Description:4. DESCRIPTION

Technical Field of the Invention

The invention relates to the development of composite superconductor materials, aimed at enhancing their performance at temperatures close to 77 K. More particularly, it focuses on method for synthesizing a precursor material which is stabilized in nanometric sizes in the Bi-2223 matrix to enhance flux pinning properties of the superconductor composite, and to enhance the critical current density up to 77 K.

Background of the Invention

High-Temperature Superconductors (HTS) such as Bi1.6Pb0.4Sr2Ca2Cu3O10 (Bi-2223) are pivotal in advanced applications like power transmission, superconducting magnets, and magnetic levitation due to their high critical temperatures. These materials allow the use of liquid nitrogen as an economical coolant. However, their potential is significantly curtailed by issues such as flux creep, especially at temperatures around 77 K, the boiling point of liquid nitrogen. Flux creep refers to the slow movement of magnetic vortices within the superconductor, leading to resistance and dissipation of energy, and a consequent loss of superconductivity under practical operating conditions. Addressing this challenge is crucial for enhancing the efficiency and reliability of superconducting materials.

Historically, several methods have been explored to mitigate the issues of flux creep and improve the performance of HTS. These include the addition of various types of dopants and the creation of microstructural barriers to stabilize the magnetic vortices. Each of these methods has its own merits and limitations, as evidenced by extensive research in this field.

One notable approach involved the addition of Nb2O3, as explored by Sözeri et al. in 2007. They aimed to enhance the flux pinning properties of Bi-2223 by introducing Nb2O3, hypothesizing that it could act as physical barriers to the movement of flux lines. Initial results were promising, showing potential improvements in the performance of the superconductor. However, the application of Nb2O3 at higher concentrations revealed significant drawbacks. The particles tended to agglomerate, leading to uneven distribution within the superconductor matrix. This agglomeration not only reduced the critical current density (Jc) but also adversely affected the superconducting properties of the matrix phase.

Another method involved the incorporation of magnesium oxide (MgO) as detailed by Guilmeau et al. in 2003. They examined the effects of MgO additions on Bi-2223 superconductors, with MgO intended to act as anchor points for magnetic vortices. While effective in minor quantities, higher concentrations of MgO led to several problems, such as a decrease in the grain size of the Bi-2223 phase and an increase in the superconducting transition width (?Tc), which indicated lowering of its performance.

Research on Nd2O3 additions by Aloysius et al. in 2005 aimed to enhance flux pinning properties in Bi-2223. Nd2O3 was hypothesized to form secondary phases within the matrix that could serve as effective pinning centers. However, like Nb2O3, higher concentrations of Nd2O3 led to the formation of precipitates that reduced the content of the Bi-2223 phase, thereby diminishing the superconductor's overall performance by disrupting matrix uniformity and reducing the effective pinning of magnetic vortices.

Recognizing these challenges, the inventors of the present invention proposed a novel method to significantly enhance flux pinning in Bi-2223 superconductor without compromising its intrinsic properties. The new method involves introducing nanometric Ca-Sr-Cu-O (referred to as I-phase) inclusions into the Bi-2223 matrix. These inclusions are designed to be non-reactive with the Bi-2223 phase even in relatively high concentrations, thereby avoiding the formation of unwanted secondary phases that could potentially degrade the superconducting properties of the Bi-2223 phase. The Ca-Sr-Cu-O (I-phase) is introduced following a procedure that generates nanometric needle-shaped precipitates in the Bi-2223 matrix phase, the precipitates generated being nearly of the same composition as the input I-phase.

Brief Summary of the Invention

The following presents a simplified summary of the disclosure to provide a basic understanding to the reader. This summary is not an extensive overview of the disclosure, and it does not identify key/critical elements of the invention or delineate the scope of the invention. Its sole purpose is to present some concepts disclosed herein in a simplified form as a prelude to the more detailed description that is presented later.

The development of High-Temperature Superconductors (HTS), especially those based on the Bi1.6Pb0.4Sr2Ca2Cu3O10 (Bi-2223) composition, represents a significant advance in materials science with broad implications for industries dependent on efficient, high-current density supporting superconductors. Applications such as power generation and transmission, magnetic levitation for transportation, and superconducting magnets for medical imaging technologies could see transformative changes with improved efficiency of these materials. However, their practical utility has been limited by significant challenges, such as flux creep, particularly at temperatures close to 77 K, the boiling point of nitrogen. This issue causes a loss of superconductivity under operational conditions due to the movement of magnetic vortices within the superconductor, leading to resistance and substantially reducing material efficiency and reliability.

This invention introduces a novel approach to significantly enhance the flux pinning capabilities of Bi-2223 superconductor without degeneration of its intrinsic properties. The primary goal is to improve the performance of the superconductor under operational conditions, particularly at higher temperatures around 77 K, by improving the critical current density (Jc) and mitigating issues like flux creep. This is achieved through the incorporation of nano-sized Ca-Sr-Cu-O (I-phase) inclusions within the Bi-2223 matrix. These I-phase particles are synthesized from a stoichiometric mixture of metal nitrates and urea through a combustion reaction, followed by a controlled heat treatment to retain their size to the submicron range. The particles are designed to be non-reactive with the Bi-2223 phase, thus maintaining the integrity of the superconducting matrix.

The innovative aspect of this invention lies in the specific composition and processing of the I-phase particles. By choosing a composition for these particles that do not react with the Bi-2223 phase, and can be uniformly distributed within the matrix, the invention effectively creates new and robust pinning centers that enhance the overall performance of the superconductor. The synthesized I-phase particles, after being mixed with the Bi-2223 precursor powder, undergo a carefully controlled heat treatment regimen to foster the formation of the Bi-2223 phase dispersed with these inclusions in nanometric sizes. The weighed in stoichiometry of the I-phase is Ca 0.86Sr 0.14CuO2 and it will be in amorphous form after synthesis by the combustion process. It was observed from Energy Dispersive Analysis using X-Rays (EDAX) that the nanometric needles formed in the matrix phase after final heat-treatment has a slightly deviated composition of Ca1.9Sr0.1CuO3, present with minor amounts of CuO (seen from XRD). The beneficial effects that we observed in this claim are promoted by the presence of this phase, and they can be expected to occur even when this phase is introduced in the Bi-2223 matrix in other ways, in combination with some other phases, and also when the phase occurs in the bulk form or the tape form of the superconductor.

Subsequent testing of the new composite material has demonstrated marked improvements in flux pinning capabilities at temperatures up to 77 K. These enhancements result in significant increases in the critical current density (Jc) compared to Bi-2223 superconductor. The enhanced Jc directly results from the effective pinning of magnetic vortices by the uniformly distributed I-phase inclusions, or defects occurring at their boundaries with the Bi-2223 phase, which act as strong pinning centers without altering the superconducting transition temperature (Tc) or the overall phase purity of the Bi-2223 matrix.

The invention offers several advantages. It significantly improves the flux pinning capabilities of Bi-2223 superconductors up to 77 K, thereby increasing the critical current density and stabilizing the superconducting state at higher operational temperatures. By using non-reactive I-phase inclusions, the structural and chemical integrity of the Bi-2223 phase is maintained, avoiding the introduction of defects or impurities that could degrade superconducting properties. This enhanced flux pinning reduces the susceptibility to flux creep, enhancing the efficiency and reliability of Bi-2223 based superconducting systems under practical conditions. Additionally, the improved current capacity of the superconductor at temperatures close to the boiling point of liquid nitrogen, broadens the potential applications of Bi-2223 superconductors, particularly in industries.

The enhanced Bi-2223 superconductors developed through this invention can be ideal for a variety of applications where high critical current density at temperatures close to the boiling point of liquid nitrogen is crucial. The current carrying capacity of the superconductor, when fabricated with uniformly distributed I-phase precipitates in optimized amount could be interesting, particularly in superconductor tapes. These applications include power transmission and superconducting magnets where superconductor tapes with higher Jc can carry current with reduced energy losses, enabling more efficient grid operations. In Magnetic levitation (Maglev) transportation, superconductors could lead to more effective and reliable maglev systems, which rely on superconductors to achieve frictionless, high-speed travel. In the field of medical imaging, particularly in Magnetic Resonance Imaging (MRI) machines, superconductors that can operate at temperatures close to 77 K, without significant flux creep could lead to more inexpensive MRI machines, at much lower cost due to the use of inexpensive liquid nitrogen refrigerant.

Further objects, features, and advantages of the invention will be readily apparent from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings.

Brief Description of the Drawings

The invention will be further understood from the following detailed description of a preferred embodiment taken in conjunction with an appended drawing, in which:

Fig. 1(a) illustrates the appearance of the I-phase particles after annealing at 500 ºC, according to the exemplary embodiment of the present invention.

Fig. 1(b) depicts the transformation of the I-phase particles into needle-shaped precipitates within the Bi-2223 matrix after annealing at 845 ºC, according to the exemplary embodiment of the present invention.

Fig. 2 (a) illustrates the prior art related to microstructural optimization in YBa2Cu3O7 superconductors by showcasing the distribution of Y 211 particles within a textured YBCO matrix.

Fig. 2 (b) illustrates the prior art related to the size distribution of Y 211 particles in the YBCO matrix, providing insight into the microstructural characteristics of the material.

Fig. 2 (c) illustrates the prior art related to the magnetization vs. magnetic field (M-H) loops recorded at different temperatures.

Fig. 2 (d) illustrates the prior art related to the magnetic field dependence of the critical current density (Jc) observed at different temperatures.

Fig. 3 illustrates the temperature dependence of magnetization for samples with varying concentrations of I-phase, indicating the onset of superconductivity around 105 K for all samples, according to the exemplary embodiment of the present invention.

Fig. 4 (a-c) presents Field Emission Scanning Electron Microscopy (FESEM) micrographs of different samples, including pure Bi-2223 (S 0) and Bi-2223 composites where proportion of I-phase added is 5 mol (S 5) and 50 mol (S 50) to 100 mol of Bi 2223 phase, according to the exemplary embodiment of the present invention.

Fig. 5 demonstrates the field dependence of critical current density (Jc) for all samples at two temperatures, according to the exemplary embodiment of the present invention.

Fig. 6 shows the field dependence of flux pinning force density (Fp) for all composites at two temperatures, highlighting the improvement in flux pinning with increasing I-phase content, even up to 77 K, according to the exemplary embodiment of the present invention.

Detailed Description of the Invention

The development of high-temperature superconductors, particularly those based on the Bi1.6Pb0.4Sr2Ca2Cu3O10 (Bi-2223) composition, marks a significant advancement in materials science with extensive implications for industries reliant on efficient, high-current supporting superconductors. Applications such as power transmission, magnetic levitation for transportation, medical imaging technologies and many more technologies, stand to undergo transformative changes owing to the efficiency and capacity of high Jc materials. Despite their potential, the practical utility of these superconductors has been limited by significant challenges like flux creep, especially at temperatures close to 77 K—the boiling point of nitrogen. This phenomenon leads to the loss of superconductivity under operational conditions due to the movement of magnetic vortices within the superconductor, resulting in resistance and substantially reduced material efficiency and reliability.

Addressing this challenge, the present invention introduces a novel approach that significantly enhances the flux pinning capabilities of Bi-2223 superconductors without compromising their intrinsic properties. The core of this innovation is the integration of nano-sized Ca-Sr-Cu-O (I-phase) inclusions within the Bi-2223 matrix. These I-phase particles are synthesized from a stoichiometric mixture of metal nitrates and urea through a combustion reaction, followed by a controlled heat treatment to adjust their particle size to the submicron range. The composition ensures that these particles are non-reactive with the Bi-2223 phase, thus maintaining the integrity of the superconducting matrix.

The method for producing a composite superconductor material involves several critical steps. Initially, Bi-2223 precursor powder is synthesized by dissolving Bi2O3, SrCO3, CuO, and CaCO3 powders in concentrated Nitric Acid, with Pb(NO3)2 added to the mix, followed by drying, grinding, and annealing. Simultaneously, Ca0.86Sr0.14CuO2 (I-phase) particles are prepared by combusting stoichiometric amounts of corresponding metal nitrates with urea. These I-phase particles are then meticulously mixed with the Bi-2223 precursor powder (100 mol) in varying concentrations, from 0 to 50 mol, to enhance flux pinning and critical current density up to 77 K.

When mixed with Bi-2223 precursor and heat-treated at 500°C, the I-phase particles attain a nearly spherical morphology, with the particles having diameters in the range 300 to 600 nm, and a composition as determined by EDAX to be Ca1.9Sr0.1CuO3.

The mixture is dispersed in a premix containing methacrylamide and methylene bisacrylamide in water, adding a dispersant to prevent agglomeration. This mixture undergoes several hours of tumbling followed by polymerization, creating a homogeneously distributed I-phase within the solid Bi-2223 matrix held together by the organic binders. The binders are removed by heat-treatment by slowly heating up to 800oC, and the maintaining at that temperature for 24 hrs. The resultant green body is then powdered, pelletized, and subjected to a dual sintering process at 845°C with an intermediate pressing, crucial for developing texture and achieving higher density to enhance the superconducting properties.

The invention's efficacy is evident from testing the new composite material, which shows marked improvements in flux pinning capabilities at temperatures up to 77 K. The critical current density (Jc) of the Bi-2223 superconductors containing I-phase inclusions is significantly higher than that of pure Bi-2223 superconductor processed under similar conditions. These enhancements are attributed to the effective pinning of magnetic vortices caused by the I-phase inclusions, acting as strong pinning centers without altering the superconducting transition temperature (Tc) or the overall phase purity of the Bi-2223 matrix.

This novel method maintains the structural and chemical integrity of the Bi-2223 phase, with the I-phase inclusions reducing susceptibility to flux creep and enhancing the efficiency and reliability of Bi-2223 system.

Overall, this invention presents a significant advancement in the application and utility of high-temperature superconductors, offering practical solutions to some of the longstanding challenges in the field. The development and implementation of this technology could revolutionize industries reliant on superconductivity, pushing the boundaries of what is possible with Bi-2223 superconductors.

Referring to the figures now, Figure 1(a) illustrates the micrograph that depicts the morphology of spherical I-phase particles, ranging from 300 to 600 nm in size, observed after annealing of the output of combustion at 500 ºC. This annealing process, following the combustion of metal nitrates with urea, maintains the particles' size and prevents agglomeration, crucially avoiding significant alterations in morphology. These nearly spherical particles act as precursors, which subsequently transform into needle-shaped precipitates.

Fig. 1(b) demonstrates the evolution of the I-phase particles into nanometer-sized needle-shaped precipitates within the Bi-2223 matrix post-annealing at 845 ºC. The presence of these precipitates contributes to the enhancement of critical current density (Jc) in the composite material.

Figure 2 (a-d) is related to the prior art on the microstructural development in high Jc YBa2Cu3O7 (YBCO) composites. The cited work shows that modifying the microstructure of YBCO by introducing a large number of insulating Y2BaCuO5 precipitates, typically around 1 micron or less in size, can significantly increase Jc at 77 K. Y2BaCuO5 is an insulating compound in the Y-Ba-Cu-O system. The work on YBCO, suggests a solution to the challenges faced by pure Bi-2223 superconductors processed into tapes in terms of supporting sufficient current density at higher magnetic fields, particularly at the boiling point of liquid nitrogen (77 K). The need to improve magnetic flux pinning at 77 K is highlighted. The microstructural modifications as in YBCO composites could be beneficial for enhancing the performance of Bi-2223 tapes.

Furthermore, the excerpt suggests that incorporating non-reacting inclusions of I-phase consisting of elements such as Ca, Sr, and Cu, into the Bi-2223 matrix, in which it can remain in large amounts without reacting with the Bi-2223 compound, could greatly benefit the performance of Bi-2223 tapes. These inclusions, ideally ranging in size from 1 micron to a few nanometers and present in significant amounts within the matrix, could enhance magnetic flux pinning and improve the current density supported by Bi-2223 tapes.

Figure 3 illustrates the temperature dependence of magnetization for samples with increasing amounts of the I-phase (labeled N0 to N4). It shows that all composites exhibit superconducting behavior, with the onset of superconductivity occurring at approximately 105 K. The same onset temperature for all samples suggests that adding up to 50 mol of the I-phase does not decrease the superconducting transition temperature of the Bi-2223 phase. Therefore, the findings highlight the robustness of the composite materials, indicating their suitability for practical applications retaining superconductivity without degradation with increasing concentrations of the I-phase.

Figure 4 (a-c) illustrates the Field Emission Scanning Electron Microscopy (FESEM) micrographs of different samples, offering insights into the microstructural evolution of the composite materials. In 4(a) the micrograph depicts pure Bi-2223, providing a baseline for comparison. Moving to 4(b), we observe Bi-2223 with 5 mol infinity phase addition, and 4 (c) illustrates Bi-2223 with 50 mol infinity phase addition, respectively. Notably, there's a systematic increase in the amount of nano-sized, needle-shaped precipitates of the I-phase evident across the samples, particularly noticeable at the grain boundaries of the Bi-2223 phase. These micrographs highlight the progressive augmentation in the content of the needle-shaped phase within the Bi-2223 matrix, as the concentration of the I-phase increases. Such structural modifications, characterized by the presence of needle-shaped precipitates, generate enhanced pinning centers. These centers can generate structural defects at the interface between the I-phase and Bi-2223 phase due to lattice mismatch. Consequently, this phenomenon contributes to the overall enhancement of critical current density (Jc) in the composite material.

Figure 5 illustrates the field dependence of the critical current density (Jc) at temperatures of 20 K and 77 K. The data reveals a systematic enhancement in Jc of the samples from S 0 to S 50, correlating with an increase in the I-phase content. This enhancement is particularly evident at 20 K and continues consistently up to 77 K in the composites. The observed trend underscores the beneficial impact of the I-phase on the superconducting properties of the composites, indicating an improvement in Jc attributed to the presence of pinning centers generated by the I-phase.

Figure 6 illustrates the field dependence of flux pinning force density (Fp) at temperatures of 20 K and 77 K. It demonstrates a notable improvement in flux pinning with increasing I-phase content, extending up to 77 K. The results affirm that the addition of the I-phase to Bi-2223 enhances both Jc and Fp, as well as their field dependence across all temperatures up to 77 K. Notably, incorporating substantial amounts of the second phase (up to 50 mol) into 100 mol of matrix phase, results in the generation of nano-sized needle-shaped precipitates that coexist with the Bi-2223 matrix without compromising Tc. This leads to a significant enhancement of Jc and Fp up to 77 K. Further optimization of the microstructures of the Bi-2223 phase can be achieved by adjusting the content of the I-phase. The material of Bi-2223 composite with nano-sized I-phase, along with the method of production, are important. Additionally, while the presented method is one approach, alternative routes for producing the I-phase material can also be utilized to improve the bulk or tapes of the superconductor. Furthermore, the incorporation of multiphase samples, which includes the I-phase as a component, extends the applicability of this approach, and the usage of such materials is also asserted.
, Claims:CLAIMS
WE CLAIM:
1. A method for producing a composite superconductor material, comprising the steps of:
synthesizing a Bi-2223 precursor powder by dissolving Bi2O3, SrCO3, CuO, and CaCO3 powders in concentrated nitric acid, adding a solution of Pb(NO3)2 in deionized water, drying, grinding, and annealing the mixture at 800°C for 24 hours with one intermediate grinding step;
synthesizing Ca0.86Sr0.14CuO2 (I-phase) particles by combusting stoichiometric amounts of corresponding metal nitrates with urea, grinding, and annealing the resulting powder at 500°C to maintain particle sizes in the submicron range, specifically aimed at achieving a size range of 300 to 600 nm;
mixing I-phase in varying concentrations ranging from 0 to 50 mol with the Bi-2223 precursor powder (100 mol) to enhance flux pinning and critical current density up to 77 K;
dispensing a premix comprising Methacrylamide (MAM) and Methylene bisacrylamide (MBAM) in water, adding the mixture of Bi-2223 precursor powder and I-phase particles along with a dispersant to prevent agglomeration;
tumbling the mixture for several hours followed by polymerization using Tetramethyl ethylenediamine (TEMED) and ammonium peroxydisulfate (APS) as catalyst and initiator to form a gelled part, ensuring homogenous distribution of I-phase particles within the Bi-2223 matrix;
removing binders by heating, followed by milling and then pelletizing the resulting Bi-2223 composite powder containing I-phase;
sintering the pelletized composite twice at 845°C with one intermediate pressing to develop texture and to achieve higher density, which enhances the superconducting properties at elevated temperatures, specifically close to the boiling point of liquid nitrogen (77 K).

2. The method as claimed in claim 1, wherein the advantageous properties of the I-phase are investigated when incorporated into the Bi-2223 matrix through diverse means, including combinations with other phases, and its presence in both bulk and tape configurations of the superconductor.

3. The method as claimed in claim 1, wherein the suspension of mixed powders further comprises a small amount of a dispersant to prevent agglomeration during tumbling, essential for maintaining the integrity and distribution of nano-sized inclusions within the superconductor matrix.

4. The method as claimed in claim 1, wherein the composite material is sintered twice at 845°C with one intermediate pressing step to facilitate texture development and to achieve higher density, crucial for enhancing the superconducting properties at temperatures up to 77 K.

5. The method as claimed in claim 1, wherein the resulting composite material includes the microstructure using Field Emission Scanning Electron Microscopy (FESEM) to observe the distribution of I-phase particles, confirming the effectiveness of the nano-sized inclusions in enhancing the critical current density and flux pinning properties at elevated temperatures.

6. The method as claimed in claim 1, wherein the I-phase particles are specifically designed to be non-reactive with the Bi-2223 phase during the synthesis and sintering processes, ensuring no degradation of the superconducting transition temperature (Tc) while enhancing the flux pinning capabilities.

7. The method as claimed in claim 1, wherein the composite material undergoes a critical current density testing at various temperatures from M-H curves, particularly focusing on performance close to the boiling point of liquid nitrogen (77 K), to quantify the enhancement in superconducting properties due to the addition of the I-phase.

8. The method as claimed in claim 1, which includes a step of characterizing the current density supported by the composite using techniques such as magnetization measurement, to evaluate the effective pinning force density and its dependence on applied magnetic field.

9. The method as claimed in claim 1, wherein the nano-sized I-phase inclusions are specifically engineered to be nanometric with needle-shaped morphology

10. The method as claimed in claim 1, wherein the pelletizing and sintering processes are controlled by varying pressure and heat treatment schedules to optimize the density of the grains within the composite, thereby maximizing the superconducting pathways and reducing macroscopic defects.

11. The method as claimed in claim 1, wherein the optimization of particle size distribution, morphology, amount of the I-phase and the resultant composition is achieved through iterative feedback based on scanning electron microscopy (SEM) and magnetic measurements, leading to continuous improvements in product performance.

12. A composite superconductor material produced by the method as claimed in claim 1, comprising:
a matrix of Bi-2223 superconductor;
nano-sized Ca0.86Sr0.14CuO2 (I-phase) particles uniformly distributed within the Bi-2223 matrix in a concentration ranging from 5 to 50 mol relative to 100 mol of Bi-2223 precursor powder;
wherein the I-phase particles are non-reactive with the Bi-2223 phase, maintaining the superconducting transition temperature while enhancing the flux pinning capabilities and critical current density at temperatures up to 77 K.

13. A superconducting system comprising the composite superconductor material as claimed in claim 1, wherein the superconducting system is:
configured for applications in power transmission, magnetic levitation transport systems, or magnetic resonance imaging machines and superconducting magnets, thereby utilizing the enhanced critical current density and flux pinning properties of the material for improved efficiency and reliability in superconducting applications at operational temperatures close to the boiling point of liquid nitrogen