Effects of Al and Co doping on the structural stability and high temperature cycling performance of LiNi_(0.5)Mn_(1.5)O_(4) spinel cathode materials

The poor structural stability and capacity retention of the high-voltage spinel-type LiNi_(0.5)Mn_(1.5)O_(4)(LNMO)limits their further application.Herein,Al and Co were doped in LNMO materials for a more stable structure and capacity.The LNMO,LiNi_(0.45)Al_(0.05)Mn_(1.5)O_(4)(LNAMO)and LiNi_(0.45)Co_(0.05)Mn_(1.5)O_(4)(LNCMO)were synthesized by calcination at 900℃ for 8 h,which was called as solid-phase method and applied universally in industry.XRD,FT-IR and CV test results showed the synthesized samples have cation disordering Fd-3m space group structures.Moreover,the incorporation of Al and Co increased the cation disordering of LNMO,thereby increasing the transfer rate of Li+.The SEM results showed that the doped samples performed more regular and ortho-octahedral.The EDS elemental analysis confirmed the uniform distribution of each metal element in the samples.Moreover,the doped samples showed better electrochemical properties than undoped LNMO.The LNAMO and LNCMO samples were discharged with specific capacities of 116.3 mA·h·g^(-1)and 122.8 mA·h·g^(-1)at 1 C charge/discharge rate with good capacity retention of 95.8% and 94.8% after 200 cycles at room temperature,respectively.The capacity fading phenomenon of the doped samples at 50℃ and 1 C rate was significantly improved.Further,cations doping also enhanced the rate performance,especially for the LNCMO,the discharge specific capacity of 117.9 mA·h·g^(-1)can be obtained at a rate of 5 C.

Long-term storage life of light source modules by temperature cycling accelerated life test

Light source modules are the most crucial and fragile devices that affect the life and reliability of the interferometric fiber optic gyroscope （IFOG）. While the light emitting chips were stable in most cases, the module packaging proved to be less satisfactory. In long-term storage or the working environment, the ambient temperature changes constantly and thus the packaging and coupling performance of light source modules are more likely to degrade slowly due to different materials with different coefficients of thermal expansion in the bonding interface. A constant temperature accelerated life test cannot evaluate the impact of temperature variation on the performance of a module package, so the temperature cycling accelerated life test was studied. The main failure mechanism affecting light source modules is package failure due to solder fatigue failure including a fiber coupling shift, loss of cooling efficiency and thermal resistor degradation, so the Norris-Landzberg model was used to model solder fatigue life and determine the activation energy related to solder fatigue failure mechanism. By analyzing the test data, activation energy was determined and then the mean life of light source modules in different storage environments with a continuously changing temperature was simulated, which has provided direct reference data for the storage life prediction of IFOG.

Quantifying the response of surface urban heat island to urbanization using the annual temperature cycle model

Urban heat island(UHI),driving by urbanization,plays an important role in urban sustainability under climate change.However,the quantification of UHI’s response to urbanization is still challenging due to the lack of robust and continuous temperature and urbanization datasets and reliable quantification methods.This study proposed a framework to quantify the response of surface UHI(SUHI)to urban expansion using the annual temperate cycle model.We built a continuous annual SUHI series at the buffer level from 2003 to 2018 in the Jing-Jin-Ji region of China using MODIS land surface temperature and imperviousness derived from Landsat.We then investigated the spatiotemporal dynamic of SUHI under urban expansion and examined the underlying mechanism.Spatially,the largest SUHI interannual variations occurred in suburban areas compared to the urban center and rural areas.Temporally,the increase in SUHI under urban expansion was more significant in daytime compare to nighttime.We found that the seasonal variation of SUHI was largely affected by the seasonal variations of vegetation in rural areas and the interannual variation was mainly attributed to urban expansion in urban areas.Additionally,urban greening led to the decrease in summer daytime SHUI in central urban areas.These findings deepen the understanding of the long-term spatiotemporal dynamic of UHI and the quantitative relationship between UHI and urban expansion,providing a scientific basis for prediction and mitigation of UHI.

Influence of Temperature Conditions on Dynamic Young’s Modulus Testing

The Young’s modulus was measured at high temperatures by impulse excitation of vibration method,and the effects of heating rate,holding time and temperature cycle on the test results were analyzed.The results show that the heating rate has obvious effect on the high temperature Young’s modulus of the green body,but has no obvious effect on that of the sintered products;the holding time of the heating process has no regular effect on the Young’s modulus,and the effect varies with the different products at a certain temperature;the method can also be used to test the Young’s modulus during cooling process.

DIMENSIONAL INSTABILITY OF LD31 Al ALLOY WELDMENTS AT ROOM TEMPERATURE AND AFTER THERMAL CYCLES

The unstable dimensional distortion of LD31 aluminum alloy weldments at room temperature and after thermal cycles was studied by use of light interference and CMM(three-coordinate measuring machines). At the same time, distortion mechanism was analyzed from the viewpoint of mechanics and micro structure. Experimental results show that there exists obvious difference of unstable dimensional distortion between LD31 welded specimens under two conditions mentioned above. Under room temperature, dimensional variation of welded specimens will decrease gradually and finally tends to be stable during 200h after welding. The relative elongation of welded specimen is 3.0×10-5; After thermal cycles, distortion of welded specimen is much larger than that at room temperature. After 11 thermal cycles, the dimension will tend to be stable. Dimensional unstable distortion of weldments mainly results from temperature condition, microstructure variation and relaxation of welding residual stress.

Spatial-temporal variations in near-surface soil freeze-thaw cycles in the source region of the Yellow River during the period 2002–2011 based on the Advanced Microwave Scanning Radiometer for the Earth Observing System(AMSR-E) data

Detecting near-surface soil freeze-thaw cycles in high-altitude cold regions is important for understanding the Earth＇s surface system, but such studies are rare. In this study, we detected the spatial-temporal variations in near-surface soil freeze-thaw cycles in the source region of the Yellow River（SRYR） during the period 2002–2011 based on data from the Advanced Microwave Scanning Radiometer for the Earth Observing System（AMSR-E）. Moreover, the trends of onset dates and durations of the soil freeze-thaw cycles under different stages were also analyzed. Results showed that the thresholds of daytime and nighttime brightness temperatures of the freeze-thaw algorithm for the SRYR were 257.59 and 261.28 K, respectively. At the spatial scale, the daily frozen surface（DFS） area and the daily surface freeze-thaw cycle surface（DFTS） area decreased by 0.08% and 0.25%, respectively, and the daily thawed surface（DTS） area increased by 0.36%. At the temporal scale, the dates of the onset of thawing and complete thawing advanced by 3.10（±1.4） and 2.46（±1.4） days, respectively; and the dates of the onset of freezing and complete freezing were delayed by 0.9（±1.4） and 1.6（±1.1） days, respectively. The duration of thawing increased by 0.72（±0.21） day/a and the duration of freezing decreased by 0.52（±0.26） day/a. In conclusion, increases in the annual minimum temperature and winter air temperature are the main factors for the advanced thawing and delayed freezing and for the increase in the duration of thawing and the decrease in the duration of freezing in the SRYR.

Discussion on New Evaluation Technology of Non-Metallic Composite Continuous Pipe for Oil and Gas Field

In view of the serious lack and lag of the test and evaluation technology of non-metallic composite continuous pipe, and focusing on the characteristics of the application of non-metallic composite continuous pipe in oil field, this paper discusses a series of new full-scale test and evaluation technologies for accurately evaluating the product quality and practical application performance of non-metallic composite continuous pipe, which effectively solves the major technical problem that the new products of non-metallic pipe cannot be accurately evaluated. Based on the characteristics of the application of non-metallic composite continuous pipe in oil field, a series of new full-scale test evaluation technologies which can accurately evaluate the product quality and practical application performance of non-metallic pipe are designed through a large number of tests. The test and evaluation technology can accurately evaluate the key performance of high and low pressure cycle, high and low temperature cycle, gas permeability resistance, minimum bending radius etc. It provides a scientific evaluation basis for the standardized application of non-metallic continuous pipe and a reliable quality control method for the selection of products in oil field.

Characteristic Surface Oxide Film Cracking Behavior of a Fe-Ni-Cr Alloy under In-phase and Out-of-phase Thermo-mechanical Fatigue

The surface oxide film cracking behavior of Fe-30Ni-20Cr alloy under in-phase and out-of-phase synchronizing thermal cycling with mechanical cycling was studied.Surface oxide film cracking along the grain boundary under in-phase overlapping was creep predominant fracture mechanisms.Strongly induced slip lines preceding were accompanied by the surface oxide film cracking under Out-of phase,and the shear cracking was dominant mode.Negative mean stress could counteract a part of the tensile component of alternative stress,so as to delay the cracking process under in-phase,but positive mean stress overlapping the tensile alternative stress could accelerate the cycling cracking process under out-of-phase.

Experimental study on the influence of temperature cycle on low-rank coal permeability

The formation temperature is a key factor affecting coalbed methane(CBM)migration in reservoirs.Both the prediction of CBM production and prevention of mine gas disasters require the understanding on the controlling mechanism of temperature on coal permeability.We experimentally examined the evolution of permeability for natural low-rank coal samples under various stresses and cyclic temperature conditions.Apparent permeability and intrinsic permeability decrease significantly when the temperature increases and they only partially recover after the temperature returns.The permeability loss decreases greatly with the increasing number of temperature cycles.The permeability loss due to the rising temperature and the irreversible permeability loss for a whole temperature cycle decrease prominently with increasing confining stress.The impacts of swelling/shrinking of coal matrix,roughness of surface,pore compressibility and weakly bound water in coal on temperature sensitivity of coal permeability are investigated.

Effect of Fe Content on the Interfacial Reliability of SnAgCu/Fe—Ni Solder Joints

Fe-Ni films with compositions of Fe-75Ni, Fe-50Ni, and Fe-30Ni were used as under bump metallization （UBM） to evaluate the interracial reliability of SnAgCu/Fe-Ni solder joints through ball shear test, high temperature storage, and temperature cycling. The shear strengths for Fe-75Ni, Fe-5ONi, and Fe-3ONi solder joints after reflow were 42.57, 53.94 and 53.98 MPa, respectively, which were all satisfied the requirement of industrialization （〉34.3 MPa）. High temperature storage was conducted at 150, 175 and 200 ℃. It was found that higher Fe content in Fe-Ni layer had the ability to inhibit the mutual diffusion at interface region below 150 ℃, and the growth speed of intermetallic compound （IMC） decreased with increasing Fe concentration. When stored at 200 ℃, the IMC thickness reached a limit for all three films after 4 days, and some cracks occurred at the interface between IMC and Fe-Ni layer. The activation energies for the growth of FeSn2 on Fe-30Ni, Fe-5ONi, and Fe-75Ni films were calculated as 246, 185, and 81 kJ/mol, respectively. Temperature cycling tests revealed that SnAgCu/Fe-5ONi solder joint had the lowest failure rate （less than 10%）, and had the best interfacial reliability among three compositions.

Microstructural Evolution and Softening Behavior of Simulated Heat-Affected Zone in 2219 Aluminum Alloy

The effect of peak temperature （Tp） at 200, 300, 400, 500 and 550 ℃ on the microstructural evolution and softening behavior of the simulated heat-affected zone （HAZ） was studied in the 2219-T87 alloy by electron-backscatter diffraction, transmission electron microscopy, X-ray diffraction, micro-hardness and micro-tensile tests. The results showed that the grain size in the HAZs at 200-500 ℃ was comparable, but the number density of the strengthening precipitates （GP zones/θ′） decreased with increasing Tp. At a Tp of 550 ℃, the grain size significantly decreased and the distribution of the misorientation angles corresponded to the MacKenzie distribution. The GP zones/θ′ phase coarsened and translated into θ phases at Tp values in the range of 200-400 ℃. Increasing the Tp to 500 ℃ and above, some θ′ phases translated into θ phases and others dissolved into the α-Al matrix which led to an increase in the solid solution strengthening. The reduction of the number density of the GP zones/θ′ was responsible for the softening behavior.

Numerical study of solar absorption heat storage system applied to Bucharest city

Buildings represent a large part in terms of fossil energy consumption,which depends on the great need for heating.Even if the solar absorption heat storage system is possible,the performance of this system is affected by the cycle limits and the climatic conditions.The goal of the present study is to control the thermal performance of the system cycle according to the imposed climatic conditions of Bucharest city,Romania,and therefore a numerical model was developed for this purpose.The scheme and the thermodynamic cycle,the energy and mass balance equations,and the computational algorithm were presented.The results show that the cycle temperature increases at the end of desorption when the heating power supplied to the desorber is increased,which is also proportional to the drop in temperature at the beginning of the desorption.The temperature at the end of absorption and the mass flow rates of the solution have a significant effect on the thermal power released from the absorber and used to heat the building.For an average daily heat power of 1.35 kW/m^(2) and 10 hours per day of heating the building,the system with a solar collector area of 3 m^(2) has the capacity of heat supply for all the cold period.However,an economic strategy remains necessary.