微波与水浴加热条件下对沸石分子筛吸附量的对比研究

为了研究微波作用对沸石分子筛吸附的影响与特点,采用静态吸附容量法,对比研究了微波与水浴两种加热条件下沸石分子筛的吸附量.实验结果表明:在相同的加热温度下,与水浴加热相比,微波加热能够快速加热分子筛,极大地缩短了加热时间;在相同的温度与压力条件下,与水浴加热相比,微波作用下分子筛吸附量总是更低.这表明微波加热沸石分子筛,...     

微波条件下PVC食品保鲜膜中DNBP在水基模拟物中的迁移行为研究

以气相色谱-质谱联用技术为分析手段,研究了在微波条件下PVC食品保鲜膜中DNBP在3种水基食品模拟物中的迁移规律。实验结果表明,DNBP的迁移量随微波功率、加热时间和加热温度的增加而增大,并与食品模拟物的种类有关;当加热温度和加热时间相同时,微波加热条件下DNBP在3种食品模拟物中的迁移量均高于常规加热方式。     

微波加热下食品球形物料温升状态的研究

微波加热温升状态研究是传热质学研究的基本内容之一，也是食品微波加热，干燥，杀菌必定涉及的内容。微波加过程是一种复杂的非稳态过程，它与物料的物性，形状尺寸，微波功率，频率及场分布等有关。本文对均匀块内球形物料加热过程进行了实验和理论研究，测定了多种料的温度分布，提出了过程的传热传质的数学模型，在若干简化条件下，求出了温度分布的数值解，与实验结果接近。关利用数学模型对程进行了分析。     

微波烧结Mn-Zn 铁氧体的微观结构演变特征

以传统氧化物法合成的Mn-Zn铁氧体前驱体和外购前驱体为实验原料,经压制成形后用频率为2.45 GHz的微波在1 200~1 400℃烧结制备Mn-Zn铁氧体软磁材料.对烧结过程样品的微观结构和形貌进行了研究,并探究了烧结过程致密化特性及微波加热温度对Mn-Zn铁氧体密度的影响.研究表明:微波烧结的Mn-Zn铁氧体具有典型的尖晶石结构,样品主体相为Mn0.4Zn0.6Fe2O4;用SEM观察样品形貌,发现在1 350~1 400℃烧结的样品结晶状况良好,晶界平直,烧结组织均匀;微波烧结温度对密度有较大影响,在1 200~1 400℃,随着烧结温度升高样品密度增高,密度为4.80~5.28 g/cm3,在1 400℃烧结样品比较致密.微波烧结可以实现样品的快速致密.     

微波加热Mg-TiO_2混合物的研究

在氩气气氛下微波辐射加热Mg-TiO_2混合物,通过XRD、SEM研究了不同n(Mg)/n(TiO_2)和反应温度对产物物相、形貌的影响。n(Mg)/n(TiO_2)影响产物中Mg-TiO_2化合物的种类和亚氧化钛的生成,对产物的形貌没有明显影响。反应温度影响产物的物相比例,温度升高会导致产物的颗粒烧结粗大。使用微波加热Mg-TiO_2虽然生成了钛酸镁及亚氧化钛,但生成量少、分离困难,因此该制备方法不可取。     

纳米羟基磷灰石粉体的水热合成

采用Ca(NO3)2·4H2O和(NH4)3PO4·3H2O作为反应前驱物,通过水热合成颗粒尺寸在100nm以下的短棒状或针状HA晶体.X射线衍射(XRD)、透射电镜(TEM)和红外光谱(FTIR)分析讨论水热温度、反应时间、表面活性剂和烧结与物相组成、晶粒尺寸和晶体形貌的关系.实验结果表明升高反应温度和延长反应时间有利于HA的生成;表面活性剂有助于改善粉体的分散性能;烧结能提高晶体的结晶程度,但粉体易团聚,当温度高于800℃时HA发生分解.     

在微波辐照下Li1+xMn2-xO4尖晶石的固相合成

采用微波直接加热方法在不同温度与氧分压条件下制各出Li1 xMn2—xO4(x＝0、0．025、0．05、0．15)尖晶石氧化物．利用XBD与SEM／EDX等手段研究了合成样品的晶体结构、形貌特征以及相交特点．在850～1200℃氧气氛下加热时，合成的样品由立方尖品石相和微量的杂相Li2MnO3组成，而且随着温度升高，晶体中阳离子混合现象减少，晶体结构的对称性增大，但是晶体结构的参数基本不变．Li1 xMn2—xO4样品中杂相Li2MnO3的含量随x的增大而增加．在相同的温度与氧分压下，用微波加热合成的尖晶石氧化物的热稳定性比用常规加热方法合成的高．用微波加热合成的尖品石氧化物结晶度好，晶体颗粒呈规则的八面体或多面体形态。     

基于固相法浸取煤矸石中有价组分铁、铝、钛

为了探索煤矸石的高效资源化利用,基于固相法和正交实验原理,通过微波辅助和传统加热方式,系统研究了其对煤矸石中铁、铝、钛浸取率的影响。结果表明:两种加热方式均可促使煤矸石中的铁、铝、钛组分达到较高的浸取率。其中,微波辅助加热最佳浸取条件为微波功率800W、酸矸比1.5(w/w)、微波辐照时间60min,此时煤矸石中的铁、铝、钛浸出率分别为98.13%、95.07%和76.33%;传统加热最佳浸取条件为加热温度170℃、酸矸比1.4(w/w)、加热时间4h,此时煤矸石中的铁、铝、钛浸出率分别为98.69%、97.43%和92.45%。采用化学分析、X射线衍射(X-ray diffraction,XRD)、扫描电镜(Scanning electron microscope,SEM)、能谱仪(Energy dispersive spectroscopy,EDS)等对煤矸石及浸取渣的化学成分、物相组成、微观形貌和微区成分进行了表征分析。     

Pb1.5Nb2O6.5型微波介质陶瓷粉体的焙烧工艺研究

探讨了合成Pb1.5Nb2O6.5型微波介质陶瓷粉体的焙烧温度、焙烧时间、添加剂等不同工艺因素对Pb1.5-Nb2O6.5粉体物相变化、晶粒生长及形貌的影响,采用X射线衍射(XRD)和扫描电子显微镜(SEM)对制备的粉体进行物相与晶体形貌检测.实验结果表明在其他工艺因素控制得当时,焙烧温度对粉体粒度和物相变化的影响最大,而不同类型的添加剂不仅可以使晶粒生长更为完整,尺寸增大,同时也可以不同程度地改变粉体颗粒的生长趋势与形貌.实验制备出的Pb1.5Nb2O6.5粉体物相单一无杂质、晶粒尺寸较小,适于进一步制备微波介质陶瓷元件.     

微波法合成锂离子电池正极材料LiCoO2

从节约能源、降低成本及保护环境出发,利用微波加热特点,采用微波技术对微波法制备LiCoO2正极材料进行了研究.在一定的微波功率、辐射时间制度下制备出LiCoO2样品并进行了电化学性能测试.通过X射线衍射(XRD)、扫描电镜(SEM)研究了样品的物相结构和形貌.结果表明:在一定的微波功率、辐射时间制度下,可以快速得到单一相的层状LiCoO2正极材料,与传统高温固相法相比,采用微波合成的LiCoO2材料不仅具有同样优越的电化学性能及形貌结构,而且合成时间短,生产成本低.     

Diverse effects of microwave heating on anatase crystallization in ionothermal synthesis of nanostructured TiO<Subscript>2</Subscript>

This article examines anatase crystallization in the ionothermal synthesis [sol gel method in the presence of ionic liquid (IL)] of nanostructured TiO₂ under microwave (MW) irradiation. MW heating can lead to rapid temperature increase of chemical reactions. In this study, we found that rapid temperature increasing effects on anatase crystallization were diverse and dependent on initial water concentration, MW irradiation time, and IL concentration. The results indicated that higher anatase crystallinity was obtained at high water amount irrespective of IL concentration. However, at lower water amounts, higher anatase crystallinity occurred only when MW heating was applied after the mixtures reacted for certain duration, especially at lower initial temperature and at a specific IL concentration. Different MW heating effects on the hydrolysis–condensation reaction and the post-treatment stage under MW/IL conditions can explain this diversity. Heating characteristics of IL/water mixtures under MW irradiation were also discussed.     

Effects of microwave irradiation on the crystalline phase of zeolite synthesized from fly ash by hydrothermal treatment

Coal fly ash was dissolved into NaOH aqueous solution and the mixture of rice husk ash as a silica source with the solution separated from the insoluble fly ash was treated hydrothermally at 373 K with microwave heating and conventional heating. Through this experiment, we investigated effects of microwave irradiation on the crystalline phase of zeolites synthesized from fly ash and clarified what process is intensively affected by the microwave irradiation. As a result, it was found that the product powder synthesized with microwave heating has a relatively higher hydroxysodalite phase than that with conventional heating, even if the synthesis conditions were the same. It was also clarified that promotion of hydroxysodalite generation by microwave irradiation is not induced by the enhancement of the crystalline phase transition from phillipsite to hydroxysodalite, but by the acceleration of hydroxysodalite formation from the precursor, aluminosilicate gel, directly. Moreover, it was found that promotion of hydroxysodalite formation is not due to the heat spot on the surface of the carbon caused by microwave irradiation. We revealed that the sensitivity, which is defined as the ratio of the quantity of generated heat to the energy of the microwave generated by the magnetron, of hydroxysodalite is almost 10 times as high as that of phillipsite. From these results, the following enhancement mechanism of hydroxysodalite crystal generation by microwave irradiation was proposed. When zeolite nuclei grow to the zeolite crystal on the interface between zeolite nuclei and aluminosilicate gel, the crystal growth of hydroxysodalite is promoted selectively as the surface temperature of hydroxysodalite is much higher than that of phillipsite in the case of microwave heating.     

The hydrothermal analogy role of ionic liquid in transforming amorphous TiO2 to anatase TiO2: elucidating effects of ionic liquids and heating method

In this study, the specific coexistence of water and ionic liquid being the lower temperature thermal annealing condition for anatase crystallization of amorphous titania at ambient pressure was found. The test ionic liquids were 1-butyl-3-methylimidazolium hexafluorophosphate and 1-butyl-3-methylimidazolium tetrafluoroborate. After deep investigation, we found that there existed an analogy between our lower temperature thermal annealing treatment system (LTTAT) and hydrothermal treatment system. In LTTAT system, the ionic liquid played an important role in driving surface crystallization of amorphous TiO₂ to the anatase phase by retaining a suitable amount of water through a dissolution–crystallization mechanism. We could observe higher hydroxyl group ratio of hydroxylated titanium compound from X-ray photoelectron spectroscopy (XPS) data during initial thermal annealing period. The self-assembly ability of ionic liquid then lead to kinetical dehydration and crystallization of hydroxylated titanium compound around it during the following annealing process. Based upon this proposition, the effects of different types of ionic liquid and its amount, temperature effect, and heating method on anatase crystallinity, characterized by X-ray diffraction (XRD), were investigated. It was found that different temperatures and microwave heating effect were observed for different types of ionic liquid. From these observations, it was pointed out that we could get better anatase crystallinity and good photodegradation performance by using the system containing ionic liquid having higher water-adsorbing ability and microwave heating annealing.     

甲基丙烯酸甲酯的微波聚合特性和产物结构

在微波辐射下进行甲基丙烯酸甲酯（MMA）的无乳化剂乳液聚合，发现在微波辐照下MMA聚合速率较加热有较大的提高，微波辐照制备的聚甲基丙烯酸甲酯（PMMA）乳液粒子形状规整，粒径分散系数1．03，达到单分散要求，微波制备乳液的数均分子量与常规加热接近，但分子量分布变窄，微波和热无乳化剂聚合的PMMA的热解过程一致，在200℃－390℃有三个分解峰，与有乳化剂聚合有很大差异，FT－IR，13C－NMR表明无乳化剂聚合的PMMA序列结构以间同为主，微波聚合略微降低PMMA的立构规整度。     

Phase transformations and phase-selective syntheses of aluminophosphate molecular sieves

A few aluminophosphate (AlPO) molecular sieves are synthesized hydrothermally under microwave irradiation and conventional electric heating. Less stable AlPO molecular sieves especially with large pore can be obtained preferentially in a short crystallization time because the inter-conversion of less stable phase into a more stable one is prohibited in short reaction time. The VFI transforms into AFI, and finally into APC, with the increase of reaction time since the relative stability is VFI < AFI < APC under the chosen reaction conditions. The relative stability can be explained with the pore size or by the framework density of each structure. Due to the rapid crystallization involved in the microwave method and instability of porous materials with large pore, these porous materials can be selectively synthesized by microwave irradiation. The synthesis of extra-large-pore VPI-5 using triethylamine is also reported for the first time, and the synthesized VPI-5 is very stable that can be dried at 100 degrees C at atmospheric pressure without the phase-transformation into AIPO-8.     

聚N-异丙基丙烯酰胺水凝胶的微波合成与性能

以水为溶剂,N-异丙基丙烯酰胺(NIPAM)为单体,N,N-亚甲基双丙烯酰胺(Bis)为交联剂,分别通过微波合成法和水浴加热法制备了聚N-异丙基丙烯酰胺(PNIPAM)水凝胶,研究了交联剂浓度、反应时间、反应温度等对反应的影响,及PNIPAM水凝胶在不同温度和pH值下的溶胀性变化。研究结果表明,与水浴加热法相比,微波合成法缩短了反应时间,从10h缩减至1h左右;适当延长反应时间和提升反应温度有利于提高单体转化率。微波法合成PNIPAM的最佳条件为:H2O为溶剂,100℃~110℃反应40 min~60 min,交联剂m(Bis)/m(NIPAM)=5/100,单体转化率97%~98%。而且,微波合成法制备的水凝胶具有更显著的温度和pH敏感性能。     

微波辅助液相还原法制备超细铜粉

以硫酸铜为原料,水合肼为还原剂,采用微波辅助液相还原法制备了超细铜粉,研究了微波的引入对超细粉体制备的影响,通过XRD、激光粒度分析和TEM表征了粉体的结晶性能、粒度度以及粉体的形貌,研究表明,微波的引入可以明显加速晶化反应的进行,在较短时间内制得的铜纳米晶发育好于传统热处理方式制得的铜纳米晶。     

A method for the evaluation of electromagnetic wave absorption potential using surface temperature change under microwave irradiation

Absorption behavior of electromagnetic wave by spherical H₂O-filled SiO₂ shell microcapsule-dispersed paraffin matrix composites is evaluated using a microwave heating and thermographic system. The composites under microwave irradiation show temperature change at the specimen surface. The temperature rises as an increase of a volume fraction of H₂O and the absorption of electromagnetic wave is strongly correlated with the temperature rise.