Thermal Radiation Calorimeter for Measuring the Specific Heat Capacity of Liquid Samples

A new thermal radiation calorimeter for measuring the specific heat capacity of liquid samples continuously in the temperature range from 280 to 360 K is described. The heat input to the sample cell from the heater by thermal radiation is estimated using the effective emissivity, which is the apparatus constant. The heat capacity of a sample can be calculated from the temperatures of the sample and the heater, and the temperature change rate of the sample. The present sample cell was made of Pyrex glass; therefore most liquid samples do not react with the sample cell, and blackening of the surface of the sample cell is not necessary in the present temperature range. The specific heat capacities for ethanol, ethylene glycol, n-heptane, n-valeric acid, and water+ethanol mixtures were measured to confirm the reliability of the present calorimeter.     

Pore water distribution in mortar during drying as determined by NMR

The drying of a saturated mortar sample was measured using Nuclear Magnetic Resonance. NMR is a technique which gives the total moisture content of a specific volume at a certain time. By looking also at the relaxation of behaviour of the NMR signal, more information can be obtained. For every time and every position, the pore size distribution of the mortar was measured. Other techniques show that NMR is a reliable method to measure pore size distributions. Two distinctive pore sizes can be seen in the pore size distribution. This corresponds to the microstructure of mortar, which has small (< 10nm) gel pores and bigger) ≈ 10 to 1000 nm) capillary pores. A one-dimensional drying experiment was carried out by blowing dry air (relative humidity =0+5%; temperature=20±1°C) ove the top of a cylindrical mortar sample, while all the other surfaces were sealed to prevent drying in other directions. The changing moisture content in the pores was followed with time during drying for about 3 days. This leads to the conclusion that the water cannot be extracted from the gel pores, while the capillary pores dry within about 20 hours under the drying conditions and time adopted.     

Early age electrical resistivity behaviour of various concrete mixtures subject to low temperature cycling

The effect of thermal cycling between −24 and + 24 °C on the electrical resistivity of five concrete mixtures was investigated at early-ages. Each mixture was subjected to two thermal cycles (initiated either 1 or 14 days after casting) wherein temperatures were changed by 1 °C/h. Electrical resistivity increased as temperature decreased. This relationship followed the Arrhenius equation until the phase transition temperature (i.e. initial freezing of the pore solution), at which point electrical resistivity increased greatly. A method of determining the phase transition temperature is presented that could be used in place of existing methods using mortar cubes. The phase transition temperature was higher during thawing cycles compared to freezing cycles for all mixtures. Mixtures with ground slag replacing cement had higher resistivity and lower phase transition temperatures than mixtures using only cement due to the change in the ionic combination of the concrete pore solution. The phase transition temperature decreases as concrete ages.     

DETERMINATION OF THE PORE STRUCTURE OF POROUS MATERIALS USING ELECTRICAL CONDUCTANCE

ABSTRACT

A new method for determining the pore structure of porous materials has been developed. The methodology combines the plastic ice model for solid-liquid phase transitions of pore water with relationships between conductance and temperature, and conductance and pore structure. With these relationships and measurements of the electrical conductance and the corresponding temperature of a saturated porous material subjected to a cycle of capillary freezing and melting, a pore size distribution is obtainable.

Baaed on this methodology a conductometric phase transition poroai-meter was constructed. The pore size distribution of porous Vycor glass was measured using this porosimeter. The modal neck and body radii measured by thia method are 28 and 55 angstroms respectively. These results are comparable to those obtained using other techniques. The modal neck and body radii measured on the same sample by mercury porosimetry are 30 and 85 angstroms and by phase transition porosimetry, 27 and 49 angstroms, respectively.     

DETERMINATION OF THE PORE STRUCTURE OF POROUS MATERIALS USING ELECTRICAL CONDUCTANCE

A new method for determining the pore structure of porous materials has been developed. The methodology combines the plastic ice model for solid-liquid phase transitions of pore water with relationships between conductance and temperature, and conductance and pore structure. With these relationships and measurements of the electrical conductance and the corresponding temperature of a saturated porous material subjected to a cycle of capillary freezing and melting, a pore size distribution is obtainable.

Baaed on this methodology a conductometric phase transition poroai-meter was constructed. The pore size distribution of porous Vycor glass was measured using this porosimeter. The modal neck and body radii measured by thia method are 28 and 55 angstroms respectively. These results are comparable to those obtained using other techniques. The modal neck and body radii measured on the same sample by mercury porosimetry are 30 and 85 angstroms and by phase transition porosimetry, 27 and 49 angstroms, respectively.     

Increased strength and related mechanisms for mortars at cryogenic temperatures

Properties of cement-based materials at cryogenic temperatures are quite different from those at room temperatures. The strength of mortars at cryogenic temperatures was experimentally studied and an empirical model was established. The freezing thermodynamic process of pore water and pore size distribution in mortars were characterized by differential scanning calorimeter (DSC) and thermoporometry (TPM), respectively. The relationship between the increased cryogenic strength and pore ice formation was discussed. The results showed that flexural strength of mortars increased at a higher rate than compressive strength. Water content and initial strength at room temperatures were the main factors influencing the cryogenic strength. Higher water content and higher initial strength resulted in higher cryogenic strength. Ice formation in pores is one of the main reasons for the mortar’s cryogenic strength increase. Nearly half of the water remained unfrozen in pores with radius less than 40 nm at −40 °C. Both ice formed in capillary pores and gel pores contributes to the strength increase observed at cryogenic temperatures.     

掺珍珠岩水泥石孔分形维数及其与孔结构、强度的关系

通过压汞法测试不同龄期掺0-40%珍珠岩掺合料水泥石的孔结构参数,利用分形理论的相关知识研究这些水化物的孔体积分形特征,计算它们的孔分形维数D=3.3～3.5,分析并探讨该水泥石孔分形维数与孔结构参数、抗压强度之间的关系.结果表明水泥石孔分形维数与孔隙率、孔径、孔表面积有密切的关系,随着孔分形维数增大,孔隙率提高,孔径扩大、孔表面积增大,孔结构就越劣化,对应的材料抗压强度下降.因此孔体积分形维数可用于综合评定材料的孔结构特性.     

多孔壳微胶囊对硬化砂浆抗渗性的影响

采用原位聚合与水解缩聚法,以四乙氧基硅烷（TEOS）、环氧树脂（E51）、苯乙烯（St）等为主要原料,合成了一种二氧化硅多孔壳微胶囊（Porous silica shell microcapsules,PSSM）。分别采用SEM、FTIR、TGA对PSSM外观形貌、化学组分、核壳比进行表征。通过对掺加PSSM的砂浆试块进行80%抗压强度荷载预压、养护（浸水或干湿循环养护）处理后,运用交流阻抗法与压汞法研究了PSSM对硬化砂浆抗渗性与孔结构的影响规律。结果表明:制备的PSSM粒径约为10~100 μm,其含有聚苯乙烯网络支架、环氧树脂和聚硅氧烷囊芯,支架聚合物和多孔壳,核壳质量比为1.54。与未预压-养护处理的试块相比,经预压-养护处理后的空白试块的连通孔溶液电阻R_CH和扩散阻抗系数σ均降低,孔隙率升高,表明预压使试块内形成微裂纹缺陷,经养护仍未愈合,因此试块抗渗性降低;而对于掺加8% PSSM的试块,经预压-养护处理后其R_CH和σ均增加,孔隙率降低,表明试块抗渗性提高。这是由于PSSM的破壳-固化作用以及长期浸水或干湿循环养护,导致试块中PSSM发生了渗出-固化作用,封堵愈合了试块内的微裂隙,抗渗性得到提高。      

Compressive strength and processing of camphene-based freeze cast calcium phosphate scaffolds with aligned pores

Porous calcium phosphate (CaP) scaffolds with aligned pores were fabricated by unidirectionally freezing a CaP/camphene slurry at 32 °C for various times (1, 2, 3 days). During this process, camphene dendrites grew preferentially from the bottom to the top of the cast body. The frozen samples were then freeze-dried to remove the solid camphene and sintered at 1200 °C for 3 h to densify the CaP walls. All of the fabricated samples showed a highly aligned pore structure with a porosity of 62-65 vol.%, regardless of the freezing time. As the freezing time was increased from 1 to 3 days, the pore size increased from 122 to 166 μm due to the continual overgrowth of camphene dendrites, while the compressive strength decreased from 9.3 ± 1.6 to 6.2 ± 1.3 MPa due to the increase in pore size. However, it should be noted that the compressive strength of the sample tested parallel to the freezing direction was much higher than that of the sample tested normal to the direction of freezing, indicating the utility of the aligned pores.     

Freeze-thaw crack determination in cementitious materials using 3D X-ray computed tomography and acoustic emission

As concrete freezes and thaws cracks may develop. These cracks can provide a path for water and ionic species to penetrate the concrete. This may reduce the service-life of the concrete element. In this study, X-ray computed tomography (CT) was used as a non-destructive technique to characterize the microstructure of mortar samples that were exposed to different levels of freeze-thaw damage by varying degree of saturation in the samples (75, 90, 95, and 100% degrees of saturation). Acoustic emission (AE) experiments were performed during freezing and thawing to investigate sample cracking behavior. The volume of cracks present within the mortar samples after freezing and thawing were determined using X-ray CT and compared to passive acoustic emission data. The location/source of cracks was also determined using X-ray CT. The crack sources (i.e., void, aggregate, interfacial transition zone, or paste) were determined using X-ray CT and were related to AE activities during cracking. Crack volumes were found to increase with increased levels of saturation, and visual observations of cracking were found to correlate with AE signatures of various crack sources.     

Resistance to freezing and thawing of mortar specimens made from sulphoaluminate—belite cement

Resistance to freezing and thawing of mortar specimens made from sulphoaluminate-belite cement (M-SAB) is compared with that of mortars made from portland cement (M-PC). The results suggest that larger median radius of the pores and total porosity of M-SAB compared to those of M-PC are primarily caused by the rapid setting of the SAB cement. The ‘coarsening’ of pore structure of mortar specimens under action of freezing and thawing is proved by the increase in the macropores portion, median pore radius, and total porosity values. This process is more intense in M-SAB. The effect of the frost attack is confirmed by lower compressive strength and dynamic modulus of elasticity on the one hand and higher absorption capacity, expansion, and crack propagation of M-SAB compared with those of M-PC on the other hand. Besides the decreased frost resistance of M-SAB as compared with that of M-PC, unsatisfactory passivation of steel in M-SAB was found. The reason of this fact is the pH value decrease to less than 11.5 of the M-SAB extract     

冷冻浇注制备多孔陶瓷的研究进展

冷冻浇注制备多孔陶瓷具有绿色经济、孔结构可控以及材料性能优良等优点,近年来受到国内外学者的广泛关注。本文在简单介绍冷冻浇注工艺原理的基础上,阐述了冷冻浇注工艺过程中孔结构的形成机理与条件,详细讨论了液相介质与冷冻条件对孔结构的影响,总结了冷冻浇注制备多孔陶瓷的材料体系以及典型工艺条件,最后指出冷冻浇注未来的研究方向是孔结构的有效控制及新型功能化多孔陶瓷的制备。     

Fibre mortar composites under fire conditions: effects of ageing and moisture content of specimens

Two small scale test series were performed using the cone calorimeter heating method to detect any differences in the way various fibres affect the thermal properties of a standard mortar. The cone shaped heater of the cone calorimeter produces a uniform heat flux on the sample surface over an area of 100×100 mm². The heat flux was adjusted to 50 kW m^?2, which corresponds to the early stage of a fully developed fire. The total exposure also corresponds roughly to the ISO 834 time-temperature curve during the first 30 minutes. Short ageing of the specimens gave very clear differences in thermal properties between fibre mortars. However, no such differences were observed with oven dried samples. This shows the importance of carrying out tests in conditions as close as possible to the end use conditions of the material or product.     

Dynamic pressurization method for measuring permeability and modulus: I. theory

The permeability of a saturated porous body can be determined from the kinetics of dilatation resulting from a change in pressure in the surrounding bath. This method was previously applied to aerogels [Gross J, Scherer GW (2003) J Non-Cryst Solids 325, 34–47]. The theory is here extended to allow for the compressibility of the solid phase, so that the method can be applied to more rigid materials, such as concrete. A viscoelastic analysis indicates that creep of the sample will have a small effect on the measured permeability for cementitious materials, in most cases. However, the effect of entrapped air in the pore liquid is shown to have a drastic effect on the relaxation behavior, so it is essential to reduce the air content below ∼0.1 volume %. For samples without entrapped air, a simple result is obtained that is tested in a companion paper.An erratum to this article can be found at     

液氮速冻对火龙果块微生物和品质的影响研究

本文以火龙果块为原料,研究了-40℃、-60℃、-80℃和-100℃喷淋式液氮速冻及-18℃冰箱缓冻处理对火龙果微生物和品质的影响,并筛选了最佳液氮速冻温度。结果表明:样品冻结速率随液氮速冻温度的降低而加快,冻结时间由1. 25 min降至0. 367 min,但-100℃出现低温断裂现象;液氮速冻处理对样品的多酚氧化酶有抑制作用,其中,-80℃液氮速冻处理后样品的多酚氧化酶活性降至47. 27%,而缓冻处理后的酶活升高至301. 09%;相比于缓冻处理,液氮速冻处理后的样品的质构保持更好,其汁液流失率在8. 88%～10. 50%之间,而缓冻处理则高达38. 29%;随着液氮速冻温度的降低,样品的可滴定酸、可溶性固形物、总酚、花色苷、抗坏血酸等品质保持更好。所以在不同温度液氮速冻处理中,-80℃对样品的品质保持最佳。     

Relevance of liquid state to solid state properties

We outline in this talk the beginning of a new programme to study physical properties of crystalline solids. It is based on considering the latter, a broken symmetry phase, in terms of the higher symmetry liquid phase. The solid is a calculable perturbation on the fluid. This is exactly opposite to the standard approach which relates mechanical properties to the behaviour of defects (mainly dislocations) etc., in an otherwise perfect crystalline solid. However, most other broken symmetry phases (e.g. ferromagnets) are discussed starting from a symmetric Hamiltonian or a free energy functional, and earlier work by one of the authors shows that the liquid-solid transition is well described, qualitatively and quantitatively, by this approach. On the other hand, defect theories of melting have a long record of nonsuccess. In the first part of the talk, the density wave theory of freezing will be outlined, and it will be shown how properties such as Debye Waller factor, entropy change of freezing etc. can be calculated with no or one free parameter. The problem of calculating shear elastic constants and dislocation core structures as well as energies in terms only of observable liquid state properties will be set up, and results presented. The method will be contrasted with zero temperature ‘atomistic’ models which obscure the essential dependence on structure and flounder in a mass of detail. The concluding part will describe further proposed applications, some suggestive experimental results extant in the literature, and some speculations. Only a summary is presented.     

The adsorption force theory of frost heaving

Presented in this paper are the theorization of a traditional concept of the mechanics of frost heaving, as well as a critical review of the recent developments in this field. The key to the theorization is the following: (1) the film water adsorbed on soil particles can build up an internal solid-like stress, and (2) the flow of film water is different from the conventionally accepted flow of pore water. It is expected that modern continuum mechanics will, in the future, improve the theory of film water which, in this paper, has been formulated by use of the classical method.The freezing film water, trying to retrieve the loss of its thickness to the frozen ice, generates a suction force that draws water to the freezing front where the frost-heaving pressure pushes up the overburden. The temperature of the freezing film water that has generated the solid-like stress, is lower than the temperature of the freezing pore water. This distribution of freezing temperatures in the region of film and pore waters explains the observation that the freezing front causing frost heaving is not a planar surface but a three-dimensional zone diffused in the direction of heat transfer. Frost-heaving pressure can be derived as part of the solution of the boundary-value problem of the frost-heaving differential equations.     

镍纳米粉的比表面积和孔结构研究

采用阳极弧放电等离子体方法制备了高纯镍纳米粉,利用X射线衍射(XBD)、透射电子显微镜(TEM)对粉末的形貌、晶体结构、粒度进行了表征。样品的N_2的吸附-脱附等温线采用静态表面吸附仪在液氮温度下(78 K)在气体饱和蒸气压力范围内测试。依据BJH理论模型计算探讨了样品的累积孔表面积、累积孔体积、孔径及其BJH脱附分布等性能。用图解法由等温吸附直线求出单层吸附量,利用BET吸附公式计算出样品的比表面积。结果表明,镍纳米粉的比表面积为14.23 m~2/g,粒径为46 nm。     

Modelling the freezing of butter

Butter is a water-in-oil emulsion so its behaviour during freezing is very different from that of most food products, for which water forms a continuous phase. The release of latent heat during freezing is controlled as much by the rate of crystallization of water in each of the water droplets as by the rate of heat transfer. Measurements of the freezing of butter show that the release of latent heat from the freezing water depends on the degree of supercooling, which, in turn, depends on the cooling medium temperature, the size of the butter item, the packaging and the type of butter. Four modelling approaches were tested against the experimental data collected for a 25 kg block of butter. A “sensible heat only model” accurately predicted the butter temperature until temperatures at which water freezing becomes significant were reached. An “equilibrium thermal properties model” predicted a temperature plateau near the initial freezing point of the butter in a manner that was inconsistent with the measured data. A third model used a stochastic approach to ice nucleation based on supercooling using classical homogeneous nucleation theory. The predicted temperatures showed that supercooling-driven nucleation alone is not sufficient to predict the freezing behaviour of butter. A fourth approach took account of time-dependent nucleation and ice crystal growth kinetics using classical Avrami crystallization theory. The relationship between the ice crystal growth rate and the supersaturation was assumed to be linear. The model predicted the experimental data accurately, particularly by predicting the slow rebound in the temperature following supercooling that is found when freezing butter under some conditions.     

加速量热仪在火炸药检测中的应用

加速量热仪(ARC)基于绝热原理设计,可使用较大的样品量,灵敏度高,能精确测得样品热分解初始温度、绝热分解过程中温度和压力随时间的变化曲线,尤其是能给出DTA和DSC等无法给出的物质在热分解初期的压力缓慢变化过程.文中简要介绍了ARC的结构、操作原理和可测参数,概述了近年来ARC在火炸药中的应用.大量研究表明,ARC是研究炸药热安定性和安全性的一种有效手段.