微波场对SrTiO3化学合成中热过程的影响

在分析微波场中 SrTiO3化学合成体系与电磁场相互作用的基础上 ,探讨合成体系在微波场中的加热机制和影响升温的主要因素（如合成体系的介电性质、保温材料的结构、生坯的致密度等） .结果表明 ,TiO2和 SrCO3在低温阶段对体系的升温速率的贡献相接近 ;高温阶段体系升温主要是 TiO2的贡献 ,同时产物对升温有较大的影响 .微波合成与常规合成在加热方式上的明显不同,对合成过程、合成时间等影响较大 .     

微波场对SrTiO3化学合成中热过程的影响

在分析微波场中SrTiO3化学合成体系与电磁场相互作用的基础上,探讨合成体系在微波场中的加热机制和影响升温的主要因素（如合成体系的介电性质、保温材料的结构、生还的致密度等）,结果表明,TiO2和SrCO3在低温阶段对体系的升温速率的贡献相接近;高温阶段体系升温主要是TiO2的贡献,同时产物对升温有较大的影响。微波合成与常规合成再加热方式上的明显不同,对合成过程、合成时间等影响较大。     

微波辐射技术在有机合成中的应用

综述了微波辐射技术应用于有机合成的研究进展，以微波加热原理，微波与物质间的相互作用该技术影响有机合成的因素及实验条件进行了较详细的讨论。     

柴油机烟碳的微波加热燃烧

本文讨论了将新颖的微波加热技术应用于柴油机烟碳燃烧的可行性。通过研究柴油机烟碳和商品碳黑的组成和结构与介电的关系，以及观察它们在微波场中的加热和燃烧行为，发现柴油机烟碳的介电性和损耗性很适宜于使用微波进行加热燃烧。实验结果表明，在含氧量为１０％的模拟排气条件下，当微波入射功率逐渐增至９００Ｗ时，可使柴油机的烧却率达５０％。文中亦考察了一次燃烧产物中ＣＯ２摩尔分离在燃烧过程中的变化 。     

柴油机烟碳的微波加热燃烧 Ⅰ．柴油机烟碳的介电性能与微波加热特征

本文讨论了将新颖的微波加热技术应用于柴油机烟碳燃烧的可行性。通过研究柴油机烟碳和商品碳黑的组成和结构与介电性能的关系，以及观察它们在微波场中的加热和燃烧行为，发现柴油机烟碳的介电性和损耗性很适宜于使用微波进行加热燃烧。实验结果表明，在含氧量为１０％的模拟排气条件下，当微波入射功率逐渐增至９００Ｗ时，可使柴油机烟碳的烧却率达５０％。文中亦考察了一次燃烧产物中ＣＯ_２摩尔分率在燃烧过程中的变化。     

交联聚苯乙烯小球的微波加热磺化

用微波加热使苯乙烯和二乙烯苯共聚小球磺化。研究了微波功率、加热时间、反应物配比、溶胀剂、反应器在微波炉内的位置等因素对磺化反应的影响。     

微波加热测定氯化钡中结晶水

分析化学实验中,常利用重量法测定水合结晶物质中结构内部的水,如氯化钡中结晶水的测定。但历来采用控温挥发失重的方法,在125°C烘箱内加热1～2h,称量至恒重,而后计算烘去的水分。近来兴起的微波加热已广泛应用于有机化合物、金属有机化合物、配位化合物和聚合物的合成等领域[1,2]。但利用微波加热法对氯化钡中结晶水的测定未见报道,本文利用微波加热法测定氯化钡中的结晶水,总结出微波法测定氯化钡中的结晶水的条件及方法。1　试验部分1.1　仪器微波炉(日本松下公司,功率800W)烘箱(重庆试验设备厂,功率3000W)分析天平(湘仪天平仪器…     

微波活性炭形成高比电容量的微结构机理

1引言 活性炭的制备目前通常采用常规加热进行，存在能耗大、环境污染严重、用作超级电容器电极的性能待提高等问题。微波加热是一种新的加热方法，它与常规加热方式不同，物体的升温不是通过热传输而是通过外场与物体相互作用完成的。微波加热具有选择性、整体性、均匀性、可快速启动与停止、节能无污染等优点，因此以微波作为加热方式制备活性炭的研究引起了人们的兴趣。     

微波在柴油机滤烟器催化再生中的应用：Ⅰ.滤烟器在氮气中的微波加热温 …

利用柴油机台架装置及微波加热装置考察了柴油机催化滤烟器的微波加热温升效应。结果表明,过滤体上捕集的烟碳量对催化滤烟器在氮气中的微波加热温升至关重要,烟碳量的微小增加,可引起滤烟体温度的显著升高。另外,当微波加热过程中隔离氧气时,滤烟体上出现了明显的金属氧化物催化剂被碳还原的现象。     

La^3＋,Co^2＋,Cu^2＋,Zn^2＋与X沸石的微波加热离子交换

用微波加热法研究了水溶液中金属阳离子Ｌａ＾３＋,Ｃｏ＾２＋,Ｃｕ＾２＋,Ｚｎ＾２＋与沸石分子筛ＮａＸ之间的离子交换反应。考察了溶液浓度、加热时间、苏州地交换度的影响并运用正交实验做了直观分析优化。对比实验及Ｘ射线粉末衍射结果表明,在相同的工艺条件下,微波加热法比传统加热法快约６０倍,微波加热对分子筛晶体结构没有破坏作用。     

Influence of microwave heating on fluoride, chloride, nitrate and sulfate concentrations in water

This paper describes a study about the influence of microwave radiation using closed vessels on fluoride, chloride, nitrate and sulfate concentrations in aqueous media. The experiments were processed by heating water using PFA vessels and a microwave cavity oven, determining the anions by ion chromatography. The influence of the exposure time, the atmospheric composition, the kind of heating (water bath or microwave radiation) and the possible formation of hydrogen peroxide were investigated. The limits of quantification for fluoride, chloride, nitrate and sulfate were respectively of 0.17, 0.15, 0.55 and 0.57 μg L⁻¹, and precision, expressed as RSD, was <4% for all considered anions. The hydrogen peroxide was quantified by spectrophotometry, and the limit of quantification and precision were 24 μg L⁻¹ and <5% (n = 10), respectively. The results demonstrate a significant increase in the anion concentration levels (between 63 and 89%) when microwave heating was used in comparison with heating by water bath. In addition, these changes observed can be mainly attributed to the species transfers, either between gaseous (atmospheric gases) and liquid (water) phases for nitrate, or between vessels walls and water for fluoride, chloride and sulfate. Additionally, hydrogen peroxide concentration higher than 45 μg L⁻¹ was determined when water was exposed to microwave radiation.     

Nonthermal microwave effects revisited: on the importance of internal temperature monitoring and agitation in microwave chemistry

The concept of nonthermal microwave effects has received considerable attention in recent years and is the subject of intense debate in the scientific community. Nonthermal microwave effects have been postulated to result from a direct stabilizing interaction of the electric field with specific (polar) molecules in the reaction medium that is not related to a macroscopic temperature effect. In order to probe the existence of nonthermal microwave effects, four synthetic transformations (Diels-Alder cycloaddition, alkylation of triphenylphosphine and 1,2,4-triazole, direct amide bond formation) were reevaluated under both microwave dielectric heating and conventional thermal heating. In all four cases, previous studies have claimed the existence of nonthermal microwave effects in these reactions. Experimentally, significant differences in conversion and/or product distribution comparing the conventionally and microwave-heated experiments performed at the same measured reaction temperature were found. The current reevaluation of these reactions was performed in a dedicated reactor setup that allowed accurate internal reaction temperature measurements using a multiple fiber-optic probe system. Using this technology, the importance of efficient stirring and internal temperature measurement in microwave-heated reactions was made evident. Inefficient agitation leads to temperature gradients within the reaction mixture due to field inhomogeneities in the microwave cavity. Using external infrared temperature sensors in some cases results in significant inaccuracies in the temperature measurement. Applying the fiber-optic probe temperature monitoring device, a critical reevaluation of all four reactions has provided no evidence for the existence of nonthermal microwave effects. Ensuring efficient agitation of the reaction mixture via magnetic stirring, no significant differences in terms of conversion and selectivity between experiments performed under microwave or oil bath conditions at the same internally measured reaction temperatures were experienced. The observed effects were purely thermal and not related to the microwave field.     

Experimental Investigation on the Mass Diffusion Behaviors of Calcium Oxide and Carbon in the Solid-State Synthesis of Calcium Carbide by Microwave Heating

Microwave (MW) heating was proven to efficiently solid-synthesize calcium carbide at 1750 °C, which was about 400 °C lower than electric heating. This study focused on the investigation of the diffusion behaviors of graphite and calcium oxide during the solid-state synthesis of calcium carbide by microwave heating and compared them with these heated by the conventional method. The phase compositions and morphologies of CaO and C pellets before and after heating were carefully characterized by inductively coupled plasma spectrograph (ICP), thermo gravimetric (TG) analyses, X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The experimental results showed that in both thermal fields, Ca and C inter-diffused at a lower temperature, but at a higher temperature, the formed calcium carbide crystals would have a negative effect on Ca diffusion to carbon. The significant enhancement of MW heating on carbon diffusion, thus on the more efficient synthesis of calcium carbide, manifested that MW heating would be a promising way for calcium carbide production, and that a sufficient enough carbon material, instead of CaO, was beneficial for calcium carbide formation in MW reactors.     

Microwave-assisted synthesis and antitumor activity of the supramolecular complexes of betulin diacetate with arabinogalactan

In this work, a water-soluble supramolecular complex was synthesized in an aqueous suspension of betulin diacetate (BDA) and arabinogalactan (AG) upon microwave heating. Microwave heating allows reducing the time required for the complex formation, compared with conventional heating in a water bath. The specific effect of microwave irradiation on the initial reagents and preparation of a supramolecular complex was studied. In contrast to conventional heating, under microwave heating AG macromolecules may break into roughly equal fragments when the temperature increases up to 100 °C. A change in the surface morphology of BDA crystals under microwave heating of the suspension suggests that microwave irradiation facilitates the dissolution of BDA in water. It has been shown that the use of dimethylsulfoxide as a reaction medium for microwave heating led to a decrease in BDA content in the product due to the inclusion of DMSO into AG macromolecules. The BDA–AG complex was isolated from the microwave-heated aqueous solution, after water evaporation, as a thin amorphous film, which exhibited antitumor activity against Ehrlich ascites carcinoma cells and can be a promising material for pharmacological applications.     

The physics of heating by time-dependent fields: microwaves and water revisited

Heating samples by microwave radiation is a particular example of the more general phenomenon where materials absorb energy from an external time-dependent field of an electric, magnetic, or mechanical nature. How this compares with conventional heating is a question of continued interest. Here, we show that the origin of the absorptivity determines whether energy accumulates in the slower configurational degrees of freedom or transfers rapidly to the phonon bath, where only the latter situation is equivalent to conventional heating. Based upon time-resolved measurements of the configurational temperatures, evidence is provided for simple liquids displaying nonthermal behavior if heated by external fields, with molecules being more mobile than expected on the basis of the actual temperature. However, water and related materials are the exception regarding absorptive heating, because energy is transferred to the phonons more rapidly than it is absorbed from the field, and nonthermal effects thus remain absent.     

微波在柴油机滤烟器催化再生中的应用 Ⅰ.滤烟器在氮气中的微波加热温升行为

利用柴油机台架装置及微波加热装置考察了柴油机催化滤烟器的微波加热温升效应． 结果表明,过滤体上捕集的烟碳量对催化滤烟器在氮气中的微波加热温升至关重要,烟碳量的微小增加,可引起滤烟体温度的显著升高． 另外,当微波加热过程中隔离氧气时,滤烟体上出现了明显的金属氧化物催化剂被碳还原的现象．     

Inductive heating with magnetic materials inside flow reactors

Superparamagnetic nanoparticles coated with silica gel or alternatively steel beads are new fixed-bed materials for flow reactors that efficiently heat reaction mixtures in an inductive field under flow conditions. The scope and limitations of these novel heating materials are investigated in comparison with conventional and microwave heating. The results suggest that inductive heating can be compared to microwave heating with respect to rate acceleration. It is also demonstrated that a very large diversity of different reactions can be performed under flow conditions by using inductively heated flow reactors. These include transfer hydrogenations, heterocyclic condensations, pericyclic reactions, organometallic reactions, multicomponent reactions, reductive cyclizations, homogeneous and heterogeneous transition-metal catalysis. Silica-coated iron oxide nanoparticles are stable under many chemical conditions and the silica shell could be utilized for further functionalization with Pd nanoparticles, rendering catalytically active heatable iron oxide particles.     

Determination of total phosphorus and nitrogen in turbid waters by oxidation with alkaline potassium peroxodisulfate and low pressure microwave digestion, autoclave heating or the use of closed vessels in a hot water bath: comparison with Kjeldahl digestion

The evaluation of the use of alkaline peroxodisulfate digestion with low pressure microwave, autoclave or hot water bath heating for the determination of total phosphorus and nitrogen in turbid lake and river waters is described. The efficiency of these digestion procedures were compared to a Kjeldahl digestion procedure with sulphuric acid-potassium sulfate and copper sulfate. The final solution before digestion was 0.045 M in potassium peroxodisulfate and 0.04 M in sodium hydroxide. Procedures were evaluated by the analysis of suspensions of two reference materials, National Institute of Environmental Science, Japan, no. 3 Chlorella and no. 2 pond sediment and natural turbid waters. Best recoveries of phosphorus and nitrogen by microwave heating were obtained when solutions were digested at 95 °C for 40 min. Quantitative recoveries of phosphorus from Chlorella suspensions up to 1000 mg/l were obtained by all three heating procedures, but incomplete recoveries of nitrogen occurred above 20 mg N/l in the digested sample. Good recoveries of phosphorus and nitrogen from suspended sediment suspensions were obtained only from solutions containing <150 mg/l of suspended sediments. Recoveries of phosphorus from phosphorus compounds containing COP and CP bonds added to distilled water were quantitative (94-113%) except for polyphosphates (microwave, 34±8; autoclave, 114±6; water bath, 96±4) and aluminium phosphate (8-23%). Recoveries of nitrogen compounds containing CN bonds added to distilled water were quantitative (94-96%). The analysis of a range of natural turbid water samples by alkaline peroxodisulfate and microwave, autoclave and water bath heating gave similar total phosphorus and nitrogen results. All procedures using alkaline peroxodisulfate underestimate phosphorus concentrations at high suspended sediment concentrations (>150 mg/l) and are only suitable for the analysis of very turbid samples when the turbidity is due to organic matter (algal cells, plant detritus). Underestimation of nitrogen occurs when samples contain more than 20 mg N/l.