高铝强化硬质瓷的制备及微观结构研究

以传统的硬质瓷配方为基础,通过提高配方中氧化铝的含量,并用烧滑石和方解石取代钾长石作为助熔剂,在1410℃下制备了具有良好半透明性的高铝强化硬质瓷.借助SEM、XRD、电子万能试验机和紫外-可见光分光光度计等测试手段研究了MgO、CaO以及MgO、CaO复合对硬质瓷显微结构和性能的影响,并探讨了其作用机理.结果表明:MgO或CaO取代K2 O作为助熔剂能够消除瓷胎中的残余刚玉晶相,并能促进瓷胎内二次须状莫来石晶体的形成,但取代量过多会导致须状莫来石粗化.一方面,引入MgO、CaO消除了折射率较大的刚玉相,使试样内部形成大量发育良好且分布均匀的莫来石晶须;另一方面,MgO、CaO的引入提高了瓷胎玻璃相的折射率,减小了晶相与玻璃相间的折射率差值,使得硬质瓷兼具高强度和良好的半透明性.随着MgO/CaO质量比的增大,试样的强度呈先增大后减小的趋势,透光度呈递增趋势,吸水率逐渐降低,当MgO/CaO质量比为0.83时,试样的综合性能最优,其抗弯强度为107.3 MPa,透光度为12.6％(厚度1 mm),吸水率为0.20％.     

真空铝热还原Li_5AlO_4制取金属锂的研究

常压煅烧氢氧化锂、氧化铝和氧化钙混合物可得到Li_5AlO_4型富锂熟料,真空铝热还原该熟料可制备金属锂,同时获得12CaO·7Al_2O_3型还原渣,该渣通过碱液溶出、碳酸化分解可制备氢氧化铝。研究了还原温度、还原时间、铝粉过量系数对真空铝热还原制取金属锂过程的影响。结果表明:在系统压强-5 Pa,还原温度1200℃,还原时间120 min,铝粉不过量的条件下,金属锂的还原率为97.76%,还原渣主要成分为12CaO·7Al_2O_3。铝粉过量超过10%不利于金属锂还原率的提高,且还原渣的主要成分为CaO·2Al_2O_3和CaO·Al_2O_3。     

CuO-TiO_2复合助剂低温烧结氧化铝陶瓷的机理(Ⅱ)

固定CuO(0.4%)和TiO_2(4%)的添加量、改变TiO_2(0-32%)和CuO(0-3.2%)的添加量(质量分数,下同),研究了CuO-TiO_2复合助剂对氧化铝陶瓷烧结性能、微观结构、物相组成以及烧结激活能的影响,以揭示复合助剂的低温烧结机理。结果表明,在1150-1200℃TiO_2固溶入Al_2O_3生成Al_2Ti_7O_(15)相,并生成大量正离子空位提高了扩散系数,从而以固相反应烧结的作用机理促进了氧化铝陶瓷的致密化;TiO_2在Al_2O_3中的极限固溶度为2%-4%,超过固溶极限的TiO_2对陶瓷烧结没有促进作用;添加适量的CuO(0.4%)可将TiO_2在Al_2O_3中的固溶温度降低到1100℃以下,并以液相润湿作用促进氧化铝陶瓷的致密烧结。陶瓷烧结激活能的计算结果定量地印证了上述烧结机理;当在Al_2O_3中添加4%的TiO_2和2.4%的CuO,可将烧结激活能降低到54.15 kJ·mol~(-1)。     

铝酸钠溶液中硫化物危害及其防治

硫化物是铝酸钠溶液中的主杂质，本文主探讨铝酸钠溶液中主杂质来源和在流程中走向分析；硫化物在氧化铝生产中的反应机理或行为，硫化物对氧化铝生产的主影响，硫化物或铝酸钠溶液中含硫离子的消除措施。     

添加氧化物对Ba2TiSi2O8极性玻璃陶瓷析晶性能的影响

采用恒温场晶粒定向晶化工艺制备了Ba2TiSi2O8极性玻璃陶瓷，在组成1．2BaO—1．0TiO2—2．6SiO2的基础玻璃中，分别加入0．2CaO和0．1ZrO2，研究了添加不同的氧化物对Ba2TiSi2O8极性玻璃陶瓷析晶性能的影响。实验结果表明，加入CaO和ZrO2都会影响主晶相的析出过程，特别是加入ZrO2造成玻璃陶瓷中产生BaZrSi3O9第二相。此外，压电性能测试显示，加入0．2CaO有利于BTS晶体的定向析晶；加入ZrO2不利于BTS晶体的定向析晶。     

一种低软化温度无机胶粘剂的制备研究

用废玻璃粉、B2O3、ZnO和P2O5等氧化物为主要原料，研制低粘接温度的无铅环保型易熔玻璃。实验中先采用四因素三水平的正交表，对废玻璃粉添加量为30％（质量分数）的样品进行了正交实验，测定其粘接温度瓦和熔化温度Tm；并对添加MgO、CaO、Al2O3等氧化物引起的易熔玻璃瓦温度的变化进行了分析。     

掺CeO2的MgO-CaO材料缺陷研究

以分析纯Ca(OH)2和Mg(OH)2为原料,CeO2为掺杂剂,利用行星球磨机混合后压制成型,经1650℃烧成,保温3h,制备了MgO-CaO材料。通过XRD和SEM对试样进行了分析表征。结果表明,随CeO2掺入量的增大,CaO的晶格常数先增大后减小,试样的体积密度不断增大,显气孔率减小,致密化程度增强;在烧结致密化过程中,MgO晶粒长大比CaO更为明显,试样晶粒间的气孔逐渐减少,但MgO晶粒中的气孔逐渐增多,而CaO晶粒中未有气孔出现;CeO2促进材料致密的实质是与CaO发生置换固溶,Ce4+进入CaO晶格内,增大了Ca2+空位浓度,有利于Ca2+的扩散。     

真空硅浴熔融还原白云石炼镁的实验研究

通过往煅烧白云石中添加适量的Al2O3和SiO2,使其在1500～1600℃之间形成熔融炉渣,并在真空下采用硅铁还原液态渣中的MgO。研究了造渣剂对MgO还原率的影响,结果表明,在能够获得熔融炉渣的情况下,增大Al2O3/SiO2比能够极大地提高渣中MgO的还原率,理想的炉渣成分为32.0%CaO-23.0%MgO-35.0%Al2O3-10%SiO2。同时,对该炉渣进行了正交实验,通过分析得出影响MgO还原率因素的顺序依次是:反应温度、还原剂硅铁添加量、反应时间、催化剂CaF2添加量。在熔融还原工艺参数为:反应温度1600℃,还原剂硅铁添加量n(Si)/n(2MgO)=1.2,反应2h,催化剂CaF2添加量3%条件下,渣中的MgO还原率高达97.3%。     

真空铝热还原LiAlO2制取金属锂的研究

真空金属热还原法是一种具有工业应用前景的炼锂方法。本文对常压下以工业碳酸锂、氧化铝和氧化钙为原料合成LiAlO2以及真空条件下铝热还原LiAlO2提取金属Li进行了实验研究。研究了不同煅烧条件对LiAlO2合成的影响以及不同还原条件对铝热还原制取金属锂过程的影响。结果表明:在制团压力50MPa、煅烧温度1073 K和煅烧时间120 min的条件下,碳酸锂的分解率为98.21%,煅烧产物为LiAlO2和CaO。在还原温度1423 K,时间180min,铝粉过量20%,物料粒度-75μm和制团压力为45MPa的条件下金属锂的还原率为95.50%,铝粉利用率为79.17%。还原渣主要成分为CaO.Al2O3和12CaO.7Al2O3,可用于溶出氧化铝。     

负载型Pd催化剂的制备及其对甲醇氧化的催化活性

采用等体积浸渍法制备了一系列负载型Pd+M(M=MgO、CaO、SrO、BaO)催化剂,运用BET、CO-化学吸附、XRD、H2-TPR和XPS等表征手段对催化剂进行了表征,并考察其对甲醇的催化氧化性能。结果表明,添加碱土金属可使Pd粒子高度分散,催化剂表面易还原氧物种量增多,还原速率加快;XPS分析可知,碱土金属可增强Pd-Ce间相互作用,促使Pd向氧化态过渡,同时增加催化剂表面Ce3+浓度,改善催化剂的氧化还原性能,进而提高催化剂的催化活性。助催化效果递变规律为BaOCaOMgOSrO。     

Raw materials selection applied to glass bonding for vitrified CBN grinding wheels

In this article the selection of more appropriate raw materials applied to alumino-borosilicate glass system for vitrified cubic boron nitride (CBN) grinding wheels was investigated. The selection of raw materials had a major effect on the performance of specimens. Mechanical properties of the specimens were measured by using three-point bending strength tester and microstructure characteristics of specimens were examined by scanning electron microscopy (SEM). The results showed that the elements barium and magnesium in the form of carbonate were more beneficial to the refractoriness and fluidity of glass binder than in the form of hydrate and oxide. Moreover, the element barium in the form of carbonate was more favorable to mechanical property of glass binder than that in form of hydroxide. But magnesium carbonate was harmful to improve the mechanical property of glass binder. Therefore, selection of appropriate raw materials used in glass binder was dependent on their natural characteristic.     

Durability of doped zinc oxide/silver/doped zinc oxide low emissivity coatings in humid environment

The relationship between internal stress of doped zinc oxide films and durability of doped zinc oxide/silver/doped zinc oxide low emissivity (low-e) coatings in humid environment was investigated. Aluminum, titanium, tin, chromium, silicon, gallium, magnesium, boron, barium, and calcium were chosen as a doping element in sputtering targets. Ratios of dopant/zinc in the oxide targets were 4/96-5/95 at.%. Films were formed by radio frequency sputtering. Doping of barium and calcium to the zinc oxide film led to a large increase in the internal stress. Doping of the other elements resulted in decreasing the internal stress. It was concluded that durability of the low-e coatings in humid environment closely correlated with the internal stress of the oxide layers.     

The machining of oxides using gas lasers

The use of CO₂-N₂-He gas lasers in the cutting and engraving of oxide materials is demonstrated. The materials investigated were vitreous silica, zirconia, alumina, magnesium aluminate spinel, magnesia and aluminous porcelain.     

Influence of alumina content on the nucleation crystallization and microstructure of barium fluorphlogopite glass-ceramics based on 8SiO2·y Al2O3·4MgO·2MgF2·BaO Part II Microstructure, microhardness and machinability

The influence of alumina content, heat treatment time and temperature on the microstructure, hardness and theoretical machinability of barium fluorphlogopite glass-ceramics were investigated. The glass-ceramics were based on glasses of the general composition 8SiO₂-yAl₂O₃-3.75MgO-2.25MgF₂-BaO. Glasses with high alumina contents with y > 2.0 were found to give fine feathery microstructures that did not coarsen readily to give the classic house of cards microstructure associated with machinability. The glass with the lowest alumina content (y = 1.5) that gave a house of cards microstructure was therefore investigated in detail. The Vickers hardness decreased slightly on formation of the barium fluorphlogopite phase, but decreased significantly on forming an interconnected house of cards microstructure. Machinability was highly dependent on the formation of an interconnected microstructure.     

熔体浸渗法制备镁/氧化铝复合材料

采用熔体浸渗法制备了Mg/Al2O3复合材料,利用X射线衍射、扫描电镜、金相显微镜等测试手段对其微观组织结构和力学性能进行了表征,并对试样断裂韧性和耐磨性进行了研究.结果表明:熔体浸渗法制备的Mg/Al2O3复合材料具有双连续相网络结构,且界面结合良好;随着Mg含量的减少,复合材料断裂韧性降低、耐磨性大幅度提高.     

The relationship between phase composition and conditions of sintering seawater derived magnesium oxide

This study has focused on the favourable effect of the TiO₂ addition (1, 2 and 5 wt%) on the reduction of B₂O₃ content during activated sintering of magnesium oxide from seawater at temperatures of 1400, 1500 and 1700°C for the duration of 1, 2 and 4 h. A mathematical model of dependence between the B₂O₃ mass fraction in the sintered sample, the temperature of isothermal sintering, the isothermal sintering time and the mass fraction of TiO₂ added have been proposed. Magnesium oxide was obtained from seawater by substoichiometric precipitation, with the addition of 80% of dolomite lime as the precipitation agent. New phases formed in magnesium oxide samples were examined by the XRD and SEM/EDS analysis. The results indicate that during activated sintering of seawater-derived magnesium oxide with a TiO₂ addition, reactions of formation of Ca₂B₂O₅, CaTiO₃ and Mg₂TiO₄ took place simultaneously. The thermodynamics analysis of experimental results, based on the Onsager reciprocity relations (symmetry relations), was applied and phenomenological coefficients were calculated to describe the interference of these three irreversible processes.     

Under-surface observation of thin-film alumina on NiAl(100) with scanning tunneling microscopy

Scanning tunneling microscopy (STM) was used to investigate the oxide structures underlying the surface of alumina thin-film grown on NiAl(100). At a bias voltage (on the sample) below 2.0 V, STM topography images of the alumina layer beneath the surface were obtained. A probe with depth of 2-8 Å was readily attained. The under-surface observation shows that the film consists of stacked layers of alumina whereas the layered alumina unnecessarily comprises entire θ-Al₂O₃ unit cells. The lattice orientation of the upper alumina layer differs from that of the lower one by 90° — the newly grown oxide structurally matching the horizontal oxide rather than the lower oxide. The results indicate a growth process competing with the typical mode of epitaxial growth for the growth of alumina film.     

卤水-石灰法制备氢氧化镁的实验研究

对以卤水和石灰乳为原料制备氢氧化镁进行了实验研究,系统考察了反应温度、卤水浓度、加料时间、陈化时间等因素对氢氧化镁质量的影响,得到了最适宜的工艺条件,即反应温度80℃、卤水浓度1.5mol/L、加料时间2h、陈化时间3h.产品中氢氧化镁含量高于98%,氧化钙含量小于0.2%.采用扫描电子显微镜(SEM)、X射线衍射(XRD)和激光粒度仪等对产品进行表征.结果表明,制备的氢氧化镁颗粒呈片状结构,粒度分布均匀.     

The corrosion resistance of high ZrO2 fusion-cast Al2O3-ZrO2-SiO2 glass refractories in soda lime glass

The corrosion resistance to soda lime glass of fusion-cast high zirconia Al₂O₃-ZrO₂-SiO₂ compositions is evaluated. It is concluded that these materials offer no improvement in corrosion resistance over the typical commercially available 40 wt% zirconia refractory in this glass. Furthermore, it is concluded that an optimum mixture of alumina and zirconia exists which has better corrosion resistance to soda lime glass than either end member. Finally, it is suggested that this trend in corrosion resistance is due to the interdependent solubilities of alumina and zirconia in the glass.     

Bond strength and interfacial structure of silicon nitride joints brazed with aluminium-silicon and aluminium-magnesium alloys

From the results of the bending strength and Weibull modulus of the joints of silicon nitride ceramics brazed using aluminium-silicon and aluminium-magnesium alloy filler metals at a temperature of 1073 K for 0.9 ksec in a vacuum of 1.3 × 10^–3 Pa, silicon, especially, present in a small amount in the filler metals, was found to be effective in improving the bond strength, while magnesium in the filler metals was harmful to the joining. This can result in the formation of a thick stable alumina layer on the surfaces of the filler metals containing magnesium during brazing which prevented contact of the filler metals with the silicon nitride ceramics.