Papers by Keyword: Thermal Expansion Coefficient

Abstract: Cellular glass composites can be made of waste flat glass or bottle glass added with eggshell powder 0, 1, 3 and 5%wt and then fired at 800° and 900°C for 1 h using compression molding process. Adding eggshell powder mixed with glass cullet affects to form open and closed pores and to decrease firing temperature, thermal expansion coefficient and light weight. However, adding high amount of eggshell powder affects to form an excessively amount of open and closed pores effect to increase water absorption. The standard Thailand Industries determines water absorption of glass foam less than 25% because high water absorption affects to decrease mechanical properties. Therefore, cellular glass composites added 1, 3 and 5%wt should not be fired at temperature higher than 800°C for 1h. In addition, the cellular glass composites added 1 %wt eggshell powder and fired at 900°C for 1 h still have low water absorption and low thermal expansion coefficient. Cellular glass composites are potential to apply for many industries such as construction, petroleum and petrochemical, insulation, medical and dental applications.

Abstract: During the curing cycle, the residual stress has influence on cure-induced deformation for carbon fiber reinforced plastics (CFRP) laminates, which is highly susceptible to the ply design. Therefore, the change laws of strain and the effect of residual stress in CFRP laminates after curing, which is of great significance to ply design, were cleared by using the combining pattern of thermocouple and fibre Bragg grating (FBG) sensors. For the FBG sensors embedded with different directions in lay-up CFRP laminates, the temperature and strain in different directions of composite laminates were obtained in real-time. Monitoring results show that compared with strain in 45° direction, the carbon fibers (CF) act stronger to inhibit strain in 0° direction and weaker to inhibit strain in 90° direction of resin. After curing, the residual strain in 0° direction is tensile strain, and the residual strain in 45° direction and 90° direction are compressive strain. Meanwhile the value of residual strain in 90° direction is greater than that in 45° direction.

Abstract: We discuss the setup of a simulation on ANSYS to predict the thermal expansion of parts made of Nitinol. A simulation is justified for working conditions in which the part heating is not homogeneous originating a temperature gradient across the part section such that an analytical estimate for the part expansion cannot be calculated. We apply the simulation to the topological optimization of a square section geometry and a bullet geometry for water assisted injection molding. For the topological optimization we consider as parameter the wall thickness and consider both the cases of fast varying temperature and fast varying temperature and pressure.

Abstract: We measured the thermal expansion coefficients of 18R-LPSO phase and α-Mg phase in a Mg₉₇Zn₁Y₂ alloy polycrystal. This was achieved by using a Gandolfi camera, which was attached on a high precision diffractometer at SPring-8 BL40XU beamline. By using this system, fine diffraction data were obtained from a Mg₉₇Zn₁Y₂ polycrystal at 6 different temperatures between 90 and 450 K. We succeeded to determine cell parameters of 18R-LPSO phase and α-Mg phase separately in the Mg₉₇Zn₁Y₂ alloy polycrystal. The thermal expansion coefficients were determined from the refined cell parameters. The differences of the thermal expansion coefficients of 18R-LPSO phase and α-Mg phase in the Mg₉₇Zn₁Y₂ alloy were much smaller than those of single-phase 18R-LPSO and α-Mg polycrystals.

Abstract: In order to synthesize cordierite ceramics with low thermal expansion coefficient and good properties, in our work, the cordierite ceramics were prepared by using talc, natural containing zirconium kyanite, common kyanite and industrial Al₂O₃ as raw materials, introducing the right amount of WO₃ (introducing tungsten acid) as catalyst. The effects of the introduced WO₃ on the phase composition, sintering characters, microstructure and thermal expansion coefficient of the cordierite ceramics were investigated. The results show that the introduction of WO₃ can eliminate the intermediate phase magnesia-alumina spinel and promote the formation of cordierite; the as-prepared cordierite ceramics synthesized by using natural containing zirconium kyanite as raw materials have high densification degree and low thermal expansion coefficient (1.53×10^-6/°C, Rt~1000 °C).

Abstract: The matrix of NZP family ceramics is natrium phosphate zirconium (for short, NZP) . NZP family ceramics have the designabolity of thermal expansion coefficient, and the average thermal expansion coefficient can be changed from negative value to positive value by means of composition adjustment, thus obtaining zero thermal expansion ceramics with good thermal shock resistance. With NZP family ceramics the thermal stress can be effectively reduced and the thermal properties of materials can be enhanced.Therefore, NZP family ceramics have become a hot topic in materials science community in recent years.The calcium phosphate zirconium powder was prepared by coprecipitation method, and NZP family ceramics were prepared after pressing molding and pressureless sintering. The results show that the compressive strength of the prepared NZP family ceramics is 199 MPa and the thermal expansion coefficient is-0.5×10^-6/°C at sintering temperature of 1100°C.

Abstract: In this work, AZ91D composite reinforced with M40 fiber was prepared by pressure impregnation method. Expansion behaviors of M40/AZ91D composite were studied with thermal expansion instrument in 25-150 °C and 25-150 °C temperature ranges of internal heat circulation, and then analyzed the influence law of hysteresis, residual strain and coefficient of thermal expansion (CTE) by different temperature change rate. The results revealed that residual stress and strain in process of pressure impregnation would lead to strain hysteresis and residual strain of composite in thermal cycling. At the same time, the CTE of the composites decreased with the increase of cycle times. Residual strain of the composite went up with the rise of temperature changed rate of the thermal cycling and CTE decreased with temperature change rate ascending in the 25-150°C temperature range. The CTE of the composites decreased with the increase of temperature during the heating process, which cut down with the increase of temperature in process of heating and cooling in the 25-495°C temperature range.

Abstract: A simple test approach named relative method is developed for determining the thermal expansion coefficient of ceramic coatings. Although ceramic coatings are hardly separated from the substrates, it was evaluated in this work simply by need only the measured thermal expansion coefficient of coated samples and substrates. This novel method was demonstrated to be valid for rectangular beam samples of two types of coating configurations: sandwich coating and around coating. The feasibility of this test method was confirmed by experimental results of SiC coating.

Abstract: Ni-Cr-Fe based alloy Inconel 690 is widely used in power plant, marine, chemical and nuclear applications due to its excellent mechanical properties, resistance to thermal creep deformation, good thermal stability and resistance to corrosive and oxidizing environments. In order to study the microstructure of the alloy and the precipitates formation during thermal exposure, the alloy was subjected to in-situ high temperature X-ray diffraction technique (HT-XRD) in the temperature range 298-1273K. Results of high temperature XRD patterns show (111), (200), (220) and (311) reflections confirming the stability of fcc structure in the temperature of investigation. With increase in the temperature, a shift in peak positions towards lower 2θ values due to lattice expansion was noticed. The average thermal expansion coefficient (TEC) of the alloy increased from 1.33 x 10^-5 K^-1 to 1.53 x 10^-5 K^-1 in the temperature range 298-1273 K. Scanning electron microscopy indicates austenitic grains of sizes in the range 100-150μm and chromium carbide precipitate at grain boundaries after the HT-XRD heat treatment.

Abstract: In this study, without changing the whole manufacturing process of T22 coiled tubes, high-temperature oxide films are formed through atmosphere adjustment by taking advantages of the cooling process after stress elimination heat treatment. The corrosion resistance of T22 heat-exchange tubes is improved, which are used in the steam generators (SG) of high-temperature gas cooled reactors (HTR). The surface microscopic morphology of the oxide films is observed using a scanning electron microscope, and the structure of these films is characterized using an X-ray diffractometer. The stability of the high-temperature oxide film forming process is investigated using TG-DTG, as well as the thermal expansion coefficient of the films. The results prove that: (1) The oxide film generated at 550 °C is uniform and dense; (2) The oxide films formed at various holding temperatures are mainly consisted by Fe₂O₃ and Fe₃O₄. When the holding temperature is 550 °C, the content of Fe₃O₄ is the highest as 70.1%; (3) The films are stable when placed in inert atmosphere (N2) below 900 °C, and there is not any change in the composition and structure of the films even after reacting with steam at 550 °C for 24 h; (4) The expansion coefficient of high-temperature oxide films is very close to that of the matrix of the heat exchange tube, and the difference between these two thermal expansion coefficients is 5.3×10^-9 mm/°C.