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。     

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。     

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。     

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。     

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.     

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.     

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...     

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.     

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     

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。     

钛合金胶接表面处理研究

钛合金表面处理方法是影响钛合金胶接耐久性的重要因素。本文介绍了各种钛合金胶接表面处理方法及其表面分析技术,评述了各种表面处理方法对胶接耐久性的贡献。以湿热耐久性为考核点的研究结果显示:电化学方法优于化学方法,化学方法优于机械方法。另外,处于研究阶段的等离子体、激光等物理方法因具有较好的耐久性和低污染特性,有望用于钛合金胶接的工业领域。     

铜粉表面磷化工艺优选

为提高铜粉的抗氧化性能,以氧化锌、磷酸、硝酸配制磷化液,通过单因素试验进行铜粉磷化工艺优选,采用扫描电镜、X射线衍射仪、激光粒度仪及烧结试验等研究了磷化液成分、磷化时间、磷化温度对所得磷化铜粉形貌、粒径和抗氧化性能的影响。结果表明:铜粉磷化后在150℃时抗氧化性得到较大改善,在300~400℃之间的抗氧化能力明显提高,但在400℃时,铜粉的抗氧化能力改善相对较小;磷化的最佳工艺为A磷化体系(8 g Zn O,14 m L HNO3,7 m L H3PO4,250 m L H2O)、磷化温度65℃、磷化时间40 min;最佳条件下磷化,能够获得粒径分布更均匀、分散性和抗氧化性更好的类球形铜粉。     

Understanding Powder Caking as a Consequence of a Range of Mechanisms by Means of Powder Rheometry

Over 70% of materials in the food, chemical, and pharmaceutical industries (from raw materials, additives, and intermediates through to manufactured products) are supplied as relatively free-flowing powders, intended to be suitable for the manufacturing process or final application. For logistical reasons however these materials will often have to be stored for extended periods during which time some powders have the potential to gain strength due to prolonged and undisturbed particle/particle interactions. This is generally referred to as “caking” and can significantly limit the ability of a powder to pass through the process train without interruption as well as detrimentally impacting product quality.

This paper will present case studies that evaluate the flow properties of different powder systems that are affected by chemical-, moisture-, and temperature-based caking mechanisms. It will show how the propensity to cake can be effectively quantified with respect to the powders’ flow properties and how this can assist in understanding and adapting the processing environment to retain optimal processability.     

机械混合法改性微纳米粉体的设备设计

粉体表面改性与复合设备是实现粉体表面改性与复合技术中的一个重要环节。在研究现有微纳米粉体表面改性与复合设备结构特点的基础上,结合微纳米粉体改性与复合的工作原理,针对微纳米粉体的表面特性,提出了机械混合法改性微纳米粉体的典型设备及其设计思想。本设计的特点在于在半椭球形容器下半部的圆柱面上设有两组8个与母线成α(α>90°)角的大小喷嘴成对角布置,以利于粉体和改性剂的分散与混合。     

无机粉体的低温等离子体表面改性

低温等离子体技术是一种新的表面改性方法,被认为是偶联剂技术的新发展。从等离子体处理方法和装置,处理后无机粉体的表面性质,使用性能等方面详细阐述了这一方法,并对该领域的研究进行了评述。