Flowing Gas Surface Characterization With Closed-Loop Concentration Control
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Solution Overview
Problem
Current methods for surface characterization of porous solids and powder materials using flowing gas techniques are relative and inferior to static volumetric techniques, lacking direct calculation of adsorptive gas concentrations and flow rates, which results in incomplete isotherm determination and measurement errors due to plugging of surface pores and non-linear thermal conductivity detectors.
Innovation Solution
A system and method for surface characterization using flowing gas, which includes mass flow controllers for carrier and adsorptive gases, a mixer, a sample cell, a chiller, and a concentration detector. The system controls the mass flow of gases to achieve a target concentration of the adsorptive gas over the sample, allowing for absolute measurements and complete isotherm determination by varying the adsorptive gas concentration from 0% to greater than 95% and using closed loop feedback for precise control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If flowing gas technique is used for surface characterization, then measurement speed and cost are improved, but measurement precision and reliability deteriorate due to plugging of surface pores and non-linear detector responses
Solution Approach 1:
The system dynamically adjusts the concentration of adsorptive gas in the flowing mixture during measurement. By varying the concentration over time rather than maintaining a static level, the system prevents pore plugging while continuously acquiring measurement data, thus maintaining both speed and precision
Solution Approach 2:
The patent changes the physical parameter of gas concentration during the measurement process. By controlling the concentration of adsorptive gas to vary from low to high levels dynamically, the system avoids the pore plugging issue that occurs with constant high concentration while still obtaining complete isotherm data
2Device complexity
If flowing gas technique is used for surface characterization, then device complexity and cost are reduced, but measurement precision deteriorates due to inability to perform direct absolute measurements
Solution Approach 1:
The system incorporates feedback control where the measured concentration of adsorptive gas downstream is used to adjust and control the mass flow rates of carrier and adsorptive gases. This closed-loop feedback enables direct absolute measurements by continuously monitoring and adjusting the gas concentrations based on actual measurement conditions
Solution Approach 2:
The patent replaces the mechanical/volumetric measurement approach of static systems with a concentration-based measurement approach using flowing gas and detectors. This substitution allows for direct measurement of adsorbate amounts through concentration changes rather than volume displacement
3Measurement precision
If static volumetric technique is used for surface characterization, then measurement precision is improved through direct absolute measurements, but device complexity and cost increase due to ultra-high vacuum requirements
Solution Approach 1:
The patent extracts the measurement function from the vacuum environment. By using a flowing gas technique with concentration detection, the system removes the requirement for ultra-high vacuum conditions while maintaining measurement precision, thus eliminating the complex vacuum system infrastructure
Solution Approach 2:
The patent introduces a carrier gas as an intermediary medium that allows the adsorptive gas to be delivered and measured in atmospheric pressure conditions. The carrier gas enables concentration-based measurements without requiring vacuum, serving as a mediator between the sample and the measurement environment
4Productivity
If high concentration of adsorptive gas is used in flowing technique, then measurement speed is improved, but harmful effects increase due to plugging of surface pores
Solution Approach 1:
The system employs periodic variation in adsorptive gas concentration during the measurement process. By cycling through different concentration levels rather than maintaining a constantly high concentration, the system achieves rapid measurements while periodically preventing pore plugging through lower concentration phases
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 system enables absolute measurements of adsorbed and desorbed gases, reduces plugging of surface pores, and provides accurate and precise isotherm determination, overcoming the limitations of existing flowing gas techniques while offering lower costs and faster measurement acquisition compared to static volumetric methods.
Implementation Method 1
a first sample cell disposed within the first measurement channel, the first sample cell configured to contain a first amount of the sample and flow the mixture over or through the first amount of the sample
Implementation Method 2
a first concentration detector coupled downstream of the first sample cell and configured to provide a signal indicative of adsorptive gas concentration in the mixture downstream of the first sample cell
Implementation Method 3
a first chiller configured to selectively cool the first sample cell
Data Source
Figure 1
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AI summary
A system and method for surface characterization of a porous solid or powder sample using flowing gas include mass flow controllers configured to deliver a controllable mass flow of a carrier gas and adsorptive gas to vary concentration of the adsorptive gas flowing through at least one measurement channel containing a sample cell. A concentration detector downstream of the sample cell provides a signal indicative of the adsorptive gas concentration to a controller that determines the amount of adsorptive gas adsorbed and/or desorbed to characterize the surface area, pore volume, pore volume distribution, etc. of the sample material. The detector may include a housing, heat exchanger, thermal conductivity detector, and a temperature regulator.