E驅≈3S Journal of the European Ceramic Society 21(2001)1027-1035 www.elsevier.com/locate/jeurc Colloidal processing of Al2O3-based composites reinforced with tiN and TiC particulates, whiskers and nanoparticles Eric laar a, Mats carlsson b,*, BenoitⅤiⅤie Mats Johnsson Mats Nygren b, Lennart Bergstrom Institute for Surface Chemistry, PO Box 5607, S-114 86 Stockholm, Swe dEpartment of Inorganic Chemistry, Stockholm University, S-1069/ Stockholm, Sweden Received 29 June 2000; received in revised form 13 October 2000: accepted 21 October 2000 o. A colloidal processing route has been developed for the preparation of dense and homogeneous Al2O3-TiN/TiC composites.The ispersion and rheological properties of mixtures of TiN or TiC particulates and Al,O3 particles were investigated using electro- kinetics and steady-shear rheology. We found that well-dispersed aqueous suspensions with low viscosity could be prepared by adding a poly(acrylic acid) dispersant and controlling ph in the alkaline range. This processing scheme was also suitable for pre paration of whisker and nanoparticle composite suspensions. The alumina-based composite suspensions with a secondary-phase concentration of 25 vol. were freeze-granulated and hot-pressed, and the resulting bodies were fully densified with well-dispersed secondary phases. Homogeneous Al2O-TiN nanoparticle composites could only be prepared with additions of up to 5 vol% nanoparticles; higher additions resulted in agglomeration and subsequent grain growth of the nanoparticles. C 2001 Elsevier Science Ltd. All rights rese Keywords: Al2Or-TiC: Al2Oy-TiN; Composites; Microstructure-final: Suspensions; TiC: TIN 1. ntroduction with homogeneous microstructure. Based on thorough powder characterization and on the results of dispersion Mechanical properties of ceramic materials are experiments, we have developed an optimized proces- strongly dependent on their microstructure. The frac- sing scheme and assessed its applicability to systems ture toughness, for instance, can be improved sub- containing TiN and TiC with a wide range of morphol- stantially by ade dding a secondary reinforcing phase to ogies. Thus, the preparation of composites containing the matrix. It has been shown that the addition of a tin micronsized TiN and TiC particles, nanosized Tin par- or TiC phase to an alumina matrix increases hardness, ticles, and TiC and Ti(C, N)whiskers has been investi fracture toughness and thermal shock resistance at gated. The results will be applied in a forthcoming temperatures up to 800oC. In order to optimize the investigation of the mechanical properties(e.g. thermal properties, the reinforcing particulate phase must be shock resistance)of Al_ O -TiN/TiC compacts. Experi- well dispersed in the matrix. Mixing, deagglomeration mentally, our study has included mainly electrokinetic and dispersion of the reinforcing components are com- and rheological characterization of aqueous composite monly performed in a liquid medium, preferably water. suspensions and microstructure evaluation of sintered Additions of dispersing agents and/ or manipulation of bodies by means of scanning electron microscopy the solution properties, e.g. the pH value, are frequently used to optimize the suspension properties In this work, we have attempted to develop an aqu- 2. Experiment eous colloidal processing route for preparating well-dis- persed powder mixtures in the AlO3-TiN/TiC systems, 2.1. Powder characterization which upon densification would yield dense compacts The manufacturer specifications of the starting pow ders are given in Table 1. For simplification we will refer to the nano-and micronsized titanium nitride powders 0955-2219/01/S. see front matter C 2001 Elsevier Science Ltd. All rights reserved. PII:S0955-2219(00)00302-2
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E. Laarz et al. Journal of the European Ceramic Society 21(2001)1027-1035 TiNnano and TiN, respectively. BET-surface area and Scanning electron microscopy, SEM (JEOL 880, particle-size distribution measurements of the as- Japan), and transmission electron microscopy, TEM received TiC, TIN and TiNnano powders were obtained (JEOL 2000FX, Japan), were employed to gain infor by means of BET nitrogen adsorption analysis(Flow mation on the particle morphology(Fig. 1). X-ray Sorb lI 2300, Micromeritics, USA)and X-ray gravita- powder diffraction(XRD) patterns of the TiC and TiN tional sedimentation analysis(Sedi Graph 5100, Micro- powders were obtained using a Guinier-Hagg focusing meritics Instrument Corporation, USA), respectively. camera with subtraction geometry. Cu-Kal radiation Table I Manufacturer specifications showing particle size and chemical ana the different powders us TIN Tinman Al2O3 H C. Starck Sumitomo STD 120 Grade c AKP 30 cle size(um) (BET equivalent pherical diameter) 0.009 O(wt % Cl(wt%) <50 o'e So 9 Fig 1. Micrographs of as-received powder and whisker materials:(a)TiC; (b)TiN;(c)Ti(C N)whiskers: (d)TINnano particles
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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 powders
6 /9L-M- O 7 ; ) P 9L->>- 9 O Q 2 ; ' ; ; A=+F!2 G+J ; ) =JJ 6=JJ 2/>7 LCL O 6=JJ 2 >/L-7 LL/C / O 2 GA M /- / /C9- 2 ) JA 6 7 6 !A /C-- /29 U 2 J V 2 3 ) B /- ,M9 9 L,- 2 ' >- ( ( 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 +4 5 /-,
E. Laarz et al / Journal of the European Ceramic Society 21(2001)1027-1035 The solubility of TiC and Tin powders in water is neg- for TiN and TiC powders are somewhat less consistent gible (However, since non- observed. The surface oxides passivate the TiN and Tic oxide ceramic powders are thermodynamically unstable materials, protecting them from further oxidation inin air and water, these differences are not unexpected aqueous environments. and can be attributed mainly to different degrees of surface oxidation. For example, it has been shown ear- 3.2. Dispersion in aqueous medium lier that the synthesis route and post-synthesis treatment of Si3N4 powders strongly affect the surface oxygen The oxidized TiC and tin powders exhibited iden content and the correlated area density of potential ical isoelectric points at pHicp 4.3 in NaCl electrolyte determining surface groups. 16, 17 Accordingly, increasing solutions(Fig. 2). The isoelectric point of TiC whiskers surface oxidation will shift the isoelectric point of the the isoelectric point of the a-alumina powder is much the value for the less acidic oxide TiO2(pHiep o/s ards was determined to be pHiepa43 as well. In comparison, acidic TiN and Tic powders more and more tow higher(pHiep9. 2). However, as shown in Fig. 2, upon Based on our studies of the surface chemistry of TiN addition of 0.5 wt. PAA to the alumina suspension and TiC, we developed the processing scheme depicted the pHiep shifts to acidic values(pHiep 3)due to poly- in Fig. 3, which can be employed for preparation of electrolyte adsorption 10-12 Measurements at various Al O -TiN/TiC composite suspensions and sintered ionic strengths confirmed that NaCl acts as an indiffer- bodies. As shown in detail in previous work, 8-l0 well- ent electrolyte in all cases(not shown). The zeta-poten- dispersed a-Al2O3 suspensions with an inherent suspen tial values for Al2O3 suspensions compare very well with sion pH value of A9 are obtained by simply mixing previous results. Previously reported pHicp-values deionized water, powder, and >0.2 wt. ammonium alt of PAA. according to our processing Table 2 done in the first milling step and in the next milling step Particle size distribution and specific surface area of the as-received tin or tic is added. In this manner heterocoagulation TiC and TiN powders is prevented, as can be seen from steady-shear measure TiN ments on suspensions with 20 vol. solids loading Fig. 4). Before and after adding tin or TiC, the sus- article size distribution(um) pensions show almost no shear thinning, thus indicating a well-dispersed suspension. However, if addition of PAA is omitted, a flocculated strongly shear-thinning ET surface area(m-g-) suspension is obtained(Fig 4). Clearly, the absence of BET equivalent spherical 0.45 0.026 diameter(um) flocculation is related to the electrostatic repulsion between alumina particles with adsorbed PAA layers e-TiC TiC(Whisker) Al O -o AL o,(0.5 wt% PAA) H Fig. 2. Zeta potentials of the powders used in 0.01 M NaCl electrolyte solution
) 6NM 7 ' ) 8 . ) ' ) 68R-2>7 ; ' 6/-- 7 ' 2 3 ' 3 5 ' 2 5,+, #$ 7 " 3 3 8 L2 ) 6? 2 72 8 L2 2 = 68 ,272 8 ' ? 2 -29 2: A 8 ' 68 7 ) ) 2/-/ ! ' ; I ) 6 72 ' ' ) ' 2/-/ A ' ) 8 ' . I 8 8R09 > , / /L 8 2/9 8 ' 3 ) ) I 3 ) I 3 2 ? 3 ) ) # ) ' ? 2 ) 01 2 ' >/- 8 ' , ) ) 3 W-2 2: A2 ; 3 2 = ' ) - '2: 6? 2 L72 # 2 8 ' A U ) 6? 2 L72 ) U A ) A ; ' - " 8 23 "/M /29 /2 0 "9- 2 2/ 0 ">L 92L 2L 0 # 6 / 7 2C 2/ LL2, # 5' 67 -2L9 -2C -2-M ? 2 2 S -2-/ ! ) 2 /-- ., / - , 0 1 . $ + 2+ 3 +4 5
E. Laarz et al /Journal of the European Ceramic Society 21(2001)1027-1035 and TIN or TiC particles which, according to Fig. 2, are not change the flow behavior compared to suspensions also highly negatively charged at pH=9 containing 25 vol. micron-sized TiN. a slight viscos- Viscosity measurements on 20 vol. TiC suspensions ity increase at 10 vol. TINnano concentration is obser Fig. 5)suggest that the negative surface charge is high vable, and even higher concentrations lead to nough at pH-77 to prevent homocoagulation. At substantial shear-thinning(Fig. 6). This effect might be lower pH the surface charge is apparently too low, related to a crowding effect or an induced aggregation though, and flocculation takes place. In comparison, the due to changes in suspension pH with addition of H of Tin samples must be increased to 10 to achieve a TiNnano. The pH of an alumina suspension dispersed well-dispersed suspension with a Newtonian shear with 0.5 wt. PAA decreases from 9.1 to 8.2 upon response(Fig. 5). Fig. 6 shows the flow curves of com- addition of 20 vol. TiNnano which can result in posite suspensions containing TINnano. USing nano- enhanced homocoagulation of the TiN particles(Fig. 5) sized TiN up to 5 vol. of the total solids loading does Another factor contributing to the high viscosity might be the interaction between TiNnano particles and PAA macromolecules. Previous results on the electrokinetics Mixing and Dispersing(I) Alos and rheology of TiNnano particles dispersed with poly Ho+ PAA acrylic-type dispersants 9. 4+ imply that PAA can be H 9 adsorbed on titanium nitride. These studies suggested that adsorption occurs even at a ph where both parti- Mixing and Dispersing(Il) cles and polymer carry negative charges. Hence, it is Addition of tintic possible that in our system weak adsorption ( 1.e adsorption below saturation level) of PAA on TiN causes bridging flocculation at high TiNnano particle Freeze Granulation and concentrations and, thus, a higher suspension viscosity Freeze Drying Summarizing the results of our dispersion experi ments, we can state that well-dispersed, low-viscous composite suspensions with 20-25 vol. solids loading (minimum viscosities of the composite suspensions were Sieving Granules in the range 3-4 mPa s)can easily be produced with all investigated alumina-based composite systems by using the same processing scheme. An additional advantage Hot Pressing in Ar of the chosen processing scheme is its tolerance towards at1700°C,28MPa,90 variations in degree of surface oxidation of the non- oxide components, which can be difficult to control in Fig 3. Processing scheme for composite preparation industrial practice A2O325%TN(no。PAA) 102[△42°325%TNQ5w%PA 103E°425%T(a5w%PA) a888. 0.5 wt% PAA 10 000 Rate [s" Fig 4. Steady-shear flow curves of 20 vol. suspensions at pHR9
? 2 ) ' ) 8R,2 & ) - '2: 6? 2 97 ' 8RC2C ' 2 8 ) U 2 = 8 /- ' 6? 2 972 ? 2 M U ' 2 F 9 '2: U ' 9 '2: 2 ' ) /- '2: ' ' 6? 2 M72 I I 8 2 8 -29 2: A ,2/ >2 - '2: 6? 2 972 ' ) A 2 A ' ) ) ) ) > , /L ) A 2 ' 8 ) ) ' 2 8 ) 62 2 ' 7 A U ' )2 < 3 ' -09 '2: 6 ' 0L A 7 ) ' ) ) 2 ' ' 3 3 X 2 ? 2 L2 < ) U ' - '2: 8,2 ? 2 2 A 2 ., / - , 0 1 . $ + 2+ 3 +4 5 /-/
E. Laarz et al / Journal of the European Ceramic Society 21(2001)1027-1035 TiG 1000 Shear Rate [s"] Fig. 5. Steady-shear flow curves of 20 vol. TiN and TiC suspensions in 0.01 M NaCl electrolyte in the range D101 O ALO-10%TiN 口A2Q25%Ti Shear Rate [s] Fig. 6. Steady-shear flow curves of 20 vol. composite suspensions containing 0.5 wt. PAA at pHA9. 3.3. Hot-pressing and microstructure evaluation However, their number decreased with increasing PAA concentration and at 0.5 wt. Paa addition the From TG studies, it was found that PAA was burned- microstructure was homogeneous with almost no out completely at 600oC in an Ar-6% H2 atmosphere. agglomerates(Fig. 7a). This may be related to the effect Accordingly, this temperature was chosen to burn out of pH changes on the colloidal stability of the secondary the organic content prior to sintering Tin phase as discussed in the foregoing section; the After hot-pressing, the TiC and TiN particle compo- higher buffer capacity of the suspension at higher PAA sites were fully densified( Table 3). The amount of PAa concentrations probably reduces the pH change that added was found to be more critical for microstructure induced by addition of the acidic Tin phase. The col- homogeneity of AlO3-TiN composites than for Al2O lodal stability of the secondary TiC phase is not sensi- TiC composites Agglomerates of Tin particles could be tive to pH changes in the alkaline range as indicated detected in the microstructure of Al2O3-TiN composites by rheology measurements (Fig. 5). Accordingly
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E. Laarz et al / Journal of the European Ceramic Society 21(2001)1027-1035 homogeneous and agglomerate-free microstructures of much dependent on the added amount of titanium 2O TiC composites were obtained at both 0. 25 and nitride. All nano composites contained micron-sized 0.5 wt. PAA content(Fig. 7b) TIN agglomerates, in amounts increasing with increas- Composites containing TiC and Ti(C, N) whiskers ing TiN content. In the samples containing 5 vol. exhibited high sintered densities, though slightly lower TiNnano the particles and particle agglomerates were than the particle reinforced composites(Table 3). With well dispersed and homogeneously distributed in the an addition of 0.5 wt. PAA, the resulting micro- matrix phase. The particles are located both within the structure show well-dispersed phases but also traces of alumina grains and at the grain boundaries(Fig. 9a) porosity(Fig 8). The whiskers have a preferred orien- However, the alumina grain coarsening during sintering tation perpendicular to the hot-press axis. Obvious was pronounced. At 10 and 20 vol. TINnano, the alu defects in the microstructure are due to fibre pull-out mina grain coarsening was suppressed; Tin particles during polishing of the samples. XPS measurements formed large agglomerates at the alumina grain bound indicated a high amount of free carbon on the whisker aries, thus acting as grain growth inhibitors(Fig. 9b and surfaces. The graphite might weaken the bonding c). Based on these results it is expected that using up to between whisker and alumina matrix, thus facilitating 5 vol. TINnano particles in combination with fibre pull-out. Possibly, the hydrophobic graphite also reduced sintering temperature will result in a micro- promotes the formation of air bubbles, which are diffi- structure with smaller TiN agglomerates and less exces cult to remove during slurry processing sive alumina grain growth Composites containing TiNnano particles were fully densified (Table 3)and exhibited microstructures very Table 3 Compositions of sintered samples and measured density after hot The aim of this study has been to develop an aqueous pressing colloidal processing route suitable for Al2O3-TIN/TIC Compositi Amount of PAA added Final density with respect to dry l2O3(wt.%) Alox 3 Al, 25 vol %o TIC 4 Al,Or25 vol% TiC 0.5 5 AlOr-25 vol% TIN 0.25 6 Al,Or-25 vol% 7 Al,Or5 vol% 8 AlOr10 vol. 10Al2O3-20vol.% 0000000098 n Ti(C, N)whiskers I1 Al,O325 vol% Fig 8. SEM micrograph of the sample cross-section perpendicular to the pressing direction of hot-pressed Al2Or-20 vol Ti(C, N)whisker composite(0.5 wt% PAA) 18 Fig. 7. SEM micrographs of the sample cross-section perpendicular to the pressing direction:(a)Al2Or-25 vol TiN composite (0.5 wt% PAA); b)Al2Or25 vol TiC composite(0.5 wt. PAA)
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E. Laarz et al / Journal of the European Ceramic Society 21(2001)1027-1035 1 Fig 9. SEM micrographs of thermally etched cross-sections parallel to the pressure direction of hot-pressed Al2Or-TiNnano composites (0.5 wt% PAA):(a)AlO3-5 vol TiNnano(the dark vertical line is a grain boundary between two large alumina grains); (b)Al2Ox-10 vol % TiNnano:(c) AO-20 vol %TIN systems, which can be used for preparation of composites 100% of the theoretical density was accomplished after with dense and homogeneous microstructures Compo- sintering. The homogeneity of Tic containing compo sites containing micron-sized TIN and TiC, nano-sized site microstructures was not affected by pH variations in TiN (30 nm mean size), TiC whiskers and Ti(C, N) the alkaline range during wet processing. For Al2O3 whiskers were investigated. By characterizing the sur- TiN composite materials, highly alkaline processing face chemistry of micron-sized TiN and Tic powders we conditions are preferred in order to prevent agglomera were able to define appropriate conditions for the wet- tion of TiN particulates. varying the content of Tinnano processing step. By first dispersing alumina with 0.5 revealed that there is an optimum concentration below wt% PAA and then adding the tiN or TiC phase, well which excessive alumina grain growth occurs whereas at dispersed and colloidally stable composite suspensions higher concentrations Tin particles tend to form with 20 vol. solids loading could be obtained. The agglomerates at the grain boundaries. The location of good colloidal stability relates to repulsive electrostatic the optimum concentration probably depends on the forces between the alumina particles with adsorbed hot pressing conditions. The role of processing para- PAA layers(pHien 3)and the TiN or TiC particles meters in the high-temperature densification step and (pHiep4.)at or above the inherent pH=9 of the sus- their influence on mechanical composite properties is pension. After freeze-granulation of the composite sus- the subject of ongoing investigations pension and freeze-drying of the granules, the organic content could be burned out by heating for 15 min at 600C in a graphite furnace Sintering was accomplished Acknowledgements in a hot-press furnace with flowing argon at 1700C and 28 MPa for 1.5 h. The assessment of composite micro- This work has been performed within the framework structures showed that the used processing scheme is of the Brinell Centre(thematic network"Ceramics and applicable to all investigated composite materials. In all nanocrystalline materials"and"The Brinell Centre- cases it is possible to obtain well-dispersed secondary Inorganic Interfacial Engineering). Financing by the TiN and TiC phases in the alumina matrix phase by Swedish Foundation for Strategic Research(SSF), the controlling suspension pH and added amount PAA. 98 Swedish National board for Industrial and Technical
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E. Laarz et al /Journal of the European Ceramic Society 21(2001)1027-1035 1035 Development (NUTEK) and the industrial partner 9. Wasche. R. Steinborn. G. Baader. F: Elektrokinetische Mes- (Erasteel Kloster AB, Ericsson Cables AB, Hoganas sungen zur Charakterisierung wassriger nanodisperser TIN-Sus- AB, Kanthal AB, OFCON Optical Fibre Consultants pensione. Fortschrittsber. DKG, 1994. 9(5), 151-158 (in AB, Sandvik AB, Seco Tools AB, Uniroc AB) is grate German 10. Cesarano Ill, J. and Aksay, I. A, Processing of highly con- fully acknowledged centrated aqueous a-alumina suspensions stabilized with poly electrolytes. J. Am. Ceram Soc., 1988, 71, 1062-1067 I1. Bergstrom, L, Rheological properties of Al2OrSiC whisker References mposite suspensions. J. Mater. Sci., 1996, 31 57-5270 12. Santhiya, D, Nandini, G, Subramanian, S, Natarajan, K. A 1. Whitney, E. D.(ed ) Ceramic cutting tools- materials, de and Malghan, S G, Effect of polymer molecular weight on the nt, and performance. Noyes Publications, Park Ridge, USA, adsorption of polyacrylic acid at the alumina-water interface. Colloid Surf..A,1998,133.157-163 2. Johansson, K.E. Palm. T and Werner. P. E, An automatic 13. Nass, R, Albayrak, S, Aslan, M. and Schmidt, M, Colloidal microdensitometer for X-ray powder diffraction photographs. J. processing and sintering of nano-scale TiN. In Ceramic Transac- Phws.Sci. Instru.,1980.13,1289-1291 ons. Vol. 51. ed. H. Hausner. G. L. Messing and S.I. Hirano 3. Werner, P. E, A fortran program for least-squa merican Ceramic Society, Westerville. 1995 rystal structure cell dimensions. Arkiv for Ken ares geg n mesta Shih. C.J. and Hon. M.-H.. Electrokinetic and rheological 516. properties of aqueous TiN suspensions with ammonium salt of 4. Ahlen, N, Johnsson, M. and Nygren, M, Carbothermal synth (methacrylic acid). Eur. Cere oc.1999,19,.2773- esis of TiC whiskers via a vapour-liquid-solid growth mechan- 2780 ism.J.Am. Ceran.Soc.,1996.79,2803-2808 15. Yeh, C.-H. and Hon, M.-H, Dispersion and stabilization of 5. Ahlen, N,Johnsson, M. and Nygren, M, Synthesis of TIN CI aqueous TiC suspensions. Ceramics International. 1995, 21,65- whiskers.J. Mater. Sci. Lett. 1999. 18. 1071-1074 6. Wagner, J, Janssen, S, Rupp, R, May, R. and Hempelmann. 16. Bergstrom, L. and Bostedt, E, Surface chemistry of silicon R. Characterization of nanoscale titanium nitride dispersions by nitride powders: electrokinetic behaviour and ESCA studies. nall-angle neutron scattering. J. 4. Ceram. Soc.. 1998. 81 3313-3317 17. Zhmud, B. V, Meurk, A. and Bergstrom, L, Evaluation of sur- 7. Greenwood, R and Bergstrom, L, Electroacoustic and rheolo- face ionization parameters from AFM data. J. Colloid Int. Sci. gical properties of aqueous Ce-zrO2(Ce-TZP) suspensions. J. 1998,207,332-343 Eur. Ceran.Soc,1997,17,537-548 18. Dupont, L and Foissy, A, Evaluation of the adsorption trends 8. Wasche. R. and Steinborn. G. Influence of the of a low molecular-weight polyelectrolyte with a site-binding casting of nanosized TiN. J. Eur. Ceram. Soc.. 1997, 17. 421-426 model. Colloids Surf. 4. 1996. 110, 235-248
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