Studies On Corrosion Of Ancient Jun Ware Glazes In China

All materials can suffer from environmental corrosion;the extent,rate,phenomenon and mechanism of corrosion depend on the material composition and structure as well as the environment.The corrosion of silicate glasses,ceramics,and metals have received a lot of attention.Moreover,ancient glazes provide effective specimens for studying the long-term corrosion of glass and porcelain under natural burial environment.Study on ancient glaze corrosion is of great significance the conservation of this cultural relics.Jun glaze is famous for its unique color and a glassy body with complex phases.Based on the unearthed materials from Juntai kiln in Henan,Duandian Kiln in Henan,Haifeng town site in Hebei,Henglong Plaza in Shandong and Qingzhou Yunmen Theater in Shandong,this work studies corrosion layer,products,phenomenon and process.Jun ware glaze analyzed in this work mainly belong to calcium glaze,and some are calcium alkali glaze.The glaze is composed of crystals and phase separation glass.The glaze corrosion displays three different types,consisting of Type ?,dendritic and columnar wollastonite crystals have a preferential corrosion relative to glassy phase,leaving dendritic or columnar pits and craters to dissolve into calcium ions and silicic acid;Type ?,the Ca-rich spherical droplets or worm-like separated phase have a preferential corrosioncompared to the Si-rich glassy matrix,forming the corroded layer.This layer preserved the morphology of uncorroded glassy phase,displaying spherical and worm-like pits.This progress could be interpreted as the result of ion exchange,and ions concern calcium and to a lesser extent magnesium,described as network modifers;Type ?,the corrosion behavior of the homogeneous glassy phase is similar to the Ca-rich separated phase.As the chemical composition results,the corroded area with crystals are is characterized by steep depletion in calcium.The corroded layer by steep depletion in calcium and lesser extent magnesium,forming Si-rich layer.Some calcium ions react with CO2 or CO32-from the soil to precipitate crystalline calcium carbonate second phase CaCO3 in the glaze surface corroded pits or on the corroded layer.The different thickness of the corroded layers can reflect the extent of corrosion.For the samples from Juntai Kiln,the thickness of corroded layer is greater in the areas with worm-like separated glassy phase than in those with spherical droplets.For the samples from Duandian Kiln,the thickness of corroded layer is greater in the areas with worm-like separated glassy phase than in those with the homogeneous glassy phase.As a whole,the glaze made up of the Ca-rich worm-like phase separation has less chemical durability for samples in the same site.The cracks formed during the cooling process and the interconnected craters caused by crystals dissolution can provide channels to facilitate the progression of the corrosion.Meanwhile,cracks formed a interconnected channel,enabling groundwater to penetrate the more durable area and to reach the less durable area for enlarge the corrosion.The appearance of glaze can be changed due to its corrosion.The corroded craters and layers in/on the glaze causing the decreasing of opacity and white color converting to light yellow.This work could change the traditional view that porcelain is corrosion-resistant and corrosion can be considered as a factor in ancient ceramic research.