Encapsulation in glass and glass-ceramic materials

Claim 1

A method of forming a composite glass-ceramic cooking vessel having a heat conducting insert fully encapsulated therewithin which comprises, supplying molten glass having a first coefficient of thermal expansion, supplying a heat conducting insert which does not chemically or fusion bond to the molten glass and which has a second coefficient of thermal expansion which is less than 20×10 -7 /°C. greater than the first coefficient of thermal expansion of the molten glass, fully encapsulating said insert within said molten glass, cooling said molten glass and the encapsulated insert to form a composite glass article having an insert fully encapsulated therewithin, contracting the insert upon cooling at a greater rate than that of the glass during said cooling, subjecting the composite article to elevated temperatures and converting the glass to a glass-ceramic article, shrinking the glass-ceramic article while at elevated temperatures about said insert and simultaneously inducing stress in said article, and cooling said composite glass-ceramic article to room temperature while simultaneously contracting said insert at a greater rate than that of said glass-ceramic article and thereby relieving the stress induced in said article to form a glass-ceramic cooking vessel having a heat conducting insert fully encapsulated therewithin.

Claim 2

A method of forming a composite glass-ceramic cooking vessel having a heat conducting insert fully encapsulated therewithin which comprises, supplying molten glass having a first coefficient of thermal expansion, supplying a heat conducting insert which does not chemically or fusion bond to the molten glass and which has a second coefficient of thermal expansion which is less than 20×10 -7 /°C. greater than the first coefficient of thermal expansion of the molten glass, fully encapsulating said insert within said molten glass, cooling said molten glass and the encapsulated insert to form a composite glass article having an insert fully encapsulated therewithin, contracting the insert upon cooling at a greater rate than that of the glass during said cooling, subjecting the composite article to elevated temperatures and converting the glass to a glass-ceramic article, shrinking the glass-ceramic article while at elevated temperatures about said insert and simultaneously inducing stress in said article, and cooling said composite glass-ceramic article to room temperature while simultaneously contracting said insert at a greater rate than that of said glass-ceramic article and thereby relieving the stress induced in said article to form a glass-ceramic cooking vessel having a heat conducting insert fully encapsulated therewithin.

Claim 5

A method of forming a composite article having an insert fully encapsulated therewithin which comprises, supplying molten glass having a first coefficient of thermal expansion, supplying a silicon insert which is bondable to said article, fully encapsulating said insert within said molten glass, cooling said molten glass and the encapsulated insert to form a composite glass article having an insert bonded thereto and fully encapsulated therewithin, subjecting said composite glass article to a thermal cycle and converting such article to a composite glass-ceramic article, said silicon insert having a second coefficient of thermal expansion which is greater than the coefficient of thermal expansion of the glass-ceramic forming said article, cooling the composite article and contracting the bonded insert at a greater rate than the glass-ceramic, and thereby placing the insert in tension and forming microcracks within said insert which relieve the tension imparted thereto by the differential contraction between the bonded insert and the encapsulating glass-ceramic article.

Claim 6

A method of forming a composite article having an insert fully encapsulated therewithin which comprises, supplying molten glass having a first coefficient of thermal expansion, supplying a silicon insert which is bondable to said article, fully encapsulating said insert within said molten glass, cooling said molten glass and the encapsulated insert to form a composite glass article having an insert bonded thereto and fully encapsulated therewithin, subjecting said composite glass article to a thermal cycle and converting such article to a composite glass-ceramic article, said silicon insert having a second coefficient of thermal expansion which is greater than the coefficient of thermal expansion of the glass-ceramic forming said article, cooling the composite article and contracting the bonded insert at a greater rate than the glass-ceramic, and thereby placing the insert in tension and forming microcracks within said insert which relieve the tension imparted thereto by the differential contraction between the bonded insert and the encapsulating glass-ceramic article.

Claim 7

A method of forming a composite glass-ceramic article having an insert fully encapsulated therewithin which comprises, supplying molten glass having a first coefficient of thermal expansion, supplying a heat conductive graphite insert having a second coefficient of thermal expansion which is greater than said first coefficient of thermal expansion, fully encapsulating said graphite insert within said molten glass and forming a composite glass article having an insert encapsulated wholly therewithin, subjecting said encapsulated glass article to a thermal cycle and converting said glass article to a glass-ceramic article, volumetrically shrinking said glass-ceramic article about said insert during said thermal cycle and inducing stresses within said article, cooling said glass-ceramic article to room temperature and contracting said insert at a rate greater than the contraction of said glass-ceramic article, and during said cooling relieving said stresses induced in said article by said volumetric shrinkage, and said coefficient of thermal expansion of said insert being selected such that said encapsulated heat conductive insert is snugly retained in a virtually stress-free relationship within said glass-ceramic article at room temperature.

Claim 8

A method of forming a composite glass-ceramic article having an insert fully encapsulated therewithin which comprises, supplying molten glass having a first coefficient of thermal expansion, supplying a heat conductive graphite insert having a second coefficient of thermal expansion which is greater than said first coefficient of thermal expansion, fully encapsulating said graphite insert within said molten glass and forming a composite glass article having an insert encapsulated wholly therewithin, subjecting said encapsulated glass article to a thermal cycle and converting said glass article to a glass-ceramic article, volumetrically shrinking said glass-ceramic article about said insert during said thermal cycle and inducing stresses within said article, cooling said glass-ceramic article to room temperature and contracting said insert at a rate greater than the contraction of said glass-ceramic article, and during said cooling relieving said stresses induced in said article by said volumetric shrinkage, and said coefficient of thermal expansion of said insert being selected such that said encapsulated heat conductive insert is snugly retained in a virtually stress-free relationship within said glass-ceramic article at room temperature.

Claim 12

A method of forming a composite glass-ceramic article having an insert fully encapsulated therewithin as defined in claims 7 or 8 including the step of supplying a disc-like heat conductive graphite insert which does not chemically or fusion bond to the glass-ceramic article, which has a modulus of elasticity less than the modulus of elasticity of said glass-ceramic material forming said article, and which has a total thickness not exceeding 1/5 of the total glass-ceramic thickness surrounding opposite sides of said insert.