Crystalline Phases And Transformation Of Silica Bricks

ورود شما به سایت کوچک مان را خیر مقدم عرض می نماییم.
به دلیل بروز بودن سایت لطفا از سایر صفحات وب هم دیدن نمایید.

تبلیغات هزینه نیست بلکه زمینه سازی برای معرفی وب خود به دیگران و درآمد زایی برای شماست .
سفارش تبلیغات سفارش تبلیغات سفارش تبلیغات سفارش تبلیغات

درباره وب

refractory, sunriserefractory

Silica bricks with identical chemical composition can have differing mineralogical compositions which can cause quite different behavior during use. Therefore, it is not always sufficient to evaluate silica bricks only by their chemical composition. It is essential to also consider the degree of transformation and the thermal expansion behavior of the bricks.

Silica brick contains cristobalite, tridymite and some residual quartz. The crystal phases each have a high and low temperature forms which can transform reversibly. The crystal structure of the individual SiO2 crystal phase can differ widely. This is of great importance during heating and cooling because of the change in the volume.

Quartz requires the smallest volume and the quartz glass the largest. During firing above approximately 900℃, quartz transforms into the other modifications and melt completely at 1725℃. It shows such a transformation at 573℃, tridymite at 117℃, and cristobalite between 225℃ and 270℃. The thermal expansion of cristobalite is considerably greater than that of the tridymite.

Because well transformed silica bricks contain little or no residual quartz, their behavior under the influence of temperature is largely determined by the ratio of cristobalite to tridymite. During heating up, silica bricks expand rapidly with the total reversible expansion being completed at around 800℃. Therefore they are insensitive to the temperature fluctuations above 800℃, but very susceptible below this temperature because of the sudden volume expansion. For this reason, sufficient time must be allowed for heating furnaces up to about 800℃.

During slow cooling , reversible volume decreases take place which are a result of the spontaneous transformation of the crystal structure from the high to the low temperature modification. The reversible and irreversible volume effects can cause considerable stress within the refractory brick structure.

During the firing process, the lime reacts with the quartzite components to form wollastonite. The matrix also contains very small quantities of calcium ferrite, hematite, magnetite, calcium olivine and hedenbergite, which are formed from impurities. These crystalline phases are the reason for the discoloration and spot formation on the silica bricks.

The degree of transformation of the bricks can be determined easily and accurately by the density of the residual quartz content. The density of a silica brick is lowest when the degree of transformation is farthest advanced.

The appearance of the bricks also indicates to the degree of transformation. The reversible thermal expansion also depends on the mineral composition. Tridymite and cristobalite do not expand linearly during heating but exhibit sudden changes in length both during heating and during cooling.

تاريخ : دوشنبه 10 آذر 1394 ساعت: 2:40 ا نویسنده : ADMIN ا
برچسب‌ها: <-TagName-> ,

دسته بندی : <-CategoryName->,

آرشیو مطالب
<-TagName-> (<-TagCount->)
امکانات وب

آمار وبلاگ

تعداد آنلاين : 1
بازديد امروز : 38
بازديد ديروز : 6
بازديد هفته : 52
بازديد کل : 35811

فروش بک لینک
خرید هاست ارزان
خرید هاست
تبدیل وبلاگ به سایت
سرور اختصاصی
ایران هاست
سرور مجازی
هاست ایران
هاست ارزان

12 Insults We Should Bring Back
تنگ کردن واژن
دکتری پژوهش محور
پایان نامه
پارکت لمینت
چت شیراز
آموزش تعمیرات موبایل
آموزش تعمیرات موبایل
شبکه حرفه ای کسب و کار
درب ضد سرقت
CCCAM Server Fast Information
دوربین مدار بسته

لینک های مفید
خرید رپورتاژ آگهی, رپورتاژاگهی, بک لینک انبوه, بک لینک, تبلیغات بنری, خرید پاپ آپ, تبلیغات پست ثابت