Thermal conductivity measurements on xonotlite-type calcium silicate by the transient hot-strip method

The experimental results of the thermal conductivities of xonotlite-type calcium silicate insulation materials were presented at different temperatures and pressures.Two appropriative surroundings,i.e.an elevated temperature surrounding from ambient temperature to 1450 K and a vacuum surrounding from atmosphere pressure to 10-3 Pa,were designed for the transient hot-strip (THS) method.The thermal conduetivities of xonotlite-type calcium silicate with four densities from ambient temperature to 1000 K and 0.045 Pa to atmospheric pressure were measured.The results show that the thermal conductivity of xunotlite-type calcium silicate decreases apparently with the fall of density,and decreases apparently with the drop of pressure,and reaches the least value at about 100 Pa.The thermal conductivity of xonotlite-type calcium silicate increases almost linearly with T3,and increases more abundantly with low density than with high density.The thermal conductivity measurement uncertainty is estimated to be approximately 3% at ambient temperature,and 6% at 800 K.     

添加氧化钙的硅酸锆陶瓷的性能

以硅酸锆和硝酸钙为原料,采用湿磨的方法实现原料的均匀混合,制备了系列的添加氧化钙的硅酸锆陶瓷,利用阿基米德法和X-射线衍射技术对硅酸锆陶瓷的密度、物相变化进行了表征,测试了其显微结构和抗折强度,重点讨论氧化钙添加量和烧成温度对硅酸锆陶瓷的影响.结果表明,1 450℃和1 500℃烧结试样的体积密度随氧化钙添加量改变有较小变化,1 550℃烧结试样密度则随着氧化钙添加量增大而减小,密度最大值可达4.19克/立方厘米;样品的物相由硅酸锆和单斜氧化锆及少量稳定氧化锆组成,主晶相为硅酸锆;硅酸锆陶瓷有较多的气孔,是其致密度小的主要原因,硅酸锆陶瓷的主要断裂方式是沿晶断裂;硅酸锆陶瓷的抗折强度随着烧成温度的升高明显降低,随氧化钙添加量增大而先减小再增大,抗折强度最高可达186.0兆帕.     

Dehydration Characteristics of C-S-H with Ca/Si Ratio 1.0 Prepared Via Precipitation

Calcium silicate hydrate(C-S-H) with Ca/Si ratio 1.0 was prepared via precipitation in solution and heated at various temperatures to investigate its dehydration behavior. The dehydration, structural collapse and recrystallization characteristics of C-S-H and its microstructural change during heating process were investigated by XRD, SEM, Raman and TG-DSC techniques. C-S-H gradually lost non-evaporable water upon heating, about 50% and 80% non-evaporable water was removed below 200 and 400 ℃, respectively, and the rest was removed up to about 1 000 ℃. At 400 ℃, dehydrated C-S-H exhibited the increasing disordering of calcium/silicon environment and the decreasing symmetrical bending vibration of Si-O-Si of Q~2 silicate chains. At 650 ℃ non-bridging oxygen atoms(O_(non)) attached to silicon were almost removed, and significant structural change occurred, and at 815 ℃ C-S-H dehydrated to wollastonite.     

Preparation and characterization of CA-MA eutectic/silicon dioxide nanoscale composite phase change material from water glass via sol-gel method

This work mainly involved the preparation of a nano-scale form-stable phase change material(PCM) consisting of capric and myristic acid(CA-MA) binary eutectic acting as thermal absorbing material and nano silicon dioxide(nano-SiO_2) serving as the supporting material. Industrial water glass for preparation of the nano silicon dioxide matrix and CA-MA eutectic mixture were compounded by single-step sol-gel method with the silane coupling agent. The morphology, chemical characterization and form stability property of the composite PCM were investigated by transmission electron microscopy(TEM), scanning electron microscopy(SEM), Fourier-transform infrared(FT-IR) spectroscopy and polarizing microscopy(POM). It was indicated that the average diameter of the composite PCM particle ranged from 30-100 nm. The CA-MA eutectic was immobilized in the network pores constructed by the Si-O bonds so that the composite PCM was allowed no liquid leakage above the melting temperature of the CA-MA eutectic. Differential scanning calorimetry(DSC) and thermogravimetric analysis(TGA) measurement were conducted to investigate the thermal properties and stability of the composite PCM. From the measurement results, the mass fraction of the CA-MA eutectic in the composite PCM was about 40%. The phase change temperature and latent heat of the composite were determined to be 21.15 ℃ and 55.67 J/g, respectively. Meanwhile, thermal conductivity of the composite was measured to be 0.208 W·m~(-1)·K~(-1) by using the transient hot-wire method. The composite PCM was able to maintain the surrounding temperature close to its phase change temperature and behaved well in thermalregulated performance which was verified by the heat storage-release experiment. This kind of form-stable PCM was supposed to complete thermal insulation even temperature regulation by the dual effect of relatively low thermal conductivity and phase change thermal storage-release properties. So it can be formulated that the nanoscale CA-MA/SiO_2 composite PCM with the form-stable property, good thermal storage capacity and relatively low thermal conductivity can be applied for energy conservation as a kind of thermal functional material.     

Modification of liquid silicone rubber by octavinyl-polyhedral oligosilsesquioxanes and silicon sol

To develop an efficient and bio-compatible way to improve the thermal and mechanical properties of addition type liquid silicone rubber(LSR), a series of modified LSR samples were prepared by introducing octavinyl-polyhedral oligosilsesquioxanes(VPOSS) and high purity silicon sol singly or in combination before vulcanization. Significant correlation was found between the loading rate of VPOSS and thermal properties. However, mechanical properties were negatively correlated with VPOSS content within the range experimented, which may be ascribed to material defect caused by uneven distribution and aggregation. Furthermore, test results approved that the introducing of silicon sol indeed affected the stabilities of the polymer by restraining the material defect caused by the aggregation of POSS molecules and improving cross link density. For example, adding 10%-20% of silicon sol into VPOSS(1.0%) modified LSR will increase tear resistance by 43.9%-85.7%, elongation at break by 31.7%-57.3%, residue at 800 ℃ in N2 atmosphere by 32.0%-37.9%, residue at 650 ℃ in air atmosphere by 70.9%-91.6%, respectively. This work proves that, to incorporate VPOSS into LSR by hydrosilylation, and to use silicon sol as dispersant and reinforce filler can become an efficient way to improve the mechanical property, thermal stability and bio-compatibility of LSR in the future.     

Preparation and Properties of Foam Glass-ceramic from Diatomite

The results of the study of raw mix preparation and foam glass-ceramics production using diatomite as a raw material were presented in the following article. A mixture of diatomite and 40% NaOH solution was subjected to heating at a constant temperature of 775 ℃. Samples of foam glass-ceramic from diatomite with an average density of 290-580 kg/m~3, compressive strength of 1.7-7.8 MPa and thermal conductivity of 0.08-0.14 W/(m·K) were obtained. The investigations have shown that the hydrothermal pretreatment of mixture at the temperature of 90 ℃ may lead to the acceleration of the leaching of amorphous SiO_2 from diatomite. It was discovered that the resulting soluble alkali silicates promote the process of foaming during heating and reduce the average density of the obtained samples. The optimal duration of the leaching process was estimated to be 30 minutes, which corresponds to the yield of SiO_2 equal to 42.5% by the weight of dry diatomite.     

MXene/二氧化硅/六水氯化钙复合相变储热材料的制备及性能

六水氯化钙作为一类低温体储热材料, 在蓄热节能方面有着巨大的应用前景。单一的六水氯化钙相变储热材料存在导热系数低和熔化时易泄漏的缺点, 具有较大的内芯和互穿介孔孔道结构的介孔二氧化硅可以解决上述 问题。介孔二氧化硅具有低密度, 热膨胀系数小, 折射率低, 比表面积大等优点, 但其导热系数低, 需要与热性能良好的材料复合来增强导热能力。选用MXene 作为导热增强材料, 在其表面上生长介孔二氧化硅, 再把相变材料六水氯 化钙负载其中。通过综合热分析仪和红外热成像仪测定, 证明复合相变材料的储热性能、热稳定性和传热速率都有显著提升; 在烘箱中观察六水氯化钙的泄漏情况也明显被载体材料所抑制, 成功制备一种热性能和稳定性俱佳的复 合相变储热材料。     

Comparison of Conventional and Microwave-assisted Synthesis and Characteristics of Aluminum-pillared Rectorite

The synthesis and characterization of aluminum-pillared rectorite were studied. The synthesis was conducted with both conventional heating and microwave irradiation. Microwave irradiation was found to enhanee the intercalation and ion-exchange during synthesis, and to be able to produce the rectorite with a larger d001 aad a better uniformity. The specific surface area is 180 m^2 / g and basal spacing is 3.2 nm.The texture change and thermal and hydrothermal stability of cross- linked rectorite were examined using XRD, FTIR, nitrogen-adsorption and TGA. The experimental results show that the aluminum-pillared rectorite, after calcined at 800℃ for 3 hours, can keep the basal aluminum-silicate texture and would not disperse in water at room or an elevated temperature. The alumimum-pillared rectorite shows a high specific surface area, good thermal and hydrothermal stability, and is promising in applications as catalyst carriers and adsorbents for waste treatment.     

New activated carbon with high thermal conductivity and its microwave regeneration performance

Using a walnut shellas a carbon source and ZnCl_2 as an activating agent,we resolved the temperature gradient problems of activated carbon in the microwave desorption process.An appropriate amount of silicon carbide was added to prepare the composite activated carbon with high thermalconductivity while developing VOC adsorption-microwave regeneration technology.The experimentalresults show that the coefficient of thermalconductivity of SiC-AC is three times as much as those of AC and SY-6.When microwave power was 480 W in its microwave desorption,the temperature of the bed thermaldesorption was 10 ℃ to 30 ℃ below that of normalactivated carbon prepared in our laboratory.The toluene desorption activation energy was 16.05 k J·mol~(-1),which was 15% less than the desorption activation energy of commercialactivated carbon.This study testified that the process could maintain its high adsorption and regeneration desorption performances.     

MPM复合保温材料导热系数的测定及实验装置的改进

MPM复合材料是一种导热系数较小的保温材料 ,单纯采用石棉作为绝热壁不能克服实验过程中大量的热损失。利用改进护热平板构造出有效的绝热壁的实验装置 ,对 MPM复合保温材料的导热系数进行了实验测试。结果表明 :在所研究的温度范围内该种材料的导热系数与温度呈线性关系 ,即λ=( 2 .0 1 8+ 0 .1 2 2 T)× 1 0 - 2 W· ( m·℃ ) - 1;导热系数的值域说明了此种材料具有较好的隔热保温性能 ;证实了该实验装置误差小于 5 %～ 1 0 %。     

Hydrothermal synthesis of zeolites-calcium silicate hydrate composite from coal fly ash with co-activation of Ca(OH)2-NaOH for aqueous heavy metals removalOA

Coal fly ash is a typical secondary aluminum/silicon resource. The preparation of zeolite-type absorbent is a potential way for its value-added utilization, while the purity and adsorption property of zeolite are limited due to the occurrence of side reactions in the synthesis process. In this study, a designated composite consisted of crystalline zeolites and amorphous calcium silicate hydrate was selected, which was direct synthesized from fly ash under conditions of a Ca/Si molar ratio of 0.8...     

Preparation of ultra-light xonotlite thermal insulation material using carbide slag

Using carbide slag as the calcareous materials, xonotlite thermal insulation material was successfully prepared via dynamic hydrothermal synthesis. The experimental results show that the xonotlite thermal insulation material is made up of large numbers of “chestnut bur shape” particles. Optimum conditions of calcination temperature of carbide slag, synthesis reaction temperature and time, stirring rate, CaO/SiO₂ mol ratio, water/solid weight ratio, amount of fiberglass, molding pressures, dryness temperatures and the presence of dispersant (glycol and polyvinyl alcohol) favor the preparation of xonotlite thermal insulation material. The evaluation of xonotlite thermal insulation material reveals that the product is ultra-light and excellent in physical performances. Such a little amount of impurities in carbide slag has no effect on the phase, morphology, stability at high temperature and physical performances of products.     

Hydration Characteristics and Humidity Control Performance of Calcium Silicate Board Prepared from Mine Tailing and Diatomite

The feasibility of utilizing molybdenum tailing and diatomite as siliceous materials to prepare calcium silicate board was explored. The influences of molybdenum tailing/diatomite proportion on hydration characteristics, thermal conductivity, water absorption, flexural strength and moisture adsorption-desorption property of calcium silicate board were investigated in detail. The experimental results reveal that molybdenum tailing is environmentally friendly to prepare building materials. The main hydration products in calcium silicate board under autoclaved condition are C-S-H with low crystallinity and tobermorite. Molybdenum tailing is favorable to the formation of tobermorite. The flexural strength and bulk density of the calcium silicate board gradually increase when the content of molybdenum tailing increases. Netlike C-S-H is formed with the increase of diatomite content during autoclaved curing process, resulting in the enhancement of moisture adsorptiondesorption performance and the reduction of thermal conductivity. The optimal content of molybdenum tailing is 20%, furthermore, the flexual strength and thermal conductivity of calcium silicate board at this content meet the Chinese standard JC/T564.1-2008.     

Preparation of Ultra-light Xonotlite Thermal Insulation Material Using Carbide Slag

Using carbide slag as the calcareous materials, xonotlite thermal insulation material was successfully prepared via dynamic hydrothermal synthesis. The experimental results show that the xonotlite thermal insulation material is made up of large numbers of chestnut bur shape particles. Optimum conditions of calcination temperature of carbide slag, synthesis reaction temperature and time, stirring rate, CaO/SiO2 mol ratio, water/solid weight ratio, amount of fiberglass, molding pressures, dryness temperatures...     

Preparation of spherical microfine silicon powder

Under certain conditions of proper temperature and pH value, sodium silicate was hydrolyzed in liquid ammonia chloride, and spherical microfine SiO2 powder in micrometer-size was prepared. In this experiment, the relationship between needed time and proper pH value, temperature, density of the solution, and its current capacity were found .The optimum conditions are pH 8.5, 70 ~C, and the concentration of sodium silicate is 0.6 mol/L for the density of the solution. The structure of spherical microfine silicon was characterized by SEM and XRD.     

Synthesis of calcium silicate hydrate based on steel slag with various alkalinities

This study aimed to improve the hydraulic potential properties of the slag. Therefore, a method of dynamic hydrothermal synthesis was applied to synthesize calcium silicate hydrate. The phases and nanostructures were characterized by XRD, FTIR, TEM, and BET nitrogen adsorption. The infl uence of alkalinity of steel slag on its structures and properties was discussed. The experimental results show that, the main product is amorphous calcium silicate hydrate gel with fl occulent or fi brous pattern with a BET specifi c surface area up to 77 m2/g and pore volume of 0.34 mL/g. Compared with low alkalinity steel slag, calcium silicate hydrate synthesized from higher alkalinity steel slag is prone to transform to tobermorite structure.     

2D finite element analysis of thermal balance for drained aluminum reduction cells

Based on the principle of energy conservation,the applicable technique for drained cell retrofitted from conventional one was analyzed with 2D finite element model. The model employed a 1D heat transfer scheme to compute iteratively the freeze profile until the thickness variable reached the terminating requirement. The calculated 2D heat dissipation from the cell surfaces was converted into the overall 3D heat loss. The potential drop of the system, freeze profile and heat balance were analyzed to evaluate their variation with technical parameters when designing the 150 kA conventional cell based drained cell. The simulation results show that the retrofitted drained cell is able to keep thermal balance under the conditions that the current is 190 kA, the anodic current density is 0.96 A/cm2, the anode-cathode distance is 2.5 cm, the alumina cover is 16 cm thick with a thermal conductivity of 0.20 W/(m·℃ ) and the electrolysis temperature is 946 ℃ .     

Preparation,Characterization, and Formation Mechanism of Calcium Sulfate Hemihydrate Whiskers

Calcium sulfate hemihydrate whiskers were synthesized successfully via one-step hydrothermal crystallization method using phosphogypsum at 130 °C for 240 min with an initial slurry mass fraction of 2.5 wt%. The phase compositions, microstructures, thermal properties and molecular structures of asprepared samples were analyzed by XRD, ESEM, EDS, TG-DTA, and FT-IR. The influence of raw materials' ball-milling time on the morphologies of whiskers was investigated. The effects of impurities on crystallization morphologies and length to diameter ratio(L/D) of calcium sulfate hemihydrate whiskers were studied. The results indicated that the calcium sulfate dihydrate crystalline could be translated directly into fibrous calcium sulfate hemihydrate whiskers. It was beneficial to form fine fiber structure when the ball-milling time of the raw material was 15 min. Aspect ratio of calcium sulfate hemihydrate whiskers decreased with increasing content of impurities. Moreover, the relative growth mechanism of whisker crystals via one-step hydrothermal crystallization method was discussed in detail.     

掺粉煤灰的保温隔热屋面材料的试验

为研究开发具有良好的保温隔热屋面材料,有效改善室内居住环境和节约能耗,通过试验,采用电厂粉煤灰为主要基料,废旧聚苯乙烯泡沫塑料为主要隔热单元,在满足保温隔热屋面材料质量要求的条件下,经水泥、外加剂复合制成具有良好的保温隔热屋面材料。这种材料具有表观密度低和导热系数小的特点,其它性能均满足屋面使用质量要求,符合国家对建筑节能和生态建材的需求,是一种有较大发展前景的绿色建筑材料。     

水化硅酸钙粉体对硅橡胶的补强作用

将在较低温度与压力条件下动态水热合成的白色水化硅酸钙粉体作为硅橡胶填料,制备通用型硅橡胶复合材料。研究了不同水热合成制度制备的水化硅酸钙粉体性质及水化硅酸钙粉体、碳酸钙、石英矿粉对硅橡胶力学性能的影响,实验结果表明：在120℃±5℃的条件下制备的水化硅酸钙粉体对硅橡胶具有良好的增强性能;除粉体粒径大小外,其表面反应活性也是影响补强作用的重要因素。