A new technology of microporous polymeric membranes

It is demonstrated that microporous membranes can be obtained by perforating polymer films with the aid of a needle cliche perforator.     

Preparation of bioactive microporous titanium surface by a new two-step chemical treatment

Microporous oxide layers allowing fast deposition of calcium phosphate layers (CPLs) were formed on commercially pure titanium (c.p.Ti) after the application of a newly developed two-step chemical treatment. The micropores were of submicrometre size. The two-step treatment was carried out by etching c.p.Ti samples with HCl and H2SO4 first and then treating them in boiling 0.2 N NaOH solution at 140 °C for 5 h. Conformal CPLs, about 20 m thick, were deposited on the two-step treated c.p.Ti surface by means of a two-day immersion in an in vitro supersaturated calcification solution. The CPL was characterized to be mainly composed of two sublayers, i.e. an outside loose octacalcium phosphate crystal sublayer and an inside dense carbonated apatite sublayer. A scratching test indicated that the apatite sublayer was strongly bonded to the c.p.Ti substrate. Moreover, it was observed that the untreated or single-step treated c.p.Ti surfaces are not only morphologically different from one another but significantly different from the two-step treated one, in that no precipitation was observed on them up to 14 d immersion in the same calcification solution. It is indicated that the two-step chemical treatment is a simple and easily controllable method to prepare bioactive titanium surfaces and subsequently to induce the rapid precipitation of conformal and adherent CPL from in vitro supersaturated calcification solutions. © 1998 Chapman & Hall     

新型微孔膜滤料的制备与除尘性能测试

针对常规除尘器滤料压力损失增长快、易磨损、易粘袋等问题,采用环氧树脂、丙酮、二乙烯三胺、有机玻璃树脂、无水乙醇等化学试剂对无纺布滤料基材进行表面改性处理,制备出新型微孔膜滤料;在对其孔径分布、透气性能、力学性能、过滤性能以及形貌结构等进行实验分析的基础上,探讨微观结构与除尘性能的关系。结果表明:无纺布滤料基材经表面改性处理后,新型微孔膜滤料的孔径尺寸为5～50μm,透气性略为降低、过滤精度和力学性能明显提升,机械强度增加;过滤风速在1.2 m/min以下时,新型微孔膜滤料的全尘过滤效率≥99%;分级过滤效率受粉尘粒径大小影响较小,对PM_(2.5)的分级过滤效率≥96%;静态过滤压损随着过滤风速的增大而增大,动态过滤压损随着过滤时间的增加而增大;新型微孔膜滤料的过滤方式为表面过滤,表面附着的三维网状光滑膜层能提高过滤精度,充当粉尘初层,降低动态过滤压损,减少粉尘沉积,提高过滤效率,降低清灰难度。     

Synthesis of new silicas with high stable and large mesopores and macropores for biocatalysis applications

Monomodal or bimodal porous silicas with large mesopores, constituted by particles or having a monolithic (block type) morphology, respectively, are synthesized using sodium silicate as siliceous species source, cetyltrimethylammonium bromide (CTAB) as pore template and ethyl acetate (EtAc) as pH modifier. The monomodal porosity is represented by 20–30 nm pores and the bimodal one by these pores and also macropores. These characteristics are modulated in function of the CTAB and EtAc concentrations as well as the pH and hydrothermal treatment. The role of these reagents upon the porosity is rationalized. The presence of high CTAB concentration and a rather low pH decreasing rate (function of EtAc concentration and hydrothermal treatment) are essential for having the already known bimodal mesoporous silicas (BMS). On the contrary a rather high pH decreasing rate promotes the formation of the new bimodal mesoporous–macroporous silicas (BMMS) synthesized in this work, where the EtAc also plays the role of emulsion forming agent. The hydrolytic stability of the synthesized silica under aqueous conditions, at different pH values, makes these silicas good candidates for application in different areas of catalysis, especially in the enzymatic one.     

Random laser action of ZnO@mesoporous silicas

ZnO@mesoporous silica nanocomposite was prepared by the impregnation method, and very efficient laser action was highlighted. As revealed by high-resolution transmission electron microscopy (HR-TEM), nanometric ZnO particles are confined inside the mesochannels of CMI-1 mesoporous silicas. Upon excitation at 3.6?eV of a femtosecond pulsed laser and at low pumping intensity, the ZnO@mesoporous silica showed a broad photoluminescence (PL) band corresponding to the excitonic recombination of ZnO. When the pumping intensity is increased up to a threshold (2.5?mJ?cm(-2)), the excitonic emission turns to stimulated emission through a mechanism which will be discussed. The same threshold value was obtained with another excitation source and nanocomposites with different ZnO loadings inside the CMI-1 mesoporous silica. These results allow a better understanding of the random laser effect in ZnO@mesoporous silica and, consequently, a model has been proposed to explain this phenomenon. Based on these new observations, many new applications can be considered since short-wavelength devices are required by industry to design new information storage supports.     

Thermodynamics of order-disorder transformations in vanadium carbide

Some of the nonstoichiometric carbides of the transition metals (e.g. VC _x ) undergo transformations to ordered phases at specific values of x. In a thermodynamic study of such order-disorder transformations the latent heats of the reactions VC_0.833=V₆C₅ and VC_0.875=V₈C₇ were measured using differential thermal analysis (DTA) and gave values of 5.7±2.8 cal g^?1 and 6.0±2.4 cal g^?1 (1 cal=4.1855 J), respectively. For well-annealed specimens intermediate in carbon-to-metal ratio between these two compositions, DTA indicated the coexistence of domains of both ordered phases. The implication is that the nonstoichiometric, disordered, NaCl-structure phase VC _x does not represent the lowest energy state of vanadium carbide at room temperature for any value of x. This result may apply to the other isomorphic carbides, i.e. TiC _x , ZrC _x , HfC _x , NbC _x and TaC _x . The measured temperatures corresponding to the onset of the transformations were 1184±12? C for V₆C₅ and 1112±8? C for V₈C₇, but the centre of the distribution was approximately 50? C higher in each case. A rationalization of the existence of first-order transitions and an estimate of the latent heats expected from the measured transition temperatures were attempted using the Bragg-Williams theory of order-disorder transformations. The results are consistent with experiment, though the adequacy of this approximation for such a complex case is questionable.     

Calculation of the adsorption deformation of a microporous adsorbent

A model of elastic adsorption deformation of microporous adsorbents is presented. The calculation results for the system argon–AUK microporous carbon adsorbent and their comparison to experimental data are given.     

A new family of tellurife glasses

Glass formation in three-component tellurite-phosphate and tellurite-borate vitreous systems has been determined, with the latter including metal oxides or metal halides (chloride, fluoride or bromide), respectively. The results obtained have served as a base for the determination of the glass forming tendency in a number of telluritemetaphosphate and tellurite-metaborate triple combinations. Hence a new family of tellurite glasses has been obtained. It has been established that the glass formation is most observed in alkaline, earth alkaline oxide and halide metaphosphate systems. The three-component tellurite-metaphosphate and metaborate systems investigated have been treated as partial three-component sections of the main four-component telluritephosphate and tellurite-borate systems also.     

Surface-modified mesoporous silicas as recyclable adsorbents of an endocrine disrupter, bisphenol A

Surface-modified mesoporous silicas (MSs) were investigated for recyclable adsorption of an endocrine disrupter, bisphenol A (BPA). Surface-modified MSs were prepared by (i) post-synthesis surface modification of MSs using surface hydroxyl groups and organosilanes (m-MS) and by (ii) co-condensation of tetraethoxysilane and the corresponding organosilanes (d-MS). Infrared measurements indicated that organic groups mainly existed on the surface of m-MS, which resulted in a surface characterized by high hydrophobicity. Both organic groups and isolated hydroxyl groups existed on the surface of d-MS, resulting in both hydrophobicity and hydrophilicity on the surface. The amount of BPA adsorbed on surface-modified MSs per organic group was similar for m-MS and d-MS, however, the d-MS established equilibrium for BPA adsorption faster than m-MS, as measured by UV-vis spectra. A larger amount of BPA per surface area could be adsorbed on carbon materials than on the surface-modified MSs, however, the regeneration of carbon materials by washing could not be done easily. The surface-modified MSs retain adsorption capacity for BPA after several regeneration cycles, demonstrating that the surface-modified MSs are effective recyclable adsorbents of the endocrine disrupter, bisphenol A.     

Use of thin films for studying order-disorder transformations

Thin films are used to investigate the transformation by heat treatment of a disordered phase into an ordered phase in two different cases: compositional disorder in the case of metallic (Au-Cu) alloys, and positional disorder in the case of an amorphous semiconductor (Ge). The transformation is followed by simultaneous resistance measurements and controlled by electron diffraction and electron microscopy; its effects on the optical properties are measured. The use of thin films allows one to characterize accurately the phases before and after the transformation, and to check that the transformation has been completed.     

Synthesis,characterization and crystal chemistry of microporous titanium-silicate materials

We attempted to synthesize crystalline, three-dimensional, microporous oxide networks composed of interconnected titanate octahedra and silicate tetrahedra. Thus, hydrothermal syntheses were performed using strongly alkaline titanium-silicate gels as reactants. Synthetic analogs of the zeolitic minerals zorite and vinogradovite were prepared and characterized, and these materials contain the desired structural features. In addition, a novel microporous titanium-silicate composition that is a structural analog of the mineral pharmacosiderite was prepared and shown to be composed of interconnected four- and six-coordinated polyhedra. These results serve to illustrate the potential for the discovery of novel molecular sieve structures and compositions that incorporate octahedral units into their frameworks.     

表面接枝防老剂的白炭黑在天然橡胶中的应用

为了提高白炭黑与橡胶的相容性,同时防止防老剂的挥发,采用γ-缩水甘油醚氧丙基三甲氧基硅烷与对氨基二苯胺(PPDA)的反应物对白炭黑进行表面改性,得到表面接枝防老剂的白炭黑。将改性白炭黑应用于天然橡胶(NR)中考察其增强与防老性能,并与炭黑/NR、未改性白炭黑/NR和Si69改性白炭黑/NR复合材料相比较(均添加防老剂4020)。结果表明,改性白炭黑/NR复合材料的焦烧时间延长,硫化时间缩短,白炭黑在橡胶中的分散性提高,同时具备更出色的力学性能。随着表面接枝防老剂含量的增加,改性白炭黑/NR复合材料的拉伸强度和撕裂强度比未改性白炭黑和Si69改性白炭黑/NR均有大幅提高。当接枝的PPDA含量达到5.27%(与白炭黑的质量比)时,其拉伸强度比未改性白炭黑/NR提高了90%,比Si69改性白炭黑/NR提高了73%,并接近炭黑/NR; 其撕裂强度是未改性白炭黑/NR的5倍,Si69改性白炭黑/NR的2.5倍,炭黑/NR的2倍。另外,表面接枝防老剂的白炭黑/NR复合材料具有优异的抗热氧、抗臭氧和湿热老化性能;其抗臭氧老化性能优于添加通用防老剂4020的对比复合材料。     

Surface properties and dispersion behaviour of precipitated silicas

Silicas of highly dispersion degree were obtained using the precipitation technique with sodium metasilicate solution and sulphuric acid. This process includes formation of silica particle and their aggregation. Studies on the surface modification of silicas using silane coupling agents are described. Application of these compounds results in the change of the hydrophilic character to the hydrophobic one. Basic physicochemical analyses of the obtained silica were presented. Moreover, studies on morphology and microstructure using scanning electron microscopy (SEM) were performed. The zeta potential, polydispersity and changes in the tendency to form agglomerates and aggregates of the particles were also described. Silicas modified with any of the examined silanes manifest a decreased tendency to secondary agglomerate formation and in many cases uniform silicas were obtained.     

Strain-dependent behaviour of microporous polyethylene with a negative Poisson's ratio

Recent papers have discussed particular forms of expanded polytetrafluoroethylene (PTFE) and ultra-high molecular weight polyethylene (UHMWPE) that exhibit large negative Poisson's ratios due to their complex microstructures. These consist of an open network of nodules interconnected by fibrils. Two geometric models have been developed to explain the effect in PTFE; one based on nodule translation and the other on nodule rotation. Data are presented for the strain-dependent variation of the Poisson's ratio of UHMWPE under compression and the models are applied. The translation model alone accurately describes the variations in Poisson's ratio as a function of compressive strain.