimental observations. The results exhibit that various types of fracture initiations in deep drawing of the laminated composite sheets are successfully predicted. Furthermore it is found that the drawability is improved by setting the mild steel sheet on the punch side for the case of aluminium alloy sheet with comparatively high ductility, and by sandwiching the aluminium alloy sheet with the mild steel sheets for the case of low ductility.     

Possibility of grain refinement for superplasticity of a Mg-AI-Zn alloy by pre-deformation

For a commercial Mg-Al-Zn alloy sheet, tensile tests are carried out under various strains, strain rates and temperatures to investigate the possibility of grain refinement by dynamic recrystallization during pre-deformation. It is found from the microstructural observations that relatively fine grains of 10 m or so, in diameter are attained under the conditions of 250°C and 8.3 × 10^–4 s^–1. The specimen pre-strained under this condition also exhibits a fairly good superplasticity of total elongation beyond 300%.     

Detailed deletion mapping of the long arm of chromosome 6 in adult T-cell leukemia

Previously, we have found that the loss of heterozygosity (LOH) was frequently observed on chromosome 6q in acute/lymphoma-type adult T-cell leukemia (ATL), suggesting a putative tumor-suppressor gene for ATL may be present on chromosome 6q. To further define a region containing this gene, we performed fine-scale deletional mapping of chromosome 6q in 22 acute/lymphomatous ATL samples using 24 highly informative microsatellite markers. LOH was found in 9 samples (40. 9%) at 1 or more of the loci examined. Of the 9 samples, 8 shared the same smallest commonly deleted region flanked by D6S1652 and D6S1644 (6q15-21). The genetic distance between these two loci is approximately 4 cM. These results suggest that a putative tumor-suppressor gene on chromosome 6q15-21 probably plays a very important role in the evolution of acute/lymphomatous ATL. Our map provides key information toward cloning the gene.     

Use of Volume Element Methods to Understand Experimental Differences in Active/Passive Transitions and Active Oxidation Rates for SiC

Quantitative evaluation of oxidation behavior of high‐temperature materials is imperative for applications in a Silicon carbide (SiC)‐based thermal protection system (TPS) of reentry space vehicles. However, the reported oxidation rates obtained using thermogravimetric analysis (TGA) have been widely varied among researchers. In this study, this variation is assumed to be attributable to differences in the oxygen partial pressure at the sample surface due to different configuration of the experimental devices. Existing data are usually given as a function of the surface temperature of a specimen T_S with the partial pressure of oxygen in the input gas as a main parameter. However, even if and T_S are set to the same, the oxygen partial pressure on specimen surface and gas temperature T_G are expected to vary widely, respectively, from , T_S, and according to the difference in the oxidative environments. To evaluate these effects in various apparatuses, numerical calculations were conducted for the case of SiC. From these results, was found to be main source of the variation in oxidation rates.