Method of fabricating an ltm perovskite product

Abstract

The present invention provides a fused product comprising LTM perovskite, L designating lanthanum, T being an element selected from strontium, calcium, magnesium, barium, yttrium, ytterbium, cerium, and mixtures of these elements, and X designating manganese.

1 . A fused product comprising LTM perovskite, L designating lanthanum, T being an element selected from the group consisting of strontium, calcium, magnesium, barium, yttrium, ytterbium, cerium, and mixtures of these elements, and M designating manganese, the product presenting the shape of a block having a thickness greater than 1 mm or the shape of a particle. 
   
   
       2 . A fused product according to  claim 1 , said perovskite presenting molar proportions l p , t p , and m p  of lanthanum, of element T, and of manganese respectively such that:
     x=t   p /( l   p   +t   p ) and  y= 1−( l   p   +t   p )/ m   p      and: x>0 and x≦0.5; and
 y≧−0.1 and y≦0.24. 
   
   
   
       3 . A fused product according to  claim 2 , in which x≦0.4. 
   
   
       4 . A fused product according to  claim 3 , in which:
 x>0.02 and x<0.35; and/or   −0.05≦y and y≦0.1.   
   
   
       5 . A fused product according to  claim 4 , in which x≦0.3. 
   
   
       6 . A fused product according to  claim 5 , in which:
 0.15<x and x<0.25; and   0≦y.   
   
   
       7 . A fused product according to  claim 1 , having an LTM perovskite percentage greater than 50%, ignoring impurities. 
   
   
       8 . A fused product according to  claim 7 , in which the LTM perovskite percentage, ignoring impurities, is greater than 90%. 
   
   
       9 . A fused product according to  claim 8 , in which the LTM perovskite percentage, ignoring impurities, is greater than 99%. 
   
   
       10 . A fused product according to  claim 9 , in which the LTM perovskite percentage, ignoring impurities, is greater than 99.9%. 
   
   
       11 . A fused product according to  claim 10 , said perovskite being a lanthanum-strontium-manganese perovskite of formula (La) 1-x Sr x ) 1-y MnO 3  with 0<x≦0.5, and −0.05≦y≦0.24, x and y being atom proportions. 
   
   
       12 . A fused product according to  claim 11 , in which the formula of said lanthanum-strontium-manganese perovskite is such that:
 (x<0.5) and (0≦y and y≦0.1).   
   
   
       13 . A fused product according to  claim 12 , in which the formula of said lanthanum-strontium-manganese perovskite is such that:
 (0.15<x and x<0.35).   
   
   
       14 . A fused product according to  claim 13 , in which the formula of said lanthanum-strontium-manganese perovskite is such that:
 x<0.25.   
   
   
       15 . A fused product according to  claim 1 , the element T being a lanthanum dopant selected from the group consisting of calcium, strontium, barium, magnesium, and mixtures thereof. 
   
   
       16 . A fused product according to  claim 15 , the element T being calcium and/or strontium. 
   
   
       17 . A fused product according to  claim 16 , presenting the following chemical composition in percentages by weight and for a total of 100%:
 36%<lanthanum expressed in the form La 2 O 3 <70.7%;   0%<strontium expressed in the form SrO<25.8%;   29.3%<manganese expressed in the form of MnO<41.2%; and   impurities<0.7%.   
   
   
       18 . A fused product according to  claim 17 , presenting the following chemical composition in percentages by weight and for a total of 100%:
 38.4%<lanthanum expressed in the form La 2 O 3 <69.7%;   0%<strontium expressed in the form SrO<25.4%;   30.3%<manganese expressed in the form of MnO<37.2%; and   impurities<0.7%.   
   
   
       19 . A fused product according to  claim 18 , presenting the following chemical composition in percentages by weight and for a total of 100%:
 47.9%<lanthanum expressed in the form La 2 O 3 <69.7%;   0%<strontium expressed in the form SrO<17%;   30.3%<manganese expressed in the form of MnO<35.7%; and   impurities<0.7%.   
   
   
       20 . A fused product according to  claim 19 , presenting the following chemical composition in percentages by weight and for a total of 100%:
 47.9%<lanthanum expressed in the form La 2 O 3 <61.6%   6.7%<strontium expressed in the form SrO<17%;   31.5%<manganese expressed in the form of MnO<35.7%; and   impurities<0.7%.   
   
   
       21 . A fused product according to  claim 20 , presenting the following chemical composition in percentages by weight and for a total of 100%:
 53.9%<lanthanum expressed in the form La 2 O 3 <61.6%;   6.7%<strontium expressed in the form SrO<11.8%;   31.5%<manganese expressed in the form of MnO<34.7%; and   impurities<0.7%.   
   
   
       22 . A fused product according to  claim 1 , that has not been subjected to annealing heat treatment after cooling and/or that does not result from any grinding. 
   
   
       23 . A fused product according to  claim 1 , in the form of a block having thickness greater than 5 cm. 
   
   
       24 . A fused product according to  claim 23 , in the form of a block having thickness greater than 15 cm. 
   
   
       25 . A fused product according to  claim 1 , in the form of a particle, the sphericity of which is greater than 0.5. 
   
   
       26 . A fused product according to  claim 25 , said particle having a size smaller than 4 mm. 
   
   
       27 . A fused product according to  claim 1 , capable of being obtained by a method of fabricating comprising the following steps:
 a′) mixing raw materials providing lanthanum, the element T, and manganese, so as to form a starting charge,   b′) fusing the starting charge to obtain a molten liquid;   c′) cooling said molten liquid until it has solidified completely, so as to obtain a fused product presenting the shape of a block having a thickness greater than 1 mm or the shape of a particle.   
   
   
       28 . A method of fabricating a fused product comprising LTM perovskite, L designating lanthanum (La), T being an element selected from the group consisting of strontium, calcium, magnesium, barium, yttrium, ytterbium, cerium, and mixtures of these elements, and M designating manganese (Mn), the method comprising the following steps:
 a′) mixing raw materials providing lanthanum, the element T, and manganese, so as to form a starting charge;   b′) fusing the starting charge to obtain a molten liquid;   c′) cooling said molten liquid until it has solidified completely, so as to obtain a fused product presenting the shape of a block having a thickness greater than 1 mm or the shape of a particle.   
   
   
       29 . A method according to  claim 28 , in which the quantities of lanthanum, of element T, and of manganese in the starting charge are determined in such a manner that the fused product obtained at the end of step c′) has said perovskite presenting molar proportions l p , t p , and m p  of lanthanum, of element T, and of manganese respectively such that:
     x=t   p /( l   p   +t   p ) and  y= 1−( l   p   +t   p )/ m   p      and: x>0 and x≦0.5; and
 y≧−0.1 and y≧0.24. 
   
   
   
       30 . A method according to  claim 28 , compounds providing the elements L, T, and M together representing more than 90% by weight of the ingredients of the starting charge. 
   
   
       31 . A method according to  claim 30 , in which the compounds providing the elements L, T, and M together represent more than 99% by weight of the ingredients of the starting charge. 
   
   
       32 . A method according to  claim 31 , in which the compounds providing the elements L, T, and M represent, together with the impurities, 100% of the ingredients of the starting charge. 
   
   
       33 . A method according to  claim 28 , in which compounds providing the elements L, T, and M are selected from: SrO; SrCO 3 ; La 2 O 3 ; CaO; CaCO 3 ; Y 2 O 3 ; Yb 2 O 3 ; MgO; MgCO 3 ; CeO 2 : BaO; MnO 2 ; MnO; or Mn 3 O 4 . 
   
   
       34 . A method according to  claim 28 , in which molar proportions l d , t d , and m d  of the elements L, T, and M respectively, in molar percentages based on the sum of the proportions l d , t d , and m d , satisfy the following conditions:
     k   1 ·(1 −x )·(1 −y )≦ l   d   /m   d   ≦k   2 ·(1 −x )·(1 −y )  (1)     and/or       k   1   ·x ·(1 −y )≦ t   d   /m   d   ≦k   2   ·x ·(1 −y )  (2)   where 0<x≦0.5 and −0.1≦y≦0.24, k 1  being equal to 0.8, and k 2  being equal to 1.2.   
   
   
       35 . A method according to  claim 28 , in which molar proportions l d , t d , and m d  of the elements L, T, and M respectively, in molar percentages based on the sum of the proportions l d , t d , and m d  satisfy the following conditions:
     k   1 ·(1 −x )·(1 −y )≦ l   d   /m   d   ≦k   2 ·(1 −x )·(1 −y )  (1)     and/or       k   1   ·x ·(1 −y )≦ t   d   /m   d   ≦k   2   ·x ·(1 −y )  (2)   where 0<x≦0.5 and −0.1≦y≦0.24, k 1  being equal to 0.9, and k 2  being equal to 1.1.   
   
   
       36 . A method according to  claim 28 , in which, in step b′), an arc furnace is used when the fused product is in the form of a particle, or an induction furnace is used when the fused product is a block. 
   
   
       37 . A method according to  claim 28 , in which the fused product is annealed. 
   
   
       38 . A method according to  claim 37 , in which annealing is performed with a soak temperature lying in the range 1050° C. to 1400° C. for a soak duration at that temperature of at least 30 minutes, the soak beginning, when the fused product is in the form of a block, once all of the fused product has reached the soak temperature. 
   
   
       39 . A method according to  claim 37 , in which annealing is performed under an atmosphere containing at least 20% by volume of oxygen. 
   
   
       40 . A method according to  claim 28 , in which step c′) comprises the following steps:
 c 1 ′) dispersing the molten liquid in the form of liquid droplets; and   d 1 ′) solidifying the liquid droplets by contact with an oxygenated fluid, so as to obtain fused particles.   
   
   
       41 . A method according to  claim 40 , in which, in step c 1 ′), said molten liquid is put into contact with an oxygenated fluid. 
   
   
       42 . A method according to  claim 40 , in which, in step c 1 ′) and/or step d 1 ′), said molten liquid is put into contact with an oxygenated fluid containing at least 20% by volume of oxygen. 
   
   
       43 . A method according to  claim 40 , in which the dispersion and solidification steps are substantially simultaneous. 
   
   
       44 . A method according to  claim 40 , in which contact is maintained between the droplets and an oxygenated fluid until said droplets have solidified completely. 
   
   
       45 . A method according to  claim 28 , in which step c′) comprises the following steps:
 c 2 ′) casting the molten liquid into a mold;   d 2 ′) solidifying the liquid cast into the mold by cooling to obtain a block that is solidified at least in part; and   e 2 ′) unmolding the block.   
   
   
       46 . A method according to  claim 45 , in which, in step c 2 ′) and/or in step d 2 ′) and/or after step e 2 ′), said molten liquid that is solidifying is put directly or indirectly into contact with an oxygenated fluid. 
   
   
       47 . A method according to  claim 46 , in which the oxygenated fluid is a gas. 
   
   
       48 . A method according to  claim 46 , in which the oxygenated fluid is air. 
   
   
       49 . A method according to  claim 46 , in which said contact is initiated immediately after unmolding the block. 
   
   
       50 . A method according to  claim 46 , in which said contact is maintained until the block has solidified completely. 
   
   
       51 . A method according to  claim 45 , in which the unmolding of step e 2 ′) is performed before the block has solidified completely. 
   
   
       52 . A method according to  claim 45 , in which the block is unmolded as soon as it presents sufficient rigidity substantially to conserve its shape. 
   
   
       53 . A method according to  claim 45 , in which the rate of cooling of the molten liquid during solidification is always less than 1000 K/s. 
   
   
       54 . A method of fabrication according to  claim 45 , in which the block, obtained at the end of step c′) optionally after annealing, is broken into pieces or powder. 
   
   
       55 . A method of fabricating of cathodes for solid oxide fuel cells (SOFC), the method comprising:
 fabricating the cathodes using a fused product according to  claim 1 .   
   
   
       56 . A fused product comprising LTM perovskite, L designating lanthanum, T designating magnesium optionally mixed with one or several elements selected from the group consisting of strontium, calcium, barium, yttrium, ytterbium, and cerium, and M designating manganese.