Papers by Keyword: Thermal Expansion

Abstract: The demand for refractory materials continues to increase, particularly in the copper smelting industry. Flash Smelting Funaces (FSF) require refractories that can withstand high temperatures and aggressive chemical interactions. This study evaluates the performance of Magnesia – Chromite as refractory materials in FSF through tests such as Thermal Expansion, Porosity, Cold Crushing Strength, Bulk Density and Thermal Conductivity. Initial test results show that the brick has high resistance to thermal shock, with a thermal expansion value of -0.3% cold crushing strength of 63.4 Mpa, bulk density of 3.22 g/cm3, porosity of 12.76% and thermal conductivity ranging from 2.8 to 2.9 W/m.K.

Abstract: Welding is a widely used and effective method of joining metals. However, serious challenges are often encountered in the process due to welding distortion. Distortions result from the thermal expansion and shrinkage of metals during the welding process. This review paper focuses on the mechanisms associated with welding distortion and various mitigation techniques adaptable by fabrication industries. Whereas full prevention of distortion is unattainable with a finite geometric accuracy, it can essentially be controlled to minimize the undesired impact of distortion on the geometric integrity, hence increasing the manufacturing efficiency and decreasing the production cost. This paper categorizes distortions into out-of-plane and in-plane deformation modes and describes the factors which influence distortions - welding parameters, sequences, and material properties. Furthermore, a review of traditional and novel mitigation strategies, such as the optimization of welding parameters and improved determination and prediction of the welding sequence schedule. In this review, based on the synthesis of current publications, efforts have been made to guide fabrication industries in determining appropriate procedures and parameters to be selected according to job requirements, with the sole aim of offering better weld quality and lowering of manufacturing cost.

Abstract: Sr-doped CaMnO₃ materials have wide applications due to their thermal and electrical properties. The importance of the synthesis of Sr-doped CaMnO₃ material for various applications encourages researchers to evaluate and refine the synthesis process. In this study, Ca_1-xSr_xMnO₃ (x = 0; 0.05; 0.1; 0.15; 0.2) system has been prepared by sol-gel method followed by conventional sintering process at 850°C for 8 hr. A thorough discussion has been made on the outcomes derived from the investigation on the structural, electrical, and thermal properties of Sr-doped CaMnO₃ system using powder x-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, DC fourprobe method, thermal expansion studies, and thermoelectric power analyses. The XRD patterns of all prepared samples exhibited single phase with orthorhombic crystal structure (space group Pnma). Rietveld refinements were performed for all the patterns by using Fullprof software to extract the structural properties. The values of unit cell volume of samples tend to increase with the increment of dopant concentration, whereas the crystallite size values were decreased with dopant concentration. The microstructures of all the samples were studied using SEM, and elemental compositions were confirmed from the EDS results. Linear thermal expansion coefficients of all the samples were found to have moderate values in the temperature range from 30°C to 800°C. The electrical properties of all the system of samples were studied in the temperature range from 30°C to 400°C using DC fourprobe conductivity setup. It was found that all the samples exhibited semiconductor nature. Sr-content on the A-site suppress the electrical resistivity up to 10% of concentration and 5% dopant content exhibited the lowest electrical resistivity. The values of Seebeck coefficient found to vary from -160 µV/K to -124 µV/K with the increase of dopant content in the parent compound.

Abstract: Changes in thermal expansion during heating of hot-extruded tube made of VT23 titanium alloy (Ti-5.45 Al-4.7 V-2.45 Mo-1.1 Cr-0.7 Fe, wt. %) were analyzed. The volume effect of α→β-transformation, β-transus temperature as well as the volume fraction of α-and β-phase formed during heating were calculated based on the received data of dilatometric analysis. Results obtained were compared to thermodynamic calculations and published data. The change in the CTE value of VT23 alloy upon heating to 975 °C was estimated, and the explanation of different CTE values obtained in the present study and published data was proposed.

Abstract: Clay of the deposit Liepa is used for the production of ceramic building and finishing bricks in the factory “Lode” in Latvia. In the present work different types of these clays were investigated and “quartz effect” was determined using quartz sand as a leaning material. The substitution of quartz sand with milled E-glass fibre from Valmiera Glass was investigated and the changes in the magnitude of the quartz inversion effect were analysed. Thermal expansion was the main method for the determination of possible formation of cracks during technological process. Powder of milled glass fibre in amount of 5–10 % affects such properties as water uptake, porosity and apparent density and provides the required material properties at a lower firing temperature.

Abstract: In the course of the repair and fire protection upgrading of an approx. 1100 m long road tunnel in Hamburg, the eleven crossings of fire protection channels were covered with sheet steel to prevent the nesting of pigeons. In this context, the mechanical strains that may occur in the event of a fire had to be determined. In particular, it was necessary to clarify which mechanical loads would result from relative movements between the substrate (fire protection board) and the cover sheets due to their different thermal expansion in case of fire. For this purpose, the thermal behavior of the CSH fire protection board was determined by means of simultaneous thermal analysis and dilatometry, and the mechanical and thermal behavior of the composite construction was studied. The studies revealed that due to the facts that thermal expansion of the both materials and due to the softening of the fire protection panel the restraint that is generated by the screwed-on perforated plate in the vicinity of the screw shafts remains low during thermal loading. As a result, the top plate does not crack or break off, which means that screwing on the perforated steel sheets not negatively affects the fire protection of the panels.

Abstract: The article is devoted to the problem of raw material base expanding and improving construction and technical properties of porous granular materials. The results of experimental studies of silicate compositions based on liquid glass and technogenic fillers containing burnable or gas-forming components are presented. Influence of molding mixtures’ composition on thermal expansion nature of granular compositions was established. Preference of a filler combined, containing glass cullet, silica clay and mineral additives was revealed. Multicomponent composition of a filler helps to intensify composition’s expansion. Electron microscopy studies of porous silicate granules have confirmed the advantages of combined fillers using. Effectiveness of sodium additive introduction to regulate technological properties of the raw material and the process of pores formation has been proven. Expediency of mechanical activation of a raw mixture to reduce the temperature of expansion and obtain granules with a bulk density of not more than 300 kg/m³ has been determined.

Abstract: Polymer composites are gaining attention due to their superior thermal properties. Especially carbon black /carbon nanotubes/ graphene filled polymer composites are used in energy harvesting, thermal actuators and MEMS. The coefficient of thermal expansion (CTE) is one of the most important properties in the polymer composite. In the present study, thermal expansion of polydimethylsiloxane (PDMS) matrix is filled with carbon black particle of varied volume fraction is modeled. Two-dimensional finite element (FE) model is computed in order to explain the thermal expansion behavior of the polymer composite and same is carried out for ambient to 70 K temperature. A 2D regular arrangement of circular particle packing model is set up and simulated. The FE model predicts that filler geometry has a little effect on the thermal expansion than the percentage of filler in the composite. Thermal expansion of composite is compared with the theoretical model. It shows that the CTE of composite reduces as the filler percentage increase, also gives good agreement in the both models. Hence, it is found that the addition of carbon black to the polymer composite could make it perform significantly better in thermal expansion.

Abstract: Strontium hexaferrite is a well-known material, due to its application in microelectronics. This paper is devoted to strontium hexaferrite single crystals, obtained by the spontaneous crystallization technique with sodium based flux. SrFe₁₂O₁₉ crystals were grounded, pressed to the tablets, and crystals cell parameters were measured by thermal X-ray diffraction technique. Coefficient of thermal expansion calculated from the X-ray thermal diffraction data is in a good agreement with dilatometric measurements.

Abstract: This study assesses the structural stability at ultra-high temperature of the following selected compositions: 6.5 and 14 mol. % of RE₂O₃ (RE = Dy, Y, Er, Yb, and Lu) doped HfO₂. Under thermal cycling and thermal shock, the structural stability was evaluated at 2400°C with water vapor flux using a specific test bench with a 3 kW CO₂ laser. The cubic phase stability, which is theoretically important in the broad temperature range from 25 to 2800°C, was determined by a quantitative analysis of the X-ray diffractograms. Fully and partially stabilized HfO₂, obtained respectively with 14 mol. % and 6.5 mol. % of dopants, showed different behaviors to thermal damage. Thermal expansion was measured up to 1650°C to anticipate dimensional changes of these stabilized samples and to be able to design an optimized material solution fitting with future combustion chamber requirements. All of these results were then considered in order to exhibit a trend on the thermal stability at 2400°C of the ionic radius of the dopants and their optimal doping rates.