Thc SPS (Spark Plasma Sintering) proccss is a new matcrials symttjesos proccssing technology recentlydcvclopcd by Sumitomo Coal Mining Co., Ltd., Japan. This paper describes the principles and fcaturcsof the SPS process, inluding the basic configuration of the Sumitom s SPS systcm, as well as the SPSproccss applications particularly in thc synthesis of thc functionally gradient inaterials and the high-density,finc-grains sintered ceramics including partly authors recent rescarch resnlts.

Thc CsNa⁺ ion exchahgc glass waveguides were made by both thermal diffusion and electrical fieldassista1lt diffusion methods. After the investigation of the temperature depcndence of the waveguides, it wasfound that these waveguides exhibit very high thermal stability below the glass transition temperature. Theion cxchangc mechanism of Cs⁺ -Na⁺ ion exchange was found to be non-Fick Diffusion. The stress gradientcanscd by the hugc dimension difference for Cs⁺ and Na⁺ ions, as the electroneutrality field gradient produced due to the large difference in diffusion coefficients between Cs⁺ and Na⁺ ions predominate the diffusion process in ion exchange. The refractive index profiles and concentration profiles obtained by SEM and X-ray energy dispersive analysis can be sell explained by the proposed ion-exchange mechanism.

The fabrication process of short chopping carbon fiber-reinforced LAS glass-ceramic matrixcomposites and tke effect of fiber length, orientation on the mechanical properties of tke composites were strudied.Tke composites witk fiber dispersed homogeneously, oriented directionally were obtdsed. Microstructureand fracture surface of tke composites were exhaned by optical microscope and SEM. It is conduded thatthe main toughening and strengthening meckanisms are based on load transfer and fiber pullout.

The isothermal crystallization kinetics of mica-containing glass ceramics with addition of TiO2 asnucleation agent was investigated by XRD, SEM and DTA. Two distinct crystallization exotherm peaksin the DTA curve were observed and resolved corresponding to the initial formation of MgTi₂O₅,followed by the formation of KMg₃AlSi₃O₁₀F₂, confirmed by X-ray diffeaction analysis (XRD). By usingJohnson-Mehl-Avrami equation, the activation energics for precipitation of MgTi₂O₅ and mica crystalswere enaluated and the crystallization mechanism of mica was analyzed. The results indicated that the growth of KMg₃AlSi₃O₁₀F₂ is a two-dimensional process, controlled by the crystal-glass in terface reaction. The average values of activation energies are 242kJ/mol and 265kJ/mol corresponding to that of MgTi₂O₅ and mica crystalized out of the glass, respectively.

The new nanocrystallites of the pyrochlore-type of rare earth complex oaldes with B-site doped,RE₂Sn_2-xB'_xO₇(RE=Sm,Ce; B'=Fe,Co,Ni: x=0～1-0), were prepared by unalcolate sol-gel method forthe first time. The nanocrystallite sizes were from 25 to 3Onm. It is found that this method can lowerreactive temperature (about 200℃) and shorten reactive time, The crystal structure of the nanocrystallitesbelongs to.cubic system and their lattice parameters are linear1y related to the content of doped ions. FromIR spectra, it is found that:(1) the data of absorption frequency of samples with RE=Ce are lower than that of with RE=Sm; (2) dopants of different ions in B-site not only bring about distortion of BO₆ octahedron, presenting relevant absorption, but also affect the vibration of RE--O bridge, causing lower frequency.

Various toughening methods, such as transformation toughening, transformation-whiskerreinforcement and transformation-particle reinforcement were used toimprove the mechanical properties of alumina.The fracture behaviors and toughening mechanisms of the composites werc studied by measuringmechanical properties, analyzing microstructures and comparing fracture morphologies. The mechanical propertiesof testing materials arc closely related with the morphologies of fracturc surfaces. The two tougheningmcchanisms in joint toughening composites will affect with each other, and produce an effect of cooperative toughening on certain conditions. The dislocations were observed in matrix of meterials undergoing property test. The tearing ridges, which are created generally in ductile fracture, were also observed on fracture surface in ZTA material.

B₄C-TiB₂ composites were prepared by hot-pressing process at 2050°C. The effects of TiB₂ particlecontent on the fracture toughness, bending strength and Vickers hardness of B₄C-TiB₂ composites werestudied. The addition of 3Ovol% TiB₂ raised the bending strength of B₄C to the peak value of 725MPa, 65%higher than monolithic B₄C. An 84% increase of composite toughness up to 6.7MP.m^1/2 was discoveredupon the incorporation of 45vol% TiB₂ particles into B₄C matrix. The crack deflection caused by theresidual stress resulting from the difference in thermal expansion coefficient between B₄C and TiB₂ is the main mechanism responsible for the increase of toughness.

The effcct of bimodal partiele size distribution on the compact cfficiency and sintering behavior ofsubmicron-sized alumina powder was investigated For two types of submicroll alumina powders with sizeratio of about 2, collsidcrably lligller compact densitics, as compared to their individuaJs, were obtainedwhen mixed in proper volumc ratios. In the casc of 33% fine particls in the mixed powder, the relativegreen density of abovc 72% was achieved by pressure filtration. Different consolidation techniqucs, namely pressure filtration and drying press, were found to yield compacts with different properties. Green compacts by pressure filtration, which had higher density, narrower pore size distribution and smaller mean pore size than those by dry-pressing, can be sintered to theoretical density with fine microstructure at relatively low temperature. The sintering behavior and the microstructure developed for the compacts by different compaction techniques were discussed with newly developed theory of sintering thermodynamics.

The compressive plastic deformation of superplastic 3 mol% yttria-stabilized zirconia polycrystalswith different grain sizes was studied by both constant cross head speed and constant load tests incompression in air. The superplastic-like phenomenon in 3Y-TZP was exhibited. The grain shape remainedequiaxed and the grains were dislocation-free after deformation. It indicated that the deformationmechanism was grain boundary sliding accommodated by diffusion. The flow stress decreased markedly with theincrease of the strain rate and grain size and with the decrease of the temperature. The stress exponent and activation energy for creep decreased from 3.2 to 1.4 and from 580jK/mol to 500kJ/mol with the increment of the grain size from 0.30μm to 1.33μm, respectively. That the change in the stress exponent and activation energy implied the change in deformation mechanism with the grain size. Cavitation occurred at triple junctions in the materials with coarser grain sizes during deformation at high strain rates and a part of the cavities developed along grain boundaries and linked as crack-like cavities.

Single phase β-Sialon powder was prepared by combustion synthesis method, with Si、A1、 A1₂O₃and Si₃N₄ as raw materials under high nitrogen pressure. The effects of nitrogen pressure and the amountof the diluent on phase composition and microstructure of combustion products were studied in detail.

Hot isostatically pressed nano-ceramics of monophasic SiC and Si₃N₄/SiC composite were studied,and the phase composition and ndcrostructure were characterized by XRD, TEM and HREM. It is skownthat fine and homogeneous microstructure with average grch size of less than 100nm for monopkasic SiC can be obtained at the HIP conditions of 1850°C, 200MPa for 1h. The starting powder materialssignificantly affect the final microstructure. At 1750°C, 150MPa for 1h, very fine and homogeneous mi-crostructure with the average grain size of about 50nm can be prepared by using the pretreated composed Si₃N₄-SiC nano-powder. Both of the different phase compositions of nano-powder and HIP conditions may be ascribed to the depression of grain growth.

SiC ceramics with rod-like grains were obtained by pressureless sintering of β-SiC powders with Y₂O₃ and Al₂O₃ as additives. The materials were densified based on liquid phase sintering mechanism. Thephase transformation of 3C→4H in SiC occurred during sintering, which was associated with the formationof rod-like grains. The mechanical properties of the materials depended on the aspect ratio of SiC grains,on the optimum, the maximum values of the flexural strength and fracture toughness reached 620MPa and 6.1MPa.m^1/2 respectively. The trajectory of indentation crack revealed that the crack deflection and grain-bridging sere the main toughening mechanisms due to the weak grain-boundary.

The YSZ film was prepared by sol-gel method. The effect of process conditions on the microstructurewas studied. Wc found that the major factors of the effect on the film cracking are the selection and cleaingof substrates, the rate of gelation, the velocity of the temperature rising and cooling in the heat treatmentprocess, XRD and SEM results showed that the YSZ film prepared by sol-gel method must be calcined atabove 8OO°C, to remove the acidic root, organic groups and carbon element, alld t0 form perfectlyl;cubic phase strcture. The film surface densified and pores decreased with the firing temperature increasing. At 1050℃, the film surface became smooth, crackfree and porefree, the spherical grain distributed uniformly. The film and substrate combined tightly, the thickness of the film was about 1.0μm.

According to the microscope theories of heat conduction, a theoretical analgsis of heat conductionfactors for the high temperaturc thermal insulation materials was studied. The main physical andchemical factors including miroscope structure, crystal phase and chemical components which cffect thermalconductivity were exmained systematically, and consequently the new technical approach for predictionand optimizing the properties of thermal insulation materials was provided.

Al₂0₃ and Li₂CO₃ were mixcd and heated at 600~700℃ f0r producing LiAlO₂ used as the matrixmaterials of the Molten Carbonate Fuel Cell. While ordinary Al₂O₃ was chosen as the reactant, because itsparticle size and bulk density were large, the fabricated particle size of LiAlO₂ was large too. While Al₂O₃made from on organic compound was selected as the reactant, the fabricated particle size of LiAlO₂ wassmall. The prepared LiAlO₂ was mixed with water soluble binder and softener, and rolled into matrix. The pprepared matrix was assembled with sintered Ni to form a Molten Carbonate Fuel Cell. The experimental results showed that the cell performance was perfect.

Because of the technical diffculty to create an ideal plannar crack with zcro root radius, macronotchedspecimen are of ten prepared for testing the fracture toughness of ceramics. In this paper, the quantitativeexpression of fracture toughness of ceramics and notch radius was investigated. Based on the theory thatthere exists a fracturc proccss zone in front of crack tip and average stress fracture model, a relationbetween fracture toughness and notch radius was derived, with this relation, the fracture toughness of ceramics can be predicted from tested value of macronotched specimens. Combined the fracture process zone with the experiment results from the available literature, it is showed that the scale of fracture process zone is four times of average grain diameter. Compared with the experimental results, we have a conclusion that when the notch radius reach to the average grain diameter, the tested results can yield the true value K_IC under 6% deviation.

Thermal properties of a recently-developed lead-barium-aluminum plLosphate glass were examined bymeans of differential thermal analysis. The glass exhibits a low melting temperature, relatively low glasstransition and softelting temperatures, and a high coefficient of thermal expansion. The infrared spectraof the glass are characterized by a very weak absorption band in the near-infrared region, the absence of acharacteristic P=O absorption band in the mid-infrared region, and three well-resolved absorption bands in the far-infrared region indicating the vibrational motion of aluminum, barium and lead ions at their network sites.

The thermal expansion coefficient of PWO crystals grown by Bridgman technology was measuredand its effects on the cracking of the crystals were discussed. The approach of overcoming the crack wasalso investigated. It was shown that the strains resulted from temperature distribution along the longitudeduring manufacture, and the large thermal expansion coefficient with tlie maked anisotropy of the crystalsare the important reason of the cracking.

The (Sr, Pb)TiO₃ ultrafine particles were prepared by oxalate-coprecipitation process, the thermolysisprocess of the coprecipitates (Sr, Pb)TiO(C₂O₄)₂ .4H₂O was analyzed and the crystallization temperatureand calcination comdition were defined. The averagc Primary particle size calcined at differenttemperaturcs, the crystal structurcs of sintered body and powders calcilled at different temperatures and thesintering condition of powders were also determined. The results show that the synthetic temperature of ceramic powder prepared by this process is much lower than by the conventional solid reaction process. the ceramic powder obtained is ultrafine and uniform, and the sintering temperature is lower. Exotic structure with fine grain was observed, that is, when the particle size is very small, the crystal structure is not the normal tetragonal ferroelectric structure but cubic paraelectric.

Nano-Y₂O₃:Eu³⁺ was prepared with the method of homogeneous precipitation. Controlling theconditions of the reaction, we obtained nano-scale powders with different grain sizes. Compared to ordinarypowders of Y₂O₃:Eu³⁺, the XRD peaks of nan-Y₂O₃:Eu³⁺ become wide, and 2θ increases. Also, it exitsthe bluc-shift in the X-ray PLS of nano-Y₂O₃:Eu³⁺.The wave length and intensity of the peak(⁵D_o →⁷F₂)are connected with the grain size of the powders.

The investigations carried out by extensive stability tests on LaCrO₃, NiMn₂O₄ and their compositematerials revealed that the composite materials are greatly superior to single-phase materials in stability.The causes of resistance variation on single phase materials during ageing were analysed applying thedefect chemistry theory. The research suggested that the reduction of oxygen vacancies concentrations,which results from that the absorbed oxygen in the surface and pores of cerandcs diffused gradually intograins, decrease the resistrivity of p-type semiconductor ceramics LaCrO₃ and increases that of n-type semiconductor ceramics NiMn₂O₄. thus it was condluded that the exceedingly good high-temperature-resistant characteristics of composite electroceramics are attributed to the compensation effect of composite materials.

The test results for Na₂MO_0．1S_0.9O₄（α）-In₂(SO₄ )₃ System studied by using of XRD, DTA, IR spectraand electrical conductivity measurcments were reported. The influcnce of In₂ (SO₄ )₃ on conductivity andphase formation of Na₂MO_0．1S_0.9O₄was discussed. Meanwhile, the reason that the conductivity increasedwas also revealed.

This paper studied a new method for preparing no-sulfur content and expandable graphite bypotassium permanganate as oxidant and a mixture of acetic anhydride and 65% nitric acid as medium. Theoptimum conditions for preparing the expandable graphite are as follows. Weight ratio of graphite: aceticanhydride: 65% nitric acid: potassium permanganate is 1.0:0.8:0.5:0.07; reacting temperature, 30℃;reacting time, 40min. The expanded volume and nitrogen content of the expandable grwphite are 280m/gand 1.27% respectively. the end product, flexble graphite does not contain nitrogen. To date, similar report has not been seen in the literature.