Automated differential scanning calorimetry at low temperatures

A Perkin-Elmer DSC-2 scanning calorimeter was operated by means of a PDP-11/34 computer with time-shared scanner and voltmeter. Special attention was paid to the problems of measurement below room temperature down to the low-temperature limit. It was found that Ne, rather than He, should be used as a purge gas, that scans should always be started at a standardized liquid nitrogen level, and that gas flow to the dry box should be stopped during measurements. Results on benzoic acid were then accurate to 0.6 % from 120 to 300 K. The specific heat of antimony was measured in the temperature interval 120–720 K.     

Differential scanning calorimetry study of constrained groove pressed low carbon steel: recovery,recrystallisation and ferrite to austenite phase transformation

Abstract

Low carbon steel sheets are subjected to severe plastic deformation (SPD) via constrained groove pressing (CGP) up to five passes. As a result of this process, strain magnitude up to 5·8 is imposed to the sheets, which leads to grain size of 225 nm. These nanostructured steel sheets, due to their high dislocation density and ultrafine microstructure, are very sensitive to heating. In the present study, recovery, recrystallisation and ferrite to austenite phase transformation phenomena for the SPD steel are investigated using differential scanning calorimetry method. The results show that with increasing the strain in steel sheets, the deformed stored energy (released through recovery and recrystallisation) and enthalpy of ferrite to austenite phase transformation are significantly increased and varied in 38·5–85·8 and 109–156·1 MJ m^?3 ranges respectively. In addition, transformation temperature is decreased from 761 to 750°C after five CGP passes. However, recovery stored energy, recovery and recrystallisation peak temperatures are not changed, considerably. Experimental data show that with increasing the hardness, the stored energy is increased. One empirical equation is developed for relationship between hardness and stored energy of severely deformed low carbon steel. In addition, using the dislocation model, this mentioned relationship is justified.     

Prediction of the self-accelerating decomposition temperature (SADT) for liquid organic peroxides from differential scanning calorimetry (DSC) measurements

We present a prediction (estimation, calculation, screening) method for the estimation of the self-accelerating decomposition temperature (SADT) for liquid organic peroxides from differential scanning calorimetry (DSC) measurements based on the concepts of thermal explosion theory originally introduced by Semonov which are adopted to our problem assuming nth-order reaction kinetics. For the peroxides under investigation, we demonstrate good agreement with the experimental SADT. This method can be used as a quick and easy applicable method for the estimation of the critical temperatures.     

Facile synthesis of MOF-5 structure with large surface area in the presence of benzoyl peroxide by room temperature synthesis

In this study, for the first time, the uniform cylindrical MOF-5-BPO (Zn₄O(BDC)₃(H₂O)·0.5ZnO, BDC = 1,4-benzenedicarboxylate, BPO = benzoyl peroxide) crystals with large Brunauer–Emmett–Teller (BET) surface area (3210.2 m² g⁻¹) was successfully synthesized by room temperature synthesis in the presence of BPO using zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O) as the zinc source. The pore volumes of MOF-5-BPO materials prepared with different concentrations of BPO were 0.84–1.07 cm³ g⁻¹, higher than that of MOF-5-NP (0.68 cm³ g⁻¹, Zn₄O(BDC)₃(H₂O)₃·2ZnO) and MOF-5-H₂O₂ (0.84 cm³ g⁻¹, Zn₄O(BDC)₃(H₂O)₂·2ZnO, H₂O₂ = hydrogen peroxide). The addition of the peroxides created new pores, which possessed the same diameters as the existing ones, thus increased the pore volume of the product. The concentration of BPO was critical for the pore texture of MOF-5-BPO. Moreover, MOF-5-BPO could store 1.24 wt% hydrogen at 77 K and 100 kPa. Thus, this study points out some information for one to realize the influence of the peroxides over MOF-5 structure and promises the potentiality of large-scale production of MOF-5 structure with large surface area.     

Cement hydration: building bridges and dams at the microstructure level

The concurrent goals of cement hydration are to percolate (bridge) the original cement particles into a load-bearing network and to depercolate (dam) the original water-filled capillary porosity. The initial volume, particle size distribution, and flocculation/dispersion state of the cement particles have a large influence on both hydration rates and microstructure development. Likewise, the capillary porosity as characterized by its pore size distribution, percolation state, and saturation state also influences both hydration kinetics and microstructure. In this paper, experimental techniques and computer modeling are applied to further understanding several of the critical connections between these physical parameters and performance properties. First, the setting or bridging process is explored via a combination of needle penetration and rheological measurements, in concert with three-dimensional microstructural modeling. Second, low temperature calorimetry is shown to be a valuable indicator of the percolation state or damming of the water-filled pores with various size entryways in the three-dimensional microstructure. Porosity percolation (or depercolation) is shown to be strongly influenced by both curing conditions and the alkali content of the cement pastes. Finally, it is proposed that future efforts in this field be directed towards a greater understanding of the (nano)structures of cement hydration products, particularly the calcium silicate hydrate gel, and their influence on performance properties.     

The possibility of high-temperature heat capacity measurements by differential scanning calorimetry

We have been conducting series of heat capacity measurements by differential scanning calorimetry (DSC) on various latent thermal storage materials such as NaOH-NaNO₃. Our concern is now shifting to higher temperature applications of latent thermal storage: space solar dynamic power systems (solar thermal electric power generation systems in space) and so on. Such applications require storage materials which can be operated above 1000 K. Needs for heat-capacity measurements at higher temperatures are increasing. In the present paper, some results of our heat capacity measurements by DSC at intermediate temperatures are presented. Several items which should be considered in order to realize the heat capacity measurements above 1000 K by DSC are discussed.Paper presented at the Second U.S.-Japan Joint Seminar on Thermophysical Properties, June 23, 1988, Gaithersburg, Maryland, U.S.A.     

Quantifying low amorphous or crystalline amounts of alpha-lactose-monohydrate using X-ray powder diffraction, near-infrared spectroscopy, and differential scanning calorimetry

Efficient and accurate quantification of low amorphous and crystalline contents within pharmaceutical materials still remains a challenging task in the pharmaceutical industry. Since X-ray powder diffraction (XRPD) equipment has improved in recent years, our aim was 1) to investigate the possibility of substantially lowering the detection limits of amorphous or crystalline material to about 1% or 0.5% w/w respectively by applying conventional Bragg Brentano optics, combined with a fast and simple evaluation technique; 2) to perform these measurements within a short time to make it suitable for routine analysis; and 3) to subject the same data sets to a partial least squares regression (PLSR) in order to investigate whether it is possible to improve accuracy and precision compared to the standard integration method. Near-infrared spectroscopy (NIRS) and differential scanning calorimetry (DSC) were chosen as reference method. As model substance, alpha lactose monohydrate was chosen to create calibration curves based on predetermined mixtures of highly crystalline and amorphous substance. In contrast to DSC, XRPD and NIRS revealed an excellent linearity, precision, and accuracy with the percent of crystalline amount and a detectability down to about 0.5% w/w. Chemometric evaluation (partial least squares regression) applied to the XRPD data further improved the quality of our calibration.     

Special features characteristic of the use of differential scanning calorimetry for the investigation of the kinetics of thermal decomposition of energetic materials

The results of analysis of mathematical models of “ideal” differential scanning calorimeter are used for determining the experimental conditions which provide for the minimal level of errors of determination of the kinetic constants of exothermal reactions of thermal decomposition of energetic materials under conditions of constant-rate heating of samples and in the isothermal mode. The predicted estimates of admissible values of the basic parameters of models (mass of samples, rate of heating, temperature range of investigations, and so on) are based on the experimental data largely obtained in the investigation of cyclotetramethylenetetranitramine (HMX).     

Effect of the TiO2 nanoparticle size on the decomposition behaviors in aluminum matrix composites

The decomposition behaviors and the effect of particle size on the kinetic rate are studied for Al–3 vol.% titanium dioxide (TiO₂) composites by using three different types of TiO₂ particles (15, 50, and 300 nm). Thermal analysis shows that the reaction is stepwise with the first reaction starting before the melting temperature of Al. Since the high chemical potential of nanoparticles enhances reactivity, the TiO, Al₃Ti, and α-Al₂O₃ phases are found to be formed during the first reaction regardless of particle size. Based on observations of microstructure, the formation mechanism of Al₃Ti and α-Al₂O₃ is understood to be solution precipitation. Non-isothermal kinetic analysis reveals that the reaction mechanism is closely related to the three-dimensional continuous nucleation and the growth limited by diffusion. Particle size is found to be having considerable effect on the kinetic rate. As the particle size decreases, the rate constant increases, while the pre-exponential factor and the activation energy decreases. A non-linear relationship between the rate constant and the reciprocal of the size is found and evaluated.     

Analysis of low temperature impact fracture data of thermoplastic polymers making use of an inverse methodology

In this work room and low temperature impact fracture data toughness of rubber modified polypropylene, polyethylene and rubber toughened polymethylmetacrylate have been assessed. In order to minimize the well-known dynamic effects a previously developed inverse methodology was used to treat force-time traces. Fracture parameters, such as K_IQ and J_C were estimated and the benefits of the inverse methodology were evaluated. The suitableness of energetic and force based toughness parameters for estimating a brittle to ductile transition was evaluated. The employment of the inverse methodology allowed us to infer the values of the crack tip loading rate, dK/dt, without the need of cushioning.     

Ultrasonic synthesis of the microporous metal-organic framework Cu3(BTC)2 at ambient temperature and pressure: An efficient and environmentally friendly method

A three-dimensional (3-D) metal-organic framework (MOF) with 3-D channels, i.e. Cu₃(BTC)₂ (HKUST-1, BTC = benzene-1,3,5-tricarboxylate), was synthesized by using ultrasonic method for the first time. The reaction of cupric acetate and H₃BTC in a mixed solution of DMF/EtOH/H₂O (3:1:2, v/v) under ultrasonic irradiation at ambient temperature and atmospheric pressure for short reaction times (5-60min) gave Cu₃(BTC)₂ in high yields (62.6-85.1%). These Cu₃(BTC)₂ nano-crystals have dimensions of a size range of 10-200 nm, which are much smaller than those synthesized using conventional solvothermal method. There were no significant differences in physicochemical properties, e.g. BET surface area, pore volume, and hydrogen storage capacity, between Cu₃(BTC)₂ nano-crystals prepared using ultrasonic method and the microcrystals obtained by using improved solvothermal method. Compared with traditional synthetic techniques, such as solvent diffusion technique, hydrothermal and solvothermal methods, ultrasonic method for the construction of porous MOFs was found to be highly efficient and environmentally friendly.     

Modeling and simulation of curing kinetics for the cardanol-based vinyl ester resin by means of non-isothermal DSC measurements

The cure kinetics of vinyl ester-styrene system was studied by non-isothermal differential scanning calorimetric (DSC) technique at four different heating rates. The kinetic parameters of the curing process were determined by isoconversional method for the kinetic analysis of the data obtained by the thermal treatment. Activation energy (E_a = 56.63 kJ mol⁻¹) was evaluated for the cure process and a two-parameter (m, n) autocatalytic model was found to be the most adequate to describe the cure kinetics of the studied cardanol-based vinyl ester resin. Non-isothermal DSC curves, as obtained by using the experimental data, show good agreement with the DSC curves obtained by theoretically calculated data.     

Hydration dynamics of collagen/PVA composites: Thermoporometric and impedance analysis

Porous scaffolds like collagen/PVA (polyvinyl alcohol) composites have potential applications in the field of biomedical engineering. The pore properties and electrical behavior of collagen/PVA composite system were investigated by thermoporometry technique and electrochemical impedance analysis. The porous composites were crosslinked by less cytotoxic genipin due to the versatility in the crosslinking reactivity between the amino groups. Different physicochemical properties like rheological behavior, thermal stability of the protein and morphological changes of the composites were investigated as a function of PVA concentration by viscosity profile, temperature dependant circular dichroic spectroscopic studies, scanning electron microscopy. Bound water constrained within the pores of collagen/PVA composites seems to provide signatures for changes induced by amount of additives on the pore diameter and distribution in composite molecules. Impedance measurements of the composites in the frequency range of 10⁻² to 10⁵ Hz reveal that concentration of the additive and crosslinking significantly influence the permittivity of the composites. The tunable physicochemical properties help to gain insight for regulating cellular events for tissue and organ regeneration.     

Effect of ageing on the mechanical properties of directly quenched copper bearing microalloyed steels

The present work aims to study the ageing behaviour of directly quenched Cu-added microalloyed steels. Temperatures related to precipitation of Cu and recovery of dislocations retained in the microstructure after quenching of the steels from finish rolling temperature are determined by differential scanning calorimetric method. Ageing of the directly quenched steels has resulted in the reduction in hardness and strength with concomitant improvement of ductility. 1.5 wt% Cu-added Ti–B microalloyed steel has yielded the most attractive combination of strength and ductility. Presence of Ni in the 1.5 wt% Cu-added Ti–B microalloyed steel indicates sluggish kinetics of Cu precipitation. Ageing has generally deteriorated the impact toughness except for Ni containing Cu-added microalloyed steel above −25 °C temperature. Formation of recovered dislocation cells and fine ?-Cu precipitates during ageing have contributed to the microstructural softening and hardening, respectively.     

Development of carbon—Low alloy steel grades for low temperature applications

Low alloy steels are processed to fulfill the requirements of low temperature applications. Besides the chemical composition, the steel should receive a suitable heat treatment to ensure the targeted mechanical properties at low temperature. In other words, the steels are designed to delay the ductile to brittle transition temperature to resist dynamic loading at subzero temperatures. Steel alloys processed for liquefied gas pipeline fittings are examples for applications that need deep subzero impact transition temperature (ITT).The main purpose of the present work was to find a suitable heat treatment sequence for alloys LC2 and LC2-1. Further, it aimed to correlate the impact toughness with the microstructure and the fracture surface at different sub-zero temperatures.The steels under investigation are carbon-low alloy grades alloyed with Ni, Cr and Mo. LC2 steel alloy has been successfully processed and then modified to LC2-1 alloy by addition of Cr and Mo. Oil quenching from 900 °C followed by tempering at 595 °C was used for toughness improvements. Hardness, tensile and impact tests at room temperature have been carried out. Further impact tests at subzero temperatures were conducted to characterize alloys behavior. Metallographic as well as SEM fractographic coupled with XRD qualitative analysis are also carried out.Non-homogenous martensite-ferrite cast structure in LC2 was altered to homogeneous tempered martensite structure using quenching-tempering treatment, which is leading to shift the ITT down to −73 °C. Addition of Cr and Mo creates a very fine martensitic structure in LC2-1 alloy. Quenching-tempering of LC2-1 accelerates ITT to −30 °C. It is expected that the steel was subjected to temper embrittlement as a result of phosphorus segregation on the grain boundary due to Cr and Mo alloying, as it was concluded in reference no. [6].     

常压放电低温等离子体辐射特性测量实验

本文在自行设计的放电电极板上实现常压下的空气辉光放电(APGD),产生出一薄层的低温等离子体,利用光栅单色仪及测试声强和温度的仪器对所产生的等离子体的光辐射、声辐射和热辐射特性进行实验测量.数据处理后的分析结果表明,该APGD等离子体的光辐射强度及声辐射和热辐射强度,以及总辐射能量基本上都与电极板的加载功率呈线性关系,而且各种形式的能量各占比例是一定的.研究结果表明可以通过沿面APGD的辐射特性与加载功率之间的关系来描述APGD等离子体的特性,以及控制等离子体的产生量.     

Application of low Ms temperature consumable to dissimilar welded joint

Abstract

The welding of dissimilar joints is very common in systems used in oil exploration and production in deep sea waters. Commonly involves welding of low carbon steel pipes with low alloy steel forgings both with inner Inconel clad. The forged steel part undergoes a process of buttering with Inconel or carbon steel electrode before the weld of the joint. The buttering process is followed by a process of residual stresses relief. The conventional way of reducing the level of residual stresses in welded joints is to apply post welding heat treatments. Depending on the size and complexity of the parts to be joined, this can become a serious problem. An alternative technique for reducing residual stresses is to use an electrode that during the cooling process undergoes a displacive transformation at a relatively low temperature so that the deformation resulting from the transformation compensates the contraction during the cooling process, and, although many papers have been published in this direction using Fe–Cr–Ni alloys, most of them report a loss of toughness in the weld metal. Maraging steel is a family of materials with M_s temperature below 200°C and even without the final heat treatment of aging has superior mechanical properties to low alloy steels used in forgings. In this work, forged piece of AISI 4130 was buttered with Maraging 350 weld consumable and subsequently welded to ASTM A36 steel using Inconel 625 filler metal. In addition, the dissimilar base metal plates were welded together using Maraging 350 steel weld consumable. The levels of residual stress, and the toughness and microstructures of heat affected zone and weld metal were investigated.     

低温共烧氮化铝复合材料基板的银金属化研究

基于氮化铝陶瓷基片厚膜导体浆料理论，开发出应用于低温共烧氮化铝流延坯、硼硅酸盐玻璃粘结相的银浆，并系统研究了共烧过程，解决了常见的导线球化问题。成功地进行了3层氮化铝复合材料基板的低温共烧银金属布线。     

金枪鱼冷藏库的设计与施工探讨

本文通过金枪鱼冷藏库工程应用实例介绍,提出了关于金枪鱼低温冷藏的通用技术要求,以供类似工程参考。     

高压低温充氧车的研制

在某些特殊场合 ,需要用到高压 (压力达 35MPa)的氧气或氮气 ,高压低温充氧车的研制就是为了满足这种特殊需求。为了在高度、容积受限制的移动工程车上实现液体泵正常工作 ,需要解决几个问题 :液体贮槽蒸发率必须严格控制 ,泵头和液体管路置于冷箱中 ,贮槽增压送液等。通过实际试车 ,该设备能较好地满足特殊需求