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1.
通过温度-应力试验研究了钙质和镁质膨胀剂(Type-CaO, Type-MgO)对混凝土早期抗开裂性能的影响。结果表明,掺10%Type-MgO和Type-CaO膨胀剂混凝土的绝热温升较基准混凝土分别提高了3.6%和14.0%,断裂温度相对基准混凝土分别降低了9.7℃和1.7℃;约束条件下,掺10%Type-MgO膨胀剂混凝土的极限拉伸值和断裂应力相对基准混凝土均提高约27%,而掺10%Type-CaO膨胀剂混凝土的极限拉伸值和断裂应力与基准混凝土无明显区别;数据表明,镁质膨胀剂相比钙质膨胀剂可以明显提高混凝土的早期抗开裂性能,钙质膨胀剂不宜用于大体积混凝土的裂缝控制。  相似文献   
2.
In the wake of increasing environmental constraints, this work is aimed at developing a catalyst purely prepared from waste biomass source as the raw material. The catalyst is investigated for its applicability in transesterification of vegetable oil with the objectives: (i) to use waste shells of mollusk as raw material for the preparation of activated carbon and CaO; (ii) to use it as heterogeneous catalyst in the transesterification of waste cooking oil; (iii) to optimize the different parameters affecting the transesterification reaction; and (iv) to study its reusability. Under optimized conditions it was observed that a conversion >90% was possible and the catalyst could be reused five times with a slight loss in activity. This study indicates that the biomass source could also be used as a potential raw material in the synthesis of environmentally benign catalysts.  相似文献   
3.
ABSTRACT

The comparative studies of grain refinement of commercial purity Mg by CaO/Ca addition have been investigated by using TP-1 tests, optical microscope, XRD characterisation and TEM (STEM) observation along with EDX analysis. Experimental results showed that Ca/CaO addition significantly refines the grain structure of commercial purity Mg. Compared with Ca addition, CaO exhibits finer grain size and the average grain size remains invariable with further CaO addition. CaO addition is readily reduced to Ca by Mg melt and forms Mg2Ca on the surface of MgO particles. First-principle calculations were used to understand the nucleation of Mg2Ca layer by a coherent interface model calculating the work of adhesion and the interface energy between Mg2Ca and α-Mg. The combination of experiments and calculations showed that the formation of Mg2Ca layer on MgO facilitates the nucleation of α-Mg and then refines the grain structure by Ca or CaO addition.  相似文献   
4.
Well-sintered CaO granules with hydration resistance are very important for the manufacturing and application of CaO-containing refractories. CaO granules with sol-processed metal oxide protective layers were prepared by granulation and surface treatment. The obtained results indicated that the usage of nano sol greatly improved the hydration resistance of CaO granules, especially when the CaO granules were treated by alumina sol. The promoting effect of nano sols in the sintering processes improved the density of CaO granules. Nanoparticles reacted with lime at lower temperature and a new phase was formed uniformly in the treated layer, which promoted densification of the treated layer. The grain size of CaO granules in the treated layer was increased obviously with the promotion of sintering. Moreover, nanoparticles were favorable for the formation of direct bonding between CaO grains by decreasing the dihedral angle.  相似文献   
5.
The effect of non-uniform temperature on the sorption-enhanced steam methane reforming (SE-SMR) in a tubular fixed-bed reactor with a constant wall temperature of 600 °C is investigated numerically by an experimentally verified unsteady two-dimensional model. The reactor uses Ni/Al2O3 as the reforming catalyst and CaO as the sorbent. The reaction of SMR is enhanced by removing the CO2 through the reaction of CaO + CO2 → CaCO3 based on the Le Chatelier's principle. A non-uniform temperature distribution instead of a uniform temperature in the reactor appears due to the rapid endothermic reaction of SMR followed by an exothermic reaction of CO2 sorption. For a small weight hourly space velocity (WHSV) of 0.67 h?1 before the CO2 breakthrough, both a low and a high temperature regions exist simultaneously in the catalyst/sorbent bed, and their sizes are enlarged and the temperature distribution is more non-uniform for a larger tube diameter (D). Both the CH4 conversion and the H2 molar fraction are slightly increased with the increase of D. Based on the parameters adopted in this work, the CH4 conversion, the H2 and CO molar fractions at D = 60 mm are 84.6%, 94.4%, and 0.63%, respectively. After CO2 breakthrough, the reaction of SMR dominates, and the reactor performance is remarkably reduced due to low reactor temperature.For a higher value of WHSV (4.03 h?1) before CO2 breakthrough, both the reaction times for SMR and CO2 sorption become much shorter. The size of low temperature region becomes larger, and the high temperature region inside the catalyst/sorbent bed doesn't exist for D ≥ 30 mm. The maximum temperature difference inside the catalyst/sorbent bed is greater than 67 °C. Both the CH4 conversion and H2 molar fraction are slightly decreased with the increase of D. However, this phenomenon is qualitatively opposite to that for small WHSV of 0.67 h?1. The CH4 conversion and H2 molar fraction at D = 60 mm are 52.6% and 78.7%, respectively, which are much lower than those for WHSV = 0.67 h?1.  相似文献   
6.
燃煤锅炉污染物超低排放标准对电厂脱硫和脱硝系统提出了更高的要求。CaO作为脱硫剂可以实现循环流化床锅炉烟气中SO2的高效脱除,焦炭作为还原剂直接还原NO,同时CaO的存在对焦炭还原NO起催化作用,可以实现燃煤烟气中SO2/NO的联合脱除。为了探究连续温度变化对CaO/生物质焦联合脱硫脱硝性能的影响,在钙循环捕集CO2技术背景下,研究了等速升温流态化下CaO/生物质焦的SO2/NO联合脱除特性。探究了烟气中O2和CO2CaO/椰壳焦脱除SO2/NO的影响。结果表明,O2通过对椰壳焦表面碳原子的活化作用降低了异相还原NO温度,在300~950℃等速升温过程中CaO/椰壳焦的NO脱除效率逐渐增加,780℃以上能实现100%脱硝。O2也提高了CaO/椰壳焦的脱硫效率。CO2CaO的碳酸化反应以及与椰壳焦的气化反应对同时脱除SO2/NO有明显抑制作用。O2和CO2共同作用下,在500~800℃内CaO/椰壳焦的脱硝效率随温度升高而增加,脱硫效率先降低后升高。NO促进了CaO/椰壳焦脱除SO2,而SO2对脱硝有抑制作用。800℃时CaO/椰壳焦同时脱除SO2和NO的效率分别为97.7%和93.9%。  相似文献   
7.
A calcified roasting−acid leaching process was developed as a highly effective method for the extraction of valuable metals from low nickel matte in the presence of CaO additive. The influences of process parameters on the metal extraction were studied, including the roasting temperature, roasting time, addition of CaO, H2SO4 concentration and liquid−solid ratio. Under the optimum condition, 94.2% of Ni, 98.1% of Cu, 92.2% of Co and 89.3% of Fe were recovered. Additionally, 99.6% of Fe was removed from the leachate as goethite by a subsequent goethite iron precipitation process. The behavior and mechanism of CaO additive in the roasting process was clarified. The role of CaO is to prevent the formation of nonferrous metal ferrite phases by a preferential reaction with Fe2O3 during the roasting process. The metal oxides (CuO and NixCu1−xO) remained stable during high-temperature roasting and were subsequently efficiently leached using a sulfuric acid solution.  相似文献   
8.
Improving the hydration resistance of CaO aggregates is the key to successful application of lime-based refractories in metallurgical industry. Additive Zr(OH)4 and Al(OH)3 were introduced in the preparation of CaO granules using granulation equipment and calcination method in this study. The results showed that the hydration resistance of CaO granules was improved significantly, especially for granules with 0.6 wt.% Zr(OH)4 and 0.9 wt.% Al(OH)3, respectively. The shell of CaO granules was relatively dense after calcination and the volume of open pores of CaO granules decreased from 3.56 × 10−2 to 1.80 × 10−2 cm3/g when additive was introduced. Zr(OH)4 and Al(OH)3 have the opposite effect on the closed porosity of CaO granules, the closed porosity of CaO granules was decreased with Zr(OH)4 addition, but increased with Al(OH)3 addition.  相似文献   
9.
Well-dispersed concentrated aqueous suspensions of Al2O3-doped Y-TZP (AY-TZP), AY-TZP with 5.4 vol% of CaO–P2O5–SiO2 (CaPSi) glass (AY-TZP5) and 10.5 vol% CaPSi glass (AY-TZP10), with ammonium polyacrylate (NH4PA) dispersant were prepared to produce slip cast compacts. The rheological properties of 35 and 40 vol% slips were studied. The densification, microstructure as well as hardness and fracture toughness were investigated as a function of CaPSi glass content at 1300°C-1500°C. The optimum NH4PA concentration of 35 vol% AY-TZP5 and AY-TZP10 slips at pH ~9 was found to be about 43% and 67% greater than that of AY-TZP slips; this behavior was related to the greater amounts of Ca2+ ions leached out from the CaPSi glass surface. The viscosity of stabilized 40 vol% slips with NH4PA attained a minimum value at 5.4 vol% CaPSi glass addition, and resulted in a more dense packing of cast samples. AY-TZP5 can be sintered at a lower temperature (1300°C) compared to that of AY-TZP. AY-TZP5 exhibited a fine microstructure of tetragonal ZrO2 (grain sizes below 0.3 µm), and ZrSiO4–Ca2P2O7 particles homogeneously distributed within the zirconia matrix. It presented similar fracture toughness and a slightly lower hardness compared to those of AY-TZP.  相似文献   
10.
Transparent MgO·1.5Al2O3 spinel ceramics were successfully prepared via reactive sintering of Al2O3 and MgO raw powders followed by hot isostatic pressing (HIP) using CaO as the sintering additive. The effects of CaO on the densification process, microstructure and optical quality of samples were investigated. It was found that the amount of CaO played an important role in the sintering process. By adding 0.05?wt% CaO, the sample with high transmittance (82.3% at 400?nm), small grain size (<5?μm) and high strength (228?±?15?MPa) was obtained after HIPing at 1550?°C. However, when the amount of CaO increased to 0.1?wt%, non-cubic and columnar-shaped grains generated at low HIP temperatures (1550–1650?°C), which severely reduced the optical quality of resulting samples. The grains were calcium aluminates, whose formation was closely related to the molar ratio of Al2O3/MgO, CaO amount and sintereing temperature.  相似文献   
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