Study On Preparation And Properties Of Encapsulated C@ZrSiO₄ And SiOC@SiO₂ Black Ceramics Pigments

Black pigments are favored for their stable and dignified color and are one of the most common ceramic decorations.At present,the black pigments are mainly composed of spinel oxides such as Co-Cr-Fe-Mn in China.Due to the high price of cobalt resources and the dissolution of heavy metals in daily use,the development and application of pigments are limited to causing harm to the human body and the environment.Carbon black is a low-priced and harmless black pigment,but it is too easy oxidized in a high-temperature environment to be applied to ceramic decorative decoration.Therefore,encapsulated carbon black material has become the development direction of non-toxic ceramic pigment.However carbon black has little affinity with water,polymers,organic solvents and is hard to be encapsulated,resulting in high chromaticity values.In this study,C@Zr Si O₄ black pigment was prepared by sol-precipitation method,using walnut shell powder,Si OC was prepared by precursor method and subsequent oxidation process to prepare Si OC@Si O₂encapsulated black pigment.The effects of heat treatment temperature,raw material mass ratio and particle size on the microstructure of precursor particles,composition,color performance and temperature stability were systematically studied by XRD,FTIR,TG-DSC,SEM,TEM,colorimeter and other characterization methods.The main research contents are as follows:（1）Zirconium silicate encapsulated carbon（C@Zr Si O₄）black pigment was prepared by sol-precipitation method,using walnut shell powder as carbon source,zirconium oxychloride（Zr OCl₂·8H₂O）as the zirconium source,ethyl silicate（TEOS）as the silicon source,and lithium fluoride（Li F）as the mineralizer.The effects of heat treatment temperature and ratio of walnut shell powder/Zr Si O₄ on the microstructure and composition of precursor particles,as well as the color performance and temperature stability of the finished pigment were systematically studied.The experimental results show that the C@Zr Si O₄ pigment with excellent coloring performance can be obtained when heat treatment temperature is 1 100℃,and the mass ratio of walnut shell powder/Zr Si O₄ is 1:3.The color values of this pigment are L^*=31.3,a^*=0.4,b^*=1.4 and parcel rate is 34.7%.When5%was added to the glaze,the chromaticity values of black glaze were L*=41.2,a*=1.2and b*=1.7,respectively,indicating that the pigment had good color rendering performance and stability in the glaze.（2）Si OC powder was prepared by thermal crosslinking and pyrolysis,and subsequent oxidation process to prepare Si OC@Si O₂ black encapsulated pigment in situ.,using hydrogen-containing polysiloxane and tetramethyltetravinylcy-clotetrasiloxane as the basic raw material,using methylvinylsiloxane platinum complex as the catalyst.The results show that when the pyrolysis temperature is between 800°C and 1100℃in argon atmosphere,the precursor is converted to Si OC amorphous state and network carbon is precipitated.When the pyrolysis temperature is higher than 1100°C,the Si OC amorphous state is phased to form free carbon,silicon carbide and silica nanodomains.This provides a good carbon source for black pigments,because Si OC contains network carbon or free carbon to make it appear black.Through the subsequent oxidation treatment of Si OC powder,silicon carbide,silica nanodomains.are oxidized,and silica encapsulated layer is formed on the surface of Si OC particles,so as to obtain Si OC@Si O₂ in situ encapsulated black pigment.（3）The affected law and mechanism of formula composition,pyrolysis temperature,oxidation time and particle size of precursors on the phase composition,microstructure and color-rendering properties of the preparation of coated pigments were explored.The results show that Si OC powder is prepared by pyrolysis at 1200℃and heat preservation for1h,when the mass ratio of hydrogen-containing polysiloxane/tetramethyltetravinylcy-clotetrasiloxane=1∶2 and the catalyst is added as 0.75%of the synthesized precursor.And Si OC@Si O₂ encapsulated pigment in situ with excellent coloring performance is prepared,when Si OC powder is oxidized at 1200°C 1h.The color values of this pigment are L*=12.3,a*=0.8,b*=-1.2.When 5%was added to the glaze,the chromaticity values of black glaze were L*=27.1,a*=0.8 and b*=-0.7,respectively,indicating that the pigment had good color rendering performance and stability in the glaze.