Name: crystal structure using x-ray diffraction
Uploaded: 2023-04-30T07:02:53.000Z
Duration: 9 min 31 s
Channel: JoVE

K12 Standards

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

9-12

Physical Geology

Minerals

Crystallinity (crystal structure)

X-ray Diffraction

以下步骤适用于特定的XRD仪器及其配套软件，使用其他仪器时步骤可能会有所差异。
<ol>
	<li>我们将使用 Panalytical Alpha-1 XRD 仪器检测一种 Ni 粉末样品。</li>
	<li>首先，根据样品直径选择掩模以固定光束尺寸。在最小的 θ 值（通常约为 70-100）下，光束的照射面积不得超过样品尺寸。对于宽度为 ε 的样品，光束尺寸应 &#60; ε sinθ。</li>
	<li>将样品装入样品旋转台，并将样品固定到位。样品旋转台有助于在空间上随机化样品对 X 射线源的暴露。</li>
	<li>选择 XRD 扫描的角度范围。例如，15–90 度是一个典型范围。</li>
	<li>选择步长，即 2θ 的增量，以及积分（计数）时间。通常情况下，大角度扫描默认采用 0.05 度的步长和 4 秒的积分时间。</li>
	<li>一旦通过初始扫描确定了所有峰位，后续扫描可围绕特定峰采用更小的角度步长，在更窄的扫描范围内进行，以获得更高分辨率的峰数据。</li>
</ol>

这是标准XRD实验的演示。本实验所检测的材料为粉末形态，但XRD同样适用于固体样品，只要样品具有平坦表面并能与样品台平面平行放置即可。
XRD 是一种广泛使用的方法，用于确定材料中是否存在（或不存在）晶体学有序结构。除了确定晶体结构这一常规应用外，XRD 还常用于获取多种其他结构信息，例如：
<ol>
	<li>材料的结构是否为非晶态（在衍射强度图谱中表现为宽泛的隆起峰，并缺乏可辨识的晶体学衍射峰），</li>
	<li>样品是否为由多种晶体学相组成的复合材料，若是，则确定各相的含量比例，</li>
	<li>判断材料是否为非晶态/晶态复合物，</li>
	<li>测定材料的晶粒/颗粒尺寸，</li>
	<li>测定材料中晶粒择优取向（织构）的程度。</li>
</ol>

衍射峰位置与晶体结构之间的关系：
当波长足够短的光波入射到晶体晶格上时，会从晶格点发生衍射。在某些入射角度下，衍射出的平行波会发生相长干涉，从而产生可检测的强度峰。W.H. 布拉格确定了图1所示的关系，并推导出相应的方程：
nλ = 2dhkl sin θ [1]
其中λ为所用X射线的波长， dhkl 是特定晶面组之间的间距 (hkl) 密勒指数*，以及 θ 是测量衍射峰时的入射角。最后，n 是表示衍射“谐波级次”的整数。例如，当 n=1 时，对应第一级谐波，意味着通过晶体衍射的 X 射线路径（相当于 2dhkl 正弦 ) 精确等于 1λ，而当 n=2 时，衍射路径为 2λ. 我们通常可以假设 n=1，且一般情况下，n=1 对于 θ &lt; 正弦-1(2λ/dh'k'l')，其中 h'k'l' 为衍射实验中首个峰（在最低 2θ 值处）所对应的晶面的密勒指数。密勒指数是一组三个整数，用于标识晶体内部方向和晶面的记号系统。对于方向，采用 [h k l] 密勒指数表示沿某一方向上两点在直角坐标系中各自x、y和z坐标之间的归一化差值。对于晶面，密勒指数 (h k l) 一个晶面的指数就是垂直于该晶面方向的h k l值。
在典型的反射模式X射线衍射（XRD）实验中，X射线源位置固定，样品相对于X射线束绕θ角旋转。探测器接收衍射束，并以两倍于样品旋转速率的角度同步转动（即当样品角度为θ时，探测器角度为2θ）。该实验的几何构型如图1所示。
<img alt="X射线衍射图；显示布拉格定律、θ角、晶体晶格、X射线源/探测器的装置示意图。" src="/files/ftp_upload/10446/10446fig1v2.jpg" data-altupdatedat="1761830439000" data-alt="图1"> 
图1：布拉格定律示意图。
当观察到强度出现峰值时，必然满足公式1。因此，我们可以根据观察到这些峰值的角度来计算晶面间距（d-spacing）。通过计算多个峰值的晶面间距，可利用数据库（例如Hanawalt检索手册或所用XRD软件附带的数据库库）确定材料样品的晶体类别及晶体结构参数。
我们假设被研究的样品不是单晶。如果样品是单晶，并且具有某个特定的(h*k*l*)晶面与样品表面平行，则需要旋转样品，直到满足该(h*k*l*)晶面的布拉格条件，才能观察到衍射强度的峰（对应n=1），并且在更高角度处还可能检测到高次谐波的(h*k*l*)峰（例如n=2时）。在其他所有角度下，单晶样品中均不会出现衍射峰。相反，我们假设样品为多晶或粉末状，其内部含有大量在统计学上具有代表性的晶粒或粉末颗粒，且被入射X射线束照射。在此假设下，样品由随机取向的晶粒组成，所有可能的晶面发生衍射的概率在统计上相近。
各因素之间的关系 dhkl 晶胞参数在以下方程2-7中分别对应7个晶系：立方、四方、六方、三方、正交、单斜和三斜。晶胞参数包括晶胞各边的长度 （a，b，c） 以及7个晶系晶胞棱边之间的夹角（α、β、γ）（图1x展示了一个晶系的示例：四方晶系，其中 a=b≠c，且 α=β=γ=90°）0）。利用多个衍射峰位置（即若干个不同的 dhkl 晶胞参数的值可以被唯一确定。
<img alt="正交晶系示意图，a≠b≠c，角度 α=β=γ=90°，标注了晶轴尺寸。" src="/files/ftp_upload/10446/10446fig2.jpg" data-altupdatedat="1761830439000" data-alt="Figure 2"> 
图2：四方结构作为七种晶体晶系之一。
立方晶系（a = b = c；α = β = γ = 900）：
<img alt="晶体学方程，d_hkl 公式，晶面间距计算公式。" src="/files/ftp_upload/10446/10446eq1.jpg" style="opacity: 0.9; font-size: 14px;" data-altupdatedat="1761830439000" data-alt="方程 1">  [2]
四方晶系（a = b ≠ c；α = β = γ = 900）：
<img alt="晶体学方程；倒易晶格间距公式；倒易晶格参数分析。" src="/files/ftp_upload/10446/10446eq2.jpg" style="opacity: 0.9; font-size: 14px;" data-altupdatedat="1761830439000" data-alt="方程 2">  [3]
六方晶系（a = b ≠ c；α = β = 900；γ = 1200）：
<img alt="六方晶格结构的晶体学方程，X射线衍射中使用的关键公式。" src="/files/ftp_upload/10446/10446eq3.jpg" style="opacity: 0.9; font-size: 14px;" data-altupdatedat="1761830439000" data-alt="方程 3">  [4]
正交晶系（a ≠ b ≠ c；α = β = γ = 900）：
<img alt="椭球体的三维几何方程；数学公式探索。" src="/files/ftp_upload/10446/10446eq4.jpg" style="opacity: 0.9; font-size: 14px;" data-altupdatedat="1761830439000" data-alt="公式 4">  [5]
菱方晶系（a = b ≠ c；α = β = γ = 900）：
<img alt="用于计算d间距的晶体学公式；数学方程；X射线衍射分析。" src="/files/ftp_upload/10446/10446eq5.jpg" style="opacity: 0.9; font-size: 14px;" data-altupdatedat="1761830439000" data-alt="方程 5">  [6]
单斜晶系（a ≠ b ≠ c；α = γ = 900 ≠ β）：
<img alt="晶体学公式，倒易点阵方程，数学推导，结构分析。" src="/files/ftp_upload/10446/10446eq6.jpg" style="opacity: 0.9; font-size: 14px;" data-altupdatedat="1761830439000" data-alt="方程 6">  [7]
三斜晶系（a ≠ b ≠ c；α ≠ β ≠ γ ≠ 900）：
      <img alt="晶体学公式示意图；用于X射线衍射分析的倒格矢计算。" src="/files/ftp_upload/10446/10446eq8v2.jpg" data-altupdatedat="1761830439000" data-alt="方程 7">  [8] 
衍射峰强度与晶体结构之间的关系：
接下来，我们分析影响XRD图谱强度的因素。这些因素可分为两类：1）由材料独特的结构特征直接导致的散射贡献（即结构中特定类型和位置的散射原子）；2）与材料本身无关的因素。前者包含两个因素：“吸收因子”和“结构因子”。吸收因子主要取决于材料在X射线入射和出射过程中对X射线的吸收能力。只要样品不是太薄（样品厚度应&gt; X射线衰减长度的3倍），该因子不随衍射角θ变化。换句话说，吸收因子对不同衍射峰强度的贡献是恒定的。结构因子则直接由晶体结构决定，影响特定衍射峰的强度。其余因素包括“多重性因子”，用于考虑因对称性相关而属于同一家族的所有晶面；以及“洛伦兹-偏振因子”，源于XRD实验的几何构型。这两个因子也会影响衍射峰的相对强度，但它们并非材料特有，可通过解析表达式准确校正（例如，XRD分析软件可利用解析函数将其去除）。
<img alt="说明光线通过棱镜时反射和折射路径的几何光学示意图。" src="/files/ftp_upload/10446/10446fig3.jpg" data-altupdatedat="1761830439000" data-alt="图3"> 
图3：三条衍射光线路径，其中光线11'和22'满足布拉格条件，而光线33'是由位于任意位置的原子（红色圆圈）散射产生的。
结构因子是唯一能够体现材料结构特征对XRD峰相对强度影响的因素，因此非常重要，需要深入分析。在图2中，假设1第级布拉格衍射条件（注意，这对应于n=1）在射线11'和射线22'之间得到满足，这两束射线在h00方向（使用前述的密勒指数表示法）上被两个间距为d的原子平面散射。在此条件下，射线11'与射线22'之间的光程差为δ(22'-11') = SA + AR = λ。因此，衍射射线1和2之间的相位差为Φ22'-11' = (δ(22'-11')/λ) 2π = 2π（假设具有立方对称性，因此在h00方向上d = a/h）。
通过解析几何的几个步骤，可以证明，由间距为任意距离 x 的某一原子平面衍射产生的射线3的相位差 Φ(33'-11') 可表示为：Φ(33'-11') = 2πhu，其中 u=x/a（a 为沿 (h00) 方向的晶胞参数）。考虑另外两个正交方向 (0k0) 和 (00l)，并令 v=y/a 和 w=z/a 为 y 和 z 方向上的分数坐标，则相位差的表达式可推广为 Φ = 2π(hu+kv+lw)。现在，由晶胞中第 j 个原子散射的X射线波具有散射振幅 fj 和相位 Φj，因此描述该波的函数为 <img alt="数学指数函数公式；物理、工程计算；e^phi 表达式。" src="/files/ftp_upload/10446/10446eq8.jpg" style="opacity: 0.9; font-size: 14px;" data-altupdatedat="1761830439000" data-alt="方程 8">。因此，我们所求的结构因子是晶胞中所有不等价原子所产生的散射函数之和。该结构因子 F 可表示为：
<img alt="晶体学方程，傅里叶变换公式，科学研究中的数学符号。" src="/files/ftp_upload/10446/10446eq9v2.jpg" data-altupdatedat="1761830439000" data-alt="方程 9">  [9]
结构因子贡献的强度因子为 I = F2。
根据原子在特定晶面（h,k,l）上的位置（u,v,w），散射波之间可能发生相长、相消或介于两者之间的干涉，这种干涉直接影响代表（hkl）晶面的X射线衍射峰的强度。
现在，绘制强度 I 随 2θ 是在XRD实验中测量的内容。晶体类型及其相关晶胞参数的确定（a, b, c, α, β 和 γ) 可通过观察峰的系统性出现/缺失，结合公式 2-9 进行计算，将数值与数据库比对，并运用推理与排除法进行解析。如今，这一过程已通过多种与晶体结构数据库相连的软件实现了高度自动化。

x射线衍射

来源：Faisal Alamgir，佐治亚理工学院材料科学与工程学院，亚特兰大，佐治亚州
X射线衍射（XRD）是材料科学中用于确定材料原子和分子结构的一种技术。该方法通过用入射X射线照射材料样品，然后测量材料散射的X射线的强度和散射角度来实现。将散射X射线的强度作为散射角度的函数进行绘图，通过分析散射强度峰的角度位置及其强度，即可确定材料的结构。除了能够测定晶体中原子的平均位置外，还可获得实际结构偏离理想结构的信息，例如由内应力或缺陷引起的变化。
X射线衍射（XRD）方法的核心——X射线的衍射现象，是广义X射线散射现象的一个子集。通常所说的XRD一般指广角X射线衍射（WAXD），属于利用弹性散射X射线波的多种方法之一。其他基于弹性散射的X射线技术包括小角X射线散射（SAXS），其中X射线以通常为0.1–100的小角度范围入射到样品上。SAXS用于测量几纳米或更大尺度的结构相关性（如晶体超结构），以及X射线反射率技术，用于测量薄膜的厚度、粗糙度和密度。WAXD涵盖的角度范围则超过100。

在图4中，我们看到了Ni粉末样品的XRD峰。请注意，所观察到的峰（例如{111}、{200}）对应于h、k和l均为偶数或均为奇数的晶面组合。Ni为面心立方（FCC）结构，在所有面心立方结构中，由于散射X射线的相消干涉，当{hkl}晶面的h、k和l为奇偶混合的整数时，相应的峰会消失。例如{210}和{211}晶面对应的峰即缺失。这一现象称为系统性存在与缺失规则，可作为分析样品晶体结构的一种工具。
<img alt="X射线衍射图谱，强度与2θ角的关系，晶体结构分析，峰的指认。" class="xfigimg" src="/files/ftp_upload/10446/10446fig4.jpg" data-altupdatedat="1761830439000" data-alt="图4"> 
图4：显示的是具有面心立方结构的Ni的X射线衍射（XRD）扫描图谱。

X射线衍射

来源：Faisal Alamgir，美国佐治亚州亚特兰大市佐治亚理工学院材料科学与工程学院  
X射线衍射（XRD）是一种技术……

X射线衍射是一种用于确定材料原子和分子结构的技术。固体具有晶体结构，对应于原子周期性重复的微观排列。通过堆叠晶面，可形成具有特定对称性的三维结构。这些结构排列形成了特定的堆积几何构型，从而决定了材料的物理和化学性质，例如磁化强度、热导率或延展性。通过将X射线反射到材料表面，可以揭示其内部结构的详细信息。本视频将阐述材料上X射线衍射的基本原理，以及该现象在实验室中如何用于确定材料的结构和化学组成。首先，让我们更仔细地观察一下晶体。晶体由原子晶格构成，这些晶格呈周期性排列，晶面之间的距离 dhkl 为几个埃。h、k、l 是密勒指数，这是一组三个整数，用于标识晶体中的方向和晶面。晶体中最小的重复结构称为晶胞。晶胞的边长 a、b、c 和夹角 α、β、γ 不同，会形成不同的对称性。晶体共有七种晶系：立方晶系、四方晶系、正交晶系、三方晶系、单斜晶系、三斜晶系和六方晶系。对于每种晶体类别，均可计算晶胞参数与密勒指数之间的关系。波长为 lambda 的电磁波，其尺寸可与晶体晶格内各晶面之间的间距相近，这对应于 X 射线光谱范围内的波长。当波长为 X 射线的光波以入射角 theta 照射晶体时，光波将穿过晶体，并在遇到晶格点时发生衍射。布拉格定律描述了这些参数之间的关系，其中 n 为表示衍射级次的整数。对于给定的 lambda，只有特定的 theta 角才能产生衍射，这是晶体结构的独特特征。在实验中，样品被旋转，而收集散射X射线的探测器在达到这些特征角度时记录到强度峰值。随后可针对满足布拉格定律的每个角度提取相应的晶面间距DHKL。利用对应于多个不同DHKL值的衍射峰位置，可唯一确定晶胞参数。影响衍射峰相对强度的主要因素有两个。首先是非结构因素，包括材料对X射线的吸收能力以及XRD实验的几何构型。这些因素可在实验数据的后期处理中予以校正。其次，也是最重要的因素，是材料的结构因素，它决定了XRD衍射峰的相对强度。实际上，每个衍射峰都是由晶胞中所有不同原子对多条射线路径散射振幅的总和构成。当散射光同相时，会发生相长干涉；而当它们异相时，则会发生相消干涉。这些干涉效应直接影响XRD峰的振幅，对应于晶体的HKL晶面。现在我们将了解这些原理如何在一个实际的X射线衍射实验中应用。开始之前，仔细检查XRD仪器，评估其状态和安全性。使用XRD仪器的人员必须在接受基本辐射安全培训后方可操作仪器。随后进行样品制备。本实验中，我们使用压制成片状的镍粉样品。样品不能过薄，其厚度应至少为X射线衰减长度的三倍。请注意，以下操作步骤适用于特定的XRD仪器及其配套软件，若使用其他仪器，步骤可能会有所差异。将样品放入样品旋转台中，并将样品固定到位，确保样品的辐照面与样品台平行。使用掩模根据样品直径调节仪器的X射线束尺寸。在最小入射角下，光束的照射范围必须小于样品宽度。现在需要选择采集参数。首先，选择XRD扫描的角度范围。通常，该范围为15至90度。然后，选择扫描每个角度时的步长以及积分时间。接下来，进行数据采集。扫描完成后，将获得一张强度随角度 theta 变化的图谱。根据此初步扫描结果，选择特定的衍射峰并确定峰位。重复采集数据，此次将扫描范围聚焦于特定峰附近的较窄区域。通过减小角度步长以获得更高分辨率的数据。数据采集完成后，可对数据进行分析以确定材料的结构。利用仪器的软件和数据库库，对光谱中的每个峰进行识别，并将其与特定的晶体排列对称性相关联。在此镍粉样品的特定情况下，光谱显示第一个峰对应于111对称性。第二个峰对应于二零零对称性，依此类推。随后，软件判定这种特定的对称性组合对应于面心立方结构，并确定该样品为镍粉。X射线衍射是确定材料中是否存在晶体结构的常规方法。该方法常用于获取多种其他结构信息，例如晶体中的内应力和缺陷，或复合材料中的多种晶体相。XRD技术也用于生物学中，以确定蛋白质和核酸等生物大分子的结构及其空间取向。特别是，DNA 的双螺旋结构正是通过这种方法被发现的，这一成果获得了1962年诺贝尔生理学或医学奖。对矿物地球化学的研究，无论是用于采矿还是行星探测，也均利用了XRD技术。以火星上的“好奇号”探测车为例，其搭载的十台科学仪器中就包括一台XRD探测器，用于分析火星土壤的成分。您刚刚观看了 JoVE 关于 X 射线衍射的简介。现在，您应该理解固体的晶体结构以及 X 射线衍射的基本原理。您还应了解 XRD 技术如何在实验室中用于获取材料的结构和化学组成。感谢观看！

Education

教育

JoVE Science Education

Engineering

工程学

Materials Engineering

材料工程

X 射线衍射

crystal structure using x-ray diffraction

X-ray diffraction is a materials science method for finding crystal structure. It uses incident X-rays that strike a sample and scatter from its atoms and molecules. The scattered X-rays are measured by their intensity and scattering angle.

The results are plotted as intensity versus angle. Scientists then analyze the position of the peaks and their strength to determine the structure of the material. This method can also show how a real crystal differs from an ideal one. It can reveal effects such as internal stress and defects.

X-ray diffraction is part of a broader group of X-ray scattering methods. It is often used to mean wide-angle X-ray diffraction, or WAXD. WAXD covers scattering at angles above 10 degrees.

Other elastic scattering methods include small angle X-ray scattering, or SAXS, and X-ray reflectivity. SAXS uses a small angular range of about 0.1 to 10 degrees and measures structural correlations on the scale of several nanometers or larger, such as crystal superstructures. X-ray reflectivity is used to measure the thickness, roughness, and density of thin films.

Crystal Structure Using X-ray Diffraction

crystal-structure-using-x-ray-diffraction

optical materialography part 1: sample preparation

optical-materialography-part-1-sample-preparation

Preparing Solid Samples for Optical Microscopy

Optical microscopy of solid materials starts with careful sample preparation. Materialography is the study of microscopic structures in solids and the features seen in those images. It helps reveal details such as porosity, grain size and shape, and whether the microstructure shows anisotropy, or direction-dependent structure. This lesson focuses on the preparation steps used before optical microscopy. It covers the techniques and procedures needed to ready a solid material sample for imaging.

optical materialography part 2: image analysis

optical-materialography-part-2-image-analysis

Quantifying Microstructure in Optical Materialography

Optical materialography can be used to measure the microstructure of solid materials. It focuses on the microscopic structures seen in an exposed surface and uses them to study the material more deeply. A common goal is to estimate the three-dimensional microstructure of a sample from a two-dimensional cross section. This approach relies on the structural features visible in the image. It helps turn surface observations into quantitative data about the material. X-ray tomography can also...

x-ray photoelectron spectroscopy

XPS Surface Analysis of Materials

X-ray photoelectron spectroscopy, or XPS, is a surface analysis method for studying materials. It measures elemental composition, empirical formula, chemical state, and electronic state of the elements in a sample. Because the signal comes from the top few nanometers, XPS is especially useful for examining surfaces. To collect an XPS spectrum, a material is irradiated with an X-ray beam. At the same time, the instrument measures the kinetic energy and number of electrons that escape from the...

x-ray diffraction

X-ray diffraction is a materials science method for finding crystal structure. It uses incident X-rays that strike a sample and scatter from its atoms and molecules. The scattered X-rays are measured by their intensity and scattering angle. The results are plotted as intensity versus angle. Scientists then analyze the position of the peaks and their strength to determine the structure of the material. This method can also show how a real crystal differs from an ideal one. It can reveal effects...

focused ion beams

Focused Ion Beams in Microfabrication

Focused ion beams are used in microfabrication and nano-fabrication. A focused ion beam, or FIB, is an instrument that can fabricate, trim, analyze, and characterize materials on micro- and nano-scales. These tools are used in many fields, from nano-electronics to medicine. FIB systems work with a beam of ions. That beam can mill, or sputter, material away. It can also deposit material and image surfaces at small scales. In many research labs, the ion column of a FIB is integrated with the...

directional solidification and phase stabilization

directional-solidification-and-phase-stabilization

Zone Melting for Alloy Refining

Zone melting directional solidification is a metallurgical process used to move a narrow molten region through a crystal, usually a bar-shaped sample. A furnace travels along the rod, so the molten zone moves from one end of the bar to the other. This controlled motion changes how material forms as it solidifies. In alloys, solute atoms tend to separate into the melt. Impurities also concentrate in the molten zone instead of staying in the solid. As the molten region moves forward, it carries...

differential scanning calorimetry

Measuring Polymer Crystallinity with DSC

Differential scanning calorimetry, or DSC, is a method used to measure the thermal properties of materials. It helps scientists see how much heat a material stores as it warms up. This heat storage is called heat capacity. DSC also measures the heat absorbed or released during chemical reactions and phase changes. From these measurements, it can help determine other properties such as glass transition temperature and polymer crystallinity. Polymers often have long, chain-like structures that...

thermal diffusivity and the laser flash method

thermal-diffusivity-and-the-laser-flash-method

How Laser Pulses Measure Heat Flow

Laser flash analysis measures thermal diffusivity, which describes how fast heat moves through a material compared with how much heat it stores. This material-specific property helps show how a sample transfers thermal energy and how it responds to temperature changes. Thermal diffusivity is related to thermal conductivity, the measure of how heat moves through a material because of a temperature difference. That relationship also depends on the material’s density, shown as ρ, and its specific...

electroplating of thin films

Fast Metal Coating Without a Vacuum

Electroplating is a way to add a thin metal coating to a surface using electric current. In this process, dissolved metal cations are reduced and form a film on an electrode. The method is also called electrodeposition. This page also compares electroplating with other thin film deposition methods. Chemical vapor deposition, or CVD, uses a gas-phase precursor. Spin coating spreads a liquid precursor by spinning it outward. Dip coating is similar, but the substrate is fully submerged instead of...

analysis of thermal expansion via dilatometry

analysis-of-thermal-expansion-via-dilatometry

Using Dilatometry to Measure Heating Effects

Dilatometry measures how a material changes in size as temperature changes. It can track changes in length, area, shape, or volume. The method is used to calculate thermal expansion, which is the expansion of a substance when it is heated. Thermal expansion matters when choosing materials for systems that face changing temperatures. Some materials need high thermal expansion, such as the liquid in a thermometer, because the change helps detect temperature shifts. Other uses need materials with...

electrochemical impedance spectroscopy

Why AC Signals Matter in Impedance

Electrical impedance describes how a circuit element resists the flow of electricity. It is a more general measure than electrical resistance, especially when a circuit is not simple enough to be described by resistance alone. Resistance is the ability of a circuit element to resist current. It is defined by Ohm's law, which relates voltage and current. That relationship works well for ideal resistors, but many real circuit elements are more complex. When an alternating current, or AC, is...

ceramic-matrix composite materials and their bending properties

ceramic-matrix-composite-materials-and-their-bending-properties

Bone-Inspired Ceramic Composites in Bending

Bone helps show how ceramic-matrix composites work. In this material system, the ceramic part gives compressive strength, while the polymer fiber reinforcement adds tensile and flexural strength. By changing the amounts of ceramic and polymer, engineers can make materials for specific uses. This idea matters in biomedical engineering, where replacing or copying bone after disease or traumatic injury is an important goal. For this study, plaster of Paris, a calcium sulfate compound, is used to...

nanocrystalline alloys and nano-grain size stability

nanocrystalline-alloys-and-nano-grain-size-stability

Keeping Nanocrystalline Alloy Grains Small

Nanocrystalline alloys are metals with grain sizes smaller than 100 nm. These tiny grains can give the material enhanced physical and mechanical properties. That is why nanocrystalline alloys are used or studied for semiconductor devices, biosensors, and aerospace parts. A major challenge is making dense bulk materials from these alloys. To reach close to 100% density, the material must be processed with elevated temperature and pressure. But as temperature and pressure rise, the small grains...

hydrogel synthesis

Hydrogels and Their Water Absorption

Hydrogels are cross-linked polymers that can absorb water and swell. They are made with relatively simple procedures and inexpensive materials, which makes them useful for many school-level chemistry and materials science topics. A hydrogel starts with a polymer backbone built from monomer reagents. An initiator makes the polymer reactive, and a crosslinking species connects the chains together. This network gives the material its final structure. Water absorption is one of the key features...

materials engineering

该系列采用尖端材料分析和表征方法，并介绍了一系列用于新技术和应用的先进材料和工艺。

Learn how X-ray diffraction uses scattered X-rays to identify crystal structure, detect defects, and distinguish WAXD, SAXS, and X-ray reflectivity.

Crystal Structure Using X-ray Diffraction | JoVE K12

criteria-mineral-crystalline-solid-occurs-nature-inorganic-defined

Criteria of a mineral (crystalline solid, occurs in nature, inorganic, defined chemical composition)

Virginia  Standards of Learning

HIgh School

Earth Science

ES.4

ES.4.c

south-carolina-college-and-career-ready-science-standards

South Carolina College and Career Ready Science Standards

High School

Chemistry

Matter and Its Interactions

C-PS1-1

C-PS1-3.

motion-and-stability-forces-and-interactions

Motion and Stability: Forces and Interactions

C-PS2-6.

Faisal Alamgir

School of Materials Science and Engineering

Georgia Institute of Technology

Overview

Principles of X-ray Diffraction

Instrument, Sample and Beam Parameters

Selection of the Parameters for the Acquisition

Acquisition and Analysis

Results

Applications

Summary

The Atomic Theory of Matter

The earliest recorded discussion of the basic structure of matter comes from ancient Greek philosophers. Leucippus and Democritus argued that all matter ...

Subatomic Particles

Dalton was only partially correct about the particles that make up matter. All matter is composed of atoms, and atoms are composed of three smaller ...

Elements: Chemical Symbols and Isotopes

A chemical symbol is an abbreviation used to indicate an element or an atom of an element. For example, the symbol for mercury is Hg. The same symbol is ...

Atomic Mass

Atoms &mdash; and the protons, neutrons, and electrons that compose them &mdash; are extremely small. For example, a carbon atom weighs less than 2 ...

physical-properties-of-minerals-ii-polymineralic-analysis

Physical Properties Of Minerals II: Polymineralic Analysis

Source: Laboratory of Alan Lester - University of Colorado Boulder
The physical properties of minerals include various measurable and discernible ...

physical-properties-of-minerals-i-crystals-and-cleavage

Physical Properties Of Minerals I: Crystals and Cleavage

Source: Laboratory of Alan Lester - University of Colorado Boulder
The physical properties of minerals comprise various measurable and discernible ...

Atoms and elements

Content elaboration: This unit builds upon the Earth and Space Science strand in grade 6, where common minerals are defined, tested and classified. It also incorporates knowledge of mineral properties and crystalline structures (chemical compositions and bonding) included in the chemistry sections of other high school courses. The emphasis in this course is to relate the chemical and physical components of minerals to the properties of the minerals. This requires extensive mineral testing, investigations, experimentation, observation, use of technology and models/modeling. The focus is on learning the ways to research, test and evaluate minerals, not in memorization of mineral names or types. Properties such as cleavage and hardness are connected to the chemical structure and bonding of the mineral. In addition, the environment in which minerals form should be part of the classification of the mineral, using mineral data to help interpret the environmental conditions that existed during the formation of the mineral.

Atoms and elements

Types of Chemical Bonds

Chemical bonding theories were pioneered by American chemist Gilbert&#xA0;N. Lewis. He developed a model called the Lewis model to explain the type and ...

Ionic Bonds

When atoms gain or lose electrons to achieve a more stable electron configuration they form ions. Ionic bonds are electrostatic attractions between ions ...

Ionic Bonding and Electron Transfer

Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence ...

Lewis Symbols and the Octet Rule

Chemical bonds are complex interactions between two or more atoms or ions, which reduce the potential energy of the molecule. Gilbert N. Lewis developed a ...

Chemical Bonds


Atoms participate in a chemical bond formation&#160;to acquire a completed valence-shell electron configuration similar to that of the noble gas nearest ...

Covalent Bonding and Lewis Structures

Compared to ionic bonds, which results from the transfer of electrons between metallic and nonmetallic atoms, covalent bonds result from the mutual ...

Bonding in Metals

Metallic bonds are formed between two metal atoms. A simplified model to describe metallic bonding has been developed by Paul Dr&#xFC;de called the ...

soil-nutrient-analysis-nitrogen-phosphorus-and-potassium

Soil Nutrient Analysis: Nitrogen, Phosphorus, and Potassium

Source: Laboratories of Margaret Workman and Kimberly Frye - Depaul University
In this experiment, three soil macronutrients are chemically extracted, ...

Chemical bonding (ionic, covalent, metallic)

Content elaboration: This unit builds upon the Earth and Space Science strand in grade 6, where common minerals are defined, tested and classified. It also incorporates knowledge of mineral properties and crystalline structures (chemical compositions and bonding) included in the chemistry sections of other high school courses. The emphasis in this course is to relate the chemical and physical components of minerals to the properties of the minerals. This requires extensive mineral testing, investigations, experimentation, observation, use of technology and models/modeling. The focus is on learning the ways to research, test and evaluate minerals, not in memorization of mineral names or types. Properties such as cleavage and hardness are connected to the chemical structure and bonding of the mineral. In addition, the environment in which minerals form should be part of the classification of the mineral, using mineral data to help interpret the environmental conditions that existed during the formation of the mineral.

Chemical bonding (ionic, covalent, metallic)

Structures of Solids

Solids in which the atoms, ions, or molecules are arranged in a definite repeating pattern are known as crystalline solids. Metals and ionic compounds ...

Ionic Crystal Structures

Ionic crystals consist of two or more different kinds of ions that usually have different sizes. The packing of these ions into a crystal structure is ...

X-ray Crystallography

The size of the unit cell and the arrangement of atoms in a crystal may be determined from measurements of the diffraction of X-rays by the crystal, ...

Classifying Matter by Composition

Matter: Pure Substances and Mixtures
According to its composition, the matter can be classified into two broad categories &mdash; pure substances and ...

Optical Materialography Part 2: Image Analysis

Source: Faisal Alamgir, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA
The imaging of microscopic structures of ...

Source: Faisal Alamgir, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA
X-ray diffraction (XRD) is a technique ...

X-ray Photoelectron Spectroscopy

Source: Faisal Alamgir, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA
X-ray photoelectron spectroscopy (XPS) ...

Crystallinity (crystal structure)

Content elaboration: This unit builds upon the Earth and Space Science strand in grade 6, where common minerals are defined, tested and classified. It also incorporates knowledge of mineral properties and crystalline structures (chemical compositions and bonding) included in the chemistry sections of other high school courses. The emphasis in this course is to relate the chemical and physical components of minerals to the properties of the minerals. This requires extensive mineral testing, investigations, experimentation, observation, use of technology and models/modeling. The focus is on learning the ways to research, test and evaluate minerals, not in memorization of mineral names or types. Properties such as cleavage and hardness are connected to the chemical structure and bonding of the mineral. In addition, the environment in which minerals form should be part of the classification of the mineral, using mineral data to help interpret the environmental conditions that existed during the formation of the mineral.

single-crystal-and-powder-x-ray-diffraction

Single Crystal and Powder X-ray Diffraction

Source: Tamara M. Powers, Department of Chemistry, Texas A&#38;M University&#160;
X-ray crystallography is a technique that uses X-rays to study the ...

determining-the-solubility-rules-of-ionic-compounds

Determining the Solubility Rules of Ionic Compounds

Source: Laboratory of Dr. Neal Abrams &#8212; SUNY College of Environmental Science and Forestry
An ionic compound&#39;s solubility can be determined via ...

Criteria of a mineral (crystalline solid, occurs in nature, inorganic, defined chemical composition)

Content elaboration: This unit builds upon the Earth and Space Science strand in grade 6, where common minerals are defined, tested and classified. It also incorporates knowledge of mineral properties and crystalline structures (chemical compositions and bonding) included in the chemistry sections of other high school courses. The emphasis in this course is to relate the chemical and physical components of minerals to the properties of the minerals. This requires extensive mineral testing, investigations, experimentation, observation, use of technology and models/modeling. The focus is on learning the ways to research, test and evaluate minerals, not in memorization of mineral names or types. Properties such as cleavage and hardness are connected to the chemical structure and bonding of the mineral. In addition, the environment in which minerals form should be part of the classification of the mineral, using mineral data to help interpret the environmental conditions that existed during the formation of the mineral.

physical-and-chemical-properties-of-matter

Physical and Chemical Properties of Matter

The characteristics that enable us to distinguish one substance from another are called properties.

Physical Properties of Matter

A physical property is ...

Metallic Solids

Metallic solids such as crystals of copper, aluminum, and iron are formed by metal atoms. The structure of metallic crystals is often described as a ...

Properties of Transition Metals

Transition metals are defined as those elements that have partially filled d orbitals. As shown in Figure 1, the d-block elements in groups 3&#8211;12 are ...

stress-strain-characteristics-of-aluminum

Stress-Strain Characteristics of Aluminum

Source:&#160;Roberto Leon, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA
Aluminum is one of the most abundant materials ...

an-overview-of-bgdgt-biomarker-analysis-for-paleoclimatology

An Overview of bGDGT Biomarker Analysis for Paleoclimatology

Source: Laboratory of Jeff Salacup&#160;- University of Massachusetts Amherst
Throughout this series of videos, natural samples were extracted and ...

an-overview-of-alkenone-biomarker-analysis-for-paleothermometry

An Overview of Alkenone Biomarker Analysis for Paleothermometry

Properties of minerals (hardness, luster, cleavage, streak, crystal shape, fluorescence, flammability, density/specific gravity, malleability)

Content elaboration: This unit builds upon the Earth and Space Science strand in grade 6, where common minerals are defined, tested and classified. It also incorporates knowledge of mineral properties and crystalline structures (chemical compositions and bonding) included in the chemistry sections of other high school courses. The emphasis in this course is to relate the chemical and physical components of minerals to the properties of the minerals. This requires extensive mineral testing, investigations, experimentation, observation, use of technology and models/modeling. The focus is on learning the ways to research, test and evaluate minerals, not in memorization of mineral names or types. Properties such as cleavage and hardness are connected to the chemical structure and bonding of the mineral. In addition, the environment in which minerals form should be part of the classification of the mineral, using mineral data to help interpret the environmental conditions that existed during the formation of the mineral.

properties-minerals-hardness-luster-cleavage-streak-crystal-shape

Properties of minerals (hardness, luster, cleavage, streak, crystal shape, fluorescence, flammability, density/specific gravity, malleability)

Crystal Structure Using X-ray Diffraction

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