微波辐射对洗涤剂用酶的作用

蛋白酶分别经过1000W微波辐射8s和10s后,在实验条件下,活性达到最大值,分别提高了11％和16％。加入标准粉后,二者去污比值几乎没有变化。微波辐射后的两种蛋白酶放置于室温下2个月,其活性均随时间变化而缓慢下降。脂肪酶分别经过1000W微波辐射5s后,活性达到最大值,分别提高了22％和7％。加入标准粉后,二者去污比值几乎没有变化。微波辐射后的两种脂肪酶放置于室温下4个月,活性均随时间变化回到未经微波辐射的最初状态。     

Drying behavior of lignite under microwave heating

Because of lignite’s high moisture content, it must be dried before most applications. Microwave radiation may be suitable for efficient drying because of its special heating properties. This study investigated the drying behavior of lignite samples from eastern Inner Mongolia by microwave thermogravimetric analysis. Three stages of microwave drying were observed: preheating, fast weight loss, and falling rate drying periods. Samples’ surface temperatures increased dramatically during preheating, dropped slightly in the second period, and rose again in the final period. The measured surface temperature was <95°C during microwave heating. The overall moisture content decreased more rapidly under higher microwave power. Fine lignite particles (diameter <0.2?mm) and lump samples (particle size 10?mm) dried better than granular lignite (particle size 1–2?mm). The samples also underwent slight natural drying (1–2% point reduction in moisture content) after microwave treatment. The critical moisture content of lignite (11–15% under experimental conditions) was redefined. Energy consumption was analyzed to evaluate the feasibility of the proposed drying process.     

微波加热制备低水硼酸锌

以硼砂和硫酸锌为原料,研究了微波加热制备低水硼酸锌(2ZnO·3B2O3·3.5H2O)的工艺,考察了反应温度、液固质量比、微波辐射时间、微波功率等因素对硼酸锌产率和粒径分布的影响,通过优化实验,确定了最佳工艺条件.实验结果表明,在反应温度85℃,液固质量比3:1,微波辐射时间50 min,微波功率630 W的条件下可制备平均粒径为10.16μm的低水硼酸锌,产率达99.18%.同时采用XRD及TG分析对产品进行表征,XRD谱图与低水硼酸锌标准谱图吻合,TG分析显示产品脱水温度与低水硼酸锌的理论脱水温度接近.     

A review: 3D printing of microwave absorption ceramics

Along with extensive research on the 3D printing and microwave absorption ceramics, 3D printing technology provides a great possibility for microwave absorption ceramics with arbitrary shapes in a faster, cheaper and more flexible way. This review focuses on the latest evolution in the raw materials, the structure design and the advanced additive manufacturing technologies of 3D printing microwave absorption ceramics. Firstly, the representative raw materials are divided into three categories, including ceramic powder, cermet powder and precursor resin. In addition, additives give rise to improvement of microwave absorption properties of ceramics. Secondly, based on two attenuation theories, structure design makes further efforts to enhance the microwave absorption performance of ceramics. Finally, comparisons are made between diversified manufacturing technologies to facilitate the selection of the best ones for different application in practical use. This study presents a summary of research that has been conducted to produce microwave absorption ceramics by additive manufacturing.     

微波消解-火焰原子吸收法测定水泥中的氧化镁

建立了微波消解-火焰原子吸收法测定水泥中氧化镁的方法。采用微波消解的方法对样品进行前处理,酸消解体系为硝酸,在特定的消解程序下对样品进行消解,经过排酸的步骤,加入氯化锶掩蔽其他元素的干扰,火焰原子吸收法测定氧化镁。在浓度范围0~0.8mg/L时呈现良好的线性,氧化镁的回收率在98.0%~101.2%,相对标准偏差为:0.09%,方法的检出限为:0.0013mg/kg。运用所建立的方法对大理市范围内的5个水泥样品及加标样品中的氧化镁进行检测,结果显示该方法选择性强、灵敏度高,前处理方法简单、快速、安全,适合水泥中氧化镁的测定。     

The effect of wetting liquid droplet size on the growth of agglomerates during wet drum granulation

Results of investigation of the effect of wetting liquid droplet size on the growth of agglomerates during wet drum granulation of dolomite flour of selected grain-size composition which guaranteed geometrical similarity were discussed.

The process of granulation was carried out batch-wise in a drum granulator 0.5 m in diameter and 0.4 m long at rotational speed 0.33 s⁻¹ and constant volumetric drum filling degree =0.1. On the bed tumbling in the drum, the wetting liquid (distilled water) was supplied at a constant flow rate Q_w=12×10⁻³ m³/h. The size of wetting droplets was changed using various air flow rates through pneumatic spray nozzles in the range Q_a=1.0 to 3.0 m³/h and applying a sprinkler which supplied (drop-wise) the liquid uniformly along the entire drum length. In the whole experimental cycle, constant mean saturation degree of the feed equal to S=0.293 was used. Relationships determining the effect of wetting droplet size and particle size distribution of the raw material on the rate of agglomerate growth during drum granulation were developed.     

Construction of plate-like magnetic heterostructure for synergistic microwave absorption

The dramatically dropped permeability of magnetic materials at gigahertz frequencies, known as the Snoek's limit, has severely constrained the microwave absorbing performance of magnetic materials. To break the Snoek's limit at high frequencies, a plate-like magnetic heterostructure composed of Ni-Fe ferrite, nitride, and Permalloy is fabricated through nitridation of Ni-Fe layered double hydroxide. It has been found that single-phase magnetic flakes or the multi-phase heterostructure with extraordinarily linked magnetic nanoplates can be obtained by simply adjusting the temperature of nitridation. Due to the highly anisotropic morphology and synergistic effect at abundant heterogeneous interfaces, the magnetic heterostructure shows enhanced imaginary permeability that is even higher than that of single-phase Permalloy. Accordingly, the magnetic loss in C and X bands is improved, leading to significant enhancement of attenuation constant in this novel microwave absorber. Combined with the moderate permittivity, the impedance matching of the heterostructure is superior compared to every single component, as well as the mixture of these components. As a result, the minimum reflection loss of −59.30 dB at a thickness of 2.02 mm and effective absorption bandwidth (RL<−10 dB) of 2.44 GHz is realized. These findings provide a novel path to designing high-performance microwave absorbers based on magnetic materials.     

石墨烯/聚合物纳米复合材料制备与微波吸收性能研究进展

二维片状的石墨烯不仅具有优异的力学、热学和电学性能,而且还具有较好的微波吸收特性。自它被发现以来,一直受到科学界的广泛关注,目前已有学者将其与聚合物复合,制备了石墨烯/聚合物纳米复合材料,这种新型微波吸收材料不仅吸波效果好而且密度小、易加工。目前石墨烯/聚合物纳米复合材料用于微波吸收的报道还比较少,该研究基本处于起步阶段。本文首先概述了石墨烯独特的物理结构和优异的力学、热学、电学性能,然后综述了石墨烯/聚合物纳米复合材料的制备方法,并分析了其微波吸收机理,最后结合国内外研究现状展望了石墨烯/聚合物纳米复合材料制备与微波吸收性能研究的发展方向,指出调控复合材料的微观形貌,对石墨烯进行磁性掺杂,探索石墨烯与聚合物微波吸收的协同效应将成为今后研究的重点和热点。     

Drying kinetics of Philippine nickel laterite by microwave heating

In this study, microwave heating was used to dry nickel laterite, which contains significant quantities of free water, crystal water, and hydroxy water. The results show that the main phase of crystal water is Ca₃Al₆Si₁₀O₃₂(H₂O)₁₃, and the main phases of hydroxy water are FeO(OH) and Mg₅(Al, Cr)AlSi₃O₁₀(OH)₈. The microwave drying process of nickel laterite can be divided into two stages: the removal of free water and the coupled removal of free water, crystal water, and hydroxy water. The effect of particle size and microwave power output were studied, and these indicate that the drying time and specific energy consumption decrease with increasing particle diameter and microwave power. The effective diffusivity and activation energy were calculated, and these are larger in the second stage than that in the first stage. The activation energies are 27.66 and 32.80?W/g for the first and second stages, respectively. The phase transition of the product, schematic drying mechanism, and feasibility analysis of the microwave drying process are also discussed.     

Two-step preparation of fly ash-based composites for microwave absorption

To develop a novel utilization avenue for fly ash (FA), the Co-loaded FA (CoFA) was constructed utilizing FA as raw material to acquire the enhanced microwave absorption (MA) performance. In this study, the CoFA composites were fabricated by a two-step method, including the construction of FA-based ceramic matrix and a subsequent loading of magnetic components. The results of XRD, SEM, and elemental mapping images revealed that Co particles generated from the carbothermal reduction were well dispersed over the interior and surface of matrix. Compared with pure FA, the as-prepared CoFA composites demonstrated the impressive MA performances, which were attributed to the good impedance matching, conduction loss, and interfacial polarization effect between the matrix and Co. When the annealing temperature kept at 700°C, the minimum reflection loss (RL_min) of as-prepared CoFA700 reached up to −40.5 dB and the broad absorption band was measured to be 4.7 GHz with a thickness of 2.0 mm, which was superior to pure FA. Our strategy might provide a new direction to the fabrication of high-efficient MA materials derived from FA.     

Microwave heating to prevent deterioration of cottonseed during storage

Fuzzy cottonseed samples of 14.5% moisture and <1.0% free fatty acids (FFA) contents heated in a conventional, home-style microwave oven at 700W and 2450 MHz for intervals up to 2.0 min. The 2.0-min treatment reduced the moisture content to 13.1%. Examination of the seed immediately after microwave heating (MWH) indicated no differences in the proteins or in the quality or quantity of the cotton linters as compared with unheated seed. Neither the oil content of the seed nor the quality of the oil were affected by the microwave treatment. After nine weeks of storage at 50°C, the unheated seed had a FFA content of >3.0% while the FFA content of the 2.0-min microwave-heated seed remained <1.0%. During this storage period there was significant deterioration of the protein quality of the unheated seed. The 2.0-min MWH treatment, however, maintained the integrity of the protein during storage.     

微波消解-冷原子吸收光谱法测定化妆品中的汞

采用密闭微波技术处理化妆品,对样品进行一次性微波消化,用冷原子吸收光谱法测定其中的汞,方法的特征浓度为2.5×10-4μg/mL,RSD为2.82%,回收率在98%～102%,方法简便、快速和准确,结果令人满意。     

正交表法测定微波脱水最佳功率和加热时间值

原油乳状液是十分复杂的分散体系,原油由于产地、开采方式、温度、压力的不同,性质也差别很大。原油含水对石油储运、加工以及产品质量造成了不利的影响,对设备造成较大的危害,因此原油破乳脱水成为石油开采及加工生产中最重要的环节之一。本实验就是在已有的试验条件下,运用正交表设计试验方案,分析了微波作用功率和加热时间对微波脱水率的影响规律,研究表明,乳状液脱水率受微波功率和加热时间的影响很大,微波加热功率和加热时间存在一个最佳值,在功率为400W,加热时间为7m in时脱水效果最好。     

微波消解-火焰原子吸收法测定水泥原料中的总铬

建立了微波消解-火焰原子吸收法测定水泥原料中总铬的方法。采用微波消解的方法对样品进行前处理,以硝酸-盐酸为消解体系,在特定的消解程序下对样品进行消解,经过排酸的步骤,加入氯化羟胺掩蔽其他元素的干扰,火焰原子吸收法测定总铬。在浓度范围0~1.0mg/L时呈现良好的线性,总铬的回收率在90.5%~99.0%,相对标准偏差为:0.32%,方法的检出限为:0.01mg/L,运用所建立的方法对5个水泥原料中的总铬进行检测,结果显示该方法选择性强、灵敏度高,前处理方法简单、快速、安全,适合水泥及原料中总铬的测定。     

Enhanced dielectric and microwave absorption properties of LiCoO2 powders by magnesium doping in the X-band

The solid-state reaction was adopted to prepare a series of LiCo_1−xMg_xO₂ powders doped with different amount of Mg²⁺. The XRD patterns reveal single phase for all the prepared materials. The shift of the electronic structure of LiCo_1−xMg_xO₂ has been investigated by X-ray photoelectron spectroscopy to confirm the single phase for material. Influence of dopant amount on the electromagnetic properties of LiCoO₂ powders was analyzed. The dielectric and the microwave absorption properties were evaluated. Results showed that with the increase in Mg the complex permittivity decreased after increasing. Maximum values of both real part (ε′ = 16.2 at 8.2 GHz) and imaginary part (ε″ = 4.1 at 8.2 GHz) were obtained for x = 0.06. Monolayer absorbent containing 75 wt% LiCo_0.94Mg_0.06O₂ had the peak microwave absorption properties in a thickness of 2.1 mm. The available bandwidth (<−10 dB) was obtained in 8.4-10.2 GHz and the minimum reflection loss was −50.4 dB, which indicated that LiCo_1−xMg_xO₂ powders would be potential materials as microwave absorption.     

Microwave absorption measurements of the electrical conductivity of small particles

A microwave absorption technique based on cavity perturbation theory is shown to be applicable for electrical conductivity measurements of both a small, single-crystal particle and finely divided powder samples when values fall in either the low (<0.1 ^–1 cm^–1) or the intermediate (0.1 100 ^–1 cm^–1) conductivity region. The results here pertain to semiconductors in the latter region. If the skin depth of the material becomes significantly smaller than the sample dimension parallel to theE-field, an appreciable error can be introduced into the calculated conductivity values; however, this discrepancy is eliminated by correcting for the field attenuation associated with the penetration depth of the microwaves. A modification of this approach utilizing the skin depth allows a first-order correction to be applied to powder samples which results in the accurate measurement of absolute values, and results with doped Si powders are compared to values obtained from one small single particle using this microwave technique as well as reported DC values determined with single crystals. The use of this microwave absorption technique with small particles having high surface/volume ratios, such as catalyst supports and oxide catalysts, under controlled environments can provide fundamental information about adsorption and catalytic processes on such semiconductor surfaces. An application to a ZnO powder demonstrates this capability.     

微波功率对油页岩热解的影响

对甘肃油页岩进行了微波热解实验研究,考察了油页岩在微波场中的升温特性及功率对页岩油、半焦、干馏气产率和组成的影响。结果表明：在微波场中油页岩干馏终温可达800℃以上;不同功率下干馏气组成不同,在480 W时干馏气中有效组分（H2＋CH4＋CO）达55%以上;随着功率的增大,半焦产率逐渐减小;页岩油产率随功率先增加后减小,在480 W时达到最大值13.5%;而干馏气产率随功率逐渐增大,在480 W时可达10%。     

微波消解—冷原子吸收光谱法测定化妆品中痕量镉

建立了微波消解冷蒸气发生—原子吸收光谱法测定化妆品中痕量镉的分析方法。化妆品样品经微波消解处理,对微波消解的温度和时间进行了优化,并对测试条件中载气流速、溶液酸度、增敏剂加入量和干扰离子的消除进行了实验。在选定的最优测试条件下,镉在0~40μg/L浓度范围内呈良好线性关系,方法的检出限为0.050μg/L,样品加标回收率为95.4%~103.3%,相对标准偏差小于4.6%。     

Morphological changes of wide polyoxymethylene rod during a microwave heating drawing process

The microwave heating drawing process for producing a polyoxymethylene (POM) rod (2.5 mm in diameter) with a sonic modulus of 40 GPa has been analysed by investigating the changes in both orientation and thermal properties during drawing. During the initial crystalline deformation in the necking region, the lamellae are oriented perpendicular to the draw direction and are then unfolded into microfibrils. The crystalline orientation function reaches a high value (0.988) at a draw ratio of 6 immediately after necking. In the advanced ultra-drawing stage, the Young modulus increases gradually with increasing amorphous orientation. At the same time, the orientation distribution in the radial direction is caused by the temperature distribution induced in the radial direction of the rod. It is noted that fine adjustments of ambient temperature and microwave power are required to get ultra-high-modulus POM rods over 40 GPa with large crosssections.     

微波辐射的功率密度对苯甲酸乙酯酯化反应影响的研究

研究在水浴和微波两种供能方式下苯甲酸乙酯酯化反应产量的影响.结果表明:在微波供能方式下,反应时间缩短明显,反应速率加快,苯甲酸乙酯产量随微波功率密度的增加而增加,和蔗糖水解反应相似该酯化反应也存在阈值(阈值在4.09～4.42 J/(s·cm3)之间),微波功率密度超过阈值后(在4.42～4.52 J/(s·cm3)时...