CN100391586C

CN100391586C - Method of synthesizing cubic boron nitride using alkali earth metal fluoride

Info

Publication number: CN100391586C
Application number: CNB200510016653XA
Authority: CN
Inventors: 郭伟力; 贾晓鹏; 马红安; 陈立学; 卜雨洲; 邹广田
Original assignee: Jilin University
Current assignee: Jilin University
Priority date: 2005-03-25
Filing date: 2005-03-25
Publication date: 2008-06-04
Anticipated expiration: 2025-03-25
Also published as: CN1686602A

Abstract

The present invention relates to a method of synthesizing cubic boron nitride with alkali earth metal fluoride, which belongs to the technical field of the synthesis of super-hard material at high temperature and high pressure. Hexagon boron nitride is used as raw material, mixture of CaF2 or/and MgF2 and Li3N is used as catalysts, and LiH is added as additive. After uniform mixing and prepressing forming, the synthesized blocks are assembled by reloading in graphite tubes. Synthesis temperature is 1000 to 1800 DEG C, synthesis pressure is 4.0 to 6.0 GPa, synthesis time is 3 to 8 minutes, and a red-yellow transparent cubic boron nitride monocrystal is obtained after a chemical treatment of the synthetic product. The present invention has the advantages of wide ranges of synthesis temperature and synthesis pressure and a high synthesis yield, which are caused by adding CaF2 or/and MgF2 as catalysts.

Description

Method with the alkali earth metal fluoride synthesizing cubic boron nitride

Technical field

The invention belongs to the HTHP synthetic method field of superhard material, particularly select the method for new catalyst synthesizing cubic boron nitride.

Background technology

The hardness of cubic boron nitride (cBN) is only second to diamond, because it has higher oxidation resistance temperature than diamond, and at high temperature not with excellent specific properties such as iron family element reacts, as abrasive material and make goods such as cutter, emery wheel and hone stone and be widely used in the iron and steel of high rigidity and the manufacture field of alloy material thereof.

Hexagonal boron nitride (hBN) mixes with catalyst, and synthetic under HTHP is the common method of producing cubic boron nitride.General cubic boron nitride synthetic method is the catalyst synthesizing cubic boron nitride with alkali metal such as Li, Mg, Ca and alkaline-earth metal or its nitride, nitrogen boride, shortcoming such as exist synthesis temperature, pressure limit is narrow, and the conversion ratio of cubic boron nitride is low.For example, Japan Patent JP56-140013 is disclosed to be raw material with hBN, and lithium nitride, CaCl2 are made catalyst, and the method for synthesizing cubic boron nitride has obtained high strength under HTHP, the cubic boron nitride monocrystal powder of low impurity content.But the used catalyst of this method is had relatively high expectations to the purity of hexagonal boron nitride and impurity content etc., the synthetic result who wants hexagonal boron nitride purity＞99.8%, boron oxide content＜0.1% and graphitization index＜2 o'clock just can obtain, as hexagonal boron nitride purity less than 98%, boron oxide content greater than 0.15% and the graphitization index greater than 3 o'clock resulting cubic boron nitride granularities just less than 300 orders, conversion ratio is also very low.

The prior art close with the present invention is that name is called " synthetic method of cubic boron nitride " Chinese patent, the patent No. 02116459.2, Granted publication CN1176009C.This patent is a synthesis material with the rough hexagonal boron nitride of purity 96%～99.8%, boron oxide content 0.01%～0.48%, graphitization index 1～6, selects LiNH ₂Make catalyst with the mixture of LiH; LiNH ₂After mixing by weight 6～12: 1 with LiH, mix by weight 1: 7～12 with the hexagonal boron nitride raw material again, pre-molding is after HTHP is synthetic, synthesis temperature is 1350～1800 ℃, synthesis pressure is 4.0～5.5GPa, generated time is 3～8 minutes, and purifying with fusion sodium carbonate obtains cubic boron nitride 70～80 orders, and breaking strength is more than 35 newton.

The cBN of the Chinese patent of " synthetic method of cubic boron nitride " synthesizing high-strength, transparent, equivalance shape under lower synthesis pressure and temperature, and synthetic district is wide, generated time is short, yield is high.Point out simultaneously, " in catalyst mixture, LiNH ₂Contribution to the cBN nucleation is bigger, uses LiNH separately ₂Can only obtain fine grain product.The nucleation amount has been controlled in the adding of LiH effectively, and promotes the g and D of cBN monocrystalline.Simultaneously, also to eliminating the boron oxide impurity influence synthetic to cBN in the raw material, inclusion enclave and defective play an important role LiH in the minimizing product.”

Summary of the invention

The technical problem to be solved in the present invention is, selects novel catalyst and raw material proportioning, makes the purity requirement of hexagonal boron nitride raw material low, and have synthesis pressure, temperature range is wide, the characteristics that conversion ratio is high.

The invention provides a kind of method of synthesizing cubic boron nitride, is raw material with the hexagonal boron nitride, uses CaF ₂Or/and MgF ₂And Li ₃N makes catalyst, and LiH is an additive, synthetic transparent cubic boron nitride.The mixed material that height is pressed into is by weight ratio: hexagonal boron nitride: CaF ₂Or/and MgF ₂: Li ₃N: LiH=1: 0.02～0.1: 0.11～0.2: 0.02～0.05, mix, synthetic under HTHP behind the pre-molding, 1000～1800 ℃ of synthesis temperatures, synthesis pressure 4.0～6.0GPa, obtains the cubic boron nitride product through chemical treatment at 3～8 minutes heat-insulation pressure keeping time.

The purity of hexagonal boron nitride can be selected more than 95%.

HTHP is synthetic down, can carry out on the special-purpose press of superhard material.

Synthetic product is reddish yellow and crystalline form percentage of head rice height, transparent cubic boron nitride crystal.

The present invention adds CaF ₂Or/and MgF ₂, the nucleation rate of cBN is improved, the temperature, pressure zone of cBN growth simultaneously broadens, and the vitellarium of cBN increases in the sample area, thereby has improved the conversion ratio that hBN transforms to cBN.Simultaneously, the present invention reduces the purity requirement of raw material hBN, and synthesis temperature also can be lower, and generated time is shorter, and product is crystalline form percentage of head rice height, transparent cubic boron nitride crystal, is more suitable for industrial production and use.

The specific embodiment

Embodiment 1

With CaF ₂, Li ₃N and LiH mixed by weight 1: 4: 1, pack into after cylindric in the graphite bush by weight mixing and in advance be pressed at 15: 85 with the hexagonal boron nitride of purity 95% again, keep the height of former stock column to equate or than the low 0.5～1mm of height of graphite-pipe with the height of graphite-pipe, put into the pyrophillite piece and be assembled into synthetic piece, synthetic at the enterprising horizontal high voltage of cubic hinge press.At 1100 ℃, under the 4.5GPa condition, heat-insulation pressure keeping 5 minutes, stop heating and treat that temperature reduces the back and takes out sample, after the soda acid purification processes, obtain the transparent cubic boron nitride crystal of reddish yellow, the cBN crystal that obtains, crystalline form percentage of head rice height, the conversion ratio of cBN are 35～40%.

With CaF ₂Use MgF ₂Substitute, by above-mentioned raw material proportioning, assembling, synthetic, purification, obtain the transparent cubic boron nitride crystal of reddish yellow equally, the conversion ratio of cBN is 35～40%.

Embodiment 2

Sample ligand ratio, assembling, synthesis device and temperature, pressure condition are all with embodiment 1, and 3 minutes heat-insulation pressure keeping time, the cBN crystal that laboratory sample obtains after purifying is with embodiment 1, and only granularity is slightly thin, and the cBN conversion ratio is 30%～40%.

Embodiment 3

Sample preparation and synthesis condition are all with embodiment 1, and the heat-insulation pressure keeping time is 8 minutes, and the cBN crystal that obtains after the synthetic product purification processes is with embodiment 1, and crystal size is thicker, crystalline form percentage of head rice height, cBN conversion ratio 35～40%.

Embodiment 4

With MgF ₂, Li ₃N and LiH mixed by weight 4: 5: 1, pack into after cylindric in the graphite bush by weight mixing and in advance be pressed at 20: 80 with the hexagonal boron nitride of purity 95% again, keep the height of former stock column to equate or than the low 0.5～1mm of height of graphite-pipe with the height of graphite-pipe, put into the pyrophillite piece and be assembled into synthetic piece, synthetic at the enterprising horizontal high voltage of cubic hinge press.At 1700 ℃, under the 5.5GPa condition, heat-insulation pressure keeping 5 minutes, stop heating and treat that temperature reduces the back and takes out sample, after the soda acid purification processes, obtain the transparent cubic boron nitride crystal of reddish yellow, the cBN crystal that obtains, crystalline form percentage of head rice height, the conversion ratio of cBN are 45～50%.

With MgF ₂Use CaF ₂Substitute, by above-mentioned raw material proportioning, assembling, synthetic, purification, obtain the transparent cubic boron nitride crystal of reddish yellow equally, and particle mean size is bigger, the conversion ratio of cBN is 40～45%.

Embodiment 5

Sample ligand is than, assembling, and synthesis device and temperature, pressure condition be all with embodiment 4,3 minutes heat-insulation pressure keeping time, and cBN crystal or embodiment 4 that laboratory sample obtains after purifying, only granularity is slightly thin, and the cBN conversion ratio is 35%～45%.

Embodiment 6

Sample preparation and synthesis condition are all with embodiment 4, and the heat-insulation pressure keeping time is 8 minutes, the same or embodiment 4 of the cBN crystal that obtains after the synthetic product purification processes, and crystal size is thicker, crystalline form percentage of head rice height, cBN conversion ratio 40～50%.

Embodiment 7

Use MgF ₂And CaF ₂Make catalyst, by weight MgF ₂: CaF ₂=1: 0.01～100.Use MgF ₂And CaF ₂The CaF of alternate embodiment 1 ₂, raw material assembling, synthesis device, temperature, pressure condition obtain the transparent cubic boron nitride crystal of reddish yellow equally all with embodiment 1, and the conversion ratio of cBN is 40～45%.

Experiment shows MgF ₂: CaF ₂Size, little to the influential effect of the transparent cubic boron nitride crystal of synthetic reddish yellow.

Claims

1. the method with the alkali earth metal fluoride synthesizing cubic boron nitride is a raw material with the hexagonal boron nitride, synthesizing cubic boron nitride product under HTHP, 1000～1800 ℃ of synthesis temperatures, synthesis pressure 4.0～6.0GPa, 3～8 minutes heat-insulation pressure keeping time; It is characterized in that, use CaF ₂Or/and MgF ₂And Li ₃N makes catalyst, and LiH is an additive; The mixed material that height is pressed into is by weight ratio: hexagonal boron nitride: CaF ₂Or/and MgF ₂: Li ₃N: LiH=1: 0.02～0.1: 0.11～0.2: 0.02～0.05; The purity of hexagonal boron nitride is more than 95%.