Glass Composition for Tube Collector Glass-Metal Bond Matching
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Solution Overview
Problem
Existing glass-metal bonds in solar energy collection apparatuses, particularly in vacuum tube collectors, face challenges with thermal expansion mismatch, high production costs, and energy-intensive processing due to the use of unsuitable glass compositions, which affect thermal insulation and mechanical stability.
Innovation Solution
A glass composition with specific oxide ratios (SiO2, B2O3, Al2O3, Na2O, K2O, CaO, MgO, and Fe2O3) is developed, allowing for a low thermal expansion coefficient matching metals, high hydrolytic stability, and low melting temperature, enabling efficient and cost-effective production of glass tubes with diameters over 120 mm for vacuum tube collectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If unmatched glass-metal bonds are used (glass and metal with different thermal expansion coefficients), then the glass can be readily meltable with low production costs, but the bond experiences thermal stress and potential failure at high temperatures
Solution Approach 1:
The patent modifies the glass composition parameters to achieve a thermal expansion coefficient matching the metal absorber tube. The glass contains specific ranges of oxides: SiO2 (70-78 wt%), B2O3 (5-10 wt%), Al2O3 (4-8 wt%), Na2O (5-8 wt%), K2O (1-4 wt%), CaO (1-4 wt%), and MgO (0.5-3 wt%), which collectively provide both matchability to metal and readiness to melt at moderate temperatures.
Solution Approach 2:
The patent creates a composite glass formulation combining multiple oxide components that work synergistically. The combination of network formers (SiO2, B2O3), network modifiers (Na2O, K2O, CaO, MgO), and intermediates (Al2O3) produces a glass with matched thermal expansion while maintaining processability and optical properties for solar collectors.
2Reliability
If matched glass-metal bonds are used with intermediate glasses, then thermal expansion matching is achieved, but production complexity and costs increase
Solution Approach 1:
The patent eliminates the need for separate intermediate glass layers by incorporating all necessary matching properties directly into the envelope glass composition. The glass itself is formulated to match the thermal expansion of the metal absorber tube, removing the complexity of multi-layer construction and simplifying the manufacturing process.
Solution Approach 2:
The envelope glass performs multiple functions simultaneously: it provides thermal insulation, matches thermal expansion with the metal, maintains structural integrity, and allows solar radiation transmission. This multi-functionality is achieved through a single optimized glass composition rather than requiring multiple specialized layers.
3Reliability
If high thermal stability glass is used for envelope tube, then the bond withstands high temperatures, but melting temperature increases and energy consumption rises
Solution Approach 1:
The patent optimizes the glass composition parameters to decouple thermal stability from melting temperature. By carefully selecting oxide ratios—particularly using B2O3 (5-10 wt%) as a network former that lowers melting point while maintaining thermal resistance, and balancing alkali oxides (Na2O 5-8 wt%, K2O 1-4 wt%) with alkaline earth oxides (CaO 1-4 wt%, MgO 0.5-3 wt%)—the glass achieves both high-temperature stability and readiness to melt at moderate temperatures.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The glass composition achieves a thermal expansion coefficient of 5.7×10−6/K, high tensile strength, and low production costs, reducing energy consumption and eliminating the need for intermediate glasses, thus enhancing the efficiency and stability of glass-metal bonds in solar energy collection systems.
Implementation Method 1
the ratio of the sum of the amounts of the alkaline-earth metal oxides (RO), in mol %, to the sum of the amounts of the alkali metal oxides (R2O), in mol %, is ≦0.6, thereby allowing the glass to have a coefficient of thermal expansion matched to a metal
Implementation Method 2
high hydrolytic stability
Implementation Method 3
low melting temperature, enabling efficient and cost-effective production
Data Source
AI summary
The glass-metal bond for a tube collector includes a glass tube and metal part bonded to the glass tube. In order to match the thermal expansion properties, the glass tube has the following composition: SiO2, 73-77 wt. %; B2O3, 6-<8 wt. %; Al2O3, 6-6.5 wt. %; Na2O, 5.5-7 wt. %; K2O, 1-3 wt. %; CaO, 0.5-3.2 wt. %; MgO, 0-2 wt. %; Fe2O3, 50-150 ppm; and TiO2 0-<100 ppm. The ratio of the sum of the alkaline-earth metal oxides (in mol %) to the sum of the alkali metal oxides (in mol %) is ≦0.6. The metal part is preferably made of metal material no. 1.3981 according to DIN 17745. The glass composition itself is also part of the invention.