Mekanisme Sintering dalam Teknologi Keramik

Dalam ilmu fisika dan teknologi keramik, pembahasan mengenai keramik bukan hanya terdiri dari struktur keramik baik secara makro maupun mikro. Keramik dalam ilmu fisika dapat diartikan sebagai sebuah bahan yang memiliki sifat mekanis yang tinggi namun memiliki kelemahan berupa sifatnya yang getas/ mudah patah. Perkembangan teknologi fisika mengenai keramik tidak seperti keramik yang kita kenal. Keramik-keramik yang ada dirumah pada umumnya merupakan satu kategori dari berbagai kategori dalam keramik fisika. Sebut saja seperti keramik gelas, keramik karbon, keramik elektronik dan lain sebagainya.

Pada umumnya, keramik tradisional yang kita lihat melewati 2 tahapan umum dalam pembentukannya. Tahapan awal berupa pembentukan keramik yang diawali dengan tanah liat yang basah kemudian dibentuk dan setelah itu dikeringkan dengan cara dijemur dengan menggunakan matahari, ataupun dibakar atau dalam ilmu fisika disebut dengan Sintering. Oleh karena itu, langsung saja berikut penjelasan sederhana mengenai Sintering.

Ilmu fisika dan teknologi keramik mengemukakan 3 tahapan dalam pembakaran keramik untuk menghilangkan sifat airnya sehingga memiliki sifat mekanik yang tinggi. 3 Tahapan tersebut dikenal dengan istilah Mekanisme Sintering yang berupa:

Proses Kalsinasi. Merupakan sebuah proses di mana keramik mendapatkan perlakuan panas untuk menghilangkan zat-zat yang tidak diinginkan (300-500 derajat celcius) dalam jangka waktu lebih dari 1 jam. Sehingga bahan keramik yang diproses melalui sintering akan terhindar dari bahan-bahan pengotor.

Proses Pembakaran. Pembakaran belum tentu sintering tetapi sintering diperoleh melalui pembakaran.

Proses Karakterisasi. Dalam proses ini bahan keramik mengalami perlakuan pengujian dan pengamatan terhadap sampel uji. Dimana dalam perlakuan pengamatan dan pengujian dapat diuraikan sebagai berikut;

• Pengujian
• Sifat Mekanik
• Sifat Listrik
• Sifat Termal
• Sifat Optik

• Pengamatan
• Permukaan Struktur Keramik
• Pengamatan secara kualitatif dan kuantitatif
• Pertumbuhan butir
• Batas butir
• Ukuran butir

A General Explanation about Periodic Table

When you learn the exact sciences, especially in the fields of science such as physics and chemistry as well as engineering sciences and the application of science of course, you will be faced with the problem of how everything around us is formed, nothing is causing it all to form. However, my point here does not mean taking the principle of causality that leads to God the creator, but rather speaks to the flow of natural phenomena. 

Once upon a time, people saw the phenomena of nature occurring is a natural power that can not be followed. However, the development of science and technology has been growing rapidly teaches us how all the good things that are objects or events that are providing a scientific perspective to analysis and identify it. In 1869, when a chemical scientist from Russia published a journal about the elements is the reason why the world was created. Dmitri Mendeleev which is a chemical scientist who publishes word form Periodic Table of Elements is the reference for every student in the world to create new technologies that can solve every human problem on earth. 

Periodic Table of Elements is a method of classifying the elements that exist in this world, especially in the planet that describes the characteristics or attributes of the elements complete with electron configuration, atomic radius, atomic number indicates the number of protons and electrons, nature of the radioactivity of an element, electronegativity and others. This method helps students, especially among students and scientists in developing the technologies of the past, present and future.

In this method the elements of the periodic system there are rules about the period and group of the periodic system of elements due to the systematic preparation in a table. The system has the form:

Group. Often called a group or family in the periodic table of elements is a vertical column of elements in the periodic table. Naming class system is often used in teaching the properties of elements such as the number of outer electrons of each element. Here are some commonly used naming groups of scientists in classifying these elements:

• alkali metal
• Alkaline earth metal
• Boron Group
• Carbon Group
• Nitrogen Group
• Oxygen Group
• Halogen Group
• Noble Gas Group
• Transition Metal

Period. It is an arrangement of elements in the periodic system of elements vertically from left to right stating atomic radii and electronegativity properties and stability elements. Arrangement is called the period commonly used is the first period, the second, third as well lanthanides and actinida period.

 

The methods commonly used in determining the elements in the polymer

When a compound is connected with the same compound is formed of a continuous chain that has certain characteristics. In a simple sense that I explain what is called the polymer. As has been mentioned in books written in general polymer as a polymer composed of long strands of each monomer binding to the monomer. The length of the string or chain can reach hundreds or even thousands of interconnected monomer. In its website, wikipedia writing A polymer is a large molecule (macromolecule) composed of repeating structural units. These sub-units are typically connected by covalent chemical bonds. Although the term polymer is sometimes taken to refer to plastics, it actually encompasses a large class of compounds comprising both natural and synthetic materials with a wide variety of properties.

Image from Wikipedia

In the current technological developments, many experts in physics, chemistry and polymer material that is the future of materials that are easy to come by. So great expectation addressed to polymeric materials to you, I am curious as well as a lot of people. No wonder that many experts in physics, chemistry, and material has been doing various kinds of research in the field of polymer so that the polymer at the present time this is a category of commercial polymers, such as call it petroleum, plastic gutter pipe PVC, textile polymers, polymer electronics and various other types.

However, in this article we will discuss what is called the polymer but rather how the methods are generally made by people to determine the constituent elements of the polymer. Of course as we know, the formation of a polymer or polymer synthesis / polymerization reactions of polycondensation and polymerization, which is then divided into a variety of methods. Because there are so-called synthetic polymer which constituent elements must exist and how to identify these polymers. The following methods are commonly used by experts that I took from the book by Mr. Anton J. Hartomo:

Classical methods. By performing the cremation-gray, fusion, acid digest or acidification and digest the bomb to the polymer.

Image from Google.com/imghp

By using the cremation-gray method consists of several ways:

• Cremation without catalytic substances. The process of cremation is done by burning the polymer in a platinum crucible with controlled conditions (as polymer), dissolved in an aqueous reagent, and then analyzed by spectrophotometry. This method is cumbersome and time consuming. Effectiveness of these elements can be different after that. Analysis of the alkali metal is more critical than on the transition metal catalyst.
• Cremation with catalytic substances. The process of cremation is required where the elements are going to be analyzed may be lost when the process is carried out. For example, copper can be reduced and attached to the crucible wall. that is why it was added a solution of inorganic salts, for example magnesium nitrate. When the bulb, the said elements in a matrix of magnesium oxide awake so easily dissolved in a suitable acid and analyzed. The addition of inorganic salts and acids taken in the presence of organic solvent (alcohol) as appropriate.
• At low temperatures the cremation furnace. The process is conducted in a furnace with air oxygen is activated by a cloud of electric charge or with ultraviolet light. Active oxygen to burn the polymer, and the risk of loss of the element being analyzed is smaller because the temperature is lower. Examples of use in the determination of rare metals in the polymer PP, PS and so on.

Then the fusion method can be performed using sodium carbonate, sodium bisulfate, and sodium peroxide. Of fusion with sodium carbonate is very good for the polymer which when in the incandescent-issued gas / vapor acids, such as PVC. Steam trap can be determined with a solid base in the reagent. Ash residue is dissolved in nitric acid, diluted acetone, potentiometric titration using standard silver nitrate.  

Digest method (Kjehldahl) acid. By using this method in addition to the determination of organic nitrogen, more or less the method is also used except in special cases. While oxygen to the combustion vessel used in the analysis of polymers such as the determination of sulfur in the polyolefin, determining chlorine in the rubber khlorobutil and PVC, phosphorus in polyolefins. 

Instrumental Methods of Engineering Analysis. This method is used to analyze the elements in the polymer consist of non-faulty techniques such as X-ray fluorescence and neutron activation analysis, as well as destructive techniques (sample described with specific reagents) such as atomic absorption spectrometry, emission Spectrograph, flame photometry, polarography, and etc..

• X-ray fluorescence spectrometry. Analysis instrument was used for the determination of micro amounts of metal or non metal; also for the content of metals such as cadmium selenide pigments in polyolefins. The advantage lies in the technique that does not destroy the sample, making the specimen is easy, fast and the measurement of content of chemical elements do not depend on the state of incorporation. However, drawbacks include the excitation of many disorders other elements in the matrix polymer. This method is often applied to the determination of industrial elements chlorine, bromine, titanium, aluminum, sodium, potassium, calcium, magnesium and vanadium on a hot plate of felt-PP and PE.
• Neutron activation analysis. This analysis technique can determine the various elements such as chlorine in polyolefins, metals in PMMA, the total oxygen in the copolymer and the PE-vinyl acetate PE-ethyl acrylate as well as the polyolefin. This method is superior because it is very sensitive and hassle free. Disadvantage, must be made in nuclear reactors. However, the results are very good and reliable.
• Atomic absorption spectroscopy (AAS). Often used for metal determination. Samples prepared in the form of an appropriate solution. Certain elements (As, Sb, Hg, Se, Sn) after the polymer has the digest, transformed into a hybrid form of gas using SnCl2 reagent or sodium borohydride.
• Electron probe microanalysis. For this method is used to determine the metal inclusions in the polymer film and sheet. Samples were fired with a narrow beam of X-ray and electron scattering a certain frequency beyond scrutiny. Scattering image corresponding atomic number elements. X-ray beam emitted is detected and enumerated with a special tool or using the detector.

By using the above methods can be determined qualitatively or quantitatively, or in both the qualitative and quantitative elements of the polymer. The goal of science can be used both in order to identify the type of polymer that is not known or commercially in order to control the process. Both of the above techniques of classical technique and modern techniques that use instruments. For so this article, may be beneficial to us all. 

 

Reference:

Penuntun Analisis Polimer Aktual work by Anton J. Hartomo. Penerbit Andi Offset Yogyakarta.

http://en.wikipedia.org/wiki/Polymer  

 

Several factors that affect plant growth and development

Plants (flora) is a unit in a living ecosystem. Plants are also part of what is called a living creature. Of course, as living beings, plants have characteristics similar to other living creatures. As with the growth and development. The process of growth and development experienced by plants in order to process a higher level. Of course, the process is also influenced by several factors relating directly or indirectly. Here are some of the processes that affect plant growth and development:

Internal factors

In influencing the development and growth in plants, internal factors related to genetic and physiological factors include the plant. Both of these factors can be described in more deeply because it contains a variety of circumstances.

• Genetic factors.  Growth and development process starts from the germination process. This process begins with water uptake (inhibition). Water is then absorbed into the body resulting in dissolution of pieces of food that is in pieces of the institution. Besides dissolving food, absorb water also serves as a substance-induced lawyer for hydrolytic enzymes. After that the enzyme will be controlled by the genes of plants. Germination process also requires that the metabolic processes of plants can live. This metabolic process requiring metabolic enzymes support that aims to regulate the metabolic rate of growth and development of plants that can be set to be optimal. And it's all arranged by the genes of plants.
• Physiologcal factors. Of origin of the word, physiological factors are factors derived from the functional processes at the cellular level in plants. All activities conducted by plant cells also affect the process of development and growth in plants. Growth and development will involve a variety of hormones and vitamins. Hormones and vitamins have specific functions at each level of growth and development. Hormones that affect growth and development are as follows Hormone auxin, gibberellin, ethylene, cytokinins, absisat acid, Kalin, traumalin acid, antokalin, filokalin, rhyzokalin and kaukokalin, addition of hormones, vitamins also affect growth and development. Examples are vitamin riboflavin, ascorbic acid, thiamine, pyridoxine, and nicotinic acid. Vitamins serve as components that are capable of activating the enzyme.

External factors 

External factors have an influence equal to the internal factors in the growth and development. In the process, external factors are factors that are outside the parts of a plant, an existing environment around the plant. These external factors that affect plant growth and development.

• Temperature. When it comes to temperature, it will not be separated from the process of photosynthesis, respiration, and evaporation in plants. Temperature affects the water content in plants that is one thing that is important in the growth and development. Temperature also affects the performance of enzymes that exist in plants. In general, temperatures will damage important parts of the plant when the temperature is high, so if too low will make the important parts do not work optimally or even not working. Optimal temperatures in plants is also different. So, temperature is the most important factor in the first category of external factors.
• Sunshine. Sun light affects green plants because sunlight will determine the photosynthesis process of plants. Photosynthesis is the fundamental process in plants to produce energy that will be used as the initial capital in the growth and development. Besides, in the process of photosynthesis, sunlight also affect plant growth physically. Plants that grow in the dark will grow faster but with the condition of pale, thin, and its leaves do not grow because of the hormone auxin is not spread and are not optimal.
• Water, pH, and oxygen. Water serves to determine the rate of photosynthesis, as the universal solvent in the process of growth and development, to determine the transport of nutrients in the soil and distribute the results to all parts of plant photosynthesis. Factor pH (or acidity) that directly affect the state of soil acidity. Minerals and nutrients derived from land, when the soil has a high acidity, it is mostly absorbed acidic compounds. So that the acid compound is absorbed so high, it is very disrupting the growth and development. Oxygen is a limiting factor in any organism. These conditions make the organisms need oxygen. Parts of plant roots require good aeration to get oxygen. Good aeration to improve root respiration process to circulate nutrients in the soil to the leaves.
• Nutrition. Plants need nutrients for its survival. Nutrients needed in large quantities such as carbon, oxygen, hydrogen, nitrogen, sulfur, potassium, calcium, phosphorus and magnesium. These elements are referred to as the mean macronutrient nutrients needed by plants in large numbers. In contrast, elements such as chlorine, iron, boron, manganese, zinc, copper, and molybdenum merupakn micronutrient elements, which means the elements needed in small amounts. Nutrients needed for plants not deficient, that is to grow and develop imperfectly. 

 

The role of food additives in human life

As it is known that a food additive used in food industries to improve the quality of processed food, and the use of food additives is justified only if it is intended for the following purposes:

• To maintain the nutritional value of food. For example, the addition of antioxidants such as BHA (butyl hydroxy-anisol) in the processing of vitamin A will maintain vitamin potency when added to food. 

• For the consumption of a particular class of people who need food. For example, the addition of artificial sweeteners such as saccharin in food or drink, so it does not add calories to the food.

• To maintain the quality or stability of food or to improve the properties of its organoleptic to not deviate from nature, and can help reduce food waste disposed. Preservatives play an important role in extending the shelf life of various types of food, making it possible for these foods are transported long distances, stored for a long time, but it still can still be safely consumed. WHO estimates that 20% of the world's food supply is lost or damaged due to decay. Without the use of preservatives such percentage will be higher.

• For the purposes of manufacture, processing, supply, treatment, the container, packaging, transfer, or transportation. Some foods in the processing process requires the use of materials, such as stabilizers, cleaning materials, and metal binder. The use of these materials allows for large-scale industrial production of food composition and quality are constant throughout the year.

• Make food more attractive. The use of food additives, such as dyes and textures repair materials varies so that the final product will have the appearance, taste, and appearance is always the same every time.

The use of food additives are not permitted for the purpose of:

• Hiding the use of incorrect or that do not meet the requirements.
• Contrary to conceal the workings of a good way for food production.
• Hide damage to food.

The Thermal Characteristic of Chromium

Chromium is hard, lustrous silvery metal which can take a high polish. It is a transition element with atomic number 24 and atomic weight 51,996. It has body-centered cubic crystalline structure and it is anti-ferromagnetic below 311.5 K and para magnetic above this Neel temperature. Naturally, occurring chromium is composed of four stable isotopes and five radioactive isotopes are known to exist, which half-lives ranging from 3.5 minutes for Cr-55 to 27.8 days for Cr-51. The most abundant isotopes from chromium is Cr-52 which has a constitutes about 83.76%.

Chromium in nature cannot move free as an unsure, but it stable with a compound called chromite (FeO.Cr2O3), from which the metal can be obtained directly by reduction with aluminum. Chromium is widely used in alloys as a hardening and anti-corrosion agent. It is the critical ingredient in all stainless steels. In combined form it is also used as a coloring agent, since all of its compounds are highly colored. In addition, it has many uses as a chemical catalyst. The structural stability of its ore, chromite, under heating makes it a useful form material in refractory processing.

Thermal Conductivity. At low temperatures a series of measurements is reported by Harper et al. On chromium specimens of increasing purity, with residual resistance ratios from 47-217 range. Below about 20 K the intrinsic thermal resistivity does not correlate well with the static defect scattering parameter beta, and consequently interpolating at these temperatures is uncertain. At higher temperature up to about 50 K, however, it is dependence for the intrinsic thermal resistivity as expected.

At temperatures above 100 K, within 1 percent with an earlier set reported for the measurement on iodide chromium having 280 of Residual Resistance Ratios (RRR). At high temperatures the thermal conductivity is obtained as a product of thermal diffusivity, specific heat, and density with thermal diffusivity. These derived thermal conductivity values lie about 3-4 percent and at temperature 1500 K and up to 1650 K the values decrease rapidly, about 20 percent at 1650 K. This reduction is attributed to effects of vacancy formations.

The recommended values for thermal conductivity are given for well-annealed chromium of purity 99.99 percent or higher. At temperatures below 100 K however, they are applicable only to chromium with residual resistivity of 0.616 nano-ohm-meter as obtained from the Wiedemann-Franz law.

Alloys composition and crystallization

An alloy is a mixture of materials which have metallic properties, composed of 2 or more components (elements) and at least a main component is metal. 

In general, inter-metal solubility is limited due to the limited replacement of atoms by other atoms or limitations of other atoms between the atoms in the crystal lattice arrangement known in the metal, namely:
Simple cubic not mean so simple but can mean that this structure has only one full unit cell as a unit again, it could be this cubic structure is the most complicated structure among the existing structure, among other example is the Carbon and Manganese. 

Face Centerred Cubic namely cubic structure similar to the BCC it appears in the presence of an atom at each corner of the unit cell and there is one atom longer at the center of each side of the cube, among others, for example, austenite Iron, Copper, Nickel, Platinum, Iridium, and Rudium. 

Based Center Cubic means every atom in the metal structure is surrounded by eight nearest atoms either atom is located at the corner or in the center of the unit cell so that each atom has approximately the same environment, among others, for example iron Ferrite, Molebdium, chromium, vanadium, thallium. 

Hexagonal arrangement of the meeting is the arrangement of the structure which has very regular basis because of certain atoms have the same angle and length, among others, for example zinc, Zirconium, Magnesium, Rhenium.
The composition of these crystals to determine the physical and mechanical properties of metals. Changes in the composition of the crystal lattice due to mixing of metal atoms resulting in changes in crystal plane spacing and number of neighboring atoms that determine the bond atoms will carry the binding effect on physical properties and mechanical.
Crystallization
Crystallization is a process of crystal formation that occurs during freezing, the phase change from liquid to solid phase. Viewed from the crystallization mechanism occurs in 2 stages: - Establishment of core or nucleation - Crystal growth
In the liquid state, the atoms do not have a regular arrangement of certain, in a liquid state, its temperature is relatively high and the atoms have enough energy so it is easy to move, no later arrangement of atoms relative to other atoms.