王亚超
, 赵江平
西安建筑科技大学材料与矿资学院 西安 710055
WANG Yachao, ZHAO Jiangping
文献标识码: 分类号 TU545 文章编号 1005-3093(2016)07-0524-07
通讯作者:
收稿日期: 2015-11-27
网络出版日期: 2016-07-25
版权声明: 2016 《材料研究学报》编辑部 《材料研究学报》编辑部
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作者简介:
本文联系人: 王亚超
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摘要
利用硅藻土松散、质轻、多孔、富含活性硅等特点, 制备用于外墙保温板的阻燃材料, 并采用多种分析手段对其进行表征。结果表明, 当同时以NaOH (2 molL-1)和Na2SiO3 (1 molL-1))为化学改性剂, 采用溶胶-凝胶法制备的硅藻土基阻燃材料可使聚苯板(EPS)的极限氧指数达到36.8%, 燃烧性能达到UL-94 V1级别。提出并阐述了NaOH和Na2SiO3对硅藻土的协同效应, 扫描电镜(SEM)结果证实NaOH和Na2SiO3同时作用时有助于硅藻土形成结构更加致密的无定型硅质层, X-射线衍射分析(XRD)和红外光谱(FT-IR)结果证实, 在碱性环境下硅藻土结构发生了“解聚-重组”, 其在燃烧过程中进一步发生重组。
关键词：
Abstract
The diatomite based flame-retardant materials for external thermal insulation board of exterior wall were preparedby sol-gels method with NaOH (2 molL-1) and Na2SiO3 (1 molL-1) simultaneously as the chemical activator, and then characterized by means of various methods. Results showed that aftera thin-plastering of the prepared flame-retardant diatomitewas applied on expandable polystyrene board, the limiting oxygen indexthe complex EPSboard can reached 36.8%, and itscombustion performance can meetthe requirement of UL-94 V1. SEM results demonstrated that the NaOH and Na2SiO3 were benefit for the diatomite to form dense amorphous silica layer, XRD and FT-IR results showed that "depolymerization-reconstruction" of the diatomite structure occurred in the alkaline media, and which would further be reconstructed during firing.
Keywords：
硅藻土具有细腻、松散、质轻、多孔、富含活性硅等特点, 以及许多特殊的技术和物理性能, 如大的孔隙度, 较强的吸附性、质轻、隔音、耐磨耐热并有一定的强度, 已被广泛用于轻工、化工、建材、石油、医药、卫生等领域。当前发展无毒、环保、高效、绿色的无机阻燃材料已成为热点, 如利用富含活性硅的云母、膨润土[1]、钙硅石、高岭土等无机硅酸盐材料制备高效阻燃材料[2]。利用硅酸盐的层状结构[3]在其中掺杂具有一定光催化性能的纳米粒子可制备出性能优异的纳米复合阻燃材料, 或者采用“微胶囊技术”制备出具有“核-壳结构”的新型阻燃材料[4]。
Vesely等[5]证明硅藻土可以作为抗腐蚀的涂料填料, 且其最佳掺量的体积分数为5%。Loganina等[6]发现改性的硅藻土可用于提高硅质溶胶的硅含量, 进而改善其亲水性能。Liang等[7]研究了硅藻土/Fe2O3复合材料作为降解有机物的异质节催化剂材料, 利用硅藻土多孔的结构作为催化剂的载体, 与TiO2、Fe2O3等均可形成性能优异的异质节催化剂[8]。但是用硅藻土作为主要填料制备防火阻燃材料, 文献资料中还鲜有报道, 尤其是通过化学改性制备阻燃材料还未见报导。结合防火材料的阻
燃机理和硅藻土的结构特点, 本文探索通过化学改性硅藻土制备防火阻燃型溶胶材料, 为硅藻土的功能化发展做出有益尝试。利用硅藻土中高含量的活性硅可在保温材料燃烧时膨胀成具有一定“隔氧隔热”的硅质层, 可达到防火阻燃的效果。并采用扫描电镜(SEM)、X-射线衍射(XRD)、热重/差式扫描量热 (TG/DSC)和红外光谱(FT-IR)等多种现代分析手段研究其微结构特征。
硅藻土取自于吉林长白山, 经X-射线荧光分析如表1所示, 其密度为0.42 g/cm3, 测得其勃氏比表面积为49 m2/g。NaOH和Na2SiO3(A.R)均购于郑州派尼化学试剂有限公司。聚苯板(Expansion polyphenyl board, EPS)购于西安海筑保温材料厂, 极限氧指数(LOI)为28.5%, 导热系数≤0.041 w/(mk)。
表1 硅藻土的化学组成
Table 1 Chemical composition of diatomite (%, mass fraction)
| Raw material | SiO2 | Al2O3 | Fe2O3 | K2O | CaO | TiO2 | Ignition loss |
|---|---|---|---|---|---|---|---|
| Diatomite | 92.93 | 3.21 | 0.73 | 0.43 | 0.85 | 0.34 | 1.51 |
分别称取40 g硅藻土和100 g水, 称取适量的NaOH和Na2SiO3·9H2O按照表2配制成NaOH溶液量浓度分别为2, 3, 4和5 molL-1, Na2SiO3溶液量浓度分别为1, 1.5, 2和2.5 molL-1。在恒温(70℃)磁力搅拌机的搅拌过程中缓慢加入硅藻土(约1 h加完), 恒温继续搅拌3 h后, 形成具有一定粘性、混合均匀的粘性溶胶, 将其按照(JB/T 7706-95)标准刷涂(3遍, 约0.3 mm厚, 200 g/m2)在EPS表面, 然后测试其LOI, 阻燃性能、矿物晶相、热重性能、键合结构和微观形貌。
采用DX8355型数显氧指数测定仪, 参照GB/T2406-93标准测试样品材料的极限氧指数, 其误差为±0.2; 采用DX8522型垂直/水平燃烧试验机检测所制备样品的阻燃性能（参照GB/T 2408-2008标准）, 其误差为±1 s, 样品的阻燃性能均以液化天然气为燃料。样品的微观形貌观察采用Quanta 200型电子扫描电镜, 工作电压为20 kV, 真空度为10-5 Torr。利用Mettler热重/差式扫描量热分析仪对样品在50-850℃的热重性能进行分析, 其测试条件为氮气氛下, 升温速率为30℃/min。采用D/MAX-2400型X射线衍射分析仪研究样品在燃烧前后的晶相变化, 其工作电压为40 kV, 工作电流为40 A, 以Cu 为靶材。样品的键合结构采用FTIR-650型红外分析仪进行表征, 其测试范围为4000~500 cm-1, 其误差小于2 cm-1, 试验时将样品粉末与KBr(样品∶KBr=1∶99)在研钵中充分混合后直接测试。
硅藻土原料及样品的XRD图谱如图1所示, 对于前者除了含有一定量的石英外, 2θ在10o~35o之间存在一个隆起的“馒头”峰, 其对应为无定型的、具有一定反应活性的物质[9]; 当硅藻土经Na2SiO3和NaOH活化后, 其XRD图谱发生了变化, 无定型的“馒头”峰发生明显的右移, 表明硅藻土在较强的碱性环境下发生了“解聚-重组”的过程, 硅藻土原料中的无定型物质在氢氧根的溶蚀下解聚成硅氧四面体, 然后再发生重组形成新的无定型的物质; 当将所形成的硅藻土基阻燃材料经燃烧后, 所形成的CO2易于和基体内OH-、SiO32-反应形成Na2CO3, 致使其XRD图谱上呈现大量的Na2CO3衍射峰。同时发现, 经燃烧处理后, 样品XRD图谱上的“馒头”峰则发生明显的“左移”, 表明在燃烧过程中, 无定型的硅质层微结构也发生了变化[9]。
表2为刷涂硅藻土基阻燃材料EPS的阻燃性能及LOI, 从表中可见, 化学改性硅藻土所制备阻燃材料均可提高EPS的阻燃性能, 其LOI都高于32%, 且大多数样品燃烧时无融滴, 其阻燃性能满足UL-94 V1级别的要求。随着NaOH溶液浓度的增大, 所制备样品的阻燃性能逐渐提高, 当NaOH浓度为2 molL-1时, 所制备材料可使EPS的极限氧指数达到32.8%, 当其浓度增大至5 molL-1时, 可使EPS的极限氧指数达到35.5%。同时发现, Na2SiO3对硅藻土活化程度低于NaOH (相同Na+浓度), 其改性样品的阻燃性能较低, 由于其不能完全水解, 形成的碱性较弱所致。
表2 刷涂硅藻土基阻燃材料EPS的阻燃性能
Table 2 Flame-retardant performances of EPS covered samples
| Samples | NaOH/molL-1 | Na2SiO3/molL-1 | LOI/ % | T1/s | T2/s | T3/s | Melting drop | UL-94 |
|---|---|---|---|---|---|---|---|---|
| S0 S1 | 0 2 | 0 0 | 28.5 32.8 | 18 9 | 24 15 | 35 28 | Yes Yes | V2 V2 |
| S2 | 3 | 0 | 33.5 | 8 | 13 | 25 | No | V1 |
| S3 | 4 | 0 | 35.2 | 7 | 13 | 20 | No | V1 |
| S4 | 5 | 0 | 35.5 | 6 | 12 | 18 | No | V1 |
| S5 | 0 | 1 | 32.5 | 15 | 26 | 32 | Yes | V2 |
| S6 | 0 | 1.5 | 33.9 | 13 | 20 | 26 | No | V1 |
| S7 | 0 | 2 | 34.5 | 12 | 13 | 20 | No | V1 |
| S8 | 0 | 2.5 | 34.7 | 11 | 12 | 16 | No | V1 |
| S9 | 1 | 0.5 | 33.2 | 8 | 20 | 23 | No | V1 |
| S10 | 1.5 | 0.75 | 34.8 | 8 | 18 | 18 | No | V1 |
| S11 | 2 | 1 | 36.6 | 7 | 10 | 16 | No | V1 |
| S12 | 2.5 | 1.25 | 36.8 | 7 | 9 | 15 | No | V1 |
但是, 当采用Na2SiO3和NaOH同时活化硅藻土时, 所制备材料的阻燃性能均高于单独采用Na2SiO3或NaOH(相同Na+浓度比较), 表明Na2SiO3和NaOH对活化硅藻土具有一定的协同效应。NaOH不仅具有较强的碱性、还具有较快的离子化速度和较强的水化程度[10, 11], 可与硅藻土中具有反应活性的-Si-OH发生反应形成硅氧四面体离子-Si-O-Na+, 其进一步反应形成具有空间网状结构的硅质层, 如反应式(1)、(2)和(3)所示, 硅质层可以有效地隔热、阻止氧气与易燃的EPS接触, 从而提高了材料的阻燃性能。
当采用Na2SiO3和NaOH同时活化硅藻土时, Na2SiO3不仅具有较强的粘性可提高材料对EPS粘附性能, 其水解产生的活性Si(OH)4可提供更多的硅氧四面单体, 其可与+Na-O-Si-O-Si-Na+等硅酸盐网络结构发生缩水反应形成结构更加致密的无定形的硅质层结构, 如反应式(4)所示。
综上所述, 在NaOH活化作用下, 硅藻土中的活性硅氧四面体经“解聚-重组”过程发展成具有-O-Si-O-Si-结构的无定形物质, 但在Na2SiO3的协同作用下, 其产生的Si(OH)4与-O-Si-O-Si-链之间发生缩聚反应形成相互交错、互穿的空间网状结构, 致使材料的阻燃性能显著提高。如图2所示, 用Na2SiO3和NaOH同时活化硅藻土时, 其中NaOH较强的水化能力和较快的离子化速度, 易于吸附和静电缔合, 可以快速形成无定形的硅质凝胶, 而Na2SiO3较强的粘性和水解产生的Si(OH)4则可拓展和密实化无定形硅凝胶, 从而提高其阻燃性能。Wang等[12]发现Na2SiO3可持续地提供OH—和促进无定型沸石类物质的形成, 而单独使用较高浓度NaOH易于使新生成的无定型硅质材料发生Si-O键断裂, 而降低其阻燃性能。
图3所示为热重/差式扫描量热(TG/DGC)曲线, 在图3a中145℃出现显著的吸热峰, 且随着温度升高其发生持续的吸热。由于单独采用NaOH活化硅藻土时, 生成无定形的-O-Si-O-Si-网状结构包裹着大量的水分子, 在基体中形成大量相互被无定形“硅质笼”包裹的水分子, 致使其在吸热峰升高至145℃(而不是100℃左右)。另外, 该NaOH活化硅藻土基材料在受热过程中发生持续的质量损失, 其失重终止温度约为201℃。
与图3a对比发现, 采用Na2SiO3和NaOH混合液活化硅藻土所制备阻燃材料的热流曲线在156℃出现明显的吸热峰, 热重曲线上其失重终止温度为215℃。表明掺入Na2SiO3水解可吸收更多的结合水, Na2SiO3与水反应形成更多的Si(OH)4, 其与-O-Si-O-Si-相互发生缩聚反应, 形成交错互穿的网状结构, 可形成结构更加致密的硅质无定形物质, 致使其热流曲线上吸热峰值温度和失重终止温度同时“右移”。
图4是硅藻土原料和样品的FT-IR光谱, 从图4a中可见, 2343 cm-1处的吸收峰对应为空气中的CO2, 硅藻土在燃烧前后, 其红外谱图没有显著变化, 表明硅藻土具有一定的高温稳定性; 从图4b可见, 经Na2SiO3和NaOH (CNa+=4 molL-1)活化硅藻土基材料在燃烧前后其红外光谱各吸收峰的强度发生变化, 但其吸收峰位置基本没有变化, 结合其TG/DGC分析结果, 再次证实硅藻土基材料具有良好的高温稳定性, 能够有效地隔热和提高材料的阻燃性能。在1092 cm-1处强而宽的吸收峰是-Si-O-Si-的反对称伸缩振动峰, 806 cm-1处的吸收峰为Si-OH的对称伸缩峰[13]。在975 cm-1处出现强而尖的吸收峰, 其对应为硅氧四面体的聚合体, 表明在Na2SiO3和NaOH溶液的活化作用下, 硅藻土中的活性物质发生了“重组”, 即活性的硅氧四面体Si(OH)4缩聚成聚合度较低的链状硅氧聚合物。3440 cm-1和1650 cm-1分别为水分子的伸缩振动和弯曲振动, 经燃烧后其强度变弱, 表明在燃烧过程中大量自由水分子和羟基蒸发散失。
图3 样品的TG/DSC曲线
Fig.3 TG/DSC curves of specimens (a) activated with NaOH (CNa+=4 molL-1), (b) activated with Na2SiO3 and NaOH (CNa+=4 molL-1)
图4 硅藻土原料和样品的傅里叶-红外光谱
Fig.4 FT-IR spectra of diatomite and specimen (a) diatomite, (b) diatomite activated with Na2SiO3 and NaOH (CNa+=4 molL-1)
在1391 cm-1处出现明显的吸收峰, 其对应为CO32-的吸收峰, 在制备过程中采用Na2SiO3和NaOH作为碱性活化剂, 它们都易与空气中的CO2反应生成CO32-, 当该硅藻土基材料经高温燃烧后, 其中还存在CO32-, 只是其浓度降低, 但是在695 cm-1处出现明显的吸收峰, 其为硅藻土基材料中的Al与硅氧四面体之间形成Al-O-Si的吸收峰[14]。表明在燃烧过程中, 硅质层结构也发生了一定的重组变化。
图5所示为硅藻土原料及化学改性硅藻土基材料的扫描电镜图片, 从图中可见, 硅藻土原料中存在大量的微孔结构, 单独采用NaOH活化硅藻土时, 其孔状结构发生破坏, 形成大量残损的微孔结构(图5b); 当采用Na2SiO3活化硅藻土时, 由于其碱性弱于NaOH, 致使残损微孔结构较大, 但其边缘上存在大量无定型的物质; 当同时采用NaOH和Na2SiO3(CNa+=4 molL-1)活化硅藻土时, 其微观形貌上不存在残损的微孔结构, 呈现无定型的片层状结构, 再次表明它们产生了一定的协同效应, 形成结构致密、较为完整的无定型硅质保护层(图5d), 进而可包覆在EPS表面, 提高其阻燃性能。
图5 硅藻土原料及样品的微观形貌
Fig.5 Morphologies of diatomite and materials (a)-diatomite; (b)-diatomite activated with 4 molL-1 NaOH; (c)- diatomite activated with 2 molL-1 Na2SiO3; (d) diatomite activated with NaOH and Na2SiO3 (CNa+= 4 molL-1)
当将所制备的硅藻土基材料经燃烧处理后, 其微观形貌如图6所示, 它们均可转变为片状物质, 其中单独以NaOH活化时, 其所形成的片状结构易于破碎(图6a), 而单独以Na2SiO3活化时形成的片状物较大(图6b); 当同时采用NaOH和Na2SiO3(CNa+=2 molL-1)时, 由于其碱性较弱, 对硅藻土的活化程度较低, 形成的片状结构也不够连续、完整, 易于破碎(图6c); 当增大碱液浓度(CNa+= 4 molL-1)后, 所制备材料经燃烧后可形成片层较大、较为完整的结构(图6d)。结合其阻燃性能, 较为完整的片层结构可有效地阻止热量、有机物的传送和氧气的传输, 进而提高材料的阻燃性能。其结果与Gu等[15]的一致, 即NaOH和Na2SiO3易于形成具有网状交联结构物质。
图6 经燃烧后样品的微观形貌
Fig.6 Morphologies of samples after firing . (a)diatomite activated with 4 molL-1 NaOH; (b)diatomite activated with 2 molL-1 Na2SiO3; (c) diatomite activated with NaOH and Na2SiO3 (CNa+= 2 molL-1); (d) diatomite activated with NaOH and Na2SiO3 (CNa+= 4 molL-1)
1. 采用硅藻土为原料, 在强碱性条件下利用溶胶-凝胶法制备出可用于外墙保温材料的阻燃材料, 其最佳的制备条件为同时以NaOH (2 molL-1)和Na2SiO3 (1 molL-1))为化学活化剂, 其可使EPS的极限氧指数达到36.8%, 同时阻燃性能达到UL-94 V1级别。
2. 研究发现NaOH和Na2SiO3在改性硅藻土时具有一定的协同效应, 其中NaOH较强的水化能力和较快的离子化速度可加速无定形硅质溶胶的形成, 而Na2SiO3较强的粘性和水解产生的Si(OH)4可促使形成更多硅质溶胶, 有助于形成更加致密的网状硅质凝胶, 从而提高其阻燃性能。
3. TG/DSC和SEM结果证实该硅藻土基材料具有良好的热稳定性, 受热过程中可产生膨胀硅质层, 达到对EPS“阻燃隔氧”的屏蔽效应。
4. XRD和FT-IR结果证实在碱性环境下硅藻土结构发生了“解聚-重组”, 先形成无定型的硅质层结构, 其在受热燃烧过程中则进一步发生重组。
The authors have declared that no competing interests exist.
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Flame retardancy of silicone-based materials ,
This review describes some recent works related to the development of the flame retardation of silicone elastomers and/or applications of silicones as flame retardant agents in other polymers. First, the thermal degradation of silicones themselves is discussed, focussing on depolymerization mechanisms, effect of structure, heating conditions, and effect of additives (i.e. less than 5wt% fillers) on thermal degradation of silicones. Then, the influence of several types of mineral fillers (of up to 80wt% content) as ceramization agents of silicones is presented. Finally, the introduction of (functionalized) silicones as flame retardants into other polymers is described.
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| [2] |
Flame retardant mechanism of organo-bentonite in polypropylene ,
Effects of organo-bentonite on the flame retardancy, mechanical and rheological properties of intumescent flame retardant (IFR) polypropylene (PP) were investigated. The X-ray diffraction and transmission electron microscopy measurements indicated that the organo-clay particles were partially exfoliated. Thermogravimetric analysis showed that incorporating 1.8 mass% organo-clay into PP/IFR considerably enhanced the thermal stability and increased the char residue by ca. 7 mass% relative to the sample without organo-clay. Limiting oxygen index (LOI) tests revealed that incorporation of organo-clay led to a further increase in LOI value of intumescent retarded PP samples. The cone calorimeter measurements demonstrated that the organo-clay cannot only further reduce the first peak heat release rate (PHRR 1 ), especially for the reduction in smoke level, but delay the time to the secondary combustion (PHRR 2 ) of intumescent flame retardant PP samples relative to PP/IFR. Unlike the plainland-like structure of residue of PP/IFR, the char residue of PP/IFR/organo-bentonite displayed a folded structure or mountain terrain-like morphology which was due to the deposition of char residue generated by IFR on the surface of clay mineral layers. This interesting morphology of residue was responsible for the enhanced thermal stability, improved flame retardancy, and higher char yields. The rheological behavior of the flame retarded PP samples suggested that the organo-clay can strengthen the three-dimensional network structure formed by the IFR particles in the flame retarded samples. The presence of organo-clay can somewhat enhance the tensile strength and Izod impact strength of PP/IFR composites. Larger organo-clay amounts decreased the above mechanical properties.
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Recent advances for microencapsulation of flame retardant ,
In this paper microencapsulation of magnesium hydroxide, red phosphorus, inorganic phosphorus and organic flame retardants have been reviewed. The effects of different shell materials on the properties of microencapsulated flame retardant and composites have been carefully and thoroughly discussed. It has been demonstrated that microencapsulation provide better water resistance, flame retardancy, compatibility and higher pyrolysis temperature, etc. With proper shell material, the microcapsules not only possess better properties, but also can be used in more rigorous situation.
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A study of diatomite and calcined kaoline properties in anticorrosion protective materials ,
Comparison of properties of diatomite and kaoline in paints were studied in dependence on their volume concentration (PVC). Model paints were prepared containing increasing filler contents, PVC=5% up to the critical volume concentration of the pigment (CPVC). The properties of the prepared coatings were tested by laboratory corrosion tests in both the neutral salt mist and the condensation moisture environments. The effect of diatomite and kaoline PVC on mechanical and anticorrosion protective properties of coats based on epoxide and epoxy-ester binders was studied. It was established that diatomite can be used as a filler in anticorrosion protective coatings. (C) 2010 Elsevier B.V. All rights reserved.
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Application of activated diatomite for dry lime mixes ,
Diatomite is a pozzolanic material containing mainly amorphous silica. In its natural form it possesses low reactivity and is a weak material. The aim of this study was to test and evaluate the diatomaceous deposits of Inza town region as a component of dry lime mixes. Methods of activation meant to change diatomite surface activity and its chemical composition were used to increase diatomite reactivity. Diatomite was activated thermally by burning in various temperatures and chemically by treatment with silicic acid. Modification of diatomite with silicic acid sol increases silica content, promotes hydrophilic properties of its surface, decreases pore dimensions, increases its activity as a mineral additive. Activated diatomite was mixed with lime in mass proportions lime:diatomite 1:4. The laboratory investigations indicated that pastes made with the modified diatomite have higher amount of bound lime and a structure with higher strength, they contain more calcium hydrosilicates and less portlandite than paste containing non-modified diatomite.
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Diatomite coated with Fe2O3 as an efficient heterogeneous catalyst for degradation of organic pollutant, J .
Heterogeneous catalysts have been attracted considerable attention for degradation of organic pollutions to overcome the disadvantages of the homogeneous Fenton process. Diatomite-Fe 2 O 3 hybrid material, honeycomb structure with circular pores synthesized as a heterogeneous catalyst for photo-Fenton degradation of organic contaminants by a novel method. The existence of Fe 2 O 3 nanoparticles in the diatomite-Fe 2 O 3 catalyst was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The catalytic activities of the diatomite-Fe 2 O 3 catalyst were evaluated by the degradation of organic dye under visible light irradiation (>420nm) in the presence of hydrogen peroxide. The results showed that the catalyst exhibited excellent catalytic property for 99.14% decoloration and 73.41% TOC removal of Rhodamine B, which could be attributed to the synergetic effects of the adsorptive power of diatomite and the hydroxyl radicals produced by heterogeneous photo-Fenton reactions. In addition, the decoloration efficiency was still higher than 90% after the catalyst being used for 5 cycles. Hence, the simplicity and cost-effectiveness of the hybrid material could be very promising for synthesizing for high-efficiency visible-light photocatalyst in the degradation of organic pollutants.
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Effect of preparation conditions on the characteristics and photocatalytic activity of TiO2/purified diatomite composite photocatalysts ,
TiO 2 /purified diatomite composite materials were prepared through a modified hydrolysis-deposition method under low temperature using titanium tetrachloride as precursor combined with a calcination crystallization process. The microstructure and crystalline phases of the obtained composites prepared under different preparation conditions were characterized by high resolution scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. The photocatalytic performance of TiO 2 /purified diatomite composites was evaluated by Rhodamine B as the target pollutant under UV irradiation, and the optimum preparation conditions of composites were obtained. The TiO 2 crystal form in composites prepared under optimum conditions was anatase, the grain size of which was 34.12nm. The relationships between structure and property of composite materials were analyzed and discussed. It is indicated that the TiO 2 nanoparticles uniformly dispersed on the surface of diatoms, and the photocatalytic performance of the composite materials was mainly determined by the dispersity and grain size of loaded TiO 2 nanoparticles.
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Synthesis, characterization and activity of an immobilized photocatalyst:Natural porous diatomite supported titania nanoparticles, J .
Abstract Diatomite, a porous non-metal mineral, was used as support to prepare TiO2/diatomite composites by a modified sol-gel method. The as-prepared composites were calcined at temperatures ranging from 450 to 950掳C. The characterization tests included X-ray powder diffraction (XRD), scanning electron microscopy (SEM) with an energy-dispersive X-ray spectrometer (EDS), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption/desorption measurements. The XRD analysis indicated that the binary mixtures of anatase and rutile exist in the composites. The morphology analysis confirmed the TiO2 particles were uniformly immobilized on the surface of diatom with a strong interfacial anchoring strength, which leads to few drain of photocatalytic components during practical applications. In further XPS studies of hybrid catalyst, we found the evidence of the presence of Ti-O-Si bond and increased percentage of surface hydroxyl. In addition, the adsorption capacity and photocatalytic activity of synthesized TiO2/diatomite composites were evaluated by studying the degradation kinetics of aqueous Rhodamine B under UV-light irradiation. The photocatalytic degradation was found to follow pseudo-first order kinetics according to the Langmuir-Hinshelwood model. The preferable removal efficiency was observed in composites by 750掳C calcination, which is attributed to a relatively appropriate anatase/rutile mixing ratio of 90/10. Copyright 漏 2014 Elsevier Inc. All rights reserved.
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New cements for the 21st century: The pursuit of an alternative to Portland cement ,
Preparation of this article entailed authors analyzing the contents of quite a number of papers, although the main objective was never to review the state of the art of new cements. Rather authors intend to discuss why they believe alkaline activated cement can be positioned at the epicentre of a new and necessary transition from today's Portland cement to the new cements of the future. A brief history of alkaline cements serves as an introduction to the technology itself. The interest roused around calcium sulfoaluminate-based cements is also reviewed, albeit summarily. The greater part of the article focuses, however, on alkaline cements which are classified into five categories. The fundamental chemical and structural characteristics of aluminosilicate-based alkaline cements are also described, and the key advances made in the understanding of synthetic gels are discussed. The paper ultimately finds hybrid cements to be technologically viable materials for contemporary construction.
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A physico-chemical basis for novel cementitious binders ,
The drive towards sustainability in construction is shaping our attitudes towards alternatives to Portland cement. Although the cement and concrete industry is essentially sustainable with respect to raw materials supply, and concrete manufacture actually gives relatively low CO 2 emissions per unit volume compared to most competitive construction materials, the current focus on climate change has led to concerns about cement industry-generated CO 2 . Thus, there is interest in developing alternative cements with lower associated CO 2 emissions. This paper seeks to provide a context for innovative development through a review of what is meant by a hydraulic cementitious binder, identification of key physico-chemical properties of successful binders and how novel systems generally rely on similar factors. Concepts such as reactivity, availability of reactive species and physico-chemical drivers for the formation of cementitious systems are discussed as a basis for introducing and reviewing recent developments in the search for ever more environmentally sustainable cements.
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Highly acidic mesoporous aluminosilicates assembled from zeolitic subunits generated by controllable desilication of ZSM-5 in Na2SiO3 solution ,
Mesoporous aluminosilicates (ZM) were hydrothermally synthesized by assembling zeolitic subunits, which were obtained by the controllable desilication of nano-sized ZSM-5 zeolite particles in Na 2 SiO 3 aqueous solution, with cetyltrimethylammonium bromide (CTAB) as the template. The characterization results indicated that ZM possessed a mesoporous structure similar to MCM-41 and ZSM-5 subunits were present in the pore walls. Compared with conventional Al-MCM-41, ZM had less isolated silanol groups, larger pore wall thickness, and higher percentage of tetrahedrally coordinated Al species. The acidity site density, the proportion of strong acidity sites, and the B/L ratio of HZM, which was obtained by ion-exchange of ZM followed by calcination, were significantly higher than those of HAl-MCM-41, but slightly lower than HZSM-5 zeolite. In cumene cracking, HZM showed higher activity than HAl-MCM-41, and much better stability than HZSM-5. In the bulky molecules-involved Friedel鈥揅rafts alkylation of benzene with 1-dodecene and in the liquid phase benzylation of benzene with benzyl alcohol, HZM exhibited higher catalytic performance than HAl-MCM-41 and HZSM-5.
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Structure characterization of hydration products generated by alkaline activation of granulated blast furnace slag. J .
The hydration mechanism and mineral phase structures by waterglass activation of granulated blast furnace slag (GBFS) are investigated in detail by means of XRD and FTIR . The results show that the network structures of glassy phases are disintegrated and there is not any new material phase formed in the early stage of hydration processes. With evolution of hydration, the polycondensation reaction takes place between [ SiO 4 ] 461 and [AlO 4 ] 561 species and some new mineral phases are produced. A hydration mechanism for the formation of geopolymer by waterglass activation of GBFS is proposed in detail.
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| [14] |
Influence of thermal treatment conditions on the formation of phase-pure mullite derived from a nanoparticulate aluminosilicate precursor ,
The crystallization of mullite derived from homogeneous, proto-imogolite allophane-resembling nanoparticulate aluminosilicate sol–gel precursors, was investigated. The kinetics of the crystal growth was studied using differential thermal analysis and the evolution of the chemical structure of the precursor was studied by Fourier transform infrared spectroscopy. Dehydroxylation of the nanoparticulate hydrogel led to the formation of an intermediate structure containing isolated M–OH groups, which temporarily favoured the formation of a co-existing spinel phase. In gels containing polymers, the interparticulate surface condensation was delayed, and further rearrangements occurring in the temperature range of 900–1000°C were found to be essential in order to induce the nucleation-growth of polymorphic mullite, without the formation of an intermediate spinel phase.
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