preparation of ultrafine boride powders by metallothermic

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Preparation of ultrafine boride powders bymetallothermic reduction methodTo cite this article Katsuhiro Nishiyama et al 2009 J Phys Conf Ser 176 012043

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Preparation of ultrafine boride powders by metallothermic reduction method

Katsuhiro Nishiyama 1 Takanobu Nakamur2 Shigenori Utsumi1 Hideki Sakai2 and Masahiko Abe2 1Department of Mechanics and Systems Faculty of System Engineering Tokyo University of Science Suwa 5000-1 Toyohira Chino Nagano 391-0292 Japan 2Department of Pure and Applied Chemistry Faculty of Science and Technology Tokyo University of Science 2641 Yamazaki Noda Chiba 278-8510 Japan E-mail nsymrssuwatusacjp

Abstract Ultrafine TiB2 ZrB2 and ReB2 powders were prepared by the metallothermic reduction method using Mg Obtained TiB2 ZrB2 and ReB2 powders were characterized by X-ray diffraction scanning electron microscopy transmission electron microscopy dynamic light scattering and scratch test The morphology of the powders was a laminar hexagonal single crystal The mean particle sizes of TiB2 and ZrB2 increased with increasing reaction temperature and that of ReB2 was 011 μm at 1093 K The obtained ReB2 powder can scratch the surface of polycrystalline synthetic diamonds (HK = 7000 kgmm2) The obtained powders will be useful for developing of new superhard alloys and pigments

1 Introduction Boron combines with various elements forming a large group of more than 200 compounds Metal borides are mostly covalent compounds with metallic appearance high electric and thermal conductivities high melting point and high hardness [1] In particular TiB2 and ZrB2 which combine with group-IV metals have high hardness and heat resistance Recently the synthesis of ReB2 which has hardness comparable to that of diamond has been reported [2] However high temperature was necessary for the synthesis of metal diboride powders by usual methods [3] At present commercially available boride powders have a large particle size of several tens μm Even after mechanical crushing treatment such as ball milling or vibration milling the smallest average particle size is 1-2 μm Impurities coming from a vessel in the crushing treatment are also a serious problem The preparation methods of metal boride powders are roughly classified into the following five groups [14-8] (i) direct reaction (ii) borothermic reduction (iii) carbothermic reduction (iv) borocarbide reduction and (v) metallothermic reduction [8 9] Commercially available metal diboride powders are mainly prepared by the methods (ii)-(iv) High temperature is necessary for these methods between 2073 and 3273 K [16] and hence the formation of coarse particles is unavoidable Therefore establishing a preparation method for ultrafine metal diboride powders is necessary for the developments of a new superhard alloy and a pigment having these characteristics of metal borides

16th International Symposium on Boron Borides and Related Materials IOP PublishingJournal of Physics Conference Series 176 (2009) 012043 doi1010881742-65961761012043

ccopy 2009 IOP Publishing Ltd 1

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ZrO2+2B+2CrarrZrB2+2CO

Zr+2BrarrZrB2

ZrO2+4BrarrZrB2+2BO

Mg

Ca

Al

Si

Zn

b ZrO2+B2O3+5CrarrZrB2+5CO

This paper reports the syntheses of ultrafine TiB2 ZrB2 and ReB2 particles by the metallothermic reduction method using Mg 2 Thermodynamic consideration Thermodynamic consideration of TiB2 and ZrB2 formations were carried out Since no thermodynamic data on ReB2 could be found in the literature we estimated the free energies of TiB2 and ZrB2 formation by metallothermic reduction The chemical equations of metallothermic reduction are listed as eqs (1)-(10) when Mg Si Zn Al and Ca are considered as a metal reduction reagent The equations of direct reaction borothermic reduction carbothermic reduction and borocarbide reduction are shown in figure 1

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TiO2+2B+2CrarrTiB2+2CO

Ti+2BrarrTiB2

TiO2+4BrarrTiB2+2BO

Mg

Ca

Al

Si

Zn

a TiO2+B2O3+5CrarrTiB2+5CO

Figure 1 Temperature dependences of the free energy of formation of TiB2 (a) and ZrB2 (b) by the usual methods and metallothermic reduction TiO2 + B2O3 + 5Mg rarr TiB2 + 5MgO 3-122-6-2-10

Mg 10141-1045310957ln10041-10721 timestimes+times+timestimes= TTTTTGΔ (1)

TiO2 + B2O3 + 25Si rarr TiB2 + 25SiO2 2-122-6-3-20

Si 10124-1065910694ln10709-10349 timestimes+times+timestimes= TTTTTGΔ (2) TiO2 + B2O3 + 5Zn rarr TiB2 + 5ZnO

107241010210342-ln10991-421 -132-6-10Zn times+times+timestimes= TTTTTGΔ (3)

TiO2 + B2O3 + 103Al rarr TiB2 + 53Al2O3 2-122-6-2-10

Al 10449-1084510047ln10071-10591 timestimes+times+timestimes= TTTTTGΔ (4) TiO2 + B2O3 + 5Ca rarr TiB2 + 5CaO

3-122-7-2-10Ca 10301-1067310541ln10052-10172 timestimes+times+timestimes= TTTTTGΔ (5)

ZrO2 + B2O3 + 5Mg rarr ZrB2 + 5MgO 2-122-6-2-10



2

ZrO2 + B2O3 + 25Si rarr ZrB2 + 25SiO2 2-122-6-2-20

Si 10732-1063910176ln10121-10619 timestimes+times+timestimes= TTTTTGΔ (7) ZrO2 + B2O3 + 5Zn rarr ZrB2 + 5ZnO

2-132-7-10Zn 10222-1010210628ln10002-421 timestimes+times+times= TTTTTGΔ (8)

ZrO2 + B2O3 + 103Al rarr ZrB2 + 53Al2O3 2-122-6-2-10

Al 10697-1083510528ln10221-10611 timestimes+times+timestimes= TTTTTGΔ (9) ZrO2 + B2O3 + 5Ca rarr TiB2 + 5CaO 3-122-7-2-10

Ca 10131-1066310691ln10202-10192 timestimes+times+timestimes= TTTTTGΔ (10)

Figure 1 shows the free energies of TiB2 and ZrB2 formations as a function of temperature It is obvious that Mg Al and Ca are suitable for metallothermic reduction because the free energies using Mg Al and Ca are smaller than free energies by usual methods at relatively low temperatures When Al and Ca are used it is difficult to remove the by-product of Al2O3 by acid treatment and to deal with Ca in the atmosphere Therefore Mg was finally selected as a metal reduction reagent because MgO formed as a slug can be easily removed by acids 3 Experimental details 31 Starting reagents Powdered TiO2 (1-2 μm Soekawa Chemical Co) ZrO2 (2 μm Soekawa Chemical Co) ReO2 (Soekawa Chemical Co) B2O3 (40-60 mesh Soekawa Chemical Co) and Mg (lt200 mesh Yamaishimetal Co) were used as starting reagents The 30 wt of MgO (200 nm Soekawa Chemical Co) was added as a negative catalyst [9] 32 Metallothermic reduction and purification procedure Figure 2 shows a flow chart of the preparation process of aimed products

Mg powder

MgOpowder

B2O3 powder

TiO2 or ZrO2 or ReO2 powder

Reaction1h Ar flow

Mixing 3h

Centrifugation 5000 rpm 10 min

Acid-treatment with 10HCl 20 min

Acid-treatment with 10NH4Cl 20 min

Drying

TiB2 or ZrB2 or ReB2 powder

XRD SEM TEM DLS Scratch test

Washing

Centrifugation 5000 rpm 10 minWashing

Mg powder

MgOpowder

B2O3 powder


Mg powder

MgOpowder

B2O3 powder


Reaction1h Ar flow

Mixing 3h




Drying



Drying



Washing

Centrifugation 5000 rpm 10 minWashing Centrifugation 5000 rpm 10 minWashing

Figure 2 Preparation process flow chart of the metal diboride products


3

The starting powders were weighed in the molar ratio of MO2 B2O3 Mg = 1 1 5 where M is Ti Zr or Re The powders were mixed by an Al2O3 ball mill at 120 rpm for 3 h and then placed into a graphite boat with an internal volume of 30 times 30 times 400 mm3 Figure 3 shows a stainless steel tubular furnace for metallothermic reduction The graphite boat with the mixed powder was put at one end of the tubular furnace and then the central part of the furnace was heated to the reaction temperature Metallothermic reduction was carried out for 1 h in an Ar flow (1 Lmin) after moving the boat to the heating zone After the reduction the boat was cooled to room temperature at the other end of the furnace The aimed products were obtained by the acid treatment with boiling 10 of NH4Cl and boiling 10 of HCl for 20 min and centrifugation at 5000 rpm followed by washing with distilled water 5 times and drying 33 Characterization of the products The obtained powders were identified by X-ray diffraction (XRD Rigaku MiniFlex II) The morphology of the powders was observed with a scanning electron microscope (SEM JEOL JSM-5910LV) and a transmission electron microscope (TEM HITACHI H-7650 accelerating voltage 120 kV) Particle size distributions were measured by dynamic light scattering (DLS NICONMP 380ZLS) Hardness test was performed on the obtained ReB2 powder using synthetic polycrystalline diamonds

Figure 3 Schematic illustration of the tubular furnace 4 Results and discussion 41 XRD patterns of the products Figure 4 shows the XRD patterns of the products obtained from TiO2-containing powders at 923 973 and 1073 K before and after purification Diffraction peaks were observed due to TiB2 MgO and other compounds such as TiO2 Ti2O3 and Mg3B2O6 TiO2 and Mg3B2O6 were formed as by-products by metallothermic reduction Because boron was used for the formation of Mg3B2O6 unreacted TiO2 remained Even after purification the diffraction peaks of Ti2O3 and Ti2O3 which are resistant to acids were observed Figure 5 shows the XRD patterns of the products obtained from ZrO2-containing powders at 923 973 and 1073 K before and after purification Diffraction peaks due to ZrO2 and Mg3B2O6 were also observed in addition to those of ZrB2 and Mg The by-product ZrO2 insoluble to acid remained after purification however the amount of ZrO2 apparently decreased with increasing reaction temperature Figure 6 shows the XRD patterns of the products obtained from ReO2-containing powders at 1073 K before and after purification Diffraction peaks of the aimed products ReB2 were prominent However many diffraction peaks were also present from by-products such as Re and Re7B3 which remained after purification More detailed investigations are necessary on the mixing ratio of starting reagents reaction temperature and purification process

Heating zone

Cooling zone Graphite boat

Ar gas inlet

Ar gas outlet

Thermocouple Water inlet Water outlet


4

1073 K

ZrO2

MgOMg3B2O6

a

973 K

923 K

Inte

nsity

( ar

b u

nits

)

1073 K

b

ZrB

2 (100

)

ZrB

2 (1

01)

ZrB

2 (0

01)

973 K

50454035302520

2θ ( degree )

923 K

1073 K

TiO2

Ti2O3

MgOMgMg3B2O6

a

973 K

923 K

Inte

nsity

( ar

b u

nits

)

1073 K

TiB

2 (0

01)

TiB

2 (1

00)

TiB

2 (1

01)b

973 K

50454035302520

2θ ( degree )

923 K

Inte

nsity

( ar

bun

its )

50454035302520

2θ ( degree )

ReB

2 (0

02)

ReB

2 (100)

ReB

2 (1

01)

ReRe7B3MgO

a

b

1073 K

1073 K

ReB

2 (102)

Figure 4 XRD patterns of the products obtained from TiO2-containing powder (a) before and (b) after purification

Figure 5 XRD patterns of the products obtained from ZrO2-containing powder (a) before and (b) after purification

Figure 6 XRD patterns of the products obtained from ReO2-containing powder (a) before and (b) after purification


5

42 Morphology and particle size of products Figures 7 and 8 show SEM and TEM images of purified products prepared at 1073 K These boride particles are laminar hexagonal single crystals and have the crystal habit characteristic of the hexagonal system The particle size was 01-04 μm indicated by the SEM and TEM images Furthermore the crystals was very thin (hundreds nm) as revealed by their transparency in the TEM images Figure 9 shows the particle size distributions of TiB2 ZrB2 and ReB2 The particle sizes of TiB2 and ZrB2 increase with increasing reaction temperature because of the coalescence of reacted particles The mean particle size of ReB2 powder prepared at 1073 K was 011 μm It is concluded that submicron powders of TiB2 ZrB2 and ReB2 powders were obtained

Figure 7 SEM images of (a) TiB2 (b) ZrB2 and (c) ReB2 obtained after purification

Figure 8 TEM images of (a) TiB2 (b) ZrB2 and (c) ReB2 obtained after purification

100nm100nm

100nm100nm100nm

a

b

c

a

b

c


6

4 5 6 7 8 9100

2 3 4 5 6 7 8 91000

Particle size (nm)

1073 K 011μm

c10

0

1073 K 020 μm 973 K 019 μm 923 K 014 μm

b

Num

ber d

istri

butio

n 10

0

1073 K 021 μm 973 K 017 μm 923 K 013 μm

a10

0

5 μm5 μm5 μm5 μm

43 Scratch test on ReB2 Scratch test was carried out using high pressure sintered synthetic diamonds which have the Knoop hardness of 7000 kgmm2 In this test the obtained ReB2 powder was sandwiched between two synthetic diamonds and then ReB2 powder rubbed by them Figure 10 shows the surface of polycrystalline synthetic diamonds before and after the test We can see the scratches on the surface of the diamond after the test revealing that the hardness of ReB2 is comparable to that of synthetic diamond 5 Conclusion Ultrafine TiB2 ZrB2 and ReB2 powders were prepared by the metallothermic reduction method using Mg Laminar hexagonal single crystals were obtained of TiB2 ZrB2 and ReB2 with submicron sizes and thickness of several nanometers ReB2 powder could scratch the surface of a synthetic diamond indicating that the hardness of ReB2 is higher than or equal to a synthetic diamond which has Knoop hardness of 7000 kgmm2 It has been reported that laminar TiB2 particles dispersed in resin improved the hardness of the resin film surface due to their hardness and particle shape which leads to increase in the face-to-face contact area between particles [11] Thus boride powders obtained in this study should be promising materials as a pigment of paint coating as well as a superhard alloy for mobile phone and automobile frames and a converter duct wall

References [1] Atouda T 1973 Titanium Diboride Titanium-Zriconium 21 145 [2] Chung H-Y 2007 Science 316 436 [3] Peshev P 1968 J Less-Common Metals 14 23 [4] Reddev D D 1994 J Alloy Compd 206 34

5 μm5 μm5 μm

Figure 9 Particle size distributions of (a) TiB2 (b) ZrB2 and (c) ReB2 powders

a

b

Figure 10 Surface of synthetic diamonds (a) before and (b) after scratch test


7

[5] Reddev D D 1996 J Alloy Compd 244 48 [6] Welham N J 2000 J Am Ceram Soc 83 1290 [7] Hwang Y 2002 Mater Lett 54 1 [8] Sundaram V 1997 Mater Lett 12 2657 [9] Nishiyama K 1990 J Jpn Soc Powder Powder Metall 37 500 [10] Smithells C J 1983 Metals Reference Book (6th ed) (Butterworths) [11] Nishiyama K 2003 Surf Coat Int B Coat Trans 86 169


8

Preparation of ultrafine boride powders by metallothermic reduction method

Katsuhiro Nishiyama 1 Takanobu Nakamur2 Shigenori Utsumi1 Hideki Sakai2 and Masahiko Abe2 1Department of Mechanics and Systems Faculty of System Engineering Tokyo University of Science Suwa 5000-1 Toyohira Chino Nagano 391-0292 Japan 2Department of Pure and Applied Chemistry Faculty of Science and Technology Tokyo University of Science 2641 Yamazaki Noda Chiba 278-8510 Japan E-mail nsymrssuwatusacjp

Abstract Ultrafine TiB2 ZrB2 and ReB2 powders were prepared by the metallothermic reduction method using Mg Obtained TiB2 ZrB2 and ReB2 powders were characterized by X-ray diffraction scanning electron microscopy transmission electron microscopy dynamic light scattering and scratch test The morphology of the powders was a laminar hexagonal single crystal The mean particle sizes of TiB2 and ZrB2 increased with increasing reaction temperature and that of ReB2 was 011 μm at 1093 K The obtained ReB2 powder can scratch the surface of polycrystalline synthetic diamonds (HK = 7000 kgmm2) The obtained powders will be useful for developing of new superhard alloys and pigments

1 Introduction Boron combines with various elements forming a large group of more than 200 compounds Metal borides are mostly covalent compounds with metallic appearance high electric and thermal conductivities high melting point and high hardness [1] In particular TiB2 and ZrB2 which combine with group-IV metals have high hardness and heat resistance Recently the synthesis of ReB2 which has hardness comparable to that of diamond has been reported [2] However high temperature was necessary for the synthesis of metal diboride powders by usual methods [3] At present commercially available boride powders have a large particle size of several tens μm Even after mechanical crushing treatment such as ball milling or vibration milling the smallest average particle size is 1-2 μm Impurities coming from a vessel in the crushing treatment are also a serious problem The preparation methods of metal boride powders are roughly classified into the following five groups [14-8] (i) direct reaction (ii) borothermic reduction (iii) carbothermic reduction (iv) borocarbide reduction and (v) metallothermic reduction [8 9] Commercially available metal diboride powders are mainly prepared by the methods (ii)-(iv) High temperature is necessary for these methods between 2073 and 3273 K [16] and hence the formation of coarse particles is unavoidable Therefore establishing a preparation method for ultrafine metal diboride powders is necessary for the developments of a new superhard alloy and a pigment having these characteristics of metal borides


ccopy 2009 IOP Publishing Ltd 1

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Zr+2BrarrZrB2

ZrO2+4BrarrZrB2+2BO

Mg

Ca

Al

Si

Zn



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Ti+2BrarrTiB2

TiO2+4BrarrTiB2+2BO

Mg

Ca

Al

Si

Zn













2








Mg powder

MgOpowder

B2O3 powder


Reaction1h Ar flow

Mixing 3h




Drying



Washing


Mg powder

MgOpowder

B2O3 powder


Mg powder

MgOpowder

B2O3 powder


Reaction1h Ar flow

Mixing 3h




Drying



Drying



Washing




3



Heating zone


Ar gas inlet

Ar gas outlet



4

1073 K

ZrO2

MgOMg3B2O6

a

973 K

923 K

Inte

nsity

( ar

b u

nits

)

1073 K

b

ZrB

2 (100

)

ZrB

2 (1

01)

ZrB

2 (0

01)

973 K

50454035302520

2θ ( degree )

923 K

1073 K

TiO2

Ti2O3

MgOMgMg3B2O6

a

973 K

923 K

Inte

nsity

( ar

b u

nits

)

1073 K

TiB

2 (0

01)

TiB

2 (1

00)

TiB

2 (1

01)b

973 K

50454035302520

2θ ( degree )

923 K

Inte

nsity

( ar

bun

its )

50454035302520

2θ ( degree )

ReB

2 (0

02)

ReB

2 (100)

ReB

2 (1

01)

ReRe7B3MgO

a

b

1073 K

1073 K

ReB

2 (102)





5




100nm100nm

100nm100nm100nm

a

b

c

a

b

c


6

4 5 6 7 8 9100

2 3 4 5 6 7 8 91000

Particle size (nm)

1073 K 011μm

c10

0

1073 K 020 μm 973 K 019 μm 923 K 014 μm

b

Num

ber d

istri

butio

n 10

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1073 K 021 μm 973 K 017 μm 923 K 013 μm

a10

0




5 μm5 μm5 μm


a

b



7



8

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1000

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(kJ

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)

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Zr+2BrarrZrB2

ZrO2+4BrarrZrB2+2BO

Mg

Ca

Al

Si

Zn



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Ti+2BrarrTiB2

TiO2+4BrarrTiB2+2BO

Mg

Ca

Al

Si

Zn













2








Mg powder

MgOpowder

B2O3 powder


Reaction1h Ar flow

Mixing 3h




Drying



Washing


Mg powder

MgOpowder

B2O3 powder


Mg powder

MgOpowder

B2O3 powder


Reaction1h Ar flow

Mixing 3h




Drying



Drying



Washing




3



Heating zone


Ar gas inlet

Ar gas outlet



4

1073 K

ZrO2

MgOMg3B2O6

a

973 K

923 K

Inte

nsity

( ar

b u

nits

)

1073 K

b

ZrB

2 (100

)

ZrB

2 (1

01)

ZrB

2 (0

01)

973 K

50454035302520

2θ ( degree )

923 K

1073 K

TiO2

Ti2O3

MgOMgMg3B2O6

a

973 K

923 K

Inte

nsity

( ar

b u

nits

)

1073 K

TiB

2 (0

01)

TiB

2 (1

00)

TiB

2 (1

01)b

973 K

50454035302520

2θ ( degree )

923 K

Inte

nsity

( ar

bun

its )

50454035302520

2θ ( degree )

ReB

2 (0

02)

ReB

2 (100)

ReB

2 (1

01)

ReRe7B3MgO

a

b

1073 K

1073 K

ReB

2 (102)





5




100nm100nm

100nm100nm100nm

a

b

c

a

b

c


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2 3 4 5 6 7 8 91000

Particle size (nm)

1073 K 011μm

c10

0

1073 K 020 μm 973 K 019 μm 923 K 014 μm

b

Num

ber d

istri

butio

n 10

0

1073 K 021 μm 973 K 017 μm 923 K 013 μm

a10

0




5 μm5 μm5 μm


a

b



7



8








Mg powder

MgOpowder

B2O3 powder


Reaction1h Ar flow

Mixing 3h




Drying



Washing


Mg powder

MgOpowder

B2O3 powder


Mg powder

MgOpowder

B2O3 powder


Reaction1h Ar flow

Mixing 3h




Drying



Drying



Washing




3



Heating zone


Ar gas inlet

Ar gas outlet



4

1073 K

ZrO2

MgOMg3B2O6

a

973 K

923 K

Inte

nsity

( ar

b u

nits

)

1073 K

b

ZrB

2 (100

)

ZrB

2 (1

01)

ZrB

2 (0

01)

973 K

50454035302520

2θ ( degree )

923 K

1073 K

TiO2

Ti2O3

MgOMgMg3B2O6

a

973 K

923 K

Inte

nsity

( ar

b u

nits

)

1073 K

TiB

2 (0

01)

TiB

2 (1

00)

TiB

2 (1

01)b

973 K

50454035302520

2θ ( degree )

923 K

Inte

nsity

( ar

bun

its )

50454035302520

2θ ( degree )

ReB

2 (0

02)

ReB

2 (100)

ReB

2 (1

01)

ReRe7B3MgO

a

b

1073 K

1073 K

ReB

2 (102)





5




100nm100nm

100nm100nm100nm

a

b

c

a

b

c


6

4 5 6 7 8 9100

2 3 4 5 6 7 8 91000

Particle size (nm)

1073 K 011μm

c10

0

1073 K 020 μm 973 K 019 μm 923 K 014 μm

b

Num

ber d

istri

butio

n 10

0

1073 K 021 μm 973 K 017 μm 923 K 013 μm

a10

0




5 μm5 μm5 μm


a

b



7



8



Heating zone


Ar gas inlet

Ar gas outlet



4

1073 K

ZrO2

MgOMg3B2O6

a

973 K

923 K

Inte

nsity

( ar

b u

nits

)

1073 K

b

ZrB

2 (100

)

ZrB

2 (1

01)

ZrB

2 (0

01)

973 K

50454035302520

2θ ( degree )

923 K

1073 K

TiO2

Ti2O3

MgOMgMg3B2O6

a

973 K

923 K

Inte

nsity

( ar

b u

nits

)

1073 K

TiB

2 (0

01)

TiB

2 (1

00)

TiB

2 (1

01)b

973 K

50454035302520

2θ ( degree )

923 K

Inte

nsity

( ar

bun

its )

50454035302520

2θ ( degree )

ReB

2 (0

02)

ReB

2 (100)

ReB

2 (1

01)

ReRe7B3MgO

a

b

1073 K

1073 K

ReB

2 (102)





5




100nm100nm

100nm100nm100nm

a

b

c

a

b

c


6

4 5 6 7 8 9100

2 3 4 5 6 7 8 91000

Particle size (nm)

1073 K 011μm

c10

0

1073 K 020 μm 973 K 019 μm 923 K 014 μm

b

Num

ber d

istri

butio

n 10

0

1073 K 021 μm 973 K 017 μm 923 K 013 μm

a10

0




5 μm5 μm5 μm


a

b



7



8

1073 K

ZrO2

MgOMg3B2O6

a

973 K

923 K

Inte

nsity

( ar

b u

nits

)

1073 K

b

ZrB

2 (100

)

ZrB

2 (1

01)

ZrB

2 (0

01)

973 K

50454035302520

2θ ( degree )

923 K

1073 K

TiO2

Ti2O3

MgOMgMg3B2O6

a

973 K

923 K

Inte

nsity

( ar

b u

nits

)

1073 K

TiB

2 (0

01)

TiB

2 (1

00)

TiB

2 (1

01)b

973 K

50454035302520

2θ ( degree )

923 K

Inte

nsity

( ar

bun

its )

50454035302520

2θ ( degree )

ReB

2 (0

02)

ReB

2 (100)

ReB

2 (1

01)

ReRe7B3MgO

a

b

1073 K

1073 K

ReB

2 (102)





5




100nm100nm

100nm100nm100nm

a

b

c

a

b

c


6

4 5 6 7 8 9100

2 3 4 5 6 7 8 91000

Particle size (nm)

1073 K 011μm

c10

0

1073 K 020 μm 973 K 019 μm 923 K 014 μm

b

Num

ber d

istri

butio

n 10

0

1073 K 021 μm 973 K 017 μm 923 K 013 μm

a10

0




5 μm5 μm5 μm


a

b



7



8




100nm100nm

100nm100nm100nm

a

b

c

a

b

c


6

4 5 6 7 8 9100

2 3 4 5 6 7 8 91000

Particle size (nm)

1073 K 011μm

c10

0

1073 K 020 μm 973 K 019 μm 923 K 014 μm

b

Num

ber d

istri

butio

n 10

0

1073 K 021 μm 973 K 017 μm 923 K 013 μm

a10

0




5 μm5 μm5 μm


a

b



7



8

4 5 6 7 8 9100

2 3 4 5 6 7 8 91000

Particle size (nm)

1073 K 011μm

c10

0

1073 K 020 μm 973 K 019 μm 923 K 014 μm

b

Num

ber d

istri

butio

n 10

0

1073 K 021 μm 973 K 017 μm 923 K 013 μm

a10

0




5 μm5 μm5 μm


a

b



7



8



8

preparation of ultrafine boride powders by metallothermic

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