Iron Oxide red pigment is mainly introduced in the form of colorant in ceramic pigment formula. Such as brown series and black series in glaze pigments; Zirconium iron red pigment in zirconium series pigments; Iron oxide red raw materials are also widely used in the black, coffee and Tan series of green body pigments, and colored cement bricks such as ceramic glazed tiles. Therefore, the amount of iron oxide red pigment used in ceramic pigments is large, and it is estimated that the annual amount is more than 10000 tons. At present, the production methods of iron oxide red pigment used in ceramic pigments are mainly divided into sulfuric ACID method and mixed acid method (nitric acid method). After processing with thin iron plate as raw material, the red and bright iron oxide red pigment is obtained. Generally, the comprehensive index of iron oxide red produced by nitric acid process is better than that produced by sulfuric acid process.
1、 Application of iron oxide red in brown series products
Brown series products occupy a large market in ceramic glaze pigments. Especially in the production of ceramic tiles and retro bricks, two series of products, golden yellow and red brown, are widely used.
Brown series products mainly have two crystal structures of Fe Cr Zn Al and Fe Cr Zn. Iron oxide red pigment is mainly added in the form of colorant. Trivalent iron ions keep red, and through compound coloring with Chrome Green, they produce golden to black brown tones. In this study, the following tests were carried out: using the frit made of chemical composition and adding 3% of the pigment to the frit, with the increase of iron oxide red pigment in the formula, the redness value and yellowness value decreased correspondingly, the hair color of the pigment changed from golden yellow to red brown, and the brightness value of the pigment also decreased correspondingly; at the same time, it was found that the number of glazed pinholes increased correspondingly.
This is because with the increase of iron oxide red pigment in the formula, the unsaturated iron ion in the pigment increases, which is easy to be separated from the high-temperature liquid phase of frit glaze. When the pinhole increases, the color saturation decreases correspondingly. From the appearance of the pigment, with the increase of iron red pigment content, the sintering degree of the pigment increases, indicating that iron red pigment can reduce the sintering temperature in brown series products.
2、 Application of iron oxide red in green black material
In the production of ceramic wall and floor tiles, three medium colors, black, yellow and coffee, are mainly used. Among them, the ceramic body black material accounts for more than 35% of the body color material, and the manufacturer consumes more than 60000 tons of body black material every year. Iron oxide red pigment is the main raw material for the formulation of green body black pigment, and its content can usually reach 50%~80%. The hue of iron oxide red products produced by different manufacturers varies greatly. For example, the quality of iron oxide red products with the specification of 130 is relatively stable in Jiangmen, while the products with the origin of Qingyuan are slightly worse in terms of temperature resistance and color tone. In this study, iron oxide red 130 products from different places were directly added into the green mud at the amount of 3%. After beating the cake, it was calcined at 1060 ℃ to test the chromaticity value of the green mud.
The experiment shows that the color and high temperature stability of the fired products are different when the iron oxide red pigments from different places are used due to the differences in the process and raw materials used by the manufacturers. Generally, the green body black product with bright red appearance has better saturation, and the product with dark purple appearance has higher blue value. At present, the price of 130 iron oxide red products in the market is about 7000 yuan / ton. Iron oxide red products with a price lower than 4500 yuan / ton generally have poor high-temperature stability and are only suitable for the production of low-grade body black products.
3、 Application of iron oxide red in black glaze
The cost of glaze black products is higher than that of other glaze pigments, and the pure blue tone is the best for cobalt black products. The cost of brilliant black products is slightly lower than that of cobalt black because they do not contain cobalt oxide. However, there are some bright black products on the market, whose pure black tone can be comparable with cobalt black. Iron oxide red pigment mainly plays a role of color aid in glaze black pigment. It is generally believed that under the condition of oxidizing atmosphere, nio-cr2o3 formed at 1000 ℃ has a cyan green tone, nio-fe2o3 has a black with red tone, and co-fe2o3 has a blue black tone, presenting a pure black through composite coloring. At the same time, cuo-fe2o3 can also show a blue black tone in the glaze.
At present, the iron red products for ceramic pigments sold in the market are mainly 110, 130, 190, etc. Due to different production processes, products of the same specification also have great differences in performance and prices, usually at 3000~7000 yuan / ton. The simple evaluation method of iron red is as follows: check whether the appearance is bright; High temperature resistance; The degree of stickiness when pinched by hand. Generally speaking, the scarlet and sticky iron red is better than the dark purple.
Because iron red has a great influence on the firing temperature and hue of the product, when selecting iron red for the production of black material for ceramic glaze, it needs to be selected according to the design requirements of the product, and whether it meets the requirements shall be tested by calcining the production formula.
In this study, the comparative test of iron oxide red pigments from various manufacturers in raw material antique glaze was conducted. The basic formula of fe:cr:ni:mn=30:35:30:10 was adopted in the test, in which Mn was introduced in the form of manganese oxide. The pigment is added to the raw glaze in the proportion of 3%. Prepare the color raw material, quickly raise the temperature to 1250 ℃ in the laboratory electric furnace for 4h, and keep the constant temperature for 2h. The burned color clinker and scraped brick sample are burned in the laboratory roller kiln at 1180 ℃ and the firing cycle is 30min. The chromaticity value of the burned sample is tested.
The results show that the iron oxide red pigment with the specification of 130 is more suitable for the production of black glaze, and its blue value is better than that of 190 iron red. For other specifications such as 110 iron red, no comparison test was conducted due to the high cost. It is generally believed that black products for glaze have better hair color in high-temperature glazes, and they also have the same hair color trend in low-temperature tiles. It should be noted that yanhei products are more suitable for use in porcelain chips. Sometimes the hair color is red and light in high-temperature glazes, but presents a pure blue tone in low-temperature glazes. Bright black nickel black products are easy to be "out of tune" during ball milling in production. Specifically, the longer the ball milling time of nickel containing black products, the more red color will be inclined, and the color depth will be significantly reduced. In particular, the less nickel in the formula, the more obvious this change will be. Cobalt black products are relatively stable.
