摘要:

The thermomechanical relationship between mullite and a lithium aluminosilicate (LAS) glass‐ceramic has been studied by a technique of bimaterial dilatometry. The viscoelastic behavior of LAS was found to result in a temperatureTrvslbelow the glass‐transformation temperatureTgat which the interfacial stresses between the materials undergo a reversal in sign. The effect ofTrvslon the high‐temperature mechanical properties of mullite or SiC fiber‐reinforced glass‐ceramic composites is discussed. It is suggested that fiber clamping by the matrix at temperatures betweenTrvslandTgcontributes to the brittle, high‐temperature behavior of such

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04844.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The resistance of a canasite glass‐ceramic to the initiation of thermal stress fracture due to a water quench was found to be higher than for the original glass, due to higher values of strength and thermal conductivity which offset increases in thermal expansion and Young's modulus. Relative strength retention behavior of the glass‐ceramic was also higher than for the glass, attributed to its crack‐size‐dependent fracture to

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04855.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Alumina ceramics were joined by hot‐pressing with polystyrene or mica sheets at temperatures of 1250° or 1350°C. The polystyrene decomposed during hot‐pressing, creating reducing conditions in the joints which enhanced interfacial diffusion and bonding. Measured fracture toughness and flexural strength of such joints approached values for monolithic alumina. Joints prepared under similar conditions but without polystyrene showed much lower KICand strength v

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04856.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Mullite (3Al2O3·2SiO2) of stoichiometric composition was prepared by mixing boehmite sol and silica dispersion and gelling at a pH of 3. Complete mullitization takes place at or above 1300°C. Ultrafine mullite powder prepared by calcining gel at 1400°C and attrition milling could be sintered to>98% (theoretical density) at 1650°C for 1.5 h. The flexural strength of the sintered body at room temperature was 405 MPa and 350 MPa at 1300°C. Only traces of a secondary phase were observed along the grain boun

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04857.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Microporous silicon dioxide thin Films were deposited on silicon substrates from a solution of tetraethoxysilane, ethanol, and water. These were converted to dense oxynitrides through a high‐temperature reaction with ammonia. The ammonia treatments yielded amorphous, compositionally homogeneous films with overall nitrogen contents ranging up to 40 mol%. For ammonia treatments below 800°C, nitrogen was incorporated into the films as an amine species, whereas higher temperature treatments produced a nitride materi

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04845.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The structures of roller‐quenched SiO2‐Al2O3glasses containing 10 to 50 wt% Al2O3were investigated by TEM and high‐resolution27Al and29Si magic angle sample spinning nuclear magnetic resonance (MASS‐NMR) spectroscopy. The chemical shifts observed in the NMR spectra of these phase‐separated (on the TEM scale) glasses provide evidence, for the existence of all three (4‐, 5‐, and 6‐jold) Al‐coordination units in these glasses and for the presence of A1 in both the Si‐rich

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04859.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Alkali‐free borosilicate films of 20B2O3. 80SiO2(in mol%) have been prepared by the sol‐gel method. The transparency of these films was found to be very sensitive to the humidity of the atmosphere during the coating process. Transparent films were obtained only in a dry atmosphere. Measurements of IR spectra and load at scratch showed that these films were densified above 60

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04860.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The fundamental question as to whether thin intergranular films can adopt an equilibrium thickness in polycrystalline ceramics is addressed. Two continuum approaches are presented, one based on interfacial energies and the other on the force balance normal to the boundary. These indicate that there will exist a stable thickness for the intergranular film and that it will be of the order of 1 nm. The origin of an equilibrium thickness is shown to be the result of two competing interactions, an attractive van der Waals‐disperson interaction between the grains on either side of the boundary acting to thin the film and a repulsive term, due to the structure of the intergranular liquid, opposing this attraction. As both of these interactions are of short range (<10 nm), it is a natural consequence that the equilibrium thickness is of the order of 1 nm, a value commensurate with that observed experimentally in a wide range of ceramics. Two further consequences of importance arc indicated. The first is that thin intergranular liquid phases can support a normal stress. The second is that the dielectric constants of the adjacent grains play an important role in determining the thicknesses of the intergranular phase. This leads to the conclusion, consistent with observations, that the thickness of the intergranular phase in polyphase ceramics is expected to be different at boundaries between dissimilar phases than that between like phase

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04846.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The effect of Ba additions on sodium potassium niobate (NKN) ceramic bodies was investigated with regard to sintering behavior, densification, and electrical properties. Small additions of Ba retard grain growth and increase density. The approximate solubility limit of Ba is 1.5 mol%. During firing the loss of Na and K was very low. Both electrical phase transitions in NKN are lowered with Ba additions. The Ba‐containing bodies show higher permittivity values than hot‐pressed materials, while radial coupling and d33were similar to or higher than those of the conventionally sintered pure materi

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04862.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Sols containing well‐mixed tetraethyl orthosilicate, sodium methylate (CH3ONa), and Ca metal dissolved in HCIO4were hydrolyzed at low pH. After gelation, controlled drying, and subsequent firing at 600°C, the mixture yielded clear glass chunks. Glasses containing 85% to<100% SiO2, which otherwise are difficult to make by conventional melting techniques, could be made using this techniq

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04863.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY