The vacuum heat treatment with carbonization pulverous boron purifies research

  • Time:
  • Click:142
  • source:KOMANG CNC Machining
Carbonization is boracic with its superior performance, like tall hardness, high standard quantity, low density, tall chemical stability and tall neutron are absorbed sectional etc, course of study already got in contemporary high-tech domain the great attention of people. Often be used to the ballproof armor of the armor Fu cover board of production battleplan, air man; Sharpener of sealing surface of the nozzle of machine of cut of high speed current, mechanical wear-resisting, cutting; Nuclear reactor dominates club and protective screen data; Pyroelectricity changeover component [1] . And the taking of these function divides carbonization boron to make a process have outside Shanghaiguan with its, still have very big concern with its composition. According to B, C phasor is knowable, carbonization boron is a single-phase compound that composition can change inside very wide range [2] , the composition with the mechanical boracic to carbonization function of its goods (B/C is compared) have stronger dependence. Document [3] points out, the hardness of carbonization boron (HV) and fracture toughness (Klc) is in only B/C ＝ 4 when have great value, in B/C ＝ 4 around, follow the accretion of B/C or reduce, HV and K1c present downtrend. Accordingly, to improve the mechanical performance of carbonization boracic goods, obtain very tall HV and KIC value, the chemical part that controls carbonization boracic powder and its product strictly will appear very important. Current, industrial carbonization boracic powder basically is with boron anhydride and coke are raw material, get through legal system of electric arc fusion. Because its reaction is very not complete, the temperature inside furnace distributings not quite even also, bring about its composition is very inhomogenous. And the B2O3 that contains certain amount, B, C. Especially the C of free, B, the agglomeration that although be in,certain moment can promote powder is compact change a course, but content of overmuch free C, B, be opposite to studying other additive again the influence of the agglomeration behavior with carbonization pulverous boron brings inconvenience. Together with, because carbonization is boracic pulverous composition (B/C is compared) inhomogenous sex, if use not via be being changed equably, the carbonization boracic product that the carbonization boracic powder that purifies processing adds the additive agglomeration such as B, C to come out, the likelihood causes its function inhomogenous sex. Accordingly, what use industrial carbonization boracic powder to the experiment is even change reach purify appear very important. For example, document [4] report, to study B is boracic to carbonization hot pressing makes the impact that tastes mechanical function, ceng Yongnong is vitriolic the free pace in as boracic as carbonization of eliminate of boil of solution of heavy chromic acerbity Potassium powder. But compare in the light of total boron and total carbon adjacent 4, the B/C of carbonization boron is inhomogenous, and the industrial carbonization boron that contains free C, B and B2O3 is pulverous, to do not make the BC element in primitive powder produces a loss, this literary grace heats with vacuum adoption method undertook handling to its, purified process and mechanism to undertake analytic discussing to its. 1 experiment method is with average bead diameter 3.

The industrial carbonization boracic powder of 5 μ M is research target, heat treatment has inside furnace of vacuum carbon canal, the vacuum inside furnace is spent be more than 1.

33 × 10-2Pa. Temperature is measured use optical fiber infra-red radiate measures Wen Yi, accuse lukewarm precision to be ± 5 ℃ . Pulverous bead diameter uses Japan to produce SFA granuality analyzer to undertake determining, free carbon content and the constant of character and morals with boracic carbonization use X, ray diffraction appearance consults document [5] undertakes determining. 2 tests result and discuss 2.

The X with pulverous boron of carbonization of 1 different position, ray diffraction pursues as a result the X with the 1 carbonization pulverous boron after be being handled to pass different temperature vacuum, ray diffraction a collection of illustrative plates. By the graph 1 visible, those who follow processing temperature is elevatory, the D ＝ of the carbon in its diffraction chart 0.

The intensity wear off of 335nm develop ray, and classics 1500-1600 ℃ is handled hind, the strongest peak of the carbon in its diffraction chart (D ＝ 0.

335nm develop ray) disappear. Lift further when temperature when 1700 ℃ , the friendly ＝ that carbon appears again in its diffraction chart 0.

335nm develop ray. Nextpage2.

Couplet of 2 processing temperature changes influence of content of carbon of the dissociate in boracic powder to express boron of the 1 carbonization after be being handled for different temperature the X of content of carbon of the dissociate in powder, ray ration analyses a result. By the watch 1 visible, everywhere manage temperature is elevatory, content of carbon of the dissociate in powder drops, and be in 1500, after 1600 ℃ are handled, the free carbon content in powder is reduced for 0. 2.

The effect that 3 temperature couplet changes constant of boracic pulverous character and morals is expressed 2 for boron of different position carbonization powder uses X, the character and morals that ray least square method determines is invariable. See by the watch, compare with primitive powder, the change of crystal lattice constant with the carbonization pulverous boron after be being handled via 1400 ℃ is not big; And in 1500 ℃ above higher temperature handles the carbonization boracic powder after, constant of its character and morals appears to be reduced apparently. 2.

The effect that couplet of 4 processing temperature changes character of boracic pulverous geometry pursues the 2 average bead diameter that are carbonization boracic powder and the relation of the area that compare a list and temperature. By the graph 2 visible, those who follow processing temperature is elevatory, the average bead diameter with carbonization pulverous boron increases, the area that compare a list decreases. Because, heat in the process, of petty powder reuniting is inevitable, lift along with temperature, will appear by soft reunite body to hard reunite the change of body. The powder when microtherm reunites degree is less, bead diameter change is not big; When temperature taller (1700 ℃ ) when, a few fine before grain, form hard reunite body, appear even the adhesion phenomenon of similar agglomeration initial stage, make pulverous dimension increases quickly. 2.

Vacuum of 5 carbonization boracic powder heats those who purify mechanism discuss a watch content of the 3 boron in be industrial carbonization boracic powder, carbon analyses a result. See by the watch, the content of this pulverous total boron and total carbon is about 90.

26 ％ , contain a few free C, B and B2O3. Atom of the B of carbonization boron, C is than making an appointment with 5.

92, and of total boron and total carbon than for 4.

46, the chemistry that is close to carbonization boron is metric than 4. Accordingly, use vacuum to add heat treatment to make mutual reaction of farther bogus of among them free B, C and B2O3 is reached diffuse each other, c of the free B in making carbonization boron pulverous, dissociate, B2O3 is able to eliminate, the composition of carbonization boron is more even, b, C is metriccer than also be close to its chemistry relatively than 4, its mechanism is as follows. (C of the free B in 1) powder, dissociate heats in vacuum the mechanism that B4C creates in the process. Element of B, C generates the reaction equation of B4C to because this reaction belongs to exothermic reaction,be 4B+C ＝ B4C (1) below constant temperature, should have only enough high temperature makes B, C former at activationing, reaction can happen. Document [6] report, element of B, C synthesizes the lowest of B4C to react temperature is 1600K below vacuum condition. Accordingly, should heat when 1600K of temperature prep above, mutual reaction of the free B in carbonization boracic powder, C builds B4C course, it is one of reasons that carbon of the dissociate in industrial carbonization boracic powder drops. By reaction (1) is knowable, about 3.

6 ％ B is used up 1.

0 ％ C, by the watch 3 knowable, 1.

The free C content that the free B place of 51 ％ uses up is 0.

428 ％ . The carbon that B4C forms below vacuum condition between the B2O3 in Nextpage(2) powder and C heats up reductive reaction mechanism, its react equation is ↑ of 2B2O3+7C ＝ B4C+6CO (2) falls in standard reference conditions, reaction (2) begins temperature to be 1772[7] . Apparent, react below vacuum condition (the temperature that 2) begins to happen will lower, response rate also is met faster. By reaction (2) is knowable, about 1.

67 ％ B2O3 is used up 1.

0 ％ C. By the watch 3 knowable, 0.

The free C content that place of 40 ％ B2O3 uses up is 0.

24 ％ . Accordingly, when carbonization boron powder heats in vacuum high temperature when, among them B2Q; With free carbon heats up reductive reaction between C, the effect since the reaction place that the reduces place to rise effect that leaves C to pulverous middle reaches makes B4C than free B and free C is bigger. (3)C diffuses mediumly to react with solid dissolve to carbonization boron mechanism. Heat in vacuum in the process, because rich B carbonization is boracic,with the photograph interface between C two side exist difference of pH indicator of atom of B, C, will produce what C atom diffuses boracicly to leave C outside with B former Yu Xiangyou to carbonization to diffuse, such, undertake ceaselessly along with what diffuse, in its the interface stands by carbonization boracic a side. C atom and primitive carbonization boron produce solid dissolve reaction to fashion new solid solution [8] , make the B of powder of primitive carbonization boracic crystal, C comparing drops, equation of solid dissolve reaction is BxC+yC ＝ BxC1+y (3) and in its the interface stands by free C a side to will press reaction (1) forms new B4C look. Accordingly, can imagine, along with heat of temperature lift and the extension of heat preservation time, reaction of dissolve of C atomic solid and reaction diffuse undertake more will thoroughly, the chemical composition with carbonization pulverous boron also more will even. The place on put together is narrated, when the processing temperature with carbonization pulverous boron is 1400 ℃ , the purify of C of carbon of the dissociate in powder is main with remaining among them the chemical reaction between the photograph is given priority to. Because by the watch 2 visible, the constant of character and morals with the carbonization pulverous boron after 1400 ℃ are handled and its savagery photograph are compared, have change, but change is not big, but by the watch L is known, former free C content is reduced however than latter more. Accordingly, can conclude, the solid dissolve reaction between the free C with right now medium powder and carbonization boron and reaction diffuse to had happened but not complete still, it is dissolve of solid of the C inside lesser around free C and the interface with boracic carbonization limits only within carbonization boracic character and morals, the free C content in bringing about powder drops, because C atom diffuses inadequate reason, because dissolve enters C atomic and the constant of character and morals that is boron of the carbonization inside local little scope only so drops [9] , but the C content in boron of the carbonization inside bigger range did not diffuse because of free C atomic and dissolve and change. So, the change of constant of character and morals with carbonization right now pulverous boron is not big. However the powder after 1700 ℃ are handled is compared with its, because of temperature elevatory, the between each composition content chemistry in powder reacts and diffuse to undertake relatively thoroughly with solid dissolve reaction each other, below the circumstance that comparatives in free C content so, change of former constant of character and morals is bigger, latter however otherwise. When classics 1500-1600 ℃ is handled, because powder is medium,the chemistry between BB2O3 of free C, dissociate reacts and between free C and carbonization boron diffuse to react with solid dissolve the result of joint action, the free C content in powder drops for 0, the character and morals of carbonization boron is invariable (A, c) value also has relatively drop substantially. This shows, carbonization boracic powder is when processing of 1500-1600 ℃ vacuum, among them between free C and carbonization boron diffuse to react with solid dissolve the purify of pair of free C is having decisive effect. 3 conclusion (1) vacuum heat treatment is B of C of the dissociate in eliminating industrial carbonization boracic powder, dissociate, B2O3 and its chemistry the efficient way that composition changes equably, its are optimal processing temperature is 1500-1600 ℃ . (2) vacuum adds heat treatment process in, the carbon of the chemical combination reaction of B of the dissociate in carbonization boracic powder and free C, B2O3 and free C heats up reductive reaction and free C and carbonization boron between diffuse and solid dissolve reaction is carbonization boron the main mechanism that powder is purified and composition changes equably. (The average bead diameter with pulverous boron of the carbonization in process of 3) vacuum heat treatment is followed heat to lift and increase of temperature, when 1600 ℃ are handled, pulverous bead diameter increases for original 2-3 times. CNC Milling CNC Machining