水泥基材料的结晶压机理研究

本文通过仪器测定了水泥基材料冻结时产生的冻胀力,试验结果发现水泥基材料冻结时也会产生冻胀力,且净浆试件冻胀力稍微大于砂浆试件,同时发现毛细孔充满液苯的砂浆试件冻结时也会产生冻胀力.结合冻胀力试验结果以及水和苯结晶过程的分析,推断冻结过程中水泥基材料内部产生冻胀力,而冻胀力产生的机理主要是结晶压.     

氯化钠、硫酸钠溶液对混凝土抗冻性的影响及其机理

研究了混凝土在质量分数为3．5％的氯化钠溶液、5．0％的硫酸钠溶液中的抗冻性,结果表明,不同的盐溶液对混凝土抗冻性有不同的影响,在氯化钠溶液中冻融时,混凝土表面产生严重的剥落;而在硫酸钠溶液中冻融时,质量损失小,原因在于氯化钠溶液冻结以后压缩塑尾较小,而硫酸钠溶液冻结后在压缩塑性很大,在溶液中冻融时混凝土的相对动弹性模量下降比在水中略为缓慢,但水灰比0．26的混凝土在硫酸钠溶液中冻融后期相对动弹性模量下降很快,过早破坏,原因在于经过一定时间硫酸盐侵蚀发挥作用以后与冻融破坏产生交互作用。     

磷酸钾镁水泥净浆抗盐冻性能研究

为了研究磷酸钾镁水泥抗盐冻性能,通过测定四种不同冻融介质中磷酸钾镁水泥净浆试件的质量损失、强度、体积变形和表观破坏形态,并与相同龄期的长期浸泡环境下的磷酸钾镁水泥净浆试件比较,借助微观手段研究磷酸钾镁水泥硬化体的物相组成和微结构.结果表明:磷酸钾镁水泥经过400次冻融循环时仍保持质量损失不超过5％、强度损失不超过25％、体积膨胀变形最大为0.275％,具有较好的抗盐冻性.四种冻融介质中,以5％硫酸钠溶液为冻融介质时破坏最严重,可作为评价磷酸钾镁水泥抗盐冻性能好坏的指标.     

路堤填垫用碱渣拌合土物理力学性能试验研究

以碱渣与粉煤灰、元明粉混合制成路堤填垫用碱渣拌合土,通过多种物理与力学性能试验对比分析元明粉的影响与拌合土的工程特性.结果表明:碱渣与粉煤灰混合后不同龄期的界限含水率和颗粒分析结果证实了两者之间存在化学作用;元明粉与碱渣中的Ca(OH)2和CaCl2发生瞬时化学反应,生成NaOH和CaSO4;粉煤灰受碱激发生成多种凝胶物质充填固体颗粒孔隙,提高土体结构胶结性;元明粉使碱渣拌合土的力学性能得到显著提高,且在掺量为0%~8%范围内,拌合土力学性能随着掺量增大呈现增大趋势;但拌合土抗冻性能差,建议加入少量水泥或NaOH活性剂来改善.     

盐碱与冻融耦合作用下再生混凝土耐久性试验研究

通过再生混凝土在3.5%NaCl、3.5%Na2SO4、3.5%NaCl+3.5%Na2SO4和水四种溶液中的冻融循环试验,分析再生混凝土在同浓度不同种类盐碱溶液中经过不同冻融次数后(N)的质量变化(△m)和动弹性模量变化(△E) ,绘制N-△m和N-△E的曲线.同时,设置单掺10%、20%粉煤灰和2%、4%硅灰为对照组,研究粉煤灰和硅灰组分别在3.5%NaCl和3.5%Na2SO4环境下混凝土的抗冻性能规律.结果表明:氯盐环境中,随冻融次数的增加,混凝土表面剥削、开裂现象明显,质量和动弹性模量损失严重,而硫酸盐环境中,冻融前期混凝土内部生成水化产物使质量增加,表面膨胀开裂,后期质量和动弹性模量急剧下降,与浓度3.5%氯盐盐冻相比,硫酸盐盐冻动弹性模量损失更大.冻融破坏强度由强到弱排序为氯盐冻、硫酸盐冻、复合盐冻、水冻;掺入粉煤灰后,氯盐环境下的混凝土抗冻性反而下降,10%掺量优于20%掺量.掺入硅灰后,硫酸盐环境下再生混凝土抗冻性提高,破坏程度要比水冻小,4%掺量优于2%掺量;最后分析了混凝土腐蚀机理.     

Experiments and insights of desalination by a freezing/thawing method at low subcooling

Desalination by freezing/thawing method was a very important method to obtain fresh water from sea water. In this work, desalination by freezing/thawing method was conducted with initial sodium chloride of 3.5 wt% in consideration of stirring speed, freezing time and subcooling. The subcooling ranged from 1.2 K to 4 K. The optimum conditions for desalination in this work were stirring speed of 200 r·min⁻¹, freezing time of 120 min, and subcooling of 3 K. The results also showed that sodium chloride cannot be effectively removed by once freezing/thawing process. The maximum removal efficiency of sodium chloride was 64.3%. Two major reasons resulting in the impurity of obtained melted water by freezing/thawing method were proposed. The first reason was the inevitable adhesion of salt solution to the surface of ice, which could be removed easily by distilled water flushing. The second reason was that salt solution was heterogeneously wrapped in the accumulated ice, which was difficult to be removed by distilled water flushing. The liquid flushing method was proposed to verify the conjecture, and the results were in accordance with the two reasons mentioned above. Additional method, such as multiple flushing liquid method, was suggested to be used during the freezing/thawing process for effectively removing sodium chloride, and obtaining fresh water.     

Experiments and insights of desalination by a freezing/thawing method at low subcooling

Desalination by freezing/thawing method was a very important method to obtain fresh water from sea water. In this work, desalination by freezing/thawing method was conducted with initial sodium chloride of 3.5 wt% in consideration of stirring speed, freezing time and subcooling. The subcooling ranged from 1.2 K to 4 K. The optimum conditions for desalination in this work were stirring speed of 200 r·min^-1, freezing time of 120 min, and subcooling of 3 K. The results also showed that sodium chloride cannot be effectively removed by once freezing/thawing process. The maximum removal efficiency of sodium chloride was 64.3%. Two major reasons resulting in the impurity of obtained melted water by freezing/thawing method were proposed. The first reason was the inevitable adhesion of salt solution to the surface of ice, which could be removed easily by distilled water flushing. The second reason was that salt solution was heterogeneously wrapped in the accumulated ice, which was difficult to be removed by distilled water flushing. The liquid flushing method was proposed to verify the conjecture, and the results were in accordance with the two reasons mentioned above. Additional method, such as multiple flushing liquid method, was suggested to be used during the freezing/thawing process for effectively removing sodium chloride, and obtaining fresh water.     

Experimental identification of ice formation in small concrete pores

Freezing of water or salt solution in the concrete pores may be the cause for severe damage and significant reduction of service life. Although being one of the main research subjects during the past decades, a complete understanding of the deterioration mechanisms is still missing. This is probably because of a lack of understanding in the freezing of a liquid solution in the very small (some 10 nm) pores. In a series of experiments, the freezing process, its initiation, continuation and the resulting damage, was studied. Calorimetric, expansion and acoustic (ultrasonic pulse transit time, acoustic emission) methods were applied to monitor heat release, mechanical deformation and damage during a series of frost cycles. The results give an insight into supercooling, salt segregation, ice front penetration and thawing characteristics. Based on these data, a qualitative sequential damage model is proposed.     

煤化工废水中硫酸钠-氯化钠-硝酸钠分离工艺研究

根据硫酸钠、氯化钠和硝酸钠溶解度曲线及Na+//Cl-、SO42--H2O三元水盐体系相图,制定了分盐结晶工艺方案,考察了一次蒸发率、冷冻温度、二次蒸发率等参数对分离效果的影响。实验结果表明:控制一次蒸发率为68%,冷冻温度为-5℃,二次蒸发率为70%,采用本方案得到了纯度为96.7%的硫酸钠、94.3%的氯化钠和98.4%的硝酸钠,产品都达到工业标准,解决了杂盐危废问题,消除了二次污染,真正实现了盐的资源化利用。     

膜法冷冻除硝工艺技术的应用

介绍了膜法冷冻除硝工艺在生产中的应用。通过采用纳滤膜法先对离子膜淡盐水中的硫酸根进行浓缩,再采用冷冻法除硝工艺使盐水中的十水硫酸钠作为产品结晶析出,达到处理硫酸根的目的。     

Reduction of fractures in dried clay-like materials due to specific surfactants

The possibility of fracture reduction as a result of application of specific surfactants during intensive drying of clay-like materials was examined in this paper. The dodecyl sulfate sodium salt (SDS) and the fluoric (FC 4430) surfactants were used for the tests. Different amounts of these surfactants were mixed with distilled water and used for wetting a dry clay material before forming clay samples. The clay samples in the form of cylinders 44 mm in diameter and 50 mm high were extruded and after leveling the moisture distribution subjected to convectively drying in hot air at 120 °C. The acoustic emission (AE) method was used to monitor on line the development of crack formation in dried samples. It was stated that application of surfactants in a prescribed amount may significantly reduce the drying induced fractures in clay during its intensive drying and thus to obtain good quality products by high drying rates.     

超硫水泥混凝土抗盐冻性能及提升研究

通过测试不同盐冻循环次数后超硫水泥混凝土的表面剥落质量和超声波相对动弹性模量,并对气泡结构参数进行表征,系统探究了引气剂对超硫水泥混凝土抗盐冻性能的影响规律,以及弱碱性激发剂——乳酸钠对超硫水泥混凝土抗盐冻性能的提升效果。研究结果表明,添加引气剂可有效提高超硫水泥混凝土抗盐冻性能,但会降低强度,复合掺加乳酸钠可避免强度降低。加入胶凝材料质量0.3%的引气剂,剥落质量仅为919.7 g/m²,较基准组降低了36.8%,且超声波相对动弹性模量未明显降低。引气剂的加入,改善了超硫水泥混凝土的气孔结构,降低了内部气孔间距系数和弦长大于100 μm的气孔数占比。这可以减缓冻融作用下内部微裂纹的发展速率,延缓冻融破坏过程。此外,乳酸钠通过促进超硫水泥水化使得混凝土抗盐冻性能得到增强,但提升效果主要体现在测试后期,且对混凝土气孔结构参数影响不大(28 d龄期)。     

冻结过程中水分盐分结晶相变对盐渍土压力的影响

冻胀和盐胀导致土体变形破坏对建筑基础、公路铁路路基等构成严重威胁。本文开展了冻结过程中水分盐分结晶相变对盐渍土压力的影响试验研究,结果表明:冰晶压力随着含水率的增加而增大;在一定干密度和含水率下,盐结晶压力随着含盐量的增大而增大。冻结过程中,土压力首先保持不变,然后迅速增大,最后迅速降低至稳定。冰晶压力与盐结晶压力作为张应力作用在孔隙壁上使得土颗粒间相互挤压,达到峰值应力后,土体结构破坏和土颗粒重分布导致土压力迅速降低至稳定。此外,还讨论了传统盐结晶压力方程和冰晶压力方程的适用性,最后对冰晶压力方程进行了修正。     

响应面优化Al3+配位改性天然高分子骨胶黏合材料的制备

采用Al³⁺配位改性天然高分子骨胶黏合材料,应用响应面优化法优化尿素用量、十二烷基硫酸钠(SDS)用量和配位反应温度3个因素对天然高分子骨胶黏合材料黏度和凝固点的影响。根据Box-Behnken实验设计原理,使用Design-Expert (V8.0.6.1)软件对实验进行设计与分析,以黏度和凝固点为响应量,建立响应量的回归模型,分析各因素的显著性与交互作用。结果表明最佳工艺条件为:m_尿素= 0.78g,m_SDS =0.5g,T_配位=60.56℃;响应量预测值为:凝固点4.2℃,黏度4.575Pa·s。     

A Novel Thermosensitive Poly(methyl 2-acetamidoacrylate)

The thermosensitive properties of aqueous poly(methyl 2-acetamidoacrylate) (PMAA) solutions were investigated in the absence or presence of sodium sulfate. Poly(methyl 2-acetamidoacrylate) with a molecular weight of 23,000 (PMAA-1) exhibited the cloud point. On heating the PMAA-1 solution, the transmittance began to decrease from near 34°C and increased again after the minimum value was shown at 36.0°C. The minimum transmittance increased linearly with an increasing concentration of the polymer although the minimum-transmittance temperature did not depend on polymer concentration. The minimum transmittance was affected by the pH and the 1-butanol added. This finding suggests that the cloudiness is controlled by a delicate balance of hydrophilicity and hydrophobicity and by intra- and/or inter-molecular hydrogen bonding. Poly(methyl 2-acetamidoacrylate) with a molecular weight of 15,000 (PMAA-2) did not exhibit cloudiness in distilled water. However, the addition of sodium sulfate caused cloudiness to appear. The cloud point of a PMAA-2 solution depended on concentrations of polymer and salt added. It decreased with an increase in polymer and salt concentrations. The salting-out constants were determined from the relationship between the cloud point and concentrations of polymer and salt.     

Partially acidulated reactive phosphate rock (PAPR) fertilizer and its reactions in soil

PAPR was made by partial acidulation of North Carolina phosphate rock with H₃PO₄. The PAPRs were incubated in bands in columns of two soils of contrasting P retention. The columns were sampled after freezing and sectioning with a cryomicrotome. The movement of P in soil incubated with³³P-labelled PAPR was followed by autoradiography of polished epoxy impregnated sections of the freeze-dried soil column. PAPR solubility was also studied by a sequential dialysis process using distilled deionised water. The acid solution resulting from the dissolution of monocalcium phosphate (MCP) in PAPR moved into the surrounding soil, solubilizing soil minerals and creating a low-pH front with a high concentration of P. Depending on the soil, phosphorus moved 6–14 mm away from the fertilizer/soil interface by mass flow and diffusion in two days. The increase in 0.5 M NaOH extractable P above that of untreated soil showed a maximum at the same position as the pH minimum in the soil. In both soils, the total P movement from the fertilizer band after a two day period for 50% PAPR was comparable to that for 100% acidulation (triple superphosphate), indicating that acidulations above 50% did not necessarily increase the movement of soluble P from the fertilizer pellet. Variations in pH in the fertilizer-affected soil could be explained by the net balance of acidity resulting from incoming acid P solution and release of OH^– during P sorption. The rock residue exhibited a transient loss in solubility which was reversed on subsequent dissolution, suggesting a possible surface alteration.     

土壤中蒽菲芘的超声萃取-恒能量同步荧光法测定

建立了土壤中蒽菲芘恒能量同步荧光测定方法,样品经甲醇丙酮超声提取,过无水硫酸钠柱。优化了测定三种多环芳烃的条件,三种多环芳烃的回收率在82%~114%之间。方法灵敏、准确,样品处理简便、快速,能同时测定土壤中的蒽菲芘,可用于土壤中多环芳烃含量测定。     

Water-soluble copolymers. VI. Dilute solution viscosity studies of random copolymers of acrylamide with sulfonated comonomers

Dilute solution viscosity of a series of random copolymers of acrylamide (AM) with sodium-2-acrylamido-2-methylpropane sulfonate (NaAMPS) and with sodium-2-sulfoethylmethacrylate (NaSEM) has been studied using a four-bulb shear dilution capillary viscometer. The hydrodynamic volume of the copolymers in aqueous media was determined as a function of salt concentration, temperature, shear rate, and time. A linear relationship was observed between the intrinsic viscosity [η]₀ and the reciprocal of the square root of ionic strength in sodium chloride solutions, with salt concentrations varying from 0.043M to 0.257M. Negative temperature coefficients for [η]₀ indicate a decrease in the hydrodynamic volume of the ionic polymer molecules with increasing temperature. The relative zero-shear-intrinsic-viscosity change in distilled water to 0.257M sodium chloride aqueous media is used to elucidate viscosity–structure relationships. A maximum value is reached for this parameter at a composition of about 30 mol % of ionic comonomers for AM–NaAMPS and AM–NaSEM copolymer series.     

Adsorption of Congo Red from Aqueous Solutions Using Chitosan Hydrogel Beads Formed by Various Anionic Surfactants

The structural organization of chitosan hydrogel beads (CSBs) formed by various anionic surfactants, sodium dodecyl sulfate (SDS), sodium decyl sulfate (DS), dodecyl benzenesulfonic acid sodium salt (SDBS), and dioctyl sulfosuccinate sodium salt (DSS), and their applications as adsorbents for environmental purifications were investigated using Congo red (CR) as a model dye. The adsorption capacities of CSB as a function of surfactant concentration revealed that CSBs formed by 5 g/L anionic surfactant were the most effective for CR adsorption. The structure of CSBs and their adsorption capacities for CR depend on the nature of anionic surfactants. The maximum adsorption capacities of CSB_SDS, CSB_DS, CSB_SDBS, and CSB_DSS obtained from the Langmuir isotherm model were 186.02, 209.28, 207.25, and 113.83 mg/g, respectively, indicating that CSB_DS was the best adsorbent for CR.     

Synthesis of poly(acrylic acid)/sodium humate superabsorbent composite for agricultural use

A novel poly (acrylic acid)/sodium humate superabsorbent composite was synthesized by graft copolymerization reaction of acrylic acid (AA) on sodium humate micropowder using N,N′‐methylenebisacrylamide (MBA) as a crosslinker and potassium peroxydisulfate (KPS) as an initiator in aqueous solution. The effects on water absorbency of factors such as reaction temperature, initial monomer concentration, and degree of neutralization of AA, amount of crosslinker, initiator, and sodium humate were investigated. The superabsorbent composite was characterized by scanning electron microscopy, and the graft copolymerization reaction of AA on sodium humate micropowder was characterized by IR spectroscopy. Results obtained from this study show that the water absorbency of the superabsorbent composite synthesized under optimal conditions for synthesis with a sodium humate content of 5.3% exhibited absorption of 684 g H₂O/g sample in distilled water. Water‐retention in soil is enhanced by the use of the superabsorbent composite. The effect of superabsorbent composite on the growth of corn is reported. The superabsorbent composite may be of use as water management materials for agriculture purposes in desert and drought‐prone areas. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5137–5143, 2006