PREPARATION OF RAW MATERIALS FOR FINE CERAMICS IN PLASMAS

(1)

HAL Id: jpa-00230808

https://hal.archives-ouvertes.fr/jpa-00230808

Submitted on 1 Jan 1990

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

PREPARATION OF RAW MATERIALS FOR FINE CERAMICS IN PLASMAS

E. Juhász, P. Lukács, F. Rosenmann, G. Szentgyörgyi, A. Imre, I. Sajó, A.

Csordás Tóth

To cite this version:

E. Juhász, P. Lukács, F. Rosenmann, G. Szentgyörgyi, A. Imre, et al.. PREPARATION OF RAW

MATERIALS FOR FINE CERAMICS IN PLASMAS. Journal de Physique Colloques, 1990, 51 (C5),

pp.C5-73-C5-81. �10.1051/jphyscol:1990510�. �jpa-00230808�

(2)

CULLOQUE DE PHYSIQUE

Colloque C5, supplgment au n018, Tome 51, 15 septembre 1990

PREPARATION OF RAW MATERIALS FOR FINE CERAMICS I N PLASMAS

E. J U H ~ ~ Z , P. L U ~ C S , F. ROSENMANN, G. SZENTGYORGYI, A. IMRE, I. S A J ~ and A.

CSORDAS

^{T ~ T H}

ALUTERV-FKI Hungalu Engineering and Development Centre, P.O. Box 128, H-1389 Budapest, Hungary

ROsum6.- Les materiaux cCramiques sont indispensables dans la technologie au temperature &levee dues d leurs qualitees mechaniques, Blectriques, magnktiques et optiques. Par celle presentation nous voulon donner les dCtails des differentes types des kquipments de plasma et des technologies qui ont et6 dgveloppees pour prkparer des poudres cCramiques.

Abstract.- Ceramic materials as silicon nitride, aluminium oxide, titanium nitride are promising materials for the high temperature technology due to their good mechanical, electrical, magnetic and optical properties. For preparation of these materials plasma technique represents a very important field, because ceramic powders have been successfully synthetized in thermal plasma reactors. Different types of plasma 'eq-uipments were developed and some technologies were evaluated in this work for preparation of the above mentioned ceramic raw materials.

Introduction

In our paper we summarize the most important parameters and results of powder analysis made by the following processes:

-

Preparation of silicon nitride by vapour-phase reaction of silicon tetrachloride and ammonia in a thermal DC plasma jet and by direct nitridation of pulverized metallic silicon in RF plasma reactor.

-

Production of fine-grain aluminium oxide by oxydation of aluminium chloride in inductively coupled RF plasma reactor with air and/or oxygen.

-

Production of titanium nitride from titanium tetraechloride in a microwave plasma equipment.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1990510

(3)

C5-74 COLLOQUE DE PHYSIQUE

1. Preparation of silicon nitride

1.1. Preparation of silicon nitride from silicon powder

There are several methods known in the literature for preparation of silicon nitride concerning both selection of raw material C metallic silicon, silicon tetrachloride, silicon oxide, organic silicon compounds etc.> and the variety of technological realizations-Taking the available equipments and possibilities into consideration the direct nitridation of metallic silicon has been investigated at first. The process is based on the following reaction:

n i t r o g e n

Si + 2N2 p l a s m a

>

Si,N,

Ammonia was also used during the operation partly as reactant partly as cooling gas. A quartz tube of 100 mm inner diameter was used as reaction chamber. The reaction zone was developed by the use of RF induction plasma <Fig.l.>. Ammonia gas and silicon powder with nitrogen carrier gas were introduced through the feed inlet arranged radially to the reactor.Place of introduction and the amount of plasma forming gas, carrier gas and ammonia gas werechanged during the process. Exhaust gas mixture comprising the fine product was conducted through a cooling/quenching unit to a bag-filter. Operational parameters adopted in the technology are given in Table 1.

Table 1 . Test conditions and ranges of operational parameters Power supply Cfrom mains> 103 kW

Frequency range 440 MHz

Plasma forming gas CN,) 7-9 ~ m ~ / h Carrier gas CN2> 0.3-1.0 ~ m ~ / h Ammonia gas <NB,> l. 6-2.9 ~ m ~ / h

Qualification of Si3N, samples resulting from individual tests was made by determination of nitrogen content. Samples have been taken from the quartz reactor, from the settling/cooling unit and the filter.

Product of best quality, finest grain size and highest nitrogen content has always been obtained in the filter, although in the optimum case nitrogen content turned out to be as low as about 20%. By further confining the operational parameters nitrogen content of the resulting product, i.e. conversion could likely be increased but the figure around 100% would hardly be approached.

This was the reason why the quality of this preliminary product of 20% nitrogen content has been improved by an aftertreatment. By the treatment at 1 4 0 0 ~ ~ in nitrogen flow nitrogen content could be increased to 36.8% (theoretical 39.9) and in the plasma unreacted silicon has become nitridated. Weight gain observed during after treatment conformed to the theoretical exceptable value of the nitridation of unreacted silicon content of the preliminary pr~duct

-

(4)

Silicon nitride appeared in the a-phase ideal for ceramic purposes. The SEM image of the silicon nitride i s given in F i g . 2 . 1 . 2 . Production o f s i l i c o n n i t r i d e from s i l i c o n t e t r a c h l o r i d e In the second phase of our activity the production from silicon tetrachloride in the DC-arc plasma has been investigated according t o the technological flowsheet given in F i g . 3 . Apart from nitride formation hydrochloric acid gas and ammonium chloride are formed in the process according t o the following equations.

n r i r o g o n

3 SiC1, + 4 NU,

p1 a s m a

>

Si,N4 + 12 HCl

n r t r o g e n

3 SiC14 + 16 NH,

>

Si,N, + 12 NH,C1

In the plasma equipment a DC arc is generated in the presence of tungsten cathode and copper anode. The plasma forming gas was nitrogen. Silicon tetrachloride was atomized with nitrogen gas into the reaction area. The exhaust gases, respectively fumes carrying the solid product are conducted t o the cooling/quenching and filtering unit, similarly a s with the previous technology.

Operational parameters of the technology are given in Table 2.

Table 2 . Test c o n d i t i o n s and range o f o p e r a t i o n a l parameters.

DC power supply 36 kW

Plasma power 26 kW

Arc current 58 A

Arc voltage 45 V

Plasma forming gas 2.7 ~ m ~ / h Ammonia

SiCl, feed rate

Carrier gas NZ 0.2 ~m,/h NH,/SiCl, ratio 12

Ammonium chloride obtained a s by-product was removed from the samples at 400 OC. The removal of oxychlorides was performed by dilute HF- solution thus nitrogen content of our best sample turned out t o be 37.8 %.

(5)

COLLOQUE DE PHYSIQUE

Distinctive feature of silicon nitride samples for the two technologies is given in T a b l e 3.

Starting material

Si SiCl,

Nitrogen content X Ctheor. 39.9) 36.8 37.8 Phase analysis: amorphous Si,N4 amorphous Si,N,

a and /3 ^Si,N4 ^{a sand}(3 Si,N,

Si NH,C1

Heat-treated sample a and f i Si,N, a and /3 Si,N,

a 0 13 Si3N, ratio 3 : l 5 : 1

Specific surface area:

green sample 28.9

-

heat-treated sample 9.2 19.4

2. Production of fine-grained high purity A 1 2 0 3

There is a growing demand world-wide for aluminium oxide products made for special purposes. Conventional processes can hardly keep abreast of the demand on purity, grain size and morphological parameters. One of the new methods could be the production of A1,0, of special feature from anhydrous aluminium chloride.

Basic reaction of the technology:

The test were carried out in a DC-arc plasma eguipment and in a RF plasma equipment, the latter having been outlined earlier. Sketch drawing of the DC-arc plasma equipment and the attached reactor is given in Fig.4.For the case of DC-arc plasma aluminium chloride vapours were introduced at 350 OC and for the case of RF plasma solid aluminium chloride of homogeneous, narrow grain size distribution was introduced with air stream into the reaction area. Operational parameters are given in T a b l e 4.

Table 4. Operational parameters for production of A1203

Nominal power Arc current Arc voltage Plasma power

Plasma forming gas

Carrier gas

DC-plasma RF-plasma

20 kW 65 kW

100 A 135 V

13.5 kW 38.2 kW

5.5 ~ m ~ 0 h air 16.0 ~ m ~ / h air 1.5 ~m,/h 0, 1.5 ~ m ~ / h air

(6)

Quality parameters of aluminium oxide produced by these technologies are given in Table 6.

Table 6. Feature of aluminium oxide powders synthetized in DC-plasma in RF-plasma Phase analysis 8 -,A1203 90 % 6-1-9

-

^A120,³⁰^%

a

-

A120, 10 % a

-

A1203 70 %

Specific surface area 10.9 30 m2/g

The SEM images of A120, powders are given in Figs.5 and 6.

3. Preparation of titanium nitride from titaniun tetrachloride in microwave plasma equipment.

Recently technology has been worked out for production of titanium nitride powder from titanium tetrachloride in a microwave plasma

eguipment. The technology is based on the following chemical reaction :

nr t r o g o n

TiC1, p l a s m a

>

TiN

The flowsheet can be seen in F i g . ? . Titanium tetrachloride vapour with hydrogen carrier gas was introduced into the plasma reactor where a nitrogen plasma is generated and the reaction takes place.

The fine product was filtered and the chlorine containing exhaust gas was introduced into the absorber.

The most important technological parameters were:

Plasma power 10 kW

Plasma generating gas <NZ> 2.0 ~ m ~ / h Carrier gas CH,> 0.4 ~m'/h

Temperature of liguid TiC1, 56 OC

In the filter-bag very fine black powder was collected and analized. The SEM image of the TiN powder is given in Fig.8.

Specific surface area of the product was 30.9 m2fg.

4. Conclusion

It has been demonstrated that different of plasma techniques are appropriate way for preparation ceramic powders, as Si3N4, TiN and A1203. Technologies have been work out for production of the above mentioned materials.

(7)

c5-78 COLLOQUE DE PHYSIQUE

Fig. l.

-

RF induction plasma

Fig. 2.

-

^SEMimage of Si,N,

(8)

Fig.

Fig. 4 . and

r

- -

₁

C3NTRCL U E i i T

>C\:!!!

--? .SU??!Y U N i T

3.

-

Technological f 10wc;hppt. fnp n ~ n d ~ ~ r t i n n nf S i N f ~ n m

SiC1,

-

DC plasma equipment the attached reactor

I

(9)

COLLOQUE DE PHYSIQUE

Fig. S .

-

^SEM^{image of}A 1 2 0 3 powder produced in DC-plasma

Fig. 6.

-

^SEM^{image of}A 1 , 0 , powder produced i n RF-plasma

(10)

Fig. 7.

-

Florsheet for production of TiN in micro-wave plasma eaui~ment

Fig. 8.

-

^SEMimage of TiN powder