Silika Dioksida 4a3d2

SILIKA DIOKSIDA (SiO2) Senyawa apakah itu? Merupakan suatu mineral yaitu mineral silikat. Secara garis besar, mineral dibagi menjadi 3 yaitu mineral silikat, mineral oksida dan mineral sulfide. Mineral silikat merupakan persenyawaan antara silicon dan oksigen dengan beberapa metal. Mineral silikat dibagi menjadi 2 yaitu feromagnetik (mengandung ion besi dan / magnesium) dan nonferomagnerik.

Nama mineral Rumus Kimia Berat jenis System Kristal Warna

: Kuarsa : SiO2 : 2.65 : heksagonal : tidak berwarna (laboratorium kristalografi dan mineralogy, 2013)

bagaimana karakteristiknya? Silikon dioksida terbentuk melalui ikatan kovalen yang kuat, serta memiliki struktur lokal yang jelas: empat atom oksigen terikat pada posisi sudut tetrahedral di sekitar atom pusat yaitu atom silikon. Berikut ini struktur lokal dari silikon dioksida:

Gambar 1. Struktur Lokal Silikon Dioksida Atom oksigen bersifat elektronegatif dan kerapatan elektron pada atom silikon sebagian ditransfer pada atom oksigen, tetapi tidaklah tepat jika silika dikatakan sebagai garam yang terdiri dari ion Si4+ dan ion O2-, yang terkadang ditemukan dalam beberapa literatur. Untuk memahami hal ini maka dapat dilihat melalui arah ikatan (momen dipol) pada struktur silika. Sudut ikatan di sekitar O-Si-O merupakan sudut tetrahedral yaitu sebesar 109⁰; jarak antara atom Si-O sebesar 1,61 Å (0,16 nm). Silikon dioksida memiliki ikatan yang disebut “jembatan” oksigen yang terdapat diantara atom silikon, hal inilah yang memberikan sifat unik pada silikon dioksida. Sudut ikatan pada Si-O-Si sekitar 145⁰, tetapi

nilai ini sangat bervariasi antara 100-170⁰ yang dipengaruhi oleh perubahan energi ikatan, Sehingga sangat memungkinkan terjadinya rotasi ikatan secara bebas.

Gambar 2. Sudut Ikatan Si-O-Si Cara yang cukup mudah untuk mengamati struktur SiO2 adalah dengan menggunakan model Zachariesen-Warren. Struktur SiO2 terbentuk melalui kelompok-kelompok SiO4 yang saling berikatan melalui atom oksigen pada sudut-sudut tetrahedralnya, ikatan ini dapat terbentuk dalam berbagai variasi sudut. (Risars, 2008). https://risars.wordpress.com/2008/11/21/struktur-padatan-silika/ Asal bahan? Even though it is poorly soluble, silica occurs widely in many plants. Plant materials with high silica phytolith content appear to be of importance to grazing animals, from chewing insects to ungulates. Studies have shown that it accelerates tooth wear, and high levels of silica in plants frequently eaten by herbivores may have developed as a defense mechanism against predation.[26][27] It is also the primary component of rice husk ash, which is used, for example, in filtration and cement manufacturing. Silicification in and by cells has been common in the biological world for well over a billion years. In the modern world it occurs in bacteria, single-celled organisms, plants, and animals (invertebrates and vertebrates). Prominent examples include: Tests or frustules (i.e. shells) of diatoms, Radiolaria and testate amoebae.[6] Silica phytoliths in the cells of many plants, including Equisetaceae, practically all grasses, and a wide range of dicotyledons. The spicules forming the skeleton of many sponges. Crystalline minerals formed in the physiological environment often show exceptional physical properties (e.g., strength, hardness, fracture toughness) and tend to form hierarchical structures that exhibit microstructural order over a range of scales. The minerals are crystallized from an environment that is undersaturated with respect to silicon, and under conditions of neutral pH and low temperature (0–40 °C). Formation of the mineral may occur either within the cell wall of an organism (such as with phytoliths), or outside the cell wall, as typically happens with tests.[clarification needed] Specific biochemical reactions exist for mineral deposition. Such reactions include those that involve lipids, proteins, and carbohydrates.

It is unclear in what ways silica is important in the nutrition of animals. This field of research is challenging because silica is ubiquitous and in most circumstances dissolves in trace quantities only. All the same it certainly does occur in the living body, leaving us with the problem that it is hard to create proper silica-free controls for purposes of research. This makes it difficult to be sure when the silica present has had operative beneficial effects, and when its presence is coincidental, or even harmful. The current consensus is that it certainly seems important in the growth, strength, and management of many connective tissues. This is true not only for hard connective tissues such as bone and tooth but possibly in the biochemistry of the subcellular enzyme-containing structures as well.[28] Aplikasi pada pangan? Berdasarkan Peraturan Menteri Kesehatan RI No. 722/Menkes/Per/IX/88 tentang Bahan Tambahan Pangan, yang dimaksud antikempal adalah bahan tambahan pangan yang dapat mencegah mengempalnya pangan berupa serbuk juga mencegah mengempalnya pangan yang berupa tepung. Bahan tambahan ini biasanya ditambahkan pada makanan yang berbentuk serbuk, misalnya garam meja atau merica bubuk dan bumbu lainnya agar pangan tersebut tidak mengempal dan mudah dituang dari wadahnya. Antikempal merupakan senyawa anhydrous yang dapat menyerap air tanpa menjadi basah. Bahan tersebut ditambahkan ke dalam produk berupa granula atau bubuk yang mempunyai sifat higroskopis, misalnya garam meja, lada bubuk, bubuk untuk pembuatan roti, dan lain sebagainya. Secara umum antikempal dapat berfungsi karena mudah menyerap air dengan melapisi partikel-partikel bubuk yang menyebabkan penolakan penyerapan air atau bubuk dan atau karena bahan tersebut tidak dapat larut air. Antikempal dapat berupa garam anhydrous atau zat yang dapat menyerap air karena pengikatan di permukaan, tetapi dia sendiri tetap mudah dicurahkan atau dapat dibuat dalam keadaan yang diperlukan denganperlakuan fisik. Banyaknya garam anhydrous bersifat polimorfi, yaitu dapat berada dalam bentuk kristal. Pada keadaan ini zat tersebut menyimpan energy yang rendah dengan ikatan antar atom yang kuat. Keadaan tersebut berubah pada waktu terjadi perubahan dari suatu bentuk kristal ke bentuk kristal yang lain. Menurut daftar dari FAO/WHO lebih dari 20 zat dapat digunakan sebagai antikempal, dan dapat dikelompokkan sebagai berikut. 1) Garam stearat yang diujikan penggunaannya ialah garam-garam aluminium, ammonium 2) Kalium fosfat 3) Kalium dan natrium ferosianida 4) Magnesium oksida 5) Garam-garam asam silikat dari aluminium, magnesium, kalsium, dan campuran aluminium. Efek yang ditimbulkan pada tubuh? Silica ingested orally is essentially nontoxic, with an LD50 of 5000 mg/kg (5 g/kg).[7] On the other hand, inhaling finely divided crystalline silica dust can lead to silicosis, bronchitis, or cancer, as the dust becomes lodged in the lungs and continuously irritates them, reducing lung capacities.[29] Studies of workers with exposure to crystalline silica have shown 10-fold higher than expected rates of lupus and other systemic autoimmune diseases compared to expected rates in the general population.[30] Prior to new rules issued in 2013, OSHA allowed 100 µg per cubic meter of air. The new regulations reduce the

amount to 50 µg/m3. The exposure limit for the construction industry is also set at 50 µg/m3 down from 250 µg/m3.[31] In the body, crystalline silica particles do not dissolve over clinically relevant periods. Silica crystals inside the lungs can activate the NLRP3 inflammasome inside macrophages and dendritic cells and thereby result in processing of pro-Interleukin 1 beta into its mature form. Chronic exposure to silica may thereby for some of its health hazards, as interleukin-1 is a highly pro-inflammatory cytokine in the immune system.[32][33][34] This effect can create an occupational hazard for people working with sandblasting equipment, products that contain powdered crystalline silica and so on. Children, asthmatics of any age, allergy sufferers, and the elderly (all of whom have reduced lung capacity) can be affected in much less time. Amorphous silica, such as fumed silica is not associated with development of silicosis, but may cause irreversible lung damage in some cases.[35] Laws restricting silica exposure with respect to the silicosis hazard specify that they are concerned only with silica that is both crystalline and dust-forming. A study that followed subjects for 15 years found that higher levels of silica in water appeared to decrease the risk of dementia. The study found an association between an increase of 10 milligram-perday of the intake of silica in drinking water with a decreased risk of dementia of 11%.[36] Crystalline silica is used in hydraulic fracturing of formation which contain tight oil and shale gas, a use which presents a health hazard to workers. In 2013 OSHA announced tightened restrictions on the amount of crystalline silica which could be present and required "green completion" of fracked wells to reduce exposure.[31] Crystalline silica is an occupational hazard for those working with stone countertops, because the process of cutting and installing the countertops creates large amounts of airborne silica.[37]