E. Laarz et al /Journal of the European Ceramic Society 21(2001)1027-1035 (=1.54060 A)was used, and finely powdered silicon bench for 4 h in order to equilibrate.Afterwards, sus- [a=5.430880(35)A] was added as an internal standard. pensions were sprayed through a nozzle into liquid The recorded films were evaluated in an automatic film nitrogen for granulation and were then freeze-dried canner, and the unit cell dimensions were refined with The obtained granules were sieved, and the the program PIRUM. The XRD peaks were identified 0.125<d<0.32 mm fraction was used for the sintering by matching them to ICdd data cards of TiC (o experiments. Rheological evaluation was performed on card No. 32-1383)a=4.3274 A, and TiN (ICDD card suspensions that had been equilibrated by 4 h of mag No. 38-1420)a= 4.2417(1)A. XPS analysis of the Tin netic stirring. All rheology experiments were carried out and TiC particle surface composition was performed with a controlled-stress rheometer(UDS 200, Physica using a Mg-Kg X-ray source and a magnetic collimator Messtechnik GmbH, Germany)equipped with a con- lens(AXIS-HS, Kratos Analytical, UK). The powder centric cylinder measuring geometry. solubility was assessed by determining the Ti con centration in solution after ageing in pH=0.8, 6, 10 and 23. Burnout and hot-pressing 12 solutions for 1750 h. Ti was analyzed with a DCP (direct current plasma) emission spectrometer(Spectra The burnout of paa was studied in a thermo- Span IIIB. SpectraMetrics Inc, USA). Microelec- gravimeter, TG (TAG24, Setaram, France)in Ar-6% rophoresis(Zeta Sizer 2000, Malvern Instruments, UK) H2 atmosphere. Prior to sintering, the organic content was used for electrokinetic characterization of TIN and was burned out in a graphite furnace(Thermal Tech TiC particles suspended in 0.01 M NaCI electrolyte. nology Inc, USA). Freeze-dried granules were poured Zeta-potential measurements of concentrated(5 vol % directly into the die of a hot press(Thermal Technology alumina suspensions(0.01 M NaCl background elec- Inc, USA), and the sample was subjected to 28 MPa at trolyte) were carried out with an AcoustoSizerT 1700C for 1.5 h in flowing argon atmosphere. Densities instrument (Matec Science, USA). We used of sintered bodies were measured according to archi analytical grade cher Merck AG, Germany) for medes' principle. The expected densities of the sintered adjustment of ionic Nacl) and pH (HCI and materials were calculated assuming no reactions to take NaOh) place between the components and by using the follow- TiC whiskers and Ti(C N)whiskers were synthesized ing densities: PAl203=3.965 g cm-3, PTin= 5.22 g at 1425 and 1250 C respectively via the carbothermal cm-3, Pric 4930 g cm-3. The microstructure was vapour-liquid-solid growth mechanism.4. 5 The whiskers evaluated with an SEM(880, JEOL, Japan). The com- have a length of about 10-30 um and an aspect ratio of posites containing TiNnano were thermally etched at 15-50(Fig. Ic). The TiNnano powder is pyrogenic and 1500C for 15 min in flowing Ar in order to reveal their was therefore suspended in a water-ethanol mixture microstructure (95/5 wt %)in a glove box filled with nitrogen to pro- mote a controlled surface oxidation .6 After this treat- ment, the solvent was evaporated at 50oC 3. Results and discussion 2. 2. Preparation and characterization of suspensions 3. Powder characterization Concentrated suspensions were prepa mIxIn The TiC and tin powders displayed similar particle Al2O3 powder with deionized water until the required morphology, particle size distribution, and surface area powder volume fraction was reached. The required Equiaxed grains with sharp edges were characteristic mount of poly(acrylic acid) dispersant(Dispex A40, features of both the TiN and the TiC particle morphol- llied Colloids, USA)had been dissolved in the deio- ogy(Fig. 1). The experimentally determined particle size nized water prior to mixing. The anionic polyelectrolyte distributions and specific surface areas are reported in used(denoted as PAA) is an ammonium salt of poly ( Table 2. The TiC and Tin powders were characterised acrylic acid) with a mean molecular weight of Mw= by Xrd to be monophasic with a cell axis of a= 10 000 and a polydispersity of Mw/Mn=1.56. PAa 4.32882(9)A for TiC and a=4.23910(18)A for TIN. In concentrations are given in wt. with respect to the previous XRD studies of nano-sized TiN with much alumina dry-powder weight. In a first milling step, alu- higher oxygen content (an order of magnitude higher mina and PAa were mixed for 30 min at 400 rpm in a than for the TiNnano used in our study ), traces of ana planetary ball mill(Pulverisette 6, Fritsch GmbH, Ger- tase and a substoichiometric TiO2-x phase could be many)equipped with a 250 ml SiAlON milling jar and detected. 8. 9 XPS analysis of the TiC and Tin powder SiAION milling spheres (0=10 mm). After this first surfaces indicated presence of an oxidized surface layer step, the other solid phase(TiC, TiN, TiNnano or whis- and a 20-25 at. level of surface contamination by ali- kers) was added and the sample was milled for another phatic carbon, which is substantially higher than the 3- 10 min. The obtained suspensions were rolled on a roll 10 at usually observed for high-purity ceramic powders6
/
9L-M- O 7     ; )      P 9
L->>- 9  O Q        2     ;   '     ;            ;      A=+F!2  G+J      ;  )      =
JJ    
6=
JJ  2/>7  L
CL O    6=
JJ  2 >/L-7  L
L/C /  O 2 GA< )     
         ! 0)
G)         6G=<8< K )  FK72    )     )               8R-2> M /-  /   /C9- 2   )    J
A 6    7      6<  < ===# < !   = 2 F<72 !     6S  <  --- !'  =  FK7              
      -2-/ ! 
) 2 S           69 '2:7    6-2-/ ! 
    ) 7         < !   6!   <    F<72 4   )      6!   H H )7  D       6
7  8 68
 872 
   6
7     )    /L9  /9-

  ' ) '    '050   2L9    '      /-0-        /909- 6? 2 / 72      )             0  3 6,919 2:7   ' 3 ;            32M         '   '   9-

2 +,+,  $  "    -  $
          ) 3             5    '       2   5    )6 )  7   6J 3 L-  
 F<7    '            3 2   ) )   6    A7      )6  )  7           6
/- ---   ) )  6
6 /
9M2C A    '   2:        )    2 =  ;       A   3   -   L--     )   6A'   M ?  H8 H  )7 5    9-  <  D  <     6TR/- 72    ;        6
      7             /- 2                 L      5 2        )       5            2         '    -2/9N"N-2           3  2 +   '            5  ) L        2   ) 3                 6FJ< -- A)  !   H8 H )7 5      )     )2 +,5,   "  $ %    A        '   H 6HL <  ? 7  0M: 8   2 A                  6     ) = 2 F<72 ?          )         6    ) = 2 F<7     D    > !A  /C--

 /29   U     2 J                     V   2  3                                 )       B /- 
,M9    9
    L
,-  2      '    <! 6>>- ( (72          )     /9--

 /9   U       '       2     5,,  !"    -  
    )     )       2 53                     
  ) 6? 2 /72  3  )          ;          2  
          ) G+J      3   L
>> ,  O  
  L
,/- />  O  2 =  ' G+J             3)    6                 )7                  2>, GA< )   
              3   )    -09 2: '    )       )      0 /- 2: )  '    )   2 ., / -   , 0 1     . $     + 2+3 +45 /-,