Linear change on reheating means that the size of refractory products is irreversible changed when the refractory products are heated to high temperature. A positive value indicates expansion which is called expansion of linear change on reheating; negative value indicates contraction which is called contraction of linear change on reheating.

1. Linear Change On Reheating Of Zircon Brick
Linear change on reheating means that the size of refractory products is irreversible changed
when the refractory products are heated to high temperature. A positive value indicates
expansion which is called expansion of linear change on reheating; negative value indicates
contraction which is called contraction of linear change on reheating.
Due to zircon brick is used at high temperature and maybe further sintered and phase
changed which will cause the change of volume, then produce expansion or contraction of
linear change on reheating. It is also an aspect to express the high temperature volume
stability and an important quality index of zircon brick. For instance, if the contraction of linear
change on reheating of the upper bricks in a glass furnace is too big, this will cause the
refractory brick shedding and the roof collapsing. So linear change on reheating of zircon
brick has great significance to discriminate its high temperature volume stability which can
ensure stability of furnace, reduce gap of masonry, improve the tightness and corrosion
resistance, and avoid the destruction of the whole structure of glass furnace.
Factors affecting the linear change on reheating
1. Chemical mineral composition and microstructure
It will expanse when the density of the reaction product is less than the density of the
reactants. Otherwise, it will shrink.
2. Sinter
Sintering is an important process in process of reheating, which is the important reason for
linear change on reheating. The porosity, liquid phase, liquid phase composition and grain
size of refractory can greatly affect the sintering. The more liquid phase it has, the smaller the
grain size is, the more porosity is, the easier the sintering, and the bigger the linear change is.
3. Manufacturing technology
It can shorten the distance between the refractory material and the thermodynamic
equilibrium state when improve the sintering temperature and prolong the holding time of the
products, which will reduce the linear change on reheating
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2. 锆砖的重烧线变化
重烧线变化是指耐火制品加热至高温后，制品尺寸（长度）发生的不可逆变化，以%表示，正
值表示膨胀，称重烧线膨胀；负值表示收缩，称重烧线收缩。
由于锆砖在高温下使用时，可能有进一步烧结和物相的继续变化，从而再次引起体积变化，产
生重烧残余收缩或膨胀。这也是表达高温体积稳定性的一个方面，是耐火制品的一项重要质量指
标。如炉顶制品重烧线收缩过大，则会引起砌砖脱落、炉顶塌落的危险，对于各种不烧制品和不
定形耐火材料，此项指标更为重要。所以锆砖重烧线的变化对判别锆砖的高温体积稳定性，从而
保证砌筑体的稳定性，减少砌筑体的缝隙，提高其密封性和耐侵蚀性，避免砌筑体整体结构的
破坏，都具有重要意义。
影响重烧线变化的因素
1.化学矿物组成与显微结构
当反应产物的密度小于反应物的密度时，发生膨胀，如红柱石、硅线石和蓝晶石的莫来石
化，氧化镁和三氧化二铝反应生成尖晶石等。如果反应产物的密度大于反应物就会产生收缩。
2.烧结
烧结是重烧过程中发生的一个重要过程，它是导致重烧线收缩的重要原因。耐火材料中气
孔率、液相量、液相组成与晶粒大小都会对烧结产生很大的影响。液相量越多，晶粒尺寸越小，气
孔率越大，烧结越容易进行，产生的重烧收缩也越大。
3.制造工艺参数
提高制品的烧成温度与延长保温时间，可以缩短耐火材料与其热力学平衡态的距离，可以
降低重烧线变化率。