蓝晶石制备莫来石晶须的研究

为了降低莫来石晶须的合成温度及生产成本,研究了以蓝晶石为主要原料烧结制备莫来石晶须的影响条件,通过烧结实验发现,原料的粒度、升温速率和催化剂添加量对莫来石晶须的制备有较大影响,影响顺序为：原料粒度〉催化剂添加量〉升温速率。晶须的最佳合成条件为：原料粒度为-325-＋400目,混合样（蓝晶石和氧化铝）与A1F3比例为10：4．0,以1150℃作为成核温度,保温lh,以1250℃作为晶化温度,保温4h,烧结过程中的升温速率为5E／rain,莫来石晶须的产率可以达到64％。     

非水解溶胶-凝胶法制备莫来石晶须

以正硅酸乙酯和无水氯化铝为前驱体,乙醚为氧供体,采用非水解溶胶-凝胶法制备了直径为0.2～20μm,长径比高达60～70的莫来石晶须.借助XRD、SEM和TEM等测试手段研究了莫来石干凝胶粉的活性、矿化剂氟化铝引入方式及其用量、成型压力以及煅烧温度等工艺参数对合成莫来石晶须的影响.结果表明:采用恒压回流工艺制备的莫来石干凝胶粉,在12MPa压力下压制成片状,以外置方式引入3wt%的氟化铝,在1200℃保温1h可制备质量较好的莫来石晶须.     

用高岭土低温制备莫来石晶须

用高岭土和硫酸铝为原料,硫酸钠为反应介质,研究了在不同温度和不同反应时间对试样产物的影响。结果表明:莫来石晶须生长的最佳温度为900℃,在1000℃开始有氧化铝生成,在1200℃主要物相为氧化铝和硅铝酸钠;在900℃条件下保温2h,制备了直径在0.5μm左右,最大长度大于7μm的莫来石晶须。     

莫来石晶须制备新工艺与生长机理

本文首次提出了用Ａｌ２Ｏ３－ＳｉＯ２玻璃粉高温热处理制取莫来石晶须的新工艺．采用ＸＲＤ、ＳＥＭ和ＴＥＭ等手段研究了热处理温度制度及气氛对莫来石晶须生长的影响，确定了制备莫来石晶须的最佳工艺参数，所得莫来石晶须的直径为０．４～１．２Ｐｍ、长径比为１０～４０，其生长方向为ｃ轴方向，生成物中莫来石晶须的含量接近９８ｖｏｌ％．探讨了用Ａｌ２Ｏ３－ＳｉＯ２玻璃粉制取莫来石晶须的生长机理．     

常压烧结SiC密封环的制备工艺与性能研究

研究了采用常压烧结方法制备碳化硅密封件,讨论了碳化硅成型及烧结工艺参数对其性能的影响.通过SEM分析了其显微结构,并测试了其力学性能和体积密度,实验结果表明:以酚醛树脂和淀粉混合物为黏结剂,通过添加2％(质量分数,下同)C和3％B4C,在2150℃、保温0.5h条件下得到了力学性能良好的致密碳化硅密封件,其洛氏硬度92,抗折强度350MPa,弹性模量300GPa,密度达到3.10g/cm3.     

硫酸钠熔盐法微硅粉制备莫来石晶须

以微硅粉和Al2(SO4)3为反应原料,硫酸钠为反应介质,反应混料分别在800℃、900℃、1000℃和1100℃下煅烧保温1h后,经溶解、过滤、烘干后得到莫来石晶须。利用XRD和FESEM对合成粉体进行物相分析和显微形貌观察,结果表明:1000℃为莫来石晶须最佳的合成温度,样品在经NaOH溶液碱处理后得到的莫来石晶须长度约为3~4μm,直径约为10~30nm。同时对合成莫来石晶须形成机理进行了探讨。     

利用煤矸石制备莫来石陶瓷

以煤矸石为原料,分别引入α-Al2 O3、工业氧化铝、氢氧化铝调整原料配比,以干压成型法制备莫来石陶瓷,研究了铝源和煅烧温度对莫来石陶瓷性能的影响.研究表明:铝硅比对莫来石生成量及制品比热容具有重要作用;随着煅烧温度的提高,试样致密化程度高,力学强度增大,比热容升高;适当延长保温时间会促进晶体发育.以氢氧化铝为铝源,铝...     

烧结温度对莫来石增强磷酸铬铝材料的制备与性能影响

以固相烧结莫来石为增强体,制备了莫来石增强磷酸铬铝基复合材料。研究了烧结温度对复合材料的微观结构和性能的影响。采用SEM、XRD、EDS等检测手段对复合材料的物相结构及断面的微观形貌进行分析,使用万能试验机测试其材料的抗折强度,并使用矢量网络分析仪分析材料的介电性能。结果表明,随着烧结温度的升高,复合材料中莫来石的晶粒依次增大,材料致密度、介电常数增加,抗弯强度增加,但过高的烧结温度下抗弯强度会降低。当烧结温度为1 500℃时,材料的抗弯强度为107 MPa,平均介电常数为3.57。     

粉末CPM10V钢常压烧结工艺研究

本文研究了CPM10V及其经不同氮势氮化的粉末钢常压烧结特性及其组织特征。结果表明:未氮化CPM10V钢在接近熔点温度(1300℃)下烧结的相对密度仅为95.8％,而氮化粉末钢存在一个相对于未氮化钢烧结温度低30℃～90℃且能使烧结密度产生突变并接近理论密度(相对密度99.3％)的最佳烧结温度,在此温度下,无共晶莱氏体出现,粉末颗粒边界消失,碳化物颗粒相对未氮化钢细小。能谱分析表明:氮化粉末钢烧结体基体上存在一种黑色氮化物共析组织,它在随后的退火、淬后过程中消失。     

Effect of rigid inclusions on the sintering of mullite synthesized by sol-gel processing

The effect of crystalline particulate inclusions of mullite or zirconia on the sintering and crystallization of a mullite powder matrix was investigated as a function of the inclusion volume fraction and size. The mullite powder was synthesized by sol-gel processing and, within the limits of X-ray diffraction, was amorphous. Composites containing up to 22.5 vol % zirconia reached almost full density after sintering at 1500 °C for 1 h. Under identical conditions, the sintered density of the composites containing crystalline mullite inclusions was considerably lower. The zirconia inclusions were inert but the mullite inclusions enhanced the independent nucleation and growth rate of the mullite crystals in the matrix. The lower sintering rate of the matrix reinforced with crystalline mullite is attributed to the enhanced matrix crystallization.     

Establishment of process parameters for producing Al-foam by dissolution and powder sintering method

Al-foams have been manufactured by a dissolution and powder sintering process using crystalline raw cane sugar, as a novel leachable pattern. The method involves mixing and compaction, leaching and sintering processes. The influence of the process parameters on the microstructure of the produced foam is investigated in order to optimize the process conditions and produce high quality Al-foams. The differences between the actual and calculated porosity of the produced foam is ascribed to the joint effect of the retained porosity of the green product and the shrinkage during sintering. The optimum ranges of compaction pressure and sintering temperature are 250–300 MPa and 680–750 °C respectively.     

Preparation of MgO-doped mullite by sol-gel method,powder characteristics and sintering

Mullite doped with MgO in quantities ranging from 0.01 to 1.5 wt% were prepared by the sol-gel method. The mullitization temperature decreases with increased MgO dopant content. The XRD patterns of the MgO-doped mullite calcined at temperatures up to 1600° C for durations ranging from 1 to 10 h did not show the presence of any other phase except mullite. The IR spectrum shows a broadening of the Al-O absorbance band at 1175cm^–1 with MgO content, indicating the solid solution of MgO. Sintering temperature decreases with increased MgO dopant content. The microstructure observed consisted of equiaxed grains. The TEM observation of the microstructure showed the presence of glassy pockets at the triple grain junctions. The thermal coefficient of expansion and dielectric constant were not changed up to 0.75wt% MgO dopant concentration. The three-point bend strength observed for 0.3wt% MgO-doped mullite at room temperature was 300 MPa and decreased below 200 MPa at 1400° C.     

工艺参数对EB-PVD制备YSZ涂层的影响

为探讨电子束物理气相沉积(EB-PVD)制备8 mol.%氧化钇稳定氧化锆(8YSZ)涂层过程中工艺参数对涂层致密性、表面粗糙度和晶粒择优取向生长的影响,利用扫描电镜、原子力显微镜和X射线衍射技术对涂层的上述性能进行了分析.分析结果表明,随沉积速率由750 nm/min下降至20 nm/min,YSZ涂层的晶粒逐渐聚合长大,晶粒之间的孔隙减少,涂层的气体扩散系数相应地由2.41×10-4cm4/(N·s)下降至6.56×10-5cm4/(N·s).YSZ涂层的表面粗糙度随靶基距的提高逐渐降低,涂层的晶体学取向随蒸汽粒子入射角的改变而改变,入射角为30°时(111)晶面具有平行于涂层表面排列的趋势,入射角为45°时(311)和(420)晶面具有平行于表面排列的趋势,而入射角为60°时(220)和(331)晶面具有平行于表面排列的趋势.     

Effect of process parameters on surface oxides on chromium-alloyed steel powder during sintering

The use of chromium in the PM steel industry today puts high demands on the choice and control of the atmosphere during the sintering process due to its high affinity to oxygen. Particular attention is required in order to control the surface chemistry of the powder which in turn is the key factor for the successful sintering and production of PM parts. Different atmosphere compositions, heating rates and green densities were employed while performing sintering trials on water atomized steel powder pre-alloyed with 3 wt.% Cr in order to evaluate the effect on surface chemical reactions. Fracture surfaces of sintered samples were examined using high resolution scanning electron microscopy combined with X-ray microanalysis. The investigation was complemented with thermogravimetric (TG) studies. Reaction products in particulate form containing strong-oxide forming elements such as Cr, Si and Mn were formed during sintering for all conditions. Processing in vacuum results in intensive inter-particle neck development during the heating stage and consequently in the excessive enclosure of surface oxide which is reflected in less good final mechanical properties. Enhanced oxide reduction was observed in samples processed in hydrogen-containing atmospheres independent of the actual content in the range of 3–10 vol.%. An optimum heating rate was required for balancing reduction/oxidation processes. A simple model for the enclosure and growth of oxide inclusions during the sinter-neck development is proposed. The obtained results show that significant reduction of the oxygen content can be achieved by adjusting the atmosphere purity/composition.     

Growth of beta-silicon carbide whiskers by the VLS process

Beta-silicon carbide whiskers are being grown by a vapour-liquid-solid (VLS) process which produces a very high purity, high strength single crystal fibre about 6m in diameter and 5–100 mm long. Details of the growth process are given along with a general explanantion of the effects of the major growth parameters on whisker growth morphology.     

The influence of sintering process and atmosphere on the non-ohmic properties of SnO2 based varistor

The non-ohmic properties of the 98.95% SnO₂ + 1.0%,CoO + 0.05%,Nb₂O₅ (all in mole%) system, as well as the influence of sintering temperature and atmosphere on these properties, were characterized in this study. The maximum non-linear coefficient ( = 32) was obtained for a sintering temperature of 1300°C in an oxygen atmosphere and this maximum is associated with the presence of O in SnO₂ grain boundaries, as interface defects. Experimental results also indicate thermionic-type conduction mechanisms, which are associated with the potential barrier of Schottky or Poole–Frenkel types.