Views: 2 Author: Site Editor Publish Time: 2022-12-08 Origin: Site
Bismuth oxide produces three variants when burned at different temperatures. α-body: yellow heavy powder or monoclinic crystal, melting point 820℃, relative density 8.9, refractive index 1.91. At 860℃, it becomes a γ-body. β-bodies: gray-black cubic crystals, with a relative density of 8.20, convert to α-bodies at 704℃. γ-body: heavy light lemon yellow powder, belongs to the square crystal system, melting point 860℃, relative density 8.55, when melting into yellowish brown, cooling is still yellow, strong red heat that is melting, after cooling condensation into crystalline mass. All three are insoluble in water, soluble in ethanol, strong acid. Preparation method: Burning bismuth carbonate or basic bismuth nitrate until the constant weight, keep the temperature at 704℃ to get α, β- body, keep above 820℃ to get γ- body.
The bismuth nitrate solution (80 ~ 90℃) was mixed by adding a CO2-free sodium hydroxide solution. In the process of precipitation, the solution remained basic and formed white bismuth oxide hydrate Bi(OH)3 precipitate. The solution was heated and dehydrated into yellow bismuth trioxide after short stirring. Bismuth oxide was prepared by water pour washing, filtration and drying.
As an advanced powder material, bismuth oxide is not only used in electronic ceramic powder materials, electrolyte materials, photoelectric materials, high temperature superconducting materials, catalysts, but also in other aspects, such as nuclear waste absorption materials. Picture tube shadow mask coating, non-toxic fireworks and so on have a good application prospect. With the deepening of the research on the application of bismuth oxide and the strengthening of people's awareness of environmental protection, bismuth oxide will be more widely used.
1. Electronic ceramic powder materials
The field of electronic ceramics is a mature and dynamic market for the application of bismuth oxide. As an important additive in electronic ceramics powder materials, bismuth oxide is generally required to be more than 99.5% pure. The main applications are zinc oxide varistors, ceramic capacitors and ferrite magnetic materials. In terms of the development of electronic ceramics, the United States is in the forefront of the world, while Japan occupies 60% of the world ceramic market by large-scale production and advanced technology. The market capacity of Chinese electronic ceramics is growing at an annual rate of 30%, which will inevitably drive the demand for bismuth oxide to grow at the same speed. With the improvement of the research and development of nanometer bismuth oxide and the innovation of homogenization manufacturing technology, It will improve the performance of electronic ceramic related components and reduce the production cost.
Bismuth oxide plays the role of liquid phase firing aid and pressure sensitive effect forming agent in zinc oxide varistors, which is the main contributor to the high nonlinear voltammetry characteristics of zinc oxide varistors. Researchers in Brazil prepared ZnO2 Bi2O3 powder mixture by combustion method to achieve the goal of homogenization, which shows good performance in the application of varistors. Researchers from Central South University have prepared nanometer bismuth oxide with an average particle size of 10nm. Its application mechanism in zinc oxide varistor, its contribution to homogenization manufacturing technology and the improvement of varistor performance are under study. Bismuth oxide can effectively improve the dielectric constant of ceramic capacitance, reduce dielectric loss and improve sintering conditions, such as in strontium titanate ceramics. The addition of Bi2O3 is a key factor for the formation of SrTiO3 and TiO2 phases. After the mechanical activation of SrBiTi4015 with the addition of BiO2, 50-100nm particles can be obtained, which are stable at room temperature. After sintering, the density reaches 98%, the dielectric constant is 2770, and the dielectric loss is 0.08. The bismuth oxide doped ferrite magnetic material has good sintering and magnetic properties. For example, when it is added to the NiZnCu ferrite by oxidation, it can be sintered into a magnet with an initial permeability greater than 250 at 850℃, a permeability greater than 300 at 10MHz and a density of 46g/cm3.
2. Electrolyte material
SBi2O3 is a special material with a cubic Yellowstone type structure. 1/4 of the oxygen ions in its lattice are vacant, so it has very high oxygen ion conductivity. Near the melting point, the conductivity is about 0.1s/cm, which is a very potential electrolyte material for solid oxide fuel cells or oxygen sensors. Its conductivity at the same temperature is 1-2 orders of magnitude higher than that of existing zirconium electrolyte materials, such as YSZ. If YSZ can be replaced in solid fuel cells, it will be of great significance to improve the efficiency and life of batteries, save battery materials and simplify the production of batteries.
3. Photoelectric material
Due to its excellent optical properties, such as high refractive index, infrared transmission and nonlinear optical properties, bismuth oxide based glass is very attractive in the application of photoelectric devices, optical fiber transmission and other materials. In such materials, bismuth oxide is used as an additive in a large amount, which is one of the important application directions of bismuth oxide. Bi2O3-B2O3-Si2O3 glasses have a high speed reaction of less than 150fs, which can be used for optical switching and broadband amplification. Bismuth glasses with cesium, such as 63.3Bi2O3-32.6B2O3-41Si2O3-0.24CeO2, have better performance, and the content of bismuth oxide is as high as 63.3%. Bismuth silicate and Bismuth germanate are both excellent light refraction materials. Bismuth germanate is used in holographic tongue storage, phase conjugation, two-dimensional exchange, real-time interferometry and other materials due to its excellent piezoelectricity and photoconductivity. Bismuth borate crystal has a large nonlinear optical coefficient and a very high light damage threshold, which can be compared with LBO with high optical quality. The crystal has a wide light transmittance and no delixing. It is a new material with great application potential.
4. High temperature superconducting material
The content of bismuth oxide in the powder of bismuth superconducting material is close to 30% and the purity is 99.99%. With the great breakthrough in the preparation technology of Bi-Sr-Ca-Cu-O high temperature superconducting materials, the high temperature superconducting wire quickly formed the industrial production capacity, which promoted the application of bismuth oxide. The current research focuses on the improvement of critical current density, mechanical properties, AC loss reduction and cost reduction.
There are three main types of applications of bismuth oxide in catalysts:
One is molybdenum-bismuth catalyst, such as bismuth-molybdenum-titanium mixed oxide obtained by sol-gel method, with a specific surface area of 32-67m2/a, which is a good and economical catalytic material for oxidation reaction. In industrial applications, it can be used as propylene oxidation to alledehyde, acrylonitrile preparation from propylene, butene oxidation, degassing to butadiene preparation. Catalysts for oxidation of butadiene to furan, etc.
The second type is yttrium bismuth catalyst, a bismuth oxide material doped with yttrium oxide, which is a very attractive catalyst for the conversion of methane to ethane or ethylene oxidation coupling reactions. For example, BY25, doped with 25% yttrium oxide bismuth, bismuth is currently used in methane oxidation coupling catalyst (such as LiMgO) efficiency is 15 times higher, and can be recycled 18 times.
The third is the burning rate catalyst. Bismuth oxide is gradually replacing lead oxide as the important catalyst in solid propellant. Because lead oxide is toxic and has direct or indirect hazards to workers and the environment, and because of the smoke produced in engine exhaust, it is not conducive to guidance. Bismuth oxide is a kind of ecological safety material with low toxicity and less smoke. Therefore, bismuth oxide has been successfully used in the former Soviet Union to replace lead oxide as a burning rate catalyst. At present, the effects of nanometer bismuth oxide on increasing burning rate and reducing pressure index of propellant are being studied.