Preparation of 3-D regenerated fibroin scaffolds with freeze drying method and freeze drying/foaming technique

Although three-dimensional fibroin scaffolds have been prepared with freeze drying method, the porosity and pore sizes still can not satisfy the requirement of tissue engineering. In this article, fibroin porous scaffold with high porosity and > 100μm diameter interconnected pores was firstly prepared with freeze drying method through adjusting fibroin concentration. The morphology of different scaffolds lyophilized from different fibroin concentration was observed by SEM. A novel freeze drying improved method, freeze drying/foaming technique, was also devised to prepare fibroin scaffolds at different fibroin concentrations. Using the said method, the porosity and pore size of fibroin scaffolds prepared from 12% concentration were 85.8 ± 4% and 109 ± 20 μm respectively with yield strength up to 450 ± 6 KPa while the porosity and pore size of fibroin scaffolds prepared from 8% concentration were 96.9 ± 3.6% and 120 ± 30 μm respectively with yield strength up to 30 ± 1 KPa. The freeze drying/foaming technique produced scaffolds with a useful combination of high yield strength, interconnected pores, and pore sizes greater than 100 μm in diameter. Through adjusting fibroin concentration and thawing time, the porosity, pore sizes and mechanical properties could be controlled to satisfy the different requirements of tissue engineering. The results suggested that fibroin scaffolds prepared with the above methods could be formed for utility in biomaterial application.     

在真空冷冻干燥中冻结温度的测定与分析

以奶牛初乳为试验材料，测定了常压状态下与真空状态下地冻结温度，是出电阻变化率约１ＭΩ／ｍｉｎ作为共晶点温度选取依据。从节能出发，试验确定了较佳冻结温度。     

New method for the measurement of stress in thin drying gel layers,produced during the formation of ceramic membranes

A new method has been developed for the measurement of stresses in thin gel layers during the drying process. The gel layers under investigation consist of boehmite, and are produced during the formation of -Al₂O₃ ceramic membranes. The method is based on the principle of the cantilever beam. Detection of beam deflections is carried out with a laser displacement meter, using a 760 nm infrared laser. Deflections of the beam can be measured continuously during the drying process, making it possible to monitor the stress in the layer also continuously. Examples illustrate that stresses may be as high as 180 MPa. Cracking of gel layers most likely manifests itself by a marked decrease in the stress. Uncracked gel layers may be stressed and subsequently unloaded by slowly lowering and increasing the relative humidity. An increase of temperature at constant air flow and relative humidity leads to an increase of the stress. Lowering the rate of air flow over the sample lowers the stress which is built up. The method which is described here can very probably also be applied to other coating materials, which are dried on rigid supports.     

Effect of formulation ingredients on the physical characteristics of salmeterol xinafoate microparticles tailored by spray freeze drying

Series of microparticles containing salmeterol xinafoate (SX) as active pharmaceutical ingredient (API) and lactose, mannitol or trehalose as a bulking agents were prepared using spray freeze drying (SFD) technique and the effects of sugar type and presence of hydroxy propyl beta cyclodextrin (HPβCD) on the physical properties of powders were evaluated. Precipitation of salmeterol in the presence of lactose and mannitol resulted in the formation of irregular shapes of microparticles with broad size distributions. However application of trehalose resulted in the formation of porous particles with spherical morphology. Addition of cyclodextrin in the formulations was generally helpful for formation of porous and spherical particles with narrow size distribution with a mean size of 10–30 μm. Dissolution of SX from processed particles was substantially higher (～90% drug release in 30 min) than that of unprocessed drug and physical mixture of drug and cyclodextrin (～22% drug release in 30 min). This study showed that, processing of SX by SFD technique could be a constructive approach to the production of various forms of drug and drastic changes in the physical characteristics of microparticles could be achieved by changing the composition of bulking agent and cyclodextrin.     

Eco-friendly approach for preparation of hybrid silica aerogel via freeze drying method

Journal of Materials Science - In this paper, an eco-friendly method of producing hybrid silica aerogels by freeze-drying method (FD) is proposed. In the freeze-drying system, deionized water was...     

Properties of porous Si3N4 ceramic electromagnetic wave transparent materials prepared by technique combining freeze drying and oxidation sintering

A simple and low-cost technique combining freeze drying and oxidation sintering is explored to prepare Si₃N₄ ceramics with high porosity and complex shape. The effects of sintering temperature and time on the phase composition, microstructure, porosity, pore size and dielectric constant of the porous Si₃N₄ ceramics are studied. Due to the variations of phase composition and microstructure, the porous Si₃N₄ ceramics sintered at different temperature possess characteristic in flexural strength. The porous Si₃N₄ ceramics sintered at 1,300 °C for 2–3 h have the highest flexural strength of 71–74 MPa. The changes of porosity and composition have much effect on the dielectric constant of porous Si₃N₄ ceramics. Because of the high porosity and SiO₂ volume fraction, the porous Si₃N₄ ceramics sintered at 1,300 °C for 2–3 h possess low dielectric constant of 3.4–3.6 and small pore size of 0.9 μm. The porous Si₃N₄ ceramics are good structural/functional and promising electromagnetic wave transparent material.     

鲜花真空冷冻干燥实验研究

为探索干燥花加工新技术,以月季、万寿菊和补血草为素材,利用冷冻干燥技术进行了冻干鲜花的实验研究。研究结果表明：采用真空冷冻干燥技术干燥较大的花朵植株,能够基本保持干燥花的形状、色泽和芳香;冻干后,红色的月季花颜色变深,而黄色的万寿菊颜色变淡;紫色的补血草颜色基本不变。采用真空冷冻干燥技术干燥鲜花是可行的。具有深入研究应用前景。     

Influence of graphite oxide drying temperature on ultra-fast microwave synthesis of graphene

Ultra-fast synthesis of graphene has been reported by microwave assisted graphene oxide reduction. In this article, the graphene oxide was initially dried above room temperature. The initial heat treatment of graphene oxide demonstrates a distinct improvement of exfoliation rate of graphene sheets. This method provides an efficient way for mass production of high quality graphene sheets. Raman spectroscopy, scanning electron microscopy, and X-ray diffraction techniques has been used to characterize reduced graphene sheets. The quality of reduced graphene was found to be affected by the initial drying temperature of graphite oxide.     

Effect of temperature on the characteristics of ZnO nanoparticles produced by laser ablation in water

Effect of the water temperature on the characteristics of zinc oxide nanoparticles (NPs) produced by laser ablation process is investigated experimentally. The fundamental wavelength of a Q-switched Nd:YAG laser was employed to irradiate a high-purity zinc plate in distilled water at different temperatures of 0, 20, 40 and 60^°C. The produced NPs were diagnosed by UV–vis–NIR spectroscopy, X-ray diffraction method, transmission electron microscopy and scanning electron microscopy. Results show that with increase in the water temperature from 20 to 60^°C, size of NPs decreases while their bandgap energy increases. Maximum ablation rate occurs at the highest temperature. Crystalinity also increases with increase in the water temperature. The abnormal behaviour of water at 0–4^°C affects the NPs characteristics.     

Investigation of characteristics of Cu based,Co-CrC reinforced composites produced by powder metallurgy method

This study was carried out to assess the contribution of Co and CrC reinforcement particles to Cu main matrix powders by powder metallurgy (P/M) method as well as to mechanical properties, abrasion resistance and microstructure properties. For this purpose, the matrix material Cu powders, Co and CrC reinforcement particles, of which the weight percents are as follows: 5% (2% Co + 3% CrC), 10% (4% Co + 6% CrC) and 15% (6% Co + 9% CrC), were added. The samples were produced by cold pressing at room temperature and 450 MPa pressure, using the P/M method. Microstructure characterization of composite samples was performed by SEM-EDS and XRD analysis. Mechanical characterization of composite samples was carried out by analyzing the data of density determinations, hardness measurements, abrasion resistance tests and tensile tests. As a result of this study, it was observed that as the reinforcement ratio increased, the relative density of the samples decreased while the hardness of the samples increased. As a result of the findings obtained from the analysis of the tensile tests and other tests performed, it was clearly seen that the reinforcement particle ratio of wt. 10% was the optimum reinforcement ratio for this study.     

Influence of calcination temperature of kaolin on the structure and properties of final geopolymer

In this paper, the structure of two types of metakaolins from kaolin calcined at 800 and 900 °C, respectively, and the obtained geopolymer were systematically characterized. It was found that calcination temperature had little effect on the environment of silicon atoms but had great effect on that of aluminum ones. ²⁷Al NMR analysis showed that tetrahedral aluminums in the metakaolin from kaolin calcined at 800 and 900 °C were in different environment, of the type AlQ₃(3Si) and AlQ₄(4Si), respectively, leading to different environment of aluminum atoms in the resulted geopolymer. Aluminum atoms in the geopolymer based on metakaolin from kaolin calcined at 800 °C were in the types of tetrahedral and octahedral, and silicon atoms were in the types of tetrahedral Q₄(3Al) together with a small amount of Q₄(0Al). However, geopolymer based on metakaolin from kaolin calcined at 900 °C consisted of Q₄(4Si) unit aluminum and Q₄(3Al) unit silicon. The results revealed that the calcination temperature had a great effect on environment of the aluminum atoms of the metakaolin, thus led to the different structure and properties including mechanical strength and thermal conductivity of the post obtained geopolymer.     

Influence of testing method on mechanical properties of ceramic matrix composites

Mechanical properties of a monolithic zircon and zircon-matrix composites reinforced with silicon carbide monofilaments and/or whiskers were measured in three-point flexure and uniaxial tension modes to study the influence of testing methods on mechanical behaviour. A number of composite characteristics, such as the first-matrix cracking stress and strain, the ultimate composite strength and strain, and the modulus were obtained from the load-deflection behaviour in flexure and tension tests. The results indicated that the modulus values and the qualitative dependence of mechanical properties on composite parameters were similar in flexure and tension tests. In contrast, all of the other mechanical properties of the monolithic and composites were different in tests performed in flexure and tension modes. Typically, the first-matrix cracking stress and strain were higher in flexure tests than in tension tests, and these stress and strain values were independent of the filament-matrix interfacial properties. Similarly, the ultimate strengths of the monolithic and composites were higher in flexure than in tension, and these strengths were independent of interfacial properties. Therefore, the mechanical properties of composites obtained in flexure should not be used for a quantitative comparison with the predictions of micromechanical models, which are derived under the assumption of a uniform tensile stress. However, the flexure data are perfectly valid in demonstrating the qualitative dependence of mechanical properties on composite parameters.     

Creep and drying shrinkage characteristics of concrete produced with coarse recycled concrete aggregate

Laboratory tests are performed to investigate the effects of a new method of mixture proportioning on the creep and shrinkage characteristics of concrete made with recycled concrete aggregate (RCA). In this method, RCA is treated as a two component composite material consisting of residual mortar and natural aggregate; accordingly, when proportioning the concrete mixture, the relative amount and properties of each component are individually considered. The test variables include the mixture proportioning method, and the aggregate type. The results show that the amounts of creep and shrinkage in concretes made with coarse RCA, and proportioned by the new method, are comparable to, or even lower than, those in similar concretes made entirely with natural aggregates. Furthermore, it is demonstrated that by applying the proposed “residual mortar factor” to the existing ACI and CEB methods for calculating creep or shrinkage of conventional concrete, these methods could be also applied to predict the creep and shrinkage of RCA-concrete.     

退火温度对sol-gel制备的ZnO薄膜的结构影响

采用sol-gel旋涂法在抛光硅〈111〉晶面生长了高度C轴取向的ZnO薄膜。DSC以及XRD测试结果显示此溶胶系统的最佳退火温度为450℃左右,更高的退火温度将对薄膜的择优取向产生不利的影响。SEM显示薄膜表面致密、均匀、光滑,组成薄膜的颗粒尺寸在50～100nm,并显示出良好的C轴择优取向。     

Structures and properties of La1−x,Sr x CoO3−y,prepared by freeze drying

Several samples of La_1–x Sr _x CoO_3–y (x = 1, 0.8, 0.5, 0.2) were prepared by calcining freezedried, stoichiometric mixtures of nitrates at different temperatures and for different lengths of time. Selected samples were characterized by powder X-ray diffraction, conductivity measurements, Brunauer-Emmett-Teller surface area measurement, and by electrochemical cyclic voltammetry in alkaline solutions and alkaline solutions containing methanol. The structures of each composition were complex and varied with composition and preparation conditions. There is evidence for non-stoichiometry caused by oxygen anion vacancies. For La_0.5Sr_0.5CoO_3–y the electrochemical activity towards the oxidation of methanol is a maximum at the fully formed cubic perovskite. The oxidation currents at La_0.8Sr_0.2CoO_3–y and La_0.2Sr_0.8CoO_3–y go through maxima at more distorted structures.     

Influence substrate temperature on structural properties of TiN/TiC bilayers produced by pulsed arc techniques

This paper presents an investigation regarding influence of substrate temperature during deposition on the characteristics of TiN/TiC bilayers grown by plasma-assisted pulsed arc discharge. The substrate temperatures were 50, 100 and 150 °C. The gases used in the experiment were N₂ for TiN and CH₄ for TiC. These coatings were studied by X-ray diffraction techniques determining the variation of the lattice parameters for each film. The Scherrer equation was used to calculate the crystallite size and the micro-strain. The X-rays analysis showed an increase in the substrate temperature made the formation of TiC in (2 0 0) orientation favorable. The sample grown at 50 °C presented low crystallinity and it was increased as the substrate temperature increases. Using a scanning probe microscopy, with atomic force microscopy, phase detection microscopy and force modulation microscopy modes, the morphology of the deposited layer was studied and macro-particles were observed using gray scales to identify differences in the friction coefficient and material composition in the coatings. It has been found that the increment of the substrate temperature decreases the condensation of microdroplets on the surface. Lateral force microscopy was used to calculate friction coefficient of the TiN and TiC monolayers and we found that the friction coefficient is smaller for TiC than for TiN.     

水平温梯冷凝法生长ZnGeP_2单晶

采用高纯(6mol/L)Ge、Zn、P单质为原料,按化学计量比并富P 0.2%配料,通过双温区法合成ZnGeP2多晶粉料,再用水平温梯冷凝法(HGF)生长出尺寸达10mm×20mm×80mm的单晶棒。对单晶进行了X射线衍射、红外透过率、热导率等测试,测试结果表明;单晶完整性好,红外透过率较高;5mm厚晶片(未退火、镀膜)在2～8μm范围内平均透过率可达54%以上;在室温附近(297.34K)热导率为35.89W/(m.K)。     

Thermophysical properties of ceramic matrix composites produced by polymer pyrolysis

A unidirectional composite and a series of bidirectionally reinforced composites were fabricated using carbon fibre reinforcement in a silicon carbide matrix, which was produced by the pyrolysis of a polymer precursor. The thermal expansion over the temperature range 20–1000 °C has been measured and the thermal diffusivity measured over the temperature range 200–1200 °C. Thermal diffusivity data was converted to conductivity data using measured density and literature specific heat data. Metallographic examination has been carried out on the composites and the results are discussed in terms of the observed microstructural features.