سنتز پودرهای نانوکامپوزیت نقره-اکسید قلع از روش هم رسوبی شیمیایی

Synthesis  of  silver  tin  oxide  nanocomposite  powders

 via  chemical coprecipitation method

سنتز پودرهای نانوکامپوزیت نقره-اکسید قلع از روش هم رسوبی شیمیایی

ABSTRACT

Introduction : Silver-metal  oxide  composite  contact  materials  have  a variety  of  applications  in  low  voltage  switches  such  as relays,  contactors  and  circuit  breakers . Until  three decades  ago,  Ag-CdO  composite  was  the  preferred material  for  these  usages  due  to  excellent  functional and  technological  properties.  However,  because  of  toxic nature  of  Cd,  especially  when  it  is  evaporated,  consider- able  efforts  have  been  made  to  replace  it  with  environ-ment-friendly  substances  such  as  Ag-SnO2. Ag-SnO2 materials,  in  addition,  have  higher  hardness,  contact resistance  and  temperature  rise  than  Ag-CdO  substances. Besides  their  arc  erosion  and  anti-welding  properties  are excellent.

 

اهمیت بیو‌فیلم‌های میکروبی در صنایع غذایی: باز‌نگری

Significance of microbial biofilms in food industry: a review

اهمیت بیو‌فیلم‌های میکروبی در صنایع غذایی: باز‌نگری

ABSTRACT

In nature and food systems, microorganisms get attracted to solid surfaces conditioned with nutrients, that are sufficient for their viability and growth. These microorganisms initially are deposited on the surfaces and later get attached, grow and actively multiply to form a colony of cells. In this regard, the formation of organic polymers are essential which helps in the proper colonization of microorganisms (Allison and Sutherland, 1987). These mass of cells further become large enough to entrap organic and inorganic debris, nutrients and other microorganisms leading to the formation of a microbial biofilm. The term biofilm refers to the biologically active matrix of cells and extracellular substances in association with a solid surface (Bakke et al., 1984). However, according to Costerton et al. (1987) a biofilm is a functional consortium of microorganisms attached to a surface and is embedded in the extracellular polymeric substances (EPS) produced by the micro- organisms.

 

روند پیشرفت نظریه انجماد غیر تعادلی

Progress of Nonequilibrium Solidification Theory

روند پیشرفت نظریه انجماد غیر تعادلی

ABSTRACT

This paper summarized the theory related to nucleation, interface kinetics, micromorphology evolution and microscopic growth during nonequilibrium alloy solidification. Methods for quantitative analysis of nucleation rate, the criterion of marginal stability, nonequilibrium partition coefficient, as well as the relationship between growth rate with undercooling and dendrite tip radius are presented. Some limitations and future developments of nonequilibrium theory are pointed out.

 

تولید کنتاکت‌های الکتریکی نقره-اکسید قلع Preparation of silver-tin oxide electrical contacts

Novel method for preparation of silver-tin oxide electrical contacts

روش جدیدی برای تولید کنتاکت‌های الکتریکی نقره-اکسید قلع

ABSTRACT

 Introduction : MOST of  the  electrical  contact materials  in  use  today  contain cadmium oxide particles that are volatile and toxic. Because of the  fact  that  vaporization of cadmium  oxide  during  switching could be detrimental  to workers' health,  its use in contact mate- rials  has  been  banned  by  health  organizations  in  some  other  countries. To replace the cadmium oxide, many foreign compa-  nies have utilized tin oxide in silver electrical contacts. 

 

آندایزینگ و عملیات حرارتی تیتانیوم متخلخل

Effects of anodizing parameters and heat treatment on 

nanotopographical features, bioactivity, and cell culture 

response of additively manufactured porous titanium 

اثر پارامترهای آندایزینگ و عملیات حرارتی بر نانو عوارض سطحی، زیست‌فعالی

و پاسخ کشت سلول در تیتانیوم متخلخل ساخته‌شده به روش افزایشی

ABSTRACT

Anodizing could be used for bio-functionalization of  the surfaces of  titanium alloys. In this study, we use anodizing for creating nanotubes on the surface of porous titanium alloy bone substitutes manufactured using selective laser melting. Different sets of anodizing parameters (voltage: 10 or 20 V anodizing time: 30 min to 3 h) are used for anodizing porous titanium  structures that were later heat treated at 500o  C. The nanotopographical features are examined  using electron microscopy while the bioactivity of anodized surfaces is measured using  immersion tests in the simulated body fluid (SBF).

 

سنتز دماپایین LaxBa1-x)B6) با تابع کار ترمویونی کوچک

Low temperature synthesis of low thermionic work function

LaxBa1x)B6)

سنتز دماپایین LaxBa1-x)B6) با تابع کار ترمویونی کوچک

ABSTRACT

This study presents investigations of the microstructure, morphology and emission properties of the promising thermionic material (LaxBa1−x)B6. The material was synthesised by solid-state reaction without post-synthesis purifications. Powder X-ray diffraction revealed that samples prepared at a temperature ⩾1500 °C had formed a significant proportion of solid solution (above 54 mass%). Subsequent sintering at 1950 °C caused the formation of a mixture of three solid solutions with the dominant phase being (La0.31Ba0.69)B6 ∼85% (by mass). The Richardson work function and emission constant for this boride mixture were found to be 1.03 eV and 8.44 × 10−6 A cm K−2 respectively.

 

طیف سنجی نشر اتمی با پلاسمای جفت شدۀ القایی

Inductively coupled plasma atomic emission spectroscopy

طیف سنجی نشر اتمی با پلاسمای جفت شدۀ القایی

ABSTRACT

Inductively coupled plasma atomic emission spectroscopy (ICP-AES) is an analytical technique for elemental determinations in the concentration range of major to trace based on the principles of atomic spectroscopy. In theory, the technique applies to all elements except argon, and samples may be introduced as liquids, gases, or solids. In practice, favorable analytical results are obtained for approximately 70 elements, with detection limits usually attainable at the parts per billion level, and most samples are introduced in liquid form as aqueous solutions. The technique has found widespread application in the metallurgical, geological, environmental, agricultural, industrial, and biological fields and is an important technique in the modem analytical laboratory.

 

تولید کامپوزیت‌های B4C-TiB2 با پرس گرم

Microstructure and mechanical properties of B4C–TiB2

composites prepared by reaction hot pressing using Ti3SiC2

ریزساختار و خواص مکانیکی کامپوزیت‌های B4C-TiB2 تولیدشده توسط پرس گرم

با استفاده از Ti3SiC2 به عنوان افزودنی

ABSTRACT

B4C–TiB2 composites were fabricated via reaction hot pressing at 2100 °C under a pressure of 25 MPa, using B4C and Ti3SiC2 powders as raw materials. The phase transformations, microstructure and mechanical properties were investigated by XRD, TG–DTA, SEM, TEM and EDS. It is found that the SiC and TiB2 particles are homogenously dispersed in the B4C–TiB2 composites, where nano-sized TiB2 particles are mainly located within the B4C matrix grains, while the large-sized TiB2 particles at the matrix grains boundaries. Due to the pinning effect of SiC and TiB2 particles on B4C grain growth, the grain size of the composite is significantly reduced, leading to a great improvement of the mechanical properties. B4C–TiB2 composite prepared from B4C-10 wt% Ti3SiC2 starting powder shows high flexural strength, fracture toughness and micro-hardness of 592 MPa, 7.01 MPa m1/2 and 3163 kg/mm2, respectively. Crack deflection and crack bridging are most likely the potential toughening mechanisms in the composites. Furthermore, according to the XRD and TG–DTA analysis, the possible reaction mechanisms leading to the in-situ formation of TiB2 were proposed.

پوشش‎های سخت با روانسازی تطبیقی دما بالا و مدیریت حرارتی محل تماس

Hard coatings with high temperature adaptive lubrication

and contact thermal management

پوشش‎های سخت با روانسازی تطبیقی دما بالا و مدیریت حرارتی محل تماس

ABSTRACT

Progress in the design and exploration of hard coatings with high temperature adaptive behavior in tribological contacts is reviewed. When coupled with most recent surface engineering strategies for high temperature contact thermal management, this progress opens a huge opportunity for adaptive coating applications on machine parts, where oils and coolants are commonly used. The adaptive mechanisms discussed here include metal diffusion and formation of lubricant phases at worn surfaces, thermally- and mechanically-induced phase transitions in hexagonal solids, contact surface tribo-chemical evolutions to form phases with low melting point, formation of easy to shear solid oxides, and others. All of these adaptive mechanisms are combined in nanocomposite coatings with synergistic self-adaptation of surface structure and chemistry to lubricate from ambient temperatures to 1000 °C and provide surface chemical and structural reversibility during temperature cycling to maintain low friction coefficients. The review also highlights emerging surface adaptive concepts, where advances with ab initio modeling of intrinsically layered solids point to new compositions for thermally stable, easy to shear ceramic coatings, load- and temperature-adaptive surfaces with arrays of compliant carbon and boron nitride nanotubes as well as low friction two-dimensional structures. Approaches for self-regulation of coating thermal conductivity, heat flow, and thermal spike mitigations are discussed in the context of surface structure evolution and phase transitions. Future progress is linked to the development of in situ exploration techniques, capable of identifying adaptive surface chemistry and structural evolutions in broad temperature regimes. When combined with predictive modeling, such approaches drastically accelerate adaptive coating developments. The review identifies opportunities, strategies, and challenges for designs and applications of hard coatings with high temperature adaptive lubrication and contact thermal management.

 

رفتار قالب پرکنندگی مذاب های تیتانیوم Mold-filling behavior of titanium melts in vertically rotating molds

Effect of centrifugal and Coriolis forces on

the mold-filling behavior of titanium melts in vertically rotating molds

اثرات نیروهای گریز از مرکز و نیروهای کوریولیس بر رفتار قالب پرکنندگی مذاب های تیتانیوم

در قالب هایی که به صورت عمودی می چرخند

ABSTRACT

The vertical centrifugal-casting technique is widely used in the manufacture of various irregularly-shaped castings of advanced structural alloys with thin walls, complex shapes and/or large sizes. These castings are used in the increasing applications in aero-space/aviation industries, human teeth/bone repairs with near-net shaped components, etc. In a vertically rotating casting system, the mold-filling processes of alloy melts, coupled with solidification-heat transfer, may be much more complicated, because they are driven simultaneously by gravity, centrifugal and Coriolis forces. In the present work, an N-S/VOF-equations-based model, solved using a SOLA-VOF algorithm, under a rotating coordinate system was applied to numerically investigate the impacts of centrifugal and Coriolis forces on metallic melt mold-filling processes in different vertical centrifugal-casting configurations with different mold-rotation rates using an authors' computer-codes system. The computational results show that the Coriolis force may cause remarkable variations in the flow patterns in the casting-part-cavities of a large horizontal-section area and directly connected to the sprue via a short ingate in a vertical centrifugal-casting process. A "turn-back" mold-filling technique, which only takes advantage of the centrifugal force in a transient rotating melt system, has been confirmed to be a rational centrifugal-casting process in order to achieve smooth and layer-by-layer casting-cavities-filling control. The simulated mold-filling processes of Ti-6AI-4V alloy melt, in a vertical centrifugal-casting system with horizontally-connected plate-casting cavities, show reasonable agreement with experimental results from the literature.