During the process of Aluminum smelting, a large amount of poisonous gas HF will be released, which will do great harm to the health of people and the growth of plants. So to scrubbing the pot room fume,to reclaim fluoride in the fume and to control the exhaust of pollutant is very important.Currently dry-scrubbing methods are mostly used all over the world. Because 90 to 95 percents of the absorption is achieved in the reactor, dry-scrubbing reactors become most important equipments in the dry-scrubbing process.In this paper, new-style charging equipment for purifying will be researched to help the alumina (Al2O3) in the fume adsorbed by the alumina, which was mixed with fume in the pot equably and sufficiently.Difference between new-style fluid bed and traditional one is that three-dimensional wire reticulation board is used for gas distribution plate. Experiment indicated that pressure loss of it is only 1/77 of pressure loss of level jet board.In new-style fluid bed, alumina is used as streaming material. Flow state and pressure loss are selected as assessment indicators. Wind speed, height of the static alumina, tiers of the wire reticulation and quantity of the feeding alumina are selected as affecting factors. Then orthogonal test tabulation is designed. Through experiments, the best operating parameters of the fluid bed are got.To 0°level gas distribution plate, air flux affects experimental results most,followed by three other factors—-alumina flux, tiers of the wire reticulation and height of static alumina. Four factors compose optimal condition in this way—-tiers of the wire reticulation are 4, air flux is 70m3/h, height of static alumina is 30mm, alumina flux is 2.5kg/h.To 2.5°oblique gas distribution plate, air flux affects experimental results most,followed by three other factors—-height of static alumina, alumina flux and tiers of the wire reticulation. Four factors compose optimal condition in this way—-tiers of wire reticulation are 4, air flux is 70m3/h, height of static alumina is 30mm, alumina flux is 5kg/h.To 5°oblique gas distribution plate, height of static alumina affects experimental results most,followed by three other factors—-air flux, tiers of wire reticulation and alumina flux. Four factors compose optimal condition in this way—-tiers of wire reticulation are 3, air flux is 70m3/h, height of static alumina is 30mm, alumina flux is 5kg/h.
Post about "alumina"
In Bayer process or Sintering process or Bayer Sintering combined process, red mud sedimentation is always an important step. Usually, the red mud sedimentation process is enhanced by adding flocculants in alumina industry. Comparing to high efficient polymeric flocculants made in abroad, domestic flocculant is produced by simple way, with poor adaptability and high addition amount. These poor conditions bear a big burden to the leaf filtering process.In this paper, dimethyl diallyl ammonium chloride (DM), acrylamide (AM) and Maleicacid (MA) have been used to synthesize amphoteric polymeric flocculent as raw materials. Reasonable ratios of these three monomers have been identified by orthogonal experiments. The amphoteric polymeric flocculent (AM-DM-MA) was remixed with anionic polyacrylamide, and then these compounds were tested by red mud sedimentation experiments. All these amphoteric polymeric flocculants were compared with flocculent produced abroad. The results show:The amphoteric polymeric flocculent (AM-DM-MA) got the best settling performance when the ratio of DM, MA and AM equal to 2:3:4.The settling performance of amphoteric polymeric flocculant (AM-DM-MA) gets better as the ratio of MA increases. The ratio of electron withdrawing groups and electro negativity groups in chain was changed as the quantity ratio of MA changed. As DM:MA:AM equal 2:2.5:4, it’s an isoelectric point. At this point, the quantity of suspended solid took a sharp rise in settling experiment.The settling performance of amphoteric polymeric flocculent (AM-DM-MA) was affect by the qualities of raw materials. Amphoteric polymeric flocculent (AM-DM-MA) made of import acrylamide had a better performance than the flocculent made of homemade acrylamide.The settling performance of G1Y (amphoteric polymeric flocculent (AM-DM-MA) made of domestic acrylamide remixed with anionic polyacrylamide) got better as the molecular weight of anionic polyacrylamide roses. However, the best settling performance of G2Y (amphoteric polymeric flocculent (AM-DM-MA) made of import acrylamide remixed with anionic polyacrylamide with different molecular weight) showed while the molecular weight of anionic polyacrylamide raised to 1.4 X 107, then got worse. G2Y was always better than G1Y. Contrast tests for G2 (AM-DM-MA), SW0801 (remixed flocculants) and Ciba (a flocculent produced by Ciba company) show that:The settling velocity decreases from SW0801 to G2 then to CIBA; The height of red mud decreases from CIBA to G2 then to SW0801; Content of suspended solids decreases from CIBA to SW0801 then to G2 as the addition amount in range of 110-250g per ton dry red mud. Meanwhile, the content of suspended solids of SW0801 and G2 showed a big reduction (0.259g/L and 0.388 g/L respectively), just as about a half to Ciba (0.512g/L). All the analysis shows that, G2 is good at decreasing content of suspended solids; SW0801 is good at enhance the settling velocity and compress ability. Both of them are better than Ciba. It can be selected as needed in practical application.
Alumina ultrafine powder is an important feedstock in preparing catalyst carrier and special ceramic products.There are diversified methods for its preparation,and the sol-gel method is widely used,which generally uses cheaper inorganic materials,simpler equipment and technical processes, meanwhile,the powder product is of high purity,small particle size and narrow size distribution.Hence,liquid preparation method is practical and quite competitive.Supercritical drying method is a very effective drying method,which has been widely used in7 organic synthesis and new advanced materials’ preparation.Using aluminum nitrate as raw material,citric acid as dispersant and anhydrous ethanol as solvent,nanosized AlOOH products were prepared by the combination of sol-gel and supercritical drying method.Upon calcination at 500-900℃,nanoγ-Al2O3 was obtained.Because sol-gel method always use water as solution,during the supercritical drying process there company with filtration and washing process.This dissertation mainly discusses use ethanol as solvent to avoid filtration process.The effect of the ammonia dripping speed and whip speed,the sort of solvent,the pH of the solution,the ageing temperature,and the ratio of aluminum nitrate to citric acid on the particle size of AlOOH as well as the calcination temperature on the particle size ofγ-Al2O3 were investigated.The morphology,particle size and structure of the products were characterized by TEM、IR and XRD analyses.Test results indicated that,the pH of the solution during the preparation of the sol-gel and additions of citric acid significantly affect the morphology and size of AlOOH.When pH=3 and n（citric acid）:n（aluminum nitrate）=1:2,fibrous nano AlOOH（a diameter of 1-10nm and a length of 30-40nm）could be prepared.Calcination of thus obtained nano AlOOH at 500-900℃converted it into fibrous nanoγ-Al2O3 with a diameter of 1-10nm and a length of 30-70nm.At the same time design the orthogonal experimental test to determine the influence of the add amount of citric acid and ammonia,ageing temperature,the concentration of aluminum nitrate to the BET of the AlOOH.Discussed the major influence factors during the supercritical drying method such as pressure,constant temperature time and pressure reliefing speed to the result.
In this paper, preparation of hollow spheres with template method were studied. The samples were characterized by transmission electron microscopy （TEM）, scanning electron microscopy （SEM）, X-ray diffraction （XRD） and energy dispersive X-ray （EDX）. The feasibility of most templates were investigated and the colloidal carbon spheres were confirmed as the best one. Then, the synthesis conditions were studied in detail and the best preparation technics of colloidal carbon spheres was determined. Alumina hollow spheres have been successfully prepared using colloidal carbon spheres as templates and the influences of the synthesis conditions such as reaction time, reaction temperature, and the concentration of A1（NO3）3 were studied. At last, the reaction mechanism of alumina hollows spheres preparation was discussesed.（1） In these technological conditions, the method of preparing alumina hollow spheres by CaCO3 and black carbon nanoparticals templates was infeasible. The results of the experiment indicated that there was no strong binding forces between alunima source and the templates.（2） The monodisperse and size-controlled colloidal carbon spheres were synthesized by hydrothermal method. The size can be controlled by changing the reaction time.（3） Novel size-tunable alumina hollow spheres have been successfully prepared using collciidal carbon spheres as templates and aluminum nitrate as alumina source. The results of the experiment indicated that, in comparison with the template, the samples had a serious shrinkage which was about 60% during the calcination process. Energy dispersive X-ray analysis illuminated that the samples was simple alumina and the X-ray diffraction analysis indicated that the alumina synthesized was amorphous. According to the experiment, the synthesized alumina hollow spheres with a narrow size distribution showed tunable shell thickness and uniform shells. The morphology of the alumina hollow spheres was influenced mainly by the reaction temperature.
The efficiency and output quality of Solid-state is controlled by pumping cavity。The materials used for pumping cavity should have provide high diffuse reflectivity during the required wavelength。In view of the weak point of the current commonly used pumping cavity ,such as metal Cavity, glass and plastic cavity ,the main goal of this thesis is to develop ceramic pumping cavity。The diffuse reflectivity of various alumina ceramics which were used for pumping cavities laser was discussed。The influence of chemical composition and physical structure on the diffuse reflectivity and mechanical properties was also studied。The pumping cavity provides high diffuse reflectivity during the the laser crystal absorption band,in addition, mechanical properties can meet the requirement。The detail work is as following:(1) the structure and preparing technology of ceramic pumping cavity have been designed(2) By comparation,Hot press injection was choosed as the reasonable molding method。the influence of molding parameters and binder materials to the green bodies were studied。Besides,the reliability of debinding was discussed to optimize the process(3) Choose the ceramics based on alumina,a series of prescription of materials were designed, compared them on reflectivity and mircostructure to determine the final ceramic materials for basal body(4) By changing the proportion of adulterant,several samples were prepared。the influence of sintering temperature and the proportion of adulterant to reflectivity was studied。combined with SEM,XRD,the reason which influence the properities was analyzed to optimize the process for the preparation of the sample which provided the best reflectivity (5) The strength and density of sample have been tested。combined with the optical properity,the most reasonable prosess condition was choosed。By testing the roughness of the sample surface ,the conclusion was fromed that the light was diffuse reflectivity(6) The enamel layer was prepared。By analizing the structure of enamel, The influence of enamel to the reflectivity of basal body was studied。
The wet forming technology is usually used to prepare Al2O3 ceramic substrate, such as tape casting, rolling casting, slip casting, gel casting and so on. The gel casting has pay close attention as it has the excellence of simple equipment, homogeneous microstructure, low distortion and extensive application. In the work, The gelcasting technology was used to prepare 96 Al2O3 ceramic substrate using highly-pure Al2O3 as raw material, and the sintered steatite, calcium carbonate and kaolin clay as sintering aid.In this casting for shaping of alumina ceramic, an essential requirement and key problem is to prepare the well-characterized suspension with high solid content and stability. The effects of pH value, dispersant content and milling time on the suspended property and stability of suspension, which includes the measurement for zeta potential of Al2O3 powder, the experiment for sedimentation of suspension and for viscosity measurements of suspension. The result of measurement for zeta potential indicates that the dispersant can greatly affect the zeta potential of powder and it can change the isoelectric point (IEP) from 8.2 to about 5. When pH value of the suspension with dispersant is 8~9, the absolute value of zeta potential of powder is the maximum. The sedimentation experiment indicates that the sedimentation is lower and the stability is better in the range of alkalescence and there exists an optimum dispersant content of 0.4%. The viscosity experiment indicates that when pH value is about 8, dispersant content is 0.4% and milling time is 24 hours, the viscosity value is the minimum in each condition and the suspension possesses good flow property.The obtained 45vol%(Al2O3 solid loading) Al2O3 matrix suspension was cast, then gelated and dried. The obtained green bodies sintered at 1530℃have a density of 3.7g/cm3, a microhardness of 1.49GPa and the bending strength of 300.78MPa.The densification of materials was investigated.The microstructure and thermal, electrical and optical properties of the sintered bodies were studied by using SEM, thermal expansion instrument and so on. The results of microstructure of the samples show that the grains arrange uniformly and orderly, and the pore ratio is low. The average coefficient of thermal expansion of sintered samples is 8.34×10-6K-1 and the thermal diffusivity is 0.0668～0.0154cm2/s from 20℃to 1000℃, and reduces with increasing the temperature. The electrical insulating performance is excellent, and volume resistivity is 6×1015～2×1010Ω·cm from 22℃to 500℃. The electrical resistivity decreases with the increment of temperature. In the range of the testing frequencies, the dielectric constant is 9.3~9.4 and the dielectric loss angle tangent is 2.2×10-3～5.4×10-3. The dielectric constant firstly decreases and then keeps constant as the frequency increases. The dielectric loss angle tangent reduces firstly, and then increases.
Polyimide （PI） has been widely used in electrical engineering, aerospace and microelectronic industries because of their outstanding dielectricity, mechanical, and thermal properties. In recent years, a number of studies have been conducted on preparation and general performance of PI by different workers at home and abroad. In order to improve properties of PI, methods of doped inorganic oxide into PI have been widely studied. However, the compatibility between PI and inorganic oxide still needs to be improved.In this paper, （3-aminopropyl）trimethoxysilane （APTMOS） was modified by reacting with pyromellitic dianhydride（PMDA）. Then, PI/SiO2 and PI/Al2O3-SiO2 composite films were prepared by sol-gel with 4,4′-oxydianiline diamine （ODA） and pyromellitic dianhydride （PMDA） as monomer, N,N-dimethyl acetamide （DMAc） as solvent, SiO2 collosol, Al2O3 collosol and modified APTMOS as dopant. The composite films have been characterized by Fourier transform infrared spectroscopy （FTIR） and scanning electron microscope （SEM）. The results showed that the size of inorganic particles in PI composite films was obvious decreasd by adding modified APTMOS. Properties of the composite films were measured by dielectric breakdown strength, corona-resistance time and dielectric spectra. Influence of modified APTMOS on properties of the composite films and the relations between properties and contents of the doped inorganic oxide contents were studied. The results revealed that the dielectric breakdown strength of PI/SiO2 composite films was 326kV/mm with SiO2 content of 20wt%, which was 1.5 time than that of pure PI films. Corona-resistance time of PI/SiO2 composite film with SiO2 content of 20wt% was 26.4h, which was 14 times than that of pure PI films. Dielectric breakdown of PI/Al2O3-SiO2 composite film with Al2O3 content of 10wt% was 242kV/mm. Corona-resistance time of PI/Al2O3-SiO2 composite film with Al2O3 content of 5wt% was 3.9h. Decomposition temperature of PI/Al2O3-SiO2 composite film with Al2O3 content of 20wt% was the maximum.
This work is concentrated on the study of solid-state conversion of single-crystal alumina. Effect of the average size of high purity alumina power and additive systems on the alumina grain growth and optical transmission was investigated. Morphology and phase analysis of alumina were observation. Optical transmission of alumina was measured.The results indicated that the average size of alumina powder can directly affect the size of the alumina grain growth. The smaller the average size of alumina powder can promote the growth of abnormal grain. Effect of additive systems on solid-state conversion of single-crystal alumina is different. MgO can improve the optical transmission of alumina. SiO2 can cause abnormal grain growth （AGG）. When MgO doping concentration was 900 ppm, SiO2 doping concentration were 300, 600, 900 ppm with 3 points for doping, samples of alumina powder B were sintering in 1900℃. Greater grain, same crystal orientation of alumina material was obtained. And its optical transmission was 5 times higher than polycrystal transparent alumina.In conclusion, greater grain, same crystal orientation and high optical transmission of alumina were obtained with addition of MgO-SiO2. At the same time, a thorough explanation and discussion on the alumina abnormal grain growth was also given based on the materials analysis technology. Therefore, this research is valuable to the low cost preparation of alumina ceramics.
The ZrO2 matrix nano-ceramic composites were fabricated by hot press sintering using nano- ZrO2 powders. The microstructures were analyzed by means of XRD, SEM, EDS and so on. The effect of the second phases Al2O3 and SiC particles on the mechanical properties and microstructure of ZrO2 nano-ceramics were investigated, and the reinforced and toughening mechanism were discussed.First of all, based on the introduction of microstructure, development of ZrO2 based ceramics, fabrication methods and sintering methods, the content and significance of this thesis were indicated. Second, fabrication techniques, testing methods of mechanical properties and observing methods of microstructure of nano-ZrO2 matrix ceramic composites were introduced.The research results showed that composite powders of Al2O3/ZrO2 can be well dispersed after being ultrasonically dispersed with dispersant agent of PHAA-NH4 and wet ball milled. The second phase Al2O3 dispersed homogeneously in the matrix grains. The second phase Al2O3 inhibited matrix grains growth, i.e. the ratio of grains is inverse proportion to the amount of Al2O3, but excessive amount of Al2O3 causes grains agglomeration decreasing the density. When the amount of doped-Al2O3 was 9mol%, the relative density, hardness and flexure strength of composite ceramics reached the maximum; but fracture toughness arrived crest value when doped-Al2O3 was 12mol%. The matrix ZrO2 grains were refined after adding Al2O3 and SiC, which induced fracture model to change from intergranular fracture to transgranular fracture.It was analyzed from SEM photos that many toughening mechanisms played roles in composite ceramics material. Firstly, the second phase Al2O3 which located at grain boundary refined matrix grains as a result of pinning effect. Secondly, the second phases Al2O3 induced crack deflection and bridging crack obviously, which Al2O3 grains shape played a very important role in performance improvement. Thirdly, transgranular microstructure formed when Al2O3 entered matrix grains. The formation of this microstructure has direct relationship with sintering temperature and second phase’s grain diameter. Transgranular fracture became the chief fracture model because that difference of thermal expansion coefficient between Al2O3, SiC and matrix ZrO2 exerted compression stress on matrix and reinforced grain boundary. Those mechanics increased fracture toughness of composite ceramics.
Ni-based alloys are used in space and medical fields as important parts because of its high heat strength, thermal shock resistance and the oxidation resistance. Alumina is especially used as a structural material in high temperature applications or as reinforcement in metal matrix composites because of its good mechanical properties, high thermal conductivity, good thermal shock behavior and high oxidation resistance. Wettability of molten Ni-based alloy / alumina system determines the property of metal matrix composites.Wettability of molten Ni-（Cr, W） alloy on polycrystal and single crystal alumina substrate was observed at 1773-1873 K in an Ar+3%H2 atmosphere, vacuum using an improved sessile drop method. The interface of Ni-based alloy / alumina and the surface of alumina substrate were observed and analyzed using X-ray diffraction （XRD）, environment scanning electron microscopy （ESEM）, scanning electron microscopy （SEM） and 3-D rotational microscope. The effects of temperature, alloy element, crystal type of substrate and protective atmosphere on the wettability and interface reaction were analyzed, and the thermodynamics analysis of interface reaction was also studied.Molten Ni / polycrystal alumina system is the base of Ni-based alloy / alumina system, Wettability of molten Ni on polycrystal alumina substrate was observed at 1773-1873 K in an Ar+3%H2 atmosphere. The contact angle of molten Ni on alumina substrate changes through rapid decrease stage and slow decrease stage, and tends to be equilibrium. Based on detection results and thermodynamic calculation, the interface reaction products include NiO, NiAl2O4, Al2O and Ni-Al intermetallic compounds. The initial contact angle and equilibrium contact angle of molten Ni tend to be smaller with increasing temperature, the time to be equilibrium becomes shorter. Reaction become stronger and interface product become more with increasing temperature.Adding alloy element Cr to Ni, the effect of Cr on wettability of Ni-Cr / alumina was analyzed. The initial contact angle and the equilibrium contact angle decreased and the decreasing rate of contact angle become larger with adding 5%-10%Cr. Adding Cr can enhance interface reaction and increase the interface adhesion, improve the wettability.The wetting of molten Ni-10%W alloy on single crystal alumina substrate was observed at 1823-1873 K. Due to anisotropies of the single crystal, the difference between the contact angles in two directions is large. The effect of anisotropies increases with increasing the temperature. Compared with polycrystal alumina, the effect of substrate crystal type on wettability of molten Ni-W/Al2O3 was analyzed.The wetting of molten Ni-10%W alloy on polycrystal alumina was observed in two protect atmospheres. Compared with Ar+3%H2 atmosphere, the decreasing rate of contact angle is larger, the time to be equilibrium is shorter and the equilibrium contact angle is smaller in vacuum. The interface reaction both occurred in the two protect atmospheres, the reaction is stronger in vacuum.