1. What are the factors that affect the plasticity of the billet?
Answer: (1) Mineral types. When the mud mass has good plasticity, it should have finer particles, complete mineral cleavage, and thicker water film on the particle surface. Conversely, plasticity will be reduced. ⑵The size and shape of solid phase particles. Generally, the coarser the particles, the lower the plasticity, and the finer the particles, the better the plasticity. The plasticity is good when the particles are in the form of plates and short columns. ⑶The type of adsorbed cations, such as H-clay>Al3+>Ba2+ ⑷The quantity and nature of the liquid phase, the water should be appropriate, not too much or too little.
2. What are the factors affecting the adaptability of blank glaze? What are the specific effects of various factors on the adaptability of blank glaze?
Answer: (1) Thermal expansion coefficient of the blank and glaze: When the thermal expansion coefficient of the blank is greater than that of the glaze, the glaze will be subjected to compressive stress and the glaze will peel off; when the thermal expansion coefficient of the blank is smaller than that of the glaze, the glaze will be subject to tension. Stress causes cracks on the glaze surface; when the thermal expansion coefficient of the glaze is slightly smaller than that of the blank, there will be little compressive stress in the glaze, and the bonding of the blank glaze is the most suitable.
(2) The chemical composition of the blank and the glaze: when the chemical composition of the blank and the glaze is close, the glaze of the blank is firmly bonded; when the chemical composition of the blank and the glaze is quite different, the glaze is easy to peel off.
(3) The modulus of elasticity of the blank glaze should be similar.
(4) The thickness of the glaze should be appropriate.
(5) The firing temperature of the billet and glaze should be compatible.
3. Try to analyze the reasons for black core defects in plate ceramic products? And point out the way to overcome it?
Answer: The reason is that the brick area is large, the brick adobe is thick, the free water and structural moisture in the inner layer are not easy to discharge, and the gas generated by the decomposition of organic matter is not easy to discharge. At the same time, because most bricks are fired quickly and at low temperature, the firing cycle is very short. Overcoming methods include: reducing the content of highly plastic clay, reducing the thickness of bricks, appropriately increasing the firing temperature and prolonging the firing time, and reducing the water content of the green body entering the kiln.
4. Analyze the reasons for the dissolution of lead in pigments? What are the current solutions to lead dissolution?
Answer: The reason for the dissolution: After the lead-containing glaze and the flux of the glaze pigment are fired, they form a lead-containing low-melting glass. Under the action of acid, Pb2+ will fall off from the silicon-oxygen network of the glass, due to Si—O The single bond strength is high, but the single bond strength of Pb—O is low, so the acid solution can interrupt Pb—O, so that the free lead on the network dissolves into the solution, and K—O, Na—O in the system containing alkali Weaker, easy to dissolve, leaving vacancies, becoming the dissolution channel of lead. At present, there are these methods to solve the dissolution of lead: (1) Select acid-resistant pigments, decals, and fluxes. (2) Appropriately design the screen. ⑶ Improve the color firing process. ⑷Steam treatment. ⑸Chemical treatment.
5. What are the factors that affect the color of ceramic pigments? (The main factor affecting the color development in the whole process from the color element to the pigment to the final color after the pigment is used as a decorative material)
Answer: (1) The valence and coordination number of coloring ions. Its color depends not only on the type of ion and the price of electricity, but also on the coordination number of the coloring ion, the polarization ability and the effect of the surrounding ions on it. (2) The composition of the flux. When the colorant is formulated into a pigment, it often needs to be used in conjunction with the flux. (3) The composition of the basic glaze, for ion-colored colored glazes, its color mainly depends on the influence of the basic glaze on the coordination state of the colored ions. ⑷Firing system, the coloration of many colored oxides is obviously affected by temperature.
6. The cause of dull glaze.
Answer: There are three reasons for the dullness of the glaze surface: one is raw firing, that is, the dullness produced by the uncooked glaze. This kind of dullness cannot be called dullness in the true sense; The third is that many microcrystals are formed in the glaze, and these microcrystals are evenly distributed on the glaze surface; when their size is larger than the wavelength of light, it will form silky or jade-like luster on the glaze surface without strong reflected light .
7. What are the principles for preparing fast melting?
Answer: ① Water-soluble and toxic raw materials should be placed in the frit; ② (R2O+R2O3)/(R2O+RO)=1:1～3:1 is the appropriate melting temperature. Alkaline salts do not evaporate. ③RO2/RO is less than 1, and the frit is insoluble in water. ④SiO2/B203 is greater than 2, and the frit is insoluble in water. ⑤Al2O3 in frit ingredients should be controlled within 0.2mol. Too much, high viscosity, difficult melting, uneven frit, and more volatile alkaline substances. ⑥Oxygen ratio (oxygen brought in by silicon dioxide and oxygen brought in by other oxides) should be 2-6.
8. What are the current methods to reduce the amount of lead and cadmium dissolved in daily-use porcelain dinnerware?
Answer: The methods are as follows: (1) Choose acid-resistant pigments, flower paper and flux, and hope to use pigments with high acid resistance of colorant and flux. ⑵ Appropriate screen design. ⑶ Improve the color firing process. ⑷Steam treatment ⑸Chemical treatment.
9. What are the performance requirements of makeup soil?
Answer: ⑴ It must be uniform and have fine particle composition. ⑵The fineness of makeup soil is required to be smaller than that of the green body but larger than that of the glaze. ⑶ The drying shrinkage and firing shrinkage of makeup soil are moderate, slightly larger than the drying shrinkage and firing shrinkage of the green body. ⑷The expansion coefficient of makeup soil should be between the body and the glaze: α blank ≥ α makeup soil ≥ α glaze. ⑸The suspending property of make-up clay should be good, and it can be well adhered to the green body before and after baking.
10. Why is the sericite porcelain in Jingdezhen white and blue?
Answer: Jingdezhen sericite porcelain was originally made of single hydromica and sericite clay as raw materials. Later, with the development of technology, kaolin was added to improve the performance of the product. The kaolin in Jingdezhen contains more iron and relatively titanium. Less, when firing sericite porcelain, use a reducing atmosphere to fire, and iron exists in a low-valence state in the porcelain, so the fired product will be white and blue.
11. What is feldspar porcelain? What is Sericite Porcelain? What are their characteristics? How do they compare?
Answer: (1) Feldspar porcelain is a three-component system porcelain of “feldspar-quartz-kaolin” with feldspar as flux. Features: Feldspar has the characteristics of melting at a lower temperature to form a high-viscosity liquid phase. The firing range is relatively wide, the porcelain is white, the thin layer is translucent, airtight, low water absorption, hard texture, and high mechanical strength. , good chemical stability, good thermal stability.
⑵ Sericite porcelain is “sericite-quartz-kaolin” system porcelain with sericite as flux. Features: In addition to the general performance characteristics of feldspar porcelain, it also has the characteristics of high transparency and “white inside and blue”.
12. The way to prepare ceramic materials with zero-order thermal expansion coefficient.
Answer: (1) Magnesium oxide can be used instead of barium oxide, and calcium oxide should be avoided. ⑵In a certain composition, intermediate oxides can be added. ⑶B2O3 can be added or other parts can be used to replace SiO2 in the glaze. ⑷Spodumene and other low expansion coefficient raw materials can be used.
13. What are the characteristics of wollastonite as ceramic raw material?
Answer: (1) Wollastonite is used as a flux in ceramic production, which can lower the firing temperature and introduce calcium carbonate and silicon dioxide.
(2) When wollastonite replaces calcite and quartz for glaze, glaze bubbles and pinholes will not occur on the glaze surface due to gas precipitation, but if the amount is too much, it will affect the gloss of the glaze surface. Wollastonite does not contain organic matter and structural water, and its drying shrinkage and firing shrinkage are very small, so its billets are very suitable for rapid firing.
(3) The needle-like crystals of wollastonite formed after firing are cross-arranged in the green body to form a network, which improves the mechanical strength of the product. At the same time, the formed glass phase containing more alkaline earth metal oxides is hygroscopic. Swells are small.
(4) The main problem of the wollastonite green body is that the firing range is small.
14. What are the characteristics of overglaze, underglaze and inglaze colors?
Answer: The main points of the answer: the glaze surface of the product is decorated with overglaze pigments or decals, and the picture obtained by firing at about 900 ℃ is called overglaze color. The characteristics are: the color is very rich and bright, but on the glaze surface, it is easy to wear and lead and cadmium are dissolved; the underglaze color is directly decorated on the green body, then covered with transparent glaze, and fired at one time. The characteristics are: overcoming the shortcomings of overglaze color, but the tone is relatively monotonous; inglaze color is decorated on the bottom glaze, then covered with transparent glaze, and fired once or several times. Or decals on the glazed surface of the product, etc., and then quickly fired at 1060-1250 °C. The characteristics are: it has the advantages of over-glaze and under-glaze decoration, and the color tone is relatively rich.
15. A factory casts plaster models for two purposes, that is, roll forming and grouting molding. The ratio of plaster to water is: a) gypsum powder: water = 1.35: 1 b) gypsum powder: water = 1.20: 1 To judge which molding method is suitable for the two plaster models? Why?
Answer: Gypsum powder: water = 1.35: 1 is suitable for making roll forming molds, gypsum powder: water = 1.20: 1 is suitable for making grouting molds, mainly because grouting uses the capillary on the inner wall of the plaster mold to absorb water, thereby Dehydrating the slurry on the inner wall of the plaster mold to form a green body layer requires the model to have a high water absorption rate. However, roll forming does not require the mold to have this performance, but requires it to have high mechanical strength.
16. What is the difference between water absorption of gypsum materials and water absorption of ceramic materials? Why?
A: The gypsum mold absorbs water through the capillary force of the inner wall to promote the absorption of water in the mud, so that it hardens into a blank, and the gypsum mold itself does not change and react. The ceramic material absorbs water by combining water in the form of free water and changing itself.
17. Review the methods to improve the thermal stability of saggers?
Answer: Use saggers made of silicon carbide and other materials as much as possible to reduce their elastic strain energy. By reducing the particle size of raw materials and uniform particle composition, a reasonable firing system should be formulated to avoid mullite formation in saggers during use. crystals, etc. to achieve.
18. What are the main causes of damage to plaster models and the ways to improve the quality of plaster models?
Answer: The main reasons for plaster mold damage are:
⑴The strength of the model itself is not high, and it is easy to be crushed or fractured.
⑵The working surface of the model is worn out by the mud particles in the blank and scrapped
(3) For grouting abrasives, due to the reaction between the model and the electrolyte in the mud, sodium sulfate crystallization occurs in the capillary pores and on the surface of the abrasive, thereby reducing the water absorption capacity. Ways to improve the quality of gypsum models ⑴: Add retarder ⑵ Synthetic resin reinforcement model ⑶ Vacuum treatment of gypsum slurry
19. Briefly describe the preparation process of plaster mold?
Answer: The master mold is used as the mold for pouring the plaster mold, and a layer of release agent is first applied on the working surface of the master mold to facilitate demoulding. Then, adjust the plaster of paris powder and water into a slurry (the ratio of model gypsum to water for general grouting molding is 100:70~90; the ratio of model gypsum to water for plastic molding is 100:60~70), pouring operation It must be completed within 5 to 8 minutes. After the model plaster has solidified and hardened, it can be demoulded to obtain the required plaster mold.
20. What are the performance requirements of kiln furniture?
Answer: The kiln is required to have good structural strength; good thermal shock resistance; good thermal conductivity, and volume stability during repeated use.
Post time: Dec-08-2022