由火山灰和铝粉在氮气中制备β-Si_3N_4固溶体

火山灰(化学组成重量百分数 SiO_263.7,Al_2O_3 19.6,FeO·Fe_2O_33.8,CaO5.4,MgO5.0,K_2O1.0,烧失量0.5)和铝粉(20—50重量%)的混合物在氮气中经1400℃加热5小时,得到β—Si_3N_4。在反应产物中β—Si_3N_4的 X射线绕射峰的角度随铝含量增加而减小,这现象标志着固溶体的生成。     

添加Al_2O_3和ZrO_2的Si_3N_4陶瓷的氧化行为以及氧化对强度的影响

研究了添加Al_2O_3和ZrO_2的Si_3N_4陶瓷材料的氧化行为,同时探讨了氧化对陶瓷材料室温强度和高温强度的影响。实验结果表明,Si_3N_4陶瓷材料在空气中的氧化行为服从抛物线规律。另外、Si_3N_4陶瓷材料在1200℃的空气中氧化后其室温强度随着氧化时间的增加呈现先增加后下降的趋势,其中在1200℃的空气中氧化50h后其室温强度提高了8％。当在1300℃的空气中氧化后其高温强度随着氧化的进行有较明显的增加,其中在1300℃的空气中氧化75h后其高温强度提高了15％。     

Si-Al-Ca-N-O系统部分亚固相关系

本文研究了Si、Al、Ca/N、O系统中以Si_3N_4、SiO_2、CaSiO_3、2CaO·Al_2O_3·SiO_2、CaO-Al_2O_3、Al_2O_3和β′-Si_2Al_4O_4N_4(β_(60))为边界的区域的亚固相关系。在此区域中发现一个新相,其组成接近CaO·1.33Al_2O_3·0.67Si_2N_2O(称S相),且与CaO·2Al_2O_3形成连续固溶体。在此区域中有14个相容性四面体,其中5个含有S相。     

基于高SiO_2含量的Si_3N_4基陶瓷显微结构与力学性能

通过在高纯Si_3N_4粉中直接加入SiO_2粉体,来模拟高氧含量的Si_3N_4粉体,然后引入三元助剂Al_2O_3-Y_2O_3-TiO_2,促进致密化。结果表明:当SiO_2含量为4.5%(质量分数)时,SiO_2主要参与晶界玻璃相的形成,显微结构粗化,长棒状β-Si_3N_4晶粒的平均直径为(0.99±0.15)μm,硬度、强度和断裂韧性分别为(15.1±0.3)GPa、(468.6±15.6)MPa和(11.0±0.4)MPa·m~(1/2)。当SiO_2含量为9%时,除了形成晶界玻璃相,部分SiO_2还与Si_3N_4和Al_2O_3反应形成O'-Sialon相;通过晶界钉扎效应,O'-Sialon抑制了β-Si_3N_4晶粒的长大,长棒状β-Si_3N_4晶粒的平均直径为(0.56±0.13)μm,硬度、抗弯强度和断裂韧性分别为(17.1±0.7)GPa、(435.3±65.0)MPa和(11.1±1.0)MPa·m~(1/2)。因此,与含4.5%SiO_2粉体制备的Si_3N_4陶瓷相比,含9%SiO_2粉体制备的Si_3N_4陶瓷具有更细小的晶粒和更高的硬度。     

Al2O3–RE2O3(RE=Lu,Y,Gd,La)烧结助剂对Si3N4陶瓷结构和性能的影响

以α-Si_3N_4粉末为原料、Al_2O_3–RE_2O_3(RE=Lu,Y,Gd和La)为烧结助剂,在1 800℃压烧结制备氮化硅陶瓷,研究了不同烧结助剂对材料的相组成、微观结构和力学性能的影响。结果表明:样品中α-Si_3N_4完全转化为β-Si_3N_4,所形成的长柱状晶粒生长发育良好。随着稀土阳离子半径的增大,材料的相对密度和力学性能呈增加趋势,其中Si_3N_4–Al_2O_3–Gd_2O_3的抗弯强度和断裂韧性分别达到860 MPa和7.2 MPa·m~(1/2)。由于稀土离子对烧结液相黏度的影响,Si_3N_4–Al_2O_3–Lu_2O_3和Si_3N_4–Al_2O_3–Y_2O_3中出现了晶粒异常长大的现象,而Si_3N_4–Al_2O_3–La_2O_3的基体与柱状晶粒界面结合较大导致材料力学性能降低。     

添加Al_2O_3-Y_2O_3烧结助剂的无压烧结Si_3N_4的研究

本文研究了 1740～1780℃范围内以Al_2O_3-Y_2O_3 为烧结助剂的 Si_3N_4 的无压烧结性能。结果表明:加少量Al_2O_3-Y_2O_3的Si_3N_4,即使含量<6.5％,只要工艺措施适当,也可获得高密度(相对密度达96～99％)的氮陶瓷,强度为500～600MN/m~2(部分达到700MN/m~2)。 试验表明,使用粒度细,α相含量高的Si_3N_4 原料,采用Si_3N_4 BN MgO 的埋粉,以及保温时间适当,是促进烧结的有效措施。研究指出:添加少量Al_2O_3-Y_2O_3 外加剂的 Si_3N_4 是以液相烧结为主。 用X射线衍射,扫描电镜和电子探针等检验了Si_3N_4的显微结构,表明 Al_2O_3已进入β-Si_3N_4 晶格,形成β’-Si_3N_4固溶体,晶格参数随 Al_2O_3 加入量增加而增大。     

刚玉-氮化硅-碳化硅复合材料的性能研究

以棕刚玉、氮化硅和碳化硅为原料在氧化气氛下制成试样.将试样分别在1500 ℃、1550 ℃和1600 ℃保温5 h进行埋炭处理.利用XRD、SEM和EDS等检测方法,结合热力学分析,研究了氧化气氛烧成后试样的物相变化以及高温埋炭条件下Si_3N_4的稳定性.结果表明:氧化气氛烧成后生成一种莫来石固溶体Si_6Al_(10)O_(21)N_4;高温埋炭处理后Si_3N_4和Si_6Al_(10)O_(21)N_4会部分转化为SiC,Si_3N_4向SiC明显转化的温度大于1500 ℃,Si_6Al_(10)O_(21)N_4向SiC明显转化的温度大于1550 ℃.     

Y_2O_3-Al_2O_3-Si_3N_4系统中Y_2O_3的含量对无压烧结Si_3N_4显微结构及性能的影响

研究了以 Y_2O_3—Al_2O_3复合氧化物为添加剂,不同 Y_2O_3含量对无压烧结 Si_3N_4性能的影响(体积密度、烧成收缩、失重、抗折强度等).材料的抗氧化性试验表明,Y_2O_3含量高的氧化增重小;Al_2O_3含量增加,氧化增重也增加。用 X-射线衍射、扫描电镜、电子探针等检验了制品的显微结构,结果表明,Al_2O_3进入了β-Si_3N_4晶格,形成了β′-Si_3N_4固溶体,固溶量为总 Al 量70%左右,与 Y_2O_3含量多少无关。Y_2O_3即使加入量达到12%,也不存在游离 Y_2O_3或形成氧氮化硅钇化合物.     

CaO-Al_2O_3-SiO_2系统玻璃的结构与电导

在CaO-Al_2O_3-SiO_2系统中,选取了三组玻璃组成。第Ⅰ组:CaO·xAl_2O_3·(4-2x)SiO_2,第Ⅱ组:(3-2x)CaO·xAl_2O_3·2SiO_2,第Ⅲ组:CaO·Al_2O_3·xSiO_2。研究了密度、折射率、克分子折射度、直流电导和玻璃组份间的关系。实验结果表明:当Al_2O_3/CaO≤1时,Al~(3+)以AlO_4四面体存在,当Al_2O_3/CaO>1时,则超过Al_2O_3/CaO=1的Al~(3+)以AlO_6六配位存在。本文并从理论计算论证了Ca~(2+)为该系统玻璃的电导载流子。     

不同助熔剂对磷矿熔融特性影响研究

利用分析纯级Ca_3(PO_4)_2、SiO_2、Al_2O_3、MgO为原料模拟磷矿组成,研究SiO_2、Al_2O_3、MgO对磷矿熔点的影响。结果表明,SiO_2、Al_2O_3、MgO单独添加均可改善物料的熔融特性,且SiO_2对降低物料熔点的促进效果优于其他两种助熔剂;SiO_2/CaO摩尔比为0.85~1.75、MgO/CaO摩尔比为0.75~1.5时SiO_2-MgO复合助熔体系磷矿存在低熔点区,熔融温度介于1260~1290℃之间;SiO_2/CaO摩尔比为0.3~1.25、Al_2O_3/CaO摩尔比为0.25~1.0,和SiO_2/CaO摩尔比为1.4~1.75、Al_2O_3/CaO摩尔比为0.3~1.25两种条件下SiO_2-Al_2O_3复合助熔体系磷矿均存在低熔点区,熔融温度介于1400~1420℃之间。研究结果为深入研究磷矿熔融还原反应提供了理论依据。     

Comparative Analysis of Boron Powders Obtained by Various Methods. I. Microstructure and Oxidation Parameters during Heating

This paper describes a study of boron powders and powder compounds, obtained by various methods, including metallothermal, electrolytic, and borane cracking methods. The crystal state, particle size and microstructure, presence and composition of impurities, and chemical composition of the oxide layer of boron particles are profoundly investigated. The effects of the above-mentioned characteristics on the particle oxidation parameters during heating with a constant rate are analyzed. The determining influence of chemical composition of the particle surface layer on the initial temperature of their intense oxidation is established. It is shown that the maximum increase in the mass and heat release value during oxidation of the boron powders is almost independent of microstructural features, crystal state, and chemical composition of and oxide layer thickness of the particles, and cannot serve as indicators of completeness of boron oxidation during heating.     

Wettability of copper and polytetrafluoroethylene surfaces with water—the influence of environmental conditions

Contact angles of water at its boiling point, measured on surfaces of copper and polytetrafluoroethylene, are reported for pressures ranging from 10–770 torr. The results suggest that not only impurities and oxidation have been responsible for the wide range of angles reported in the literature but that inconsistencies may be created because of an adsorbed layer of water vapour on the solid surface.     

激光重熔NiCrAlY涂层研究

采用空气等离子喷涂技术(APS)将NiCrAlY粉末作为粘结层材料喷涂在IN718镍基合金上,再用5 kW CO2连续激光器对其进行激光重熔处理,利用扫描电镜(SEM)、能谱分析(EDX)和X射线衍射(XRD)等手段对等离子喷涂层和激光重熔层的微观组织与成分进行了比较分析.结果表明:应用优化激光重熔工艺进行重熔后,涂层...     

PASSIVATION OF COPPER BY LOW TEMPERATURE ANNEALING OF Cu/Mg/SiO2 BILAYERS

Annealed thin films of Cu/Mg/SiO₂ are studied as possible conductors for microelectronics. Rutherford backscattering and sheet resistance measurements show that vacuum annealing at 350-400°C results in transport of Mg from the buried layer to the surface of the copper where it reacts with impurities to form a thin surface layer of MgO. Such films are then exceedingly resistant to further oxidation. These films have a resistivity of 2·μω-cm and are adherent to the SiO₂ substrate. However, at temperatures 450-500°C there is a reaction between Mg and the SiO₂ substrate releasing free Si into the copper.     

高纯度黄磷生产工艺研究初探

阐述了采用氧化剂及氧化增强剂脱除黄磷中有机及无机杂质的方法,对黄磷中的砷及有机物有较高的脱除率。找到了几种氧化剂和氧化增强剂,初步确定了它们之间的组合和优化工艺条件。确定了高纯黄磷中几个主要杂质指标的分析方法,特别是有机物的分析方法。试验所得产品为5N级黄磷。     

Impurity Effects on Alumina Scale Growth

Most high-temperature-resistant alloys oxidize to form an external alumina layer, or scale, whose slow growth protects the underlying alloy from continued aggressive oxidation. The growth of the Al₂O₃ scale is controlled by the transport of oxygen inward and aluminum outward through it, with the rate dominated by the fastest diffusing species down the fastest path. Components in the alloy can be incorporated into the growing Al₂O₃ layer, hence affect the transport rates of oxygen and/or aluminum. This paper summarizes existing experimental data to assess the possible effect of these incorporated impurities on the growth rate and transport properties of Al₂O₃ scales formed on Fe-, Ni-, and Pt-based alloys. The amount and distribution of the alloy base metal, sulfur impurity, and reactive elements, such as Hf, Y, Zr, and Ce, in the alumina scale are evaluated. Their effect on the oxidation and transport rates through the scale are discussed and compared with Al and O diffusion rates deduced from creep studies.     

环己烷仿生催化氧化产物及杂质浅析

对环己烷仿生催化氧化产物与无催化氧化产物进行了分析,对氧化液中各组分的比例和烷四釜中各杂质的含量进行了对比。结果表明:与环己烷无催化氧化相比,仿生催化氧化环己烷转化率高,产物中醇、酮、酸、酯含量高,过氧化物含量降低;烷四釜中杂质种类相同,各组分的含量不同,其杂质总量约为无催化氧化的1．5倍,杂质可在精馏过程中分离。     

EIS investigation of zinc dissolution in aerated sulphate medium. Part II: zinc coatings

The kinetics of anodic dissolution and corrosion of zinc coatings deposited onto steel sheet either by electrodeposition or by hot dipping are investigated by electrochemical impedance spectroscopy in aerated sulfate medium. The results are compared with those obtained previously on pure bulk zinc and interpreted on the basis of the model derived in the first part of this paper. It is shown that zinc coatings are less sensitive to corrosion than pure bulk zinc and changes of their behavior with time are not identical. Important differences are observed between the various coatings in the respective contributions of the three parallel paths of the dissolution process. Three kinds of oxidation products were identified by Raman spectroscopy. A compact non-stoichiometric zinc oxide was formed by surface reaction on zinc. Above it, a thick and porous layer made of zinc hydroxi-sulfate and stoichiometric ZnO, was formed by precipitation from a local saturation of the solution. A strong correlation was evidenced between the oxidation products and the various paths of the reaction model. It was assumed that the impurities, initially present in the metal, may affect the interfacial reactions, the increase of the micro-roughness, and may also reinforce the protective properties of oxidation product layers. The differences between the various zinc coating behaviors result mainly from their impurities. Their crystal preferred orientations have no significant influence.     

Changes in oxyreactivity of carbons due to heat treatment and prehydrogenation

Evidence from deactivation due to heating chars at elevated temperatures supports the suggestion that impurities catalyse all oxidation reactions of carbons in similar ways. Data on deactivation by both thermal treatment and prehydrogenation how that the concentration of sites at which oxidation reactions proceed is dependent on the morphology of impurities and possibly their chemical type. The rate limiting step, or steps, during oxidation of chars and cokes are not redox reactions between the carbon and catalytic impurities. An assumption of steady reaction conditions during gasification of chars and cokes will not be valid generally. Impurities may be capable of catalysing the carbon-hydrogen reaction, but such catalytic activity will decay due to aggregation of impurities.     

Growth of Oxide Layers on Thin Aluminum Nitride Samples Measured by Electron Energy-Loss Spectroscopy

AlN ceramics with different amounts of oxygen impurities were investigated by electron energy-loss Spectroscopy (EELS). Because of the high dynamics of EEL spectra, a method was developed to record partial spectra and then to join them together to form a complete spectrum. The data obtained from EEL spectra were the nitrogen/oxygen concentration ratio, sample thickness, and energy-loss nearedge structures (ELNES). Because of spontaneous formation of an oxide layer on AlN samples immediately after ion milling, a method had to be developed which yielded the oxide layer thickness and the bulk oxygen content. The growth kinetics of the oxide layer were investigated by exposing the AIN samples at room temperature to air and to water for various times. From these measurements a logarithmic rate law for the oxidation of AlN at room temperature was obtained.