Nanoparticles for conservation of bio-calcarenite stone

In the present study, the consolidation effectiveness of some inorganic nanoparticles dispersions (silica, calcium hydroxide, and strontium hydroxide) has been evaluated when applied on a very porous stone substrate, i.e., Lecce stone. The strengthening effect of the nanoparticle-based treatments was compared to that exhibited by the well-known consolidant tetraethoxysilane. Ca(OH)₂ and Sr(OH)₂ nanoparticles were prepared in laboratory and characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), dynamic light scattering (DLS), and Fourier transform infrared spectroscopy (FTIR). The kinetic stability of nanoparticles dispersions was determined by UV-vis spectrophotometric studies. Moreover, the study of the nanolime carbonatation process was carried out using FTIR spectroscopy. Distribution of the applied product into the stone substrate was examined by SEM-EDS. The chemical weathering effect of salt crystallization of the treated specimens was evaluated by performing the dry weight loss (DWL) test. All the results suggested that Ca(OH)₂ and Sr(OH)₂ nanoparticles, applied as 2-propanol dispersions, display some good properties as consolidating agents for a very porous bio-calcarenite such as Lecce stone.     

Nanoparticles of Sr(OH)<Subscript>2</Subscript>: synthesis in homogeneous phase at low temperature and application for cultural heritage artefacts

This paper concerns the synthesis and the characterization of nanometer particles of Sr(OH)₂, a moderately high water soluble hydroxide (Ksp= 3.2×10^-4 at 25 °C). The reported process yields strontium hydroxide nanoparticles starting from low cost raw materials in aqueous medium (homogeneous phase) at low temperature (below 100 °C) by chemical precipitation from salt solutions, involving very simple operational steps and avoiding the use of organic solvents. Observations by X-ray diffraction (XRD), scanning electron microscopy (SEM), electron dispersive X-Ray (EDX) and Fourier transform infrared spectroscopy (FTIR) indicate that the particles are well-crystallized and have nanometer dimensions (∼ 30 nm in diameter). Moreover, experimental evidence shows the potential use of this material for the protection and the consolidation of wall paintings (frescoes), paper, stone, wood and other artistic artefacts. PACS  81.16.Be; 82.70.Dd; 68.37.Hk; 68.37.Xy; 61.46.Df     

Experience with the [13C2]Oxalate Absorption Test

Abstract

Hyperoxaluria is the most important risk factor for a formation of calcium oxalate-urinary stones. Usually, the bulk of oxalate will be formed in the human body, but in many patients the oxalate from food plays the decisive role. Conventionally, in urine the endogenous oxalate can not be distinguished from food derived oxalate. We have developed a standardized oxalate-absorption test, applying a physiological dose (50 mg disodium salt of [¹³C₂]oxalic acid) of labelled oxalate. The assay has been published. Now we report on the first extensive applications of this test in 86 volunteers and 135 patients from different groups with calcium oxalate stones or an increased risk of the formation of such stones. In one-third of the patients with calcium oxalate-urinary stones an oxalate hyperabsorption was diagnosed. For these patients, a dietetic stone prophylaxis and/or therapy is indicated.     

Salt crystallization as damage mechanism in porous building materials--a nuclear magnetic resonance study

Salts can damage building materials by chemical reactions or crystallization, which is a serious threat to cultural heritage. In order to develop better conservation techniques, more knowledge of the crystallization processes is needed. In a porous material, the size of a salt crystal is limited by the sizes of the pores. It has been predicted that as a consequence, the solubility of a salt increases with decreasing pore size. This increase seems to be related to an increase of the stress generated by a crystal on the pore wall. It has been suggested that the resulting stress could become high enough to induce failure. We have studied the crystallization of salts in porous materials with well-defined pore sizes. Samples were saturated at 40 degrees C with saturated Na2SO4 and Na2CO3 solutions. Next we have cooled the samples to 0 degrees C and waited for nucleation. After nucleation occurred, the solubility in the porous material was measured with nuclear magnetic resonance (NMR) as a function of the temperature. The measurements on Na2CO3 indeed show an increase in solubility with a decrease in pore size. For Na2SO4, we did not observe a pore size-dependent solubility. However, we have to remark that these results show a metastable crystal phase. The results can be used to calculate the actual pressure exerted by the crystals onto the pore wall.     

Solution-based metal induced crystallization of a-Si

This paper investigates a simplified metal induced crystallization (MIC) of a-Si, named solution-based MIC (S-MIC). The nickel inducing source was formed on a-Si from salt solution dissolved in de-ionized water or ethanol. a-Si thin film was deposited with low pressure chemical vapour deposition or plasma enhanced chemical vapour deposition as precursor material for MIC. It finds that the content of nickel source formed on a-Si can be controlled by solution concentration and dipping time. The dependence of crystallization rate of a-Si on annealing time illustrated that the linear density of nickel source was another critical factor that affects the crystallization of a-Si, besides the diffusion of nickel disilicide. The highest electron Hall mobility of thus prepared S-MIC poly-Si is 45.6cm²/(V.s). By using this S-MIC poly-Si, thin film transistors and display scan drivers were made, and their characteristics are presented.     

Luminescent properties of Eu activated tungstate based novel red-emitting phosphors

A novel red-emission phosphor of Eu³⁺-doped tungstate was prepared at 950 °C by a modified solid-state reaction. Photoluminescence (PL) results showed that the phosphor can be efficiently excited by irradiation at wavelengths in the near-UV and blue regions of the spectrum. The material has potential application as the fluorescent material for ultraviolet light-emitting diodes (UV-LEDs). The crystallization and particle sizes of the phosphor have been investigated by using powder X-ray diffraction (XRD) and transmission electron microscopy (TEM).     

Crystallization of a Mechanically Activated CuTi Alloy

The atomic structure and amorphous-crystalline transition dynamics in CuTi metallic glass synthesized by high-energy ball milling have been studied. Using high-resolution transmission electron microscopy (HRTEM), it has been shown that the initial amorphous phase contains crystalline inclusions, which are up to 8 nm in size and may serve as crystallization centers. In contrast to the earlier studied amorphous CuTi alloys synthesized by melt spinning, the process of crystallization in the mechanically generated amorphous alloy begins at a lower temperature (250°C) and lasts for 20–30 s. A conclusion about the diffusion mechanism of crystallization in this material has been made.     

Optimization of salt concentration in PEG-based crystallization solutions

Although polyethylene glycol (PEG) is the most widely used precipitant in protein crystallization, the concentration of co-existing salt in the solution has not been well discussed. To determine the optimum salt concentration range, several kinds of protein were crystallized in a 30% PEG 4000 solution at various NaCl concentrations with various pH levels. It was found that, if crystallization occurred, the lowest effective salt concentration depended on the pH of the protein solution and the pI of the protein molecule; that is, higher salt concentrations were required for crystal growth if the difference between pH and pI was increasing. The linear relationship between the charge density of the protein and the ionic strength of the crystallization solution was further verified. These results suggested that the lowest effective concentration of salt in a crystallization solution can be predicted before performing a crystallization experiment. Our results can be a tip for tuning crystallization conditions by the vapor-diffusion method.     

Degradation of stone materials in the archaeological context of the Greek–Roman Theatre in Taormina (Sicily, Italy)

In the present work results on the degradation phenomena of stone materials in the Ancient Theatre of Taormina, one of the most important Greek–Roman monuments of Sicily, are reported. Artificial stone materials in different conservation conditions were investigated. Samples of salt efflorescences from brick walls and degraded setting mortars were taken from the open gallery in “summa cavea”. The chemical, physical and structural characterization was performed by means of X-Ray Photoelectron Spectroscopy (XPS), X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF), both in situ and ex situ.     

Nonisothermal Crystallization Behaviors of Flame-Retardant Copolyester/Montmorillonite Nanocomposites

In order to obtain poly(ethylene terephthalate) (PET) engineering plastics with good flame retardancy, heat resistance, and mechanical properties, a novel phosphorus-containing copolyester (PET-co-DDP)/organo-montmorillonite (OMMT 1%) nanocomposite (PET-co-DDP/OMMT) was prepared by in situ intercalating polymerization. Nonisothermal crystallization kinetics and nanoscale morphology of this composite have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). Based on the results of the nonisothermal crystallization kinetics, the flame-retardant copolyester PET-co-DDP has a lower crystallization rate than pure PET, while PET-co-DDP/OMMT nanocomposite has a higher crystallization rate than pure PET. Based on the Augis and Bennett method, the activation energies for nonisothermal crystallization of pure PET, PET-co-DDP, and PET-co-DDP/OMMT nanocomposite were evaluated as 101, 138, and 76 kJ mol^?1, respectively. All the evidence shows that PET-co-DDP strongly influences the crystallization behavior because of its irregular chain structure, while the addition of nanoscale OMMT to this copolymer can significantly enhance the crystallization rate owing to its remarkable nucleating effect. An understanding of the above crystalline behaviors will be beneficial in preparing PET engineering plastics with good overall comprehensive performance.     

Characterization of blend polymer PVA-PVP complexed with ammonium thiocyanate

Thin films of blend polymer electrolytes comprising poly(vinyl alcohol) (PVA) and poly(vinyl pyrrolidone) (PVP) complexed with ammonium thiocyanate (NH₄SCN) salt in different compositions have been prepared by solution casting technique using distilled water as solvent. The prepared films have been investigated by different experimental techniques. The complexation of these films has been studied by FTIR spectroscopy. The increase in amorphousness of the films with increase in NH₄SCN content has been confirmed by XRD analysis. The addition of ammonium thiocyanate salt to PVA-PVP polymer blend shows a shift in T_g of the blend. The effect of salt concentration and temperature on the ionic conductivity of the polymer blend films has been analyzed using AC impedance spectroscopy. The maximum conductivity of 6.85 × 10^?4 S cm^?1 at room temperature has been observed for the blend with 50 mol% PVA-50 mol% PVP complexed with 40 mol% NH₄SCN. The activation energy has been found to be minimum (0.24 eV) for this sample. Wagner’s polarization technique shows that the charge transport in these blend films is predominantly due to ions. Using the highest conductivity blend polymer electrolyte, a proton battery has been fabricated and its discharge characteristics have been studied.     

在硅片上沉积厚二氧化硅的火焰水解法研究

用火焰水解和高温烧结的方法在单晶硅基片上制备了厚SiO2和B2O2-P2O2-SiO2光波导包层材料。并用扫描电镜(SEM)和X射线粉末衍射(XRD)方法对其微观形貌和物相结构进行了观察和检测。重点对硅基片上沉积厚SiO2时的龟裂和析晶问题进行了深入研究。从扫描电镜照片可以看出．火焰水解法形成的SiO2粉末呈多孔的蜂窝状结构。这种粉末具有很高的比表面积,因而很容易烧结成玻璃。X射线衍射图谱表明．这种粉末是完全非晶态的。经过烧结以后,从扫描电镜照片可以明显看出硅基片上的SiO2薄膜出现龟裂。同时,X射线衍射测试结果表明有少量SiO2析晶。而通过在SiO2中掺入B2O3、P2O5,上述龟裂和析晶完全消失。用这种工艺制备的SiO2波导包层材料厚度达到20μm以上,表面光滑、没有龟裂,而且是完全玻璃态的,可以用于制备性能优良的各种硅基二氧化硅波导器件。     

Charge carriers dynamics in PEO + NaSCN polymer electrolytes

Sodium-ion-conducting poly(ethylene oxide) (PEO)-based solid polymer electrolyte films mixed with salt sodium thiocyanate (NaSCN) have been prepared by solution-cast method. Films were characterized in detail using optical microscopy, differential scanning calorimetry, and impedance spectroscopy. The drop in ionic conductivity with increasing salt concentration is supported by a decrease in number of charge carriers. Dielectric constant is supported by decreases in numbers of charge carriers and increase in mobility. The maximum ionic conductivity and number of charge carriers for material are found 9.86 × 10^?6 S/m and 1.21 × 10²⁰, respectively, for weight % ratio (95:05) of PEO:NaSCN polymer salt complex. The maximum mobility of material is found 2.58 × 10^?6 m²/Vs for weight % ratio (80:20) of PEO:NaSCN polymer salt complex.     

A multianalytical approach to investigate stone biodeterioration at a UNESCO world heritage site: the volcanic rock-hewn churches of Lalibela, Northern Ethiopia

A multianalytical approach combining Optical Microscopy (OM), Backscattered Variable Pressure Scanning Electron Microscopy + Energy Dispersive X-ray Spectroscopy (VP-BSEM + EDS), Powder X-ray Diffractometry (PXRD), Raman Spectroscopy, and Microbiological techniques has been applied to characterize decay products and processes occurring at the surface of two rock-hewn churches (Bete Gyorgis and Bete Amanuel) at the UNESCO’s World Heritage site of Lalibela, Northern Ethiopia. The two churches were carved into volcanic scoria deposits of basaltic composition. In their geological history, the Lalibela volcanic rocks underwent late to post-magmatic hydrothermal alteration together with partial laterization and are therefore characterized by a decay-prone highly vesicular microtexture with late stage to post-magmatic precipitation of secondary mineral phases (calcite–zeolite–smectite). The main objective of the study was to gain a better insight into the weathering products and mechanisms affecting the surface of the stone monuments and to assess the relative contribution of natural “geological” weathering processes versus biological/salt attack in stone decay at this unique heritage site. Results indicate that while the main cause of bulk rock deterioration and structural failure could be related to the stone inherited “geological” features, biological attack by micro- (bacteria) and/or macro- (lichens) organisms is currently responsible for severe stone surface physical and chemical weathering leading to significant weakening of the stone texture and to material loss at the surface of the churches walls. A prompt and careful removal of the biological patinas with the correct biocidal treatment is therefore recommended.     

非晶态Li+导体分相和晶化过程中的相界效应

非晶态Li⁺导体B₂O₃-0.7Li₂O-0.7LiCl-0.1Al₂O₃在等温处理过程中,其电导率先随时间升高,出现峰值后下降,随后出现两个平台。这是由于材料的分相和晶化所致。本文据相界效应观点,认为不同相之间界面附近有一高电导率层,它对电导率的贡献补偿和超过了由于分相和晶化的体效应所引起的电导率下降。由此,对这种材料的电导率随时间变化曲线给出了解释。 关键词：     

Effect on ion dissociation in MWCNT-based polymer nanocomposite

Polymer nanocomposite has been proven to improve the property of polymer salt complex. Organo-modified clay and inorganic oxides are the most commonly used filler for polymer nanocomposite (PNC). However, single wall carbon nanotube (SWCNT)/multiwall carbon nanotube (MWCNT) are becoming popular filler for PNC for their high surface area and high mechanical stability. In this work, a series of PNC sample has been prepared by using polyethylene oxide (PEO)-polydimethylsiloxane (PDMS) blend as polymer matrix, an optimized salt stoichiometry of Ö/Li ~15, and surface-modified MWCNT as filler. The effect of ion-polymer and ion-MWCNT interaction in the polymer nanocomposite has been investigated by using XRD, SEM, FTIR, and electrical study. X-ray diffraction pattern confirms the dispersion of MWCNT inside the polymer chain and modifies the structural parameter of the polymer matrix. FTIR spectra indicate inclusion of MWCNT inside the polymer salt complex which changes the ion dissociation/association in the polymer host matrix. Further, the changes in structural, thermal, and electrical property of the polymer salt complex system have been studied by using SEM, DSC, and impedance analysis. Dc conductivity study shows that optimized PNC sample has conductivity of 8.04 × 10⁻⁵ S cm⁻¹. This is almost two order enhancement from pure polymer salt system (10⁻⁶ S cm⁻¹).

     

Ultrasound-assisted depolymerization of kappa-carrageenan and characterization of degradation product

Degradation of polysaccharides to afford low-molecular-weight oligosaccharides have been shown to produce new bioactivities that are not present in the starting material. The simplicity of ultrasonic treatment in the degradation of a polysaccharide, such as κ-carrageenan, offers practical advantage in producing degraded products with lower molecular weight that may have new interesting potential activities. This study embarked on investigating the effects in molecular weights and structural changes of κ-carrageenan under varying ultrasonic conditions. Molecular weight (MW) monitoring of ultrasonically-treated κ-carrageenan at various conditions were done by gel permeation chromatography. The product formed using the optimized condition was characterized using FTIR and NMR. The decrease in MW has been shown to be dependent on low concentration (5.0 mg mL⁻¹), high amplitude (85%), and long treatment time (180 mins) to afford a degraded κ-carrageenan with average molecular weight (AMW) of 41,864 Da, which is a 96.33% reduction from the raw sample with initial AMW of 1,139,927 Da. Structural analysis reveals that most of the peaks of the raw κ-carrageenan was retained with minor change. 1D and 2D NMR analyses showed that the sonic process afforded a product where the sulfate group at the G4S-4 position was cleaved forming a methylene in the G4S ring. The results would be useful in the structure–activity relationship of κ-carrageenan oligosaccharides and in understanding the effect in the various potential applications of degraded κ-carrageenan.     

影响聚合物离子导体电导率的一些因素

本文研究了极性基团浓度、碱金属盐阳离子和阴离子尺寸对均聚物聚环氧氯丙烷(PECH)和共聚物聚环氧氯丙烷-聚环氧乙烷(PECH-PEO)电导率的影响。对锂盐络合物,极性基团浓度增高,电导率降低。钠盐络合物则正好相反,极性基团浓度越高,电导率越高。碱金属盐阳离子和阴离子尺寸对聚合物离子导体电导率都有明显影响。所研究的聚环氧氯丙烷与三种碱金属盐络合物PECH-MI(M=Li,Na,K)的电导率数据表明,钠盐络合物的电导率最高,锂盐和钾盐络合物的电导率较低。碱金属盐阴离子越大,PECH络合物的电导率越低。此外,还 关键词：     

On the Elastic Modulus of Powders

For the design of silos and similar equipment for storage, handling and processing of particulate materials, a thorough understanding of the mechanical behaviour of powders is of great importance. Whereas strength properties of powders have been investigated by many workers, the elastic behaviour at small deformations has been much less in focus. In that respect, a simple preliminary theory of uniaxial elasticity has been derived for particles, based on a simple system of spherical and monosized particles of a homogenous and elastically isotropic material. The equation σ = E_p?_el² gives the relationship between stress, elastic modulus and elastic deformation for the unloading of a given powder at a specific consolidation stress/ compression level. Comparisons with experimental results of real powders in a uniaxial tester show surprisingly good agreement in many cases. The equation seems to describe the elasticity of powders fairly well, although it is only a preliminary derivation based on simple considerations.