Iron Oxide Red Pigments via Nitrate Process pH Control
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Solution Overview
Problem
Current iron oxide red pigments produced by the Penniman red process have low color saturation, limiting their use in applications requiring intense red shades, and face challenges in achieving consistent color quality due to reaction conditions that can lead to passivation or incomplete hematite formation.
Innovation Solution
The process involves reacting iron with an aqueous hematite nucleus suspension and an iron (II) nitrate solution in the presence of an oxygen-containing gas at controlled temperatures and pH levels, with nitrogen introduction to maintain optimal pH, resulting in hematite pigments with enhanced color properties and improved process control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If iron is reacted with dilute nitric acid at elevated temperature to produce hematite nuclei, then hematite pigment suspension is formed, but the reaction can lead to passivation of iron surface or dissolution to form iron nitrate, both of which are undesirable
Solution Approach 1:
The patent optimizes specific parameters including maintaining temperature at 90-99°C, controlling nitric acid concentration at 5-15% by weight, and regulating pH in the range 1.5-3.5 during the reaction. These parameter changes ensure consistent hematite formation while preventing passivation and iron nitrate dissolution, resolving the reliability issue.
2Quantity of substance
If conventional Penniman red process is used to produce iron oxide red pigments, then pigment suspension is obtained, but the color saturation is comparatively low (similar to commercial 130 standard)
Solution Approach 1:
The patent achieves enhanced color saturation (a* values exceeding 58 CIELAB units) by optimizing reaction parameters including temperature (90-99°C), pH control (1.5-3.5), and the use of nitrogen introduction to maintain optimal conditions. These changes produce intense red shades that expand the pigment's application range beyond conventional building industry uses.
3Manufacturing precision
If nitrogen is introduced to maintain optimal pH during reaction, then consistent color quality is achieved, but process complexity increases
Solution Approach 1:
The patent implements pH monitoring and feedback control during the reaction process. By continuously measuring pH and adjusting nitrogen introduction accordingly, the system maintains pH within the optimal range of 1.5-3.5, ensuring consistent color quality while providing a systematic approach to process control.
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 method produces iron oxide red pigments with significantly higher color saturation, achieving a* values exceeding 58 CIELAB units, ensuring intense red shades both in full shade and with reduction, and exhibits Newtonian flow behavior, simplifying processing and achieving consistent color quality.
Implementation Method 1
iron metal being dissolved and oxidized with addition of an iron salt and an iron oxide nucleus
Implementation Method 2
aqueous production of finely divided hematite
Implementation Method 3
in the presence of an oxygen-containing gas
Implementation Method 4
at controlled temperatures
Implementation Method 5
exhibits Newtonian flow behavior, simplifying processing
Data Source
AI summary
The present invention relates to iron oxide red pigments having improved color values, a process for producing these improved iron oxide red pigments by the Penniman red process using nitrate (also referred to as nitrate process or direct red process) and an apparatus for the production thereof.