WO2000051948A1 - A method for producing nano-engineered precursors - Google Patents

A method for producing nano-engineered precursors Download PDF

Info

Publication number
WO2000051948A1
WO2000051948A1 PCT/SE2000/000429 SE0000429W WO0051948A1 WO 2000051948 A1 WO2000051948 A1 WO 2000051948A1 SE 0000429 W SE0000429 W SE 0000429W WO 0051948 A1 WO0051948 A1 WO 0051948A1
Authority
WO
WIPO (PCT)
Prior art keywords
reactor
solid
solutions
solution
feed solutions
Prior art date
Application number
PCT/SE2000/000429
Other languages
French (fr)
Inventor
Mamoun Muhammed
Yu Zhang
Lingna Wang
Original Assignee
Mamoun Muhammed
Yu Zhang
Lingna Wang
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Mamoun Muhammed, Yu Zhang, Lingna Wang filed Critical Mamoun Muhammed
Priority to AU36881/00A priority Critical patent/AU3688100A/en
Priority to EP00915656A priority patent/EP1089951A1/en
Publication of WO2000051948A1 publication Critical patent/WO2000051948A1/en

Links

Classifications

    • BPERFORMING OPERATIONS; TRANSPORTING
    • B82NANOTECHNOLOGY
    • B82YSPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00Nanotechnology for materials or surface science, e.g. nanocomposites
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B13/00Oxygen; Ozone; Oxides or hydroxides in general
    • C01B13/14Methods for preparing oxides or hydroxides in general
    • C01B13/18Methods for preparing oxides or hydroxides in general by thermal decomposition of compounds, e.g. of salts or hydroxides
    • C01B13/185Preparing mixtures of oxides
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01GCOMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G21/00Compounds of lead
    • C01G21/006Compounds containing, besides lead, two or more other elements, with the exception of oxygen or hydrogen
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01GCOMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G29/00Compounds of bismuth
    • C01G29/006Compounds containing, besides bismuth, two or more other elements, with the exception of oxygen or hydrogen
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01PINDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00Particle morphology
    • C01P2004/60Particles characterised by their size
    • C01P2004/64Nanometer sized, i.e. from 1-100 nanometer

Definitions

  • the present invention relates to a method for producing nano-engineered precursors, and more particularly precursors of superconductors.
  • HTSC High Temperature Superconductors
  • Co-precipitation in solution is a technique for preparation of precursors, so that they are very well mixed.
  • the different components such as metal salts
  • the dissolved components are precipitated from the solution by the addition of precipi- taring agents, such as carbonates, formates, hydroxides and oxalates.
  • precipi- taring agents such as carbonates, formates, hydroxides and oxalates.
  • the resultant precipitate is filtered and thereafter calcined to remove or decompose the anion to obtain a mixture of the respective cation oxide.
  • Further heating at high temperature, above 900 °C result in transformation of the cation oxides to a high temperature super conducting material (HTSC).
  • the co-precipitation technique of HTSC precursors is generally based on the solid formation reactions between desired metals ions (M 3+ and M 2+ ) and a specified precipitant ligand (L n- ) as follows,
  • M + Y + , Bi 3+ , etc
  • M 2+ Ba 2+ , Sr 2+ , Ca 2+ , Cu 2+ , Pb 2+ , etc.
  • n 1 or 2
  • L- OH
  • I C0 3 2 ", C 2 0 4 2 -, etc.
  • the conventional co-precipitation based method generally comprises the following steps:
  • the solution mixing can also be obtained by adding the solution(s) of metal ions into the precipitant solution or vice versa. In order to enhance the precipitation, ad- dition of the precipitant solution in excess is always required.
  • the pH of the mixed solution is adjusted, for instance by adding an alkaline solution, to the optimal level for co-precipitation during, or after, the third step. Subsequently, the co-precipitated solid is then filtered, washed, dried and calcined to obtain the desired super conducting oxide.
  • a co-precipitation method described as above can provide improved precursors.
  • a more uniform and smaller particle size ( ⁇ 1 urn) such a co-precipitated powder is not only better in mixing the different metal components, but also more reactive to form the superconductive oxide.
  • the conventional solu- tion addition/mixing process could hardly accomplish a simultaneous co-precipitation of all the desired metal components but "precipitation-in-sequence" of the individual components.
  • the precipitation sequence of the metal ions is Y> Ba »Cu, if the solution of metal ions is added into the precipitant solution. If the precipitant solution is added into the solution of metal ions, the precipitation sequence is Y>Cu» Ba. In either way, the precipitate could hardly be a uniform mixture of various oxalates formed in the respective particles of individual components. Large scale production implies more serious drawbacks, which could even overcome the advantages of the co-precipitation technique.
  • an object of the present invention is to provide a new co-precipitation based method that will overcome the drawbacks of the conventional methods, while enhancing their advantages as mentioned above.
  • the object of the invention is to provide a method that can easily control the quality in overall chemical composition of the co-precipitated solid, as well as the uniformity in compositional distribution among the individual particles, while reducing the particles size down to the nanometer scale ⁇ 100 nm, for producing nano-particle size precursors.
  • An inventive method is primarily characterised in that the metal components, i. e. the metal compounds, are dissolved to form separate solutions before being mixed together, or a solution of known concentrations before being mixed together
  • Another object of the invention is to improve the quality of powder products to obtain high reactivity, particularly for meta-stable co-precipitated powders for HTSC precursors.
  • the process claimed in this invention can be used to produce high quality precur- sors of rare earth oxide and/or alkaline earth oxide and/or copper oxide based ceramics in general, and oxide superconductors in particular.
  • the method involves the knowledge that the dissolution of the metal compounds to form a feed solution of all the desired metal components at a fixed ratio of known concentrations, or two separate feed solutions: one containing a metal component(s) that can only be soluble at relatively high acidity, and another containing the other metal components at a fixed ratio of known concentrations, result in a co-precipitate solid having a high and consistent purity and a narrow variation in particle size.
  • a method for producing nano- particle size precursors comprises the steps of:
  • the feed solutions are added to a buffer solution under controlled conditions, e. g. pH.
  • the buffer solution is preferably added to the reactor and re-circulated by means of a buffer tank and a corresponding pump.
  • the HTSC components are those which form high temperature superconductors.
  • Such compounds are described for instance in WO- A 1-94/00385.
  • the metal compounds are preferably selected from those which form high temperature superconductors, including for example compounds of Y, Bi, Ba, Sr, Ca, Cu, Pb. Compounds of other metals having similar or suitable properties are also included in the scope of the invention.
  • the separated solid is heated after the filtration to remove water and carbon contents and form a precursor of oxides, preferably being superconducting.
  • the precipitating agent is selected from a carboxylic acid, or its salt, an oxalic acid, an oxalate salt, or a carbonate salt.
  • the pH-adjusting agents are a solution of nitric acid to decrease the pH, and a solution of an alkali hydroxide, such as sodium hydroxide to increase the pH.
  • Fig. 1 is a schematic process scheme of the method according to the invention.
  • Fig. 2 is a more detailed process scheme of the method according to a preferred embodiment of the invention.
  • Fig. 1 shows a general process scheme.
  • the overall operation can be generalised as follows:
  • the precipitating agent and pH-adjusting agents are separately dissolved in water in stirred tanks forming separate solutions 10, 20, 30, while the metal compounds are dissolved in water or acid in other tanks, forming solutions 40, 50.
  • the prepared solutions 60 referred to as "feed solutions” are sampled for analysis of the accurate concentrations of the respective chemicals.
  • the feed solutions 60 of metal components can also be combined in one tank (not illustrated). Then, a defined molar ratio of the metal ions should be fixed if the feed solution contains more than one metal ion. Moreover, some metal compounds may have to be dissolved in an acid solution, instead of water.
  • the feed solutions 60 of the reactants i. e. the precipitating agent 20 and metal ion 40, 50 solutions, are pumped at a defined flow rate into a buffer solution 85 in a batch reactor 70 under stirring.
  • a recycled flow from a buffer tank 80 is also simul- taneously pumped into the reactor 70.
  • the pH of the buffer solution in the reactor 70 is conveniently monitored via a combined glass electrode or the like to assure it is within a defined range.
  • the pH of the buffer solution is adjusted by adding a certain amount of the base 30 (or acid 20) solution into the reactor 70.
  • the overflow of the buffer solution in the reactor 70 is conducted to the buffer tank 80 and recycled. After defined quantities of the reactants have been added into the reactor 70, the feeding pumps 90 are stopped.
  • the precipitated solid is sampled for analysis in a given time interval until its composition does not change.
  • the stirring, as well as the pumping is then stopped to allow the suspension to sedimentate. After a certain period, the suspension is thickened at the bottom of the reactor 70, and the clear solution is drained off through a conduit to the buffer tank 80.
  • the stirring is restarted and the bottom valve 100 is turned on to let the suspension flow to a thickener 110.
  • the suspension from the reactor 70 is mixed with the filtrate solution in the thickener 110 under stirring for a certain period of time.
  • the stirring and pumping are then stopped to allow the suspension to sedimentate.
  • the suspension is thickened at the bottom of the thickener 110 and the clear upper solution is drained off to the buffer tank 80 via a valve.
  • the stirring is restarted and the bottom valve 111 is turned on to let the suspension flow to a filter 120.
  • the solid product 130 is separated from its mother liquor, washed with water and then dried.
  • the filtrate solutions comprising the mother liquor and wash- ing water are returned to the thickener 110.
  • the controlled operating conditions for mixing and co-precipitation include the overall addition ratios between the feed solutions, the respective flow rates of the feed solutions, the stirring rates and the pH ranges of the reaction mixture, and its residence period in both the reactor and thickener.
  • the overall addition ratios between the feed solutions are predetermined according to the chemical equilibrium calculation for said co-precipitation.
  • the actual overall addition ratios between the metal components and precipitating agent are continuously monitored and kept constant within 0.1% derivation by controlling the respective flow rates of the feed so- lutions during operation.
  • the operational conditions of the respective flow rates of the feed solutions are designed according to the predetermination of the overall addition ratios, as well as the optimal residence period in the reactor.
  • the operational condition of the stirring rates of the reaction mixture in the reactor is designed according to the predetermination for its influence on the solution mixing and particle growth/dispersion.
  • the actual stirring rate is con- tinuously monitored and kept constant within 5% variation during operation.
  • the metastable product (powder) as obtained is specified by its well-defined composition, high uniformity in compositional distribution among the individual grains on nanometer scale, its low crystalinity or amorphous phase, and its high uniformity in phase distribution.
  • the metastable product is specified by its ultrafine particle size, or nanometer grain size, and its high uniformity in size distribution.
  • the product i. e. the nano-engineered precursor is specified by its nano-sized grains with high reactivity for further processing toward high performance oxide superconductors.
  • a stable high-Tc (1 10 K) phase like Bil.6Pb0.4Sr2Ca2Cu3O10+8 is mostly preferred.
  • BiPbSrCaCuO is only referred to as Bil.6Pb0.4Sr2Ca2Cu3O10 in the following.
  • the precipitating agent solution 10 is prepared by dissolving oxalic acid or sodium oxalate in water at a concentration of 0.1-0.5 M. The accurate concentration should be analysed.
  • the acid solution 20 is approximately 1 M nitric acid in water.
  • the basic solution 30 is 1-5 M sodium hydroxide in water.
  • the solutions of metal components of Bi,Pb,Sr,Ca and Cu are prepared, either by dissolving the respective oxides, hydroxides or carbonates in 4 M nitric acid, or by dissolving the respective nitrates in water or acid. Excess nitric acid of 1-3 M is required in the solution of 0.1-1 M Bi to avoid the precipitation. The concentrations of other metal components in the respective solutions are 0.5-2 M.
  • the accurate concentration should be analysed;
  • the reactor 70 is half-filled with a recycled solution 85 pumped from a buffer tank
  • the pH of the solution 85 should be between 4-5;
  • the feed solutions 60 of 20, 30, 10, 40 and 50, are simultaneously and continuously pumped at the respective flow rates into the reactor 70 under constant stirring.
  • the pH of the solution mixture 75 is continuously momtored and controlled controlled within a range of 3-5 by adjusting the flow rate of 30.
  • the stirring of the suspension should continue until the bulk composition of the precipitated oxalate precursor is independent on time.
  • the residence time of the suspension in the thickener 110 is about one hour.
  • the operational condition to filtration are mostly dependent upon the filter 120 to be used.
  • the washing operation should lower the impurity to ⁇ 0.1% in the oxalate product.
  • the nano-engineered precursors are synthesised via a controlled co-precipitation procedure that produces the metastable solids of multiple metal components of well- defined composition, such as low crystalinity, ultrafine particle size, and high uniformity in their distributions within the nanometer scale ( ⁇ 100 n ).
  • the actual residence period is controlled by adjusting the flow rate of the recycled solution from the buffer tank during operation.
  • the operational criteria of the average residence period of the reaction mixture in the reactor can be designed according to the predetermination for completion of more than 99% of co-precipitation equilibrium.
  • the actual residence period is regularly verified by on-line analysis of the soluble metal component that is known to have the slowest precipitation rate, and adjusted accordingly during operation.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Nanotechnology (AREA)
  • Inorganic Compounds Of Heavy Metals (AREA)
  • Physics & Mathematics (AREA)
  • Composite Materials (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Materials Engineering (AREA)
  • Crystallography & Structural Chemistry (AREA)

Abstract

A method for producing nano-engineered precursors, in particular superconductor precursors is disclosed, said method comprising the steps of: dissolving at least two metal compounds, precipitating agents and optionally pH-adjusting agents to form feed solutions (60) of known concentrations; mixing the feed solutions (60) by adding them, preferably into a reactor (70); co-precipitating a solid from the mixed solutions (60), preferably in the reactor (70) under controlled operating conditions; thickening the co-precipitated solid; separating the precipitated solid from the mother liquor, for instance by filtration, which mother liquor preferably is recycled to the reactor (70), and; optionally washing the solid during filtration to remove impurities; wherein said at least two metal compounds are dissolved to form separate solutions (40, 50) before being mixed together. The co-precipitated solid is then filtered, washed, dried and calcined to obtain a desired super conducting oxide.

Description

A method for producing nano-engineered precursors
Field of the invention
The present invention relates to a method for producing nano-engineered precursors, and more particularly precursors of superconductors.
Background art
Methods for producing precursors of the aforesaid kind are well known within this field. The two main techniques to obtain to precursors such as High Temperature Superconductors (HTSC) are grinding/mixing the respective HTSC components together or co-precipitating the respective components in liquid solution.
One well known problem with grinding/mixing technique is that it is a lengthy process, requiring several grinding and sorting stages to be able to obtain a mixture which will be suitable for the production of the HTSC. However, it is difficult to obtain phase purity and reproducibility, especially in large scale. Phase purity is critical as regards the efficiency of the HTSC:s, since even slight deviations from the correct ratio of the different HTSC components will result in degradation or loss of HTSC properties.
Co-precipitation in solution is a technique for preparation of precursors, so that they are very well mixed. In solution precipitation, the different components, such as metal salts, are initially dissolved in aqueous solution, thereby forming ions. The dissolved components are precipitated from the solution by the addition of precipi- taring agents, such as carbonates, formates, hydroxides and oxalates. Thereafter, the resultant precipitate is filtered and thereafter calcined to remove or decompose the anion to obtain a mixture of the respective cation oxide. Further heating at high temperature, above 900 °C result in transformation of the cation oxides to a high temperature super conducting material (HTSC). The co-precipitation technique of HTSC precursors is generally based on the solid formation reactions between desired metals ions (M3+ and M2+) and a specified precipitant ligand (Ln-) as follows,
nM + +3Ln" → Mn L (s) (Eq. la)
and
M2+ + 2/n Ln" → ML2/n (s) (Eq lb)
where M + =Y +, Bi3+, etc; M2+ = Ba2+, Sr2+, Ca2+, Cu2+, Pb2+, etc.; n = 1 or 2, L- = OH", I = C03 2", C204 2-, etc.
The conventional co-precipitation based method generally comprises the following steps:
-Dissolving the metal salts in water and/or acid to obtain the respective aqueous solutions of single-metal ions. However, it is also possible to obtain a solution mixture containing all desired metal ions at a defined molar ratio; -Dissolving a precipitating agent in water or acid; -Precipitating the desired metal ions, according to Eq. la and lb, by mixing the solutions of the precipitating agent and the metal ions, preferably under stirring.
The solution mixing can also be obtained by adding the solution(s) of metal ions into the precipitant solution or vice versa. In order to enhance the precipitation, ad- dition of the precipitant solution in excess is always required.
The pH of the mixed solution is adjusted, for instance by adding an alkaline solution, to the optimal level for co-precipitation during, or after, the third step. Subsequently, the co-precipitated solid is then filtered, washed, dried and calcined to obtain the desired super conducting oxide.
Compared to the traditional reaction method based on intensively mechanical grinding/mixing, a co-precipitation method described as above can provide improved precursors. With a more uniform and smaller particle size (< 1 urn), such a co-precipitated powder is not only better in mixing the different metal components, but also more reactive to form the superconductive oxide.
However, there are several serious drawbacks when performing the above method, since co-precipitation of multiple-metal components is generally a complicated chemical process. The precipitation rates, i. e. the kinetics, as well as the thermodynamics, of individual components are significantly different from each other and depending on many parameters. In addition to the two mostly recognised parame- ters, type of the precipitant and respective pH range of the reaction media, the following parameters are also of importance: initial concentrations of the reactants, solution addition/mixing sequence, addition rates, ratio of the reactants, and residence time of the precipitating suspension. As the control and optimisation of these parameters have not been well established, reproducibility of the conventional co- precipitation routines has been always questionable, especially when the quality of chemical composition of the co-precipitated solid is of great importance.
In an oxalate co-precipitation method for precursors of Y-Ba-Cu-0 superconductors, for instance, the conventional method of adding excess oxalate precipitant re- suits in increasing the solubility of copper oxalate though enhancing the precipitation of others. Therefore, a certain amount of excess addition of copper ions is always required. To maintain a constant ratio of dissolved to solid copper species, such a process becomes very sensitive regarding the operating conditions as mentioned above, and a quality control of the overall chemical composition of the co- precipitated powder is always a problem. On the other hand, the conventional solu- tion addition/mixing process, as described above in the third step, could hardly accomplish a simultaneous co-precipitation of all the desired metal components but "precipitation-in-sequence" of the individual components. In case of a Y-Ba-Cu-0 precursor, for instance, the precipitation sequence of the metal ions is Y> Ba »Cu, if the solution of metal ions is added into the precipitant solution. If the precipitant solution is added into the solution of metal ions, the precipitation sequence is Y>Cu» Ba. In either way, the precipitate could hardly be a uniform mixture of various oxalates formed in the respective particles of individual components. Large scale production implies more serious drawbacks, which could even overcome the advantages of the co-precipitation technique.
To obtain HTSC precursors having high efficiency and high transition temperature, it is of great importance to provide that the components are present in the correct ratio. The ratio must be extremely carefully controlled to obtain the high phase pu- rity as required.
Thus, it is generally desirable from several aspects to be able to control the ratio of the components. Unfortunately, however, this is not taught by any known technique.
There is thus a need of a solution which will allow the control of the components.
Summary of the invention
The aforesaid problems are avoided essentially completely by the present invention.
Thus, an object of the present invention is to provide a new co-precipitation based method that will overcome the drawbacks of the conventional methods, while enhancing their advantages as mentioned above. In other words, the object of the invention is to provide a method that can easily control the quality in overall chemical composition of the co-precipitated solid, as well as the uniformity in compositional distribution among the individual particles, while reducing the particles size down to the nanometer scale < 100 nm, for producing nano-particle size precursors. An inventive method is primarily characterised in that the metal components, i. e. the metal compounds, are dissolved to form separate solutions before being mixed together, or a solution of known concentrations before being mixed together
Furthermore, another object of the invention is to improve the quality of powder products to obtain high reactivity, particularly for meta-stable co-precipitated powders for HTSC precursors.
The process claimed in this invention can be used to produce high quality precur- sors of rare earth oxide and/or alkaline earth oxide and/or copper oxide based ceramics in general, and oxide superconductors in particular.
Moreover, the method involves the knowledge that the dissolution of the metal compounds to form a feed solution of all the desired metal components at a fixed ratio of known concentrations, or two separate feed solutions: one containing a metal component(s) that can only be soluble at relatively high acidity, and another containing the other metal components at a fixed ratio of known concentrations, result in a co-precipitate solid having a high and consistent purity and a narrow variation in particle size.
According to one embodiment of the invention, a method for producing nano- particle size precursors, in particular superconductor precursors, comprises the steps of:
-dissolving at least two metal compounds, precipitating agents and optionally pH- adjusting agents to form feed solutions of known concentrations;
-mixing the feed solutions by adding them, preferably into a reactor; -co-precipitating a solid from the mixed solutions, preferably in the reactor under controlled operating conditions; -thickening the co-precipitated solid; -separating the precipitated solid from the mother liquor, for instance by filtration, whereby the mother liquor preferably is recycled to the mixer/reactor, and; -optionally washing the solid during filtration to remove impurities; wherein said at least two metal compounds are dissolved to form separate solutions before being mixed simultaneously together, in the mixer/reactor (70).
According to a preferred embodiment of the invention, the feed solutions are added to a buffer solution under controlled conditions, e. g. pH. The buffer solution is preferably added to the reactor and re-circulated by means of a buffer tank and a corresponding pump.
Suitably, the HTSC components are those which form high temperature superconductors. Such compounds are described for instance in WO- A 1-94/00385.
The metal compounds are preferably selected from those which form high temperature superconductors, including for example compounds of Y, Bi, Ba, Sr, Ca, Cu, Pb. Compounds of other metals having similar or suitable properties are also included in the scope of the invention.
According to another preferred embodiment of the invention, the separated solid is heated after the filtration to remove water and carbon contents and form a precursor of oxides, preferably being superconducting.
Suitably, the precipitating agent is selected from a carboxylic acid, or its salt, an oxalic acid, an oxalate salt, or a carbonate salt. Preferably, the pH-adjusting agents are a solution of nitric acid to decrease the pH, and a solution of an alkali hydroxide, such as sodium hydroxide to increase the pH.
These and other objectives, advantaged and features of features of the present invention will be better understood and appreciated by reference to the written specification. Brief description of the drawings
The present invention will now be described in more detail with reference to the accompanying drawings, in which:
Fig. 1 is a schematic process scheme of the method according to the invention.
Fig. 2 is a more detailed process scheme of the method according to a preferred embodiment of the invention.
Detailed description of preferred embodiments Fig. 1 shows a general process scheme. The overall operation can be generalised as follows:
The precipitating agent and pH-adjusting agents (acid and base) are separately dissolved in water in stirred tanks forming separate solutions 10, 20, 30, while the metal compounds are dissolved in water or acid in other tanks, forming solutions 40, 50. The prepared solutions 60, referred to as "feed solutions" are sampled for analysis of the accurate concentrations of the respective chemicals. The feed solutions 60 of metal components can also be combined in one tank (not illustrated). Then, a defined molar ratio of the metal ions should be fixed if the feed solution contains more than one metal ion. Moreover, some metal compounds may have to be dissolved in an acid solution, instead of water.
The feed solutions 60 of the reactants, i. e. the precipitating agent 20 and metal ion 40, 50 solutions, are pumped at a defined flow rate into a buffer solution 85 in a batch reactor 70 under stirring. A recycled flow from a buffer tank 80 is also simul- taneously pumped into the reactor 70. The pH of the buffer solution in the reactor 70 is conveniently monitored via a combined glass electrode or the like to assure it is within a defined range. The pH of the buffer solution is adjusted by adding a certain amount of the base 30 (or acid 20) solution into the reactor 70. The overflow of the buffer solution in the reactor 70 is conducted to the buffer tank 80 and recycled. After defined quantities of the reactants have been added into the reactor 70, the feeding pumps 90 are stopped. The precipitated solid is sampled for analysis in a given time interval until its composition does not change. The stirring, as well as the pumping is then stopped to allow the suspension to sedimentate. After a certain period, the suspension is thickened at the bottom of the reactor 70, and the clear solution is drained off through a conduit to the buffer tank 80. The stirring is restarted and the bottom valve 100 is turned on to let the suspension flow to a thickener 110.
The suspension from the reactor 70 is mixed with the filtrate solution in the thickener 110 under stirring for a certain period of time. The stirring and pumping are then stopped to allow the suspension to sedimentate. After a certain settling period, the suspension is thickened at the bottom of the thickener 110 and the clear upper solution is drained off to the buffer tank 80 via a valve. The stirring is restarted and the bottom valve 111 is turned on to let the suspension flow to a filter 120. During the filtration, the solid product 130 is separated from its mother liquor, washed with water and then dried. The filtrate solutions comprising the mother liquor and wash- ing water are returned to the thickener 110.
The controlled operating conditions for mixing and co-precipitation include the overall addition ratios between the feed solutions, the respective flow rates of the feed solutions, the stirring rates and the pH ranges of the reaction mixture, and its residence period in both the reactor and thickener. The overall addition ratios between the feed solutions are predetermined according to the chemical equilibrium calculation for said co-precipitation. The actual overall addition ratios between the metal components and precipitating agent are continuously monitored and kept constant within 0.1% derivation by controlling the respective flow rates of the feed so- lutions during operation.
Preferably, the operational conditions of the respective flow rates of the feed solutions are designed according to the predetermination of the overall addition ratios, as well as the optimal residence period in the reactor. The operational condition of the stirring rates of the reaction mixture in the reactor is designed according to the predetermination for its influence on the solution mixing and particle growth/dispersion.
According to another embodiment of the invention, the actual stirring rate is con- tinuously monitored and kept constant within 5% variation during operation.
The actual pH values of the reaction mixture in both the reactor and thickener, may be continuously monitored and controlled within a relatively insensitive range of two pH units (pH=3-5, or 10-12) by occasionally modifying the flow rate of one or more pH-adjusting agent solution(s) during operation.
The metastable product (powder) as obtained is specified by its well-defined composition, high uniformity in compositional distribution among the individual grains on nanometer scale, its low crystalinity or amorphous phase, and its high uniformity in phase distribution.
The metastable product (powder) is specified by its ultrafine particle size, or nanometer grain size, and its high uniformity in size distribution.
The product, i. e. the nano-engineered precursor is specified by its nano-sized grains with high reactivity for further processing toward high performance oxide superconductors.
The invention will now be described by means of examples.
Example 1 :
This example illustrates the production of oxalate precursors if BiPbSrCaCuO superconductors; BiPbSrCaCuO actually represents a homological series of superconducting phases of (BIl-xPbx)2Sr2Can-lCun02n+4+5with x =0-0.3 and n =1,2,3,...Among them, a stable high-Tc (1 10 K) phase like Bil.6Pb0.4Sr2Ca2Cu3O10+8 is mostly preferred. For simplicity, BiPbSrCaCuO is only referred to as Bil.6Pb0.4Sr2Ca2Cu3O10 in the following.
As shown in Fig. 2, the co-precipitation procedure compromises three major steps:
1. Dissolution — preparation of the feed solutions
The precipitating agent solution 10 is prepared by dissolving oxalic acid or sodium oxalate in water at a concentration of 0.1-0.5 M. The accurate concentration should be analysed.
The acid solution 20 is approximately 1 M nitric acid in water. The basic solution 30 is 1-5 M sodium hydroxide in water. The solutions of metal components of Bi,Pb,Sr,Ca and Cu are prepared, either by dissolving the respective oxides, hydroxides or carbonates in 4 M nitric acid, or by dissolving the respective nitrates in water or acid. Excess nitric acid of 1-3 M is required in the solution of 0.1-1 M Bi to avoid the precipitation. The concentrations of other metal components in the respective solutions are 0.5-2 M. The accurate concentration should be analysed; The solutions of Pb, Sr, Ca, and Cu are mixed and stored at a molar ratio of Pb:Sr:Ca:Cu = 0.4:2x:2.0;3.0 (x=l.1-2.0) in one tank, while the solution 50 of Bi is in another tank.
2) Co-precipitation of the oxalate solid.
The reactor 70 is half-filled with a recycled solution 85 pumped from a buffer tank
80. The pH of the solution 85 should be between 4-5; The feed solutions 60 of 20, 30, 10, 40 and 50, are simultaneously and continuously pumped at the respective flow rates into the reactor 70 under constant stirring. The flow rates of the feed solutions 60 are continuously monitored and controlled at such a constant ratio that the molar ratio of the added reactants in the reactor 70 should always be maintained at C204:Cu:Bi = 9.8:3.0: 1.6; The pH of the solution mixture 75 is continuously momtored and controlled controlled within a range of 3-5 by adjusting the flow rate of 30. After the addition of the reactants 60 is complete , the stirring of the suspension should continue until the bulk composition of the precipitated oxalate precursor is independent on time. The final composition of the precursor should be Bi:Pb:Sr:Ca:Cu=* 1.6:0.4:2:2:3 with a derivation <2%.
3) Separation of the oxalate precursor from the process flows The residence time of the suspension in the thickener 110 is about one hour. The operational condition to filtration are mostly dependent upon the filter 120 to be used. The washing operation should lower the impurity to <0.1% in the oxalate product.
The process claimed has the following technological features:
On-line operation/analysis facilities , sampling and adjusting the process operating conditions;
Computerised data acquisition & control facilities for process control, optimisation and automation;
Operational variability for both batch and continuous processing regardless the scale; Product variability for synthesising various types and compositions of the precursors;
Quality control availability for tailoring the metastable powder precursors with well-defined composition, low crystalinity, ultrafine particle size and high uniformity in their distributions.
The nano-engineered precursors are synthesised via a controlled co-precipitation procedure that produces the metastable solids of multiple metal components of well- defined composition, such as low crystalinity, ultrafine particle size, and high uniformity in their distributions within the nanometer scale (< 100 n ). The actual residence period is controlled by adjusting the flow rate of the recycled solution from the buffer tank during operation.
The operational criteria of the average residence period of the reaction mixture in the reactor can be designed according to the predetermination for completion of more than 99% of co-precipitation equilibrium.
The actual residence period is regularly verified by on-line analysis of the soluble metal component that is known to have the slowest precipitation rate, and adjusted accordingly during operation.
The invention shall therefore not be considered limited to the aforedescribed exemplifying embodiments thereof, since other embodiments are conceivable within the scope of the following claims.

Claims

Claims
1. A method for producing nano-engineered precursors, in particular superconductor precursors, said method comprising the steps of:
-dissolving at least two metal compounds, precipitating agents and optionally pH- adjusting agents to form feed solutions (60) of known concentrations; -mixing the feed solutions (60) by adding them, preferably into a reactor (70); -co-precipitating a solid from the mixed solutions, preferably in the reactor (70) un- der controlled operating conditions;
-thickening the co-precipitated solid, preferably in a thickener (110); -separating the precipitated solid from the mother liquor, for instance by filtration, whereby the mother liquor preferably is recycled to the mixer/reactor (70), and; -optionally washing the solid during filtration to remove impurities; characterised in that said at least two metal compounds are dissolved to form separate solutions (40, 50) before being mixed simultaneously together in the mixer/reactor (70).
2. A method according to claim 1, wherein said feed solutions (60) are added to a buffer solution under controlled conditions.
3. A method according to claim 1 or 2, wherein the separated solid is heated to remove water and carbon contents and form a precursor of oxides, preferably super conducting.
4. A method according to any one of the claims 1-3, wherein the metal compounds are selected from those which form high temperature superconductors, such as compounds of Y, Bi, Ba, Sr, Ca, Cu or Pb.
5. A method according to any one of the claims 1-4, wherein the precipitating agent is selected from a carboxylic acid, or its salt, an oxalic acid, an oxalate salt, or a carbonate salt.
6. A method according to any one of the preceding claims, wherein the pH- adjusting agents are a solution (20) of nitric acid to decrease the pH, and a solution (30) of an alkali hydroxide, such as sodium hydroxide to increase the pH.
7. A method according to any one of the preceding claims, wherein the controlled operating conditions for mixing and co-precipitation include the overall addition ratios between the feed solutions (60), the respective flow rates of the feed solutions (60), the stirring rates and the pH ranges of the reaction mixture, and its residence periods in the reactor (70) and thickener (110).
8. A method according to claim 7, wherein the overall addition ratios between the feed solutions (60) are predetermined according to the chemical equilibrium calculation for said co-precipitation.
9. A method according to any one of the preceding claims, wherein the actual over- all addition ratios between the metal compounds (40, 50) and precipitating agent are continuously monitored and kept constant within 0.1% derivation by controlling the respective flow rates of the feed solutions (60) during operation.
10. A method according to any one of the preceding claims, wherein the operational conditions of the respective flow rates of the feed solutions (60) are designed according to the predetermination for the overall addition ratios, as well as the optimal residence period in the reactor (70).
11. A method according to any one of the preceding claims, wherein the operational condition of the stirring rate of the reaction mixture in the reactor (70) is de- signed according to the predetermination for its influence on the solution mixing and particle growth/dispersion.
12. A method according to claim 11, wherein the actual stirring rate is continuously monitored and kept constant within 5% variation during operation.
13. A method according to any one of the preceding claims, wherein the actual pH values of the reaction mixture in the reactor (70) and thickener (110) are continuously momtored and controlled within a range of two pH units (pH=3-5, or 10- I2) by occasionally modifying the flow rate of one or more-pH-adjusting agent solution (20, 30) during operation.
14. A solid produced by the method according to any one of the claims 1-13.
15. A precursor produced by the method according to claim 3, wherein the solid is heated to a temperature sufficient to convert the co-precipitated solid to a HTSC.
PCT/SE2000/000429 1999-03-02 2000-03-02 A method for producing nano-engineered precursors WO2000051948A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
AU36881/00A AU3688100A (en) 1999-03-02 2000-03-02 A method for producing nano-engineered precursors
EP00915656A EP1089951A1 (en) 1999-03-02 2000-03-02 A method for producing nano-engineered precursors

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE9900759A SE9900759D0 (en) 1999-03-02 1999-03-02 A method for producing nano-engineered precursors
SE9900759-3 1999-03-02

Publications (1)

Publication Number Publication Date
WO2000051948A1 true WO2000051948A1 (en) 2000-09-08

Family

ID=20414703

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/SE2000/000429 WO2000051948A1 (en) 1999-03-02 2000-03-02 A method for producing nano-engineered precursors

Country Status (4)

Country Link
EP (1) EP1089951A1 (en)
AU (1) AU3688100A (en)
SE (1) SE9900759D0 (en)
WO (1) WO2000051948A1 (en)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4804649A (en) * 1987-10-16 1989-02-14 Akzo America Inc. Alkaline oxalate precipitation process for forming metal oxide ceramic superconductors
US5206215A (en) * 1991-03-18 1993-04-27 Alcatel Alsthom Compagnie Generale D'electricite Process for obtaining precursors for high critical temperature superconductor ceramics comprising a first and second precipitation
WO1994000385A1 (en) * 1992-06-23 1994-01-06 The University Of Queensland SUPERCONDUCTING OXIDES BY COPRECIPITATION AT CONSTANT pH
US5484766A (en) * 1994-02-14 1996-01-16 Electric Power Research Institute, Inc. Preparation of Bi-Pb-Sr-Ca-Cu-O (2223) superconductors

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4804649A (en) * 1987-10-16 1989-02-14 Akzo America Inc. Alkaline oxalate precipitation process for forming metal oxide ceramic superconductors
US5206215A (en) * 1991-03-18 1993-04-27 Alcatel Alsthom Compagnie Generale D'electricite Process for obtaining precursors for high critical temperature superconductor ceramics comprising a first and second precipitation
WO1994000385A1 (en) * 1992-06-23 1994-01-06 The University Of Queensland SUPERCONDUCTING OXIDES BY COPRECIPITATION AT CONSTANT pH
US5484766A (en) * 1994-02-14 1996-01-16 Electric Power Research Institute, Inc. Preparation of Bi-Pb-Sr-Ca-Cu-O (2223) superconductors

Also Published As

Publication number Publication date
SE9900759D0 (en) 1999-03-02
EP1089951A1 (en) 2001-04-11
AU3688100A (en) 2000-09-21

Similar Documents

Publication Publication Date Title
KR101605559B1 (en) Device and method for the production of compounds by precipitation
KR100442079B1 (en) Niobium and Tantalum Pentoxide Compounds
US4839339A (en) Superconductor precursor mixtures made by precipitation method
EP1494968B1 (en) Method for preparing single crystalline cerium oxide powders
US4497785A (en) Production of rare earth compounds
US3393055A (en) Precipitation processes
CN1068267C (en) Method of preparing powders for hard materials
CN112479241A (en) Method for preparing flake aluminum oxide by utilizing flake aluminum hydroxide
CN103878362A (en) Cobalt-based alloy powder for cemented carbide and preparing method of cobalt-based alloy powder for cemented carbide
CN111943240B (en) Method for preparing coarse-grained aluminum hydroxide by decomposing sodium aluminate solution with ultralow seed crystal amount
CN100413785C (en) Method for producing fluorinated potassium tantalate crystal and fluorinated potassium tantalate crystal
CN1114639A (en) Method for producing cobalt oxide nickel oxide powder for electronic industry
EP1089951A1 (en) A method for producing nano-engineered precursors
RU2389690C2 (en) Tungstic acid powder consisting of spherical particles and method of preparing said powder
AU2017227207B2 (en) Nickel powder production method
JP3321902B2 (en) Production method of electronic ceramic raw material powder
CN1565976A (en) Nano-class silver oxide and preparation method thereof
CN1046684C (en) Method for preparing lead titanate powder
CN115340126B (en) Rare earth zirconate particles and preparation method thereof
CN116924450A (en) Method for preparing basic rare earth carbonate by using rare earth chloride feed liquid
JPH0733292B2 (en) Method for producing powder for ceramic raw material
JPS59232920A (en) Manufacture of zirconium oxide powder containing yttrium as solid solution
JPS62216916A (en) Production of metallic hydrated oxide
CN118324516A (en) Preparation method of zirconia granulated powder with low chloride ion content
Yoshizawa et al. Preparation of Precursor Powders

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A1

Designated state(s): AE AL AM AT AU AZ BA BB BG BR BY CA CH CN CR CU CZ DE DK DM EE ES FI GB GD GE GH GM HR HU ID IL IN IS JP KE KG KP KR KZ LC LK LR LS LT LU LV MA MD MG MK MN MW MX NO NZ PL PT RO RU SD SE SG SI SK SL TJ TM TR TT TZ UA UG US UZ VN YU ZA ZW

AL Designated countries for regional patents

Kind code of ref document: A1

Designated state(s): GH GM KE LS MW SD SL SZ TZ UG ZW AM AZ BY KG KZ MD RU TJ TM AT BE CH CY DE DK ES FI FR GB GR IE IT LU MC NL PT SE BF BJ CF CG CI CM GA GN GW ML MR NE SN TD TG

121 Ep: the epo has been informed by wipo that ep was designated in this application
WWE Wipo information: entry into national phase

Ref document number: 2000915656

Country of ref document: EP

WWP Wipo information: published in national office

Ref document number: 2000915656

Country of ref document: EP

REG Reference to national code

Ref country code: DE

Ref legal event code: 8642

WWW Wipo information: withdrawn in national office

Ref document number: 2000915656

Country of ref document: EP