Silver/Polyaniline Nanocomposite for the Electrocatalytic Hydrazine Oxidation
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Silver/polyaniline (Ag-PANi) nanocomposites were prepared via in situ reduction of silver in aniline by mild photolysis performed with short wavelength (365 nm) radiation from UV lamp for 12 h. Reduction of the silver in aqueous aniline leads to the formation of silver nanoparticles which in turn catalyze oxidation of aniline into polyaniline. A slightly broadened X-ray diffraction (XRD) pattern suggests small particle which was size consistent with cubic silver nanoparticles. The UV–Vis absorption revealed that the bands at about 400–420 nm due to benzonoid ring of the polyaniline are overlapped and blue-shifted due to the presence of silver nanoparticles in powdered state. Scanning electron microscopy (SEM) of the silver/polyaniline (Ag-PANi) nanocomposite showed a size distribution with nanofibers and granular morphology of silver nanoparticles. Our findings are not only the promising approach for electro-catalytic hydrazine oxidation but also utilized in the other bio-sensing applications.
KeywordsSilver/polyaniline (Ag-PANi) Chemical synthesis Polymer Nanocomposite
The silver nanoparticles have potential in technological applications due to its interesting properties including catalysis, conductive inks, thick film pastes, and adhesives for various electronic components, in photonics and in photography [1, 2, 3]. The conducting polymers have the excellent hosts for trapping nanoparticles of metals and semiconductors, because of their ability to act as stabilizers or surface capping agents. The nanoparticles embedded or encapsulated in a polymer; the polymer terminates the growth of the particles by controlling the nucleation. For application in opto-electronics and electronics, the control of particle size and their uniform distribution within the polymer is the key to technology. Conducting organic polymers especially doped polyaniline, which have high electrical conductivity with great environmental stability in organic, inorganic, and aqueous medium. The methods of preparation may lead to small differences in physical and chemical properties of the product culminated into the electronic applications such as sensing . However, the synthesis of Ag-PANi nanocomposite via photo-polymerization process has reported for the first time for the electrocatalytical hydrazine oxidation. Hydrazine is an agricultural chemicals (pesticides), blowing agents, pharmaceutical intermediates, photographic developers, treatment of water for corrosion protection, textile dyes, and jet and rocket fuels . Besides these, individuals occupationally exposed to hydrazine in the workplace or from accidental discharges into water, air, and soil, which may also occur during storage, handling, transport, and improper waste disposal . The photolysis of aniline into polyaniline utilizing AgNO3 is an alternate strategy for in situ polymerization of aniline was established. This method has considered more suitable for synthesis of not only nanoparticles but also nanocomposite. The preparations of nanoparticles of silver by photolysis are rather scarce, although a large number of chemical methods have reported. However, the synthesis of silver nanoparticles of desired shape and size with uniform distribution within the matrix remains highly challenging and meaningful.
Polyaniline-AgNPs nanocomposites show enhanced sensing, electrical and catalytic capabilities, as compared with those of pure PANi. Khanna et al.  have reported the synthesis of Ag-PANi nanocomposites via in situ photo-redox mechanism by which radiation from UV lamps have used to reduce silver salt in aniline. Kang et al.  have prepared nanocomposites by oxidative polymerization of aniline-stabilized Ag colloids by gamma-irradiation. Karim et al.  jave synthesized core–shell silver nanocomposites by in situ gamma radiation-induced chemical polymerization method. Du et al.  have employed one-pot synthesis method for Ag/polyaniline nanoparticles; whereas Pillalamarri et al.  have also used one-pot synthesis method in which composite materials consisting of polyaniline nanofibres decorated with noble-metal (Ag or Au) nanoparticles were synthesized with γ-radiolysis. Zhou et al. . have applied the unsymmetrical square wave current method, and characterized by the combination of an anodic process of aniline monomer polymerization and a cathodic process of metal ionic electrodeposition to produce the PANi silver nanocomposite film.
Although the limitations associated with these methods are very hard to avoid, like sub-micrometre size diameter, risk of contamination and complex process control. To the best of our knowledge, the PANi/silver nanocomposite films for the elctrocatalytic oxidation of hydrazine have not reported until date. The advantage of the present method requires no other template for the reduction of silver salt into AgNPs. In this manuscript, an easy route to a silver/polyaniline nanocomposite powder was prepared using UV lamp at 365 nm wavelength. Silver nitrate has reduced by aniline in an aqueous medium via photolysis to produce PANi, in which silver acts as a catalyst to initiate the polymerization in aqueous medium.
Aniline, silver nitrate and ethanol were obtained from Merck, India. Aqueous solutions were prepared using deionized water. Aniline stored in dark at low temperature in the concentration of 0.5 M aniline mixed with 0.5 M of silver nitrate in total volume (5.0 mL) of mixture. The assay mixture had irradiated using 365 nm wavelength for 12 h at room temperature in UV chamber. The colour of the solution changes from whitish to blue and then finally it becomes green.The solution kept inrefrigerator at rest for 24 h to complete the polymerization process and then this solution was centrifuged at 5,000 rpm for 30 min. The mass obtained was washed with acetone, ethanol and double distilled water to remove excess of monomer, oligomer. The powdered sample have characterized by several techniques. ITO substrates were cleaned using distilled water with several times and air-dried. The reaction mixture well vortexes and put on the desired area of the substrate. After that, put inside the UV lamp chamber (365 nm) carefully for 12 h. The presence of a green thin PANi film on ITO substrate has observed, suggesting the protonation of the emeraldine base. The AgNPs/PAni film on the ITO electrode washed with buffer solution.
Morphology of nanocomposites are studied by a Scanning electron microscopy (SEM) FEI, model Quanta 200, Netherland. The optical absorption band has measured with UV–Vis spectroscopy (Perkin Elmer model L35, Germany). Photoluminescence spectra of the samples have obtained out using LS 55 Fluorescence spectrophotometer (Perkin Elmer). The excitation wavelength for the PL study of the sample is 330 nm. TGA of the samples have carried out on Pyris 1 TGA instrument at a heating rate of 10 °C per minute in N2 atmosphere over a temperature range of 25–700 °C. FTIR is recorded with a FTIR-NEXUS, NICOLET instrument in the region of 500–4000 cm−1 using KBr pellet. XRD was performed on Rigaku D/max-2200 PC diffractometer operated at 40 kV/20 mA, using Cu Kα1 radiation with wavelength of 1.54 Å in the wide angle region from 20 to 80°. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were performed on electrochemistry workstation CHI 660A (Austin, USA). Electrochemical measurements have performed in one-compartment cell containing the ITO modified electrode (geometric area of 1.0 cm2) as working electrode, a platinum auxiliary electrode, and Ag/AgCl sat electrode as reference. DPV experiments have performed at a scan rate of 20 mVs−1 using instrumental conditions of 50 mV pulse amplitude, pulse width of 50 ms and pulse time of 200 ms.
3 Results and Discussions
The excitation of aniline monomer by UV light @ 365 nm is playing role for the polyaniline formation and controlling of silver particle sizes. The speculation to this mechanism is also due to Ag+ ions, which oxidize the aniline monomer and as result reduce it into metal Ag0 and finally PANi and Ag0 particles are formed. Possibly, in another way, the decomposition of NO3− by UV light yields hydroxyl radicals (OH) as oxidizing agent and they are responsible for aniline photopolymerization rather than rather than due to Ag+. Thus, we can propose that NO3− ions are able to promote the polymerization of aniline monomer by UV light. Strongly we can state that the exact mechanism of photopolymerization process are still not fully understand, probably UV light interacts with aniline and silver nitrate to yield PANi and Ag0 due to photo-excitation process.
The synthesis of Ag-PANi nanocomposite by simple route is established in presence of aniline as a starting material. The photolysis is effective in the initial reduction of silver nitrate into AgNPs and then simulataneously act as photocatalyst to oxidize aniline to polyaniline. This nanocomposite is more thermally stable and more crystalline than standard polyaniline. Confirmation of the presence of silver nanoparticles in polyaniline is obtained by UV–Vis, PL, FTIR, XRD, TGA, SEM and CV analysis. The modified electrode are used for the first time to confirm the utility and application of this, towards the electrocatalytic oxidation of hydrazine.
Work supported by DST Nano-Mission (SR/NM/NS-87/2008), Department of Science and Technology.
This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.
Open AccessThis is an open access article distributed under the terms of the Creative Commons Attribution Noncommercial License (https://creativecommons.org/licenses/by-nc/2.0), which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.


Is glucose a product of respiration?
Most of the steps of cellular respiration take place in the mitochondria. Oxygen and glucose are both reactants in the process of cellular respiration. The main product of cellular respiration is ATP; waste products include carbon dioxide and water.
What are the products of respiration?
Cellular respiration converts oxygen and glucose into water and carbon dioxide. Water and carbon dioxide are by- products and ATP is energy that is transformed from the process.
What does oxygen and glucose make the body?
Through the process of cellular respiration, the energy in food is converted into energy that can be used by the body’s cells. During cellular respiration, glucose and oxygen are converted into carbon dioxide and water, and the energy is transferred to ATP.
What is energy called that is made in respiration?
The source of the energy required to regenerate ATP is the chemical energy stored in food (e.g. glucose). The cellular process of releasing energy from food through a series of enzyme-controlled reactions is called respiration . Some of the energy released is used to produce ATP.
How do we get energy from respiration?
Respiration releases energy – it is an exothermic process. The energy is stored in molecules of ATP . ATP can be broken down in other processes in cells to release the stored energy. Don’t confuse respiration with photosynthesis.
Is energy made during respiration?
Metabolic pathways provide resources and energy that allow cells to grow and divide.
What is the role of oxygen in anaerobic respiration?
Anaerobic respiration is respiration using electron acceptors other than molecular oxygen (O2). Although oxygen is not the final electron acceptor, the process still uses a respiratory electron transport chain. Molecular oxygen is a high-energy oxidizing agent and, therefore, is an excellent electron acceptor.
How is energy released from glucose?
During cellular respiration, glucose is broken down in the presence of oxygen to produce carbon dioxide and water. Energy released during the reaction is captured by the energy-carrying molecule ATP (adenosine triphosphate).
How much oxygen is in our body?
Normal: A normal ABG oxygen level for healthy lungs falls between 80 and 100 millimeters of mercury (mm Hg). If a pulse ox measured your blood oxygen level (SpO2), a normal reading is typically between 95 and 100 percent.
What is normal oxygen consumption?
Results: The human lung consumes about 5-6 ml oxygen per minute at an esophageal temperature of 28 degrees C. Prebypass whole-body oxygen consumption measured at nearly normothermic conditions was 198 +/- 28 ml/min. Mean lung and whole-body respiratory quotients were similar (0.84 and 0.77, respectively).
What is the fastest healing organ in the body?
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Sulfur-Enriched Bone Char as Alternative P Fertilizer: Spectroscopic, Wet Chemical, and Yield Response Evaluation (2018)
Zimmer D., Panten K., Frank M., Springer A., Leinweber P.
Agriculture, 9 (1), 21
Phosphorus- (P) rich bone char (BC) could be an alternative P fertilizer in sustainable agriculture; however, it has a low P solubility. Therefore, sulfur-enriched BC (BCplus) was tested for chemical composition and fertilization effects in a pot experiment. In BCplus sulfur, concentrations increased from <0.1% to 27% and pH decreased from 8.6 to 5.0. These modifications did not change P solubility in water, neutral ammonium citrate, and citric acid. A pot experiment with annual rye grass (Lolium multiflorum L.) and treatments without P (P0), BC, BCplus and triple superphosphate (TSP) was set up. The cumulative dry matter yield of the BC treatment was similar to P0, and that of BCplus similar to TSP. The plant P uptake was in the order P0 = BC < BCplus < TSP. Consequently, the apparent nutrient recovery efficiency differed significantly between BC (<3%), BCplus (10% to 15%), and TSP (>18%). The tested equilibrium extractions, regularly used to classify mineral P-fertilizers, failed to predict differences in plant yield and P uptake. Therefore, non-equilibrium extraction methods should be tested in combination with pot experiments. Additionally, particle-plant root scale analyses and long-term experiments are necessary to gain insights into fertilizer-plant interactions.


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What is a Glycol Dehydration Unit?
Triethylene glycol (TEG) unit or glycol dehydrator is a liquid desiccant system used for the removal of water from natural gas and NGLs. It is the most commonly used means of water removal from natural gas. A TEG Unit also referred to as a glycol unit, uses absorption, which occurs when the water vapor is taken out by a dehydrating agent, or liquid desiccant.
A TEG unit removes water vapor from the gas or liquids such as natural gas or oil. Water vapor in gas is like humidity in the air; it can only be removed through a dehydration process such as a liquid or solid desiccant dehydrator or with refrigeration. Water vapor is the amount of water contained in gas at a given temperature and pressure. There are three main characteristics that affect the water vapor in gas; temperature, pressure, and volume.
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Here at CROFT, we like to first find out what the volume, temperature and pressure is, so we can determine how much water vapor needs to be removed and what size equipment will be needed to appropriately dehydrate the gas.
There are different types of dehydration products, but this blog will focus specifically on glycol dehydration units which are a non-regenerative system utilizing liquid glycol absorbents to hydrate the gas.
Components that make up a Glycol Dehydration Unit:
There are several components on a TEG unit that are critical to the function or can greatly improve the efficiency of the system. We partner with Surplus Energy Equipment to provide our clients with components to repair or upgrade their existing Tglycol dehy unit. These components are available as-is or for re-certification.
- Reboilers– Reboilers drive the water from the wet desiccant into the atmosphere. Reboilers, also referred to as regenerators are either direct-fired or steam-heated with a stripping column on top. Stripping columns can be packed or contain trays. Reboilers are often fueled by fuel gas from the gas stream of the contractor. In this case, the fuel gas quality may need to be improved using a fuel gas conditioning system.
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How a Glycol Dehydrator works:
We discussed some of the components a TEG, but keep reading for a better understanding of how those components work together to achieve the overall function.
- Wet gas enters the inlet scrubber, which is placed before the contact tower to remove any free water, dust, condensed hydrocarbons, and other impurities
- After going through the separator, the wet gas enters through the contact tower where it rises through the column. As its rises through the contact tower the gas meets the lean glycol solution flowing downward across either bubble trays, random packed or structured packed towers
- Next, the rich TEG exchanges heat with the lean TEG and enters the still column. The TEG then flows downward through the still column to the reboiler where it is heated around 375°F and removes all but a small percentage of the water from the regenerator
- The hot, dry glycol then flows through an overflow system to the surge section of the reboiler, where the glycol pump then pulls lean TEG and pumps the glycol back into the top of the contact tower, where the drying process is repeated
Croft Production Systems, Inc. has developed a glycol dehydration design that combines the best practices through the industry. CROFT will properly size and sell a system to meet your needs. For efficiency gains and environmental consideration, CROFT promotes this baseline product with upgraded features like BTEX, Burner Management Systems (BMS), and sensors with control kills.
Read more about TEG units.
Shop for TEG parts.
Shop for used or surplus components for TEG units.


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Protecting Workers and the Public from Acrylamide and Other Chemical Exposure Risks
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In this work, we review the progress in recent studies on glass patterning including technologies and applications. Four technologies for glass micromachining including wet etching, sandblasting, reactive ion etching, and glass reflow process are analyzed. Advantages as well as disadvantages of each method are presented and discussed in light of the experiments. Various microsystem applications using the above glass patterning technologies like thermal sensors, hermetically packaged capacitive silicon resonators, optical modulator devices, glass microfluidics, micro-heaters, and vacuum-sealed capacitive micromachined ultrasonic transducer arrays are reported.
Part of the book: Advances in Glass Science and Technology


A lot of diseases been recently related to heavy metal toxicity, which also known as heavy metal poisoning for most and so far has been a reason for the problem for several.
When considerably more an exposure to toxic heavy metals, is just usually thought to be a huge factor each morning symptoms, like low energy, change in moods as well as other types of changes. Basically, this is what happens; these metals usually enter the bloodstream once there is an exposure to contaminated water, dental fillings, and even common household products. They now travel all through the body and enter into the cells quite a few tissues also as organs, staying stored up at as long as years.
How To take care of Heavy Metal Toxicity?
You end up being wondering, how do you treat heavy metal toxicity? Well, it’s pretty easy. It is mostly by using a heavy metal detox strategy. When you set up a plan while this, have got to be aware of symptoms would most likely get just a little worse before they become better, understanding that should be anticipated. Some of major you would most likely experience when you start a heavy metal detox includes:
Loss of appetite
What The particular Foods That Be Used for Removing Heavy metals From The body?
There are foods which can in removing heavy metals from requires and they include quite a lot of vegetables. Some of the vegetables which can be used for heavy metal detox include Herbs and spices, Leafy greens, Bone broth, superfoods such as algae.
When start out a detoxification process, supplements can be used as well as other styles of detoxifying treatments which help in improving both your liver, brain, nervous system, some other forms of important organs.
Why Should we Detox Off Heavy Metals?
There are numerous dangers of heavy metals and hair band poisoning. This is because heavy metals are elements which can be very toxic as well as dangerous. However, the concentration amount of the chemical toxins.
Which will be metals can easily be lead to such toxicity or poisoning, you might wonder? There are a lot of metals end up being cause this in the long or short run, and they include:
These your main and quite popular factors behind heavy metal poisoning, plus some of the studies have shown that under certain conditions, taking a top level of calcium could be quite dangerous to your body.
This form of poisoning can cause quite fantastic of issues when entire body gets exposed to metals all around the environment, and they even teach tend to accumulate inside the body. According to some reports and thus Study, metals sick as lead, cadmium, mercury, and arsenic will not absolute and beneficial role to the human body or contribute anyway to a person's homeostasis and instead rend to contribute more to more forms of noncommunicable chronic diseases.
More researches have conducted researches which proved whenever the body is exposed a few number with a minimum of 23 different environmental heavy metals, it tends staying detrimental on the health and cause a serious form of toxicity.
The reasons Tnrse metals are said to be heavy is considering that they tend to keep in the body, and additionally they also tend to hide in the fat cells, which are impending as adipose muscle. They are very stubborn and cause great difficulty in protection. They will often be compared to fat-soluble toxins as well.
The truth is, that can no way you can a person can completely stay away from heavy metal exposure, that makes sense as this a very necessary supply found inside food supply all over the world nicely in water as well as the grounds of the environment. But as this happens, trouble to cause more damage without as well as the individual actually realizing, being the rationality why we decide to detoxify more than possible. These damage of heavy metal toxicity includes the fact it can affect the central nervous function, reduce as well as damage the mental health, plus affect the vital organs in human body which include the heart, liver, kidneys and also the endocrine glands.
Longer Term Exposure To Heavy Metals
When the body is exposed longer on the heavy metals, it may lead to very serious damages and lead to physical and muscular degeneration as we as also a neurological damage. When these become more severe, it does imitate regarding other problems such as Parkinson’s diseases, Alzheimer’s plus multiple sclerosis.
This is generally related individuals who are old enough to get aging issues such as memory loss as well as constant and increased fatigue and although a lot of of people tend to blame the associated with old age, these cause be triggered by other things without actually realizing or considering will be able to be as a result the contact with heavy alloys.
So Why Exactly Will we Do Great Metal Detox?
To Remove Toxins Among the Body.
These chemical toxins tend to affect human metabolism and also tends to open ways for plenty of diseases. And let’s take into account they are stored in each parts of your body, including the brain to have a very very long time.
Increases The Body’s energy
After detoxing, you will feel a wide lot stronger and be willing to be more active both physically, mentally and emotionally and additionally you get rest a lot better and do not require often of sleep for minimal energy. It assists in giving you more clarity and making decisions wouldn’t be too hard of a chore.
It Works well for Preventing chronic diseases.
As mentioned, when these toxins are removed, process, which is no longer be the boss of things pertaining to instance strokes, cancer, neurological diseases, etc. Detoxing helps in assisting your body fight off these points.
Helps In Enhancing The Body’s Natural immunity
Detoxing helps the defense system function a whole lot healthier. It strengthens it and helps it to fight off infections which you could end up colds and flushed.
Improves Skin Quality.
Getting gone toxins and taking in a good diet is sure to help your skin glow current you a generally healthy and wonderful appearance.
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Retinyl palmitate (helps increase collagen production); vitamin C (antioxidant); omega-3 oils (reduce inflammation); dermaxyl (peptide)
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posted by Sophia .
The solubility of CaCO3 at 25 degrees celsius is 6.90*10-5M. The reaction is CaCO3(s)-->Ca 2+(aq) + CO3 2-(aq)
a. Calculate the concentration of Ca +2 and CO3 -2 at equilibrium.
b. Calculate the equilibrium constant for the dissolution reaction. (also known as the solubility product).
The solubility of CaCO3 is quite complex due to the potential reaction of the carbonate ion with H2O to form bicarbonate and carbonic acid. I think the intent of this problem is to ignore that which I shall do.
CaCO3 ==> Ca^+ + CO3^=
Ksp = (Ca^+2)(CO3^=)
(Ca^+2) = 6.90 x 10^-5 M at equilibrium.
(CO3^=) = 6.90 x 10^-5 M at equilibrium.
Substitute into the Ksp expresion and solve for Ksp.


PolyPid, an Israeli drug-delivery company, has introduced a new family of drug carriers based on a melding of two drug delivery systems: polymers and lipid-based systems. The PolyPid carrier carrier can be tailored to small molecules, peptides, protein and nucleic acids-based drugs.
The company's technology ensnares a large variety of one or more biologically active molecules and releases them at a pre-programmed rate for up to several months. PolyPid produces a product called BonyPid, a biodegradable bone void filler. After BonyPid releases its coating, over time, the bone void filler scaffold remains and supports bone recovery. This way, according to the company, physicians can "obtain the benefits of conventional bone void filler combined with an effective local drug delivery system."
"Due to its flexibility, the PolyPid platform can be utilized to address numerous medical indications in various fields, such as orthopedics, urology, periodontal, anti-cancer/anti-fungal treatments and surgical accessories," PolyPid CTO Noam Emanuel said in a news release.
- read PolyPid's release
- and a brief report on PBR


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Various guidelines are to be found in the literature for evaluation of soil corrosivity based on parameters like resistivity, pH, water content, redox-potential, content of salt, and bacterial activity. Corrosion studies of steel piles and pipes in Norwegian marine clayey sediments show that these parameters are not always applicable. Studies of piles in undisturbed marine clays below the groundwater table indicate a limited correlation between the resistivity and the corrosion rate. The highest corrosion rates found amount to 30 μm/year indicating that pile corrosion is not a severe problem under the aforementioned conditions. The environmental conditions for pipes are generally much more complex than for piles, as the backfill is disturbed and often includes material other than the original sediment. Studies of pipes in a heterogeneous environment indicate differential aeration to be the most common corrosion cause.
Corrosivity evaluations are also performed with electrochemical probes.
steels, corrosions, soils, corrosion tests, environments, underground corrosion
Senior research engineer, The Ship Research Institute of Norway, Sandefjord,
Research scientist, Norsk Hydro, Sandvika,


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GlobalFoundries, Inc. (Essex Junction, VT)
The GlobalFoundries Vermont facility (FAB9) manufactures semiconductor chips for global telecommunications and consumer electronics markets. The following projects were driven by the team’s goals to improve tool utilization and increase process efficiency and become the best in class for ‘cost per wafer pass’ in the industry. All this while developing sustainable processes that are safe and healthful with reduced environmental impact.
Solvent Pre-Rinse Elimination: The Team discovered an older process running for one technology. For this technology, the process was rinsing the wafer with solvent prior to the application of photoresist to clean the wafer. This was a legacy process left over from many years prior, and this process had been instituted due to an upstream tool causing organic defects on the wafer surface. That upstream process had changed and the problem was resolved, but this process was not removed. The Team qualified the elimination of this solvent pre-rinse with no increase in defectivity or degradation off yield. This project reduced solvent usage by 16,304 liters and saved approximately $45,000 in chemical costs.
FSI Polaris 25% Pre-Wet Reduction: The goal was to reduce solvent use without impacting the process integrity and product quality and reliability. The work involved creating an extensive matrix, running, and evaluating the optimal solvent use against the key process parameters. There was an extensive qualification effort associated with this conversion which enabled the reduction of solvent used by 25% for a total of 5,606 liters annually and saved $91,930 in chemical costs.
The qualification effort encompassed all different substrate types coming to this group of tools and evaluating each one with product wafers. The team used a macro defect inspection tool tuned to find striations or missing photoresist, reviewed several thousand wafer images across incoming film or substrate types. Solvent for this fleet of tools is delivered to the tool in 10 Liter bottles, and this project eliminated 500 bottle changes per year on the tool set. The elimination of bottle changes reduced the need for chemical handling which removes contact risk exposure to the operators and the possibility for an accidental spill or release.
HD4004 Develop Solvent Reduction: Photo sensitive polyimide uses a solvent with high solubility as a developer for the photo process. This developer process also uses an additional solvent as a rinse agent. The project objective was to find the process window which allowed for significant reduction of the use of these solvents without changing the resultant developed polyimide structure. To ensure this process was equivalent to the process of record, the Team ran a matrix around volume of each chemical while doing both visual inspection of the wafer and its cross section. The resulting process exhibited equivalent results within acceptable process margins and achieved a 55% reduction of the highly soluble, higher cost developer solvent while reducing the rinse solvent by 36%. Overall, this project reduced over 40,000 liters of solvent usage which prevented this from becoming waste. In addition, this project saved $248,403 in chemical costs.
Blended Pre-Wet: FAB9 developed an innovative process to both reduce the amount of solvent used on a large subset of photo tools and significantly decreased the cost of solvent required for this process step. This process step is critical to the application of the photoresist on the wafer. The photoresist has to be applied defect free and at a uniformity across the wafer of less than 45 angstroms. The process is unique in the industry, it leverages a lower cost bulk chemical over a higher cost chemical that is delivered to the tool from a 10 Liter bottle that is resident on the tool. The overall process reduced the volume of solvent used on the wafer by 25% while reducing the higher cost chemical volume by 75% for a total of 7,636 liters. By lowering the volume of the higher cost chemical, they were able to achieve significant cost savings ($267,021) but also reduce the labor required to replace these bottles. They effectively eliminated 2,300 bottle changes per year from FAB9 which is performed by operators. The elimination of bottle changes reduced the need for chemical handling which removes contact risk exposure to the operators and the possibility for an accidental spill or release.
GlobalFoundries, Inc. (Malta, NY)
The GlobalFoundries Malta, New York (FAB8) Chemical Mechanical Polish (CMP) team has implemented six projects that reduced usage of eleven different types of slurries for a total of 29,067 gallons annually. This increased the manufacturing capacity while reducing loading demands upon local wastewater treatment systems. The following projects were implemented over the recent 24 months:
Barrier Slurry Flow Reductions: In the copper CMP process, different slurries are used to remove the copper film and the barrier/oxide films. In this project, the team was able to reduce the flow rate of the slurry used in the barrier/oxide polish step by 10% on specific process layers without impacting the process time or other parameters. This reduced the amount of slurry that is used and therefore the amount of material sent to the local municipal wastewater plant (POTW) for treatment with lower azole and organic acid content.
CMP Downforce Increase: In the copper CMP process, the team was able to increase the downforce used in processing specific layers, which in turn reduced the amount of slurry used in both the copper removal and the barrier/oxide removal steps. This reduced the amount of slurry that is used and therefore the amount of material sent to local POTW for treatment with lower azole and organic acid content.
Slurry Reduction and New Pad Qualification: Also in the copper CMP process, the team was able to qualify a new polishing pad with improved hydrodynamic properties to improve the slurry distribution across the pad surface. This increased the polish rate of the process and in turn reduced the amount of copper polish slurry used in specific process layers. This reduced the amount of slurry that is used and consequently the volume of azole discharged.
Cleaning Chemical Reduction: In the CMP process, cleaning chemicals are used in the brush clean steps to clean the wafer surface after the polishing operation completes. In these projects, the team was able to reduce the cleaning chemistry used in as set of tools by reducing the amount of chemical used to clean both production wafers and non-production test wafers. For the production wafers, the team optimized the cleaning operation steps by eliminating a cleaning step, which in turn reduced the amount of cleaning chemistry used in the process. For the non-production test wafers, the team further reduced the cleaning chemistry utilized by reducing the chemical flow rate needed to clean the wafers. This reduced the amount of chemical used in the processes and as a result lowered the discharge of ammonia and highly corrosive wastewater to the local POTW.
Slurry Flow Reduction (Bulk & Buff): In the tungsten CMP process, multiple slurries are utilized to remove the tungsten film and the barrier/oxide films. In this project, the team was able to qualify a 10% reduction of all the slurries used in the bulk and buff operations without incurring significant differences in the process performance. This reduced the amount of slurry that is used and consequently the volume of azoles discharged.
Slurry Prime Removal: In the CMP process tool setup, a slurry priming step is utilized, where slurry is pumped to drain at the start of the process to ensure fresh slurry is available when the first wafers of a lot arrive. This step has historically been needed in order to maintain stable wafer processing throughout the entire lot of wafers, but in this project, the team calculated the volume of slurry in the supply lines and was able to qualify a reduced slurry priming step. In some cases, the team was even able to eliminate the need for the priming step by showing no change in initial wafer process performance without the slurry priming. This reduced the amount of slurry that is used and therefore the amount of material sent to local POTW for treatment with lower azole, ethylene glycol, and organic acid content.


For those who have been or are being exposed to fungi mold in water damaged buildings, please follow these important treatment strategies. Especially if anyone is noticing any of the symptoms of mold sickness (see previous post), here are helpful measures to employ:
Antihistamines such as Benadryl, Claritin or Zyrtec combined with Pepcid can reduce allergic symptoms.
Antileukotrienes such as Singulair can further reduce and prevent allergy symptoms from mold sickness.
Toxin Binders soak up mycotoxins in the gut to ensure their proper elimination, rather than allowing them to be reabsorbed into the system. Calcium d-glucarate, triphala, Hemp fiber, Psyllium and activated charcoal aids the process or binding mucotoxins.
Use of gentle laxatives, magnesium citrate, or buffered C powder to keep bowels functioning normally while on toxin binders.
Metabolic Detoxification Supplements are used to detox mycotoxins from inside your body. Examples include liposomal glutathione, milk thistle, n-acetylcysteine, glycine, glutamine, alpha lipoic acid, and taurine.
Antioxidants such as vitamins A, C and E block the harmful effects of the toxins.
Frequent use of saunas, when available, promotes toxin elimination through sweat.
Antifungals are prescription medications that may be required when someone actually has fungus mold growing in their body. This is happening frequently, especially in people with health issues like diabetes and other on certain medications that suppress their immune system.
Avoid steroid creams and nasal sprays because this will suppress your immune system in a way that will amplify mold sickness!
Avoid antibiotics because this will also allow for mold overgrowth in your body.
It has been nearly impossible to get a restock of these medications in my clinic and the local pharmacies. For this reason, I have reached out to doctor friends for help. Here is the plan we have in place so far. It is a good plan. Please help us!
We are proposing putting together packets of 3 custom formulas designed to reduce the harmful effects of mycotoxins and mold spores. These packets are to be used preventatively for persons with prolonged mold exposure, and for others who are experiencing symptoms after exposures. Working with California medical and naturopathic doctors, we have been able to secure significant discounts. The mold detox packets contain these natural, safe products listed above.
Please consider making a grant to Freeport Rotary club specifically for purchase of these essential mold sickness nutriceuticals.
Website for donations: Rotary6990.org and donate to the Robbins fund. PLEASE: Specify your donation is for mold toxicity treatment and prevention in Grand Bahama.


US 4537735 A
In a method of producing a silicon carbide sintered compact comprising steps of placing silicon carbide fines, a sintering additive and a shaping additive as required into a dispersing medium solution to form a supensoid, sieving operation on said suspensoid, forming a green shape from powders obtained in said sieving operation, and pressureless sintering process; an improvement characterized is that solid content comprising said silicon carbide fines and sintering additive is limited within a range of 10-50% by volume to said suspensoid, and that in the sieving operation, the suspensoid is passed through a sieve having an opening less than 65 μm under a pressure differential between before and after the sieve to remove coarse particles in the silicon carbide fines, sintering additive and others to form silicon carbide sintered compact having a high strength.
1. In a method of producing a silicon carbide sintered compact comprising steps of placing silicon carbide fines, at least one sintering additive selected from a group consisting of boron containing additives, carbonaceous additives, beryllium containing additives and aluminum containing additives, and at least one shaping additive selected from a group consisting of polyethylene glycol, magnesium stearate, barium stearate, aluminum stearate, zinc stearate, stearic acid, starch, dextrin, gum arabic, casein, sugar, molasses, na-carboxymethyl cellulose, methyl cellulose, polyvinyl alcohol, polyvinyl methyl ether, polyacrylic amide, tannic acid, liquid paraffin, wax emulsion, ethyl cellulose, polyvinyl acetate, phenol resin, cellulose acetate, glycerol and polyethylene glycol, as required into a dispersing medium solution of water or organic liquid to form a suspensoid, performing a sieving operation of said suspensoid, processing and forming said suspensoid into a green compact from powders obtained in said sieving operation, and subjecting said green compact to a pressureless sintering process to produce a sintered compact:
the improvement comprising limiting the solid content comprising said silicon carbide fines and sintering additive within a range of 10-50% by volume to said suspensoid; when water is used as said dispersing medium solution, adding and dispersing at least one of the dispersing agents in the following group A, while when an organic liquid is used as said dispersing medium solution, adding and dispersing at least one of the dispersing agents in the following group B, in said solution to form a suspensoid, said organic liquid being selected from a group consisting of acetone, methenol, ethanol, butanol, hexane, heptane, nonane, toluene, xylene, ethyl methyl ketone, methyl isobutyl ketone, ethyl benzene, ethylene glycol, trichloroethylene, cyclohexane, nitromethane, nitroethane, isopropyl alcohol, benzene and carbon tetrachloride; applying a pressure differential to promote the sieving operation retarded by a pressure loss between, before and after said sieve, with or without vibration, to said suspensoid to pass a sieve having an opening less than 65 μm, removing coarse foreign matters which cause pores or inclusion affecting adversely the bending strength of said compact;
A. amines, organic compounds containing carboxyl group, organic compounds containing sulfo group, esters, ammonium compounds, organic compounds containing ether linkage, carboxylic acid salts, aluminates, phosphates, phosphoric acid complex salts, sulfonates and silicates;
B. amines, organic compounds containing carboxyl group, organic compounds containing sulfo group and esters.
2. Method as defined in claim 1, wherein said dispersing agent is added in a range of 0.05-15 parts by weight to 100 parts by weight of a mixture comprising silicon carbide fines and sintering additive.
3. Method as defined in claim 1, wherein said pressure differential in said suspensoid between before and after the sieve is fluctuated periodically in a range of 1/400-2 seconds.
4. Method as defined in claims 1 or 2, wherein a vibration in a range of frequency of 1-400 Hz is applied to said suspensoid.
The present invention relates generally to manufacture of sintered products of silicon carbide, especially to manufacturing process of sintered compacts of silicon carbide having high strength and high reliability.
Silicon carbide is one of the most suitable materials for use under severe high temperature condition for example, gas turbine parts or high temperature heat exchangers due to its excellent chemical and physical properties.
Hithertofore, the pressure sintering and reaction sintering processes are widely known for sintering of silicon carbide. However, there have been some disadvantages in these processes, i.e., in the former it is difficult to obtain complicated configuration of the sintered body and of its low productivity, and in the latter it is difficult to obtain the sintered products having high strength and to use under high temperature due to its high content of free silicon.
Meanwhile, silicon carbide is one of variety of materials to be sintered with difficulty, and it has been observed difficult to apply the pressureless sintering generally adopted to manufacture of oxide ceramics wherein a green compact shaped under the normal temperature is sintered without pressure. Recently new pressureless sintering process have been reported wherein a mixed powder comprising silicon carbide, boron containing additive and carbonaceous additive is compacted and sintered under an inert atmosphere. For example, in accordance with U.S. Pat. No. 4,004,934, it is disclosed that silicon carbide is admixed with a boron containing additive (0.3-3.0% by weight of boron) and a carbon containing additive (0.1-1.0% by weight of carbon) is compacted and then sintered without pressure under an inert atmosphere and temperature of 1900°-2100° C. to give a sintered product having at least 85% of theoretical density.
As mentioned above, in the pressureless sintering process of silicon carbide the raw material for making sintered silicon carbide compacts (hereinafter referred to as sintering material) includes a boron containing additives and a carbonaceous additives as main sintering additives, and further includes in some cases, for example U.S. Pat. No. 4,172,109, beryllium etc. The reason for addition of the boron containing additive is to form an adhesive layer around the surface of the silicon carbide particles due to the coexistence of boron and to promote adhesion between the particles and to advance the uniform shrinkage, while the reason for addition of the carbonaceous additive is to remove silica membrane around the silicon carbide particle formed by reduction which hinders the self-sintering and promote the sintering process and at the same time to control the growth of crystalline grain. The carbonaceous material includes various organic substances or inorganic carbon fines. Therefore uniform dispersion of the above-mentioned additives in the sintering material is effective to obtain high quality products.
Meanwhile sintered silicon carbide compacts having high strength and reliability are desired due to the characteristics of silicon carbide. However, known compacts of high strength have been prepared by use of expensive beta-silicon carbide produced by thermal decomposition of organic silicon compound or silicon carbide produced by specific processes disclosed in for example Japanese Patent Disclosure No. 54-67599. It has been observed extremely difficult to produce high quality of sintered products with silica and carbon with conventional manner.
Inventors of the present application have studied the reason of inferior strength of sintered silicon carbide compacts resulting from the conventional process using silica and carbon, and found that inclusion of relatively coarse foreign matters cause pores and faults in sintered compacts resulting in the above-mentioned inferior strength. Thus it is most important that such inclusion should be avoided as possible.
Conventional methods for obtaining the sintering material without inclusion of such foreign matters which deteriorate the strength of sintered silicon carbide compacts are: (1) the production of the sintering material is performed in an isolated chamber without coarse foreign matters or dusts, and (2) foreign matters and dusts are removed by screen classification or sieve separation. However, the method (1) may be practised in a laboratory scale, but in an industrial scale bulk equipments are required and further a complete prevention of the inclusion is almost impossible. The method (2) is classified into wet and dry filtering processes. The dry filtering process is eventually not practical because of aggregating property of fine powders such as the sintering material which makes dispersion of the powders infeasible. On the other hand, in wet filtering process as disclosed in U.S. Pat. No. 4,004,934, the sintering material is mixed in a dispersing medium solution and passed through a sieve. Unfortunately the sieve shown in the above U.S. patent is of over 200 mesh (74 μm) and insufficient to remove foreign matter larger than 65 μm. Thus it can not be expected to appreciably promote the strength by use of sintering material obtained by filtering process.
One of the inventors has proposed an invention disclosed in Japanese Patent Disclosure No. 57-145076 wherein silicon carbide fine powders preferably admixed with sintering additive or shaping additively is shaped into a green compact and then pressureless sintered at least said silicon carbide fine being dispersed in an organic medium to form a suspensoid. The suspensoid is passed through a sieve of less than 44 μm under the influence of ultrasonic vibration, and then the powder is separated from the medium.
In the above-mentioned process it is not adequate to pass the powder through the sieve after admixture of silicon carbide fines, sintering additive and shaping additive because uniform dispersion of silicon carbide fines, sintering additive and shaping additive having respectively different properties such as specific weight and aggregating property for a long period of time resulting in segregation of the additive and varied proportion of silicon carbide fine, sintering additive and shaping additive giving adverse effects on the property of sintered products.
The present invention provides an improvement of the above-mentioned procedure wherein silicon carbide fine, sintering additive, or shaping additive added as required are placed in a dispersing medium solution to form a suspensoid, said suspensoid is treated through a sieve under pressure differential to remove relatively coarse foreign matters effectively.
As object of the present invention is to provide a feasible procedure for manufacturing silicon carbide sintered compact having high strength and reliability.
According to the present invention silicon carbide fine, sintering additive and shaping additive added as required are placed in a dispersing medium solution to form a suspensoid which is treated with a sieve, then the separated particles are formed into a green shape and pressureless sintered, said solid content of silicon carbide fine and sintering additive in the suspensoid being limited within 10-50% by volume, dispersing medium being added to said suspensoid, pressure differential being given to overcome the pressure loss generated between before and after a sieve of less than 65 μm with or without vibration of the suspensoid to remove relatively coarse foreign matters which cause faults of pores and inclusion thereof to achieve the above-mentioned object.
Since it is important as described above, the sintering material comprising silicon carbide fine, sintering additive and shaping additive added as require should be in a form of uniformly dispersed condition and that said uniform mixture as it is should be subjected to the sieve treatment. As stated above, since silicon carbide fine and the sintering additive respectively having high aggregating property, it is difficult to maintain in a dispersing medium solution. Accordingly, no effective procedure is known to treat the solution with a sieve of less than 65 μm under an uniform suspended condition.
After extensive studies the inventors discovered a new group of dispersing media or agents having high affinity to silicon carbide and the sintering additive to form a suspensoid maintaining its stable suspensing condition for a long period of time to be passed through a sieve of less than 65 μm.
The dispersing medium solutions which may be used for the present invention are classified roughly into water and organic liquids.
According to the present invention when water is used for the dispersing liquid, the dispersing media is at least one selected from a group consisting of amines, organic compounds having carboxyl group, organic compound having sulfo group, esters, ammonium compounds, organic compounds having ether linkage, carboxylic acid salts, aluminates, phosphates, complex phosphates, sulphonates and silicates. These include tetramethyl ammonium hydroxide, monoethanol amine, monoethyl amine, diethyl amine, trimethyl amine, propyl amine, isobutyl amine, monobutyl amine, di-n-propyl amine, tannic acid, sodium alginate, ammonium alginate, polyacrylic acid, polyacrylic acid amine, polyacrylic acid esters, polyacrylic acid ammonium, sodium lignin sulfonate, ammonium lignin sulfonate, sodium aluminate, ammonium aluminate and water glass.
The carbonaceous additives to disperse inorganic carbon fine when used include fatty acid salts, alkylbenzene sulphonates, straight-chain alkylbenzene sulphonates, alpha-olefin sulphonates, sulphonates of naphthalene-formalin condensate, and polyoxyethylene alkyl phenyl ether. These media may be used alone or combination thereof. The pH of the suspensoid may be adjusted with aqueous ammonia to promote the dispersion. It is preferred to adjust the pH within a range of 5.5-11.
On the other hand, when organic liquids are used as dispersing media, one or more members should be selected from a group consisting of amines, organic compounds having carboxyl group or sulfo group, and esters which include polyoxy fatty acid amines, sorbitan fatty acid esters, di-alkylsulfo succinic acid esters, fatty acids, alkyl amine salts and benzene sulfonic acid. When inorganic carbon fine is used as carbonaceous additive preferred dispersing media include polyoxysorbitan fatty acid esters, polyoxyethylene grycerine fatty acid esters, polyethylene glycol fatty acid esters, pentaerythritol fatty acid esters, propylene glycolic acid esters, cane sugar fatty acid esters, polyglycerine fatty acid esters, fatty acid alkanol amide and amineoxides. These may used alone or combination thereof.
The above-mentioned organic liquid include acetone, methanol, ethanol, butanol, hexane, butane, nonan, toluene, oxylene, ethylmethyl ketone, methyl isobutyl ketone, ethyl benzene, ethylene glycol, trichloroethylene, cryclohexane, nitro methane, nitro ethane, isopropyl alcohol, benzene and carbon tetrachloride.
The above-mentioned dispersing media or agents exhibit the effects which disintegrate aggregation of silicon carbide fines and sintering additives in the suspensoid, enhance the uniform dispersion of these particles, and lower the viscosity of the suspensoid to facilate the sieving operation.
According to the present invention, it is required that when silicon carbide fines, sintering additive and shaping additive added as required are suspended in a dispersing medium solution the solid content comprising the silicon carbide fines and the sintering additive should be present in a range of 10-50% by volume of the solution. The larger proportion of the solid content than 50% makes difficult to obtain an uniform dispersion, and to pass the sieve due to a high viscosity, while the smaller proportion than 10% enhances the uniform dispersion but gives an economical disadvantage due to a vast volume in the sieving process. Therefore the preferred rage is within 15-40% by volume.
According to the present invention the preferred range of addition of dispersing medium is 0.05-15% by weight to total weight of 100% of fines plus medium. Because the smaller amount makes difficult to maintain the uniform dispersion which causes ineffective sieving operation, while the larger amount of the medium to be used is not only uneconomical but also remaining medium adversely affect on the sintering operation.
Silicon carbide fines may be alpha-type-crystalline, beta-type crystalline, or amorphous powder, and combination thereof, and have preferably specific surface area of 5-50 m2 /g and oxygen content of 0.1-1.0% by weight, and beta-type crystalline is advantageously used. Sintering additives which may be used for the present invention are primarily boron containing additives and/or carbonaceous additives, and other additives containing beryllium and aluminum.
The above-mentioned boron containing additives include boron, boron carbide, boron nitride, aluminum boride, boron phosphate and combination thereof, and the preferred range of addition is 0.1-3.0% by weight on a basis of boron content. Specifically the additive powder having at least specific surface area of 10 m2 /g is advantageously used.
The above-mentioned carbonaceous additives include phenol resin, lignin sulfonate, polyvinyl alcohol, corn starch, sugar, molasses, coal tar pitch, alginate, polyphenylene, polymethyl phenylene and other organic compounds existing in the form of carbon at the beginning of sintering operation, and thermal decomposing carbon such as carbon black and acetylene black. The preferred range of the addition is 0.5-4.0% by weight, and the particles having at least 50 m2 /g of specific surface area at the beginning of sintering operation are advantageously used.
According to the present invention, a shaping additive may be added to the sintering material as required. Such shaping additive serves as lubricant or binder during shaping operation to minimize shaping defect. These additives serving as lubricant include CARBOWAX (a Registered Trademark of Union Carbide Corporation identifying polyethylene glycol), magnesium stearate, barium stearate, aluminum stearate, zinc stearate and stearic acid. The additive serving as binder include starch, dextrin, gum arabic, casein, sugar, molasses, Na-carboxymethyl cellulose, methyl cellulose, polyvinyl alcohol, polyvinyl methyl ether, polyacrylic amide, tannic acid, liquid paraffin, wax emulsion, ethyl cellulose, polyvinyl acetate and phenol resin etc. The additives having both effects as lubricant and binder include cellulose acetate, glycerol and polyethylene glycol, and these may be used alone or combination.
In the present invention, it is required to uniformly disperse the suspensoid before the sieving operation. Since the silicon carbide fines and sintering additives used for the invention have high aggregating property, when they are dispersed in a dispersing medium solution they are in the coagulating condition which hinders the sieving operation.
Uniform dispersing treatment may be carried through vibrating mill, Attoritor, ball mill, colloid mill, or high speed mixer. When a dispersing process is carried with agitation using impeller or screw, disintegration of the coagulation is insufficient, and the sieving operation can not be performed effectively. The former devices provide a strong shearing force and produce the desired uniform dispersion for short period of time.
Alternatively, the suspensoid is advantageously subjected to vibration of 1-400 Hz, because a standing suspensoid often settle the powders into coagulation which makes almost impossible the sintering operation. Also the vibration lowers the viscosity of the suspensoid to facilitate the sieving operation. A lower frequency than 1 Hz is insufficient for a uniform dispersion and lowering viscosity, while a higher frequency than 400 Hz exhibits a poor transmittance through the suspensoid. Thus the range of 1-400 Hz preferably 2-100 Hz is suitable.
Vibration applied to the suspensoid may be generated from mechanical or magnetic sourse or pulsating pump.
In the present invention, the pressure loss in the suspensoid before and after the sieve which causes stagnation of the flow may be compensated by an application of pressure differential to promote the flow through the sieve.
In accordance with the present invention the pressure applied above the sieve is desirably varied periodically in a range of 1/400-2 seconds. The periodical application of pressure may cause agitation in the suspensoid to promote the dispersion of silicon carbide fines and sintering additive and facilitate the sieve passage. A shorter period than 1/400 second retards the transmittance of the pressure fluctuation while a longer period than 2 seconds causes a low agitation. The preferred range is of 1/100-1.5 seconds.
In accordance with the present invention, the pressure applied above the sieve should have a pressure differential at least 0.5 kg/cm2 between the maximum and minimum values, and at the maximum pressure application the pressure differential between the before and after sides of the sieve should be in a range of 0.2-5 kg/cm2, while at the minimum pressure application such range should be -0.5-2 kg/cm2. The above-mentioned pressure differential means the pressure value before the sieve substracted by the pressure value after the sieve.
When a pressure is applied to the suspensoid, various devices may be used, but a pulsating pump is advantageously used because it provides both pressurization and vibration simultaneously. One type of the pulsating pump is diaphragm pump.
In the present invention, an ultrasonic vibration may be applied to the suspensoid just above the sieve to further promote the dispersion of silicon carbide fines and sintering additive.
The sieve used for the present invention should have an opening less than 65 μm. A larger opening than 65 μm can not remove coarse foreign matters, and hence an opening lesser than 44 μm is to be used to obtain a sintered product having the desired characteristics. Fine foreign matters passing through an opening of 5 μm do not adversely affect the product but require a long sieving operation. Therefore, the preferred range of opening of 5-44 μm is selected for the present invention.
The suspensoid after the sieving operation or filtering may be processed through the wet shaping as it is, or through dry process after the removal of the dispersing medium solution and drying into a green shape.
The removal of the solution from the suspensoid and drying should be carried out maintaining a uniform mixing condition.
The removal of the solution may be performed; (1) spray drying for removing the solution in a short period of time by evaporation, or (2) freeze drying wherein a suspensoid is freezed in an atmosphere at a temperature lower than the melting point of the dispersing medium solution which may be removed by sublimation.
In the above (1) spray drying, segregation of sintering additive or shaping additive may be prevented due to the removal of the dispersing medium solution with evaporation, and the process may be carried out for a relatively short period of time. Therefore, in this process it is advantageous that the sprayed dropplet has as smaller diameter as possible. Further this process has an advantage to obtain powder material having an excellent fluidity.
In the above (2) freeze drying, the dispersing medium solution may be selected from a group consisting of cyclohexane and benzene, and water also may be used. In this drying process, the suspensoid is sprayed in an atmosphere maintained at a lower temperature than the melting point of the dispersing medium solution, then the frozen solution is dried up under a reduced pressure by sublimation. Since the sprayed dropplet provides a rapid heat exchange preventing the segregation of the fines and additives. The drying with sublimation also prevents the segregation of the fines, sintering additives and/or shaping additive while the uniform mixing condition is maintained. The freeze drying process also gives powder material having excellent fluidity and compactibility.
In the present invention, the process from the sieving or filtering operation to the shaping or compacting operation is advantageously practised in an isolated chamber free from coarse foreign matters, but subsequent operation after the shaping to green compact does not require such chamber.
According to the present invention, green shape produced as above are placed in a sintering furnace and sintered under an inert gas stream under a temperature range of 1900°-2300° C. to produce silicon carbide sintered compacts having a high strength and reliability.
The present invention will be described in detail on preferred embodiment with relation to the accompanying drawings.
FIG. 1 shows a diagram representing relationships between fracture strength and fracture probability of sintered compacts described in Example 1.
FIG. 2 shows a diagram representing relationships between fracture strength and fracture probability of sintered compacts described in Comparative Example 1.
FIG. 3 shows a diagram representing relationships between fracture strength and fracture probability of sintered compact described in Comparative Example 2.
Silicon carbide fines consisting primarily of beta-type crystalline are produced by a process disclosed as in U.S. Pat. No. 4,162,167, refined and classified.
The silicon carbide fines comprise 97.6% by weight of beta-type crystalline, 0.41% by weight of free carbon and 0.14% by weight of oxygen, having the specific surface area of 17.8 m2 /g.
As a carbonaceous additive oil furnace black having an average particle size of 210 A and a specific surface area of 125 m2 /g was used.
10 g of said oil furnace black was mixed with 10.0 g of polyoxyethylene nonylphenol ether and 100 ml of distilled water, and the mixture was blended in a ball mill for 20 hours. 500 g of silicon carbide fines, 6.5 g of boron carbide powder having a specific surface area of 22.7 m2 /g, 190 ml of distilled water, 5.0 g of cellulose acetate and 5.0 g of tetramethyl ammonium hydroxide were added to the mixture and dispersed in Attoritor for 5 hours. The suspensoid was discharged from Attoritor, then passed through a sieve with a diaphragm pump under an application of vibration of 15 Hz. A sieve having an opening of 25 μm and a sieve frame of 200 mm diameter were used, and ultrasonic vibration of 26 KHZ, 600 W was applied to the suspensoid above the sieve. A pulsating pressure having the maximum value of 2.0 kg/cm2, the minimum value of 0 kg/cm2 and a fluctuation period of 1 second was applied to the suspensoid, and the pressure below the sieve was opened to the atmosphere. The passing rate of the suspensoid was 0.13 g/cm2 ·sec. Discharged suspensoid from Attoritor was measured of its viscosity as 59 g/cm2 ·sec with a B-type viscosimeter provided with Roter No. 4 at a rotating speed of 60 rpm.
The dispersed suspensoid was sprayed into a chamber maintained at a temperature of -60° C. to obtain freezed powder having an average particle size of 0.11 mm. The powder were dried in a chamber maintained at a pressure of 0.01-20 mmHg and a temperature of -5°--10° C. to obtain dried powder having a bulk density of 0.72 g/cm3.
An amount of the powder was preshaped into a shape with a metal die under a pressure of 0.15 t/cm2 into a green shape. The shape was sintered in Tammann furnace under argon atmosphere. The sintering operation was held at the maximum temperature of 2100° C. for 30 minutes.
The sintered compact showed a density of 3.14 g/cm3. Then the compact was machined into a bar of 3×3×30 mm and finished with diamond dusts of 2 μm size. The finished bar was measured of its bending strength as 70.8 kg/mm2 at the room temperature by the three point bending test machine having a span of 20 mm and the cross-head speed of 0.5 mm/min. Weibull factor of the compact is shown in FIG. 1 of a value of 15 which ensures high strength and reliability. The tests were carried on 30 pieces of sample and Weibull factor was calculated from Weibull logarithmic chart. The above-mentioned Weibull factor is calculated from a diagram showing the relationship between fracture stress and remaining probability in Weibull statistics generally used for measurement of ceramic strength which represents the reliability of fracture.
Same materials and procedure as in Example 1 were used provided that silicon carbide fines and sintering additive powder were passed through a sieve of 25 μm to remove coarse foreign matters. A sintered compact was produced without sieving operation after the uniform mixing of the materials.
The sintered compact exhibited a density of 3.15 g/cm3. The compact was measured of its strength in the same manner as in Example 1 and the average strength at the room temperature was 65.7 kg/mm2. Weibull factor is 11 as shown in FIG. 2, and the average strength and reliability were inferior to that obtained in Example 1.
Same materials and procedure were used provided that volumetric proportion of solid content comprising silicon carbide fines and sintering additive powder, amount of dispersing agent added, vibration applied to suspensoid, sieve opening, period of pressure fluctuation, maximum and minimum pressure to suspensoid and passing rate through a sieve were varied as shown in Table 1 with the results.
TABLE 1__________________________________________________________________________ Dispersing agent C Dispersing Tetra- oil medium Suspensoid Polyoxy- methyl furnace solution Viscosity ethylens ammonium SiC B4 C black water Conc. (g/cm, nonyl hydroxide (g) (g) (g) (ml) (Vol %) sec) phenol (g) (g)__________________________________________________________________________Ex.1 500 6.5 10 290 36 59 10.0 5.02-1 500 6.5 10 200 45 205 10.0 5.02-2 500 6.5 10 650 20 18 10.0 5.02-3 500 6.5 10 290 36 43 34.0 17.02-4 500 6.5 10 290 36 71 2.0 1.02-5 500 6.5 10 245 40 113 10.0 5.02-6 500 6.5 10 245 40 113 10.0 5.0Compara- 500 6.5 10 135 55 420 10.0 5.0tiveExample 3__________________________________________________________________________Sieving operation Rate Pressure to suspensoid Sintered compactOpening (g/cm3, Freq. Max. Min. Period Density Strength Weibull(m) sec) (Hz) (kg/cm2) (kg/cm2) (Sec.) (kg/cm3) (kg/mm2) factor__________________________________________________________________________Ex.1 25 0.13 15 2 0 1 3.14 70.8 152-1 25 0.02 15 4 -0.2 1/10 3.15 68.8 162-2 25 1.2 4 1 0 1/10 3.12 67.4 152-3 25 0.13 15 1.5 0 1 3.14 69.4 152-4 25 0.08 15 2.5 0.5 1 3.14 69.9 142-5 63 0.46 100 2 0 1/2 3.15 62.6 112-6 25 0.02 350 3 -0.3 1/2 3.15 68.5 15Compara-63 -- 10 1.5 -0.2 1/2 -- -- --tiveExample 3__________________________________________________________________________
Similar mixtures to Example 1 were used provided that in place of polyoxyethylene nonyl phenol ether, fatty acid salts, alkyl benzene sulfonates, straight chain alkyl benzene sulfonates, alpha-olefin sulfonates, sulfonate of naphthalene-formalin condensate and polyoxy ethylene alkyl ether were used respectively to prepare the suspensoids. The same procedure as Example 1 was repeated to obtain sintered compacts which showed the desired properties.
Similar mixtures to Example 1 were used provided that in place of tetramethyl ammonium hydroxide, monoethanol amine, monoethyl amine, diethyl amine, triethyl amine, propyl amine, isobutyl amine, monobutyl amine, di-n-propyl amine, tannic acid, sodium alginate, ammonium alginate, polyacrylic acid, polyacrylic acid amine, polyacrylic acid ester, polyacrylic acid ammonium, sodium lignin sulfonate, ammonium lignin sulfonate, carboxymethyl cellulose, sodium aluminate, ammonium aluminate and water glass were used respectively to prepare the suspensoids. The same procedure was repeated to obtain sintered compacts which showed the desired properties.
10 g of polyoxyethylene dodecyl amine and 100 ml of benzene were added to 10 g of oil furnace black used in Example 1 then mixed in a ball mill for 3 hours. To the resulting mixture, 500 g of silicon carbide fines used in Example 1, 6.5 g of boron carbide powder used in Example 1, 25 ml of benzene, 5.0 g of dioctyl succinic acid ammonium and 5.0 g of polyethylene glycol were added and dispersed in a vibrating mill for 4 hours. The resulting suspensoid is discharged under the operation of the mill, and subjected to the sieving operation under the conditions of 200 Hz of vibration, maximum pressure of 1.5 kg/cm2 and minimum pressure of -0.2 kg/cm2, pressure fluctuation period of 1/2 second and sieve passing rate of 0.28 g/cm2 ·sec. Viscosity measured as in Example 1 was 42 g/cm·sec.
Suspensoid resulting from the above procedure was sprayed into a vessel maintained at a temperature of -50° C. to obtain freezed powders having an average particle size of 0.11 mm. The powders were dried in a vessel maintained at a pressure of 0.11-20 mmHg and a temperature of 0°--5° C. The resulting dried mixture had a bulk density of 0.68 g/cm3.
An amount of the dried mixture was pressed and sintered under the same procedure as Example 1 to obtain a compact having a density of 3.16 g/cm3. The compact showed a strength at room temperature of 69.2 kg/mm2 (average) and Weibull factor of 14.
8 g of propylene glycol fatty acid ester and 100 ml of acetone were added to oil furnace black used in Example 5 and the mixture was blended in a vibrating mill for 1 hour. 500 g of silicon carbide fines used in Example 1, 6.5 g of boron carbide powder used in Example 1, 470 ml of acetone, 5 g of polyethylene glycol, and 5 g of sodium dioctyl sulfosuccinate were added to the mixture, and dispersed in Attoritor for 4 hours to form suspensoid. The suspensoid was subjected to sieving operation as in Example 5 and sprayed into a vessel maintained at a temperature of -80° C. to obtain dried mixture in powder form. Viscosity of the suspensoid was 15 g/cm·sec.
An amount of the dried mixture was compacted and sintered as similar procedure as Example 1.
The sintered compact showed a bending strength at room temperature of 62.4 kg/mm2 (average) and Weibull factor of 13.
350 ml of benzene, 10 g of sorbitan mono-oleate and 10 g of polyethylene glycol were added to a mixture comprising 500 g of silicon carbide fines used in Example 1, boron carbide powder used in Example 1 and 19.4 g of novolak-phenol resin containing 51.6% by volume of fixed carbon, and dispersed in a vibrating mill for 6 hours to obtain a suspensoid. Viscosity of the suspensoid was 48 g/cm·sec. The suspensoid was subjected to sieving operation as in Example 5 and spray dried to form powders. Sintered compacts were obtained under the same procedure as in Example 5.
The compact showed a density of 3.14 g/cm3, a bending strength at the room temperature of 68.5 kg/mm2 (average) and Weibull factor of 14.
As mentioned as above, in accordance with the present invention coarse foreign matters may be removed from sintering materials with which a sintered compacted having high bending strength and reliability may be produced at a relatively low cost.