مواد دارای تغییر شکل در اثر الکتریسیته

Electroheological Materials

مواد دارای تغییر شکل در اثر الکتریسیته (Electrorheological)

ABSTRACT

The electroheological effect refers to the abrupt change in viscosity in certain colloidal sols when subjected to an electric field . The phenomenon of electroheology (ER) was first reported by w . M. Winslow in 1947 and therefor is also known as the Winslow effect . An ER fluid changes is flow characteristics ( due to the viscosity changes ) in the presence of a high voltage low current electric field and if the strength of the electric field is sufficient the fluid behaves much like a solid . The adaptive response of an ER fluid ( which takes only milliseconds )is in the from of progressive gelling which is proportional to the field strength . In the absence of electric field the fluid flows freely like water .

مواد چیرال الکترومغناطیس

Electromagnetic chiral Material

مواد چیرال الکترومغناطیس

ABSTRACT

A special class of electromagnetic (EM) material referred to as chiral materials are emerging in engineering application . A chiral medium is one whose electric and magnetic fields are cross-coupled . The characteristic aspect of such materials is the intrinsic handedness (right or left ) present in their physical structure . Optically active natural  materials exhibit mirror-asymmetric molecular structure(s) and have been originally known as chiral materials ,Natural chiral structurs include a diverse array of sugars amino acids DNA and certain mollusks as well as winding vegetation while the man-made versions encompass such objects as a helix a Mobius strip or an irregular tetrahedron.

مواد سرامیکی و پلیمری دارای مواد رسانا

Conductor-Loaded Polymeric and ceramic Material

مواد سرامیکی و پلیمری دارای مواد رسانا (دارای ذرات تقویت کننده رسانا)

ABSTRACT

Conductor-filled polymers and ceramic are specific subsets of the conductor-Loaded dielectrics . The primary reason for adding conducting particles in polymers plastics or ceramics is to enhance the electrical conductance of the medium . In general polymers and ceramics when loaded with conductors become very good conductors of electricity and are useful in a wide range of electromagnetic applications. However inclusion of a metallic constituent in a polymer matrix may affect the low density and high strength or impact resistance properties of the plastics or the ceramics .

مواد پلیمری رسانا

Conducting Polymeric Materials

مواد پلیمری رسانا

ABSTRACT

A highly conjugated organic polymer ( having unsaturated bonds spaced along the polymer chain intermittently ) such as polyacetylene has been known to exhibit high electronic conductivity when oxidized by suitable reagents . Likewise a number of conjugated hydrocarbon and aromatic heterocyclic polymers ( such as poly-p-phenylene،  poly-p- phenylene-vinylene  ،  poly-p-phenylene sulfide ، polypyrrole and polythiophene as well as radical salts like tetracyanoquinodimethane ( TCQN) complexes have also been identified as conducting Polymers organometallics.In terms of technological applications of these materials they have been deployed as rectifiers sensors solar energy conversion elements fuel cell components switching devices photoresist elements chemoselective electrodes electrophotographic devices and durable synthetic materials replacing metals. Speculative applications on possible high temperature superconductive applications of these materials also prevail .

 

مواد محافظ الکترومغناطیسی

Electromagnetic Shieldig Materials

مواد محافظ الکترومغناطیسی

ABSTRACT

Electromagnetic Shieldig Materials are the structural constituents of the so-called electromagnetic Shields used for the purpose of confining electromagnetic energy within the bounds of a specific region and/or to prevent the proliferation of such energy into a designated locale .   Electromagnetic energy in general manifests as :

• Energy associated with static and/or time-varying electric force field
• Energy associated with static and/or time-varying magnetic force field
• Radiated electromagnetic energy

Depending on the Shieldig requirements vis-à-vis the interference due to any of the above forms of electromagnetic (EM) energy a variety of materials have been developed avd deployed in the fabrication of Shieldig partitions or enclosures which confine the EM energy within a specified region there by preventing its invasion elsewhere .

نانومرکب ­های سرامیکی برای چاپگرهای چهاررنگه جوهرافشان

Nano-sized Ceramic Inks for Drop-on-Demand Ink-Jet Printing in Quadrichromy

نانومرکب ­های سرامیکی برای چاپگرهای چهاررنگه جوهرافشان drop-on-demand (با فناوری چکانش روی موضع موردنظر)

ABSTRACT

Nano –sized ceramic inks suitable for ink –jet printing have been developed for the four-colours CMYK ( cyan ، magentah ، yellow ، black ) process . Nano- inks of different pigment composition ( Co _1-x O ، Au⁰ ،TiO₂ ، Sb ،Cr ،CoFe₂O₄ )  have been with various solid loading and their chemico-physical  properties ( particle size ، viscosity ، surface tension ، potential ) were tailored for the ink-jet application. The pigment particle size is in the 20-80 nm rang . All these nano-suspensions are stable for long time (i .e  several months ) due to either electrostatic ( high – potential values ) or steric stabilization mechanisms.

سنتز پودر ZrB2بوسیله احیا حرارتی بور

ZrB2 Powders Synthesis by Borothermal Reduction

سنتز پودر ZrB₂بوسیله احیا حرارتی بور

ABSTRACT

IHigh-purity zirconium diboride (ZrB2) powders with submicrometer particle size were synthesized by borothermal reduction of nanometric ZrO2 powders in vacuum. The reaction process was experimentally and thermodynamically assessed. B2O3 was identified as a possible intermediate reaction product. ZrO2 completely converted to ZrB2 when thermally treated at 10001C for 2 h in a vacuum, but the removal of residual boron-related species required a temperature above ۱۵۰۰۱C. ZrB2 powders obtained at 10001–۱۲۰۰۱C showed a faceted morphology, whereas those prepared above 15001C had a nearly spherical morphology. The particle size that was calculated from the measured surface area increased with the increasing synthesis temperature from 0.15 lm at 10001C to ۰٫۶۶ lm at 16501C. The oxygen content of the ZrB2 powders synthesized at 16501C was as low as 0.43 wt%.

 

سرامیک­ های فوق ­دمابالا جهت کاربرد در محیط­ های سرسخت

Ultra-High Temperature Ceramic Materials for
Extreme Environment Applications

سرامیک­ های فوق ­دمابالا جهت کاربرد در محیط­ های سرسخت

ABSTRACT

For the purposes of this paper, we will simply define UHTC materials by their usefulness in a real structural (load-bearing) application where the very high temperatures are generated rapidly by burning fuels or friction with the atmosphere (not steady state). This will quickly eliminate most of the materials mentioned above. While oxides are reasonable to consider for use in oxidizing environments, poor thermal shock resistance due to high thermal expansion and low thermal conductivity eliminates them from further discussion. The silicon based refractory compounds (SiC, Si3N4, MoSi2, etc.) possess excellent oxidation resistance up to 1700°C due to the formation of a layer of SiO2 glass that inhibits oxygen diffusion to the parent material.4 This is the primary reason for the popularity of these materials for a wide variety of applications. However, active oxidation (the direct formation ofSiO(g) instead of a protective SiO2 layer) can occur at very high temperatures (> 1350°C, depending on PO2) and reduced system pressures. In addition, decomposition of already-formed SiO2, or the interface reaction between SiC and SiO2 results in SiO(g) formation at high temperatures and reduced pressure environments. Other materials, such as TiB2, TiC, NbB2, NbC, while having high melting temperatures, form oxides with low melting points (TiO2 – Tm = 1840°C and Nb2O5 – Tm = 1485°C). Graphite has the highest melting temperature of any material known, but starts to burn thet 800°C. While it is a most widely used material in high-temperature applications, it must be protected by coatings for long-term use.

مینرال­ های گروه سیلیمانیت؛ سیلیمانیت، کیانیت و آندالوزیت

The Sillimanite Minerals: Andalusite, Kyanite, and Sillimanite

 مینرال­ های گروه سیلیمانیت؛

سیلیمانیت، کیانیت و آندالوزیت

ABSTRACT

The chemistry and the mineralogy of the three Al2O3.SiO2 sillimanite minerals (anadlusite, kyanite, and sillimanite) are described. Their P–T diagram is discussed. The structural differences among the three are reviewed, emphasizing the coordination of the Al3+ cations that link the double octahedral chains within the structures. Their decompositions to produce mullite and silica are described and contrasted. The effect of nanomilling on those decompositions is discussed. Finally, the locations of commercial deposits and the industrial applications are addressed.The sillimanite minerals are the three anhydrous aluminosilicates: andalusite, kyanite, and sillimanite [1,2]. Kyanite is also referred to as cyanita, cyanite, and disthene. Because all three have the same 1:1 molar ratio of alumina (Al2O3) to silica (SiO2), they are often written simply as Al2O3·SiO2 or Al2SiO5. Their ideal composition is 62.92 wt% alumina and 37.08 wt% silica. However, in natural states involving significant impurities, the alumina content is usually less than 60 wt%. There are reports of higher alumina content deposits associated with the presence of higher alumina content minerals. That such a mineral group exists is not surprising, for the three most common elements in the Earth’s crust are O, Si, and Al.

 

زیرکنیا

Zirconia

زیرکنیا

ABSTRACT

Zirconia is a very important industrial ceramic for structural applications because of its high toughness, which has proven to be superior to other ceramics. In addition, it has applications making use of its high ionic conductivity. The thermodynamically stable, room temperature form of zirconia is baddeleyite. However, this mineral is not used for the great majority of industrial applications of zirconia. The intermediate-temperature phase of zirconia, which has a tetragonal structure, can be stabilized at room temperature by the addition of modest amounts (below ∼۸ mol%) of dopants such as Y3+ and Ca2+. This doped zirconia has mechanical toughness values as high as 17 MPa • m1/2. On the other hand, the high-temperature phase of zirconia, which has a cubic structure, can be stabilized at room temperature by the addition of significant amounts (above ∼۸ mol%) of dopants. This form of zirconia has one of the highest ionic conductivity values associated with ceramics, allowing the use of the material in oxygen sensors and solid-oxide fuel cells. Research on this material actively continues and many improvements can be expected in the years to come.