A particulate inorganic oxide contains an aluminum oxide, a metal oxide forming no composite oxide with an aluminum oxide, and at least one additional element selected from the group consisting of rare earth elements and alkaline earth elements. In the inorganic oxide, a percentage content of the additional element to a total amount of aluminum in the aluminum oxide, a metal element in the metal oxide, and the additional element is in a range from 1.1 at % to 8.0 at % in terms of element content. At least 80% of primary particles in the inorganic oxide have a particle diameter of 100 nm or smaller. At least a part of the primary particles have a surface concentrated region where a percentage content of the additional element is locally increased in a surface layer part thereof. The content of the additional element in the surface concentrated region to a whole amount of the inorganic oxide is in a range from 0.06% by mass to 0.98% by mass in terms of oxide amount.
一种颗粒状无机氧化物包含氧化铝,一种与氧化铝不形成复合氧化物的金属氧化物,以及至少一种从稀土元素和碱土
金属元素组成的附加元素。在无机氧化物中,附加元素的百分含量与氧化铝中的铝总量,金属氧化物中的
金属元素和附加元素的总量之比在元素含量方面为1.1至8.0at%的范围内。在无机氧化物中,至少80%的初级颗粒具有100nm或更小的粒径。至少部分初级颗粒具有表面浓缩区域,在表面层部分中,附加元素的百分含量局部增加。表面浓缩区域中的附加元素含量与整个无机氧化物的含量在氧化物量方面为0.06%至0.98%的范围内。