Silica Fume in Refractory Castables

{"news_id":8176,"is_preview":0,"news_info":{"id":8176,"company_id":176,"user_id":411,"author":"","website_id":781,"pub_date":"2023-10-07 11:13:20","urla":"silica-fume-in-refractory-castables","description":"Silica fume is used as a fine spherical filler in refractory castables to reduce the water \u2026","image_url":"https:\/\/oss.matchpages.cn\/matchpages\/common\/2023\/1007\/2059\/6520cbda09314\/undensified-silica-fume-800-600.webp","image_alt":"undensified silica fume","title":"Silica Fume in Refractory Castables","content":"<div class=\"bg-ch-pro mb-5\">\n<div class=\"container py-5\">\n<h1 style=\"line-height: 1.75;\"><strong><span style=\"color: #169179; font-size: 18pt;\">Silica Fume in Refractory Castables<\/span><\/strong><\/h1>\n<h2 style=\"line-height: 1.75;\"><strong><span id=\"The-effect-of-silica-fume-on-refractory-castables\" style=\"color: #169179; font-size: 14pt;\">1.The effect of silica fume on refractory castables<\/span><\/strong><\/h2>\n<p style=\"line-height: 1.75;\"><span style=\"text-decoration: underline;\"><strong><span style=\"color: #169179; text-decoration: underline;\"><a style=\"color: #169179; text-decoration: underline;\" href=\"http:\/\/www.allcarbon.com.cn\/microsilica\" data-page_id=\"0\" data-page_name=\"\" data-page_type=\"\">Silica fume<\/a><\/span><\/strong><\/span> <span style=\"color: #000000;\">consists of ultra-fine spherical particles that can fill the pores among the particles of the castables. So the water consumption and porosity of the castables are both reduced. And between particles, the sliding friction becomes rolling resistance. Because the coefficient of rolling resistance is generally much smaller than that of the sliding friction, the resisting force between the particles reduces, and leads to the reduction of viscosity of the castables and the improvement of flowability.<\/span><\/p>\n<h2 style=\"line-height: 1.75;\"><span style=\"color: #169179;\"><strong><span id=\"Bonding-mechanism\" style=\"font-size: 14pt;\">2.Bonding mechanism<\/span><\/strong><\/span><\/h2>\n<p style=\"line-height: 1.75;\"><span style=\"color: #000000;\">Silica fume reacts with water to form silanol groups (Si-OH) on the surface. During drying, a large number of silanol groups condense to siloxane bonds (Si&minus;O&minus;Si) after the temperature reaches 80&deg;C, and subsequently form a siloxane network structure that provides high strength at low temperature and remains unchanged till 250&deg;C. And this high strength provided by silica fume is not only limited under low-temperature conditions, castable products added with silica fume also have high strength at mid- and high-temperatures as the network structure has no apparent changes at temperatures up to 1200&deg;C.<\/span><\/p>\n<p style=\"line-height: 1.75;\"><span style=\"color: #000000;\">And due to silica fume&rsquo;s high activity, it is easy to form mullite with Al<sub>2<\/sub>O<sub>3<\/sub>&nbsp;in high alumina based refractory castables by solid state reaction at high temperature, thereby improving the strength and stability of low cement castables. Thanks to the combination of the network structure and mullite, the products can have a cold crushing strength of more than 100 MPa after firing at medium temperature (about 1000&deg;C).<\/span><\/p>\n<h2 style=\"line-height: 1.75;\"><strong><span id=\"The-use-of-silica-fume-in-refractory-castables\" style=\"color: #169179; font-size: 14pt;\">3.The use of silica fume in refractory castables<\/span><\/strong><\/h2>\n<h3 style=\"line-height: 1.75;\"><strong><span style=\"color: #000000; font-size: 12pt;\">3.1Using high SiO<sub>2<\/sub>&nbsp;content silica fume to improve flowability<\/span><\/strong><\/h3>\n<p style=\"line-height: 1.75;\"><span style=\"color: #000000;\">As&nbsp;silica fume&nbsp;has a direct influence on the flowability of refractory castables, silica fume with high SiO<sub>2<\/sub>&nbsp;content is beneficial to the enhancement of material flowability. Under the premise of the same flow value, using low SiO<sub>2<\/sub>&nbsp;content silica fume will inevitably lead to the increase of water content of castables. If the water content is too high, the porosity of castables left after drying will increase, causing a decrease in the bulk density and the physical strength of products.<\/span><\/p>\n<h3 style=\"line-height: 1.75;\"><strong><span id=\"The-influence-of-the-pH-value-of-silica-fume\" style=\"color: #000000; font-size: 12pt;\">3.2The influence of the pH value of silica fume<\/span><\/strong><\/h3>\n<p style=\"line-height: 1.75;\"><span style=\"color: #000000;\">A study found that the influence of pH on the flow value of the high-alumina low-cement castables showed a similar trend at different water additions: With the increase of pH value of silica fume, the flow value of the castables first increases.&nbsp;When the pH value of silica fume is 5.5-8.5, the castables have relatively good and stable flowability. And when the pH value exceeds 8.5, the flow value of the castables decreases significantly.<\/span><\/p>\n<p style=\"line-height: 1.75;\"><span style=\"color: #000000;\">The study also showed that the hardening time of the castable is shortened as the pH value of silica fume increases, and it is shortened sharply when the pH value exceeds 8.5. When the pH value of silica fume is between 7 and 8, the castables have higher strength.<\/span><\/p>\n<h3 style=\"line-height: 1.75;\"><strong><span id=\"Dispersant\" style=\"color: #000000; font-size: 12pt;\">3.3Dispersant<\/span><\/strong><\/h3>\n<p style=\"line-height: 1.75;\"><span style=\"color: #000000;\">Ultra-fine silica fume has a large surface free energy, so the particles agglomerate easily. Generally,<\/span>&nbsp;<span style=\"text-decoration: underline;\"><strong><span style=\"color: #169179; text-decoration: underline;\"><a style=\"color: #169179; text-decoration: underline;\" href=\"https:\/\/www.allcarbon.com.cn\/undensified-microsilica\" target=\"\" data-page_id=\"0\">undensified silica fume<\/a><\/span><\/strong><\/span>&nbsp;<span style=\"color: #000000;\">is used in low cement refractory castables because of its better dispersion efficiency. In addition, using high efficient dispersant allows silica fume to give full play to its pore filling effect, so as to produce low cement castables with high density, high strength, and good high temperature performance.<\/span><\/p>\n<\/div>\n<\/div>","discuss":0,"seo_title":"Silica Fume in Refractory Castables | ACC","seo_keyword":"silica fume,micro silica,castable refractory,castable refractory cement,silica fume concrete","seo_describe":"Silica fume is used as a fine spherical filler in refractory castables to reduce the water content and porosity of the products, and improve their strength.","track_code":"","viewer":"","source_copy_id":0,"sort":127,"status":0,"data_time":"2023-12-07 14:56:08","create_time":"2023-10-07 11:13:20","update_time":"2025-04-02 09:56:43","type_items":[{"id":2204,"website_id":781,"name":"Microsilica","urla":""}],"tag_items":[]}}

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<h1 style="line-height: 1.75;"><strong><span style="color: #169179; font-size: 18pt;">Silica Fume in Refractory Castables</span></strong></h1>
<h2 style="line-height: 1.75;"><strong><span id="The-effect-of-silica-fume-on-refractory-castables" style="color: #169179; font-size: 14pt;">1.The effect of silica fume on refractory castables</span></strong></h2>
<p style="line-height: 1.75;"><span style="text-decoration: underline;"><strong><span style="color: #169179; text-decoration: underline;"><a style="color: #169179; text-decoration: underline;" href="http://www.allcarbon.com.cn/microsilica" data-page_id="0" data-page_name="" data-page_type="">Silica fume</a></span></strong></span> <span style="color: #000000;">consists of ultra-fine spherical particles that can fill the pores among the particles of the castables. So the water consumption and porosity of the castables are both reduced. And between particles, the sliding friction becomes rolling resistance. Because the coefficient of rolling resistance is generally much smaller than that of the sliding friction, the resisting force between the particles reduces, and leads to the reduction of viscosity of the castables and the improvement of flowability.</span></p>
<h2 style="line-height: 1.75;"><span style="color: #169179;"><strong><span id="Bonding-mechanism" style="font-size: 14pt;">2.Bonding mechanism</span></strong></span></h2>
<p style="line-height: 1.75;"><span style="color: #000000;">Silica fume reacts with water to form silanol groups (Si-OH) on the surface. During drying, a large number of silanol groups condense to siloxane bonds (Si−O−Si) after the temperature reaches 80°C, and subsequently form a siloxane network structure that provides high strength at low temperature and remains unchanged till 250°C. And this high strength provided by silica fume is not only limited under low-temperature conditions, castable products added with silica fume also have high strength at mid- and high-temperatures as the network structure has no apparent changes at temperatures up to 1200°C.</span></p>
<p style="line-height: 1.75;"><span style="color: #000000;">And due to silica fume’s high activity, it is easy to form mullite with Al<sub>2</sub>O<sub>3</sub> in high alumina based refractory castables by solid state reaction at high temperature, thereby improving the strength and stability of low cement castables. Thanks to the combination of the network structure and mullite, the products can have a cold crushing strength of more than 100 MPa after firing at medium temperature (about 1000°C).</span></p>
<h2 style="line-height: 1.75;"><strong><span id="The-use-of-silica-fume-in-refractory-castables" style="color: #169179; font-size: 14pt;">3.The use of silica fume in refractory castables</span></strong></h2>
<h3 style="line-height: 1.75;"><strong><span style="color: #000000; font-size: 12pt;">3.1Using high SiO<sub>2</sub> content silica fume to improve flowability</span></strong></h3>
<p style="line-height: 1.75;"><span style="color: #000000;">As silica fume has a direct influence on the flowability of refractory castables, silica fume with high SiO<sub>2</sub> content is beneficial to the enhancement of material flowability. Under the premise of the same flow value, using low SiO<sub>2</sub> content silica fume will inevitably lead to the increase of water content of castables. If the water content is too high, the porosity of castables left after drying will increase, causing a decrease in the bulk density and the physical strength of products.</span></p>
<h3 style="line-height: 1.75;"><strong><span id="The-influence-of-the-pH-value-of-silica-fume" style="color: #000000; font-size: 12pt;">3.2The influence of the pH value of silica fume</span></strong></h3>
<p style="line-height: 1.75;"><span style="color: #000000;">A study found that the influence of pH on the flow value of the high-alumina low-cement castables showed a similar trend at different water additions: With the increase of pH value of silica fume, the flow value of the castables first increases. When the pH value of silica fume is 5.5-8.5, the castables have relatively good and stable flowability. And when the pH value exceeds 8.5, the flow value of the castables decreases significantly.</span></p>
<p style="line-height: 1.75;"><span style="color: #000000;">The study also showed that the hardening time of the castable is shortened as the pH value of silica fume increases, and it is shortened sharply when the pH value exceeds 8.5. When the pH value of silica fume is between 7 and 8, the castables have higher strength.</span></p>
<h3 style="line-height: 1.75;"><strong><span id="Dispersant" style="color: #000000; font-size: 12pt;">3.3Dispersant</span></strong></h3>
<p style="line-height: 1.75;"><span style="color: #000000;">Ultra-fine silica fume has a large surface free energy, so the particles agglomerate easily. Generally,</span> <span style="text-decoration: underline;"><strong><span style="color: #169179; text-decoration: underline;"><a style="color: #169179; text-decoration: underline;" href="https://www.allcarbon.com.cn/undensified-microsilica" target="" data-page_id="0">undensified silica fume</a></span></strong></span> <span style="color: #000000;">is used in low cement refractory castables because of its better dispersion efficiency. In addition, using high efficient dispersant allows silica fume to give full play to its pore filling effect, so as to produce low cement castables with high density, high strength, and good high temperature performance.</span></p>
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