Effect of some metallic additives (Ag, Cd, and Sn) on thermal transport properties of a-Se

In this study, we have studied the effect of elements Ag, Cd, and Sn as chemical modifiers on some thermal transport properties (thermal conductivity, diffusivity, and specific heat per unit volume) of amorphous Se. Concurrent measurements of thermal transport properties such as effective thermal conductivity (??_e), thermal diffusivity (??_e), and specific heat per unit volume (??C _v) are used at room temperature for twin pellets of pure Se- and Se-based binary Se₉₈M₂ (M?=?Ag, Cd, and Sn) alloys using transient plane source technique. We have also determined the thermal inertia I _T using the experimental values of thermal conductivity and specific heat per unit volume for present amorphous alloys. The increasing sequence of measured thermal transport properties is also discussed.     

Thermodynamic insights into n-alkanes phase change materials for thermal energy storage

n-Alkanes have been widely used as phase change materials (PCMs) for thermal energy storage applications because of their exceptional phase transition performance, high chemical stability, long term cyclic stability and non-toxicity. However, the thermodynamic properties, especially heat capacity, of n-alkanes have rarely been comprehensively investigated in a wide temperature range, which would be insufficient for design and utilization of n-alkanes-based thermal energy storage techniques. In this study, the thermal properties of n-alkanes (C₁₈H₃₈-C₂₂H₄₆), such as thermal stability, thermal conductivity, phase transition temperature and enthalpy were systematically studied by different thermal analysis and calorimetry methods, and compared with previous results. Thermodynamic property of these n-alkanes was studied in a wide temperature range from 1.9 K to 370 K using a combined relaxation (Physical Property Measurement System, PPMS), differential scanning and adiabatic calorimetry method, and the corresponding thermodynamic functions, such as entropy and enthalpy, were calculated based on the heat capacity curve fitting. Most importantly, the heat capacities and related thermodynamic functions of n-heneicosane and n-docosane were reported for the first time in this work, as far as we know. This research work would provide accurate and reliable thermodynamic properties for further study of n-alkanes-based PCMs for thermal energy storage applications.     

Effect of indium additive on thermal transport properties of Se–Te–Cd multi-component chalcogenide glasses

The thermal conductivity, thermal diffusivity and specific heat per unit volume of twin pellets of Se₇₅Te_15?Cx Cd₁₀In _x (x?=?0, 5, 10 and 15) glasses, were carried out at room temperature by transient plane source technique. Results indicated that both values of thermal conductivity (??) and thermal diffusivity (??) are varied with In (indium) content and highest for 5?at.% of In, whereas the specific heat per unit volume is almost constant with increase of indium concentration. This shows that Se₇₅Te₁₀Cd₁₀In₅ glass can be considered as a critical composition at which the alloy becomes chemically ordered and most thermally stable than other compositions. This compositional dependence behaviour of thermal conductivity and thermal diffusivity can explained in terms of iono-covalent type bond which In makes with Se and Te as it is incorporated in Se?CTe?CCd glasses.     

Studies on the thermal properties of caprolactam/long chain lactam copolymer

The thermal properties of caprolactam/long chain lactam copolymer were studied with a Perkin-Elmer DSC 7. The melting point (T _m), heat of fusion (δH _m), crystalline degree (X _c), crystallization temperature (T _c) and glass transition temperature (T _g) of the copolymers increase with decrease of the content of the log chain lactam. From the changes in the mechanical properties with corresponding changes in the thermal properties, it is clear that the copolymers are thermal plastic and elastic. In addition, it is found that the results at a heating rate of 10 deg·min^?1 are almost the same as that at 20 deg·min^?1 after thermal history is erased.     

The thermal properties of monochloro-para-xylylene

The three thermal properties that describe the heat transfer in a material were determined for a thin, tough, transparent, highly crystalline film of poly-monochloro-para-xylylene (PCPX). These three properties, viz. thermal conductivity (K), thermal diffusivity (α), and specific heat (C_p) were determined using a transient heating method.The experimental method used involved the heating of a sample of stacked polymer sheets by an ultrathin heating foil. The heating foil, located in the center plane of the stack provided a source of constant heat flux when a current of known amperage was passed through it. By careful consideration of sample dimensions, the sample simulated an infinite solid. The thermal properties were calculated using standard solutions of the heat transfer equations of an infinite solid over a temperature range of ?192 to 130°C. The experimental method was repeated to check the reproducibility of the results and compared with differential scanning calorimeter results.A data acquisition system was developed to facilitate data handling for the transient experiments. The system included hardware capable of punching data on paper tape and a software package to analyze these data.The conclusions drawn include: (1) the reproducibility of the experiments was well within the experimental errors; (2) the data acquisition system greatly facilitates acquisition of thermal data; (3) an incremental change occurs in C_p of PCPX in the vicinity of the γ relaxation reported by dynamical relaxation measurements and its occurrence indicates that this relaxation involves a cooperative motion of molecules; (4) owing to the significant magnitude of the C_p jump and the appreciable degree of crystallinity of PCPX, these internal motions occurring at the γ transition probably involve both amorphous and crystalline regions; (5) a direct relationship between thermal expansion and specific heat was indicated in PCPX as well as for polystyrene (PS) at relatively low temperatures (?200 to ?20°C); (6) the overall low values of thermal conductivity (1.0 to 2.5 × 10^?4 cal sec^?1 cm^?1) and thermal diffusivity (9.5 to 5.3 × 10^?4 cm² sec^?1) of PCPX indicate that it is ideally suited for insulation applications.     

Temperature dependence of the thermophysical properties of Bi1.5Sb0.5Te3

The thermophysical properties (thermal diffusivitya, specific heatC _p and thermal conductivity λ), of Bi_1.5Sb_0.5Te₃ were measured in the temperature range 300–700 K. The results showed that the contribution of the charge carriers to the thermal conduction is negligibly small in comparison with the contribution of phonons at high temperatures. On the other hand, the heat conduction due to the simultaneous thermal diffusion of electrons and holes is important as well as the lattice thermal conduction. The explanation of the results was supported by using electrical conductivity measurements and X-ray diffraction.     

Anomalous changes in the specific heat and thermal conductivity of LiKSO4 crystals around the high-temperature phase

The thermophysical properties of LiKSO₄ crystals were studied around the high-temperature phase, atT _{c 2}=943 K. A Heraeus (DSC) technique was used to measure the specific heat,c _p, while the thermal conductivity,K, was measured by the linear heat flow steady-state method. The measured parameters showed an anomaly in the temperature dependence of bothc _p andK. Anisotropy in the thermal conductivity coefficient was also observed in the different crystallographic axes.     

Heat transfer in microsphere insulation

The results of an investigation of heat transfer in a new type of insulation (microsphere insulation) are presented. The effects of the microsphere diameter, the concentration of metallized microspheres and the residual gas pressure on the thermal conductivity of the insulation were investigated. Measurements were made of the thermal conductivity at 77 to 300 K of microspheres with differing diameters (e.g. 95, 130 and 270 μm) and of samples with silver metallized microsphere concentrations of 7 and 32%. Measurements of average thermal conductivity (77–296 K) were made at residual gas pressuresk(p) in the range from 10^?3 Pa to 10⁵ Pa for pure nitrogen. The component of heat transfer by gas,k _gc (p), was estimated.     

Effect of in and Zn additives on some thermal properties of a-Se

In the present work, the effect of In and Zn on some thermo–physical properties (thermal conductivity, diffusivity and specific heat per unit volume) of amorphous Se (a-Se) have been studied. For this, simultaneous measurements of effective thermal conductivity (λ_e) and effective thermal diffusivity (χ_e) are used at room temperature for twin pellets of Se, Se₉₀In₁₀ and Se₉₀Zn₁₀ alloys using transient plane source (TPS) technique. It has been found that In and Zn additives changes significantly the values of thermo-physical properties (thermal conductivity, diffusivity and specific heat per unit volume) of a-Se studied in the present work. The results have been analyzed in terms of average bond strength and effective molecular weight of the binary alloys.     

A new method of determining the thermal conductivities of energetic materials by microcalorimeter

A device of measuring the thermal conductivity of pellet of propellants and explosives has been constructed. A method and a calculation formula for determining the thermal conductivity of pellet of propellants and explosives under constant radial heat flow conditions by use of Joule effect is presented. Using this device and a microcalorimeter, type RD496-II, and two standard samples with known thermal conductivity, two instrument constant have been determined and the thermal conductivities of seven materials: plexiglass, teflon, DB propellant DB-2 (nitrocellulose(NC)/nitroglycerine(NG)/dinitrotoluene/dimethyl centralite/vaseline/PbO/CaCO₃, 59.6/25/8.8/3/1.2/1.2/1.2), DB propellant SQ(NC/NG/diethyl phthalate(DEP)/binder, 59/29/7/5), DB propellant RHN-149 (NC/NG/triacetin (TA)/binder-I, 52/25/8/15), DB propellant RHN-190 (NC/NG/TA/ binder-II, 52/26/7/15), 2, 4, 6-trinitrotoluene (TNT) at 298 K are measured. The results show that (1) the reproducibility of measurement for the heat (q) retained in investigated system after cutting the Joule current and the amount of heat flux through the wall of the investigated cylinder (Q _s) are less than 0.50% and within 0.10%, respectively; (2) the standard deviation of the thermal conductivity determined by using this method is less than 1.0%; (3) the values ofq, Q _s and internal radius of the cylinder are three principal factors affecting the magnitude of the thermal conductivity of these materials.     

Explosion evaluation and safety storage analyses of cumene hydroperoxide using various calorimeters

Plenty of thermal explosions and runaway reactions of cumene hydroperoxide (CHP) were described from 1981 to 2010 in Taiwan. Therefore, a thermal explosion accident of CHP in oxidation tower in 2010 in Taiwan was investigated because of piping breakage. In general, high concentration of CHP for thermal analysis using the calorimeter is dangerous. Therefore, a simulation method and a kinetic parameter were used to simulate thermal hazard of high concentrations of CHP only by the researcher. This study was applied to evaluate thermal hazard and to analyze storage parameters of 80 and 88 mass% CHP using three calorimeters for the oxidation tower, transportation, and 50-gallon drum. Differential scanning calorimetry (DSC) (a non-isothermal calorimeter), thermal activity monitor III (TAM III) (an isothermal calorimeter), and vent sizing package 2 (VSP2) (an adiabatic calorimeter) were employed to detect the exothermic behavior and runaway reaction model of 80 and 88 mass% CHP. Exothermic onset temperature (T ₀), heat of decomposition (ΔH _d), maximum temperature (T _max), time to maximum rate under isothermal condition (TMR_iso) (as an emergency response time), maximum pressure (P _max), maximum of self-heating rate ((dT/dt)_max), maximum of pressure rise rate ((dP/dt)_max), half-life time (t _1/2), reaction order (n), activation energy (E _a), frequency factor (A), etc., of 80 and 88 mass% CHP were applied to prevent thermal explosion and runaway reaction accident and to calculate the critical temperature (T _c). Experimental results displayed that the n of 80 and 88 mass% CHP was determined to be 0.5 and the E _a of 80 and 88 mass% CHP were evaluated to be 132 and 134 kJ mol^?1, respectively.     

BTATz–HNIW–CMDB propellants

The high nitrogen compound 3,6-bis(1H-1,2,3,4-tetrazol-5-yl-amino)-1,2,4,5-tetrazine and the high energy density material hexanitrohexaazaisowurtzitane (HNIW), were used as substitute of hexogen (RDX) in the composite modified double base (CMDB) propellant formulations, the propellant samples were prepared, the thermal behaviors, nonisothermal reaction kinetics, and thermal safety were carried out, and the eight important parameters were calculated and obtained as the self-accelerating decomposition temperature (T _SADT), thermal ignition temperature (T _TIT), critical temperatures of thermal explosion (T _b), critical temperature of hot-spot initiation (T _cr,hot-spot), characteristic drop height of impact sensitivity (H ₅₀), critical thermal explosion ambient temperature (T _acr), safety degree (S _d), and thermal explosion probability (P _TE). It shows that the content of HNIW has a large effect on the decomposition reaction mechanism of the CMDB propellant, when the content of HNIW is 10 %, the decomposition reaction are controlled by the random nucleation and subsequent growth (n = l), and the reaction mechanism obeys Mampel law; but when the content of HNIW is 20 %, the decomposition reaction are controlled by the chemical reaction (n = 1/4). The mechanism can not be changed by the catalysts, and they just make the apparent activation energy change slightly. For the sample, from BC01 to BC04, the values of T _SADT and T _TIT making an upward tendency, show the resistivity to heat: BC04 > BC03 > BC02 > BC01; the values of T _acr and S _d, BC01 are the maximum and BC02 are the minimum, show the heat sensitivity: BC01 > BC03 > BC04 > BC02. For the same radius, the thermal safety of the sphere sample is greater than that of the infinite cylinder one.     

2,2,2-三硝基乙基-N-硝基甲胺的热安全性

为评价2,2,2-三硝基乙基-N-硝基甲胺(TNMA)的热安全性, 得到计算TNMA热安全性参数用的基本数据, 用经验式估算了TNMA的比热容(C_p)和热导率(λ). 用键能贡献于生成热Q_f的加和法, 估算了TNMA的标准生成焓Δ_cH_m^θ(TNMA, s, 298.15 K). 用热力学公式计算了TNMA的标准燃烧焓ΔU_m^θ(TNMA, s, 298.15 K)和标准燃烧能Δ_cH_m^θ(TNMA, s, 298.15 K). 用Kamlet-Jacobs 公式估算了爆速、爆压和爆热. 用经验式估算了分解热(Q_d). 通过差示扫描量热(DSC)曲线和高灵敏度布鲁顿玻璃薄膜压力计测得的逸出气体标准体积(V_H)-时间(t)曲线, 得到了TNMA放热分解反应的动力学参数. 用上述基本数据得到了评价TNMA的热安全性参数: 自加速分解温度(T_SADT), 热爆炸临界温度(T_be0和T_bp0), 绝热至爆时间(t_TIad), 撞击感度50%落高(H₅₀), 热点起爆临界温度(T_cr), 被300 K环境包围的半厚和半径为1 m的无限大平板、无限长圆柱和球形TNMA的热感度概率密度函数S(T), 相应于S(T)-T关系曲线最大值的峰温(T_S(T)max), 安全度(SD), 临界热爆炸环境温度(T_acr)和热爆炸概率(P_TE). 结果表明: (1) TNMA有较好的热安全性和对热抵抗能力, 与环三亚甲基三硝胺(RDX)相比, TNMA易从热分解过渡到热爆炸; (2) 不同形状大药量TNMA 热安全性降低的次序为: 球>无限长圆柱>无限大平板; (3)TNMA有高的燃烧能、高的爆轰化学能(爆热)和接近环四亚甲基四硝胺(HMX)的爆炸性能, 其对冲击敏感, 冲击感度与季戊四醇四硝酸酯(PETN)和特屈尔接近, 可用作混合炸药主组分.     

Thermal hazard evaluations of 18650 lithium-ion batteries by an adiabatic calorimeter

In this study, the thermal hazard features of various lithium-ion batteries, such as LiCoO₂ and LiFePO₄, were assessed properly by calorimetric techniques. Vent sizing package 2 (VSP2), an adiabatic calorimeter, was used to measure the thermal hazards and runaway characteristics of the 18650 lithium-ion batteries under an adiabatic condition. The thermal behaviors of the lithium-ion batteries were obtained at normal and abnormal conditions in this study. The critical parameters for thermal hazardous behavior of lithium-ion batteries were obtained including the exothermic onset temperature (T ₀), heat of decomposition (ΔH), maximum temperature (T _max), maximum pressure (P _max), self-heating rate (dT/dt), and pressure rise rate (dP/dt). Therefore, the result indicates the thermal runaway situation of the lithium-ion battery with different materials and voltages in view the of TNT-equivalent method by VSP2. The hazard gets greater with higher voltage. Without the consideration of other anti-pressure measurements, different voltages involving 3.3, 3.6, 3.7, and 4.2 V are evaluated to 0.11, 0.23, 0.88, and 1.77 g of TNT. Further estimation of thermal runaway reaction and decomposition reaction of lithium-ion battery can also be confirmed by VSP2. It shows that the battery of a fully charged state is more dangerous than that of a storage state. The technique results showed that VSP2 can be used to strictly evaluate thermal runaway reaction and thermal decomposition behaviors of lithium-ion batteries. The loss prevention and thermal hazard assessment are very important for development of electric vehicles as well as other appliances in the future. Therefore, our results could be applied to define important safety indices of lithium-ion batteries for safety concerns.     

Thermal decomposition behavior, kinetics, and thermal hazard evaluation of CMDB propellant containing CL-20 by microcalorimetry

The thermal decomposition behavior of composite modified double-base propellant containing hexanitrohexaazaisowurtzitane (CL-20/CMDB propellant) was studied by microcalorimetry. The kinetic and thermodynamic parameters were obtained from the analysis of the heat flow curves. The effect of different proportion of CL-20 to the thermal decomposition behavior, kinetics, and thermal hazard was investigated at the same time. The critical temperature of thermal explosion (T _b), the self acceleration decomposition temperature (T _SADT), and the adiabatic decomposition temperature rise (??T _ad) were calculated to evaluate the thermal hazard of the CL-20/CMDB propellant. It shows that the CMDB propellant with 38% CL-20 has relative lower values of E and lgA, and with 18% CL-20 has the highest potential hazard.     

Thermal conductivity of the ferrites Ni0.65Zn0.35CuxFe2−xO4

A series of samples of the type Ni_0.65Zn_0.35Cu_xFe_2?xO₄ (x=0, 0.1, 0.2, 0.3, 0.4 and 0.5) were prepared by a ceramic technique. The existence of a single phase was confirmed by X-ray studies. The thermal conductivity and specific heat were measured at 53°C. The thermal conductivity had a minimum value atx=0.3, due to the maximum porosity at this composition. The phonon frequency was estimated to have an optimum value at x=0.3, due to the increase in phonon scattering.     

Magnetic,transport and thermodynamic properties of Ce5Ni2Si3 compound

The magnetization M(T,H), specific heat C_p(T,H), electrical resistivity ρ(T), magnetoresistance MR(T,H), thermal conductivity κ(T) and thermopower S(T) measurements were performed on the antiferromagnetic compound Ce₅Ni₂Si₃ with the Néel temperature T_N = 5.7 K. The estimated effective moment μ_eff is close to the free ion value of Ce in its trivalent state. The negative sign of the paramagnetic Curie temperature θ_p indicate the antiferromagnetic nature of the magnetic ordering. The variation of magnetic resistivity ρ_mag with temperature in Ce₅Ni₂Si₃ can be explained by a competition of the crystal electric field (CEF) splitting, the Kondo effect and the magnetic order. Based on the thermopower and employing a simple single-ion Kondo model the Kondo temperature have been estimated. Magnetocaloric effect is small but shows a sign change, which may be caused by a metamagnetic behavior.     

Numerical study on thermal performance of TiO2, Fe3O4 and NiCr/engine oil in an inclined wavy pip

The essential intention of the existing article is to illustrate the effect of wall properties on flow and thermal behavior, through a sinusoidal inclined wavy pipe. To succeed this phenomena we assume a sinusoidal pipe consist of wavy surface, whose walls traveling down to its borders and located at an inclined position, moreover titanium dioxide (TiO₂), ferrosoferric oxide (Fe₃O₄) and nichrome (80% Ni and 20% Cr) are considered as nano-particles and unused engine oil is assumed as a base fluid. The arising mathematical equations for thermal and flow ratio with wall slip impact are solved by mathematica. Also, evaluate graphically the thermal and flow behavior of nanofluids for multi values of solid volume fractions (η), rigidity parameter (M₁), stiffness parameter (M₂), viscous damping parameter (M₃), Grashof number (G_r), slip parameter (β) and heat generation parameter (H) also discuss the streamlines for different values of solid volume fraction.     

Thermal hazard evaluation of tert-butyl peroxide using non-isothermal and adiabatic calorimetric approaches

Tert-butyl peroxide (TBPO), is a typical organic peroxides (OPs),which is widely applied as initiator in poly-glycidyl methacrylate (PGMA) reaction, and is employed to provide a free-radical in frontal polymerization, and which has also caused many thermal runaway reactions and explosions worldwide. To find an unknown and insufficient hazard information for an energetic material, differential scanning calorimetry (DSC) and vent sizing package 2 (VSP2) were employed to detect the fundamental thermokinetic parameters involving the exothermic onset temperature (T ₀), heat of decomposition (??H _d), temperature rise rate (dT · dt ^?1), time to maximum rate under adiabatic situation (TMR_ad), pressure rise rate (dP · dt ^?1), and maximum pressure (P _max), etc. The T ₀ was calculated to be 130?°C using DSC and VSP2. Activation energy (E _a) of TBPO was evaluated to be 136?kJ?mol^?1 by VSP2. In view of the loss prevention, calorimetric applications and model evaluation to integrate thermal hazard development are adequate means for inherently safer design.     

Thermal properties of the pyrochlore, Y2Ti2O7

The thermal conductivity and heat capacity of high-purity single crystals of yttrium titanate, Y₂Ti₂O_7, have been determined over the temperature range 2 K?T?300 K. The experimental heat capacity is in very good agreement with an analysis based on three acoustic modes per unit cell (with the Debye characteristic temperature, θ_D, of ca. 970 K) and an assignment of the remaining 63 optic modes, as well as a correction for C_p−C_v. From the integrated heat capacity data, the enthalpy and entropy relative to absolute zero, are, respectively, H(T=298.15 K)−H₀=34.69 kJ mol⁻¹ and S(T=298.15 K)−S₀=211.2 J K⁻¹ mol⁻¹. The thermal conductivity shows a peak at ca. θ_D/50, characteristic of a highly purified crystal in which the phonon mean free path is about 10 μm in the defect/boundary low-temperature limit. The room-temperature thermal conductivity of Y₂Ti₂O₇ is 2.8 W m⁻¹ K⁻¹, close to the calculated theoretical thermal conductivity, κ_min, for fully coupled phonons at high temperatures.