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相关概念视频

Hybridization of Atomic Orbitals I03:24

Hybridization of Atomic Orbitals I

The mathematical expression known as the wave function, ψ, contains information about each orbital and the wavelike properties of electrons in an isolated atom. When atoms are bound together in a molecule, the wave functions combine to produce new mathematical descriptions that have different shapes. This process of combining the wave functions for atomic orbitals is called hybridization and is mathematically accomplished by the linear combination of atomic orbitals. The new orbitals that...
Hydroboration-Oxidation of Alkenes03:08

Hydroboration-Oxidation of Alkenes

In addition to the oxymercuration–demercuration method, which converts the alkenes to alcohols with Markovnikov orientation, a complementary hydroboration-oxidation method yields the anti-Markovnikov product. The hydroboration reaction, discovered in 1959 by H.C. Brown, involves the addition of a B–H bond of borane to an alkene giving an organoborane intermediate. The oxidation of this intermediate with basic hydrogen peroxide forms an alcohol.
Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation02:47

Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation

Introduction
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
Plastic Behavior01:21

Plastic Behavior

A material's elastic behavior is characterized by the disappearance of stress once the load is removed, allowing the material to return to its original state. However, when stress surpasses the yield point, yielding commences, marking the onset of plastic deformation or permanent set. This change from elastic to plastic behavior is influenced by the peak stress value and the duration before the load is removed. An intriguing observation occurs when a specimen is loaded, unloaded, and reloaded.
Imperfections in Crystal Structure: Stoichiometric Point Defects01:26

Imperfections in Crystal Structure: Stoichiometric Point Defects

Schottky defects arise when some lattice points in a crystal, such as those in NaCl, remain unoccupied, creating lattice vacancies without disturbing the overall electrical neutrality of the crystal. This defect is common in ionic crystals where the positive and negative ions are similar in size, as seen in sodium chloride and cesium chloride. The presence of Schottky defects enables the crystal to conduct electricity to a small extent through an ionic mechanism. Electric fields cause nearby...
Imperfections in Crystal Structure: Non-Stoichiometric Defects01:29

Imperfections in Crystal Structure: Non-Stoichiometric Defects

Non-stoichiometric defects refer to a type of defect in the crystal structure of a compound where the ratio of its constituent elements deviates from the ideal stoichiometric ratio. There are two main types of non-stoichiometric defects: metal excess defects and metal deficiency defects.Metal excess defects occur when there is a slight surplus of metal ions than what is required by the stoichiometric ratio of the compound. For example, heating a sodium chloride crystal in sodium vapor results...

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相关实验视频

Updated: Jun 4, 2026

Assessment of Boron Doped Diamond Electrode Quality and Application to In Situ Modification of Local pH by Water Electrolysis
13:09

Assessment of Boron Doped Diamond Electrode Quality and Application to In Situ Modification of Local pH by Water Electrolysis

Published on: January 6, 2016

在碳化物中的冲击诱导局部无形化.

Mingwei Chen1, James W McCauley, Kevin J Hemker

  • 1Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218, USA.

Science (New York, N.Y.)
|March 8, 2003
PubMed
概括

冲击载荷碳化物产生纳米级无形带,解释其在高冲击速率下降的弹道性能. 这个过程还合成了具有改变性质的新材料.

科学领域:

  • 材料科学 材料科学 材料科学
  • 固体力学 固体力学是什么
  • 纳米技术纳米技术

背景情况:

  • 碳化在高压冲击负载下表现出复杂的行为.
  • 以前对碳化物的弹道性能降解的理解是不完整的.

研究的目的:

  • 调查冲击载荷碳化弹道性能下降背后的微观结构机制.
  • 阐明纳米尺度结构变化对材料特性中的作用.

主要方法:

  • 使用高分辨率电子显微镜观察冲击负荷的碳化物.
  • 分析的重点是内粒状特征及其与断裂表面的关系.

主要成果:

  • 观察到纳米级无形带与特定的晶体平面平行形成.
  • 这些无形带被发现连续与切割的断裂表面.
  • 波段形成和弹道性能降低之间确立了直接的相关性.

结论:

  • 纳米级无形带的形成是导致碳化物在高冲击下弹道性能下降的主要损伤机制.
  • 冲击负荷可以诱导具有显著改变材料特性的新型纳米结构的合成.
  • 这项研究提供了在极端条件下材料故障的机制性理解.

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Negative Additive Manufacturing of Complex Shaped Boron Carbides

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Assessment of Boron Doped Diamond Electrode Quality and Application to In Situ Modification of Local pH by Water Electrolysis
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Negative Additive Manufacturing of Complex Shaped Boron Carbides

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