纯铝酸钙水泥和α-Al2O3微粉的反应机理研究

研究了纯铝酸钙水泥和α-Al2O3微粉的反应过程,利用XRD,DTA-TG,SEM等方法来表征物相组成与结构变化.实验结果表明:在室温主要为CA的水化过程生成CAH10,在升高温度的过程中,有一些过渡相C3A5,900℃时开始有C12A7的生成,1100℃时,CA基本完全反应,在1400℃和1500℃热处理后主要是CA2和Al2O3,也有少部分的C12A7.试样经过不同的温度热处理(1100-1500℃),热处理温度越高,试样的颗粒粒径明显减小.     

Fe（OH）3中微量金属离子对水热合成α—Fe2O3粒径的影响

本文研究了某些金属离子（Ａｌ＾３＋、Ｍｎ＾２＋、Ｚｎ＾２＋、Ｃｒ＾２＋、Ｎｉ＾２＋、Ｃｏ＾２＋）Ｆｅ（ＯＨ）３凝胶经水热法合成的α－Ｆｅ２Ｏ３微粉颗粒大小的影响。研究结果出现，随着金属离子的浓度在一定范围内（０．０１０－０．０５０ｍｏｌ·Ｌ＾－１）的增加，α－Ｆｅ２Ｏ３颗粒有减小的趋势。其中加入Ｃｏ＾２＋（０．０５０ｍｏｌ·Ｌ＾－１）、Ｍｎ＾２＋（０．１００ｍｏｌ·Ｌ＾－１）可以得到粒径为７５ｎｍ     

铁基催化剂组成对热解火焰法合成碳纳米管的影响

为了改善碳纳米管的产量和质量,改变催化剂的组成是一个重要的途径。在热解火焰法制备碳纳米管实验中,主要对比了催化剂中铁和镍含量对碳纳米管质量和产量的影响。通过扫描电子显微镜、拉曼光谱和透射电子显微镜等方法对生成的碳纳米管进行系统分析表征,结果表明Fe含量较低时,得到的碳纳米管质量较好,但产量很少;Fe含量较高时,得到的碳纳米管产量较高,但杂质会明显增加,石墨化程度明显下降。实验发现,当催化剂中各元素物质的量比Fe∶Mo∶Al=1∶0.17∶16时碳管的综合质量最好。在铁基催化剂Fe/Mo/Al_2O_3中加入少量Ni会提高碳纳米管的质量,但是若Ni过量碳纳米管的质量反而会下降,当Fe/Ni-Mo/Al_2O_3中元素的物质的量比Fe∶Ni∶Mo∶Al=1∶0.5∶0.17∶16时,合成的碳纳米管的产量较高、质量较好,且具有更好的定向性。     

第二组元掺杂对ATO纳米粉体电学和光学性能的影响

以醇盐水解法制备掺杂第二组元金属氧化物的ATO纳米粉末,通过高速剪切、超声波方法制备分散均匀的ATO浆料,用该浆料以匀胶法在玻璃片上镀膜.对粉末用XRD、TEM、SEM进行了检测.粉末电阻率用数字式微欧表测量,以多功能光谱仪测定不同波长下的薄膜的透射率.结果表明,Cr2O3增大ATO纳米粉末晶粒尺寸,对ATO粉体电阻率急剧增加,搀杂ZnO增加ATO纳米粉末晶粒尺寸,但降低ATO粉末的电阻率,搀杂Fe2O3能大大减少ATO纳米粉末晶粒长大,当Fe2O3搀杂量超过一定值时使电阻率急剧上升,3种氧化物均降低ATO薄膜的透射率,其程度为Cr2O3＞Fe2O3＞ZnO.     

一种液相制备均匀α-Fe2O3微粉的新方法

利用沸腾回流强迫水解法由FeCl3或Fe(NO3)3溶液(0.5-1.0mol.L)在弱酸性环境下,制备了均匀亚微米级α-Fe2O3胶粒.如果在反应液中加入微量Na2SO3,完全转化为α-Fe2O3粒子的时间可缩短至几小时.使用XRD和TEM对产品的物相及形貌进行了表征.     

SiO2包覆Fe2O3纳米粒子的制备和性能

在近球形α-Fe2O3颗粒的悬浮液中,以正硅酸乙酯（TEOS）为硅源,氨水和尿素为催化剂,合成了Fe2O3-SiO2核-壳粒子．应用TEM、XRD对Fe2O3-SiO2核-壳粒子结构进行了测定．研究了TEOS、氨水的浓度对核-壳粒子结构的影响．UV—Vis吸收光谱表明,SiO2壳层消除了Fe2O3纳米粒子的表面悬挂键,产生增强的激子发射,使得核-壳粒子的吸收峰发生蓝移．根据带边吸收峰的波长计算出核-壳粒子中Fe2O3的禁带宽度为2．25eV．     

SiO2包覆Fe2O3纳米粒子的制备和性能

在近球形α-Fe2O3颗粒的悬浮液中,以正硅酸乙酯(TEOS)为硅源,氨水和尿素为催化剂,合成了Fe2O3-SiO2核-壳粒子.应用TEM.XRD对Fe2O3-SiO2核-壳粒子结构进行了测定.研究了TEOS.氨水的浓度对核-壳粒子结构的影响.UV-Vis吸收光谱表明,SiO2壳层消除了Fe2O3纳米粒子的表面悬挂键,产生增强的激子发射,使得核-壳粒子的吸收峰发生蓝移.根据带边吸收峰的波长计算出核-壳粒子中Fe2O3的禁带宽度为2.25 eV.     

磁性纳米TiO2/SiO2/Fe3O4光催化剂的制备及表征

以纳米Fe3O4磁粉为核心，采用溶胶一凝胶法制备了TiO2／SiO2／Fe3O4复合光催化剂．用XRD、TEM及元素分析对其结构和表面形貌进行了表征．以具有偶氮染料结构的甲基橙水溶液为目标反应物，评价其光催化活性．结果表明，所制TiO2／SiO2／FeaO4样品为双层包覆型结构，SiO2为中间层，最外层是锐钛矿型的TiO2,该复合光催化剂对甲基橙溶液有较高的光催化活性，并具有可利用其磁性回收重用的特点，应用前景广泛。     

强磁性纳米Fe3O4/SiO2复合粒子的制备及其性能研究

本文采用液相沉积法制备出了满足免疫磁珠用磁核的粒径和磁性要求的纳米Fe3O4/SiO2复合粒子.考察了不同的制备条件对复合粒子的粒径和磁性能的影响,并借助不同的分析测试手段对复合粒子的性能进行表征.结果表明:该复合粒子的最佳制备条件为正硅酸乙酯(TEOS)的浓度为0.6mol·L-1,Fe3O4/TEOS物质的量的比为5:1,反应温度为50℃,搅拌速度为800rpm;在此实验条件下制得的复合粒子的平均粒径在20nm左右,呈球形且分散较均匀,比饱和磁化强度为60.5emu·g-1.     

过渡族金属掺杂对TiO2薄膜光催化性能的影响

本文采用溶胶凝胶旋涂法在普通玻璃上制备了掺杂不同Fe3+浓度及不同Zn2+浓度的TiO2薄膜,并对薄膜进行了500℃退火处理。分析讨论不同Fe3+及Zn2+掺杂浓度下TiO2薄膜的光催化性能,得出了铁离子最佳掺杂浓度为0.5%,锌离子最佳掺杂浓度为5%。并利用XRD、SEM、UV-Vis对不同掺杂离子的薄膜进行了对比分析,结果表明:Fe2O3/TiO2和ZnO/TiO2薄膜在可见光范围内均具有很好的光透过性(>80%),ZnO/TiO2薄膜光催化性能略优于Fe2O3/TiO2薄膜,最佳状态下ZnO/TiO2薄膜的光降解率能达到Fe2O3/TiO2薄膜的两倍。     

High temperature mechanical spectroscopy and creep of calcium hexaluminate

Samples of calcium hexaluminate (CA₆) were studied by four-point bending creep tests and mechanical spectroscopy at temperatures between 1300 and 1600 K. By using the temperature-compensated time concept, proposed by Dorn (1954, 1956), activation enthalpies of the order of 620 kJ/mol were deduced from both the isothermal creep and the internal friction measurements. A generic curve, “ master curve”, is obtained by a superposition of the isothermal mechanical loss spectrum along the temperature-compensated frequency axis. The master curve is composed of two components: a high-frequency part (peak) and a low-frequency part (exponential background). Both the peak and the background decrease after performing torsional creep. Additionally, the peak shifts towards higher frequency after annealing. The high temperature mechanical loss behavior of CA₆ is discussed in terms of a dislocation model invoking anelastic and viscoplastic relaxation phenomena.     

Effects of additives on sintering and some properties of calcium phosphates with various Ca/P ratios

The effects were studied of additives on the sintering and properties such as the compressive strength and chemical durability of ceramics of calcium pyrophosphate, tricalcium phosphate and hydroxyapatite. In improving the compressive strength of these calcium phosphates, the effect of additives was found to be in the order Na₂OCaF₂>MgOgAl₂O₃, SiO₂ for the case of single-doping, and was most marked in the combination of Na₂O-MgO-Al₂O₃ for the complex addition. It was also found that the chemical durability of the calcium phosphates was improved greatly by using a single or complex additives.     

Control of calcium hexaluminate grain morphology in in-situ toughened ceramic composites

The influence of processing conditions on the morphology of calcium hexaluminate (CA₆) grains in Al₂O₃: 30 vol% CaO·6Al₂O₃ (CA₆) ceramic composites was investigated. Specimens were prepared by in-situ reaction sintering using precursor powders of alumina, and either calcium carbonate or calcium oxide. In some samples, 1 vol% anorthite glass was added as a sintering aid. X-ray diffraction was used to study the phase development in the as-calcined and sintered states. The resultant microstructures were characterized using both scanning electron microscopy (SEM), and imaging secondary ion mass spectrometry (SIMS). It was found that the CA₆ grains developed a platelike morphology when CaCO₃ was used as the starting calcium-rich powder. In contrast, samples prepared using CaO resulted in equiaxed CA₆ grains. This result was observed to be independent of the anorthite glass addition. The findings are rationalized in terms of distinct CA₆ reaction mechanisms, resulting from differences in the reactivity of the powders during the early stages of calcining.Cement Nomenclature C CaO - A Al₂O₃     

Optical properties of Eu-activated calcium aluminosilicates synthesized in different atmospheres

The optical properties of Eu-activated CaAl₂Si₂O₈ appear to be totally dependent on the atmosphere during the synthesis processing. Compared with oxidizing/reducing-sintered samples, a significant enhancement in both the photoluminescence and afterglow for the vacuum-sintered sample is observed. The deficiency of energy transfer among the different emission centers is the prevailing contribution to the highest photoluminescence intensity of the vacuum-sintered sample. A distinction in afterglow characteristics of CaAl₂Si₂O₈:Eu prepared in different atmosphere is suggested to be mainly due to the distribution of different trap depths at three types of emission centers.     

Effect of various additives and temperature on some properties of an apatitic calcium phosphate cement

The effect of additives and temperature on setting time, swelling time and compressive strength of a previously developed apatitic calcium phosphate cement was investigated. Setting was faster at body temperature than at room temperature. Early contact with aqueous solutions resembling blood and other body fluids had no effect. Deliberate additions of soluble carbonates, pyrophosphate or magnesium salts to the cement powder retarded or even inhibited setting. However, additions of calcium pyrophosphate, -tertiary calcium phosphate or sintered hydroxyapatite to the cement powder in amounts up to 10% had no effect on the cement properties. Several organic substances were used as additives. They all retarded the setting and decreased the strength of the cement considerably.     

Effects of porous carbon additives and induced fluorine on low dielectric constant polyimide synthesized with an e-beam

We report the synthesis of a polyimide matrix with a low dielectric constant for application as an intercalation material between metal interconnections in electronic devices. Porous activated carbon was embedded in the polyimide to reduce the dielectric constant, and a thin film of the complex was obtained using the spin-coating and e-beam irradiation methods. The surface of the thin film was modified with fluorine functional groups to impart water resistance and reduce the dielectric constant further. The water resistance was significantly improved by the modification with hydrophobic fluorine groups. The dielectric constant was effectively decreased by porous activated carbon. The fluorine modification also resulted in a low dielectric constant on the polyimide surface by reducing the polar surface free energy. The dielectric constant of polyimide film decreased from 2.98 to 1.9 by effects of porous activated carbon additive and fluorine surface modification.     

Effect of several additives and their admixtures on the physico-chemical properties of a calcium phosphate cement

Combinations of citrate (C₆H₅O ₇ ^3-– ), pyrophosphate (P₂O ₇ ^4– ) and sulfate (SO ₄ ^2– ) ions were used to modify the physico-chemical properties of a calcium phosphate cement (CPC) composed of -tricalcium phosphate (-TCP) and phosphoric acid (PA) solution. The results obtained with only one additive at a time are similar to those previously published. New facts are: the positive effect of C₆H₅O ₇ ^3– ions on cement failure strain and their negative effect on cement pH. The position of the setting time maximum measured at an SO ₄ ^2– concentration of 0.09 M was not displaced by the addition of C₆H₅O ₇ ^3– and P₂O ₇ ^4– ions. However, the effect of SO ₄ ^2– ions on the setting time was depressed by C₆H₅O ₇ ^3– ions. Moreover, no increase in tensile strength was observed when increasing amounts of SO ₄ ^2– were added into a C₆H₅O ₇ ^3– -containing cement. The latter results suggest a competitive effect of C₆H₅O ₇ ^3– and SO ₄ ^2– on setting time and tensile strength. Anhydrous dicalcium phosphate (DCP; CaHPO₄) appeared in cement samples dried just after setting, but not in cement samples incubated for 24 h in deionized water before the drying step. It is believed that the setting reaction is stopped by the drying step, leaving a low internal pH in the sample, hence providing favorable conditions for the transformation of dicalcium phosphate dihydrate (DCPD) into DCP. Interestingly, even though C₆H₅O ₇ ^3– ions dramatically lowered the equilibrium pH of the cement with 5 ml of deionized water, they still prevented the occurrence of the transformation of DCPD into DCP.     

Effects of organic additives on the morphology of calcium carbonate particles in the presence of CTAB

In this paper, calcium carbonate particles with unusual morphologies could be easily obtained by a precipitation reaction of sodium carbonate with calcium chloride from mixed solution of organic solvents and water in the presence of cetyltrimethylammonium bromide (CTAB) at 80 °C. The as-prepared products were characterized with scanning electron microscopy and X-ray diffraction. The effects of different organic additives–glycol, glycerine, formaldehyde, acetaldehyde, glycol-methyl ether and glycol-ethylether, on the crystal form and morphology of the as-prepared CaCO₃–were investigated and discussed. The results show that organic additives can have great influence on the forms and morphologies of CaCO₃ at relative high temperature in the presence of CTAB. Various unusual crystal morphologies, such as dendrite-shaped, flower-like, wheatgrass-like, needle-like, whiskers, double-taper-like, etc., can be obtained depending on the experimental conditions. In particular, pure aragonite with unusual morphologies can be produced in the presence of glycol, glycerine, glycol-methyl ether at 80 °C, respectively.