Synthesis of perovskite-type LaAl1-xCrxO3 for application in transparent glaze

ABSTRACT In Brazil, studies on ceramic pigments are still very scarce. For this reason, most of the pigments consumed by the ceramic industry are imported to European countries. Another part of these pigments is obtained by the ceramic route, however, this route of synthesis results in pigments with very heterogeneous properties, reducing the quality of the coating. For this reason, several studies are aimed at developing synthetic routes that result in pigments with more homogenous properties, being environmentally friendly and economically viable. In context, the aim of this work was to synthesize oxides with perovskite structure of LaAl1-xCrxO3 composition (x = 0.1; x = 0.05) by the gelatin method, aiming its application as pigment for color transparent glazes. The powders resulting from the synthesis process were calcined at 800 and 1000 °C. Then they were characterized using thermal analysis, X-ray diffraction, UV–visible diffuse reflectance spectroscopy and CIElab colorimetry. The perovskite was used for the preparation of ceramic glazes by addition of 2 wt.% pigments on transparent glazes. X-ray patterns revealed single-phase powders with trigonal perovskite structure. The color of the samples varied as a function of the substituent content. The reddish hue was observed in the perovskites obtained with lower substitution of the Cr3+ ion and calcined at higher temperatures. No changes in the pigment color when introduced into transparent glazes were observed.

摘要
在巴西，陶瓷颜料相关研究仍极为匮乏。因此，该国陶瓷工业所消耗的大部分颜料均从欧洲国家进口；其余部分颜料则通过陶瓷工艺路线制备，但该合成路线所得颜料的性能极不均匀，会降低涂层质量。有鉴于此，多项研究致力于开发合成路线，以制备性能更均匀、环保且经济可行的颜料。
在此背景下，本研究旨在通过凝胶法（gelatin method）合成组分为LaAl₁₋ₓCrₓO₃（x=0.1、x=0.05）的钙钛矿（perovskite）结构氧化物，以期将其用作有色透明釉料的颜料。将合成过程所得粉体分别在800℃与1000℃下进行煅烧。随后通过热分析（thermal analysis）、X射线衍射（X-ray diffraction）、紫外-可见漫反射光谱（UV–visible diffuse reflectance spectroscopy）以及CIELab色度法对粉体进行表征。将该钙钛矿以2 wt.%的添加量掺入透明釉料中，用于制备陶瓷釉料。
X射线衍射图谱显示，所得粉体为单相三角晶系钙钛矿结构。样品的颜色随取代剂含量的变化而改变：Cr³+离子取代率较低且经高温煅烧所得的钙钛矿样品呈现出偏红的色调。将颜料掺入透明釉料后，其颜色未发生变化。