Investigation of thermal properties of some basalt samples in Egypt

This work aims in studying the temperature dependence of the thermal properties (thermal diffusivity, k, specific heat, C _p and thermal conductivity, ) of some basalt group samples, collected from different regions in the eastern desert of Egypt. The thermal properties of these samples were measured in the temperature range from r.t. to 900 K. The average values of the thermal conductivity of these investigated samples lie in the range from 0.4·10^–3 to 2.01·10^–3 cal cm^–1 s^–1 K^–1. This means that these samples are considered as thermal insulating materials. The thermogravimetric analysis (TG) confirmed that these investigated samples are dry rocks. X-ray fluorescence (XRF) and X-ray diffraction (XRD) confirmed that these rock samples have a crystalline phase, the peaks of XRD have a small change in their location as a result of heat treatment. This behaviour was attributed to the oxidation and firing of some minerals after the heat treatment.This revised version was published online in November 2005 with corrections to the Cover Date.     

Characterization of very low thermal conductivity thin films

Characterization of thermal transport in nanoscale thin films with very low thermal conductivity (<1 W m^?1 K^?1) is challenging due to the difficulties in accurately measuring spatial variations in temperature field as well as the heat losses. In this paper, we present a new experimental technique involving freestanding nanofabricated specimens that are anchored at the ends, while the entire chip is heated by a macroscopic heater. The unique aspect of this technique is to remove uncertainty in measurement of convective heat transfer, which can be of the same magnitude as through the specimen in a low conductivity material. Spatial mapping of temperature field as well as the natural convective heat transfer coefficient allows us to calculate the thermal conductivity of the specimen using an energy balance modeling approach. The technique is demonstrated on thermally grown silicon oxide and low dielectric constant carbon-doped oxide films. The thermal conductivity of 400 nm silicon dioxide films was found to be 1.2 W m^?1 K^?1, and is in good agreement with the literature. Experimental results for 200 nm thin low dielectric constant oxide films demonstrate that the model is also capable of accurately determining the thermal conductivity for materials with values <1 W m^?1 K^?1.     

Reversible Melting of Thermally Fractionated Polyethylene

Different grades of linear low density polyethylenes (LLDPEs) have been quenched cooled step-wise and crystallised isothermally at (a series of increasing) temperatures in a DSC (thermal fractionated samples). These samples have been investigated by temperature modulated DSC (MDSC). The heat flow curves of the thermal fractionated materials were compared with those obtained from samples crystallised at a relatively slow cooling rate of 2 K min^-1(standard samples). The melting enthalpy obtained from the total heat flow of the thermal fractionated samples was 0-10 J g^-1higher than those of standard samples. The melting enthalpy obtained from the reversing heat flows was 13-31 J g^-1lower in the thermal fractionated samples than in the standard samples. The ratio of the reversing melting enthalpy to the total melting enthalpy increased with decreasing density of the PE. The melting temperature of the endotherms formed by the step-wise cooling was 9 K higher than the crystallisation temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Nanocomposite phase change materials based on NaCl–CaCl2 and mesoporous silica

The synthesis of phase change materials based on NaCl–CaCl₂ molten salt mixture and mesoporous silica was investigated. The influence of mesoporous silica porosity and salt concentration on the thermal energy storage properties of the resulting materials is discussed. The nanocomposite samples were characterized by X-ray diffraction, differential scanning calorimetry, infrared spectroscopy, thermogravimetry, scanning electron microscopy and X-ray photoelectron spectroscopy. The mesoporous silica was found to act as a reactive matrix for the molten salts. Composite samples with up 95% wt. salt can be obtained and used as shape-stabilized phase change materials. The materials have heat of fusion values of up to 60.8 J g^?1 and specific heat capacity between 1.0 and 1.1 J g^?1 K^?1. The samples exhibit thermal stability up to 700 °C and can be used for high-temperature thermal energy storage through both latent and sensible heat storage mechanisms.

     

Thermal analysis of low alloy Cr-Mo steel

The paper deals with results of thermal analysis of low-alloyed chromium-molybdenum steel. The methods of analysis were dilatometry, differential thermal analysis (DTA) and differential scanning calorimetry (DSC). The Ac₁ and Ac₃ temperatures of the steel samples measured by dilatometry and DTA during the heating period were in good agreement. Generated by cooling a martensitic structure first became apparent at 503 K. Tempering of the as-quenched samples showed the presence of the second tempering stage in the region between 473 and 573 K. At that stage heat capacity decreased from 0.48 to 0.32 J g^-1 K^-1, as a result of conversion of transition carbide due to heat consumption. After normalization of the as-quenched samples the heat capacity values were restored to between 0.42 and 0.47 J g^-1 K^-1 in the temperature range from 373 to 673 K. This revised version was published online in August 2006 with corrections to the Cover Date.     

Influences of temperature and atmosphere on thermal stability of BaCrO4

In this article, the influences of temperature and atmosphere on thermal stability of BaCrO₄ were investigated. BaCrO₄ powders with an orthorhombic structure were synthesized by a facile aqueous solution route. The synthesized BaCrO₄ products were then heat treated at different atmospheres to evaluate their thermal stability by differential thermal analysis–thermogravimetry (DTA–TG), X-ray photoelectron spectroscopy and X-ray diffraction. BaCrO₄ has a good thermal stability and does not decompose in air up to 1,400 °C. However, the decomposition of BaCrO₄ in vacuum depends mainly upon a two-stage chemical reaction. BaCrO₄ is finally decomposed into BaCr₂O₄ with trivalent Cr³⁺ cations and Ba₃(Cr⁶⁺ Cr⁵⁺)₂O_9?x with both pentavalent Cr⁵⁺ and hexavalent Cr⁶⁺ cations after heat treatments in vacuum.     

Synthesis and thermal behavior of a new high-energy organic potassium salt

A new high-energy organic potassium salt, 1-amino-1-hydrazino-2,2-dinitroethylene potassium salt [K(AHDNE)], was synthesized by reacting of 1-amino-1-hydrazino-2,2-dinitroethylene (AHDNE) and potassium hydroxide in methanol aqueous solution. The thermal behavior of K(AHDNE) was studied using DSC and TG/DTG methods and can be divided into three obvious exothermic decomposition processes. The decomposition enthalpy, apparent activation energy and pre-exponential factor of the first decomposition process were ?2662.5?J?g^?1, 185.2?kJ?mol^?1 and 10^19.63 s^?1, respectively. The critical temperature of thermal explosion of K(AHDNE) is 171.38?°C. The specific heat capacity of K(AHDNE) was determined using a micro-DSC method, and the molar heat capacity is 208.57?J?mol^?1 K^?1 at 298.15?K. Adiabatic time-to-explosion of K(AHDNE) was also calculated. K(AHDNE) presents higher thermal stability than AHDNE.     

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.     

Improvement of thermal decomposition properties of ammonium perchlorate particles using some polymer coating agents

This research aimed to investigate the optimum conditions for modification of thermal decomposition properties of ammonium perchlorate (AP) particles through microencapsulation techniques. A solvent/non-solvent method has been used to perform microencapsulation of AP particles with some polymer-coating agents such as viton A and nitrocellulose (NC). Differential scanning calorimetry, thermogravimetry, and scanning electron microscopy have been exploited to investigate the thermal properties, heat of decomposition, and coating morphology of pure and coated samples. The preliminary results revealed that AP microparticle could be effectively coated with both NC and viton, but the latter significantly and unfavorably attenuated heat of decomposition of AP so NC was chosen as an appropriate coating agent for modification of thermal properties of AP. The thermal analysis of NC-coated samples, prepared at optimized coating conditions, showed that its first stage decomposition temperature increases about 12 °C with respect to uncoated sample and reaches to 305 °C. Also, the apparent activation energy (E), ΔG ^≠, ΔH ^≠, and ΔS ^≠ of the decomposition processes of the pure and coated AP particles at the optimum conditions were obtained by non-isothermal methods that proposed by ASTM and Ozawa. Finally, the results of this investigation showed that microencapsulation of AP particles with fibrous NC enhance its heat of decomposition (~120 J g^?1) with no obvious effect on kinetic parameters and thermal decomposition temperature.     

Carbon isotopic composition effects on interatomic interactions and the properties of diamond

The interatomic interaction potential parameters were determined for ¹²C and ¹³C in diamond. The results were used to obtain the isotopic dependences of such diamond properties as the Debye temperature, molar heat capacity, thermal expansion coefficient, energies of vacancy formation and self-diffusion, surface energy, and longitudinal velocity of sound. The isotopic dependence of isochoric heat capacity disappeared as the temperature increased. Sign inversion was observed for the isotopic dependence of the thermal expansion coefficient at a certain temperature: its growth changed into a drop. This approach was also used to estimate changes in the interatomic interaction potential and crystal bulk compression modulus of lithium in going from ⁷Li to ⁶Li. The isotopic dependences of phase transition parameters and the whole p-T phase diagram of a simple substance were predicted.     

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.     

Synthesis and characterization of the n-butyl palmitate as an organic phase change material

In this research, the n-butyl palmitate was synthesized using the esterification reaction of the PA with n-butanol. The ¹H nuclear magnetic resonance and Fourier transform infrared illustrated that the hydroxyl group and carboxyl group disappeared, and the ester bond appeared after the reaction, explaining that n-butyl palmitate was successfully fabricated. The differential scanning calorimetry indicated that the phase-transition temperature and latent heat are 12.6 °C and 127.1 J g^?1, which was suited to use in low-temperature fields such as food, pharmaceutical, and biomedical. The thermogravimetric analysis suggested that it had great thermal stability during the phase change process. In addition, the thermal conductivity of the n-butyl palmitate was slightly higher than other fatty acid ester, and the 500 thermal cycles test results indicated that it had excellent thermal reliability. Therefore, the n-butyl palmitate is deduced to share great thermal energy storage ability in terms of latent heat thermal energy system applications.

     

Thermo-physical characterization of some paraffins used as phase change materials for thermal energy storage

Three phase change paraffinic materials (PCMs) were thermophysically (phase-transition temperatures, latent heat, heat capacity at constant pressure, density, and thermal conductivity) investigated in order to be used as latent heat storage media in a pilot plant developed in Plovdiv Bulgaria. Raman structural investigation probes aliphatic character of the E53 sample, while the E46 and ECP samples contain also unsaturated components due to their Raman features within 1,500–1,700 cm^?1 range. Orthorhombic structure of the three PCMs was evidenced by the Raman modes at the 1,417 cm^?1. The highest latent heat value, ΔH, of phase transitions among the three materials was represented by summation of a solid order–disorder, and melting latent heat was encountered by the E53 paraffin, i.e., 194.32 J g^?1 during a μ-DSC scan of 1 °C min^?1. Conversely, the ECP composite containing ceresin component shows the lowest latent heat value of 143.89 J g^?1 and the highest thermal conductivity of 0.46 W m^?1 K^?1 among the three phase change materials (PCMs). More facile melt-disordered solid transition with the activation energy of 525.45 kJ mol^?1 than the lower temperature transition of disorder–order (E _a of 631.73 kJ mol^?1) during the two-step process of solidification for the E53 melt are discussed in terms of structural and molecular motion changes.     

An intrinsic antistatic polyethylene glycol-based solid–solid phase change material for thermal energy storage and thermal management

Polyethylene glycol (PEG) is an important and popular phase change material (PCM), but is not a good antistatic material, which would cause the accumulation of static electricity and electrostatic discharge when used for the thermal energy storage and thermal management of electrical devices. Herein, we prepared a PEG-based solid–solid PCM (SSPCM) with good antistatic property by introducing an ionic liquid onto the macromolecular chains. This SSPCM is in solid state even at 90°C, avoiding the leakage issue of pure PEG. Its latent heat values in the melting and solidifying processes are 56.2 and 30.6 J g⁻¹, respectively. Additionally, this SSPCM has good thermal stability and thermal reliability for thermal storage and thermal management according to thermogravimetric and thermal cycling tests. The volume- and surface resistivity of the SSPCM at ambient temperature are 10^8.87 Ω m and 10^8.92 Ω, respectively, showing good antistatic performance.     

Low-Temperature Heat Capacities and Thermodynamic Properties of Octahydrated Barium Dihydroxide,Ba（OH）2·8H2O（s）

Low-temperature heat capacities of octahydrated barium dihydroxide, Ba（OH）2·8H2O（s）, were measured by a precision automated adiabatic calorimeter in the temperature range from T=78 to 370 K. An obvious endothermic process took place in the temperature range of 345-356 K. The peak in the heat capacity curve was correspondent to the sum of both the fusion and the first thermal decomposition or dehydration. The experimental molar heat capacifies in the temperature ranges of 78-345 K and 356-369 K were fitted to two polynomials. The peak temperature, molar enthalpy and entropy of the phase change have been determined to be （355.007±0.076） K, （73.506±0.011） kJ·ol^-1 and （207.140±0.074） J·K^-1·mol^-1, respectively, by three series of repeated heat capacity measurements in the temperature region of 298-370 K. The thermodynamic functions, （Hr-H298.15 k ）and （Sr-S298.15k）, of the compound have been calculated by the numerical integral of the two heat-eapacity polynomials. In addition, DSC and TG-DTG techniques were used for the further study of thermal behavior of the compound. The latent heat of the phase change became into a value larger than that of the normal compound because the melfing process of the compound must be accompanied by the thermal decomposition or dehydration of 71-120.     

Thermal analysis of protein–metallic ion systems

Advanced thermal analysis methods, such as temperature modulated DSC (differential scanning calorimetry) and quasi-isothermal TMDSC were used to analyze the protein–metallic ion interactions in silk fibroin proteins. The precise heat capacities were measured and theoretically predicted in this study. To remove bound water and simplify the system, a thermal cycling treatment through both standard DSC and TMDSC was used to detect the underlying heat capacity and reveal the phase transitions of the silk–metallic salts system. Results show that K⁺ metallic salts play the role of plasticizer in silk fibroin proteins, which reduces the glass transition (T_g) of the pure silk protein and negatively affects its structural thermal stability. On the other hand, Ca²⁺ metallic salts act as an anti-plasticizer, and increase the glass transition and the thermal stability of the silk protein structure. This indicates that the thermal analysis methods offer a new pathway to study protein–metallic ion systems, yielding very fruitful information for the study of protein structures in the future.     

Multichanneled hierarchical porous nanocomposite CuO/carbonized butterfly wing and its excellent catalytic performance for thermal decomposition of ammonium perchlorate

To meet the requirement of generating more apparent specific heat release at lower temperatures for ammonium perchlorate (AP)-based composite solid propellants, the development of high-performance catalysts for improving the thermal decomposition properties of AP still remains essential and challenging. Herein, a novel catalyst, multichanneled hierarchical porous nanocomposite of CuO and carbonized butterfly wing (CuO/CBW), has been prepared through an in-situ reaction on original butterfly wing scales. Owing to the high active surface area and the good electrical and thermal conductivity, as well as the synergistic effect of CuO nanoparticles (20–25 nm) and CBW, CuO/CBW nanocomposite exhibits excellent catalytic activity for AP thermal decomposition in reducing the high-temperature decomposition temperature by 88.3°C, lowering the apparent activation energy from 190.0 to 103.1 kJ mol⁻¹ and increasing the heat release from 255 to 1841 J g⁻¹.     

Structural Characterization and Thermal Properties of 1-Amino-1-ethylamino-2,2-dinitroethylene

1-amino-1-ethylamino-2,2-dinitroethylene (AEFOX-7) was synthesized by the reaction of 1,1-diamino-2,2-dinitroethylene (FOX-7) and ethylamine aqueous solution at 92 oC. The the-oretical investigation on AEFOX-7 was carried out by B3LYP/6-311++G^**method. The IR frequencies and NMR chemical shifts were performed and compared with the experi-mental results. The thermal behavior of AEFOX-7 was studied with differential scanning calorimetry and thermal gravity-derivative thermogravimetry methods, and can be divided into a melting process and an exothermic decomposition process. The enthalpy, apparent activation energy and pre-exponential factor of the exothermic decomposition reaction were obtained as 374.88 kJ/mol, 169.7 kJ/mol, and 10^19.24 s^-1, respectively. The critical temper-ature of thermal explosion of AEFOX-7 is 145.2 oC. The specific heat capacity of AEFOX-7 was determined with micro-DSC method and theoretical calculation method, and the molar heat capacity is 214.50 J/(mol K) at 298.15 K. The adiabatic time-to-explosion of AEFOX-7 was calculated to be a certain value between 1.38-1.40 s. The thermal stability of AEFOX-7 is much lower than that of FOX-7.     

Thermal and kinetic study of the ferroelectric phase transition in deuterated triglycine selenate

The specific heat and the enthalpy variation of a highly deuterated crystal of ferroelectric triglycine selenate have been measured around its first-order phase transition using the technique square modulated differential thermal analysis (SMDTA). The low temperature variation rate has allowed analyzing the kinetics of the phase transition. Due to an internal crack in the sample, the transition is carried out in two steps and an intermediate region where the transition is blocked and both phases coexist without transformation has been found. The latent heat on cooling (L _c=1.32±0.02 J g^–1) is higher than on heating (L _h=1.08±0.02 J g^–1) due to the thermal hysteresis and the great difference between the specific heat in both phases. Nevertheless, the enthalpy balance is fulfilled on heating and on cooling.