Al2O3 nanoparticles in concrete and different curing media

In the present study, the effect of limewater on strength and percentage of water absorption of Al₂O₃ nanoparticles blended concrete has been investigated. Portland cement was partially replaced by Al₂O₃ nanoparticles with the average particle size of 15 nm with different amount and the specimens were cured in water and saturated limewater for specific ages. Utilizing up to 2.0 wt% Al₂O₃ nanoparticles could produce concrete with improved strength and water permeability when the specimens cured in saturated limewater while this content is 1.0 wt% for the specimens cured in tap water. The high action of fine nanoparticles substantially increases the quantity of C-S-H gel. Although the limewater reduces the strength of concrete without nanoparticles when compared with that cured in water, curing the specimens in saturated limewater results in more strengthening gel formation around Al₂O₃ nanoparticles and causes improved permeability together with high strength. In addition, Al₂O₃ nanoparticles are able to act as nanofillers and recover the pore structure of the specimens by decreasing harmful pores. Accelerated peak appearance in conduction calorimetry tests, more weight loss in thermogravimetric analysis and more rapid appearance of peaks related to hydrated products in X-ray diffraction results, all indicate that Al₂O₃ nanoparticles could improve mechanical and physical properties of the specimens.     

Physical, mechanical and thermal properties of concrete in different curing media containing ZnO2 nanoparticles

In the present work, the effect of curing medium on microstructure together with physical, mechanical and thermal properties of concrete containing ZnO₂ nanoparticles have been investigated. Portland cement was partially replaced by ZnO₂ nanoparticles with the average particle size of 15 nm and the specimens were cured in water and saturated limewater for specific ages. The results indicate that ZnO₂ nanoparticles up to maximum of 2.0% produces concrete with improved compressive strength and setting time when the specimens cured in saturated limewater. The optimum level of replacement for cured specimens in water is 1.0 wt%. Although the limewater reduces the strength of concrete without nanoparticles when it is compared with the specimens cured in water, curing the specimens bearing nanoparticles in saturated limewater results in more strengthening gel formation around ZnO₂ nanoparticles causes more rapid setting time together with high strength. Accelerated peak appearance in conduction calorimetry tests, more weight loss in thermogravimetric analysis and more rapid appearance of peaks related to hydrated products in X-ray diffraction results, all indicate that ZnO₂ nanoparticles could improve mechanical and physical properties of the specimens.     

Splitting tensile strength of concrete using ground granulated blast furnace slag and SiO2 nanoparticles as binder

In the present study, split tensile strength together with pore structure, thermal behavior and microstructure of concrete containing ground granulated blast furnace slag and SiO₂ nanoparticles have been investigated. Portland cement was replaced by different amounts of ground granulated blast furnace slag and the properties of concrete specimens were measured. Although it negatively impacts the properties of concrete at early ages, ground granulated blast furnace slag was found to improve the physical and mechanical properties of concrete up to 45 wt% at later ages. SiO₂ nanoparticles with the average particle size of 15 nm were partially added to concrete with the optimum content of ground granulated blast furnace slag and physical and mechanical properties of the specimens were studied. SiO₂ nanoparticle as a partial replacement of cement up to 3 wt% could accelerate C-S-H gel formation as a result of increased crystalline Ca(OH)₂ amount at the early age of hydration and hence increase split tensile strength of concrete specimens. The increased the SiO₂ nanoparticles’ content more than 3 wt% causes the reduced the split tensile strength because of the decreased crystalline Ca(OH)₂ content required for C-S-H gel formation. SiO₂ nanoparticles could improve the pore structure of concrete and shift the distributed pores to harmless and few-harm pores.     

TiO2 nanoparticles effects on physical, thermal and mechanical properties of self compacting concrete with ground granulated blast furnace slag as binder

In this work, strength assessments and percentage of water absorption of self compacting concrete containing different amounts of ground granulated blast furnace slag and TiO₂ nanoparticles as binder have been investigated. Portland cement was replaced by 45 wt% of ground granulated blast furnace slag and up to 4.0 wt% TiO₂ nanoparticles and the properties of concrete specimens were investigated. TiO₂ nanoparticle as a partial replacement of cement up to 3.0 wt% could accelerate C-S-H gel formation as a result of increased crystalline Ca(OH)₂ amount at the early age of hydration and hence increase strength and improve the resistance to water permeability of concrete specimens. Several empirical relationships have been presented to predict flexural and split tensile strength of the specimens by means of the corresponding compressive strength at a certain age of curing.     

纳米颗粒对水工混凝土抗冲磨性的影响及其机理研究

目前,纳米材料因其优异的性能已经在水泥基材料中得到了广泛应用。利用两种类型的纳米颗粒,即纳米二氧化硅(NS)和纳米碳化硅(NC)掺入粉煤灰水泥砂浆制备水工混凝土试样,在强度测试的基础上,研究了纳米颗粒含量对不同试样耐冲磨性的影响,并对其作用机理进行理论分析。结果表明,纳米颗粒在提高粉煤灰混凝土抗压和抗弯强度得同时也改善了抗冲磨性能;单掺NS和NC最佳添加量分别为2%和为3%,而双掺2%NS和2%NC的水工混凝土具有最优抗冲磨性能,磨损量仅为0.64 kg/m2,比参照组的磨损量降低了75%;从SEM扫描图像中得到改性机理为纳米颗粒的表面效应、火山灰反应和微观骨料填充效应,增大了骨料得表面能,改变了界面过渡区的结构,同时也填充了微结构孔隙,从而提高了粉煤灰混凝土的耐冲磨性。研究结果对设计高强度和抗冲磨性的水工混凝土具有一定指导意义。     

纳米SiO2对掺污泥焚烧灰水泥胶砂性能的影响

研究了纳米SiO₂对污泥焚烧灰-水泥复合胶凝体系性能的影响,并对其水化程度进行了分析。结果表明:随着污泥焚烧灰掺量的增加,复合胶凝体系的标准稠度用水量增加、凝结时间延长,水泥胶砂流动度降低、抗压和抗折强度降低;纳米SiO₂的掺入在一定程度上缩短了复合胶凝体系的凝结时间,提高了水泥胶砂的强度,但对工作性不利;掺入纳米SiO₂后,复合胶凝体系7 d内的化学结合水生成量和生成速率较高,纳米SiO₂对复合胶凝体系早期水化影响较大。     

Synergistic effects of inorganic tin compounds and Sb2O3 on thermal properties and flame retardancy of flexible poly(vinyl chloride)

The effects of inorganic tin compounds such as zinc hydroxystannate (ZHS), tin dioxide (SnO₂), and tin monoxide (SnO), Sb₂O₃, and their mixtures on the flame retardant and smoke suppressant properties of flexible poly(vinyl chloride) (PVC), and their flame retardant and smoke suppressant actions, were studied using the limiting oxygen index (LOI) test, the smoke density rating (SDR) test, thermogravimetric analysis/differential thermogravimetry/differential thermal analysis (TGA/DTG/DTA), scanning electron microscopy (SEM), and quantitative analysis. The results showed that the incorporation of small amounts of inorganic tin compounds and their mixtures with Sb₂O₃ can increase the LOI of PVC and decrease the SDR during combustion. Partial replacement of Sb₂O₃ in flexible PVC by ZHS resulted in a significant synergistic improvement in flame retardant behavior. TGA/DTG/DTA, SEM, and quantitative analysis showed that ZHS acts as a flame retardant in the solid phase, Zn²⁺ can catalyze dehydrochlorination of PVC and promote early cross-linking, leading to rapid charring, and Sn⁴⁺ can react with the char, thereby increasing the char stability. These actions, combined with the vapor-phase role of Sb₂O₃, can significantly enhance the flame retardancy of PVC.     

X射线荧光光谱法测定电解铝灰中SiO2、Fe2O3、MgO、CaO、K2O、Na2O、MnO、TiO2、P2O5的含量

电解铝灰、铝渣是铝在电解过程中产生的一种浮渣,电解过程中漂浮在电解槽铝液的上方,主要成分为电解过程中未反应的冰晶石、氧化铝、金属铝等混合物,回收价值较高。对电解铝灰的成分分析,相对于化学滴定等分析方法,X射线荧光光谱法样品前处理更加简单方便,且可以同时对多组分进行分析。用粉末压片-X射线荧光光谱法测定电解铝灰中SiO₂、Fe₂O₃、MgO、CaO、K₂O、Na₂O、MnO、TiO₂、P₂O₅的含量。以成分含量相近的铝土矿国家标准物质样品绘制具有一定浓度梯度的标准曲线,通过理论α系数校正方法和经验校正法校正。所得结果表明:各元素含量在标准工作曲线中标准样品的含量范围内时,测定结果和常规分析方法测定结果相符。在方法的精密度实验中,含量较高的SiO₂的极差为0.2%,其他元素值也较为稳定,满足质量要求。     

g-C3N4光催化混凝土对NO降解性能研究

研究了不同制备工艺及掺量的石墨相氮化碳(g-C₃N₄)对混凝土的力学性能及对NO气体光催化降解性能的影响及变化规律。通过TEM、SEM、XRD分别对材料的物相及微观结构进行了表征,利用微机控制全自动压力试验机和氮氧化物分析仪分别研究了掺g-C₃N₄后混凝土的抗压强度及对NO的降解性能。结果表明,四种不同种类的g-C₃N₄掺入后混凝土都具有对NO的降解作用,其中,少层g-C₃N₄的降解率最高,且在紫外线等照射24 h后其仍能保持较高的降解率;g-C₃N₄掺量不超过0.8%时混凝土的抗压强度不会有太大影响,在此范围内尽可能提高g-C₃N₄的掺量来提高其对NO的降解作用。     

Ceramsite obtained from water and wastewater sludge and its characteristics affected by (Fe2O3 + CaO + MgO)/(SiO2 + Al2O3)

To control and optimize the process for making ceramsite from wastewater treatment sludge (WWTS) and drinking-water treatment one (DWTS), the effect of mass ratios of (Fe₂O₃ + CaO + MgO)/(SiO₂ + Al₂O₃) (defined as F/SA ratios); SiO₂:Al₂O₃ and Fe₂O₃:CaO:MgO (under the condition of fixed F/SA ratio) on the characteristics of ceramsite were investigated. It was found that the optimal F/SA ratios for making ceramsite range 0.175-0.45. Na-Ca feldspars and amorphous phases increase in ceramsite as F/SA ratios increase. Ceramsite with porous surfaces, expanded structures, and complex crystalline phases can be obtained at 0.275 ≤ F/SA ≤ 0.45, which accordingly cause the decrease in compressive strength. Higher strength of ceramsite with lower porosity can be obtained at 0.175 ≤ F/SA < 0.275, and under the condition of F/SA ratio = 0.275, the raw materials can produce ceramsite with desired physical properties at 18.2:35 ≤ SiO₂:Al₂O₃ ≤ 45:10.2 and 10:2.7:1.4 ≤ Fe₂O₃:CaO:MgO ≤ 5.3:6:1.6. Ceramsite with higher compressive strength and lower porosity can be obtained at SiO₂:Al₂O₃ > 27.2:15.8 and Fe₂O₃:CaO:MgO > 6:3.5:1.8. Results indicate that F/SA ratios could be used as an important parameter to control the production process of ceramsite with desired physicochemical properties and resolve the disposal problems of residual sludges.     

某石灰窑耐热混凝土胀裂机理研究分析

针对某钢铁公司石灰窑平台混凝土胀裂现象,通过对混凝土试样进行化学分析、XRD射线衍射试验分析及扫描电子显微镜微观试验分析,并对平台结构承载能力进行验算,认为造成混凝土胀裂的主要原因为混凝土骨料中MgO含量过高,在高温条件下发生水化反应,体积膨胀而造成混凝土开裂,当混凝土开裂后造成结构承载能力不足及混凝土碳化收缩加速了混凝土的开裂.研究分析成果对相关工程的研究具有一定的参考价值.     

活性Al2O3对碱—骨料反应（ASR）的抑制与制动作用

通过试验发现,在富含活性Ａｌ２Ｏ３的混凝土体系中,虽然仍有可能发生碱－骨料反应（ＡＳＲ）,但在相同条件下,总膨胀率减小,膨胀期缩短,并最终趋于稳定,也就是说,活性Ａｌ２Ｏ３既能抑制又能制动ＡＳＲ膨胀,其原因是：在活性ＡｌｗＯ３存在的情况下,ＡＳＲ的反应产物不再是无限吸水膨胀的碱－硅酸凝胶,而是碱－铝硅酸盐凝胶,这类凝胶具有很强的结晶倾向,一旦结晶成沸石类矿物,其体积将不再因水分子的进出而胀缩,倘若     

Na2SO4对低硫水泥及其混凝土性能的影响

本文探讨了单掺Na2SO4对低硫水泥及其混凝土性能的影响。结果表明:少量的Na2SO4缩短了水泥凝结时间,有利于提高混凝土的坍落度、改善混凝土坍落度损失,而且在低温时可以明显改善混凝土的早期强度。     

Effect of different catalysts in SO2 oxidation over polymeric concrete

Polymeric concrete performance in polluted environment has been studied in order to determine outdoor pollutant transfer process. SO₂ oxidation process over different building materials in laboratory-based atmospheric flow chambers is well known; however, the effect of NO_x is not very clear. In order to clarify this process, the effect of NO_x in SO₂ oxidation over the surface of a porcelain material was studied under wetted and unwetted conditions. In the chamber, NO_x can either catalyse SO₂ reaction or undergo oxidation to NO₃⁻. The main conclusion in this work is that for the porcelain samples under wetted conditions NO and NO₂ catalysed the reaction. But in unwetted conditions NO reacts with the sample instead of SO₂.     

Performing a microfiltration integrated with photocatalysis using an Ag-TiO2/HAP/Al2O3 composite membrane for water treatment: Evaluating effectiveness for humic acid removal and anti-fouling properties

Membrane filtration has been increasingly used for water treatment and wastewater reclamation in recent years. To further improve the effectiveness of membrane process and reduce membrane fouling, a highly reactive photocatalytic membrane, Ag-TiO₂/hydroxiapiate (HAP, Ca₁₀(PO₄)₆(OH)₂)/Al₂O₃, was employed to realize microfiltration (MF) coupling photocatalysis for surface water treatment. The effectiveness on the potential of membrane was investigated by removing humic acid (HA) test under different feed total organic carbon (TOC), light intensity and transmembrane pressure (TMP). The HA removal and anti-fouling property of as-prepared membrane was improved under UV irradiation, likely due to photocatalytic degradation of foulants along with filtration simultaneously. Under given feed water composition, increasing the light intensity resulted in increased removal of HA from aqueous solution. However, a limiting TMP seems to exist beyond which the increased HA removal cannot be sustained. Fouling behavior analysis indicated that the transition in fouling mode from initial pore blocking to cake filtration occurred much slower as UV irradiated. Furthermore, a superior efficiency on removal of trace organic contaminants, as well as milder flux reduction, was presented from surface water treatment, which demonstrated that the integrated system with enhanced performance is foreseen as an emerging technique for water treatment.     

Degradation of selected pharmaceuticals in aqueous solution with UV and UV/H2O2

The degradation of four pharmaceutical compounds (PhACs), ibuprofen (IBU), diphenhydramine (DP), phenazone (PZ), and phenytoin (PHT) was investigated via ultraviolet (UV) photolysis and UV/H₂O₂ process with a low-pressure (LP) UV lamp. For each PhAC tested, direct photolysis quantum yields at 254 nm were found to be ranging from 6.32 × 10⁻² to 2.79 × 10⁻¹ mol E⁻¹ at pH 7. The second-order rate constants of the reaction between the PhACs and OH were determined to be from 4.86 × 10⁹ to 6.67 × 10⁹ M⁻¹ s⁻¹ by using a competition kinetic model which utilized para-chlorobenzoic acid (pCBA) as a reference compound. The overall effect of OH radical scavenging from humic acid (HA) and anions HCO₃⁻, NO₃⁻ was measured utilizing R_OH,UV method through examining the aqueous photodegradation of pCBA as a probe compound. Moreover, these fundamental direct and indirect photolysis parameters were applied in the model prediction for oxidation rate constants of the PhACs in UV/H₂O₂ process. It was found that the predicted oxidation rate constants approximated the observed ones. The results indicated that the new R_OH,UV probe compound method was applicable for measuring background OH radical scavenging effects in water treatment process of UV/H₂O₂. Furthermore, by GC-MS analysis, most of the intermediates created during the photodegradation of the selected PhACs in UV/H₂O₂ process were identified. For the photodegradation of PZ, a competition mechanism existed between the direct UV photolysis and the oxidation of OH. An appropriate dosage of H₂O₂ could hinder the occurrence of the direct photolysis.     

Ce^(3+)和Fe^(3+)共掺杂CaAl_(2)O_(4)高近红外反射颜料的制备与表征

离子掺杂能够调谐颜料的反射性能和颜色。采用溶胶-凝胶法制备了一系列新型低毒的Fe^(3+)、Ce^(3+)共掺杂Ca_(1-x)Ce_(x)Al_(2-y)Fe_(y)O_(4)(x=0、0.15;y=0.15、0.25、0.35)高近红外反射无机颜料。采用X-射线衍射仪(XRD)、扫描电子显微镜(SEM)、紫外/可见/近红外光谱仪及Color CIE色度分析软件对所合成复合颜料的晶体结构、微观形貌、光学性质(反射性能)和颜色等进行了表征。XRD分析表明,煅烧温度为1100℃时,所合成的样品为磷石英结构;光学性能分析表明,随着Fe^(3+)掺杂量的增加,颜料的颜色由白色逐渐变为黄色再变为深棕色。Fe^(3+)、Ce^(3+)共掺杂所制备的颜料在780~2500 nm波长范围内具有较高的近红外反射率(NIR≥61.5%)。该Ca_(1-x)Ce_(x)Al_(2-y)Fe_(y)O_(4)“冷”颜料粉体在建筑涂料等方面具有广阔的应用前景。     

TiO2 nanoparticles aggregation and disaggregation in presence of alginate and Suwannee River humic acids. pH and concentration effects on nanoparticle stability

The behavior of manufactured TiO₂ nanoparticles is studied in a systematic way in presence of alginate and Suwannee River humic acids at variable concentrations. TiO₂ nanoparticles aggregation, disaggregation and stabilization are investigated using dynamic light scattering and electrophoretic experiments allowing the measurement of z-average hydrodynamic diameters and zeta potential values. Stability of the TiO₂ nanoparticles is discussed by considering three pH-dependent electrostatic scenarios. In the first scenario, when pH is below the TiO₂ nanoparticle point of zero charge, nanoparticles exhibit a positively charged surface whereas alginate and Suwannee River humic acids are negatively charged. Fast adsorption at the TiO₂ nanoparticles occurs, promotes surface charge neutralization and aggregation. By increasing further alginate and Suwannee River humic acids concentrations charge inversion and stabilization of TiO₂ nanoparticles are obtained. In the second electrostatic scenario, at the surface charge neutralization pH, TiO₂ nanoparticles are rapidly forming aggregates. Adsorption of alginate and Suwannee River humic acids on aggregates leads to their partial fragmentation. In the third electrostatic scenario, when nanoparticles, alginate and Suwannee River humic acids are negatively charged, only a small amount of Suwannee River humic acids is adsorbed on TiO₂ nanoparticles surface. It is found that the fate and behavior of individual and aggregated TiO₂ nanoparticles in presence of environmental compounds are mainly driven by the complex interplay between electrostatic attractive and repulsive interactions, steric and van der Waals interactions, as well as concentration ratio. Results also suggest that environmental aquatic concentration ranges of humic acids and biopolymers largely modify the stability of aggregated or dispersed TiO₂ nanoparticles.     

Synthesis of mesoporous magnetic γ-Fe2O3 and its application to Cr(VI) removal from contaminated water

In this study, mesoporous magnetic iron-oxide (γ-Fe₂O₃) was synthesized as an adsorbent for Cr(VI) removal. For material synthesis, mesoporous silica (KIT-6) was used as a hard template and to drive iron precursor into KIT-6, a ‘greener’, affinity based impregnation method was employed, which involved using a nonpolar solvent (xylene) and led to recycling of the solvent. The results of Cr(VI) removal experiments showed that the synthesized mesoporous γ-Fe₂O₃ has a Cr(VI) adsorption capacity comparable with 10 nm nonporous γ-Fe₂O₃ but simultaneously has a much faster separation than 10 nm nonporous γ-Fe₂O₃ in the presence of an external magnetic field under the same experimental conditions. Cr(VI) adsorption capacity onto the mesoporous γ-Fe₂O₃ increased with decreasing solution pH and could be readily regenerated. Therefore, mesoporous γ-Fe₂O₃ presents a reusable adsorbent for a fast, convenient, and highly efficient removal of Cr(VI) from contaminated water.