X-ray or gamma ray systems or devices – Specific application – Diffraction – reflection – or scattering analysis
Reexamination Certificate
2002-02-05
2004-06-15
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Diffraction, reflection, or scattering analysis
C378S072000, C378S073000, C378S075000
Reexamination Certificate
active
06751287
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a method and apparatus for x-ray analysis of particle size, XAPS for short, and more specifically to a method and apparatus for determining particle size and particle size distribution of crystalline particles comprising powders, suspensions or solids non-intrusively without the need to extractor separate the particles from the other ingredients of the materials.
2. Related Art
The overwhelming majority of materials handled by industry, such as mining, chemicals, construction, agriculture and waste products, are in particle or “powder” form. Many technologically important materials such as ceramics, metals, composites, solid propellants, catalysts, magnets and high-T
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superconductors all constitute particles or “grains” and are manufactured by consolidation of powders. Particle size is one dominant parameter in all these industrial products that dictates their properties and performance. Determination and control of particle characteristics, especially the particle size distribution, are essential for product quality control and performance.
Various methods have been developed in the past to determine the particle size distribution in powders. These range from sieve elimination to laser scattering. Each one of these techniques has its unique advantage and limitations.
The early techniques for characterizing fine particles depended heavily on sieves, elutriators and microscopes. These techniques are time consuming and do not lend themselves to fast and practical measurements. In the period from the mid-1950's to the mid-1970's the methodology of fine particle characterization improved rapidly with the introduction of the instruments as the Coulter Counter, other resista-zone counters and image analyzers. Since mid-seventies the fine particle characterization studies have expanded substantially and many new techniques and instrumentation have been developed. The highlights of this era include holography for characterization of particles in mist and suspension systems; laser Doppler velocimetry (laser-photon correlation spectroscopy) for characterization of particles in aerosols and Brownian motion; eriometry (light/laser diffraction) for evaluating fine particle populations based upon group diffraction patterns; signature-waveform characterization of scattered light for fine particle analysis; fractal description of fine particle profiles; and a new generation of image analyzers with powerful digitization and computer routines for fine particle size and shape analysis.
Most of the recent techniques for particle size determination are based on indirect measurements such as the optical properties of particles obtained from scattering, diffraction, etc., of light or laser directed at the particle surface, or the disturbance of a homogeneous electrical field by a passing particle. If an irregular shaped particle is measured using these physical properties, the “size”of this particle will differ and depend on the particular property chosen. In these techniques, particle size is described by its so-called equivalent diameter, the diameter of a sphere, which yields the same response when analyzing a certain property as the irregularly shaped particle. For these reasons significant differences are found in the particle size distribution results obtained by different commercially available instruments. For measurement of particle size in loose powders the scanning electron microscope (SEM) is a very useful tool because of its superior depth-of-focus compared to optical microscopes. However, use of SEM is extremely time consuming in order to obtain statistically significant measurements. It also needs to operate under vacuum and is not amenable for on-line applications.
On the other hand, none of the current particle-size analysis techniques is applicable to multi-particle mixed solid materials, except for microscopy in certain cases. Microscopy, however, requires destructive sectioning of the solids followed by tedious polishing and etching procedures. These procedures are difficult and time consuming, and sometimes unsuccessful for many ceramics, intermetallics, composites, energetics, and some metals. Particle size analysis of fillers in viscous suspensions (uncured) where the particles are encapsulated is yet another area, which is not feasible even with microscopy.
Analysis of particles in some of the suspensions and solids by these techniques might be feasible only after their constituents are separated effectively. One such technique involves the separation of particles, e.g. separation of solid filler particles from a suspension by heating in an oven to pyrolyze and eliminate the viscous phase. Thereafter, the remaining particulate can be characterized by the known methods. Such intrusive approaches, however, are usually ineffective and expensive.
All the methods mentioned so far, including the early methods, do not provide information on the constitution of the fine particles, i.e., when the fine particles contain more than one material or phase-polymorph, they are not differentiated by these techniques. Scanning electron microscopy (SEM) combined with energy dispersive x-ray fluorescence analysis (EDX) can differentiate compositional differences between the particles in a mixed material. However, SEM with EDX is applicable in general only if the components contain different and contrasting elements that are heavier than oxygen and are not affected by the vacuum. The EDX technique is also limited to submicron thick surface layers and prone to errors due to surface films. Use of SEM with EDX is time consuming and is not amenable for on-line applications.
X-ray diffraction methods can be applied to determine the size of particles in some special cases. Early work has been done with Debye and back-reflection cameras. In these x-ray diffraction techniques particles or grains of a polycrystalline material are irradiated with a collimated beam and diffraction takes place in the coherently reflecting planes of the particles. When large numbers of particles are irradiated under the incident beam, their diffraction spots overlap and form continuous diffraction lines on appropriate Debye rings. Continuity of the rings breakdown and individual diffraction spots are resolved if the number of diffraction particles is reduced. However, the number of diffracting particles is reduced and diffraction spots from individual particles are resolved only if the particle size is very large. Furthermore, these x-ray techniques are very tedious and cannot be applied routinely.
Previous efforts in this area include:
Mack, U.S. Pat. No. 3,148,275 discloses a x-ray technique that is not for particle size analysis. Rather, it relates to a special sample holder to hold a curved specimen to improve wide-angle x-ray diffractometer (WAXRD).
Goebel, U.S. Pat. No. 4,144,450 does not disclose a particle size analyzer, but rather relates to a wide-angle x-ray powder diffractometer equipped with a horizontal linear position sensitive proportional counter (PSPC) for simultaneous data collection from a range of 2&thgr; angles, on the equatorial diffraction plane. This is a regular WAXRD technique with a horizontal linear position-sensitive detector (PSD). This is not a particle size analyzer.
Ladell, U.S. Pat. No. 4,199,678 does not disclose a particle size analyzer. Rather, it relates to a modified WAXRD for texture (preferred orientation) analysis with a point detector.
Rinik. et al., U.S. Pat. No. 4,649,556 discloses an indirect method to get information on the “average” particle size by making use of the variation of diffracted intensity with WAXRD 2&thgr; angle using a point detector. It does not obtain direct information on the particle size and cannot do measurements on individual particles to get particle size distribution.
Cocks. et al., U.S. Pat. No. 4,821,301 discloses a technique for glancing-angle x-ray-absorbance chemical analyses of thin (1000 Å) films. It does not relate to particle size a
Kalyon Dilhan M.
Yazici Dostum F.
Yazici Rahmi
Bruce David V.
Ho Allen C.
The Trustees of the Stevens Institute of Technology
Wolff & Samson PC
Yazici Dostum F.
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