The Role of Lattice Matching Techniques in the Characterization of Polymorphic Forms

An inspection of the recent literature reveals that polymorphism is a frequently encountered phenomenon. The recognition of polymorphic forms plays a vital role in the materials sciences because such structures are characterized by different crystal packing and accordingly have different physical properties. In the pharmaceutical industry, recognition of polymorphic forms can be critical for, in certain cases, a polymorphic form of a drug may be an ineffective therapeutic agent due to its unfavorable physical properties. A check of the recent literature has revealed that in some cases new polymorphic forms are not recognized. In other instances, a supposedly new polymeric form is actually the result of an incorrect structure determination. Fortunately, lattice-matching techniques, which have proved invaluable in the identification and characterization of crystal structures, represent a powerful tool for analyzing polymorphic forms. These lattice-matching methods are based on either of two strategies: (a) the reduced cell strategy–the matching of reduced cells of the respective lattices or (b) the matrix strategy–the determination of a matrix or matrices relating the two lattices coupled with an analysis of the matrix elements. Herein, these techniques are applied to three typical cases–(a) the identification of a new polymorphic form, (b) the demonstration that a substance may not be a new polymorphic form due to missed symmetry, and (c) the evaluation of pseudo polymorphism because of a missed lattice. To identify new polymorphic forms and to prevent errors, it is recommended that these lattice matching techniques become an integral part of the editorial review process of crystallography journals.     

The effects of post annealing on the mechanical properties, microstructure and texture evolutions of pure copper deformed by twist extrusion process

X-ray diffraction peak broadening analysis showed that performing a proper heat treatment between the twist extrusion passes of commercially pure copper decreased the coherent domain size and increased the microstrain. Moreover, SEM micrographs illustrated that annealed material contained new formed grains that could not grow due to lack of sufficient time. Under such circumstances, the ultimate strength was elevated about 45 MPa. The deformed material showed texture of simple shear deformation, changing by applying the post annealing.     

Effect of NiCrAlY platelets inclusion on the mechanical and thermal shock properties of glass matrix composites

NiCrAlY platelets modified glass matrix composites were prepared. Their microstructures were characterized, their Young's modulus, fracture strength in bending, Vickers hardness, and indentation toughness were measured, and their thermal shock resistance was studied using quenching-strength and indentation-quench methods. With increasing NiCrAlY content, evident enhancements of the Young's modulus and indentation toughness were obtained. The NiCrAlY alloy inclusion could exert significant influences on the retained bending strength of the samples after quench tests, from 9.6 MPa for NiCrAlY-free glass to 32.0 MPa for 30 wt.% NiCrAlY-containing composites. The indentation-quench tests showed that NiCrAlY alloy inclusion elevated the critical quenching temperatures for propagation of pre-crack, from 150 °C for NiCrAlY-free glass to 225 °C for 30 wt.% NiCrAlY-containing composites. Inclusion debonding and intersection, crack deflection and bridging were observed, and are likely the micromechanisms accounted for the improvement of fracture resistance.     

八氯甲基笼型倍半硅氧烷的合成及表征

以氯甲基三氯硅烷为原料,甲醇、氯仿和石油醚为混合溶剂,在浓盐酸和无水三氯化铁为催化剂的条件下水解缩合制备了八氯甲基笼型倍半硅氧烷(CM-POSS)。利用FT-IR、GPC、1 H-NMR、29Si-NMR和XRD等技术对产物的结构进行了表征,并通过TGA研究了其热稳定性。结果表明产物为八氯甲基笼型倍半硅氧烷,且热稳定性良好。     

抛光用氧化锆固体粉体的表征与制备研究

为筛选合适的氧化锆粉制备抛光液,采用固体紫外光谱、粉末衍射谱、晶体结构拟合、红外光谱、电子探针显微镜等对进口抛光液Zox-N粉体的成分及其品质进行了分析,确定了抛光粉的组成及国产锆粉制备抛光粉的工艺。结果表明,在氧化锆粉中加入0.18%的氧化铁红,混合均匀后在680～720℃煅烧24h,得到的粉体晶型与Zox-N基本一致。     

FeS2薄膜光电性能的影响因素

综述了黄铁矿(FeS2)的晶体结构、制备方法、硫化工艺、薄膜厚度及掺杂元素对FeS2薄膜光电性能的影响,指出了现阶段在FeS2薄膜光电性能研究中出现的问题,并指出了今后的发展方向。     

Thermo-mechanical test rig for experimental evaluation of thermal conductivity of ceramic pebble beds

The experimental determination of mechanical and thermal properties of ceramic pebble beds, such as the lithium orthosilicate or lithium metatitanate, is a key issue in the framework of fusion power technology, for the reason that they are possible candidates in the design of breeder blankets.The paper deals with an experimental method for the evaluation of the thermal conductivity of ceramic pebble beds versus the temperature and compressive strain, based on a steady state heat flux through a material (alumina) of known conductivity. The alumina thermal conductivity is determined by means of the hot wire method. To assess the experimental method, a thermo-mechanical characterization of alumina pebble beds (a material largely available), having different diameters, considering a wide range of temperatures and compression forces has been carried out.Moreover preliminary tests have been performed on lithium orthosilicate and lithium metatitanate pebble beds.     

Effect of plasma treatment on the surface properties of polydimethylsiloxane

In this work, the analysis of the plasma modification of polydimethylsiloxane (PDMS) substrates was conducted. The influence of the modification onto the changes occurred within the geometrical structure and chemical composition of the surface was analyzed. Due to the study of the atomic force microscopy, it was possible to determine the relationships between the surface development and applied process parameters, defining the conditions facilitating to obtain isotropic or anisotropic orientations of wrinkles. A precise analysis of the chemical composition of the surface, executed before and after the modification processes, enabled to define the changes in their elementary composition. Moreover, the modification influence onto the changes of the contact angle and the surface free energy were also analyzed. So, based on the research it was stated that the increase of value of the surface free energy is proportional to the sp³ phase contents in the DLC coatings. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41635.     

Formation mechanism and microhardness characterization of the ultrasonic hardening layer in cementitious materials

Ultrasonic surface treatment (UST) is a novel treatment method to improve the durability of cementitious materials, resulting in the formation of an ultrasonic hardening layer (UHL). The UHL acts as an effective natural coating, offering penetration and erosion protection. However, the formation mechanism and the quantitative characterization of the UHL have not been studied, and the validity of the UST on the top and side surfaces of cementitious materials is still unknown. Therefore, in this study, we investigated and proposed a formation mechanism for the UHL, and defined a transition layer between the UHL and the matrix. We also utilized HV microhardness testing to provide an effective quantitative characterization method for the UHL. Finally, using a set of custom-designed ultrasonic molds, we confirmed the validity of the UST on the top and side surfaces of the cementitious materials.