Papers by Keyword: Thermal Expansion Coefficient

Abstract: In this paper we have focused on the study of the thermal expansion coefficient of a dental alloy, WBC, and its compatibility with a ceramic mass ,VITA VM 13, following thermal treatment according to the technological stages of production of a metal-ceramic prosthetic restoration.

Abstract: An improved model with polygonal aggregates is proposed to analyze the thermal stability of the resin concrete in this paper. A 2D polygonal aggregates model is established to make the calculating results closer to the reality and the 2D model is the slice directly captured from the 3D model based on the predecessors theory. A comparison is made between the conventional model with spherical aggregates and the polygonal aggregates model in this paper. The results of the analysis on the improved model are closer to the previous research results and more accurate than the spherical aggregates model. It confirms that the polygonal aggregates model is accurate enough to analyze the properties of the resin concrete.

Abstract: In this work, an experimental set for determining the linear thermal expansion coefficient (α) of a metal was designed and constructed. It was divided into three parts: metal rod holder, light source, and heating system. A cylindrical plastic pipe with an inner diameter of 16 cm was used as a metal rod holder. The sample metal rod with unknown linear thermal expansion coefficient was inserted vertically into a holder and covered by the first razor blade at one end, while the other end was fixed. The second razor blade was attached with posts. Two razor blades were aligned and separated with a distance of 0.05 cm; therefore, two razor blades were acted as a thin single slit. The steam generated from heating system was transferred into metal rod holder; subsequently, the length of metal rod increased with increasing temperature. The design of the apparatus for this proposed method based on decreasing the width of single slit with the same amount of increasing the metal rod length due to linear thermal expansion. A He-Ne laser with a wavelength of 632.8 nm used as a light source was passed through a single slit and produced a diffraction pattern on a screen. The decrease in slit width was determined by measuring the fringe width. The value of linear thermal expansion coefficient of a metal can be calculated from alteration of fringe width. In our case, stainless steel (314), copper (UNS C11000), and aluminium (6063) rods with the original length of 45.3 cm were used as samples. The experimental values of α for stainless steel, copper, and aluminium are 15.25 × 10^-6, 17.74 × 10^-6, and 23.13 × 10^-6 (°C)^-1, respectively. These values are in good agreement with the standard values as reported by the National Metal and Materials Technology Center (MTEC), Thailand. The error of this proposed method is found to be less than 1.2%.

Abstract: One of the components of the vehicle are of particular interest is the brake system , because its main function is to stop the rotation axis, set the axis of rotation and to prevent unwanted rotation. One classification system is the brake drum that has been widely made of cast iron, cast iron and cast steel special. This study makes brake drum of composite materials aluminum-based, with reinforcement is silicon carbide (SiC), obtained optimum composition of 15%, so it is written (Al-Si)-SiC/15%. Physics testing includes testing of thermal conductivity and thermal expansion coefficient, and Chemistry testing the corrosion penetration rate when the test material was coating with regular polish, with chrome, with nickel and with nickel + chrome. The final results showed that the value of conductivity and thermal expansion coefficient of the composite material is lower than cast iron, aluminum and other alloys. That is pretty good heat resistance when applied to brake drum material. The lowest of corrosion penetration rate on coating material with a layer of Ni-Cr.

Abstract: The novel high aluminum zinc-based alloy is prepared by changing composition of the alloy and adding 0.05% mixed rare earth with lanthanum-rich. The microstructure, mechanical properties and thermal expansion coefficient are investigated under as casting condition. The results showed that the novel high aluminum zinc-based alloy had fine microstructure, higher mechanical properties and smaller thermal expansion coefficient compared to the ZA27 alloy.

Abstract: CaZr₄(PO₄)₆ ceramics were prepared with solid reaction of two-steps method. CaZr₄(PO₄)₆ powders were synthesized by solid-phase reaction with Ca (OH)₂, ZrO₂ and (NH₄)₂HPO₄ as raw materials. Then the powders precursor were sintered to CaZr₄(PO₄)₆ ceramics with single phase structure at 1400°C for 8 hours. The relative density was measured, the phase structure of the materials synthesized at different temperatures and the average coefficients of thermal expansion were investigated. The results showed that the relative density of CaZr₄(PO₄)₆ ceramics sintered at 1400°C was 93%. The average thermal expansion coefficients was 1.8×10^-6/°C from 25°C to 1400°C. The CaZr₄(PO₄)₆ ceramics obtained possesses low thermal expansion property in a broad range of temperatures.

Abstract: In order to control cutting depth of preheating ZrO₂ sintered ceramics accurately, linear expansion elongation of preheating ZrO₂ multiple phase is measured; on the base of the measured data a mathematical model of thermal expansion coefficient given at different preheating temperature is put forward. Its fitting-error from-9μm to +2μm is very small compared to the data of linear expansion elongation measured. Some milling experiments that cutting force is following preheating temperature have been done by the amending cutting-depth from the model. The experimental results show that the cutting performance of ZrO₂ sintered ceramics preheated not only turns better but also extends cutter life.

Abstract: In order to accelerate the commercialization of SOFCs technology, the key is the development of high performance cathode materials operated at intermediate temperature. Sr and Cu doped rare earth oxide La_1-xSr_xFe_1-yCu_.yO_3-δ (x=0.1, 0.3 ; y=0.1, 0.2, denoted as LSFCu-11, LSFCu-31 and LSFCu-32 ) were synthesized by solid state reaction method (SSR). The formation process, phase structure and microstructure of the synthesized samples were characterized using TG/DSC, XRD and SEM. The thermal expansion coefficients (TEC) of the samples were analyzed by thermal dilatometry. The electrical conductivities of the samples were measured with DC four-terminal method from 25 to 950 °C. The results indicate that the samples exhibit a single phase with orthorhombic and hexagonal perovskite structure after sintered at 1200 °C for 4h. The electrical conductivity of the samples increases with temperature up to a maximum value, and then decreases gradually. The small polaron hopping is regarded as the conducting mechanism for synthesized samples at T 550 °C. The negative temperature dependence occurring at higher temperature is due to the creation of oxygen vacancies for charge balance. LSFCu-32 has higher mixed conductivity (> 100 S·cm^-1) at intermediate temperature and can meet the demand of cathode material for IT-SOFC. In addition, the average TECs of LSFCu-11, LSFCu-31 and LSFCu-32 are 1.22 × 10^-6 K^-1 , 1.30 × 10^-6 K^-1 and 1.34 × 10^-6 K^-1 respectively.

Abstract: Optical equipments especially those for aerospace application are expected to work over a wide temperature range. The change of temperature could cause the refractive index change of infrared glass elements. Furthermore, it would lead to the defocus of the image surface and the performance degradation, so the method of temperature compensation must be adopted, which could make sure that optical system would adapt to the change of ambient temperature. A method of temperature compensation with mechanical passive compensation is briefly described, and an example is also given. The quality of image could be optimized through mechanical passive compensation,depending on the differences of metal and non-metallic thermal expansion coefficient. The results show that the optical system works stablely in the designed temperature range. It is of great importance to the athermalisation design of infrared optical system.

Abstract: The Nb₂O₅-Al₂O₃ binary system ceramics were prepared by high temperature solid state reaction sintering, using Nb₂O₅ and Al₂O₃ micro powder as the raw materials. The samples were characterized by XRD, SEM, thermodilatometric analysis and mechanical strength measurement. The influences of Al₂O₃ content on the phase composition, microstructure, thermal expansion properties and bending strength were investigated. Results show the samples shows obvious changes in phase composition and microstructure with the addition of Al₂O₃ from 2.5% to 15%. The pure Nb₂O₅ ceramic is composed of monoclinic phase Nb₂O₅, while different monoclinic aluminum niobates were formed with different Al₂O₃ additions. Obvious microcracking can be observed for the samples without and with 2.5% and 7.5% Al₂O₃ additions. The addition of Al₂O₃ leads to significant increase of bending strength, and all the samples keep relatively low thermal expansion coefficient (TEC). The Nb₂O₅-Al₂O₃ binary system ceramics with ultra low TEC (0.55~0.86×10^-6°C^-1) and improved bending strength (50.4~70.6MPa) could be obtained with the addition of 7.5~15% Al₂O₃ when sintered at 1390°C for 2h.