FR2707083A1 - New ultrahard materials based on tetravalent metal oxides - Google Patents

Abstract

Use as ultrahard material of at least one oxide of formula MO2, in which M denotes at least one tetravalent metal chosen from Ti, Zr, Hf, V, Nb, Cr, Mo, U, Mn, Re, Ru, Os, Rh, Ir, Pd, Pt, Ce, Pr, Nd, Tb, Ge, Sn, Pb and Te, in the form of metastable phase obtained at high pressure or at high pressure and high temperature. When powders of such oxides are compressed, in fact, new phases are seen to appear whose hardness, estimated especially by determining the compression modulus, is very high. These ultrahard phases can be characterised especially by their X-ray diffraction pattern.

Description

The subject of the invention is the use of high pressure phases

of metal oxides

  tetravalent as ultra-hard materials.

  Diamond is known to be the hardest material currently known, and synthetic diamonds are manufactured industrially, under high pressure and at high temperature, which are used especially in the production of cutting or abrasive tools. The use of diamond, however, has various disadvantages. For example, the

  diamond reacts with ferrous materials and is unsuitable for their machining.

  Other ultra-hard materials are used, such as cubic boron nitride or

  tungsten carbonate. However, their hardness is less than that of diamond.

  The use of ultra-hard materials has been increasing since the 1970s, and even more since the 1980s; see for example IDR (Industrial Diamond

  Review) Volume 50, No. 541, pp. 291-293 (1990).

  There is therefore a considerable interest in obtaining ultra-hard chemically neutral and stable materials, especially for machining metals or other materials, sawing, or polishing materials such as ceramics, minerals, concrete etc. It is also important to look for materials that are harder than diamonds, which allow the machining of diamonds, which is currently impossible: we essentially proceed by cleaving and polishing with diamond powder. Obtaining materials that are harder than diamonds would make machined diamond parts (for example for micromechanics, optics, or electronics), and diamond engraving would be possible (for example to carry out diamond markings). identification or for the realization of

optical networks).

  It has now been discovered that certain tetravalent metal oxides can be obtained in allotropic forms referred to herein as "high pressure phases" constituting

  ultra-hard materials, some of these phases being even harder than diamond.

  It is known that the hardness of a material is conventionally defined as its resistance to scratching (using a material harder than the studied material). However, it is possible to indirectly evaluate the hardness of a material using its compression modulus, which is the inverse of compressibility; see, for example, R. J. GOBLE, Canadian Mineralogist, vol.

  23, pp.273-285 (1985) and R. RIEDEL Adv. Mater., 4, No. 11 pp. 759-761 (1992).

  The subject of the invention is therefore the use as ultra-hard material of at least one oxide of formula MO 2, in which M represents at least one tetravalent metal chosen from Ti, Zr, Hf, V, Nb, Cr, Mo, U, Mn, Re, Ru, Os, Rh, Ir, Pd, Pt, Ce, Pr, Nd, Tb, Ge, Sn, Pb and Te, as a metastable phase obtained at high pressure or at high pressure and high

temperature.

  In particular embodiments, said material may be chosen in particular from those containing a high pressure phase of at least one selected MO2 oxide.

  among those for which M represents Ru, Hf, Ti, Zr.

  Here, the term "high pressure phase" refers to a phase obtained at a pressure at least equal to 1 GPa, at a temperature between room temperature and 2000 C. The invention furthermore relates to a process for the preparation of a ultra-hard material, characterized in that it comprises the step of subjecting a material MO2, in powder form or in sintered form, to compression to a pressure sufficient for a new crystalline phase to appear, and that the materials obtained having a hardness, estimated in particular by the compression modulus, greater than a predetermined threshold are selected. To prepare an ultra-hard material according to the invention, it is possible to use, for example, a powder containing one or more materials MO2, in particular in one of the allotropic forms existing in the natural state. The starting material is subjected to compression, according to

  known methods, up to a pressure sufficient for an ultra-hard phase to appear.

  This compression step can be carried out either statically with known high pressure generators, of the "high pressure" type or of the "high pressure-high" type.

  temperature ", or by the action of a shock wave.

  The devices used are devices of the high pressure or high type

  pressure and high temperature. Such devices are known.

  In some cases, it is possible to operate at room temperature. However, it may be desirable to heat the material to higher temperatures, for example up to 2000 ° C (and generally at temperatures no greater than about 1600 ° C) to operate at lower pressures than those required for training. of phases

  ultra-hard at room temperature, and / or to accelerate the kinetics of the phase transition.

  After a sufficient compression time, which can be determined by simple routine experiments, the material is decompressed to ambient atmospheric pressure. Rapid decompression or possibly slow decompression can be performed when it does not significantly affect the desired hardness properties. Here again, the decompression procedure can be developed in

  each case, by simple routine experiments.

  Of course, for the use as ultra-hard material, only those phases having a hardness, estimated for example according to the compression module, greater than a predetermined threshold, will be retained. For example, it will be possible to retain only the high pressure phases having

  a compression module greater than 300 GPa.

  The materials of the invention can also be obtained by chemical vapor deposition on suitable substrates from the corresponding metals or oxides to which catalysts or solvents are optionally added. They take

  then the form of coating deposited on these substrates.

  The invention also relates to a cutting tool or abrasion, characterized in that it contains at least one ultra-hard material as defined above. Such tools are prepared in a manner known per se, for example by incorporating the ultra-hard material, in the form of a powder of appropriate particle size, into a binder (especially metal powder or resin), and giving the mixture obtained the desired shape by compression molding to

suitable temperature.

  The following examples illustrate the invention.

EXAMPLE 1

  The behavior under high pressures, at room temperature, of

  powders of various MO2 oxides, M being a transition metal such as Hf, Ru, Zr, Ti.

  The starting materials are powders with a particle size of less than 1 pan.

  For compression, a diamond anvil cell of the lever arm type is used.

  A silicone oil is used as a pressure transmitter medium.

  A wide slot in the back face of the diamond allows the recording of the X-ray diffraction pattern on a photographic film placed on a cylindrical support. The X-ray diffraction spectrum is studied in situ by the powder method. X-ray are produced by an anticathode molybdenum tube. Indexing powder diagrams

  is performed using the DICVOL program (D. LOUER and M. LOUER, J. Appl.

, 271, 1972).

  The pressure can be calculated for example, either from the displacement of the fluorescence line of the ruby (HK Mao et al., J. Appl Phys 49,3276,1978), or from the reduction of the parameter of the crystal lattice of silver (K. Syassen and WB HolzapfeL J. Appl Phys 49, 4427, 1978). For this, we add a grain (monocrystal) of ruby or

  silver powder in the sample, in known manner.

  The compression tests of the materials studied gave the results mentioned

below.

  HfO2: The starting product (monoclinic phase I) is transformed into an IL phase,

  orthorhombic for a pressure of about 10 GPa.

  Above 26 GPa a new transition is observed, corresponding to a

  phase i =, new, orthorhombic as phase II, but with a new mesh.

  Above about 40 GPa, we observe the appearance of a new phase IV, quadratic mesh according to the X-ray diagram.

  Between 40 and 47.5 GPa, phases m1 and IV coexist.

  The characteristics of the various phases observed, and in particular: pressure (P) of study of the sample, - interreicular distances observed (d obs.), In. (1010m), - mesh parameters (a, b, c), number of HfO2 units per mesh (Z), -4- are summarized in the following Table 1:

TABLE 1

HfO2

PHASE III IV

P (GPa) 29.5 42.5

3,519 3,529

2,570 2,705

2,419 2,489

2,262 1,813

d obs 1,758 1,550

(A) 1,700 1,365

  1,618 1,530 1,466 1,349 1,242 1,214 a () * 4.85 4.98 b (A) 7.03 c () 3.38 4.26 V / Vo 0.833 0.763

4 4

* = IO-1 m.

  RuO: The starting material (RuO2 with rutile type structure) gives rise to a first phase transition towards 5 GPa (phase II, orthorhombic, coming from a distortion of the rutile phase). Above 12 GPa appears a new phase III cubic, fluorite structure. The characteristics of the phases obtained are summarized in the following table 2:

TABLE 2

RuO2 PHASE II mI P (GPa) 11.3 40

3.134 2.716

2,573 2,367

2,494 1,668

2,194 1,427

d obs 1,698 1,355

() 1,636

1,556 1,449 1,394

1,288

  1,153 1,104 a () 4,615 4,727 b () 4,230 c (A) 3,112 V / Vo 0.966 0.839

Z 2 4

  TiO, 2: The starting material is anatase (phase I). Below 5 GPa appears a phase

  orthorhombic type a-PbO2 (phase II).

  Above 10 GPa, a new phase appears (IT phase), monoclinic.

  No new transition is observed up to 49 OPa.

  The characteristics of phase III (at pressure P = 23.2 GPa) are given in the

table 3.

-6-

TABLE 3

  TiO2 III monoclinic back (3,319 2,860 2,584

2,386

1,967 1,816 1,664 1,606

1,501

1,450

  a = 4.266, b = 4.778, c = 4.794, 3 = 99.15, Z = 4.

  At the compression of the monoclinic starting material, a new phase appears between 8 and 11 GPa. This phase is orthorhombic (orthorhombic phase-I). Between 22 and 27 GPa, a new transition is observed. We get another phase

orthorhombic (orthorhombic-II).

  Although some authors have assigned to such a phase a PbCI2 type structure,

  the results observed here correspond to an orthorhombic structure.

  A new transition appears between 37.5 and 42.5 GPa. The observed results

  correspond to an orthorhombic phase (orthorhombic phase-II).

  The characteristics of the phases obtained are summarized in Table 4.

-7 -

TABLE 4

  ZrO2 PHASE ORTHO II ORTHO mI P (GPa) 27.5 48.5

2,871 2,837

2,729 2,681

2,563 2,498

2,448 1,738

d obs 1,761 1,663

(A) 1,630 1,595

1,556 1,552

1,490 1,470

1,368 1,360

1,253 1,246

  1,224 a () 8,607 6,22 b () 3,707 4, 98 c () 7,044 6.33

V (3) 224.72 197.42

V / Vo 0.798 0.701

Z 8 8

  Compression Modules: Experimental data, obtained from X-ray diffraction patterns, on the relative volume V / V0 versus pressure were interpreted using Birch's state equation: P = (3/2) B0x (I + x) 512 (1 + ax)

  wherein x = (V / Vo) -2/3 -1 and a = (3/4) (B'o-04).

  B is the compression module and B 'is its first derivative with respect to the pressure;

  the subscript zero refers to values at normal pressure (one atmosphere).

  Reference: F. Birch, Phys. Rev. 71, 809 (1947).

  The results obtained are summarized in Table 5 below.

-8-

TABLE 5

OBTAINED MODULE

OXIDE PHASE HAS ONE

COMPRESSION PRESSURE

from (GPa) B (GPa) HfO2 III 26,475

IV 42,553

RuO2 II 5> 300

III 12 399

TiO2 III 10 522 ZrO2 II 22> 300

III 37> 300

  Conclusion: The highlighted phases, namely the mT and IV phases of HfO2, II and mI of RuO2, HI of TiO2 and the orthorhombic phases [I and III of ZrO2, are usable as

ultra-hard materials.

EXAMPLE 2

  A high-pressure generating device of the type with 6 converging anvils is used which is similar in configuration to the apparatuses used in diamond sintering.

  In the compression cell, 50 mg of RuO2 are introduced.

  The pressure is increased to 16 GPa, and the cell is heated to a temperature of 300 C. Then decompressed in a few hours. We obtain the phase III described in

Example 1

  It is also possible to use a "Belt" type device of configuration similar to

  that of apparatus used in the manufacture of diamond and cubic boron nitride.

  In the compression cell, 100 mg of PbO 2 is introduced. The cell is heated to a temperature of 500 C at a pressure of 8 GPa. We observe the appearance of a

new phase, ultra-hard.

-9 -

Claims (9)

  1. Use as ultra-hard material of at least one oxide of formula MO 2, in which M represents at least one tetravalent metal selected from Ti, Zr, Hf, V, Nb, Cr, Mo, U, Mn, Re, Ru , Os, Rh, Ir, Pd, Pt, Ce, Pr, Nd, Tb, Ge, Sn, Pb and Te, in phase form   metastable obtained at high pressure or at high pressure and at high temperature.   2. Use according to claim 1, characterized in that said material   contains at least one high pressure phase of HfO2.   3. Use according to claim 1 or 2, characterized in that said material   contains at least one high pressure phase of RuO2.   4. Use according to any one of the preceding claims, characterized   in that said material contains at least one high pressure phase of TiO2.   5. Use according to any one of the preceding claims, characterized by   the fact that said material contains at least one high pressure phase of ZrO2.   6. Use according to any one of the preceding claims, characterized by   the fact that said material contains at least one high pressure phase of PbO2.   7. Use according to any one of the preceding claims, characterized   in that said material is a high pressure phase of a solid solution of at least   two oxides MO2, M being defined as in claim 1.   8. Use according to any one of the preceding claims, characterized   in that said material is in the form of a powder or in the form of a   coating deposited on a solid substrate.   9. Cutting or abrasive tool, characterized in that it contains a material such as   as defined in any one of the preceding claims.