FAFB与Al(OH)3质量比对莫来石质材料显微结构及性能的影响

以固体废弃物粉煤灰漂珠(FAFB)和工业氢氧化铝为主要原料,并添加AlF3和V2 O5作为矿化剂,采用原位生长法合成了莫来石质材料,研究了粉煤灰漂珠和氢氧化铝质量配比对材料的显微结构及其性能的影响.采用X射线衍射仪(XRD)和扫描电子显微镜(SEM)对材料的晶相和显微结构进行了表征.实验结果表明,当粉煤灰漂珠与氢氧化铝的质量比为25:75时,样品是由棒状的莫来石相和片状的刚玉相组成,当质量比从35:65变化到55:45时,可以获得针状的纯莫来石质空心球材料,且在该配方组成范围内合成的莫来石材料具有优良的性能,高的抗压强度7.6～10.5 MPa,低的体积密度0.48～0.66 g/cm3,当质量比达到65:35时,伴随有石英相的产生.     

铝源对煤矸石烧结合成莫来石结构与性能的影响

分别以w(Al_2O_3) 99. 0%的煅烧氧化铝、w(Al_2O_3)=83. 94%的煅烧铝土矿、w(Al_2O_3) 64. 5%的氢氧化铝为铝源,w(SiO_2)=65. 21%的煤矸石为硅源,AlF_3和V_2O_5为添加剂,干压成型后,于1 500℃保温1 h固相烧结合成了主晶相为莫来石的试样,并研究了三种铝源对煤矸石烧结合成莫来石结构和性能的影响。结果表明:铝源为氢氧化铝的试样相比其他铝源试样,相组成中莫来石比例更高,莫来石晶体更加细长,试样更致密,抗折强度相差不大,其显气孔率为2. 15%,抗折强度为76. 2 MPa。     

煤矸石合成莫来石晶须工艺的研究

以煤矸石和硫酸铝为原料,硫酸钠为反应介质,采用烧结法制备莫来石晶须。利用XRD、SEM、DSC等测试方法,研究了煅烧温度和保温时间对莫来石晶须的影响。研究结果表明:温度过低时熔融性差不利于莫来石晶须形成;而温度过高时,已合成的莫来石晶须相发生二次分解,均使莫来石产率降低。经过实验,得出最佳条件:1 100℃保温3h时,合成莫来石晶须长为3~4μm、直径为50~100nm。     

莫来石的低温合成及结构组成变化

以九水硝酸铝和正硅酸乙酯为原料,以无水乙醇为溶剂,用溶胶-凝胶法制备出分子级均匀混合的莫来石前驱体.热重-差示扫描量热、X射线衍射和红外分析结果表明:前驱体在985℃直接由非晶态转化为富铝莫来石晶体,没有经历尖晶石相变过程,随着热处理温度的提高,富铝莫来石逐渐转化为结构为3Al2O3·2SiO2的稳定莫来石.前驱体粉末经1 000℃煅烧4h后,用放电等离子烧结技术在1 450℃烧结10min能制成透明莫来石陶瓷.     

综合利用粉煤灰制备莫来石系列材料研究进展及展望

粉煤灰是燃煤发电过程产生的固体废弃物,其大量堆积不仅会侵占土地资源,而且会造成严重的环境污染,甚至危及人体健康。但粉煤灰中富含氧化硅和氧化铝等资源,尤其在内蒙西部和山西北部产生的高铝粉煤灰中氧化铝和氧化硅含量达80%~85%,极具资源化利用的前景。莫来石材料因其优异的理化性质被广泛应用于冶金、催化、水处理和航空等领域,利用天然铝硅酸盐矿物或高纯试剂制备莫来石不仅会消耗大量矿产资源,而且存在生产成本高的问题,而以粉煤灰为原料制备莫来石系列材料可有效减少天然矿物的消耗、降低生产成本和缓解环境污染。因此,利用粉煤灰制备莫来石系列材料成为了粉煤灰高值与资源化利用的重要途径之一。在总结和概括莫来石的组成、性质、合成方法与应用的基础上,从成分、矿相调控制备粉煤灰基莫来石及其性能与应用出发,综述了综合利用粉煤灰制备莫来石系列材料的研究进展,系统总结了当前粉煤灰制备莫来石系列材料的类型及其技术方法,分析了粉煤灰铝硅比调控、杂质控制以及莫来石生成机理机制,阐述了不同粉煤灰基莫来石材料的性能及其性能影响因素,以期实现粉煤灰基莫来石系列材料结构和性能的调控、推动粉煤灰高值与资源化利用。     

NaOH激发粉煤灰基胶凝材料的水化产物

以粉煤灰为原料,NaOH为激发剂,制备出高抗压强度的粉煤灰基碱激发胶凝材料,研究养护条件对粉煤灰基碱激发胶凝材料抗压强度的影响。用x射线衍射分析不同龄期粉煤灰基碱激发胶凝材料的矿物组成,并用带能谱分析的扫描电镜观察不同龄期材料的微观形貌和区域元素组成。结果表明：蒸汽养护可以显著提高材料的抗压强度：粉煤灰中的玻璃相参加材料的水化反应,莫来石、石英等晶相则为惰性物质,不参加反应：在水化过程早期,粉煤灰基碱激发胶凝材料的气孔内会形成钠系菱沸石的前驱体,蒸汽养护1d后长大为表面呈十字交叉状的1pm左右颗粒,随着时间延长,这些颗粒可长至5μm左右,交错重叠充满整个气孔内壁,形成致密的空间网状结构,使材料强度得到提高。     

莫来石含量对堇青石-莫来石复相陶瓷性能的影响

以合成堇青石(≤0.074 mm)和合成莫来石(0.45～0.9 mm)为主要原料,a-Al2O3微粉(≤0.044 mm)、镁砂(≤0.054 mm)和熔融石英(≤0.054 mm)为添加剂,经细磨、造粒、成型后,于1 370℃4 h烧成后制备了莫来石质量分数分别为15%、20%、25%、30%、35%和40%的堇青石-莫来石复相陶瓷材料,研究了莫来石含量对复相陶瓷材料烧结性能、抗折强度、热膨胀性及抗热震性的影响.结果表明:随着莫来石含量的增加,堇青石一莫来石复相陶瓷材料的体积密度、显气孔率和热膨胀系数都呈上升趋势,而抗折强度呈降低趋势;适当提高莫来石含量有利于复相陶瓷材料的抗热震性,当莫来石含量达到30%时,材料的抗热震性最好.     

用不同硅质原料来制备莫来石结合碳化硅多孔陶瓷

分别以Al(OH)3为铝质原料,气相白炭黑和硅灰为硅质原料,在1330 ℃下实现了莫来石的低温合成,莫来石转化率达90%以上.以碳化硅为骨料,以20%结合剂制得了莫来石结合碳化硅复相陶瓷多孔材料.当材料的气孔率为31.46%时,抗折强度达85.75 MPa.利用XRD和SEM分别研究了不同硅质原料合成莫来石结合碳化硅材料中莫来石转化率及材料烧成温度对材料性能的影响.作为比较,研究了以红柱石为合成莫来石原料来制备Mullite/SiC复相陶瓷多孔材料.     

莫来石晶须的特性及应用

通过溶胶─凝胶工艺制备了莫来石前驱体,加入适当矿化剂经高温煅烧合成了高纯、单相莫来石晶须。XRD及SEM分析结果显示:晶须直径为50～100nm,长度为3～8μm,晶须尺寸均匀性好,表面光洁,直晶率高。运用所制备的晶须制备了多孔基板试样,并与普通粒子堆积法烧成样品显微结构与性能进行比较,进而分析了低维晶须材料与普通粒子的堆积成孔方式的异同。在此基础上,对莫来石晶须在其它方面的应用进行了展望。     

原位合成莫来石晶须-氧化铝复合体系

为改善氧化铝陶瓷的韧性,以Al_2O_3、Si O2和AlF_3·3H_2O为原料,原位合成了莫来石晶须-氧化铝复合体系。探讨了AlF_3·3H_2O加入量(质量分数分别为2.9%、9.1%和16.6%)和热处理温度(1 400、1 500和1 600℃)对在Al_2O_3为80%~90%(w)的粉体中原位合成莫来石晶须的影响,并研究了莫来石晶须的生长机制。结果表明:原位合成莫来石晶须-氧化铝复合体系的最佳工艺条件是Al F3·3H2O加入量为9.1%(w),热处理条件为1 600℃保温5 h;生成的莫来石晶须长度可达50μm,长径比可达25;莫来石晶须的原位生长遵循气-固(VS)机制。     

Preparation of Mullite Ceramics from Coprecipitated Aluminum Hydroxide and Kaolinite Using Hexamethylenediamine

Mullite ceramics have been prepared from an aqueous suspension of kaolinite (raw or ground) and aluminum hydroxide. The precursor was coprecipitated in the mixture using hexamethylenediamine (HMDA) or ammonium hydroxide, and a solution of aluminum chloride from acid dissolution of wastes of aluminum metal. The precursor and the resulting materials were characterized and studied by X-ray diffraction, thermal methods, and mechanical strength and porosity measurements. The feasibility of the proposed chemical processing route for mullite preparation was demonstrated, in particular using HMDA as a precipitating agent for aluminum hydroxide instead of ammonium hydroxide, which adversely affects the system reactivity. The use of HMDA, as compared with ammonium hydroxide, and ground kaolinite produces single-phase mullite and enhances the flexural strength (maximum of 49 MPa) of the resultant ceramic porous bodies (porosity ca. 52–45 vol%) fired at 1550–1600°C for 30 min.     

V2O5掺杂对莫来石晶须增强型陶粒支撑剂的性能影响

以高岭石质煤矸石为主要原料,V2O5为添加剂,于1400 ℃下制备了莫来石晶须增强的陶粒支撑剂,讨论了V2O5促进莫来石晶须生长机制及其添加量对支撑剂样品性能的影响.结果表明:随着V2O5的加入,支撑剂样品的主晶相莫来石逐渐生长形成莫来石晶须;当V2O5添加量为1wt％时,试样的性能最佳;体积密度1.25 g/cm3,视密度2.69 g/cm3,52 MPa闭合压力下的破碎率5.18％.     

Aluminum K-Edge Absorption (XANES) Studies of Noncrystalline Mullite Precursors

Noncrystalline aluminum silicate precursors MP1 and MP3 with different ratios of Al in tetrahedral (^[4]A1), pentahedral (^[5]A1), and octahedral (^[6]A1) position were prepared from aluminum sec-butylate and tetraethoxysilane (Al/Si ratio: 3/1) making use of a slow and rapid hydrolysis process, respectively. The MP2 precursor was synthesized from aluminum sec-butylate and silicon tetrachloride (Al/Si ratio: 4/1) by rapid hydrolysis. All aluminum silicate gels were heat-treated to temperatures just prior to crystallization to mullite and γ-Al₂O₃, respectively (MP1 and MP3: 800°C; MP2: 300°C). Al K near-edge absorption spectra (XANES) of the mullite precursors and of several suitable crystalline reference materials were measured using monochromatic synchrotron radiation. The reference XANES spectra yielded a linear correlation between the energy position of the first inflection point of the white lines and the frequency of sixfold-coordinated Al (^[6]A1) in the samples. A similar though less straightforward correlation seems to hold also for the white line intensities. From these findings, the actual ^[61]A1 frequencies for the mullite precursors under investigation were derived to be <10% (MP1), =30% (MP3), and =60% (MP2). The ^[6]A1 frequency distribution in the mullite precursors displays a trend similar to that determined by ²⁷A1 NMR spectroscopy.     

Preparation of Mullite Fiber

Transparent mullite fibers have been prepared using aluminum carboxylates (ACs) and tetraethyl orthosilicate (TEOS) as starting materials. The ACs are derived from the catalyzed dissolution of elemental aluminum in a mixture of formic acid and acetic acid. The solubility of aluminum in the acids is influenced by the concentrations of the acids, water, and additives and the preparation temperature. A 1:4:3:24 molar ratio of aluminum, formic acid, acetic acid, and water dissolves the aluminum completely to give a colorless, clear solution suitable for fiber synthesis. The mixture of the ACs and TEOS, in the presence of ethyl alcohol as a mutual solvent at 50°–60°C, is concentrated to give a spinnable dope, from which mullite precursor fibers can be drawn. Heat treatment of the precursor at 1250°C yields crystallized and transparent mullite fibers.     

利用太阳能多晶硅片生产过程中产生的固体废弃物合成莫来石晶须

以太阳能多晶硅片生产过程中产生的废弃石英坩埚及废弃超细氧化铝磨料为原料,以硫酸钠、硫酸钾复合盐作为熔盐体系制备莫来石晶须.同时,采用XRD,SEM等测试手段研究了不同温度下所合成粉体的物相及形貌分析.结果表明,在1100℃高火保温3h制备出了直径为0.1～2μm,长径比高达50～60的莫来石晶须,其形成机理属于熔解-沉淀反应机制.     

Formation and Densification Behavior of Mullite Aggregates from Beach Sand Sillimanite

Dense mullite aggregates with 60% and 70% Al₂O₃ have been prepared from precursor mixtures consisting of beach sand sillimanite and a high-purity aluminum hydroxide following conventional single- and double-stage firing processes. The bulk density (BD), apparent porosity (AP), and water absorption (WA) capacity of sintered mullite aggregates were found to be strongly influenced by the premullitization step of this precursor mixture. Mullite aggregates formed in a double-stage firing process exhibited higher BD and mullite content and lower AP and WA capacity in comparison with those obtained by the single-stage firing process. The values of coefficient of thermal expansion of sintered mullite aggregates are close to those found in the literature reports for high-purity stoichiometric mullite.     

Colloidal Processing and Mechanical Properties of Whisker-Reinforced Mullite Matrix Composites

Aqueous colloidal suspensions in the two systems of CVD-processed ultrafine mullite powder (<0.1 μm), -Si₃N₄ whisker and -mullite whisker, were prepared near the isoelectric point of mullite (pH 7.0) to prevent cracking during drying of wet green compacts consolidated by filtration. The freeze-dried porous green compacts were hot-pressed with a carbon die at 1500°C for 1 h at a pressure of 39 MPa in N₂ atmosphere. The relative densities of the mullite matrix composites with whiskers of 0 to 10 vol% were in the range of 95.2% to 99.8%. Increasing the fraction of Si₃N₄ whisker increased the density, flexural strength, and fracture toughness of the hot-pressed composites. On the other hand, addition of the mullite whisker increased the fracture toughness but decreased the density and strength of the composites.     

粉煤灰提铝残渣低温碱溶过程工艺研究

循环流化床粉煤灰“一步酸溶法”提取氧化铝工艺过程中产生的尾渣主要成分为无定形二氧化硅,且具有较高的活性,是制备白炭黑、分子筛、硅酸钠水玻璃的理想原料。对该提铝残渣在氢氧化钠溶液中的溶出过程做了研究,探讨了液固比、碱浓度、溶出时间、溶出温度工艺条件对二氧化硅和氧化铝溶出效果的影响。研究结果表明：在氢氧化钠碱液的浓度为4 mol/L、反应温度为70 ℃、液固比为6、反应时间为4 h的条件下,二氧化硅的溶出率最高,达到93%。提铝残渣碱溶后固体渣经XRD分析,其无定形二氧化硅基本已溶出,剩余物主要为锐钛矿与莫来石等。     

Coprecipitation and Processing of Mullite Precursor Phases

Ultrafine powders of aluminum-rich mullite precursor phases were prepared by spraying mixed acid solutions of silicic acid and aluminum chloride into ammonium hydroxide at different pH values. The aluminum-rich composition was chosen to avoid abnormal grain growth of the mullite grains caused by silica-rich liquid phases. The influence of coprecipitation pH on particle size, zeta potential, and the mixing degree of aluminum and silicon in the precipitated powders and on the sintered microstructures have been described. In the basic pH region, the degree of mixing of both components increased as the pH of coprecipitation decreased. Under these conditions, direct slip casting of the coprecipitated slurries was possible, and fine and equiaxed microstructures could be obtained in the sintered bodies.     

复合型絮凝剂聚合氯化铝铁的合成

粉煤灰中含有铝、铁,可以用其制备聚合氯化铝铁絮凝剂。但是,粉煤灰中的铝、硅以复杂的玻璃体红柱石形式存在,酸溶性非常差,需要通过焙烧破坏其中的SiO₂-Al₂O₃键,提高其酸溶性。在粉煤灰中通过添加一定量赤泥来调节混合物中铝铁比值关系,然后用改性粉煤灰和盐酸为主要原料,制备聚合氯化铝铁絮凝剂。粉煤灰活化最佳条件：粉煤灰与赤泥的质量比为0.3、焙烧温度为750 ℃、焙烧时间为2 h。粉煤灰中铝铁溶出最佳条件：盐酸浓度为7 mol/L,液固比为3.5 mL/g,反应温度为85 ℃,反应时间为2.0 h,在此条件下铝铁溶出率高达90.5%。将所得溶液陈化18 h即得到聚合氯化铝铁（PAFC）絮凝剂。絮凝实验结果表明：制得的PAFC的絮凝性能优于聚合氯化铝（PAC）、聚合氯化铁（PFC）。