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The Hydrolytic Cleavage of Methyl and Chloromethyl Siloxanes

TEOS-40 hydrolysis

Colloids and Surfaces A: Physicochemical and Engineering Aspects, Volume 70, Issue 3, 31 March 1993, Pages 253–268

Colloids and Surfaces A: Physicochemical and Engineering Aspects

Volume 70, Issue 3, 31 March 1993, Pages 253–268

Hydrolysis and polycondensation of ethyl silicates. 2. Hydrolysis and polycondensation of ETS40 (ethyl silicate 40)

• J. Cihlář

• Technical University of Brno, Technická 2, 616 69 Brno, Czechoslovakia

• Received 15 June 1992. Accepted 15 September 1992. Available online 7 November 2001.

http://www.sciencedirect.com/science/article/pii/092777579380299T

Making Silica Aerogels

 http://eetd.lbl.gov/ecs/aerogels/sa-making.html

The discussion below relies upon the following terms:

Hydrolysis:

The reaction of a metal alkoxide (M-OR) with water, forming a metal hydroxide (M-OH).

Condensation:

A condensation reaction occurs when two metal hydroxides (M-OH + HO-M) combine to give a metal oxide species (M-O-M). The reaction forms one water molecule.

Sol:

A solution of various reactants that are undergoing hydrolysis and condensation reactions. The molecular weight of the oxide species produced continuously increases. As these species grow, they may begin to link together in a three-dimensional network.

Gel Point:

The point in time at which the network of linked oxide particles spans the container holding the Sol. At the gel point the Sol becomes an Alcogel.

Alcogel (wet gel):

At the gel point, the mixture forms a rigid substance called an alcogel. The alcogel can be removed from its original container and can stand on its own. An alcogel consists of two parts, a solid part and a liquid part. The solid part is formed by the three-dimensional network of linked oxide particles. The liquid part (the original solvent of the Sol) fills the free space surrounding the solid part. The liquid and solid parts of an alcogel occupy the same apparent volume.

Supercritical fluid:

A substance that is above its critical pressure and critical temperature. A supercritical fluid possesses some properties in common with liquids (density, thermal conductivity) and some in common with gases (fills its container, does not have surface tension).

Aerogel:

What remains when the liquid part of an alcogel is removed without damaging the solid part (most often achieved by supercritical extraction). If made correctly, the aerogel retains the original shape of the alcogel and at least 50% (typically >85%) of the alcogel's volume.

Xerogel:

What remains when the liquid part of an alcogel is removed by evaporation, or similar methods. Xerogels may retain their original shape, but often crack. The shrinkage during drying is often extreme (~90%) for xerogels.

Sol-Gel Chemistry

The formation of aerogels, in general, involves two major steps, the formation of a wet gel, and the drying of the wet gel to form an aerogel. Originally, wet gels were made by the aqueous condensation of sodium silicate, or a similar material. While this process worked well, the reaction formed salts within the gel that needed to be removed by many repetitive washings (a long, laborious procedure). With the rapid development of sol-gel chemistry over the last few decades, the vast majority of silica aerogels prepared today utilize silicon alkoxide precursors. The most common of these are tetramethyl orthosilicate (TMOS, Si(OCH₃)₄), and tetraethyl orthosilicate (TEOS, Si(OCH₂CH₃)₄). However, many other alkoxides, containing various organic functional groups, can be used to impart different properties to the gel. Alkoxide-based sol-gel chemistry avoids the formation of undesirable salt by-products, and allows a much greater degree of control over the final product. The balanced chemical equation for the formation of a silica gel from TEOS is:

Si(OCH₂CH₃)_{4 (liq.)} + 2H₂O _(liq.) = SiO_{2 (solid)} + 4HOCH₂CH₃ (liq.)

The above reaction is typically performed in ethanol, with the final density of the aerogel dependent on the concentration of silicon alkoxide monomers in the solution. Note that the stoichiometry of the reaction requires two moles of water per mole of TEOS. In practice, this amount of water leads to incomplete reaction and weak, cloudy aerogels. Most aerogel recipes, therefore, use a higher water ratio than is required by the balanced equation (anywhere from 4-30 equivalents).

Catalysts

The kinetics of the above reaction are impracticably slow at room temperature, often requiring several days to reach completion. For this reason, acid or base catalysts are added to the formulation. The amount and type of catalyst used play key roles in the microstructural, physical and optical properties of the final aerogel product.
Acid catalysts can be any protic acid, such as HCl. Basic catalysis usually uses ammonia, or, more commonly, ammonia and ammonium fluoride. Aerogels prepared with acid catalysts often show more shrinkage during supercritical drying and may be less transparent than base catalyzed aerogels. The microstructural effects of various catalysts are harder to describe accurately, as the substructure of the primary particles of aerogels can be difficult to image with electron microscopy. All show small (2-5 nm diameter) particles that are generally spherical or egg-shaped. With acid catalysis, however, these particles may appear "less solid" (looking something like a ball of string) than those in base-catalyzed gels.
As condensation reactions progress the sol will set into a rigid gel. At this point, the gel is usually removed from its mold. However, the gel must be kept covered by alcohol to prevent evaporation of the liquid contained in the pores of the gel. Evaporation causes severe damage to the gel and will lead to poor quality aerogels

Single-Step vs. Two-Step Aerogels

Typical acid or base catalyzed TEOS gels are often classified as "single-step" gels, referring to the "one-pot" nature of this reaction. A more recently developed approach uses pre-polymerized TEOS as the silica source. Pre-polymerized TEOS is prepared by heating an ethanol solution of TEOS with a sub-stoichiometric amount of water and an acid catalyst. The solvent is removed by distillation, leaving a viscous fluid containing higher molecular weight silicon alkoxy-oxides. This material is redissolved in ethanol and reacted with additional water under basic conditions until gelation occurs. Gels prepared in this way are known as "two-step" acid-base catalyzed gels. Pre-polymerized TEOS is available commercially in the U.S. from Silbond Corp. (Silbond H-5).
These slightly different processing conditions impart subtle, but important changes to the final aerogel product. Single-step base catalyzed aerogels are typically mechanically stronger, but more brittle, than two-step aerogels. While two-step aerogels have a smaller and narrower pore size distribution and are often optically clearer than single-step aerogels.

Aging and Soaking

When a sol reaches the gel point, it is often assumed that the hydrolysis and condensation reactions of the silicon alkoxide reactant are complete. This is far from the case. The gel point simply represents the time when the polymerizing silica species span the container containing the sol. At this point the silica backbone of the gel contains a significant number of unreacted alkoxide groups. In fact, hydrolysis and condensation can continue for several times the time needed for gelation. Failure to realize, and to accommodate this fact is one of the most common mistakes made in preparing silica aerogels. The solution is simple--patience. Sufficient time must be given for the strengthening of the silica network. This can be enhanced by controlling the pH and water content of the covering solution. Common aging procedures for base catalyzed gels typically involve soaking the gel in an alcohol/water mixture of equal proportions to the original sol at a pH of 8-9 (ammonia). The gels are best left undisturbed in this solution for up to 48 hours.
This step, and all subsequent processing steps, are diffusion controlled. That is, transport of material into, and out of, the gel is unaffected by convection or mixing (due to the solid silica network). Diffusion, in turn, is affected by the thickness of the gel. In short, the time required for each processing step increases dramatically as the thickness of the gel increases. This limits the practical production of aerogels to 1-2 cm-thick pieces.
After aging the gel, all water still contained within its pores must be removed prior to drying. This is simply accomplished by soaking the gel in pure alcohol several times until all the water is removed. Again, the length of time required for this process is dependent on the thickness of the gel. Any water left in the gel will not be removed by supercritical drying, and will lead to an opaque, white, and very dense aerogel.

Supercritical Drying

Process conditions for both the carbon dioxide substitution/drying process and the alcohol drying process.

The final, and most important, process in making silica aerogels is supercritical drying. This is where the liquid within the gel is removed, leaving only the linked silica network. The process can be performed by venting the ethanol above its critical point (high temperature-very dangerous) or by prior solvent exchange with CO₂followed by supercritical venting (lower temperatures-less dangerous) It is imperative that this process only be performed in an autoclave specially designed for this purpose (small autoclaves used by electron microscopists to prepare biological samples are acceptable for CO₂ drying). The process is as follows. The alcogels are placed in the autoclave (which has been filled with ethanol). The system is pressurized to at least 750-850 psi with CO₂ and cooled to 5-10 degrees C. Liquid CO₂ is then flushed through the vessel until all the ethanol has been removed from the vessel and from within the gels. When the gels are ethanol-free the vessel is heated to a temperature above the critical temperature of CO₂ (31 degrees C). As the vessel is heated the pressure of the system rises. CO₂ is carefully released to maintain a pressure slightly above the critical pressure of CO₂ (1050 psi). The system is held at these conditions for a short time, followed by the slow, controlled release of CO₂ to ambient pressure. As with previous steps, the length of time required for this process is dependent on the thickness of the gels. The process may last anywhere from 12 hours to 6 days.
At this point the vessel can be opened and the aerogels admired for their intrinsic beauty.

Typical Recipes

Single-Step Base Catalyzed Silica Aerogel

This will produce an aerogel with a density of approx. 0.08 g/cm³. The gel time should be 60-120 minutes, depending on temperature.

1. Mix two solutions:
   1. Silica solution containing 50 mL of TEOS, 40 mL of ethanol
   2. Catalyst solution containing 35 mL of ethanol, 70 mL of water, 0.275 mL of 30% aqueous ammonia, and 1.21 mL of 0.5 M ammonium fluoride.
2. Slowly add the catalyst solution to the silica solution with stirring.
3. Pour the mixture into an appropriate mold until gelation.
4. Process as described above.

Two-Step Acid-Base Catalyzed Silica Aerogel

This will produce an aerogel with a density of approx. 0.08 g/cm³. The gel time should be 30-90 minutes, depending on temperature.

1. Mix two solutions:
   1. Silica solution containing 50 mL of precondensed silica (Silbond H-5, or equivalent), 50mL of ethanol
   2. Catalyst solution containing 35 mL of ethanol, 75 mL of water, and 0.35 mL of 30% aqueous ammonia.
2. Slowly add the catalyst solution to the silica solution with stirring.
3. Pour the mixture into an appropriate mold until gelation.
4. Process as described above.

Synthesis and preliminary characterization of octakis (chloropropyldimethylsiloxy) octasilsesquioxane

Synthesis and preliminary characterization of octakis (chloropropyldimethylsiloxy) octasilsesquioxane

http://www.scielo.br/scielo.php?pid=S1516-14392004000300020&script=sci_arttext

Tetraethyl orthosilicate (TEOS) 矽酸乙酯

Tetraethyl orthosilicate

From :http://en.wikipedia.org/wiki/Tetraethyl_orthosilicate


性質：Si（OC2H5）4 又名正矽酸乙酯、原矽酸乙酯。無色或淡棕色液體。
略有香味。
密度0.9320。
沸點168.8℃，熔點-82.5℃，折射率1.3928。
在潮濕空氣(水解)中變渾濁。靜置後又澄清而析出矽酸沉澱。
用於製造耐化學品塗料和耐熱塗料。也用作製備有機矽的溶劑。
由四氯化矽和無水乙醇作用後經蒸餾而製得。


Alternatively TEOS can be considered to be the ethyl ester of orthosilicic acid, Si(OH)4. It is a prototypical alkoxide.

製備
TEOS is a tetrahedral molecule. Many analogues exist, and most are prepared by alcoholysis of silicon tetrachloride:
SiCl4 + 4 ROH → Si(OR)4 + 4 HCl
where R = alkyl such as methyl, ethyl, propyl, etc.
水解反應( hydrolysis reaction )
Si(OC2H5)4 + 2 H2O → SiO2 + 4 C2H5OH
This hydrolysis reaction is an example of a sol-gel process. The side product is ethanol.

The reaction proceeds via a series of condensation reactions that convert the TEOS molecule into a mineral-like solid via the formation of Si-O-Si linkages.

Rates of this conversion are sensitive to the presence of acids and bases, both of which serve as catalysts.
The Stöber process allows the formation of monodisperse silica particles.

At elevated temperatures (>600 °C), TEOS converts to silicon dioxide:
Si(OC2H5)4 → SiO2 + 2O(C2H5)2
The volatile coproduct is diethylether.

=======================================================
Stöber process
http://en.wikipedia.org/wiki/St%C3%B6ber_process

太陽能燈具和LED燈具專業英語翻譯

工作環境溫度：Working temperature工作電壓：Supply voltage額定電源頻率Rated power frequency額定功率Rated power驅動電源效率Power supply efficiency功率因數Power-factor(PF)LED發光效率LED luminoue efficiency燈具初始光通量Luminous flux燈具出光效率 Lamp Flux色溫Color temperature顯色指數CRI: Ra>75防護等級IP rating:IP65使用壽命 Working life外殼材質Shell material character產品尺寸 Size(A*B*C mm)重量 Net weight (kg)包裝尺寸 Packing dimensions(mm)
太陽能的相對多一點：

交流電兩種電的形態之一: 交變電流, 常用於住家中.
非晶具有無週期型的原子結構.
非晶矽有時簡稱為'a-矽'作為一種無序半導體材料用於增強等離子體化學蒸汽沉積(PECVD)工藝中. 此工藝可用來在不銹鋼的基片上產生薄膜太陽能發電層.
安培 (Amps)電流單位. 可視為電力流動的數量單位
光伏矩陣或發電板陣(Array - photovoltaic)太陽能發電板串聯或併聯連接在一起形成矩陣.
阻流二極管 (Blocking Diode)用來防止反向電流, 在發電板陣中, 阻流二極管用來防止電流流向一個或數個失效或有遮影的發電板(或一連串的太陽能發電板) 上. 在夜間或低電流出的期間, 防止電流從蓄電池流向光伏發電板矩陣."
光伏發電系統平衡(BOS or Balance of System - photovoltaic)光伏發電系統除發電板矩陣以外的部分. 例如開關, 控制儀表, 電力溫控設備, 矩陣的支撐結構, 儲電組件等等.
旁路二極管 (Bypass Diode)是與光伏發電板並聯的二極管. 用來在光電板被遮影或出故障時提供另外的電流通路.
光伏發電板 (電池) (Cell-photovoltaic)太陽能發電板中最小的組件.
充電顯示器 (表) (Charge Monitor/Meter)用以測量電流安培量的裝置, 安培表.
充電調節器 (Charge Regulator)"用來控制蓄電池充電速度和/或充電狀態的裝置, 連接於光伏發電板矩陣和蓄電池組之間. 它的主要作用是防止蓄電池被光伏發電板過度充電, 同時監控光伏發電矩陣和/或蓄電池的電壓."
組件 (Components)指用於建立太陽能電源系統所需的其他裝置.
交直流轉換器 (Converter)將交流電轉換成直流電的裝置.
晶體狀 (Crystalline)具有三維的重複的原子結構.
直流電 (DC)"兩種電流的形態之一, 常見於使用電池的物件中, 如收音機, 汽車, 手提電腦, 手機等等."
無序結構 (Disordered)減小並消除晶格的局限性. 提供新的自由度, 從而可在多維空間中放置其他元素. 使它們以前所未有的方式互相作用. 這種技術應用多種元素以及復合材料. 它們在位置,移動及成分上的不規則可消除結構的局限性, 因而產生新的局部規則環境. 而這些新的局部環境決定了這些材料的物理性質, 電子性質以及化學性質. 因此使得合成具有新潁機理的新型材料成為可能.
電網連接- 光伏發電(Grid-Connected - photovoltaic)是一種由光伏發電板陣向電網提供電力的光伏發電系統. 這些系統可由供電公司或個別樓宇來運作.
直流交流轉換器 (Inverter)用來將直流電轉換成交流電的裝置.
千瓦 (Kilowatt)1000瓦特, 一個燈泡通常使用40至100瓦特的電力.
百萬瓦特 (Megawatt)1,000,000瓦特
光伏發電板 (Module - photovoltaic)光伏電池以串聯方式連在一起組成發電板.
奧佛電子 (Ovonic)[以SR 奧佛辛斯基(聯合太陽能公司創始人)及電子的組合命名] - 用來描述我們獨有的材料, 產品和技術的術語.
奧佛辛斯基效應 (Ovshinsky effect)一種特別的玻璃狀薄膜在極小電壓的作用下從一種非導體轉變成一種半導體的效應..
並聯連接 (Parallel Connection)一種發電板連接方法. 這種連接法使電壓保持相同, 但電流成倍數增加
峰值輸出功能 (Peak Power)持續一段時間(通常是10到30秒)的最大能量輸出.
光伏 (Photovoltaic - PV)光能到電能的直接轉換.
光伏發電板 (電池) (Photovoltaic Cell)經過特殊處理可將太陽能輻射轉換成電力的半導體材料.
捲到卷工序 (Roll-to-Roll Process)將整捲的基件連續地轉變成整捲的產品的工序.
串聯連接 (Series Connection)電流不變電壓倍增的連接方式.
太陽能 (Solar)來自太陽的能量.
太陽能收集器 (Solar Collectors)用以捕獲來自太陽的光能或熱能的裝置. 太陽收集器用於太陽能熱水器系統中(常見於住家), 而光伏能收集器則是用於太陽能電力系統.
太陽能加熱 (Solar Heating)利用來自太陽的熱能發電的技術或系統. 太陽能收集器用於太陽能熱水器系統中(常見於住家), 而光伏能收集器則是用於太陽能電力系統中
太陽能發電模塊或太陽能發電板(Solar Module or Solar Panel)一些由太陽能發電板單元所組成的太陽能發電板板塊.
穩定能量轉換效率(Stabilized Energy Conversion Efficiency)長期的電力輸出與光能輸入比例.
系統, 平衡系統(Systems; Balance of Systems)"太陽能電力系統包括了光伏發電板矩陣和其它的部件. 這些部件可使這些太陽能發電板得以應用在需要可控直流電或交流電的住家和商業設施中. 用於太陽能電力系統的其它部件包括:接線和短路裝置, 充電調壓器,逆變器, 儀表和接地部件."
薄膜 (Thin-Film)在基片上形成的很薄的材料層.
伏特 (Volts)電動勢能單位. 能促使一安培的電流通過一歐姆的電阻.
電壓 (Voltage)電勢的量.
電壓表 (Voltage Meter)用以測量電壓的裝置.
瓦特 (Watts)用電壓乘以電流的值來衡量的電力度.
英文
ACOne of two types of electricity: Alternating Current; found in homes.
Amorphoushaving an atomic structure that is not periodic.
Amorphous Silicon"Sometimes abbreviated as ""a-Si"", amorphous silicon is used as a disordered semi-conductor material in the plasma-enhanced chemical vapor deposition (PECVD) process used to create thin-film solar cells on a stainless-steel substrate"
Amps"The unit of electrical current. Can be thought of as the ""flow rate"" of electricity."
Array (photovoltaic)modules wired together in series or parallel form an array.
Blocking Diode"Used to prevent undesired current flow. In a PV array, the diode is used to prevent current flow towards a failed or shaded module (or string of modules) or from the battery to the PV array during periods of darkness or low current production. "
BOS or Balance of System (photovoltaic)the parts of a photovoltaic system other than the array. For instance: switches, controls, meters, power conditioning equipment, supporting structure for the array, storage components, etc.
Bypass DiodeA diode connected in parallel with a PV cell to provide an alternative current path in case of cell shading or failure.
Cell (photovoltaic)the smallest unit of a solar module.
Charge Monitor/MeterA device that measures amperage; amp meter.
Charge Regulator" A device that controls the changing rate and/or state of charge for batteries. Wired between a photovoltaic array and a battery bank., its main job is to prevent the battery from being overcharged from the PV array, while monitoring the array and/ or battery voltage."
ComponentsRefers to other devices used and needed when building a solar system
ConverterAn Electroic Device that changes alternating current (ac) to direct current (dc).
Crystallinehaving a repeating atomic structure in all three dimensions.
DC"One of two types of Electricity Direct Current; found in anything that uses batteries. Radios, cars laptops, cell phones, etc."
Disorderedminimizing and lifting of lattice constraints, which provides new degrees of freedom, permitting the placement of elements in multi-dimensional spaces where they interact in ways not previously available. This allows the use of multi-elements and complex materials where positional, translational, and compositional disorder remove restrictions so new local order environments can be generated controlling the physical, electronic, and chemical properties of the material, thereby permitting the synthesis of new materials with new mechanisms.
Grid-Connected (photovoltaic)a photovoltaic (PV) system in which the PV array supplies power to the grid. Systems can be operated by the utility or by individual buildings.
InverterAn Electronic Device that changes direct current (dc) to alternating current (ac).
Kilowatt1000 watts; a light bulb uses 40-100 watts.
Megawatt"1,000,000 watts"
Module (photovoltaic)cells wired together in series form a module.
Ovonic[after SR Ov(shinsky) + (electr)onic] - the term used to describe our proprietary materials, products, and technologies.
Ovshinsky effectThe effect by which a specific glassy thin film switches from a nonconductor to a semiconductor upon application of a minimum voltage.
Parallel Connection"Connection in which the voltage stays the same, but the amperage multiplies."
Peak Powerthe maximum amount of energy available for a sustained period of time, typically 10 to 30 seconds.
Photovoltaic (PV)direct conversion of light into electrical energy.
Photovoltaic CellThe treated semi-conductor material that converts solar irradiance to electricity.
Roll-to-Roll Processa process where a roll of substrate is continuously converted into a roll of product.
Series ConnectionConnection in which the current (amps) stays the same but the voltage multiplies.
SolarEnergy from the sun.
Solar CollectorsA device designed to capture light or heat energy from the sun. Solar thermal collectors are used in solar hot water systems (often found in homes) and photovoltaic collectors are used in solar electric systems
Solar HeatingTechnologies or systems that take advantage of the heat energy coming from the sun. Solar thermal collectors are used in solar hot water systems (often found in homes) and photovoltaic collectors are used in solar electric systems.
Solar Module or Solar PanelA collection of solar cells interconnected to form a solar panel or module.
Stabilized Energy Conversion Efficiencythe long-term ratio of electrical output to light input.
Systems; Balance of Systems"Solar electric systems include the photovoltaic array and the other components that allow these solar panels to be used in homes and commercial facilities where a regulated DC power supply or an AC power supply is required. Components used in solar electric systems include; wire and disconnect devices, charge regulators, inverters, metering, and grounding components."
Thin-Filma very thin layer of material formed on a substrate.
VoltsThe unit of electromotive force that will force a current of one amp through a resistor or one ohm.
VoltageThe measurement of the force of electricity.
Voltage MeterA device that measures voltage.
WattsA measure of electrical power that is determined by multiplying the voltage by the amperage.