The effects of starting composition, sintering temperature and porosity on the mechanical properties of hydroxyapatite ceramics were investigated. The hydroxyapatite powder were prepared by precipitation method using Ca(NO3)2.4H2O and (NH4)2.HPO4. The obtained powders were Ca-deficient hydroxyapatites and as the Ca/P mole ration in the initial solution was increased, the particle size of the precipitates was decreased, and the decomposition of hydroxyapatite to -TCP was controlled. The porosity, as well as Ca/P mole ratio in starting composition and sintering temperature, plays major role in the mechanical properties of dense hydroxyapatite ceramics.

The effect of pH variation in starting solution on the characteristics of hydroxyapatite precipitates and powder prepared by the wet method was investigated. Hydroxyapatite precipitates was agglomerated, the average agglomerated particle size was decreased in the range from 2 to 6 with increasing pH values in starting solution. The aspect ratio of rod-shaped hydroxyapatite particle was rapidly increased at pH 11 and 11.5. The maximum specific surface area, 91.1/g, was at pH 10.5. Dried powder prepared at high pH values contained more minutes CO2 than that prepared at low pH values. The poor crystallinity was maintained up to regardless of the pH values in starting solutions. However, the second phase or high crsytalline hydroxypatite phase appeared above 80. In pH 9.5 and pH 10, -whitlockite transformed to -whitlockite at 120, while in pH 10.5-11.5, hydroxyapatite phase was maintained up to 120.

Al2O3/SiC composite-material was synthesized by the birth-spread mechanism through the carbothermal reduction reaction of SiO2 in Ha-Dong Kaolin with carbon powder under H2 gas atmosphere at 1300~140. Average diameter of synthesized SiC whiskers were 1 and aspect ratio (c/a) was 10~100. Al2O3 particles and SiC whiskers were mixed homogeneously in the reacted pellet.

In order to develope hydroxyapatite ceramics which has mechanical strength as bio-implant materials and get the basic data for the study and application of biocompatibility, hydroxyapatite was synthesized at Ca/P=1.67~1.75, pH 7~11 by precipitation method. Using prepared powders, the sintered body, fluorine substituted body and the porous body was formed and their properties were investigated. The sample obtained in condition of Ca/P=1.67, pH 7 and sintering at 1,15 was decomposed to -tricalcium phosphate, and co-existed with hydroxyapatite. Hydroxyapatite synthesized at pH 11 was not easily decomposed to -tricalcium phosphate at sintering process. The substitution of a small amount of fluorine for hydroxyapatite prevented hydroxyapatite from being decompsed to -tricalcium phosphate. Hydroxyapatite ceramics which substited of 10% fluorine was prepared at 1,15, and the valueof bending strength for this body were found to be 112MPa.

The preparation of the fine BN powders by ammonia-nitridation of ammonia-decaborane derivate was attempted at temperature between 300 to 150. The formation mechanism of BN was examined and the resulant BN powder was characterized by means of IR, XRD, SEM and PSA method. In the nitridation below 80 bonding materials were identified with mainly BH and NH but above 80 with BN by IR spectra and X-ray patterns. Crystalite size, lattice constant and particle size distribution of hexagonal BN prepared at 1, 50 were La=470, Lc=180, a=2.50621, c=6.82852 and 2.0-5.4, respectively.

Synthesis of spinel pigment on ZnO-Fe2O3 system. The object of this research is the synthesis of new spinel pigments on the basic of ZnO-Fe2O3 system which was substituted by ZnO-Fe2O3 by MgO-Al2O3. This research was progressed by measuring the X-ray diffraction and the reflectances of the substitued ZnO-Fe2O3 group. Which was obtained by sintering at the temperature of 1,00, 1,10, 1,20 and 1,25 and them by regrinding. In order to coloring test, here basic compositions of Barium glaze, Zinc glaze, Lime glaze, Lead glaze and Talc glaze used in this experiment are obtained from the ceramic work. Adding synthetic stains in these basic glazes with 3%, mixing and glazing on the specimen. The specimens was fired at 1,28 in reducing and oxidizing atmosphere in the gas kiln. The results of the research as follow. 1. Many kinds of spinel pigment was produced on ZnO-Fe2O3 system that is to say, not always only spinel. 2. Spinel peak was observed strongly on the ZnO-Fe2O3 system withsubstituting by MgO-Fe2O3 and MgO-Al2O3 group(the ratio of MgO, Al2O3 being increased, observed more strongly). 3. The most effective temperature ranges was 1,20~1,25. 4. The color of spinel pigments on this system was observed by "stable YR". 5. It was yellow red in oxidizing and green in reducing atmosphere on the coloring test.ring test.

The Silica-Carbon mixture was made with addition of carbon black in the composition which monodispersed spherical fine silica was formed by the hydrolysis of ethylsilicate, mole ratio of Carbon/Alkoxide was 3.1 and -SiC powder was synthesized by reacting this mixture at 1,350~1,50 in Ar atmosphere. The results of this study are as follow : (1) The purity of synthesized -SiC powder was above 99.98% and it was in cubic modification with lattice constant of 4.3476. (2) The rate-controlling steps varied with the reaction temperature for the syntehsis of -SiC in this study ; nucleation and growth of -SiC at 1,350~1,40, interfacial reaction at 1,45 and diffusion described by Jander Equation at 1,50. (3) When the rate-determining step was nucleation and growth, the activation energy was about 87.8kcal/mol.

Fine Si-Al-OH coprecipitate powders were prepared from Si- and Al-alkoxides by the hydrolysis method. -Sialon powder was obtained from prepared Si-Al-OH coprecipitate by the simultaneous reduction and nitridation method. The syntehsized Sialon powder was pressureless sintered at 175 for 90 min in N2 atmosphere. The characterization of the Sialon powder was performed with XRD, BET, SEM, TEM and particle size analysis. The sinterability and mechanical properties of sintered bodies were investigated in terms of relative density, M.O.R., fracture toughness, hardness and the morphology of microstructure. The highest values of their mechanical properties were obtained for the -Sialon ceramics at Z=1 and those values are as follows : M.O.R., KIC and HV of -Sialon ceramics(Z=1) are 499.1 MPa, 5.9MN/m3/2 and 18.7GPa, respectively.

The properties of the powder of Al2O3-15v/o ZrO2(＋3m/o Y2O3) system prepared by co-precipitation method at the pH values of 7, 9, 10 and 11 were investigated. Al2(SO4)3.18H2O, ZrOCl2.8H2O and YCl3.6H2O were used as starting materials and NH4OH as a precipitation agent. Zirconium hydroxide decreased the specific surface area of aluminum hydroxide of AlOOH type, while increased the specific surface area of aluminum hydroxide of Al(OH)3 type, and formed co-network structure of Al-O-Zr type with the aluminum hydroxides. The rate of transition to -Al2O3 from co-precipitated materials occurred in the order of 7≒10, 9 and 11 of pH values. Al2O3 and ZrO2 interacted to bring about coupled grain growth, and the growth of ZrO2 crystallite size rapidly occurred within -Al2O3 matrix. Segregation did not occur in the system Al2O3-15v/o ZrO2(＋3m/o Y2O3) and Y2O3 acted as a stabilizer to ZrO2. The lattice strain of tetragonal ZrO2 was increased by the constraint effect of Al2O3 matrix.

To investigate the development and densification YBa2Cu3O7-x(1-2-3) superconducting phase, the 1-2-3 phase powders have been prepared by citrate and nitrate processes with changing calcination temperature. Nearly pure 1-2-3 phase peaks have been obtained by calcining the precursor in air at 90 for 2.5h in citrate process but at 95 for 2.5h in nitrate process. The sintering density of citrate derived sample calcined at 80 has been about 4% higher than that calcined at 90, although the compacting density has been lower at 80 calcination. This can be explained that the 1-2-3 phase particles formed at 80 have reactive sub-micron size which has good sinterbililty.

Pressureless-sintering of SiC with additions of yttria and alumina was studied. SiC could be densified to about 97% of its theoretical density at 185 which is about 20 below the normal sintering temperature of SiC with boron and carbon. Yttria and alumina formed intergranular liquid phases at the sintering temperature and promoted densification by the liquid phase sintering mechanism. The microstructure of sintered specimens was equiaxed and the liquid phase appeared to wet and dissolve SiC grains. The fracture toughness was measured by indentation method and found to be 5.3MPa.m1/2. Processing flaws near the surface of specimens appeared to be the major fracture origin during 3-point bending tests.

A study on the APCVD(atmospheric pressure chemical vapor deposition) Al2O3 was done by using the aluminum-tri-isopropoxide/N2 reaction system at 40. When the flow rate of the carrier gas(N2) was over 2SLPM, heterogeneous reaction was observed. However, when the flow rate of the carrier gas was below 2SLPM, a porously deposited film or powder formation was observed. The film formed by a heterogeneous reaction was optically dense. The dense film is thought to be a kind of a hydrated alumina. After a thermal treatment of the film in the range of temperature from to 1, 20, properties of the film seems to be changed due to dehydration and densification process. In the case of the powder on heat treatment(600~1, 20), both a phase transformation and the change of OH peak was observed.

The powder properties and sinterability of ZrO2-8m/o Y2O3 prepared by coprecipitation were investigated. The specific surface area and the total pore volume were increased with increasing pH of sediment and using of ethyl alcohol for washing. The powders of prepared by freeze drying method were showed the smallest particle size and lowest agglomerate rate, and the powders obtained from spray drying method were showed porous structure. At 130, their relative density were 94-96%, so these sintered bodies have revealed high sinterability in spite of low sintering temperature.

Dielectric properties and the stability of the perovskite phase in the Pb(Mg1/3Nb2/3)O3 system have been investigated as a function of amount of BaTiO3 and firing temperature. In the specimens fired at 120, the pyrochlore phase was eliminated by the addition of 10-15m/o BaTiO3 and also the dielectric constant increased. However, the dielectric constant decreased with further addition of BaTiO3 even though no pyrochlore phase was found to be present. The reducing tendency of the pyrochlore phase decreased with lowering the firing temperature in the system of Pb(Mg1/3Nb2/3)O3 with BaTiO3. Dielectric properties in PMN ceramics were affected by the character of the BaTiO3 rather than the pyrochlore phase.

The effects of grain size and dopant ZnO on the photoelectrochemical conversion in TiO2 ceramic electrodes have been investigated. The photocurrent increases with increasing grain size in the undoped TiO2 ceramic electrode. In ZnO-doped TiO2 electrodes, the photocurrent decreases with increasing ZnO up to 0.4 wt% due to decrease of donor concentration, and then with further addition of ZnO, photocurrent increases according to the formation of second phase. However, the photoresponse appears at wavelength of 420nm, which is very close to the energy band gap of TiO2, regardless of grain size and amount of ZnO.

YBa2Cu3O7-x oxide superconductors were fabricated by sintering and hotisostatic pressing (HIP), and their microstructures and properties were compared with each other. Thougha part of the second phase was observed along grain boundaries, their structures were consisted of single (123) phase and they had many porosities. But, porosities were remakably reduced by Hiping and the densification was brought about. The structure of (123) compound also showed a number of twins, which are typical of high Tc superconductors. The on-set temperature of YBa2Cu3O7-x compound sintered at 96 in oxygen and hipped at 88 was highest, but that shwoed 0 resistance at 87K, which is a little lower than the compound sintered at 96. HIP treatment also increased the critical current density of as-sintered compound. However, its value was low, which may be ascribed to the many pores of starting-sintered compact and partially to the second phase along grain boundaries.

Interpretation of high-resolution transmission electron microscopy images of defects and complex structures such as found in ceramics generally requires matching of the images with compound image simulations for reliable interpretation. A transmission electron microscopy study of the aluminum oxide was carried out at high-resolution, so that the crystal structure of the aluminum oxide could be modelled on an atomic level. In conjunction with computer simulation comparisons, the images reveal directly the atomic structure of the oxide. Results show that comparison between experimental high-resolution electron microscopy images and simulated images leads to a one to one correspondence of the image to the atomic model of the aluminum oxide. The aluminum atoms are disordered in the octahedral sites and the tetrahedral sites in the spinel aluminum oxide.

The properteis of the composition of second reports with Al2O3 and CaO have been investigated. The amount of Al2O3 addition was 5-20w/o, the composition ranges of maximum strength and the microstructure have been studied. In the same method, the effects of CaO on the theoretical composition of tricalcium phosphate have been studied.