میکروسیلیس ماده اولیه دیرگداز

MICROSILICA A versatile Refractory Raw Material

میکروسیلیس ماده اولیه دیرگداز؛ کاملاً انعطافپذیر و پرکاربرد

ABSTRACT

An overview is given on the applications of microsilica in refractories starting more than 40 years ago . The role of microsilica in binder systems for briks and castables are discussed including reaction mechanisms at various temperatures . Critical parameters in these reactions are pointed out . Examples of application in castables are presented.

خواص یک نانوکامپوزیت شفاف در برابر مادون قرمز

Properties of an Infrared-Transparent MgO:Y2O3 Nanocomposite

خواص یک نانوکامپوزیت شفاف در برابر مادون قرمز از نوع MgO:Y₂O₃

ABSTRACT

A 50:50 vol% MgO–Y2O3 nanocomposite with ~150 nm grain size was prepared in an attempt to make 3–5 lm infraredtransmitting windows with increased durability and thermal shock resistance. Flexure strength of the composite at 21°C is 679 MPa for 0.88 cm2 under load. Hardness is consistent with that of the constituents with similar grain size. For 3-mm-thick material at 4.85 lm, the total scatter loss is 1.5%, forward scatter is 0.2%, and absorptance is 1.8%. Optical scatter below 2 lm is 100%. Variable intensity OH absorption (~6% absorptance) is observed near 3 lm. The refractive index is ~0.4% below the volume-fraction-weighted average of those of the constituents. Thermal expansion is equal to the volumefraction- weighted average of expansion of the constituents. Specific heat capacity is equal to the mass-fraction-weighted average of heat capacities of the constituents. Thermal conductivity lies between those of the constituents up to 1200 K. Elastic constants lie between those of the constituents. The Hasselman mild thermal shock resistance parameter for the composite is twice as great as that of common 3–5 lm window materials, buthalf as great as that of c-plane sapphire.

مدل سازی تفرق در محیط های کامپوزیتی

Modeling Scatter in Composite Media

مدل سازی تفرق در محیط های کامپوزیتی 

ABSTRACT

A theoretical model of optical scattering in materials consisting of densely packed spherical particles is developed that can be used to predict its optical properties given its physical characteristics. The inputs to this model are the waveband of interest, the complex refractive indices and particle size distribution of the materials that comprise the media (including any contaminants), the density and sizes of any contaminants in the media, and the dimensions of the media slab. The outputs of this model are the specular transmittance and emissivity vs. wavelength of the media, and it’s Bidirectional Scattering Distribution Function (BSDF) vs. scatter angle vs. wavelength. The results of this model are compared to measured transmittance and BSDF data from optical ceramics comprised of densified nanopowders (nanocomposite optical ceramics).

جایگزین های بافت نرم Soft Tissue Replacements

Soft Tissue Replacements

جایگزین های بافت نرم 

ABSTRACT

Blood comes in contact with foreign materials for a short term in extracorporeal devices such as dialyzers , blood oxygenators , ventricular assist devices, and catheters . Long-term vascular implants include heart valve prostheses, vascular grafts , and cardiac pacemakers , among others. In this section, we will be concerned with development of biomaterials for long-term implants, specifically for heart valve prostheses, total artificial heart ( TAH ), and vascular grafts. The primary requirements for biomaterials for long-term implants are biocompatibility, nontoxicity, and durability. Furthermore, the material should be nonirritating to the tissue, resistant to platelet and thrombus deposition, nondegradable in the physiological environment, and neither absorb blood constituents nor release foreign substances into the blood stream [Shim and Lenker, 1988]. In addition, design considerations include that the implant should mimic the function of the organ that it replaces without interfering with the surrounding anatomical structures and must be of suitable size and weight. The biomaterials chosen must be easily available, inexpensive, easily machinable, and sterilizable and have a long storage life.

قابلیت تزریق شدن خمیرهای کلسیم فسفات

Injectability of calcium phosphate pastes

قابلیت تزریق شدن خمیرهای کلسیم فسفات 

ABSTRACT

A theoretical model was developed to assess ways to improve the injectability of calcium phosphate pastes. The theoretical results were then compared to experimental data obtained on calcium phosphate slips. The theoretical approach predicted that the injectability of a cement paste could be improved by an increase of the liquid-to-powder ratio, and a decrease of the particle size and the plastic limit (PL) of the powder. The theoretical results were confirmed by experimental data. Interestingly, an increase of the viscosity of the mixing liquid with small additions of xanthan had a positive effect on the paste injectability. This effect could be due to a change of the PL of the powder or to the lubricating effect of the polymer.

سنتز، شناسایی و خواص نوری نانوذرات اکسید روی

Synthesis, characterization and optical properties of zinc oxide nanoparticles

سنتز، شناسایی و خواص نوری نانوذرات اکسید روی

ABSTRACT

Zinc oxide nanoparticles were synthesized using a simple precipitation method with zinc sulfate and sodium hydroxide as starting materials. The synthesized sample was calcined at different temperatures for 2 h. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and proton-induced X-ray emission (PIXE) analysis. SEM images show various morphological changes of ZnO obtained by the above method. The average crystallite sizes of the samples were calculated from the full width at half maximum of XRD peaks by using Debye-Scherrer's formula and were found to be in the nanorange. EDS shows that the above route produced highly pure ZnO nanostructures. PIXE technique was used for trace elemental analysis of ZnO. The optical band gaps of various ZnO powders were calculated from UV-visible diffuse reflectance spectroscopic studies.

خواص ساختاری منیزیم و آلومینیوم جانشین شده در فریت لیتیم

Structural properties of magnesium and aluminium co-substituted lithium ferrite

خواص ساختاری منیزیم و آلومینیوم جانشین شده در فریت لیتیم

 

ABSTRACT

The structural properties of Mg2 + and Al3 + co-substituted Li0.5Fe2.5O4 are studied by synthesizing the spinel solid solution series MgxAl2xLi0.5(1
x)Fe2.5(1
x)O4. Polycrystalline samples of this series with x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5 have been prepared by double-sintering ceramic method. The structural details like: lattice constant and distribution of cations in the tetrahedral and octahedral interstitial voids have been deduced through X-ray diffraction (XRD) data analysis. The x dependence of bond length, oxygen positional parameter, site ionic radii, bulk density, porosity and shrinkages have also been determined.

راهنمای عملیات حرارتی آلیاژ های منیزیم

Heat Treater's Guide: Mg Alloys
راهنمای عملیات حرارتی آلیاژ های منیزیم

آلیاژ منیزیم ، آلومینیوم، روی

آلیاژ منیزیم، زیر کونیوم

آلیاژ منیزیم، کروم

 AZ91C ،AZ92A،EQ21A،EZ33A،HK31A،HZ32A،AZ91A،AZ91B،AZ91D،AZ91E،AZ81A

ABSTRACT

The principles which govern heat treatment of metals and alloys are applicable to both ferrous and nonferrous alloys. However, in practice there are sufficient differences to make it convenient to emphasize as separate topics the peculiarities of the alloys of each class in their response to heat treatment. For example, in nonferrous alloys, eutectoid transformations, which play such a prominent role in steels, are seldom encountered, so there is less concern with principles associated with time-temperaturetransformation diagrams and with martensite formation. On the other hand, the principles associated with chemical homogenization of cast structures are applicable to many alloys in both classes. Diffusion Process The diffusion process is involved in nearly all heat treatments for nonferrous alloys. Common treatments include:

• Annealing after cold working
• Homogenization of castings
• Precipitation hardening treatments
• Development of two-phase structures

پایداری ساختاری مواد نانوکریستالین – رشد دانه

Stability of structural nanocrystalline materials grain growth

پایداری ساختاری مواد نانوکریستالین – رشد دانه

ABSTRACT

Knowledge of the thermal stability of nanocrystalline materials is important for both tech­  nological and scientific reasons. From a technological point of view, the thermal stabil­ ity  is important for consolidation of nanocrystalline particulates without coarsening the  microstructure.That is, many methods, as described in Chapter 2, for synthesis ofnanocrys­ talline  materials result in particulate products which must be consolidated into bulk form. Since most  consolidation processes involve both heat and pressure, the thermal stability of the nanoscale  microstructure is always at risk. The goal of particulate consolidation is to attain essentially  100% theoretical density and good particulate bonding while preventing or minimizing grain growth  of the nanocrystalline grains. Understanding the scientific nature of stability, grain growth of nanocrystalline  microstructures is a criterion for allowing strategies for minimizing grain growth to be devel­  oped. A basic scientific question with regard to nanocrystalline materials is whether their  behavior involves ''new physics" or is simply the expected grain-size-dependent behavior  extrapolated to nanocrystalline grain sizes. Thermal stability is an important phenomenon to be  addressed in this regard. The thermal stability in a broader sense involves not only the  stability of the grain structure, that is the microstructure, but also the stability of the  structure of the grain boundaries in nanocrystalline materials. A number of investigations on the  thermal stability of nanocrystalline materials have been conducted. Grain growth in  nanocrystalline materials has been reviewed by Suryanarayana (1995), Weissmuller (1996), and  Malow and Koch (1996a,b). In this chapter we will discuss the thermal sta­ bility, grain growth  of nanocrystalline materials with reference to experimental methods for measuring grain growth,  grain-growth theories for conventional grain-size materials which may be applicable, grain growth  (secondary recrystallization) at ambient tempera­ tures in nanocrystalline metals, strategies for  inhibition of grain growth in nanocrystalline materials, and examples of experimental studies of  grain-growth kinetics in nanocrystalline materials.

اثر عملیات حرارتی در جوشکاری انفجاری فولاد زنگ نزن/مس

Effect of heat treatment on bonding interface in explosive welded
copper/stainless steel

اثر عملیات حرارتی روی فصل مشترک اتصال در جوشکاری انفجاری فولاد زنگ نزن/مس

ABSTRACT

In this investigation, explosive welding and heat treatment processes provided an effective method for manufacturing high-strength and high-ductility copper/ austenitic stainless steel couple. In order to improve diffusion in the interface of copper/stainless steel, first the tensile samples were provided from the welded part, then they were subjected to annealing at 300 C (below recrystallization temperature) for 8–32 h with 8 h intervals and then samples were cooled in the furnace. Optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were utilized to evaluate the possibility of diffusion in the joints. Moreover, in order to measure the hardness of the samples, microhardness test was performed. Microstructural evaluations showed that the stainless steel 304L had a wavy interface. Furthermore, the post heat treatment process resulted in great enhancement of diffusion. Microhardness measurements showed that the hardness of the sample near to the interface is greatly higher than other parts; this is due to plastic deformation and work hardening of copper and stainless steel 304L in these regions. The interface of samples with and without the post heat treatment was exhibited ductile and brittle fracture, respectively.