506111437 BRA GIRI

Prof.Dr. Onuralp YCEL

Prof.Dr. Filiz INAR AHN

PRODUCTION OF

CHROMIUM BORIDE

(CRB , CRB2 )

CONTENTS

1. Generel Information About CHROMIUM BORIDE (CrB , CrB2 )

2. Production of CHROMIUM BORIDE (CrB , CrB2 )

2.1. Mechanochemical Synthesis

2.2. Solid state Reaction

2.3. Molten Salt Method

2.4. Low Temperature Synthesis of Chromium Borides

2.5. Chromium Borides by Combustion Synthesis Involving

Borothermic and Aluminothermic Reduction of Cr2O3

3. Suppliers and Price of CHROMIUM BORIDE (CrB , CrB2 )

4. References

1. GENEREL INFORMATION ABOUT CHROMIUM BORIDE (CRB , CRB2 )

Borides of transition metals have attracted considerable interest for their various unique properties. Among these borides, chromium boride (CrB) is currently of great technological importance because of its high melting point, high chemical stability, high hardness and strength. So it has found applications in structure materials.

Chromium borides are used in plasma technology and for high-performance electrodes in electron microscopes, metal matrix composites (MMCs), cutting tools and cermets for machining aluminum.

For the CrB system, six chromium borides (Cr2B, Cr5B3,CrB, Cr3B4, CrB2, and CrB4) shown in next figure . Among them,CrB2 is the most stable compound with a melting point of 2200 C and is a potential candidate as the structural material, hard coating on cutting tools, and protective layer on mechanical parts to resist wear and corrosion.

1. GENEREL INFORMATION ABOUT CHROMIUM BORIDE (CRB , CRB2 )

1. GENEREL INFORMATION ABOUT CHROMIUM BORIDE (CRB , CRB2 )

CrB CrB2

Formula Weight 62.81 73.62

Color - Gray

Theoretical Density

(Kg/m3 X 10-3 )

6,14 5,20

Crystal Structure tetragonal hexagonal

Thermal Expansion

Coefficient (10-6/K)*

12.3 10.5

Thermal Conductivity

(W/M. K) **

20.1 31.8

2. PRODUCTION OF CHROMIUM BORIDE (CRB , CRB2 )

2.1. MECHANOCHEMICAL SYNTHESIS

Ball-milling of elemental powder mixtures without external heat application

has been processed as a mechanism for the mechanochemical synthesis of high

melting point compounds.

Chromium and amorphous boron elemental powder mixtures at atomic ratios

of 1:1 and 1:2 were processed for 10-40h in a planetary ball-mill. CrB2 was

formed at a low yield after 10-30h of milling the 1:2 mixture using tungsten

carbide balls. However, a single phase of CrB2 was found by XRD, after the

as-milled Cr-B (1:2) mixture was annealed at 900 C for 2h. A single phase of

CrB was formed by annealing the Cr-B (1:1) mixture at 1000 C for 2h. Ball-

milling of the elemental powder mixtures before annealing significantly

reduced the reaction temperature necessary for chromium boride synthesis. The

as-milled Cr-B (1:2) mixture contained fewer contaminations (tungsten and

cobalt) than the as milled Cr-B (1:1) mixture. The lattice parameters of the

chromium borides obtained agree with previously reported measurements.

2. PRODUCTION OF CHROMIUM BORIDE (CRB , CRB2 )

2.2. SOLID STATE REACTION

Chromium boride powders can be synthesized at 600 C through a solid-state reaction. The synthesis is carried out in an autoclave by using CrCl3 , Mg and

MgB2 as reactants.The Xray powder diffraction pattern indicates the formation

of orthorhombic CrB. Trassion electron microscopy image shows that typical

CrB crystallites are compossed of floss-like particles with less than 10 nm in

diameter and about 50-100 nm in leght.

2CrCl3 + MgB2 + 2Mg 2 CrB + 3 MgCl2

2. PRODUCTION OF CHROMIUM BORIDE (CRB , CRB2 )

2.3. MOLTEN SALT METHOD

A molten salt (anhydrous aluminum trichloride) method to prepare CrB

nanorods via a reductionboronation route at 650 C in an autoclave be described as follows,

CrCl3 + B + 3Na CrB +3NaCl

Below the temperature of 500 C, the weight gain almost has not changed. From 500 to 1000 C, the weight gain of CrB nanorods experiences four different steps. Below

the temperature of 630 C, the weight gain increases gradually, which indicates that the sample is oxidized by oxygen slowly forming chromium oxide and

boron oxides.

When the temperature is within 630660 C, the weight gain increases significantly indicating that the sample is oxidized rapidly forming oxide layer

gradually at the surface of the nanorods.

2. PRODUCTION OF CHROMIUM BORIDE (CRB , CRB2 )

2.3. MOLTEN SALT METHOD

If the temperature was higher than

700 C, the diameters of the CrB nanorods increased obviously. An

optimum reaction temperature for

the CrB nanorods was about 650

C. The reaction time must be sufficient to ensure the process of

boronation. It was found that 10 h

was needed for the synthesis of

nanorods.

2. PRODUCTION OF CHROMIUM BORIDE (CRB , CRB2 )

2.4. LOW TEMPERATURE SYNTHESIS OF CHROMIUM BORIDES

Commercially available chromium acetate, Cr(CH3COO)3 and boron powder

were used as starting materials. The boron powder was purified by refluxing in

acid to an ethanolic solution of chromium acetate, boron was added .The

resulting dispersion was sonicated for 2 h and evaporated to make a dry mass.

The product was further annealed in inert atmosphere under three different

conditions (i) 400 C for 12 h, (ii) 600 C for 12 h and (iii) 400 C for 6 h and

subsequently at 1000 C for 12 h in an argon atmosphere.

2. PRODUCTION OF CHROMIUM BORIDE (CRB , CRB2 )

2.4. LOW TEMPERATURE SYNTHESIS OF CHROMIUM BORIDES

2. PRODUCTION OF CHROMIUM BORIDE (CRB , CRB2 )

2.4. LOW TEMPERATURE SYNTHESIS OF CHROMIUM BORIDES

a - On heating the mixture of chromium acetate and boron at 400 C, powder X-ray diffraction shows the formation of poorly crystalline CrB .

b - Further heating of the product at 600 C leads to improvement in the crystallinity.

c - Synthesis of CrB at ambient pressure can be achieved above 1400 C and pure phases of CrB have been obtained only at 1600 C

2. PRODUCTION OF CHROMIUM BORIDE (CRB , CRB2 )

2.4. LOW TEMPERATURE SYNTHESIS OF CHROMIUM BORIDES

Chromium boride (CrB) nanowires obtained at

400 C

Chromium boride (CrB)

nanoparticles obtained at

600 C

Chromium

diboride

nanoparticles

obtained at

1000 C

2. PRODUCTION OF CHROMIUM BORIDE (CRB , CRB2 )

2.5. CHROMIUM BORIDES BY COMBUSTION SYNTHESIS INVOLVING

BOROTHERMIC AND ALUMINOTHERMIC REDUCTION OF CR2O3

A variety of transition metal borides have been produced from their constituent

elements through combustion synthesis in the mode of self-propagating high-

temperature synthesis (SHS). When direct combustion between the metal and

boron is not feasible due largely to insufcient exothermicity, the SHS process

involving borothermic reduction of metaloxides has been considered as an

alternative of preparing the corresponding chromium borides.

On the preparation of chromium borides, CrB2 has been the most produced

phase. Obtained CrB and CrB2 in pure form by milling chromium and boron

powders in a planetary ball mill for 2040 h, followed by annealing at 900

1000 C for 2 h. Conducted borothermic reduction of Cr2O3 at 1600 C to produce CrB2.

Through self-propagating combustion involving reduction of Cr2O3 by

amorphous boron.

2. PRODUCTION OF CHROMIUM BORIDE (CRB , CRB2 )

2.5. CHROMIUM BORIDES BY COMBUSTION SYNTHESIS INVOLVING

BOROTHERMIC AND ALUMINOTHERMIC REDUCTION OF CR2O3

Chromiumoxide Cr2O3 ,amorphous boron, and Al powders were employed as

the starting materials to prepare two types of the powder mixtures.

One is composed of Cr2O3 and boron with a molar composition of Cr2O3+ xB.

The other type of the sample adopts Al as the reducing agent and is formulated

by the molar proportion of Cr2O3+ 2Al + yB . The synthesis process of the

Cr2O3B sample essentially combines the reduction of Cr2O3 by B to form

elemental Cr and B2O3 as a by product and the interaction between the reduced

Cr and B to yield boride compounds. On the other hand, chromium borides are

produced along with Al2O3 from the samples containing Cr2O3, Al, and B

powders. The following reactions are two examples of the formation of CrB

and CrB2 from stoichiometric Cr2O3B and Cr2O3AlB samples, respectively.

CrO3 + 4B 2CrB + B2O3

Cr2O3 + 2Al + 4B 2CrB2 + Al2O3

3. SUPPLIERS AND PRICE OF CHROMIUM BORIDE (CRB , CRB2 )

Alfa Aesar / CHINA www.alfa.com

Energy Chemical / CHINA www.energy-chemical.com

Aladdin Reagents / CHINA www.aladdin-e.com

Guangzhou WeiBo / CHINA www.weibochem.com

ABCR / GERMANY www.abcrestore.com

Service Chemical / GERMANY www.chemos-group.com

Price of Alfa Aesar ;

-325 Mesh Powder form 100gr price is 141 Euro.

4. REFERENCES

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