Bonding Surface area and Bonding Mechanism-Two Important Factors fir the Understanding of Powder Comparability

Two factors could be regarded as primary factors for the compactability of powders: the dominating bond mechanism and the surface area over which these bonds are active. Owing to considerable experimental difficulties, these factors have not been evaluated in any detail for pharmaceutical materials. Instead, more indirect, secondary factors are normally studied and used for correlations with tablet strength. Such secondary factors are particle size, shape and surface texture. Also the importance of volume reduction mechanisms, i.e. elastic deformation, plastic deformation and particle fragmentation have been studied in detail.

For the investigation of dominating bond mechanisms and estimation of the magnitude of the surface area of the solids involved in interparticulate attraction in compacts several pharmaceutical excipients representing both plastically deforming materials (sodium chloride, Avicel® PH 101, Sta-Rx 1500®, and sodium bicarbonate) and fragmenting materials (lactose, sucrose, paracetamol and Emcompress®) have been used in a series of publications from our laboratory.

The bonding mechanisms discussed have been solid bridges, representing continous solid bridges between tablet particles, intermolecular forces, representing weaker attraction forces active over distances and mechanical interlocking, representing a bond type dependent on hooking and twisting of irregularly shaped particles. To characterize the dominating bond mechanisms, measurements of compact strength has been performed in media known to reduce bonding with intermolecular forces. The media used were liquids with different dielectric constants and films of magnesium stearate. The results establish that the intermolecular forces constitute the dominating bond mechanism for pharmaceutical materials. Bonding with solid bridges contribute to the compact strength only for coarse plastically deforming materials that can melt during compaction. Only for sodium chloride, of the materials tested, is there substantial evidence for the existence of solid bridges. Bonding with mechanical interlocking is a bonding mechanism of minor importance for most of the investigated materials with the possible exception of Avicel® PH 101.

The results indicate that the surface area utilized for bonding with solid bridges for sodium chloride as measured with gas adsorption is small in relation to the total surface area of the compact. For all the materials bonding with intermolecular forces, only a proportional relation between compact surface area and bonding surface area could be possible. By using permeametry surface area data, the surface specific compact strength was characterized and found similar for all materials bonding primarily with intermolecular forces. For such materials a large bonding surface area will thus be obtained if the surface area of the particles in the tablet is large. This could either be achieved by the use of materials that undergo extensive fragmentation or by the use of very fine paniculate materials or qualities with pronounced surface roughness. It is suggested that most of the so called plastically deforming pharmaceutical materials often possess inadequate plasticity for the development of large zones that could take part in the interparticulate attraction by intermolecular forces.     

Surface quality of thermally compressed Douglas fir veneer

The objective of this study is to evaluate surface quality of compressed Douglas fir (Pseudotsuga menziesii) veneer sheets in the form of its roughness. Veneer samples were compressed using pressure levels of 1.0 N/mm², 2.0 N/mm², and 2.5 N/mm² at two temperatures of 180 °C and 210 °C for 3 min. A fine stylus profilometer was used to evaluate surface roughness of the veneer samples. Three roughness parameters, namely average roughness (R_a), mean peak-to-valley height (R_z), and maximum roughness (R_max) values were determined. The results obtained in this study showed that the surface roughness parameters of the thermally compressed veneers decreased with increasing press temperature and pressure level. It appears that initial data found in this work would provide some benefit to more efficient use of adhesive to manufacture plywood and laminated veneer lumber (LVL) panels with enhanced properties.     

Cu-Fe基粉末烧结金刚石复合材料界面结合特性

以Cu-Fe基粉末为基体材料,在真空压力烧结条件下制备了金刚石复合材料。利用扫描电镜、能谱仪、X射线衍射仪等研究粉末与金刚石颗粒界面结合特性。结果表明,930℃、15MPa烧结温度和压力下,烧结胎体中Fe原子向金刚石表面扩散,形成一定厚度的扩散层,并与金刚石中的C发生化学反应生成Cfe15,呈非连续层片状分布于金刚石颗粒表面,实现了金刚石颗粒与金属的化学键结合。     

铝粉的表面改性

铝粉的表面改性是功能铝粉生产中非常重要的工艺。本文中综合铝粉改性的手段及改性后铝粉的功能,介绍了铝粉表面改性常用的几种方法,包括机械化学改性、氧化改性、表面化学改性、胶囊改性、包覆改性和沉淀改性等。     

碳粉表面金属化研究

研究了在碳粉表面电镀铜的工艺。首先对碳粉表面进行亲水、敏化、活化和还原处理,然后在其表面化学镀铜,形成导电膜,再采用电磁搅拌的方法电镀铜,使镀层加厚。     

SiC纳米粉表面研究

借助于TEM、IR和XPS分析;对新鲜的SiC纳米粉表面和不同存放时间及处理条件下的样品表面进行分析比较,发现新鲜的作品表面主要以物理吸附氧为主（78.25％）,化合态氧为辅（21.75％）,在空气中存放一个月后,O／Si比由新鲜样品表面的0.49上升至0.70表面发生氧化,继续存放一个月,O／Si比增至0．77;但表面氧化速度变缓,在潮湿空气中SiC纳米粉更易氧化．离子刻蚀分析表明,O主要分布在粉末表面．     

a－Si：H表面键合光敏染料及其光电导

本文报导了用低温等离子体法使ａ－Ｓｉ：Ｈ表面活化，经多步化学反应，将３种菁键合于其表面，并经激光拉曼光谱和Ｘ－光电子能谱表征。测定了键合染料的ａ－Ｓｉ：Ｈ的吸收光谱和光电导。结果表明，光敏染料可使ａ－Ｓｉ：Ｈ敏化，改善其光吸收和光电导。     

钛表面的氧化对钛瓷结合强度的影响

研究了钛表面氧化对钛/瓷结合强度的影响, 并采用溶胶凝胶技术在钛表面制备SnO_x中间层, 研究SnO_x层对钛/瓷结合强度的影响. 结果表明：空气炉中800℃氧化3min后, 钛/瓷结合强度明显下降; 烤瓷炉中预氧化3min, 钛/瓷结合强度无明显变化. 热处理使钛表面生成一层金红石型氧化层, 钛/瓷剥脱主要发生在金红石氧化层与钛之间. 采用溶胶-凝胶法经300℃处理后在钛表面制得的SnO_x涂层, 可有效隔绝氧向Ti表面的扩散, 防止钛表面的过度氧化, 提高了钛/瓷结合强度. 经SnO_x涂层处理后, 钛/瓷剥脱主要发生在SnO_x涂层内.     

聚丙烯粉料表面的紫外光和射线辐照接枝

以马来酸酐（ＭＡＨ）、丙烯酸（ＡＡ）、丙烯酸乙酯（ＥＡ）、丙烯酰胺（ＡＡ）为单体，对预氧化和未处理的聚丙烯（ＰＰ）粉进行固相光接枝、溶液光接枝，固相γ射线接枝以及γ射线预辐照溶液接枝，用ＦＴ－ＩＲ、ＥＳＣＡ和化学滴定法对接枝聚丙烯进行了定性和定量表征。结果表明，各单位均在聚丙烯表面发生了不同程度的接枝共聚。     

双金属热轧复合的界面结合影响因素及结合机理

在综合了不同材料热轧复合的实验基础上,分析了双金属热轧复合过程中不同工艺条件对结合质量的影响.结果表明:轧制前清除材料表面的覆盖膜有助于轧制过程中形成结合点;轧制过程中适当的轧制温度和轧制压下量能大量消除轧制过程中在金属表面形成的氧化膜,从而使组元材料能形成机械结合;在热烧结过程中,原子通过界面扩散可以消除轧制过程中由于界面微观不平整形成的空洞,同时通过原子间的相互作用使组元材料间形成冶金结合.依据固相结合理论分析得出,双金属热轧复合的界面结合过程包括:金属间物理接触形成机械结合阶段,原子通过化学作用形成化学键及通过界面扩散消除空洞的冶金结合阶段,以及互扩散阶段.     

Chirality and Surface Bonding Correlation in Atomically Precise Metal Nanoclusters

Chirality is ubiquitous in nature and occurs at all length scales. The development of applications for chiral nanostructures is rising rapidly. With the recent achievements of atomically precise nanochemistry, total structures of ligand-protected Au and other metal nanoclusters (NCs) are successfully obtained, and the origins of chirality are discovered to be associated with different parts of the cluster, including the surface ligands (e.g., swirl patterns), the organic–inorganic interface (e.g., helical stripes), and the kernel. Herein, a unified picture of metal–ligand surface bonding-induced chirality for the nanoclusters is proposed. The different bonding modes of M–X (where M = metal and X = the binding atom of ligand) lead to different surface structures on nanoclusters, which in turn give rise to various characteristic features of chirality. A comparison of Au–thiolate NCs with Au–phosphine ones further reveals the important roles of surface bonding. Compared to the Au–thiolate NCs, the Ag/Cu/Cd–thiolate systems exhibit different coordination modes between the metal and the thiolate. Other than thiolate and phosphine ligands, alkynyls are also briefly discussed. Several methods of obtaining chiroptically active nanoclusters are introduced, such as enantioseparation by high-performance liquid chromatography and enantioselective synthesis. Future perspectives on chiral NCs are also proposed.     

Diffusion Bonding of Laser Surface Melted Nickel Alloy Material

Diffusion bonding studies were performed on Laser Surface Melted (LSM) Ni-Cr-Fe material. LSM generates metastable microstructures with extended solid solution. The rapid quenching associated with LSM generates a zone that is void of intragranular precipitates, consists of well-defined grain boundaries via intergranular carbides, and contains fine-grained material. Grain growth across the bondlineand precipitate morphology were studied as a function of laser beam power (energy density) and bonding temperature. LSM at low energy density produced excellent grain growth across the bondline even when bonding at low temperature.     

粉末置换包覆的热力学及其影响因素

从热力学角度分析了置换包覆粉末的原理,并探讨了原料粉末、镀液浓度、温度、搅拌速度、添加剂等因素对置换包覆的影响.通过热力学计算表明,置换反应速度随镀液浓度的增大和温度的升高而增大.过程为化学反应控制时,搅拌不影响置换包覆速度;过程为扩散控制时,随着温度升高,置换包覆速度增加.镀液pH值过大会发生析氢反应,过小会使金属离子水解降低置换包覆速度.另外在镀液中加入合适的添加剂有利于改善镀层的质量.     

具有键合功能热塑性聚氨酯的表面性能

通过反相气相色谱法(IGC),采用非极性和极性探针分子研究了新型热塑性聚氨酯弹性体(DTPU)的色散表面自由能和表面Lewis酸碱性质,并与传统的推进剂用热塑性聚氨酯粘合剂(BTPU)做了对比。结果表明,DTPU与BTPU的色散表面自由能较为接近,并且随着温度的升高而线性降低;DTPU的酸常数Ka和碱常数Kb分别为0.09和0.48,而BTPU的酸常数Ka和碱常数Kb分别为0.06和0.37,DTPU的酸性和表面总的酸碱作用能力较大,与推进剂中高能固体填料具有更好的相互作用。     

纳米二氧化硅表面改性研究

采用甲苯二异氰酸酯(TDI)接枝聚乙二醇(PEG)对纳米SiO2进行表面改性,并利用红外光谱(FTIR)和热重(TG)、扫描电镜(SEM)、粒径分析、重力沉降法等方法对改性前后的纳米SiO2的表面形貌和在介质中的分散稳定性进行了表征和分析.结果表明,改性后的纳米SiO2表面接枝上了TDI、PEG的有机官能团,降低了颗粒...     

焊前处理方式对LF6铝合金扩散焊的影响

利用Ｇｌｅｅｂｌｅ－１５００热／力模拟试验机，研究了ＬＦ６铝合金的扩散焊工艺，通过对焊接温度、压力、时间的调整和选用不同的料前处理方法，确定了最佳的扩散规范，研究结果表明：在一定的温度和时间范围内，ＬＦ６５铝合金扩散焊接头的剪切哟度随焊接温度和时间的增加而提高；化学浸蚀法比机械打磨法能更有效的去除铝合金表面的氧化膜；在现有试验条件下，得到ＬＦ６铝合金扩散焊的最佳规范参数，搭接试扩散焊接头的剪切强度     

超细氢氧化镁阻粉体表面改性研究

采用硅烷偶联剂对超细氢氧化镁粉体进行表面改性,研究了偶联剂用量、时间、温度等因素对粉体改性效果的影响,并以活化指数作为衡量指标,获得了硅烷偶联剂对氢氧化镁表面改性的最佳工艺条件。能量色散谱仪(EDS)测试结果表明,改性后氢氧化镁表面结合了硅烷偶联剂;红外光谱显示,硅烷偶联剂与氢氧化镁之间形成了化学键。提出了硅烷偶联剂对氢氧化镁表面改性的机理。     

铜金粉表面改性技术的研究

为了提高铜金粉的表面其泽度采用3种表面活性剂对铜金粉进行表面改性研究,从而证明降低粘结料对铜金粉的润湿性,可提高粉末在粘结料中的漂浮性能,有效提高铜金粉颜料的印金光泽度。探明了铜金粉颜料化处理的原理和努力的方向。同时分析了表面活性剂的种类及其浓度对铜金粉印金光泽度的影响。结果表明,铜金粉的润湿性随表面活性剂浓度变化而存在极值点;复合改性剂比硬脂酸系列的改性剂能更好的降低铜金粉的润湿性。     

纳米级二氧化钛的表面包覆技术

表面包覆技术是继成功制备出纳米ＴｉＯ２ 后,为获得特异性能及适应多种应用场合而发展起来的新研究项目。本文综述了近年来纳米级ＴｉＯ２ 表面包覆技术的研究成果及进展,并提出当前和今后的研究方向。     

冷轧带钢粘结缺陷的影响因素与控制措施

对八钢冷轧薄板厂钢卷产生的粘结缺陷进行追踪，从热轧卷来料、冷轧轧机、罩式炉退火、平整工艺对粘结进行系统的研究，找出各机组粘结缺陷的影响因素和影响方式，并提出冷轧厂及其各机组的控制措施。