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Abstract: Al2O3–ZrB2 in situ composites of 97% of theoretical density were successfully fabricated by a novel self-propagating high temperature synthesis (SHS) dynamic compaction, using less expensive raw materials zirconium oxide, boron oxide, and aluminium. The process is fast, energy efficient, where no furnace sintering is required. The process inhibits and controls the grain growth and microstructure. The densification behaviour and correlation with microstructure of the SHS dynamic compacts were compared with the furnace sintered composite samples where the composite powder was prepared by SHS process. The furnace sintered samples showed coarser grain growth and maximum density of 94.5% of theoretical density was achieved. The SHS dynamic compacted in situ composite had much finer grains in the range of 0.5–3μm with density 95.5% of the theoretical value. The average grain size was found to decrease from 10μm to 1.4μm for alumina and from 5.4μm to 1.0μm for zirconium diboride from furnace sintering to SHS dynamic compaction, respectively. Addition of Al2O3 as a diluent during SHS reaction enhanced the density to 97%. During SHS dynamic compaction, the amount of liquid and the time interval at which the sample stays at high temperature are the controlling factor of the final microstructure and the densification of the composite. [Copyright &y& Elsevier]

Abstract: The sintering behaviour of magnetic bulk glassy compact has been addressed. Rapidly quenched ribbons of Fe71Nb3.7Cu1Al3Mn0.8Si13.5B7 alloy were ball milled to powder and consolidated using binder to get bulk glassy compacts. Structural and crystallization behaviour of glassy and heat-treated powders was evaluated. Differential scanning calorimetry (DSC) of the powders showed transition from amorphous to nanocrystalline phase at 800K. Magnetic evaluation of the bulk glassy cores revealed best soft magnetic property at a sintering temperature of 775K which was due to the formation of α-Fe(Si,Al) and Fe3(Si,Al) nanoparticles evidenced by transmission electron microscopy (TEM) and X-ray analysis. However, at this temperature the glassy compact exhibited low value of remanence, which was attributed to the demagnetization field due to porosity in the material that developed from the escaped mineral binder. At subsequent higher sintering temperature of 785K the glassy core exhibited inferior soft magnetic properties with a low coercivity due to the formation of strongly anisotropic boride phases. Remanence value increased due to reduced demagnetization effect arising from a more compact morphology. Such reduced porosity was due to the coalescence of powder particle as observed from scanning electron microscopy (SEM). [Copyright &y& Elsevier]

Abstract: A detailed investigation on sintering behaviour of SHS produced ZrB2–Al2O3 composite was carried out, which showed a maximum densification of 94% of the theoretical density after sintering at 1800°C for 30min. Further enhancement on sintering temperatures increased the porosity and decreased the densification due to evaporation of alumina from the surface of pellets during sintering. Severe reaction of the ZrB2–Al2O3 composite with C was observed during high temperature sintering in a graphite furnace. The C was found to react at the surface forming ZrC and further increase in temperature led to formation of AlO vapour and aluminium carbide. The C reaction could be lowered by covering the pellets with alumina powder. The inter-diffusion between ZrB2 and Al2O3 and the formation of a complex boride or oxyboride of Zr and Al was established near the grain-boundary region. [Copyright &y& Elsevier]

Abstract: The addition of TiC (5–10 wt.%) and C (5 wt.%) was found to enhance the sinterability of SHS produced ZrB2 powder. The densification increased to 94% of the theoretical density with the addition of carbon and TiC. The oxygen impurities normally present on the surface of this diboride powder leads to exaggerated grain-growth during sintering and hinders densification. The addition of C and TiC reduced the surface oxide layer and resulted in improved densification. Less grain-growth was also observed during sintering. [Copyright &y& Elsevier]

The effect of sintering temperature on structural, electrical and magnetic behaviours of polycrystalline samples of Ho0.9Ca0.1Mn0.9Co0.1O3 prepared by the solid state reaction route sintered at three different temperature 1250°C, 1350°C, 1450°C for 10h are investigated. XRD, SEM, magnetization, dielectric and ferroelectric measurements were carried out. Experimental results showed the nucleation of orthorhombic phase as the sintering temperature increases from 1250°C to 1450°C. Ferroelectric (T c ) and antiferromagnetic transition temperature (T N ) increases with increase in sintering temperature. Strong bifurcation of FC and ZFC curve in sample sintered at 1450°C showed a clear onset of ferromagnetic state around 165°K, which is confirmed from M to H graph at 165°K. All the sample showed ferroelectric behaviour at room temperature which are leaky in nature. Sintering temperature along with Ca and Co doping in HoMnO3 ceramics plays an important role in phase transformation along with enhancement in multiferroic properties. [ABSTRACT FROM AUTHOR]

Abstract: We have observed good ferroelectric loops at room temperature in hexagonal HoMnO3 (HMO) bulk ceramics sintered at 1250°C. Microstructure and ferroelectric hysteresis loops are observed to be dependent on sintering temperature. It is observed that with an increase of sintering temperature, hexagonal a-axis is compressed and c-axis is marginally dilated with overall contraction of the hexagonal unit-cell volume. We explain the origin of ferroelectricity through relative movement of Ho ion and Mn ion within its unit-cell volume, resulting in the distortion of unit-cell volume. We argue that ferroelectric origin of hexagonal HMO at room temperature may be due to the marginal displacement of Ho ion along a-axis, that influences the exchange interaction among the Mn3+ and Ho3+ ions, causing magnetically induced ferroelectricity at room temperature. [Copyright &y& Elsevier]

Abstract: Magnesite-chrome aggregates have been prepared from friable chrome ore and magnesia of different reactivity in the presence of an additive, ZrO2. Two types of batch compositions using sintered magnesia, caustic magnesia and chrome ore have been selected for preparing mag-chrome composites. The batch consisting of sintered magnesia and friable chrome ore (SMC) was vibromilled for 8h, whereas caustic magnesia compositions were added directly to a vibromilled chrome ore (CMC) and mixed in a fluidized bed mixer. Additions of 1–5wt.% ZrO2 were made to the batches. Firings were carried out between 1700 and 1750°C with 2h soaking. Aggregates were characterized by evaluating densification, hot modulus of rupture and microstructure. The reactivity of magnesia was found to play an important role in the final properties of samples. Introducing less reactive sintered magnesia improved all the properties of the aggregates. ZrO2 was found to be a good sintering aid in the magnesite-chrome composites. [Copyright &y& Elsevier]

This paper reports the effect of sintering temperature on ferroelectric properties of GdMnO3 (GMO) bulk ceramics at room temperature prepared by the conventional solid state reaction route following slow step sintering schedule. Ferroelectric hysteresis loop as well as sharp dielectric anomaly in pure (99.999%) GMO sintered ceramics has been clearly observed. Samples sintered at 1350°C become orthorhombic with Pbnm space group and showed frequency independent sharp dielectric anomalies at 373K and a square type of novel ferroelectric hysteresis loop was observed at room temperature. Interestingly, dielectric anomalies and ferroelectric behavior were observed to be dependent upon sintering temperature of GdMnO3. Room temperature dielectric constant (ε r ) value at different frequencies is observed to be abnormally high. The magnetic field and temperature dependent magnetization show antiferromagnetic behavior at 40K for both 1350°C and 1700°C sintered GMO. Present findings showed the possibility of application of GdMnO3 at room temperature as multifunctional materials. [ABSTRACT FROM AUTHOR]

Sintering of lime was carried out in the presence of V2O5 by a single firing process. A pure limestone was crushed, mixed with 1, 2 and 4 wt.% V2O5, pelletised and fired between 1550 and 1650 °C. The sintered lime was evaluated by bulk density, apparent porosity, microstructure, hydration resistance and hot modulus of rupture (HMOR) at 1300 °C. Incorporation of V2O5 forms liquid phase with lime at elevated temperature and influences the densification process by liquid phase sintering. As a result bulk density of sinters improved and they become more hydration resistant due to the larger grain size of the lime phase. The hot strength increased up to a certain temperature followed by deterioration because of the pressure of higher amount of liquid phase. [Copyright &y& Elsevier]

Stoichiometric magnesium aluminate spinel was synthesized by reaction sintering of alumina with caustic and sintered magnesia. The volume expansion of 5–7% during MgAl2O4 formation was utilized to identify the starting temperature of spinel formation and densification by high temperature dilatometry. The magnesia reactivity was determined by measurement of crystallite size and specific surface area. Caustic magnesia and sintered magnesia behave differently vis-a`-vis phase formation and densification of spinel. Densification of stoichiometric Mag-Al spinel was carried out between 1650 and 1750 °C. Attempts were made to correlate the MgO reactivity with microstructure and densification of spinel. [Copyright &y& Elsevier]

Densification of two different nonstoichiometric spinels (Al2O3 content 66 wt.% and 90 wt.%) was studied by using the reaction sintering technique. Sintered sea water magnesia and commercial alumina were used as starting materials. Reactivity of alumina was changed by calcinations between 800 and 1600 °C. Sintering for all the batches was carried out in the temperature range of 1600 and 1700 °C. Sintered products were characterized by bulk density, phase analysis and microstructure. Alumina calcined at 1200 °C was found to be optimum for densification of non-stoichiometric spinels. [Copyright &y& Elsevier]

Fabrication of Al–TiN (10, 30 wt.%) composites by a powder metallurgical route has been investigated using pressureless sintering and hot pressing techniques. Results indicate that sintering followed by hot pressing is required for significant densification and improvement of mechanical properties. The presence of titanium nitride (TiN) particles at grain boundaries played a significant role in improving the densification, and results in improved mechanical properties. Dry sliding wear results showed improved wear resistance of the composite (Al–TiN) compared to the base material (Al) metal due to presence of TiN particles. The wear rates of the Al–TiN composites decrease by an order of magnitude after hot pressing. [Copyright &y& Elsevier]