12,515 research outputs found
Silicon carbide equipments for process intensification of silicon reactions.
Bluestar Silicones, one of the worldwide leaders in silicones chemistry, proposes a
R&D project, aiming to design new equipment for the transposition of batch to continuous
processes. The safety and environmental issues linked to this type of chemicals, and the
productivity targets as well require innovative technologies characterized by a fair corrosion
resistance and high heat and mass transfer performances. A preliminary prototype of heat
exchanger reactor made of silicon carbide plates has been developed by the LGC in
collaboration with a SME specialist of SiC, Boostec. It has allowed the pilot feasibility with
some reactions of industrial interest for a Bluestar Silicones to be highlighted. Now, it is
necessary to pursue this effort and beyond the feasibility step to go on up to the design of an
industrial reactor. This project corresponds to a programme of innovative process development
in order to design cleaner, safer and less consuming devices
Development of material specifications and qualifications of polymeric materials for the JPL Spacecraft Materials Guidebook Monthly technical progress report no. 11, 10 Apr. - 10 May 1965
Outgassing characteristics of liquid and paste silicones and effects of postcuring procedure
Molecular Devices. Chiral, Bichromophoric Silicones
The interaction of chromophores is proposed as a basis for the construction of devices with high complexity. Silicones are promising elements of structure to control the function of such devices
Brief overview on bio-based adhesives and sealants
Adhesives and sealants (AS) are materials with excellent properties, versatility, and simple curing mechanisms, being widely used in different areas ranging from the construction to the medical sectors. Due to the fast-growing demand for petroleum-based products and the consequent negative environmental impact, there is an increasing need to develop novel and more sustainable sources to obtain raw materials (monomers). This reality is particularly relevant for AS industries, which are generally dependent on non-sustainable fossil raw materials. In this respect, biopolymers, such as cellulose, starch, lignin, or proteins, emerge as important alternatives. Nevertheless, substantial improvements and developments are still required in order to simplify the synthetic routes, as well as to improve the biopolymer stability and performance of these new bio-based AS formulations. This environmentally friendly strategy will hopefully lead to the future partial or even total replacement of non-renewable petroleum-based feedstock. In this brief overview, the general features of typical AS are reviewed and critically discussed regarding their drawbacks and advantages. Moreover, the challenges faced by novel and more ecological alternatives, in particular lignocellulose-based solutions, are highlighted.Funding Agency
Portuguese Foundation for Science and Technology
PTDC/AGR-TEC/4814/2014;
PTDC/ASP-SIL/30619/2017;
IF/01005/2014.info:eu-repo/semantics/publishedVersio
Ultra-high molecular weight silphenylene-siloxane polymers
Silphenylene-siloxane copolymers with molecular weights above one million were prepared using a two stage polymerization technique. The technique was successfully scaled up to produce 50 grams of this high polymer in a single run. The reactive monomer approach was also investigated using the following aminosilanes: bis(dimethylamino)dimethylsilane, N,N-bis(pyrrolidinyl)dimethylsilane and N,N-bis(gamma-butyrolactam)dimethylsilane). Thermal analyses were performed in both air and nitrogen. The experimental polymers decomposed at 540 to 562 C, as opposed to 408 to 426 C for commercial silicones. Differential scanning calorimetry showed a glass transition (Tg) at -50 to -55 C for the silphenylene-siloxane copolymer while the commercial silicones had Tg's at -96 to -112 C
Silicone elastomers filled with rare earth oxides
Silicones which possess, amongst others, remarkable mechanical properties, thermal stability over a
wide range of temperatures and processability, and rare earth oxides(REO), known for their unique
optic, magnetic and catalytic properties can be coupled into multifunctional composite materials(SREOs). In addition, the intrinsic hydrophobicity of REO and polysiloxanes makes them easily
compatible without the need for surface treatments of the former. Thus, europium oxide (Eu2O3),
gadolinium oxide (Gd2O3) and dysprosium oxide (Dy2O3)in amounts of 20 pph are incorporated as
fillers into silicone matrices, followed by processing mixture as thin films and crosslinking at room
temperature. The analysis of the obtained films reveals the changes induced by these fillers in the
thermal, mechanical, dielectric and optical properties, as well as the hydrophobicity of the silicones.
The luminescence properties of S-REO composites were investigated by fluorescence spectra and
lifetime - resolved measurements with a multiemission peaks from blue to greenish register. The
thermogravimetrical analysis indicates an increasing of thermal stability of the composites that
contain REO, compared to pure silicone. As expected, the dielectric permittivity significantly
increased due to nature of the fillers, while the dielectric loss values are relatively low for all samples,
indicating a minimal conversion of electrical energy in the form of heat within bulk composites. The
presence of rare earth oxides into the silicone matrix facilitates the motions of long-range charge
carriers through the network resulting in higher values of conductivity of the composite films. The
stress-strain measurements revealed the reinforcing effect of the rare earth metal oxides on a silicone
matrix, leading to a significant increase of Young modulus. The known hydrophobicity of silicones is
further enhanced by the presence of REO
An evaluation of two flat-black silicone paints for space application
Tests were conducted on two flat-black silicone paints suggested for space applications to determine their optical, electrical, and mechanical properties. Three different types of substrate materials were chosen for these paint tests; the application of the paints onto the primed substrates was carried out by spray coating. The adhesion properties were verified by thermal shock and sudden immersion into liquid nitrogen. A controlled thermal vacuum tests was also carried out by varying the temperature of the paint from -100 to 225 C. The measured optical properties included normal and hemispherical emittance, and solar absorption/reflectance. A simultaneous exposure to low-energy proton/UV irradiation in vacuum, and high-energy proton/electron irradiation was carried out. Additional tests of the paints are described
Trends in Materials' Outgassing Technology
Test sample acquisition and chemical analysis techniques for outgassing products from spacecraft, experiment modules, and support equipment is described. The reduction of test data to a computer compatible format to implement materials selection policies is described. A list of the most troublesome outgassing species is given and several materials correlations are discussed. Outgassing from solar panels, thermal blankets, and wire insulation are examined individually
Sources and transport of silicone NVR
The retrieved LDEF had varying amounts of visible contamination films (brown stains) at many locations. FTIR spectra of heavy film deposits at vents and of optical windows from tray E5 indicated methyl silicone and silica in the contaminant films. Two possible sources of the methyl silicone are DC-710 phenyl methyl silicone in the shuttle-bay-liner beta cloth, and the shuttle tile waterproofing silane. It is concluded that much of the silicon and silica contamination came from ground operations and the orbiter
Stability and reactivity of dimethylethoxysilane
The chemistry of the compound dimethylethoxysilane (DMES) is discussed especially as it relates to waterproofing silica surfaces. Some of the desirable properties of this compound are that it readily reacts with silica in the vapor phase, it is a low boiling point liquid (54 C), and the by-product of its reaction with silica is the rather inert substances ethanol. It is currently used by NASA to re-waterproof the HRSI shuttle tiles before relaunching the vehicle. Very little information is available on this particular compound in the literature or even on related silane compounds that have both a hydride group and an alkoxy group. Since the close proximity of two groups often drastically affects the chemical behavior of each group, chemical reactions were carried out in the laboratory with DMES to verify the expected behavior of these two functional groups located on DMES. Some of the reactions tested would be potentially useful for quantitative or qualitative measurements on DMES. To study the reactions of DMES with silica surfaces, cabosil was used as a silica substrate because of its high surface area and the ease of detection by infrared spectroscopy as well as other techniques
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