Influence of gadolinium on microstructure and magnetic properties of sintered NdGdFeB magnets

The effect of Gd content on microstructure and magnetic properties of sintered Nd33.03-xGdxFe65.65B1.32 (x=0-2) was studied in this paper to improve the thermal stability of NdFeB and to reduce the raw material cost. The results showed that better magnet performance could be obtained by adding Gd (0-1.5 wt.%) with partial substitution of Nd in Nd33.03-xGdxFe65.65B1.32. It was also found that the Nd33.03-xGdxFe65.65B1.32 magnets showed the best performance when Gd addition increased to 1.0 wt.%. The temperature coefficient Br (α) could be improved from -0.15%/oC to -0.063%/oC (maximum work temperature 120 oC) and the Curie temperature could be improved from 315 oC to 323 oC because the Gd2Fe14B had positive temperature coefficient Br (α) and higher Curie temperature than that of Nd2Fe14B. The coercivity could be improved from 10.2 to 11.48 kOe and the microstructure was close to ideal microstructure. The magnetic performance decreased sharply by adding Gd (above 2 wt.%) with partial substitution of Nd in Nd33.03-xGdxFe65.65B1.32 because the Gd element concen-trated in the grain boundaries.     

列管式换热器管束振动特性分析

管束换热器之所以振动是由于流体与管束等传热元件的冲击从而产生了诱导振动,而当流体诱发振动的频率与后者的固有频率一致或相当接近时,就会发生共振。用解析法导出了换热器管束固有频率的计算方法,并提出了预防和解决共振问题的措施。     

固定化脂肪酶在离子液体中催化合成生物柴油

通过硅胶载体涂布法对细菌Burkholderia cepacia GX-35所产的脂肪酶进行固定化。比较了自制固定化脂肪酶在4种离子液体中催化合成生物柴油的效果,其中文章研究新设计并合成的一种离子液体溴代1-乙基-2-甲基咪唑[EMIM]Br对催化反应起促进作用。通过对转酯率的测定,研究了固定化脂肪酶在[EMIM]Br中的最适反应条件:最适反应温度为35℃,[EMIM]Br加入量为花生油质量分数的60%,最佳醇类为乙醇,加水量为花生油质量分数的5%,乙醇与花生油之比为9∶1,固定化脂肪酶加入量为花生油的20%,反应时间为6 h。固定化脂肪酶在[EMIM]Br中稳定性好,使用6次之后转酯率下降不明显。试验结果表明,与不加[EMIM]Br相比,加[EMIM]Br能有效提高生物柴油的转化率。     

离子液体中间体1-丁基-3-甲基咪唑溴盐的合成

以N-甲基咪唑和1-溴代正丁烷为原料合成1-丁基-3-甲基咪唑溴盐[Bmim]Br,研究了反应时间、反应温度、N-甲基咪唑与1一溴代正丁烷的摩尔比及溶剂对[Bmim]Br收率的影响,产物结构通过。HNMR及FT—IR表征。实验结果表明,在反应温度60℃、反应时间24h、N-甲基咪唑与1-溴代正丁烷的摩尔比1：1．2时,收率为91．93％。     

Brφnsted酸性离子液体中苯甲酸酯、苄酯的无溶剂微波合成

该文以1-甲基咪唑、吡啶、苄基氯、硫酸、磷酸为原料,合成了4种B r nsted酸性离子液体:1-甲基-3-苄基咪唑硫酸氢根盐(a),1-甲基-3-苄基咪唑磷酸二氢根盐(b),N-苄基吡啶硫酸氢根盐(c),N-苄基吡啶磷酸二氢根盐(d),以它们作为催化剂和反应介质,考察了苯甲酸与系列脂肪醇、苄醇与系列脂肪酸、苯甲酸在无溶剂和微波辐射反应条件下的F ischer酯化反应,结果表明,当苯甲酸或苄醇与离子液体的摩尔比为1∶0.5时,无需外加催化剂,反应即可在化学计量条件下进行,12~20 m in完成反应,苯甲酸酯与苄酯的收率分别为77%~98%和78%~98.5%,气相色谱纯度≥95%。离子液体循环使用3次,催化活性仅下降1.8%~3.4%。     

I2/Bronsted酸性离子液体介导的ε-环己内酯的合成研究

以I₂/Bronsted酸性功能化离子液体1-羧甲基-3-甲基咪唑硫酸氢根盐(［MCMIM］HSO₄)作为反应体系,H₂O₂（35%）为氧化剂,考察环己酮的Baeyer-Villiger氧化反应,结果表明,n（环己酮）∶n（H₂O₂）∶n（离子液体）=1∶3.5∶（0.2～0.6）时,只需加入微量I₂,反应即可在室温下顺利进行,反应时间2 h,ε-环己内酯收率72.7%～78.2%。离子液体经萃取、减压蒸馏除水和真空干燥即可循环使用,循环使用3次,产物酯收率略有下降。     

5-Br-DMPAP 分光光度法测定食品中微量锌

研究了以５－Ｂｒ－ＤＭＰＡＰ分光光度法测定食品中微量锌，对实验条件和共存离子的干扰及掩蔽进行了探讨。在ＯＰ存在下，Ｚｎ（Ⅱ）和５－Ｂｒ－ＤＭＰＡＰ在ｐＨ８．０～１０．０氨性缓冲液中形成有色络合物；λｍａｘ＝５５５ｎｍ，ε＝８．８１×１０４Ｌｍｏｌ－１ｃｍ－１，Ｚｎ在０～５６０μｇ／Ｌ范围内符合比耳定律，变异系数和回收率分别在１．６％～４．６％和９１．１％～１０５％之间。     

［EMIM］Br-AlCl3离子液体的合成

采用N-甲基咪唑、溴乙烷、AlCl₃常规回流法以及微波法合成离子液体,研究［EMIM］Br中间体的产率;采用量子化学方法计算离子液体结构,明确合成反应的机理;通过紫外光谱和红外光谱表征［EMIM］Br-AlCl₃离子液体的结构;测试离子液体的密度、电导率等性质。结果表明：常规回流法以N-甲基咪唑和溴乙烷为原料,在70℃温度下反应5 h,反应产率为87.9%;微波法反应时间1000 s,产率为94.2%;40℃下密度为1.46 g·cm^-3,电导率为21 S·m^-1;用DFT B3LYP 量子化学计算方法研究离子液体的构型,离子液体的合成反应遵循SN2反应机理;紫外光谱和红外光谱表征了［EMIM］Br和AlCl₃/［EMIM］Br离子液体的结构。     

1,2,3-三甲氧基苯的绿色合成工艺研究

采用碳酸二甲酯(DMC)代替传统的有毒有害试剂作为甲基化试剂和以廉价的焦性没食子酸(PA)为原料,在离子液体[ Bmim] Br催化作用下合成1,2,3-三甲氧基苯(TMB).通过单因素和正交试验考察了PA和DMC的摩尔比、催化剂的用量、反应温度以及反应时间等因素对甲基化反应的影响.结果表明:各因素的影响程度为反应温度...     

Reverse micellar extraction of bovine serum albumin – A comparison between the effects of gemini surfactant and its corresponding monomeric surfactant

Gemini surfactant displayed distinct advantages over monomeric surfactant in the liquid–liquid reverse micellar extraction process. First, less amount of gemini surfactant than monomeric surfactant was needed for transferring almost complete bovine serum albumin (BSA) into organic phase from aqueous phase. Second, the loading capacity of gemini surfactant reverse micelle phase was much higher than that of the corresponding monomeric surfactant reverse micelle. Third, efficient backward extraction (75–92%) of BSA could be effected in a wide pH range from 4 to 9 with gemini surfactant reverse micelle while a pH of ca. 4.3 is prerequisite to the recovery of BSA from monomeric surfactant reverse micelle. So far, the reports about the effect of surfactant structure on protein extraction have been limited. This study indicates the important role of the spacer of gemini surfactant in protein extraction process and may provide more knowledge on how to optimise surfactant structure.