Title of Invention	"AN IMPROVED PROCESS FOR THE PRODUCTION OF NEODYMIUM-IRON-BORON PERMANENT MAGNET ALLOY POWDER"
Abstract	An improved process for the production of neodymium-rion-boron permanent magnet alloy powder by mixing neodymium salt solution of strength in the range of 0.25 - 2.0 M, iron salt solution of strength in the range 0.25 - 2.0 M adjusting the pH of the solution in the range of 1 - 2.5, adding the alkaline borohydride solution, slowly and continuously to the mixture such as herein described neodymium-iron salt solution and maintaining a temperature in the range of 5 to 15 deg.C, with continuous stirring to get a black precipitate having a composition in the range of Neodymium 10 to 40 wt% ,iron 60 to 90 wt% boron 1 to 10 wt%; filtering, washing the precipitate with water and organic solvents, heat treating the precipitate with argon/hydrogen at a temperature in the range of 500 to 750°C. to obtain neodymium iron - boron permanent magnet alloy powder .

Title of Invention

"AN IMPROVED PROCESS FOR THE PRODUCTION OF NEODYMIUM-IRON-BORON PERMANENT MAGNET ALLOY POWDER"

Abstract

An improved process for the production of neodymium-rion-boron permanent magnet alloy powder by mixing neodymium salt solution of strength in the range of 0.25 - 2.0 M, iron salt solution of strength in the range 0.25 - 2.0 M adjusting the pH of the solution in the range of 1 - 2.5, adding the alkaline borohydride solution, slowly and continuously to the mixture such as herein described neodymium-iron salt solution and maintaining a temperature in the range of 5 to 15 deg.C, with continuous stirring to get a black precipitate having a composition in the range of Neodymium 10 to 40 wt% ,iron 60 to 90 wt% boron 1 to 10 wt%; filtering, washing the precipitate with water and organic solvents, heat treating the precipitate with argon/hydrogen at a temperature in the range of 500 to 750°C. to obtain neodymium iron - boron permanent magnet alloy powder .

Full Text	This invention relates to an improved process for the production of neodymium-iron-boron permanent magnet alloy powder. The neodymium-iron-boron alloy prepared by the process of the present invention can be processed further to get anisotropic permanent magnets, bonded as well as sintered. Neodymium-iron-boron magnets find wide application due to their excellent magnetic properties, viz., a very high coercivity, a high remanence and a very high maximum energy product. They are increasingly used in motors, generators, measuring and control devices, telecommunications, acoustic devices and magneto-mechanical applications. They also find applications in aerospace components, instrumentation, medical diagnosis and treatment. In the conventional methods of production of neodymium-iron-boron magnets, the individual elements such as neodymium, iron and boron or ferroboron are melted crushed and milled to micron size, compacted under magnetic field and then sintered. This known process is energy intensive as well as costly. The rare earth metal, neodymium which is the raw material for the process is very expensive because of the difficulties in the separation of neodymium oxide/salt from the mixture of rare earth oxides/salts and the reduction of neodymium oxide/salt into metal. In another known process wherein metallothermic reduction diffusion is involved, neodymium chloride/fluoride or oxide, iron and boron or ferroboron are reacted with calcium in the presence of hydrogen to get neodymium-iron-boron alloy along with calcium oxide and unreacted calcium. This is further reacted with water/moist nitrogen to remove calcium and then leached with acetic acid to remove calcium oxide. This process also requires considerable amount of energy input in preparation of alloy during reduction with calcium at high temperature in the range of 1000 to 1200 degree centigrade. In our copending application No. 374/Del/94 dated 31.3.94, we have disclosed a process for the production of nano sized neodymium-iron-boron permanent magnet alloy powder. The process employs neodymium oxide/salt, iron salt and borohydride for making for making neodymium-iron-boron alloy powder with particle size in the range of 20-100nm (nm : nanometer) . The use of borohydride as a reductant helps in the reduction of neodymium and iron salt to their metallic state and formation of the compound is accomplish through suitable heat treatment. The as produced powder being highly pyrophoric needs specific surface treatment to stabilize it, however, this coating some times leads to problems when the powder is subjected to further heat treatment.. Therefore, further R&D efforts have been made to improve the process and the present invention differs from the copending application 374/Del/94 in the following way : The new process, with a heat-treatment schedule, using both hydrogen and argon at 750 degree centigrade, provides a bulk alloy of Nd-Fe-B system with the required Nd2Fe14B and NdFe4B4 phases, grain size being in the range of sub-micron. This heat treatment directly provides the optimum concentration of boron in the alloy, as the excess boron being driven away from the system in the form of volatile borohydrides. The main object of the present invention is to provide a process for the, production of neodymium-iron-boron permanent magnet alloy powder by overcoming the above mentioned drawbacks. The process of present invention employs a chemical route involving a reaction of neodymium oxide/salt, iron salt and a borohydride under specific conditions of concentration, pH, temperature and time for the reaction followed by a heat treatment at ambient temperature under controlled atmosphere for making neodymium-iron-born alloy. The use of borohydride as reductant helps in the reduction of neodymium and iron salts to Their metallic state. The formation of alloy with optimum number of phases is accomplished through suitable heat treatment. Accordingly, the present invention provides An improved process for the production of neodymium-rion-boron permanent magnet alloy powder which comprises: i) mixing neodymium salt solution of strength in the range of 0.25 - 2.0 M, iron salt solution of strength in the range 0.25 - 2.0 M ii) adjusting the pH of the solution in the range of 1 - 2.5, iii) adding the athalive borohydride solution, slowly and continuously to the mixture such as herein described neodymium-iron salt solution and maintaining a temperature in the range of 5 to 15 deg.C, with continuous stirring to get a black precipitate having a composition in the range of; Nedodymium : 10to40wt% Iron : 60 to 90 wt% Boron : Itol0wt%; iv) filtering, washing the precipitate, obtained from step (iii), with water and organic solvents such as herein described v) heat treating the precipitate with argon/hydrogen at a temperature in the range of 500 to 750 deg.C. to obtain neodymium iron - boron permanent magnet alloy powder. According to the feature of the invention, the amount of the solutions used are in the following range : Neodymium salt : 1 volume iron salt : 3-7 volumes alkali borohydride : 4-10 volumes. All the salts used may be of commercial grade. The mixing of the neodymium and iron salt solutions with alkali borohydride may be done in inert atmosphere preferably using argon. By the process of present invention a two phase material with grains of size 200 - 500nm with composition close to Nd2Fel4B and grain boundary with composition close to NdFe4B4 is produced. The following examples are given by way of illustration and should not be construed to limit . the scope of the present invention. Example 1: 40 ml. of 1M ferrous sulphate solution was mixed with 8ml. of 1M neodymium chloride and cooled to 10 degree centigrade. The pH of the solution was adjusted to 1.5. To this was added 100 ml.of 4M sodium borohydride solution with continuous stirring. The black precipitate formed was filtered, washed with water, methanol and acetone. The powder was heat treated in pure argon at 450 deg.C. and upto 700 deg.C. in hydrogen. Sample was held at this temperature for 2 hours and then cooled in Argon. The material as identified by SEM (EDX) and x-ray diffraction,indicated a mixture of two phases namely iron rich phase and neodymium rich phase. The product was further tested for ensuring the presence of elements in their metallic forms. The result obtained are as follows : Iron rich phase gave the following chemical analysis (By EDX) : Fe 96.97 wt% Nd 3.03 wt% Neodymium rich phase gave the following chemical analysis (By EDX) : Fe 30.31 wt% Nd 69.96 wt% The boron was found to be 5Wt% in the alloy. Example 2: 40 ml. of 1M ferrous sulphate solution was mixed with 8ml. of 1M neodymium chloride and cooled to 10 degree centigrade. The pH of the solution was adjusted to 1.5. To this was added 100 ml.of 4M sodium borohydride solution with continuous stirring. The black precipitate formed was filtered, washed with water, methanol and acetone. The powder was heat treated in pure argon at 150 deg.C. and up to 700 deg.C. in hydrogen. Sample was held at this temperature for 2 hours and then cooled in Argon.This material was further annealed in Argon for 96 hours. The material was identified by SEM (EDX) and x-ray diffraction, a mixture of two phases namely Nd2Fe14B (Phase - 1) and NdFe4B4 (Phase - II). The product was further tested for ensuring the presence of elements in their metallic forms. The result obtained are as follows : Phase -I gave the chemical analysis (By EDX) as follows : Fe 73.79 wt% Nd 26.21 wt% Phase -II gave the chemical analysis (By EDX) as follows : Fe 58.73 wt% Nd 39.27 wt% The boron was found to be 2wt% in the bulk alloy. The main advantages of the present invention are : a) neodymium - iron - boron alloy is produced in two steps only whereas other relevant known processes require several steps and time consuming. b)neodymium - iron - boron alloy produced has characteristic microstructure and phases as required for the production of permanent magnet. This has not been achieved in known processes. c) the required compositions and phases have been obtained by heat treating the very fine neodymium-iron-boron alloy (particle size in the range 20-80nm) at much lower temperature than that required by any other known processes. d)the cost of production of the product of the present invention is far less compared to the existing processes which involves melting and milling or metallothermic reduction. We Claim: 1. An improved process for the production of neodymium-iron-boron permanent magnet alloy powder which comprises: i) mixing neodymium salt solution of strength in the range of 0.25 - 2.0 M, iron salt solution of strength in the range 0.25 - 2.0 M ii) adjusting the pH of the solution in the range of 1 - 2.5, iii) adding the alkaline borohydride solution, slowly and continuously to the mixture such as herein described neodymium-iron salt solution and maintaining a temperature in the range of 5 to 15 deg.C, with continuous stirring to get a black precipitate having a composition in the range of; Neodymium : 10to40wt% Iron : 60 to 90 wt% Boron : Itol0wt%; iv) filtering, washing the precipitate, obtained from step (iii), with water and organic solvents such as herein described v) heat treating the precipitate with argon/hydrogen at a temperature in the range of 500 to 750 deg.C. to obtain neodymium iron - boron permanent magnet alloy powder . 2. An improved process as claimed in claim 1 wherein the amounts of solutions used are in the following ranges : Neodymium salt : 3-7 volumes Alkali borohydride : 4-10 volumes. 3. An improved process for the production of neodymium - iron-boron permanent magnet alloy powder substantially as herein described with reference to the examples.

Full Text

This invention relates to an improved process for the production of neodymium-iron-boron permanent magnet alloy powder.
The neodymium-iron-boron alloy prepared by the process of the present invention can be processed further to get anisotropic permanent magnets, bonded as well as sintered.
Neodymium-iron-boron magnets find wide application due to their excellent magnetic properties, viz., a very high coercivity, a high remanence and a very high maximum energy product. They are increasingly used in motors, generators, measuring and control devices, telecommunications, acoustic devices and magneto-mechanical applications. They also find applications in aerospace components, instrumentation, medical diagnosis and treatment.
In the conventional methods of production of neodymium-iron-boron magnets, the individual elements such as neodymium, iron and boron or ferroboron are melted crushed and milled to micron size, compacted under magnetic field and then sintered. This known process is energy intensive as well as costly. The rare earth metal, neodymium which is the raw material for the process is very expensive because of the difficulties in the separation of neodymium oxide/salt from the mixture of rare earth oxides/salts and the reduction of neodymium oxide/salt into metal.
In another known process wherein metallothermic reduction diffusion is involved, neodymium chloride/fluoride or oxide, iron and boron or ferroboron are reacted with calcium in the presence of hydrogen to get neodymium-iron-boron alloy along with calcium oxide and unreacted calcium. This is further reacted with water/moist nitrogen to remove calcium and then leached with acetic acid to remove calcium oxide. This process also requires considerable amount of energy input in preparation of alloy during reduction with calcium at high temperature in the range of 1000 to 1200 degree centigrade.

In our copending application No. 374/Del/94 dated 31.3.94, we have disclosed a process for the production of nano sized neodymium-iron-boron permanent magnet alloy powder. The process employs neodymium oxide/salt, iron salt and borohydride for making for making neodymium-iron-boron alloy powder with particle size in the range of 20-100nm (nm : nanometer) . The use of borohydride as a reductant helps in the reduction of neodymium and iron salt to their metallic state and formation of the compound is accomplish through suitable heat treatment. The as produced powder being highly pyrophoric needs specific surface treatment to stabilize it, however, this coating some times leads to problems when the powder is subjected to further heat treatment..
Therefore, further R&D efforts have been made to improve the process and the present invention differs from the copending application 374/Del/94 in the following way :
The new process, with a heat-treatment schedule, using both hydrogen and argon at 750 degree centigrade, provides a bulk alloy of Nd-Fe-B system with the required Nd2Fe14B and NdFe4B4 phases, grain size being in the range of sub-micron. This heat treatment directly provides the optimum concentration of boron in the alloy, as the excess boron being driven away from the system in the form of volatile borohydrides.
The main object of the present invention is to provide a process for the, production of neodymium-iron-boron permanent
magnet alloy powder by overcoming the above mentioned drawbacks.
The process of present invention employs a chemical route involving a reaction of neodymium oxide/salt, iron salt and a borohydride under specific conditions of concentration, pH, temperature and time for the reaction followed by a heat treatment at ambient temperature under controlled atmosphere for making neodymium-iron-born alloy. The use of borohydride as reductant helps in the reduction of neodymium and iron salts to

Their metallic state. The formation of alloy with optimum number of phases is accomplished through suitable heat treatment.
Accordingly, the present invention provides An improved process for the production of neodymium-rion-boron permanent magnet alloy powder which comprises:
i) mixing neodymium salt solution of strength in the range of 0.25 - 2.0 M, iron
salt solution of strength in the range 0.25 - 2.0 M ii) adjusting the pH of the solution in the range of 1 - 2.5, iii) adding the athalive borohydride solution, slowly and continuously to the mixture such as herein described neodymium-iron salt solution and maintaining a temperature in the range of 5 to 15 deg.C, with continuous stirring to get a black precipitate having a composition in the range of;
Nedodymium : 10to40wt%
Iron : 60 to 90 wt%
Boron : Itol0wt%;
iv) filtering, washing the precipitate, obtained from step (iii), with water and
organic solvents such as herein described
v) heat treating the precipitate with argon/hydrogen at a temperature in the range of 500 to 750 deg.C. to obtain neodymium iron - boron permanent magnet alloy powder.
According to the feature of the invention, the amount of the solutions used are in the following range :
Neodymium salt : 1 volume

iron salt : 3-7 volumes
alkali borohydride : 4-10 volumes. All the salts used may be of commercial grade.
The mixing of the neodymium and iron salt solutions with alkali borohydride may be done in inert atmosphere preferably using argon.
By the process of present invention a two phase material with grains of size 200 - 500nm with composition close to Nd2Fel4B and grain boundary with composition close to NdFe4B4 is produced.
The following examples are given by way of illustration and should not be construed to limit . the scope of the present invention.
Example 1:
40 ml. of 1M ferrous sulphate solution was mixed with 8ml. of 1M neodymium chloride and cooled to 10 degree centigrade. The pH of the solution was adjusted to 1.5. To this was added 100 ml.of 4M sodium borohydride solution with continuous stirring. The black precipitate formed was filtered, washed with water, methanol and acetone. The powder was heat treated in pure argon at 450 deg.C. and upto 700 deg.C. in hydrogen. Sample was held at this temperature for 2 hours and then cooled in Argon. The material as identified by SEM (EDX) and x-ray diffraction,indicated a mixture of two phases namely iron rich phase and neodymium rich phase.
The product was further tested for ensuring the presence of elements in their metallic forms. The result obtained are as follows :
Iron rich phase gave the following chemical analysis (By EDX) :
Fe 96.97 wt%
Nd 3.03 wt%

Neodymium rich phase gave the following chemical analysis (By EDX) :
Fe 30.31 wt%
Nd 69.96 wt% The boron was found to be 5Wt% in the alloy.
Example 2:
40 ml. of 1M ferrous sulphate solution was mixed with 8ml. of 1M neodymium chloride and cooled to 10 degree centigrade. The pH of the solution was adjusted to 1.5. To this was added 100 ml.of 4M sodium borohydride solution with continuous stirring. The black precipitate formed was filtered, washed with water, methanol and acetone. The powder was heat treated in pure argon at 150 deg.C. and up to 700 deg.C. in hydrogen. Sample was held at this temperature for 2 hours and then cooled in Argon.This material was further annealed in Argon for 96 hours. The material was identified by SEM (EDX) and x-ray diffraction, a mixture of two phases namely Nd2Fe14B (Phase - 1) and NdFe4B4 (Phase - II).
The product was further tested for ensuring the presence of elements in their metallic forms. The result obtained are as follows :
Phase -I gave the chemical analysis (By EDX) as follows :
Fe 73.79 wt% Nd 26.21 wt%
Phase -II gave the chemical analysis (By EDX) as follows :
Fe 58.73 wt%
Nd 39.27 wt% The boron was found to be 2wt% in the bulk alloy.
The main advantages of the present invention are : a) neodymium - iron - boron alloy is produced in two steps only whereas other relevant known processes require several steps and time consuming.
b)neodymium - iron - boron alloy produced has characteristic microstructure and phases as required for the production of

permanent magnet. This has not been achieved in known processes.
c) the required compositions and phases have been obtained by heat treating the very fine neodymium-iron-boron alloy (particle size in the range 20-80nm) at much lower temperature than that required by any other known processes.
d)the cost of production of the product of the present invention is far less compared to the existing processes which involves melting and milling or metallothermic reduction.

We Claim:
1. An improved process for the production of neodymium-iron-boron permanent
magnet alloy powder which comprises:
i) mixing neodymium salt solution of strength in the range of 0.25 - 2.0 M,
iron salt solution of strength in the range 0.25 - 2.0 M ii) adjusting the pH of the solution in the range of 1 - 2.5, iii) adding the alkaline borohydride solution, slowly and continuously to the mixture such as herein described neodymium-iron salt solution and maintaining a temperature in the range of 5 to 15 deg.C, with continuous stirring to get a black precipitate having a composition in the range of;
Neodymium : 10to40wt%
Iron : 60 to 90 wt%
Boron : Itol0wt%;
iv) filtering, washing the precipitate, obtained from step (iii), with water and
organic solvents such as herein described v) heat treating the precipitate with argon/hydrogen at a temperature in the
range of 500 to 750 deg.C. to obtain neodymium iron - boron permanent
magnet alloy powder .
2. An improved process as claimed in claim 1 wherein the amounts of solutions used
are in the following ranges :
Neodymium salt : 3-7 volumes
Alkali borohydride : 4-10 volumes.
3. An improved process for the production of neodymium - iron-boron permanent
magnet alloy powder substantially as herein described with reference to the
examples.

Documents:

287-del-1999-abstract.pdf

287-del-1999-claims.pdf

287-del-1999-correspondence-others.pdf

287-del-1999-correspondence-po.pdf

287-del-1999-description (complete).pdf

287-del-1999-form-1.pdf

287-del-1999-form-19.pdf

287-del-1999-form-2.pdf

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Patent Number

215853

Indian Patent Application Number

287/DEL/1999

PG Journal Number

12/2008

Publication Date

21-Mar-2008

Grant Date

04-Mar-2008

Date of Filing

19-Feb-1999

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG. NEW DELHI-110001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	PATCHA RAMACHANDRA RAO	NATIONAL METALLURGICAL LABORATORY, JAMSHEDPUR, BIHAR, INDIA.
2	VENKATESH RAO	NATIONAL METALLURGICAL LABORATORY, JAMSHEDPUR, BIHAR, INDIA.
3	ARVIND SINHA	NATIONAL METALLURGICAL LABORATORY, JAMSHEDPUR, BIHAR, INDIA.

PCT International Classification Number

C22C 1/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA