Progress in pressureless sintering of boron carbide ceramics – a review

ABSTRACT

Boron carbide (B₄C) ceramics has many outstanding performance, such as extremely high hardness, low density, high melting point, high elastic modulus, high thermoelectromotive force, high chemical resistance, high neutron absorption cross section, high impact and excellent wear resistance. Therefore, B₄C ceramics can be used in various industrial applications, such as lightweight ceramic armour, high temperature thermocouples, neutron absorber, reactor control rods in nuclear power engineering, polishing media for hard materials, abrasive media for lapping and grinding, and wear resistant components (blasting nozzles, die tips and grinding wheels). Pressureless sintering is the method with industrialised application value for B₄C ceramics, however, it is impossible to sinter pure B₄C ceramics to high densities without additives by pressureless sintering. So sintering additives must be used to promote the densification of B₄C ceramics. The different sintering additives used to promote the densification of boron carbide will be described in this review, including carbon additives, metallic additives, oxide additives, non-oxide additives, combined additives and rare earth oxide additives. Finally, the recent research trends for sintering methods and sintering additives of B₄C ceramics will also be proposed.     

Extended vertical lists for temporal pattern mining from multivariate time series

In this paper, the problem of mining complex temporal patterns in the context of multivariate time series is considered. A new method called the Fast Temporal Pattern Mining with Extended Vertical Lists is introduced. The method is based on an extension of the level‐wise property, which requires a more complex pattern to start at positions within a record where all of the subpatterns of the pattern start. The approach is built around a novel data structure called the Extended Vertical List that tracks positions of the first state of the pattern inside records and links them to appropriate positions of a specific subpattern of the pattern called the prefix. Extensive computational results indicate that the new method performs significantly faster than the previous version of the algorithm for Temporal Pattern Mining; however, the increase in speed comes at the expense of increased memory usage.     

Fluidizing effects of polymers with various anchoring groups in cement pastes and their sensitivity to environmental temperatures

We synthesized various polymers with different functional groups of ─COO⁻, ─SO₃⁻, and ≡N⁺─ to study the impact of the environmental temperature (25, 50, and 80 °C) on the dispersing capability by measuring the fluidity of fresh cement paste, total organic carbon, ζ potential, and isothermal calorimetry. The results show that no adsorption was observed for the cement pastes containing acrylic acid, 2-acrylamido-2-methyl propane sulfonic acid, and [3-(methacryloylamino)propyl] trimethyl ammonium chloride, probably because of the trace amount of adsorption, whereas the fluidity of the pastes was indeed improved by the addition of these chemicals. Generally, for the polymers containing various functional groups, the adsorption capability was in the order ─COO⁻ > ─SO₃⁻ > ≡N⁺─. The dispersing capability for the carboxylate superplasticizer was robust to the change in the temperature, whereas it was dramatically weakened by the increase in temperature for sulfonate superplasticizer, although the adsorption amount increased along with the temperature rise. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47494.     

工业硝酸铵添加剂对乳胶基质的影响

为了改善工业硝酸铵的吸湿结块性能,通常会加入添加剂(有机包覆剂或无机改性剂),而工业硝酸铵作为乳化炸药的主要原料,其添加剂对乳化炸药的制备和性能会产生影响。因此,分别对采用有机包覆剂蜡的泰国产工业硝酸铵和采用无机改性剂的俄罗斯产工业硝酸铵,开展了制备现场散装乳胶基质的工业试验。结果表明:两类工业硝酸铵均可作为乳化炸药原材料使用,但有机包覆剂会沉入水相罐底部或粘附在输送管道内壁,对水相和乳胶基质制备造成不利影响,因此需要在水相制备环节分离去除包覆剂蜡;硝酸镁、硝酸钙等无机改性剂对乳胶基质制备无影响,但生产的乳胶基质稳定性较差,通过调整乳化剂的种类和配比以及乳化器的转速可得到一定改进。     

纸基底印刷无芯片RFID湿度传感器* .txt

摘要：提出了一种基于纸基底的喷墨印刷无芯片RFID湿度传感器，通过遗传算法与射频仿真软件HFSS相结合，对常规开口环谐振器结构进行分布式加载，得到目标频率为245 GHz的谐振特性良好的传感器模型；采用DMP3000型材料打印机，在不同纸基底上喷墨印刷银墨水制作传感器，以纸张本身的吸水性实现湿度传感；研究不同纸基底对湿度传感器感湿灵敏度和恢复度的影响。结果表明，柯达相纸传感器的灵敏度最高，高湿灵敏度可达到8 MHz%RH，双铜纸湿度传感器恢复度高且恢复时间短，仅为2 min；两种基底湿度传感器皆有较好的一致性、中长期稳定性，且湿敏特性在20℃～30℃范围内受温度影响较小。对纸基湿度传感器的感湿机理进行了分析，纸主要成分纤维素表面的羟基与吸附的水分子作用形成氢键，改变了基底的介电参数，传感器的湿敏特性与纸的成分和结构有关。 .txt     

Physicochemical,textural and volatile characteristics of fermented milk co-cultured with Streptococcus thermophilus,Bifidobacterium animalis or Lactobacillus plantarum

Fermented milks were prepared with various culture combinations of Lactobacillus plantarum or Bifidobacterium animalis with Streptococcus thermophilus, and the impact of microbes combinations on acidification, proteolysis, lipolysis, texture, volatiles and sensory quality of fermented milk was investigated during 21-day storage at 4 °C. The results showed that products from the co-cultures displayed higher titratable acidity, more peptides, higher proteolytic activity and lipolysis capacity compared with that from the pure strains of S. thermophilus. When L. plantarum and B. animalis combined in a ratio of 2:1 with S. thermophilus, the products maintained relatively more viable cell counts of the 3 strains, strong proteolysis ability and lipolysis capacity during the storage. Milk fermented by co-cultures of the 3 strains exhibited higher cohesiveness, more volatiles and better sensory quality compared with these fermented by S. thermophilus only or in co-cultures with either B. animalis or L. plantarum based on principal component analysis.     

Microstructure and mechanical properties of Mg-5Li-1Al sheets prepared by accumulative roll bonding

Ultrafine-grain and high-strength Mg-5Li-1Al sheets were prepared by accumulative roll bonding (ARB) process. Evolution of microstructure and mechanical properties of ARB-processed Mg-5Li-1Al sheets was investigated.Results show that, during ARB process, the evolution of deformation mechanism of t Mg-5Li-1Al alloy is as follows: twinning deformation, shear deformation, forming macro shear zone, and finally dynamic recrystallization (DRX). The grain refining mechanism changes from twin DRX to rotation DRX. With the increase in ARB cycles, strength of the Mg-5Li-1Al sheets is enhanced, whilst elongation varies slightly. With the increase in rolling cycles, anisotropy of mechanical properties decreases. It is conclusive that strain hardening and grain refinement dominate the strengthening mechanism of Mg-5Li-1Al alloy.     

Modeling of quantitative relationships between physicochemical properties of active pharmaceutical ingredients and tensile strength of tablets using a boosted tree

Objectives: The aim of this study was to explore the potential of boosted tree (BT) to develop a correlation model between active pharmaceutical ingredient (API) characteristics and a tensile strength (TS) of tablets as critical quality attributes.

Methods: First, we evaluated 81 kinds of API characteristics, such as particle size distribution, bulk density, tapped density, Hausner ratio, moisture content, elastic recovery, molecular weight, and partition coefficient. Next, we prepared tablets containing 50% API, 49% microcrystalline cellulose, and 1% magnesium stearate using direct compression at 6, 8, and 10?kN, and measured TS. Then, we applied BT to our dataset to develop a correlation model. Finally, the constructed BT model was validated using k-fold cross-validation.

Results: Results showed that the BT model achieved high-performance statistics, whereas multiple regression analysis resulted in poor estimations. Sensitivity analysis of the BT model revealed that diameter of powder particles at the 10th percentile of the cumulative percentage size distribution was the most crucial factor for TS. In addition, the influences of moisture content, partition coefficients, and modal diameter were appreciably meaningful factors.

Conclusions: This study demonstrates that BT model could provide comprehensive understanding of the latent structure underlying APIs and TS of tablets.     

碳纳米管改性水泥石力学性能研究

随着非常规油气的勘探开发，超深井、复杂井、页岩气井等对固井质量的要求越来越高，现有水泥基材料性能已经不能满足要求，需要探索新型材料在水泥基材料中的应用以及对水泥石的性能改造。从碳纳米管自身的特点出发，制备稳定性较好的碳纳米管分散液，通过水泥石抗压强度、抗折强度测试、单轴三轴力学性能实验以及微观结构测试对碳纳米管的加量范围、分散效果进行了讨论，分析碳纳米管对水泥石力学性能的影响规律。实验结果表明，0.05%~0.1%碳纳米管加量能够提高水泥石的抗压、抗折性能，并且随着龄期的增长其增强效果更加明显；碳纳米管能够降低水泥石的弹性模量，同时增大塑性形变，使水泥石韧性增加；碳纳米管对微观结构的增强增韧机理表现为拨出、桥联、纳米诱导效应和网状填充效应，经过分散的碳纳米管与基体的相容性较好。