Effect Of Pulse Electric Current On The Preparation Of Yttria Powders And Its Sintering Behavior

As a rare earth material,yttrium oxide(Y2O3)has been interested by lots of researchers.On the other hand,the technology of external field treatment has been favored by researchers in recent years.Till now,the precipitation of yttria under external electric field and its influence on the grain nucleation and growth has seldom been reported.Moreover,due to difficult sintering of Y2O3,pulse electric current sintering(PECS)as a new sintering technology with high efficiency might be suitable for the sintering of yttria.In this experiment uses yttrium nitrate hexahydrate as raw material to synthesize yttria precursor by precipitation method in the way of forward titration.During the precipitation in which pulse current is imposed,We investigate the effects of the current intensity,pulse frequency,precipitants agents,the content of Na+,Y3+ molar concentration on the precipitation precursor and calcined yttrium oxide by the contrast method.At the same time,the mechanism is analyzed simply.The yttria powder is pressed into form and sintered with conventional sintering method and PECS.The density,the thermal shock resistance and other properties of yttria bulk materials are investigated after sintering.Based on the work,the main results are listed in the follows:(1)The precipitation precursor of chemical formular for Y2(CO3)3·2H2O can be obtained by using ammonium hydrogen carbonate and ammonium carbonate as precipitant,while with ammonia as the precipitating agent can get precipitated precursor of chemical formular for Y2(OH)x(NO3)(6-x)·1.5H2O(where x is 5 and 5.14),and the precursors calcinned under 750? were the Y2O3 powders.(2)Small pulse current in the precipitation process has little effect on the precursor,while the pulse current is large(electric current is 6.0A,10A),it is in a favour of the crystallinity of precursor,and to a certain degree,it can change the advantage growth surface of precipitation,which eventually resulting in the generation of difference in the morphology of yttria.(3)When the concentration of Y3+ is 0.1mol·L-1,the obtained Y2O3 is in the form of sheets,to galvanize the 10A pulse current can get the yttria whose type tends to granluar;while the density of Y3 + is O.5mol·L-1,the morphology of Y2O3 tends to be in acicular,with 10A pulse current along,the acicular yttrium oxide becomes finer,and the length to diameter ratio is greater.(4)By changing the process parameters,we have obtained the yttria powder with different morphologies,such as diamond,needle and granular.The different morphologies of the yttrium oxide have different sitering property,the needle yttria is higher bulk density than the diamond plate but lower thermal shock resistance.(5)Compared to the conventional sintering method,higher performance of yttria bulk material can be obtained at comparatively lower sintering temperature and shorter holding time by PECS.The relative density can reach to 99.6%.