SITALL

SITALL ÑÎ-115Ì is a crystalline glass ceramic material with ultra low Coefficient of thermal expansion.
SITALL ÑÎ-115Ì is an ideal material to be used for manufacturing of astr6onomical telescopes mirrors and other optical parts that require linear dimensions and surface figure stability at significant temperature changes.
Thermal stability of SITALL ÑÎ-115Ì material enables the fabrication of high precision mirrors within quicker time of treatment process since testing measurements are able to be conducted not waiting until thermal equilibrium is achieved.

sitall blanks with various forms of lightweightening

THERMAL PROPERTIES
mean linear coefficient of thermal expansion (CTE) within temperature range -60 to 60 oÑ	10-7 oC-1	0±1.5
CTE homogeneity	10-7 oC-1	<= 0.2
specific heat capacity	kilocalorie kg-1 oC-1	0.22
heat conductivity	kilocalorie h-1 m-1 oC-1	1.71
thermal resistance	oC	550
MECHANICAL PROPERTIES
density	g cm-3	2.46
micro hardness	10-7Pa	860
lapping relative hardness (with reference to glass, K-8 type)	-	1.78
modulus of elasticity (Young’s)	GPa	92
bending strength	10-7Pa	16.6
Poisson’s coefficient	-	0.28
OPTICAL PROPERTIES
refractive index ne	-	1.538
refractive index nd	-	1.536
average variance nF - nC	-	0.0102
quality	-	as per requirements
bubbles and striae	-	as per requirements
stress birefringence	nm/cm	up to 15

Sitall material shapes and forms of supply:
Sitall is made in form of flat round and rectangular plates, with maximum dimensions up to 3000mm. More detailed information about sitall material is submitted in reply to your request.