Embodiments of the present invention relate to methods and systems for treating materials, characterizing materials, and for both treating and characterizing materials.
Positrons are the charged particles that have a mass equal to the mass of an electron and a positive charge equal in magnitude to the negative charge of an electron, and are considered the anti-particle or anti-matter of electrons. When a positron and an electron collide, the particles can annihilate one other. In other words, their mass is combined and converted into energy in the form of gamma rays. In general, two gamma ray photons each having an energy of about 511 keV are emitted in generally opposite directions (in directions oriented about 180 degrees relative to one another) upon annihilation of a positron-electron pair, although the precise direction of emission and energy of the gamma ray photons may be affected by the kinetic energy of the electron and the positron at the time of annihilation.
A positron within a material will diffuse away from the location of injection or generation due to thermal energy until it encounters and is annihilated with an electron. During this diffusion process, the positrons are repelled by positively charged nuclei and thus accumulate at locations within the lattice structure where the concentration of nuclei is relatively low, such as at the location of dislocations, vacant lattice sites, vacancy clusters, vacancy-impurity complexes, grain boundaries, interfaces, and pores, and other defects in the material, all of which are collectively referred to hereinafter as “lattice anomalies”.
The gamma ray photons emitted upon annihilation of a positron-electron pair can be detected. Furthermore, the energy of the detected gamma ray photons can be determined. By detecting the emitted gamma rays and determining their energy, certain characteristics of the material may be determined. As a result, positrons have been injected into or generated within materials, and gamma rays emitted upon annihilation of positron-electron pairs within the materials have been detected and used to gather information relating to the presence of lattice anomalies within the crystal lattice of the materials. Such information can be used to characterize embrittlement, fatigue, and other material characteristics.
Positrons can be injected into a material to be tested by directing positrons generated outside the material from a positron source toward the material. Such positron sources include, for example, radioactive isotopes such as 22Na, 68Ge, and 58Co which emit positrons during radioactive decay. Positrons injected into a material in this manner, however, generally migrate into the material to a limited depth, and material analysis techniques employing such positron injection methods are limited by the depth to which the positrons will migrate into the material. In other words, such injection techniques may be used to analyze material characteristics at or near the surface of the material.
To analyze material properties deeper within a material, radioactive isotopes may be generated or provided within the material itself, and the radioactive isotopes then generate positrons within the material as the radioactive isotopes decay. Positron-emitting radioactive isotopes may be generated or provided within a material by, for example, bombarding the material with neutrons (to add neutrons to atoms to form the positron-emitting radioactive isotopes) or photons (to remove neutrons from atoms to form the positron-emitting radioactive isotopes), which will penetrate into a material to a greater depth than will positrons. In such processes, however, the material must include atoms that will form positron emitting radioactive isotopes upon bombardment with neutrons or photons.
References that disclose systems and methods for characterizing materials that employ the detection of gamma rays emitted upon annihilation of positron-electron pairs include, for example, U.S. Pat. No. 6,178,218, issued Jan. 23, 2001 and entitled NONDESTRUCTIVE EXAMINATION USING NEUTRON ACTIVATED POSITRON ANNIHILATION, U.S. Pat. No. 7,231,011, issued Jun. 12, 2007 and entitled APPARATUS FOR PHOTON ACTIVATION POSITRON ANNIHILATION ANALYSIS, U.S. Patent Application Publication No. 2003/0161431, published Aug. 28, 2003 and entitled METHOD AND APPARATUS FOR EVALUATING MATERIALS USING PROMPT GAMMA RAY ANALYIS, and U.S. Patent Application Publication No. 2005/0117682, published Jun. 2, 2005 and entitled METHOD FOR ON-LINE EVALUATION OF MATERIALS USING PROMPT GAMMA RAY ANALYSIS, and U.S. Patent Application Publication No. 2006/0013350, published Jan. 19, 2006 and entitled METHOD AND APPARATUS FOR NON-DESTRUCTIVE TESTING, the entire disclosure of each of which document is incorporated herein by this reference.
Materials may be subjected to thermal treatment processes to change or tailor the microstructure of the material in such a way as to impart certain desirable physical or chemical characteristics to the material. Such thermal treatment processes include, for example, annealing processes, quenching processes, and phase precipitation processes. Thermal treatment processes may be carried out in a controlled environment, and certain process parameters including, for example, temperature, time at temperature, rate of temperature change, pressure, and chemical composition of the atmosphere may be controlled throughout the process.
The effects of varying process parameters in thermal treatment processes on the material being treated may be assessed by performing multiple thermal treatment processes and varying the parameters of the process in a predetermined, calculated, and controlled manner during those processes. The resulting microstructures of the materials treated in such thermal treatment processes then may be analyzed, and the microstructural characteristics of the materials may be correlated to the respective variations in the process parameters to determine how variations in each of the process parameters will affect the resulting microstructure. The results of such parametric studies often do not allow accurate prediction of the microstructural characteristics that will result in a particular material upon treating the material using any given set of process parameters.
In some embodiments, the present invention includes methods of treating materials that include providing positrons within a material and detecting electromagnetic radiation emitted upon annihilation of positron-electron pairs within the material as the material is treated. For example, the methods may be used to thermally treat a material, and may include changing a temperature of a material while detecting radiation emitted upon annihilation of positron-electron pairs.
In additional embodiments, the present invention includes methods of treating materials that include subjecting a material to a controlled environment, detecting radiation emitted upon annihilation of positron-electron pairs within the material, and adjusting at least one of a temperature, a pressure, and a chemical composition of an atmosphere within the environment in response to the detected radiation.
In additional embodiments, the present invention includes methods of characterizing a material that include detecting a change in one or more physical or chemical characteristics of a material in a non-equilibrium state using radiation emitted upon annihilation of positron-electron pairs within the material.
In yet other embodiments, the present invention includes material treatment systems that include an enclosure, a positron-generating device for providing positrons within material to be treated within the enclosure, and a radiation detection device configured to detect radiation emitted upon annihilation of positron-electron pairs within material to be treated within the enclosure.
While the specification concludes with claims particularly pointing out and distinctly claiming that which is regarded as the present invention, the advantages of this invention may be more readily ascertained from the following description of the invention when read in conjunction with the accompanying drawings in which:
The illustrations presented herein are not meant to be actual views of any particular apparatus or system, but are merely idealized representations that are employed to describe various embodiments of the present invention. It is noted that elements that are common between figures may retain the same numerical designation.
As used herein, the term “thermal treatment process” means and includes any process in which matter is subjected to an environment in which at least the temperature of the environment is controlled either to form a particular material from the matter, or to alter one or more physical or chemical characteristics of a material (e.g., average grain size, phase composition, phase distribution, hardness, strength, modulus, etc.) comprising the matter. Other parameters also may be controlled in thermal treatment processes such as, for example, rate of temperature change, pressure, rate of pressure change, and atmosphere composition. Thermal treatment processes include, for example, sintering processes, annealing processes, quenching processes, and phase precipitation processes.
As used herein, the term “non-equilibrium state” means any state of a material in which one or more physical and/or chemical characteristics of the material are changing appreciably with time. Non-equilibrium states, as used herein, do not include metastable states, in which the free energy of the material system is not at a minimum, but the characteristics of the material system are not changing or are changing so slowly with time that the changes are not appreciable.
As used herein, the term “controlled environment” means any environment in which one or more of a temperature, a pressure, and a chemical composition of the atmosphere within the environment is controlled. By way of nonlimiting example, the environment within a temperature controlled furnace is a controlled environment.
According to embodiments of the present invention, electromagnetic radiation emitted from a material upon annihilation of positron-electron pairs within the material is detected while a thermal treatment process is being performed on the material. The emitted electromagnetic radiation may be used to identify one or more characteristics of the material in real time during the thermal treatment, and information obtained from such electromagnetic radiation may be used to adjust one or more parameters (e.g., temperature, rate of temperature change, pressure, rate of pressure change, or atmosphere composition) of the thermal treatment process to tailor one or more physical or chemical characteristics of the material being treated. In further embodiments of the invention, material treatment systems are configured to perform such methods.
An embodiment of a material treatment system 10 of the present invention is schematically illustrated in
In some embodiments, the enclosure 12 may comprise a furnace for thermally treating material 14, and the material treatment system 10 may further comprise a temperature control device 20 for controlling the temperature within the furnace.
In addition or as an alternative, the material treatment system 10 may further include one or both of a pressure control device 22 for controlling the pressure within the enclosure 12, and an atmosphere control device for controlling the chemical composition of the atmosphere within the enclosure 12. A position translation device also may be used to provide relative movement between the positron-generating device 16 and the material 14 to be treated within the enclosure 12. For example, the positron-generating device 16 may be mounted on a position translation device 26A configured to move the positron-generating device 16 relative to the material 14, the material 14 may be disposed on a position translation device 26B configured to move the material 14 relative to the positron-generating device 16, or both.
The material treatment system 10 may further include a system controller 28 configured to selectively control one or more of the various controllable components of the system 10, such as, for example, the radiation detector 18, the temperature control device 20, the pressure control device 22, the atmosphere control device 24, and the one or more position translation devices 26A, 26B.
Each of the various components of the material treatment system 10 is described in further detail below.
With continued reference to
The temperature control device 20 may be used to control (e.g., selectively vary) the temperature within the enclosure 12, and hence, to control the temperature of the material 14. By way of example and not limitation, the temperature control device 20 may comprise a burner (not shown) for causing combustion of one or more fuels to generate heat within the enclosure 12, one or more temperature sensors (e.g., one or more thermocouples) (not shown) for sensing a temperature within the enclosure 12, and a controller (not shown), such as, for example, a programmable logic controller (PLC), for igniting the burner and/or controlling the rate of flow of fuel to the burner in response to signals received from the one or more temperature sensors. As another example, the enclosure 12 may comprise or be part of an induction furnace, and the temperature control device 20 may comprise one or more conductive coils (not shown) configured to surround the material 14, a power supply (not shown) configured to pass electrical current through the conductive coils to generate magnetic fields in a region comprising the material 14, one or more temperature sensors (e.g., one or more thermocouples) (not shown) for sensing a temperature within the enclosure 12, and a controller (not shown), such as, for example, a programmable logic controller (PLC), for controlling the flow of electrical current (e.g., the direction of current flow and the magnitude of the current flow) through the conductive coils in response to electrical signals received from the one or more temperature sensors.
In some embodiments, the temperature control device 20 also may comprise a cooling device configured to reduce the temperature within the enclosure 12 and, hence, the temperature of the material 14. For example, the temperature control device 20 may comprise a heat exchanger system for removing heat out from within the enclosure 20 and the material 14. In one non-limiting example embodiment, the temperature control device 20 may comprise a fluid pump configured to pump cooling fluid (e.g., liquid or gas) through associated plumbing within the enclosure 12, and a controller device may be used to control operation of the pump and the rate of flow of fluid through the associated plumbing. In such embodiments, the fluid pump also be used to provide heat within the enclosure (e.g., to function as a heat pump).
In the embodiments described above, the temperature control device 20 may be adapted to initiate and regulate heating and/or cooling of the material 14 within the enclosure 12 to one or more predetermined temperatures for predetermined amounts of time, and to further control the rate(s) of temperature change as the temperature of the material 14 is selectively varied using the temperature control device 20.
The positron-generating device 16 is configured to provide positrons within the material 14 while the material 14 is disposed within the enclosure 12 before, during, and/or after treatment of material 14 by the material treatment system 10. By way of example and not limitation, the positron-generating device 16 may comprise any of the positron-generating devices disclosed in U.S. Pat. No. 6,178,218 to Akers et al. In some embodiments, the positron-generating device 16 may comprise, for example, a positron-emitting material or device configured to emit positrons toward the material 14. As one non-limiting example, the positron-generating device 16 may comprise a quantity of one or more of 22Na, 68Ge, and 58Co, and optionally, such materials may be encapsulated in a material such as titanium. Such positron sources are commercially available from, for example, Eckert & Ziegler Isotope Products of Valencia, Calif. Optionally, the positron-generating device 16 may be configured to emit a beam of positrons toward the material 14. In other embodiments, if one or more elements within the material 14 is capable of generating positrons upon input of energy to the material (e.g., through impingement by photons, neutrons, or other particles) the positron-generating device 16 may comprise a device configured to input energy into the material 14 (e.g., by emitting photons, neutrons, other particles, or another form of energy toward the material 14) to cause the material 14 itself to generate positrons therein.
As previously discussed herein, positrons provided within the material 14 by the positron-generating device 16 are repelled by positively charged nuclei and accumulate at lattice anomalies within the lattice structure or structures of the material 14, where the concentration of nuclei is relatively low. As the photons combine with electrons and are annihilated, the resulting gamma ray emissions may be detected using the radiation detection device 18.
The radiation detection device 18 may comprise, for example, a high purity germanium (HPGe) photon detector device, such as, for example, those commercially sold under the Trademark ORTEC by Advanced Measurement Technology, Inc. of Oakridge, Tenn.
As previously mentioned, the material treatment system 10 optionally may further include one or both of a pressure control device 22 and an atmosphere control device 24. In some embodiments, the pressure control device 22 and the atmosphere control device 24 may be separate devices or systems, as represented schematically in
The pressure control device 22 may comprise, for example, one or more pumps (not shown) configured to pump gas or gasses into the enclosure 12 and/or to pump gas or gasses out from the enclosure 12. The pressure control device 22 may further include a pressure sensor (not shown) for sensing the pressure within the enclosure 12, and a control device (not shown) for controlling operation of the one or more pumps in response to electrical signals received from the pressure sensor to provide or maintain predetermined pressure(s) within the container 12 during treatment of the material 14.
The atmosphere control device 24 may comprise, for example, a source of reactive gasses (e.g., reducing or oxidizing gasses) and/or inert gases (e.g., argon gas) and plumbing configured to allow the reactive and/or inert gases to flow into, through, and out from the enclosure 12. Optionally, one or more pumps may be used to drive the flow of the reactive and/or inert gases through the enclosure 12, although, such pumps may not be needed if, for example, the reactive and/or inert gases are supplied by a pressurized gas source.
As previously mentioned, the material treatment system 10 may further comprise a position translation device configured to provide relative movement between the material 14 and the positron-generating device 16, such as the position translation device 26A and/or the position translation device 26B. As non-limiting examples, the position translation device 26A may comprise a robotic arm (not shown) configured to move the positron-generating device 16 in one, two, or three dimensions relative to the material 14. The positron translation device 26B may comprise a platform on which the material 14 is supported during treatment and an electromechanical device (not shown) configured to move the platform in one, two, or three dimensions relative to the positron-generating device 16.
The system controller 28 may comprise a computer device, such as, for example, a desktop computer, a laptop computer, a server, or a programmable logic controller. The system controller 28 may be used both for controlling the various controllable components of the system 10 (e.g., the radiation detector 18, the temperature control device 20, the pressure control device 22, the atmosphere control device 24, and the one or more position translation devices 26A, 26B) and for collecting and processing data received from the radiation detection device 18. Optionally, the system controller 28 may be configured to create one or more graphical representations of the data. Furthermore, the system controller 28 may be configured under control of a software program to automatically adjust one or more operating parameters of the material treatment system 10 in response to data obtained from the radiation detection device 18.
The robotic arm 45 may be used to selectively move the positron-generating device 16 relative to the material 14 within the enclosure 12 before, during, and/or after the material 14 is subjected to a thermal treatment process within the enclosure 12. In this manner, various regions or areas of the material 14 may be analyzed before, during, or after the material 14 is subjected to a thermal treatment process within the enclosure 12.
The probe 44 may be formed from a material that is capable of withstanding the temperatures within the furnace. For example, the probe 44 may be formed from high-temperature ceramic or metal materials. Furthermore, a cooling system may be used to cool the probe 44 and/or the positron-generating device 16 within the furnace. By way of example and not limitation, a cooled liquid or gas (e.g., nitrogen) may be caused to flow over at least a portion of the interior and/or exterior surfaces of the probe 44 and/or the positron-generating device 16 within the furnace. For example, such cooled liquid or gas may be caused to flow over the exterior surfaces of the probe 44 and/or the positron-generating device 16 within the furnace through a cooling jacket 48 provided thereover, as shown in
With continued reference to
The particular configuration shown in
Embodiments of material treatment systems of the present invention, such as the material treatment system previously described with reference to
As positrons are provided within a material 14, positrons will combine and annihilate with electrons, which results in the emission of gamma rays. The radiation detector device 18 may be used to detect the intensity (as measured by counts) of the detected gamma rays as a function of their wavelength, or energy. As previously mentioned, two gamma ray photons each having an energy of about 511 keV are emitted in generally opposite directions (in directions oriented about 180 degrees relative to one another) upon annihilation of a positron-electron pair, although the precise direction of emission and energy of the gamma ray photons may be affected by the kinetic energy of the electron and the positron at the time of annihilation. Therefore, when the radiation detector device 18 is used to detect the intensity (or counts) of the gamma rays as a function of their energy or wavelength, the resulting graph may appear generally as a bell curve that is centered at or near 511 keV, like the bell curve shown in
Referring to
Furthermore, the kinetic energy of positron-electron pairs within a material 14 at the time of annihilation may be at least partially related to the energy band structure of the bulk material 14. As different materials have different energy band structures, different bulk materials 14 will exhibit intensity/energy curves, like the energy curves 50, 52 of
Referring again to
In additional embodiments, the data obtained from the radiation detection device 18 may be subjected to a Doppler broadening algorithm to facilitate analysis thereof, as disclosed in any one of previously referenced U.S. Pat. No. 6,178,218, issued Jan. 23, 2001 and entitled NONDESTRUCTIVE EXAMINATION USING NEUTRON ACTIVATED POSITRON ANNIHILATION, U.S. Pat. No. 7,231,011, issued Jun. 12, 2007 and entitled APPARATUS FOR PHOTON ACTIVATION POSITRON ANNIHILATION ANALYSIS, U.S. Patent Application Publication No. 2003/0161431, published Aug. 28, 2003 and entitled METHOD AND APPARATUS FOR EVALUATING MATERIALS USING PROMPT GAMMA RAY ANALYIS, and U.S. Patent Application Publication No. 2005/0117682, published Jun. 2, 2005 and entitled METHOD FOR ON-LINE EVALUATION OF MATERIALS USING PROMPT GAMMA RAY ANALYSIS.
Referring again to
For example, each time a relatively small area or volume of material 14 is tested using the positron-generating device 16 and the radiation detection device 18, the data accumulated may be used to generate a curve (like the curves 50, 52 of
As shown in
Data regarding the shape of the intensity/energy curve for a particular material may be collected at least substantially continuously, or at predetermined intervals over a period of time, before, during, and/or after a material is treated using the material treatment system 10. For example, data regarding the shape of the intensity/energy curve for a particular material may be collected before, during, and/or after a material is subjected to a thermal treatment process using the material treatment system 10. For example, positrons may be provided within the material 14 using the positron-generating device 16. The temperature of the material 14 may be selectively changed or varied within the enclosure 12 to conduct a thermal treatment process. As the temperature is selectively changed or varied within the enclosure 12, electromagnetic radiation emitted upon annihilation of positron-electron pairs within the material 14 may be detected using the radiation detection device 18. As part of the thermal treatment process, at least one change in a physical or chemical characteristic of the material 14 may be induced by subjecting the material 14 to elevated or reduced temperatures within the enclosure 12, and the at least one change may be detected using the detected radiation emitted upon annihilation of positron-electron pairs within the material 14. Such changes in the material 14 may include phase changes, a change in a lattice structure of a material, a change in a density of defects within the material (e.g., dislocations and pores), a change in average grain size within the material, a change in a chemical composition of the material, etc.
Embodiments of the present invention are not limited to methods and systems for thermally treating materials. By subjecting a material 14 to, for example, elevated or reduced pressures or to atmospheres comprising one or more reagents (i.e., a reactive atmosphere) within the enclosure (in addition to, or as an alternative to subjecting the material 14 to elevated or reduced temperatures), the material 14 may be provided in a non-equilibrium state. As the material 14 transforms from a non-equilibrium state toward an equilibrium state, a change in one or more physical or chemical characteristics of the material 14 may be detected and identified by detecting and analyzing electromagnetic radiation emitted upon annihilation of positron-electron pairs within the material 14.
Embodiments of the invention may be used to determine what parameters and parameter changes of a thermal treatment process will result in the formation of a desirable microstructure in a material. Using embodiments of material treatment systems 10 as described herein, data may obtained from the detected gamma radiation emitted from the material 14 in situ during a material treatment process (e.g., a thermal treatment process), and the data may be represented visually as two dimensional curves (like those shown in
In utilizing embodiments of material treatment systems of the present invention (like the material treatment system 10 of
As embodiments of the present invention facilitate in situ monitoring of physical and or characteristics of materials 14 as they are treated, embodiments of the present invention may be used to adjust treatment parameters in real time during a material treatment process in response to data obtained from detected radiation emitted upon annihilation of positron-electron pairs within the material 14 in situ. For example, the material 14 may be subjected to a controlled environment within the enclosure 12, and at least one of a temperature, a pressure, and a chemical composition of the atmosphere within the enclosure 12 may be adjusted in response to information about the material 14 obtained by detecting the radiation emitted upon annihilation of positron-electron pairs within the material 14 as part of a material treatment process. More particularly, the system controller 28 may be configured under control of a software program to continuously receive the data obtained from the radiation detection device 18 during a material treatment process, to perform one or more algorithms on the data, and to adjust one or more operating parameters of one or more of the temperature control device 20, the pressure control device 22, and the atmosphere control device 24 to affect one or more changes in the material 14, which could be detected by the system controller 28 using the data obtained from the radiation detection device 18.
Embodiments of methods and systems of the present invention also may include performing a positron lifetime algorithm to produce positron lifetime data, as disclosed in any one of previously referenced U.S. Pat. No. 7,231,011, issued Jun. 12, 2007 and entitled APPARATUS FOR PHOTON ACTIVATION POSITRON ANNIHILATION ANALYSIS, U.S. Patent Application Publication No. 2003/0161431, published Aug. 28, 2003 and entitled METHOD AND APPARATUS FOR EVALUATING MATERIALS USING PROMPT GAMMA RAY ANALYIS, and U.S. Patent Application Publication No. 2005/0117682, published Jun. 2, 2005 and entitled METHOD FOR ON-LINE EVALUATION OF MATERIALS USING PROMPT GAMMA RAY ANALYSIS. As disclosed therein, such methods and systems may employ more than one radiation detection device 18.
Embodiments of methods and systems of the present invention may be used to treat many types of materials including metals, ceramics, polymers, and composite materials.
Furthermore, in some embodiments of the present invention, portable material treatment systems may be provided that include at least a positron-generating device 16, a radiation detection device 18, and a system controller 28. Such portable material treatment systems then may be used with existing enclosures (e.g., furnaces) to perform material treatment processes, as disclosed herein.
While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention includes all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the following appended claims and their legal equivalents.
The United States Government has certain rights in this invention pursuant to Contract No. DE-AC07-05ID14517 between the United States Department of Energy and Battelle Energy Alliance, LLC.