Instantaneous Thermal Expansion Research Articles

Structure and Stability of Charge-Coupled Lanthanide-Substituted Ca10(PO4)6F2 as a Potential Fluoride Bearing Nuclear Waste Form.

The structure and stability of charge-coupled lanthanide-substituted Ca10(PO4)6F2 as a potential fluoride-bearing nuclear waste form for the back-end fuel cycle of Gen-IV molten salt reactor have been studied in detail. Here, calcium fluorapatite (CaFAp) as a model structure was taken for incorporation of trivalent lanthanides (Lns, La-Lu except Pm) in a charge-coupled fashion, i.e., 2Ca2+ = Na+ + Ln3+. In these fluorapatite phases, Na+ is substituted exclusively at nine coordinated sites, Ca1, while Ln3+ is preferentially substituted at seven coordinated sites, Ca2. These compositions are further characterized for the local structure by Fourier transform infrared (FTIR) and Raman spectroscopy. Thermal expansion was measured by high-temperature X-ray diffraction (XRD) and the instantaneous thermal expansion coefficient correlates well with the unsubstituted CaFAp. The heat capacities of these solids were measured by differential scanning calorimetry and drop calorimetry, whereas enthalpies of formation were obtained by high-temperature oxide melt solution calorimetry. The thermodynamic analysis demonstrated that lanthanides having ionic radii closure to Ca2+ (Sm3+ and Gd3+) imparted higher thermodynamic stability to the substituted CaFAp as compared to that of other Ln3+. According to structural and thermodynamic investigations, entropy-stabilized fluorapatite waste from NaPr0.125Nd0.125Sm0.125Eu0.125Gd0.125Tb0.125Dy0.125Ho0.125Ca8(PO4)6F2 (WF-Ln) was successfully synthesized for the first time. Furthermore, electron beam irradiation studies probed by XRD, FTIR, Raman, and X-ray absorption (XAS) spectroscopy implied the radiation resistance nature of this substituted CaFAps up to 20 MGy.

Thermal expansion studies of Li2TiO3 by dilatometry and in-situ high-temperature X-ray diffraction

Li2TiO3 (lithium titanate) is a material of interest in the field of fusion reactors due to its potential application as a tritium breeder material. Because of the extreme working conditions and temperature gradients involved, thermal expansion properties are critical to consider when assessing a material for a fusion reactor. The reactor is subjected to severe neutron flux, high temperature and thermal cycling, which can cause significant stress on the material. A low coefficient of thermal expansion (CTE) of Li2TiO3 is important as it mitigates mechanical stress and minimized the risk of structural damage resulting from thermal cycling. Material degradation, cracking, or delamination might result from a mismatch in CTE between different materials in the reactor. Therefore the estimations of material's thermal expansion properties hold significance for the designing and fabrication of structural material. In this study, Li2TiO3 material was compacted into pellets and high-temperature X-ray diffraction (HT-XRD) was employed to obtain X-ray diffraction patterns from room temperature to 1273 K at 100 K intervals. The lattice parameters (a, b, and c) of Li2TiO3 polycrystals were determined and corresponding unit cell volumes were estimated at each temperature. The thermal expansion percentages for the lattice parameters a, b, and c between room temperature and 1273 K were found to be 1.21%, 1.84%, and 1.83% respectively. The calculated coefficient of thermal expansion (CTE) were determined as 12.5 × 10−6 K−1, 19 × 10−6 K−1, and 18.9 × 10−6 K−1for lattice parameters a, b and c respectively. The crystallographic density at room temperature was estimated to be 3.42 g/cm3. The molar volume was calculated to range between 32.12 and 33.72 cm3/mol from room temperature to 1273 K. Additionally, high-temperature dilatometry was employed to measure the thermal expansion of Li2TiO3, resulting in the estimation of coefficient of thermal expansion. From room temperature to 1290 K, the thermal expansion percentage and mean coefficient of thermal expansion were calculated to be 1.91% and 19.64 × 10−6 1/K, respectively. Furthermore, the temperature dependent mean and instantaneous thermal expansion values were also determined. The differential scanning calorimetry (DSC) method was used to estimate the temperature of the monoclinic to cubic transformation, which was determined to be 1416 K. This paper provides a comprehensive description of the conducted experiments, accompanied by the detailed analysis of the thermal expansion properties derived through the use of High-Temperature X-Ray Diffraction (HT-XRD) and HT-dilatometry (High-Temperature Dilatometry).

Thermal chemical erosion behavior of the burning-free Al2O3–C–Si bottom nozzle

Burning-free Al2O3–C–Si bottom nozzle, a key refractory component connecting the intermediate ladle slide to the immersion spout, is always prone to failure under the extreme environment of repeated exposure to chemical attack and thermal shock of the steel. Here, an approach of adding Si powder and the change in Al2O3 aggregate aims to enhance the product's quality and performance of the burning-free Al2O3–C–Si bottom nozzle. And the different composition ratios effects on the chemical erosion behavior of the burning-free Al2O3–C–Si bottom nozzle were investigated based on the measured instantaneous thermal-expansion coefficient and young's modulus of the bottom nozzle materials in the high-temperature range of 300–1473 K. Moreover, the high-temperature folding resistance, thermal-shock resistance test and slag resistance experiments have also been probed. Obtained results reveal that the absence of 6 wt.% Si can promote the formation of SiC phases in the form of flakes and whiskers inside the bottom nozzles, which significantly improves the density, strength, thermal shock resistance and slag erosion resistance of refractory materials. Compared with the bauxite-Al sample, the slab corundum-Si-Al sample reduced the porosity by 7.8% and the erosion index decreased by 4.7% due to the formation of SiC and a thin protective layer of SiO2, as well as the mullite crystals structure. Here, an optimized bottom nozzle with a composite structure has also been proposed. This work can make significant contribution to improve the performance of burning-free refractory materials, bottom nozzles and reducing costs.

Dislocation structure evolution under electroplastic effect

In this study, the effect of high current density electropulsing (103 A/mm2 for 150 μs) on the residual stress of quenched steel was investigated with the objective of determining the electroplastic effect on plastic strain and dislocation evolution. The residual stress and dislocation density, which were closely related to the plastic strain, were significantly reduced through electropulsing. The direct effect of drift electrons on the dislocation motion, instead of side effects such as skin, pinch, instantaneous thermal expansion stress, and Joule heating, primarily contributes to the plastic strain. Employing the thermally activated plastic flow concept, the drift electrons were also found to have an effect on the thermally activated dislocation motion in addition to the force exerted on the dislocations by an electron wind. Under the action of drift electrons, the movement of vacancies and dislocations were enhanced, which accelerated the dislocation annihilation. In contrast, affected by the electron wind force, Frank-Read source failed to produce a large amount of dislocations, thereby simultaneously decreasing the dislocation multiplication rate. Finally, the dislocation density decreased and the dislocation structure was rearranged parallel to the direction of motion of the drift electrons.

Quality monitoring of end plug resistance weldment for nuclear fuel rods by electrode displacement

The welds on the fuel rods in a nuclear power fuel assembly are the most likely places to leak during combustion, and therefore, the integrity of the welds is critical. The end plug welding method used for the nuclear fuel rod was upset butt resistance welding, and the welding time was a very short 1 cycle. The purpose of this research was to investigate factors that could be used to monitor the welding quality of end plug welds on nuclear fuel rods. In this study, to assess the integrity of the nuclear fuel rod welds, the waveform of the variables during the short welding time was measured using a waveform measurement device, and the quality assessment factors that can impact the welding quality were determined. To deduce the quality assessment factors, this study chose to use instantaneous displacement, which was calculated from electrode displacement. To observe electrode movements resulting from instantaneous thermal expansion on welds, a displacement sensor was installed on the welding machine, and physical phenomena were analyzed per half-cycle by measuring displacement signals during welding. In addition, damage to major components of the welding equipment was simulated. Welding testing was carried out to determine the waveforms, and the quality assessment factor values here were compared with the values corresponding to a normal welding condition. Through this study, the major components of welding equipment were monitored to ensure the integrity of the welding.

Anisotropic Thermal Expansion of Zirconium Diboride: An Energy-Dispersive X-Ray Diffraction Study

Zirconium diboride (ZrB2) is an attractive material due to its thermal and electrical properties. In recent years, ZrB2 has been investigated as a superior replacement for sapphire when used as a substrate for gallium nitride devices. Like sapphire, ZrB2 has an anisotropic hexagonal structure which defines its directionally dependent properties. However, the anisotropic behavior of ZrB2 is not well understood. In this paper, we use energy-dispersive synchrotron X-ray diffraction to measure the thermal expansion of polycrystalline ZrB2 powder from 300 to 1150 K. Nine Bragg reflections are fit using Pseudo-Voigt peak profiles and used to compute the a and c lattice parameters using a nonlinear least-squares approximation. The temperature-dependent instantaneous thermal expansion coefficients are determined for each a-axis and c-axis direction and are described by the following equations: αa = (4.1507×10-6 + 5.1086 × 10-9(T-293.15))/(1+4.1507 × 10-6(T-293.15) + 2.5543×10-9(T-293.15)2) and αc = (4.5374×10-6 + 4.3004×10-9(T-293.15))/(1+4.5374×10-6(T-293.15) + 2.1502×10-9(T-293.15)2). Our results are within range of previously reported values but describe the temperature anisotropy in more detail. We show that anisotropic expansion coefficients converge to the same value at about 780 K and diverge at higher temperatures. Results are compared with other reported values.

Mean and Instantaneous Thermal Expansion of Uncoated and Ti Coated Diamond/Copper Composite Materials

Heat sink materials not only should have higher thermal conductivity, but also have smaller difference of thermal expansion with cooled material. diamond/copper composites were made by the powder metallurgy method. Vacuum slowly vapor deposition technique was employed to deposit a titanium film on diamond particles before mixing with Cu powder in order to improve the bonding strength between Cu and diamond particles during sintering. The thermal expansion of diamond/Cu d composite was measured in the temperature range from 50 to 600 °C. The results show that the titanium film on diamond improves the interfacial bonding and reduces the coefficient of thermal expansion (CTE) of Cu/diamond composites. The CTE of diamond/Cu composites decreases with increasing diamond volume fraction as the results of mixture rule and the intense restriction effect of diamond reinforcement on the copper matrix. The residual stresses and pores in the composites affect instantaneous thermal expansion of diamond/Cu composites.

Chemical Imaging: Chemical Imaging Beyond the Diffraction Limit: Experimental Validation of the PTIR Technique (Small 3/2013)

Photothermal-induced resonance for chemical imaging at the nanoscale is described by A. Centrone and co-workers on page 439. An AFM cantilever measures instantaneous thermal expansion induced by light absorption in a sample. A pulsed laser, tunable across the mid-IR is used to illuminate the sample in a total internal reflection confi guration. If the laser wavelength matches the sample vibrational absorptions, the sample heats, expands, and deflects the cantilever faster than the AFM feedback. The tip deflection is proportional to the energy absorbed, and it allows extraction of spectroscopic information with nanoscale resolution, many-fold better than the diffraction limit. Topological images and chemical images are obtained simultaneously.

Analysis of instantaneous thermal expansion coefficient curve during thermal cycling in short fiber reinforced AlSi12CuMgNi composites

Short fiber reinforced AlSi12CuMgNi composites have potential applications as engine components in automobile industry. In these engine components, the dimensional stability is of great concern. Thermal cycling experiments can approximately simulate the real working conditions of the materials and give an evaluation of the dimensional changes during their service in the changing temperature environments. Due to the fact that in metal matrix composites the thermal strain is dependent on the phase transformation, the matrix plastic yielding and the physical damage of reinforcement, analysis of thermal strain curves could allow not only insight into their thermal expansion behavior but also into the phase transformation and possible matrix plastic deformation behavior caused by large internal thermal stresses. Compared with the thermal strain curve, the instantaneous CTE curve can clearly supply more information because it is the differential of thermal strain over temperature. It is useful to differentiate whether the appearance of a knee on the thermal strain curve is caused by the phase transformation and/or by the matrix plastic deformation, especially in metal matrix composites with age hardenable matrix. In the present paper, the aging behaviors in both the unreinforced and ceramic reinforced AlSi12CuMgNi piston alloys are investigated and discussed by analyzing the instantaneous CTE curve, DTA curve and hardness tests. The matrix plastic deformation caused by thermal stresses is discussed based on the observation of CTE divergence in the longitudinal and transverse directions. The effects of both the SiO 2 content and subsequent heat treatment on the critical temperature, above which the CTE divergence occurs, are discussed. Finally, the effects of precipitation and matrix plastic deformation on the residual strain after thermal cycling are also preliminary evaluated.

Some dilatometric observations on the α-β transformation in zirconium- [formula omitted] niobium alloy

The effects of repeated heating and cooling on the dilatometric curves in the region of the α /ai β transformation range have been investigated with particular reference to the effect of oxygen contamination at reduced pressures. Data have been obtained on specimen length changes, instantaneous thermal expansion coefficient, dilation change at transformation and transition temperatures. The Goldschmidt expansion on cooling from just below the (α + β) β transition in a vacuum of 2 × 10 −6 mm Hg is ten times greater than when the specimen is cooled from just above this transition, whilst the final length change is ~1% elongation compared with ~1% contraction in the second case. Repeated α /ai β cycling leads to a reduced dilation change and small specimen elongation. The structural implications are discussed. Oxygen contamination at 3 × 10 −4 mm Hg virtually eliminates the dilation change through transformation. The mechanism of formation of horizontal portions to the cooling curve is discussed and on cooling is attributed to the interaction of the transforming outer layers with the still contracting untransformed β core region. Pressure variations in the range 10 −6-10 −4 mm Hg have an important influence on transition temperatures.