On the enhanced properties of composite asphalt via adding surface modified calcium sulfate whisker-SBR

With the aim of improving the durability and safety,erosion time,and cost-effective of asphalt road,a composite of modified calcium sulfate whisker-styrene butadiene rubber modified asphalt(MCSWSBRMA)was prepared via thermal doping.Firstly,stearic acid and titanate coupling agent(NDZ-201)were used as a modifier to transform calcium sulfate whisker(CSW)into MCSW via wet modification method at 60℃and anhydrous ethanol as a dispersant.What is more,the optimum loading of modifier(a mixture of 25%stearic acid+75%NDZ-201)was found to be at 2%to prepare MCSW.Subsequently,a composite of MCSW-SBRMA was prepared with different loading of MCSW(i.e.2%to 8%)to enhance the softening point of asphalt.In this study,it was found that 4%of modifiers was the best composition to improve the MCSW-SBRMA properties as elucidated in the orthogonal experiment table L_(16)(42).The effects of MCSW and SBR addition on several properties of asphalt were studied by multiple routine tests including penetration,segregation test,and so on.The results show that:2%to 8%MCSW can increase the softening point of SBR modified asphalt(SBRMA)by 7%to 8%.4%MCSW increased the PG of SBRMA from 64 to 70,which greatly improved the high temperature characteristics of asphalt.The 5℃ductility of MCSW-SBRMA is greater than 100 cm,which greatly improves the low temperature performance of asphalt.Through the application of fluorescence microscopy(FM),Fourier transform infrared spectroscopy(FTIR),Scanning electron microscopy(SEM),and energy dispersive spectroscopy(SEM-EDS),it has been demonstrated that MCSW-SBR effectively alters asphalt in a highly uniform manner,with some MCSW still retaining large cross sections,thereby facilitating the dispersion of shear stress and enhancing the durability of asphalt.

Exploration of As(Ⅲ)/As(V) Uptake from Aqueous Solution by Synthesized Calcium Sulfate Whisker

Although common calcium-containing minerals such as calcite and gypsum may fix arsenic, the interaction between modified calcic minerals and arsenic has seldom been reported. The uptake behavior of As(Ⅲ)/As(V) from aqueous solutions by calcium sulfate whisker(CSW, dihydrate or anhydrite) synthesized through a cooling recrystallization method was explored. A series of batch experiments were conducted to examine the effect of p H, reaction time, whisker dosage, and initial As concentration. X-ray diffraction(XRD) and scanning electron microscopy(SEM) were used to characterize the samples prepared. The results showed that p H of the aqueous solution was an important parameter for As(Ⅲ)/As(V) uptake, and an excellent removal efficiency could be achieved under strongly alkaline condition. The data from batch experiments for reaction of As(V) with calcium sulfate dihydrate whisker(CSDW) and calcium sulfate anhydrous whisker(CSAW) were well described with extended Langmuir EXT1 model, from which theoretic maximum adsorption capacity of 46.57 mg As(V)·(g CSDW)-1and 39.18 mg As(V)·(g CSAW)-1were obtained. Some calcium arsenate solids products,such as Ca As O3(OH)(weilite, syn), Ca3(As O4)2(calcium arsenate), Ca O–As2O5, Ca–As–O, Ca5(As O4)3OH·x H2O(calcium arsenate hydroxide hydrate), and Ca H(As O4)·2H2O(hydrogen calcium arsenic oxide hydrate), were detected at p H = 12.5 through XRD analysis. This indicates that the interaction mechanism between As(V) and CSW is a complex adsorption process combined with surface dissolution and chemical precipitation.

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.

Calcium sulfate whisker prepared by flue gas desulfurization gypsum:A physical–chemical coupling production process

In this paper,the solid waste desulfurization gypsum produced by coal-fired power plants was used as a raw material to prepare calcium sulfate whiskers with high application prospects.Calcium sulfate whiskers with uniform morphology and high aspect ratio can be prepared by hydrothermal method in sulfuric acid solution.A new process of desulfurization gypsum activated by high-energy grinding to reduce the reaction temperature and sulfuric acid concentration was developed.Through the comparison of product morphology,the best grinding time was determined to be 3.5 h.The mechanism of desulfurization gypsum through physical–chemical coupling to reduce energy consumption was clarified.The activation of desulfurization gypsum by grinding and the acidic environment provided by the sulfuric acid solution made the calcium sulfate solution reached rapid saturation and accelerated the nucleation rate.By calculating the conversion and crystallization rate of calcium sulfate whiskers,it was found that there were obvious"autocatalytic"kinetic characteristics during the crystallization process.

Hydrothermal synthesis of calcium sulfate whisker from flue gas desulfurization gypsum

Plenty of flue gas desulfurization(FGD) gypsum generated from coal-fired power plants for sulfur dioxide sequestration caused many environmental issues. Preparing calcium sulfate whisker(CSW) from FGD gypsum by hydrothermal synthesis is considered to be a promising approach to solve this troublesome problem and utilize calcium sulfate in a high-value-added way. The effects of particle size of FGD gypsum, slurry concentration,and additives on CSW were investigated in this work. The results indicated that fine particle size of FGD gypsum and moderately high slurry concentration were beneficial for crystal nucleation and growth. Three additives of magnesium chloride, citric acid, and sodium dodecyl benzene sulfonate(SDBS) were employed in this study. It was found that mean length and aspect ratio of CSW were both decreased by the usage of magnesium chloride,while a small quantity of citric acid or SDBS could improve the CSW morphology. When multi-additives of citric acid-SDBS were employed, the mean length and aspect ratio increased more than 20%. Moreover, surface morphology of CSW went better, and the particle size and crystal shape became more uniform.

Removal and utilization of calcite existed in scheelite by preparation of calcium sulfate whiskers

In order to eliminate the effect of calcite associated with scheelite on the scheelite flotation, hydrochloric acid was used to dissolve the calcite, and the soaking solution was used to prepare CaSO_4 whiskers by hydrothermal reaction with sulfuric acid at ambient pressure. First, the condition experiments of preparing CaSO_4 whiskers by using CaCl_2 and H_2SO_4 were carried out to optimize reaction parameters of the crystallization process. The optimal conditions were: at 102 ℃ reaction temperature, 0,5 mol/L reactant concentration and 60 min reaction time. Then based on the condition experiments and considering keeping acid concentration stable for achieving HCl recycling, Calcium sulfate whiskers with the average diameter of 1.41 μm and the average aspect ratio of 109 were prepared by the soaking solution after evaporating to half of its volume and 1.0 mol/L H_2SO_4 at 102 ℃ for 60 min: After ion exchange processing,the filtrate could be used as HCl in the process of HCl dissolution.

稀土石膏母液循环法制备硫酸钙晶须及其晶型转换和性能研究

以稀土冶金过程产生的废渣(稀土石膏)为原料,采用微波法制备硫酸钙晶须,随后探讨母液循环对硫酸钙晶须制备及其晶型转化的影响,明确了硫酸钙晶须晶型转换条件,最后探究硫酸钙的性能。通过X射线衍射仪(XRD)、扫描电子显微镜(SEM)、热重-差热分析仪(TG)、傅里叶红外光谱仪(FT-IR)和原子力-拉曼光谱仪和荧光光谱仪(F-4600)等仪器对硫酸钙晶须的结构、形貌和性能进行表征和分析。结果表明:母液循环3次后,晶须的形貌和晶体结构稳定,平均长度为92.4μm,长径比为13.7,可见母液循环方案可行。循环后的产物通过调控干燥温度进行烘干,在80℃、90℃和420℃下分别制备出二水、半水和无水硫酸钙晶须,3种硫酸钙晶须均具有吸收紫外光和发射蓝光的性能,其中半水硫酸钙晶须的发光性能最好。固废与母液循环提高了废渣和废液处理过程中的资源利用效率,减少了对环境的不良影响。通过对硫酸钙晶须晶型的调控并赋予硫酸钙晶须发光特性,为探究硫酸钙晶须应用领域提供新方向,同时为稀土冶金的清洁化生产提供了新思路。

Mechanical Properties and Microstructure of CaSO4 Whisker Reinforced Cement Mortar

Calcium sulfate whisker(CaSO4 whiskers), a new type of microfiber material, was used in cement matrix to increase the strength of the cement based composites. Effect of CaSO4 whiskers on the mechanical properties of the resulting cement mortar was also studied. The results showed that the flexural strength and compressive strength of the mortar specimen was improved as high as 28.3% and 8.5% by incorporating 5 wt% CaSO4 whiskers. Also, the chemical composition and structural transformation of the hardened cement matrix with CaSO4 whiskers were identified by X-ray diffraction(XRD) and scanning electron microscope(SEM). Conclusion can be drawn that CaSO4 whiskers can effectively retard the formation and restrict the coalescence of micro-crack expansion. The interaction mechanism of CaSO4 whisker on the reinforcement is mainly on three aspects: whisker pullout, crack deflection, and crack bridging. Mercury intrusion porosimetry(MIP) tests have confirmed that for 28 d cement mortar, the harmless pores increased from 9.33% to 10.62%, and the harmful pores decreased from 2.08% to 1.90%. Therefore, the whisker can optimize the pore size distribution of the resulting cement mortar.

硫酸钙晶须混凝土冻融性能研究

研究目的:在我国北方寒冷地区,河流众多,混凝土结构不仅承受冻融循环的影响,还会在汛期遭受河流中泥砂和碎石的反复冲击与摩擦,导致耐久性显著劣化。为提高混凝土的耐久性,加入高强度、高弹性模量的纤维材料是一种有效的解决方案。本文以华北地区某高铁桥梁工程的桥用混凝土为研究对象,通过加入一定掺量的硫酸钙晶须,开展C40和C60硫酸钙晶须混凝土(calcium sulfate whisker concrete,CSWC)的冻融试验和冲磨试验,分析冻融循环作用和冲磨作用对CSWC耐久性的影响。研究结论:(1)掺入CSW后,CSWC的冻融性能和力学性能均较普通混凝土有显著改善;(2)当CSW掺量为5 kg/m^(3)时,冻融循环及冲磨耦合作用下的表面性能提升效果最佳;(3)建立了基于塑性微应变的CSWC冻融损伤发展模型,并据此预测了其抗冻耐久性寿命;(4)本研究结果可为混凝土耐久性提升提供理论依据,并对CSWC在我国北方寒冷地区的实际应用具有指导意义。

硫酸钙晶须/SBS复合改性沥青性能研究

为分析硫酸钙晶须(Calcium Sulfate Whisker,CSW)与苯乙烯-丁二烯-苯乙烯嵌段共聚物(Styrene⁃buta⁃diene⁃styrene Block Copolymer,SBS)复合改性沥青的常规物理性能和高低温流变性,采用沥青三大指标、动态剪切流变(Dynamic Shear Rheology,DSR)和弯曲梁流变(Bending Beam Rheology,BBR)试验,研究了不同CSW掺量对复合改性沥青基本性能和高低温流变性能的影响,并设置CSW改性沥青为对照组。研究结果表明:随着CSW掺量增加,CSW改性沥青的温度敏感性和高温性能提高而低温性能下降;掺量10%CSW改性沥青的针入度指数PI为-0.83,车辙因子G^(*)/sinδ为27.70 kPa,蠕变劲度模量S为368 MPa,蠕变速率m为0.271;CSW/SBS复合改性沥青的温度敏感性和高低温流变性能较CSW改性沥青均明显提高,其中,PI、G^(*)/sinδ和m分别提升了147.0%、82.3%和7.4%,S降低了19.5%。同时,掺量8%CSW/SBS复合改性沥青的高温、低温PG等级分别为82℃和-18℃,比CSW改性沥青的高低温等级分别升了两级和一级。因此,CSW可明显改善沥青的高温性能和温度敏感性,但对沥青低温性能稍微不利,若将其与SBS进行复合改性,可保证沥青的低温性能。

固相反应合成MgAl_(2)O_(4)多孔纤维的研究

MgAl_(2)O_(4)纤维的主要制备方法为气相法,但该方法存在反应温度高、制备成本高以及产率低等问题。将碱式硫酸镁晶须作为模板,分别与铝溶胶或α-Al_(2)O_(3)微粉混合,通过固相反应制备了MgAl_(2)O_(4)多孔纤维,研究了热处理温度(1000、1100和1300℃)和保温时间(3、10 h)以及铝源(铝溶胶和α-Al_(2)O_(3)微粉)对MgAl_(2)O_(4)多孔纤维合成的影响。结果表明:1)与α-Al_(2)O_(3)微粉相比,以铝溶胶为铝源时,纤维中MgAl_(2)O_(4)生成量更高;2)随着热处理温度的升高,Al_(2)O_(3)与MgO逐渐反应完全,MgAl_(2)O_(4)的生成量不断增加,MgAl_(2)O_(4)多孔纤维上有小而均匀的纳米孔;3)最佳制备工艺是以铝溶胶为铝源,在1300℃保温3 h。

硫酸钙晶须的制备及应用研究进展

硫酸钙晶须是一种性能优良的改性增强材料,但由于目前制备的硫酸钙晶须的产率较低、质量较差,致使其在实际应用中受到一定的限制。为推动该问题的解决,本文介绍了当前硫酸钙晶须的制备方法,分析了各方法的优缺点,并介绍了硫酸钙晶须在材料改性及环境材料等方面的应用,对今后硫酸钙晶须的开发及应用研究提出了一些建议。

Mg^(2+)、Al^(3+)对制备半水硫酸钙晶须形貌和尺寸的影响

以二水硫酸钙为原料,通过水热法制备半水硫酸钙晶须,在探究反应温度、反应时间对晶须形貌和尺寸影响基础上,分别系统考察了Mg^(2+)、Al^(3+)浓度对其形貌和尺寸的影响。实验结果表明:在料浆质量分数为2%、反应温度为160℃、反应时间为6 h条件下制备的产物其平均长度为273.4μm,平均长径比达到30.4,晶须的形貌为针状且较为均一。在低浓度的Mg^(2+)存在下,半水硫酸钙晶须的直径小,长径比高;Al^(3+)对半水硫酸钙晶须沿c轴的生长有较强的抑制作用,得到的晶须呈现棒状或者纺锤体状。

阳离子对制备半水硫酸钙晶须影响的研究进展

可溶性离子对半水硫酸钙晶须的形貌和晶体生长的影响非常显著,为了深入理解晶须调控的基础理论,本文总结了脱硫石膏中不同种类和浓度的可溶性阳离子对晶须制备影响的研究进展。低浓度的Na^(+)对半水硫酸钙晶须的影响较小,几乎不影响晶须的形貌和表面光滑程度;K^(+)的含量适宜在3%(质量分数)及以下,较高含量下反而对半水硫酸钙晶须的生长有不利影响;Mg^(2+)使晶须表面更均匀,结晶度更高;微量具有选择性吸附作用的Al^(3+)对晶须长径比几乎没有影响;与K^(+)相类似,Fe^(3+)也具有最佳浓度,适宜低于2 mmol/L;与上述各阳离子不同的是,Cu^(2+)并非来自原料之中,是一种额外引入的离子,掺加适量的Cu^(2+)有利于形成表面光滑均匀的晶须。

磷石膏常压制备二水硫酸钙晶须机理研究

磷石膏是湿法磷酸工艺产生的大宗固体废弃物,堆存量大且对环境污染严重,因此,亟需对磷石膏进行除杂提纯以实现其高值化利用。本文以盐酸为溶剂对磷石膏进行热析提纯,得到了高品质、高长径比二水硫酸钙晶须,基于分子动力学对晶须生长机理进行了模拟。结果表明:在反应温度80℃、反应时间1.5 h、盐酸浓度4 mol/L条件下,热析提纯后磷石膏中二水硫酸钙质量分数由82.50%提升至99.80%,P_(2)O_(5)含量由1.78%(质量分数,下同)降低至0.03%,SiO_(2)含量由7.37%降低至0.02%,氟几乎完全去除,最终得到二水硫酸钙晶须制品。模拟计算表明:298 K条件下,二水硫酸钙在盐酸中比在纯水中更易溶解,且随温度升高,二水硫酸钙溶解度降低。此外,二水硫酸钙(020)面间距最小,该面硫酸钙离子排列更加紧密,有利于形成完整有序的晶体。晶须生长机制为二水硫酸钙在盐酸环境下先逐渐溶解,随着温度升高,溶液开始过饱和,析出硫酸钙晶体并形成晶核,晶体沿二水硫酸钙(020)面螺旋位错生长,形成二水硫酸钙晶须。

Direct transformation of FGD gypsum to calcium sulfate hemihydrate whiskers:Preparation,simulations,and process analysis

Calcium sulfate hemihydrate （CSH） whiskers were synthesized by phase transition in CaCl2 solution under atmospheric pressure. Analytical-grade calcium sulfate dihydrate （AR CSD） was used as the raw material for the synthesis of CSH whiskers, according to orthogonal experiments. The effects of reaction tem- perature, AR CSD content, H2SO4 content, and reaction time were investigated, and the crystallization conditions were optimized. The as-prepared CSH whiskers displayed a regular morphology and a highly uniform size, with an aspect ratio of 105, A simulation system was also established by blending various sulfates with AR CSD, to evaluate the effects of impurities in flue gas desulfurization （FGD） gypsum. The main aim was to prepare CSH whiskers directly from FGD gypsum, without any purification, using the optimized conditions. This is a facile potential alternative process for large-scale production of CSH whiskers using abundant FGD gypsum as source materials.

Preparation of calcium sulfate whiskers from FGD gypsum via hydrothermal crystallization in the H_2SO_4-NaCl-H_2O system

Little attention has thus far been paid to the potential effect of solution composition on the hydrothermal crystallization of calcium sulfate whiskers prepared from flue-gas desulfurization（FGD） gypsum.When purified FGD gypsum was used as raw material,the morphology and phase structure of the hydrothermal products grown in pure water,H2SO4-H2O,NaCl-H2O,and H2SO4-NaCl-H2O solutions as well as the solubility of purified FGD gypsum in these solutions were investigated.The results indicate that calcium sulfate whiskers grow favorably in the H2SO4-NaCl-H2O system.When prepared using 10-70 g NaCl/kg gypsum-0.01 M H2SO4-H2O at 130 ℃ for 60 min,the obtained calcium sulfate whiskers had diameters ranging from 3 to 5 ｜xm and lengths from 200 to 600 ｜xm,and their phase structure was calcium sulfate hemihydrate（HH）.Opposing effects of sulfuric acid and sodium chloride on the solubility of the purified FGD gypsum were observed.With the co-presence of sulfuric acid and sodium chloride in the reaction solution,the concentrations of Ca2＋ and SO42- can be kept relatively stable,which implies that the crystallization of the hydrothermal products can be controlled by changing the concentrations of sulfuric acid and sodium chloride.

Influence of disodium hydrogen phosphate dodecahydrate on hydrothermal formation of hemihydrate calcium sulfate whiskers

The influence of Na2HPO4·12H2O on the hydrothermal formation of hemihydrate calcium sulfate（CaSO4·0.5H2O） whiskers from dihydrate calcium sulfate（CaSO4·2H2O）at 135 ℃ was investigated.Experimental results indicate that the addition of phosphorus accelerates the hydrothermal conversion of CaSO4·2H2O to CaSO4·0.5H2O via the formation of Ca3（PO4）2 and produces CaSO4-0.5H2O whiskers with thinner diameters and shorter lengths.Compared with the blank experiment without Na2HPO4·12H2O,the existence of minor amounts（8.65 ×10-4-4.36 × 10-3 mol/L） of Na2HPO4·12H2O led to a decrease in the diameter of CaSO4·0.5H2O whiskers from 1.0-10.0 to 0.5-2.0 μm and lengths from 70-300 to50-200 μm.

硫酸钙晶须制备与应用研究进展

工业副产石膏是我国重要大宗固废,但综合利用率偏低,其大量堆积会浪费土地资源及污染环境。硫酸钙晶须是一种新型无机材料,广泛应用于建筑、医学、高分子材料改性等领域。将工业副产石膏转变为硫酸钙晶须,使其变废为宝资源化利用,可以提高企业经济效益,符合我国绿色发展的主题,具有广阔的市场前景。介绍了硫酸钙晶须各相态间的相互转换关系、制备硫酸钙晶须常见的工业石膏种类、硫酸钙晶须的制备方法及特点,总结了硫酸钙晶须的最新应用进展,并对硫酸钙晶须资源综合利用前景提出展望和建议。

One-step synthesis of basic magnesium sulfate whiskers by atmospheric pressure reflux

We have developed a one-step process for the synthesis of basic magnesium sulfate （5Mg（OH）2-MgSO4-3H20, abbreviated as 513MOS） whiskers from MgSO4,7H20 and MgO by refluxing at atmospheric pressure. The process shows potential for the low-cost mass production of controlled- structure whiskers. Their 0.3-1.0 μm diameter and 40-80 μm length correspond to an aspect ratio of 40-260. The 513MOS whisker morphology is related closely to MgSO4 concentration and reflux time. The optimized MgSO4 concentration is 1.2-1.5 mol/L with a 25-30 h reflux time. X-ray diffractometry revealed that the b-axis is the predominant growth direction of the whiskers. Their growth mechanism is by the relatively slow liquid-phase deposition of Mg2＋, OH-, and SO42-. The long reaction time and high MgSO4 concentration are conducive to the formation of 513MOS whiskers under gentle reaction conditions. Porous MgO whiskers with a fibrous structure were obtained after calcination of the 513MOS whiskers at 1020 ℃.