What is x-ray powder diffractometer?
X-ray diffractometer (XRD)
uses the phenomenon of diffraction of X-rays in crystals to obtain the characteristics of X-ray signals after diffraction, and after processing to obtain diffraction patterns.
Characteristic X-rays and their diffraction X-rays are electromagnetic waves with a short wavelength (0.06-20nm) that can penetrate substances of a certain thickness and cause fluorescent substances to glow, camera emulsions to be photographed, and gases to be ionized. X-rays are produced by bombarding a metal target with a high-energy electron beam, which has a specific wavelength corresponding to the element in the target, called characteristic X-rays. For example, the copper target corresponds to the X-ray wavelength of 0.154056 nm.
Application of x-ray powder diffractometer
XRD analysis instrument
is the basic means to study and identify the composition and atomic level structure of substances and materials. It is widely used in metallurgy, petroleum, chemical industry, scientific research, aerospace, teaching, material production, and other fields.Materials scienceX-ray diffraction
is a major technique for the study of advanced materials and includes the following functions: phase identification and quantification, phase crystallinity determination, crystal structure, crystal orientation and weave, polar maps, etc. The effects of non-environmental conditions on these functions are also frequently studied together with the XRD technique. A wide range of sample types can be targeted, from powders to solid materials of various shapes and sizes, liquids, and semiconductor wafers.Geology, minerals, and mining
In the study of planetary processes and Earth's tectonics, geographers need to analyze the composition of rock and mineral samples. x-ray diffractometer analysis techniques such as small spot excitation, distribution analysis, and label-free quantitative analysis are increasingly becoming the main instruments in the field of geological and mineralogical research. x-ray diffractometer (XRD) allows quantitative measurement of phase composition. x-ray diffraction data Rietveld analysis is considered to be Rietveld analysis of X-ray diffraction data is considered a suitable method for quantitative analysis of crystal phases.Metals
Foundries, smelters, and steel mills, as well as other aspects of the metal industry, are in continuous production and require day and night control of the production and quality of the incoming and outgoing material. The chemical content of alloys, and residual stresses are important characteristics associated with structural failure. x-ray diffractometry is a non-destructive and accurate method of measuring residual stresses. x-ray diffraction has a high spatial resolution and the ability to measure hardened materials provides non-contact measurements.Coatings
Whether it is a thin film of a barrier layer on an integrated circuit chip or a coating on an aluminum beverage can, X-rays are an analytical technique for research and development, product process control, and quality assurance*. As an important method for nanotechnology research, X-ray diffraction (XRD) and ancillary techniques are used to determine the nature of the molecular structure of thin films.
How does x-ray powder diffractometer work?
XRD works on the principle that the wavelength of x-rays is similar to the spacing between the atomic planes inside the crystal, and the crystal can act as a spatial diffraction grating for x-rays, i.e., when a beam of x-rays hits an object, it is scattered by the atoms in the object, and each atom produces scattered waves, which interfere with each other and result in diffraction. The superposition of diffraction waves results in the intensity of the rays strengthening in some directions and weakening in others. The analysis of the diffraction results leads to the crystal structure. In 1913, the British physicists W.H. Bragg and W.L. Bragg not only succeeded in determining the crystal structure of NaCl, KCl, etc. based on Laue's discovery but also proposed the famous formula for diffraction as the basis of crystal diffraction The famous formula of Bragg's equation: 2dsinθ=nλ.
For crystalline materials, when the crystals to be measured are at different angles to the incident beam, those crystalline surfaces that satisfy Bragg diffraction will be detected, which is represented in the XRD Pattern as diffractive crests having different diffraction intensity. For non-crystalline materials, the XRD pattern of non-crystalline materials is some diffuse scattering bun peaks because the structure does not have the long-range ordering of atomic arrangement in the crystal structure, but only the short-range ordering in the range of a few atoms.
Structure of x-ray diffractometer
X-ray generator - device for generating X-rays
X-ray generators consist of X-ray tubes, high-voltage generators, tube voltage and tube current stabilization circuits, and various protection circuits, among other components.
An X-ray tube is essentially a vacuum diode. Working principle: when the cathode is heated with a certain current, it can emit thermal radiation electrons. Under the action of a high-voltage electric field of tens of thousands of volts, these electrons are accelerated and bombard the anode (also known as the target). The anode target surface by the electron beam bombardment of the focal point is an elongated rectangular shape (called the line focus or line focal spot), from the center of the ray window, and the target surface of the X-ray grazing angle of 3 ° -6 °. From the direction of emission perpendicular to the long side of the focal spot of the two outgoing window observations, the focal spot is line-shaped called line light source; from the other two outgoing window observations, the focal spot such as point-shaped called point light source. In the diffractometer, each time the installation of the tube must identify whether the X-ray emission window is used for the line focus direction. In addition, it is also required that the goniometer should have a proper tilt angle concerning the target plane.
Goniometer - device for measuring angle 2θ
The goniometer is the most central part of the X-ray diffractometer measurement and is used to accurately measure the diffraction angle.
Working principle: The specimen is mounted at specimen table C. The incident rays are emitted from the X-ray tube focus S, projected onto the specimen surface through the incident diaphragm system A to produce diffraction, and the diffraction lines enter the pedometer E through the receiving diaphragm system B, F and G. S and F are on the same circumference (goniometer circle). The specimen stage and the counter are fixed on two coaxial discs driven by two stepper motors, respectively. Constantly changing θ, the counter moves along the goniometer circle and receives the diffraction intensity corresponding to each diffraction angle 2θ.
X-ray detectors - counting devices for measuring the intensity of X-rays
The main function of the counter is to convert the energy of X-ray photons into an electrical pulse signal. Radiation detectors usually used in X-ray diffractometers are proportional counters, scintillation counters, and bit-sensitive proportional detectors.
X-ray system control device - data acquisition system and various electrical systems, protection systems.
X-rays can cause damage to human tissue, and it is important to ensure the safety of the protection system while taking protective measures yourself. Equipment should be regularly inspected and maintained, and operators should learn about radiation protection and also undergo radiation occupational health checks.
Types of x-ray powder diffractometer
Single crystal x-ray diffractometer
Single crystal x-ray diffractometer is used to determine the crystal structure of an unknown crystalline material. Basic principle: In a single crystal the atoms or groups of atoms are arranged periodically. X-rays (e.g. Kα radiation of Cu) are diffracted onto a single crystal, and by analyzing the diffraction lines, the arrangement of the atoms in the crystal can be resolved, i.e.
Polycrystalline x-ray diffractometer
Polycrystalline x-ray diffractometer is also known as a powder diffractometer, and the object to be measured is usually a bulk material such as powder, polycrystalline metal, or polymer. Basic principle: When a continuous beam of x-rays is irradiated onto a crystal, it is scattered by the atoms on the crystal. Since each atom is periodically arranged in the crystal, there is a fixed phase relationship between these scattered waves, and they interfere with each other spatially, resulting in mutual superposition in some directions and mutual cancellation in some directions, producing scattered ray-enhanced diffraction spots only in specific directions.
How to maintain x-ray powder diffractometer?
a. The lifetime of an XRD tube
can be very long, and the main determining factor is how it is used and maintained.
b. The service life of XRF tubes depends mainly on natural aging, and the influence of the user is less. But high currents are always a bad thing.
c. Both XRD and XRF tubes are expected to be in working condition (heated) at all times, where the "getter" remains in working condition and a good vacuum is maintained.
d. The standby power and especially the current should not be too high, because it will consume the tube life.
e. The high voltage in standby is not a problem, it helps to keep the tube stable to avoid firing.
f. The beryllium window is fragile and toxic. Do not touch the beryllium window under any circumstances, including cleaning. Avoid dropping any sample onto the beryllium window.
g. Cooling water is always important including composition, temperature, and flow rate.
h. Cooler water does not cool better than hotter water, and the optimal cooling water temperature is 20 ºC to 25 ºC. In hotter and more humid environments, the cooling water temperature should also be higher. It is better to be higher than the dew point temperature.
i. When the x-ray diffractometer is not used for more than one hour, set the x-ray tube to standby.
j. When the x-ray diffractometer is not used for more than two weeks, turn off the high voltage of the x-ray tube.
k. When the x-ray diffractometer is not used for more than 10 weeks, remove the x-ray tube.
l. For new X-ray tubes, X-ray tubes that have not been used for more than 100 hours, and X-ray tubes that have been removed from the instrument, normal aging must be performed. For more than 24 hours but less than 100 hours of an unused X-ray tube for automatic rapid aging.
m. When raising the voltage, first raise the voltage and then raise the current. 14.
n. When lowering the high voltage, lower the current first and then lower the voltage.
Precautions for using x-ray powder diffractometer
1. When using an x-ray diffractometer to test metal samples such as a block, plate, or round crutch, it is required to grind into a flat surface with an area not less than 10X10 mm, if the area is too small you can use several pieces to paste together.
2. For lamellar, round crutch samples there will be a serious selection of orientation, x-ray diffractometer diffraction intensity abnormal. Therefore, the test requires a reasonable choice of response direction plane.
3. For the measurement of metal samples of microscopic stress (lattice distortion), the measurement of residual austenite, requires the sample can not simply coarse grinding, requires the preparation of metallographic samples, and ordinary polishing or electrolytic polishing to eliminate the surface strain layer.
4. When using an x-ray diffractometer to measure powder samples, it is required to grind to a particle size of 320 mesh, about 40 microns. Coarse particle size diffraction intensity is low, the peak shape is not good, low resolution. To understand the physical and chemical properties of the sample, such as whether it is flammable, easy to deliquescence, easy to corrosion, toxic, or volatile.
5. The requirements of the sample for the x-ray diffractometer can be metal, non-metal, organic, or inorganic material powder.
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