Mechanical and optical properties in precipitated regions of alumina‐rich magnesium aluminate spinel

The toughening and strengthening of transparent ceramics is challenging because microstructural alterations typically lead to light scattering. Here, controlled precipitation of α‐Al₂O₃ from nonstoichiometric spinel is explored to demonstrate unique control over the evolution of second phase Al₂O₃ and how the microstructure might be altered to enhance fracture toughness while minimizing light scatter. Alumina‐rich magnesium aluminate spinel, MgO·nAl₂O₃, where n=2, was hot pressed and HIPed to produce fully dense, single‐phase material. The material was then heat treated in air at 1573 K for up to 20 hours to create a two‐phase spinel‐Al₂O₃ composite. The fracture toughness varies from 0.88 to 2.47 MPa√m depending on the microstructure; enhanced toughness at the surface was due to increased crack tortuosity at phase boundaries, but residual tensile stresses were observed in the interior of the material. Precipitation causes local volume contraction and the formation of porosity, decreasing optical transmission, especially for heat treatment times longer than 5 hours.     

铸造多晶硅中铜沉淀的电子束诱生电流

利用电子束诱生电流(EBIC)研究了不同热处理条件下太阳电池用铸造多晶硅材料中的铜的沉淀特性，并与铜在普通直拉硅单晶中的沉淀行为进行了比较。EBIC观察发现，在铸造多晶硅中，热处理的冷却速率和结晶学缺陷(如晶界和位错)共同影响着铜在多晶硅中的扩散和沉淀性质。样品在快速冷却时，在晶界以及晶粒内形成了很高密度且分布较均匀的细小铜沉淀；而在慢速冷却时，则是形成密度较低，较大尺寸的铜沉淀。EBIC的衬度计算显示，慢速冷却下形成的铜沉淀具有更强的复合特性，且铜沉淀在晶界上的分布具有选择性。最后，讨论了铜沉淀在铸造多晶硅中的形成机理。     

EFFECT OF PRETREATMENT ON COLOR OF DEHYDRATED PRODUCTS

ABSTRACT

The effect of pretreatment on color of convective dried products (namely apple, banana, potato and carrot) was investigated. Five different types of pretreatment were taken into consideration; microwave, osmotic, sulfite, water blanching and steam blanching. Color characteristics were identified by measuring the color parameters (namely, Lightness (L), Redness (a) and Yellowness (b)) using a Hunter Lab chromatometer. The type of pretreatment was found to significantly affect the three color parameters. In addition, Redness (a) and Yellowness (b) were found to follow a first order kinetic model. Untreated dried materials showed an extensive browning, indicated by a significant drop of the L parameter and a corresponding increase of a, b parameters. Osmotically and microwave pretreated samples supressed browning compared to the untreated samples. In this case, lightness decreased slightly, while a, b increased slightly. Sulfite pretreatment prevented significantly color deterioration, while water and steam blanching also prevented enzymatic browning during convective drying.     

Effects of Four Different Drying Methods on the Quality Characteristics of Peeled Litchis (Litchi chinensis Sonn.)

Four different drying methods, namely, air drying (AD), microwave-assisted vacuum drying (MWVD), coupled microwave–hot air drying (MWAD), and freeze drying (FD), were studied, in terms of drying time, color, reducing sugar content, shrinkage, microstructure, and sensory evaluation. The drying rate of MWVD and MWAD were notably faster than that of AD and FD. The highest reducing sugar content was observed in MWAD, followed by MWVD. No significant differences were observed in reducing sugar between air-dried and freeze-dried products. FD had the best color and shrinkage among the other drying methods. The color and shrinkage of MWVD drying is close to the fresh litchis and much better than hot air and MWAD. Scanning electron microscopy (SEM) images showed that the MWVD and FD litchis have a porous structure, whereas AD and MWAD litchis have a compact structure. The sensory evaluation suggests that peeled litchis dried by the four studied drying methods are of a quality that is accepted by consumers.     

Effect of post-treatment microwave vacuum drying on the quality of 3D-printed mango juice gel

Abstract

This paper presents the development of three-dimensional (3D)-printed mango juice gel with microwave vacuum drying (MVD) post-treatment. In this study, the post-treatment MVD was used to improve the quality of the 3D-printed mango juice gel. The flavor, texture, water status distribution, and dielectric properties of products with different drying times (0, 2, and 4?min) were compared. We found that 3D printed products under a post-treatment of 4?min of MVD had the best shape retention and shape accuracy. 3D-printed mango juice gel under 4?min of MVD post-treatment exhibited a compact gel system with the highest ratio of bound water, as well as the highest hardness (445.19?g) and gumminess (89.11), and the lowest the relative dielectric constant (26.40) and dielectric dissipation factor (14.74). Also, samples evaluated under different drying times could be distinguished by comparing the responding signals of the e-nose. Based on these results, it was concluded that the MVD method is a promising way to improve the quality of 3D printed food.     

离子液体中羟丙基纤维素的合成

使用离子液体1,3-二乙基咪唑磷酸二乙酯盐([EEIM][DEP])为反应溶剂主组分来溶解微晶纤维素进行羟丙基化衍生,微晶纤维素和醚化剂在离子液体中均可形成均相,通过碱化、醚化、酸化及洗涤等步骤制备得到不同取代度的羟丙基纤维素。考察了碱化反应温度、反应原料摩尔比、醚化反应时间及酸化剂的种类对羟丙基纤维素产品的收率和摩尔取代度的影响,并采用红外、核磁、TGA等手段对产品结构进行了表征。     

酸处理改性Hβ分子筛催化合成乙基蒽醌

采用微波辐射法,对Hβ分子筛进行酸处理改性,并通过NH₃-TPD、XRD和吡啶－IR对分子筛进行表征,考察改性前后分子筛酸性质和晶相变化,采用改性的Hβ分子筛催化乙苯和苯酐合成乙基蒽醌。结果表明,无机酸改性分子筛时,由于酸性太强,溶解了大量分子筛的铝物种,减小了分子筛固有的酸催化中心数,使分子筛的催化活性大幅度下降,不适合作为Hβ分子筛的改性试剂。有机酸对Hβ分子筛的改性效果较好,以0.1 mol·L^-1马来酸处理后的分子筛催化效果最好,苯酐转化率为51.53%,乙基蒽醌选择性为39.10%,乙基蒽醌收率最高可达20.15%。采用马来酸和Ce(NO₃)·6H₂O复合改性分子筛,乙基蒽醌选择性为54.0%,乙基蒽醌收率最高可达23.5%,选择性比马来酸单独改性时提高约15个百分点,催化效果明显提高。     

邻二甲苯-4-磺酸从猪血粉水解液中沉淀提取L-亮氨酸的工艺

考察了pH值、邻二甲苯–4–磺酸与L–亮氨酸的物质的量比、氯化铵浓度和温度等因素对邻二甲苯–4–磺酸反应沉淀L–亮氨酸的影响。结果表明：邻二甲苯–4–磺酸沉淀L-亮氨酸的适宜pH值为不高于1.5;邻二甲苯–4–磺酸与L-亮氨酸的最适物质的量比为3∶1;溶液中氯化铵浓度增大使L–亮氨酸的沉淀率缓慢下降;温度升高L–亮氨酸的沉淀率迅速降低,反应应于低温下进行,实际生产中可选择在0 ℃。按上述最佳工艺条件从除酸后猪血粉水解液中提取L–亮氨酸,沉淀率达到90.62%,经精制L-亮氨酸产品达到《中华人民共和国药典》(2000年版二部)的标准。     

微波动态循环阶段连续逆流提取二氢杨梅素

引言 微波提取是一项新型的中药有效成分提取技术,具有加热速度快、能耗低、提取效率高等优点[1-3].动态循环阶段连续逆流提取是一种增大传质推动力、提高提取效率的提取技术[4].它是将多个提取单元科学组合,使单位时间内固液两相保持较高的浓度差,从而提高提取效率.     

微波合成对-香豆酸的工艺研究

采用微波辐射法,利用正交设计,以对-羟基苯甲醛和丙二酸为原料,甲苯、吡啶作为溶剂,苯胺作催化剂合成了对-香豆酸.最佳反应条件:在微波辐射下,反应物摩尔比为1:2(0.015mol:0.03mol),催化剂苯胺用量0.54g,辐射时间50min,产率达到72.76%.与传统法比较,微波辐射具有反应速度快、产率高的优点.