FR2625491A1 - PROCESS FOR OBTAINING PULVERULENT LEAD TITANATE - Google Patents

Abstract

The invention relates to a process for obtaining powdered lead titanate. According to the invention, it consists in preparing a charge from powders of titanium dioxide and litharge or of minium, in calcining the charge obtained at 750-1000 degree (s) C for 10-50 hours and in grinding the product obtained. The Pb0: TiO2 molar ratio in the feed is 1.01: 1.05. The particle size composition of titanium dioxide is as follows: 45-60 microns 5% by weight at most 2-45 microns 90-98% by weight less than 2 microns 5% by weight at most, that of litharge or minium is : 50-100 microns 1% by weight at most 4-40 microns 89-95% by weight less than 4 microns 10% by weight at most. The invention applies in particular to the sealing of parts of electronic devices.

Description

The present invention relates to the field of electronic techniques, and

  more precisely, the processes for obtaining the pulverulent lead titanate. The indicated product can be used as a filler for composite glass-based materials for

  sealing electronic devices.

  The low thermal expansion of lead titanate makes it possible to use the powder-based easily fusible glass composite material comprising, as a filler, powdered lead titanate, for welding ceramic, glass and metal parts in cases where it is necessary to combine a relatively low thermal expansion of the parts to

  combine with a low welding temperature.

  A process is known for obtaining powdered lead titanate by calcining titanyloxalates or lead titanyltartrates isolated in aqueous solutions of corresponding compounds (US, A,

3352632).

  A major disadvantage of the indicated process is the use of expensive and deficient oxalic and tartaric acids. There is also known a process for obtaining powdered lead titanate by calcining the titanium and lead compounds precipitated together in aqueous solutions, such as carbonates and hydroxides taken at the ratio necessary to obtain the lead titanate (EG Smazhevskaya, NB Feldman "Piezoelectric Ceramics", 1971, Publishers "Sovetskoe

radio "(Moscow), pages 50-56).

  However, carrying out the indicated process requires a special stage of preparation of the titanium and lead compounds solutions as well as the neutralization of E solutions and wash water. In addition, the process requires complicated technical equipment. A substantially simpler process is that of obtaining powdered lead titanate from titanium dioxide and litharge or minium, consisting in preparing a charge of powders of the starting constituents and calcining it at a temperature of 600 to 60.degree. 750 C. The litharge or the titanium dioxide and the titanium dioxide are then taken in such quantities that the molar ratio of PbO: TiO 2 in the feedstock is 0.85. The particle size of litharge or minium and titanium dioxide is less than 0.5

micron (US, A, 2607659).

  However, the use in the indicated process of minium or litharge and titanium dioxide having a particle size of less than 0.5 micron results in the production of powdered lead titanate with a particle size of less than 0.5 microns. 2 microns, which renders the latter unsuitable for use as a filler for a readily fusible glass-based composite solder, since lead titanate particles having a particle size less than 2 microns tend to form aggregates and, as part of the composition of the glass-based composite braze material, they form, during its fusion, coagulums preventing the welding of the parts. In addition, the molar ratio of PbO: TiO 2 in the feedstock of 0.85 is insufficient to obtain lead titanate suitable for use as a filler for a composite solder based on since the non-reacted titanium dioxide contained in the obtained pulverulent lead titanate leads to the reduction of the spreading capacity of the composite solder and to

  the deterioration of the quality of the welding of the parts.

  It has therefore been proposed, in a process for obtaining the pulverulent lead titanate, to find a ratio of the charge constituents and a particle size of the starting constituents, as well as to modify the calcination conditions of the charge, so that is ensured to obtain a lead titanate suitable for use as a filler for a glass-based composite material for welding and for hermetically sealing the parts

electronic components.

  The solution to the problem lies in the fact that a process is proposed for producing powdered lead titanate from titanium dioxide and litharge or from minium, a process comprising the preparation of the filler of initial pulverulent constituents. calcination of the charge and the grinding of the product obtained, and according to the invention, the litharge or the titanium dioxide and the titanium dioxide are then used in such quantities that the molar ratio PbO: TiO 2 in the feed is equal to 1 , 01-1.05, the calcination being carried out at a temperature of 750 to 1000 C for 10-50 hours, using the titanium dioxide at the following particle sizes: -60 microns 5% by weight at most 2-45 microns 90- 98% by weight less than 2 microns 5% by weight at most, the litharge or the minium with the following granulometries: -100 microns 1% by weight at most 4-40 microns 89-95% by weight

  less than 2 microns 10% by weight at most.

  The proposed process provides pulverulent lead titanate of the required quality with a particle size of 2-45 microns, whose use as a filler for glass-based composite solders provides hermetic sealing of parts electronic devices, for example parts of integrated circuit envelopes of the DIP type, cathodoluminescent indicators, etc. In this case, when titanium dioxide having a particle size of less than 2 microns in an amount of greater than 5% by weight is used, the spreading capacity of the composite glass-based solder is insufficient and does not achieve hermetic sealing of parts. When using titanium dioxide with a particle size of -60 microns in excess of 5% by weight, more than 1% by weight of lead oxide does not enter lead titanate in reaction, this fact being inadmissible, because during the calcination of the glass-based composite material and during the welding of the parts, there is the dissolution of the lead oxide in the easily fusible glass, leading to the alteration properties of the glass-based composites and

  the appearance of seal leaks.

  When using titanium dioxide with a particle size of between 2 and 45 microns at less than 90% by weight, in the composite glass solder, after welding, microcracks appear, and therefore,

  leaks at the sealing site.

  If one takes the litharge or the minium of a granulometry lower than 5 microns with more than 10% by weight, a caking of these materials, the composition of the initial charge becomes heterogeneous, the content of oxide of lead not entered in reaction of lead titanate increases, and leakage defects

appear in the welds.

  If litharge or minium of a particle size of 50 to 100 microns in an amount greater than 1% by weight is used, the non-reacted lead oxide content of the lead titanate increases and defects occur.

sealing.

  In the case of the use of the litharge or minium of a particle size of 4-40 microns in an amount of less than 89% by weight, the non-reacted lead oxide content of the lead titanate also increases; which becomes the cause of defects

sealing in the welds.

  As mentioned above, the calcination of the initial charge is carried out at a temperature of 750 to 1000lC. At a calcination temperature of less than 750 ° C., the amount of lead oxide not reacted in lead titanate is more than 1% by weight, which is not permissible for the reasons set out above; in addition, this requires an increase

  considerable duration of calcination.

  The pulverulent lead titanate obtained at a calcination temperature greater than 10000C is coarse grains and this fact increases the duration of its grinding. In addition, the loss of lead oxide due to its volatility increases with the increase in the temperature of

calcination.

  It is disadvantageous to perform the calcination for less than 10 hours, the synthesis of the titanate of

lead remaining unfinished.

  It is also disadvantageous to carry out the calcination for more than 50 hours, since this does not give any additional effect but leads to

  unjustified consumption of energy.

  -In the initial charge, an excess of lead oxide (PbO), equal to the losses due to

  evaporation during the calcination of the charge.

  The molar ratio of PbO: TiO2 in the feedstock must not exceed 1.05 since, in this case, unconverted lead oxide may remain in lead titanate in an amount greater than 1% by weight, which leads to the alteration of the properties of the glass-based composite solder and to defects

welding sealing.

  On the other hand, the molar ratio PbO: TiO2 should not be less than 1, 01, since in the interaction mixture (of PbO and TiO2), after the volatilization of PbO, may be a deficiency of PbO resulting in altered properties of the

powdery lead titanate.

  The process for obtaining lead titanate

  powder is carried out as follows.

  To prepare the initial charge, the powdered litharge or minium is used at the following granulometries: -100 microns 1% by weight at most 4-40 microns 89-95% by weight less than 4 microns 10% by weight at most powdered titanium dioxide with the following particle sizes: 60 microns 5% by weight at most 2-45 microns 90-98% by weight

  less than 2 microns 5% by weight at most.

  The constituents indicated are taken in such quantities that the molar ratio PbO: TiO 2 in the feed is 1.01-1.05. The stirring of the initial constituents is carried out in a kneader, making it possible to obtain a load of homogeneous composition, for example

  in a planetary screw mixer.

  The prepared filler is placed in ceramic capsules which are closed with ceramic lids. The capsules are placed in an electric oven, the temperature is raised to 750-1000 ° C. and calcination is carried out in the indicated temperature range.

  for 10-50 hours, to obtain lead titanate.

  The pulverulent lead titanate obtained, after cooling, is discharged from the capsules and subjected to grinding, for example in a ball mill. Then, the pulverulent lead titanate undergoes vibration sieving and the target product is obtained.

  particles are from 2 to 45 microns in size.

  The pulverulent lead titanate obtained as a filler in the glass-based composite solder is used for sealing electronic device parts. Other features and advantages of the invention will be better understood when reading the

  description that will follow of concrete examples of his

production.

Examples 1

  To prepare the initial charge, the following sizes are used: 50-100 microns 0.5% by weight 4-40 microns 92.0 by weight less than 4 microns 7.5% by weight as well as titanium dioxide powder at the following granulometries: -60 microns 4.0% by weight 2-45 microns 95.0% by weight less than 2 microns 1.0% by weight. 74.3 kg of pulverulent litharge and 26.6 kg of powdered titanium dioxide were

  a charge whose molar ratio is 1.04.

  The charge obtained is fired in an electric oven at a temperature of 850 C. The duration of

cooking is 45 hours.

  The titanate of lead formed is milled in a ball mill until a specific surface of 1800 cm 2 / g is obtained, then it undergoes sieving and a powder with a particle size of between 2 is obtained.

and 45 microns.

  Below, all the examples (1 to 9) of realization of the proposed method are shown in Table 1

TABLE I

  ## EQU1 ## ## 1 ## EQU1 ## ##

  of germanulometry, X by weight of the acrylonitrile, by weight of the monomer, and by weight of the monomers.

  ______________________________________ ______________________________________________________________________________________________________________________ ______________________________________ ______________________________________ ## EQU0000 ## ## STR1 ## where: ## STR1 ## (1), (4), (4), (1), (1), (1), (1), (1), (1) (1), (1), (1), (1), (1), (1), (1) and (1). lll 2 5 4 5 6 '7 0n 9 kJ t 11 Il121 3 g 14 i 15 16 g0.5 92.0 7.574, 3 .. 4, 95, [1,26.6 1 34 50 i 45 2 ons 92 , 7.5, 740 - 3 -I i g1

  , 92.0, 7 - - - 4 ,, 095,, 111, (26.6 1.04 750 45

  2 10.5 192.0 7.51 74.3 I. 4.0 1 9-, I, -1 1 26.61, 114I110 ID) 0)

  10.5] 92.0 17.574.3 - - - - 4.0 95.111.1 26.6.01 8fn50 4) 1, O 89, 01, O74, 5 ... 4, 95, 1), 126,61,1158 t5045 - 1,090,0,0) 1,074,43.0,191,1115,026.6 1,103,850,745 FF, 51} 92.0 17,574,3 -, 5-- -. I 9], (11,526.6m1.01 4850g 45 1] 0.5192.0 i7.5 1 74.3- 3- - - 5.0 90, i11, (1 g 26.61.104 g850 4'5 G - 1.0 - 190.0: 9.0 175.84, 95, (1 [5, 1 126, 6 61.05 '51 4, ::':}; 0 1 i The invention relates to the following methods: The invention relates to the following methods: powdered lead titanate obtained in Examples 1 to 9 by the process proposed as well as that obtained according to US, A, 2607659 were subjected to a test on the content of non-reacted (residual) lead oxide (PbO), also determined the plating capacity of glass-based solder composites containing, as a filler, the indicated piomb titanate powders, the sealing temperature using the indicated composite materials of the integrated circuit envelopes

  and sealing the welds of the envelopes.

  The spreadability of glass-based solder composites was determined as follows. The glass solder composite material powder, at a rate of 6.85 g, is cylindrical in pressing at 7.0 MPa and 20 mm tablets are obtained. The tablets indicated are placed on a glass pane, brought to 450 C and maintained at this temperature for 10 minutes. the spreading capacity of the glass-based brazing composite material is expressed by the diameter of a tablet

softened and spread.

  For the tests, 200 DIP-type glass-ceramic integrated-circuit envelopes were prepared for each lead titanate powder obtained in Examples 1-9. For this purpose, pulverulent lead titanate was stirred with another filler material. that is, powdery zircon and the easily fusible glass powder of the following composition, - wt.%: PbO: 85, B203: 13, SiO2: 1, Al2O3: 1. The result is a glass composite material. (welding glass) of the following composition,% by weight: glass easily

  fuse: 53, lead titanate: 42, zircon '5.

  Then, welding, by the known method, glass-ceramic envelopes of the integrated circuits, using the glass-based composite materials of the indicated composition. The welding is carried out in a continuous oven at a temperature of 450 C with a hold of 10 minutes. The test relating to the control of the sealing tightness of the envelopes of the integrated circuits has been carried out by the known method on a heli-searchcher of leakage. The leakproofness of the seal has been determined by the leakage level of h-elium, which must not be

exceed 1.10 -W.

  Below, in Table 2, are summarized the

test results.

TABLE 2

  Capacitance Content Sealing NO Spreading Oxide Lead Welding Temperature Non Material (composite welding level, helium leakage), full reaction OC-based glass W titanate, mm lead, weight

1 1 2 I 23 _4 _5

1 0.4 25.6 450 does not exceed

1-10'9

2 0.3 26.0 - "-

3 0.5 25.1 ---

4 0.2 26.5 - "- -

0.5 25.7 ---

6 0.4 26.8 - "-

7 0.3 27.2 - -

8 0.5 25.8 - -

9 0.6 24.8 - -_

  According to at most welding is impossible - the composite material

  US, A 0.02 of glass solder does not spread.

  As can be seen from the data in Table 2, the proposed process provides pulverulent lead titanate whose use in the glass-based solder composite material provides reliable sealing to the envelopes of the DIP-type integrated circuits. Sealing of the envelopes is then performed at a relatively low temperature (450 C), which keeps the electrical parameters of the integrated circuits. The use of the pulverulent lead titanate obtained by the process proposed in the solder composite materials based on a more fusible glass than the one having undergone the above tests makes it possible to hermetically seal the pieces of

  electronic technique at lower temperatures.

  Thus the welding of the bodies of integrated DIP-type diagrams can be carried out at a temperature of not more than 415 ° C and the welding of the cathodoluminescent indicators - at a temperature no greater than

430 C.

Claims (1)

R E V E N D I C A T I ON   Process for producing pulverulent lead titanate from titanium dioxide and litharge or minium, of the type comprising the preparation of a charge of powders of initial constituents, the firing of the filler and the grinding of the product obtained, characterized in that the litharge or the titanium dioxide and the titanium dioxide are used in such quantities that the molar ratio PbO: TiO 2 in the feedstock is 1.01 to 1.05, the firing of the filler is carried out at a rate of temperature of 750 to 10,000 ° C for 10 to 50 hours, using titanium dioxide at the following particle sizes: -60 microns 5% by weight at most 2-45 microns 90-98% by weight less than 2 microns 5% by weight at most , and the litharge or minium with particle sizes of: -100 microns 1% by weight at most 4-40 microns 89-95% by weight   less than 4 microns 10% by weight at most.