地聚合物胶凝材料的性能研究

在以往对地聚合物胶凝材料的研究中,碱性激发剂的制备都需要经过24h或者更长时间的陈化,这不利于地聚合物的实际应用.以偏高岭土和粉煤灰为硅铝酸盐材料,采用不经过陈化的双组分作碱性激发剂制备地聚合物胶凝材料.研究了激发剂的掺加方式、种类、含量以及粉煤灰对地聚合物胶凝材料力学性能的影响;初步研究了地聚合物的抗硫酸盐侵蚀性能以及耐高温性能.结果表明:不经过陈化的双组分作碱性激发剂制备的地聚合物3天抗压强度可以达到45MPa,抗硫酸盐侵蚀及耐高温性能比普通硅酸盐水泥更为优异,是一种值得关注的新型胶凝材料.     

常温制备赤泥-低钙粉煤灰基地聚物的试验和微观研究

低钙粉煤灰在常温条件下合成地聚物存在反应度低、强度低的问题。本研究在低钙粉煤灰中掺入20%赤泥制备地聚物,研究其力学性质,并通过SEM、EDS和FT-IR分析地聚物的微观结构变化。进一步研究了化学配比n(Si)/n(Al)=1.8～2.5、n(Na)/n(Al)=0.8～1.1以及在100%相对湿度养护0～7 d对赤泥-粉煤灰基地聚物性质的影响。试验发现常温养护的赤泥-粉煤灰基地聚物的力学性质明显优于低钙粉煤灰基地聚物,且n(Si)/n(Al)=2.0～2.2、n(Na)/n(Al)=1.0为前者制备的最优配比,而较高的养护湿度可提高其早期强度。这证明赤泥对常温合成粉煤灰基地聚物有促进作用,并揭示了赤泥-粉煤灰基地聚物比粉煤灰基地聚物更密实的微观结构、更多的地聚物胶凝体形成和更高的反应度是前者力学性质优于后者的主要原因。     

不同活化方法对煤矸石胶凝性能的影响

主要研究了煅烧和增钙煅烧这两种活化方法对煤矸石胶凝性能的影响,同时通过NMR方法从Si、Al 原子所处环境和相互间的关系角度上对煤矸石活化过程作结构层次的研究.     

CaO增强复合胶凝材料的性能

使用重金属污泥制备免烧砖。使用CaO钙源优化配置复合胶凝材料的组分,并调控胶凝浆体中的水化产物和未水化相。先基于免烧砖原料的配合比计算复合胶凝体系的钙硅比(Ca/Si)并控制其值为0.8~1.2,设计添加CaO的免烧砖实验方案。使用核磁共振(NMR)、透射电镜-能谱等手段和PCAS分析软件,研究了CaO使高硅复合胶凝材料性能提高的机理。结果表明：随着高硅胶凝体系Ca/Si比在0.8~1.2范围内的提高,免烧砖的力学性能先提高后降低,Ca/Si比的最佳值为1.0,CaO也有一个最佳调控值。随着Ca/Si比的提高7 d试样的吸水率先降低后提高,28 d试样的吸水率线性降低。随着Ca/Si比的提高,试样中平面孔径大于200 μm的孔隙率递减,分形维数先减小后增大;对于孔径小于200 μm的孔结构,随着Ca/Si比的提高孔径为200~200 μm的孔减少,孔径小于200 nm的孔增多,孔的体积呈减小的趋势。复合胶凝体系能抑制污泥免烧砖70%以上的重金属浸出量。     

不同钙源对地聚合物反应机制的影响研究

在地聚合物体系中,反应产物会随原材料化学组成与激发条件的不同产生巨大差异,钙掺杂地聚合物的反应机理、产物组成与结构更为复杂。试验采用5种外加晶体钙源和2种非晶体外加钙源以不同比例与偏高岭土复掺制备地聚合物,研究了外加钙源对地聚合物性能和反应机制的影响。研究表明:外加钙源中Si、Al的溶出量与钙源的结构有关,Si和Al的溶出量之间存在很强的正相关性,而Ca与Si、Al的溶出量之间不存在相关性。外加钙源会降低偏高龄土基地聚合物体系的抗压强度,掺杂非晶体钙源地聚合物的抗压强度均大于掺杂晶体钙源的。外加钙源中Ca的溶出量与抗压强度之间存在负相关性。本研究为拓宽地聚合物原材料的来源和资源化利用含钙工业固体废弃物研制复合地聚合物提供了理论和试验依据。     

粉煤灰微珠表面热碱活化镀银层的制备及机理研究

对粉煤灰微珠进行热碱液活化,以葡萄糖为还原剂,通过向碱性溶液中缓慢滴入Ag NO3溶液来制备镀银复合粉体;采用扫描电子显微镜、X射线能量色散谱和X射线衍射进行形貌观察及成分分析,并探讨热碱活化化学镀银机理。结果表明:银镀层为均匀致密的纳米晶;镀银复合粉体的电阻率达到0.05Ω·cm;热碱活化化学镀银机理为强碱与Si O2和Al2O3发生强烈作用,在粉煤灰微珠表面生成大量羟基基团,其亲核性对银铵阳离子产生极性吸引并在葡萄糖的还原作用下还原为单质银。     

煤矸石质硅铝基材料胶凝机理的研究

系统地开展了利用低温煅烧煤矸石为主要原料制备早期强度高、水化热低且具有良好固土特性的硅铝基胶凝材料的基础研究.采用结构分析的方法,运用高分辨固体核磁共振、液体核磁共振和红外光谱等分析手段研究了煤矸石和高岭石在煅烧、碱介质中溶出和胶凝过程中硅、铝配位的变化,结合其胶凝产物的物相、形貌和水化热,从结构、配位和物相转变的角度来研究煤矸石质硅铝基胶凝材料胶凝机理.揭示了煤矸石的煅烧过程就是铝氧八面体中铝的四配位转化以及铝氧四面体和硅氧四面体解聚过程的重要规律,其中铝氧八面体中铝的四配位转化是煤矸石产生胶凝活性的本源.证明了煤矸石和高岭石在煅烧过程中铝配位的变化与地质界Thompson定律相吻合.比较研究了煤矸石和高岭石的活性与其结构之间的关系,发现低于900℃煅烧煤矸石的红外光谱中,560cm-1附近吸收峰的强度与Si、Al离子的溶出量具有正相关性;五配位铝是偏高岭石具有高活性的主要原因.证明了由于一价和二价阳离子的存在,以高岭石为主要矿物的煤矸石在煅烧过程中没有出现五配位铝.通过对硅铝质物料Si2p、Al2p和Ols结合能与其胶凝材料力学性能之间关系的研究,提出用硅、铝电子结合能评价硅铝物料胶凝活性的新方法.深入研究了不同介质条件下煅烧煤矸石的溶出特性及其胶凝机理.研究表明:煅烧煤矸石在碱性溶液中是以单聚体硅酸根离子和单聚体铝酸根离子的形式溶出;(HO)3SiO-和Al(OH)4-的溶出证明硅铝基胶凝材料反应初期是硅氧四面体和铝氧四面体的再解聚过程,体现在反应后,27Al和29Si NMR谱的共振峰向低场偏移;以硅酸钾为溶出介质,煅烧煤矸石溶出渣29Si MAS NMR谱中-97.36×10-6共振峰的出现揭示了硅铝基胶凝材料胶凝过程中原位键合的作用;随着反应的进行,27Al和29Si NMR共振峰都向高场偏移,表明胶凝过程中与中心铝原子在次级配位圈上直接连接[SiO4]四面体数量增多以及反应产物中硅氧四面体聚合度的增加.根据胶凝过程中硅、铝配位的变化,提出了硅铝基胶凝材料原位键合的反应机理,并将胶凝过程概括为解聚过程、胶结过程、原位键合过程和缩聚过程.     

中性盐-矿渣-粉煤灰胶结材固结核废料的适应性研究

研究了组成不同的中性盐-矿渣-粉煤灰胶结材的强度、碱度、自由水含量以及对金属Al的腐蚀性.结果表明,Na2SO4-矿渣-粉煤灰胶结材、CaSO4-矿渣-粉煤灰胶结材以及Na2SO4-CaSO4-矿渣-粉煤灰胶结材具有强度和碱度适中、对金属Al腐蚀性弱、自由水含量低的特点,可作为固结放射性废物的胶凝材料系统.     

辅助胶凝材料玻璃体结构与胶凝活性的研究进展

大宗工业副产品或废弃物(如粒化高炉矿渣、粉煤灰等)作为辅助胶凝材料用于硅酸盐水泥及混凝土中已有不短的时间.利用辅助胶凝材料可有效缓解水泥生产所带来的制备能耗高、自然资源消耗大、二氧化碳排放等问题.在胶凝材料性能不大幅降低的前提下,要实现大比例取代(≥30％(质量分数))硅酸盐水泥,激发辅助胶凝材料的活性是关键.然而,从材料学观点出发,过往基于宏观性能的经验测试方法,对辅助胶凝材料活性的理解仍相当碎片化.除比表面积等物理性质外,多数辅助胶凝材料的水硬活性取决于其中玻璃相的溶解-沉淀反应.辅助胶凝材料中的玻璃体结构可简化为网络调整体(如Ca、Na等)和网络形成体(如Si、Al等)的物质的量比,如解聚度.近来对CaO-SiO2-Al2 O3体系玻璃体的研究,进一步增强了对玻璃体聚合度的理解.玻璃体的溶解与聚合程度及溶液组成(如溶液的饱和程度、阴阳离子类型及浓度、pH等)密切相关.同时,沉淀的生成也会显著改变玻璃体的溶解动力学.本文归纳了辅助胶凝材料玻璃体结构与水硬活性的研究进展,分别对表征辅助胶凝材料玻璃体结构的解聚度及玻璃体中Si(Qn(mAl))聚合程度进行了介绍,分析了玻璃体结构在不同激发条件下的反应活性,以期为制备性能稳定和耐久性优良的低碳建筑材料提供参考.     

Al_2O_3无机薄膜的制备、热稳定性及表面自由能计算

以异丙醇铝(AIP)为前体,硝酸为胶溶剂,采用溶胶-凝胶法制备Al_2O_3无机薄膜.通过X射线衍射(XRD)、能谱分析(EDS)、红外光谱(FTIR)、热重-微分热重(TG-DTG)、接触角测试等表征,对无机薄膜的热稳定性及表面自由能进行研究.结果表明,随着焙烧温度的升高,C—H吸收峰减弱,Al—O—H键逐渐断裂,表面自由能先减小后增大;350℃时化学结构以Al—O键为主,物相结构由γ-AlOOH转变为γ-Al_2O_3,对应最强衍射峰(440)晶面处的晶粒尺寸达到4.2nm,膜材料对应的Al/O元素原子及重量百分比与Al_2O_3化学组成匹配,表面自由能达到最小值46.24×10~(-5) N/cm.     

Assessing the suitability of three Australian fly ashes as an aluminosilicate source for geopolymers in high temperature applications

Fly ash characteristics cannot be assumed to be constant between power stations as they are highly dependent on the coal source and burning conditions. It is critical to understand the characteristics of fly ash in order to produce geopolymers suitable for high temperature applications. We report on the characterisation of fly ash from three Australian power stations in terms of elemental composition, phase composition, particle size, density and morphology. Geopolymers were synthesised from each of the fly ashes using sodium silicate and sodium aluminate solutions to achieve a range of Si:Al compositional ratios. Mechanical properties of geopolymer binders are presented and the effect of the source fly ash characteristics on the hardened product is discussed, as well as implications for high temperature applications. It was found that the twenty eight day strength of geopolymers is largely dependent on the sub 20 μm size fraction of the fly ash. Strength loss after high temperature exposure was found to be dependent on the concentration of iron in the fly ash precursor and the Si:Al ratio of the geopolymer mixture.     

Fly ash-based geopolymer for Pb removal from aqueous solution

The aim of this work was to synthesis highly amorphous geopolymer from waste coal fly ash, to be used as an adsorbent for lead Pb(II) removal from aqueous wastewater. The effect of various parameters including geopolymer dosage, initial concentration, contact time, pH and temperature on lead adsorption were investigated. The major components of the used ash in the current study were SiO(2), Al(2)O(3) and Fe(2)O(3) representing 91.53 wt% of its mass. It was found that the synthesized geopolymer has higher removal capacity for lead ions when compared with that of raw coal fly ash. The removal efficiency increases with increasing geopolymer dosage, contact time, temperature, and the decrease of Pb(2+) initial concentration. The optimum removal efficiency was obtained at pH 5. Adsorption isotherm study indicated that Langmuir isotherm model is the best fit for the experimental data than Freundlich model. It was found also that the adsorption process is endothermic and more favorable at higher temperatures.     

Reduction of metal leaching in brown coal fly ash using geopolymers

Current regulations classify fly ash as a prescribed waste and prohibit its disposal in regular landfill. Treatment of the fly ash can reduce the leach rate of metals, and allow it to be disposed in less prescribed landfill. A geopolymer matrix was investigated as a potential stabilisation method for brown coal fly ash. Precipitator fly ash was obtained from electrostatic precipitators and leached fly ash was collected from ash disposal ponds, and leaching tests were conducted on both types of geopolymer stabilised fly ashes. The ratio of fly ash to geopolymer was varied to determine the effects of different compositions on leaching rates. Fourteen metals and heavy metals were targeted during the leaching tests and the results indicate that a geopolymer is effective at reducing the leach rates of many metals from the fly ash, such as calcium, arsenic, selenium, strontium and barium. The major element leachate concentrations obtained from leached fly ash were in general lower than that of precipitator fly ash. Conversely, heavy metal leachate concentrations were lower in precipitator fly ash than leached pond fly ash. The maximum addition of fly ash to this geopolymer was found to be 60wt% for fly ash obtained from the electrostatic precipitators and 70wt% for fly ash obtained from ash disposal ponds. The formation of geopolymer in the presence of fly ash was studied using 29Si MAS-NMR and showed that a geopolymer matrix was formed. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) imaging showed the interaction of the fly ash with the geopolymer, which was related to the leachate data and also the maximum percentage fly ash addition.     

Characterisation of class F fly ash geopolymer pastes immersed in acid and alkaline solutions

Acid and alkaline resistance of class F fly ash based geopolymer pastes has been investigated. As prepared geopolymers showed high solubility in both strong alkali and acid solutions. Calcination of the fly ash based geopolymers at 600 °C resulted in a decrease of amorphous component from 63.4 to 61.6 wt.%. However, the solubility of the Al, Si and Fe ions in 14 M NaOH and 18% HCl after 5 days immersion decreased from 1.3 to 16-fold in comparison to as prepared geopolymer samples. Calcination of the geopolymers also resulted in a 30% reduction in compressive strength. Acid and alkali resistance of the geopolymers investigated strongly depends on mineralogical composition change of the calcined geopolymer. Partial crystallisation of non-reacted fly ash particles in the geopolymer decreases its solubility in acid and alkali solutions.     

Reaction mechanisms in the geopolymeric conversion of inorganic waste to useful products

High-performance materials for construction, waste immobilisation and an ever-growing range of niche applications are produced by the reaction sequence known as 'geopolymerisation'. In this process, an alkaline activating solution reacts with a solid aluminosilicate source, with solidification possible within minutes and very rapid early strength development. Geopolymers have been observed to display remarkable chemical and thermal stability, but due to their largely X-ray amorphous nature have only recently been accurately characterised. It has previously been shown that both fly ash and ground granulated blast furnace slag are highly effective as solid constituents of geopolymer reaction slurries, providing readily soluble alumina and silica that undergo a dissolution-reorientation-solidification process to form a geopolymeric material. Here a conceptual model for geopolymerisation is presented, allowing elucidation of the individual mechanistic steps involved in this complex and rapid process. The model is based on the reactions known to occur in the weathering of aluminosilicate minerals under alkaline conditions, which occur in a highly accelerated manner under the conditions required for geopolymerisation. Transformation of the waste materials to the mixture of gel and nanocrystalline/semicrystalline phases comprising the geopolymeric product is described. Presence of calcium in the solid waste materials affects the process of geopolymerisation by providing extra nucleation sites for precipitation of dissolved species, which may be used to tailor setting times and material properties if desired. Application of geopolymer technology in remediation of toxic or radioactive contaminants will depend on the ability to analyse and predict long-term durability and stability based on initial mix formulation. The model presented here provides a framework by which this will be made possible.     

醋酸钙/飞灰复合脱硫脱硝剂热解性能实验研究

为了提高脱硫脱硝效率同时合理利用火电厂产生的飞灰,研究了醋酸钙中加入飞灰制备的复合脱硫脱硝剂的热解性能。对不同条件下制得的醋酸钙/飞灰复合脱硫脱硝剂的热重特性、X射线衍射图谱、比表面积、扫描电镜结果等进行了分析,结果表明:利用醋酸钙和飞灰水合制备的脱硫脱硝剂具有比单纯的醋酸钙和飞灰更大的比表面积;经过900℃煅烧后脱硫脱硝剂孔隙结构最好;脱硫脱硝剂经过900℃煅烧后的热解产物(SiO2、Al2O3、Fe2O3和CaO)有助于脱除烟气中的硫氧化物和氮氧化物。     

Characterization of geopolymers from compositionally and physically different Class F fly ashes

The alkali-activation technology of coal fly ash is one of several potential solutions to minimize the harmful disposal of fly ash. This study reports high-resolution characterization of the alkali-activated reaction products for two representative Korean Class F fly ashes, which are significantly different in compositional and physical characteristics. The analysis confirms that differences in the network modifying element content, the amorphous phase content, and the particle size lead to large differences in compressive strength. Chabazite-Na and Al-rich chabazite-Na are identified as major crystalline phases in the high strength samples, supporting the favoring formation of ABC-6 family of zeolitic precursors for the higher mechanical strength while the C–S–H formation from the high CaO content (or crystalline CaO) is not a major source of the strength. The XRD analysis shows that the presence of amorphous humps located at 27–29° 2θ is not a sufficient indicator of geopolymeric gel formation. In the ²⁹Si MAS NMR, some portion of −108 ppm Q₄(0Al) peak is not related to quartz, implying that this portion of Si atoms actively participate in geopolymerization. The ²⁷Al MAS NMR spectra exhibit more conversion of Al(V) and Al(VI) aluminum atoms into Al(IV) units in the higher strength sample, which can be an indication of more geopolymeric reaction.     

Factors affecting the performance of metakaolin geopolymers exposed to elevated temperatures

The effects of geopolymer binder systems exposed to elevated temperatures are examined. Geopolymers investigated were synthesized from metakaolin, activated by combinations of sodium/potassium silicate and sodium/potassium hydroxide. The specimens were then exposed to temperatures of 800 °C. The factors studied were: (1) calcining temperatures of kaolin; (2) Si/Al ratio of the geopolymer; (3) activator/metakaolin ratio; (4) curing temperature; and (5) alkali cation type. Altogether 30 geopolymer formulations were studied. The samples were subjected to compressive strength, thermogravimetry, and scanning electron microscopy tests. Results showed that Si/Al ratio has a significant influence on elevated temperature exposure deterioration. Lesser strength loss due to elevated temperature exposures were observed in geopolymer with high Si/Al ratios (>1.5). The geopolymer binders activated by potassium-based activators showed an enhanced post-elevated temperature exposure performance compared to sodium-based systems. The optimum calcining temperature of kaolin and curing temperatures for improved temperature performance are also reported.     

Compressive strength and microstructural characteristics of class C fly ash geopolymer

Geopolymers prepared from a class C fly ash (CFA) and a mixed alkali activator of sodium hydroxide and sodium silicate solution were investigated. A high compressive strength was obtained when the modulus of the activator viz., molar ratio of SiO₂/Na₂O was 1.5, and the proper content of this activator as evaluated by the mass proportion of Na₂O to CFA was 10%. The compressive strength of these samples was 63.4 MPa when they were cured at 75 °C for 8 h followed by curing at 23 °C for 28 d. In FTIR spectroscopy, the main peaks at 1036 and 1400 cm^?1 have been attributed to asymmetric stretching of Al–O/Si–O bonds, while those at 747 cm^?1 are due to the Si–O–Si/Si–O–Al bending band. The main geopolymeric gel and calcium silicate hydrate (C–S–H) gel co-exist and bond some remaining unreacted CFA spheres as observed in XRD and SEM–EXDA. The presence of gismondine (zeolite) was also observed in the XRD pattern.     

Stabilization/solidification of a municipal solid waste incineration residue using fly ash-based geopolymers

The stabilization/solidification (S/S) of a municipal solid waste incineration (MSWI) fly ash containing hazardous metals such as Pb, Cd, Cr, Zn or Ba by means of geopolymerization technology is described in this paper. Different reagents such as sodium hydroxide, potassium hydroxide, sodium silicate, potassium silicate, kaolin, metakaolin and ground blast furnace slag have been used. Mixtures of MSWI waste with these kinds of geopolymeric materials and class F coal fly ash used as silica and alumina source have been processed to study the potential of geopolymers as waste immobilizing agents. To this end, the effects of curing conditions and composition have been tested. S/S solids are submitted to compressive strength and leaching tests to assess the results obtained and to evaluate the efficiency of the treatment. Compressive strength values in the range 1-9 MPa were easily obtained at 7 and 28 days. Concentrations of the metals leached from S/S products were strongly pH dependent, showing that the leachate pH was the most important variable for the immobilization of metals. Comparison of fly ash-based geopolymer systems with classical Portland cement stabilization methods has also been accomplished.