Pernilla Pettersson

Thermal decomposition of fibrous TiOSO4·2H2O to TiO2

Abstract Fibres of TiOSO4·2H2O are used as precursor material for the preparation of TiO2 fibres and/or particles with controlled morphology. This is achieved by heat treatment in air in the temperature range 580–1250°C for times ranging from 0.1 to 100 h. Thermogravimetric studies showed that water was expelled at temperatures below 500°C, and the conversion of TiOSO4 to TiO2 took place in the temperature range 540 to 580°C. Heat treatment at temperatures below 650°C yielded anatase, whereas rutile started to appear after extended holding times (100 h) at 650°C. Heat treatment at 950°C and higher yielded monophasic rutile samples. In the temperature region 650–950°C, both anatase and rutile appeared in the product in various relative amounts depending on the temperature and time of annealing. The original fibre morphology was preserved in the low-temperature region where anatase was formed. In the rutile region, however, the fibres became degraded due to growth of TiO2 particles, resulting in pearl strings of particles. The final morphology of the product depended strongly on the time and temperature of heat treatment. The time dependence of the conversion of anatase to rutile at 750°C was monitored. The rate of conversion is rather high in the beginning of the process but substantially slower at the end. The obtained data can be fitted by the extended rate law proposed by Prout-Tomkins.

Thermal shock properties of alumina reinforced with Ti(C,N) whiskers

Abstract Alumina composites reinforced with Ti(C,N) whiskers were produced to evaluate the thermal shock properties. The indentation fracture toughness (49 N load) increased from 2.6 MPa m 1 2 for pure alumina to 5.0 MPa m 1 2 for the sample with 30 vol.% Ti(C,N) whiskers. The hardness also increased, from 17.6 to 24.2 GPa. A clear R-curve behaviour was observed. An indentation–quench test was used to measure the thermal shock resistance. The best thermal shock resistance was observed at 30 vol.% Ti(C,N) whiskers.

Thermal shock resistance of α/β-sialon ceramic composites

Abstract The thermal shock properties of α/β-sialon composites have been evaluated with an indentation-quench method based on propagation of Vickers cracks. Nominally the z value of the β-phase (Si 6- z Al z O z N 8- z ) was held constant at 0.6, and the composition of the α-sialon phase Y x Si 12-( m + n ) Al m + n O n N 16- n was x =0.33, m =1.0, n =1.2. Different α/(α+β) ratios were tested, and the amount of sintering aid (a yttrium-containing glass phase) was varied between 0 and 20 vol.%. The thermal shock resistance increases with increasing fraction of β-phase, and the presence of a glass phase also has a positive influence on the thermal shock resistance.